Copper imbalance in Alzheimer’s disease: Convergence of the chemistry and the clinic

Association between Copper Exposure and Cognitive Function: A Cross-Sectional Study in a County, Guangxi, China

There has been growing attention to the impact of copper exposure on cognitive function; however, current research on the specific information regarding urinary copper and cognitive function is limited, particularly detailed analyses in the Chinese adult population. This study aimed to explore the association between copper exposure and cognitive function in a cross-sectional design. A total of 2617 participants in a county, Guangxi Zhuang Autonomous Region (Guangxi), China, were included. The mini-mental state examination (MMSE) was used to assess cognitive function, and inductively coupled plasma mass spectrometry was used to measure urinary metal levels. Spearman's rank correlation was used to analyze the correlation between urinary copper levels and various cognitive function assessment indices. After adjusting for potential confounders, binary logistic regression was used to explore the association between urinary copper levels and the risk of cognitive impairment (CI) as revealed by MMSE, and restricted cubic spline regression was further used to explore the dose-response relationship. The results showed a negative correlation between urinary copper levels and orientation, attention and calculation, memory, language ability, and MMSE total scores (P < 0.05). Compared with the low copper exposure group, the high exposure group showed a 58.5% increased risk of CI (OR = 1.585, 95%CI: 1.125 to 2.235, P = 0.008). A significant linear dose-response relationship was observed between urinary copper levels and the risk of CI (P overall = 0.045, P nonlinearity = 0.081). Our findings suggest that higher copper exposure may be associated with CI in the population of a county, Guangxi, China.

Active Site Environment and Reactivity of Copper-Aβ in Membrane Mimetic SDS Micellar Environment

Alzheimer's disease (AD) is characterized by the abnormal aggregation of amyloid β (Aβ) peptide in extracellular deposits generated upon proteolysis of Amyloid Precursor Protein (APP). While copper (Cu(II)) binds to Aβ in soluble oligomeric and aggregated forms, its interaction with membrane-bound Aβ remains elusive. Investigating these interactions is crucial for understanding AD pathogenesis. Here, utilizing SDS micelles as a simplified membrane mimic, we focus on elucidating the interplay between membrane-anchored Aβ and copper, given their pivotal roles in AD. We employed spectroscopic techniques including UV, CD, and EPR to characterize the active site of Cu-Aβ complexes. Our findings demonstrate that copper interacts with Aβ peptides in membrane-mimicking micellar environments similarly to aqueous buffer solutions. Cu-Aβ complexes in this medium also induce higher hydrogen peroxide (H2O2) production, potentially contributing to AD-related oxidative stress. Moreover, we observe an increased oxidation rate of neurotransmitter such as dopamine by Cu-Aβ complexes. These results enhance our understanding of Cu-Aβ interactions in AD pathology and offer insights into potential therapeutic interventions targeting this interaction.

Fluorescent DNA-Silver nanoclusters in food safety detection: From synthesis to application

In recent years, the conventional preparation of silver nanoclusters (AgNCs) has attracted much attention due to their ultra-small size, tunable fluorescence, easy-to-engineer, as well as biocompatible material. Moreover, its great affinity towards cytosine bases on single-stranded DNA has led to the construction of biosensors, especially aptamers, for a broad variety of applications in food safety and environmental protection. In past years, numerous researchers paid attention to the construction of AgNCs aptasensor. Therefore, this review will be an effort to summarize the synthetic strategy along with the influences of factors on synthesis, categorize the sensing mechanism of aptamer-functionalized AgNCs biosensors, as well as their specific applications in food safety detection including heavy metal, toxin, and foodborne pathogenic bacteria. Furthermore, a brief conclusion and outlook regarding the prospects and challenges of their applications in food safety were drawn in line with the developments in DNA-AgNCs.

Tracking mitochondrial Cu(I) fluctuations through a ratiometric fluorescent probe in AD model cells: Towards understanding how AβOs induce mitochondrial Cu(I) dyshomeostasis

Mitochondrial copper signaling pathway plays a role in Alzheimer's disease (AD), especially in relevant Amyloid-β oligomers (AβOs) neurotoxicity and mitochondrial dysfunction. Clarifying the relationship between mitochondrial copper homeostasis and both of mitochondrial dysfunction and AβOs neurotoxicity is important for understanding AD pathogenesis. Herein, we designed and synthesized a ratiometric fluorescent probe CHC-NS4 for Cu(I). CHC-NS4 possesses excellent ratiometric response, high selectivity to Cu(I) and specific ability to target mitochondria. Under mitochondrial dysfunction induced by oligomycin, mitochondrial Cu(I) levels gradually increased, which may be related to inhibition of ATP7A-mediated Cu(I) exportation and/or high expression of COX. On this basis, CHC-NS4 was further utilized to visualize the fluctuations of mitochondrial Cu(I) levels during progression of AD model cells induced by AβOs. It was found that mitochondrial Cu(I) levels were gradually elevated during the AD progression, which depended on not only AβOs concentration but also incubation time. Moreover, endocytosis maybe served as a prime pathway mode for mitochondrial Cu(I) dyshomeostasis induced by AβOs during AD progression. These results have provided a novel inspiration into mitochondrial copper biology in AD pathogenesis.

