Nitric oxide donors as generators and scavengers of superoxide anions.

Three classical direct nitric oxide (NO) donors, 3-morpholine-sydnonimine (SIN-1), S-nitroso-N-acetyl-d,l-penicillamine (SNAP) and sodium nitroprusside (NaNP) as well as two indirect NO donors, molsidomine (MSL) and glyceryl trinitrate (GTN) were studied for their potencies to generate O2-, to scavenge O2-, to consume molecular oxygen and to inhibit lipid oxidation. Out of five NO donors only those which were spontaneous releasers of NO at physiological pH were also scavengers of O2- which has been generated by xanthine:xanthine oxidase system (SIN-1 IC50 19 microM, SNAP IC50 416 microM) and inhibitors of the Fe3+ and ascorbate stimulated oxidation of rat liver lipids (SIN-1 IC50 76 microM, SNAP IC50 12 microM). Only SIN-1 at high concentrations of 300-5000 microM generated O2- as detected by a SOD inhibitable reduction of nitroblue tetrazolium. None of the in vitro studied activities were exerted by NaNP, MLS and GTN.