Historically, much of the focus on monoamine oxidases and their substrates has been in the area of depression
and the monoamine neurotransmitters serotonin (5-hydroxytryptamine), noradrenaline, and to a lesser extent, dopamine.
With both forms of monoamine oxidase (A and B), the production of hydrogen peroxide as a byproduct of the reaction between
the monoamine oxidases and their monoamine substrates has also implicated monoamine oxidase-sensitive events
in intrinsic cell death pathways, particularly those centered on oxidative stress and peroxyradical-mediated mechanisms.
Consequently, and perhaps not unexpectedly, the inhibition of monoamine oxidase has been considered as adjunctive
therapy in neurodegenerative disorders such as Alzheimer’s disease and Parkinson’s disease, both of which involve a significant
oxidative stress component. Yet the literature also provides ambiguities; indeed, not all of the functions of monoamine
oxidases are dependent on catalytic activity nor can they all be ascribed to expression levels of the monoamine oxidase
protein per se. Recent reports strongly suggest that the functions of monoamine oxidases also rely on posttranslational
modifications, epigenetic influences, interactions with other proteins, the cell phenotype and its localization
to specific subcellular compartments. These recent developments certainly complicate the issue, yet they need to be duly
considered when implicating monoamine oxidases and their inhibitors in both in vitro and in vivo pathological contexts.
Keywords: Monoamine oxidase, oxidative stress, apoptosis, phosphorylation, splice variant, catalytic independent, mitochondria, nucleus, Alzheimer disease, Parkinson’s disease
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