Cupric-amyloid beta peptide complex stimulates oxidation of ascorbate and generation of hydroxyl radical

Role of Metal Cations of Copper, Iron, and Aluminum and Multifunctional Ligands in Alzheimer's Disease: Experimental and Computational Insights

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of people around the world. Even though the causes of AD are not completely understood due to its multifactorial nature, some neuropathological hallmarks of its development have been related to the high concentration of some metal cations. These roles include the participation of these metal cations in the production of reactive oxygen species, which have been involved in neuronal damage. In order to avoid the increment in the oxidative stress, multifunctional ligands used to coordinate these metal cations have been proposed as a possible treatment to AD. In this review, we present the recent advances in experimental and computational works aiming to understand the role of two redox active and essential transition-metal cations (Cu and Fe) and one nonbiological metal (Al) and the recent proposals on the development of multifunctional ligands to stop or revert the damaging effects promoted by these metal cations.

Why the Ala-His-His Peptide Is an Appropriate Scaffold to Remove and Redox Silence Copper Ions from the Alzheimer’s-Related Aβ Peptide

The progressive, neurodegenerative Alzheimer’s disease (AD) is the most widespread dementia. Due to the ageing of the population and the current lack of molecules able to prevent or stop the disease, AD will be even more impactful for society in the future. AD is a multifactorial disease, and, among other factors, metal ions have been regarded as potential therapeutic targets. This is the case for the redox-competent Cu ions involved in the production of reactive oxygen species (ROS) when bound to the Alzheimer-related Aβ peptide, a process that contributes to the overall oxidative stress and inflammation observed in AD. Here, we made use of peptide ligands to stop the Cu(Aβ)-induced ROS production and we showed why the AHH sequence is fully appropriate, while the two parents, AH and AAH, are not. The AHH peptide keeps its beneficial ability against Cu(Aβ)-induced ROS, even in the presence of Zn^II-competing ions and other biologically relevant ions. The detailed kinetic mechanism by which AHH could exert its action against Cu(Aβ)-induced ROS is also proposed.

Aβ and Tau Interact with Metal Ions, Lipid Membranes and Peptide-Based Amyloid Inhibitors: Are These Common Features Relevant in Alzheimer’s Disease?

In the last two decades, the amyloid hypothesis, i.e., the abnormal accumulation of toxic Aβ assemblies in the brain, has been considered the mainstream concept sustaining research in Alzheimer’s Disease (AD). However, the course of cognitive decline and AD development better correlates with tau accumulation rather than amyloid peptide deposition. Moreover, all clinical trials of amyloid-targeting drug candidates have been unsuccessful, implicitly suggesting that the amyloid hypothesis needs significant amendments. Accumulating evidence supports the existence of a series of potentially dangerous relationships between Aβ oligomeric species and tau protein in AD. However, the molecular determinants underlying pathogenic Aβ/tau cross interactions are not fully understood. Here, we discuss the common features of Aβ and tau molecules, with special emphasis on: (i) the critical role played by metal dyshomeostasis in promoting both Aβ and tau aggregation and oxidative stress, in AD; (ii) the effects of lipid membranes on Aβ and tau (co)-aggregation at the membrane interface; (iii) the potential of small peptide-based inhibitors of Aβ and tau misfolding as therapeutic tools in AD. Although the molecular mechanism underlying the direct Aβ/tau interaction remains largely unknown, the arguments discussed in this review may help reinforcing the current view of a synergistic Aβ/tau molecular crosstalk in AD and stimulate further research to mechanism elucidation and next-generation AD therapeutics.

The Hidden Notes of Redox Balance in Neurodegenerative Diseases

Reactive oxygen species (ROS) are versatile molecules that, even if produced in the background of many biological processes and responses, possess pleiotropic roles categorized in two interactive yet opposite domains. In particular, ROS can either function as signaling molecules that shape physiological cell functions, or act as deleterious end products of unbalanced redox reactions. Indeed, cellular redox status needs to be tightly regulated to ensure proper cellular functioning, and either excessive ROS accumulation or the dysfunction of antioxidant systems can perturb the redox homeostasis, leading to supraphysiological concentrations of ROS and potentially harmful outcomes. Therefore, whether ROS would act as signaling molecules or as detrimental factors strictly relies on a dynamic equilibrium between free radical production and scavenging resources. Of notice, the mammalian brain is particularly vulnerable to ROS-mediated toxicity, because it possesses relatively poor antioxidant defenses to cope with the redox burden imposed by the elevated oxygen consumption rate and metabolic activity. Many features of neurodegenerative diseases can in fact be traced back to causes of oxidative stress, which may influence both the onset and progression of brain demise. This review focuses on the description of the dual roles of ROS as double-edge sword in both physiological and pathological settings, with reference to Alzheimer's and Parkinson's diseases.

