title: Mechanisms underlying activation of soluble guanylate cyclase by the nitroxyl donor Angeli's salt.
abstract: Nitroxyl (HNO) may be formed endogenously by uncoupled nitric-oxide (NO) synthases, enzymatic reduction of NO or as product of vascular nitroglycerin bioactivation. The established HNO donor Angeli's salt (trioxodinitrate, AS) causes cGMP-dependent vasodilation through activation of soluble guanylate cyclase (sGC). We investigated the mechanisms underlying this effect using purified sGC and cultured endothelial cells. AS (up to 0.1 mM) had no significant effect on sGC activity in the absence of superoxide dismutase (SOD) or dithiothreitol (DTT). In the presence of SOD, AS caused biphasic sGC activation (apparent EC(50) approximately 10 nM, maximum at 1 microM) that was accompanied by the formation of NO. DTT (2 mM) inhibited the effects of <10 microM AS but led to sGC activation and NO release at 0.1 mM AS even without SOD. AS had no effect on ferric sGC, excluding activation of the oxidized enzyme by HNO. The NO scavenger carboxy-PTIO inhibited endothelial cGMP accumulation induced by AS in the presence but not in the absence of SOD (EC(50) approximately 50 nM and approximately 16 microM, respectively). Carboxy-PTIO (0.1 mM) inhibited the effect of <or=10 microM AS in the presence of SOD but caused NO release from 0.1 mM AS in the absence of SOD. These data indicate that AS activates sGC exclusively via NO, formed either via SOD-catalyzed oxidation of HNO or through a minor AS decomposition pathway that is unmasked in the presence of HNO scavenging thiols.
authors.affiliation: Department of Pharmacology and Toxicology, Karl-Franzens-Universität Graz, Graz, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Zeller
authors.forename: M Verena
authors.initials: MV
authors.lastname: Wenzl
authors.forename: Matteo
authors.initials: M
authors.lastname: Beretta
authors.forename: Heike
authors.initials: H
authors.lastname: Stessel
authors.forename: Michael
authors.initials: M
authors.lastname: Russwurm
authors.forename: Doris
authors.initials: D
authors.lastname: Koesling
authors.forename: Kurt
authors.initials: K
authors.lastname: Schmidt
authors.forename: Bernd
authors.initials: B
authors.lastname: Mayer
mesh_terms: D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D006162:Guanylate Cyclase / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D009573:Nitrites / Q000494:pharmacology*; D009589:Nitrogen Oxides / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D000071756:Soluble Guanylyl Cyclase; D013552:Swine
chemical_list: D020030:Nitric Oxide Donors; D009573:Nitrites; D009589:Nitrogen Oxides; D018160:Receptors, Cytoplasmic and Nuclear; C021229:oxyhyponitrite; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase; C039900:nitroxyl