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. A state of cellular resistance to insulin action subtends the observed hyperinsulinism. With the insulin/glucose-clamp technique, in combination with tracer glucose infusion and indirect calorimetry, it has been demonstrated that the insulin resistance of essential hypertension is located in peripheral tissues (muscle), is limited to nonoxidative pathways of glucose disposal (glycogen synthesis), and 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. Physiological maneuvers, such as calorie restriction (in the overweight patient) and regular physical exercise, can improve tissue sensitivity to insulin; evidence indicates that these maneuvers can also lower blood pressure in both normotensive and hypertensive individuals. 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. 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.

Insulin Resistance: A Multifaceted Syndrome Responsible for NIDDM, Obesity, Hypertension, Dyslipidemia, and Atherosclerotic Cardiovascular Disease

Background Although it is generally accepted that lowering elevated serum levels of low-density lipoprotein (LDL) cholesterol in patients with coronary heart disease is beneficial, there are few data to guide decisions about therapy for patients whose primary lipid abnormality is a low level of high-density lipoprotein (HDL) cholesterol. Methods We conducted a double-blind trial comparing gemfibrozil (1200 mg per day) with placebo in 2531 men with coronary heart disease, an HDL cholesterol level of 40 mg per deciliter (1.0 mmol per liter) or less, and an LDL cholesterol level of 140 mg per deciliter (3.6 mmol per liter) or less. The primary study outcome was nonfatal myocardial infarction or death from coronary causes. Results The median follow-up was 5.1 years. At one year, the mean HDL cholesterol level was 6 percent higher, the mean triglyceride level was 31 percent lower, and the mean total cholesterol level was 4 percent lower in the gemfibrozil group than in the placebo group. LDL cholesterol levels...

https://www.nejm.org/doi/pdf/10.1056/NEJM199908053410604

Gemfibrozil for the Secondary Prevention of Coronary Heart Disease in Men with Low Levels of High-Density Lipoprotein Cholesterol

Context: The prevalence of abnormal thyroid function in the United States and the significance of thyroid dysfunction remain controversial. Systemic effects of abnormal thyroid function have not been fully delineated, particularly in cases of mild thyroid failure. Also, the relationship between traditional hypothyroid symptoms and biochemical thyroid function is unclear. Objective: To determine the prevalence of abnormal thyroid function and the relationship between (1) abnormal thyroid function and lipid levels and (2) abnormal thyroid function and symptoms using modern and sensitive thyroid tests. Design: Cross-sectional study.

https://jamanetwork.com/journals/jamainternalmedicine/articlepdf/415184/ioi90027.pdf

The Colorado Thyroid Disease Prevalence Study

The apo E locus contributes to determining the variation in plasma cholesterol levels of healthy and diseased populations. It also influences the expression of hyperlipidemia and appears to modulate the susceptibility to atherosclerosis in a complex multifactorial interaction. There is evidence that the presence of apo E2 is protective, whereas that of apo E4 predisposes to coronary artery disease. The burden of proof, however, lies on future, well-designed clinical trials and prospective studies. The study of the biological significance of the apo E polymorphism in humans has emphasized the importance of gene-gene and gene-environment interactions in the pathogenesis of hyperlipidemia and atherosclerosis. The apo E polymorphism involves the coding region of the apo E gene and results in alterations of the gene product which, in turn, either directly or secondarily affect the metabolic fate of the lipoprotein particles. Rapid advances in knowledge over the last decade have provided a metabolic explanation for the observation of the opposite effects of the epsilon 4 and the epsilon 2 alleles on lipoprotein levels. Apo E2 has lower receptor binding affinity which results in delayed clearance of apo E2-bearing lipoprotein particles from plasma. Apo E4 is distributed differently from apo E3 between VLDL and HDL, is degraded more rapidly than apo E3, and may enhance the catabolism of E4-bearing particles, leading to other alterations in lipoprotein metabolism which result in elevated levels of LDL. In view of the significant opposite impacts of the epsilon 4 and the epsilon 2 alleles on plasma LDL cholesterol concentrations, it is evident that determination of the apo E phenotype will become a useful adjunct to the assessment of the cardiovascular risk profile of an individual. In addition, the relationship between the epsilon 2 allele and type III hyperlipoproteinemia provides a valuable model for the study of complex genetic interactions in the pathogenesis of hyperlipidemia. The further study of apo E and its interactions shows great promise for a deeper comprehension of the pathogenesis of atherosclerosis.

