Amyloid-β peptides (Aβ) are key molecules in Alzheimer's disease (AD) pathology as they form amyloid plaques that are primary hallmarks of AD. There i

Aggregation of amyloid‐β (Aβ) peptides is a central phenomenon in Alzheimer’s disease. Zn(II) and Cu(II) have profound effects on Aβ aggregation; however, their impact on amyloidogenesis is unclear. Here we show that Zn(II) and Cu(II) inhibit Aβ₄₂ fibrillization and initiate formation of non‐fibrillar Aβ₄₂ aggregates, and that the inhibitory effect of Zn(II) (IC₅₀ = 1.8 μmol/L) is three times stronger than that of Cu(II). Medium and high‐affinity metal chelators including metallothioneins prevented metal‐induced Aβ₄₂ aggregation. Moreover, their addition to preformed aggregates initiated fast Aβ₄₂ fibrillization. Upon prolonged incubation the metal‐induced aggregates also transformed spontaneously into fibrils, that appear to represent the most stable state of Aβ₄₂. H13A and H14A mutations in Aβ₄₂ reduced the inhibitory effect of metal ions, whereas an H6A mutation had no significant impact. We suggest that metal binding by H13 and H14 prevents the formation of a cross‐β core structure within region 10–23 of the amyloid fibril. Cu(II)‐Aβ₄₂ aggregates were neurotoxic to neurons in vitro only in the presence of ascorbate, whereas monomers and Zn(II)‐Aβ₄₂ aggregates were non‐toxic. Disturbed metal homeostasis in the vicinity of zinc‐enriched neurons might pre‐dispose formation of metal‐induced Aβ aggregates, subsequent fibrillization of which can lead to amyloid formation. The molecular background underlying metal‐chelating therapies for Alzheimer’s disease is discussed in this light.

The progression of Alzheimer’s disease is causatively linked to the accumulation of amyloid-β aggregates in the brain, however, it is not clear how the amyloid aggregates initiate the death of neuronal cells. The in vitro toxic effects of amyloid peptides are most commonly examined using the human neuroblastoma derived SH-SY5Y cell line and here we show that differentiated neuron-like SH-SY5Y cells are more sensitive to amyloid peptides than non-differentiated cells, because the latter lack long neurites. Exogenous soluble amyloid-β 1–42 covered cell bodies and whole neurites in differentiated cells with dense fibrils, causing neurite beading and fragmentation, whereas preformed amyloid-β 1–42 fibrils had no toxic effects. Importantly, spontaneously fibrillizing amyloid-β 1–42 peptide exhibited substantially higher cellular toxicity than amyloid-β 1–40, which did not form fibrils under the experimental conditions. These results support the hypothesis that peptide toxicity is related to the active fibrillization process in the incubation mixture.

The amyloid deposition in the form of extracellular fibrillar aggregates of amyloid-β (Aβ) peptide is a critical pathological event in Alzheimer’s disease. Here, we report a systematic investigation of the effects of environmental factors on the kinetics of Aβ fibrillization in vitro. The effects of Aβ42 peptide concentration, temperature, pH, added solvents and the ratio of Aβ40 and Aβ42 on the peptide fibrillization under agitated conditions was studied. The analysis show that the rate of fibril growth by monomer addition is not limited by diffusion but by rearrangement in the monomer structure, which is enhanced by low concentrations of fluorinated alcohols and characterized by the activation energy of 12 kcal/mol. Fibrillization rate decreases at pH values below 7.0 where simultaneous protonation of His 13 and 14 inhibits fibril formation. The lag period for Aβ42 was only twofold shorter and the fibril growth rate twofold faster than those of Aβ40. Lag period was shortened and the fibrillization rate was increased only at 90% content of Aβ42.