The effect of cholesterol feeding on primate serum lipoproteins: I. Low density lipoprotein characterization from rhesus monkeys with high serum cholesterol

Abstract

The effect of dietary cholesterol on the serum low density lipoproteins (LDL 2) of the rhesus monkey ( Macaca mulatta) was studied by comparison of monkeys on a standard commercial monkey chow diet to those on a high cholesterol, high fat diet. The serum lipoproteins were fractionated by ultracentrifugation. Monkeys ingesting the control diet had 2% of the serum cholesterol in VLDL and an equal amount in the LDL 1 (1.006–1.019 g/ml) fraction. Upon ingesting the high cholesterol, high fat diet, the percentage in the VLDL and the LDL 1 fractions increased to 34–40% of the total. There was little change in the percentage of the serum cholesterol in the LDL 2 fraction except the absolute amount was higher in the cholesterol-fed animals. A 50% reduction in the percentage of serum cholesterol in the HDL was found upon cholesterol feeding (60% for controls vs 30% for cholesterol fed). A comparison of the LDL 2 composition of the control and cholesterolfed monkeys showed that the cholesteryl esters increased while protein and triglyceride decreased. The cholesterol/phospholipid ratio increased from 1.34 to 1.69 after cholesterol feeding. Cholesterol feeding had little effect on the phospholipid composition other than a twofold increase in phosphatidylethanolamine of LDL 2. The percentage of unsaturated fatty acids in LDL 2 increased in the triglycerides, decreased in the phospholipids, and were unchanged in the cholesteryl esters after cholesterol-fat feeding. However, individual changes in unsaturated fatty acids seemed unrelated. In the LDL 2 phospholipid, arachidonic acid rose eightfold to 23% of the total while other unsaturated fatty acids showed little change. In the LDL 2 triglycerides, linoleic acid fell 73%, oleic 37%, and palmitoleic doubled upon cholesterol feeding. These changes were not a reflection of the dietary fatty acid composition except that four times as much fat was available to the cholesterol-fed animals. The amino acid composition of the apo-LDL 2 was not affected by cholesterol feeding. Determination of the molecular weights on the native LDL 2 showed that cholesterol feeding resulted in an increase of about 12% (3.1 to 3.5 million).