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.

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.

As insulin goes up so does the danger of arterial plaques

Most readers of these posts, practitioner and layperson alike, have probably long been aware of the role of insulin resistance in cardiovascular disease, chronic inflammation and cancer as described in last week’s New York Times article. A fascinating study that adds to the mountain of scientific evidence was just published in the Public Library of Science (PLoS One) in which the authors show that higher insulin levels are associated with the unstable form of carotid artery plaque:

“The stability of atherosclerotic plaques determines the risk for rupture, which may lead to thrombus formation and potentially severe clinical complications such as myocardial infarction and stroke. Although the rate of plaque formation may be important for plaque stability, this process is not well understood. We took advantage of the atmospheric 14C-declination curve (a result of the atomic bomb tests in the 1950s and 1960s) to determine the average biological age of carotid plaques.”

The authors dissected the cores of carotid plaques from 29 patients with carotid stenosis and analyzed them for 14C. Their findings are fascinating:

“The average plaque age (i.e. formation time) was 9.6±3.3 years. All but two plaques had formed within 5–15 years before surgery. Plaque age was not associated with the chronological ages of the patients but was inversely related to plasma insulin levels…plaques in the lowest tercile of plaque age (most recently formed) were characterized by further instability with a higher content of lipids and macrophages…Microarray analysis of plaques in the lowest tercile also showed increased activity of genes involved in immune responses and oxidative phosphorylation.”

As readers here know, a heart attack or stroke occurs when a vulnerable plaque ruptures and blocks a smaller vessel downstream. These investigators show that unstable plaque is associated with higher insulin levels. Intervening to reduce insulin resistance is one of the most important things that clinicians and patients can do for a host of conditions. The authors conclude:

“Our results show, for the first time, that plaque age, as judge[d] by relative incorporation of 14C, can improve our understanding of carotid plaque stability and therefore risk for clinical complications. Our results also suggest that levels of plasma insulin might be involved in determining carotid plaque age.”

Regarding laboratory testing to determine the presence of inflamed vulnerable plaque, see the earlier post on Lp-PLA2.

Cholesterol crystals are a trigger for local and systemic inflammation. What then?

Journal of Clinical LipidologyThere is an evidence-based middle ground between the dogmas of those who assert that cholesterol is the main cause of cardiovascular disease and those who insist that its contribution is trivial. An interesting paper just published in the Journal of Clinical Lipidology illustrates an important mechanism by which cholesterol crystals trigger an inflammatory response.

“The response to arterial wall injury is an inflammatory process, which over time becomes integral to the development of atherosclerosis and subsequent plaque instability…In this review, a model of plaque rupture is hypothesized with two stages of inflammatory activity.”

In the first stage buildup of cholesterol crystals inside the “foam” cells that accumulate cholesterol induces their death (“apoptosis”); these dead cells elicit an inflammatory response that gathers more lipids into a vulnerable plaque. In stage two further expansion of crystals leads to intimal (blood vessel wall) injury…

“…which can manifest as a clinical syndrome with a systemic inflammation response…We recently demonstrated that when cholesterol crystallizes from a liquid to a solid state, it undergoes volume expansion, which can tear the plaque cap. This observation of cholesterol crystals perforating the cap and intimal surface was made in the plaques of patients who died with acute coronary syndrome.”

The authors refer to their previous work showing that alcohol, aspirin and statins can dissolve cholesterol crystals. Their conclusion:

“…we propose that cholesterol crystallization could help explain in part both local and systemic inflammation associated with atherosclerosis.”

American Journal of CardiologyOf course there are a number of other pathways to  inflammation in cardiovascular disease (please see related posts) but this is one of the reasons why I prefer that patients who have both high cholesterol and evidence of inflammation have the benefit of the natural statin derived from red rice yeast with the necessary supportive and protective cofactors including coenzyme Q10. This paper published recently in the American Journal of Cardiology provides evidence that red rice yeast is as effective and better tolerated than the commonly prescribed drug pravastatin:

“The present trial evaluated the tolerability of red yeast rice versus pravastatin in patients unable to tolerate other statins because of myalgia.”

The authors enrolled adults who had to discontinue statins due to muscle pain. Their findings are reassuring for those who prefer a natural alternative to pharma statins:

“The low-density lipoprotein cholesterol level decreased 30% in the red yeast rice group and 27% in the pravastatin group. In conclusion, red yeast rice was tolerated as well as pravastatin and achieved a comparable reduction of low-density lipoprotein cholesterol in a population previously intolerant to statins.”

This is a serious issue. Statin-associated myalgia or the diagnosis rhabdomyolysis does not do justice to the devastating side effects I recently observed in a patient who had a bad reaction to lovastatin.