Copper-Mediated β-Amyloid Toxicity and its Chelation Therapy in Alzheimer's Disease

The link between bio-metals, Alzheimer's disease (AD), and its associated protein, amyloid-β (Aβ) is very complex and one of the most studied aspects currently. Alzheimer's disease, a progressive neurodegenerative disease, is proposed to occurs due to the misfolding and aggregation of Aβ. Dyshomeostasis of metal ions and their interaction with Aβ has largely been implicated in AD. Copper plays a crucial role in amyloid-β toxicity and AD development potentially occurs through direct interaction with the copper-binding motif of APP and different amino acid residues of Aβ. Previous reports suggest that high levels of copper accumulation in the AD brain result in modulation of toxic Aβ peptide levels, implicating the role of copper in the pathophysiology of AD. In this review, we explore the possible mode of copper ion interaction with Aβ which accelerates the kinetics of fibril formation and promote amyloid-β mediated cell toxicity in Alzheimer's disease and the potential use of various copper chelators in the prevention of copper-mediated Aβ toxicity.

Do glutathione and copper interact to modify Alzheimer's disease pathogenesis?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder first described in 1906 that is currently estimated to impact ∼40 million people worldwide. Extensive research activities have led to a wealth of information on the pathogenesis, hallmarks, and risk factors of AD; however, therapeutic options remain extremely limited. The large number of pathogenic factors that have been reported to potentially contribute to AD include copper dyshomeostasis as well as increased oxidative stress, which is related to alterations to molecular antioxidants like glutathione (GSH). While the individual roles of GSH and copper in AD have been studied by many research groups, their interactions have received relatively little attention, although they appear to interact and affect each other's regulation. Existing knowledge on how GSH-copper interactions may affect AD is sparse and lacks focus. This review first highlights the most relevant individual roles that GSH and copper play in physiology and AD, and then collects and assesses research concerning their interactions, in an effort to provide a more accessible and understandable picture of the role of GSH, copper, and their interactions in AD.

Rational Design of a Cu Chelator That Mitigates Cu-Induced ROS Production by Amyloid Beta

Alzheimer's disease severely perturbs transition metal homeostasis in the brain leading to the accumulation of excess metals in extracellular and intraneuronal locations. The amyloid beta protein binds these transition metals, ultimately causing severe oxidative stress in the brain. Metal chelation therapy is an approach to sequester metals from amyloid beta and relieve the oxidative stress. Here we have designed a mixed N/O donor Cu chelator inspired by the proposed ligand set of Cu in amyloid beta. We demonstrate that the chelator effectively removes Cu from amyloid beta and suppresses reactive oxygen species (ROS) production by redox silencing and radical scavenging both in vitro and in cellulo. The impact of ROS on the extent of oxidation of the different aggregated forms of the peptide is studied by mass spectrometry, which, along with other ROS assays, shows that the oligomers are pro-oxidants in nature. The aliphatic Leu34, which was previously unobserved, has been identified as a new oxidation site.

A Novel Cu(II)-Binding Peptide Identified by Phage Display Inhibits Cu2+-Mediated Aβ Aggregation

Copper (Cu) has been implicated in the progression of Alzheimer’s disease (AD), and aggregation of Cu and amyloid β peptide (Aβ) are considered key pathological features of AD. Metal chelators are considered to be potential therapeutic agents for AD because of their capacity to reduce metal ion-induced Aβ aggregation through the regulation of metal ion distribution. Here, we used phage display technology to screen, synthesize, and evaluate a novel Cu(II)-binding peptide that specifically blocked Cu-triggered Aβ aggregation. The Cu(II)-binding peptide (S-A-Q-I-A-P-H, PCu) identified from the phage display heptapeptide library was used to explore the mechanism of PCu inhibition of Cu²⁺-mediated Aβ aggregation and Aβ production. In vitro experiments revealed that PCu directly inhibited Cu²⁺-mediated Aβ aggregation and regulated copper levels to reduce biological toxicity. Furthermore, PCu reduced the production of Aβ by inhibiting Cu²⁺-induced BACE1 expression and improving Cu(II)-mediated cell oxidative damage. Cell culture experiments further demonstrated that PCu had relatively low toxicity. This Cu(II)-binding peptide that we have identified using phage display technology provides a potential therapeutic approach to prevent or treat AD.

