OBJECTIVES: Several studies revealed that the proportion of hepatocellular carcinoma (HCC) without hepatitis virus infection (NBNC-HCC) is increasing. On the other hand, epigenetic alterations are reportedly responsible for HCC development. Here, we identified HCC risk factors that are associated with DNA methylation in the background liver tissue of NBNC-HCC patients. METHODS: We performed methylation analysis in 37 pairs of virus-positive and 22 pairs of NBNC-HCC and non-cancerous livers using a HumanMethylation450 BeadChip array. After the selection of differentially methylated CpGs (DM-CpGs) in cancerous and non-cancerous livers, we analyzed DNA methylation of DM-CpGs within the adjacent non-cancerous liver tissue that is affected by specific HCC risk factors. RESULTS: A total of 38,331 CpGs were selected as DM-CpGs using the following criteria: difference of β-value between HCC and non-cancerous liver ≥0.15 and false discovery rate (FDR) q < 1.0E-12. We subsequently selected the DM-CpGs that had methylation differences with the background liver tissue (that has FDR q < 0.35). Among the virus-positive patients, the type of hepatitis virus was mostly associated with differences in methylation within the background liver tissues. However, we found that background methylation patterns were most significantly associated with aging in NBNC patients. Interestingly, age-related methylation differences in DM-CpGs were also observed in NBNC-HCC tissues. CONCLUSIONS: Hepatitis viruses affect the methylation profiles within background liver tissues. However, difference in background methylation was mostly associated with age in NCBC-HCC patients; some age-related methylation events could contribute to emergence of NBNC-HCC in elderly individuals.
OBJECTIVES: Several studies revealed that the proportion of hepatocellular carcinoma (HCC) without hepatitis virus infection (NBNC-HCC) is increasing. On the other hand, epigenetic alterations are reportedly responsible for HCC development. Here, we identified HCC risk factors that are associated with DNA methylation in the background liver tissue of NBNC-HCC patients. METHODS: We performed methylation analysis in 37 pairs of virus-positive and 22 pairs of NBNC-HCC and non-cancerous livers using a HumanMethylation450 BeadChip array. After the selection of differentially methylated CpGs (DM-CpGs) in cancerous and non-cancerous livers, we analyzed DNA methylation of DM-CpGs within the adjacent non-cancerous liver tissue that is affected by specific HCC risk factors. RESULTS: A total of 38,331 CpGs were selected as DM-CpGs using the following criteria: difference of β-value between HCC and non-cancerous liver ≥0.15 and false discovery rate (FDR) q < 1.0E-12. We subsequently selected the DM-CpGs that had methylation differences with the background liver tissue (that has FDR q < 0.35). Among the virus-positive patients, the type of hepatitis virus was mostly associated with differences in methylation within the background liver tissues. However, we found that background methylation patterns were most significantly associated with aging in NBNC patients. Interestingly, age-related methylation differences in DM-CpGs were also observed in NBNC-HCC tissues. CONCLUSIONS:Hepatitis viruses affect the methylation profiles within background liver tissues. However, difference in background methylation was mostly associated with age in NCBC-HCC patients; some age-related methylation events could contribute to emergence of NBNC-HCC in elderly individuals.