Regulation of Human Renal Transporters by Pregnancy-Related Hormones in Primary Proximal Tubular Epithelial Cells

Background/Objectives: Pregnancy is associated with increased renal secretory clearance of drugs mediated by organic anion transporters (OATs) and organic cation transporter 2 (OCT2). Circulating concentrations of pregnancy-related hormones (PRHs) increase with gestational age, providing a plausible mechanism for renal OAT and OCT2 regulation. Methods: Using primary human proximal tubular epithelial cells (PTECs), we quantified the effects of PRHs, at trimester-specific concentrations, on the mRNA expression of renal drug transporters (apical and basal) and metabolizing enzymes (DMETs), as well as endocytic receptors. PTECs from three female, premenopausal donors were cultured in an optimized Transwell system that maintains measurable OAT activity. PTECs were then exposed for 72 h to trimester-matched PRH cocktails at physiologic (1×) or supraphysiologic (10×) concentrations, with medium replaced every 24 h. DMET and endocytic receptor mRNA were quantified by RT-qPCR, and uptake activities of OAT1/2/3, OCT2, OAT4, and OCTN1 were measured with selective substrates or substrate-inhibitor pairs. Results: At 1× PRHs, renal DMET and endocytic receptor mRNA expression was unchanged across trimester-related PRH concentration except for consistent downregulation of PEPT2. Uptake activity for all measured transporters was unchanged. At 10× PRHs, selective changes in mRNA expression of transporters were observed (e.g., induction of OAT1), but these changes did not translate into changes in activity. Conclusions: Our data argue against PRHs as the main driver of the increase in OAT-mediated drug secretion during pregnancy. Alternative mechanisms (e.g., flow-dependent mechanotransduction and untested hormones [e.g., prolactin, hCG]) should be evaluated to explain gestation-dependent changes in renal secretory clearance of drugs.