Quantitation of spin probe-detectable oxidants in cells using electron paramagnetic resonance spectroscopy: To probe or to trap?

Electron Paramagnetic Resonance (EPR) spectroscopy coupled with spin traps/probes enables quantitative determination of reactive nitrogen and oxygen species (RNOS). Even with numerous studies using spin probes, the methodology has not been rigorously investigated. The autoxidation of spin probes has been commonly overlooked. Using the spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH), the present study has tested the effects of metal chelators, temperature, and oxygen content on the autoxidation of spin probes, where an optimized condition is refined for cell studies. The apparent rate of CMH autoxidation under this condition is 7.01 ± 1.60 nM/min, indicating low sensitivity and great variation of the CMH method and that CMH autoxidation rate should be subtracted from the generation rate of CMH-detectable oxidants (simplified as oxidants below) in samples. Oxidants in RAW264.7 cells are detected at an initial rate of 4.0 ± 0.7 pmol/min/10⁶ cells, which is not considered as the rate of basal oxidants generation because the same method has failed to detect oxidant generation from the stimulation of phorbol-12-mysirate-13-acetate (PMA, 0.1 nmol/10⁶ cells) in cells (2.5 ± 0.9 for PMA vs. 2.1 ± 1.5 pmol/min/10⁶ cells for dimethyl sulfoxide (DMSO)-treated cells). In contrast, the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), which exhibits minimal autoxidation, reveals differences between PMA and DMSO treatment (0.26 ± 0.09 vs. -0.06 ± 0.12 pmol/min/10⁶ cells), which challenges previous claims that spin probes are more sensitive than spin traps. We have also found that low temperature EPR measurements of frozen samples of CMH autoxidation provide lower signal intensity and greater variation compared to RT measurements of fresh samples. The current study establishes an example for method development of RNOS detection, where experimental details are rigorously considered and tested, and raises questions on the applications of spin probes and spin traps.

ROS-mediated lipid peroxidation as a result of Cu(ii) interaction with FomA protein fragments of F. nucleatum: relevance to colorectal carcinogenesis

The ability of the studied FomA protein fragments of Fusobacterium nucleatum (Fn) with copper(ii) ions (Cu(ii)-Ac-KGHGNGEEGTPTVHNE-NH2 (1Cu) and its cyclic analogue Cu(ii)-cyclo(KGHGNGEEGTPTVHNE) (2Cu)) to induce reactive oxygen species (ROS) generation, as a result of red-ox processes, was determined by UV-Vis, luminescence methods, spin trapping and cyclic voltamperometry. The contribution of 1O2 and ˙OH to DNA degradation was proved using gel electrophoresis. Furthermore, the pronounced generation of ROS by mouse colon carcinoma cells (CT26) stimulated by both copper(ii) complexes was confirmed. A fluorescence method allowed the total amounts of ROS generated inside the CT26 cells to be detected, while the spin trapping technique proved that free radicals mainly attached to the membrane surface. These last results are in agreement with the data obtained from the ICP-MS method, which demonstrates that 1Cu and 2Cu complexes are not efficiently accumulated inside the cell. Furthermore, the role of ROS in lipid peroxidation was established. The above-mentioned factors may clearly indicate the contribution of ROS generated by the studied copper(ii) complexes to colonic cell damage, which can lead to a carcinogenesis process. This study may be an important step to recognize and understand the mechanism of colon cancer initiation.

Redox active metals in neurodegenerative diseases

Copper (Cu) and iron (Fe) are redox active metals essential for the regulation of cellular pathways that are fundamental for brain function, including neurotransmitter synthesis and release, neurotransmission, and protein turnover. Cu and Fe are tightly regulated by sophisticated homeostatic systems that tune the levels and localization of these redox active metals. The regulation of Cu and Fe necessitates their coordination to small organic molecules and metal chaperone proteins that restrict their reactions to specific protein centres, where Cu and Fe cycle between reduced (Fe²⁺, Cu⁺) and oxidised states (Fe³⁺, Cu²⁺). Perturbation of this regulation is evident in the brain affected by neurodegeneration. Here we review the evidence that links Cu and Fe dyshomeostasis to neurodegeneration as well as the promising preclinical and clinical studies reporting pharmacological intervention to remedy Cu and Fe abnormalities in the treatment of Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS).

