Cholesterol feeding increases plasma and aortic tissue cholesterol oxide levels in parallel: further evidence for the role of cholesterol oxidation in atherosclerosis

Abstract

To determine the relationship between plasma and arterial wall oxysterols, plasma and aortic tissue from 7 New Zealand White rabbits fed a high cholesterol (1%) diet for 6 weeks was compared to plasma and aortic tissue from 7 normocholesterolemic rabbits fed standard rabbit chow. Cholesterol and cholesterol oxide fractions were isolated and analyzed by gas chromatography. Normocholesterolemic plasma and aortic tissue contained low levels of cholest-5-ene-3β,7α-diol, cholesta-3,5-dien-7-one, 5,6α-epoxy-5α-cholestan-3α-ol, cholest-5-ene-3β,7β-diol, and 5α-cholestane-3β,5,6/gb-triol while hypercholesterolemic plasma and atherosclerotic aorta contained significantly higher levels (P < 0.05) of these products. Furthermore, 5,6β3-epoxy-5α-cholestan-3/gb-ol not found in normocholesterolemic plasma or aortic tissue was present in substantial amounts in both hypercholesterolemic plasma and atherosclerotic aortic tissue. Cholest-5-ene-3(3β,25-diol and 3/3-hydroxycholest-5-ene-7-one not present in normocholesterolemic aorta were present in the atherosclerotic aorta. The oxysterol chromatographic patterns of normocholesterolemic plasma and normocholesterolemic aortic tissue were similar to each other as were the oxysterol chromatographic patterns of hypercholesterolemic plasma and atherosclerotic aortic tissue. The chromatographic patterns between the normocholesterolemic and hypercholesterolemic samples differed however. Possible absorption of the low levels of cholesterol oxides present in the cholesterol feed could account for the elevation of only some of the oxysterols. We conclude that cholesterol oxides exist at some basal level in normocholesterolemia and that these levels are increased by cholesterol-feeding which results in hypercholesterolemia. Our findings demonstrate that there is a strong relationship between plasma and aortic arterial wall levels of cholesterol oxides and suggest that in addition to exogenous sources, formation of cholesterol oxides proceeds via free radical oxidation acting upon elevated cholesterol levels resulting in the accumulation of these potentially cytotoxic and atherogenic products.