Inhibition of nitric oxide synthesis during induced cholestasis ameliorates hepatocellular injury by facilitating S-nitrosothiol homeostasis

Abstract

Cholestatic liver injury following extra-or intrahepatic bile duct obstruction causes nonparenchymal cell proliferation and matrix deposition leading to end-stage liver disease and cirrhosis. In cholestatic conditions, nitric oxide (NO) is mainly produced by a hepatocyte-inducible NO synthase (iNOS) as a result of enhanced inflow of endotoxins to the liver and also by accumulation of bile salts in hepatocytes and subsequent hepatocellular injury. This study was aimed to investigate the role of NO and S-nitrosothiol (SNO) homeostasis in the development of hepatocellular injury during cholestasis induced by bile duct ligation (BDL) in rats. Male Wistar rats (200-250 g) were divided into four groups (n ¼ 10 each), including sham-operated (SO), bile duct-ligated (BDL), tauroursodeoxycholic acid (TUDCA, 50 mg/kg) and S-methylisothiourea (SMT, 25 mg/kg) treated. After 7 days, BDL rats showed elevated serum levels of g-glutamiltranspeptidase, aspartate aminotransferase, alanine aminotransferase, LDH, and bilirubin, bile duct proliferation and fibrosis, compared with the SO group. TUDCA treatment did not significantly alter these parameters, but the iNOS inhibitor SMT ameliorated hepatocellular injury, as shown by lower levels of circulating hepatic enzymes and bilirubin, and a decreased grade of bile duct proliferation and fibrosis. Both TUDCA and SMT treatments reversed Mrp2 canalicular pump expression to control levels. However, only SMT treatment significantly lowered the increased levels of plasma NO and S-nitrosation (S-nitrosylation) of liver proteins in BDL rats. Moreover, BDL resulted in a reduction of the S-nitrosoglutathione reductase (GSNOR/Adh5) enzymatic activity and a downregulation of the GSNOR/Adh5 mRNA expression that was reverted by SMT, but not TUDCA, treatment. A total of 25 liver proteins, including S-adenosyl methionine synthetase, betainehomocysteine S-methyltransferase, Hsp90 and protein disulfide isomerase, were found to be S-nitrosated in BDL rats. In conclusion, the inhibition of NO production during induced cholestasis ameliorates hepatocellular injury. This effect is in part mediated by the improvement of cell proficiency in maintaining SNO homeostasis.

GCDCA down-regulates gene expression by increasing Sp1 binding to the NOS-3 promoter in an oxidative stress dependent manner

“…We have previously shown that NOS-2 overexpression in the BDL group is associated with the hepatocellular injury [15]. According to the results of the present study, the adverse effects exerted by NO during cholestatic injury might be due to both the increase in NOS-2 and the reduction in NOS-3 expression.…”

“…This result is not surprising since the hepatic cholestasis was associated with tissue fibrosis [15], and liver fibrosis has been previously linked to changes in the expression of commonly used loading control proteins [42,43]. We have previously shown that NOS-2 overexpression in the BDL group is associated with the hepatocellular injury [15].…”

“…Animals were randomized into two groups: Sham operated control group (SO group, n = 13) and bile duct ligation group (BDL group, n = 13). Surgical procedure and sample collection were carried out as we described before [15]. Briefly, 13 animals in each group were killed 7 days after surgery under sevofluorane anaesthesia.…”

The effect of albumin administration on renal dysfunction after experimental surgical obstructive jaundice in male rats

“…The excessive generation of NO has been observed both in experimental cholestasis [34,35] and in primary biliary cirrhosis patients [36,37]. Renal impairment occurs in cirrhotic patients with a high concentration of NO in the plasma and ascitic fluid.…”

Nitric oxide-mediated inhibition of taurocholate uptake involvesS-nitrosylation of NTCP

“…It has also been shown that overall Snitrosylation levels increase in NO donor-treated hepatic stellate cells (29). Recent work has shown that inhibition of nitric oxide synthesis during induced cholestasis can ameliorate hepatocellular injury by facilitating S-nitrosothiol homeostasis (23). Despite these findings, very little work has been done investigating a role for S-nitrosylation in the regulation of hepatic transporters.…”