Abstract
Cytochrome P450-dependent oxidation and glutathione (GSH)-dependent conjugation are the primary routes of metabolism of haloalkanes. Using rat liver microsomes and cytosol, we investigated the metabolism of two halopropanes found on the U.S. Environmental Protection Agency Contaminant Candidate List, 1,3-dichloropropane (1,3-DCP) and 2,2-dichloropropane (2,2-DCP). An automated headspace technique using gas chromatography was developed to determine rates of metabolism. Additional dihaloalkanes (1,2-dichloroethane, 1,2-dichloropropane, 1,4-dichlorobutane, 1,2-dibromoethane, 1,2-dibromopropane, 1,4-dibromobutane) were evaluated to assess structure-activity relationships. In general, brominated dihaloalkanes were eliminated from rat cytosol faster than chlorinated dihaloalkanes, reflecting the expected halide order of reactivity (Br > Cl). Furthermore, the rate of GSH conjugation was proportional to α,ω-haloalkane chain length. The clearance of 1,3-DCP via the GSH conjugation pathway (1.6 × 10–4 l/h/mg cytosol protein) was minor relative to the P450 pathway (2.8 × 10–2 l/h/mg microsomal protein). In contrast, we did not observe metabolism of 2,2-DCP via the GSH-dependent conjugation pathway and observed only a minor level of clearance via the P450 pathway (7 × 10–4 l/h/mg microsomal protein). Neither compound was mutagenic in various strains of Salmonella, including those containing GSTT1–1, indicating that GSTT1–1 does not metabolize 1,3-DCP or 2,2-DCP to mutagens. Analysis of the reaction products of 1,3-DCP and GSH in cytosol by liquid chromatography/mass spectrometry revealed significant production of S-(3-chloropropyl) glutathione conjugate, indicating that the conjugate half-mustard does not rearrange to form a sulfonium ion, as typically occurs with vicinal dihaloalkanes.
Footnotes
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↵1 Abbreviations used are: EPA, Environmental Protection Agency; 1,3-DCP, 1,3-dichloropropane; 2,2-DCP, 2,2-dichloropropane; P450, cytochrome P450; GSTs, glutathione S-transferases; GSH, glutathione; 1,2-DCE, 1,2-dichloroethane; 1,2-DBE, 1,2-dibromoethane; 1,3-DBP, 1,3-dibromopropane; 1,4-DCB, 1,4-dichlorobutane; PRR, predicted relative rate; HPLC, high-performance liquid chromatography; LC-MS, liquid chromatography/mass spectrometry.
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C.G. and R.T.-V. were supported by University of North Carolina/EPA Training Agreements CT826513.
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M.K.R. was supported by UNC/EPA Training Agreements CT827206 and by National Institute of Environmental Health Services Fellowship F32ES11111–01.
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J.P.J. received support through NIEHS ES-009122.
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This manuscript has been reviewed by the National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.
- Received June 30, 2003.
- Accepted September 2, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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