Phenothiazine appended thiophene derivative: a trilateral approach to copper ion detection in living cells and aqueous samples

This research paper unveils a fluorescent probe (PTZ-SCN) engineered for the specific detection of Cu2+, featuring a 10-ethyl-10H-phenothiazine-3-carbaldehyde and 2-(thiophen-2-yl) acetonitrile moiety. The fluorescence sensing behavior of PTZ-SCN towards various metal cations was scrutinized in CH3CN : HEPES (9 : 1) buffer aqueous solution. The UV absorbance of PTZ-SCN displayed a distinct red shift in the presence of Cu2+ cations, whereas other metal cations did not cause any interference. Similarly, the fluorescence emission of the probe was also only quenched by Cu2+ cations. The limit of detection (LOD) was calculated as 1.0461 × 10-8 M. PTZ-SCN showed the ability to identify Cu2+ using the colorimetric method, the fluorometric method and even through visual observation in a trilateral detection. We studied the recognition mechanism of PTZ-SCN for Cu2+ using 1H-NMR, HRMS analysis, and time-dependent density functional theory (TDDFT) calculations. Furthermore, our study encompassed the investigation of PTZ-SCN's practical applicability, bridging the gap from research to real-world implementation. This was achieved by employing test strips and water samples for the detection of Cu2+. Additionally, the PTZ-SCN probe's low cytotoxicity and effective imaging properties for Cu2+ in living cells were confirmed, indicating that PTZ-SCN shows the potential to serve as a promising probe for detecting Cu2+in vivo.

Natural Acceptor of Coumarin-Isomerized Red-Emissive BioAIEgen for Monitoring Cu2+ Concentration in Live Cells via FLIM

Artificial aggregation-induced emission luminogens (AIEgens) have flourished in bio-applications with the development of synthetic chemistry, which however are plagued by issues like singularity in structures and non-renewability. The unique structures and renewability of biomass moieties can compensate for these drawbacks, but their properties are hard to design and regulate due to their confined structures. Therefore, it appears to be a reasonable approach to derive AIEgens from abundant biomass (BioAIEgens), integrating the bilateral advantages of both synthetic and natural AIEgens. In this work, the blue-violet emissive coumarin with its lactone structure serving as a rare natural acceptor, is utilized to construct donor-π-acceptor typed BioAIE isomers incorporating the propeller-like and electron-donating triphenylamine (TPA) unit. The results show that Cm-p-TPA undergoes charge transfer with its keto form, emitting red light at 600 nm, which can be applied to monitor Cu2+ concentration during mitophagy using fluorescence lifetime imaging microscopy because of the excellent biocompatibility, photostability, and specific recognition to Cu2+ . This work not only demonstrates the feasibility of utilizing positional isomerization to modulate excited-state evolutions and resultant optical properties, but also provides evidence for the rationality of constructing biologically-active BioAIEgens via a biomass-derivatization concept.

Using a cotton thread-based colorimetric sensor modified by carboxymethylcellulose and cuprizone with smartphone detection for quantification of copper

In the present work, we report the development of a novel cotton thread-based colorimetric sensor modified by carboxymethylcellulose (CMC) and cuprizone (CPZ) with smartphone detection and its application for the quantitative determination of cupric ions in water and cachaça. The cotton thread/smartphone detection-based colorimetric method is an easily affordable, low-cost technique which allows one to perform real-time and on-field determination analyses, especially with limited financial resources. The method involves the complexation of Cu(II) with CPZ, which causes a change in the coloration of the cotton thread from a shade of white to blue in the detection zone of the colorimetric sensor. The immobilization of CPZ on CMC in the cotton thread leads to the pre-concentration of Cu(II) via a complexation mechanism with colorimetric reaction. The application of the colorimetric sensor allows the quantification of copper in the range from 1 to 12 mg L-1, with a low limit of detection of 0.21 mg L-1. In addition, the recovery assays conducted in samples of water and cachaça resulted in recovery percentages ranging from 84.9% to 107%, which is indicative of a precise method. To validate the precision of the proposed colorimetric method, the values obtained from the quantification analysis were compared with those of the flame atomic absorption spectrometry and a good agreement at the 95% confidence level was obtained.

Copper trafficking systems in cells: insights into coordination chemistry and toxicity

Transition metal ions, such as copper, are indispensable components in the biological system. Copper ions which primarily exist in two major oxidation states Cu(I) and Cu(II) play crucial roles in various cellular processes including antioxidant defense, biosynthesis of neurotransmitters, and energy metabolism, owing to their inherent redox activity. The disturbance in copper homeostasis can contribute to the development of copper metabolism disorders, cancer, and neurodegenerative diseases, highlighting the significance of understanding the copper trafficking system in cellular environments. This review aims to offer a comprehensive overview of copper homeostatic machinery, with an emphasis on the coordination chemistry of copper transporters and trafficking proteins. While copper chaperones and the corresponding metalloenzymes are thoroughly discussed, we also explore the potential existence of low-molecular-mass metal complexes within cellular systems. Furthermore, we summarize the toxicity mechanisms originating from copper deficiency or accumulation, which include the dysregulation of oxidative stress, signaling pathways, signal transduction, and amyloidosis. This perspective review delves into the current knowledge regarding the intricate aspects of the copper trafficking system, providing valuable insights into potential treatment strategies from the standpoint of bioinorganic chemistry.

The amyloid cascade hypothesis: an updated critical review

Results from recent clinical trials of antibodies that target amyloid-β (Aβ) for Alzheimer's disease have created excitement and have been heralded as corroboration of the amyloid cascade hypothesis. However, while Aβ may contribute to disease, genetic, clinical, imaging and biochemical data suggest a more complex aetiology. Here we review the history and weaknesses of the amyloid cascade hypothesis in view of the new evidence obtained from clinical trials of anti-amyloid antibodies. These trials indicate that the treatments have either no or uncertain clinical effect on cognition. Despite the importance of amyloid in the definition of Alzheimer's disease, we argue that the data point to Aβ playing a minor aetiological role. We also discuss data suggesting that the concerted activity of many pathogenic factors contribute to Alzheimer's disease and propose that evolving multi-factor disease models will better underpin the search for more effective strategies to treat the disease.

