Copper in Alzheimer disease: too much, too little, or misplaced?

Facile Separation of Cu2+ from Water by Novel Sandwich NaY Zeolite Adsorptive Membrane

Polyethersulfone-sulfonated polyethersulfone (PES-SPES)/NaY zeolite/nylon sandwich structure membranes were prepared and used to adsorb Cu2+ from water. The adsorption kinetics, adsorption isotherm, dynamic adsorption experiment, and reusability were discussed. The experimental data showed that the Langmuir isotherm model, Dubinin–Radushkevich (D-R) isotherm model, and the pseudo-first-order kinetic model can well represent the adsorption of Cu2+ on the membrane, indicating an ion exchange mechanism, with the maximum adsorption capacity of 111.25 mg·g−1. Repeatability experiments show that the sandwich film still has good adsorption performance after five times of adsorption and desorption. The as-prepared membrane showed considerable separation performance in removing Cu2+ from aspirin solution, providing a feasible method to remove heavy metals from drugs.

Two mixed-ligand Cd(ii)–organic frameworks with unique topologies: selective luminescence sensing of TNP and Cu2+ ions with recyclable performances

Two luminescent Cd(ii)–organic frameworks exhibit unprecedented (4,4,5,5)-c and (4,4,4,6,7)-c topologies, and highly sensitive and selective sensing of 2,4,6-trinitrophenol and Cu²⁺.

An anionic layered europium(iii) coordination polymer for solvent-dependent selective luminescence sensing of Fe3+ and Cu2+ ions and latent fingerprint detection

An anionic layered coordination polymer [Eu(BTEC)0.5(HCOO)(H2O)2] (1) has been successfully synthesized via a solvothermal method (H4BTEC = 1,2,4,5-benzenetetracarboxylic acid, HCOOH = formic acid). Compound 1 possesses two-dimensional layers, which further generate a three-dimensional supramolecular network by hydrogen bonds existing between carboxylic oxygen, formate anion and H2O molecules of two adjacent layers. Interestingly, 1 shows high luminescence quenching efficiency upon addition of Fe3+ ions when it was dispersed in water even in the presence of interfering ions such as Na+, Ag+, Ca2+, Cd2+, Co2+, Cu2+, Mg2+, Mn2+, Zn2+ and Al3+. When dispersed in DMSO solution, 1 displays excellent sensitivity and selectivity towards both Cu2+ and Fe3+ ions. Possible quenching mechanisms for detection of Fe3+ and Cu2+ ions were carefully investigated and proposed based on a dynamic quenching process, static quenching process and fluorescence inner filter effect. Moreover, the as-prepared particles can be used for visualizing latent fingerprints on various substrates. These results indicate that a Eu(iii)-based coordination polymer has great potential in detection and security application.

Cu and Zn coordination to amyloid peptides: From fascinating chemistry to debated pathological relevance

Several diseases share misfolding of different peptides and proteins as a key feature for their development. This is the case of important neurodegenerative diseases such as Alzheimer's and Parkinson's diseases and type II diabetes mellitus. Even more, metal ions such as copper and zinc might play an important role upon interaction with amyloidogenic peptides and proteins, which could impact their aggregation and toxicity abilities. In this review, the different coordination modes proposed for copper and zinc with amyloid-β, α-synuclein and IAPP will be reviewed as well as their impact on the aggregation, and ROS production in the case of copper. In addition, a special focus will be given to the mutations that affect metal binding and lead to familial cases of the diseases. Different modifications of the peptides that have been observed in vivo and could be relevant for the coordination of metal ions are also described.

