Differential modulation of Alzheimer's disease amyloid beta-peptide accumulation by diverse classes of metal ligands

Transdermal Application of Soluble CuII(atsm) Increases Brain and Spinal Cord Uptake Compared to Gavage with an Insoluble Suspension

Cu^II(atsm) is a blood-brain barrier permeant copper(II) compound that is under investigation in human clinical trials for the treatment of neurodegenerative diseases of the central nervous system (CNS). Imaging in humans by positron emission tomography shows the compound accumulates in affected regions of the CNS in patients. Most therapeutic studies to date have utilised oral administration of Cu^II(atsm) in an insoluble form, as either solid tablets or a liquid suspension. However, two pre-clinical studies have demonstrated disease-modifying outcomes following transdermal application of soluble Cu^II(atsm) prepared in dimethyl sulphoxide. Whether differences in the method of administration lead to different degrees of tissue accumulation of the compound has never been examined. Here, we compare the two methods of administration in wild-type mice by assessing changes in tissue concentrations of copper. Both administration methods resulted in elevated copper concentrations in numerous tissues, with the largest increases evident in the liver, brain and spinal cord. In all instances where treatment with Cu^II(atsm) resulted in elevated tissue copper, transdermal application of soluble Cu^II(atsm) led to higher concentrations of copper. In contrast to Cu^II(atsm), an equivalent dose of copper(II) chloride resulted in minimal changes to tissue copper concentrations, regardless of the administration method. Data presented herein provide quantitative insight to transdermal application of soluble Cu^II(atsm) as a potential alternative to oral administration of the compound in an insoluble formulation.

His-Rich Domain of Selenoprotein P Ameliorates Neuropathology and Cognitive Deficits by Regulating TrkB Pathway and Zinc Homeostasis in an Alzheimer Model of Mice

Selenoproteins are a family of special proteins that contain the 21st amino acid, selenocysteine (Sec), in their sequence. Selenoprotein P has 10 Sec residues and modulates selenium homeostasis and redox balance in the brain. Previously, we found that the Sec-devoid His-rich motif of selenoprotein P (Selenop-H) suppressed metal-induced aggregation and neurotoxicities of both Aβ and tau in vitro. To investigate the intervening capacity of Selenop-H on the neuropathology and cognitive deficits of triple transgenic AD (3 × Tg-AD) mice, the Selenop-H gene packaged in rAAV9 was delivered into the hippocampal CA3 regions of mice via stereotaxic injection. Four months later, we demonstrated that Selenop-H (1) improved the spatial learning and memory deficits, (2) alleviated neuron damage and synaptic protein loss, (3) inhibited both tau pathology and amyloid beta protein (Aβ) aggregation, (4) activated both BDNF- and Src-mediated TrkB signaling, and (5) increased MT3 and ZnT3 levels and restored Zn²⁺ homeostasis in the mice model of AD. The study revealed that Selenop-H is potent in ameliorating AD-related neuropathology and cognitive deficits by modulating TrkB signaling and Zn²⁺ homeostasis.

Protein Tyrosine Phosphatase 1B Inhibitors: A Novel Therapeutic Strategy for the Management of type 2 Diabetes Mellitus

Diabetes is one of the most common endocrine non-communicable metabolic disorders which is mainly caused either due to insufficient insulin or inefficient insulin or both together and is characterized by hyperglycemia. Diabetes emerged as a serious health issue in the industrialized and developing country especially in the Asian pacific region. Out of the two major categories of diabetes mellitus, type 2 diabetes is more prevalent, almost 90 to 95% cases, and the main cause of this is insulin resistance. The main cause of the progression of type 2 diabetes mellitus has been found to be insulin resistance. The type 2 diabetes mellitus may be managed by the change in lifestyle, physical activities, dietary modifications and medications. The major currently available management strategies are sulfonylureas, biguanides, thiazolidinediones, α-glucosidase inhibitors, dipeptidyl peptidase-IV inhibitors, and glucagon-like peptide-1 (GLP-1) agonist. Binding of insulin on the extracellular unit of insulin receptor sparks tyrosine kinase of the insulin receptor which induces autophosphorylation. The phosphorylation of the tyrosine is regulated by insulin and leptin molecules. Protein tyrosine phosphatase-1B (PTP1B) works as a negative governor for the insulin signalling pathways, as it dephosphorylates the tyrosine of the insulin receptor and suppresses the insulin signalling cascade. The compounds or molecules which inhibit the negative regulation of PTP1B can have an inductive effect on the insulin pathway and finally help in the management of diabetes mellitus. PTP1B could be an emerging therapeutic strategy for diabetes management. There are a number of clinical and basic research results which suggest that induced expression of PTP1B reduces insulin resistance. In this review, we briefly elaborate and explain the place of PTP1B and its significance in diabetes as well as a recent development in the PTP1B inhibitors as an antidiabetic therapy.

