Adenosine Triphosphate–Binding Cassette Subfamily C Member 2 Is the Major Transporter of the Hepatobiliary Imaging Agent 99mTc-Mebrofenin
Kuldeep K. Bhargava 1,
Brigid Joseph 2,
Meenakshisundaram Ananthanarayanan 3,
Natarajan Balasubramaniyan 3,
Gene G. Tronco 1,
Christopher J. Palestro 1,
and
Sanjeev Gupta 2*
1 Division of Nuclear Medicine and Molecular Imaging, North Shore–Long Island Health System, New Hyde Park, New York and Albert Einstein College of Medicine, Bronx, New York; Bronx, New York
2 Departments of Medicine and Pathology, Marion Bessin Liver Research Center, Cancer Research Center, Diabetes Center and Institute for Clinical and Translational Research, Jack and Pearl Resnick Campus, Albert Einstein College of Medicine, Bronx, New York
3 Department of Pediatrics, Mount Sinai School of Medicine, New York, New York
* To whom correspondence should be addressed. E-mail: sanjvgupta{at}pol.net.
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Abstract |
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The organic anion 99mTc-N-[2-[(3-bromo-2,4,6-trimethylphenyl)-amino]-2-oxoethyl]-N-(carboxymethyl)-glycine (99mTc-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 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 99mTc-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 99mTc-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% ± 3% of the peak 99mTc-mebrofenin activity was retained after 60 min. By contrast, in HsdAMC:TR-Abcc2 mutant rats, 73% ± 5% of the peak 99mTc-mebrofenin activity was retained (P < 0.001). Moreover, the administration of cyclosporin A markedly inhibited 99mTc-mebrofenin excretion in healthy rats, with no further effect on already impaired 99mTc-mebrofenin excretion in HsdAMC:TR-Abcc2 mutant rats. Hepatic excretion of 99mTc-mebrofenin was largely dependent on Abcc2. This molecular basis of 99mTc-mebrofenin excretion will advance studies of pathophysiologic mechanisms in hepatic Abcc2 pathways.
Key Words:
canalicular, gene, liver, 99mTc-mebrofenin, transport
