Transport of gabapentin by LAT1 (SLC7A5)

Gabapentin is used in the treatment of epilepsy and neuropathic pain. Gabapentin has high and saturable permeability across the BBB, but no mechanistic studies underpinning this process have been reported. The aim of the current study was to investigate the transport of gabapentin in a model of the BBB, identify the important drug transporter(s) and to use mathematical modelling to quantify the processes involved. A human brain endothelial cell line (hCMEC/D3) was utilised as an in-vitro model of the BBB. Uptake of radiolabeled gabapentin into cells in the presence of chemical inhibitors, siRNA or overexpressed drug transporters of interest was investigated. Gabapentin was demonstrated to be a LAT1 substrate in brain endothelial cells (LAT1-process; K-m = 530 mu M and V-max = 7039 pmoles/million cells/min versus other-processes; K-m = 923 mu M and V-max = 3656 pmoles/million cells/min) and in transfected HEK 293 LAT1 cells (LAT1-process; K-m = 217 mu M and V-max = 5192 pmoles/million cells/min versus other-processes; K-m = 1546 mu M and V-max = 3375 pmoles/million cells/min). At physiological concentrations of gabapentin, LAT1 mediated transport was 3 or similar to 10-fold higher than the other transport processes in the two systems, respectively, demonstrating clear selectivity for gabapentin. In-silico structural homology modelling confirmed that LAT1 could have the LeuT conserved fold and functions by the alternative access mechanism. Mathematical modelling of this mechanism revealed revised significance of V-max and K-m so that a low K-m may not necessarily imply a high affinity transport process. Gabapentin was negative for OCT like transport and LAT2 activity in the hCMEC/D3 and OCT1 transfected cells. Our data shows that gabapentin is a substrate for the influx transporter LAT1 at therapeutic concentrations. (C) 2013 Elsevier Inc. All rights reserved.