Hypocholesterolemic Effect of Lycopene and β-Carotene Is Related to Suppression of Cholesterol Synthesis and Augmentation of LDL Receptor Activity in Macrophages

Abstract

β-Carotene and lycopene are derived from plants, and they share similar initial synthetic pathway with cholesterol, which is synthesized in animal but not in plant cells. Thus, we sought to analyze the effect of carotenoids on macrophage cholesterol metabolism, in comparison to the effect of LDL cholesterol and of the cholesterol synthesis inhibitor, fluvastatin. In J-774 A. 1 macrophage cell line, the cellular cholesterol synthesis from [3H]-acetate, but not from [14C] mevalonate, was suppressed by 63% and by 73% following cell incubation with β-carotene or lycopene (10μM) respectively, in comparison to a 90% and 91% inhibition by LDL (100μg of cholesterol), or by fluvastatin (10μg/ml) respectively. However, unlike LDL derived cholesterol, which also suppresses macrophage LDL receptor activity, lycopene and β-carotene augmented the activity of the macrophage LDL receptor, similarly to the effect of fluvastatin. In agreement with these in vitro observations, dietary supplementation of tomato's lycopene (60mg/day) to 6 males for a 3 months period resulted in a significant 14% reduction in their plasma LDL cholesterol concentrations. We thus conclude that dietary supplementation of carotenoids may act as moderate hypocholesterolemic agents, secondary to their inhibitory effect on macrophage 3-hydroxy-3-methyl glutaryl coenzyme A (HMGCoA) reductase, the rate limiting enzyme in cholesterol synthesis.