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

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 (IC₅₀) 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 μm, 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 (IC₅₀) 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.