Adenosine triphosphate-binding cassette subfamily C member 2 is the major transporter of the hepatobiliary imaging agent (99m)Tc-mebrofenin.
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 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% +/- 3% of the peak (99m)Tc-mebrofenin activity was retained after 60 min. By contrast, in HsdAMC:TR-Abcc2 mutant rats, 73% +/- 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.
Bhargava
Kuldeep K
KK
Division of Nuclear Medicine and Molecular Imaging, North Shore-Long Island Health System, New Hyde Park, New York, USA.
Joseph
Brigid
B
Ananthanarayanan
Meenakshisundaram
M
Balasubramaniyan
Natarajan
N
Tronco
Gene G
GG
Palestro
Christopher J
CJ
Gupta
Sanjeev
S
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000814:Aniline Compounds; D000818:Animals; D002251:Carbon Tetrachloride; D005998:Glycine; D007098:Imino Acids / Q000493:pharmacokinetics*; D008099:Liver / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008106:Liver Cirrhosis, Experimental / Q000139:chemically induced / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics*; D011877:Radionuclide Imaging; D051381:Rats; D011916:Rats, Inbred F344; D017208:Rats, Wistar; D014018:Tissue Distribution
D018528:ATP-Binding Cassette Transporters; C423013:Abcc2 protein, rat; D000814:Aniline Compounds; D007098:Imino Acids; D015609:Organotechnetium Compounds; D002251:Carbon Tetrachloride; C034837:technetium Tc 99m mebrofenin; D005998:Glycine