Adenosine Triphosphate-Binding Cassette Subfamily C Member 2 Is the Major Transporter of the Hepatobiliary Imaging Agent 99mTc-Mebrofenin
Journal of Nuclear Medicine
The organic anion 99m Tc-N-[2-[(3-bromo-2,4,6-trimethylphenyl)amino]-2-oxoethyl]-N-(carboxymethyl)-glycine ( 99m Tc-mebrofenin) and its analogs are widely used for hepatobiliary imaging. Identification of the mechanisms directing bile canalicular transport of these agents will provide insights into the basis of their hepatic handling for assessing perturbations. Methods: We performed studies in animals, including healthy Fischer 344 rats or rats treated with carbon tetrachloride or intrasplenic
... ide or intrasplenic cell transplantation and healthy Wistar rats or HsdAMC:TR-Abcc2 mutant rats in Wistar background. Onset of hepatic inflammation was verified by analysis of carbon uptake in Kupffer cells. Hepatic clearance of 99m Tc-mebrofenin was studied with dynamic imaging, and fractional retention of peak hepatic mebrofenin activity after 60 min was determined. Changes in the expression of bile canalicular transporters were analyzed by real-time polymerase chain reaction and Western blots. Results: Carbon tetrachloride and cell transplantation produced hepatic inflammation with activation of Kupffer cells, resulting in a rapid decline in the expression of the bile canalicular transporters Abcb4, Abcb11, and Abcc2. Among these transporters, decreased expression of Abcc2 was most prominent, and this decline persisted for 4 wk. Next, we examined 99m Tc-mebrofenin excretion in HsdAMC:TR-Abcc2 mutant rats (in which Abcc2 expression is naturally inactivated), compared with their healthy counterparts. In healthy HsdRccHan:WIST rats, only 23% 6 3% of the peak 99m Tc-mebrofenin activity was retained after 60 min. By contrast, in HsdAMC:TR-Abcc2 mutant rats, 73% 6 5% of the peak 99m Tc-mebrofenin activity was retained (P , 0.001). Moreover, the administration of cyclosporin A markedly inhibited 99m Tc-mebrofenin excretion in healthy rats, with no further effect on already impaired 99m Tc-mebrofenin excretion in HsdAMC:TR-Abcc2 mutant rats. Hepatic excretion of 99m Tc-mebrofenin was largely dependent on Abcc2. This molecular basis of 99m Tc-mebrofenin excretion will advance studies of pathophysiologic mechanisms in hepatic Abcc2 pathways.