Conjugative metabolism of 1,2-dibromoethane in mitochondria: disruption ofoxidative phosphorylation and alkylation of mitochondrial DNA

1,2-Dibromoethane (DBE) is an environmental contaminant that is metabolized by glutathione S-transferases to a haloethane-glutathione conjugate. Since haloethane-glutathione conjugates are known to alkylate nuclear DNA and cy toplasmic proteins, these effects were investigated in isolated rat liver m itochondria exposed to DBE by measuring guanine adducts and several aspects of oxidative phosphorylation including respiratory control ratios, respira tory enzyme activity, and ATP levels. Mitochondrial large-amplitude swellin g and glutathione status were assessed to evaluate mitochondrial membrane i ntegrity and function. When exposed to DBE, mitochondria became uncoupled r apidly, yet no large-amplitude swelling or extramitochondrial glutathione w as observed. Mitochondrial GSH was depleted to 2-53% of controls after a 60 -min exposure to micromolar quantities of DBE; however, no extramitochondri al GSH or GSSG was detected. The depletion of mitochondrial glutathione cor responded to an increase of an intramitochondrial GSH-conjugate which, base d on HPLC elution profiles and retention times, appeared to be S,S'-(1,2-et hanediyl)bis(glutathione). Activities of the NADH oxidase and succinate oxi dase respiratory enzyme systems were inhibited 10-74% at micromolar levels of DBE, with succinate oxidase inactivation occurring at lower doses. ATP c oncentrations in DBE-exposed mitochondria in the presence of succinate were 5-90% lower than in the controls. The DNA adduct S-[2-(N-7-guanyl)ethyl]gl utathione was detected by HPLC in mtDNA isolated from DBE-exposed mitochond ria. The results suggest that respiratory enzyme inhibition, glutathione de pletion, decreased ATP levels, and DNA alkylation in DBE-exposed mitochondr ia occur via the formation of an S-(2-bromoethyl)glutathione conjugate, the precursor of the episulfonium ion alkylating species of DBE. (C) 2001 Else vier Science Inc. All rights reserved.