Suppression of β-catenin mutation by dietary exposure of auraptene, a citrus antioxidant, in N,N-diethylnitrosamine-induced hepatocellular carcinomas in rats

Alteration of β-catenin expression in hepatocellular carcinomas (HCCs) may play an important role in tumor progression by stimulating cell proliferation. We have previously reported that auraptene (AUR), an antioxidant agent isolated from citrus fruit, effectively inhibits chemically induced hepatocarcinogenesis in rats. In this study, we investigated the molecular mechanism of the inhibitory effects of dietary supplementation with AUR on N,N-diethylnitrosamine (DEN)-initiated hepatocarcinogenesis. Male F344 rats initiated with DEN were fed the AUR-containing diet during either the initiation stage (initiation feeding for 7 weeks) or post-initiation phase (post-initiation feeding for 25 weeks) of hepatocarcinogenesis. Liver tumors >5 mm in diameter were used for the analysis of β-catenin gene mutation and β-catenin protein expression. After PCR amplification of exon 2 of the β-catenin gene, the products were sequenced directly. Mutations in the β-catenin gene were detected in 8 of 24 HCCs (33.3%) in the DEN alone group, 7 of 15 HCCs (46.7%) in the DEN + AUR (initiation feeding) group, and 0 of 8 HCCs (0%) in the DEN↷AUR (post-initiation feeding) group. No mutations of β-catenin gene were detected in liver cell adenomas of any group. These results demonstrate that AUR exposure in post-initiation period suppresses the occurrence of HCCs with β-catenin mutation, presumably by negative selection for neoplastic cells harboring the mutation.