A high-fat/high-cholesterol diet, but not high-cholesterol alone, increases free cholesterol and apoE-rich HDL serum levels in rats and upregulates hepatic ABCA1 expression

A high-fat/high-cholesterol (HFC) diet, but not a high-cholesterol (HC) diet, is known to induce elevated serum apolipoprotein E (apoE)-rich high-density lipoprotein (HDL) levels in animal models. However, the exact mechanisms by which the combination of dietary fat and cholesterol induces apoE-rich HDL production is not well understood. Here, we investigated the effects of dietary fat and cholesterol on serum lipoprotein profiles and hepatic mRNA expression that are associated with HDL production, cholesterol transport, and bile acid metabolism. Male Sprague-Dawley rats were fed HFC, HC, high-fat, or control diets and then evaluated. The HFC diet induced significant increases in hepatic free-cholesterol accumulation (1.4-fold, p < 0.01) and serum apoE-rich HDL cholesterol (8.7-fold, p < 0.001) levels compared with the HC diet. The apoE-rich HDL induced by the HFC diet was remarkably rich in free cholesterol. Liver gene-expression was mostly similar between the HC and HFC diet groups. However, there was a significant increase of ATP-binding cassette transporter A1 (ABCA1) levels in the HFC group compared to the HC group for both mRNA (1.9-fold, p < 0.001) and protein (6.6-fold, p < 0.01). These results suggest that an increase in apoE-rich HDL induced by dietary fat and cholesterol may be involved in cholesterol efflux from the liver through increased ABCA1-mediated free-cholesterol efflux.