Human Multidrug Resistance Protein 2 (MRP2/ABCC2) transports 3α, 6α, 7α, 12α‐(OH)4‐5β‐cholyl taurine (6α‐OH‐TC)

Abstract

Background and AimGenetic defects in the bile salt export pump (ABCB11) gene lead to fatal Type 2 progressive familial intrahepatic cholestasis (PFIC2). However, Abcb11 knockout (KO) mice exhibit only mild cholestasis and secrete large amounts of unusual tetrahydroxyl bile salts into bile (PNAS 98:2011). The formation of hydrophilic bile salts is postulated to detoxify the hydrophobic bile salts and prevent a severe cholestatic phenotype in the KO mice. An unidentified alternative canalicular non‐Abcb11‐mediated transport system is proposed to efflux these tetrahydroxyl bile salts. Furthermore, 6a‐OH‐TC is present in human amniotic fluid, neonatal urine and urine of cholestatic patients. Here we investigate human MRP2 as a possible alternative transporter for 6a‐OH‐TC.MethodsTauro‐Δ22‐3a, 6a, 7a, 12a ‐tetrahydroxy‐5 β‐cholan‐24‐oic acid was synthesized, reductively tritiated, and purified by TLC and HPLC (98% purity). Human MRP2 was expressed in Sf9 insect cells and the kinetic parameters (Km, Vmax, Hill coefficient [HC]) of ATP dependant transport of 3H‐6a‐OH‐TC determined in Sf9 plasma membrane vesicles.ResultsSaturation kinetics studies (6a‐OH‐TC 0.1‐1mM) yielded uptake that fit best to the Hill equation with Vmax = 509 pmol/mg/min; Km = 128 µM; Hill coefficient = 1.6.Conclusion6α‐OH‐TC is a substrate of MRP2 with evidence of positive cooperativity. (HD 58299)