The pathogenesis of
nonalcoholic steatohepatitis (NASH) is a two-stage process in which steatosis is the "first hit" and an unknown "second hit." We hypothesized that "a binge" could be a "second hit" to develop NASH from
obesity-induced simple steatosis. Thirty-week-old male Otsuka Long-Evans Tokushima fatty (OLETF) rats were administered 10 mL of 10%
ethanol orally for 5, 3, 2, and 1 d/wk for 3 consecutive weeks. As control, male Otsuka Long-Evans Tokushima (OLET) rats were administered the same amount of alcohol. Various biochemical parameters of
obesity, steatosis and NASH were monitored in serum and liver specimens in untreated and
ethanol-treated rats. The liver sections were evaluated for histopathological alterations of NASH and stained for
cytochrome P-4502E1 (
CYP2E1) and 4-hydroxy-nonenal (4-HNE). Simple steatosis,
hyperinsulinemia,
hyperglycemia,
insulin resistance, hypertriglycemia and marked increases in hepatic
CYP2E1 and 4-HNE were present in 30-wk-old untreated OLETF rats. Massive
steatohepatitis with hepatocyte ballooning was observed in the livers of all OLETF rats treated with
ethanol. Serum and hepatic
triglyceride levels as well as
tumor necrosis factor (TNF)-α
mRNA were markedly increased in all
ethanol-treated OLETF rats. Staining for
CYP2E1 and 4-NHE demonstrated marked increases in the hepatic tissue of all the groups of OLETF rats treated with
ethanol compared with OLET rats. Our data demonstrated that "a binge" serves as a "second hit" for development of NASH from
obesity-induced simple steatosis through aggravation of oxidative stress. The enhanced levels of
CYP2E1 and increased oxidative stress in
obesity play a significant role in this process.