Insulin resistance increases cardiovascular disease

Insulin resistance (IR), resistance of the insulin receptor due to overstimulation, elicits a rise of insulin levels to overcome the reduced receptor sensitivity. The resulting elevated insulin levels damage tissues throughout the body, and are a major contributing cause of cardiovascular disease. This is well known to many practitioners, so it was disturbing to read an article in the New York Times describing endocrinologists who are baffled by the fact that medications for type 2 diabetes that increase insulin levels worsen the risk for cardiovascular disease. The wealth of scientific evidence has been accumulating for a long time.

Insulin resistance and coronary artery disease

Insulin resistance and CADA study published in 1996 in the journal Diabetologia described the strong connection between CAD (coronary artery disease) and insulin resistance with its consequent hyperinsulinemia.

“The purpose of the present study was to quantitate insulin-mediated glucose disposal in normal glucose tolerant patients with angiographically documented coronary artery disease (CAD) and to define the pathways responsible for the insulin resistance.”

Of particular interest is that all the study subjects, both those with CAD and controls, had a normal oral glucose tolerance test. HOWEVER…

Fasting plasma insulin concentration and area under the plasma insulin curve following glucose ingestion were increased in CAD vs control subjects. Insulin-mediated whole body glucose disposal was significantly decreased in CAD subjects and this was entirely due to diminished non-oxidative glucose disposal. The magnitude of insulin resistance was positively correlated with the severity of CAD.”

It is hard to over emphasize the importance to clinicians of being vigilant in recognizing insulin resistance in the presence of normal glucose levels.

“In the CAD subjects basal and insulin-mediated rates of glucose and lipid oxidation were normal and insulin caused a normal suppression of hepatic glucose production. In conclusion, subjects with angiographically documented CAD are characterized by moderate-severe insulin resistance and hyperinsulinaemia and should be included in the metabolic and cardiovascular cluster of disorders that comprise the insulin resistance syndrome or ’syndrome X’.

Hypertension, Dyslipidemia, and Atherosclerotic Cardiovascular Disease

In 1991 a paper published in Diabetes Care described how insulin resistance promotes multiple factors that cause atherosclerosis.

“Diabetes mellitus is commonly associated with systolic/diastolic hypertension, and a wealth of epidemiological data suggest that this association is independent of age and obesity. Much evidence indicates that the link between diabetes and essential hypertension is hyperinsulinemia. Thus, when hypertensive patients, whether obese or of normal body weight, are compared with age- and weight-matched normotensive control subjects, a heightened plasma insulin response to a glucose challenge is consistently found.”

Moreover…

“…insulin resistance…correlates directly with the severity of hypertension. The reasons for the association of insulin resistance and essential hypertension can be sought in at least four general types of mechanisms: Na+ retention, sympathetic nervous system overactivity, disturbed membrane ion transport, and proliferation of vascular smooth muscle cells.”

It is also well-known that IR with its hyperinsulinemia cause elevated lipid levels.

Insulin resistance and hyperinsulinemia are also associated with an atherogenic plasma lipid profile. Elevated plasma insulin concentrations enhance very-low-density lipoprotein (VLDL) synthesis, leading to hypertriglyceridemia. Progressive elimination of lipid and apolipoproteins from the VLDL particle leads to an increased formation of intermediate-density and low-density lipoproteins, both of which are atherogenic.”

And elevated insulin directly fosters atherosclerosis:

“Last, insulin, independent of its effects on blood pressure and plasma lipids, is known to be atherogenic. The hormone enhances cholesterol transport into arteriolar smooth muscle cells and increases endogenous lipid synthesis by these cells. Insulin also stimulates the proliferation of arteriolar smooth muscle cells, augments collagen synthesis in the vascular wall, increases the formation of and decreases the regression of lipid plaques, and stimulates the production of various growth factors. In summary, insulin resistance appears to be a syndrome that is associated with a clustering of metabolic disorders, including non-insulin-dependent diabetes mellitus, obesity, hypertension, lipid abnormalities, and atherosclerotic cardiovascular disease.”

 

Controlling insulin resistance more important than glucose or LDLA more recent study in Diabetes Care presents striking data demonstrating the massive impact reduction in heart attacks that would occur by preventing insulin resistance. In setting out to determine what portion of coronary artery disease is caused by IR, the authors used data from the National Health and Nutrition Examination Survey 1998–2004 to simulate a population representative of young adults in the U.S. They applied the Archimedes model was to estimate the proportion of heart attacks that would be prevented by maintaining insulin resistance at healthy levels. Their data painted a dramatic picture:

“In young adults, preventing insulin resistance would prevent ∼42% of myocardial infarctions. The next most important determinant of CAD is systolic hypertension, prevention of which would reduce myocardial infarctions by ∼36%. Following systolic blood pressure, the most important determinants are HDL cholesterol (31%), BMI (21%), LDL cholesterol (16%), triglycerides (10%), fasting plasma glucose and smoking (both ∼9%), and family history (4%).”

Preventing insulin resistance beat the pants off controlling LDL cholesterol and smoking! Interestingly, they found that the effects were especially important for women:

“The effects of insulin resistance are also affected by sex. Today’s young men face a higher rate of myocardial infarctions than today’s young women: 55 vs. 32%. However, insulin resistance plays a larger relative role in women than in men, with normalization of insulin resistance reducing the myocardial infarction rate ∼57% for women (from 32 to 14%), compared with ∼29% (from 55 to 39%) for men.”

Preventing insulin resistance carries more weight than controlling glucose

In their conclusion the authors make points that are crucial for clinicians to bear in mind:

“Of the risk factors that we believe are sufficiently well studied to permit quantitative analysis, insulin resistance is the most important single risk factor for CAD. Our results indicate that insulin resistance is responsible for approximately 42% of myocardial infarctions. Its effect on CAD is indirect, mediated through its effects on other variables such as SBP, HDL cholesterol, triglycerides, glucose, and apoB.”

Effect of insulin resistance on myocardial infarction

In comparing their results with other research, the authors highlight the critical error made by depending on medications that increase insulin to control glucose:

“Our results are not directly comparable with those of clinical trials, where the effects of glucose lowering on CAD were either much smaller or null. The reason is that in the clinical trials, the focus was on lowering blood glucose—not preventing or curing insulin resistance. The drugs used in the trials either lowered glucose without affecting insulin resistance (e.g., sulfonylureas and insulin) or lowered insulin resistance to some extent but did not eliminate it (e.g., metformin and rosiglitazone). Furthermore, we normalized insulin resistance over the entire lifetimes of the subjects, whereas the treatments in the trials were given only after individuals had developed diabetes and were given only for the limited durations of the studies. Thus, the results of the trials do not represent the full eff

ect of normalizing insulin resistance and are actually consistent with our results.”

Note the implication that cardiovascular damage by IR occurs long before losing glucose control and crossing the border into diabetes territory.

Insulin resistance without diabetes causes cardiovascular disease

Investigators publishing in PLoS One make the same point about cardiovascular damage caused by IR well before diabetes sets in.

“To enable a comparison between cardiovascular disease risks for glucose, insulin and HOMA-IR, we calculated pooled relative risks per increase of one standard deviation…We included 65 studies (involving 516,325 participants) in this meta-analysis. In a random-effect meta-analysis the pooled relative risk of CHD (95% CI; I2) comparing high to low concentrations was 1.52 (1.31, 1.76; 62.4%) for glucose, 1.12 (0.92, 1.37; 41.0%) for insulin and 1.64 (1.35, 2.00; 0%) for HOMA-IR. The pooled relative risk of CHD per one standard deviation increase was 1.21 (1.13, 1.30; 64.9%) for glucose, 1.04 (0.96, 1.12; 43.0%) for insulin and 1.46 (1.26, 1.69; 0.0%) for HOMA-IR.”

They concluded that insulin resistance (HOMA-IR) was the leading culprit:

“The relative risk of cardiovascular disease was higher for an increase of one standard deviation in HOMA-IR compared to an increase of one standard deviation in fasting glucose or fasting insulin concentration.”

The authors also demonstrate that IR is a much better biomarker than fasting insulin:

 “The present meta-analyses showed that fasting glucose, fasting insulin and HOMA-IR were all associated with incident cardiovascular disease in individuals without diabetes. In a standardized meta-analysis we found that coronary heart disease risk increased with 46% for an increase of one standard deviation in HOMA-IR concentration compared to an increase of 21% for fasting glucose concentration and an increase of 4% for fasting insulin concentration.”

