A LINOLEIC-ACID ENRICHED DIET INCREASES SERUM-CHOLESTEROL ESTERIFICATION BY LECITHIN - CHOLESTEROL ACYLTRANSFERASE IN MEAL-FED RATS

Dietary fats are known to influence the fatty acid profile of plasma l ipids, including phospholipids which are substrates of lecithin:choles terol acyltransferase (LCAT; EC 2.3.1.43), an important enzyme in lipo protein metabolism. We tested whether the dietary fatty acid profile h as an effect on LCAT activity in an animal model. Rats were conditione d to eat two meals per day, which were enriched in either palmitic, ol eic or Linoleic acids, far 10 weeks. Serum was isolated from blood sam ples taken prior to the meal. The LCAT activity was determined in two ways: (I)by measuring serum cholesterol esterification rates, which ar e an estimate of LCAT action on endogenous lipoproteins, and (2) by me asuring serum LCAT activity levels with excess exogenous substrates, a n estimate of LCAT mass. Animals receiving the linoleic acid diet had lower serum concentrations of unesterified cholesterol and triglycerid es, if compared with animals fed oleic acid or palmitic acid diets (p < 0.05). Serum LCAT activity levels (measured with excess exogenous su bstrates) were not different. but both the absolute and fractional rat es of cholesterol esterification were highest on the linoleic acid ric h diet (p < 0.01), showing that LCAT action on endogenous lipoproteins is improved. No differences were found in serum apolipoprotein B and A-TV concentrations between the dietary groups. Apolipoprotein A-I lev els were lowest in the palmitic acid group (oleic and linoleic > palmi tic; p < 0.05), and apolipoprotein E levels were highest in the palmit ic acid group (palmitic > oleic and linoleic, p < 0.05). II is conclud ed that a linoleic acid rich diet may cause increased metabolism of se rum cholesterol by LCAT in rats. This effect is not due to elevated se rum concentrations of LCAT or of its apolipoprotein activators, but mo st likely to changes in the chemical composition of endogenous lipopro tein substrates. It remains to be established whether the serum choles terol esterification rates measured in vitro are related to in vivo ra tes of reverse cholesterol transport.