Udp-glucuronosyltransferase 2b7 is the major enzyme responsible for gemcabene glucuronidation in human liver microsomes.
The predominant metabolic pathway of gemcabene in humans is glucuronidation. The principal human UDP-glucuronosyltransferases (UGTs) involved in the glucuronidation of gemcabene were determined in this study. Glucuronidation of gemcabene was catalyzed by recombinant UGT1A3, recombinant UGT2B7, and recombinant UGT2B17, as well as by human liver microsomes (HLM). Gemcabene glucuronidation in recombinant UGTs and HLM followed non-Michaelis-Menten kinetics consistent with homotropic activation, but pharmacokinetics in humans were linear over the dose range tested (total plasma C(max), 0.06-0.88 mM). Gemcabene showed similar affinity (S(50)) for recombinant UGTs (0.92-1.45 mM) and HLM (1.37 mM). S-Flurbiprofen was identified as a more selective inhibitor of recombinant UGT2B7-catalyzed gemcabene glucuronidation (>23-fold lower IC(50)) when compared with recombinant UGT1A3- or recombinant UGT2B17-catalyzed gemcabene glucuronidation. The IC(50) for S-flurbiprofen inhibition of gemcabene glucuronidation was similar in HLM (60.6 microM) compared with recombinant UGT2B7 (27.4 microM), consistent with a major role for UGT2B7 in gemcabene glucuronidation in HLM. In addition, 5,6,7,3',4',5'-hexamethoxyflavone inhibited recombinant UGT1A3 and recombinant UGT2B17-catalyzed gemcabene glucuronidation (with 4-fold greater potency for recombinant UGT1A3) but did not inhibit gemcabene glucuronidation in HLM, suggesting that UGT1A3 and UGT2B17 do not contribute significantly to gemcabene glucuronidation. Reaction rates for gemcabene glucuronidation from a human liver bank correlated well (r(2)=0.722, P<0.0001; n=24) with rates of glucuronidation of the UGT2B7 probe substrate 3'-azido-3'-deoxythymidine. In conclusion, using the three independent experimental approaches typically used for cytochrome P450 reaction phenotyping, UGT2B7 is the major enzyme contributing to gemcabene glucuronidation in human liver microsomes.
Department of Pharmacokinetics, Dynamics and Metabolism, Pfizer Global Research and Development, Ann Arbor, MI 48105, USA. jonathan.bauman@pfizer.com.
Jonathan N
JN
Bauman
Theunis C
TC
Goosen
Meera
M
Tugnait
Vincent
V
Peterkin
Susan I
SI
Hurst
Lee C
LC
Menning
Mark
M
Milad
Michael H
MH
Court
J Andrew
JA
Williams
D002208:Caproates / Q000378:metabolism*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D008862:Microsomes, Liver / Q000201:enzymology; D015778:Minor Histocompatibility Antigens; D010641:Phenotype; D011994:Recombinant Proteins / Q000378:metabolism; D015215:Zidovudine / Q000031:analogs & derivatives / Q000378:metabolism
D002208:Caproates; D004791:Enzyme Inhibitors; D015778:Minor Histocompatibility Antigens; D011994:Recombinant Proteins; D015215:Zidovudine; C111024:gemcabene; C055886:3'-azido-3'-deoxy-5'-O-beta-glucopyranuronosylthymidine; C122075:UDP-glucuronosyltransferase, UGT1A3; C491474:UGT2B7 protein, human; D014453:Glucuronosyltransferase; C500513:UGT2B17 protein, human