Inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) expression in fulminant hepatic failure

Background/Aims: Inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) have important functions in inflammation and vasoregulation but their role in fulminant hepatic failure (FHF) is not well understood. Methods: Intrahepatic in situ staining and semi-quantification of iNOS and eNOS by immunohistochemistry in 25 patients with FHF, in 40 patients with chronic liver diseases (CLD) and in ten normal controls (NC). Results: Expression patterns of iNOS and eNOS differed. While in NC only faint iNOS expression was found in some Kupffer cells/macrophages and hepatocytes, eNOS was expressed constitutively in sinusoidal and vascular endothelial cells. In CLD, iNOS expression was induced in Kupffer cells/macrophages and hepatocytes, representing the main iNOS expressing cell types. Additionally, bile ducts, vascular endothelial cells and lymphocytes also expressed iNOS (P=0.001). In contrast, no differences were found between eNOS expression in CLD and NC (P=0.64). The same cell types expressed eNOS and iNOS in FHF but numbers of both were significantly enhanced, exceeding the levels seen in CLD (P<0.001, P=0.017). Conclusions: Our data demonstrate that iNOS and eNOS are differently regulated in physiologic conditions and in liver disease. While eNOS seems to be involved in the physiological regulation of hepatic perfusion, strong upregulation of iNOS might contribute to inflammatory processes in FHF.