Vagus nerve regulates inflammation and metabolism

Vagus and inflammation, metabolismVagus nerve (cranial nerve X) function, a key regulator of inflammation and metabolism, is under assault in the modern environment. An excellent paper published in Nature Reviews Endocrinology presents a lucid review of the clinically important vagal inflammatory reflex, the role of impaired vagal function in type 2 diabetes and obesity, with therapeutic implications for reducing inflammation and regulating appetite. The authors state:

“The vagus nerve has an important role in regulation of metabolic homeostasis, and efferent vagus nerve-mediated cholinergic signalling controls immune function and proinflammatory responses via the inflammatory reflex. Dysregulation of metabolism and immune function in obesity are associated with chronic inflammation, a critical step in the pathogenesis of insulin resistance and type 2 diabetes mellitus.”

The vagus inflammatory reflex

Functional anatomy of the vagal inflammatory reflexThe vagal inflammatory reflex is a crucial factor in the brain’s regulation of inflammation…

Communication between the immune system and the brain is vital for controlling inflammation. The inflammatory reflex is a centrally integrated physiological mechanism in which afferent vagus nerve signaling, activated by cytokines or pathogen-derived products, is functionally associated with efferent vagus nerve-mediated output to regulate proinflammatory cytokine production and inflammation. The absence of this inflammatory reflex…results in excessive innate immune responses and cytokine toxicity.”

Vagal cholinergic control of inflammationWhen cytokines or pathogen-derived products activate the vagus nerve, it acts to regulate proinflammatory cytokine production and inflammation. When function of the inflammatory reflex is diminished there is excessive innate immune inflammatory activity. Disrupted immune regulation results in persistent pro-inflammatory cytokine activity and chronic inflammation.

“This state underlies the pathogenesis of a range of disease syndromes, including sepsis, rheumatoid arthritis, inflammatory bowel disease and other inflammatory and autoimmune disorders.”

Vagal output is a crucial mechanism for calming inflammation in the digestive tract and throughout the body.

Association with metabolism and obesity

Metabolic and immune dysregulation both contribute to chronic inflammation, and vagal stimulation can help remediate both.

“Chronic inflammation as a result of immune and metabolic dysregulation is a characteristic feature in patients with obesity and is causally linked with insulin resistance and other metabolic complications. Decreased vagus nerve activity in the context of obesity has been reported. Selective cholinergic activation within the efferent vagus nerve-mediated arm of the inflammatory reflex can suppress obesity-associated inflammation and reverse metabolic complications. These findings raise the intriguing possibility that dysregulation of vagus nerve-mediated signalling might contribute to the pathogenesis of obesity and its related comorbidities.

Importantly, the vagus nerve also acts to control appetite and feeding.

“Vagus nerve afferent and efferent signalling has an important role in the regulation of feeding behaviour and metabolic homeostasis. This finely tuned regulation is aimed at preserving energy balance and preventing fluctuations in body weight and metabolism that can be detrimental to the individual.”

It sends functional and metabolic information from the digestive and hepatic systems to the brain, and instructions from brain in return:

“Vagus nerve afferents innervating the gastrointestinal tract and liver are major constituents of a sensory system that detects changes in micronutrient and metabolic molecules. These nerve fibres transmit information detected by associated mechanoreceptors, chemoreceptors and specific metabolite receptors in the gut and hepatic portal system concerning levels of lipids, cholecystokinin, leptin, peptide YY, insulin and glucose to the brain…Vagus nerve efferents, on the other hand, provide brain-derived output to the gastrointestinal tract, liver and pancreas.”

Morever, vagal stimulation is necessary to maintain the gut barrier:

“…truncal vagotomy is associated with increased bacterial trans location across the intestinal mucosa, which suggests a tonic vagus nerve control of intestinal permeability and postprandial endotoxaemia.”

Vagal dysregulation in the inflammation of obesity

Inflammation is characteristic of obesity, associated with impaired vagal function…

“Disruption in metabolic and immune homeostasis in obesity is associated with hyperglycaemia, insulin resistance, dyslipidaemia and hypertension. This cluster of conditions characterizes the metabolic syndrome. Moreover, levels of proinflammatory cytokines and acute-phase proteins such as CRP are increased in individuals with obesity, indicating chronic inflammation. This inflammatory state is considered to be an essential pathophysiological constituent in obesity, underlying its adverse consequences and linking it to the other components of the metabolic syndrome. Several lines of evidence indicate that vagus nerve activity could be impaired in obesity, and enhancing cholinergic signaling within the inflammatory reflex can suppress obesity-associated inflammation and its adverse implications.”

There are numerous mechanisms by which obesity promotes systemic inflammation i association with disturbed vagal function.

Autonomic dysfunction and diminished vagus nerve activity occur frequently in individuals with obesity and type 2 diabetes mellitus. A 15-year follow-up study has revealed a strong relationship between autonomic dysfunction and insufficient vagus nerve activity (revealed by impaired heart rate recovery following exercise cessation), impaired glucose homeostasis and development of type 2 diabetes mellitus. Together, these preclinical and clinical findings support the hypothesis that diminished vagus nerve signaling in obesity could lead to enhanced inflammation and metabolic complications.”

Reducing obesity-associated inflammation with vagal support

Vagal cholinergic stimulation can alleviate the inflammation and metabolic complications of obesity:

“Targeting cholinergic mechanisms in the inflammatory reflex using α7nAChR agonists or a centrally-acting acetylcholinesterase inhibitor could alleviate inflammation and metabolic complications in obesity.”

Type 2 diabetes and cardiovascular risk can both be ameliorated by reducing inflammation through vagal support.

“The chronic inflammatory state associated with obesity is one such common step that could be targeted. Some anti-inflammatory approaches have already been explored in the treatment of obesity-linked disorders in preclinical and clinical scenarios. For example, patients with type 2 diabetes mellitus who were treated with a recombinant human IL-1 receptor antagonist (anakinra) experienced reductions in levels of IL-6 and CRP. Additionally, HbA1c levels in these patients were reduced and their pancreatic β-cell secretory function improved. Administration of salicylate—a known IKK inhibitor in rodents, which propagates proinflammatory signals—significantly improved glucose homeostasis, reduced free fatty acid levels and increased adiponectin levels in patients with type 2 diabetes mellitus.”

Therapeutic Considerations

In addition to stimulation of the vagus by devices and pharmacotherapy, there are numerous ‘hands-on’ therapies that stimulate the CNS from the periphery (chiropractic, cranial therapy, auriculotherapy, acupuncture, etc.) that, when properly rendered, increase parasympathetic (vagal) activity. The authors conclude:

“The inflammatory reflex mediated by the vagus nerve has been successfully exploited therapeutically in preclinical models of diseases with aetiologies characterized by excessive inflammatory responses. Insufficient efferent vagus nerve cholinergic output might have a causative role in the dysfunctional immune and metabolic regulation observed in obesity, as selective activation of the efferent cholinergic arm of the inflammatory reflex attenuates both inflammation and metabolic derangements. Although cholinergic suppression of inflammation can contribute specifically to alleviating metabolic complications, direct cholinergic effects on metabolic pathways could also have a role in alleviating symptoms associated with the metabolic syndrome and type 2 diabetes mellitus. These complex interactions and the contribution of central and peripheral mechanisms in this regulation are topics of ongoing study. Additionally, intracellular mechanisms by which cholinergic signals control obesity-associated inflammation and modulate insulin signaling are under investigation…The use of cholinergic modalities in combination with existing or new therapeutic approaches to target neural, endocrine and immune functions for therapeutic benefit in patients with obesity-related disorders should also be considered.”

They offer a summary by way of these key points:

  • The inflammatory reflex is a physiological mechanism through which the vagus nerve regulates immune function and inhibits excessive proinflammatory cytokine production
  • Vagus nerve signaling has an important role in the regulation of feeding behaviour and metabolic homeostasis
  • Disruption of metabolic and immune regulation in obesity results in inflammation, which mediates insulin resistance and the development of type 2 diabetes mellitus as well as other debilitating and life-threatening conditions
  • Activation of cholinergic signaling in the efferent arm of the inflammatory reflex alleviates obesity-associated inflammation and metabolic derangements
  • The inflammatory reflex can potentially be exploited for treatment of the metabolic syndrome, type 2 diabetes mellitus and other obesity-driven disorders

Readers may also be interested in how vagal activity regulates the brain-immune relationship.

Skipping breakfast worsens blood glucose and insulin later

Diabetes CareBreakfast is a cornerstone of healthy metabolism. A study just published in the journal Diabetes Care now shows that skipping breakfast damages the blood glucose and insulin response to meals later in the day. The authors note:

Skipping breakfast has been consistently associated with high HbA1c and postprandial hyperglycemia (PPHG) in patients with type 2 diabetes. Our aim was to explore the effect of skipping breakfast on glycemia after a subsequent isocaloric (700 kcal) lunch and dinner. “

They compared postprandial plasma glucose, insulin, C-peptide, free fatty acids (FFA), glucagon, and intact glucagon-like peptide-1 (iGLP-1) for subjects randomly assigned to one day with breakfast, lunch, and dinner (YesB) and another with lunch and dinner but no breakfast (NoB). Their data show that skipping the morning meal messed up metabolism for the rest of the day:

“Compared with YesB, lunch area under the curves for 0–180 min (AUC0–180) for plasma glucose, FFA, and glucagon were 36.8, 41.1, and 14.8% higher, respectively, whereas the AUC0-180 for insulin and iGLP-1 were 17% and 19% lower, respectively, on the NoB day (P < 0.0001). Similarly, dinner AUC0-180 for glucose, FFA, and glucagon were 26.6, 29.6, and 11.5% higher, respectively, and AUC0-180 for insulin and iGLP-1 were 7.9% and 16.5% lower on the NoB day compared with the YesB day (P < 0.0001). Furthermore, insulin peak was delayed 30 min after lunch and dinner on the NoB day compared with the YesB day. “

In other words, it worsened hyperglycemia and insulin resistance after both lunch and dinner. The authors conclude:

“Skipping breakfast increases PPHG after lunch and dinner in association with lower iGLP-1 and impaired insulin response. This study shows a long-term influence of breakfast on glucose regulation that persists throughout the day. Breakfast consumption could be a successful strategy for reduction of PPHG in type 2 diabetes.”

It’s also clearly important for prevention of type 2 diabetes and all the depredations of insulin resistance and dysregulated blood sugar.

Insulin resistance indicated by neutrophil-lymphocyte ratio

BMC Endocrine DisordersInsulin resistance (IR) is central to type 2 diabetes and a contributing cause to cardiovascular and neurodegenerative disorders, chronic kidney disease (CKD), a number of cancers and more. A study recently published in BMC Endocrine Disorders the ratio between neutrophils and lymphocytes (neutrophil-lymphocyte ratio, NLR) is a valuable and inexpensive predictive marker for insulin resistance. The authors note:

“Insulin resistance (IR) is a reduction in reaction or sensitivity to insulin and is considered to be the common cause of impaired glucose tolerance, diabetes, obesity, dyslipidemia, and hypertensive diseases….several studies have confirmed the relationship between systemic inflammation and insulin resistance, in which an altered immune system plays a decisive role in the pathogenesis of DM. The immune response to various physiological challenges is characterized by increased neutrophil and decreased lymphocyte counts, and NLR is often recognized as an inflammatory marker to assess the severity of the disease.”

Furthermore…

“Scholars have rarely investigated the relationship between IR and NLR. This study aims to evaluate the relationship between IR and NLR, and determine whether or not NLR is a reliable marker for IR.”

