Chlorophyllin as a protector of mitochondrial membranes against gamma-radiation and photosensitization

Ionizing radiation and photosensitization are highly damaging events and th ey generate oxygen-derived free radicals as well as excited species. Howeve r, the types as well as extent of reactive oxygen species (ROS) differ. The y have been linked to Various pathological conditions. Hence natural compou nds capable of preventing oxidative damage induced by these agents may have potential applications. Chlorophyllin (CHL), the water-soluble analogue of chlorophyll, has been examined for its ability to inhibit membrane damage induced by gamma -radiation and photosensitization involving methylene blue plus visible light. Using rat liver mitochondria as model systems the mech anisms of damage induced by these two agents as well as its possible preven tion by CHL have been examined. The parameters used were lipid peroxidation as assessed by formation of thiobarbituric acid reactive substances (TBARS ) and 4-hydroxynonenal (4-HNE), protein oxidation besides glutathione (GSH) and superoxide dismutase (SOD). Peroxidation increases with radiation dose , in the range of 75-600 Gy. A similar observation also was observed with p hotosensitization, as a function of time. CHL, at a concentration of 10 muM offered a high degree of protection against radiation and photosensitizati on as indicated by decreased peroxidation, protein oxidation as well as the restoration of GSH and SOD. When compared with the established antioxidant s, ascorbic acid and GSH, CHL offered a much higher degree of protection. P ulse radiolysis studies show that this compound has a relatively high rate constant with hydroxyl radical ((OH)-O-.), a crucial species generated duri ng gamma -radiation. Hence the studies show that CHL is a potent antioxidan t in mitochondrial membranes. (C) 2000 Elsevier Science Ireland Ltd. All ri ghts reserved.