NADPH- and adriamycin-dependent microsomal release of iron and lipid peroxidation.
In a previous study (Minotti, G., 1989, Arch. Biochem. Biophys. 268, 398-403) NADPH-supplemented microsomes were found to reduce adriamycin (ADR) to semiquinone free radical (ADR-.), which in turn autoxidized at the expense of oxygen to regenerate ADR and form O2-. Redox cycling of ADR was paralleled by reductive release of membrane-bound nonheme iron, as evidenced by mobilization of bathophenanthroline-chelatable Fe2+. In the present study, iron release was found to increase with concentration of ADR in a superoxide dismutase- and catalase-insensitive manner. This suggested that membrane-bound iron was reduced by ADR-. with negligible contribution by O2-. or interference by its dismutation product H2O2. Following release from microsomes, Fe2+ was reconverted to Fe3+ via two distinct mechanisms: (i) catalase-inhibitable oxidation by H2O2 and (ii) catalase-insensitive autoxidation at the expense of oxygen, which occurred upon chelation by ADR and increased with the ADR:Fe2+ molar ratio. Malondialdehyde formation, indicative of membrane lipid peroxidation, was observed when approximately 50% of Fe2+ was converted to Fe3+. This occurred in presence of catalase and low concentrations of ADR, which prevented Fe2+ oxidation and favored only partial Fe2+ autoxidation, respectively. Lipid peroxidation was inhibited by superoxide dismutase via increased formation of H2O2 from O2-. and excessive Fe2+ oxidation. Lipid peroxidation was also inhibited by high concentrations of ADR, which favored maximum Fe2+ release but also caused excessive Fe2+ autoxidation via formation of very high ADR:Fe2+ molar ratios. These results highlighted multiple and diverging effects of ADR, O2-., and H2O2 on iron release, iron (auto-)oxidation and lipid peroxidation. Stimulation of malondialdehyde formation by catalase suggested that lipid peroxidation was not promoted by reaction of Fe2+ with H2O2 and formation of hydroxyl radical. The requirement for both Fe2+ and Fe3+ was indicative of initiation by some type of Fe2+/Fe3+ complex.
Minotti
G
G
Institute of General Pathology, Catholic University School of Medicine, Largo F. Vito 1, Rome, Italy.
D000818:Animals; D002374:Catalase / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology*; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values
D009249:NADP; D004317:Doxorubicin; D003577:Cytochrome P-450 Enzyme System; D007501:Iron; D002374:Catalase; D010634:Phenobarbital