Modification of Biodistribution and Brain Uptake of Copper Bis(thiosemicarbazonato) Complexes by the Incorporation of Amine and Polyamine Functional Groups

The synthesis of new bis(thiosemicarbazonato)copper(II) complexes featuring polyamine substituents via selective transamination reactions is presented. Polyamines of different lengths, with different ionizable substituent groups, were used to modify and adjust the hydrophilic/lipophilic balance of the copper complexes. The new analogues were radiolabeled with copper-64 and their lipophilicities estimated using distribution coefficients. The cell uptake of the new polyamine complexes was investigated with preliminary in vitro biological studies using a neuroblastoma cancer cell line. The in vivo biodistribution of three of the new analogues was investigated in vivo in mice using positron-emission tomography imaging, and one of the new complexes was compared to [⁶⁴Cu]Cu(atsm) in an A431 squamous cell carcinoma xenograft model. Modification of the copper complexes with various amine-containing functional groups alters the biodistribution of the complexes in mice. One complex, with a pendent ( N, N-dimethylamino)ethane functional group, displayed tumor uptake similar to that of [⁶⁴Cu]Cu(atsm) but higher brain uptake, suggesting that this compound has the potential to be of use in the diagnostic brain imaging of tumors and neurodegenerative diseases.

Iron and Copper Intracellular Chelation as an Anticancer Drug Strategy

A very promising direction in the development of anticancer drugs is inhibiting the molecular pathways that keep cancer cells alive and able to metastasize. Copper and iron are two essential metals that play significant roles in the rapid proliferation of cancer cells and several chelators have been studied to suppress the bioavailability of these metals in the cells. This review discusses the major contributions that Cu and Fe play in the progression and spreading of cancer and evaluates select Cu and Fe chelators that demonstrate great promise as anticancer drugs. Efforts to improve the cellular delivery, efficacy, and tumor responsiveness of these chelators are also presented including a transmetallation strategy for dual targeting of Cu and Fe. To elucidate the effectiveness and specificity of Cu and Fe chelators for treating cancer, analytical tools are described for measuring Cu and Fe levels and for tracking the metals in cells, tissue, and the body.

Iron and Copper Intracellular Chelation as an Anticancer Drug Strategy

A very promising direction in the development of anticancer drugs is inhibiting the molecular pathways that keep cancer cells alive and able to metastasize. Copper and iron are two essential metals that play significant roles in the rapid proliferation of cancer cells and several chelators have been studied to suppress the bioavailability of these metals in the cells. This review discusses the major contributions that Cu and Fe play in the progression and spreading of cancer and evaluates select Cu and Fe chelators that demonstrate great promise as anticancer drugs. Efforts to improve the cellular delivery, efficacy, and tumor responsiveness of these chelators are also presented including a transmetallation strategy for dual targeting of Cu and Fe. To elucidate the effectiveness and specificity of Cu and Fe chelators for treating cancer, analytical tools are described for measuring Cu and Fe levels and for tracking the metals in cells, tissue, and the body.

Copper and Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of adult neurode-generation and is characterised by progressive loss of cognitive function leading to death. The neuropathological hallmarks include extracellular amyloid plaque accumulation in affected regions of the brain, formation of intraneuronal neurofibrillary tangles, chronic neuroinflammation, oxidative stress, and abnormal biometal homeostasis. Of the latter, major changes in copper (Cu) levels and localisation have been identified in AD brain, with accumulation of Cu in amyloid deposits, together with deficiency of Cu in some brain regions. The amyloid precursor protein (APP) and the amyloid beta (Aβ) peptide both have Cu binding sites, and interaction with Cu can lead to potentially neurotoxic outcomes through generation of reactive oxygen species. In addition, AD patients have systemic changes to Cu metabolism, and altered Cu may also affect neuroinflammatory outcomes in AD. Although we still have much to learn about Cu homeostasis in AD patients and its role in disease aetiopathology, therapeutic approaches for regulating Cu levels and interactions with Cu-binding proteins in the brain are currently being developed. This review will examine how Cu is associated with pathological changes in the AD brain and how these may be targeted for therapeutic intervention.

Protein tyrosine phosphatase 1B inhibitors as antidiabetic agents - A brief review

Diabetes mellitus and obesity are one of the most common health issues spread throughout world and raised the medical attention to find the new effective agents to treat these disease state. Occurrence of the drug resistance to the insulin and leptin receptor is also challenging major issues. The molecules that can overcome this resistance problem could be effective for the treatment of both type II diabetes and obesity. Protein Tyrosine Phosphatase (PTP) has emerged as new promising targets for therapeutic purpose in recent years. Protein Tyrosine Phosphatase 1B (PTP 1B) act as a negative regulator of insulin and leptin receptor signalling pathways. Several approaches have been successfully applied to find out potent and selective inhibitors. This article reviews PTP 1B inhibitors; natural, synthetic and semi-synthetic that showed inhibition towards enzyme as a major target for the management of type II diabetes. These studies could be contributing the future development of PTP 1B inhibitors as drugs.