Insulin resistance causes fat expansion and vascular endothelial damage

An excellent paper published in Arteriosclerosis, Thrombosis, and Vascular Biology details how IR causes cardiovascular disease beyond abnormal glucose, lipids, hypertension, and its proinflammatory effects.

“…insulin’s action directly on vascular endothelium, atherosclerotic plaque macrophages, and in the heart, kidney, and retina has now been described, and impaired insulin signaling in these locations can alter progression of cardiovascular disease in the metabolic syndrome and affect development of microvascular complications.”

The authors describe how IR causes vascular inflammation and atherosclerosis:

“Insulin action directly on vascular endothelial cells affects endothelial function beyond regulating blood flow or capillary recruitment. Conditional knockout of the insulin receptor in endothelial cells causes a 2- to 3-fold increase in the atherosclerotic lesion size in apolipoprotein E–null mice…the increased atherogenesis in this model can be attributed to insulin action directly on endothelial cells rather than effects mediated through systemic parameters. The accelerated atherosclerosis in mice with endothelial cell insulin receptor knockout is preceded by a dramatic increase in leukocyte rolling and adhesion to endothelium and an increase in expression of vascular cell adhesion molecule-1…insulin signaling independent of NO is responsible for this effect.”

They state that IR promotes the necrotic core at the heart of vulnerable plaque:

Insulin resistance in macrophages, however, promotes formation of a necrotic core in atherosclerotic plaques by enhancing macrophage apoptosis. This is an important event in advanced atherosclerosis because exposure of the necrotic core to circulating blood in the event of plaque rupture can precipitate thrombosis, leading to unstable angina pectoris, transitory cerebral ischemia, stroke, or myocardial infarction.”

Regarding cardiomyocyte function…

“…it is likely that the changes in metabolic substrate inflexibility and increased mitochondrial production of oxidants caused by cardiomyocyte insulin resistance can contribute to development of heart failure in the metabolic syndrome.”

The authors conclude with important clinical points:

“Research on insulin receptor signaling using tissue–specific gene manipulation in mice as well as other methods has provided important insights into insulin action and revealed insulin effects in tissues that a decade or 2 ago were considered nonresponsive to insulin….insulin sensitizers would theoretically have better profiles of action if they improved insulin resistance in tissues regulating glucose and lipid metabolism, as well as in the endothelium and other vascular tissues where impaired insulin signaling is proatherosclerotic independent of metabolic effects. Second, insulin analogues should be carefully evaluated for deleterious effects on insulin signaling pathways which are not affected by insulin resistance, such as those pathways which promote dyslipidemia or increase vascular expression of endothelin-1.”

Insulin resistance promotes advanced plaque progression

A paper published in Cell Metabolism details additional mechanisms by which IR promotes atherosclerosis. The authors note that…

“…the pathophysiological processes involved in the initiation and progression of early lesions are quite different from those that cause the formation of clinically dangerous plaques,…advanced plaque progression is influenced primarily by processes that promote plaque necrosis and thinning of a collagenous “scar” overlying the lesion called the fibrous cap… and distinguishing the effects of insulin resistance and hyperglycemia on these processes is critically important.”

They echo other investigators who point out the crucial fact that insulin resistance does damage before glucose control is lost:

“There is ample clinical evidence that insulin resistance increases the risk for coronary artery disease (CAD) even in the absence of hyperglycemia. Insulin resistance syndromes can promote both atherogenesis and advanced plaque progression, and the mechanisms likely involve both systemic factors that promote these processes, particularly dyslipidemia but also hypertension and a proinflammatory state, as well as the effect of perturbed insulin signaling at the level of the intimal cells that participate in atherosclerosis, including endothelial cells, vascular smooth muscle cells, and macrophages.”

They highlight the critical clinical implication that insulin resistance also entails overstimulation of various tissues by insulin elevated in compensation for receptor resistance or by insulin-elevating medications:

“…“insulin resistance” can mean either defective insulin receptor signaling or, ironically, overstimulation of insulin receptor pathways caused by hyperinsulinemia.”

They also note the difference between ‘ordinary’ atherosclerosis and the lesions, vulnerable plaque, that actually cause heart attacks and ischemic strokes.

“Most importantly, the primary objective of this study was to address an entirely different question, namely, the effect of myeloid IR deficiency on advanced lesional macrophage apoptosis and plaque necrosis. Recall that most atherosclerotic lesions in humans do not cause acute coronary artery disease, because they undergo outward remodeling of the arterial wall, which preserves lumen patency, and do not undergo plaque rupture or erosion and thus do not trigger acute lumenal thrombosis. The small percentage of lesions that do cause acute vascular disease are distinguished by the presence of large areas of necrosis and thin fibrous caps, which promote plaque disruption, acute lumenal thrombosis, and tissue infarction. This concept is particularly important for the topic of this review, because advanced atherosclerotic lesions in diabetic subjects are characterized by large necrotic cores when compared with similarly sized lesions from nondiabetic individuals”

In their conclusion the authors state the role of insulin resistance over hyperglycemia:

“These studies have provided evidence that insulin resistance in macrophages and endothelial cells may play important roles in both atherogenesis and clinically relevant advanced plaque progression. Hyperglycemia, on the other hand, appears to primarily promote early stages of lesion formation…”

Insulin resistance inhibits nitric oxide synthase

An interesting paper published in the Italian journal Panminerva Medica further elucidates key mechanisms, including the damage by IR to nitric oxide regulation done by increasing asymmetric dimethylarginine, which inhibits nitric oxide synthase. The author includes this under the rubric ‘insulin resistance syndrome’.

“…the more insulin resistant an individual, the more insulin they must secrete in order to prevent the development of type 2 diabetes. However, the combination of insulin resistance and compensatory hyperinsulinemia increases the likelihood that an individual will be hypertensive, and have a dyslipidemia characterized by a high plasma triglyceride (TG) and low high-density lipoprotein cholesterol (HDL-C) concentration….Several other clinical syndromes are now known to be associated with insulin resistance and compensatory hyperinsulinemia. For example, polycystic ovary syndrome appears to be secondary to insulin resistance and compensatory hyperinsulinemia. More recently, studies have shown that the prevalence of insulin resistance/hyperinsulinemia is increased in patients with nonalcoholic fatty liver disease, and there are reports that certain forms of cancer are more likely to occur in insulin resistant/hyperinsulinemic persons. Finally, there is substantial evidence of an association between insulin resistance/hyperinsulinemia, and sleep disordered breathing. Given the rapid increase in the number of clinical syndromes and abnormalities associated with insulin resistance/hyperinsulinemia, it seems reasonable to suggest that the cluster of these changes related to the defect in insulin action be subsumed under the term of the insulin resistance syndrome.”

Specifically in regard to cardiovascular disease…

“…in addition to a high TG and a low HDL-C, the atherogenic lipoprotein profile in insulin resistant/hyperinsulinemic individuals also includes the appearance of smaller and denser low density lipoprotein particles, and the enhanced postprandial accumulation of remnant lipoproteins; changes identified as increasing risk of CVD. Elevated plasma concentrations of plasminogen activator inhibitor-1 (PAI-1) have been shown to be associated with increased CVD, and there is evidence of a significant relationship between PAI-1 and fibrinogen levels and both insulin resistance and hyperinsulinemia. Evidence is also accumulating that sympathetic nervous system (SNS) activity is increased in insulin resistant, hyperinsulinemic individuals, and, along with the salt sensitivity associated with insulin resistance/hyperinsulinemia, increases the likelihood that these individuals will develop essential hypertension.”

Moreover…

“The first step in the process of atherogenesis is the binding of mononuclear cells to the endothelium, and mononuclear cells isolated from insulin resistant/hyperinsulinemic individuals adhere with greater avidity. This process is modulated by adhesion molecules produced by endothelial cells, and there is a significant relationship between degree of insulin resistance and the plasma concentration of the several of these adhesion molecules. Further evidence of the relationship between insulin resistance and endothelial dysfunction is the finding that asymmetric dimethylarginine, an endogenous inhibitor of the enzyme nitric oxide synthase, is increased in insulin resistant/hyperinsulinemic individuals. Finally, plasma concentrations of several inflammatory markers are elevated in insulin resistant subjects.”

 

A paper published in Diabetes Metabolism Research and Reviews draws this point further.

