Inhibition of cytochrome P450 2A participating in coumarin 7-hydroxylation in pig liver microsomes.
Five commonly used human cytochrome P450 (CYP) inhibitors were examined for their effects on coumarin 7-hydroxylase (CYP2A) activity in pig liver microsomes. The K(m) and V(max) values for coumarin 7-hydroxylation in pig liver microsomes were estimated to be 1 μm and 0.26 nmol·mg/min, respectively. The following human CYP inhibitors caused little or no inhibition of CYP2A as defined by a K(i) > 200 μm: quinidine (CYP2D6), troleandomycin (CYP3A4), and sulfaphenazole (CYP2C9). The other two human CYP inhibitors were classified as strong inhibitors of CYP2A: 8-methoxypsoralen (CYP2A6) and α-naphthoflavone (CYP1A1/2). In the absence of a preincubation period, 8-MOP inhibited the 7-hydroxylation of coumarin with a K(i) value of 1.1 μm, which decreased to 0.1 μm when 8-MOP was preincubated with pig liver microsomes for 3 min. α-Naphthoflavone inhibited the 7-hydroxylation of coumarin with a K(i) value of 32 μm, which did not increase ability to inhibitor CYP2A when α-naphthoflavone was preincubated with pig liver microsomes for 3 min. These results of this study suggest that 8-MOP is a potent, mechanism-based inhibitor of pig CYP2A activity in pig liver microsomes.
National Reference Laboratory of Veterinary Drug Residues (HZAU)/MAO Key Laboratory of Food Safety Evaluation, Huazhong Agricultural University, Wuhan, Hubei, China.
Z-Y
ZY
Liu
M-H
MH
Dai
Y-F
YF
Tao
D-M
DM
Chen
Z-H
ZH
Yuan
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors*; D003374:Coumarins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006900:Hydroxylation; D007093:Imidazoles / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D020033:Protein Isoforms; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors*; D013552:Swine
D003374:Coumarins; D004791:Enzyme Inhibitors; D007093:Imidazoles; D020033:Protein Isoforms; C517283:coumarin 7; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C029009:steroid hormone 7-alpha-hydroxylase