title: Recombinant cytochrome P450 2D18 metabolism of dopamine and arachidonic acid.
abstract: The function of cytochrome P450 (P450) in the mammalian brain is not well understood. In an effort to further this understanding, this study identifies two endogenous substrates for P450 2D18. Previous reports have shown that this isoform is expressed in the rat brain, and the recombinant enzyme catalyzes the N-demethylation of the antidepressants imipramine and desipramine. By further examining the substrate profile of P450 2D18, inferences can be made as to potential endogenous P450 substrates. Herein we demonstrate the metabolism of the central nervous system-acting compounds chlorpromazine and chlorzoxazone with turnover numbers of 1.8 and 0. 9 nmol/min/nmol, respectively. Because the four aforementioned pharmaceutical substrates work by binding to neurotransmitter receptors, binding assays and oxidation reactions were performed to test whether dopamine is a substrate for P450 2D18. These data indicate a K(S) value of 678 microM and that P450 2D18 can support the oxidation of dopamine to aminochrome through a peroxide-shunt mechanism. We also report the P450 2D18-mediated omega-hydroxylation and epoxygenation of arachidonic acid, primarily leading to the formation of 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids, compounds that have been shown to have vasoactive properties in brain, kidney, and heart tissues. The data presented herein suggest a possible role for P450 involvement in membrane and receptor regulation via epoxyeicosatrienoic acid formation and a potential involvement of P450 in the oxidation of dopamine to reactive oxygen species under aberrant physiological conditions where the sequestering of dopamine becomes compromised, such as in Parkinson's disease.
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Texas Medical School, Houston 77225, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Thompson
authors.forename: J H
authors.initials: JH
authors.lastname: Capdevila
authors.forename: H W
authors.initials: HW
authors.lastname: Strobel
mesh_terms: D000818:Animals; D014150:Antipsychotic Agents / Q000737:chemistry; D016718:Arachidonic Acid / Q000737:chemistry* / Q000378:metabolism; D001189:Aryl Hydrocarbon Hydroxylases; D001921:Brain / Q000378:metabolism; D002746:Chlorpromazine / Q000737:chemistry; D002753:Chlorzoxazone / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry* / Q000378:metabolism; D004298:Dopamine / Q000737:chemistry*; D005978:Glutathione / Q000737:chemistry; D006900:Hydroxylation; D066298:In Vitro Techniques; D045563:Indolequinones; D007211:Indoles / Q000032:analysis; D007700:Kinetics; D008054:Lipid Peroxides / Q000737:chemistry; D009125:Muscle Relaxants, Central / Q000737:chemistry; D010084:Oxidation-Reduction; D011485:Protein Binding; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D014150:Antipsychotic Agents; D045563:Indolequinones; D007211:Indoles; D008054:Lipid Peroxides; D009125:Muscle Relaxants, Central; D011994:Recombinant Proteins; D016718:Arachidonic Acid; C091584:aminochrome 1; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C115670:Cyp2d4 protein, rat; D005978:Glutathione; D002753:Chlorzoxazone; D002746:Chlorpromazine; D004298:Dopamine