Aminochrome associated mechanisms for methamphetamine-induced neurotoxicity

Although the mechanism underlying methamphetamine-induced neurotoxicity is unknown, several lines of evidence implicate oxidative stress driven by dopamine quinones as contributing factors. To test the hypothesis, aminochrome was proposed as a possible dopamine quinone responsible for methamphetamine-induced oxidative damage because: (i) it is an oxidative product of dopamine, (ii) its formation has been found to occur in vivo in the brain, (iii) it can potentially undergo redox cycling reactions to produce reactive oxygen species, and (iv) it can potentially participate in electrophilic addition reactions with sulfhydryls on cysteinyl residues to alter thiol balance in the cell.; First, the ability of aminochrome to participate in electrophilic addition reactions with sulfhydryls non-protein and protein was determined in an in vitro reaction assay with glutathione and glutathione reductase. Reaction of aminochrome and glutathione resulted in decreased free glutathione, indicating covalent modification of glutathione. Reaction of aminochrome with glutathione reductase resulted in decreased glutathione reductase function, indicating inactivation of glutathione reductase by aminochrome.; Second, the ability of aminochrome to participate in redox cycling reactions was determined in striatal homogenates by an oxygen consumption assay. Striatal homogenates treated with aminochrome resulted in increase oxygen consumption, indicating redox cycling. Addition of catalase to the homogenate reaction decreased oxygen consumption. Reactions without added NADPH, striatal homogenate or aminochrome resulted in little or no oxygen consumption. Oxygen consumption assays with phenanthrenequinone, a known redox cycler, indicated similar pattern of oxygen consumption as aminochrome. These results indicate aminochrome is capable of undergoing redox cycling reactions.; Third, the effects of aminochrome activation in pheochromocytoma (PC) 12 cells were determined in parallel with methamphetamine-treated cells. PC 12 cells treated with either methamphetamine or aminochrome were observed to induce significant increases in reactive oxygen species formation, lipid peroxidation and oxidized glutathione concentration as well as decreases in dopamine levels. In addition, these effects were observed in PC 12 cells at 4 h post-methamphetamine and post-aminochrome treatment. Taken together, the parallel results in methamphetamine and aminochrome studies provide suggestive evidence that methamphetamine may mediate its toxicity through dopamine quinones such as aminochrome.