“In recent years, it has become clear that insulin resistance and endothelial dysfunction play a central role in the pathogenesis of atherosclerosis. Much evidence supports the presence of insulin resistance as the fundamental pathophysiologic disturbance responsible for the cluster of metabolic and cardiovascular disorders, known collectively as the metabolic syndrome. Endothelial dysfunction is an important component of the metabolic or insulin resistance syndrome and this is demonstrated by inadequate vasodilation and/or paradoxical vasoconstriction in coronary and peripheral arteries in response to stimuli that release nitric oxide (NO). Deficiency of endothelial-derived NO is believed to be the primary defect that links insulin resistance and endothelial dysfunction. NO deficiency results from decreased synthesis and/or release, in combination with exaggerated consumption in tissues by high levels of reactive oxygen (ROS) and nitrogen (RNS) species, which are produced by cellular disturbances in glucose and lipid metabolism.”

And a vicious cycle ensues…

“Endothelial dysfunction contributes to impaired insulin action, by altering the transcapillary passage of insulin to target tissues. Reduced expansion of the capillary network, with attenuation of microcirculatory blood flow to metabolically active tissues, contributes to the impairment of insulin-stimulated glucose and lipid metabolism. This establishes a reverberating negative feedback cycle in which progressive endothelial dysfunction and disturbances in glucose and lipid metabolism develop secondary to the insulin resistance. Vascular damage, which results from lipid deposition and oxidative stress to the vessel wall, triggers an inflammatory reaction, and the release of chemoattractants and cytokines worsens the insulin resistance and endothelial dysfunction.”

In their conclusion the authors state:

“…endothelial dysfunction and insulin resistance commonly occur together and can be detected early in the pathogenesis of atherosclerosis. Insulin resistance can be inferred by the presence of a cluster of metabolic and cardiovascular abnormalities known collectively as the metabolic syndrome or by direct measurement of impaired insulin-stimulated glucose and lipid metabolism . Endothelial dysfunction can be documented by the demonstration of inadequate vasodilation and/or paradoxical vasoconstriction in coronary and peripheral arteries. Lack of endothelial-derived NO may provide the link between insulin resistance and endothelial dysfunction.”

Plea to clinicians

Many resources are available for practitioners to apply a functional medicine model of objectively targeted treatment to resuscitate insulin receptor function and address lifestyle issues, especially diet, for the management of type 2 diabetes that minimizes the use of agents that lower glucose by increasing insulin, and therefore insulin resistance. It is my sincere wish that not only endocrinologists, but all clinicians, recall the mechanisms by which medications that promote insulin resistance increase cardiovascular disease, and act accordingly to protect their patients.

Insulin resistance is a huge topic, and there are numerous posts here pertaining to IR an conditions as diverse as Alzheimer’s disease and breast cancer that can be viewed by using the search box. They include the earlier post on the correlation of IR with blood vessel damage leading to heart attack and stroke.

Oxidized LDL promotes atherosclerosis

Science SignalingOxidized LDL, low density lipoprotein that has been that has been subject to oxidation as participates in a vascular infllammatory process, is a direct risk factor for heart attacks and ischemic strokes and a more accurate predictor than ‘ordinary’ undamaged LDL. Research recently published in Science Signaling elucidates one of the mechanisms by which oxidized LDL promotes atherosclerosis.

Oxidized LDL promotes foam cell generation

Foam cells are the macrophages (white blood cells) filled with fat that accumulate in the build-up of atherosclerotic plaque.

“One characteristic of atherosclerosis is the accumulation of lipid-laden macrophage foam cells in the arterial wall. We have previously shown that the binding of oxidized low-density lipoprotein (oxLDL) to the scavenger receptor CD36 activates the kinase Lyn, initiating a cascade that inhibits macrophage migration and is necessary for foam cell generation.”

The authors demonstrated that blocking the ion transporter Na+/K+-ATPase, a key link in this signaling chain, protects against diet-induced atherosclerosis:

“We identified the plasma membrane ion transporter Na+/K+-ATPase as a key component in the macrophage oxLDL-CD36 signaling axis. Using peritoneal macrophages isolated from Atp1a1 heterozygous or Cd36-null mice, we demonstrated that CD36 recruited an Na+/K+-ATPase–Lyn complex for Lyn activation in response to oxLDL. Macrophages deficient in the α1 Na+/K+-ATPase catalytic subunit did not respond to activation of CD36, showing attenuated oxLDL uptake and foam cell formation, and oxLDL failed to inhibit migration of these macrophages. Furthermore, Apoe-null mice, which are a model of atherosclerosis, were protected from diet-induced atherosclerosis by global deletion of a single allele encoding the α1 Na+/K+-ATPase subunit or reconstitution with macrophages that lacked an allele encoding the α1 Na+/K+-ATPase subunit. These findings identify Na+/K+-ATPase as a potential target for preventing or treating atherosclerosis.”

Clinical Note

Case management of cardiovascular risk entails the measurement of oxidized LDL as a key predictive biomarker, and interval changes are important to objectively gauge the effectiveness of lifestyle and other interventions.

Low-normal thyroid function and cardiometabolic disorders

European Journal of Clinical InvestigationLow-normal thyroid function commonly shows up in lab results in my general practice, mostly due to the diffuse autoimmune phenomena so widespread now, but it seems to be often overlooked. A study just published in the European Journal of Clinical Investigation offers more evidence that low-normal thyroid function should be respected as a risk factor, in this case for cardiovascular and metabolic disorders. The authors state:

“Subclinical hypothyroidism may adversely affect the development of cardiovascular disease (CVD). Less is known about the role of low-normal thyroid function, that is higher thyroid-stimulating hormone and/or lower free thyroxine levels within the euthyroid [‘normal’] reference range, in the development of cardio-metabolic disorders. This review is focused on the relationship of low-normal thyroid function with CVD, plasma lipids and lipoprotein function, as well as with metabolic syndrome (MetS), chronic kidney disease (CKD) and nonalcoholic fatty liver disease (NAFLD).”

The authors surveyed a range of reviews and meta-analyses derived from clinical and basic research papers, obtained published up to November 2014 and found:

Low-normal thyroid function could adversely affect the development of (subclinical) atherosclerotic manifestations. It is likely that low-normal thyroid function relates to modest increases in plasma total cholesterol, LDL cholesterol and triglycerides, and may convey pro-atherogenic changes in lipoprotein metabolism and in HDL function. Most available data support the concept that low-normal thyroid function is associated with MetS, insulin resistance and CKD, but not with high blood pressure. Inconsistent effects of low-normal thyroid function on NAFLD have been reported so far.”

See earlier posts for studies reporting additional adverse effects from low-normal thyroid and low-normal free T3. Practitioners should be alert to anti-thyroid antibodies indicating a pre-Hashimoto’s state and test for iodine insufficiency (by 24 hour urine collection) when indicated. The authors conclude:

“Observational studies suggest that low-normal thyroid function may be implicated in the pathogenesis of CVD. Low-normal thyroid function could also play a role in the development of MetS, insulin resistance and CKD, but the relationship with NAFLD is uncertain.”

Antioxidants in excess can increase inflammation and blunt benefits of exercise

PLOS ONEAntioxidants, even glutathione, taken in excess can increase rather than ameliorate harmful inflammation as attested by two revealing papers recently published in PLOS (Public Library of Science). In a fascinating study on experimental colitis, the authors demonstrate that certain levels of ROS (reactive oxygen species, well known to be damaging at higher levels) are critically necessary to regulate the Treg (regulatory T cell) function that controls autoimmune inflammation. Moreover, of premiere clinical importance is their observation that higher levels of glutathione that excessively dampened ROS blocked Treg function and thus worsened the inflammation of inflammatory bowel disease (IBD). Antioxidants, of course, are employed to keep the lid on ROS. And with good reason:

Reactive oxygen species (ROS) are highly reactive and interact with many bio-molecules. At high concentrations, they are likely to destroy biological structures, promoting cellular damage and tissue destruction. Traditionally, ROS have been implicated in ageing and the progression of inflammatory and autoimmune diseases, including inflammatory bowel diseases (IBD).

However…

Meanwhile, many recent observations are opposing the traditional concept on ROS, suggesting the protective role of ROS in immune-mediated inflammatory diseases.”