Mean neutrophil-lymphocyte ratio (NLR) values of the groups. Group 1 is diabetic w/o IR, Group 2 is diabetic with IR.

Mean neutrophil-lymphocyte ratio (NLR) values of the groups. Group 1 is diabetic w/o IR, Group 2 is diabetic with IR.

So they investigated the neutrophil-lymphocyte ratio in 413 patients with T2DM, 310 of whom had a HOMA-IR value (fasting plasma glucose (mmol/L) multiplied by fasting serum insulin (mIU/L) divided by 22.5) of > 2.0, indicating insulin resistance. They were compared to a control group of 130 healthy subjects and found a strong association:

“The NLR values of the diabetic patients were significantly higher than those of the healthy control, and the NLR values of the patients with a HOMA-IR value of > 2.0 are notably greater than those of the patients with a HOMA-IR value of ≤ 2.0. Pearson correlation analysis showed a significant positive correlation of NLR with HOMA-IR. Logistic regression analysis showed that the risk predictors of IR include NLR, TG and HbA1c. NLR levels correlated positively with IR. The IR odds ratio increased by a factor of 7.231 (95%) for every one unit increase in NLR.”

 Diabetes, cancer and cardiovascular diseases

In relation to their confirmation of NLR as a predictor for insulin resistance the authors observe…

“Many epidemiological studies have determined that DM is associated with chronic inflammation, which may contribute to the acceleration of diabetic microangiopathy and the development of macroangiopathy; IR is a characterized of T2DM, whereas the exact molecular action leading to IR is not yet understood, several studies have associated IR with inflammation, experimental studies have demonstrated a link between chronic inflammation and insulin resistance through mechanisms involving obesity and atherosclerosis. NLR has been recently defined as a novel potential inflammation marker in cancer and cardiovascular diseases. NLR can easily be calculated using the neutrophil-lymphocyte ratio in peripheral blood count. Calculating NLR is simpler and cheaper than measuring other inflammatory cytokines, such as IL-6, IL-1β, and TNF-α.”

Diabetes and chronic inflammation

These findings highlight the relationship between chronic inflammation, insulin resistance and type 2 diabetes.

“he pathological activation of innate immunity leads to inflammation of the islet cells, resulting in a decrease in pancreatic beta-cell mass and impaired insulin secretion. Patients with T2DM are in a state of low-degree chronic inflammation that induces hypersecretion of inflammatory factors, such as CRP, IL-6, TNF-α, and MCP-1, which results in a constantly elevated neutrophilic granulocyte count. One mechanism by which increased levels of neutrophils could mediate IR may be through augmented inflammation. The increase in NLR appears to underlie the elevated levels of pro-inflammation, as evident from the persistent neutrophil activation and enhanced release of neutrophil proteases with T2DM.”

 NLR tracks HgbA1c and triglycerides

Glycation of hemoglobin (HgbA1c) and triglycerides (TG) both go up as insulin resistance progresses along with the neutrophil-lymphocyte ratio.

“A logistic regression analysis of the following risk factors was conducted: NLR, TG and HbA1c. In our study, in conjunction with the rising of the level of HbAlc, the degree of IR increased significantly. HbA1c showed an association with early-phase insulin secretion assessed by insulinogenic index. Heianza et al. reported that elevated HbA1c levels of above 41 mmol/mol (>5.9%) were associated with a substantial reduction in insulin secretion and insulin sensitivity as well as an association with β-cell dysfunction in Japanese individuals without a history of treatment of diabetes. Increased accumulation of TG has been observed in human muscle tissue of obese and type 2 diabetic subjects, and associated with IR, which is in agreement with the present study. IR reduces the inhibition effect of lipolysis in adipose tissue, resulting in the increase of the free fatty acid (FFA) level in plasma.”

NLR is a superior biomarker

Although susceptible to modification by dehydration, elevated PSA or catecholamine release induced by exercise, the NLR is more sensitive than the neutrophil count alone or CRP levels.

“NLR represents a combination of two markers where neutrophils represent the active nonspecific inflammatory mediator initiating the first line of defense, whereas lymphocytes represent the regulatory or protective component of inflammation. NLR is superior to other leukocyte parameters (e.g., neutrophil, lymphocyte, and total leukocyte counts) because of its better stability compared with the other parameters that can be altered by various physiological, pathological, and physical factors. Thus, as a simple clinical indicator of IR, NLR is more sensitive compared with the neutrophilic granulocyte count and CRP levels, which are widely used as markers of IR.”

Clinical bottom line

Practitioners should not fail to make use of this significant, inexpensive biomarker that is under our noses every day. The authors sum it up:

“…in the present study, NLR serves an important function in predicting the risk of IR. IR in diabetic patients is related to chronic inflammation, and NLR may be helpful in assessing the prognoses of these patients…We recommend that the NLR values of diabetic patients be calculated as NLR is a cheap, predictive, and prognostic marker for IR. High NLR values were independently related to IR.”

Stroke risk reduced by magnesium

StrokeStroke risk is reduced by higher plasma magnesium levels according to data from 32,826 women in the Nurses’ Health Study presented in a paper just published in the journal Stroke. The authors note:

Lower plasma magnesium levels may be associated with higher blood pressure and endothelial dysfunction, but sparse prospective data are available for stroke.”

So they compared plasma magnesium in stroke cases with controls matched for age, race/ethnicity, smoking status, date of blood draw, fasting status, menopausal status, and hormone use. Women with magnesium levels* that I see in lab reports had a signficantly increased risk for stroke:

“Conditional on matching factors, women in the lowest magnesium quintile had a relative risk of 1.34 for total ischemic stroke compared with women in the highest quintile. Additional adjustment for risk factors and confounders did not substantially alter the risk estimates for total ischemic stroke. Women with magnesium levels <0.82 mmol/L* had significantly greater risk of total ischemic stroke (multivariable relative risk, 1.57) and thrombotic stroke (multivariable relative risk, 1.66) compared with women with magnesium levels ≥0.82 mmol/L. No significant effect modification was observed by age, body mass index, hypertension, or diabetes mellitus.”

Magnesium is an anti-inflammatory agent

Clinical key  point: Cardiovascular and cerebrovascular disease have a well-known inflammatory component. Besides lowering blood pressure and promoting healthy endothelial function, magnesium is ‘nature’s anti-inflammatory mineral’ that supports parasympathetic nervous system function with a calming, anti-spasmodic effect.

* Plasma magnesium <0.82 mmol/L = 2.0 mg/dL.

The authors conclude:

Lower plasma magnesium levels may contribute to higher risk of ischemic stroke among women.”

Magnesium, inflammation and endothelial function

American Journal of Clinical NutritionRegarding additional mechanisms by which magnesium status is linked to stroke and cardiovascular disease, a study published in the American Journal of Clinical Nutrition provides evidence that magnesium is important for endothelial (blood vessel lining) health:

“We conducted a cross-sectional study of 657 women from the Nurses’ Health Study cohort who were aged 43-69 y and free of cardiovascular disease, cancer, and diabetes mellitus when blood was drawn in 1989 and 1990. Plasma concentrations of C-reactive protein (CRP), interleukin 6 (IL-6), soluble tumor necrosis factor alpha receptor 2 (sTNF-R2), E-selectin, soluble intercellular adhesion molecule 1 (sICAM-1), and soluble vascular cell adhesion molecule 1 (sVCAM-1) were measured. Estimates from 2 semiquantitative food-frequency questionnaires, administered in 1986 and 1990, were averaged to assess dietary intakes.”

E-selectin recruits white blood cells to engage in the endothelial inflammatory process. The authors demonstrated a  role for magnesium significant for stroke:

“…magnesium intake was inversely associated with plasma concentrations of CRP, E-selectin, and sICAM-1. After further adjustment for physical activity, smoking status, alcohol use, postmenopausal hormone use, and body mass index, dietary magnesium intake remained inversely associated with CRP and E-selectin. Multivariate-adjusted geometric means for women in the highest quintile of dietary magnesium intake were 24% lower for CRP and 14% lower for E-selectin than those for women in the lowest quintile.”

Magnesium reduces CRP

Archives of Medical ResearchA recent study published in Archives of Medical Research also shows anti-inflammatory effect of magnesium in lowering CRP:

“It has been suggested that magnesium deficiency is associated with the triggering of acute phase response, which may contribute to type 2 diabetes and cardiovascular disease risk. We undertook this study to determine whether oral magnesium supplementation modifies serum levels of high-sensitivity C-reactive protein (hsCRP) in apparently healthy subjects with prediabetes and hypomagnesemia.”

The authors examined the effect of magnesium supplementation on 62 men and non-pregnant women aged 18–65 years who were newly diagnosed with prediabetes and hypomagnesemia (serum magnesium levels <0.74 mmol/L/1.8 mg/dL) for the effects of daily supplementation with magnesium in a double-blind placebo-controlled trial, leading to their conclusion…

Oral magnesium supplementation decreases hsCRP levels in apparently healthy subjects with prediabetes and hypomagnesemia.”

Nuts reduce inflammation and all-cause mortality

Asia Pacific Journal of Clinical NutritionNuts have been shown to confer multiple health benefits, so it’s disconcerting to see  some apparently popular paleo diet plans that forbid them. In the absence of a nut allergy it’s a shame to forgo the benefit of such a healthful and convenient food. The intent of the paleo diet is to reduce inflammation, so it’s worth considering a paper published in the Asia Pacific Journal of Clinical Nutrition offering evidence that nuts reduce inflammation. The authors note:

“Several large epidemiological studies have associated the frequency of nut consumption with reduced risk of coronary heart disease (CHD), CVD, myocardial infarction, sudden death, and all causes of mortality, Type 2 diabetes (T2D) and other chronic disease.

Nuts are anti-inflammatory

Key inflammatory markers including CRP and IL-6 are reduced by nut consumption:

“Epidemiological and clinical studies suggest that some dietary factors, such as n–3 polyunsaturated fatty acids, antioxidant vitamins, dietary fiber, L-arginine and magnesium may play an important role in modulating inflammation. The relationship observed between frequent nut consumption and the reduced risk of cardiovascular mortality and type 2 diabetes in some prospective studies could be explained by the fact that nuts are rich in all of these modulator nutrients. In fact, frequent nut consumption has been associated with lower concentrations of some peripheral inflammation markers in cross-sectional studies. Nut consumption has also been shown to decrease the plasma concentration of CRP, IL-6 and some endothelial markers in recent clinical trials.”

Nuts also benefit cholesterol and lipids

“In the last two decades, a considerable number of clinical trials have consistently demonstrated beneficial effects on blood lipids and lipoproteins, primarily a decrease in Low-density lipoprotein (LDL) cholesterol, a classical CHD risk factor. This effect has been demonstrated consistently in different population groups, using different types of nuts (walnuts, hazelnuts, almonds, pecan, pistachio and macadamia nuts) and study designs. The favourable effects of tree nuts or tree nut oils on plasma lipid and lipoprotein profiles is a mechanism that appears to account for some of the cardio protective effects observed in the epidemiological studies.”

Nuts and olive oil are a great combination for cardiovascular risk:

“…in a cross-sectional study we evaluated the association between components of the Mediterranean diet and circulating markers of inflammation in a large cohort of asymptomatic subjects with high risk of cardiovascular disease. Subjects with the highest consumption of nuts and virgin olive oil showed the lowest concentrations of VCAM-1, ICAM-1, IL-6 and CRP; although this difference was statistically significant for ICAM-1 only in the case of nuts and for VCAM-1 in the case of olive oil.”