Metallothionein-3 attenuates the effect of Cu2+ ions on actin filaments

Metallothionein 3 (MT-3) is a cysteine-rich metal-binding protein that is expressed in the mammalian central nervous system and kidney. Various reports have posited a role for MT-3 in regulating the actin cytoskeleton by promoting the assembly of actin filaments. We generated purified, recombinant mouse MT-3 of known metal compositions, either with zinc (Zn), lead (Pb), or copper/zinc (Cu/Zn) bound. None of these forms of MT-3 accelerated actin filament polymerization in vitro, either with or without the actin binding protein profilin. Furthermore, using a co-sedimentation assay, we did not observe Zn-bound MT-3 in complex with actin filaments. Cu²⁺ ions on their own induced rapid actin polymerization, an effect that we attribute to filament fragmentation. This effect of Cu²⁺ is reversed by adding either EGTA or Zn-bound MT-3, indicating that either molecule can chelate Cu²⁺ from actin. Altogether, our data indicate that purified recombinant MT-3 does not directly bind actin but it does attenuate the Cu-induced fragmentation of actin filaments.

Imbalance of Essential Metals in Traumatic Brain Injury and Its Possible Link with Disorders of Consciousness

Dysfunction of the complex cerebral networks underlying wakefulness and awareness is responsible for Disorders of Consciousness (DoC). Traumatic Brain Injury (TBI) is a common cause of DoC, and it is responsible for a multi-dimensional pathological cascade that affects the proper functioning of the brainstem and brain consciousness pathways. Iron (Fe), Zinc (Zn), and Copper (Cu) have a role in the neurophysiology of both the ascending reticular activating system, a multi-neurotransmitter network located in the brainstem that is crucial for consciousness, and several brain regions. We aimed to summarize the role of these essential metals in TBI and its possible link with consciousness alterations. We found that TBI alters many neuronal molecular mechanisms involving essential metals, causing neurodegeneration, neural apoptosis, synaptic dysfunction, oxidative stress, and inflammation. This final pattern resembles that described for Alzheimer's disease (AD) and other neurological and psychiatric diseases. Furthermore, we found that amantadine, zolpidem, and transcranial direct current stimulation (tDCS)-the most used treatments for DoC recovery-seem to have an effect on essential metals-related pathways and that Zn might be a promising new therapeutic approach. This review summarizes the neurophysiology of essential metals in the brain structures of consciousness and focuses on the mechanisms underlying their imbalance following TBI, suggesting their possible role in DoC. The scenario supports further studies aimed at getting a deeper insight into metals' role in DoC, in order to evaluate metal-based drugs, such as metal complexes and metal chelating agents, as potential therapeutic options.

Current understanding of metal-dependent amyloid-β aggregation and toxicity

The discovery of effective therapeutics targeting amyloid-β (Aβ) aggregates for Alzheimer's disease (AD) has been very challenging, which suggests its complicated etiology associated with multiple pathogenic elements. In AD-affected brains, highly concentrated metals, such as copper and zinc, are found in senile plaques mainly composed of Aβ aggregates. These metal ions are coordinated to Aβ and affect its aggregation and toxicity profiles. In this review, we illustrate the current view on molecular insights into the assembly of Aβ peptides in the absence and presence of metal ions as well as the effect of metal ions on their toxicity.

Naked-eye chemosensor with high absolute fluorescence quantum yield for selective detection of Cu(II) and cell imaging

The regulation of copper in the human body is important for the prevention of several diseases. Therefore, a rhodamine B-based chemosensor 1 that demonstrates substantial affinity and selectivity was synthesized for the fluorescence imaging of copper(II). In the presence of Cu²⁺, the chemosensor underwent a color change from colorless to amaranth that was visible to the naked eye, and the fluorescence intensity did not change when excess EDTA was added to the solution. Furthermore, strong fluorescence was observed at 575 nm. The limit of detection was determined as 12.1 nM. The absolute fluorescence quantum yield was as high as 77 % and the stoichiometry between 1 and Cu²⁺ was determined to be 1:1 using a job plot. An analytical method was developed and successfully used to evaluate the sensor's ability for the fluorescence imaging of Cu²⁺ in HeLa tumor cells.

Role of the Cysteine in R3 Tau Peptide in Copper Binding and Reactivity

Tau is a widespread neuroprotein that regulates the cytoskeleton assembly. In some neurological disorders, known as tauopathies, tau is dissociated from the microtubule and forms insoluble neurofibrillary tangles. Tau comprises four pseudorepeats (R1-R4), containing one (R1, R2, R4) or two (R3) histidines, that potentially act as metal binding sites. Moreover, Cys291 and Cys322 in R2 and R3, respectively, might have an important role in protein aggregation, through possible disulfide bond formation, and/or affecting the binding and reactivity of redox-active metal ions, as copper. We, therefore, compare the interaction of copper with octadeca-R3-peptide (R3C) and with the mutant containing an alanine residue (R3A) to assess the role of thiol group. Spectrophotometric titrations allow to calculate the formation constant of the copper(I) complexes, showing a remarkable stronger interaction in the case of R3C (l log Kf = 13.4 and 10.5 for copper(I)-R3C and copper(I)-R3A, respectively). We also evaluate the oxidative reactivity associated to these copper complexes in the presence of dopamine and ascorbate. Both R3A and R3C peptides increase the capability of copper to oxidize catechols, but copper-R3C displays a peculiar mechanism due to the presence of cysteine. HPLC-MS analysis shows that cysteine can form disulfide bonds and dopamine-Cys covalent adducts, with potential implication in tau aggregation process.

