Hepatobiliary transport of a nonpeptidic endothelin antagonist, (+)-(5S,6R,7R)-2-butyl-7-[2((2S)-2-carboxypropyl)-4-methoxyphenyl]-5-(3,4-methylenedioxyphenyl) cyclopentenol[1,2-b]pyridine-6-carboxylic acid: uptake by isolated rat hepatocytes and canalicular membrane vesicles.
OBJECTIVE
Hepatobiliary excretions of drugs from the blood to the bile include two essential transmembrane processes: uptake into hepatocytes and secretion from hepatocytes. The purpose of this study was to clarify the transport mechanisms underlying these processes for a new non-peptide endothelin antagonist, (+)-(5S,6R,7R)-2-butyl-7-[2((2S)-2-carboxypropyl)-4-methoxyphenyl]-5-(3,4-methylenedioxy-phenyl)cyclopentenol[1,2-b]pyridine-6-carboxylic acid (J-104132).


METHODS
Biliary excretion of J-104132 was assessed in rats after intravenous injection. To evaluate the hepatic uptake process, J-104132 was incubated with freshly isolated rat hepatocytes and the uptake of J-104132 was calculated. To evaluate the biliary secretion process, the uptake of J-104132 into rat canalicular membrane vesicles that were isolated from normal Sprague-Dawley rats or Eisai hyperbilirubinemic rats was measured.


RESULTS
After intravenous injection, J-104132 was recovered from the bile quantitatively (99.7 +/- 1.3%) as its intact form. J-104132 was taken up by isolated rat hepatocytes in a time- and temperature-dependent manner. The uptake was saturable with Km and Vmax of 5.7 microM and 564 pmol/min/10(6) cells, respectively. The uptake was Na+ independent and was reduced in the presence of ATP depleters (rotenone and carbonyl cyanide-p-(trifluoromethoxy)-phenylhydrazone), organic anions (dibromosulfophthalein, indocyanine green, BQ-123, and pravastatin), and bile acids (taurecholate and cholate). In Sprague-Dawley rats, J-104132 was taken up by canalicular membrane vesicle ATP-dependently with Km and Vmax values of 6.1 microM and 552 pmol/min/mg protein, respectively. However, ATP-dependent uptake disappeared in Eisai hyperbilirubinemic rats.


CONCLUSIONS
These data suggest that energy-dependent and carrier-mediated transport systems play important roles in hepatobiliary excretion of J-104132 (both uptake and secretion processes), which is the main excretion route in rats. As for the secretion process of J-104132, an involvement of mrp2 was demonstrated.
Kobayashi
Naoko
N
Drug Metabolism, Tsukuba Research Institute, Banyu Pharmaceutical Co., Ltd., 3 Okubo, Tsukuba, Ibaraki 300-2611, Japan.
Tani
Takeshi
T
Hisaka
Akihiro
A
Hara
Ken-ichi
K
Yasumori
Toshio
T
D000818:Animals; D001648:Bile Canaliculi / Q000378:metabolism; D001659:Biliary Tract / Q000166:cytology / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D016232:Endothelins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D011725:Pyridines / Q000737:chemistry / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley
D016232:Endothelins; D011725:Pyridines; C119319:J 104132