After reviewing several other studies documenting improvements in inflammation and endothelial function the authors conclude:

“In conclusion, nuts are complex food matrices containing diverse nutrients and other chemical constituents that may favourably influence human physiology. These sub- stances may inhibit the activation of the innate immune system, probably by decreasing the production of proinflammatory cytokines such as CRP, IL-6, TNF-α or IL-18, and increase the production of antiinflammatory cytokines such as adiponectin. This may improve the proinflammatory milieu, which in turn ameliorates endothelial dysfunction at the vascular level, and ultimately decreases the risk of insulin resistance, type 2 diabetes and coronary heart disease. The capacity of nuts to modulate inflammation may explain at least in part why frequent nut consumption is associated with reduced risk of diabetes and cardiovascular disease in epidemiological studies.”

Nut consumption reduces total and cause-specific mortality

New England Journal of MedicineA paper published earlier this year in The New England Journal of Medicine add more extensive data presenting evidence that eating nuts reduces death from cancer, heart disease, respiratory disease and ‘all causes’.

“Observational and intervention studies of nut consumption have also shown reductions in various mediators of chronic diseases, including oxidative stress, inflammation, visceral adiposity, hyperglycemia, insulin resistance, and endothelial dysfunction. In prospective cohort studies, increased nut intake has been associated with reduced risks of type 2 diabetes mellitus, the metabolic syndrome, colon cancer, hypertension, gallstone disease, diverticulitis, and death from inflammatory diseases.”

To extend the data to encompass the effects of eating nuts and all causes of death the authors:

“…examined the association of nut consumption with total and cause-specific mortality in two large, independent cohort studies of nurses and other health professionals. These studies provide repeated measures of diet (including separate data on peanuts and tree nuts), extensive data on known or suspected confounding variables, 30 years of follow-up, and data on more than 27,000 deaths for analysis.”

Their data suggest that nuts are among the healthiest foods to eat:

“In two large prospective U.S. cohorts, we found a significant, dose-dependent inverse association between nut consumption and total mortality, after adjusting for potential confounders. As compared with participants who did not eat nuts, those who consumed nuts seven or more times per week had a 20% lower death rate. Inverse associations were observed for most major causes of death, including heart disease, cancer, and respiratory diseases. Results were similar for peanuts and tree nuts, and the inverse association persisted across all subgroups.”

Some nuts every day was the best:

“Our results are consistent with the findings in previous, smaller studies. The Adventist Health Study showed that, as compared with nut consumption less than once per week, consumption five or more times per week was associated with reduced total mortality among whites, blacks, and elderly persons, with hazard ratios ranging from 0.56 to 0.82. Similarly, a study of a U.K. cohort, the Iowa Women’s Health Study, the Netherlands Cohort Study, and an earlier analysis of the NHS all showed significant inverse associations between nut intake and total mortality. Finally, in a recent secondary analysis within the PREDIMED (Prevención con Dieta Mediterránea) trial, a hazard ratio for death of 0.61 (95% CI, 0.45 to 0.83) was found for consumption of more than three servings of nuts per week, as compared with no nut consumption.”

Bottom line: ‘paleo’ and ‘autoimmune’ paleo diets can be fine healing diets for many, but like everything else should not be applied dogmatically or in a ‘rubber stamp’, ‘one-size-fits-all’ manner. In the absence of allergy, the evidence supports the consumption of nuts as wholesome foods with anti-inflammatory and metabolic benefits, exactly what paleo diets intend to accomplish.

Type 2 diabetes risk associated with high normal serum calcium

Diabetes CareType 2 diabetes, characterized by impaired insulin action, is linked to elevated serum calcium according to a study just published in the journal Diabetes Care. The authors state:

Insulin resistance and secretion depend on calcium homeostasis. Cross-sectional studies have associated elevated serum calcium levels with markers of impaired glucose metabolism… The aim of the current study was to prospectively investigate the association between albumin-adjusted serum calcium concentrations and type 2 diabetes in subjects at high cardiovascular risk.”

They collected data for 7447 men (aged 55 to 80 years) and women (aged 60 to 80 years) at high cardiovascular risk, including 707 individuals who did not have diabetes at baseline over an average of 4.8 years and found a significant correlation between type 2 diabetes and higher serum calcium:

An increase in serum calcium levels during follow-up was related to an increased risk of diabetes. In comparison with individuals in the lowest tertile (−0.78 ± 0.29 mg/dL), the hazard ratio (HR) and 95% CI for diabetes incidence in individuals in the higher tertile of change (0.52 ± 0.13 mg/dL) during follow-up was 3.48. When albumin-adjusted serum calcium was analyzed as a continuous variable, per 1 mg/dL increase, the HR of diabetes incidence was 2.87. These associations remained significant after individuals taking calcium supplements or having calcium levels out of normal range had been excluded.

In other words, even with albumin-adjusted serum calcium, for every 1 mg/dL increase there was a 287% increase in the risk for type 2 diabetes. Note that this refers to ‘high normal’ levels of serum calcium, and that calcium supplements had no role.

Medscape Medical News quoted study co-author Mònica Bulló, PhD, professor in the Faculty of Medicine and Health Sciences at the Universitat Rovira i Virgili, Reus, Spain:

“Measurement [of serum calcium] could add significance to measurement of fasting glucose…Calcium is involved in several metabolic pathways, and it is important to integrate all of them. However, our results suggest that [one consider] calcium levels as a risk factor for the development of T2D [as] an additional tool for clinicians in the management of the population at risk.”

The authors’ conclusion should be borne in mind by practitioners involved in case management of individuals with indications of insulin resistance commonly associated with cardiovascular and type 2 diabetes risk:

An increase in serum calcium concentrations is associated with an increased risk of type 2 diabetes in individuals at high cardiovascular risk.”

Thyroid in heart, metabolism, brain, kidney; vital importance of T3

The American Journal of MedicineNote: Scroll to the bottom of this post for an ‘executive summary.’

Thyroid disorders have widespread impact and although subclinical hypothyroidism and low triiodothyronine (T3) syndrome are common they are frequently overlooked in practice.

Thyroid function is very important for cardiovascular health. The authors of freshly published paper in The American Journal of Medicine remind readers:

Thyroid hormones modulate every component of the cardiovascular system necessary for normal cardiovascular development and function. When cardiovascular disease is present, thyroid function tests are characteristically indicated to determine if overt thyroid disorders or even subclinical dysfunction exists.”

The authors apparently rely on TSH as do many others, but in my opinion and as subsequent papers illustrate, this can result in many missed diagnoses…

“As hypothyroidism, hypertension and cardiovascular disease all increase with advancing age monitoring of TSH, the most sensitive test for hypothyroidism, is important in this expanding segment of our population. A better understanding of the impact of thyroid hormonal status on cardiovascular physiology will enable health care providers to make decisions regarding thyroid hormone evaluation and therapy in concert with evaluating and treating hypertension and cardiovascular disease.”

This includes the…

“…potential role of overt and subclinical hypothyroidism and hyperthyroidism in a variety of cardiovascular diseases.”

 

The Annals Of Thoracic SurgeryMore inspiration to  not overlook the widespread occurrence and clinical importance of low T3 (triiodothyronine, the ‘active’ thyroid hormone) is offered in a study just published in The Annals of Thoracic Surgery differentiates low triiodothyronine syndrome from gross hypothyroid in the context of coronary artery disease.

“There is strong clinical and experimental evidence that altered thyroid homeostasis negatively affects survival in cardiac patients, but a negative effect of the low triiodothyronine (T3) syndrome on the outcome of coronary artery bypass grafting (CABG) has not been demonstrated. This study was designed to evaluate the prognostic significance of low T3 syndrome in patients undergoing CABG.”

The authors evaluated 806 consecutive CABG patients for any effect of baseline free T3 (fT3) concentration and of preoperative low T3 syndrome (fT3 <2.23 pmol/L) on the risk of low cardiac output (CO) and death, finding a significant association:

“There were 19 (2.3%) deaths, and 64 (7.8%) patients experienced major complications. After univariate analysis, fT3, low T3, New York Heart Association class greater than II, low left ventricular ejection fraction (LVEF), and emergency were associated with low CO and hospital death…At multivariate analysis, only fT3, low T3, emergency, and LVEF were associated with low CO, and fT3 and LVEF were the only independent predictors of death.”

They summarize these striking results in their conclusion:

“Our study demonstrates that low T3 is a strong predictor of death and low CO in CABG patients. For this reason, the thyroid profile should be evaluated before CABG, and patients with low T3 should be considered at higher risk and treated accordingly.”

 

Acta CardiologicaIn this vein a very interesting paper was published in the journal Acta Cardiologica (Official Journal of the Belgian Society of Cardiology) that identifies low free (bioactive) T3 as a contributor to the development of cardiac dysfunction. The authors outline their intent:

“A low T3 syndrome was described in patients with heart failure (HF), and it appears to be associated with adverse outcome, representing an independent predictor of mortality. However, it is not known if low T3 levels contribute to the pathophysiology of HF. On the other hand, it has been seen that an elevation of brain natriuretic peptides (BNP and NT-proBNP) may represent a warning signal for future cardiovascular disease and may be an early marker of diastolic dysfunction. Therefore we tested the hypothesis that low levels of free-triiodothyronine (FT3) are sufficient to determine an increased concentration of the amino-terminal fragment of pro-brain natriuretic peptide (NT-proBNP), as the result of an initial and asymptomatic cardiac impairment.”

They evaluated thyroid function and measured NT-proBNP in 52 consecutive non-cardiac patients. Dividing them into a low T3 group (19 patients) and a normal T3 group (33 patients) they found…

“The median NT-proBNP concentration of patients with low T3 syndrome was significantly higher than in those with normal FT3 (370 vs. 120 pg/ml). There is a strong and inverse correlation between FT3 and Log NT-proBNP (R = -0.47); this relation persists in a multivariable regression analysis, after adjustment for other potentially confounding variables.”

The authors articulate the clinical significance in their conclusion:

“In absence of overt cardiovascular disease, patients with low T3 syndrome present an increased concentration of NT-proBNP. These data suggest that low FT3 levels may be a contributing factor for the development of cardiac dysfunction.”

 

European Journal of Clinical InvestigationThe same syndrome of subclinical low thyroid manifesting as low T3 applies to stroke as well according to a study published in the European Journal of Clinical Investigation. The authors state:

Low triiodothyronine (T3) has been associated with increased short-term mortality in intensive care unit patients and long-term mortality in patients with heart disease. The objective of this study was to investigate possible associations of thyroid hormone status with clinical outcome in patients admitted for acute stroke.”

Considering T3 values ≤ 78 ng dL (1·2 nmol L as ‘low T3’ and T4 values ≤ 4·66 µg dL (60 nmol L) were as ‘low T4′, they examined data for 737 consecutive patients with acute first ever stroke within 24 hours of onset. They measured total T3, thyroxin (T4) and thyroid-stimulating hormone (TSH) levels and evaluated the basic clinical characteristics, stroke risk factors, and brain imaging. Low thyroid (T3) turned out to be a significant predictor:

“Four hundred and seventeen (56%) patients had T3 values ≤ 78 ng dL−1 and 320 had normal T3 values. The 1-year mortality was 27·34% for low T3 and 19·37% for normal T3 cases. A smaller percentage of patients with low T3 values were independent at 1 year compared to those with normal T3 values [54·2% vs. 68·7%, odds ratio (OR) = 0·53]. Cox regression analysis revealed that increased age, haemorrhagic stroke, low Scandinavian Stroke Scale score, increased glucose and low T3 values (hazards ratio 0·69) were significant predictors of 1-year mortality.”

