HISTOLOGY AND HISTOPATHOLOGY
Cellular and Molecular Biology

 

Inhibitors of inducible nitric oxide (NO) synthase are more effective than an NO donor in reducing carbon-tetrachloride induced acute liver injury

G.L.Tipoe1,6, T.M. Leung1,6, E. Liong2, H. So5, K.M. Leung1, T.Y.H. Lau1,7, W.M. Tom3, M.L. Fung2, S.T. Fan4,6 and A.A. Nanji8

Departments of 1Anatomy, 2Physiology, 3Pharmacology and 4Surgery, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 5Laboratory Animal Unit, The University of Hong Kong, 6Centre for the Study of Liver Disease, The University of Hong Kong, 7Department of Health Technology and Informatics, Hong Kong Polytechnic University and 8Department of Pathology and Laboratory Medicine, Dalhousie University School of Medicine, Halifax, Nova Scotia, Canada

Offprint requests to: Dr. George L. Tipoe, Department of Anatomy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR. e-mail: tgeorge@hkucc.hku.hk


Summary. The exact functional role of nitric oxide (NO) in liver injury is currently a source of controversy. NO is enzymatically synthesized by nitric oxide synthase (NOS). In this study, we assessed the role of inducible NOS (iNOS) in carbon tetrachloride (CCl4)-induced acute liver injury using inhibitors of iNOS, and an NO donor. Adult ICR mice were injected with CCl4 with or without the iNOS inhibitors (5-methylisothiourea hemisulfate [SMT] and l-N6-(1-iminoethyl)-lysine [L-NIL]) and an NO donor (Sodium Nitroprusside [SNP]). Blood and liver tissues were collected for analysis. Immunohistochemistry (IHC), serum alanine aminotransferase (ALT), serum total 8-isoprostane analysis, RT-PCR, Western Blotting (WB) and EMSA were done. Our results showed increased levels of ALT, necrosis, total 8-isoprostane and nitrotyrosine after CCl4 administration. iNOS inhibitors and SNP abrogated these effects but the effect was more pronounced with SMT and L-NIL. RT-PCR, WB and IHC in CCl4–treated mice demonstrated upregulation of TNF-alpha, iNOS, and COX-2. The administration of iNOS inhibitors with CCl4 diminished the expression of these proinflammatory mediators. NF-kappaB was also upregulated in CCl4-treated mice and was reversed in mice pretreated with iNOS inhibitors. SNP pretreated mice also showed a lower expression of COX-2 when compared with CCl4 treated mice but TNF-alpha, iNOS and NF-kappaB activity were unaffected. We propose that a high level of nitric oxide is associated with CCl4-induced acute liver injury and the liver injury can be ameliorated by decreasing the NO level with iNOS inhibitors and an NO donor with the former more effective in reducing CCl4-induced liver injury. Histol Histopathol 21,1157-1165 (2006)

Key words:
Nitric oxide, Liver injury, Oxidative stress; Lipid peroxidation, Inflammation

DOI: 10.14670/HH-21.1157