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.

BackgroundA major pathological hallmark of AD is the deposition of insoluble extracellular β-amyloid (Aβ) plaques. There are compelling data suggesting that Aβ aggregation is catalysed by reaction with the metals zinc and copper.Methodology/Principal FindingsWe now report that the major human-expressed metallothionein (MT) subtype, MT-2A, is capable of preventing the in vitro copper-mediated aggregation of Aβ1–40 and Aβ1–42. This action of MT-2A appears to involve a metal-swap between Zn7MT-2A and Cu(II)-Aβ, since neither Cu10MT-2A or carboxymethylated MT-2A blocked Cu(II)-Aβ aggregation. Furthermore, Zn7MT-2A blocked Cu(II)-Aβ induced changes in ionic homeostasis and subsequent neurotoxicity of cultured cortical neurons.Conclusions/SignificanceThese results indicate that MTs of the type represented by MT-2A are capable of protecting against Aβ aggregation and toxicity. Given the recent interest in metal-chelation therapies for AD that remove metal from Aβ leaving a metal-free Aβ that can readily bind metals again, we believe that MT-2A might represent a different therapeutic approach as the metal exchange between MT and Aβ leaves the Aβ in a Zn-bound, relatively inert form.

Neuronal growth‐inhibitory factor, later renamed metallothionein‐3, is one of four members of the mammalian metallothionein family. Metallothioneins are a family of ubiquitous, low‐molecular‐weight, cysteine‐rich proteins. Although neuronal growth‐inhibitory factor shares metal‐binding and reactive oxygen species scavenging properties with the other metallothioneins, it displays several distinct biological properties. In this review, we examine the recent developments regarding the function of neuronal growth‐inhibitory factor within the brain, particularly in response to brain injury or during neurodegenerative disease progression.

BackgroundAlzheimer's disease (AD) is a progressive neurodegenerative disease, characterised by the formation of insoluble amyloidogenic plaques and neurofibrillary tangles. Beta amyloid (Aβ) peptide is one of the main constituents in Aβ plaques, and is thought to be a primary causative agent in AD. Neurons are likely to be exposed to chronic, sublethal doses of Aβ over an extended time during the pathogenesis of AD, however most studies published to date using in vitro models have focussed on acute studies. To experimentally model the progressive pathogenesis of AD, we exposed primary cortical neurons daily to 1 μM of Aβ1-40 over 7 days and compared their survival with age-similar untreated cells. We also investigated whether chronic Aβ exposure affects neuronal susceptibility to the subsequent acute excitotoxicity induced by 10 μM glutamate and assessed how Ca2+ and K+ homeostasis were affected by either treatment.ResultsWe show that continuous exposure to 1 μM Aβ1-40 for seven days decreased survival of cultured cortical neurons by 20%. This decrease in survival correlated with increased K+ efflux from the cells. One day treatment with 1 μM Aβ followed by glutamate led to a substantially higher K+ efflux than in the age-similar untreated control. This difference further increased with the duration of the treatment. K+ efflux also remained higher in Aβ treated cells 20 min after glutamate application leading to 2.8-fold higher total K+ effluxed from the cells compared to controls. Ca2+ uptake was significantly higher only after prolonged Aβ treatment with 2.5-fold increase in total Ca2+ uptake over 20 min post glutamate application after six days of Aβ treatment or longer (P < 0.05).ConclusionsOur data suggest that long term exposure to Aβ is detrimental because it reduces the ability of cortical neurons to maintain K+ and Ca2+ homeostasis in response to glutamate challenge, a response that might underlie the early symptoms of AD. The observed inability to maintain K+ homeostasis might furthermore be useful in future studies as an early indicator of pathological changes in response to Aβ.

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