antioxidant; beta carotene; free radical; lipid peroxide; tert butyl hydroperoxide; triphenylmethane; autooxidation; cancer inhibition; dose response; drug comparison; drug interaction; drug mechanism; drug response; drug stability; linoleic acid methyl ester; oxygen tension; preliminary communication; tetralin; theoretical study; carotenoids; chemistry; free radicals; linoleic acids; lipid; oxidation-reduction; oxygen; partial pressure; peroxides; support, non-U. S. Gov't; tetrahydronaphthalenes
The mechanism of lipid peroxidation and the manner in which antioxidants function is reviewed. β-Carotene is a purported anticancer agent, which is believed by some to have antioxidant action of a radical-trapping type. However, definitive experimental support for such action has been lacking. New experiments in vitro show that β-carotene belongs to a previously unknown class of biological antioxidants. Specifically, it exhibits good radical-trapping antioxidant behavior only at partial pressures of oxygen significantly less than 150 torr, the pressure of oxygen in normal air. Such low oxygen partial pressures are found in most tissues under physiological conditions. At high oxygen pressures, β-carotene loses its antioxidant activity and shows an autocatalytic, prooxidant effect, particularly at relatively high concentrations. Similar oxygen-pressure-dependent behavior may be shown by other compounds containing many conjugated double bonds.