Redox reactions of neurotransmitters possibly involved in the progression of Parkinson's Disease.

In Parkinson's Disease the neuromelanin in the substania nigra is known to contain considerably increased amounts of iron suggesting the presence of free, unprotected iron ions during its formation. Iron(II) is known to interact with peroxide via Fenton's reaction producing OH-radicals or ferryl (Fe(IV)) species. This can readily oxidize the neurotransmitter dopamine to the neurotoxic 6-hydroxydopamine (6-OHDA) which is a strong reducing agent. The produced 6-OHDA is, in turn, able to reduce and possibly release iron, as iron(II), from the iron storage protein ferritin. This cycle of events could well explain the development of Parkinson's Disease due to a continuous production of cell damaging species. The contrasting behaviour of 6-OHDA with some other important catecholamines is discussed.