Comparison of blood–brain barrier permeability assays: in situ brain perfusion, MDR1-MDCKII and PAMPA-BBB

Permeability data from MDR1-MDCKII and PAMPA-BBB assays were compared to data from in situ brain perfusion to evaluate the accuracy of in vitro assays in predicting in vivo blood-brain barrier (BBB) permeability. PAMPA-BBB significantly correlated to in situ brain perfusion, however, MDR1-MDCKII had no correlation with in situ brain perfusion. PAMPA-BBB also significantly correlated with MDR1-MDCKII. The differential correlation of PAMPA-BBB and MDR1-MDCKII to in situ brain perfusion appears to be mainly due to the difference in membrane characteristics rather than binding to brain tissue. The MDR1-MDCKII cell membrane has lower ratios of: phospholipid to cholesterol, unsaturated to saturated acyl chains, and phosphatidyl-choline (PC) to sphingomyelin (SM) than brain endothelial cells, making it a poor passive permeability model for BBB. The BBB is more hydrophobic, rigid, and less fluidic than MDR1-MDCKII cell membrane. PAMPA-BBB more closely matches the BBB membrane in these characteristics and is a more accurate passive diffusion permeability model for BBB than MDR1-MDCKII. PAMPA-BBB is high throughput, low cost and has good prediction of in vivo BBB permeability, and therefore, it is a valuable tool in drug discovery to screen compounds for the rate of brain penetration.