Chronic and excessive ethanol intake decreases hepatic retinoic acid (RA) concentrations, which may play a critical role in ethanol-induced hyperproliferation in hepatocytes. The present study was conducted to determine whether RA supplementation in chronic ethanol-fed rats could restore hepatic RA concentrations to normal levels and modulate hepatocyte hyperproliferation. Male Sprague–Dawley rats were divided into four groups: control, ethanol-fed, ethanol-fed + 50 μg all-trans-RA/kg body wt and ethanol-fed + 100 μg all-trans-RA/kg body wt. Ethanol was given to rats at 6.2% (v/v) in a liquid diet to provide 36% of total caloric intake. Control animals received the same amount of liquid diet with isocaloric maltodextrin in place of ethanol. Results show that the ethanol treatment in rats for a month significantly increased the mean number of proliferating cell nuclear antigen (PCNA)-positive hepatocytes [4.96 ± 1.36% (ethanol-fed) versus 0.29 ± 0.08% (control), P < 0.05]. This increase was associated with the induction of hepatic c-Jun protein (6.5-fold increase) and cyclin D1 protein (3-fold increase) in ethanol-fed animals as compared with controls. Furthermore, activator protein 1 (AP-1) DNA-binding activity was significantly higher in hepatic nuclear extracts from ethanol-fed rats than those from controls. In contrast, RA supplementation in ethanol-fed rats raised hepatic RA concentration to normal levels and almost completely abolished the ethanol-enhanced c-Jun, cyclin D and AP-1 DNA-binding activities. Moreover, RA supplementation at both doses markedly suppressed the ethanol-induced PCNA-positive hepatocytes by ~80%. These results demonstrate that the restoration of hepatic RA concentrations by dietary RA supplementation suppresses ethanol-induced hepatocyte proliferation via inhibiting c-Jun overexpression, and suggest that RA may play a role in preventing or reversing certain types of ethanol-induced liver injury.
Keywords: AP-1, activator protein 1; HPLC, high performance liquid chromatography; JNK, c-Jun N-terminal kinase; PCNA, proliferating cell nuclear antigen; RA, retinoic acid.
Journal Article. 6104 words. Illustrated.
Subjects: Clinical Cytogenetics and Molecular Genetics
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