The authors relate the fascinating background to this study on ROS, antioxidants and autoimmune inflammation:

“Mice with lower level of ROS than WT mice due to defects in ROS-producing enzyme system, such as Ncf1−/− or Nox2−/−, are more susceptible to autoimmune diseases, such as arthritis and encephalomyelitis. Humans with lower levels ROS than normal persons, such as chronic granulomatous disease (CGD) patients and carriers, are also more susceptible to autoimmune diseases. By contrast, mice with higher level ROS than WT mice due to the defect in a ROS metabolizing enzyme, glutathione peroxidase-1 (GPx-1), are resistant to immune-mediated inflammatory diseases, such as allergen-induced airway inflammation and high fat diet-induced atherosclerosis. In particular, mice with higher level of ROS due to defect of a non-enzymatic cellular anti-oxidant, peroxiredoxin (Prx) II, are resistant to dextran sodium sulfate (DSS)-induced colitis.”

In other words, more enzyme activity producing antioxidants such as glutathione and peroxiredoxin increased susceptibility to autoimmune inflammatory disorders. Moreover…

“These clinical or experimental observations implicated the immunoregulatory role of ROS, and adoptive-transfer of CD4+ cells from rats with lower ROS level induced arthritis in rats with normal ROS level, demonstrating the key role of CD4+ cells in the hyperinflammatory response in lowered levels of ROS. On the other hand, oxidative stress induces T cell hyporesponsiveness in several human pathologies (e.g. cancer, rheumatoid arthritis, AIDS and leprosy). Accordingly, ROS level is supposed to be closely associated with T cell responsiveness. In particular, regulatory T cell (Treg) function seems to be closely linked to ROS level. Tregs isolated from mice with lower level of ROS, such as Ncf1−/− mice, were hypofunctional than WT Tregs. Tregs were also hypofunctional in vitro at lowered levels of ROS by adding antioxidants or NADPH oxidase inhibitors. Differentiation of inducible Treg (iTreg) seems also linked to the level of ROS. Induction of FoxP3+ iTreg was attenuated, whereas that of Th17 cells was enhanced in lowered levels of ROS due to Nox2 deficiency or addition of apocynin. By contrast, induction of FoxP3+ Treg was enhanced in elevated levels of ROS due to PrxII deficiency.”

Thus, whereas excessive oxidative stress (ROS) with insufficient antioxidants can contribute to T cell hypoactivity in some pathologies including cancer and AIDS, levels of regulatory T cell (FoxP3+ iTreg) that rein in autoimmune Th17 inflammation are suppressed in the presence to ROS levels that are too low.

Colitis inflammation attenuated in KO mice, aggravated by NACSo the authors set out to investigate the suppressive function of Tregs isolated from mice with elevated levels of ROS due to defects in the enzymes that make the antioxidatns glutathione (GPx1) and catalase. Their results illuminated the aspects of ROS and antioxidants that are critical to case management of inflammatory disorders:

“In the present study, we demonstrated for the first time that Tregs were hyperfunctional in elevated level of ROS by using GPx1−/− × Cat−/− Tregs. As it has been already reported that Tregs were hypofunctional in lowered levels of ROS, it could be argued that Treg function is closely linked to ROS level. Actually in the present study, IP injection of NAC [N-acetylcysteine] into GPx1−/− × Cat−/− mice reduced the suppressive function of Tregs to the level comparable to WT Tregs. Administration of NAC also has made GPx1−/− × Cat−/− mice, which are naturally resistant, susceptible to DSS-induced colitis, suggesting the critical role of ROS in the prevention of DSS-induced colitis. The importance of Tregs in the maintenance of intestinal immune balance has been already shown in many other studies. Consequently, ROS level might be critical in the maintenance of intestinal immune homeostasis, providing an insight for the immunomodulation by ROS.”

In other words, elevated ROS increase the antiinflammatory activity of Treg cells, while administration of NAC (which increases glutathione production) suppressed Tregs by reducing ROS, resulting in increased intestinal inflammation.

Clinical note: Excessive suppression of ROS by overenthusiastic application of antioxidants can disturb immune homeostasis resulting in increased autoimmune inflammation.

The authors also shed light on the association of ROS and inflammation with tryptophan metabolism:

At molecular level, the expression of an immunoregulatory enzyme, IDO, is also associated with ROS level. IDO catabolizes the essential amino acid tryptophan into the stable metabolite, kynurenine. Consequently, IDO depletes tryptophan from the environment, thus starving effector cells. It was also found that tryptophan depletion resulted in inhibition of Th17 cell differentiation and expansion of Foxp3+ Tregs….Thus, IDO expression might be induced as a consequence of the inflammatory reaction, contributing to the feedback regulation…Elevated levels of ROS not only contribute to the induction but also enhance the enzyme activity of IDO, as superoxide radical acts as a cofactor of IDO. Therefore, high expression and strong activity of IDO from the beginning in GPx1−/− × Cat−/− mice might contribute to the preparation of immunosuppressive environment preventing inflammatory tissue damage during treatment with DSS.”

Clinical note: antioxidant and ROS status can be investigated with a urinary organic acid analysis that includes p-Hydroxyphenyllactate, 8-Hydroxy-2′-deoxyguanosine, kynurenate and quinolinate; and a blood assay for oxidative stress that includes cysteine, cystine, glutathione, glutathione peroxidase, lipid peroxides, sulfate, superoxide dismutase (SOD), and total antioxidant capacity (TAC).

The authors summarize implications for modulation of ROS by antioxidants:

“Actually in the present study, the frequency of FoxP3+ cells was significantly increased in parallel with significantly attenuated inflammatory reaction in the lesions of DSS-induced colitis in mice with elevated level of ROS due to defects in GPx1 and Cat. By contrast, IP injection of NAC significantly reduced the frequency of FoxP3+ cells and aggravated inflammatory reaction in the lesions of DSS-induced colitis… we demonstrated an experimental colitis was attenuated in elevated level of ROS. Enhancement of Treg function and IDO expression, investigated in the present study, might be involved in the underlying mechanism…Taken together, the results of the present study suggest the potential therapeutic strategy for IBD through immunomodulation by ROS.”

ROS and Psoriasis

The same team of scientists a study also in PLOS One similarly investigating the role of ROS and by implication the use of antioxidants in regard to psoriatic dermatitis:

Psoriasis is a chronic inflammatory skin disease resulting from immune dysregulation. Regulatory T cells (Tregs) are important in the prevention of psoriasis. Traditionally, reactive oxygen species (ROS) are known to be implicated in the progression of inflammatory diseases, including psoriasis, but many recent studies suggested the protective role of ROS in immune-mediated diseases. In particular, severe cases of psoriasis vulgaris have been reported to be successfully treated by hyperbaric oxygen therapy (HBOT), which raises tissue level of ROS. Also it was reported that Treg function was closely associated with ROS level. However, it has been only investigated in lowered levels of ROS so far.”

The authors state:

Psoriasis is known to develop as a result of immune dysregulation, in particular hyperfunction of T helper 17 (Th17) cells. In steady state, immune homeostasis is maintained by regulatory T cells (Tregs) that suppress immune effectors including Th17 cells. It was also reported that psoriasis is associated with impaired suppressive function of Tregs. Therefore, in order to restore the dysregulated immune status in psoriasis, it is necessary to suppress immune effectors including Th17 cells and/or to enhance Tregs.”

Consonant with their study on colitis:

“Traditionally, reactive oxygen species (ROS) are known to be implicated in the progression of many inflammatory diseases. As ROS are highly reactive and interact with many bio-molecules, they are likely to destroy biological structures, promoting cellular damage and tissue destruction. In contrast, many recent evidences are accumulating on the protective role of ROS in immune-mediated diseases. Autoimmune arthritis was aggravated in rodents with lower levels of ROS than wildtype (WT) mice due to defects in ROS-producing enzyme system, such as mutation in the neutrophil cytosolic factor (Ncf)-1 or NADPH oxidase (NOX)2. In human, too, many autoimmune diseases develop more frequently in chronic granulomatous disease (CGD) patients with lower level of ROS than normal persons due to defect in ROS-producing NOX. To the contrary, experimentally induced asthmatic inflammation was attenuated in mice with higher level of ROS than WT mice due to the defect of a ROS metabolizing enzyme, glutathione peroxidase-1 (GPx-1). Atherosclerotic lesions induced by high-fat diet were also decreased in GPx-1−/− mice. In addition, experimental colitis was attenuated in mice with a higher level of ROS due to defect in a non-enzymatic anti-oxidant, peroxiredoxin II.”

