Cytochrome P450 2E1 (CYP2E1) is essential for acrylonitrile metabolism to cyanide: comparative studies using CYP2E1-null and wild-type mice.
Acrylonitrile (AN) is a rodent carcinogen and suspected human carcinogen. Metabolism of AN proceeds via conjugation with glutathione or epoxidation via cytochrome P4502E1 (CYP2E1) to cyanoethylene oxide (CEO). It was hypothesized that CEO metabolism via epoxide hydrolase (EH) is the primary pathway for cyanide formation. The objective of this work is to assess the enzymatic basis of metabolism to cyanide. Male wild-type and CYP2E1-null mice received 0, 2.5, 10, 20, or 40 mg of AN/kg by gavage, and cyanide was measured in blood and tissues. CYP2E1 and EH expression were assessed using Western blot analyses. Present results demonstrated that cyanide concentrations in blood and tissues of AN-treated wild-type mice were higher at 1 versus 3 h, increased in a dose-dependent manner, and were significantly higher in AN-treated versus vehicle-treated mice. In contrast, cyanide concentrations in the blood and tissues of AN-treated CYP2E1-null mice were not statistically different from those of vehicle-treated mice. Furthermore, this work showed that EH is expressed in CYP2E1-null and wild-type mice. In conclusion, under the current experimental conditions using CYP2E1-null mice, current work demonstrated for the first time that CYP2E1-mediated oxidation is a prerequisite for AN metabolism to cyanide. Since earlier studies showed that CYP2E1 is the only enzyme responsible for AN epoxidation, it is concluded that AN metabolism to CEO is a prerequisite for cyanide formation, and this pathway is exclusively catalyzed by CYP2E1. Finally, this work confirmed that cyanide plays an essential role in the causation of the acute toxicity/mortality of AN.
Laboratory of Pharmacology and Chemistry, Environmental Toxicology Program, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
Hongbing
H
Wang
Brian
B
Chanas
Burhan I
BI
Ghanayem
D000181:Acrylonitrile / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D019392:Cytochrome P-450 CYP2E1 / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004851:Epoxide Hydrolases / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D008168:Lung / Q000187:drug effects / Q000201:enzymology; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D013045:Species Specificity; D014018:Tissue Distribution; D023382:Toxicity Tests, Acute
D019392:Cytochrome P-450 CYP2E1; D004851:Epoxide Hydrolases; D000181:Acrylonitrile