Zn(II)‐ and Cu(II)‐induced non‐fibrillar aggregates of amyloid‐β (1–42) peptide are transformed to amyloid fibrils, both spontaneously and under the influence of metal chelators

Abstract

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.

β-Amyloid Fibrils in Alzheimer Disease Are Not Inert When Bound to Copper Ions but Can Degrade Hydrogen Peroxide and Generate Reactive Oxygen Species

“…When the Zn(II):A␤(1-42) ratio is 1:1 (but in the absence of added Cu(II)), somewhat spherical amorphous aggregates are seen. This type of aggregate has been noted before in the case of A␤(1-40) (27,53,54). However, the images obtained for samples prepared when both metal ions and the peptide are present at a 1:1:1 ratio show the coexistence of fibrillar and amorphous aggregates.…”

Pulsed hydrogen–deuterium exchange mass spectrometry probes conformational changes in amyloid beta (Aβ) peptide aggregation

“…By using this method, we successfully decoupled the aggregation from the HDX process. Importantly, we extracted kinetic information on the Aβ 42 aggregation at 25°C, indicating that the middle region of the Aβ 42 peptide (i.e., [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] was the "seeding" region in aggregation, followed by the C-terminus hydrophobic region (i.e., [36][37][38][39][40][41][42] and then the N-terminus hydrophilic region (i.e., [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Finally, we showed that this approach allowed us to examine directly the factors that affect the oligomerization of Aβ 42 .…”

“…Upon pulsed HDX of the preformed fibrils we observed both the peptides formed by pepsin digestion (i.e., [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and the undigested Aβ 42 . The peptides and the full Aβ 42 are similarly protected (89 ± 1% for the undigested Aβ 42 and 85 ± 1%, 84 ± 1%, and 91 ± 2% for 1-19, 20-35 and 36-42, respectively), consistent with the peptides' being proteolytic fragments from the amyloid fibrils.…”

“…The amyloid plaques in AD-affected brains contain high levels of copper, zinc, and iron (14)(15)(16)(17)(18)(19)(20). Among these, Cu has drawn the most attention because the Aβ precursor protein is likely a Cuchaperone protein (21).…”

Biometals and Their Therapeutic Implications in Alzheimer's Disease

“…Copper can also accelerate Aβ aggregation but, unlike zinc, copper induces oligomer, rather than fibril, structures [171][172][173][174][175]. Toxicity of Aβ oligomers can be attenuated in cultures by copper chelation [176,177].…”