THE COMPARATIVE TOXICITY OF NITRIC-OXIDE AND PEROXYNITRITE TO ESCHERICHIA-COLI

The reactivity and toxicity of nitric oxide is modest in comparison to oxidants derived from nitric oxide. Exposure of Escherichia coli to 1 mM nitric oxide under aerobic or anaerobic conditions did not decreas e viability of the bacteria, Peroxynitrite (1 mM), the reaction produc t of superoxide and nitric oxide, was completely bactericidal after 5 s, The nitrovasodilator, 3-morpholinosydnonimine-N-ethylcarbamide (SIN -1), slowly decomposes to release both nitric oxide and superoxide and thereby produces peroxynitrite, SIN-1 killed E. coli in direct propor tion to its concentration with an LD(50) of 0.5 mM, Copper, zinc super oxide dismutase (50-400 units/ml) provided substantial but not complet e protection against SIN-1 killing, Catalase (500-10,000 units/ml) par tially protected in direct proportion to its concentration, while inac tivated catalase was not protective, Superoxide dismutase and catalase together completely protected E. coli against SIN-1 toxicity. Oxy-hem oglobin eliminated both SIN-1 and peroxynitrite toxicity, The bacteric idal activity of SIN-1 was further enhanced by pterin plus xanthine ox idase. Pterin plus xanthine oxidase alone or together with Fe3+ ethyle nediamine tetraacetate produced no significant decrease in E, coli via bility, Hydrogen peroxide was not directly toxic to the bacteria, but E, coli pretreated with hydrogen peroxide were more susceptible to per oxynitrite, SIN-1, and the aerobic oxidation products of nitric oxide, Hydrogen peroxide pretreatment did not increase significantly the tox icity of nitric oxide under anaerobic conditions. Our results suggest that peroxynitrite is far more toxic to E, coli than nitric oxide or i ts byproducts from aerobic oxidation, (C) 1995 Academic Press, Inc.