Matrix metalloproteinases in the brain and blood-brain barrier: Versatile breakers and makers

Matrix metalloproteinases are versatile endopeptidases with many different functions in the body in health and disease. In the brain, matrix metalloproteinases are critical for tissue formation, neuronal network remodeling, and blood-brain barrier integrity. Many reviews have been published on matrix metalloproteinases before, most of which focus on the two best studied matrix metalloproteinases, the gelatinases MMP-2 and MMP-9, and their role in one or two diseases. In this review, we provide a broad overview of the role various matrix metalloproteinases play in brain disorders. We summarize and review current knowledge and understanding of matrix metalloproteinases in the brain and at the blood-brain barrier in neuroinflammation, multiple sclerosis, cerebral aneurysms, stroke, epilepsy, Alzheimer's disease, Parkinson's disease, and brain cancer. We discuss the detrimental effects matrix metalloproteinases can have in these conditions, contributing to blood-brain barrier leakage, neuroinflammation, neurotoxicity, demyelination, tumor angiogenesis, and cancer metastasis. We also discuss the beneficial role matrix metalloproteinases can play in neuroprotection and anti-inflammation. Finally, we address matrix metalloproteinases as potential therapeutic targets. Together, in this comprehensive review, we summarize current understanding and knowledge of matrix metalloproteinases in the brain and at the blood-brain barrier in brain disorders.

Melatonin regulates the transcription of βAPP-cleaving secretases mediated through melatonin receptors in human neuroblastoma SH-SY5Y cells

Melatonin is involved in the control of various physiological functions, such as sleep, cell growth and free radical scavenging. The ability of melatonin to behave as an antioxidant, together with the fact that the Alzheimer-related amyloid β-peptide (Aβ) triggers oxidative stress through hydroxyl radical-induced cell death, suggests that melatonin could reduce Alzheimer's pathology. Although the exact etiology of Alzheimer's disease (AD) remains to be established, excess Aβ is believed to be the primary contributor to the dysfunction and degeneration of neurons that occurs in AD. Aβ peptides are produced via the sequential cleavage of β-secretase β-site APP-cleaving enzyme 1 (BACE1) and γ-secretase (PS1/PS2), while α-secretase (ADAM10) prevents the production of Aβ peptides. We hypothesized that melatonin could inhibit BACE1 and PS1/PS2 and enhance ADAM10 expression. Using the human neuronal SH-SY5Y cell line, we found that melatonin inhibited BACE1 and PS1 and activated ADAM10 mRNA level and protein expression in a concentration-dependent manner and mediated via melatonin G protein-coupled receptors. Melatonin inhibits BACE1 and PS1 protein expressions through the attenuation of nuclear factor-κB phosphorylation (pNF-κB). Moreover, melatonin reduced BACE1 promoter transactivation and consequently downregulated β-secretase catalytic activity. The present data show that melatonin is not only a potential regulator of β/γ-secretase but also an activator of α-secretase expression through the activation of protein kinase C, thereby favoring the nonamyloidogenic pathway over the amyloidogenic pathway. Altogether, our findings suggest that melatonin may be a potential therapeutic agent for reducing the risk of AD in humans.

Metal complexes and metalloproteases: targeting conformational diseases

In recent years many metalloproteases (MPs) have been shown to play important roles in the development of various pathological conditions. Although most of the literature is focused on matrix MPs (MMPs), many other MPs have been demonstrated to be involved in the degradation of peptides or proteins whose accumulation and dyshomeostasis are considered as being responsible for the development of conformational diseases, i.e., diseases where non-native protein conformations lead to protein aggregation. It seems clear that, at least in principle, it must be possible to control the levels of many aggregation-prone proteins not only by reducing their production, but also by enhancing their catabolism. Metal complexes that can perform this function were designed and tested according to at least two different strategies: (i) intervening on the endogenous MPs by directly or indirectly modulating their activity; (ii) acting as artificial MPs, replacing or synergistically functioning with endogenous MPs. These two different bioinorganic approaches are widely represented in the current literature and the aim of this review is to rationally organize and discuss both of them so as to give a critical insight into these approaches and highlighting their limitations and future perspectives.

The role of copper ions in pathophysiology and fluorescent sensors for the detection thereof

Copper ions are crucial to life, and some fundamental roles of copper in pathophysiology have been elucidated using fluorescent sensors.