Mono and dihydroxy coumarin derivatives: Copper chelation and reduction ability

Due to the limited array of the currently available copper chelators, research of such compounds continues to be of clinical interest. Notably, o-dihydroxycoumarins have been previously shown to be potent iron chelators under neutral conditions. Within this study, the interaction of a series of natural coumarins and their synthetic analogs with copper has been evaluated in order to obtain structure-activity relationships under different pathophysiological pH conditions. Both competitive and non-competitive methods have been employed. Analysis of cupric ion reduction has also been performed. Under mildly competitive conditions, cupric chelation was observed for o-dihydroxycoumarins, and partially for o-diacetoxycoumarin. Non-competitive studies showed that cuprous ions are not chelated at all and that the stoichiometries of the most active 6,7- and 7,8-dihydroxycoumarins to cupric ions ranged from 1:1 to 2:1 depending on pH and concentration. Interestingly, under highly competitive conditions, coumarins were not capable of chelating cupric ions, either. Reduction experiments have shown that 13 out of the 15 coumarins included in this study reduced cupric ions. However, significant differences depending on their structures were apparent in their potencies. O-dihydroxycoumarins were the most potent ones again.

CONCLUSION

O-dihydroxycoumarins are moderately active cupric ion chelators with potent copper reducing properties.

Copper(I/II), α/β-Synuclein and Amyloid-β: Menage à Trois?

Copper binding to α-synuclein (aS) and to amyloid-β (Ab) has been connected to Parkinson's and Alzheimer's disease (AD), respectively, because Cu ions can modulate the peptide aggregation, and these Cu ⋅ peptide complexes can catalyse the production of reactive oxygen species (ROS). In a significant proportion of AD brains, aggregation of aS and Ab has been detected, and it was proposed that Ab and aS interact with each other. Thus, we investigated the potential interactions of Ab and aS through their binding of copper(I) and copper(II). Additionally, β-synuclein (bS) was investigated, due to its additional methionine residue, a potential Cu(I) ligand. We found that: 1) the peptides containing the Cu-binding domains Ab1-16, aS1-15 and bS1-15 have similar affinities towards Cu(II) and towards Cu(I), with Ab1-16 being slightly stronger, 2) in the case of Cu(I), the additional Met residue in bS1-15 increased the affinity slightly, 3) the exchange of Cu(I/II) between the two peptides is rapid (≤ ms), 4) a/bS1-15 and Ab1-16 form a heterodimeric complex with Cu(II), 5) Cu(I) probably promotes a transient ternary complex, 6) the different Cu(I/II) coordination of Ab1-16, aS1-15 and bS1-15 impacts the capacity to produce ROS and to oxidise catechol, and 7) when Ab1-16, aS1-15 and Cu are present, the ROS production more closely resembles that by Ab1-16. The work gives insights into the coordination chemistry of these related peptides, and the relevance of coordination differences, the ternary complex and ROS production are discussed.

Memory restorative ability of clioquinol in copper-cholesterol-induced experimental dementia in mice

CONTEXT

Results from various studies indicate that the presence of certain heavy metals such as aluminum (Al), arsenic (As), copper (Cu), lead (Pb), and mercury (Hg) may enhance the aggregation of Aβ and oxidative stress levels leading to neuronal toxicity and Alzheimer's disease (AD). Studies also reveal that anomalous brain copper-cholesterol (Cu-Ch) homeostasis may lead to memory deficits in Swiss albino mice.

OBJECTIVE

The present study investigates the anti-amnesic potential of clioquinol (5-chloro-7-iodoquinolin-8-ol) in cognitive deficits associated with experimental dementia induced by Cu-Ch.

MATERIALS AND METHODS

Administration of Cu-Ch {0.21 mg/kg, per os - 2% w/v, per os for 8 weeks} was used to induce dementia in Swiss albino mice. The Morris water maze (MWM) test was performed to assess the effect on learning and memory. A battery of biochemical estimations was performed following the MWM test such as brain-reduced glutathione (GSH), superoxide dismutase (SOD), thiobarbituric acid reactive species (TBARS), acetylcholinestrase (AChE) activity, and serum cholesterol levels.

