INCREASE IN PLASMA CHOLESTERYL ESTER TRANSFER PROTEIN DURING PROBUCOL TREATMENT - RELATION TO CHANGES IN HIGH-DENSITY-LIPOPROTEIN COMPOSITION

Probucol is a hypolipidemic agent that causes a marked decrease in high density lipoprotein (HDL) cholesterol. To investigate the mechanism of this effect, two studies were performed in hypercholesterolemic patients who had been stabilized previously on diet and were not receiving other lipid-lowering medication. Plasma cholesteryl ester transfer protein (CETP) concentrations were measured in fasting plasma samples before and after 10 weeks of probucol therapy using a sensitive and specific radioimmunoassay. Plasma total and low density lipoprotein cholesterol concentrations decreased, whereas apolipoprotein (apo) B was unchanged. Plasma apo E concentrations increased markedly. HDL cholesterol and apo A-I decreased in all subjects. These effects of probucol were accompanied by even more striking changes in plasma CETP concentrations, which increased by a mean of 64%. In a second study of six hypercholesterolemic subjects, the time-course effects of probucol on CETP and HDL subspecies were studied. Significant increases in plasma apo E and in CETP occurred after 4 weeks, and CETP, but not apo E, increased further after 16 weeks of treatment. Concomitant and opposite changes occurred in HDL composition, with decreases in HDL cholesterol and lipoprotein containing apo A-I. The increase in plasma CETP concentrations, the decrease in HDL cholesterol, and the increase in plasma apo E concentrations observed during probucol treatment are changes consistent with a postulated increase in reverse cholesterol transport via the remnant pathway.