Role of nitric oxide in the regulation of fibrogenic factors in experimental liver fibrosis in mice
Tung-Ming Leung1,2*, Man-Lung Fung4*, Emily C. Liong2, Thomas Y.H. Lau3, Amin A. Nanji1 and George L. Tipoe2*
1Department of Pathology and Laboratory Medicine, Faculty of Medicine, Dalhousie University, Halifax, NS, Canada, 2Department of Anatomy, Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, 3Department of Health Technology and Informatics, Hong Kong Polytechnic University, Hong Kong SAR and 4Department of Physiology, Faculty of Medicine, The University of Hong Kong, Hong Kong SAR.
*These authors contributed equally to this work (TML, MLF, GLT).
Offprint requests to: Dr. George L. Tipoe, Department of Anatomy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong. e-mail: email@example.com
Summary. Previously, we have shown that an increased expression level of iNOS but a reduction in the expression of eNOS is associated with increased oxidative stress markers in CCl4-induced experimental liver fibrosis. The present study aimed to investigate the effect of L-arginine and 5-methylisothiourea hemisulfate (SMT) in the expression of profibrogenic factors in chronic liver injury. ICR mice were treated with CCl4 with or without treatment of L-arginine, an NO donor, or SMT, an iNOS inhibitor. The expression of matrix metalloptroteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs), α-smooth muscle actin (α-SMA), tumor necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX-2) were investigated by RT-PCR. The activity of the MMP-2 and MMP-9 were measured by zymography. Our results showed that CCl4-treated mice showed significant up-regulation of expression of pro-fibrogenic factors, TNF-α and COX-2. Treatment with L-arginine or SMT showed a significant reduction in CCl4-induced expression of these pro-fibrogenic factors, TNF-α and COX-2. In conclusion, both SMT and L-arginine effectively attenuated the progression of CCl4-induced liver fibrosis. SMT suppresses iNOS mediated NO production. However, L-arginine augments NO production. The similar effect of the two drugs on liver fibrosis indicates that there may be two distinct pathways of NOS mediated fibrogenesis in chronic liver injury by iNOS and eNOS. Our results suggest that eNOS-mediated liver fibrogenesis may play a more important role than that of iNOS in chronic liver injury. Taken together, these results support the contention that NO plays an active role in the progression of liver fibrosis and hepatocellular damage. Histol Histopathol 26, 201-211 (2011)
Key words: Liver fibrosis, SMT, L-arginine, Nitric oxide, Nitric oxide synthases