Abstract
Involvement of LST-1 (a human liver-specific transporter, also called OATP2) as the major transporter in the uptake of pravastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, by human liver was demonstrated. The hepatic uptake of pravastatin evaluated using human hepatocytes was Na+-independent and reached saturation with a Michaelis constant (Km) of 11.5 ± 2.2 μM. The uptake of pravastatin was temperature-dependent and was inhibited by estradiol-17β-d-glucuronide, taurocholic acid, bromosulfophthalein, and simvastatin acid, but not byp-aminohippurate. Estradiol-17β-d-glucuronide competitively inhibited pravastatin uptake with an inhibition constant comparable to theKm value for estradiol-17β-d-glucuronide transport, indicating that a common transporter mediates the transport of pravastatin and estradiol-17β-d-glucuronide in human hepatocytes. The results obtained with human hepatocytes agreed with those obtained with LST-1 expressing Xenopus oocytes. Oocytes microinjected with human liver polyadenylated mRNA showed Na+-independent uptake of pravastatin and estradiol-17β-d-glucuronide. A simultaneous injection of LST-1 antisense oligonucleotides completely abolished this uptake. Expression of LST-1 was immunohistochemically demonstrated in the human hepatocytes, but not in Hep G2 cells, which showed very low uptake of pravastatin. Therefore, LST-1 was regarded as a key molecule for pravastatin in liver-specific inhibition of cholesterol synthesis, making pravastatin accessible to the target enzyme, which would otherwise not be inhibited by this hydrophilic drug.
Footnotes
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Send reprint requests to: Dr. Taro Tokui, Drug Metabolism and Pharmacokinetics Research Laboratories, Sankyo Co., Ltd., 2-58 Hiromachi, Shinagawa-ku, Tokyo, 140-8710, Japan. E-mail:tokuit{at}shina.sankyo.co.jp
- Abbreviations:
- HMG-CoA
- 3-hydroxy-3-methylglutaryl coenzyme A
- OATP2
- organic anion transporting polypeptide 2
- LST-1
- human liver-specific organic anion transporter
- KHL
- keyhole limpet hemocyanin
- Km
- Michaelis constant
- Vmax
- maximum uptake rate
- Pdif
- nonspecific uptake clearance
- Ki
- inhibition constant
- Received October 19, 2000.
- Accepted January 2, 2001.
- The American Society for Pharmacology and Experimental Therapeutics