Copper as a key regulator of cell signalling pathways. Expert Rev Mol Med. 2014;16:e11. [PMID: 24849048 DOI: 10.1017/erm.2014.11]

Copper is an essential element in many biological processes. The critical functions associated with copper have resulted from evolutionary harnessing of its potent redox activity. This same property also places copper in a unique role as a key modulator of cell signal transduction pathways. These pathways are the complex sequence of molecular interactions that drive all cellular mechanisms and are often associated with the interplay of key enzymes including kinases and phosphatases but also including intracellular changes in pools of smaller molecules. A growing body of evidence is beginning to delineate the how, when and where of copper-mediated control over cell signal transduction. This has been driven by research demonstrating critical changes to copper homeostasis in many disorders including cancer and neurodegeneration and therapeutic potential through control of disease-associated cell signalling changes by modulation of copper-protein interactions. This timely review brings together for the first time the diverse actions of copper as a key regulator of cell signalling pathways and discusses the potential strategies for controlling disease-associated signalling processes using copper modulators. It is hoped that this review will provide a valuable insight into copper as a key signal regulator and stimulate further research to promote our understanding of copper in disease and therapy.

Protein tyrosine phosphatase inhibition by metals and metal complexes

SIGNIFICANCE

Protein tyrosine phosphatases (PTPs) play essential roles in controlling cell proliferation, differentiation, communication, and adhesion. The dysregulated activities of PTPs are involved in the pathogenesis of a number of human diseases such as cancer, diabetes, and autoimmune diseases.

RECENT ADVANCES

Many PTPs have emerged as potential new targets for novel drug discovery. PTP inhibitors have attracted much attention. Many PTP inhibitors have been developed. Some of them have been proven to be efficient in lowering blood glucose levels in vivo or inhibiting tumor xenograft growth.

CRITICAL ISSUES

Some metal ions and metal complexes potently inhibit PTPs. The metal atoms within metal complexes play an important role in PTP binding, while ligand structures influence the inhibitory potency and selectivity. Some metal complexes can penetrate the cell membrane and selectively bind to their targeting PTPs, enhancing the phosphorylation of the related substrates and influencing cellular metabolism. PTP inhibition is potentially involved in the pathophysiological and toxicological processes of metals and some PTPs may be cellular targets of certain metal-based therapeutic agents.

FUTURE DIRECTIONS

Investigating the structural basis of the interactions between metal complexes and PTPs would facilitate a comprehensive understanding of the structure-activity relationship and accelerate the development of promising metal-based drugs targeting specific PTPs.

Biological metals and metal-targeting compounds in major neurodegenerative diseases

Metals are functionally essential, but redistribute in neurodegenerative disease where they induce protein aggregates, catalyze radical formation, and lose bioavailability.

Lipophilic adamantyl- or deferasirox-based conjugates of desferrioxamine B have enhanced neuroprotective capacity: implications for Parkinson disease

Parkinson disease (PD) is a neurodegenerative disease characterized by death of dopaminergic neurons in the substantia nigra region of the brain. Iron content is also elevated in this region in PD and is implicated in the pathobiology of the disease. Desferrioxamine B (DFOB) is a high-affinity iron chelator and has shown efficacy in animal models of Parkinson disease. The high water solubility of DFOB, however, attenuates its ability to enter the brain. In this study, we have conjugated DFOB to derivatives of adamantane or the clinical iron chelator deferasirox to produce lipophilic compounds designed to increase the bioavailability of DFOB to brain cells. We found that the novel compounds are highly effective in preventing iron-mediated paraquat and hydrogen peroxide toxicity in neuronal-like BE2-M17 dopaminergic cells, primary neurons, and iron-loaded or glutathione-depleted primary astrocytes. The compounds also alleviated paraquat toxicity in BE2-M17 cells that express the PD-causing A30P mutation of α-synuclein. This protection was ∼66-fold more potent than DFOB alone and also more effective than other cell-permeative metal chelators, clioquinol and phenanthroline. These results demonstrate that increasing the bioavailability of DFOB through the conjugation of lipophilic fragments greatly enhances its protective capacity. These novel compounds have potential as therapeutics for the treatment of PD and other conditions of Fe dyshomeostasis.