So they set out to…

“…clarify the relationship between ROS level and Treg function, as well as their role in the pathogenesis of psoriasis, we investigated imiquimod-induced psoriatic dermatitis (PD) in association with Treg function both in elevated and lowered levels of ROS by using knockout mice, such as glutathione peroxidase-1−/− and neutrophil cytosolic factor-1−/− mice, as well as by using HBOT or chemicals, such as 2,3-dimethoxy-1,4-naphthoquinone and N-acetylcysteine.

Reactive Oxygen Species Prevent Imiquimod-Induced Psoriatic Dermatitis through Enhancing Regulatory T Cell FunctionHere too they found that moderately high levels of ROS were protective against autoimmune inflammation PD (psoriatic dermatitis):

The results consistently showed Tregs were hyperfunctional in elevated levels of ROS, whereas hypofunctional in lowered levels of ROS. In addition, imiquimod-induced PD was attenuated in elevated levels of ROS, whereas aggravated in lowered levels of ROS. For the molecular mechanism that may link ROS level and Treg function, we investigated the expression of an immunoregulatory enzyme, indoleamine 2,3-dioxygenase (IDO) which is induced by ROS, in PD lesions. Taken together, it was implied that appropriately elevated levels of ROS might prevent psoriasis through enhancing IDO expression and Treg function.”

Reflecting on the clinical significance of these results and the crucial difference between moderately high levels of ROS which are protective versus higher levels that are damaging:

“In the present study, we demonstrated that imiquimod-induced PD was attenuated in elevated levels of ROS, whereas aggravated in lowered levels of ROS. This observation provides experimental evidence supporting the immunoregulatory role of ROS, that is contradictory to the traditional concept. Traditionally, ROS is implicated in the progression of inflammatory diseases by promoting cellular damage and tissue destruction as well as ageing. At the moment, it is necessary to establish a new conceptual framework where the recent observations and the traditional concept can be compromised…Taken together, we can imagine a threshold level of ROS that divides the moderately high tolerable range and the intolerably higher levels. In the higher levels such as GPx-1−/−×GPx-2−/− mice, inflammatory reactions are augmented due to the direct tissue damage by ROS. Many evident previous observations that contribute to establish the traditional concept of ROS, such as vascular reperfusion injury and other in vitro observations, might fall in this range of intolerably higher levels of ROS. In contrast, as demonstrated previously by others and by us in the present study, inflammatory diseases are attenuated in the moderately high tolerably ranges such as in GPx-1−/− or PrxII−/− mice. Thus, we suppose some kinds of anti-inflammatory mechanisms are operating in the moderately high tolerable range of ROS. As ROS can induce direct tissue damages at high levels, it would be natural to develop defensive or compensatory mechanisms counteracting the destructive effects of ROS in the body.”

Clinical note: Here is where the rubber meets the road in clinical case management of autoimmune diseases in respect to ROS versus excessive use of antioxidants:

“In this aspect, enhancement of Treg function depending on ROS level is quite pertinent to counteract the destructive damages induced by ROS, as Tregs suppress every arm of immune response, including Th1, Th2, Th17, B, NK cells and DCsTregs play a critical role in the prevention of autoimmune diseases, and functional impairment of Tregs is important in the pathogenesis of psoriasis. Therefore, restoration or strengthening of impaired Treg function would be a desirable therapeutic strategy for psoriasis. The results of the present study suggested appropriately elevated levels of ROS could enhance Treg function, and thus might attenuate psoriasis.”

In particular for clinicians involved in case management of autoimmune disorders, from a personal communication with one of the lead authors Ju-young Seoh, MD, Ph,D.:

“Your understanding, “too much as well as too little antioxidant activity can be harmful, and too aggressive use of antioxidant agent, such as vitamin C, could impair Treg activity and accelerate autoimmune inflammatory activity.” is exact our message.”

 

Clinical Chimica ActaThe authors of a paper just published in Clinica Chimica Acta also note the distinction between low and high levels of ROS and the role of antioxidants:

“Oxidative stress plays a pivotal role in the development of human diseases. Reactive oxygen species (ROS) that includes hydrogen peroxide, hyphochlorus acid, superoxide anion, singlet oxygen, lipid peroxides, hypochlorite and hydroxyl radical are involved in growth, differentiation, progression and death of the cell. They can react with membrane lipids, nucleic acids, proteins, enzymes and other small molecules. Low concentrations of ROS has an indispensable role in intracellular signalling and defence against pathogens, while, higher amounts of ROS play a role in number of human diseases, including arthritis, cancer, diabetes, atherosclerosis, ischemia, failures in immunity and endocrine functions. Antioxidants presumably act as safeguard against the accumulation of ROS and their elimination from the system.”

Antioxidants and Exercise

Journal of the International Society of Sports NutritionIt’s edifying in this context to consider the effects of antioxidants on desirable physiological adaptations to the stress of exercise. In a study recently published in the Journal of the International Society of Sports Nutrition the investigators documented that while antioxidants increased the strength of muscle contraction acutely, there was also a suppression of the desirable growth hormone (GH) response to exercise (which increases muscle mass).

Antioxidant supplementation is known to increase human endogenous antioxidant (AOX) capacity providing a means of blunting exercise induced reactive oxygen species (ROS). The purpose of this study was to compare the effects of a single acute dose of an AOX (vs blinded placebo) on muscle contractile performance and hormonal responses to a single bout of lower limb ‘hypertrophic’ resistance training (RT).”

Their data should be considered in the context of antioxidant supplementation and exercise:

“It was found that in comparison to a placebo mixture, subjects were able to perform 3.75% more work (W), and generate greater mean concentric power and velocity throughout the HTS after consuming the AOX mixture…however circulating GH levels was significantly reduced in the AOX trial compared to the placebo trial…This would suggest that the GH results from this study indicate they may be undesirable in regards to promoting muscular hypertrophy. It is therefore of interest for future studies to examine whether this decreased circulating GH would affect muscular hypertrophy after a prolonged period of use or whether it acutely affects IGF-1 levels. Moreover, recent research suggests excessive AOX supplementation may hinder important physiological training adaptations. This has prompted the suggestion that optimal oxidant content for maximal force production exists within the muscle…GH secretion is involved in MH and strength development and its attenuation may negatively impact training adaptations…These recent findings and the GH results in this study, highlight the need to further our understanding of the effect of AOX supplementation on training adaptations.”

 

Sports MedicineThese results further validate the findings documented in paper published a couple of years earlier in the journal Sports Medicine:

“High levels of reactive oxygen species (ROS) produced in skeletal muscle during exercise have been associated with muscle damage and impaired muscle function. Supporting endogenous defence systems with additional oral doses of antioxidants has received much attention as a noninvasive strategy to prevent or reduce oxidative stress, decrease muscle damage and improve exercise performance…The consistent finding is that antioxidant supplementation attenuates exercise-induced oxidative stress. However, any physiological implications of this have yet to be consistently demonstrated, with most studies reporting no effects on exercise- induced muscle damage and performance. Moreover, a growing body of evidence indicates detrimental effects of antioxidant supplementation on the health and performance benefits of exercise training. Indeed, although ROS are associated with harmful biological events, they are also essential to the development and optimal function of every cell. The aim of this review is to present and discuss 23 studies that have shown that antioxidant supplementation interferes with exercise training-induced adaptations.”

Here again we see that antioxidants have both positive and negative effects:

“The main findings of these studies are that, in certain situations, loading the cell with high doses of antioxidants leads to a blunting of the positive effects of exercise training and interferes with important ROS-mediated physiological processes, such as vasodilation and insulin signalling. More research is needed to produce evidence-based guidelines regarding the use of antioxidant supplementation during exercise training.”

 

Bottom line: The use of antioxidants must be calibrated with careful consideration of the balance between protective and suppressive effects according to the needs of the individual patient by observing appropriate lab values for ROS and oxidative damage, outcomes for regulation of inflammation, and the patient’s subjective impression of energy versus fatigue.

Treating atherosclerosis as an autoimmune inflammatory disease

Immunology LettersAtherosclerosis is a disease characterized by plaque formation in an artery in response to inflammation in the lining (endothelium) of the vessel. It is referred to also as vulnerable plaque because it is subject to rupture followed by the blocking of a smaller downstream artery, the immediate cause of most heart attacks and strokes. A paper recently published in Immunology Letters discusses the treatment of the vascular inflammation of atherosclerosis as an autoimmune inflammatory disorder. The authors state:

Atherosclerosis is a chronic inflammatory disease, in which multiple types of immune cells are involved. Th1 and Th17 cells play a prominent role in induction and progression of local inflammation in the atherosclerotic plaque.”

