Glucuronidation of Antiallergic Drug, Tranilast: Identification of Human UDP-Glucuronosyltransferase Isoforms and Effect of Its Phase I Metabolite

Abstract

ABSTRACT:Tranilast is an oral antiallergic agent widely used in Japan. Recently, in Western populations, hyperbilirubinemia induced by tranilast was suspected during clinical trials. Tranilast has been reported to be mainly metabolized to a glucuronide and a phase I metabolite, 4-demethyltranilast (N-3). In the present study, we investigated the in vitro metabolism of tranilast in human liver and jejunum microsomes and recombinant UDP-glucuronosyltransferases (UGTs). The glucuronidation of tranilast was clarified to be mainly catalyzed by UGT1A1 in human liver and intestine. The K m values of tranilast glucuronosyltransferase activity were 51.5, 50.6, and 38.0 M in human liver microsomes, human jejunum microsomes, and recombinant UGT1A1, respectively. The V max values were 10.4, 42.9, and 19.7 pmol/min/mg protein in human liver microsomes, human jejunum microsomes, and recombinant UGT1A1, respectively. When the intrinsic clearance was calculated using the in vitro kinetic parameters, microsomal protein content, and weight of tissues, tranilast glucuronosyltransferase activity was 2.5-fold higher in liver than in intestine. Tranilast glucuronosyltransferase activity was strongly inhibited by bilirubin, a typical UGT1A1 substrate, and N-3, indicating that the phase I metabolite could affect the tranilast glucuronosyltransferase activity. In the case of N-3 formation, the K m and V max values were 37.1 M and 27.6 pmol/min/mg protein in human liver microsomes. The bilirubin glucuronosyltransferase activity was strongly inhibited by both tranilast and N-3, suggesting that tranilast-induced hyperbilirubinemia would be responsible for the inhibition by tranilast and N-3 of the bilirubin glucuronosyltransferase activity, as would the UGT1A1 genotype.Tranilast (N-(3Ј,4Ј-demethoxycinnamoyl)-anthranilic acid) is an oral antiallergic agent developed by Kissei Pharmaceutical Co. Ltd. (Nagano, Japan) and widely used in Japan for bronchial asthma, allergic rhinitis, atopic dermatitis, keloid, and hypertrophic scar. The mechanism of its efficacy is to inhibit chemical mediators from mast cells (Azuma et al., 1976) and the accumulation of collagen in granulation tissue (Isaji et al., 1987). Recently, a clinical trial regarding the prevention of restenosis after percutaneous transluminal coronary revascularization was performed in Western populations (Holmes et al., 2000). During that trial, it was found that hyperbilirubinemia might be induced by tranilast and the risk of hyperbilirubinemia was increased in individuals with Gilbert's syndrome (Danoff et al., 2004).Major metabolic pathways of tranilast have been shown to be glucuronidation, 4-demethylation (N-3), and sulfation of N-3 in the data sheet of tranilast provided by Kissei Pharmaceutical (Fig. 1). Tranilast, N-3, and N-3 sulfate were reported to be detected in human urine (Slobodzian et al., 1985). Since the urine sample was hydrolyzed by glucuronidase and/or base in that article, the formation of glucuronide could be speculated by a comparison of the chromatograms befo...

Assessment of cryopreserved human hepatocytes as a model system to investigate sulfation and glucuronidation and to evaluate inhibitors of drug conjugation

“…This would suggest that the inhibition of glucuronidation was non-competitive, and this has previously been shown to be the case in vitro, using rat liver microsomes (Kamali 1993). Tranilast is an anti-allergy agent that strongly inhibits UGT1A1 and is associated with drug-induced hyperbilirubinaemia (Katoh et al 2007). We found tranilast inhibited a substantial proportion of both the glucuronidation and sulfation of paracetamol in cryopreserved hepatocytes, suggesting UGT1A1 and SULT1A1 may be important contributors to paracetamol metabolism.…”

Anti-Allergic Drugs Tranilast and Ketotifen Dose-Dependently Exert Mast Cell-Stabilizing Properties

“…1A). In human, the serum concentration of tranilast ranges between 30 and 300 µM when orally administered for the treatment of systemic diseases [27,28]. However, in in vitro studies using rat peritoneal mast cells, doses as high as 1 mM tranilast were required to effectively elicit its inhibitory property on the release of histamine [9,29].…”

Product Inhibition of UDP-Glucuronosyltransferase (UGT) Enzymes by UDP Obfuscates the Inhibitory Effects of UGT Substrates

“…Group B included 3 compounds of which the inhibitory effects on the activities of both human liver microsomes and recombinant UGT1A1 were potent (residual activities were Ͻ40%). Ethynylestradiol and tranilast are the substrates of UGT1A1 (McGinnity et al, 2004;Katoh et al, 2007). Propofol, a substrate of UGT1A9, has been reported to inhibit UGT1A1 activities (Williams et al, 2004;Kaji and Kume, 2005).…”