AtherosclerosisBut how do we know when to intervene since high cholesterol alone is not a reliable risk factor and CRP (c-reactive protein) may not be elevated if the inflammation it is supposed to report is also preventing the liver from making it? One very helpful test for discriminating whether high cholesterol is contributing to vascular disease is the lipoprotein-associated phospholipase A2 (Lp-PLA2, PLAC) test, described here in an earlier post, that is associated specifically with inflammation in plaques. Another relies on the fact that it is cholesterol that has been damaged by oxidation that participates in the vascular lesion. To gauge this we can measure lipid peroxides. As this paper published in the journal Atherosclerosis documents, atherosclerosis is strongly associated with the presence of oxidized LDL:

“We investigated the relation between serum lipids including oxidized LDL and the severity of coronary atherosclerosis. Serum lipids and oxidized LDL was measured in 62 men (33–66 years), who underwent diagnostic coronary angiography and sonography to measure the carotid intima-media thickness…Regression analysis indicated that the carotid intima-media thickness and…the ox-LDL:LDL ratio…were the only factors associated independently with the severity of coronary atherosclerosis.”

Seminars in Thrombosis & HemostasisWe have also a fascinating study just published in the German medical journal Seminars in Thrombosis & Hemostasis that shows how oxidized LDL taken up by platelets induces inflammation in the blood vessel:

“Platelets are involved in the initiation of atherosclerosis by adherence to inflamed endothelium…In this study we investigated the functional consequences of oxidized low-density lipoprotein (oxLDL) uptake on platelet function and interaction with the endothelium.”

The authors were actually able to visualize the intracellular vesicles (microscopic sacs) containing the oxidized LDL using immunoflorescence microscopy. They made a fascinating observation: the platelets containing oxLDL provoked more cellular stickiness than regular LDL, oxLDL in the bloodstream or platelets without oxLDL.

“Furthermore, oxLDL-laden platelets induced foam cell development from CD34+ progenitor cells. On endothelial regeneration, oxLDL-laden platelets had the opposite effect: The number of CD34+ progenitor cells (colony-forming units) able to transform into endothelial cells was significantly reduced in the presence of oxLDL-platelets, whereas native LDL had no effect.”

This is a striking insight: it was only the oxidized LDL that prevented the endothelial cells (lining the blood vessel wall) from repairing, not the ‘native’ LDL.

Doctors and patients alike need to bear in mind the summary of their findings:

“Our results demonstrate that activated platelets internalize oxLDL and that oxLDL-laden platelets activate endothelium, inhibit endothelial regeneration, and promote foam cell development. Platelet oxLDL contributes significantly to vascular inflammation and is able to promote atherosclerosis.”

LipidsBut, you may ask, since diabetes and pre-diabetes (metabolic syndrome) are so strongly associated with cardiovascular disease shouldn’t there be some kind of connection here? This study published in the journal Lipids shows the evidence that there is.

Oxidized low-density lipoprotein (ox-LDL) plays a key role in the progression of atherosclerosis and diabetes complications. The aim of this study was first, to evaluate the association between ox-LDL and diabetes duration, and second, to examine serum level of ox-LDL in patients with prolonged diabetes and a desirable LDL-cholesterol level.”

It’s important to appreciate that the study group had ‘regular’ LDL in the desirable range, so a typical blood test would appear to be fine. Their very interesting observation is that the longer the person had diabetes (= the longer the risk factor for cardiovascular disease was building up) the more oxLDL they had in proportion to regular LDL:

“The ox-LDL-to-LDL ratio was dramatically higher in patients with diabetes duration >5 years in comparison to newly diagnosed patients and healthy participants. Ox-LDL was significantly associated with diabetes duration.”

Their final comments must be borne in mind by anyone caring for patients with both diabetes and a significant burden of insulin resistance:

“In conclusion, this study showed that the serum ox-LDL level increases with the length of diabetes, even though the patients’ LDL-cholesterol level is maintained at a desirable level. Our findings highlight that possibly more attention should be focused on markers of oxidative stress in the management of lipids in diabetic patients.”

Blood PressureCan we reliably measure oxidized LDL as implied by the lab test mentioned above? This study published in the journal Blood Pressure assure us that we can:

Cardiovascular diseases are accompanied by the presence of active oxygen species and organic free radical generation. The aim of this study was to examine the possibility of using malondialdehyde (MDA)-modified low-density lipoprotein (LDL) analyses as a diagnostic and prognostic biomarker.”

MDA-modified LDL is the same as oxLDL. What conclusion did they draw from their data?

“MDA-modified LDL estimation has a diagnostic accuracy and may be used as an independent biochemical marker for atherosclerosis.”

Truthfully, the functional approach to cardiovascular disease encompasses a number of other important aspects, but I’m wondering if you’ve gotten this far. As a reward for your diligence I’ll conclude this limited post with a few interesting items of satisfying practical significance. First we have a paper just published in The Journal of Steroid Biochemistry & Molecular Biology that reassures us of the benefit of vitamin D in the prevention and treatment of cardiovascular disease.

Journal of Steroid Biochem & Molec Bio“Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in patients with type 2 diabetes mellitus (T2DM). In type 2 diabetics, the prevalence of vitamin D deficiency is 20% higher than in non-diabetics, and low vitamin D levels nearly double the relative risk of developing CVD compared to diabetic patients with normal vitamin D levels.”

