Distribution, properties, and inhibitor sensitivity of zebrafish catechol-O-methyl transferases (COMT)

Abstract

Catechol-O-methyltransferase (COMT; EC 2.1.1.6) is an enzyme with multiple functions in vertebrates. COMT methylates and thus inactivates catecholamine neurotransmitters and metabolizes xenobiotic catechols. Gene polymorphism rs4680 that influences the enzymatic activity of COMT affects cognition and behavior in humans. The zebrafish is widely used as an experimental animal in many areas of biomedical research, but most aspects of COMT function in this species have remained uncharacterized. We hypothesized that both comt genes play essential roles in zebrafish. Both comt-a and comt-b were widely expressed in zebrafish tissues, but their relative abundance varied considerably. Homogenates of zebrafish organs, including the brain, showed enzymatic COMT activity that was the highest in the liver and kidney. Treatment of larval zebrafish with the COMT inhibitor Ro41-0960 shifted the balance of catecholamine metabolic pathways towards increased oxidative metabolism. Whole-body concentrations of dioxyphenylacetic acid (DOPAC), a product of dopamine oxidation, were increased in the inhibitor-treated larvae, although the dopamine levels were unchanged. Thus, COMT is likely to participate in the processing of catecholamine neurotransmitters in the zebrafish, but the inhibition of COMT in larval fish is compensated efficiently and does not have pronounced effects on dopamine levels.

Keywords: 3-MT—3-methoxytyramine (1669); 5-HIAA—5-hydroxindoleacetic acid (1826); BCA—bicinchoninic acid (71068); BCIP—5-bromo-4-chloro-3-indolylphosphate (65409); Brain; CHRM1—cholinergic receptor muscarinic 1; COMT; DHBAC—dihydroxybenzylacetic acid (72); DIG—digoxigenin (15478); DOPAC—dihydroxyphenylacetic acid (547); Dopamine; Enzyme activity; GAD67—glutamic acid decarboxylase (brain, 67kDa); GFAP—glial fibrillary acidic protein; GST—glutathione-S-transferase; GluN2A—glutamate ionotropic receptor NMDA type subunit 2A; Gut; L-DOPA—3,4-dihydroxy-l-phenylalanine (6047); NBT—nitro blue tetrazolium chloride (9281); PFA—paraformaldehyde (712); Ro41-0960—2′-fluoro-3,4-dihydroxy-5-nitrobenzophenone (3495594); SAM—S-adenosyl methionine (34756); Zebrafish; nNOS—neuronal nitric acid synthase.