Clinicians should bear in mind the authors’ conclusion about low T3 thyroid syndrome and stroke:

“A high proportion of patients with acute stroke were found soon after the event with low T3 values. The low-T3 syndrome is an independent predictor of early and late survival in patients with acute stroke, and predicts handicap at 1 year.”

 

Saudi Medical JournalA valuable paper published in the Saudi Medical Journal offers evidence that low T3 is the strongest correlate of suboptimal thyroid function with metabolic syndrome and insulin resistance. The authors determined to…

“…determine the association between thyroid hormones, insulin resistance, and metabolic syndrome in euthyroid women.”

They examine forty-five women free of past medical conditions by estimating body fat and measuring fasting blood for total triiodothyronine (T3), total thyroxine (T4), thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), lipids, insulin, and glucose. T3 turned out to be a much more significant indicator than T4:

“The mean age of the participants was 32.6 +/= 9.6 years with a body mass index (BMI) of 29.9 +/= 3.8 kg/m2. Evidence of homeostasis model assessment index for insulin resistance (HOMA-IR) more than 3 was seen in 34 (75%) and metabolic syndrome in 29 (64%) participants. Total T3 showed a positive correlation with triglycerides, low density lipoprotein- cholesterol (LDL-C), total cholesterol, insulin, HOMA-IR and negatively with body fat. Thyroid-stimulating hormone correlated positively with BMI, insulin, HOMA-IR, LDL-C and negatively with HDL-cholesterol (p<0.05). Free triiodothyronine correlated positively with waist circumference and T4 did not correlate with metabolic syndrome parameters.”

The authors conclude:

“Our preliminary data show an association between thyroid hormones and some components specific of the metabolic syndrome in euthyroid women. Total triiodothyronine and TSH correlated more with variables of metabolic syndrome than FT3 and T4.”

 

Endocrine JournalLow-grade systemic inflammation is a common denominator of aging and almost every chronic disease. It is, of course, a key factor in both type 2 diabetes and thyroid disorders. A study published recently in the Endocrine Journal (Japan Endocrine Society) demonstrates the association of type 2 diabetes with low T3 in the context of low-grade systemic inflammation:

“Previous reports highlight the role of systemic inflammation in the genesis of non-thyroidal illness syndrome and type 2 diabetes mellitus (T2DM). Our objective was to assess whether body mass index and the low-grade systemic inflammation would be associated with changes in thyroid hormone metabolism in patients with type 2 diabetes.”

They examined data for 104 subjects, half with type 2 diabetes and half comprised a control group who were paired by age, gender and body mass index. They measured total (T) and free (F) thyroxine (T4) and triiodothyronine (T3), reverse T3 (rT3), the ratios FT3/rT3, FT3/FT4 and FT4/rT3, and obtained additional data on diabetes duration and complications, body mass index, waist circumference, hypertension, HbA1c, and high sensitivity C-reactive protein. T3 stands out here as well:

“Patients with DM presented lower levels of TT4, TT3 and FT3 and higher of FT4, waist circumference and C-reactive protein. Body mass index was inversely correlated with FT4 and TT3. C-reactive protein was positively correlated with rT3 and inversely with FT4/rT3 and FT3/rT3. Body mass index was an independent predictor for FT4 and TT3 levels. Inflammation predicted the FT4/rT3 ratio. C-reactive protein and body mass index were independent predictors for rT3.”

Clinical note: this implies that thyroid assessment is incomplete if it doesn’t include at least free and total T3 and T4 (along with TSH). The authors conclude with a statement of great significance because it is so common to encounter in clinical practice:

“In conclusion, type 2 diabetes was associated with a low T3 state. Body mass index and the low-grade systemic inflammation are related to the non-thyroidal illness syndrome in these patients, possibly by altering the activity of peripheral deiodinases.”

I find low-grade systemic inflammation impairment of the activity of deiodinase enzymes to convert T4 into the metabolically active T3 regularly in my patient population.

 

Journal of Clinical Endocrinology & MetabolismMore complete assessment of seemingly euthyroid (‘normal’ thyroid) patients is often dismissed with the  test data limited meagerly to TSH and total T4 levels, a practical flaw that likely fails to uncover many diagnoses. In a study published in the Journal of Clinical Endocrinology & Metabolism, the authors demonstrate that ‘low normal’ free T4 correlated significantly with metabolic syndrome and cardiovascular risk factors. The authors state:

“Thyroid disease and the metabolic syndrome are both associated with cardiovascular disease…The aim of this study was to explore the hypothesis that thyroid function, in euthyroid subjects, is associated with components of the metabolic syndrome, including serum lipid concentrations and insulin resistance.”

They assessed data for 2703 euthyroid adult subjects that included homeostasis model assessment for insulin resistance (HOMA-IR and usual criteria for metabolic syndrome:

“After adjustment for age and sex, free T4 (FT4) was significantly associated with total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglycerides. Both FT4 and TSH were significantly associated with HOMA-IR. Median HOMA-IR increased from 1.42 in the highest tertile of FT4 to 1.66 in the lowest tertile of FT4. FT4 was significantly related to four of five components of the metabolic syndrome (abdominal obesity, triglycerides, high-density lipoprotein cholesterol, and blood pressure), independent of insulin resistance.”

Clinical note: so-called euthyroid = ‘normal’ thyroid or ‘subclinical hypothyroid’ must not be overlooked in case management of metabolic syndrome and cardiovascular risk. The authors conclude by asserting:

“We have demonstrated an association between FT4 levels within the normal reference range and lipids, in accordance with the earlier observed association between (sub)clinical hypothyroidism and hyperlipidemia. Moreover, low normal FT4 levels were significantly associated with increased insulin resistance. These findings are consistent with an increased cardiovascular risk in subjects with low normal thyroid function.”

 

Metabolic Syndrome and Related DisordersMore on T3 and metabolic syndrome was presented in a study published in the journal Metabolic Syndrome and Related Disorders (yes, there is a journal by that title) in which the authors examined date for 211 patients with a mean age of about 40 years who had a body mass index (BMI) >30 kg/m(2) without any other hormonal disorder related to obesity. Measurements included fasting blood glucose (FBG), insulin, insulin resistance (HOMA-IR),total cholesterol, triglycerides, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), thyroid-stimulating hormone (TSH), total triiodothyronine (TT3), total thyroxine (TT4), free T3 (FT3), and free T4 (FT4). They used TSH cutoff value of 2.5 mU/L. Sure enough T3 stood out:

Metabolic syndrome positive patients had significantly higher FBG, triglycerides, FT4, systolic (SBP) and diastolic blood pressure (DBP), and statistically lower HDL-C and FT3/FT4 ratio than metabolic syndrome negative patients. TSH decreased with age and was not related with any metabolic syndrome parameters. The FT3/FT4 ratio negatively correlated with FBG, triglycerides, SBP, and DBP; TT3 positively correlated with HOMA-IR, FBG, and waist circumference.”

In other words, as free T3 went down in relation to free T4 fasting blood glucose, triglycerides, and both systolic and diastolic blood pressure went up. And as total T3 went down insulin resistance, fasting blood glucose and waist circumference went up. The authors conclude:

“”Metabolic syndrome parameters (except HDL) correlated with TT3, FT4, and the FT3/FT4 ratio. FT4 levels were associated with obesity and metabolic syndrome independently of insulin resistance, whereas TT3 levels were associated with both insulin resistance and metabolic syndrome. This relationship can be explained by compensatory effects of TT3, and probably FT4, on energy expenditure and thermogenesis in obese people.”

 

Journal of Clinical InvestigationAt the crux of the matter is the manner in which low grade chronic inflammation impairs conversion of the relatively inactive T4 thyroid hormone to the active T3. The authors of a very valuable paper published in The Journal of Clinical Investigation shed light on an important mechanism by describing the role of the pro-inflammatory cytokine IL-6.

Nonthyroidal illness syndrome (NTIS) is a state of low serum 3,5,3′ triiodothyronine (T₃) that occurs in chronically ill patients; the degree of reduction in T₃ is associated with overall prognosis and survival. Iodthyronine deiodinases are enzymes that catalyze iodine removal from thyroid hormones; type I and II deiodinase (D1 and D2, respectively) convert the prohormone thyroxine T₄ to active T₃, whereas the type III enzyme (D3) inactivates T₄ and T₃. Increased production of cytokines, including IL-6, is a hallmark of the acute phase of NTIS.”

They investigated this by measuring the effect of IL-6 the different types deiodinase activities in human cell lines. (Recall that deiodinase enzyme activity is required to convert T4 to T3.) Their results reveal not only the role of pro-inflammatory IL-6, but implicate glutathione (GSH) as a likely key factor:

Active T₃ generation by D1 and D2 in intact cells was suppressed by IL-6, despite an increase in sonicate deiodinases (and mRNAs). N-acetyl-cysteine (NAC), an antioxidant that restores intracellular glutathione (GSH) concentrations, prevented the IL-6-induced inhibitory effect on D1- and D2-mediated T₃ production, which suggests that IL-6 might function by depleting an intracellular thiol cofactor, perhaps GSH. In contrast, IL-6 stimulated endogenous D3-mediated inactivation of T₃.”

The authors’ conclusion contains comments of great clinical significance:

“In conclusion, our findings demonstrated that pathophysiologically relevant concentrations of IL-6 reduce D1 and D2 function and increase that of D3, providing a single mechanistic explanation for the decreased serum T3 and increased rT3 observed in the acute phase of NTIS. The decrease in D1 will both reduce plasma T3 production and impair rT3 deiodination, while the decrease in D2 will supplement this by impairing intracellular T4-to-T3 conversion. On the other hand, the increased D3 protein, which has its function preserved by its more ready access to GSH (or other extracellular reducing agents), will further decrease plasma T3 and increase the production of rT3 from T4. The general increase in the cellular deiodinase proteins is caused by a combination of IL-6–induced ROS (also found with H2O2) and specific activation of JAK/STAT pathways by this cytokine.”

In a larger context…

“Although other factors in sick patients may also contribute to NTIS, these observations and unifying hypothesis represent a major step forward in unraveling this longstanding enigma, leading to what we believe to be a previously unrecognized combinatorial pathway that may be viewed largely as a general response to oxidative stress. Our results therefore suggest that rather than a protective or a maladaptive process, the changes in plasma T4, T3, and rT3 are a consequence of cellular stress. Whether antioxidants, such as NAC, could be beneficial as an adjuvant therapy together with other therapeutic measures in critically ill patients remains to be evaluated.”

 

Nephrology Dialysis TransplantationFurther insight into the nature of the low T3 in thyroid dysregulation associated with chronic disease is offered in a study published in the journal Nephrology Dialysis Transplantation on chronic kidney diseae (CKD) and low T3. These authors observe:

“The evaluation of thyroid function in systemic illness remains complex because the changes occur at all levels of the hypothalamic-pituitary-thyroid axis. During illness, a decrease in triiodothyronine (T3) and pulsatile thyroid-stimulating hormone (TSH) release and increases in reverse T3 occur. This constellation of findings is termed the low T3 syndrome, the euthyroid sick syndrome or non-thyroid illness. Low T3 syndrome is the most common manifestation in non-thyroid illness and this phenomenon has been believed to be due to inhibition of 5′-deiodinase, which is a catalyzing enzyme for production of T3 from circulating T4. To date, a variety of alterations in thyroid hormone levels and metabolism have been reported in patients with chronic renal failure and low T3 has been consistently found to be the most common disturbance.”

