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

1 We studied the functional interaction between transport and metabolism by comparing the transport of losartan and its active metabolite EXP 3174 (EX P) across cell monolayers. 2 Epithelial layers of Caco-2 cells as well as MDR1, MRP-1 and MRP-2 overex pressing cells, in comparison to the respective wildtypes, were used to cha racterize the transcellular transport of losartan and EXP. 3 Losartan transport in MDCK-MDR1 and Caco-2 cells was saturable and energy -dependent with a significantly greater basolateral-to-apical (B/A) than ap ical-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 cyclospori ne and vinblastine, inhibitors of P-glycoprotein and MRP. In contrast, no a ctive losartan transport was observed in MRP-I or MRP-2 overexpressing cell s. 4 The metabolite was only transported in Caco-2 cells with a B/A-to-A/B rat io of 5 +/- 1, while lacking active transport in the MDR1, MRP-1 or MRP-2 o verexpressing cells. The B/A flux of EXP was significantly inhibited by cyc losporine and vinblastine. 5 In conclusion, losartan is transported by P-glycoprotein and other intest inal transporters, that do not include MRP-1 and MRP-2. In contrast, the ca rboxylic acid metabolite is not a P-glycoprotein substrate, but displays co nsiderably higher affinity for other transporters than losartan, that again most probably do not include MRP-1 and MRP-2.