Nitrite reductase activity of heme and copper bound Aβ peptides

A significant abundance of copper (Cu) and iron in amyloid β (Aβ) plaques, and several heme related metabolic disorders are directly correlated with Alzheimer's disease (AD), and these together with co-localization of Aβ plaques with heme rich deposits in the brains of AD sufferers indicates a possible association of the said metals with the disease. Recently, the Aβ peptides have been found to bind heme and Cu individually as well as simultaneously. Another significant finding relevant to this is the lower levels of nitrite and nitrate found in the brains of patients suffering from AD. In this study, a combination of absorption and electron paramagnetic resonance spectroscopy and kinetic assays have been used to study the interaction of nitrite with the metal bound Aβ complexes. The data indicate that heme(III)-Cu(i)-Aβ, heme(II)-Cu(i)-Aβ, heme(II)-Aβ and Cu(i)-Aβ can reduce nitrite to nitric oxide (NO), an important biological messenger also related to AD, and thus behave as nitrite reductases. However these complexes reduce nitrite at different rates with heme(III)-Cu(i)-Aβ being the fastest following an inner sphere electron transfer mechanism. The rest of the metal-Aβ adducts follow an outer sphere electron transfer mechanism during nitrite reduction. Protonation from the Arg5 residue triggering the N-O bond heterolysis in heme(III) bound nitrite with a simultaneous electron transfer from the Cu(i) center to produce NO is the rate determining step, indicating a proton transfer followed by electron transfer (PTET) mechanism.

Metal Binding to Aβ Peptides Inhibits Interaction with Cytochrome c: Insights from Abiological Constructs

Aβ(1-40) peptide is mutated to introduce cysteine residue to allow formation of organized self-assembled monolayers (SAMs) on Au electrodes. Three mutants of this peptide are produced, which vary in the position of the inserted cysteine residue. Fourier transform infrared data on these peptide SAMs show the presence of both α helices and β sheet in these Aβ constructs. These peptide constructs interact with cytochrome c (Cytc), allowing electron transfer between Cytc and the electrode via the Aβ peptides. Binding of metals like Zn²⁺ or Cu²⁺ induces changes in the morphologies of these assemblies, making them fold, which inhibits their spontaneous interaction with Cytc.

Brain Energy and Oxygen Metabolism: Emerging Role in Normal Function and Disease

Dynamic metabolic changes occurring in neurons are critically important in directing brain plasticity and cognitive function. In other tissue types, disruptions to metabolism and the resultant changes in cellular oxidative state, such as increased reactive oxygen species (ROS) or induction of hypoxia, are associated with cellular stress. In the brain however, where drastic metabolic shifts occur to support physiological processes, subsequent changes to cellular oxidative state and induction of transcriptional sensors of oxidative stress likely play a significant role in regulating physiological neuronal function. Understanding the role of metabolism and metabolically-regulated genes in neuronal function will be critical in elucidating how cognitive functions are disrupted in pathological conditions where neuronal metabolism is affected. Here, we discuss known mechanisms regulating neuronal metabolism as well as the role of hypoxia and oxidative stress during normal and disrupted neuronal function. We also summarize recent studies implicating a role for metabolism in regulating neuronal plasticity as an emerging neuroscience paradigm.

Water Quality and Brain Function

In the United States, regulations are in place to ensure the quality of drinking water. Such precautions are intended to safeguard the health of the population. However, regulatory guidelines may at times fail to achieve their purpose. This may be due to lack of sufficient data regarding the health hazards of chronic low dose exposure to contaminants or the introduction of new substances that pose a health hazard risk that has yet to be identified. In this review, examples of different sources of contaminants in drinking water will be discussed, followed by an evaluation of some select individual toxicants with known adverse neurological impact. The ability of mixtures to potentially cause additive, synergistic, or antagonistic neurotoxic responses will be briefly addressed. The last section of the review will provide examples of select mechanisms by which different classes of contaminants may lead to neurological impairments. The main objective of this review is to bring to light the importance of considering trace amounts of chemicals in the drinking water and potential brain abnormalities. There is continued need for toxicology studies to better understand negative consequences of trace amounts of toxins and although it is beyond the scope of this brief overview it is hoped that the review will underscore the paucity of studies focused on determining how long-term exposure to minute levels of contaminants in drinking water may pose a significant health hazard.