Of widespread importance:

“Several lines of evidence suggested that low T3 was an independent predictor of survival in various illness states. Furthermore, the recent data proposed that biomarkers of inflammation were associated with low T3 levels in haemodialysis and peritoneal dialysis patients and thyroid dysfunction might be implicated in the pathogenetic pathway which link microinflammation to survival in dialysis patients.”

They determined to see if low T3 correlated to chronic kidney disease prior to the stage of dialysis:

“However, there are no data about the prevalence of low T3 in persons with chronic kidney disease (CKD) who do not require maintenance dialysis. We hypothesized that the prevalence of low T3 would be increased according to the increase of a CKD stage. This study was performed to explore the prevalence in each stage of CKD and relationship with eGFR.”

Their data on 2284 subjects with normal serum TSH and not taking thyroid hormones confirmed their hypothesis, leading to the conclusion:

“This study showed that low T3 syndrome was highly prevalent in CKD and was a remarkable finding in early CKD. Furthermore, serum T3 levels were associated with severity of CKD even in the normal TSH level.”

 

Iranian Journal of Kidney DiseasesAlong these lines a study showing that low T3 in various conditions including CKD is linked to systemic low grade inflammation reflected in altered cytokines was published in the Iranian Journal of Kidney Diseases. The authors evaluated the interleukins (IL) IL-6 and IL-10 and euthyroid sick syndrome (ESS) in patients with nonthyroidal illnesses (NTI) including chronic kidney disease (CKD), congestive heart failure (CHF), or acute myocardial infarction (MI) while measuring serum levels of IL-6 and IL-10, thyroid stimulating hormone (TSH), total T4, and T3:

“In the 60 patients with NTI, we detected a significantly lower T3 and T4 levels compared to controls, while TSH level was within the reference range. Also, IL-6 level was substantially higher than that in controls and correlated with T3 and T4. Similarly was IL-10 level that correlated with T3, but not with T4. The ILs correlated positively with each other. Only IL-6 was a predictor of low T3. The proportion of patients with subnormal T3, T4, and TSH levels was highest in those with MI along with greatest IL-6 and IL-10 levels compared to patients with CHF and CKD. Patients with CKD showed the least disturbance in IL-6 and IL-10 despite the lower levels of T3, T4, and TSH in a higher proportion of them compared to patients with CHF.”

Their discussion of these results contains some key points for clinicians:

“In the current study, we observed a considerably lower serum T3 and total T4 concentrations, signifying thyroid dysfunction, in patients with variable NTIs, while serum TSH showed a mean value that was not significantly different from that in the healthy controls…In this study, we detected a substantially high level of the pro-inflammatory cytokine, IL-6, in patients with NTI, supporting its possible role as an endocrine cytokine with a regulatory effect on many endocrine systems including the thyroid gland.”

Here is something readers who test cytokines may have seen too that illustrates a fundamental principal in case management and disease progression: suppression of receptors due to chronically high levels of signaling agents (in this case anti-inflammatory IL-10):

We also detected a considerably high level of the anti-inflammatory cytokine, IL-10 in the patients with NTI.Therefore, within the cytokine network, activation of pro-inflammatory mediators such as IL-6 is followed by increased production of endogenous inhibitory molecules including the antagonistic cytokine IL-10 in an attempt to suppress release of pro-inflammatory cytokines. This dimorphic response may be related to macrophages resistance to the suppressive effect of IL-10 as a result of down-regulation of the expression of soluble IL-10 receptors. The high IL-10 levels was hoped for to minimize the deleterious effect of the raised IL-6. Taniguchi and colleagues highlighted this potential protective effect of IL-10 in their 25 patients with systemic inflammatory states…In this study, the suppressed thyroid hormones were inversely associated with serum IL-6 elevations.”

There was a particularly strong association with heart attacks (MI), consonant with the degree of thyroid dysfunction tracking the severity of non-thyroidal illness:

“We observed a highest level of IL-6 along with lowest measurements of both serum T3 and serum T4 in the patients with MI, while the least changes were noticed in patients with chronic illness exemplified by CHF. This is in accordance with the hypothesis that the magnitude of thyroid hormones’ alteration parallels the severity of the associated NTI.”

 

Clinical note: It is very important for practitioners to bear in mind that thyroid effect, in addition to thyroid hormone production and conversion, encompasses thyroid hormone transporters and receptors. The felt metabolic and brain effects of thyroid activation depends on all of these. Failing to take them into consideration is a common reason why ‘subclinical hypothyroidism’, NTIS (nonthyroidal illness syndrome) or ESS (euthyroid sick syndrome) is often overlooked.

Journal of Molecular EndocrinologyA paper published in the Journal of Molecular Endocrinology sheds light on the role of MCT8, MCT10, organic anion transporting polypeptides (OATP) transporters:

“Thyroid hormone is a pleiotropic hormone with widespread biological actions. The follicular cells of the thyroid gland produce predominantly thyroxine (T4), but it is mainly 3,3′,5-tri-iodothyronine (T3) that binds to the nuclear thyroid hormone receptor. The biological activity of T3 is therefore largely determined by the intracellular T3 concentration which is dependent on a) the circulating T3 concentration; b) the transport of thyroid hormone across the cell membrane; and c) the presence of iodothyronine deiodinases, which activate or inactivate thyroid hormone. To date, three deiodinases have been characterized as homologous selenoproteins. Both D1 and D2 converts T4 to T3, whereas D3 catalyzes the degradation of T4 to reverse T3 (rT3) and of T3 to 3,3′-T2.”

The enzymes that convert T4 to T3 have their active portions inside the cell, and transporters are required to get T4 through the cell membrane into the cytoplasm where the action happens:

“The deiodinases are membrane proteins with their active sites located in the cytoplasm. Therefore, transport across the cell membrane is essential for thyroid hormone action and metabolism. Based on the lipophilic structure of thyroid hormones, it is long thought that thyroid hormone enters the cell through passive diffusion. However, it has become increasingly clear that there are specific thyroid hormone transporters, and that the activity of these transporters in part determines the intracellular thyroid hormone concentration.”

Thyroid hormone transporters MCT8 and MCT10Transporters MCT8, MCT10 and OATP have been the most studied:

“To date, several transporters with high affinity for thyroid hormone, but with different tissue distributions and ligand affinities have been identified. This review will focus on the molecular aspects of the monocarboxylate transporter 8 (MCT8) and MCT10, and several members of the organic anion transporting polypeptide (OATP) family…both MCT8 and MCT10 increase the intracellular availability of iodothyronines, as evidenced by the marked increase in their intracellular deiodination by co-transfected deiodinases. However, both MCT8 and MCT10 facilitate not only the cellular uptake but also the efflux of iodothyronines.”

In other words, they get necessary thyroid stuff both into and out of the cell. These transporters are subject to genetic variation of course, and some mutations in the MCT8 gene can cause severe psychomotor retardation:

Mutations in the MCT8 gene cause a syndrome of severe psychomotor retardation and high serum T3 levels in affected male patients, known as the Allan–Herndon–Dudley syndrome. The neurological deficits are probably explained by an impeded uptake of T3 in MCT8-expressing central neurons and, hence, an impaired brain development. This has been reviewed in detail elsewhere. Since mutations in the MCT8 gene have such profound effects, the question arises whether small changes in the MCT8 gene may affect transport activity as well.”

Such as depression, etc. The implication is that much milder disruption of MCT8 transporter function can significantly diminish metabolism in the brain that impairs cognition and mood. The authors conclude their lengthy paper detailing the action of other transports with comments of great clinical significance:

“…it has become clear that thyroid hormone requires active transport across cell membrane to carry out its biological functions…It is surprising that few studies have been published investigating the association of polymorphisms in these transporters with serum thyroid parameters or thyroid hormone-related endpoints, especially since polymorphism studies have yielded new insights into the role of thyroid hormone in several processes in the human body. For instance, a genome-wide linkage scan identified the type 2 deiodinase as a susceptibility locus for osteoarthritis. In addition, genetic variation seems to play a role in psychological well-being…”

 

Thyroid ResearchThe authors of a paper published in the journal Thyroid Research chime in with an expansion of these observations:

Thyroid hormones are of crucial importance for the functioning of nearly every organ. Remarkably, disturbances of thyroid hormone synthesis and function are among the most common endocrine disorders affecting approximately one third of the working German population. Over the last ten years our understanding of biosynthesis and functioning of these hormones has increased tremendously. This includes the identification of proteins involved in thyroid hormone biosynthesis like Thox2 and Dehal where mutations in these genes are responsible for certain degrees of hypothyroidism. One of the most important findings was the identification of a specific transporter for triiodothyronine (T3), the monocarboxylate transporter 8 (MCT8) responsible for directed transport of T3 into target cells and for export of thyroid hormones out of thyroid epithelial cells.”

They remind of the role of thyroid dysregulation in depression and dementia:

“Disturbed TH action is linked with major health problems especially in critical life phases such as development, disease or ageing. Thus, lack of TH action in the adult brain causes impaired neuro-cognitive function and psychiatric states such as severe depression and dementia. Not only hypothyroidism but also hyperthyroidism affects the CNS and frequently results in agitation, increased irritability and dysregulation of body temperature.”

Cardiovascular disease can also have a thyroid component:

“There is ample epidemiological evidence that both, hyper- and hypothyroidism confer an increased risk for cardiovascular morbidity(e.g. arrhythmia, heart failure and stroke) and mortality.”

Interestingly in regard to obesity:

“Besides the classic hormones T4 and T3 new data demonstrate that the rare thyroid hormone metabolite 3,5-T2 is effective in the prevention of high fat diet-induced adiposity and prevents hepatic steatosis, however, without exerting the severe side effects on the cardiac system that have been observed with T3-based treatments. The vital importance of thyroid hormones for regulation of thermogenesis and for maintenance of the homeostasis of the mitochondrial energy metabolism has long been established. However, the functional interactions between the activities of uncoupling proteins (UCP) which are triggered by T3 and catecholamines affecting brown adipose tissue (BAT) as well as skeletal muscle of the adult, provide new possibilities for therapeutic intervention in obesity that have only recently become apparent.”

Old and new concepts of thyroid hormone actionThey summarize a ‘bird’s-eye’ view of hormone physiology:

“Thus in the present concept of thyroid hormone action, the cellular thyroid hormone status is defined by thyroid hormone transporters, thyroid hormone membrane receptors, thyroid hormone molecules and TAM mediated actions.

There is no question that aging increases the tendency to subclinical hypothyroid conditions:

“Epidemiology has shown unequivocally that with age the ratio of subclinical to clinically manifest thyroid disorders increases, thus thyroid disorders are a disease of the ageing population. In light of the demographic changes of our societies, improvements of human health care systems should not be limited to better management of only cardiovascular disorders, cancer, and neurodegenerative diseases. We believe that modern and future-oriented health politics and policy making institutions need to take an endocrine organ into account that has been known for decades, but is still not fully “revealed”, the thyroid gland.”

 

Journal of EndocrinologyAppreciation of the weighty influence of the MCT8 transporter is enhanced by recognition of its role in the global neurological impairment of intrauterine growth restriction (IUGR) as described in a study published in the Journal of Endocrinology:

Intrauterine growth restriction (IUGR) describes the failure of a fetus to attain its genetically determined growth potential, with the most common underlying etiology being uteroplacental failure associated with abnormal placental development. IUGR is often characterized by continued head and brain growth at the expense of other less vital organs resulting in an elevated brain:liver weight ratio postnatally. IUGR complicates 5–10% of pregnancies and is associated with increased perinatal mortality. Survivors demonstrate an increased prevalence of cognitive impairment compared with babies born appropriately grown for gestational age.”