Is There a Connection between the Metabolism of Copper, Sulfur, and Molybdenum in Alzheimer’s Disease? New Insights on Disease Etiology

Alzheimer’s disease (AD) and other forms of dementia was ranked 3rd in both the Americas and Europe in 2019 in a World Health Organization (WHO) publication listing the leading causes of death and disability worldwide. Copper (Cu) imbalance has been reported in AD and increasing evidence suggests metal imbalance, including molybdenum (Mo), as a potential link with AD occurrence.We conducted an extensive literature review of the last 60 years of research on AD and its relationship with Cu, sulfur (S), and Mo at out of range levels.Weanalyzed the interactions among metallic elements’ metabolisms;Cu and Mo are biological antagonists, Mo is a sulfite oxidase and xanthine oxidase co-factor, and their low activities impair S metabolism and reduce uric acid, respectively. We found significant evidence in the literature of a new potential mechanism linking Cu imbalance to Mo and S abnormalities in AD etiology: under certain circumstances, the accumulation of Cu not bound to ceruloplasmin might affect the transport of Mo outside the blood vessels, causing a mild Mo deficiency that might lowerthe activity of Mo and S enzymes essential for neuronal activity. The current review provides an updated discussion of the plausible mechanisms combining Cu, S, and Mo alterations in AD.

Conformational and functional changes of the native neuropeptide somatostatin occur in the presence of copper and amyloid-β

The progression of neurodegenerative disorders can lead to impaired neurotransmission; however, the role of pathogenic factors associated with these diseases and their impact on the structures and functions of neurotransmitters have not been clearly established. Here we report the discovery that conformational and functional changes of a native neuropeptide, somatostatin (SST), occur in the presence of copper ions, metal-free amyloid-β (Aβ) and metal-bound Aβ (metal-Aβ) found as pathological factors in the brains of patients with Alzheimer's disease. These pathological elements induce the self-assembly of SST and, consequently, prevent it from binding to the receptor. In the reverse direction, SST notably modifies the aggregation profiles of Aβ species in the presence of metal ions, attenuating their cytotoxicity and interactions with cell membranes. Our work demonstrates a loss of normal function of SST as a neurotransmitter and a gain of its modulative function against metal-Aβ under pathological conditions.

Regulatory miRNAs in Cardiovascular and Alzheimer's Disease: A Focus on Copper

Non-coding RNAs (ncRNAs), including microRNAs (miRNAs), are key regulators of differentiation and development. In the cell, transcription factors regulate the production of miRNA in response to different external stimuli. Copper (Cu) is a heavy metal and an essential micronutrient with widespread industrial applications. It is involved in a number of vital biological processes encompassing respiration, blood cell line maturation, and immune responses. In recent years, the link between deregulation of miRNAs' functionality and the development of various pathologies as well as cardiovascular diseases (CVDs) has been extensively studied. Alzheimer's disease (AD) is the most common cause of dementia in the elderly with a complex disease etiology, and its link with Cu abnormalities is being increasingly studied. A direct interaction between COMMD1, a regulator of the Cu pathway, and hypoxia-inducible factor (HIF) HIF-1a does exist in ischemic injury, but little information has been collected on the role of Cu in hypoxia associated with AD thus far. The current review deals with this matter in an attempt to structurally discuss the link between miRNA expression and Cu dysregulation in AD and CVDs.

Increased Serum Beta-Secretase 1 Activity is an Early Marker of Alzheimer's Disease

BACKGROUND

Beta-site APP cleaving enzyme 1 (BACE1) is the rate-limiting enzyme in amyloid-β (Aβ) plaques formation. BACE1 activity is increased in brains of patients with AD and mild cognitive impairment (MCI) and plasma levels of BACE1 appears to reflect those in the brains.

OBJECTIVE

In this work, we investigated the role of serum BACE1 activity as biomarker for AD, estimating the diagnostic accuracy of the assay and assessing the correlation of BACE1 activity with levels of Aβ 1 - 40, Aβ 1 - 42, and Aβ 40/42 ratio in serum, known biomarkers of brain amyloidosis.

METHODS

Serum BACE1 activity and levels of Aβ 1 - 40, Aβ 1 - 42, were assessed in 31 AD, 28 MCI, diagnosed as AD at follow-up (MCI-AD), and 30 controls. The BACE1 analysis was performed with a luciferase assay, where interpolation of relative fluorescence units with a standard curve of concentration reveals BACE1 activity. Serum levels of Aβ 1 - 40, Aβ 1 - 42 were measured with the ultrasensitive Single Molecule Array technology.

RESULTS

BACE1 was increased (higher than 60%) in AD and MCI-AD: a cut-off of 11.04 kU/L discriminated patients with high sensitivity (98.31%) and specificity (100%). Diagnostic accuracy was higher for BACE1 than Aβ 40/42 ratio. High BACE1 levels were associated with worse cognitive performance and earlier disease onset, which was anticipated by 8 years in patients with BACE1 values above the median value (>  16.67 kU/L).

CONCLUSION

Our results provide new evidence supporting serum/plasma BACE1 activity as an early biomarker of AD.

Simultaneous visualization and quantification of copper (II) ions in Alzheimer's disease by a near-infrared fluorescence probe

The abnormal accumulation of copper ions (Cu²⁺) is considered to be one of the pathological factors of Alzheimer's disease (AD), but the internal relationship between Cu²⁺ and AD progression is still not fully clear. In this work, a sensitive and selective near-infrared fluorescent copper ion probe (DDP-Cu) was designed for quantification and visualization of Cu²⁺ level in lysates, living cells, living zebrafish and brain tissues of drosophila and mice with AD. By using this probe, we demonstrated that the content of Cu²⁺ in the brains of AD mice and drosophila enhanced nearly 3.5-fold and 4-fold than that of normal mice and drosophila, respectively. More importantly, pathogenesis analysis revealed that elevated Cu²⁺ led to changes in factors closely associated with AD, such as the increasing of reactive oxygen species(ROS), the aggregation of amyloid-β protein (Aβ) and nerve cell cytotoxicity. These findings could promote the understanding of the roles between Cu²⁺ and AD.

