Modulation of Aflatoxin Metabolism, Aflatoxin-7V7-guanineFormation, and Hepatic Tumorigenesis in Rats Fed Ethoxyquin: Role of Induction of Glutathione S-Transferases1

The effects of dietary administration of ethoxyquin (EQ) on aflatoxin li, (AFBi) metabolism, DNA adduct formation and removal, and hepatic tumorigenesis were examined in male Fischer rats. Rats were fed a semipurified diet containing 0.4% EQ for 1 wk, gavaged with 250 Mgof AFBi per kg 5 times a wk during the next 2 wk, and, finally, restored to the control diet 1 wk after cessation of dosing. At 4 mo, focal areas of hepatocellular alteration were identified and quantitated by staining sections of liver for f-glutamyl transpeptidase. Treatment with EQ reduced by >95% both area and volume of liver occupied by •y-glutamyl transpeptidase-positive foci. Utilizing the same multiple dosing protocol, patterns of covalent modifications of DNA by AFBt were determined. EQ produced a dramatic reduction in the binding of AFBi to hepatic DNA: 18-fold initially and 3-fold at the end of the dosing period. Although binding was detectable at 3 and 4 mo postdosing, no effect of EQ was observed, suggesting that these persistent adducts are not of primary relevance to AFBi carcinogenesis. Analysis of nucleic acid bases by highperformance liquid chromatography revealed no qualitative differences in adduct species between treatment groups. The inhibitory effect of EQ on AFBi binding to DNA and tumorigenesis appears related to induction of detoxication enzymes. Rats fed 0.4% EQ for 7 days showed a 5-fold increase in hepatic cytosolic glutathione 5-transferase (GST)-specific activities. Multiple molecular forms of GST were induced, and concomi tant elevations in messenger RNA levels coding for the synthesis of GST subunits were observed. Correspondingly, biliary elimination of AFBiglutathione conjugate was increased 4.5-fold in animals on the EQ diet during the first 2 h following p.o. administration of 250 jig of AFBi per kg. Thus, induction by EQ of enzymes important to AFBi detoxication, such as GST, can lead to enhanced carcinogen elimination, as well as reductions of VKB, -1)\ A adduct formation and subsequent expression of preneoplastic lesions, and, ultimately, neoplasia.