ANTIOXIDANT AND PROOXIDANT ROLE OF BETA-CAROTENE IN MURINE NORMAL ANDTUMOR THYMOCYTES - EFFECTS OF OXYGEN PARTIAL-PRESSURE

The effects of the partial pressure of oxygen (pO(2)) on antioxidant e fficiency of beta-carotene in inhibiting radical-initiated lipid perox idation were studied in murine normal and tumor thymocytes. At 150 mm Hg pO(2) (the pressure of oxygen in normal air), beta-carotene acted a s an antioxidant, inhibiting radical-induced lipid peroxidation in bot h normal and tumor thymocytes. At 760 mm Hg pO(2), beta-carotene lost its antioxidant activity in normal thymocytes and exhibited a dose-dep endent prooxidant effect in tumor thymocytes. In these cells, the proo xidant effect of beta-carotene was also accompanied by an increase of endogenous alpha-tocopherol loss. beta-carotene radical-trapping and a utooxidation reactions were faster at 760 mm Hg pO(2) than at 150 mm H g pO(2) in both normal and tumor thymocytes and the carotenoid was mor e rapidly consumed in tumor cells. These data point out a key role of the oxygen tension on the antioxidant effectiveness of beta-carotene. They also show a selective prooxidant effect of beta-carotene under 10 0% oxygen in tumor cells. Copyright (C) 1997 Elsevier Science Inc.