Therapeutic redistribution of metal ions to treat Alzheimer's disease

Currently, therapeutics that modify Alzheimer's disease (AD)are not available. Increasing age is the primary risk factor for AD and due to an aging global population the urgent need for effective therapeutics increases every year. This Account presents the development of an AD treatment strategy that incorporates diverse compounds with a common characteristic: the ability to redistribute metal ions within the brain. Central to cognitive decline in AD is the amyloid-β peptide (Aβ) that accumulates in the AD brain. A range of therapeutic strategies have been developed based on the premise that decreasing the brain Aβ burden will attenuate the severity of the disease symptoms. Unfortunately these treatments have failed to show any positive outcomes in large-scale clinical trials, raising many questions regarding whether therapeutics for AD can rely solely on decreasing Aβ levels. An alternate strategy is to target the interaction between Aβ and metal ions using compounds with the potential to redistribute metal ions within the brain. The original rationale for this strategy came from studies showing that metal ions promote Aβ toxicity and aggregation. In initial studies using the prototype metal-chelating compound clioquinol (CQ), CQ prevented Aβ toxicity in vitro, out-competed Aβ for metal ions without affecting the activity of metal-dependent enzymes, and attenuated the rate of cognitive decline in AD subjects in a small phase II clinical trial. All these outcomes were consistent with the original hypothesized mechanism of action for CQ where prevention or reversal of the extracellular Aβ-metal interactions could prevent Aβ toxicity. Soon after the completion of these studies, a new body of work began to suggest that this hypothesized mechanism of action for CQ was simplistic and that other factors were also important for the positive therapeutic outcomes. Perhaps most significantly, it was shown that after CQ sequesters metal ions the neutral CQ-metal complex crosses cell membranes to increase intracellular levels of the metals, thereby initiating protective cell signaling cascades. The activity of CQ therefore appeared to be two-fold: it prevented toxic interactions between Aβ and metal ions outside the cell, and it redistributed the metal ions into the cell to promote healthy cell function. To determine the significance of redistributing metal ions into the cell, glyoxalbis(N(4)-methylthiosemicarbazonato)Cu(II) [Cu(II)(gtsm)] was tested in models of AD. Cu(II)(gtsm) delivers Cu into cells, but, unlike CQ, it cannot out-compete Aβ for metal ions. When tested in AD model mice, the Cu(II)(gtsm) treatment restored cognitive function back to levels expected for cognitively healthy mice. The most advanced compound from this therapeutic strategy, PBT2, can sequester metal ions from Aβ and redistribute them into the cell like CQ. PBT2 improved cognition in a phase II clinical trial with AD patients, and further clinical testing is currently underway.

Modulating metals as a therapeutic strategy for Alzheimer's disease

In 1906, Alois Alzheimer first characterized the disease that bears his name. Despite intensive research, which has led to a better understanding of the pathology, there is no effective treatment for this disease. Of the drugs approved by the US FDA, none are disease modifying, only symptomatic. Unfortunately, there have been a number of failed clinical trials in the past 10 years where studies show either no cognitive improvement or, worse, serious side effects associated with treatment. Hence, there is a need for the field to look at alternative approaches to therapy. In this review, we will discuss how metal dyshomeostasis occurs in aging and Alzheimer's disease. Concomitantly, we will discuss how targeting this dyshomeostasis offers an effective and novel therapeutic approach. Thus far, compounds that mediate these effects have shown great potential in both preclinical animal studies as well as in early-stage clinical trials.

Micronutrient (Zn, Cu, Fe)-gene interactions in ageing and inflammatory age-related diseases: implications for treatments

In ageing, alterations in inflammatory/immune response and antioxidant capacity lead to increased susceptibility to diseases and loss of mobility and agility. Various essential micronutrients in the diet are involved in age-altered biological functions. Micronutrients (zinc, copper, iron) play a pivotal role either in maintaining and reinforcing the immune and antioxidant performances or in affecting the complex network of genes (nutrigenomic approach) involved in encoding proteins for a correct inflammatory/immune response. By the other side, the genetic inter-individual variability may affect the absorption and uptake of the micronutrients (nutrigenetic approach) with subsequent altered effects on inflammatory/immune response and antioxidant activity. Therefore, the individual micronutrient-gene interactions are fundamental to achieve healthy ageing. In this review, we report and discuss the role of micronutrients (Zn, Cu, Fe)-gene interactions in relation to the inflammatory status and the possibility of a supplement in the event of a micronutrient deficiency or chelation in presence of micronutrient overload in relation to specific polymorphisms of inflammatory proteins or proteins related of the delivery of the micronutriemts to various organs and tissues. In this last context, we report the protein-metal speciation analysis in order to have, coupled with micronutrient-gene interactions, a more complete picture of the individual need in micronutrient supplementation or chelation to achieve healthy ageing and longevity.

