Higher susceptibility to aflatoxin B₁-related hepatocellular carcinoma in glycine N-methyltransferase knockout mice

In both humans and rodents, males are known to be more susceptible than females to hepatocarcinogenesis. We have previously reported that glycine N-methyltransferase (GNMT) interacts with aflatoxin B₁ (AFB ₁) and reduces both AFB₁-DNA adduct formation and hepatocellular carcinoma (HCC) in mice. We also reported that 50% of the males and 100% of the females in a small group of Gnmt null (Gnmt-/-) mice developed HCC, with first dysplastic hepatocellular nodules detected at mean ages of 17 and 16.5 months, respectively. In our study, we tested our hypothesis that male and female Gnmt-/- mice are susceptible to AFB₁ carcinogenesis, and that the absence of Gnmt expression may accelerate AFB₁-induced liver tumorigenesis. We inoculated Gnmt-/- and wild-type mice intraperitoneally with AFB₁ at 7 days and 9 weeks of age and periodically examined them using ultrasound. Dysplastic hepatocellular nodules were detected in six of eight males and five of five females at 12.7 and 12 months of ages, respectively. Dysplastic hepatocellular nodules from 5/8 (62.5%) male and 4/5 (80%) female Gnmt-/- mice were diagnosed as having HCC, ∼6 months earlier than AFB₁-treated wild-type mice. Results from microarray and real-time PCR analyses indicate that five detoxification pathway-related genes were downregulated in AFB₁-treated Gnmt-/- mice: Cyp1a2, Cyp3a44, Cyp2d22, Gsta4 and Abca8a. In summary, we observed overall higher susceptibility to AFB₁-related HCC in Gnmt-/- mice, further evidence that GNMT overexpression is an important contributing factor to liver cancer resistance.