Analyses of (1-chloroethenyl)oxirane headspace and hemoglobin N-valine adducts in erythrocytes indicate selective detoxification of (1-chloroethenyl)oxirane enantiomers

• Published in: Chemico-biological interactions 2007-03, Vol.166 (1), p.332-340
• Main Authors: Hurst, Harrell E., Ali, Md. Yeakub
• Format: Article
• Language: English
• Subjects: Animals; Chiral analysis; Chloroprene; Chloroprene epoxide; Chromatography, Gas; Detoxification; Epoxide enantiomers; Erythrocytes - drug effects; Erythrocytes - metabolism; Ethylene Oxide - analogs & derivatives; Ethylene Oxide - analysis; Ethylene Oxide - chemistry; Ethylene Oxide - isolation & purification; Ethylene Oxide - toxicity; GC/MS; Glutathione - metabolism; Glutathione Transferase - metabolism; Hemoglobin adducts; Hemoglobins - analysis; Inactivation, Metabolic; Kinetics; Mass Spectrometry; Mice; Mice, Inbred C57BL; Oxidation-Reduction; R- and S-(1-Chloroethenyl)oxirane; Stereoisomerism; Valine - analysis; Volatilization - drug effects
• ISSN: 0009-2797; 1872-7786
• DOI: 10.1016/j.cbi.2006.04.016

Chloroprene (2-chloro-1,3-butadiene, CAS 126-99-8, CP) is a colorless volatile liquid used in manufacture of polychloroprene, a synthetic rubber polymer. National Toxicology Program inhalation studies of CP in rats and mice gave clear evidence of carcinogenic activity. CP is metabolized by CYP2E1 to electrophilic epoxides, including R- and S-(1-chloroethenyl)oxirane (CEO), which form adducts with nucleic acids and other nucleophiles including glutathione and hemoglobin. As detection of these epoxide metabolites in vivo is technically challenging, measurements of CEO-Hb adducts may provide biomarkers of exposure to bioactivated metabolites of CP. The present studies involved exposure of C57BL/6 mouse erythrocytes (RBC) in vitro to pure enantiomers of CEO. Headspace analysis of CEO using Cyclodex-B capillary GC/MS with selected ion monitoring enabled separation, specific detection, and quantification of CEO enantiomers as reactions proceeded in vitro with RBC. These analyses indicated that R-CEO was much more persistent when incubated in vitro with RBC, while S-CEO disappeared rapidly. After periods of exposure of RBC to various concentrations of R- or S-CEO, erythrocytes were lysed and globin isolated. Covalent adducts, formed by reaction of CEO with N-terminal valine in Hb, were analyzed following Edman cleavage and trimethylsilylation. SIM-GC/MS analyses using a 5%-phenyl-dimethylsiloxane capillary column enabled quantification of CEO-Hb adducts. These analyses produced two chromatographic peaks of CEO-valine adduct derivatives, which were tentatively identified from mass spectra, reaction, and abundance data to be 1-(3-chloro-2-trimethylsilyloxybut-3-en-1-yl)-5-isopropyl-3-phenyl-2-thiohydantoin and 1-[2-chloro-1-(trimethylsilyloxymethyl)prop-2-en-1-yl]-5-isopropyl-3-phenyl-2-thiohydantoin. Analyses quantified significantly greater levels of adducts formed from R-CEO than from S-CEO. Studies involving pretreatment of RBC with glutathione-depleting diethyl maleate diminished the selective detoxification of S-CEO, and suggest enantiomeric selectivity of mouse glutathione- S-transferase as a mechanism of differential detoxification of CEO enantiomers. These results indicate more rapid detoxification of S-CEO by mouse RBC in vitro, while R-CEO may persist to react with cellular nucleophiles.