Probable Reasons for Neuron Copper Deficiency in the Brain of Patients with Alzheimer’s Disease: The Complex Role of Amyloid

Alzheimer’s disease is a progressive neurodegenerative disorder that eventually leads the affected patients to die. The appearance of senile plaques in the brains of Alzheimer’s patients is known as a main symptom of this disease. The plaques consist of different components, and according to numerous reports, their main components include beta-amyloid peptide and transition metals such as copper. In this disease, metal dyshomeostasis leads the number of copper ions to simultaneously increase in the plaques and decrease in neurons. Copper ions are essential for proper brain functioning, and one of the possible mechanisms of neuronal death in Alzheimer’s disease is the copper depletion of neurons. However, the reason for the copper depletion is as yet unknown. Based on the available evidence, we suggest two possible reasons: the first is copper released from neurons (along with beta-amyloid peptides), which is deposited outside the neurons, and the second is the uptake of copper ions by activated microglia.

Interactions between copper (II) and β-amyloid peptide using capillary electrophoresis-ICP-MS: Kd measurements at the nanogram scale

Although the interaction between the β-amyloid peptide and copper (II) appears to play an important role in Alzheimer's disease, the affinity constant is still controversial and values are ranging from 10⁷ to 10¹¹ M^-1. With the aim of clarifying this point, a complementary method, based on the capillary electrophoresis-ICP-MS hyphenation, was developed and competitive binding experiments were conducted in the presence of nitrilotriacetic acid. The effect of the capillary surface (neutral or positively charged) and nature of the buffer (Tris or Hepes) have been studied. Tris buffer was found to be inappropriate for such determination as it enhances the dissociation of copper (II) complexes, already occurring in the presence of an electric field in capillary electrophoresis. Using Hepes, a value of 10¹⁰ M^-1 was found for the affinity of the small β-amyloid peptide 1-16 for copper (II), which is in agreement with the values obtained for other proteins involved in neurodegenerative diseases. These constants were also determined in conditions closer to those of biological media (higher ionic strength, presence of carbonates).

Copper in tumors and the use of copper-based compounds in cancer treatment

Copper homeostasis is strictly regulated by protein transporters and chaperones, to allow its correct distribution and avoid uncontrolled redox reactions. Several studies address copper as involved in cancer development and spreading (epithelial to mesenchymal transition, angiogenesis). However, being endogenous and displaying a tremendous potential to generate free radicals, copper is a perfect candidate, once opportunely complexed, to be used as a drug in cancer therapy with low adverse effects. Copper ions can be modulated by the organic counterpart, after complexed to their metalcore, either in redox potential or geometry and consequently reactivity. During the last four decades, many copper complexes were studied regarding their reactivity toward cancer cells, and many of them could be a drug choice for phase II and III in cancer therapy. Also, there is promising evidence of using ⁶⁴Cu in nanoparticles as radiopharmaceuticals for both positron emission tomography (PET) imaging and treatment of hypoxic tumors. However, few compounds have gone beyond testing in animal models, and none of them got the status of a drug for cancer chemotherapy. The main challenge is their solubility in physiological buffers and their different and non-predictable mechanism of action. Moreover, it is difficult to rationalize a structure-based activity for drug design and delivery. In this review, we describe the role of copper in cancer, the effects of copper-complexes on tumor cell death mechanisms, and point to the new copper complexes applicable as drugs, suggesting that they may represent at least one component of a multi-action combination in cancer therapy.

Microglia and Astrocytes in Alzheimer's Disease in the Context of the Aberrant Copper Homeostasis Hypothesis

Evidence of copper's (Cu) involvement in Alzheimer's disease (AD) is available, but information on Cu involvement in microglia and astrocytes during the course of AD has yet to be structurally discussed. This review deals with this matter in an attempt to provide an updated discussion on the role of reactive glia challenged by excess labile Cu in a wide picture that embraces all the major processes identified as playing a role in toxicity induced by an imbalance of Cu in AD.

Non-Ceruloplasmin Copper as a Stratification Biomarker of Alzheimer's Disease Patients: How to Measure and Use It

Alzheimer's disease (AD) is a type of dementia very common in the elderly. A growing body of recent evidence has linked AD pathogenesis to copper (Cu) dysmetabolism in the body. In fact, a subset of patients affected either by AD or by its prodromal form known as Mild Cognitive Impairment (MCI) have been observed to be unable to maintain a proper balance of Cu metabolism and distribution and are characterized by the presence in their serum of increased levels of Cu not bound to ceruloplasmin (non-ceruloplasmin Cu). Since serum non-ceruloplasmin Cu is a biomark- er of Wilson's disease (WD), a well-known condition of Cu-driven toxicosis, in this review, we pro- pose that in close analogy with WD, the assessment of non-ceruloplasmin Cu levels can be exploit- ed as a cost-effective stratification and susceptibility/risk biomarker for the identification of some AD/MCI individuals. The approach can also be used as an eligibility criterion for clinical trials aim- ing at investigating Cu-related interventions against AD/MCI.

Fluorescent noble metal nanoclusters for contaminants analysis in food matrix

Recently, food safety issues caused by contaminants have aroused great public concern. The development of innovative and efficient sensing techniques for contaminants detection in food matrix is in urgent demand. As fluorescent nanomaterials, noble metal nanoclusters have attracted much attention because of their ease of synthesis, enhanced catalytic activity and biocompatibility, and most importantly, excellent photoluminescence property that provides promising analytical applications. This review comprehensively introduced the synthesis method of noble metal nanoclusters, and summarized the application of metal nanoclusters as fluorescent sensing materials in the detection of pollutants, including pesticides, heavy metal, mycotoxin, food additives, and other contaminants in food. The detection mechanism of pesticide residues mostly relies on the inhibition of natural enzymes. For heavy metals, the detection mechanism is mainly related to the interaction between metal ions and nanoclusters or ligands. It is evidenced that metal nanoclusters have great potential application in the field of food safety monitoring. Moreover, challenges and future trends of nanoclusters were discussed. We hope that this review can provide insights and directions for the application of nanoclusters in contaminants detection.

