In vitro metabolic characteristics of cytochrome P-450 2A6 in Chinese liver microsomes.
OBJECTIVE
To investigate the metabolic characteristics of cytochrome P-450 C YP2A6 in human liver microsomes.


METHODS
Cytochrome P-450 enzyme activities were measured by biochemical assays. Xenobiotics were employed to observe their effects on CYP2A6 in vitro. The kinetics of coumarin 7-hydroxylase was determined, and the correlation between CYP2A6 and UDP-glucuronosyltransferase (UGT) was analyzed.


RESULTS
CYP2A6 activities of human liver microsomes were from 0.47 to 4.14 micromol . min-1 . g-1, with a 8.8-fold variation. The Km and Vmax of CYP2A6 ranged from 0.25 to 1.56 micromol/L and 1.41 to 8.70 micromol . min-1 . g-1, respectively. CYP2A6 activity was markedly inhibited (> 50 %) by pilocarpine, diethyldithio carbamic (DDC), and rifampicin, the IC50 was 5.31 micromol/L, 156.35 micromol/L, and 38.81 micromol/L, respectively. alpha-Naphthoflavone, sulfaphenazole, troleandomycin (TAO), ketoconazole, phenobarbital, prednisolone, and azithromycin had little or no effects on coumarin 7-hydroxylation. A significant correlation was observed between CYP2A6 and UGT2 (r = 0.9453, P < 0.05).


CONCLUSIONS
CYP2A6 activity and kinetics exhibited a considerable variation in human liver microsomes in vitro, and a significant correlation was existed between CYP2A6 and phase II enzyme UGT2. Not only pilocarpine, CYP2A6 specific inhibitor, but also rifampicin and DDC inhibited CYP2A6 activity selectively.
Xia
Xue-Yan
XY
Department of Pharmacology, Medical College of Wuhan University, Wuhan 430071, China.
Peng
Ren-Xiu
RX
Yu
Jie-Ping
JP
Wang
Hui
H
Wang
Jun
J
D000328:Adult; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D044466:Asian People; D065637:Cytochrome P-450 CYP2A6; D004791:Enzyme Inhibitors / Q000494:pharmacology; D014453:Glucuronosyltransferase / Q000378:metabolism; D006801:Humans; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010862:Pilocarpine / Q000494:pharmacology*; D012293:Rifampin / Q000494:pharmacology
D004791:Enzyme Inhibitors; D010862:Pilocarpine; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6; D014453:Glucuronosyltransferase; D012293:Rifampin