Abstract
Elimination of hydrogen sulfide from glutathione (GSH) converts a well known cellular nucleophile to an electrophilic species, γ-glutamyldehydroalanylglycine (EdAG). We have found that a sulfonium metabolite formed from GSH and busulfan undergoes a facile β-elimination reaction to give EdAG, which is an α,β-unsaturated dehydroalanyl analog of GSH. EdAG was identified as a metabolite of busulfan in a human liver cytosol fraction. EdAG condenses with GSH in a Michael addition reaction to produce a lanthionine thioether [(2-amino-5-[[3-[2-[[4-amino-5-hydroxy-5-oxopentanoyl]amino]-3-(carboxymethylamino)-3-oxopropyl]sulfanyl-1-(carboxymethylamino)-1-oxopropan-2-yl]amino]-5-oxopentanoic acid); GSG], which is a nonreducible analog of glutathione disulfide. EdAG was less cytotoxic than busulfan to C6 rat glioma cells. GSH and EdAG were equally effective in displacing a glutathione S-transferase (GST) isozyme (human GSTA1-1) from a GSH-agarose column. The finding of an electrophilic metabolite of GSH suggests that alteration of cellular GSH concentrations, irreversible nonreducible glutathionylation of proteins, and interference with GST function may contribute to the toxicity of busulfan.
Footnotes
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The work reported herein was supported in part by National Institutes of Health (NIH) Grant RO1 ES08421 (to A.J.L.C.), NIH-National Cancer Institute Grant 5-PO1-CA47741, the Mylan Chair of Pharmacology at West Virginia University Health Sciences Center (to W.P.P.), and National Institute of Justice Grant IJ-CX-K014 (to P.S.C.).
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.108.142208.
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ABBREVIATIONS: GSH, glutathione; EdAG, γ-glutamyldehydroalanylglycine; GS+THT, γ-glutamyl-β-(S-tetrahydrothiophenium)alanylglycine; GST, glutathione S-transferase; DMSO, dimethyl sulfoxide; MS, mass spectrometry; MS/MS, tandem mass spectrometry; GSG, (2-amino-5-[[3-[2-[[4-amino-5-hydroxy-5-oxopentanoyl]amino]-3-(carboxymethylamino)-3-oxopropyl]sulfanyl-1-(carboxymethylamino)-1-oxopropan-2-yl]amino]-5-oxopentanoic acid); LC, liquid chromatography; HVOD, hepatic venoocclusive disease.
- Received June 11, 2008.
- Accepted September 11, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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