Intracellular alpha-synuclein (alpha-syn) aggregates are the pathological hallmark in several neurodegenerative diseases including Parkinson's disease, dementia with Lewy bodies and multiple system atrophy. Recent evidence suggests that small oligomeric aggregates rather than large amyloid fibrils represent the main toxic particle species in these diseases. We recently characterized iron-dependent toxic alpha-syn oligomer species by confocal single molecule fluorescence techniques and used this aggregation model to identify several N'-benzylidene-benzohydrazide (NBB) derivatives inhibiting oligomer formation in vitro. In our current work, we used the bioluminescent protein-fragment complementation assay (BPCA) to directly analyze the formation of toxic alpha-syn oligomers in cell culture and to investigate the effect of iron and potential drug-like compounds in living cells. Similar to our previous findings in vitro, we found a converse modulation of toxic alpha-syn oligomers by NBB derivates and ferric iron, which was characterized by an increase in aggregate formation by iron and an inhibitory effect of certain NBB compounds. Inhibition of alpha-syn oligomer formation by the NBB compound 293G02 was paralleled by a reduction in cytotoxicity indicating that toxic alpha-syn oligomers are present in the BPCA cell culture model and that pharmacological inhibition of oligomer formation can reduce toxicity. Thus, this approach provides a suitable model system for the development of new disease-modifying drugs targeting toxic oligomer species. Moreover, NBB compounds such as 293G02 may provide useful tool compounds to dissect the functional role of toxic oligomer species in cell culture models and in vivo.
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