RESULTS

Administration of Cu-Ch produced a marked decline in MWM performance measured during the acquisition (78.9 ± 3.3) and retrieval trials (9.5 ± 2.4), reflecting impairment of learning and memory. Cu-Ch-treated mice also exhibited a marked accentuation of AChE activity (5.8 ± 0.55) and TBARS levels (9.74 ± 1.9) along with a decline in the GSH level (15.4 ± 3.3) and the SOD level (26 ± 2.5) when compared with the untreated control group. Administration of clioquinol significantly attenuated Cu-Ch-induced memory deficits and biochemical alterations.

DISCUSSION AND CONCLUSION

The findings demonstrate memory restorative ability of clioquinol which may be attributed to its anti-cholinesterase, antioxidative, and cholesterol-lowering potential.

Chitooligosaccharides attenuate Cu2+-induced cellular oxidative damage and cell apoptosis involving Nrf2 activation

Alzheimer's disease (AD) is one of the common neurodegenerative diseases. Increase of labile copper pool plays an important role in the pathogenesis of AD. Nrf2(NF-E2-related factor-2)-ARE (antioxidant response element) signaling is an important intracellular manner to defend against oxidative stress. In this study, we used SH-SY5Y cells as a model of neuron to test the effect of chitooligosaccharides (COSs) on Cu(2+)-induced oxidative damage. SH-SY5Y cells were treated with different concentrations of COSs (100-800 mg/L) before incubated with Cu(2+). Cell viability and cell damage and apoptosis were assessed. Both extracellular H(2)O(2) and intracellular ROS were measured and the relative levels of Nrf2, phosphorylated Nrf2, and HO-1 were analyzed by Western blotting, and further HO-1 mRNA was relatively quantified by real-time quantitative PCR. The results indicated that Cu(2+)-induced decrease of cell viability and increase of LDH release. In cell-free solution, COSs alone or with Cu(2+) cannot scavenge O(2)(-); however, COSs downregulate the levels of cellular oxidative stress and activated Caspase-3 induced by Cu(2+). Further, the levels of pSer40-Nrf2 protein and both the transcription and the translation of HO-1 gene are dramatically increased in COSs-protective group compared with Cu(2+) damage group. Therefore, these results indicate that Nrf2 activation might be involved in the protection of COSs against Cu(2+)-induced cellular oxidative damage. COSs contribute to the attenuation of oxidative damage and could be used as a nutritional agent for AD treatment.

Synthetic Flavonoids, Aminoisoflavones: Interaction and Reactivity with Metal-Free and Metal-Associated Amyloid-β Species

Metal ion homeostasis in conjunction with amyloid-β (Aβ) aggregation in the brain has been implicated in Alzheimer's disease (AD) pathogenesis. To uncover the interplay between metal ions and Aβ peptides, synthetic, multifunctional small molecules have been employed to modulate Aβ aggregation in vitro. Naturally occurring flavonoids have emerged as a valuable class of compounds for this purpose due to their ability to modulate both metal-free and metal-induced Aβ aggregation. Although, flavonoids have shown anti-amyloidogenic effects, the structural moieties of flavonoids responsible for such reactivity have not been fully identified. In order to understand the structure-interaction-reactivity relationship within the flavonoid family for metal-free and metal-associated Aβ, we designed, synthesized, and characterized a set of isoflavone derivatives, aminoisoflavones (1-4), that displayed reactivity (i.e., modulation of Aβ aggregation) in vitro. NMR studies revealed a potential binding site for aminoisoflavones between the N-terminal loop and central helix on prefibrillar Aβ different from the non-specific binding observed for other flavonoids. The absence or presence of the catechol group differentiated the binding affinities and enthalpy/entropy balance between aminoisoflavones and Aβ. Furthermore, having a catechol group influenced the binding mode with fibrillar Aβ. Inclusion of additional substituents moderately tuned the impact of aminoisoflavones on Aβ aggregation. Overall, through these studies, we obtained valuable insights on the requirements for parity among metal chelation, intermolecular interactions, and substituent variation for Aβ interaction.

