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Drug Metabolism and Disposition Fast Forward
First published on March 28, 2007; DOI: 10.1124/dmd.106.013862

0090-9556/07/3507-1089-1095$20.00
DMD 35:1089-1095, 2007

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Intestinal First-Pass Metabolism via Carboxylesterase in Rat Jejunum and Ileum

Kenji Masaki, Mitsuru Hashimoto, and Teruko Imai

Graduate School of Pharmaceutical Sciences, Kumamoto University, Oe-Honmachi, Kumamoto, Japan

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.

Address correspondence to: Dr. Teruko Imai, Professor, Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-Honmachi, Kumamoto, 862-0973, Japan. E-mail: iteruko{at}gpo.kumamoto-u.ac.jp






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