Colorimetric analysis of the early oxidation of dopamine by hypochlorous acid as preliminary screening tool for chemical determinants of neuronal oxidative stress

The hypochlorous acid produced by the innate immune system during inflammation characteristic of several neurodegenerative disorders is responsible for the generation of chlorinated byproducts of dopamine in neurons where this neurotransmitter reaches the highest concentration. Therefore, this physiological acid could play a key role in neuronal oxidative stress associated to aberrant dopamine-quinones (DQ) production. Here we report a model study simulating simplified conditions of HOCl reaction with dopamine (DA) in neurons, showing for the first time that DA is immediately converted by HOCl to the yellow colored DQ molecule. The DQ originated from dopamine oxidation results directly proportional to the total amount of the oxidant with excellent reproducibility. Furthermore, following the several evidences of the interplay between cytosolic dopamine and calcium in neurodegenerative disorders, we have verified that the presence of calcium cation influences the dopamine oxidation pathway likely due to the metal chelation by semiquinone formed in the early stage of dopamine oxidation. This experimental approach, based on the isolation of the highly reactive DQ molecule, could be useful for prelaminar investigation of the (putative) determinants of dopamine-poisoning derivatives formation.