Differential mRNA expression and the uptake of methotrexate in primary MAEC and MLF cells: involvement of the Abc and Slco/Oatp transporters in alveolar epithelial cell toxicity.

Drug transporters play a pivotal role in the disposition and elimination of a wide variety of organic compounds across the biological membrane of the body. Recent studies have revealed that some drug transporters are involved in drug-induced toxicity. We have previously reported that methotrexate (MTX)-induced cytotoxicity and apoptosis in primary mouse alveolar epithelial cells (MAEC) are more sensitive than primary mouse lung fibroblasts (MLF). In the present study, we investigated the mRNA expression of ABCs, Slco/Slc/Oatp transporters by RT-PCR and quantitative real-time PCR (qRT-PCR) techniques in mouse lung tissues and primary lung cells. The ABC transporters (Mdr1, Mrp1, 3, 4, 5, and Bcrp) and the Slco/Oatp transporters (Rfc, Oatp1a1, 1a4, 1a5, 1b2, 2a1, 2b1, 3a1, 4c1, and 5a1) were detected in mouse lung tissues, whereas some ABCs, Slcs/Oats, and Slco/Oatps transporters were not expressed in the mouse lung. Additionally, we found that some Abc transporters are expressed predominantly in MLF whereas Mrp3 and Oatp4c1 are expressed predominantly in MAEC. The transport activity of [(3)H]MTX mediated via MAEC was significantly higher than the MLF-mediated transport. When MLF was treated with MK571, accumulated [(3)H]MTX significantly increased when compared with MAEC. Thus, our results indicate that depending on the type of cells, several types of drug transporters are expressed in mouse lung tissues. Our results also suggest that MTX-induced fibrosis with cell dysfunction may be caused by the accumulation within the alveolar epithelial cells of MTX in the lung.