Disturbances in dietary fat metabolism and their role in the development of atherosclerosis

Abstract

It was suggested that postprandial lipoproteins (PPLp) may play an important role in atherogenesis. To examine this hypothesis, we studied PPLp metabolism in normolipidemic individuals and hyperlipoproteinemic (HLP) patients on various diets, physical activity programs and hypolipidemic drugs as well as in patients with coronary artery disease (CAD). We used the vitamin A-fat loading test, which labels intestinally derived lipoproteins with retinyl palmitate. Type IV HLP patients demonstrated a severe defect in chylomicron clearance. Type III HLP patients showed severely disordered clearance of chylomicron remnants. Compared to the saturated fatty acid enriched diet, the omega 6 polyunsaturated acid enriched diet reduced chylomicrons and their remnant levels by 56% and 38%, respectively. The diet enriched in omega 3 polyunsaturated acid decreased chylomicrons and their remnant levels by 67% and 53%, respectively. Physical conditioning reduced chylomicron levels by 37%. Gemfibrozil decreased chylomicron levels in type IV HLP patients. Cholestyramine increased chylomicron levels by 88%. Bezafibrate reduced chylomicrons and their remnants levels and increased fasting HDL-C in patients with isolated low HDL-C levels. Continuous prolonged intravenous heparin administration inhibited chylomicron clearance. Normolipidemic patients with CAD had significantly higher plasma levels of chylomicron remnants than matched controls with normal coronary arteries. The studies reported here demonstrate that both chylomicrons and their remnants are present in the plasma of normolipidemic people and more so for hyper- or dyslipidemic patients for a prolonged period of time after fat ingestion. The duration and magnitude of this postprandial lipemia can be regulated or altered by such interventions as diet, physical activity, and drugs. Our case control studies strongly support the hypothesis that PPLp may play a crucial part in atherogenesis, and therefore justify measuring their levels in high risk patients. We believe that in selected patient groups the use of one or more of the interventions mentioned here is warranted.