Conjugation of anti-dihydrodiol epoxides of benzo[ a]pyrene, chrysene, benzo[ c]phenanthrene and dibenz[ a, h]anthracene with glutathione catalyzed by cytosol and by the Mu-class glutathione transferase HTP II from rat liver

Abstract

The (±)- anti-dihydrodiol epoxides (DE) of benzo[ a]pyrene (BP), chrysene (Chr), benzo-[ c]phenanthrene (BcPh) and dibenz[ a, h]anthracene (DBA) were incubated in the presence of glutathione (GSH) with hepatic cytosol from untreated and Aroclor 1254 pretreated rats and with the Mu-class glutathione transferase (GST) HTP II from rat liver. The diastereoisomeric GSH conjugates formed were separated, identified and quantified by HPLC employing synthetic reference compounds. All (±)- anti-dihydrodiol epoxides investigated in this study were proven to be substrates of the cytosolic GSTs. The highly mutagenic and carcinogenic (+)- anti-DE with R, S, S, R absolute configuration was preferentially conjugated in the case of BP and Chr. Aroclor 1254 pretreatment increased the turnover 2–3-fold and changed the enantioselectivity. The previously purified GST HTP II exhibited a high degree of enantioselectivity (≥ 95%) towards the R, S, S, R-configurated enantiomer in the case of the bay-region (±)-anti-BPDE, (±)- anti-ChrDE and (±)- anti-DBADE, whereas in the case of the fjord-region (±)- anti-BcPhDE both enantiomers were good substrates. The contribution of HTP II to the enzymatic activity of the cytosolic GST pool was estimated to be in the range of 11–32%. In agreement with previous results, the observed enantioselectivity of the purified enzyme seems to be of minor significance considering the total GST pool in the liver.