Note that Th17 cells play a key role in the cascade of factors that produce autoimmune inflammation. Inadequate regulatory T cell (Treg) activity contributes by failing to restrain the autoimmune attack:

Regulatory T cells (Tregs) can be also found in the plaque but their numbers are decreased and function may be impaired. Tregs are the master modulators of the immune system possessing the immunosuppressive capacity to prevent unfavorable immune responses and maintain tolerance to self-antigens. These cells play the atheroprotective role by inhibiting Th1/Th17-mediated proinflammatory response and down-regulating the antigen-presenting function of dendritic cells (DCs). Tregs mediate the immune response through the cell-to-cell contacts and secretion of anti-inflammatory cytokines IL-10 and TNF-beta.”

Improving the function of regulatory T cells is one of the important tactics to ameliorate underlying contributing causes of autoimmune disorders:

“In addition to the natural CD4+CD25+Foxp3+ Tregs presented in the thymus, there are several subtypes of inducible Tregs that can be induced from naïve CD4+ T cells by tolerogenic DCs in the periphery. Thus, stimulation of the immunosuppressive activity of Tregs and increasing numbers of Tregs and immunocompetent DCs has a great clinical potential in prevention and treatment of atherosclerosis and its vascular complications.”

In addition to ascertaining adequate 25-OH Vitamin D levels and ensuring that vitamin D receptors (VDR) are working well (both necessary for Treg production), I suggest that clinicians consider low dose cytokine therapy* to promote IL-10 activity. The authors conclude:

“A promising strategy to induce the anti-atherogenic immune response is an oral administration of anti-inflammatory immunomodulators capable to activate the intestine immune tolerance by recruiting mucosal tolerogenic DCs and inducing Tregs. Induced Tregs can then migrate to the inflamed vascular sites and reduce atherogenesis.”

* Practitioners are welcome to contact me to discuss low dose cytokine therapy.

Erectile Dysfunction is a risk factor for cardiovascular disease and mortality

PLoS MedicineMore evidence that erectile dysfunction is a risk factor for cardiovascular disease is presented in a study just published in PLoS Medicine (Public Library of Science). This should come as no surprise considering that health of vascular  endothelium is one of the elements necessary to ensure blood delivery to the ‘periphery’. The authors added to literature on this topic by examining the degree of erectile dysfunction in relation to cardiovascular risk:

Erectile dysfunction is an emerging risk marker for future cardiovascular disease (CVD) events; however, evidence on dose response and specific CVD outcomes is limited. This study investigates the relationship between severity of erectile dysfunction and specific CVD outcomes.”

To do so they examined hospitalisation and death data for 95,038 men 45 years and older, analyzing the relationship of reported severity of erectile dysfunction to all-cause mortality and hospitalisation for cardiovascular disease. Men with and without previous CVD were, adjusting for age, smoking, alcohol consumption, marital status, income, education, physical activity, body mass index, diabetes, and treatment for hypertension and/or high cholesterol. The data describe a strong association:

“There were 7,855 incident admissions for CVD and 2,304 deaths during follow-up (mean time from recruitment, 2.2 y for CVD admission and 2.8 y for mortality). Risks of CVD and death increased steadily with severity of erectile dysfunction. Among men without previous CVD, those with severe versus no erectile dysfunction had significantly increased risks of ischaemic heart disease (adjusted relative risk [RR] = 1.60), heart failure (8.00), peripheral vascular disease (1.92), “other” CVD (1.26), all CVD combined (1.35), and all-cause mortality (1.93). For men with previous CVD, corresponding RRs (95% CI) were 1.70, 4.40, 2.46, 1.40, 1.64, and 2.37, respectively. Among men without previous CVD, RRs of more specific CVDs increased significantly with severe versus no erectile dysfunction, including acute myocardial infarction (1.66), atrioventricular and left bundle branch block (6.62), and (peripheral) atherosclerosis (2.47), with no significant difference in risk for conditions such as primary hypertension (0.61) and intracerebral haemorrhage (0.78).”

Clinicians’ notes: (1) Phosphodiesterase type 5 inhibitors (Viagra®, etc.) do not remediate the underlying causes. (2) Don’t forget to check ADMA (asymmetric dimethyl arginine levels for endothelial nitric oxide capacity. As authors conclude, erectile dysfunction is an alert to examine all the risk factors for CVD:

These findings give support for CVD risk assessment in men with erectile dysfunction who have not already undergone assessment…The findings of this study highlight the need to consider erectile dysfunction in relation to the risk of a wide range of CVDs that extends beyond ischaemic heart disease and stroke and includes conditions such as heart failure and conduction disorders. They also provide evidence that CVD risk is elevated across a spectrum of severity of erectile dysfunction and that men with mild or moderate erectile dysfunction should be considered at increased risk, in addition to those with severe disease.”

The important role of autoimmunity in cardiovascular disease

Summary: Inflammation of the blood vessels is the fundamental factor in cardiovascular diseases including heart attack and stroke. Vascular inflammation due to autoimmunity, a widespread phenomenon, is not encompassed by the ‘traditional’ metabolic risk factors. In the clinic the autoimmune components of vascular disease must be investigated and treated.

The authors of a paper published in the clinical journal Mædica observe:

“Inflammation plays a crucial role in atherogenesis either by local cellular mechanisms or humoral consequences…inflammation and endothelial dysfunction are triggered by cardiovascular risk factors: hypercholesterolemia, hypertension, smoking or diabetes. In other cases inflammation precedes atherosclerotic changes that occur in autoimmune diseases, as systemic lupus erythematosus and rheumatoid arthritis. In these diseases atherogenesis is mostly independent from conventional risk factors. Irrespective of its cause systemic inflammation is correlated with cardiovascular events.”

They also note:

“The pathogenic mechanisms of autoimmune disorders include an important localized or systemic inflammatory response. This may trigger as an “innocent bystander” reaction a peculiar type of endothelial injury that predisposes to atherogenesis. Many of these diseases are associated with early, accelerated atherosclerosis. This can also be due to concomitant presence of conventional risk factors, but is determined mainly by specific autoimmune and pro-inflammatory mechanisms or by specific medication (i.e. long term systemic corticosteroid use). In these cases atherosclerosis occurs in population subgroups traditionally protected from the atherosclerotic process, as young women that develop systemic lupus erythematosus. Atherothrombosis became the main cause of mortality in autoimmune disorders…Endothelial dysfunction found in early stages of athero genesis in autoimmune diseases is independent from traditional risk factors, depends only on the severity of systemic inflammation.”

As stated by the authors of a paper published in The Netherlands Journal of Medicine, autoimmune conditions such as rheumatoid arthritis and SLE have long been known to increase cardiovascular risk:

Immune-mediated inflammatory diseases (IMIDs), including rheumatoid arthritis and spondyloarthritis, are associated with increased cardiovascular morbidity and mortality, independent of the established cardiovascular risk factors. The chronic inflammatory state, a hallmark of IMIDs, is considered to be a driving force for accelerated atherogenesis.”

They discuss autoimmunity and cardiovascular disease using as models RA, psoriatic arthritis and ankylosing spondyloarthritis, SLE and role of innate and adaptive immunity, concluding:

“Over the past two decades it has become increasingly clear that chronic inflammation is an independent risk factor for cardiovascular events, with an impact over and above established risk factors. Since IMIDs are protracted disorders, the focus on adequate cardiovascular prevention in these patients is long overdue. Pathophysiologically, chronic inflammation provides a direct link between IMIDs and accelerated atherogenesis.”

A fascinating review article, rich with references to other valuable citations, was published recently in the International Journal of Inflammation that expands on the role of oxidative stress in eliciting an autoimmune response that produces cardiovascular inflammation. The authors state:

“Recently, it has become clear that atherosclerosis is a chronic inflammatory disease in which inflammation and immune responses play a key role. Accelerated atherosclerosis has been reported in patients with autoimmune diseases, suggesting an involvement of autoimmune mechanisms in atherogenesis. Different self-antigens or modified self-molecules have been identified as target of humoral and cellular immune responses in patients with atherosclerotic disease. Oxidative stress, increasingly reported in these patients, is the major event causing structural modification of proteins with consequent appearance of neoepitopes. Self-molecules modified by oxidative events can become targets of autoimmune reactions, thus sustaining the inflammatory mechanisms involved in endothelial dysfunction and plaque development.”

