Hepatofibrosis, which leads to cirrhosis and eventual hepatocellular carcinoma, is a common response to chronic toxin-mediated liver injury. Nitrosamines are potent hepatotoxic agents that cause necrosis and subsequent fibrosis in the liver as a result of cytochrome P450 2E1 (CYP2E1)-dependent metabolism, which generates toxic metabolites that form adducts with nucleic acids, leading to hepatotoxicity and mutagenesis. Herein, CYP2E1 activity and content were determined in fibrotic liver tissue from patients with hepatocellular carcinoma. The relationship between CYP2E1 innate activity and hepatofibrogenesis was evaluated, the effect of inhibition of CYP2E1 activity on hepatofibrosis was determined in a Sprague-Dawley rat model of diethylnitrosamine-induced hepatofibrosis. The results demonstrated that the CYP2E1 activities in human fibrotic tissues are significantly higher than that in normal liver tissues. In rats treated with diethylnitrosamine, the livers demonstrated various degree of fibrotic changes and collagen deposition in individual rats. The Ishak score, which determines the stage of fibrosis, correlated with CYP2E1 innate activity, with greater fibrosis in rat livers with higher CYP2E1 innate activity. Inhibition of CYP2E1 during diethylnitrosamine treatment decreased hepatofibrosis and there was an inverse correlation between the degree of inhibition and the extent of hepatofibrosis. Therefore, high CYP2E1 activity is a risk factor for hepatofibrogenesis induced by nitrosamines.
Hepatofibrosis is an important susceptibility factor for hepatocarcinogenesis. However, only a handful of cases of hepatofibrosis will develop into hepatocellular carcinoma (HCC). As cytochrome P450 2E1 (CYP2E1) is involved in the metabolism and activation of many known environmental toxicants and procarcinogens, this enzyme may play a role in the development of hepatocarcinogenesis subsequent to hepatofibrosis. Herein, we evaluated whether higher CYP2E1 activity is a risk factor for the development of hepatocarcinogenesis from hepatofibrosis. CYP2E1 activity in fibrotic tissues from 72 HCC patients and in normal liver tissues from 59 control subjects was determined along with the severity of hepatofibrosis in hepatocarcinogenesis patients. Similarly, using a rat diethylnitrosamine-induced hepatocarcinogenesis model, CYP2E1 activity at the hepatofibrosis and hepatocarcinogenesis stages was determined, the correlation between CYP2E1 activity at the hepatofibrosis stage and hepatocarcinogenesis was explored, and the impact of inhibition of CYP2E1 activity on hepatocarcinogenesis was studied. The results showed that while CYP2E1 activity in HCC patients with underlying hepatofibrosis was increased, the severity of hepatofibrosis did not correlate with CYP2E1 activity. In the rat hepatocarcinogenesis model, unexpectedly, CYP2E1 activity was found to decrease from hepatofibrosis to hepatocarcinogenesis. Importantly, however, hepatofibrotic rats with higher CYP2E1 activity developed a more severe form of HCC. Moreover, inhibition of CYP2E1 activity could decrease the occurrence and development of HCC in rats. In conclusion, higher CYP2E1 activity may be a risk factor for hepatocarcinogenesis from hepatofibrosis, which raises the possibility of screening patients with hepatofibrosis for CYP2E1 activity to better estimate their risk for hepatocarcinogenesis.
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