Characterization of Organic Anion Transporter 2 (SLC22A7): A Highly Efficient Transporter for Creatinine and Species-Dependent Renal Tubular Expression

Abstract

The contribution of organic anion transporter OAT2 (SLC22A7) to the renal tubular secretion of creatinine and its exact localization in the kidney are reportedly controversial. In the present investigation, the transport of creatinine was assessed in human embryonic kidney (HEK) cells that stably expressed human OAT2 (OAT2-HEK) and isolated human renal proximal tubule cells (HRPTCs). The tubular localization of OAT2 in human, monkey, and rat kidney was characterized. The overexpression of OAT2 significantly enhanced the uptake of creatinine in OAT2-HEK cells. Under physiologic conditions (creatinine concentrations of 41.2 and 123.5 mM), the initial rate of OAT2-mediated creatinine transport was approximately 11-, 80-, and 80-fold higher than OCT2, multidrug and toxin extrusion protein (MATE)1, and MATE2K, respectively, resulting in approximately 37-, 1850-, and 80-fold increase of the intrinsic transport clearance when normalized to the transporter protein concentrations. Creatinine intracellular uptake and transcellular transport in HRPTCs were decreased in the presence of 50 mM bromosulfophthalein and 100 mM indomethacin, which inhibited OAT2 more potently than other known creatinine transporters, OCT2 and multidrug and toxin extrusion proteins MATE1 and MATE2K (IC 50 : 1.3 mM vs. > 100 mM and 2.1 mM vs. > 200 mM for bromosulfophthalein and indomethacin, respectively) Immunohistochemistry analysis showed that OAT2 protein was localized to both basolateral and apical membranes of human and cynomolgus monkey renal proximal tubules, but appeared only on the apical membrane of rat proximal tubules. Collectively, the findings revealed the important role of OAT2 in renal secretion and possible reabsorption of creatinine and suggested a molecular basis for potential species difference in the transporter handling of creatinine.

The Complexities of Interpreting Reversible Elevated Serum Creatinine Levels in Drug Development: Does a Correlation with Inhibition of Renal Transporters Exist?

“…OAT2 is expressed in the basolateral membrane of renal proximal tubule cells as well as in the sinusoidal membrane of hepatocytes (Kobayashi et al, 2005;Cheng et al, 2012). One group showed that OAT2 was localized in both basolateral and apical membranes of human and cynomolgus monkey renal proximal tubules, but only in the apical membrane of rat proximal tubules (Shen et al, 2015). These findings suggest species differences for OAT2/Oat2 localization and possibly a role in reabsorption of OAT2 in primates.…”

“…Creatinine showed a somewhat higher affinity toward OAT2 (K m = 986 mM) as compared with OCT2 and OCT3. Other groups also observed higher affinity transport of creatinine by OAT2 compared with that by other transporters (Shen et al, 2015). OAT2 might contribute to creatinine secretion, and possibly reabsorption in human renal proximal tubules, but clinical data are needed to support this hypothesis.…”

“…In contrast to OAT1 and OAT3, the role of OAT2 is less well characterized. More studies have emerged this decade focusing on OAT2 expression in the human kidney as well as its role in renal tubular handling of drugs (Cheng et al, 2012;Lepist et al, 2014;Shen et al, 2015). OAT2 is expressed in the basolateral membrane of renal proximal tubule cells as well as in the sinusoidal membrane of hepatocytes (Kobayashi et al, 2005;Cheng et al, 2012).…”

“…Based on current evidence, OCT3 is likely less important than OCT2 for creatinine uptake in the kidney. Opposing the traditional view of organic cationic pathways as the sole mechanism of creatinine secretion in the kidney, creatinine has been reported to be an in vitro substrate for OAT2 (Ciarimboli et al, 2012;Lepist et al, 2014;Shen et al, 2015). A comprehensive analysis to identify the transporters for creatinine was performed, in which each transporter's mRNA and function were measured (Lepist et al, 2014).…”

Cynomolgus Monkey as a Clinically Relevant Model to Study Transport Involving Renal Organic Cation Transporters: In Vitro and In Vivo Evaluation

“…Use of Monkey to Assess Transport by OCT2 and MATEs 245 at ASPET Journals on March 31, 2019 dmd.aspetjournals.org counterparts, likely function to mediated the secretion of substrates such as MFM, creatinine, and cisplatin (Urakami et al, 2004;Tanihara et al, 2007Tanihara et al, , 2009Imamura et al, 2011;Shen et al, 2015a). It is worth noting that although the impact of transporters on systemic exposure is relatively modest (less than threefold), their effects on drug distribution or tissue exposure could be more dramatic.…”