Temocaprilat, a Novel Angiotensin-Converting Enzyme Inhibitor, is Excreted in Bile via an ATP-dependent Active Transporter (cMOAT) That is Deficient in Eisai Hyperbilirubinemic Mutant Rats (EHBR)
- Hitoshi Ishizuka1,
- Kumiko Konno1,
- Hideo Naganuma1,
- Kunihiro Sasahara1,
- Yukinori Kawahara1,
- Kayoko Niinuma2,
- Hiroshi Suzuki2 and
- Yuichi Sugiyama2
- 1Analytical and Metabolic Research Laboratories (H.I., K.K., H.N., K.S., Y.K.), Sankyo Co., Ltd., Tokyo, Japan and the 2Faculty of Pharmaceutical Sciences (K.N., H.S., Y.S.), The University of Tokyo, Tokyo, Japan
Abstract
Temocapril · HCl (α-{(2S,6R)-6-[(1S)-1-ethoxy-carbonyl-3-phenyl-propyl]amino-5-oxo-2-(2-thienyl)perhydro-1,4-thiazepin-4yl}acetic acid hydrochloride) is a novel prodrug of an angiotensin-converting enzyme (ACE) inhibitor. Unlike many other ACE inhibitors, its pharmacologically active metabolite,temocaprilat, is excreted predominantly in bile. To investigate the mechanism for the biliary excretion of temocaprilat, we performed in vivo and in vitro experiments using mutant Eisai hyperbilirubinemic rats EHBR) whose canalicular multispecific organic anion transporter (cMOAT) is hereditarily defective. Biliary clearance of temocaprilat after i.v. administration of [14C]temocapril · HCl (1.0 mg/kg) in EHBR was significantly lower than that in Sprague-Dawley rats (5.00 ml/min/kg for Sprague-Dawley rats vs. 0.25 ml/min/kg for EHBR). The uptake of temocaprilat into canalicular membrane vesicles (CMVs) prepared from Sprague-Dawley rats was stimulated in the presence of ATP, whereas little stimulation was observed in CMVs from EHBR. The initial uptake rate of ATP-dependent transport of temocaprilat showed saturation kinetics; we obtained an apparentV max value of 1.14 nmol/min/mg protein and aKm value 92.5 μM. ATP-dependent transport of temocaprilat was competitively inhibited by 2,4-dinitrophenyl-S-glutathione, a typical substrate for cMOAT with an inhibition constant (Ki) of 25.8 μM. The Km value for the uptake of 2,4-dinitrophenyl-S-glutathione into CMVs (Km = 29.6 μM) was consistent with thisKi value. In addition, the ATP-dependent uptake of 2,4-dinitrophenyl-S-glutathione was inhibited by temocaprilat in a concentration-dependent manner. Active forms of some ACE inhibitors (benazepril, cilazapril, delapril, enalapril and imidapril) did not affect the transport of temocaprilat into CMVs even at concentrations as high as 200 μM. These data suggest that temocaprilat is effectively excreted in bile via cMOAT that is deficient in EHBR and that many of other ACE inhibitors have low affinity for cMOAT.
Footnotes
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Send reprint requests to: Hitoshi Ishizuka, Analytical and Metabolic Research Laboratories, Sankyo Co., Ltd., 2-58, Hiromachi 1-chome, Shinagawa-ku, Tokyo 140, Japan.
- Abbreviations:
- cMOAT
- canalicular multispecific organic anion transporter
- CMVs
- canalicular membrane vesicles
- SDR
- Sprague-Dawley rats
- EHBR
- Eisai hyperbilirubinemic rats
- DNP-SG
- 2,4-dinitrophenyl-S-glutathione
- ACE
- angiotensin-converting enzyme
- ALP
- alkaline phosphatase
- LAP
- leucine aminopeptidase
- γ-GTPase
- γ-glutamyl transpeptidase
- Cmax
- maximum concentration
- AUC
- area under the curve
- Tmax
- time to maximum concentration
- CLbile
- biliary clearance
- DBSP
- dibromosulfophthalein
- ICG
- indocyanine green
- LG
- liquiritigenin
- E3040
- 6-hydroxy-5, 7-dimethyl-2-methylamino-4-(3-pyridylmethyl) benzothiazole
- hMRP
- human multidrug resistance-associated protein
- ABC
- ATP-binding cassette
- PCR
- polymerase chain reaction
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- Received July 9, 1996.
- Accepted November 8, 1996.
- The American Society for Pharmacology and Experimental Therapeutics
