Inhibitory effect of flavonoids on low-density lipoprotein peroxidation catalyzed by mammalian 15-lipoxygenase

Lipoxygenase-dependent low-density lipoprotein (LDL) oxidation is believed to be involved in atherogenesis, Inhibition of lipoxygenase-induced lipid p eroxidation might, therefore, be an important mode to suppress the developm ent of atherosclerosis, Because dietary antioxidants inhibit LDL oxidation in vitro and their intake is inversely associated with coronary heart disea ses, we compared the inhibitory effect of three typical flavonoids-querceti n, epicatechin, and flavone-with alpha-tocopherol and ascorbic acid against human LDL oxidation catalyzed by mammalian 15-lipoxygenase. The oxidative modification of LDL was monitored by measurement of cholesteryl ester hydro peroxide (CE-OOH) formation and consumption of antioxidants by using HLPC. Quercetin and epicatechin were the strongest inhibitors of LDL oxidation ca talyzed by 15-lipoxygenase; ascorbic acid was an effective inhibitor in the first 3 h of oxidation; and fivefold alpha-tocopherol-enriched LDL showed a partial inhibition of CE-OOH formation only after 4-6 h of incubation. Fl avone had no effect. Quercetin, ascorbic acid, and alpha-tocopherol were co nsumed in the first 3 h of incubation, Consumption of LDL alpha-tocopherol was partially inhibited by ascorbic acid and quercetin, whereas epicatechin and flavone were without effect. These results emphasize the inhibitory ef fect of the flavonoids quercetin and epicatechin on 15-lipoxygenase-mediate d LDL lipid peroxidation. At similar concentrations, they are stronger anti oxidants than ascorbic acid, alpha-tocopherol, and flavone.