Cytochrome P450 isoenzymes involved in rat liver microsomal metabolism of californine and protopine

Studies are described on the cytochrome P450 (CYP) isoenzyme dependence of the main metabolic steps of the Eschscholtzia californica alkaloids californine and protopine using rat liver microsomes. Preparations of E. californica are in use as phytopharmaceuticals and as herbal drugs of abuse. CYP isoenyzme dependences were studied using specific chemical inhibitors for CYP1A2, CYP2D1, and CYP3A2 (alpha-naphthoflavone, quinine, and ketoconazole, respectively). CYP2C11 was inhibited by specific antibodies for lack of specific chemical inhibitors. Californine N-demethylation was mainly catalyzed by CYP3A2 and to a minor extent by CYP1A2 and CYP2D1, but not by CYP2C11. CYP2D1 and CYP2C11 were shown to be mainly involved in demethylenation of both, californine and protopine, while CYP1A2 and CYP3A2 showed only minor contribution. Kinetic parameters of the reactions were established. K-m and V-max values for the californine N-dernethylation were 4.5 +/- 4.7 muM and 22.9 +/- 13.7 min/mg protein (high affinity) and 161.3 +/- 16.7 muM and 311.8 +/- 39.4 min/mg protein (low affinity), respectively. Californine demethylenation and protopine demethylenation showed substrate inhibition and K-m and V-max values were 5.0 +/- 0.5 and 7.1 +/- 0.6 muM and 83.3 +/- 2.6 and 160.7 +/- 4.0 min/mg protein, respectively. (C) 2003 Elsevier B.V. All rights reserved.