DNA sequence analysis of methylene chloride-induced HPRT mutations in Chinese hamster ovary cells: comparison with the mutation spectrum obtained for 1,2-dibromoethane and formaldehyde.
Glutathione-S-transferase-mediated metabolism of methylene chloride (MC) generates S-chloromethylglutathione, which has the potential to react with DNA, and formaldehyde, which is a known mutagen. MC-induced mutations in the HPRT gene of Chinese hamster ovary cells have been sequenced and compared with the mutations induced by 1, 2-dibromoethane (1,2-DEB), which is known to act through a glutathione conjugate, and formaldehyde. All three compounds induced primarily point mutations, with a small number of insertion and deletion events. The most common point mutations induced by MC were GC-->AT transitions (4/8), with two GC-->CG transversions and two AT-->TA transversions. This pattern of mutations showed greater similarity with 1,2-DBE, where the dominant point mutations were GC-->AT transitions (7/9), than formaldehyde, where all mutations were single base transversions and 5/6 occurred from AT base pairs. The mutation sequence results for MC suggest that S-chloromethylglutathione plays a major role in MC mutagenesis, with only a limited contribution from formaldehyde. The involvement of a glutathione (GSH) conjugate in MC mutagenicity would be analogous to the well-characterized pathway of activation of 1,2-DBE.
Graves
R J
RJ
Zeneca Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire SK10 4TJ, UK.
Trueman
P
P
Jones
S
S
Green
T
T
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism; D015946:Ethylene Dibromide / Q000633:toxicity*; D005557:Formaldehyde / Q000633:toxicity*; D007041:Hypoxanthine Phosphoribosyltransferase / Q000187:drug effects / Q000235:genetics*; D008099:Liver / Q000737:chemistry; D008752:Methylene Chloride / Q000378:metabolism / Q000633:toxicity*; D051379:Mice; D009153:Mutagens / Q000633:toxicity; D009154:Mutation; D017422:Sequence Analysis, DNA
D009153:Mutagens; D005557:Formaldehyde; D015946:Ethylene Dibromide; D008752:Methylene Chloride; D007041:Hypoxanthine Phosphoribosyltransferase