Reduced folate carrier-mediated methotrexate transport in human distal lung epithelial NCl-H441 cells

OBJECTIVES: We had previously found that reduced folate carrier (RFC; SLC19A1) is mainly involved in an influx of transport of methotrexate (MTX), a folate analogue, using alveolar epithelial A549 cells. Therefore, we examined MTX uptake in NCl-H441 (H441) cells, another in vitro alveolar epithelial model, focusing on the localization of RFC in the present study. METHODS: H]MTX. KEY FINDINGS: The uptake of MTX was increased remarkably after pretreatment of the cell monolayer with ethylenediaminetetraacetic acid (EDTA) in H441 cells but not in A549 cells, indicating the contribution of the basolaterally located transporter. In addition, folic acid and thiamine monophosphate, RFC inhibitors, inhibited the uptake of MTX from the basolateral side of the H441 cells. In order to compare the function of RFC on the apical and basolateral sides of the cells, the uptake of MTX from each side was examined using a Transwell chamber. Intracellular MTX amounts from the basolateral side were found to be significantly higher than those from the apical side. CONCLUSIONS: These findings suggest that the distribution of MTX in the lung alveolar epithelial cells may be mediated by basolaterally located RFC in alveolar epithelial cells.