Increased formation of S-nitrothiols and nitrotyrosine in cirrhotic rats during endotoxemia

Plasma S-nitrosothiols are believed to function as a circulating form of nitric oxide that affects both vascular function and platelet aggregation. However, the formation of circulating S-nitrosothiols in relation to acute and chronic disease is largely unknown. Plasma S-nitrosothiols were measured by chemiluminescence in rats with biliary cirrhosis or controls, and the effect of lipopolysaccharide (LPS) on their formation was determined. Plasma S-nitrosothiols were increased in rats with cirrhosis (206 ± 59 nM) compared to controls (51 ± 6 nM, p < .001). Two hours following injection of LPS (0.5 mg/kg) plasma S-nitrosothiols increased to 108 ± 23 nM in controls (p < .01) and to 1335 ± 423 nM in cirrhotic rats (p < .001). The plasma clearance and half-life of S-nitrosoalbumin, the predominant circulating S-nitrosothiol, were similar in control and cirrhotic rats, confirming that the increased plasma concentrations were due to increased synthesis. Because reactive nitrogen species, such as peroxynitrite, may cause the formation of S-nitrosothiols in vivo, we determined the levels of nitrotyrosine by gas chromatography/mass spectrometry as an index for these nitrating and nitrosating radicals. Hepatic nitrotyrosine levels were increased at 7.0 ± 1.2 ng/mg in cirrhotic rats compared to controls (2.0 ± 0.2 ng/mg, p < .01). Hepatic nitrotyrosine levels increased by 2.3-fold and 1.5-fold in control and cirrhotic rats, respectively, at 2 h following injection of LPS (p < .01). Strong positive staining for nitrotyrosine was shown by immunohistochemistry in all the livers of the rats with cirrhosis. We conclude that there is increased formation of S-nitrosothiols and nitrotyrosine in biliary cirrhosis, and this is markedly upregulated during endotoxemia.