The authors endeavored to uncover the mechanism behind vitamin D’s benefit:

“We found that 1,25-dihydroxy vitamin D3 [1,25(OH)2D3] suppressed foam cell formation by reducing acetylated low density lipoprotein (AcLDL) and oxidized low density lipoprotein (oxLDL) cholesterol uptake in diabetics only. …In addition, 1,25(OH)2D3…improved insulin signaling, downregulated SR-A1 expression, and prevented oxLDL- and AcLDL-derived cholesterol uptake.”

You can remember their conclusion when getting your vitamin D level checked:

“The results of this research reveal novel insights into the mechanisms linking vitamin D signaling to foam cell formation in diabetics and suggest a potential new therapeutic target to reduce cardiovascular risk in this population.”

Anatolian Journal of CardiologyThrow some nuts in there too. A nice original study was published not long ago in The Anatolian Journal of Cardiology evaluated the benefit of hazelnuts (filberts) on atherosclerosis. The authors observed a number of interesting effects:

“Lag time for oxidation and α-tocopherol content of LDL were found to be increased while ox-LDL levels decreased during the study period. Total cholesterol, LDL-cholesterol, apolipoprotein (apo) B and apo B/apo AI ratio were found to be significantly lower while apo AI was higher. In respect to LDL subfraction, ratio of large/small LDL was significantly increased at the end of the study.”

They summed up their ‘take home’ message  on hazelnuts (which earlier posts suggest applies to most if not all nuts) accordingly:

“Hazelnut-enriched diet may play important role in decrease in atherogenic tendency of LDL by lowering the susceptibility of LDL to oxidation and plasma ox-LDL levels, and increasing the ratio of large/small LDL beyond its beneficial effect on lipid and lipoprotein levels.”

Digestive Diseases and SciencesHelicobacter pylori infection is, as you likely know, extremely common—according to WHO the most common infection in the world. It is a causative agent in almost all gastric ulcers. We see it here all the time. Finding out if you have it and getting it treated is another important therapeutic point for cardiovascular disease as this paper just published in the journal Digestive Diseases and Sciences reminds us. The authors investigated the impact of H. pylori infection on coronary atherosclerosis by examining the effects of infection on levels of serum lipid, high-sensitivity C-reactive protein (hsCRP) and oxidized low-density protein (oxLDL). What did their data show?

“The levels of total cholesterol, LDL, apolipoprotein B, serum hsCRP, oxLDL were significantly elevated and the severity of coronary atherosclerosis was significantly increased in H. pylorigroup.”

Their conclusion echoes the findings of other investigators:

“More serious coronary atherosclerosis was observed in CHD patients with H. pylori…infection. H. pylori…infection might be involved in coronary atherosclerosis by modifying serum lipids, enhancing LDL oxidation, and activating the inflammatory responses.”

Remember, the most reliable ways to diagnose H. pylori infection are by stool antigens, a provoked breath test, or PCR (DNA amplification). H. pylori antibodies are not dependable.

AngiologyAlthough it’s a major topic that deserves more space, mention at least much be made of the autoimmune aspect of cardiovascular disease as described in this recent paper published in the journal Angiology:

Atherosclerosis is now recognized as a chronic inflammatory disease and is characterized by features of inflammation at all stages of its development. It also appears to display elements of autoimmunity, and several autoantibodies including those directed against oxidized low-density lipoprotein (ox-LDL) and heat shock proteins (Hsps) have been identified in atherosclerosis.”

The authors then describe their investigation of immune complexes, antibodies and receptor signaling in this process. Certain cases demand a thorough evaluation of the autoimmune component of their CVD.

EndocrinologyIt would also not be appropriate to close without at least alluding to the influence of hormones on cardiovascular disease, a topic that has many aspects treated in other posts. This paper recently published in the journal Endocrinology makes a very important but little known point for men (for whom most everyone knows that too little testosterone or excess conversion to estrogen is a big risk factor for CVD). Testosterone is normally converted into its dihydrotestosterone form (DHT) which does a lot of the heavy lifting because it’s ten times stronger than the original. Men with prostate disease are commonly prescribed medications (including saw palmetto) that block the conversion of testosterone to DHT, but without first measuring the levels of the bioactive forms of these hormones. These medications don’t always help because not everyone with a prostate condition has too much DHT. Moreover, DHT is important for protection against cardiovascular disease. The authors…

“…investigated the effect of…dihydrotestosterone (DHT) on the rabbit atherogenesis in relation to…oxidized-low-density lipoprotein receptor-1 (LOX-1) and its downstream molecules.”

What did they find?

“…DHT significantly reduced HCD-induced [high cholesterol diet-induced] foam cell formation…DHT inhibited the formation of foam cells induced by oxidized low-density lipoprotein. Moreover, the expression of LOX-1 and inflammatory cytokines in the cultured macrophages was significantly suppressed by DHT.”

Inappropriately blocking the conversion of testosterone to DHT can thus open a door to cardiovascular disease. So remember, both gentlemen and ladies: no hormone interventions without measuring the free-fraction bioactive levels before and after!