UPTAKE OF THE MYCOTOXIN OCHRATOXIN-A IN LIVER-CELLS OCCURS VIA THE CLONED ORGANIC ANION TRANSPORTING POLYPEPTIDE

Ochratoxin A (OTA) is a mycotoxin produced by mold. It mainly causes n ephropathies in humans and domestic animals as a major pathogenic cont aminant of cereals and animal feed. Upon p.o. uptake and intestinal ab sorption, a large part of OTA is taken up by hepatocytes and eliminate d into bile. In the present study, hepatocellular uptake of radiolabel ed [H-3]OTA in isolated rat hepatocytes was characterized; a saturable (K-m = 18.9 mu M, V-max = 473 pmol/mg/min), temperature (A(app) = 30. 4 and 76.6 kilo Joule/mol) and energy-dependent mycotoxin transport wa s found. This OTA uptake was inhibited by various bile acids, sulfobro mophthalein and the thrombin inhibitor CRC 220. Because all inhibitors are substrates of the organic aniontransporting polypeptide (oatp), a recently cloned hepatic carrier, uptake experiments were performed in oatp-cRNA-injected Xenopus laevis oocytes. These studies revealed an oatp-specific OTA uptake (K-m = 16.6 mu M). In contrast, OTA was not t ransported by the hepatic Na+/taurocholate-cotransporting polypeptide. Known oatp substrates cis-inhibited OTA uptake in oatp-cRNA-injected oocytes in close correlation with the results derived from isolated he patocytes. These results identify OTA as a new substrate for oatp. The y further support the multispecific nature of oatp-mediated transport and stress the importance of this carrier for hepatic clearance of xen obiotics.