Investigation into UDP-Glucuronosyltransferase (UGT) Enzyme Kinetics of Imidazole- and Triazole-Containing Antifungal Drugs in Human Liver Microsomes and Recombinant UGT Enzymes

Abstract

ABSTRACT:Imidazoles and triazoles represent major classes of antifungal azole derivatives. With respect to UDP-glucuronosyltransferase (UGT) enzymes, the drug metabolism focus has mainly concentrated on their inhibitory effects with little known about azoles as substrates for UGTs. N-Glucuronide metabolites of the imidazole antifungals, tioconazole and croconazole, have been reported, but there are currently no reports of N-glucuronidation of triazole antifungal agents. In this study, evidence for glucuronidation of azole-containing compounds was studied in human liver microsomes (HLM). When a glucuronide metabolite was identified, azoles were incubated in 12 recombinant UGT (rUGT) enzymes, and enzyme kinetics were determined for the UGT with the most intense glucuronide peak. Six imidazole antifungals, three triazoles, and the benzodiazepine alprazolam (triazole) were evaluated in this study. All compounds investigated were identified as substrates of UGT. UGT1A4 was the main enzyme involved in the metabolism of all compounds except for fluconazole, which was mainly metabolized by UGT2B7, probably mediating its O-glucuronide metabolism. UGT1A3 was also found to be involved in the metabolism of all imidazoles but not triazoles. In both HLM and rUGT K m values were lower for imidazoles (14.8-144 M) than for triazoles (158-3037 M), with the exception of itraconazole (8.4 M). All of the imidazoles studied inhibited their own metabolism at high substrate concentrations. In terms of UGT1A4 metabolism, itraconazole showed kinetic features characteristic of imidazole rather than triazole antifungals. This behavior is attributed to the physicochemical properties of itraconazole that are similar to those of imidazoles in terms of clogP.

Physiologically Based Pharmacokinetic Approach to Determine Dosing on Extracorporeal Life Support: Fluconazole in Children on ECMO

“…Expected CL R is the renal plasma clearance expected due to GFR if there was no reabsorption or tubular secretion (expected CL R  = fraction unbound × GFR =  f u  × 110 mL/minute). Metabolism was attributed to glucuronidation via UGT2B7, and unbound intrinsic clearance (${\text{CL}}_{\mathrm{normalI}}^{\prime }$) was calculated using hepatic clearance (CL H ) 24. The CL H was assumed to be 15% of total empiric clearance 23.…”

Has the era of individualised medicine arrived for antifungals? A review of antifungal pharmacogenomics

“…76 Voriconazole is also a low-affinity substrate for UGT1A4 in vitro. 49 An understanding of how genetic polymorphism affects voriconazole metabolism has been pivotal in explaining the pharmacokinetic variability observed in patients. The occurrence of genetic variants in the CYP alleles (Table 4) has a significant impact on the levels of drug achieved in those patients and probably upon the therapeutic efficacy of voriconazole.…”

“…59 Recently, itraconazole was shown to be a substrate for the phase II enzyme UGT1A4, with an affinity similar to that of the imidazole antifungal agents, and it may also be an inhibitor of UGT1A4. 49 Itraconazole interacts with several genetically variable drug transporters and CYP enzymes, thus implicating them in the observed variability of itraconazole levels. Moreover, because CYP3A4 and P-glycoprotein also play a crucial role in the metabolism of many other drugs used in HSCT patients, this effect is likely to be compounded.…”

“…Its ability to inhibit 2C9 and 2C19 causes potential drug interactions particularly relevant to HSCT recipients; for example, the interaction with CY may result in increased formation of toxic metabolites, 47 although others have noted a protective effect of co-administration. 48 Fluconazole is both a substrate 49 and an inhibitor 50 of the UGT isoform, UGT2B7, the enzyme involved in its metabolism to the urinary metabolite fluconazole glucuronide. 43 It also inhibits UGT2B4, hence inhibiting, for example, the glucuronidation of codeine that may potentiate codeine-induced analgesia.…”

Evaluation and Comparison of the Inhibition Effect of Astragaloside IV and Aglycone Cycloastragenol on Various UDP-Glucuronosyltransferase (UGT) Isoforms

“…The disposition and clearance of drugs may be significantly changed when UGT are modulated by co-administrated drugs or herbal medicines. For example, fluconazole itself is not metabolized by UGT but alter pharmacokinetic parameters of co-administrated zidovudine in AIDS patients, because the glucuronidation of zidovudine by UGT2B7 is strongly inhibited by fluconazole [12]; indinavir Although much research has been carried on the in vitro and in vivo metabolism profiles of AST and CAG, only a few articles that deal with metabolism enzymes elucidate the potential toxicity and herb-drug interactions. Shan et al [10] reported that AST was a competitive inhibitor of CYP2C9 and a non-competitive inhibitor of CYP3A4 in an in vitro study.…”