Changes in adult metabolism of aflatoxin B1 in rats neonatally exposed to diethylstilbestrol. Alterations in alpha-class glutathione S-transferases.

Abstract

Neonatal exposure of rats to xenobiotics has been shown to produce long-term alterations in hepatic enzyme activities and in levels of DNA adducts following carcinogen exposure. We exposed newborn male rats to diethylstilbestrol (DES), pregnenolone-16 alpha-carbonitrile, 7,12-dimethylbenz[a]anthracene or phenobarbital on days 1, 3 and 5 of age. At five months of age, males were injected with 1 mg/kg of [3H]aflatoxin B1 (AFB1), killed after 2 h and examined for AF-DNA adduction in the liver. Males neonatally exposed to DES showed a 35% decrease in DNA adduction levels. Analysis of the adducted DNA bases failed to show any changes in relative proportions of individual adducts in the DES samples compared to controls. Hepatic glutathione concentrations were unchanged. However, Western blot analysis of alpha-class glutathione S-transferases (alpha GST), enzymes known to inactivate the toxic AFB1-8,9-epoxide, showed a 2-fold increase in subunit levels in the DES-treated males, suggesting that the detoxifying activity of the cytosol may have been increased. To confirm this, in vitro tests were undertaken using butylated hydroxyanisole (BHA) induced mouse microsomes to activate [3H]AFB1 in the presence of treated cytosol and GSH. Analysis of metabolites by HPLC showed that DES-treated males formed 245% of the AFB-SG conjugate relative to vehicle controls. These results indicate that neonatal DES treatment resulted in long-term changes in basal alpha GST levels and suggest that these changes were responsible for lower levels of DNA adduction following adult exposure to AFB1.