Carotenoid oxidative degradation products inhibit Na+-K+-ATPase

This study investigates the biological significance of carotenoid oxidation products using inhibition of Na+-K+-ATPase activity as an index. beta-Caro tene was completely oxidized by hypochlorous acid and the oxidation product s were analyzed by capillary gas-liquid chromatography and high performance liquid chromatography. The Na+-K+-ATPase activity was assayed in the prese nce of these oxidized carotenoids and was rapidly and potently inhibited. T his was demonstrated for a mixture of beta-carotene oxidative breakdown pro ducts, beta-Apo-10'-carotenal and retinal. Most of the beta-carotene oxidat ion products were identified as aldehydic. The concentration of the oxidize d carotenoid mixture that inhibited Na+-K+-ATPase activity by 50% (IC50) wa s equivalent to 10 mu M nondegraded beta-carotene, whereas the IC50 for 4-h ydroxy-2-nonenal, a major lipid peroxidation product, was 120 mu M. Caroten oid oxidation products are more potent inhibitors of Na+-K+-ATPase than 4-h ydroxy-2-nonenal. Enzyme activity was only partially restored with hydroxyl amine and/or beta-mercaptoethanol. Thus, in vitro binding of carotenoid oxi dation products results in strong enzyme inhibition. These data indicate th e potential toxicity of oxidative carotenoid metabolites and their activity on key enzyme regulators and signal modulators.