Polyunsaturated fatty acids up-regulate hepatic scavenger receptor B1 (SR-BI) expression and HDL cholesteryl ester uptake in the hamster

Diets rich in polyunsaturated fatty acids lower plasma HDL cholesterol conc entrations when compared to diets rich in saturated fatty acids. We investi gated the mechanistic basis for this effect in the hamster and sought to de termine whether reduced plasma HDL cholesterol concentrations resulting fro m a high polyunsaturated fat diet are associated with a decrease in reverse cholesterol transport. Animals were fed semisynthetic diets enriched with polyunsaturated or saturated fatty acids for 6 weeks. We then determined th e effect of these diets on the following parameters: 1) hepatic scavenger r eceptor B1 (SR-BI) mRNA and protein levels, 2) the rate of hepatic HDL chol esteryl ester uptake, and 3) the rate of cholesterol acquisition by the ext rahepatic tissues (from de novo synthesis, LDL and HDL) as a measure of the rate of reverse cholesterol transport. Compared to saturated fatty acids, dietary polyunsaturated fatty acids up-regulated hepatic SR-BI expression b y similar to 50% and increased HDL cholesteryl ester transport to the liver ; as a consequence, plasma HDL cholesteryl ester concentrations were reduce d. Although dietary polyunsaturated fatty acids increased hepatic HDL chole steryl ester uptake and lowered plasma HDL cholesterol concentrations, ther e was no change in the cholesterol content or in the rate of cholesterol ac quisition (via de novo synthesis and lipoprotein uptake) by the extrahepati c tissues. These studies indicate that substitution of polyunsaturated for saturated fatty acids in the diet increases SR-EI expression and lowers pla sma HDL cholesteryl ester concentrations but does not affect reverse choles terol transport.