Bile duct ligation impairs function and expression of breast cancer resistance protein in rat blood-retinal barrier mainly due to both the increased ammonia and bilirubin.

Patients with liver failure often suffer from hepatic retinopathy, partly due to the blood-retinal barrier (BRB) impairment. BRB includes the inner BRB formed by retinal microvascular endothelial cells and the outer BRB formed by retinal pigment epithelial cells. Breast cancer resistance protein (BCRP), highly expressed in the inner BRB, regulates retinal homeostasis. To investigate the effects of liver failure on retina BCRP function and expression, we used bile duct ligation (BDL) rats as an animal model, and the BCRP function and BRB integrity were evaluated via retinal prazosin/sulfasalazine distribution and fluorescein isothiocyanate-conjugated dextran permeability using total 18 BDL and 18 sham rats (n = 6 per group), respectively. The results demonstrated that BDL significantly downregulated retina BCRP expression (decrease 1.7-fold of sham rats) and function without affecting BRB permeability, alongside 50%-75% reductions in JNK and p-JNK expression, as well as 30% increases in reactive oxygen species (ROS) levels and 2-fold elevations in p-ERK1/2 expression. The primarily cultured rat retinal microvascular endothelial cells were used to investigate the mechanism of BCRP expression impairment by BDL. In vitro, NH4Cl significantly downregulated the expression of BCRP, JNK, and p-JNK protein, which were attenuated by JNK activator, metformin. Bilirubin could also decrease BCRP expression, accompanied by increased levels of ROS and p-ERK1/2. N-Acetyl-L-cysteine and U0126 attenuated the bilirubin- or H2O2-induced downregulation of BCRP protein. Confirming this in vivo, bilirubin and ammonium acetate recapitulated BCRP suppression via ROS-ERK1/2 and JNK pathways, respectively (n = 6 per group). In summary, BDL downregulated the expression and function of BCRP in rat retina, partly due to increases in levels of both ammonia and bilirubin. Ammonia impaired BCRP expression by inactivating the JNK pathway, while bilirubin suppressed BCRP expression by activating the ROS-ERK1/2 pathway. SIGNIFICANCE STATEMENT: Bile duct ligation-induced ammonia and bilirubin accumulation downregulated retinal breast cancer resistance protein (BCRP) expression and function. Ammonia impaired the expression of BCRP by inactivating the JNK pathway, while bilirubin suppressed BCRP expression through activating the ROS-ERK1/2 pathway.