Formation of the quaternary ammonium-linked glucuronide of nicotine in human liver microsomes: identification and stereoselectivity in the kinetics.
The formation of the N1-glucuronide metabolite of each nicotine enantiomer was studied in pooled human liver microsomes (n = 6). The metabolite formed from natural S(-)-nicotine was identified by comparison of the high-pressure liquid chromatography (HPLC) retention time and positive ion electrospray ionization-mass spectral characteristics with a synthetic reference standard. A radiometric HPLC method was used to quantify the metabolite. The specificity of the assay method was demonstrated by experiments in which beta-glucuronidase treatment of incubated assay samples resulted in elimination of the peak due to the N1-glucuronide metabolite. The glucuronides of S(-)- and R(+)-nicotine were formed by one-enzyme kinetics, with K(m) values of 0.11 and 0.23 mM and V(max) values of 132 and 70 pmol/min/mg of protein, respectively. There is marked stereoselectivity in the apparent intrinsic clearance values (V(max)/K(m)) in that the value for S(-)-nicotine is 4 times greater than for the R(+)-isomer (1.2 versus 0.31 microl/min/mg of protein).
Ghosheh
O
O
Drug Metabolism and Drug Disposition Group, College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Vashishtha
S C
SC
Hawes
E M
EM
D002851:Chromatography, High Pressure Liquid; D005260:Female; D020719:Glucuronides / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D009538:Nicotine / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D013237:Stereoisomerism
D020719:Glucuronides; D018722:Nicotinic Agonists; D000644:Quaternary Ammonium Compounds; D009538:Nicotine