Summary

Neuromelanin (NM) is a complex polymer pigment found in catecholaminergic neurons of the human brain. The structure, formation pathway and physiological function of NM have not yet been clarified, but interest in this polymer has been sparked by the suggestion that NM is involved in cell death in Parkinson's disease. Indeed, the pallor of the parkinsonian substantia nigra is one of the most characteristic pathological features of this disorder. A direct relationship between the loss of the dopaminergic substantia nigra cells and their NM content has been reported, while other work suggests that NM may play a protective function within the cell. Evidence to date suggests that NM is capable of acting as a protective mechanism within the cell via its ability to bind a variety of potentially toxic substances, such as exogenous cytotoxins and heavy metals, and via its ability to inactivate damaging free radicals; on the other hand, in the presence of increased tissue iron NM appears to potentiate cell damage. This is particularly relevant because iron is increased in the parkinsonian substantia nigra; the interaction between the increased tissue iron and NM may result in an increased rate of free radical production, leading to dopaminergic cell loss. The interaction between iron and NM within the vulnerable dopaminergic neurons may underlie, at least partially, the measured increase in indices of oxidative stress in this disorder and may potentiate the rate of neurodegeneration. © 1999 Prous Science. All rights reserved.

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