Nonalcoholic steatohepatitis (NASH) may cause fibrosis, cirrhosis, and hepatocellular carcinoma (HCC); however, the exact mechanism of disease progression is not fully understood. Angiogenesis has been shown to play an important role in the progression of chronic liver disease. The aim of this study was to elucidate the role of angiogenesis in the development of liver fibrosis and hepatocarcinogenesis in NASH. Zucker rats, which naturally develop leptin receptor mutations, and their lean littermate rats were fed a choline-deficient, amino acid-defined diet. Both Zucker and littermate rats showed marked steatohepatitis and elevation of oxidative stress markers (e.g., thiobarbital acid reactive substances and 8-hydroxydeoxyguanosine). In sharp contrast, liver fibrosis, glutathione-S-transferase placental form (GST-P)-positive preneoplastic lesions, and HCC developed in littermate rats but not in Zucker rats. Hepatic neovascularization and the expression of vascular endothelial growth factor (VEGF), a potent angiogenic factor, only increased in littermate rats, almost in parallel with fibrogenesis and carcinogenesis. The CD31-immunopositive neovessels were mainly localized either along the fibrotic septa or in the GST-P-positive lesions. Our in vitro study revealed that leptin exerted a proangiogenic activity in the presence of VEGF. In conclusion, these results suggest that leptin-mediated neovascularization coordinated with VEGF plays an important role in the development of liver fibrosis and hepatocarcinogenesis in NASH.
Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html). (HEPATOLOGY 2006;
44:983-991.) N onalcoholic steatohepatitis (NASH), a progressive metabolic liver disease, is one of the major consequences of the current obesity epidemic. 1 It lies on a spectrum of nonalcoholic fatty liver disease that ranges from simple steatosis to cirrhosis. 2 Whereas simple steatosis seems to be a benign and nonprogressive condi-tion, NASH is recognized as a potentially progressive disease that may cause cirrhosis, an end-stage liver disease, and hepatocellular carcinoma (HCC). 3,4 The pathogenesis of NASH is known to be a multifactorial process. 3,5 The current concept in the pathogenesis of NASH involves a "two-hit" theory in which an initial metabolic disturbance, such as insulin resistance, causes steatosis, and a second pathogenic stimulus causes oxidative stress and reactive oxygen species, leading to steatohepatitis. It has been reported that hepatic thiobarbital acid reactive substances (TBARSs) and 8-hydroxydeoxyguanosine (8-OHdG), as reliable markers of lipid peroxidation and oxidative DNA-damage, respectively, were significantly increased both in the animal models and human samples of NASH. 6-8 However, it is not known whether reactive oxygen species can result in progression of liver fibrosis and hepatocarcinogenesis, beccause, like diabetes mellitus, NASH is almost certainly a polygenic disease affected by several factors, with disease pathogenesis related to multiple "hits." 3