Mechanisms for Transport of Methotrexate across Apical and Basolateral Membranes in Human Intestinal Epithelial Caco-2 Cells

To investigate the intestinal absorption mechanisms of methotrexate,we examined the apical uptake and transcellular transport of the drug in human intestinal epithelial Caco-2 cells.In these cells,the mRNA expression of proton-coupled folate transporter (PCFT) was much higher than that of reduced folate carrier (RFC).The apical uptake of 1μM methotrexate by Caco-2 cells grown on plastic dishes was markedly increased by acidification (pH 6.5→4.citation=5)of the apical medium,and diminished at a low temperature (4°C).The transcellular transport of 1μM methotrexate across Caco-2 cell monolayers grown on porous membrane filters was only slightly greater in the apical-to-basolateral direction than in the opposite direction.Pharmacokinetic analysis of the transcellular transport revealed that the influx clearance of methotrexate at the apical membrane was greater than that at the basolateral membrane,with significant gradual decreases in the low concentration range (1→10μM).On the other hand,the efflux clearance of methotrexate was much lower than the influx clearance at both apical and basolateral membranes.These findings indicated that high-affinity PCFT was involved in the uptake of methotrexate across the apical membrane in Caco-2 cells,and that there was little or no efflux of the drug at the basolateral membrane.