Interplay of salicylaldehyde, lysine, and M2+ ions on α-synuclein aggregation: Cancellation of aggregation effects and determination of salicylaldehyde neurotoxicity

In this study, α-synuclein was treated in vitro with salicylaldehyde (SA), lysine (lys) and Mn+ (Cu2+ or Zn2+) in various ratios. SA induced aggregation of α-syn in the ratio of 1:500 (α-syn:SA) after incubation (pH 7.4, PBS buffer, 16–24 h). Free lys can thus scavenge SA, inhibiting the aggregation of α-syn up to ∼63% (α-syn:SA:lys = 1:1000:5000). When Cu2+ and Zn2+ are added to SA and α-syn, protein aggregation is induced. In the case of Zn2+, the aggregation of α-syn increased to 74% (ratio = 1:1000:50). Fluorescence studies support the production of protein-bound Zn2+-salicylaldimine species. For Cu2+, aggregation of α-syn was shown (138%). Thus, possible protective or inducing effects of lys, Cu2+ and Zn2+ may exist with α-syn. α-Syn, SA and Cu2+ can undergo complexation (fluorescence, CD and MALDI data). Cellular toxicity of SA (700 μM), Zn2+ (700 μM) and Cu2+ (700 μM) on SH-SY5Y (1 × 105 cells) showed 9.8%, 38.0% and 14.4% compared to control values. Combinations showed more severe toxicities: 71.9% and 93.1% for SA (70 μM) + Cu2+ (700 μM) and SA (70 μM) + Zn2+ (700 μM), respectively, suggesting complexation itself may be toxic.

Figure optionsDownload high-quality image (211 K)Download as PowerPoint slideHighlights
► SA induced aggregation of syn in the ratio of 1:500 (α-syn:SA).
► Free Lys can scavenge SA, inhibiting aggregation of α-syn up to ∼63%.
► Cu2+ and Zn2+ induced α-syn aggregation when added to α-syn and SA.
► Zn2+ and Cu2+ can attach α-syn with SA to change fluorescence and protein structure.
► Combinations showed more severe toxicities than just one chemical species in WST assay.