Oxidative stress and the amyloid beta peptide in Alzheimer's disease

Oxidative stress is known to play an important role in the pathogenesis of a number of diseases. In particular, it is linked to the etiology of Alzheimer’s disease (AD), an age-related neurodegenerative disease and the most common cause of dementia in the elderly. Histopathological hallmarks of AD are intracellular neurofibrillary tangles and extracellular formation of senile plaques composed of the amyloid-beta peptide (Aβ) in aggregated form along with metal-ions such as copper, iron or zinc. Redox active metal ions, as for example copper, can catalyze the production of Reactive Oxygen Species (ROS) when bound to the amyloid-β (Aβ). The ROS thus produced, in particular the hydroxyl radical which is the most reactive one, may contribute to oxidative damage on both the Aβ peptide itself and on surrounding molecule (proteins, lipids, …). This review highlights the existing link between oxidative stress and AD, and the consequences towards the Aβ peptide and surrounding molecules in terms of oxidative damage. In addition, the implication of metal ions in AD, their interaction with the Aβ peptide and redox properties leading to ROS production are discussed, along with both in vitro and in vivo oxidation of the Aβ peptide, at the molecular level.

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Oxidative stress plays a role in Alzheimer’s disease (AD), a multifactorial disease leading to loss of cognitive functions.

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Metal ions can bind the amyloid beta peptide (Aβ) and are involved in the production of reactive oxygen species (ROS).

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Oxidation targets neuronal membrane biomolecules and leads to disruption of membrane integrity.

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Aβ is damaged during ROS production, with consequences regarding aggregation, ROS production and cell toxicity.

Control of DNA integrity in skeletal muscle under physiological and pathological conditions

Skeletal muscle is a highly oxygen-consuming tissue that ensures body support and movement, as well as nutrient and temperature regulation. DNA damage induced by reactive oxygen species is present in muscles and tends to accumulate with age. Here, we present a summary of data obtained on DNA damage and its implication in muscle homeostasis, myogenic differentiation and neuromuscular disorders. Controlled and transient DNA damage appears to be essential for muscular homeostasis and differentiation while uncontrolled and chronic DNA damage negatively affects muscle health.

Blood free Radicals Concentration Determined by Electron Paramagnetic Resonance Spectroscopy and Delayed Cerebral Ischemia Occurrence in Patients with Aneurysmal Subarachnoid Hemorrhage

Pathophysiology of delayed cerebral ischemia and cerebral vasospasm following aneurysmal subarachnoid hemorrhage is still poorly recognized, however free radicals are postulated as one of the crucial players. This study was designed to scrutinize whether the concentration of free radicals in the peripheral venous blood is related to the occurrence of delayed cerebral ischemia associated with cerebral vasospasm. Twenty-four aneurysmal subarachnoid hemorrhage patients and seven patients with unruptured intracranial aneurysm (control group) have been studied. Free radicals in patients’ blood have been detected by the electron paramagnetic resonance (CMH.HCl spin probe, 150 K, ELEXSYS E500 spectrometer) on admission and at least 72 h from disease onset. Delayed cerebral ischemia monitoring was performed by daily neurological follow-up and transcranial color coded Doppler. Delayed cerebral ischemia observed in six aneurysmal subarachnoid hemorrhage patients was accompanied by cerebral vasospasm in all six cases. No statistically significant difference in average free radicals concentration between controls and study subgroups was noticed on admission (p = .3; Kruskal–Wallis test). After 72 h free radicals concentration in delayed cerebral ischemia patients (3.19 ± 1.52 mmol/l) differed significantly from the concentration in aneurysmal subarachnoid hemorrhage patients without delayed cerebral ischemia (0.65 ± 0.37 mmol/l) (p = .012; Mann–Whitney test). These findings are consistent with our assumptions and seem to confirm the role of free radicals in delayed cerebral ischemia development. Preliminary results presented above are promising and we need perform further investigation to establish whether blood free radicals concentration may serve as the biomarker of delayed cerebral ischemia associated with cerebral vasospasm.

