β‐Amyloid protein oligomers induced by metal ions and acid pH are distinct from those generated by slow spontaneous ageing at neutral pH

• DOI: 10.1046/j.1432-1033.2003.03815.x
• Publication Date: 2003-10-16T15:14:59Z
• Authors: Genevieve M. J. A...; Dusan Losic; ; S. Subasinghe; Marie‐Isabel Aguilar; Lisandra L. Martin; David H. Small
• Keywords: Kinetics; 0303 health sciences; 03 medical and health sciences; Amyloid beta-Peptides; Biopolymers; Metals; Electrophoresis, Polyacrylamide Gel; Hydrogen-Ion Concentration; Microscopy, Atomic Force

Amyloid protein (Aβ1–40) aggregation and conformation was examined using native and sodium dodecyl sulfate/polyacrylamide gel electrophoresis, and the results compared with those obtained by atomic force microscopy, and with Congo red binding, sedimentation and turbidity assays. The amount of Aβ aggregation measured was different, depending upon the method used. Incubation for 15 min at pH 5.0 or in the presence of Fe2+, Cu2+ or Zn2+ did not alter the level of Aβ oligomers observed on SDS and native gels. However, the slow aggregation of Aβ to form high molecular mass species over 5 days was inhibited. In contrast, when Aβ aggregation was monitored using a Congo red binding assay or sedimentation assay, a rapid increase in Aβ aggregation was observed after incubation for 15 min at pH 5.0, or in the presence of Fe2+, Cu2+ or Zn2+. The low pH‐, Zn2+‐ or Cu2+‐induced Aβ aggregation measured in a turbidity assay was reversible. In contrast, a considerable proportion of the Aβ aggregation measured by native and SDS/PAGE was stable. Atomic force microscopy studies showed that Aβ aged at pH 5.0 or in the presence of Zn2+ produced larger looser rod‐shaped aggregates than at pH 7.4. Aβ that had been aged at pH 7.4 was more cytotoxic than Aβ aged at pH 5.0. Taken together, the results suggest that Aβ oligomerizes via two mutually exclusive mechanisms to form two different types of aggregates, which differ in their cytotoxic properties.