Multifunctional Small Molecules as Potential Anti-Alzheimer's Disease Agents

Alzheimer's disease (AD) is a severe multifactorial neurodegenerative disorder characterized by a progressive loss of neurons in the brain. Despite research efforts, the pathogenesis and mechanism of AD progression are not yet completely understood. There are only a few symptomatic drugs approved for the treatment of AD. The multifactorial character of AD suggests that it is important to develop molecules able to target the numerous pathological mechanisms associated with the disease. Thus, in the context of the worldwide recognized interest of multifunctional ligand therapy, we report herein the synthesis, characterization, physicochemical and biological evaluation of a set of five (1a-e) new ferulic acid-based hybrid compounds, namely feroyl-benzyloxyamidic derivatives enclosing different substituent groups, as potential anti-Alzheimer's disease agents. These hybrids can keep both the radical scavenging activity and metal chelation capacity of the naturally occurring ferulic acid scaffold, presenting also good/mild capacity for inhibition of self-Aβ aggregation and fairly good inhibition of Cu-induced Aβ aggregation. The predicted pharmacokinetic properties point towards good absorption, comparable to known oral drugs.

Nerve Growth Factor-Based Therapy in Alzheimer's Disease and Age-Related Macular Degeneration

Alzheimer's disease (AD) is an age-associated neurodegenerative disease which is the most common cause of dementia among the elderly. Imbalance in nerve growth factor (NGF) signaling, metabolism, and/or defect in NGF transport to the basal forebrain cholinergic neurons occurs in patients affected with AD. According to the cholinergic hypothesis, an early and progressive synaptic and neuronal loss in a vulnerable population of basal forebrain involved in memory and learning processes leads to degeneration of cortical and hippocampal projections followed by cognitive impairment with accumulation of misfolded/aggregated Aβ and tau protein. The neuroprotective and regenerative effects of NGF on cholinergic neurons have been largely demonstrated, both in animal models of AD and in living patients. However, the development of this neurotrophin as a disease-modifying therapy in humans is challenged by both delivery limitations (inability to cross the blood-brain barrier (BBB), poor pharmacokinetic profile) and unwanted side effects (pain and weight loss). Age-related macular degeneration (AMD) is a retinal disease which represents the major cause of blindness in developed countries and shares several clinical and pathological features with AD, including alterations in NGF transduction pathways. Interestingly, nerve fiber layer thinning, degeneration of retinal ganglion cells and changes of vascular parameters, aggregation of Aβ and tau protein, and apoptosis also occur in the retina of both AD and AMD. A protective effect of ocular administration of NGF on both photoreceptor and retinal ganglion cell degeneration has been recently described. Besides, the current knowledge about the detection of essential trace metals associated with AD and AMD and their changes depending on the severity of diseases, either systemic or locally detected, further pave the way for a promising diagnostic approach. This review is aimed at describing the employment of NGF as a common therapeutic approach to AMD and AD and the diagnostic power of detection of essential trace metals associated with both diseases. The multiple approaches employed to allow a sustained release/targeting of NGF to the brain and its neurosensorial ocular extensions will be also discussed, highlighting innovative technologies and future translational prospects.

Copper Imbalance in Alzheimer's Disease and Its Link with the Amyloid Hypothesis: Towards a Combined Clinical, Chemical, and Genetic Etiology

The cause of Alzheimer's disease (AD) is incompletely defined. To date, no mono-causal treatment has so far reached its primary clinical endpoints, probably due to the complexity and diverse neuropathology contributing to the neurodegenerative process. In the present paper, we describe the plausible etiological role of copper (Cu) imbalance in the disease. Cu imbalance is strongly associated with neurodegeneration in dementia, but a complete biochemical etiology consistent with the clinical, chemical, and genetic data is required to support a causative association, rather than just correlation with disease. We hypothesize that a Cu imbalance in the aging human brain evolves as a gradual shift from bound metal ion pools, associated with both loss of energy production and antioxidant function, to pools of loosely bound metal ions, involved in gain-of-function oxidative stress, a shift that may be aggravated by chemical aging. We explain how this may cause mitochondrial deficits, energy depletion of high-energy demanding neurons, and aggravated protein misfolding/oligomerization to produce different clinical consequences shaped by the severity of risk factors, additional comorbidities, and combinations with other types of pathology. Cu imbalance should be viewed and integrated with concomitant genetic risk factors, aging, metabolic abnormalities, energetic deficits, neuroinflammation, and the relation to tau, prion proteins, α-synuclein, TAR DNA binding protein-43 (TDP-43) as well as systemic comorbidity. Specifically, the Amyloid Hypothesis is strongly intertwined with Cu imbalance because amyloid-β protein precursor (AβPP)/Aβ are probable Cu/Zn binding proteins with a potential role as natural Cu/Zn buffering proteins (loss of function), and via the plausible pathogenic role of Cu-Aβ.

