Characterization of uptake of folates by rat and human blood-brain barrier endothelial cells

This study aimed to characterize 3H-folic acid ( 3H-FA) and 14C-methyltetrahydrofolic acid ( 14C-MTHF) uptake by rat (RBE4) and human (hCMEC/D3) blood-brain barrier (BBB) endothelial cell lines. Uptake of 3H-FA and 14C-MTHF by RBE4 cells was time dependent and linear for the first 2 min of incubation; uptake by hCMEC/D3 cells showed a less marked time-dependency and a greater experimental variability. So, further experiments were performed in RBE4 cells only. Uptake of 3H-FA was stimulated at acidic and alkaline pH, Na+ dependent, stimulated when F- substituted for Cl-, energy independent, inhibited by premetrexed, stimulated by cytochalasin D, and unaffected by MTHF, DIDS, SITS, methotrexate, monensin, and FA. Uptake of 14C-MTHF was found to be pH-, Na+-, Cl --and energy independent, inhibited by premetrexed and methotrexate, stimulated by cytochalasin D, and unaffected by FA, DIDS, SITS, monensin, and MTHF. RT-PCR analysis showed mRNA expression of reduced folate transporter (RFC), but neither of FRα nor of proton-coupled folate transporter (PCFT) in RBE4 cells, and mRNA expression of RFC and PCFT, but not of FRα, in hCMEC/D3 cells. In conclusion, both human and rat BBB endothelial cells show little capacity for 3H-FA and 14C-MTHF apical uptake. Hence, these cell lines do not appear to be a good model to study the transport of folates at the BBB. © 2010 International Union of Biochemistry and Molecular Biology, Inc.