Apolipoprotein E polymorphism and atherosclerosis.

ContextElevated nonfasting triglycerides indicate the presence of remnant lipoproteins, which may promote atherosclerosis.ObjectiveTo test the hypothesis that very high levels of nonfasting triglycerides predict myocardial infarction (MI), ischemic heart disease (IHD), and death.Design, Setting, and ParticipantsA prospective cohort study of 7587 women and 6394 men from the general population of Copenhagen, Denmark, aged 20 to 93 years, followed up from baseline (1976-1978) until 2004.Main Outcome MeasuresHazard ratios (HRs) for incident MI, IHD, and total death according to baseline nonfasting triglyceride level categories of 1 to 1.99 mmol/L (88.5-176.1 mg/dL), 2 to 2.99 mmol/L (177.0-264.6 mg/dL), 3 to 3.99 mmol/L (265.5-353.0 mg/dL), 4 to 4.99 mmol/L (354.0-441.6 mg/dL), and 5 mmol/L or more (≥442.5 mg/dL) vs triglyceride levels of less than 1 mmol/L (<88.5 mg/dL).ResultsWith increasing levels of nonfasting triglycerides, levels of remnant lipoprotein cholesterol increased. During a mean follow-up of 26 years, 1793 participants (691 women and 1102 men) developed MI, 3479 (1567 women and 1912 men) developed IHD, and 7818 (3731 women and 4087 men) died. For MI, among women, the age-adjusted HRs and multifactorially adjusted HRs (aHRs) for each respective category per 1-mmol/L increase in nonfasting triglyceride levels were 2.2 (aHR, 1.7), 4.4 (aHR, 2.5), 3.9 (aHR, 2.1), 5.1 (aHR, 2.4), and 16.8 (aHR, 5.4); for both, P for trend < .001. For MI, among men, the values were 1.6 (aHR, 1.4), 2.3 (aHR, 1.6), 3.6 (aHR, 2.3), 3.3 (aHR, 1.9), and 4.6 (aHR, 2.4); for both, P for trend < .001. For IHD, among women, the values were 1.7 (aHR, 1.4), 2.8 (aHR, 1.8), 3.0 (aHR, 1.8), 2.1 (aHR, 1.2), and 5.9 (aHR, 2.6); for both, P for trend < .001. For IHD, among men, the values were 1.3 (aHR, 1.1), 1.7 (aHR, 1.3), 2.1 (aHR, 1.3), 2.0 (aHR, 1.2), and 2.9 (aHR, 1.5); P for trend < .001 for age-adjusted and P for trend = .03 for multifactorially adjusted. For total death, among women, the values were 1.3 (aHR, 1.3), 1.7 (aHR, 1.6), 2.2 (aHR, 2.2), 2.2 (aHR, 1.9), and 4.3 (aHR, 3.3); for both, P for trend < .001. For total death, among men, the values were 1.3 (aHR, 1.2), 1.4 (aHR, 1.4), 1.7 (aHR, 1.5), 1.8 (aHR, 1.6), and 2.0 (aHR, 1.8); for both, P for trend < .001.ConclusionIn this general population cohort, elevated nonfasting triglyceride levels were associated with increased risk of MI, IHD, and death in men and women.

https://jamanetwork.com/journals/jama/articlepdf/208012/joc70073_299_308.pdf

Nonfasting triglycerides and risk of myocardial infarction, ischemic heart disease, and death in men and women