The anti-neurodegenerative agent clioquinol regulates the transcription factor FOXO1a

Many diseases of aging including AD (Alzheimer's disease) and T2D (Type 2 diabetes) are strongly associated with common risk factors, suggesting that there may be shared aging mechanisms underlying these diseases, with the scope to identify common cellular targets for therapy. In the present study we have examined the insulin-like signalling properties of an experimental AD 8-hydroxyquinoline drug known as CQ (clioquinol). The IIS [insulin/IGF-1 (insulin-like growth factor-1) signalling] kinase Akt/PKB (protein kinase B) inhibits the transcription factor FOXO1a (forkhead box O1a) by phosphorylating it on residues that trigger its exit from the nucleus. In HEK (human embryonic kidney)-293 cells, we found that CQ treatment induces similar responses. A key transcriptional response to IIS is the inhibition of hepatic gluconeogenic gene expression, and, in rat liver cells, CQ represses expression of the key gluconeogenic regulatory enzymes PEPCK (phosphoenolpyruvate carboxykinase) and G6Pase (glucose-6-phosphatase). The effects on FOXO1a and gluconeogenic gene expression require the presence of Zn2+ ions, reminiscent of much earlier studies examining diabetogenic properties of 8-hydroxyquinolines. Comparative investigation of the signalling properties of a panel of these compounds demonstrates that CQ alone exhibits FOXO1a regulation without diabetogenicity. Our results suggest that Zn2+-dependent regulation of FOXOs and gluconeogenesis may contribute to the therapeutic properties of this drug. Further investigation of this signalling response might illuminate novel pharmacological strategies for the treatment of age-related diseases.

Neurodegeneration in Alzheimer disease: role of amyloid precursor protein and presenilin 1 intracellular signaling

Alzheimer disease (AD) is a heterogeneous neurodegenerative disorder characterized by (1) progressive loss of synapses and neurons, (2) intracellular neurofibrillary tangles, composed of hyperphosphorylated Tau protein, and (3) amyloid plaques. Genetically, AD is linked to mutations in few proteins amyloid precursor protein (APP) and presenilin 1 and 2 (PS1 and PS2). The molecular mechanisms underlying neurodegeneration in AD as well as the physiological function of APP are not yet known. A recent theory has proposed that APP and PS1 modulate intracellular signals to induce cell-cycle abnormalities responsible for neuronal death and possibly amyloid deposition. This hypothesis is supported by the presence of a complex network of proteins, clearly involved in the regulation of signal transduction mechanisms that interact with both APP and PS1. In this review we discuss the significance of novel finding related to cell-signaling events modulated by APP and PS1 in the development of neurodegeneration.

Alzheimer's disease & metals: therapeutic opportunities

Alzheimer's disease (AD) is the most common age related neurodegenerative disease. Currently, there are no disease modifying drugs, existing therapies only offer short-term symptomatic relief. Two of the pathognomonic indicators of AD are the presence of extracellular protein aggregates consisting primarily of the Aβ peptide and oxidative stress. Both of these phenomena can potentially be explained by the interactions of Aβ with metal ions. In addition, metal ions play a pivotal role in synaptic function and their homeostasis is tightly regulated. A breakdown in this metal homeostasis and the generation of toxic Aβ oligomers are likely to be responsible for the synaptic dysfunction associated with AD. Therefore, approaches that are designed to prevent Aβ metal interactions, inhibiting the formation of toxic Aβ species as well as restoring metal homeostasis may have potential as disease modifying strategies for treating AD. This review summarizes the physiological and pathological interactions that metal ions play in synaptic function with particular emphasis placed on interactions with Aβ. A variety of therapeutic strategies designed to address these pathological processes are also described. The most advanced of these strategies is the so-called 'metal protein attenuating compound' approach, with the lead molecule PBT2 having successfully completed early phase clinical trials. The success of these various strategies suggests that manipulating metal ion interactions offers multiple opportunities to develop disease modifying therapies for AD.

Mononuclear copper(II) complexes with 3,5-substituted-4-salicylidene-amino-3,5-dimethyl-1,2,4-triazole: synthesis, structure and potent inhibition of protein tyrosine phosphatases

Six copper complexes of Schiff base ligands containing 3,5-substituted-4-salicylideneamino-3,5-dimethyl-1,2,4-triazole have been synthesized and well characterized. The structures of complexes 1 and 2 were determined by X-ray crystal analysis. Fluorescence and potentiometric study indicated that in the physiological pH range, one ligand was dissociated from the complexes to form 1:1 mononucleus copper complexes. The complexes potently inhibit protein tyrosine phosphatase 1B (PTP1B), T-cell protein tyrosine phosphatase (TCPTP), megakaryocyte protein tyrosine phosphatase 2 (PTP-MEG2) and Src homology phosphatase 1 (SHP-1) with 3-4 fold selectivity against PTP1B over TCPTP and PTP-MEG2, and 3-9 fold over SHP-1, but display almost no inhibition against Src homology phosphatase 2 (SHP-2). Complex 1 inhibits PTP1B with a competitive model with K(i) of 30 nM. Substitution with small groups at the phenyl of the ligand does not obviously influence the inhibitory ability of the complexes.

