Kinetic studies of aflatoxin B1-glutathione conjugate formation in liver and kidneys of adult and weanling rats

Abstract

Aflatoxin B1(AFB1)-glutathione(GSH) conjugation is the major pathway for the detoxification of aflatoxin metabolites. This reaction is catalysed by GSH S-transferase (GST) and play a major role in modulation of AFB1 adduct formation to nuclear DNA. Changes recorded in hepatic GST activity during development of rats can alter the balance between AFB1-GSH conjugation and AFB1-DNA adduct formation. Measurment of cytosolic GST using 1-chloro-2,4-dinitrobenzene (CDNB) as the substrate showed that the enzyme activity is initially lower in weanling tissues as compared to that of adults. But nevertheless hepatic and renal cytosolic GST activity is increased significantly in growing rats pretreated with AFB1. Kinetic studies of AFB1-GSH conjugate formation in kidneys and livers of the two-age groups of rats treated with a single i.p. dose of AFB1 (400 microg/kg b.w.) revealed that at the end of 24 h of AFB1 administration the rate of the conjugate formation in kidneys of immature rats was approximately twice of that measured in adults. Age-related differences in the GST activity as well as AFB1-GSH conjugation was more pronounced in kidneys. The conjugate formation in kidneys of growing rats during 6-24 h following AFB1 administration shows that urinary excretion of aflatoxin metabolites is relatively rapid in growing rats. The major portion of the AFB1-GSH is formed in liver but contribution of the renal tissue to the formation of detoxification metabolites can not be ruled out. These data demonstrate that aflatoxin metabolites are eliminated more efficiently from kidneys of a growing rat. AFB1-induced GST induction in renal tissues of growing animals during 24 h of the carcinogen administration could be considered as an important mechanism for GSH conjugate formation and aflatoxin detoxification. Therefore GST induction in response to hepatotoxic drugs can confer resistance to young animals being exposed for the first time to such drugs. It is also worthmentioning that the GST activity measured before AFB1 administration does not reflect the rate of AFB1 detoxification via GSH conjugation.