A new paradigm for enzymatic control of α-cleavage and β-cleavage of the prion protein

The cellular form of the prion protein (PrP(C)) is found in both full-length and several different cleaved forms in vivo. Although the precise functions of the PrP(C) proteolytic products are not known, cleavage between the unstructured N-terminal domain and the structured C-terminal domain at Lys-109↓His-110 (mouse sequence), termed α-cleavage, has been shown to produce the anti-apoptotic N1 and the scrapie-resistant C1 peptide fragments. β-Cleavage, residing adjacent to the octarepeat domain and N-terminal to the α-cleavage site, is thought to arise from the action of reactive oxygen species produced from redox cycling of coordinated copper. We sought to elucidate the role of key members of the ADAM (a disintegrin and metalloproteinase) enzyme family, as well as Cu(2+) redox cycling, in recombinant mouse PrP (MoPrP) cleavage through LC/MS analysis. Our findings show that although Cu(2+) redox-generated reactive oxygen species do produce fragmentation corresponding to β-cleavage, ADAM8 also cleaves MoPrP in the octarepeat domain in a Cu(2+)- and Zn(2+)-dependent manner. Additional cleavage by ADAM8 was observed at the previously proposed location of α-cleavage, Lys-109↓His-110 (MoPrP sequencing); however, upon addition of Cu(2+), the location of α-cleavage shifted by several amino acids toward the C terminus. ADAM10 and ADAM17 have also been implicated in α-cleavage at Lys-109↓His-110; however, we observed that they instead cleaved MoPrP at a novel location, Ala-119↓Val-120, with additional cleavage by ADAM10 at Gly-227↓Arg-228 near the C terminus. Together, our results show that MoPrP cleavage is far more complex than previously thought and suggest a mechanism by which PrP(C) fragmentation responds to Cu(2+) and Zn(2+).

Linkage disequilibrium and haplotype analysis of the ATP7B gene in Alzheimer's disease

Copper dyshomeostasis leading to a labile Cu(2+) not bound to ceruloplasmin ("free" copper) may influence Alzheimer's disease (AD) onset or progression. To investigate this hypothesis, we investigated ATP7B, the gene that controls copper excretion through the bile and concentrations of free copper in systemic circulation. Our study analyzed informative ATP7B single-nucleotide polymorphisms (SNPs) in a case-control population (n=515). In particular, we evaluated the genetic structure of the ATP7B gene using the HapMap database and carried out a genetic association investigation. Linkage disequilibrium (LD) analysis highlighted that our informative SNPs and their LD SNPs covered 96% of the ATP7B gene sequence, distinguishing two "strong LD" blocks. The first LD block contains the gene region encoding for transmembrane and copper-binding, whereas the second LD block encodes for copper-binding domains. The genetic association analysis showed significant results after multiple testing correction for all investigated variants (rs1801243, odds ratio [OR]=1.52, 95% confidence interval [CI]=1.10-2.09, p=0.010; rs2147363, OR=1.58, 95% CI=1.11-2.25, p=0.010; rs1061472, OR=1.73, 95% CI=1.23-2.43, p=0.002; rs732774, OR=2.31, 95% CI=1.41-3.77, p<0.001), indicating that SNPs in transmembrane domains may have a stronger association with AD risk than variants in copper-binding domains. Our study provides novel insights that confirm the role of ATP7B as a potential genetic risk factor for AD. The analysis of ATP7B informative SNPs confirms our previous hypothesis about the absence of ATP7B in the significant loci of genome-wide association studies of AD and the genetic association study suggests that transmembrane and adenosine triphosphate (ATP) domains in the ATP7B gene may harbor variants/haplotypes associated with AD risk.

A bioinorganic view of Alzheimer's disease: when misplaced metal ions (re)direct the electrons to the wrong target

Metal ions Cu, Zn and Fe, seem to play a pivotal role in Alzheimer's disease and other neurodegenerative diseases. In order to understand this in a broader sense, one has to considerer the peculiarities of metal metabolism in the brain compared to most other tissues, as well as the importance of the redox active metal ions, Fe and Cu, in oxygen metabolism and the connected oxidative stress.

