Unconjugated bilirubin elevation impairs the function and expression of breast cancer resistance protein (BCRP) at the blood-brain barrier in bile duct-ligated rats

Abstract

Aim: Liver failure is associated with dyshomeostasis of efflux transporters at the blood-brain barrier (BBB), which contributes to hepatic encephalopathy. In this study we examined whether breast cancer resistance protein (BCRP), a major efflux transporter at the BBB, was altered during liver failure in rats. Methods: Rats underwent bile duct ligation (BDL) surgery, and then were sacrificed after intravenous injection of prazosin on d3, d7 and d14. The brains and blood samples were collected. BCRP function at the BBB was assessed by the brain-to-plasma prazosin concentration ratio; Evans Blue extravasation in the brain tissues was used as an indicator of BBB integrity. The protein levels of BCRP in the brain tissues were detected. Human cerebral microvessel endothelial cells (HCMEC/D3) and Madin-Darby canine kidney cells expressing human BCRP (MDCK-BCRP) were tested in vitro. In addition, hyperbilirubinemia (HB) was induced in rats by intravenous injection of unconjugated bilirubin (UCB). Results: BDL rats exhibited progressive decline of liver function and HB from d3 to d14. In the brain tissues of BDL rats, both the function and protein levels of BCRP were progressively decreased, whereas the BBB integrity was intact. Furthermore, BDL rat serum significantly decreased BCRP function and protein levels in HCMEC/D3 cells. Among the abnormally altered components in BDL rat serum tested, UCB (10, 25 µmol/L) dose-dependently inhibit BCRP function and protein levels in HCMEC/D3 cells, whereas 3 bile acids (CDCA, UDCA and DCA) had no effect. Similar results were obtained in MDCK-BCRP cells and in the brains of HB rats. Correlation analysis revealed that UCB levels were negatively correlated with BCRP expression in the brain tissues of BDL rats and HB rats as well as in two types of cells tested in vitro. Conclusion: UCB elevation in BDL rats impairs the function and expression of BCRP at the BBB, thus contributing to hepatic encephalopathy.

Altered Function and Expression of ABC Transporters at the Blood–Brain Barrier and Increased Brain Distribution of Phenobarbital in Acute Liver Failure Mice

“…The effects of unconjugated bilirubin (UCB), cholic acid (CA), deoxycholic acid (DCA), lithocholic acid (LCA), chenodeoxycholic acid (CDCA), and ursodeoxycholic acid (UDCA) on P-GP function and expression were investigated in HCMEC/D3 and MDCK-BCRP (MDCK type II cells transfected with human BCRP) cells. In brief, sub-confluent (80%) cells were incubated with medium containing different concentrations of UCB (0, 10, or 25 μM) and bile acids (0, 10, or 100 μM) for 24 h. The concentrations of UCB and individual bile acids were chosen based on previous studies ( Komori et al, 2014 ; Liu et al, 2014 ; Xu et al, 2016 ). It is noted that the data from a MTT study demonstrated that cell viability was not impaired by these agents at the tested concentrations ( Figures 2A,B ).…”

“…We once reported that both acute and chronic liver failure induced by thioacetamide (TAA) downregulated P-GP function and expression, and upregulated MRP2 function and expression at the BBB of rats ( Jin et al, 2013 ). Similarly, both function and expression of BCRP at the BBB of rats were decreased by ALF or bile duct ligation, leading to increases in brain distribution of prazosin ( Li et al, 2016 ; Xu et al, 2016 ). These results indicated that the altered function of ABC transporters at the BBB by ALF might affect the brain distribution, CNS activity, and toxicity of their substrates.…”

Alterations in Expression and Function of ABC Family Transporters at Blood-Brain Barrier under Liver Failure and Their Clinical Significances

“…Accumulating evidence [ 26 , 27 , 28 , 53 , 72 , 73 , 74 , 75 ] has demonstrated that liver failure altered the expression and function of ABC transporters at the BBB, and that the alterations were dependent on types of the developed liver failure and the species of ABC transporters. ALF rats were developed using intraperitoneal injection of thioacetamide (TAA) (300 mg/kg) for two days with a 24-h interval [ 26 , 53 ].…”

“…Furthermore, incubation with BDL rat serum significantly decreased BCRP function and protein levels in both HCMEC/D3 and MDCK-BCRP cells, indicating that some abnormal components in BDL rat serum might impair BCRP function at the BBB. BDL rats exhibited significant elevations of UCB and bile acids [ 72 ]. In vitro data showed that only incubation with 25 μmol/L UCB significantly increased the uptake of prazosin, and downregulated the expression of BCRP protein in HCMEC/D3 and MDCK-BCRP cells.…”

“…Correlation analysis revealed that the level of UCB negatively correlated with BCRP expression in the brains of BDL rats and hyperbilirubinemia rats. Two types of cells tested in vitro further demonstrated that UCB elevation in plasma of BDL rats contributed to the impaired function, and expression of BCRP at the BBB of BDL rats [ 72 ].…”