Identification of 2‐Piperidone as a Biomarker of CYP2E1 Activity through Metabolomic Phenotyping

Cytochrome P450 2E1 (CYP2E1) is a key enzyme in the metabolic activation of small‐molecule toxicants and carcinogens. Since CYP2E1 contributes to alcohol‐induced liver injury and chemical‐induced carcinogenesis, it is important to establish a noninvasive method to monitor CYP2E1 activity in vivo. A mass spectrometry‐based metabolomics approach was applied to examine the metabolomic differences between wild‐type (WT), cyp2e1 ‐null (KO), and CYP2E1 ‐humanized (hCYP2E1) mice. Results of urinary chemicals revealed a clear separation of KO from WT and hCYP2E1 mice in the multivariate models, and further identified 2‐piperidone (2P) as a potential biomarker of CYP2E1 activity because of its consistently higher abundance in the urine samples of KO compared to that in WT and hCYP2E1 mice. Backcrossing of WT and KO as well as the targeted analysis of 2P in serum confirmed the genotype‐dependent appearance of 2P. The accumulation of 2P in KO mice is due to the altered balance between biosynthesis and degradation of 2P since the conversion of cadeverine to 2P by amine oxidase is much higher in KO mice while the metabolism of 2P to 6‐hydroxylated‐2P is meager. Overall, this untargeted metabolomic analysis identified a novel correlation between the levels of 2P in urine and the activity of CYP2E1, and establish a clinically applicable biomarker that monitor CYP2E1 activity via noninvasive measurements.