Prooxidant activity of β-carotene under 100% oxygen pressure in rat liver microsomes

The effects of the partial pressure of oxygen (pO2 on antioxidant efficiency of β-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°C is markedly higher at 150 than 760 mm Hg pO2. At 150 mm Hg pO2 β-carotene acts as an antioxidant, inhibiting 2,2′-azobis(2-amidinopropane) (AAPH)-induced Malondialdehyde (MDA) formation. At 760 mm Hg pO2, it loses its antioxidant activity and shows a prooxidant effect, increasing lipid peroxidation products, α-Tocopherol prevents the prooxidant effect of β-carotene in a dose-dependent manner. Our data provide the first evidence of a prooxidant effect of β-carotene under 100% oxygen pressure in a biological membrane model and point out the existence of cooperative interactions between β-carotene and α-tocopherol.