Enhanced adsorption of Cu(II) and Zn(II) from aqueous solution by polyethyleneimine modified straw hydrochar

Heavy metals removal from aqueous phase by adsorption technique has recently attracted a considerable interest. Although various adsorbing materials have been developed, introducing more functional groups is considered as the most efficient way to promote the adsorption capacity of the selected adsorbent. However, this approach is usually limited in costly modification precursor and unguaranteed loading efficacy. In this study, waste corn straw was converted to adsorbent precursor by hydrothermal carbonization. The obtained hydrochar (HC) was chemically activated before being modified by polyethyleneimine (PEI). Multiple analysis methods including Scanning Electron Microscopy, Fourier Transform Infrared analysis, and X-ray Photoelectron Spectroscopy analysis verified the alkali activated hydrochar (alkali-HC) was more efficacy to enhance PEI grafting than acid activation. Based on this, the modified HC materials obtained a better adsorption performance. The sorption process of Cu(II) and Zn(II) on the acid-PEI-HC, alkali-PEI-HC, and pristine HC fitted the pseudo second order kinetic and Freundlich model well, and was dominated by chemisorption. Among these adsorbents, the adsorption capacity of alkali-PEI-HC to metal ions was the maximum, which was 207.6 mg/g to Zn(II) and 56.1 mg/g to Cu(II) at 298 K. Regeneration tests showed a result of no less than 60% of its removal capacity was achieved after five cycles. Therefore, alkali-PEI-HC performed as a promising composite sorbent for metal ions. In addition, the study described here has provided a new basis for the utilization of hydrochar (1.08 kWh kg^-1) derived from agricultural resources as a promising adsorbent precursor.

Copper Imbalance in Alzheimer's Disease: Meta-Analysis of Serum, Plasma, and Brain Specimens, and Replication Study Evaluating ATP7B Gene Variants

Evidence indicates that patients with Alzheimer's dementia (AD) show signs of copper (Cu) dyshomeostasis. This study aimed at evaluating the potential of Cu dysregulation as an AD susceptibility factor. We performed a meta-analysis of 56 studies investigating Cu biomarkers in brain specimens (pooled total of 182 AD and 166 healthy controls, HC) and in serum/plasma (pooled total of 2929 AD and 3547 HC). We also completed a replication study of serum Cu biomarkers in 97 AD patients and 70 HC screened for rs732774 and rs1061472 ATP7B, the gene encoding for the Cu transporter ATPase7B. Our meta-analysis showed decreased Cu in AD brain specimens, increased Cu and nonbound ceruloplasmin (Non-Cp) Cu in serum/plasma samples, and unchanged ceruloplasmin. Serum/plasma Cu excess was associated with a three to fourfold increase in the risk of having AD. Our replication study confirmed meta-analysis results and showed that carriers of the ATP7B AG haplotype were significantly more frequent in the AD group. Overall, our study shows that AD patients fail to maintain a Cu metabolic balance and reveals the presence of a percentage of AD patients carrying ATP7B AG haplotype and presenting Non-Cp Cu excess, which suggest that a subset of AD subjects is prone to Cu imbalance. This AD subtype can be the target of precision medicine-based strategies tackling Cu dysregulation.

Copper Dependent Modulation of α-Synuclein Phosphorylation in Differentiated SHSY5Y Neuroblastoma Cells

Copper (Cu) dyshomeostasis plays a pivotal role in several neuropathologies, such as Parkinson's disease (PD). Metal accumulation in the central nervous system (CNS) could result in loss-of-function of proteins involved in Cu metabolism and redox cycling, generating reactive oxygen species (ROS). Moreover, neurodegenerative disorders imply the presence of an excess of misfolded proteins known to lead to neuronal damage. In PD, Cu accumulates in the brain, binds α-synuclein, and initiates its aggregation. We assessed the correlation between neuronal differentiation, Cu homeostasis regulation, and α-synuclein phosphorylation. At this purpose, we used differentiated SHSY5Y neuroblastoma cells to reproduce some of the characteristics of the dopaminergic neurons. Here, we reported that differentiated cells expressed a significantly higher amount of a copper transporter protein 1 (CTR1), increasing the copper uptake. Cells also showed a significantly more phosphorylated form of α-synuclein, further increased by copper treatment, without modifications in α-synuclein levels. This effect depended on the upregulation of the polo-like kinase 2 (PLK2), whereas the levels of the relative protein phosphatase 2A (PP2A) remained unvaried. No changes in the oxidative state of the cells were identified. The Cu dependent alteration of α-synuclein phosphorylation pattern might potentially offer new opportunities for clinical intervention.

A Cu-bis(imidazole) Substrate Intermediate Is the Catalytically Competent Center for Catechol Oxidase Activity of Copper Amyloid-β

Interaction of copper ions with Aβ peptides alters the redox activity of the metal ion and can be associated with neurodegeneration. Many studies deal with the characterization of the copper binding mode responsible for the reactivity. Oxidation experiments of dopamine and related catechols by copper(II) complexes with the N-terminal amyloid-β peptides Aβ₁₆ and Aβ₉, and the Aβ₁₆[H6A] and Aβ₁₆[H13A] mutant forms, both in their free amine and N-acetylated forms show that efficient reactivity requires the oxygenation of a Cu^I-bis(imidazole) complex with a bound substrate. Therefore, the active intermediate for catechol oxidation differs from the proposed “in-between state” for the catalytic oxidation of ascorbate. During the catechol oxidation process, hydrogen peroxide and superoxide anion are formed but give only a minor contribution to the reaction.

The redox cycling of copper bound to amyloid-β peptide requires the generation of a Cu(I)-Aβ-catecholate complex. When copper(II) is confined in the N-terminal portion, its reduction is slow and causes a shift toward a bis-His coordination environment. The addition of catechol to the Cu(I)-bis(imidazole) complex results in a faster reaction with dioxygen. The reactive species for catechol oxidation does not correspond to the proposed “in-between state” for ascorbate oxidation.

Novel Quinoline-Based Thiazole Derivatives for Selective Detection of Fe3+, Fe2+, and Cu2+ Ions

New quinoline-based thiazole derivatives QPT and QBT were synthesized and characterized by various spectroscopic and single-crystal X-ray crystallographic studies. The metal-sensing properties of the probes were further examined by absorption and fluorescence spectrometry. The fluorescence intensity of QPT and QBT was remarkably quenched during the addition of Fe³⁺, Fe²⁺, and Cu²⁺ ions in THF/H₂O (1:1) at pH = 7.4 in HEPES buffer, while the addition of other metal ions did not affect the fluorescence intensity of the ligands. The detection ability of the probes QPT and QBT was further investigated by titration with various equivalents of metal ions, optimized pH ranges for detection, and reversibility with Na₂EDTA for biological applications.

