Cell proliferation and hepatocarcinogenesis in rat initiated by diethylnitrosamine and promoted by phenobarbital: potential roles of early DNA damage and liver metallothionein expression

Cell proliferation plays an important role in multistage chemical carcinogenesis. Again, several reports demonstrated that upregulation of metallothionein (MT) expression is associated with increased cell proliferation that may contribute to the pathogenesis of preneoplastic phenotype to frank malignancy. In this study, we evaluated the roles of early DNA damage, altered expressions of liver MT and Ki-67 nuclear antigen, and altered hepatic levels of zinc (Zn) and copper (Cu) on cell proliferation and the progression of hepatocarcinogenesis through premalignant, late premalignant and malignant transformation phases in male Sprague-Dawley rats. We have further studied the association between MT expression and cell proliferation in hepatocarcinogenesis. There was substantial induction of DNA single-strand breaks (SSBs) (P < 0.001) and development of hepatocellular premalignant lesions along with significant decrease in hepatic levels of Zn and increase in Cu content following a single, necrogenic, intraperitoneal (i.p.) injection (200 mg/Kg body weight) of diethylnitrosamine (DEN) at week 4 of the experimental protocol. Moreover, DEN + phenobarbital (PB)-treatment significantly elevated MT-, Ki-67-, and BrdU-immunoexpressions along with their immunolabeling indices. Furthermore, positive correlations between MT- and Ki-67- labeling (P = 0.0006) at various time intervals, as well as, between MT immunoreactivity and 5’-bromo-2’-deoxyuridine-labeling index (BrdU-LI) (P = 0.0007) indicate that, MT expression might be associated with Ki-67 expression and cell proliferation thereby. The study suggests that DEN treatment may lead to alteration of Zn and Cu levels resulting in early DNA damage along with elevation of MT expression that may ultimately lead to hepatic cell proliferation. The results thus provide evidence in support of the role of MT as a potential positive regulator of cell growth during the early stages of hepatocellular transformation in rats.