Several antioxidants widely used as preservatives in human and animal diets are known to inhibit cancer induction in various rodent tissues by a wide group of chemical carcinogens. Experimental studies from several laboratories suggest that these antioxidants play an important inhibitory role both in the initiation and promotion stages of carcinogenesis. However, exact mechanism of inhibition by these compounds is not yet known. Preliminary studies from our laboratory indicate that stimulation of hepatic cytosolic glutathione (GSH) S-tranferases by administration of an antioxidant, butylated hydroxyanisole (BHA) to rats may be an important factor responsible for inhibition of aflatoxin B1 (AFB1) binding to hepatic DNA. The overall aim of this project is to investigate further the effect of dietary BHA administration on the metabolism of AFB1 in vivo and in vitro studies in the rat.
The specific aims of this program are (1) to examine the kinetics of AFB1-DNA binding, AFB1-GSH conjugation, formation and conjugation of hydroxy metabolites of AFB1 after dietary administration of BHA to male rats using as experimental models hepatosubcellular studies, isolated hepatocytes, the perfused liver and whole animals. Liver perfusion and whole animal studies will allow measurements of biliary excretion of AFB1-GSH and related thiol conjugates as well as conjugates of hydroxy metabolites. Depletion of hepatic GSH levels by the administration of buthione sulfoximine will also be examined to assess the role of AFB1-GSH conjugation in inhibition of AFB1-DNA binding in BHA-treated animals. In some of these studies, AFB1-DNA adduct profiles will also be examined. (2) Since dietary BHA consists of 2 isomers, the effects of these two isomers will be examined separately on the total metabolism of AFB1 including modulation of hepatic AFB1-DNA binding in all the systems described above. (3) Final aim is to investigate which GSH S-transferases induced by dietary BHA treatment is responsible for conversion of AFB1-epoxide to AFB1-GSH conjugate. These studies would involve purification of various GSH S-transferases from BHA-treated rat livers and examining their catalytic and kinetic properties in a reconstituted system. The overall studies would enable us to determine the role of various pathways in the modulation of AFB1-DNA binding in the initiation of AFB1 hepatocarcinogenesis in the rat after BHA pretreatment.
| Jhee, E C; Ho, L L; Lotlikar, P D (1988) Effect of butylated hydroxyanisole pretreatment on in vitro hepatic aflatoxin B1-DNA binding and aflatoxin B1-glutathione conjugation in rats. Cancer Res 48:2688-92 |
| Lotlikar, P D; Raj, H G; Prasanna, H R et al. (1987) Role of glutathione (GSH) and GSH S-transferases in conjugation of reactive metabolites of chemical carcinogens. Indian J Biochem Biophys 24:suppl 36-43 |
