Inhibitory effects of water-soluble cationic manganese porphyrins on peroxynitrite-induced SOS response in Salmonella typhimurium TA4107/pSK1002

We have investigated the protective effects of water-soluble cationic Mn(III) porphyrins against peroxynitrite (ONOO^-)-induced DNA damage in the cells of Salmonella typhimurium TA4107/pSK1002 and lipid peroxidation of red blood cell membranes. Mn(III) tetrakis (N-methylpyridinium-4-yl) porphine (TMPyP) and the brominated form, Mn(III) octabromo-tetrakis (N-methylpyridinium- 4-yl) porphine (OBTMPyP) effectively reduced the damage and peroxidation induced by N-morpholino sydnonimine (SIN-1), which gradually generates ONOO^- from O₂·^- and·NO produced through hydrolysis. Mn(III)OBTMPyP became 10-fold more active than the non-brominated form. In the presence of authentic ONOO^-, the Mn(III) porphyrins were ineffective against damage and strongly enhanced lipid peroxidation, while the coexistence of ascorbic acid inhibited peroxidation. Using a diode array spectrophotometry, the reactions of Mn(III)TMPyP with authentic ONOO^- and SIN-1 were measured. Mn(III)TMPyP is known to be catalytic for ONOO ^- decomposition in the presence of antioxidants. OxoMn(IV)TMPyP with SIN-1 was rapidly reduced back to Mn(III) without adding any oxidants. Further, in the SIN-1 system, the concentration of NO₂^- and NO ₃^- were colorimetrically determined by Griess reaction based on the two-step diazotization. NO₂^- increased by addition of Mn(III) porphyrin and the ratio of NO₂^- to NO₃^- was 4-7 times higher than that (1.05) of SIN-1 alone. This result suggests that O₂·^- from SIN-1 acts as a reductant and·NO cogenerated is oxidized to NO₂^-, a primarily decomposition product of·NO. Under the pathological conditions where biological antioxidants are depleted and ONOO^- and O₂·^- are extensively generated, the Mn(III) porphyrins will effectively cycle ONOO^- decomposition using O ₂·^-.