Search

Acamprosate is an anionic drug substance widely used in treating symptoms of alcohol withdrawal. It was recently shown that oral acamprosate absorption is likely due to paracellular transport. In contrast, little is known about the eliminating mechanism clearing acamprosate from the blood in the kidneys, despite the fact that studies have shown renal secretion of acamprosate. The hypothesis of the present study was therefore that renal organic anion transporters (OATs) facilitate the renal excretion of acamprosate in humans. The aim of the present study was to establish and apply OAT1 (gene product of SLC22A6) and OAT3 (gene product of SLC22A8) expressing cell lines to investigate whether acamprosate is a substrate or inhibitor of OAT1 and/or OAT3. The studies were performed in HEK293-Flp-In cells stably transfected with SLC22A6 or SLC22A8. Protein and functional data showed that the established cell lines are useful for studying OAT1- and OAT3-mediated transport in bi-laboratory studies. Acamprosate inhibited OAT1-mediated p-aminohippuric acid (PAH) uptake but did not inhibit substrate uptake via OAT3 expressing cells, neither when applied concomitantly nor after a 3 h preincubation with acamprosate. The uptake of PAH via OAT1 was inhibited in a competitive manner by acamprosate and cellular uptake studies showed that acamprosate is a substrate for OAT1 with a Km-value of approximately 700 &micro, M. Probenecid inhibited OAT1-mediated acamprosate uptake with a Ki-value of approximately 13 &micro, M, which may translate into an estimated clinically significant DDI index. In conclusion, acamprosate was identified as a substrate of OAT1 but not OAT3.

Introduction. Acamprosate is a BCS class III, non-metabolized, anionic drug substance for which the excretion mechanism is not fully understood. Intravenous administration in rats of acamprosate together with probenecid, a known substrate and inhibitor of the organic anion transporter (OAT) 1 (SLC22A6) (1), decreased the renal clearance (ClR) of acamprosate in a dose-dependent manner (2). The hypothesis of the present study was that renal OATs expressed in the basolateral membrane of the proximal tubule epithelium (3) could be the carrier contributing to renal excretion of acamprosate and the reason for potential acamprosate-drug (e.g. probenecid) interactions.Aim. To investigate if acamprosate interacts with OAT1 by measuring the concentration-dependent effect of acamprosate on the uptake of [14C]-p-aminohippuric acid ([14C]-PAH), a well-established substrate of OAT1 (4).Method. The apical uptake of 0.5 μCi/mL [14C]-PAH was measured for 5 minutes at 37°C and 100 rpm in the presence of 0 – 33 000 μM acamprosate in human embryonic kidney (HEK)293 cells transiently expressing OAT1 (Corning TransportoCells OAT1), or in a HEK293-Flp-in cell line stably expressing OAT1 (developed in-house). The uptake was in both series measured in parallel in mock-transfected HEK293 cells grown under similar cell culture conditions.Results. A significant, time-dependent and saturable increase of [14C]-PAH apical uptake was observed in the OAT1-transfected HEK293 cells compared to mock-transfected cells. The apical uptake of [14C]-PAH in OAT1-transfected cells was decreased in the presence of acamprosate in a concentration-dependent manner, while no effect of acamprosate was observed in the mock-transfected cells. The mean (+/- SD) inhibition constant for [14C]-PAH uptake (IC50) was 1 042 ± 134 and 902 ± 20 μM in the transiently (n=3) and stably transfected (N=3, n=2) HEK293-OAT1 cells, respectively.Conclusion. Acamprosate inhibits OAT1 in vitro at concentrations close to the maximum unbound plasma concentration of acamprosate, cmax = 154-768 μM (5), obtained after intravenous administration [333-2130 mg].References1. Nigam SK, Bush KT, Martovetsky G, Ahn SY, Liu HC, Richard E, et al. The organic anion transporter (OAT) family: a systems biology perspective. Physiol Rev. 2015;95(1):83-123.2. Zornoza T, Guerri C, Polache A, Granero L. Disposition of acamprosate in the rat: influence of probenecid. Biopharm Drug Dispos. 2002;23(7):283-91.3. Wright SH, Dantzler WH. Molecular and cellular physiology of renal organic cation and anion transport. Physiol Rev. 2004;84(3):987-1049.4. FDA. In Vitro Metabolism and Transporter-Mediated Drug-Drug Interaction Studies - Guidance for Industry. In: CDER, editor. Silver Spring, MD: U.S. Department of Health and Human Services; 2017. p. 1-37.5. Approval package for application number 21-431: Campral clinical pharmacology and biopharmaceutics review: Center for drug evaluation and research; 2004 [cited 2018 08 13]. Available from: https://www.accessdata.fda.gov/drugsatfda_docs/nda/2004/21-431_Campral_BioPharmr.pdf.