Abstract
To determine the activity of a major intestinal esterase in the first-pass hydrolysis of O-isovaleryl-propranolol (isovaleryl-PL), a model ester compound, rat intestinal jejunum and blood vessels were perfused simultaneously after inhibition of a carboxylesterase (CES) by bis-p-nitrophenyl phosphate (BNPP). BNPP specifically inhibits approximately 90% of CES activity without influencing aminopeptidase activity or the transport of l-leucyl-p-nitroanilide and p-nitroaniline, nonester compounds. When isovaleryl-PL was perfused into the jejunal lumen after BNPP treatment, its absorption clearance (7.60 ± 0.74 μl/min) increased approximately 3-fold compared with control, whereas its degradation clearance (32.5 ± 5.40 μl/min) decreased to 23% of control. Therefore, CES seems to be mainly responsible for the intestinal first-pass hydrolysis of isovaleryl-PL. This finding is consistent with the results from studies of in vitro BNPP inhibition in the mucosal S9 fraction. Vmax values for valeryl-PL, isovaleryl-PL, and p-nitrophenyl acetate in the jejunal S9 fraction were 1.7- to 2.5-fold higher than that in the ileal S9 fraction, which agreed with the jejunum/ileum ratio (approximately 1.5-fold) of mRNA expression levels for the CES2 isozymes, AB010635 and AY034877. These findings indicated that CESs expressed in the intestine markedly contribute to first-pass hydrolysis in both jejunum and ileum.
Footnotes
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This work was supported in part by a Grant-in-Aid for Scientific Research (16590085) from the Japan Society for the Promotion of Science.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.106.013862.
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ABBREVIATIONS: P450, cytochrome P450; CES, carboxylesterase; PL, propranolol; PNPA, p-nitrophenyl acetate; BBM, brush border membrane; BNPP, bis-p-nitrophenyl phosphate; HPLC, high-performance liquid chromatography; l-Leu-p-NA, l-leucyl-p-nitroanilide; MES, 2-(N-morpholino)ethanesulfonic acid; BSA, bovine serum albumin; FD-4, fluorescein isothiocyanate dextran 4000; DMSO, dimethyl sulfoxide; RT, reverse transcription; PCR, polymerase chain reaction.
- Received November 13, 2006.
- Accepted March 27, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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