Effect of diet on aflatoxin B1-DNA binding and aflatoxin B1-induced glutathione S-transferase placental form positive hepatic foci in the rat

Effects of diets on hepatic aflatoxin B1 (AFB1)- DNA binding and AFB1-induced glutathione S- transferase placental (GST-P) form positive hepatic foci have been examined in young male Fischer rats. Animals were fed either AIN-76A or Purina Chow (PC) diet for 1 wk before AFB1- DNA binding studies in vivo and in vitro. Animals were injected i.p. with AFB1 (1 mg/kg body wt) and 3 days later were given either AIN-76A or PC diet with or without 0.1% phenobarbital (PB) in their drinking water. All animals were sacrificed 10 wks after AFB1 dosing for analysis of AFB1-induced GST-P positive hepatic foci by immunochemistry. Two h after i.p. injection of AFB1, hepatic AFB1-DNA binding in AIN-76A fed rats was twice as much as those in PC fed animals without affecting GSH levels. There was no significant effect of diet on either cytochrome P-450 content, GSH levels or microsomal cytochrome P-450 mediated AFB1-DNA binding to exogenous DNA. There was a 40% increase in cytosolic GSH S-transferase activity with 1-chloro-2,4-dinitrobenzene as a substrate in PC fed animals compared to those given AIN- 76A diet. The number and area of AFB1-induced GST-P positive hepatic foci were twice and fivefold as much in AIN-76A fed compared to those in PC fed rats. The number of AFB1-induced GST-P positive foci was increased 5-10 fold in the presence of PB in both groups. In summary, the present data indicate that feeding of PC diet compared to AIN-76A diet inhibits the initiation phase whereas AIN-76A stimulates the promotion phase of AFB1 hepatocarcinogenesis in rats by inhibiting AFB1-DNA binding and increasing AFB1-induced hepatic foci respectively.

Enhancement of aflatoxin B1-induced enzyme altered hepatic foci in rats by treatment with carbon tetrachloride

The effect of carbon tetrachloride (CCl4) on aflatoxin B1 (AFB1)-induced enzyme altered hepatic foci has been examined in young male Fischer rats given AIN-76A diet. A single i.p. dose of AFB1 (0.2 mg/kg body wt) was given to rats 24 h after partial hepatectomy. Two weeks later, CCl4 (0.8 ml/kg body wt) was injected i.p. once a week for 9 weeks. Animals were sacrificed 24 h after the last dose of CCl4 and glutathione S-transferase placental form (GST-P) and gamma-glutamyl transpeptidase (GGT) positive hepatic foci were analyzed by immunohistochemical and histochemical methods, respectively. Ten weeks after AFB1 dosing, treatment with CCl4 increased the number of AFB1-induced enzyme altered foci several fold and produced a ten to twenty-fold increase in area and volume. GST-P was more sensitive than GGT in detecting AFB1-induced enzyme altered foci. Treatment with AFB1 or CCl4 produced mild hepatic fibrosis in zones 1 and 3 respectively, whereas both treatments produced severe fibrosis in zones 1 to 3 areas. Treatment with CCl4 after AFB1 dosing lowered hepatic GSH levels by 20% and increased lipid peroxidation by 40%. It appears that CCl4, by being an effective enhancer of AFB1-induced enzyme altered hepatic foci in the rat, may mimic cirrhosis observed in human hepatocellular carcinoma.

Expression of p53 gene in hepatocellular carcinomas induced by aflatoxin B1 with or without human hepatitis B virus in tree shrews

Using tree shrew as an animal model, our previous studies have demonstrated synergistic effects of aflatoxin B-1 (AFB(1)) and human hepatitis B virus (HHBV) in the induction of hepatocellular carcinoma (HCC). In the present study, we have examined expression of p53 gene in HCCs induced by AFB(1) with or without HHBV infection in tree shrews. Avidin-biotin-peroxidase complex immunohistochemical method with human p53-CM1 polyclonal antibody has been used to detect p53 expression in serial sections of paraffin-embedded liver and HCC tissues. Five out of 9 animals with HCCs (55.6%) induced by AFB(1) with HHBV infection and 2/3 animals with HCCs (66.7%) induced by AFB(1) alone expressed the p53 protein. Out of 18 HCCs examined, expression of p53 protein was observed in 9/10 moderately and poorly differentiated HCCs (0/8). None of the well differentiated HCCs (0/8) expressed p53 (0%). Similarly, no p53 expression was observed in either non-tumorous or hyperplastic liver tissues or nodules. These results suggest that p53 expression associated with p53 mutation is a late event occurring probably during tumor progression in AFB(1) and HHBV induced hepatocarcinogenesis in the tree shrew. This report is the first example of an experimental animal model where combination of human HBV and AFB(1)-induced HCCs demonstrate p53 expression.