PNNL

Abstract

The chloro- and bromo- haloacetates are drinking water disinfection by-products and rodent carcinogens. Chloro, bromo di-haloacetates are also mechanism based inhibitors of glutathione-S- transferase zeta (GSTZ1-1). We studied the stereospecific toxicokinetics and in-vitro metabolism of two chiral di-haloacetates in male F344 rats: (-), (+)bromochloro-acetate (BCA), and racemic chlorofluoro-acetate (CFA), a non GST-zeta inhibiting di-haloacetate. These experiments were repeated in animals that had previously been treated with dichloroacetate (DCA) to deplete GST-zeta activity. Results indicated that in naive rats the elimination half-life of (-)BCA was 0.07 hrs compared to 0.40 hrs for (+)BCA. A comparable difference in elimination half-life was also observed for the CFA stereoisomers (0.79 hr vs. 0.11 hrs). In GST-zeta depleted rats, stereospecific elimination of (-), (+) BCA was absent with both stereoisomers having an elimination half-life of approximately 0.4 hrs. This finding was in contrast to results for CFA, which still maintained the same relative difference in elimination rate between its stereoisomers although overall elimination was diminished in GST-zeta depleted rats. Results of in-vitro metabolism experiments indicated (-)BCA was affected by modulating GST-zeta activity, with the intrinsic metabolic clearance decreasing from 2.81 to 0.15 ml hr-1 mg-protein-1 (naive, GST-zeta depleted) compared with values for (+)BCA (0.30 and 0.31 ml hr-1 mg-protein-1). Incubations with 350 mM DDTC (IC50 for GST-theta inhibition) or polyclonal antibodies recognizing GST-theta (hGSTT1-1) preferentially decreased (+)BCA metabolism in both GST-zeta depleted and human cytosol. These results indicate (+)BCA is a poor substrate for GST-zeta and its metabolism is controlled by an additional GST isoenzyme, possibly GST-theta.