Received for publication October 18, 2005.
Revised February 2, 2006.
Accepted for publication February 13, 2006.

Oxidative metabolism of the alkaloid rutaecarpine by human cytochrome P450s

Abstract

Rutaecarpine is the main active alkaloid of the herbal medicine, Evodia rutaecarpa. To identify the major human cytochrome P450 (P450, CYP) participating in rutaecarpine oxidative metabolism, human liver microsomes and bacteria-expressed recombinant human P450 were studied. In liver microsomes, rutaecarpine was oxidized to 10-, 11-, 12-, and 3-hydroxyrutaecarpine. Microsomal 10- and 3-hydroxylation activities were strongly inhibited by ketoconazole. The 11- and 12-hydroxylation activities were inhibited by -naphthoflavone, quinidine, and ketoconazole. These results indicated that multiple hepatic CYPs including CYP1A2, CYP2D6, and CYP3A4 participate in rutaecarpine hydroxylations. Among recombinant CYPs, CYP1A1 had the highest rutaecarpine hydroxylation activities. Decreased metabolite formation at high substrate concentration indicated that there was substrate inhibition of CYP1A1- and CYP1A2-catalyzed hydroxylations. CYP1A1-catalyzed rutaecarpine hydroxylations had V_max values of 1388 ~ 1893 pmol/min/nmol P450, K_m values of 4.1 ~ 9.5 µM, and K_i values of 45 ~ 103 µM. These results indicated that more than one molecule of rutaecarpine is accessible to the CYP1A active site. The major metabolite 10-hydroxyrutaecarpine decreased CYP1A1, CYP1A2 and CYP1B1 activities with respective IC₅₀ values of 2.56 ± 0.04, 2.57 ± 0.11, and 0.09 ± 0.01 µM, suggesting that product inhibition might occur during rutaecarpine hydroxylation. The metabolite profile and kinetic properties of rutaecarpine hydroxylation by human CYPs provides important information relevant to the clinical application of rutaecarpine and E. rutaecarpa.

Key words: cytochrome P450 catalyzed oxidations, drug disposition, human CYP enzymes

This article has been cited by other articles:

				R. Kitamura, H. Asanoma, S. Nagayama, and M. Otagiri Identification of Human Liver Cytochrome P450 Isoforms Involved in Autoinduced Metabolism of the Antiangiogenic Agent (Z)-5-[(1,2-Dihydro-2-oxo-3H-indol-3-ylidene)methyl]-2,4-dimethyl-1H-pyrrole-3-propanoic Acid (TSU-68) Drug Metab. Dispos., June 1, 2008; 36(6): 1003 - 1009. [Abstract] [Full Text] [PDF]

				D. Wu and Z. Hu Rutaecarpine Induces Chloride Secretion across Rat Isolated Distal Colon J. Pharmacol. Exp. Ther., April 1, 2008; 325(1): 256 - 266. [Abstract] [Full Text] [PDF]