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

Abstract

This study investigated alterations in the function and expression of P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), and multidrug resistance-associated protein 2 (MRP2) at the blood–brain barrier (BBB) of acute liver failure (ALF) mice and its clinical significance. ALF mice were developed using intraperitoneal injection of thioacetamide. P-GP, BCRP, and MRP2 functions were determined by measuring the ratios of brain-to-plasma concentration of rhodamine 123, prazosin, and dinitrophenyl-S-glutathione, respectively. The mRNA and proteins expression levels of P-GP, BCRP, and MRP2 were evaluated with quantitative real-time PCR and western blot, respectively. MDCK-MDR1 and HCMEC/D3 cells were used to document the effects of the abnormally altered components in serum of ALF mice on the function and expression of P-GP. The clinical significance of alteration in P-GP function and expression was investigated by determining the distribution of the P-GP substrate phenobarbital (60 mg/kg, intravenous administration) in the brain and loss of righting reflex (LORR) induced by the drug (100 mg/kg). The results showed that ALF significantly downregulated the function and expression of both P-GP and BCRP, but increased the function and expression of MRP2 in the brain of mice. Cell study showed that increased chenodeoxycholic acid may be a reason behind the downregulated P-GP function and expression. Compared with control mice, ALF mice showed a significantly higher brain concentration of phenobarbital and higher brain-to-plasma concentration ratios. In accordance, ALF mice showed a significantly larger duration of LORR and shorter latency time of LORR by phenobarbital, inferring the enhanced pharmacological effect of phenobarbital on the central nervous system (CNS). In conclusion, the function and expression of P-GP and BCRP decreased, while the function and expression of MRP2 increased in the brain of ALF mice. The attenuated function and expression of P-GP at the BBB might enhance phenobarbital distribution in the brain and increase phenobarbital efficacy on the CNS of ALF mice.

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

“…Being different from P-GP and BCRP, the expression and function of Mrp2 at brain of ALF rats were significantly upregulated, leading to lower brain-to-plasma ratios of its substrates [ 26 ]. These findings were further confirmed in TAA-induced ALF mice [ 28 ]. Moreover, TAA-induced chronic liver failure also downregulated the expression and function of P-GP and upregulated the expression and function of Mrp2 at the BBB of rats, although BBB integrity of chronic liver failure rats was impaired [ 27 ].…”

“…Clinical trials and animal experiments have demonstrated that Alzheimer’s disease (AD) significantly downregulated the expression and function of P-GP at brain [ 19 , 20 , 21 , 22 ]. Some peripheral diseases, such as diabetes [ 23 , 24 , 25 ] and liver failure [ 26 , 27 , 28 ], also downregulated brain P-GP expression and function—enhancing pharmacological effect on CNS. Conversely, overexpression of P-GP also occurred in capillary endothelial cells of epilepsia patients [ 29 ] or epilepsia animals [ 30 ].…”

“…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 ].…”

“…Effects of several bile acids (cholic acid, deoxycholic acid, lithocholic acid, chenodeoxycholic acid, and ursodeoxycholic acid) and unconjugated bilirubin (UCB) on P-GP function and expression in HCMEC/D3 and MDCK-BCRP cells were investigated. The results showed that only chenodeoxycholic acid downregulated P-GP expression, and function in both HCMEC/D3 and MDCK-BCRP cells in a concentration-dependent manner [ 28 ]. These results indicated that increased chenodeoxycholic acid might be partly attributed to the downregulation of P-GP function and expression in brain of TAA-induced ALF rats and mice.…”

“…Transport of phenobarbital across the BBB is mediated by P-GP. TAA-induced ALF was reported to significantly increase brain concentration of phenobarbital, and brain-to-plasma concentration ratios of phenobarbital in mice—which was in consistence with the reduction of P-GP function and expression [ 28 ]. The ALF mice showed a significantly larger duration and shorter latency in the loss of righting reflex by phenobarbital, which was in line with increases in phenobarbital distribution of phenobarbital [ 28 ].…”