Selective acetylcholinesterase inhibitor activated by acetylcholinesterase releases an active chelator with neurorescuing and anti-amyloid activities

The finding that acetylcholinesterase (AChE) colocalizes with β-amyloid (Aβ) and promotes and accelerates Aβ aggregation has renewed an intense interest in developing new multifunctional AChE inhibitors as potential disease-modifying drugs for Alzheimer's therapy. To this end, we have developed a new class of selective AChE inhibitors with site-activated chelating activity. The identified lead, HLA20A, exhibits little affinity for metal (Fe, Cu, and Zn) ions but can be activated following inhibition of AChE to liberate an active chelator, HLA20. HLA20 has been shown to possess neuroprotective and neurorescuing activities in vitro and in vivo with the ability to lower amyloid precursor holoprotein (APP) expression and Aβ generation and inhibit Aβ aggregation induced by metal (Fe, Cu, and Zn) ion. HLA20A inhibited AChE in a time and concentration dependent manner with an HLA20A-AChE complex constant (K(i)) of 9.66 × 10(-6) M, a carbamylation rate (k(+2)) of 0.14 min(-1), and a second-order rate (k(i)) of 1.45 × 10 (4) M(-1) min(-1), comparable to those of rivastigmine. HLA20A showed little iron-binding capacity and activity against iron-induced lipid peroxidation (LPO) at concentrations of 1-50 μM, while HLA20 exhibited high potency in iron-binding and in inhibiting iron-induced LPO. At a concentration of 10 μM, HLA20A showed some activity against monoamine oxidase (MAO)-A and -B when tested in rat brain homogenates. Defined restrictively by Lipinski's rules, both HLA20A and HLA20 satisfied drug-like criteria and possible oral and brain permeability, but HLA20A was more lipophilic and considerably less toxic in human SHSY5Y neuroblastoma cells at high concentrations (25 or 50 μM). Together our data suggest that HLA20A may represent a promising lead for further development for Alzheimer's disease therapy.

Aluminum does not enhance beta-amyloid toxicity in rat hippocampal cultures

A number of environmental factors have been implicated in neurodegenerative disorders, including metallotoxins such as aluminum (Al). In the present study, the toxicity of Al-quinate (AlQ), a well-characterized Al complex, was investigated in primary rat hippocampal cultures in comparison to inorganic Al (Al-S). AlQ was significantly less toxic than Al-S during both short- (3h) and long-term (24h) incubations. The neuroprotective properties of quinic acid (which constitutes the quinate moiety of AlQ) against short-term incubations with Al-S were subsequently assessed, and the organic compound was found to provide full protection, comparable to synthetic metal chelating agents desferrioxamine and clioquinol. Finally, potential synergistic actions between Al (AlQ and Al-S) and beta-amyloid (Abeta) were investigated. Neither Al form appeared to enhance Abeta toxicity, in fact, AlQ significantly reduced Abeta toxicity. Collectively, this study highlights further the impact of structural features and physiological ligands of metal complexes on toxicity profiles, and reveals promising properties of quinic acid as a metal chelator. Despite previous reports suggesting synergistic toxicity between Al and Abeta, we could not identify such a mechanism in our investigation.

Cu(II) interaction with amyloid-beta peptide: a review of neuroactive mechanisms in AD brains

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by the dys-homeostasis of biometal metabolism, the extracellular accumulation of neurotoxic amyloid-beta (Abeta) peptide, the intracellular accumulation of hyperphosphorylated tau and the loss of synapses. Copper plays a key role in AD development. The Abeta peptide and amyloid precursor protein (APP), the parental molecule of Abeta, are modulated by copper in the brain. Increased copper concentration has been found in the AD brain that implies that copper may participate in the pathophysiology of AD. Copper can bind to APP and Abeta, then affects the structure and toxic of APP and Abeta. Some researchers have reported that copper could affect the formation of beta-sheet structure that is widely accepted as toxic secondary structure of Abeta. This review explores the role of copper on the conformation and aggregation of Abeta, and the copper-induced neuroactive mechanisms. Copper may be involved in the following pathways to affect the neuroactivation of Abeta: (1) change of the secondary structure of Abeta; (2) induction of oxidative stress in AD brains, and (3) regulation of cellular signal pathway. Thus, correcting brain copper imbalance may represent a relevant therapeutic target for Alzheimer's disease.

