β-Carotene inhibits the oxidative modification of low-density lipoprotein

Several lines of evidence indicate that oxidized LDL (Ox-LDL) may promote atherogenesis. Hence, the role of antioxidants in the prevention of LDL oxidation needs to be determined. β-Carotene, in addition to being an efficient quencher of singlet oxygen, can also function as a radical-trapping antioxidant. Since previous studies have failed to show that β-carotene inhibits LDL oxidation, we re-examined its effect on the oxidative modification of LDL. For these studies, LDL was oxidized in both a cell-free (2.5 μM Cu²⁺ in PBS) and a cellular system (human monocyte macrophages in Ham's F-10 medium). β-Carotene inhibited the oxidative modification of LDL in both systems as evidenced by a decrease in the lipid peroxide content (thiobarbituric-acid-reacting substances activity), the negative charge of LDL (electrophoretic mobility) and the formation of conjugated dienes. By inhibiting LDL oxidation, β-carotene substantially decreased its degradation by macrophages. β-Carotene (2 μM) was more potent than α-tocopherol (40 μM) in inhibiting LDL oxidation. Thus, β-carotene, like ascorbate and α-tocopherol, inhibits LDL oxidation and might have an important role in the prevention of atherosclerosis.