Catechins delay lipid oxidation and alpha-tocopherol and beta-carotene depletion following ascorbate depletion in human plasma

Blood plasma was incubated with 50 mM AAPH [2,2'-azobis-(2-amidinopropane) hydrochloride] in the absence or presence of catechins (5-100 mu M). Lipid oxidation was evaluated by measuring the formation of 2-thiobarbituric acid reactive substances (TBARS). The concentration of alpha-tocopherol (AT), b eta-carotene (BC), ascorbic acid (AA), and catechins was determined by reve rse phase high performance liquid chromatography (HPLC) with electrochemica l detection. All the assayed catechins inhibited plasma TBARS formation. Ba sed on the calculated IC50, the order of effectiveness was: epicatechin gal late (ECG) > epigallocatechin gallate (EGCG) > epigallocatechin (EGC) > epi catechin (EC) > catechin (C). Catechins protected plasma AT and BC from AAP H-mediated oxidation. The order of effectiveness for AT protection was ECG > EGCG > EC = C > EGG; and for BC protection, the order was EGCG > ECG > EG C > > EC > C. The addition of catechins modified the kinetics of TEARS form ation and AT depletion, but the rate of AA depletion was not affected. Cate chin oxidation did not start until the complete depletion of AA, and it pre ceded AT depletion. These results indicate that catechins are effective ant ioxidants in human blood plasma, delaying the lipid oxidation and depletion of endogenous lipid-soluble antioxidants (AT and BC).