Autoxidation of dopamine: a comparison of luminescent and spectrophotometric detection in basic solutions

Oxidation products of catecholamines, particularly dopamine, could play an important role in the physiology and pathology of the nervous system. This study has therefore characterised autoxidation of dopamine monitored in a variety of systems. Lucigenin-dependent chemiluminescence and reduction of cytochrome c were exploited to register generation of the byproduct superoxide anion, whereas the quinone product was detected by a direct spectrophotometric measurement. Accumulation of hydrogen peroxide was followed as an increase in luminol-dependent chemiluminescence. In all cases, basic solutions were used to initiate the oxidation of dopamine. The results obtained could be interpreted as specific reactions at the particular stages of the autoxidation process: the luminol-dependent chemiluminescence system detected accumulation of hydrogen peroxide during dopamine oxidation, whereas the lucigenin-dependent chemiluminescence indicated generation of superoxide anion. Furthermore, cytochrome c reduction, observed during dopamine oxidation, was probably attributed to a direct interaction with dopamine semiquinone. In addition, the effects of superoxide dismutase, catalase, and peroxidase were examined in each of the systems: Each enzyme exhibited a different effect in each system used. The possible reaction mechanisms leading to different action of enzymes affecting reactive oxygen species are discussed. The methods described here of monitoring dopamine autoxidation could thus be used in parallel to detect the effects of different preparations on various stages of the dopamine autoxidation process.