Bacterial and mammalian DNA alkyltransferases sensitize Escherichia coli to the lethal and mutagenic effects of dibromoalkanes.
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Here we confirm and extend our previous studies demonstrating that the mutagenic potency of 1,2-dibromoethane (DBE) and dibromomethane (DBM) is markedly enhanced (not prevented) in bacteria expressing the O6-alkylguanine-DNA alkyltransferase (ATase) encoded by the Escherichia coli ogt gene. We demonstrate that, in close parallel with mutagenesis, the Ogt ATase sensitizes the bacteria to the lethal effects of these carcinogens, suggesting that one or more of the potentially mutagenic lesions induced by DBE and DBM in the presence of Ogt has additional lethal capacity. We further demonstrate that the sensitization to both lethality and mutagenesis by DBE and DBM is a property shared by other DNA alkyltransferases. This objective was accomplished by quantifying the induction of mutations and lethal events in ogt- ada- E. coli expressing an exogenous bacterial or mammalian ATase from a multicopy plasmid. Mammalian recombinant ATases enhanced the lethal and mutagenic actions of DBE and suppressed the lack of sensitivity of the vector-transformed bacteria to DBM. In most cases the order of effectiveness of the ATases ranked: murine > human > Ogt > rat. Further comparisons included the full-length Ada ATase from E. coli and a truncated Ada version (T-ada) that retains the O6-methylguanine binding domain of the protein. The full-length Ada ATase was effective in enhancing the lethality but not the mutagenicity induced by DBE and DBM. The T-ada ATase provided less sensitization than Ada to lethality by DBE, but of the three bacterial ATases T-ada yielded the highest sensitization to mutagenesis by this compound. T-ada and Ada ATases were in general less effective than the mammalian versions, with the exception of the rat recombinant ATase. The effectiveness of the different mammalian and bacterial ATases in promoting the deleterious actions of dibromoalkanes was compared with the effectiveness of these proteins in suppressing the lethal and mutagenic effects induced by N-nitroso-N-methylurea. The ability to sensitize E. coli to the lethal and mutagenic effects of DBE and DBM seems restricted to DNA alkyltransferase, since overexpression of thioredoxin (Trx) or glutaredoxin (Grx1) in ogt- ada- cells showed no effect, in spite of the reported potential of bioactive dihaloethane-derived species to alkylate Trx. (+info)
Disposition of 1,2-[14C]Dibromoethane in male Wistar rats.
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In this study the disposition of 1,2-[14C]dibromoethane (1, 2-[14C]DBE) was investigated in male Wistar rats. 1,2-DBE is a cytotoxic and carcinogenic compound that has been used as an additive in leaded gasoline and as a fumigant. 1,2-[14C]DBE was administered orally or iv. Radioactivity was recovered (mostly within 48 hr after administration) in urine (75-82% of the dose), feces (3.2-4% of the dose), and expired air (0.53-7.2% of the dose). One hundred-sixty-eight hours after administration of 1,2-[14C]DBE, most of the radioactivity in tissues was found in the liver, lungs, and kidneys (<1% of the dose) and the red blood cells (0.3% of the dose). Identified urinary metabolites were S-(2-hydroxyethyl)mercapturic acid, thiodiacetic acid, and thiodiacetic acid sulfoxide, together accounting for, on average, 78% of the total amount of radioactivity in urine. In addition to S-(2-hydroxyethyl)mercapturic acid, thiodiacetic acid, and thiodiacetic acid sulfoxide, several compounds were anticipated as potential urinary metabolites of 1,2-DBE, i.e. S-(carboxymethyl)mercapturic acid, S-(2-hydroxyethyl)thioacetic acid, S-(2-hydroxyethyl)thiopyruvic acid, S-(carboxymethyl)thiopyruvic acid, S-(2-hydroxyethyl)thiolactic acid, and S-(carboxymethyl)thiolactic acid. All of the postulated urinary metabolites were synthesized and searched for in urine samples. None of these metabolites could be detected in urine, however. The data obtained in the present study might be useful for risk assessment and biomonitoring studies of 1,2-DBE and will also be used to further validate a physiologically based pharmacokinetic model for 1, 2-DBE in rats and humans that was recently developed. (+info)