Aldosterone glucuronidation by human liver and kidney microsomes and recombinant UDP-glucuronosyltransferases: Inhibition by NSAIDs

center dot Carboxylic acid NSAIDs are extensively glucuronidated as either the parent drug or hydroxylated metabolites and UGT2B7 is ranked highest in terms of NSAID-glucuronidation activity. center dot NSAIDs cause adverse renal effects including sodium and water retention and hyperkalaemia. center dot In human kidney the mineralocorticoid aldosterone is glucuronidated directly to form aldosterone 18 beta-glucuronide. WHAT THIS STUDY ADDS center dot Human liver and kidney microsomes and UGT1A10 and UGT2B7 catalyze aldosterone18 beta-glucuronidation. center dot Non-selective NSAIDs inhibit renal and hepatic aldosterone18 beta-glucuronidation and in vivo this may lead to elevated intra-renal concentrations of this hormone. center dot Common involvement of UGT2B7 in NSAID and aldosterone glucuronidation predicates an intra-renal NSAID-aldosterone interaction that may explain in part the clinical observations of variable effects of NSAIDs on electrolytes, fluid retention and blood pressure. AIMS To characterize: i) the kinetics of aldosterone (ALDO) 18 beta-glucuronidation using human liver and human kidney microsomes and identify the human UGT enzyme(s) responsible for ALDO 18 beta-glucuronidation and ii) the inhibition of ALDO 18 beta-glucuronidation by non-selective NSAIDs. METHODS Using HPLC and LC-MS methods, ALDO 18 beta-glucuronidation was characterized using human liver (n = 6), human kidney microsomes (n = 5) and recombinant human UGT 1A1, 1A3, 1A4, 1A5, 1A6, 1A7, 1A8, 1A9, 1A10, 2B4, 2B7, 2B10, 2B15, 2B17 and 2B28 as the enzyme sources. Inhibition of ALDO 18 beta-glucuronidation was investigated using alclofenac, cicloprofen, diclofenac, diflunisal, fenoprofen, R- and S-ibuprofen, indomethacin, ketoprofen, ketorolac, meclofenamic acid, mefenamic acid, S-naproxen, pirprofen and tiaprofenic acid. A rank order of inhibition (IC50) was established and the mechanism of inhibition investigated using diclofenac, S-ibuprofen, indomethacin, mefenamic acid and S-naproxen. RESULTS ALDO 18 beta-glucuronidation by hepatic and renal microsomes exhibited Michaelis-Menten kinetics. Mean (+/- SD) K-m, V-max and CLint values for HLM and HKCM were 509 +/- 137 and 367 +/- 170 mu m, 1075 +/- 429 and 1110 +/- 522 pmol min(-1) mg(-1), and 2.36 +/- 1.12 and 3.91 +/- 2.35 mu l min(-1) mg(-1), respectively. Of the UGT proteins, only UGT1A10 and UGT2B7 converted ALDO to its 18 beta-glucuronide. All NSAIDs investigated inhibited ALDO 18 beta-G formation by HLM, HKCM and UGT2B7. The rank order of inhibition (IC50) of renal and hepatic ALDO 18 beta-glucuronidation followed the general trend: fenamates > diclofenac > arylpropionates. CONCLUSION A NSAID-ALDO interaction in vivo may result in elevated intra-renal concentrations of ALDO that may contribute to the adverse renal effects of NSAIDs and their effects on antihypertensive drug response.