They measured changes in cortical MCT8 expression with IUGR by immunohistochemistry performed on brain sections obtained from appropriately grown for gestational age (AGA) human fetuses and MCT8 immunostaining in the occipital cortex of stillborn IUGR human fetuses which was compared with that in the occipital cortex of gestationally matched AGA fetuses:

“When complicated by IUGR, fetuses showed a significant fivefold reduction in the percentage area of cortical plate immunostained for MCT8 compared with AGA fetuses… Cortical MCT8 expression was negatively correlated with the severity of IUGR indicated by the brain:liver weight ratios at post-mortem. Our results support the hypothesis that a reduction in MCT8 expression in the IUGR fetal brain could further compromise TH-dependent brain development…This study is the first to demonstrate significantly reduced cortical MCT8 expression within the developing CNS of human fetuses stillborn with severe IUGR. Our results suggest that altered TH transporter activity in cerebral neurons could be a contributory factor to the pathophysiology of neurodevelopmental impairment associated with IUGR.”

 

Molecular and Cellular EndocrinologyAs described in an earlier post (Depression, aging and brain inflammation: indications for sustainable treatment) there is evidence that the global driving factor of biological aging is inflammation in the hypothalamus, practitioners doing case management of thyroid conditions should know the importance of thyroid hormone feedback in the hypothalamus and pituitary as described in a paper published in Molecular and Cellular Endocrinology:

“A major change in thyroid setpoint regulation occurs in various clinical conditions such as critical illness and psychiatric disorders. As a first step towards identifying determinants of these setpoint changes, we have studied the distribution and expression of thyroid hormone receptor (TR) isoforms, type 2 and type 3 deiodinase (D2 and D3), and the thyroid hormone transporter monocarboxylate transporter 8 (MCT8) in the human hypothalamus and anterior pituitary.”

Their examination of these agents through immunoreactivity and immunostaining revealed important activity of hypothalamic glial cells:

“These findings suggest that the prohormone thyroxine (T4) is taken up in hypothalamic glial cells that convert T4 into the biologically active triiodothyronine (T3) via the enzyme D2, and that T3 is subsequently transported to TRH producing neurons in the PVN. In these neurons, T3 may either bind to TRs or be metabolized into inactive iodothyronines by D3. By inference, local changes in thyroid hormone metabolism resulting from altered hypothalamic deiodinase or MCT8 expression may underlie the decrease in TRH mRNA reported earlier in the PVN of patients with critical illness and depression.”

The pituitary, of course, also comes into play:

“In the anterior pituitary, D2 and MCT8 immunoreactivity occurred exclusively in folliculostellate (FS) cells. Both TR and D3 immunoreactivity was observed in gonadotropes and to a lesser extent in thyrotropes and other hormone producing cell types.”

The authors summarize their results:

“Based upon these neuroanatomical findings, we propose a novel model for central thyroid hormone feedback in humans, with a pivotal role for hypothalamic glial cells and pituitary FS cells in processing and activation of T4. Production and action of T3 appear to occur in separate cell types of the human hypothalamus and anterior pituitary.”

 

Pediatric Endocrinology ReviewsHormone receptors are a critical link in the signaling chain for thyroid as for other hormones and neurotransmitters. Receptor function can be impaired by elevated hormone levels, genetic mutation and chronic inflammation. A paper published in Pediatric Endocrinology Reviews serves as a reminder to consider thyroid hormone receptor function in case management:

The important physiological actions of the thyroid hormones are mediated by binding to nuclear thyroid hormone receptors (TRs), encoded by two genes TRalpha and TRbeta. These receptors act as hormone-dependent transcription factors by binding to DNA motifs located in the regulatory regions of target genes…”

Receptor resistance to thyroid hormones can cause a hypothyroid state in the presence of normal TSH and thyroid hormone levels:

“TRbeta gene mutations cause resistance to thyroid hormones (RTH), characterized by inappropriately high thyroid-stimulating hormone (TSH) levels due to lack of feedback inhibition of thyroid hormones on the hypothalamus and pituitary gland, and to reduced sensitivity of other TRbeta target tissues to thyroid hormones. Very recently, patients heterozygous for TRalpha mutations have been identified. These patients exhibit clinical symptoms of hypothyroidism in TRalpha target tissues such as intestine or heart and near normal circulating TSH and thyroid hormone levels.”

 

Nephrology Dialysis TransplantationChronic low-grade inflammation, also termed micro-inflammation, is an almost universal ‘fact of life’ in chronic disorders and aging. Its link to peripheral thyroid resistance and low T3 is seen in high magnification in Nephrology Dialysis Transplantation in which the authors observe its role in continuous ambulatory peritoneal dialysis (CAPD) patients with end-stage renal disease (ESRD):

Low T3 is a frequent alteration in patients with ESRD. This derangement has been recently linked to inflammation in haemodialysis patients. Whether this association holds true in peritoneal dialysis patients has not been studied…We investigated the relationship between low-grade inflammation [IL-6, C-reactive protein (CRP) and serum albumin levels] and free tri-iodothyronine (fT3) in a cohort of 41 CAPD patients without heart failure and inter-current illnesses.”

 

They found multiple correlations, including low free T3 as a predictor of mortality:

“CAPD patients had lower fT3 levels than healthy subjects of similar age. Free T3 levels were directly related to those of serum albumin and inversely to IL-6 and CRP. Age, haemoglobin levels and diastolic blood pressure were also related to fT3. In multiple regression models adjusting for all variables related to fT3, CRP and albumin were retained as independent correlates of fT3…Plasma fT3 levels were lower in patients who died compared with survivors. In Cox analyses, fT3 was a significant predictor of mortality independent of the main traditional as well as non-traditional risk factors.”

 

The association of micro-inflammation and low free T3 noted by the authors likely applies to numerous other conditions:

“The relationship between fT3, CRP and serum albumin suggests that inflammation–malnutrition might be involved in the low T3 syndrome in CAPD patients. Thyroid dysfunction might be implicated in the pathogenic pathway which links micro-inflammation to survival in PD patients.”

 

Journal of Endocrinological InvestigationClinicians should also keep in mind that low T3 can be the only thyroid abnormality contributing to psychiatric depression. A paper published in the Journal of Endocrinological Investigation focuses on the link between low T3 syndrome and depression.

“In euthyroid sick syndrome [non-thyroidal illness (NTI)], a number of investigators have described TSH and serum thyroid hormone abnormalities, low T3, low T3 and T4, increased T4, low TSH, etc. Those cases of NTI where there is only T3 decrease [and normal serum T4, free T4 (FT4), and TSH levels] are specifically referred to as low T3 syndrome. However, the information in regard to low T3 syndrome in psychiatric subjects who are clinically euthyroid and do not have any other systemic illness is scanty. In our facility, since thyroid function is routinely assessed in psychiatric patients at admission, this provided the opportunity to study low T3 syndrome in a large group of psychiatric patients.”

The authors found low T3 syndrome in a substantial percentage of depressed patients:

Out of 250 subjects with major psychiatric depression, 6.4% exhibited low T3 syndrome (mean serum T3 concentration 0.94 nmol/l vs normal mean serum concentration of 1.77 nmol/l). The low T3 levels could not be ascribed to malnutrition or any other illness and the metabolic parameters were all normal…The depression might constitute an illness having the same relation to low T3 as found in the low T3 syndrome previously described in euthyroid sick subjects. The present findings, besides describing low T3 syndrome in psychiatric patients without systemic illnesses, suggest the possibility of subgrouping in clinical psychiatric depression which may have a broader clinical significance.”

 

Minerva EndocrinologicaA point of premiere clinical importance is that supplemental T3 can be the treatment of choice in depression with hypothyroid as asserted by the authors of an excellent paper published in Minerva Endocrinologica:

Hypothyroidism has been linked to depression as there is irrefutable evidence that it triggers affective disease and psychic disorders. Depressive patients have a higher frequency of hypothyroidism and patients with hypothyroidism have a higher occurrence of depressive syndrome. Hypothyroidism exhibits considerable alterations in blood flow and glucose metabolism in the brain. Furthermore, patients with major depression may have structural abnormalities of the hippocampus that can affect memory performance. Thyroid peroxidase antibodies have, moreover, been positively associated with trait markers of depression.”

Remember that more than 90% of hypothyroid in developed countries is autoimmune thyroiditis (Hashimoto’s disease) with the presence of thyroid peroxidase antibodies, a frequent finding on laboratory tests that can be very significant even at ‘predictive’ (low) levels. Furthermore…

Depressive symptomatology is variable and is influenced by susceptibility and the degree, though not always, of thyroid failure. In addition, glucose homeostasis and rapid weight loss have been associated to thyroid hormones and increased depressive symptoms. Thyroxine treatment in patients older than 65 years does not improve cognition. In contrast, T3 administration is the therapy of choice in patients with resistance to antidepressive drugs, and especially to SSIR. Genetic variants of thyroid hormone transporters or of deiodinases I and II may predispose to depression and, therefore, a personalized approach should be implemented.”

 

BMC CancerAlso of great interest is the finding that treatment of subclinical hypothyroid/non-thyroidal illness syndrome (NTIS) with T3 can improve the response to chemotherapy in breast cancer as reported in a study published in BMC Cancer:

Thyroid hormones have been shown to regulate breast cancer cells growth, the absence or reduction of thyroid hormones in cells could provoke a proliferation arrest in G0-G1 or weak mitochondrial activity, which makes cells insensitive to therapies for cancers through transforming into low metabolism status. This biological phenomenon may help explain why treatment efficacy and prognosis vary among breast cancer patients having hypothyroid, hyperthyroid and normal function. Nevertheless, the abnormal thyroid function in breast cancer patients has been considered being mainly caused by thyroid diseases, few studied influence of chemotherapy on thyroid function and whether its alteration during chemotherapy can influence the response to chemotherapy is still unclear. So, we aimed to find the alterations of thyroid function and non-thyroidal illness syndrome (NTIS) prevalence during chemotherapy in breast cancer patients, and investigate the influence of thyroid hormones on chemotherapeutic efficacy.”

The authors examined thyroid hormone levels and NTIS prevalence at initial diagnosis of breast cancer and during chemotherapy in 685 patients (369 with breast cancer, 316 with breast benign lesions). They also measured the influence of thyroid hormones on chemotherapeutic efficacy by the chemosensitization test and compared chemotherapeutic efficacy between breast cancer cells with chemotherapeutics plus triiodothyronine (T3) versus chemotherapeutics only. A distinct benefit from treatment by T3 emerged from their data:

“In breast cancer, NTIS prevalence at the initial diagnosis was higher and increased during chemotherapy, but declined before the next chemotherapeutic course. Thyroid hormones decreased significantly during chemotherapy. T3 can enhance the chemosensitivity of MCF-7 to 5-Fu and taxol, with progression from G0-G1 phase to S phase. The similar chemosensitization role of T3 were found in MDA-MB-231. We compared chemotherapeutic efficacy among groups with different usage modes of T3, finding pretreatment with lower dose of T3, using higher dose of T3 together with 5-Fu or during chemotherapy with 5-Fu were all available to achieve chemosensitization, but pretreatment with lower dose of T3 until the end of chemotherapy may be a safer and more efficient therapy.”

