Nonalcoholic steatohepatitis induced by a high-fat diet promotes diethylnitrosamine-initiated early hepatocarcinogenesis in rats

It has been suggested that patients with nonalcoholic steatohepatitis {(NASH)} may have high risk for liver cancer. However, it is unknown whether high-fat diet {(HFD)} induced {NASH} promotes hepatocarcinogenesis. In this study, {Sprague-Dawley} rats were injected with a low dose of hepatic carcinogen diethylnitrosamine {(DEN)} and then fed either {Lieber-DeCarli} control diet {(CD)} or {HFD} for 6 weeks. Liver histology and the hepatic placental form of glutathione S-transferase {(P-GST)} positive foci were examined. Expression levels of proliferating cell nuclear antigen {(PCNA),} {cyclinD1,} phosphorylated mitogen-activated protein kinase {(MAPK)} including extracellular signal-regulated kinase {(ERK)} and p38, as well as tumor necrosis factor-alpha {(TNF-alpha),} and nuclear {factor-kappaB} {(NF-kappaB)} were measured in the liver. Induction of lipid peroxidation end products (malondialdehyde plus 4-hydroxynonenal) in liver and apoptotic hepatocytes were also assessed. Results showed that {HFD-fed} rats developed significantly higher incidence and multiplicity of {P-GST} positive foci along with more fat accumulation, infiltration of inflammatory cells and higher lipid peroxidation in the liver, when compared with rats fed the {CD.} This high prevalence of hepatic lesions in the liver was accompanied by greater {PCNA} expression and {cyclinD1} protein concentration but little change in hepatocyte apoptosis. {HFD} feeding elevated hepatic phosphorylated {ERK} but reduced phosphorylated p38 when compared with the {CD} feeding. In addition, a significantly higher expression of {TNF-alpha} {mRNA} and nuclear {NF-kappaB} p65 protein were observed in {HFD} group than in {CD} group. These data clearly demonstrate that {NASH} induced by {HFD} promoted {DEN-initiated} early hepatocarcinogenesis, which was associated with elevated {TNF-alpha/NF-kappaB} signaling and {MAPK} related hepatocyte proliferation.