Active transport of the angiotensin‐II antagonist losartan and its main metabolite EXP 3174 across MDCK‐MDR1 and Caco‐2 cell monolayers

We studied the functional interaction between transport and metabolism by comparing the transport of losartan and its active metabolite EXP 3174 (EXP) across cell monolayers. Epithelial layers of Caco‐2 cells as well as MDR1, MRP‐1 and MRP‐2 overexpressing cells, in comparison to the respective wildtypes, were used to characterize the transcellular transport of losartan and EXP. Losartan transport in MDCK‐MDR1 and Caco‐2 cells was saturable and energy‐dependent with a significantly greater basolateral‐to‐apical (B/A) than apical‐to‐basolateral (A/B) flux (ratio=31±1 in MDCK‐MDR1 and ratio 4±1 in Caco‐2 cells). The B/A flux of losartan was inhibited by cyclosporine and vinblastine, inhibitors of P‐glycoprotein and MRP. In contrast, no active losartan transport was observed in MRP‐1 or MRP‐2 overexpressing cells. The metabolite was only transported in Caco‐2 cells with a B/A‐to‐A/B ratio of 5±1, while lacking active transport in the MDR1, MRP‐1 or MRP‐2 overexpressing cells. The B/A flux of EXP was significantly inhibited by cyclosporine and vinblastine. In conclusion, losartan is transported by P‐glycoprotein and other intestinal transporters, that do not include MRP‐1 and MRP‐2. In contrast, the carboxylic acid metabolite is not a P‐glycoprotein substrate, but displays considerably higher affinity for other transporters than losartan, that again most probably do not include MRP‐1 and MRP‐2. British Journal of Pharmacology (2000) 129, 1235–1243; doi:10.1038/sj.bjp.0703150