MRP-1 and BCRP Promote the Externalization of Phosphatidylserine in Oxalate-Treated Renal Epithelial Cells: Implications for Calcium Oxalate Urolithiasis

To investigate the possible involvement of multidrug resistance-associated protein 1 (MRP-1) and breast cancer resistance protein (BCRP) in the oxalate-induced redistribution of phosphatidylserine (PS) in renal epithelial cell membranes.

A western blot analysis was used to examine the MRP-1 and BCRP expression levels. Surface-expressed PS was detected by the annexin V-binding assay. The cell-permeable fluorogenic probe 2,7-dichlorofluorescein diacetate (DCFH-DA) was used to measure the intracellular reactive oxygen species (ROS) level. A rat model of hyperoxaluria was obtained using 0.5% ethylene glycol (EG) and 1.0% ammonium chloride (NH4Cl). In addition, certain animals received verapamil (50 mg/kg body weight), which is a common inhibitor of MRP-1 and BCRP. The degree of nephrolithiasis was assessed histomorphometrically using sections stained by Pizzolato's method and by measuring the calcium oxalate crystal content in the renal tissue.

Oxalate produced a concentration-dependent increase in the synthesis of MRP-1 and BCRP. Treatment with MK571 and Ko143 (MRP-1- and BCRP-specific inhibitors, respectively) significantly attenuated the oxalate-induced PS externalization. Adding the antioxidant N-acetyl-L-cysteine (NAC) significantly reduced MRP-1 and BCRP expression. In vivo, markedly decreased nephrocalcinosis was observed compared with that in the rat model of hyperoxaluria without verapamil treatment.

Oxalate induces the up-regulation of MRP-1 and BCRP, which act as phospholipid floppases to cause PS externalization in the renal epithelial cell membrane. The process is mediated by intracellular ROS production. The ROS-mediated increase in the synthesis of MRP-1 and BCRP, can play an important role in hyperoxaluria-promoted calcium oxalate urolithiasis by facilitating phosphatidylserine redistribution in renal epithelial cells.

Urology. 2017 May 31 [Epub ahead of print]

YiFu Li, ShiLiang Yu, XiuGuo Gan, Ze Zhang, Yan Wang, YingWei Wang, RuiHua An

Department of Urology, First Affiliated Hospital of Harbin Medical University, Harbin, People's Republic of China., Department of Pathology, First Affiliated Hospital of Harbin Medical University, Harbin, People's Republic of China., Department of Urology, First Affiliated Hospital of Harbin Medical University, Harbin, People's Republic of China. Electronic address: .