title: Glucuronidation of fenamates: kinetic studies using human kidney cortical microsomes and recombinant UDP-glucuronosyltransferase (UGT) 1A9 and 2B7.
abstract: Mefenamic acid, a non-steroidal anti-inflammatory drug (NSAID), is used commonly to treat menorrhagia. This study investigated the glucuronidation kinetics of flufenamic, mefenamic and niflumic acid using human kidney cortical microsomes (HKCM) and recombinant UGT1A9 and UGT2B7. Using HKCM Michaelis-Menten (MM) kinetics were observed for mefenamic (K(m)(app) 23 microM) and niflumic acid (K(m)(app) 123 microM) glucuronidation, while flufenamic acid exhibited non-hyperbolic (atypical) glucuronidation kinetics. Notably, the intrinsic renal clearance of mefenamic acid (CL(int) 17+/-5.5 microL/minmg protein) was fifteen fold higher than that of niflumic acid (CL(int) 1.1+/-0.8 microL/minmg protein). These data suggest that renal glucuronidation of mefenamic acid may result in high intrarenal exposure to mefenamic acyl-glucuronide and subsequent binding to renal proteins. Diverse kinetics were observed for fenamate glucuronidation by UGT2B7 and UGT1A9. Using UGT2B7 MM kinetics were observed for flufenamic (K(m)(app) 48 microM) and niflumic acid (K(m)(app) 135 microM) glucuronidation and atypical kinetics with mefenamic acid. Similarity in K(m)(app) between HKCM and UGT2B7 suggests that UGT2B7 may be the predominant renal UGT isoform catalysing niflumic acid glucuronidation. In contrast, UGT1A9 glucuronidation kinetics were characterised by negative cooperativity with mefenamic (S(50) 449 microM, h 0.4) and niflumic acid (S(50) 7344 microM, h 0.4) while atypical kinetics were observed with flufenamic acid. Additionally, potent inhibition of the renal glucuronidation of the UGT substrate 'probe' 4-methylumbelliferone by flufenamic, mefenamic and niflumic acid was observed. These data suggest that inhibitory metabolic interactions may occur between fenamates and other substrates metabolised by UGT2B7 and UGT1A9 in human kidney.
authors.affiliation: Department of Clinical Pharmacology, Flinders University and Flinders Medical Centre, Bedford Park, Adelaide, Australia.
authors.forename: Paraskevi
authors.initials: P
authors.lastname: Gaganis
authors.forename: John O
authors.initials: JO
authors.lastname: Miners
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Knights
mesh_terms: D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000378:metabolism* / Q000494:pharmacology; D005439:Flufenamic Acid / Q000378:metabolism / Q000494:pharmacology; D020719:Glucuronides / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006801:Humans; D007668:Kidney; D007672:Kidney Cortex; D007700:Kinetics; D008528:Mefenamic Acid / Q000378:metabolism / Q000494:pharmacology; D008861:Microsomes / Q000378:metabolism*; D009544:Niflumic Acid / Q000378:metabolism / Q000494:pharmacology; D011994:Recombinant Proteins; D000090264:UDP-Glucuronosyltransferase 1A9; D062367:ortho-Aminobenzoates / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D020719:Glucuronides; D011994:Recombinant Proteins; C000715591:UGT1A9 protein, human; D062367:ortho-Aminobenzoates; D008528:Mefenamic Acid; D009544:Niflumic Acid; D005439:Flufenamic Acid; C001209:fenamic acid; C491474:UGT2B7 protein, human; D014453:Glucuronosyltransferase; D000090264:UDP-Glucuronosyltransferase 1A9