Inhibitory effect of tea flavonoids on the ability of cells to oxidize lowdensity lipoprotein

Dietary flavonoid intake has been reported to be inversely related to morta lity from coronary heart disease, and the anti-atherosclerotic effect of fl avonoids is considered to be due probably to their antioxidant properties. Oxidation of low density Lipoprotein (LDL) has been reported to be induced by the constituent cells of the arterial wall. Accordingly, we examined the effect of pretreatment with tea flavonoids, such as theaflavin digallate, on the ability of cells to oxidize LDL. Theaflavin digallate pretreatment o f macrophages or endothelial cells reduced cell-mediated LDL oxidation in a concentration- (0-400 mu M) and time- (0-4 hr) dependent manner. This inhi bitory effect: of flavonoids on cell-mediated LDL oxidation was in the orde r of theaflavin digallate > theaflavin greater than or equal to epigallocat echin gallate > epigallocatechin > gallic acid. Further, we investigated th e mechanisms by which flavonoids inhibited cell-mediated LDL oxidation usin g macrophages and theaflavin digallate. Theaflavin digallate pretreatment d ecreased superoxide production of macrophages and chelated iron ions signif icantly. These results suggest that tea flavonoids attenuate the ability of the cell to oxidize LDL, probably by reducing superoxide production in cel ls and chelating iron ions. BIOCHEM PHARMACOL 58;11:1695-1703, 1999. (C) 19 99 Elsevier Science Inc.