Gemfibrozil treatment of endogenous hypertriglyceridemia: effect on insulin-mediated glucose disposal and plasma insulin concentrations

The Interplay between Non-Esterified Fatty Acids and Plasma Zinc and Its Influence on Thrombotic Risk in Obesity and Type 2 Diabetes

Thrombosis is a major comorbidity of obesity and type-2 diabetes mellitus (T2DM). Despite the development of numerous effective treatments and preventative strategies to address thrombotic disease in such individuals, the incidence of thrombotic complications remains high. This suggests that not all the pathophysiological mechanisms underlying these events have been identified or targeted. Non-esterified fatty acids (NEFAs) are increasingly regarded as a nexus between obesity, insulin resistance, and vascular disease. Notably, plasma NEFA levels are consistently elevated in obesity and T2DM and may impact hemostasis in several ways. A potentially unrecognized route of NEFA-mediated thrombotic activity is their ability to disturb Zn²⁺ speciation in the plasma. Zn²⁺ is a potent regulator of coagulation and its availability in the plasma is monitored carefully through buffering by human serum albumin (HSA). The binding of long-chain NEFAs such as palmitate and stearate, however, trigger a conformational change in HSA that reduces its ability to bind Zn²⁺, thus increasing the ion’s availability to bind and activate coagulation proteins. NEFA-mediated perturbation of HSA-Zn²⁺ binding is thus predicted to contribute to the prothrombotic milieu in obesity and T2DM, representing a novel targetable disease mechanism in these disorders.

Changes in Plasma Free Fatty Acids Associated with Type-2 Diabetes

Type 2 diabetes mellitus (T2DM) is associated with increased total plasma free fatty acid (FFA) concentrations and an elevated risk of cardiovascular disease. The exact mechanisms by which the plasma FFA profile of subjects with T2DM changes is unclear, but it is thought that dietary fats and changes to lipid metabolism are likely to contribute. Therefore, establishing the changes in concentrations of specific FFAs in an individual’s plasma is important. Each type of FFA has different effects on physiological processes, including the regulation of lipolysis and lipogenesis in adipose tissue, inflammation, endocrine signalling and the composition and properties of cellular membranes. Alterations in such processes due to altered plasma FFA concentrations/profiles can potentially result in the development of insulin resistance and coagulatory defects. Finally, fibrates and statins, lipid-regulating drugs prescribed to subjects with T2DM, are also thought to exert part of their beneficial effects by impacting on plasma FFA concentrations. Thus, it is also interesting to consider their effects on the concentration of FFAs in plasma. Collectively, we review how FFAs are altered in T2DM and explore the likely downstream physiological and pathological implications of such changes.

PPARalpha activation elevates blood pressure and does not correct glucocorticoid-induced insulin resistance in humans

Fibrates, activators of the nuclear receptor PPARalpha, improve dyslipidemia, but their effects on insulin resistance and vascular disease are unresolved. To test the hypothesis that PPARalpha activation improves insulin resistance and vascular function, we determined the effects of fenofibrate in healthy adults with insulin resistance induced by short-term glucocorticoid administration. Eighteen normal-weight subjects were studied in four stages: at baseline, after 21 days of fenofibrate (160 mg/day) alone, after 3 days of dexamethasone (8 mg/day) added to fenofibrate, and after 3 days of dexamethasone added to placebo (dexamethasone alone). Dexamethasone alone caused hyperinsulinemia, increased glucose, decreased glucose disposal, and reduced insulin-induced suppression of hepatic glucose production as determined by hyperinsulinemic euglycemic clamp and increased systolic blood pressure as determined by ambulatory monitoring, features associated with an insulin-resistant state. Fenofibrate improved fasting LDL and total cholesterol in the setting of dexamethasone treatment but had no significant effect on levels of insulin or glucose, insulin-stimulated glucose disposal, or insulin suppression of glucose production during clamps, or ambulatory monitored blood pressure. In the absence of dexamethasone, fenofibrate lowered fasting triglycerides and cholesterol but unexpectedly increased systolic blood pressure by ambulatory monitoring. These data suggest that PPARalpha activation in humans does not correct insulin resistance induced by glucocorticoids and may adversely affect blood pressure.

Insulin resistance and cardiovascular events with low HDL cholesterol: the Veterans Affairs HDL Intervention Trial (VA-HIT)

OBJECTIVE

To assess the effect of insulin resistance and the benefit of the fibrate, gemfibrozil, on the incidence of major cardiovascular events in subjects with low HDL cholesterol and a broad range of triglyceride values who participated in the Veterans Affairs High Density Lipoprotein Intervention Trial (VA-HIT).

RESEARCH DESIGN AND METHODS

This intention-to-treat analysis, specified as a secondary objective in VA-HIT, determined using Cox proportional hazards models the 5-year combined incidence of nonfatal myocardial infarction, coronary heart disease (CHD) death, or stroke in relation to the presence or absence of insulin resistance (defined by the highest tertile of the homeostasis model assessment of insulin resistance, HOMA-IR) in conjunction with lower and higher levels of HDL cholesterol and triglycerides. The study population consisted of 2,283 men with known coronary heart disease (CHD), treated with either placebo or gemfibrozil, who could be subdivided into groups with diabetes with or without insulin resistance, with no diabetes but insulin resistance, and with neither diabetes nor insulin resistance.

RESULTS

With insulin resistance there was a significantly higher relative risk (RR) of a cardiovascular event both with diabetes (RR of 1.62 with 95% CI of 1.28-2.06) and without diabetes (RR of 1.43 with 95% CI of 1.03-1.98) than without insulin resistance. Throughout both lower and higher ranges of HDL cholesterol and triglycerides, the rate of new cardiovascular events and the reduction of events with gemfibrozil was greater in subjects with insulin resistance than without, despite the finding that an increase in HDL cholesterol and a decrease in triglycerides with gemfibrozil was less with insulin resistance than without insulin resistance.

CONCLUSIONS

Results show that in VA-HIT the occurrence of a new cardiovascular event and the benefit of fibrate therapy was much less dependent on levels of HDL cholesterol or triglycerides than on the presence or absence of insulin resistance.