An analysis of the mutagenicity of 1,2-dibromoethane to Escherichia coli: Influence of DNA repair activities and metabolic pathways

Abstract

SummaryThe mutagenicity of 1,2-dibromoethane (EDB) to Escherichia coli was reduced by the UV lightinduced excision repair system but unaffected by the loss of a major apurinic/apyrimidinic site repair function. At high doses, 70-90% of the EDB-induced mutations were independent of SOS-mutagenic processing and approximately 50% were independent of glutathione conjugation. The SOSindependent mutations induced by EDB were unaffected by the enzymes that repair alkylationinduced DNA lesions. EDB-induced base substitutions were dominated by GC to AT and AT to GC transitions. These results suggest that EDB-induced premutagenic lesions have some, but not all, of the characteristics of simple alkyl lesions. KeywordsDibromoethane; EDB; Escherichia coil; Miscoding lesions; DNA repair 1,2-Dibromoethane (EDB or DBE; has been used as an antiknock additive in leaded gasoline, an industrial solvent, a pesticide, and a food disinfectant (NIOSH, 1977). It is one of a class of potentially hazardous compounds, the haloalkanes, that has become widely distributed in the environment . EDB is highly toxic, causing liver and kidney necrosis and reproductive abnormalities (reviews Shih and Hill, 1981;Rannug, 1980;Ter Haar, 1980). It has been repeatedly shown to be carcinogenic to rodents, resulting in tumors in a number of organs, including the forestomach, liver, spleen and thyroid (NCI, 1978). Thus environmental exposure to EDB is a potential health hazard.The mutagenicity of EDB has been demonstrated in a number of genetic systems, including bacteria, yeast and other fungi, plants, insects, mammals and human cells (reviews, Fabricant and Chalmers, 1980;Rannug, 1980). Although EDB is a direct-acting mutagen in the Salmonella/microsome assay (McCann et al., 1975a), its mutagenicity has been shown to be further enhanced by metabolic activation (Rannug, 1980). Metabolic activation of EDB to its ultimate mutagenic and carcinogenic form has been hypothesized to occur by two different (Rannug, 1980; Anders and Livesey, 1980). One, mediated by the mixed-function oxygenases of liver microsomes, would yield bromoacetaldehyde and 2-bromoethanol as potential DNA-damaging agents (Hill et al., 1978;Banerjee et al., 1979). The other pathway, conjugation with glutathione mediated by enzymes present in liver cytosol, would yield as reactive products a half-sulfur-mustard or an episulfonium ion (Rannug, 1980;van Bladeren et al., 1980). The binding of EDB to DNA in vitro has been shown to be dependent on glutathione conjugation, and an S- [2-(N 7 -guanyl)ethyl]glutathione adduct has been identified (Ozawa and Guengerich, 1983;Inskeep and Guengerich, 1984). However, bromoacetaldehyde is a metabolite of EDB (Hill et al., 1978) and can bind to DNA without enzymatic activation (Banerjee et al., 1979). Both 2-bromoethanol and chloroacetaldehyde are bacterial mutagens (McCann et al., 1975b;Rannug et al., 1976;Rosenkranz, 1977), but bromoacetaldehyde is not, possibly due to its extreme toxicity (Rosenkranz, 1977). Thus, the identity of the genotoxic metabol...

Recharacterization of ancient DNA miscoding lesions: insights in the era of sequencing-by-synthesis

“…Although various modifications of guanine are known to cause miscoding lesions, during enzymatic replication these result in the generation of transversions; for example, a common product of oxidative degradation, 8-oxoguanine, generates G→T transversions (21), whereas other guanine products such as 8-methyl-2′-deoxyguanosine generate both G→C and G→T transversions (22). Furthermore, the mutagen ethylene dibromide, a once common insecticide, fumigant and anti-knock agent for gasoline has been observed to indirectly cause G→A miscoding lesions in living cells (23). However, it is unlikely that this is the cause in this situation, as the process requires enzymatic conjugation to form the half-mustard S -(2-bromoethyl)glutathione (GSCH 2 CH 2 Br), which clearly could not happen in post mortem systems.…”

Characterization of a Mutagenic DNA Adduct Formed from 1,2-Dibromoethane by O6-Alkylguanine-DNA Alkyltransferase

“…Future studies are also needed to test the role that other DNA repair pathways play in protecting from DBE (4,6).…”

“…AGT is inactivated by the alkyl group transfer, and therefore additional repair requires new protein synthesis. Although an early study reported that the mutagenicity of 1,2-dibromoethane (DBE) was not affected by enzymes that repair alkylation lesions (4), there is now convincing data that AGT paradoxically promotes the toxicity of DBE (5,6). Overexpression of human AGT (hAGT) or AGTs from other species enhances the mutagenicity and lethality of DBE in Escherichia coli (5)(6)(7)(8)(9) and induces growth retardation in mammalian cells (10).…”

Screening and characterization of variant Theta‐class glutathione transferases catalyzing the activation of ethylene dibromide to a mutagen

“…The characteristic event dominating EDB mutational spectra is the G:C ? A:T transition [Foster et al, 1988;Cmarik et al, 1992], which is also commonly seen with alkylating agents. The episomal lacZ allele of strain CC102 reverts by a G:C ?…”

“…A:T transition (GGG, encoding glycine, to GAG, encoding glutamic acid) [Cupples and Miller, 1989]. The mutagenicity of EDB in E. coli is reduced in the presence of an active DNA excision repair system [Foster et al, 1988] but does not require the activity of Y-class DNA polymerases such as UmuDC or MucAB. Therefore, to establish an E. coli lacZ tester strain suitable for the detection of EDB mutagenicity, we moved (by conjugation) the episome of strain CC102 into a previously constructed E. coli strain that lacks DNA nucleotide excision repair [Josephy, 2000].…”