Their conclusions are highly important for breast cancer management:

“Taken together, thyroid hormones decreasing during chemotherapy was found in lots of breast cancer patients. On the other hand, thyroid hormones can enhance the chemotherapeutic efficacy through gathering tumor cells in actively proliferating stage, which may provide a new adjuvant therapy for breast cancer in future, especially for those have hypothyroidism during chemotherapy.”

 

Clinical Endocrinology & MetabolismThyroid function tests may be often oversimplified to the detriment of the patient. As studies shown above and many more have shown, low T3 can be a complicating factor in a wide range of disorders. Dysregulation of thyroid function has multiple forms and causes. In a paper entitled Pitfalls in the measurement and interpretation of thyroid function tests published in Clinical Endocrinology & Metabolism the authors review conditions in which measuring TSH alone can be be particularly misleading:

When measuring TSH alone may misleadAnd they offer a diagram of different patterns of thyroid function tests and their causes:

Microsoft PowerPoint - ybeem_930_Koulouri et al - FIGURES - FINA

 

Nature Reviews EndocrinologyFinally, a paper recently published in Nature Reviews Endocrinology articulates an eloquent case for adding T3 to T4 and the need to recognize the patients who may need it:

Impaired psychological well-being, depression or anxiety are observed in 5–10% of hypothyroid patients receiving levothyroxine, despite normal TSH levels. Such complaints might hypothetically be related to increased free T4 and decreased free T3 serum concentrations, which result in the abnormally low free T4:free T3 ratios observed in 30% of patients on levothyroxine.”

Furthermore…

“Evidence is mounting that levothyroxine monotherapy cannot assure a euthyroid state in all tissues simultaneously, and that normal serum TSH levels in patients receiving levothyroxine reflect pituitary euthyroidism alone.”

No wonder then that more are resorting to the combination of T4 (levothyroxine) and T3 (liothyronine):

Levothyroxine plus liothyronine combination therapy is gaining in popularity; although the evidence suggests it is generally not superior to levothyroxine monotherapy, in some of the 14 published trials this combination was definitely preferred by patients and associated with improved metabolic profiles. Disappointing results with combination therapy could be related to use of inappropriate levothyroxine and liothyronine doses, resulting in abnormal serum free T4:free T3 ratios. Alternatively, its potential benefit might be confined to patients with specific genetic polymorphisms in thyroid hormone transporters and deiodinases that affect the intracellular levels of T3 available for binding to T3 receptors. Levothyroxine monotherapy remains the standard treatment for hypothyroidism. However, in selected patients, new guidelines suggest that experimental combination therapy might be considered.”

 

‘Executive Summary’

This post is merely a ‘sampling’ of the vast subject of thyroid hormone regulation and case management. Forthcoming posts will examine other aspects. Here are key points contained in this limited presentation:

  • Thyroid activity is vitally important for all systems throughout the body. Thyroid dysfunction can play a role in common cardiovascular, metabolic, renal and brain disorders.
  • Low T3 syndrome, also known as subclinical hypothyroidism, ‘euthyroid sick syndrome’ and ‘non-thyroidal illness syndrome’ occurs frequently and contributes to morbidity and mortality in numerous ways, adding to the burden of cardiovascular disease, metabolic syndrome (insulin resistance), type 2 diabetes, kidney disease, overweight, depression and dementia.
  • Low T3 is often overlooked due to insufficient testing in clinical practice when TSH and T4 are appear normal.
  • Chronic low grade inflammation is ubiquitous contributing cause to low T3.
  • Disturbances of enzymes that convert T4 to T3, transporters that usher thyroid agents into and out of cells, and peripheral receptor resistance are common and also contribute to Impaired thyroid function.
  • T3 can enhance to response to chemotherapy in the treatment of breast cancer.
  • Treatment of a hypothyroid component in depression can require T3.

Type 2 diabetes – autoimmune aspects

GerontologyType 2 diabetes (T2DM) causation is not restricted to metabolic factors but can include loss of immune tolerance for components of the glucose and insulin regulating systems. A paper published recently in the journal Gerontology reminds that interventions that ameliorate autoimmune inflammation can help to lower blood sugar. The authors state:

“Sustained research over the last 30 years has challenged the stereotypical view that T2DM is solely a metabolic disease by identifying autoimmunity as an overlapping feature of type 1 diabetes (T1DM) and T2DM, which leads to impaired insulin secretion in β cells and promotes hyperglycaemia. Diabetes development based on combined cellular autoimmunity and insulin resistance has been reflected by various terms, such as double diabetes, latent autoimmune diabetes of the adult (LADA) or the young (LADY) or type 1.5 diabetes mellitus.”

It’s of great importance in type 2 diabetes that…

“Its nosographic characterization is yet a matter of debate, thus many T2DM patients may go undiagnosed for autoimmune β-cell alterations, which may have therapeutic consequences. LADA patients, who are generally defined by age of diagnosis >30 years, presence of circulating islet autoantibodies, and lack of insulin requirement for 6 months after diagnosis, need insulin earlier during disease progression, are likely to respond poorly to oral anti-diabetic mediation, but they could respond favourably to immunomodulator therapy. However, anti-inflammatory and immunomodulatory therapies have also proven effective in improving the metabolic profile of many T2DM patients, possibly by interfering with autoimmune processes and thereby halting the decline of β-cell function.”

Important mechanisms for autoimmunity in type 2 diabetes include:

“The chronic inflammatory state in T2DM is characterized by an increased production of cytokines, most notably interleukin (IL)-1β, which destroy [pancreatic] β cells. When tissue inflammation-induced tissue destruction occurs, ‘self’ antigens, which are generally not accessible to T cells, can be released from the affected tissues and thus promote autoimmune activation. Concomitantly, many more alarm signals such as various cytokines or extracellular matrix breakdown products can be released into the circulation if cellular death occurs by dysfunctional apoptosis. For approaching autoimmunity in the context of T2DM, one also has to take into account the role of apoptosis-related molecules Fas and Fas ligand and defects in active suppression of self-reactivity by regulatory T cells (Tregs), immune deviations in the T-helper 1/T-helper 2 (Th1/Th2) ratio or defects in B-cell tolerance.”

The authors elaborate further on factors associated with loss of immune tolerance in type 2 diabetes that apply to numerous other conditions as well:

“Depending on the immunological model one adheres to, autoimmunity occurs due to defects in self-tolerance or the persistence of danger signals stemming from chronic inflammation and tissue destruction. The latter model…would favour the concept of autoimmune activation in T2DM, as plenty of pathological alterations characteristic of this disease – such as obesity-associated chronic adipose tissue inflammation and β-cell stress induced by gluco- and lipotoxicity – continuously provide danger signals which cause an activation of both innate and adaptive immunity. Danger signals can include any molecules resulting from cellular distress which binds to pattern recognition receptors, such as toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD) receptors and cause a local or generalized immune response. This response…triggers IL-1β production.”

Islet cell autoimmunity in T2DMSimply higher levels of glucose and fatty acids in circulation can promote autoimmunity in type 2 diabetes:

“Increased circulating glucose concentrations activate the NLRP3 inflammasome while increased free fatty acid concentration activate TLR2 and TLR4, which leads to recruitment of macrophages and eventually β-cell stress…‘Glucolipotoxicity’-induced β-cell apoptosis could favour the release of ‘danger signals’, autoantibody production, and activation of T cells reactive to β-cell antigens, culminating in further autoimmune destruction of β cells. Indeed, the expression of several β-cell antigens is increased when β cells are stimulated by glucose and decreased when the β cells are less active.”

Furthermore…

“From the perspective of the ‘self/non-self’ model, the release of ‘cryptic’ β-cell antigens through β-cell destruction can have immunogenic potential too: if self-reactive T cells, which have escaped deletion in the thymus, encounter such a β-cell antigen presented in primary lymph nodes by dendritic cells, T-cell priming might occur, followed by further T-cell-mediated β-cell destruction. Stress antigens might drive inflammation in β cells, but also in other metabolically affected tissues in T2DM, such as adipose tissue or the vessel wall.”

As for Th17 activity which plays a role in most autoimmune disorders:

“Th17, participates in the induction of autoimmunity and inflammation and their abundance is enhanced in obesity. The increased number of Th17 and CD8+ T cells in T2DM and obesity may also link inflammation to islet autoimmune destruction.”

And there is good reason for clinicians to bear in mind the importance of vitamin D in type 2 diabetes considering the necessity of vitamin D for Treg activity and IL-10 production:

“When compared to B cells of healthy subjects, B cells of patients with T2DM fail to secrete the anti-inflammatory interleukin-10 (IL-10) in response to stimulation through TLR2, TLR4 or TLR9. IL-10 secreted by B cells is important for controlling autoimmune processes. Accordingly, low IL-10 production in response to stimulation with lipopolysaccharide was associated with a high risk for T2DM in elderly subjects. It is thus conceivable that dysfunctional B cells might add to altered IL-10 production observed in T2DM….Tregs [regulatory T cells] are necessary for maintaining self-tolerance and immune regulation and include several subsets. They exert their suppressive function through direct cell-cell contact and production of anti-inflammatory cytokines such as IL-10. In mouse models of obesity and T2DM, the number of Tregs in visceral adipose tissue is drastically reduced, whereas induction of Tregs reduces inflammation and mitigates autoimmune reactions, insulin resistance and end-organ complications.”

Clinical note: there are the usual wide range of considerations in case management of autoimmunity in type 2 diabetes and a simplistic approach to suppressing inflammation is hardly sufficient, but the authors include interesting comments on a few agents:

“…keeping in mind the prominent role of innate immune system activation in adipose tissue inflammation and T2DM, anti-inflammatory and immunomodulatory therapeutic approaches may be beneficial in improving metabolic regulation in T2DM…Promising results have initially been achieved by targeting IL-1β, an inflammatory cytokine with a pivotal role in islet inflammation in T2DM.”

This certainly suggests the use of low dose cytokine therapy with anti-interleukin-1 combined with IL-10. Interestingly…

“High doses of salicylates block the NF-κB pathway and increase circulating adiponectin, an important adipokine counteracting insulin resistance. In a randomized clinical trial, a high dose of salsalate improved metabolic control and HbA1c levels in T2DM patients.”

Although high doses of salsalate come with a serious warning for cardiovascular complications and GI bleeding. Omega-3 fatty acids, however, come up benignly as usual:

Long-chain n-3 polyunsaturated fatty acids (PUFA) are known for their anti-inflammatory actions and immunomodulating effects on T cells. We have recently shown in a randomized controlled trial that treatment of obese, mostly insulin-resistant but non-diabetic patients that the resolving lipid mediator precursors eicosapentaenoic acid (EPA) and docosahexaenoidic acid (DHA) lead to a reduced expression of key inflammatory genes adipose tissue, lower circulating IL-6 concentration parallel to a substantial increase in anti-inflammatory resolving lipid mediators resolvins D1 and E1 as well as protectin D1.”

A common anti-hypertensive could possibly do double duty:

“TLRs can be inappropriately activated by self-components and cause inflammation and autoimmunity and have been hypothesized to play a role in the pathogenesis of T2DM. TLRs are downregulated by angiotensin receptor blockers and these substances protected pancreatic islets and reduced adipose tissue inflammation in mice fed a high-fat diet.”

And the diabetes drug sitagliplin may have potential to oppose autoimmunity:

“Dipeptidyl peptidase (DPP) inhibitors and GLP-1 analogues alter the inflammatory profile and reduce inflammatory cytokine secretion, while improving glucose metabolism [55]. Interestingly, the DPP-4 inhibitor sitagliplin reduces autoimmunity by decreasing the homing of CD4+ cells into pancreatic β cells in NOD mice and helps preserve islet cell mass.”