In the Helsinki Heart Study, a randomized five-year, double-blind trial, a 34% reduction in the incidence of coronary heart disease (CHD) was observed in dyslipidemic men treated with gemfibrozil. Averaged over the five years of the trial, gemfibrozil therapy produced, compared with placebo, mean decreases of 10% in serum total cholesterol level, 14% in non-high-density lipoprotein (HDL) cholesterol level, 11% in low-density lipoprotein (LDL) cholesterol level, 35% in triglyceride level, and a mean increase of 11% in HDL cholesterol level from baseline levels measured prior to treatment. While changes in HDL cholesterol level were similar in all Fredrickson types, the effect on concentrations of total cholesterol and LDL cholesterol was largest in type IIA and on LDL minimal in type IV. The reduction of CHD incidence over placebo was largest in type IIB and smallest in type IIA. The lipid changes were dependent on lipid levels prior to treatment and on compliance with the medication regimen. When risk factors for CHD, including age, blood pressure, smoking and drinking habits, baseline lipid levels, and exercise and relative weight, were controlled by applying the Cox proportional hazards model, the changes in serum HDL and LDL cholesterol levels were both statistically significantly associated with the decline in CHD incidence within the gemfibrozil-treated group. The large decrease in serum triglyceride levels had relatively small effect on CHD incidence. Thus, the results of this study, together with earlier observations, suggest that both elevating HDL and lowering LDL cholesterol levels are effective in the primary prevention of CHD. (JAMA1988;260:641-651)

Lipid Alterations and Decline in the Incidence of Coronary Heart Disease in the Helsinki Heart Study

Apolipoprotein E polymorphism in the Finnish population: gene frequencies and relation to lipoprotein concentrations.

Evidence for the role of hepatic endothelial lipase in the metabolism of plasma high density lipoprotein2 in man

Physically well-trained people generally have lower VLDL-triglyceride and higher HDL-cholesterol levels than sedentary subjects. To examine the underlying mechanisms of this lipoprotein pattern, we measured the lipoprotein lipase (LPL) activity in needle biopsy specimens of adipose tissue and skeletal muscle of competitive runners and of body weight-matched, physically less-active controls. The active sportsmen were either sprinters, whose training program consisted mainly of athletics of short duration or long distance runners undergoing a strenuous endurance exercise program. In sprinters (all males) the serum lipid and lipoprotein concentrations did not differ significantly from those of controls and the mean LPL activities in muscle and adipose tissue were also similar in these two groups. The long distance runners (both sexes), on the other hand, had higher means levels of HDL-cholesterol than the respective controls. The LPL-activity of both adipose tissue (p less than 0.05) and skeletal muscle (p less than 0.01) was significantly higher in male long distance runners than in control males. Female runners had higher muscle LPL activity than controls (p less than 0.01) but in adipose tissue the difference in LPL activity was not significant. Rough estimates calculated for LPL activity present in whole body adipose tissue and skeletal muscle indicated that total LPL activity was 2.3 times higher in male long distance runners and 1.5 times higher in female long distance runners than in the respective controls. In combined groups of male runners and controls, there was a highly significant positive correlation between the serum HDL-cholesterol level and the LPL activity of adipose tissue expressed per tissue weight (r = +0.72, p less than 0.001) or per whole body fat (r = +0.62, p less than 0.001). The group means of HDL-cholesterol and adipose tissue LPL activity in the five cohorts studied (male sprinters, distance runners and controls and female distance runners and controls) were also positively correlated (r = +0.94). It is concluded that endurance training is associated with an adaptive increase of LPL activity not only in skeletal muscle but also in adipose tissue. These changes are not observed in sprinters who are trained by exercises of shorter duration. The high HDL-cholesterol levels of physically well-trained people are probably accounted for, at least partly, by the increased LPL activity and the concomitant rapid turnover or triglyceride-rich lipoproteins.

Esko A. Nikkilä

Papers

Lipid Alterations and Decline in the Incidence of Coronary Heart Disease in the Helsinki Heart Study

Apolipoprotein E polymorphism in the Finnish population: gene frequencies and relation to lipoprotein concentrations.

Evidence for the role of hepatic endothelial lipase in the metabolism of plasma high density lipoprotein2 in man

Lipoprotein lipase activity in adipose tissue and skeletal muscle of runners: relation to serum lipoproteins.

An immunochemical method for the selective measurement of two triglyceride lipases in human postheparin plasma.