The authors acknowledge the role of infectious agents as instigators of autoimmune activity, but emphasize the role of modified self-antigens:

“Although infectious agents have been associated with the activation of immune mechanisms, evidence exist that the main antigenic targets in atherosclerosis are modified endogenous structures [12]. Atherosclerotic plaques express autoantigens that are targeted by both IgM and IgG. It is likely that these autoimmune responses initially have a beneficial effect facilitating the removal of potentially harmful antigens [13, 14]. However, studies performed on hypercholesterolaemic mice deficient in different components of innate and adaptive immunity uniformly indicate that the net effect of immune activation is proatherogenic and that atherosclerosis, at least to some extent, should be regarded as an autoimmune disease.”

They go on to discuss the roles of oxidized LDL, heat shock proteins, Beta2-glycoprotein I (β2-GPI), and oxidized hemoglobin as oxidized agents that act as autoantigens eliciting an autoimmune response implicated in atherogenesis and cardiovascular disease, then conclude by stating:

“Excessive oxidative stress and low-grade chronic inflammation are major pathophysiological factors contributing to the development of cardiovascular diseases…In addition to pro-inflammatory properties, self molecules modified by oxidative events can become targets of autoimmune reactions, thus sustaining the inflammatory mechanisms involved in endothelial dysfunction and plaque development…Modulation of the immune system could represent a useful approach to prevent and/or treat these diseases.”

An excellent paper published in the journal Nature Reviews Rheumatology (formerly Nature Clinical Practice Rheumatology) discusses the mechanisms of atherosclerosis in autoimmune diseases. The authors note:

Many components of the immune system are involved in the pathologic processes underlying the development of atherosclerosis: macrophages that develop into foam cells; T cells; autoantibodies; autoantigens that are components of vessel walls and cholesterol particles; and cytokines that are secreted by cells within atherosclerotic plaques, including interleukin (IL)-1, IL-2, IL-6, IL-8, IL-12, IL-10, tumor-necrosis factor, interferon-gamma and platelet-derived growth factor.”

They note evidence for the role of cellular immunity…

“Several autoimmune diseases are characterized as being TYPE 1 T HELPER (TH1) CELL-mediated or TYPE 2 T HELPER (TH2) CELL-mediated conditions. A study in which ApoE-/- mice were treated with pentoxifylline (an inhibitor of the TH1 differentiation pathway) for 12 weeks suggested that atherosclerosis is a TH1-mediated process.”

And the participation of humoral immunity is characterized by antibodies to oxidized LDL cholesterol and to heat-shock proteins (HSPs):

Oxidized LDL (oxLDL) is the type of LDL cholesterol most likely to be taken up by macrophages that develop into foam cells. Increased levels of anti-oxLDL antibodies have been detected in patients with early-onset peripheral vascular disease, severe carotid atherosclerosis, and angiographically verified coronary artery disease (CAD). In addition, raised levels of oxLDL antibodies were found to be predictive of progression of carotid atherosclerosis, MI, and death…it was found that individuals with atherosclerosis had significantly higher levels of anti-HSP65 antibodies than controls.”

It has long been known that antiphospholipid antibodies (aPL) and anticardiolipin antibodies (aCL) can be associated with cardiovascular disease, and the authors discuss their relation to arterial intima–media thickness (IMT, pathological thickening of the blood vessel wall). They conclude:

“The complex involvement of the immune system in the pathogenesis of atherosclerosis is most evident in patients with autoimmune diseases, but is also important in the general population. Immunomodulation of atherosclerosis carries great potential for future human therapies…

  • Autoimmune rheumatic diseases are characterized by enhanced atherosclerosis, which leads to cardiovascular disease
  • Some forms of atherosclerosis can be detected at the preclinical stage
  • Both cellular and humoral components of the immune system are involved in the pathogenesis of atherosclerosis
  • Classical and nonclassical risk factors for atherosclerosis are associated with accelerated atherosclerosis in autoimmune rheumatic diseases
  • Atherosclerosis can be immunomodulated in experimental models in various ways, which include induction of immune tolerance”

The authors of a paper published in the journal Stroke observe that inflammation plays the critical role in arterial plaque destabilization:

Inflammation is not only instrumental in the development of human atheromatous plaques, but, importantly, plays a crucial role in the destabilization of internal carotid artery plaques, thus converting chronic atherosclerosis into an acute thrombo-embolic disorder.”

Expanding on this…

“…a complex endothelial dysfunction induced by elevated and modified low-density lipoproteins (LDL), free radicals, infectious microorganisms, shear stress, hypertension, toxins after smoking or combinations of these and other factors leads to a compensatory inflammatory response. Endothelial dysfunction is characterized by decreased nitric oxide synthesis, local oxidation of circulating lipoproteins and their entry into the vessel wall. Intracellular reactive oxygen species similarly induced by the multiple atherosclerosis risk factors lead to enhanced oxidative stress in vascular cells and further activate intracellular signaling molecules involved in gene expression. Upregulation of cell adhesion molecules facilitates adherence of leukocytes to the dysfunctional endothelium and their subsequent transmigration into the vessel wall. As outlined in this review, the evolving inflammatory reaction is instrumental in the initiation of atherosclerotic plaques and their destabilization.”

The authors summarize the stream of events leading to plaque rupture:

Inflammation plays an important role in the progression of atherosclerosis and ICA plaque destabilization converting a chronic process into an acute disorder with ensuing thrombo-embolism. During atherosclerosis, T cells and macrophages infiltrate the vessel wall triggered by endothelial dysfunction, and locally interact in a synergistic manner. Autoreactive T cells recognize oxLDL, HSP and shared microbial antigens by molecular mimicry and locally release proinflammatory cytokines. Macrophages on stimulation by T-cell-derived cytokines and transformation into foam cells after uptake of oxLDL secrete MMP predisposing the plaques to subsequent rupture. Plaque-associated macrophages, moreover, are an important cellular source of TF. On plaque rupture TF-rich plaque material gets in contact with the circulation and activates the extrinsic coagulation pathway…Vaccination against modified LDL and HSP can slow development of atherosclerotic plaques. Current therapeutics effective in preventing atherosclerosis and stroke such as statins, ASS [aspirin] and renin-angiotensin system inhibitors may exert part of their effects by modulating inflammatory responses in the vessel wall.”

The authors of a review article published in Clinical and Developmental Immunology consider epigenetic mechanisms involved in autoimmune cardiovascular risk. They state:

Autoimmune diseases (AIDs) have been associated with accelerated atherosclerosis (AT) leading to increased cardio- and cerebrovascular disease risk…many new genes and signalling pathways involved in autoimmunity…have been further detected. Epigenetics, the control of gene packaging and expression independent of alterations in the DNA sequence, is providing new directions linking genetics and environmental factors. Epigenetic regulatory mechanisms comprise DNA methylation, histone modifications, and microRNA activity, all of which act upon gene and protein expression levels. Recent findings have contributed to our understanding of how epigenetic modifications could influence AID development.

In other words, environmental factors that modulate gene expression play a role in ‘turning on’ autoimmunity that promotes heart attacks and strokes. As the authors note:

“It is widely known that AIDs are the result of interaction between predisposing genetic factors, deregulation of the immune system, and environmental triggering factors.”

Of great importance is that these factors can be modified:

“Moreover, epigenetic changes may be reversed. A remarkable example of disease in which epigenetic abnormalities and patterns of inheritance are extremely complex is SLE. The high incidence of twin pairs in which SLE develops in only one of the siblings supports the notion that environmental factors and their involvement in epigenetic modifications could affect the onset of disease.”

And there seem to be differences of autoimmune expression depending on the disease and the individual:

“Significant evidence has shown that there is heterogeneity in the characteristics of vasculopathies underlying different autoimmune diseases such as APS, SLE, RA, and pSS. It has been also shown a relevant heterogeneity with respect to inflammatory risk factors. The data presented in this revision further indicated that epigenetic mechanisms also seem to influence inflammation and cardiovascular disease in those autoimmune conditions.”

