Cytochrome P450 (CYP) enzymes carry out oxidative metabolism of a variety of endogenous and foreign chemicals. Cytochrome P450 2E1 (CYP2E1) is thought to be responsible for the oxidative metabolism of ethanol and a number of other chemicals of importance to the NTP including 1,3- butadiene, benzene, and vinyl chloride. In the present work the role of CYP2E1 in the oxidative metabolism of acrylonitrile, methacrylonitrile (MAN), and acrylamide was determined. 2-14C-MAN was administered to CYP2E1-/- or CYP2E1+/+ mice by gavage at 12 mg/kg. Urine analysis from these animals revealed a significant decline in the ratio of mercapturic acids originating from the epoxide-glutathione vs. MAN-glutathione conjugates in CYP 2E1-null mice in comparison to wild-type animals. Exhalation of MAN-derived organic volatiles was 12 and 42 fold greater in female and male CYP2E1-null vs. wild-type mice, respectively. Parent MAN is the main constituent of exhaled organic volatiles. Additionally, exhalation of CO2 derived from metabolism of MAN via the CYP2E1 pathway was 3-5 fold greater in wild-type vs. CYP2E1- null animals. In conclusion, these data indicated that while CYP2E1 plays a major role in MAN metabolism, however, other CYP isozymes may be involved in the its oxidatiion. Assessment of MAN metabolism in CYP2E1-null mice pretreated with 1- Aminobenzotriazole (CYP inhibitor) resulted in further reduction of oxidative metabolites of MAN. Tissue concentrations of MAN-derived radioactivity tissues suggested that there is a direct relationship between MAN oxidative metabolism and tissue binding. Additional studies were also conducted to investigate the metabolism of 13C- acrylonitrile and 13C-acrylamide using CYP2E1-null and wild-type mice. Identification and quantification of urinary metabolites demonstrated that both chemicals were metabolized via the epoxide intermediates in wild-type animals. In contrast, no metabolites originating from the epoxide intermediates were detected in the urine of CYP2E1-null mice.
