Abstract
The mechanism for hepatic uptake of temocaprilat, an angiotensin-converting enzyme inhibitor that is predominantly excreted into bile was studied using isolated rat hepatocytes and COS-7 cells expressing the organic anion transporting polypeptide (oatp1). The uptake of temocaprilat into isolated rat hepatocytes exhibited saturation with a Km of 20.9 μM and a Vmax of 0.21 nmol/min/mg protein. This uptake was temperature sensitive and was significantly reduced by metabolic inhibitors, a sulfhydryl-modifying reagent and an anion-exchange inhibitor, although the replacement of Na+ with Li+ in the medium did not affect the uptake. [3H]Temocaprilat uptake was inhibited by estradiol-17β-d-glucuronide and dibromosulphophthalein, typical substrates for the Na+-independent organic anion transporter, in a concentration-dependent manner, whereas excess estradiol-17β-d-glucuronide did not completely inhibit the uptake. Temocaprilat uptake into COS-7 cells transfected with oatp1 cDNA revealed a concentration-dependency with aKm of 46.7 μM, a value comparable with that obtained in isolated hepatocytes. The contribution of oatp1 to carrier-mediated hepatic uptake of temocaprilat was less than 50% by correcting the uptake clearance with that of estradiol-17β-d-glucuronide. A good linear correlation was observed for the inhibitory effect of angiotensin-converting enzyme inhibitors (benazeprilat, cilazaprilat, delaprilat and enalaprilat) between isolated hepatocytes and oatp1-expressing cells. These data suggest that oatp1, along with another transporter(s), mediates the uptake of angiotensin-converting enzyme inhibitors into rat hepatocytes.
Footnotes
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Send reprint requests to: Dr. Hitoshi Ishizuka, Analytical and Metabolic Research Laboratories, Sankyo Co., Ltd., 2-58, Hiromachi 1-chome, Shinagawa-ku, Tokyo 140, Japan.
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↵1 This work was supported in part by the Swiss National Science Foundation Grant 31-45536.95 to P.J.M.
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↵2 This work was supported in part by a grant-in-aid from the Ministry of Education, Science, Sports and Culture of Japan, and the Core Research for Evolutional Sciences and Technology of Japan Sciences and Technology Corporation.
- Abbreviations:
- ACE
- angiotensin-converting enzyme
- oatp1
- organic anion transporting polypeptide
- Ntcp
- Na+/taurocholate co-transporting polypeptide
- cMOAT
- canalicular multispecific organic anion transporter
- E217βG
- estradiol-17β-d-glucuronide
- BSP
- bromosulfophthalein
- DBSP
- dibromosulfophthalein
- DIDS
- 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid
- FCCP
- carbonyl cyanide p-(trifluoro-methoxy)phenylhydrazone
- PCMBS
- p-choloromercuriphenylsulfonic acid
- HEPES
- 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid
- SD rats
- Sprague-Dawley rats
- EHBR
- Eisai hyperbilirubinemic rats
- DMEM
- Dulbecco’s modified Eagle’s medium
- Received January 17, 1998.
- Accepted May 18, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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