Interferon (IFN) is a multifunctional cytokine which works as a suppressor of hepatocarcinogenesis. Pegylated interferon (PEG-IFN) is a modified form of IFN with different pharmacokinetics. We evaluated the anti-tumor effect of PEG-IFN using a rat hepatocarcinogenesis model. Male Fisher Rats were treated using the Solt and Faber model to induce liver cancer. IFN and PEG-IFN were administered from chemical initiation, and pre-neoplastic foci and neoplastic hepatocellular carcinoma (HCC) were examined at 4 and 40 weeks after chemical initiation, respectively. Apoptosis-related molecules such as p53 and Fas-L, proliferating cell nuclear antigen (PCNA), and oxidative stress-related molecules such as 8-hydroxydeoxyguanosine (8-OHdG) and thioredoxin (TRX) were assessed by immunohistochemical analysis and reverse transcriptase-polymerase chain reaction (RT-PCR). The expression of Notch-1, a molecule related to the regenerative and oncogenic processes was also examined. The generation of foci and HCC were significantly suppressed in IFN and PEG-IFN groups compared with the control group. Whereas PCNA and Notch-1 were strongly expressed in the foci and HCC, Fas-L was mainly detected in the surrounding hepatocytes. 8-OHdG and TRX were also detected in the foci. Although PCNA and Notch-1 were down-regulated in IFN- and PEG-IFN-treated groups, Fas-L was up-regulated in those groups. The activation of Notch-1 signaling and the accumulation of oxidative stress in the pre-neoplastic foci might be associated with the progression of HCC in the DEN-induced hepatocarcinogenesis model. The inhibitory effect of the PEG-IFN and IFN on hepatocarcinogenesis was almost the same, and this might be induced by the Fas-related apoptosis in the surrounding tissues.

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