Finally, practitioners should bear these points in mind:

“Autoimmunity may be both cause and consequence of β-cell dysfunction, imposing in either case a further disturbance in glucose homeostasis. The prevalence of T2DM is on the rise and if 10% of these patients are positive for islet autoantibodies, then testing for islet autoantibodies as part of the diagnostic assessment in T2DM is relevant to a great number of adult patients, as it may contribute to the rate of progression to insulin requirement, particularly in the absence of gross visceral obesity. Autoantibodies indeed help distinguish adult patients with T1DM, LADA or T2DM, but also the presence of self-reactive T cells in autoantibody-negative T2DM patients identifies an autoimmunity that is associated with the metabolic dysregulation…Surely sustained future research is needed in order to understand the complex immune interactions relevant to T2DM, but we should remember that basic measures in the prevention and management of T2DM such as lifestyle changes also repress inflammation and autoimmune reactions, and are therefore a major tool to help decrease β-cell stress and compensate for the relative lack of insulin.”

Metabolic health status and aging determined by inflammation, not weight

JCEM Vol 98 Number 9Metabolic health is not reliably determined by weight or BMI (body mass index). Lean individuals can suffer from cardiovascular and other diseases involving metabolism, and  evidence has been mounting that supports the notion of a subtype of obesity that is metabolically healthy. A study recently published in JCEM (The Journal of Clinical Endocrinology & Metabolism) shows that inflammation can determine metabolic health in both obese and non-obese populations. The authors state:

Inflammation is a potential mechanism linking obesity and cardiometabolic risk… The aim of the study was to investigate the extent to which differences between metabolically healthy and unhealthy obese and nonobese adults, defined using a range of metabolic health definitions, are correlated with a range of inflammatory markers.”

To do so they measured serum acute-phase reactants, adipocytokines, proinflammatory cytokines, and white blood cell counts in 2047 men and women who they classified as obese (BMI more than 30 kg/m2) and nonobese (BMI less than kg/m2). They established metabolic health status with five definitions that included markers such as blood pressure, triglycerides, LDL, HDL, total cholesterol, fasting glucose, and insulin resistance (HOMA). Several of the inflammatory markers were more strongly associated with metabolic health:

“According to most definitions, metabolically healthy obese and nonobese individuals presented with lower concentrations of complement component 3, C-reactive protein, TNF-α, IL-6, and plasminogen activator inhibitor-1; higher adiponectin levels; and reduced white blood cell count compared to their metabolically unhealthy counterparts. Logistic regression analysis identified greater likelihood of metabolically healthy obesity among individuals with lower levels of complement component 3 (odds ratios [ORs], 2–3.5), IL-6 (ORs, 1.7–2.9), plasminogen activator inhibitor-1 (ORs, 1.7–2.9), and white blood cells (ORs, 2.1–2.5) and higher adiponectin concentrations (ORs, 2.6–4.0).”

In other words, lower C3, CRP, TNF-α, IL-6, PAI-1, and white blood cells, along with higher adiponectin were associated with metabolic health in both groups. Lower C3, IL-6, PAI-1 and higher adiponectin were most strongly indicative of metabolic health among the obese. The authors’ conclusion highlights what clinicians should bear in mind:

Favorable inflammatory status is positively associated with metabolic health in obese and nonobese individuals. These findings are of public health and clinical significance in terms of screening and stratification based on metabolic health phenotype to identify those at greatest cardiometabolic risk for whom appropriate therapeutic or intervention strategies should be developed. “

 

CMAJ Vol 185 Num 13Furthermore, inflammation is turning out to be a key determinant of the quality of aging. The authors of a paper recently published in CMAJ (Canadian Medical Association Journal) state:

Chronic inflammation has been implicated in the pathogenesis of age-related conditions, such as type 2 diabetes, cardiovascular disease, cognitive impairment and brain atrophy… For example, obesity increases inflammation, and chronic inflammation, in turn, contributes to the development of type 2 diabetes by inducing insulin resistance, and to coronary artery disease by promoting atherogenesis. Thus, raised levels of inflammation appear to be implicated in various pathological processes leading to diseases in older age… We assessed inflammatory markers twice over a 5-year exposure period to examine the association between chronic inflammation and future aging phenotypes in a large population of men and women.”

They examined interleukin-6 (IL-6) levels for 3044 middle-aged adults at baseline and 5 years earlier and correlated it with cause-specific mortality, chronic disease and functioning from hospital and register data and clinical examinations. The authors focused on IL-6 because:

“Of the various markers of systemic inflammation, interleukin-6 is particularly relevant to aging outcomes. There is increasing evidence that interleukin-6 is the pro-inflammatory cytokine that “drives” downstream inflammatory markers, such as C-reactive protein and fibrinogen. Interleukin-6, in contrast to C-reactive protein and fibrinogen, is also likely to play a causal role in aging owing to its direct effects on the brain and skeletal muscles. In addition, results of Mendelian randomization studies of interleukin-6 and studies of antagonists are consistent with a causal role for interleukin-6 in relation to coronary artery disease, again in contrast to C-reactive protein and fibrinogen.”

They created four aging phenotypes at the 10-year follow-up defined as:

  • Successful aging (free of major chronic disease and with optimal physical, mental and cognitive functioning)
  • Incident fatal or nonfatal cardiovascular disease
  • Death from noncardiovascular causes
  • Normal aging (all other participants)

Chronic inflammation as determined by higher IL-6 levels was clearly associated with the poorer aging phenotypes:

“Of the 3044 participants, 721 (23.7%) met the criteria for successful aging at the 10-year follow-up, 321 (10.6%) had cardiovascular disease events, 147 (4.8%) died from noncardiovascular causes, and the remaining 1855 (60.9%) were included in the normal aging phenotype. After adjustment for potential confounders, having a high interleukin-6 level (> 2.0 ng/L) twice over the 5-year exposure period nearly halved the odds of successful aging at the 10-year follow-up (odds ratio [OR] 0.53) and increased the risk of future cardiovascular events (OR 1.64) and noncardiovascular death (OR 2.43).”

IL-6 is not the only useful metric for chronic inflammation in aging, but the authors interpret their data as offering good evidence for its use:

Chronic inflammation, as ascertained by repeat measurements, was associated with a range of unhealthy aging phenotypes and a decreased likelihood of successful aging. Our results suggest that assessing long-term chronic inflammation by repeat measurement of interleukin-6 has the potential to guide clinical practice.

And, not surprisingly, two measurements of IL-6 were better than one:

“Our results on the associations between inflammation, cardiovascular events and death from noncardiovascular causes are concordant with those reported in the literature. However, our results also show that measuring chronic inflammation twice may be a better predictor of future cardiovascular disease and noncardiovascular death than measuring inflammation only once.”

In conclusion:

“We found that chronic inflammation characterized by a high interleukin-6 level (> 2.0 ng/L) measured twice over the 5-year exposure period nearly halved the odds of successful aging after 10 years of follow-up compared with maintaining a low level of interleukin-6 (< 1.0 ng/L twice over the exposure period). Our study showed that high interleukin-6 levels at baseline were inversely associated with most of the individual components that characterize successful aging…”

 

Experimental GerontologyIn this context it’s important to consider the role of autoimmunity in inflammation that produces poor aging outcomes. A paper just published in Experimental Gerontology shows how an increase in the Th17/Treg ratio, a pro-inflammatory shift that is a hallmark of autoimmune phenomena, is also associated with increased inflammation of aging called ‘inflammaging‘.

Aging is associated with multiple changes in the proliferative and functional abilities of the immune system which are not related to any pathology but consequences in immunosenescence and inflammagingT helper (TH) 17 cells have been implicated in the development of autoimmune and chronic inflammatory diseases in humans. Additionally, a reciprocal relationship between these pro-inflammatory TH17 and the anti-inflammatory regulatory T cells (Tregs) has been described.”

The authors investigated the proportion of pro-inflammatory TH17 cells (CD4 + IL23R +) and anti-inflammatory Tregs (regulatory T cells that modulate the immune response and depend on vitamin D) along with their respective cytokines IL-17 and IL-10 in human healthy donors:

“The data revealed a continual increase of basal CD4 + IL23R + cell amounts in the different age groups. By analyzing the balance of both T-cell subsets it was observed that, on a basal resting level, TH17 cells were significantly increased in older individuals whereas Tregs were reduced.”

Clinical note: This is of great practical significance since almost all the manifold disorders associated with aging, from diminished cognitive function to osteoporosis, have an inflammatory component. The authors conclude:

“…changes of the TH17/Treg ratios in combination with altered cytokine expression during aging may contribute to an imbalance between the pro-inflammatory and the anti-inflammatory immune response. This indicates a higher susceptibility to develop inflammatory diseases with increasing age.”

Type 2 diabetes is associated with brain atrophy

Diabetes Care August 2013Type 2 diabetes subjects the brain to insult by high levels of both insulin and glucose. A study just published in the journal Diabetes Care shows that brain atrophy resembling Alzheimer’s disease exceeds cerebrovascular disease (brain ischemia and stroke) in type 2 diabetes. The authors determined to resolve whether cognitive dysfunction in T2DM was linked more to brain atrophy or vascular disease in the brain:

Type 2 diabetes (T2DM) is associated with brain atrophy and cerebrovascular disease. We aimed to define the regional distribution of brain atrophy in T2DM and to examine whether atrophy or cerebrovascular lesions are feasible links between T2DM and cognitive function.”

They examined 350 type 2 diabetes subjects with MRI and cognitive tests (and 363 controls without T2DM). With the MRI they mapped the regional distribution of brain atrophy. They also measured cerebrovascular lesions (infarcts, microbleeds, and white matter hyperintensity [WMH] volume) and atrophy (gray matter, white matter, and hippocampal volumes), and looked for links with loss of cognitive function.

T2DM was associated with more cerebral infarcts and lower total gray, white, and hippocampal volumes but not with microbleeds or WMH [white matter hyperintensity]. T2DM-related gray matter loss was distributed mainly in medial temporal, anterior cingulate, and medial frontal lobes, and white matter loss was distributed in frontal and temporal regions. T2DM was associated with poorer visuospatial construction, planning, visual memory, and speed independent of age, sex, education, and vascular risk factors. The strength of these associations was attenuated by almost one-half when adjusted for hippocampal and total gray volumes but was unchanged by adjustment for cerebrovascular lesions or white matter volume.”

In other words, as the authors were quoted in Medscape Family Medicine:

“This study is the first to demonstrate that brain atrophy rather than cerebrovascular lesions may substantially mediate the relationship between [type 2 diabetes] and cognitive impairment.”

Additionally as noted in Medscape Family Medicine

Gray-matter atrophy associated with [type 2 diabetes] is widely and bilaterally distributed in hippocampi, temporal, frontal, and cingulate cortices and subcortical nuclei,” they summarize. “It appears to be the primary driver of cognitive dysfunction in people with [type 2 diabetes].”

Clinical note: Brain atrophy doesn’t occur overnight. Practitioners should bear in mind that early elevations of HgbA1c and other markers of insulin resistance are a risk factor for cognitive dysfunction associated with brain atrophy. Biological functions regulated by brain arousal and inhibition are also vulnerable. The authors conclude:

Cortical atrophy in T2DM resembles patterns seen in preclinical Alzheimer disease. Neurodegeneration rather than cerebrovascular lesions may play a key role in T2DM-related cognitive impairment.”