title: Celery extract inhibits mouse CYP2A5 and human CYP2A6 activities via different mechanisms.
abstract: Human cytochrome P450 (CYP) 2A6 participates in the metabolism of nicotine and precarcinogens, thus the deliberate inhibition of CYP2A6 may reduce cigarette consumption and therefore reduce the risk of developing the types of cancer associated with smoking. The inhibitory effects and mechanisms of celery (Apium graveolens) extract on mouse CYP2A5 and human CYP2A6 activity remain unclear. These effects were investigated in mouse and human liver microsomes using coumarin 7-hydroxylation in a probe reaction. Celery extract reduced CYP2A5 and CYP2A6 activitiesin vitroin a dose-dependent manner.In vivoexperiments also showed that celery extract markedly decreased CYP2A5 activity. The inhibition of celery extract on CYP2A5 was time- and nicotinamide adenine dinucleotide phosphate (NADPH)-independent, and was markedly reduced by ultracentrifugation. Additionally, the inhibition of celery extract on CYP2A6 was time and NADPH-dependent. Levels of inhibition were characterized by a Ki, the measure of the tightness of bonds between the enzyme and its inhibitor, of 266.4 µg/ml for CYP2A5, and a Kiof 1,018 µg/ml and Kinactof 0.3/min for CYP2A6. Kinactis the maximal rate of enzyme inactivation at a saturating concentration of inhibitor. The coumarin derivative 5-methoxypsoralen present in celery extract did not solely to the inhibition of CYP2A5/6 activity. In conclusion, celery extract inhibited the levels of mouse CYP2A5 and human CYP2A6 activity via different mechanisms: Mixed competitive inhibition for CYP2A5 and mechanism-based inhibition for CYP2A6.
authors.affiliation: Institute of Life Sciences, Chongqing Medical University, Chongqing 400016, P.R. China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Deng
authors.affiliation: Institute of Life Sciences, Chongqing Medical University, Chongqing 400016, P.R. China.
authors.forename: Qianghong
authors.initials: Q
authors.lastname: Pu
authors.affiliation: Institute of Life Sciences, Chongqing Medical University, Chongqing 400016, P.R. China.
authors.forename: Erhao
authors.initials: E
authors.lastname: Wang
authors.affiliation: Institute of Life Sciences, Chongqing Medical University, Chongqing 400016, P.R. China.
authors.forename: Chao
authors.initials: C
authors.lastname: Yu
keywords: Apium graveolens; coumarin 7-hydroxylase; mechanism-based inhibition