Received for publication August 4, 2004.
Revised May 6, 2005.
Accepted for publication May 10, 2005.

Functional involvement of rat organic anion transporter 2 (Slc22a7) in the hepatic uptake of the non-steroidal anti-inflammatory drug, ketoprofen

Abstract

Rat organic anion transporter 2 (rOat2, Slc22a7) is a sinusoidal multispecific organic anion transporter in the liver. The role of rOat2 in the hepatic uptake of drugs has not been thoroughly investigated yet. rOat2 substrates include non-steroidal anti-inflammatory drugs, such as ketoprofen, indomethacin and salicylate. In the present study, the uptake of ketoprofen, indomethacin and salicylate by freshly isolated rat hepatocytes was characterized. The uptake of ketoprofen, indomethacin and salicylate by hepatocytes was sodium-independent, and the rank order of their uptake activities was indomethacin > ketoprofen > salicylate. Kinetic analysis based on Akaike's Information Criterion suggested that the uptake of ketoprofen and indomethacin by hepatocytes consists of two saturable components and one non-saturable one. The K_m and V_max values for the high and low affinity components for ketoprofen uptake were 0.84 and 97 µM, and 35 and 1800 pmol/min/mg protein, respectively, while those for indomethacin were 1.1 and 140 µM, and 130 and 16000 pmol/min/mg protein, respectively. The K_m values of the high affinity component were similar to those for rOat2 (3.3 and 0.37 µM for ketoprofen and indomethacin, respectively). The uptake of ketoprofen by hepatocytes was significantly inhibited by probenecid and rOat2 inhibitors (indocyanine green, indomethacin, glibenclamide and salicylate). Other inhibitors of rOatps (taurocholate and pravastatin) and rOat3 (pravastatin and p-aminohippurate) had a slight effect, but digoxin had no effect. These results suggest that rOat2 accounts partly for the hepatic uptake of ketoprofen and, presumably, indomethacin as a high affinity site, and that other transporters, such as rOatps, but not rOatp2, and rOat3, are also involved.

Key words: hepatic uptake, hepatocytes, non-steroidal anti-inflammatory drugs, organic anion transport, transporters