nitroarginine and sodium-arsenite

Reactive oxygen species have been shown to be involved in the mutagenicity, clastogenicity, and apoptosis of mammalian cells treated with arsenic or cadmium. As these endpoints require several hours of cellular processing, it is not clear that reactive oxygen species damage DNA directly or interfere with DNA replication and repair. Using single-cell alkaline electrophoresis, we have detected DNA strand breaks (DSBs) in bovine aortic endothelial cells by a 4-h treatment with sodium arsenite (As) and cadmium chloride (Cd) in sublethal concentrations. As-induced DSBs could be decreased by nitric oxide (NO) synthase inhibitors, superoxide scavengers, and peroxynitrite scavengers and could be increased by superoxide generators and NO generators. Treatment with As also increased nitrite production. These results suggest that As-increased NO may react with O2*- to produce peroxynitrite and cause DNA damage. The results showing that Cd increased cellular H2O2 levels and that Cd-induced DSBs could be modulated by various oxidant modulators suggest that Cd may induce DSBs via O2*-, H2O2, and *OH. Nevertheless, the DSBs in both As- and Cd-treated cells seem to come from the excision of oxidized bases such as formamidopyrimidine and 8-oxoguanine, as the Escherichia coli enzyme formamidopyrimidine-DNA glycosylase (Fpg) increased DSBs in cells treated with As, 3-morpholinosydnonimine (a peroxynitrite-generating agent), Cd, or H2O2.

Topics: Amitrole; Animals; Antioxidants; Aorta; Arsenites; Bacterial Proteins; Cadmium Chloride; Catalase; Cattle; Cells, Cultured; Chromans; Citrulline; Ditiocarb; DNA Damage; DNA-Formamidopyrimidine Glycosylase; Endothelium, Vascular; Enzyme Inhibitors; Escherichia coli Proteins; Free Radical Scavengers; Hydrogen Peroxide; Molsidomine; Mutagens; N-Glycosyl Hydrolases; Nitrates; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Onium Compounds; Phenanthrolines; Reactive Oxygen Species; Sodium Compounds; Sodium Selenite; Superoxide Dismutase; Superoxides; Thiomalates; Thiourea; Uric Acid

Chronic hypoxic exposure has been previously demonstrated to attenuate systemic vasoconstrictor activity to a variety of agents. This attenuated responsiveness is observed not only in conscious animals but in isolated vascular preparations as well. Because hypoxia has been documented to increase heme oxygenase (HO) levels and the subsequent production of the vasodilator CO in vitro, we hypothesized that the blunted reactivity observed with chronic hypoxia (CH) may be in part due to increased HO activity. In thoracic aortic rings from CH rats, cumulative dose-response curves to phenylephrine (PE) in the presence of the nitric oxide (NO) synthase inhibitor Nomega-nitro-L-arginine (L-NNA) and the HO inhibitor zinc protoporphyrin 9 (ZnPPIX) elicited increased contractility compared with CH rings treated with only L-NNA. Similar results were observed in rings incubated overnight with the HO-inducing agent sodium m-arsenite. In contrast, contractile responses in rings from control rats were unaffected by the HO inhibitor. Furthermore, endothelium-denuded rings from either control or CH rats did not exhibit an increase in reactivity to PE following ZnPPIX incubation. ZnPPIX had no effect on relaxant responses to the NO donor S-nitroso-N-penicillamine, suggesting that its actions were specific to HO inhibition. Finally, aortic rings exhibited dose-dependent relaxant responses to exogenous CO that were endothelium independent and blocked by an inhibitor of soluble guanylyl cyclase. The other products of HO enzyme activity, iron and biliverdin, were without effect on vasoreactivity. Thus we conclude that the attenuated vasoreactivity to PE following CH is likely to involve the induction of endothelial HO and the subsequent enhanced production of CO.

Topics: Animals; Aorta, Thoracic; Arsenites; Carbon Monoxide; Endothelium, Vascular; Enzyme Inhibitors; Guanylate Cyclase; Heme Oxygenase (Decyclizing); Hypoxia; In Vitro Techniques; Kinetics; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nitric Oxide Donors; Nitroarginine; Oxadiazoles; Penicillamine; Phenylephrine; Protoporphyrins; Quinoxalines; Rats; Rats, Sprague-Dawley; Reference Values; S-Nitroso-N-Acetylpenicillamine; Sodium Compounds