Lack of inducible nitric oxide synthase leads to increased hepatic apoptosis and decreased fibrosis in mice after chronic carbon tetrachloride administration

Abstract

The role of nitric oxide (NO) in liver injury and fibrosis is unclear. The purpose of this study was to determine whether inducible NO synthase deficiency (iNOS ؊/؊ ) affects liver injury and fibrosis produced in mice by chronic carbon tetrachloride (CCl 4 ) administration. Wildtype (WT) or iNOS ؊/؊ mice were subjected to biweekly CCl 4 injections over 8 weeks, whereas controls were given isovolumetric injections of olive oil. Serum aminotransferases were lower after CCl 4 in the iNOS ؊/؊ than in the WT mice, which correlated with decreased necrosis on liver histology. There was increased apoptosis, a lower number of stellate cells, and a lesser degree of fibrosis after CCl 4 in the iNOS ؊/؊ as compared with the WT mice. ␣ 1 (I) collagen messenger RNA (mRNA) was markedly increased after CCl 4 in the WT and to a significantly lesser extent in the iNOS ؊/؊ mice. Liver matrix metalloproteinase-9 (MMP-9) mRNA and MMP-2 mRNA were increased more in the WT than in the iNOS ؊/؊ mice after CCl 4 . Also tissue inhibitor metalloproteinase 1 (TIMP-1) mRNA was increased to a much greater extent in the WT than in the iNOS ؊/؊ mice after CCl 4 (P < 0.05). However, MMP-9 and TIMP-1 protein, determined by western blot, were similarly increased after CCl 4 in both groups of mice. Conclusion: NO protects against CCl 4 -induced apoptosis. In the absence of iNOS, there is decreased necrosis, increased apoptosis, and reduced liver fibrosis. (HEPATOLOGY 2008;47:2051-2058 N itric oxide (NO) is a free radical that has a broad range of functions. It is synthesized from L-arginine by three known NO synthase isoforms: neuronal NO synthase, inducible NO synthase (iNOS-2), and endothelial NO synthase. NO has many roles ranging from neurotransmission, prevention of blood clotting, and regulation of blood pressure (mainly through the constitutive expression of neuronal NO synthase or endothelial NO synthase). In the liver, NO production by endothelial NO synthase has a protective role by maintaining perfusion and preventing platelet aggregation, whereas the exact role of iNOS remains unclear. There are differing results on whether NO production by iNOS is hepatoprotective or detrimental, depending on the level, intensity, and duration of an insult. In response to inflammation, iNOS is up-regulated in hepatocytes and macrophages. 1 In the presence of iNOS inhibitors, apoptotic cell death is increased, suggesting that NO has antiapoptotic properties. 2 Interactions between NO and reactive oxygen species (ROS)

Pigment Epithelium-Derived Factor Is an Intrinsic Antifibrosis Factor Targeting Hepatic Stellate Cells

“…Additionally, since tissue inhibitor of metalloproteinase is reportedly also synthesized in the liver along with MMPs after CCl 4 treatment, there may be a fine balance between MMPs and tissue inhibitor of metalloproteinase. 34,35 Our data have also shown that the majority of PEDFinduced PPAR␥ in HSCs remains in the cytoplasm, rather than the nucleus. Similar subcellular retention of PPAR␥ has been reported by others in macrophage-like RAW 264 cells, differentiating 3T3-L1 preadipocytes, and normal human urothelial cells, and this cytoplasmic retention is related to the nitration, lipid droplet interaction, and tyrosine phosphorylation of PPAR␥.…”

Serum Oxidative/anti-oxidative Stress Balance Is Dysregulated in Potentially Pulmonary Hypertensive Patients with Liver Cirrhosis: A Case Control Study

“…Moreover, NO is hypothesized to be a potential regulatory effector for prolidase and may regulate matrix metalloproteinase activity. An iNOS knockout study revealed decreased collagen accumulation in chemically-induced liver fibrosis, (24). ADMA promotes the dissociation of the ferrous-dioxy species from the heme group of NOS, resulting in the production of superoxide rather than NO.…”

Reversal of liver fibrosis by the antagonism of endocannabinoid CB1 receptor in a rat model of CCl4-induced advanced cirrhosis

“…22,23 Moreover, the NO generated by the activity of the inducible form of NO synthase, which is highly responsive to pro-inflammatory cytokines and endotoxemia, has been proposed to induce liver damage and facilitate the deposition of collagen. 24 TNF-a and MCP-1 have an important role in the development of fibrosis as pro-inflammatory molecules contributing to the activation of HSC and to the recruitment of myofibroblasts, macrophages and other effector cells to sites of tissue injury. 16,17 As we have recently showed in a model of acute liver injury produced by ischemia-reperfusion complicated by endotoxemia, 13 Rimonabant appears to exert its protective activity also by promoting the synthesis of IL-10 and SOCS-3.…”