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

Abstract

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • 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. • NSAIDs cause adverse renal effects including sodium and water retention and hyperkalaemia. • In human kidney the mineralocorticoid aldosterone is glucuronidated directly to form aldosterone 18β‐glucuronide. WHAT THIS STUDY ADDS • Human liver and kidney microsomes and UGT1A10 and UGT2B7 catalyze aldosterone18β‐glucuronidation. • Non‐selective NSAIDs inhibit renal and hepatic aldosterone18β‐glucuronidation and in vivo this may lead to elevated intra‐renal concentrations of this hormone. • 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) 18β‐glucuronidation using human liver and human kidney microsomes and identify the human UGT enzyme(s) responsible for ALDO 18β‐glucuronidation and ii) the inhibition of ALDO 18β‐glucuronidation by non‐selective NSAIDs. METHODS Using HPLC and LC‐MS methods, ALDO 18β‐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 18β‐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 (I C 50 ) was established and the mechanism of inhibition investigated using diclofenac, S ‐ibuprofen, indomethacin, mefenamic acid and S ‐naproxen. RESULTS ALDO 18β‐glucuronidation by hepatic and renal microsomes exhibited Michaelis‐Menten kinetics. Mean (±SD) K m , V max and CL int values for HLM and HKCM were 509 ± 137 and 367 ± 170 µ m , 1075 ± 429 and 1110 ± 522 pmol min −1 mg −1 , and 2.36 ± 1.12 and 3.91 ± 2.35 µl min −1 mg −1 , respectively. Of the UGT proteins, only UGT1A10 and UGT2B7 converted ALDO to its 18β‐glucuronide. All NSAIDs investigated inhibited ALDO 18β‐G formation by HLM, HKCM and UGT2B7. The rank order of inhibition (I C 50 ) of renal and hepatic ALDO 18β‐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.