Interplay of salicylaldehyde, lysine, and M(2+) ions on alpha-synuclein aggregation: Cancellation of aggregation effects and determination of salicylaldehyde neurotoxicity

Abstract

In this study, alpha-synuclein was treated in vitro with salicylaldehyde (SA), lysine (lys) and Mn+ (Cu2+ or Zn2+) in various ratios. SA induced aggregation of alpha-syn in the ratio of 1:500 (alpha-syn:SA) after incubation (pH 7.4, PBS buffer, 16-24 h). Free lys can thus scavenge SA, inhibiting the aggregation of alpha-syn up to similar to 63% (alpha-syn:SA:lys = 1:1000:5000). When Cu2+ and Zn2+ are added to SA and alpha-syn, protein aggregation is induced. In the case of Zn2+, the aggregation of alpha-syn increased to 74% (ratio = 1:1000:50). Fluorescence studies support the production of protein-bound Zn2+-salicylaldimine species. For Cu2+, aggregation of alpha-syn was shown (138%). Thus, possible protective or inducing effects of lys, Cu2+ and Zn2+ may exist with alpha-syn. alpha-Syn, SA and Cu2+ can undergo complexation (fluorescence. CD and MALDI data). Cellular toxicity of SA (700 mu M). Zn2+ (700 mu M) and Cu2+ (700 mu M) on SH-SY5Y (1 x 10(5) 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 mu M) + Cu2+ (700 mu M) and SA (70 mu M) + Zn2+ (700 mu M), respectively, suggesting complexation itself may be toxic. (C) 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.