Modeling copper binding to the amyloid-β peptide at different pH: toward a molecular mechanism for Cu reduction

Oxidative stress, including the production of reactive oxygen species (ROS), has been reported to be a key event in the etiology of Alzheimer's disease (AD). Cu has been found in high concentrations in amyloid plaques, a hallmark of AD, where it is bound to the main constituent amyloid-β (Aβ) peptide. Whereas it has been proposed that Cu-Aβ complexes catalyze the production of ROS via redox-cycling between the Cu(I) and Cu(II) state, the redox chemistry of Cu-Aβ and the precise mechanism of redox reactions are still unclear. Because experiments indicate different coordination environments for Cu(II) and Cu(I), it is expected that the electron is not transferred between Cu-Aβ and reactants in a straightforward manner but involves structural rearrangement. In this work the structures indicated by experimental data are modeled at the level of modern density-functional theory approximations. Possible pathways for Cu(II) reduction in different coordination sites are investigated by means of first-principles molecular dynamics simulations in the water solvent and at room temperature. The models of the ligand reorganization around Cu allow the proposal of a preferential mechanism for Cu-Aβ complex reduction at physiological pH. Models reveal that for efficient reduction the deprotonated amide N in the Ala 2-Glu 3 peptide bond has to be protonated and that interactions in the second coordination sphere make important contributions to the reductive pathway, in particular the interaction between COO(-) and NH(2) groups of Asp 1. The proposed mechanism is an important step forward to a clear understanding of the redox chemistry of Cu-Aβ, a difficult task for spectroscopic approaches as the Cu-peptide interactions are weak and dynamical in nature.

Divalent copper is a potent extracellular blocker for TRPM2 channel

Transient receptor potential melastatin 2 (TRPM2) is a Ca(2+)-permeable cationic channel in the TRP channel family. The channel activity can be regulated by reactive oxygen species (ROS) and cellular acidification, which has been implicated to the pathogenesis of diabetes and some neuronal disorders. However, little is known about the effect of redox-active metal ions, such as copper, on TRPM2 channels. Here we investigated the effect of divalent copper on TRPM2. TRPM2 channel was over-expressed in HEK-293 cells and the whole-cell current was recorded by patch clamp. We found the whole-cell current evoked by intracellular ADP-ribose was potently inhibited by Cu(2+) with a half maximal inhibitory concentration (IC(50)) of 2.59 μM. The inhibitory effect was irreversible. The single channel activity was abolished in the outside-out patches, and intracellular application of Cu(2+) did not prevent the channel activation, suggesting that the action site of Cu(2+) is located in the extracellular domains of the channel. TRPM2 current was also blocked by Hg(2+), Pb(2+), Fe(2+) and Se(2+). We concluded that Cu(2+) is a potent TRPM2 channel blocker. The sensitivity of TRPM2 channel to heavy metal ions could be a new mechanism for the pathogenesis of some metal ion-related diseases.

Chelation therapy in Wilson's disease: from D-penicillamine to the design of selective bioinspired intracellular Cu(I) chelators

Wilson's disease is an orphan disease due to copper homeostasis dysfunction. Mutations of the ATP7B gene induces an impaired functioning of a Cu-ATPase, impaired Cu detoxification in the liver and copper overload in the body. Indeed, even though copper is an essential element, which is used as cofactor by many enzymes playing vital roles, it becomes toxic when in excess as it promotes cytotoxic reactions leading to oxidative stress. In this perspective, human copper homeostasis is first described in order to explain the mechanisms promoting copper overload in Wilson's disease. We will see that the liver is the main organ for copper distribution and detoxification in the body. Nowadays this disease is treated life-long by systemic chelation therapy, which is not satisfactory in many cases. Therefore the design of more selective and efficient drugs is of great interest. A strategy to design more specific chelators to treat localized copper accumulation in the liver will then be presented. In particular we will show how bioinorganic chemistry may help in the design of such novel chelators by taking inspiration from the biological copper cell transporters.