On the propagation of the OH radical produced by Cu-amyloid beta peptide model complexes. Insight from molecular modelling

Oxidative stress and metal dyshomeostasis are considered as crucial factors in the pathogenesis of Alzheimer's disease (AD). Indeed, transition metal ions such as Cu(ii) can generate Reactive Oxygen Species (ROS) via O₂ Fenton-like reduction, catalyzed by Cu(ii) coordinated to the Amyloid beta (Aβ) peptide. Despite intensive effort, the mechanisms of ROS-induced molecular damage remain poorly understood. In the present paper, we investigate on the basis of molecular modelling computations the mechanism of OH radical propagation toward the Aβ peptide, starting from the end-product of OH radical generation by Cu(ii)·Aβ. We evaluate (i) the OH oxidative capacity, as well as the energetics of the possible Aβ oxidation target residues, by quantum chemistry Density Functional Theory (DFT) on coordination models of Cu(ii)/OH/Aβ and (ii) the motion of the OH˙ approaching the Aβ target residues by classical Molecular Dynamics (MD) on the full peptide Cu(ii)/OH/Aβ(1-16). The results show that the oxidative capacity of OH coordinated Cu(ii)Aβ is significantly lower than that of the free OH radical and that propagation toward Aβ Asp and His residues is favoured over Tyr residues. These results are discussed on the basis of the recent literature on in vitro Aβ metal-catalyzed oxidation and on the possible implications for the AD oxidative stress mechanism.

Zinc Therapy in Early Alzheimer's Disease: Safety and Potential Therapeutic Efficacy

Zinc therapy is normally utilized for treatment of Wilson disease (WD), an inherited condition that is characterized by increased levels of non-ceruloplasmin bound ('free') copper in serum and urine. A subset of patients with Alzheimer's disease (AD) or its prodromal form, known as Mild Cognitive Impairment (MCI), fail to maintain a normal copper metabolic balance and exhibit higher than normal values of non-ceruloplasmin copper. Zinc's action mechanism involves the induction of intestinal cell metallothionein, which blocks copper absorption from the intestinal tract, thus restoring physiological levels of non-ceruloplasmin copper in the body. On this basis, it is employed in WD. Zinc therapy has shown potential beneficial effects in preliminary AD clinical trials, even though the studies have missed their primary endpoints, since they have study design and other important weaknesses. Nevertheless, in the studied AD patients, zinc effectively decreased non-ceruloplasmin copper levels and showed potential for improved cognitive performances with no major side effects. This review discusses zinc therapy safety and the potential therapeutic effects that might be expected on a subset of individuals showing both cognitive complaints and signs of copper imbalance.

Copper homeostasis: Emerging target for cancer treatment

Copper (Cu) is an essential micronutrient involved in a variety of fundamental biological processes. Recently, disorder of Cu homeostasis can be observed in many malignancies. Elevated Cu levels in serum and tissue are correlated with cancer progression. Hence, targeting Cu has emerged as a novel strategy in cancer treatment. This review provides an overview of physiological Cu metabolism and its homeostasis, followed by a discussion of the dysregulation of Cu homeostasis in cancer and the effects of Cu on cancer progression. Finally, recent therapeutic advances using Cu coordination complexes as anticancer agents, as well as the mechanisms of their anti-cancer action are discussed. This review contributes full comprehension to the role of Cu in cancer and demonstrates the broad application prospect of Cu coordination compounds as potential therapeutic agents.

Agricultural Use of Copper and Its Link to Alzheimer's Disease

Copper is an essential nutrient for plants, animals, and humans because it is an indispensable component of several essential proteins and either lack or excess are harmful to human health. Recent studies revealed that the breakdown of the regulation of copper homeostasis could be associated with Alzheimer's disease (AD), the most common form of dementia. Copper accumulation occurs in human aging and is thought to increase the risk of AD for individuals with a susceptibility to copper exposure. This review reports that one of the leading causes of copper accumulation in the environment and the human food chain is its use in agriculture as a plant protection product against numerous diseases, especially in organic production. In the past two decades, some countries and the EU have invested in research to reduce the reliance on copper. However, no single alternative able to replace copper has been identified. We suggest that agroecological approaches are urgently needed to design crop protection strategies based on the complementary actions of the wide variety of crop protection tools for disease control.

Mechanistic approaches for chemically modifying the coordination sphere of copper-amyloid-β complexes

Neurotoxic implications of the interactions between Cu(I/II) and amyloid-β (Aβ) indicate a connection between amyloid cascade hypothesis and metal ion hypothesis with respect to the neurodegeneration associated with Alzheimer's disease (AD). Herein, we report a mechanistic strategy for modifying the first coordination sphere of Cu(II) bound to Aβ utilizing a rationally designed peptide modifier, L1. Upon reacting with L1, a metal-binding histidine (His) residue, His14, in Cu(II)-Aβ was modified through either covalent adduct formation, oxidation, or both. Consequently, the reactivity of L1 with Cu(II)-Aβ was able to disrupt binding of Cu(II) to Aβ and result in chemically modified Aβ with altered aggregation and toxicity profiles. Our molecular-level mechanistic studies revealed that such L1-mediated modifications toward Cu(II)-Aβ could stem from the molecule's ability to 1) interact with Cu(II)-Aβ and 2) foster copper-O₂ chemistry. Collectively, our work demonstrates the development of an effective approach to modify Cu(II)-Aβ at a metal-binding amino acid residue and consequently alter Aβ's coordination to copper, aggregation, and toxicity, supplemented with an in-depth mechanistic perspective regarding such reactivity.