Taketo Ogiso

Inhibition of microsomal lipid peroxidation by baicalein: A possible formation of an iron‐baicalein complex

Baicalein decreased the production of thiobarbituric acid reactive substances, the rate of oxygen consumption and iron reduction in the reaction system of ascorbic acid with FeCl3. Superoxide dismutase, catalase and hydroxyl radical scavengers had no significant effect. Ironchelators had an inhibitory effect similar to that of baicalein. The production of thiobarbituric acid reactive substances of baicalein‐treated microsomes obtained by centrifugation after incubation with baicalein was not observed in the reaction system, but was stimulated by adding iron with increases in concentration. The amount of bound iron to microsomal membranes increased by increasing both the concentration of baicalein and iron. The amount of baicalein bound to microsomal membranes increased with increasing concentration of added baicalein. These results suggest that baicalein bound to microsomal membranes inhibits lipid peroxidation by formating an iron‐baicalein complex.

Oxidative damage to bovine serum albumin induced by hydroxyl radical generating systems of xanthine oxidase + EDTA−Fe3+ and ascorbate + EDTA−Fe3+

Oxidative damage to bovine serum albumin (BSA) was induced by hydroxyl radical (HO.) generating systems of xanthine oxidase (XO) + EDTA-Fe3+ and ascorbate + EDTA-Fe3+. Formation of bityrosine and loss of tryptophan were observed in the ascorbate + EDTA-Fe3+ system and carbonyl formation was induced by both systems. Mannitol and ethanol very strongly inhibited the carbonyl and/or bityrosine formation, indicating that the oxidative damage to BSA was due to HO(.). The sulfhydryl (SH) groups of BSA were very sensitive to the XO + EDTA-Fe3+ but not to the ascorbate + EDTA-Fe3+ system. Catalase but not hydroxyl radical scavengers or superoxide dismutase strongly inhibited the loss of SH groups, indicating that H2O2 is involved in their oxidation. Fragmentation of BSA was observed during exposure to the XO + EDTA-Fe3+ and ascorbate + EDTA-Fe3+ systems and the products presented a broad band on sodium dodecyl sulfate polyacrylamide gel electrophoresis. Little formation of amine groups was observed in these systems, indicating that little peptide bond cleavage occurred. BSA exposed to the ascorbate + EDTA-Fe3+ system was more readily degraded by trypsin than that exposed to the XO + EDTA-Fe3+ system. Elastase degraded BSA exposed to the ascorbate + EDTA-Fe3+ system but not to the XO + EDTA-Fe3+ system.

Protective effects of β-blockers against 2,2′-azobis(2-amidinopropane)-dihydrochlorideinduced damage

Abstract The protective effects of β-blockers against 2,2′-azobis(2-amidinopropane)-dihydrochloride (AAPH)-induced damage were investigated. With the exception of pindolol, none of the β-blockers tested inhibited arachidonate peroxidation induced by AAPH in the absence of iron. In contrast, ADP-Fe3+- and NADPH-dependent microsomal lipid peroxidation was inhibited by all the β-blockers tested, although the inhibitory effects of atenolol and metoprolol were very slight. Oxidation of tryptophan residues in bovine serum albumin (BSA) induced by AAPH was strongly inhibited by pindolol and propranolol but not by atenolol or metoprolol. All the β-blockers tested, however, inhibited AAPH-induced carbonyl formation of BSA. Furthermore, all the β-blockers tested also strongly inhibited the deoxyribose degradation induced by AAPH, suggesting that these agents act as hydroxyl radical scavengers to inhibit carbonyl formation. DNA strand scission was induced by AAPH in the absence or presence of O2. Only pindolol strongly inhibited the DNA damage in the absence of O2. In the presence of O2, however, all the β-blockers tested effectively prevented the DNA damage. These results suggested that the hydroxyl radicals produced from AAPH damaged DNA and, that β-blockers might act as hydroxyl radical scavengers to protect DNA against the AAPH-induced oxidative damage.