PROOXIDANT ACTIVITY OF BETA-CAROTENE UNDER 100-PERCENT OXYGEN-PRESSURE IN RAT-LIVER MICROSOMES

The effects of the partial pressure of oxygen (pO(2)) on antioxidant efficiency of beta-carotene in inhibiting 2,2'-azobis(2-amidinopropane) (AAPH)-induced lipid peroxidation are investigated in rat liver microsomal membranes. The rate of peroxyl radicals generated by thermolysis of AAPH at 37 degrees C is markedly higher at 150 than 760 mm Hg pO,. At 150 mm Hg pO(2) beta-carotene acts as an antioxidant, inhibiting 2,2'-azobis(2-amidinopropane) (AAPH)-induced Malondialdehyde (MDA) formation. At 760 mm Hg pO(2), it loses its antioxidant activity and shows a prooxidant effect, increasing lipid peroxidation products. alpha-Tocopherol prevents the prooxidant effect of beta-carotene in a dose-dependent manner. Our data provide the first evidence of a prooxidant effect of beta-carotene under 100% oxygen pressure in a biological membrane model and point out the existence of cooperative interactions between beta-carotene and alpha-tocopherol.