Zinc Inhibits Amyloid beta Production from Alzheimer's Amyloid Precursor Protein in SH-SY5Y Cells

Zinc released from excited glutamatergic neurons accelerates amyloid beta (Abeta) aggregation, underscoring the therapeutic potential of zinc chelation for the treatment of Alzheimer's disease (AD). Zinc can also alter Abeta concentration by affecting its degradation. In order to elucidate the possible role of zinc influx in secretase-processed Abeta production, SH-SY5Y cells stably expressing amyloid precursor protein (APP) were treated with pyrrolidine dithiocarbamate (PDTC), a zinc ionophore, and the resultant changes in APP processing were examined. PDTC decreased Abeta40 and Abeta42 concentrations in culture media bathing APP-expressing SH-SY5Y cells. Measuring the levels of a series of C-terminal APP fragments generated by enzymatic cutting at different APP-cleavage sites showed that both beta- and alpha-cleavage of APP were inhibited by zinc influx. PDTC also interfered with the maturation of APP. PDTC, however, paradoxically increased the intracellular levels of Abeta40. These results indicate that inhibition of secretase-mediated APP cleavage accounts -at least in part- for zinc inhibition of Abeta secretion.

Increasing Cu bioavailability inhibits Abeta oligomers and tau phosphorylation

Cognitive decline in Alzheimer's disease (AD) involves pathological accumulation of synaptotoxic amyloid-beta (Abeta) oligomers and hyperphosphorylated tau. Because recent evidence indicates that glycogen synthase kinase 3beta (GSK3beta) activity regulates these neurotoxic pathways, we developed an AD therapeutic strategy to target GSK3beta. The strategy involves the use of copper-bis(thiosemicarbazonoto) complexes to increase intracellular copper bioavailability and inhibit GSK3beta through activation of an Akt signaling pathway. Our lead compound Cu(II)(gtsm) significantly inhibited GSK3beta in the brains of APP/PS1 transgenic AD model mice. Cu(II)(gtsm) also decreased the abundance of Abeta trimers and phosphorylated tau, and restored performance of AD mice in the Y-maze test to levels expected for cognitively normal animals. Improvement in the Y-maze correlated directly with decreased Abeta trimer levels. This study demonstrates that increasing intracellular copper bioavailability can restore cognitive function by inhibiting the accumulation of neurotoxic Abeta trimers and phosphorylated tau.

Disordered proteins: biological membranes as two-dimensional aggregation matrices

Aberrant folded proteins and peptides are hallmarks of amyloidogenic diseases. However, the molecular processes that cause these proteins to adopt non-native structures in vivo and become cytotoxic are still largely unknown, despite intense efforts to establish a general molecular description of their behavior. Clearly, the fate of these proteins is ultimately linked to their immediate biochemical environment in vivo. In this review, we focus on the role of biological membranes, reactive interfaces that not only affect the conformational stability of amyloidogenic proteins, but also their aggregation rates and, probably, their toxicity. We first provide an overview of recent work, starting with findings regarding the amphiphatic amyloid-beta protein (Abeta), which give evidence that membranes can directly promote aggregation, and that the effectiveness in this process can be related to the presence of specific neuronal ganglioside lipids. In addition, we discuss the implications of recent research (medin as an detailed example) regarding putative roles of membranes in the misfolding behavior of soluble, non-amphiphatic proteins, which are attracting increasing interest. The potential role of membranes in exerting the toxic action of misfolded proteins will also be highlighted in a molecular context. In this review, we discuss novel NMR-based approaches for exploring membrane-protein interactions, and findings obtained using them, which we use to develop a molecular concept to describe membrane-mediated protein misfolding as a quasi-two-dimensional process rather than a three-dimensional event in a biochemical environment. The aim of the review is to provide researchers with a general understanding of the involvement of membranes in folding/misfolding processes in vivo, which might be quite universal and important for future research concerning amyloidogenic and misfolding proteins, and possible ways to prevent their toxic actions.

The anti-neurodegeneration drug clioquinol inhibits the aging-associated protein CLK-1

The development of neurodegenerative diseases such as Alzheimer, Parkinson, and Huntington disease is strongly age-dependent. Discovering drugs that act on the high rate of aging in older individuals could be a means of combating these diseases. Reduction of the activity of the mitochondrial enzyme CLK-1 (also known as COQ7) slows down aging in Caenorhabditis elegans and in mice. Clioquinol is a metal chelator that has beneficial effects in several cellular and animal models of neurodegenerative diseases as well as on Alzheimer disease patients. Here we show that clioquinol inhibits the activity of mammalian CLK-1 in cultured cells, an inhibition that can be blocked by iron or cobalt cations, suggesting that chelation is involved in the mechanism of action of clioquinol on CLK-1. We also show that treatment of nematodes and mice with clioquinol mimics a variety of phenotypes produced by mutational reduction of CLK-1 activity in these organisms. These results suggest that the surprising action of clioquinol on several age-dependent neurodegenerative diseases with distinct etiologies might result from a slowing down of the aging process through action of the drug on CLK-1. Our findings support the hypothesis that pharmacologically targeting aging-associated proteins could help relieve age-dependent diseases.