Role of ascorbate and protein thiols in the release of nitric oxide from S-nitroso-albumin and S-nitroso-glutathione in human plasma.
In this work we investigated the stability in aerobic plasma of two naturally occurring S-nitrosothiols, the S-nitroso adduct of serum albumin (S-NO-albumin) and the S-nitroso adduct of glutathione (S-NO-glutathione). In contrast to their behavior in physiological buffers, in which they are stable, in plasma these S-nitrosothiols showed a slow but continuous release of .NO. In the presence of red blood cells, the .NO was quantitatively oxidized to NO3- with stoichiometric formation of methemoglobin. In the absence of red blood cells, the principal oxidation product was NO2- with small amounts of NO3- (about 1/5 of the amount of NO2-). The release of .NO was also proven by spin trapping experiments with 2-(4-Carboxyphenyl)4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide which, when added to plasma in the presence of S-NO-glutathione, was transformed into 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl. Both dialysable and nondialysable compounds are involved in the release of .NO from S-nitrosothiols. Ascorbate and the thiol group of serum albumin are the plasma components mainly involved in the release of .NO, while endogenous L-cysteine and glutathione play a minor role due to their relative low concentrations. However, in contrast to the thiol-dependent release that is known to induce the formation of disulfides, the ascorbate-dependent release of .NO from S-NO-glutathione resulted in the formation of free sulfhydryls. Our results suggest that in plasma the .NO release from S-NO-albumin and S-NO-glutathione may be regulated by heterolytic NO+ transfer and reductive activation to .NO, rather than by homolytic decomposition of labile S-nitrosothiols.
Scorza
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Laboratorio di Biologia Cellulare, Istituto Superiore di Sanità, Roma, Italy.
Pietraforte
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Minetti
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D001205:Ascorbic Acid / Q000097:blood* / Q000494:pharmacology*; D004578:Electron Spin Resonance Spectroscopy; D004912:Erythrocytes / Q000378:metabolism; D005609:Free Radicals / Q000097:blood; D005978:Glutathione / Q000031:analogs & derivatives* / Q000097:blood; D006801:Humans; D066298:In Vitro Techniques; D009569:Nitric Oxide / Q000097:blood*; D009603:Nitroso Compounds / Q000097:blood*; D026422:S-Nitrosoglutathione; D012709:Serum Albumin / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000097:blood
D005609:Free Radicals; D009603:Nitroso Compounds; C091665:S-nitrosoalbumin; D012709:Serum Albumin; D013438:Sulfhydryl Compounds; D012710:Serum Albumin, Bovine; D009569:Nitric Oxide; D026422:S-Nitrosoglutathione; D005978:Glutathione; D001205:Ascorbic Acid