The role of formaldehyde and S-chloromethylglutathione in the bacterial mutagenicity of methylene chloride.
Methylene chloride was less mutagenic in Salmonella typhimurium TA100/NG-11 (glutathione-deficient) compared to TA100, indicating that glutathione is involved in the activation of methylene chloride to a mutagen in bacteria. In rodents, the pathway of methylene chloride metabolism utilizing glutathione produces formaldehyde via a postulated S-chloromethylglutathione conjugate (GSCH2Cl). Formaldehyde is known to cause DNA-protein cross-links, and GSCH2Cl may act as a monofunctional DNA alkylator by analogy with the glutathione conjugates of 1,2-dihaloalkanes. The lack of sensitivity of Salmonella TA100 towards formaldehyde (Schmid et al., Mutagenesis, 1 (1986) No. 6, 427-431) suggests that GSCH2Cl is responsible for methylene chloride mutagenicity in Salmonella. In Escherichia coli K12 (AB1157), formaldehyde was mutagenic only in the wild-type, a characteristic shared with cross-linking agents, whereas 1,2-dibromoethane (1,2-DBE) was more mutagenic in uvrA cells (AB1886). Methylene chloride, activated by S9 from mouse liver, was mutagenic only in wild-type cells, suggesting a mutagenic role for metabolically derived formaldehyde in E. coli. Mouse-liver S9 also enhanced the cell-killing effect of methylene chloride in the uvrA, and a recA/uvrA double mutant (AB2480) which is very sensitive to DNA damage. This pattern was consistent with formaldehyde damage. However, a mutagenic role in bacteria for the glutathione conjugate of methylene chloride cannot be ruled out by these E. coli experiments because S9 fractions did not increase 1,2-DBE mutagenicity, suggesting lack of cell wall penetration by this reactive species. Rat-liver S9 did not activate methylene chloride to a bacterial mutagen or enhance methylene chloride-induced cell-killing, which is consistent with the carcinogenicity difference between the species.
Graves
R J
RJ
Zeneca Central Toxicology Laboratory, Alderley Park, Macclesfield, Ches, UK.
Callander
R D
RD
Green
T
T
D000818:Animals; D001711:Biotransformation; D004926:Escherichia coli / Q000235:genetics; D015946:Ethylene Dibromide / Q000633:toxicity; D005557:Formaldehyde / Q000378:metabolism*; D005978:Glutathione / Q000031:analogs & derivatives* / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D008297:Male; D008741:Methyl Methanesulfonate / Q000633:toxicity; D008752:Methylene Chloride / Q000378:metabolism / Q000633:toxicity*; D051379:Mice; D016685:Mitomycin / Q000633:toxicity; D009152:Mutagenicity Tests; D009603:Nitroso Compounds / Q000633:toxicity; D051381:Rats; D012486:Salmonella typhimurium / Q000235:genetics
D009603:Nitroso Compounds; C008651:4-nitrosodimethylaniline; C085664:S-chloromethylglutathione; D005557:Formaldehyde; D015946:Ethylene Dibromide; D016685:Mitomycin; D008752:Methylene Chloride; D008741:Methyl Methanesulfonate; D005982:Glutathione Transferase; D005978:Glutathione