Dietary fat amount and carbohydrate type regulate hepatic acyl CoA:cholesterol acyltransferase (ACAT) activity. Possible links between ACAT activity and plasma cholesterol levels

Abstract

The effects of dietary fat amount and carbohydrate type were evaluated on hepatic acyl CoA:cholesterol acyltransferase (ACAT) activity in guinea pigs to determine whether there was a correlation between plasma LDL cholesterol concentrations induced by diet and rates of hepatic cholesterol esterification. Animals were fed two different fat:carbohydrate ratios: 2.5:58% ( w w ) (low fat) or 25:29% ( w w ) (high fat) with either sucrose or starch as the sole carbohydrate source. Fat contributed 6.9 and 53% of total calories respectively. Consumption of high fat diets resulted in higher plasma cholesterol concentrations (P < 0.001) while simple carbohydrate intake increased plasma triacylglycerol levels (P < 0.01). Animals fed the high fat:sucrose diet exhibited the highest plasma and hepatic cholesterol concentrations. The type of carbohydrate affected the distribution of hepatic cholesterol pools in that animals fed sucrose had higher concentrations of free while those fed starch had higher levels of esterified cholesterol (P < 0.01). Hepatic ACAT activity was up-regulated in animals fed high fat diets (P < 0.01) with no effect due to carbohydrate type. A significant correlation was found between hepatic ACAT activity and plasma LDL cholesterol concentrations (r = 0.69, P < 0.001) and between hepatic ACAT activity and cholesterol influx to the liver (r = 0.97, P < 0.01). These results demonstrate that modifications in hepatic ACAT activity induced by dietary factors could be a response to the influx of cholesterol to the liver or could be related to the rates of incorporation of cholesteryl ester into lipoproteins secreted by the liver.