Bile duct ligation enhances AZT CNS toxicity partly by impairing the expression and function of BCRP in rat brain.

Breast cancer resistance protein (BCRP) is one of ATP-binding cassette (ABC) transporters in brain microvessel endothelial cells that transport their substrates from brain to blood, thus limiting substrates to crossing into brain through blood-brain barrier. Our previous works show that bile duct ligation (BDL) impairs expression and function of brain BCRP in rats. Since zidovudine (AZT) is BCRP substrate, we investigated whether impaired expression and function of BCRP increased brain distribution and toxicity of AZT in BDL-D7 rats. After administration of AZT (10 mg/kg, i.v.), BDL markedly increased brain AZT concentrations, compared with sham-operated (SO) rats. The ratio of AZT brain-to-plasma area under concentration curve (AUC) in BDL rats was increased to 1.6-folds of SO rats. After treatment with AZT (100 mg/kg every day, i.v.) for 7 days, BDL significantly impaired cognitive functions compared with SO rats, evidenced by the significantly decreased percentage of alternation in Y-maze test and prolonged escaped latency in two-way passive avoidance trial. Furthermore, AZT treatment caused significant decrease in copies of mitochondrial DNA and mitochondrial membrane potential in hippocampus of BDL rats. Moreover, AZT treatment caused a significant decrease of cortex microtubule-associated protein 2 and hippocampus synaptophysin levels in BDL rats. AZT-induced CNS adverse alterations in BDL rats were not observed in SO rats treated with AZT. In conclusion, BDL decreases the function and expression of brain BCRP in rats, leading to increased brain distribution of AZT, which in turn enhances AZT CNS toxicity, leading to mitochondrial dysfunction, neuronal damage, and ultimately cognitive dysfunction.

Simultaneously predict pharmacokinetic interaction of rifampicin with oral versus intravenous substrates of cytochrome P450 3A/P­glycoprotein to healthy human using a semi-physiologically based pharmacokinetic model involving both enzyme and transporter turnover.

Several reports demonstrated that rifampicin affected pharmacokinetics of victim drugs following oral more than intravenous administration. We aimed to establish a semi-physiologically based pharmacokinetic (semi-PBPK) model involving both enzyme and transporter turnover to simultaneously predict pharmacokinetic interaction of rifampicin with oral versus intravenous substrates of cytochrome P450 (CYP) 3A4/P­glycoprotein (P-GP) in human. Rifampicin was chosen as the CYP3A /P-GP inducer. Thirteen victim drugs including P-GP substrates (digoxin and talinolol), CYP3A substrates (alfentanil, midazolam, nifedipine, ondansetron and oxycodone), dual substrates of CYP3A/P-GP (quinidine, cyclosporine A, tacrolimus and verapamil) and complex substrates (S-ketamine and tramadol) were chosen to investigate drug-drug interactions (DDIs) with rifampicin. Corresponding parameters were cited from literatures. Before and after multi-dose of oral rifampicin, the pharmacokinetic profiles of victim drugs for oral or intravenous administration to human were predicted using the semi-PBPK model and compared with the observed values. Contribution of both CYP3A and P-GP induction in intestine and liver by rifampicin to pharmacokinetic profiles of victim drugs was investigated. The predicted pharmacokinetic profiles of drugs before and after rifampicin administration accorded with the observations. The predicted pharmacokinetic parameters and DDIs were successful, whose fold-errors were within 2. It was consistent with observations that the DDIs of rifampicin with oral victim drugs were larger than those with intravenous victim drugs. DDIs of rifampicin with CYP3A or P-GP substrates following oral versus intravenous administration to human were successfully predicted using the developed semi-PBPK model.