No abstract

Acrylonitrile (AN) and acrylamide (AM) are commonly used in the synthesis of plastics and polymers. In rodents, AM and AN are metabolized to the epoxides glycidamide and cyanoethylene oxide, respectively. The aim of this study was to determine the role of cytochrome P450 in the metabolism of AM and AN in vivo. Wild-type (WT) mice, WT mice pretreated with aminobenzotriazole (ABT, 50 mg/kg ip, 2 h pre-exposure), and mice devoid of cytochrome P450 2E1 (P450 2E1-null) were treated with 50 mg/kg [(13)C]AM po. WT mice and P450 2E1-null mice were treated with 2.5 or 10 mg/kg [(13)C]AN po. Urine was collected for 24 h, and metabolites were characterized using (13)C NMR. WT mice excreted metabolites derived from the epoxides and from direct GSH conjugation with AM or AN. Only metabolites derived from direct GSH conjugation with AM or AN were observed in the urine from ABT-pretreated WT mice and P450 2E1-null mice. On the basis of evaluation of urinary metabolites at these doses, these data suggest that P450 2E1 is possibly the only cytochrome P450 enzyme involved in the metabolism of AM and AN in mice, that inhibiting total P450 activity does not result in new pathways of non-P450 metabolism of AM, and that mice devoid of P450 2E1 do not excrete metabolites of AM or AN that would be produced by oxidation by other cytochrome P450s. P450 2E1-null mice may be an appropriate model for the investigation of the role of oxidative metabolism in the toxicity or carcinogenicity of these compounds.

Acrylamide (AA) is an animal carcinogen, neurotoxin, and reproductive toxin. AA is formed in baked and fried carbohydrate-rich foods. Metabolism of AA occurs via epoxidation to glycidamide (GA) or direct conjugation with glutathione. Using CYP2E1-null mice, recent studies in this laboratory demonstrated that induction of somatic and germ cell mutagenicity in AA-treated mice is dependent on CYP2E1. We hypothesized that AA metabolism to GA is a prerequisite for the induction of AA-induced mutagenicity. Current studies were undertaken to assess the role of CYP2E1 in the epoxidation of AA to GA and the formation of DNA and hemoglobin (HGB) adducts. AA was administered to CYP2E1-null or wild-type mice at 50 mg/kg ip. Mice were euthanized 6 h later and blood and tissues were collected. Using LC-ES/MS/MS, AA, GA, and DNA- and HGB-adducts were measured. While the plasma levels of AA and GA were 115 +/- 14.0 and 1.7 +/- 0.31 microM in CYP2E1-null mice, they were 0.84 +/- 0.80 and 33.0 +/- 6.3 microM in the plasma of AA-treated wild-type mice. Administration of AA to wild-type mice caused a large increase in N7-GA-Gua and N3-GA-Ade adducts in the liver, lung, and testes. While traces of N7-GA-Gua adducts were measured in the tissues of AA-treated CYP2E1-null mice, these levels were 52- to 66-fold lower than in wild-type mice. Significant elevation of both AA- and GA-HGB adducts was detected in AA-treated wild-type mice. In AA-treated CYP2E1-null mice, levels of AA-HGB adducts were roughly twice as high as those in wild-type mice. In conclusion, current work demonstrated that CYP2E1 is the primary enzyme responsible for the epoxidation of AA to GA, which leads to the formation of GA-DNA and HGB adducts.

Acrylamide (AM), used in the manufacture of polyacrylamide and grouting agents, is produced during the cooking of foods. Workplace exposure to AM can occur through the dermal and inhalation routes. The objective of this study was to define the kinetics of elimination of AM and its metabolites following oral and dermal administration. This is the second part of a study in which metabolites and hemoglobin adducts of AM were determined in people (Fennell et al., 2005, Toxicol. Sci. 85, 447-459). (1,2,3-(13)C(3))AM was administered in an aqueous solution orally (single dose of 0.5, 1.0, or 3.0 mg/kg) or dermally (three daily doses of 3.0 mg/kg) to sterile male volunteers. Urine samples were collected at 0-2, 2-4, 4-8, 8-16, and 16-24 h following administration orally, or at 0-2, 2-4, 4-8, 8-16, and 16-24 h following each of three daily dermal doses. (13)C(3)-AM and its metabolites in urine, (13)C(3)-glycidamide, (13)C(3)-N-acetyl-S-(3-amino-3-oxopropyl)cysteine and its S-oxide, and (13)C(3)-N-acetyl-S-(3-amino-2-hydroxy-3-oxopropyl)cysteine, were quantitated using liquid chromatography-tandem mass spectrometry. The recovered urinary metabolites accounted for 45.6, 49.9, and 39.9% of a 0.5, 1.0, and 3.0 mg/kg oral dose (0-24 h), respectively, and for 4.5% of the dose after 3 mg/kg was administered daily for 3 days dermally (0-4 days). These results indicate that after oral administration AM is rapidly absorbed and eliminated. The half-life estimated for elimination of AM in urine was 3.1-3.5 h. After dermal administration, AM uptake is slow. This study indicated that skin provides a barrier that slows the absorption of AM, and results in limited systemic availability following dermal exposure to AM.