L-carnitine effects on chemical composition of plasma lipoproteins of rabbits fed with normal and high cholesterol diets

L-Carnitine plays an important role in the mitochondrial uptake of long-cha in fatty acids in mammals. It has recently been shown that this compound ha s a marked hypo-cholesterolemic effect when used in conjunction with lipid- rich diets. The aim of this study was to investigate the effects of L-carni tine on the fatty acid composition of plasma lipoproteins in rabbits fed wi th different diets. Four different groups were investigated: group I (stand ard diet), group II (standard diet supplemented with L-carnitine at 80 mg/k g), group III (standard diet supplemented with 0.5% cholesterol), and group IV (standard diet supplemented with 0.5% cholesterol plus L-carnitine at 8 0 mg/kg). The feeding period was 126 d. Total plasma cholesterol was indist inguishable in groups I and II, but increased nearly 40-fold in group III. This increment was reduced by 50% in group IV. Correspondingly, total chole sterol content in lipoprotein fractions very low density lipoprotein (VLDL) , low density lipoprotein (LDL), high density lipoprotein (HDL) separated b y agarose gel chromatography was the same for groups I and II, while for an imals fed a cholesterol-rich diet (III) total cholesterol in VLDL + LDL inc reased nearly 100-fold when compared with groups I and II but, again, the i ncrement was reduced by 50% in group IV. In contrast, total cholesterol in HDL increased only fivefold for both groups III and IV when compared with g roups I and II, indicating no effects of L-carnitine on this parameter. The reduction of total cholesterol in VLDL + LDL particles in animals fed a ch olesterol-rich diet plus L-carnitine was associated with a marked decrease in the ratio of cholesteryl ester to free cholesterol and a dramatic increa se in their phospholipid content; opposite effects were observed for HDL. L -Carnitine induced a marked decrease in the saturated to unsaturated C-16 C-18 fatty acid ratio in cholesteryl esters associated with VLDL and LDL f rom animals fed with both normal and cholesterol-rich diets. The opposite e ffect (a large increase in the saturated to unsaturated fatty acid ratio) w as observed for both cholesteryl esters and phospholipids associated with H DL in animals fed with both diets. The results suggested that the hypochole sterolemic effects of L-carnitine could be associated with increased system ic breakdown of cholesteryl esters, a probable increase in reverse choleste rol transport, and the stabilization of a phospholipid-based structure of V LDL + LDL particles.