Persistent hepatocyte apoptosis promotes tumorigenesis from diethylnitrosamine-transformed hepatocytes through increased oxidative stress, independent of compensatory liver regeneration

Hepatocellular carcinoma highly occurs in chronic hepatitis livers, where hepatocyte apoptosis is frequently detected. Apoptosis is a mechanism that eliminates mutated cells. Hepatocyte apoptosis induces compensatory liver regeneration, which is believed to contribute to tumor formation. Hepatocyte-specific Mcl-1 knockout mice (Mcl-1(Δhep) mice) developed persistent hepatocyte apoptosis and compensatory liver regeneration with increased oxidative stress in adulthood but had not yet developed hepatocyte apoptosis at the age of 2 weeks. When diethylnitrosamine (DEN) was administered to 2-week-old Mcl-1(Δhep) mice, multiple liver tumors were formed at 4 months, while wild-type mice did not develop any tumors. These tumors contained the B-Raf V637E mutation, indicating that DEN-initiated tumorigenesis was promoted by persistent hepatocyte apoptosis. When N-acetyl-L-cysteine was given from 6 weeks of age, DEN-administered Mcl-1(Δhep) mice had reduced oxidative stress and suppressed tumorigenesis in the liver but showed no changes in hepatocyte apoptosis or proliferation. In conclusion, enhanced tumor formation from DEN-transformed hepatocytes by persistent hepatocyte apoptosis is mediated by increased oxidative stress, independent of compensatory liver regeneration. For patients with livers harboring transformed cells, the control of oxidative stress may suppress hepatocarcinogenesis based on chronic liver injury.