Effect of melatonin on α-synuclein self-assembly and cytotoxicity

alpha-Synuclein (alpha S) assembly has been implicated as a critical step in the development of Lewy body diseases such as Parkinson's disease and dementia with Lewy bodies. Melatonin (Mel), a secretory product of the pineal gland, is known to have beneficial effects such as an antioxidant function and neuroprotection. To elucidate whether Mel has an antiassembly effect, here we used circular dichroism spectroscopy, photoinduced crosslinking of unmodified proteins, thioflavin S fluorescence, size exclusion chromatography, electron microscopy and atomic force microscopy to examine the effects of Mel on the alpha S assembly. We also examined the effects of Mel on alpha S-induced cytotoxicity by assaying 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide metabolism in alpha S-treated, primary neuronal cells. Initial studies revealed that Mel blocked alpha S fibril formation as well as destabilizing preformed alpha S fibrils. Subsequent evaluation of the assembly-stage specificity of the effect showed that Mel was able to inhibit protofibril formation, oligomerization, and secondary structure transitions. Importantly, Mel decreased alpha S-induced cytotoxicity. These data suggest a mechanism of action for Mel, inhibition of assembly of toxic polymers and protection of neurons from their effect. (C) 2012 Elsevier Inc. All rights reserved.