The authors of a paper published in Zeitschrift für Rheumatologie (Journal of Rheumatology) note that EULAR (the European League Against Rheumatism) recommends aggressive cardiovascular risk factor management for rheumatoid arthritis, which would be reasonable extrapolate to other autoimmune diseases:

“Beyond the traditional CV risk factors, chronic systemic inflammation has been shown to be a crucial factor in atherosclerosis development and progression from endothelial dysfunction to plaque rupture and thrombosis. Numerous studies have shown that atherosclerosis is not a passive process characterized by accumulation of lipids in the vessel walls, but rather represents active inflammation of the vasculature…According to the recently published EULAR recommendations for CV risk screening and management in patients with inflammatory arthritis, annual CV risk assessment is recommended for all patients with RA. Any CV risk factors identified should be optimally managed. In addition to appropriate CV risk management, aggressive suppression of the inflammatory process is recommended to further lower CV risk.”

Stroke in young women, particularly in the absence of ‘traditional’ risk factors such as elevated cholesterol, hypertension, metabolic syndrome and obesity, etc. is a great concern. In a paper published recently in the Canadian Journal of Neurological Sciences the authors state:

“In women ages 15-45 years, an additional set of risk factors are important in the pathogenesis of ischemic stroke. Some of these pertain strictly to women, and relate to exogenous hormones and pregnancy. Various other conditions are more common in women, which include migraine with aura, selected vascular disorders and autoimmune conditions. These differences do have implications for management in both the primary and secondary prevention of stroke in this age group.”

Of interest to clinicians is another paper in the same journal drawing attention to the role of the cytokine transforming growth factor-β (TGF-β) in vascular inflammation. The authors investigated polymorphisms of the TGF-β gene in ischemic stroke:

“Inflammation plays a pivotal role in the pathogenesis of atherosclerosis and of cerebrovascular complications. Transforming growth factor-β (TGF-β) is a pleiotropic cytokine with a central role in inflammation. To investigate whether polymorphisms of the TGF-β1 gene can modify the risk of ischemic stroke (IS) in Chinese population, we conduct this hospital-based, case-control study.”

They determined the transforming growth factor-β1 genotype in 450 Chinese patients (306 male and 144 female) with ischemic stroke compared to 450 control subjects (326 male and 124 female).

“Subjects carrying 869TT were susceptible to IS (odds ratio [OR] =1.58). Further analysis of IS data partitioned by gender revealed the female-specific association with 869T/C (OR=2.64).”

While the 869TT genotype of the TGF-β1 gene increased the risk of stroke for both sexes, the increase in risk for stroke was 264% for females.

The authors of an interesting paper published recently in the Endocrine Journal investigate the association of chronic inflammation in autoimmune thyroiditis with endothelial (vascular) dysfunction:

“Our study aims to investigate the presence of the well known preceding clinical situations of atherosclerosis like endothelial dysfunction and inflammation in subclinical hypothyroidism.”

They evaluated 37 patients with subclinical hypothyroidism (29 women, 8 men) in comparison to 23 healthy volunteers (19 women, 4 men) for endothelial dysfunction as measured by brachial artery responses to endothelium-dependent (flow mediated dilation, FMD) and endothelium-independent stimuli (sublingual nitroglycerin (NTG)). They also measured serum TNF-alpha, interleukin-6, and hs-CRP, and estimated insulin resistance by HOMA score. The data make paint an interesting picture:

“There were no significant differences in age, body mass index, waist circumference, HOMA scores. There was a statistically significant difference in endothelium-dependent (FMD) and endothelium-independent vascular responses (NTG) between the patients with subclinical hypothyroidism and the normal healthy controls…The TSH and LDL, IL-6, TNF-alpha and hs-CRP levels in the patient group were significantly higher than those in control group. A positive correlation was found only between endothelium-dependent vasodilation and TNF-alpha, hs-CRP and IL-6, TSH, total cholesterol, LDL and triglycerides. Neither of the groups were insulin resistant and there was not any difference either in fasting insulin or in glucose levels. We found endothelial dysfunction in subclinical hypothyroidism group.”

The vascular inflammation associated with autoimmune thyroiditis stands out in high relief against a background of normal traditional risk factors like BMI, waist circumference and insulin resistance. The authors conclude:

“Our findings suggest that there is endothelial dysfunction and low grade chronic inflammation in SH due to autoimmune thyroiditis. There are several contributing factors which can cause endothelial dysfunction in SH such as changes in lipid profile, hyperhomocysteinemia. According to our results low grade chronic inflammation may be one of these factors.”

Finally, in the journal Circulation Research the authors of a commentary  on a study just published in the Journal of Clinical Investigation ask the question “Is Atherosclerosis an Allergic Disease?“:

“A new report in the Journal of Clinical Investigation adds to the ever-increasing evidence that immunological mechanisms play an important role in atherogenesis. These new observations suggest involvement of IgE and its FcϵR1α receptor in the promotion of atherosclerosis, and specifically in plaque instability and clinical events.”

They further note, importantly…

“In addition, aside from conditions in which there are generalized increases in IgE levels, such as parasitic infections and hyper-IgE syndromes, elevated IgE levels usually reflect allergic-type immune responses.”

This is one mechanism by which food and other allergies contribute to the inflammation of cardiovascular disease. The authors conclude:

“The report by Wang et al and other reports describing the potential importance of mast cells to CVD have provided a compelling case to study the role of IgE in inflammatory conditions such as atherosclerosis. It adds to the growing evidence of the importance of immune function in atherogenesis and in particular of the role that immunoglobulins play, both through antigen-specific interactions and antigen-independent regulatory roles.”

Bottom line: In clinical management of cardiovascular disease the autoimmune components should be investigated and addressed with a rational treatment strategy.

Full-fat dairy reduces cardiovascular disease?

European Journal of Clinical Nutrition 0310Studies examining the epidemiological effect of a food rarely disclose its quality and source. Do you ever wonder if a study on meat, for example, might give different results if the subjects consumed only organic grass-fed meat rather than meat from hormone and antibiotic-laced feedlot animals fed on grain silage and offal? A study recently published in the European Journal of Clinical Nutrition came up with a surprise when it investigated the effect of full-fat dairy on cardiovascular disease in Australian adults.

“Dairy foods contain various nutrients that may affect health. We investigated whether intake of dairy products or related nutrients is associated with mortality due to cardiovascular disease (CVD), cancer and all causes.”

The authors studied 1529 adult Australians over 16 years, correlating habitual intakes of dairy products with mortality and cause of death. When the numbers were analyzed an unexpected finding emerged:

“…compared with those with the lowest intake of full-fat dairy, participants with the highest intake had reduced death due to CVD after adjustment for calcium intake and other confounders.”

The data compelled them to record conclusions contrary to popular dogma:

Overall intake of dairy products was not associated with mortality. A possible beneficial association between intake of full-fat dairy and cardiovascular mortality needs further assessment and confirmation.”

Veterinary Research CommunicationsPerhaps it has something to with what the cows were eating. A study published just last month in the journal Veterinary Research Communications compared the effect of grass hay versus grain (maize = corn) on the properties of the milk to promote cardiovascular disease.

“14 Holstein dairy cows were fed…either grass hay (GH) or maize silage (MS). Milk samples were collected…and fatty acid (FA) profiles were analyzed…Milk from animals fed the GH-diet contained lower concentrations of saturated FAs and higher levels of polyunsaturated FAs (PUFAs). Feeding additional hay also increased conjugated linoleic acid and n-3 FA levels and decreased C16:0 levels.”

What do these differences in fatty acids mean for cardiovascular disease risk?

“Increases in both PUFAs and n-3 FAs resulted in lower atherogenic and thrombogenic indices in milk from animals fed the GH diet compared with those fed the MS diet. A complete substitution of GH for MS appeared to improve milk FA profiles….”

American Journal of Clinical NutritionToo bad the authors of the Australian study weren’t able to specify what those Australian cows ate. But another fascinating study just published in the American Journal of Clinical Nutrition sheds more light on the matter. The authors begin by observing:

“Despite the high saturated fat content of dairy products, no clear association between dairy product intake and risk of myocardial infarction (MI) has been observed. Dairy products are the main source of conjugated linoleic acid (CLA; 18:2n–7t), which is produced by the ruminal biohydrogenation of grasses eaten by cows. Pasture-grazing dairy cows have more CLA in their milk than do grain-fed cows. Some animal models have reported beneficial effects of CLA on atherosclerosis.”

The authors wanted to determine the association between CLA in adipose tissue and risk of MI [myocardial infarction]. They used 1813 individuals with non-fatal heart attacks compared to matched controls, in Costa Rica where people use traditional pasture-grazing for dairy cows. What did their data show?

Adipose tissue CLA was associated with a lower risk of MIDairy intake was not associated with risk of MI, despite a strong risk associated with saturated fat intake.”