Formation of reactive oxygen species during one-electron reduction of noradrenochrome catalyzed by NADPH-cytochrome P-450 reductase

Physical exercise and catecholamines response: benefits and health risk: possible mechanisms

Beneficial effect of regular moderate physical exercise (PE) and negative effect of severe exercise and/or overtraining as an activator of the sympathetic nervous system (SNS) have been shown in numerous aspects of human health, including reduced risk of cardiovascular disease, neurological disease, depression, and some types of cancer. Moderate-to-vigorous PE stimulates the SNS activation, releasing catecholamines (CATs) adrenaline, noradrenaline, dopamine that play an important regulatory and modulatory actions by affecting metabolic processes and the immune system. Summary of the dispersed literature in this area and explanation of the biological mechanisms operating between PE-CATs and the immune system would lead to a better understanding of the beneficial and negative effects of PE on health. This overview aimed to: demonstrate representative literature findings on the exercise released CATs levels, major functions performed by these hormones, their interactions with the immune system and their effects on carbohydrate and lipid metabolism. Also, mechanisms of cytotoxic free radicals and reactive oxygen species (ROS) generation during CATs oxidation, and molecular mechanisms of CATs response to exercise are discussed to demonstrate positive and negative on human health effects. Owing to the large body of the subject literature, we present a representative cross-section of the published studies in this area. The results show a significant role of CATs in carbohydrate and lipid metabolism, immunity and as generators of ROS, depending on PE intensity and duration. Further investigation of the PE-CATs relationship should validate CATs levels to optimize safe intensity and duration of exercise and individualize their prescription, considering CATs to be applied as markers for a dose of exercise. Also, a better understanding of the biological mechanisms is also needed.

Leucoisoprenochrome-o-semiquinone Formation in Freshly Isolated Adult Rat Cardiomyocytes

Sustained high levels of circulating catecholamines can lead to cardiotoxicity. There is increasing evidence that this process may result from metal-catalyzed catecholamine oxidation into semiquinones, quinones, and aminochromes. We have previously shown that Cu2+-induced oxidation of isoproterenol into isoprenochrome induces toxic effects in isolated cardiomyocytes. The aim of this study was to characterize the isoproterenol oxidation process and to locate the formation of semiquinone radicals in cardiomyocyte suspensions. Freshly isolated rat cardiomyocytes were incubated with 1 or 10 mM isoproterenol and 20 microM Cu2+ for 4 h. The formation of an isoproterenol oxidation radical was detected in the extracellular medium, cells, membranes, and heavy organelles by electron spin resonance spectroscopy. An electron spin resonance signal assigned to leucoisoprenochrome-o-semiquinone increased in a time-dependent manner in the extracellular medium. A second electron spin resonance signal, characteristic of an immobilized radical, was also found in the cardiomyocytes. The latter was attributed to leucoisoprenochrome-o-semiquinone immobilized on cellular components such as membranes, cytoskeleton, nucleus, and heavy organelles. In addition, the levels of leucoisoprenochrome-o-semiquinone decreased in the presence of glutathione. Computer simulations of the experimental spectra indicate the formation of two distinct isomeric leucoisoprenochrome-o-semiquinone radicals during isoproterenol oxidation. The present study shows that the isoproterenol oxidation in isolated rat cardiomyocytes correlates with the formation of leucoisoprenochrome-o-semiquinone in the cells and in the extracellular medium, suggesting that it might be involved in cardiotoxicity induced by the oxidation of catecholamines.

Human class Mu glutathione transferases, in particular isoenzyme M2-2, catalyze detoxication of the dopamine metabolite aminochrome

Human glutathione transferases (GSTs) were shown to catalyze the reductive glutathione conjugation of aminochrome (2, 3-dihydroindole-5,6-dione). The class Mu enzyme GST M2-2 displayed the highest specific activity (148 micromol/min/mg), whereas GSTs A1-1, A2-2, M1-1, M3-3, and P1-1 had markedly lower activities (<1 micromol/min/mg). The product of the conjugation, with a UV spectrum exhibiting absorption peaks at 277 and 295 nm, was 4-S-glutathionyl-5,6-dihydroxyindoline as determined by NMR spectroscopy. In contrast to reduced forms of aminochrome (leucoaminochrome and o-semiquinone), 4-S-glutathionyl-5, 6-dihydroxyindoline was stable in the presence of molecular oxygen, superoxide radicals, and hydrogen peroxide. However, the strongly oxidizing complex of Mn3+ and pyrophosphate oxidizes 4-S-glutathionyl-5,6-dihydroxyindoline to 4-S-glutathionylaminochrome, a new quinone derivative with an absorption peak at 620 nm. GST M2-2 (and to a lower degree, GST M1-1) prevents the formation of reactive oxygen species linked to one-electron reduction of aminochrome catalyzed by NADPH-cytochrome P450 reductase. The results suggest that the reductive conjugation of aminochrome catalyzed by GSTs, in particular GST M2-2, is an important cellular antioxidant activity preventing the formation of o-semiquinone and thereby the generation of reactive oxygen species.