title: Autoxidation and MAO-mediated metabolism of dopamine as a potential cause of oxidative stress: role of ferrous and ferric ions.
abstract: The autoxidation and monoamine oxidase (MAO)-mediated metabolism of dopamine (3-hydroxytyramine; DA) cause a continuous production of hydroxyl radical (*OH), which is further enhanced by the presence of iron (ferrous iron, Fe(2+) and ferric ion, Fe(3+)). The accumulation of hydrogen peroxide (H2O2) in the presence of Fe(2+) appears to discard the involvement of the Fenton reaction in this process. It has been found that the presence of DA significantly reduces the formation of thiobarbituric acid reagent substances (TBARS), which under physiological conditions takes place in mitochondrial preparations. The presence of DA is also able to reduce TBARS formation in mitochondrial preparations even in the presence of iron (Fe(2+) and Fe(3+)). However, DA boosted the carbonyl content of mitochondrial proteins, which was further increased in the presence of iron (Fe(2+) and Fe(3+)). This latter effect is also accompanied by a significant reduction in thiol content of mitochondrial proteins. It has also been observed how the pre-incubation of mitochondria with pargyline, an acetylenic MAO inhibitor, reduces the production of *OH and increases the formation of TBARS. Although, the MAO-mediated metabolism of DA increases MAO-B activity, the presence of iron inhibits both MAO-A and MAO-B activities. Consequently, DA has been shown to be a double-edged sword, because it displays antioxidant properties in relation to both the Fenton reaction and lipid peroxidation and exhibits pro-oxidant properties by causing both generation *OH and oxidation of mitochondrial proteins. Evidently, these pro-oxidant properties of DA help explain the long-term side effects derived from l-DOPA treatment of Parkinson's disease and its exacerbation by the concomitant use of DA metabolism inhibitors.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Grupo de Neuroquímica, Facultad de Medicina, Universidad de Santiago de Compostela, San Francisco 1, E-15782 Santiago de Compostela, Spain.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Hermida-Ameijeiras
authors.forename: Estefanía
authors.initials: E
authors.lastname: Méndez-Alvarez
authors.forename: Sofía
authors.initials: S
authors.lastname: Sánchez-Iglesias
authors.forename: Carolina
authors.initials: C
authors.lastname: Sanmartín-Suárez
authors.forename: Ramón
authors.initials: R
authors.lastname: Soto-Otero
mesh_terms: D000818:Animals; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D005290:Ferric Compounds / Q000494:pharmacology*; D005296:Ferrous Compounds / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008995:Monoamine Oxidase / Q000378:metabolism*; D016877:Oxidants / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D016877:Oxidants; D017392:Thiobarbituric Acid Reactive Substances; D006861:Hydrogen Peroxide; D008995:Monoamine Oxidase; D004298:Dopamine