DISPARATE EFFECTS OF A TRIGLYCERIDE LOWERING DIET AND OF BEZAFIBRATE ON THE HDL SYSTEM - A STUDY IN PATIENTS WITH HYPERTRIGLYCERIDEMIA AND LOW HDL-CHOLESTEROL LEVELS

The response of plasma triglyceride and of the high density lipoprotein (HDL) system to a triglyceride lowering diet and to a bezafibrate was compared in a group of 24 human subjects with mild to moderate hypertriglyceridaemia and low HDL-cholesterol levels. Post-heparin plasma lipoprotein (LPL) and hepatic (HL) lipase activities were determined before the initiation of the study and at the end of the diet (12 weeks) and bezafibrate (12 weeks) periods. HDL structure and composition were determined on a zonal centrifugation system at the end of the diet and bezafibrate periods. Diet caused a 9-20% reduction of plasma triglycerides but there was no change in LPL, HL or HDL levels. The individual responses between plasma triglycerides and HDL cholesterol levels however were highly correlated (r=0.60 to 0.78). Combined diet plus bezafibrate therapy caused a further 38% decrease of plasma triglycerides with a 28% increase of HDL-cholesterol and a 47% increase of LPL activity. HDL3 density decreased and the contribution of cholesteryl ester to the HDL mass was increased while the contribution of proteins and triglycerides decreased. In the majority of the subjects (61%) HDL cholesterol levels increased by 20% or more and in these subjects the change of HDL was highly correlated with the change of the LPL/HL ratio (r=0.74) but not with the change of the plasma triglyceride levels. In the remaining subjects (39%), HDL cholesterol levels remained unchanged or increased by less than 20%. The change of HDL cholesterol levels in these subjects was unrelated to the decrease of plasma triglycerides or the change of post-heparin lipase activities. It is suggested that during triglyceride-lowering diets HDL levels change in relation to the reduction of plasma triglycerides due to a decreased cholesteryl ester transfer between lipoproteins (a weak effect) while during combined diet plus bezafibrate therapy, an additional strong effect on HDL due to the increased LPL activity exists at least in the majority of the subjects.