Elsevier

Biochemical Pharmacology

Volume 74, Issue 1, 30 June 2007, Pages 161-168
Biochemical Pharmacology

Interaction and transport characteristics of mycophenolic acid and its glucuronide via human organic anion transporters hOAT1 and hOAT3

https://doi.org/10.1016/j.bcp.2007.03.024Get rights and content

Abstract

The immunosuppressant mycophenolate mofetil (MMF) is frequently administered with calcineurin inhibitors and corticosteroids to recipients of organ transplantations. However, the renal handling of the active metabolite mycophenolic acid (MPA) and 7-O-MPA-glucuronide (MPAG) has been unclear. The purpose of the present study was to assess the interaction of MPA and MPAG with the human renal organic anion transporters hOAT1 (SLC22A6) and hOAT3 (SLC22A8), by conducting uptake experiments using HEK293 cells stably expressing these transporters. MPA and MPAG inhibited the time-dependent uptake of p-[14C]aminohippurate by hOAT1 and that of [3H]estrone sulfate by hOAT3. The apparent 50% inhibitory concentration (IC50) of MPA for hOAT1 and hOAT3 was estimated at 10.7 and 1.5 μM, respectively. In the case of MPAG, the IC50 values were calculated at 512.3 μM for hOAT1 and 69.1 μM for hOAT3. Eadie–Hofstee plot analyses showed that they inhibited hOAT1 noncompetitively and hOAT3 competitively. No inhibitory effects of tacrolimus, cyclosporin A and azathioprine on transport of p-[14C]aminohippurate by hOAT1 and of [3H]estrone sulfate by hOAT3 were observed. No transport of MPA by these transporters was observed. On the other hand, the uptake of MPAG into cells was stimulated by the expression of hOAT3, but not hOAT1. These findings propose the possibility that the administration of MMF decreases the renal clearance of drugs which are substrates of hOAT1 and hOAT3. Present data suggest that hOAT3 contributes to the renal tubular secretion of MPAG.

Introduction

An immunosuppressive agent, mycophenolate mofetil (MMF) is commonly prescribed with the calcineurin inhibitor tacrolimus or cyclosporin A and corticosteroids for patients who have received a solid organ transplantation. After orally administered and absorbed, MMF is converted to an active metabolite, mycophenolic acid (MPA; Fig. 1) by serum esterases. MPA is mainly excreted into urine after being metabolized to 7-O-MPA-glucuronide (MPAG) by the hepatic uridine diphosphate-glucuronosyltransferases [1], [2]. The genetic variants of uridine diphosphate-glucuronosyltransferases contribute to the extensive variability in the pharmacokinetics of the immunosuppressant [3], [4]. Furthermore, the enterohepatic circulation of MPAG/MPA exists, and tubular secretion as well as glomerular filtration is responsible for the urinary excretion of MPAG [1]. Thus, the process by which MMF is eliminated, is very intricate.

Besides immunosuppressive agents, many drugs are given to recipients of organ transplantations, to prevent or treat infections, gastrointestinal ulcers, thrombus, ascites, pleural fluid, hypertension, diabetes, osteoporosis, gout, bronchitis and so on. Accordingly, side effects caused by drug interactions often occur. In addition to tacrolimus and cyclosporin A, MMF was shown to interact with various drugs. For instance, MMF reduced the renal clearance of acyclovir and ganciclovir, and the pharmacokinetics of MPA or MPAG were affected by cyclosporin A, glucocorticoids and non-steroidal anti-inflammatory drugs [1], [5], [6], [7], [8]. Taking these MPA and/or MPAG-mediated drug interactions into account, together with the complexity of the fate of MMF, it is important to identify the drug-metabolizing enzymes and drug transporters interacting with this immunosuppressive agent for a successful organ transplantation.

The human organic anion transporters (hOATs) mediate transport of clinically important drugs, such as diuretics, antibiotics, antivirals, histamine H2 receptor antagonists, non-steroidal anti-inflammatory drugs and so on [9], [10]. Among the family, hOAT1 (SLC22A6) and hOAT3 (SLC22A8) were shown to be predominantly expressed in the basolateral membrane of the renal proximal tubules [11], suggesting that they play main roles in the renal tubular uptake of organic compounds from blood. Furthermore, as previously reported [12], it is possible that hOAT1 and hOAT3 are targets of the interaction between methotrexate and non-steroidal anti-inflammatory drugs.

This background suggests that the renal organic anion transporters are concerned with the renal excretion of the metabolites of MMF and drug interaction with them, but to our knowledge, no report has examined the interaction of MPA and MPAG with the renal organic anion transporters at a molecular level. In the present study, the inhibitory effects of MPA and MPAG on hOAT1 and hOAT3 were assessed. In addition, the contribution of hOAT1 and hOAT3 to the renal tubular secretion of MPA and MPAG was investigated.

Section snippets

Materials

p-[glycyl-1-14C]Aminohippurate (1.9 GBq/mmol) and [6,7-3H(N)]estrone sulfate, ammonium salt (2.1 TBq/mmol) were obtained from NEN™ Life Science Products Inc. (Boston, MA, USA) and Perkin-Elmer Life Sciences Inc. (Boston, MA, USA), respectively. MPA and its glucuronide were from Wako Pure Chemical Industries (Osaka, Japan) and Analytical Services International Ltd. (London, UK), respectively. Tacrolimus and cyclosporin A were kindly supplied by Fujisawa Pharmaceutical (Newly, Astellas Pharma Inc.,

Inhibitory effects of MPA and MPAG on hOAT1 and hOAT3

First, to examine whether MPA and MPAG interact with hOAT1 and hOAT3, the effects of MPA and MPAG on the time-dependent uptake of p-[14C]aminohippurate by HEK-hOAT1 and of [3H]estrone sulfate by HEK-hOAT3 were investigated. As shown in Fig. 2A, the amount of p-[14C]aminohippurate taken up by HEK-hOAT1 increased linearly for 2 min. MPA at 300 μM completely inhibited the hOAT1-mediated transport of p-[14C]aminohippurate. MPAG at 300 μM also inhibited the uptake of p-[14C]aminohippurate by hOAT1, but

Discussion

In organ transplantation, many drugs, including immunosuppressants, antibiotics, antivirals, antifungals, diuretics, histamine H2 receptor antagonists, proton pump inhibitors, anticoagulants, bronchodilators and hypouricemic agents are administered to recipients. Accordingly, drugs should be prescribed with predictions of drug interactions [14]. To avoid adverse effects via drug interactions, information on the routes of elimination of a drug and its inhibitory effects on drug-metabolizing

Acknowledgements

This work was supported in part by a grant-in-aid for Research on Advanced Medical Technology from the Ministry of Health, Labor and Welfare of Japan, by a Japan Health Science Foundation “Research on Health Sciences Focusing on Drug Innovation”, by a grant-in-aid for Scientific Research from the Ministry of Education, Science, Culture and Sports of Japan and by the 21st Century COE program “Knowledge Information Infrastructure for Genome Science”.

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