Vitamin C, Aging and Alzheimer's Disease

Accumulating evidence in mice models of accelerated senescence indicates a rescuing role of ascorbic acid in premature aging. Supplementation of ascorbic acid appeared to halt cell growth, oxidative stress, telomere attrition, disorganization of chromatin, and excessive secretion of inflammatory factors, and extend lifespan. Interestingly, ascorbic acid (AA) was also found to positively modulate inflamm-aging and immunosenescence, two hallmarks of biological aging. Moreover, ascorbic acid has been shown to epigenetically regulate genome integrity and stability, indicating a key role of targeted nutrition in healthy aging. Growing in vivo evidence supports the role of ascorbic acid in ameliorating factors linked to Alzheimer’s disease (AD) pathogenesis, although evidence in humans yielded equivocal results. The neuroprotective role of ascorbic acid not only relies on the general free radical trapping, but also on the suppression of pro-inflammatory genes, mitigating neuroinflammation, on the chelation of iron, copper, and zinc, and on the suppression of amyloid-beta peptide (Aβ) fibrillogenesis. Epidemiological evidence linking diet, one of the most important modifiable lifestyle factors, and risk of Alzheimer's disease is rapidly increasing. Thus, dietary interventions, as a way to epigenetically modulate the human genome, may play a role in the prevention of AD. The present review is aimed at providing an up to date overview of the main biological mechanisms that are associated with ascorbic acid supplementation/bioavailability in the process of aging and Alzheimer’s disease. In addition, we will address new fields of research and future directions.

Alpha-crystallin-derived peptides as therapeutic chaperones

BACKGROUND

The demonstration of chaperone-like activity in peptides (mini-chaperones) derived from α-crystallin's chaperone region has generated significant interest in exploring the therapeutic potential of peptide chaperones in diseases of protein aggregation. Recent studies in experimental animals show that mini-chaperones could reach intended targets and alter the disease phenotype. Although mini-chaperones show potential benefits against protein aggregation diseases, they do tend to form aggregates on storage. There is thus a need to fine-tune peptide chaperones to increase their solubility, pharmacokinetics, and biological efficacy.

SCOPE OF REVIEW

This review summarizes the properties and the potential therapeutic roles of mini-chaperones in protein aggregation diseases and highlights some of the refinements needed to increase the stability and biological efficacy of mini-chaperones while maintaining or enhancing their chaperone-like activity against precipitation of unfolding proteins.

MAJOR CONCLUSIONS

Mini-chaperones suppress the aggregation of proteins, block amyloid fibril formation, stabilize mutant proteins, sequester metal ions, and exhibit antiapoptotic properties. Much work must be done to fine-tune mini-chaperones and increase their stability and biological efficacy. Peptide chaperones could have a great therapeutic value in diseases associated with protein aggregation and apoptosis.

GENERAL SIGNIFICANCE

Accumulation of misfolded proteins is a primary cause for many age-related diseases, including cataract, macular degeneration, and various neurological diseases. Stabilization of native proteins is a logical therapeutic approach for such diseases. Mini-chaperones, with their inherent antiaggregation and antiapoptotic properties, may represent an effective therapeutic molecule to prevent the cascade of protein conformational disorders. Future studies will further uncover the therapeutic potential of mini-chaperones. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

The use of metabolomics in the study of metals in biological systems

Metabolomics and systems biology/toxicology can elucidate novel pathways and mechanistic networks of metals and metalloids in biological systems, as well as providing useful biomarkers of the metal status of organisms.

Fatty acids in energy metabolism of the central nervous system

In this review, we analyze the current hypotheses regarding energy metabolism in the neurons and astroglia. Recently, it was shown that up to 20% of the total brain's energy is provided by mitochondrial oxidation of fatty acids. However, the existing hypotheses consider glucose, or its derivative lactate, as the only main energy substrate for the brain. Astroglia metabolically supports the neurons by providing lactate as a substrate for neuronal mitochondria. In addition, a significant amount of neuromediators, glutamate and GABA, is transported into neurons and also serves as substrates for mitochondria. Thus, neuronal mitochondria may simultaneously oxidize several substrates. Astrocytes have to replenish the pool of neuromediators by synthesis de novo, which requires large amounts of energy. In this review, we made an attempt to reconcile β-oxidation of fatty acids by astrocytic mitochondria with the existing hypothesis on regulation of aerobic glycolysis. We suggest that, under condition of neuronal excitation, both metabolic pathways may exist simultaneously. We provide experimental evidence that isolated neuronal mitochondria may oxidize palmitoyl carnitine in the presence of other mitochondrial substrates. We also suggest that variations in the brain mitochondrial metabolic phenotype may be associated with different mtDNA haplogroups.

Capturing a reactive state of amyloid aggregates: NMR-based characterization of copper-bound Alzheimer disease amyloid β-fibrils in a redox cycle

The interaction of redox-active copper ions with misfolded amyloid β (Aβ) is linked to production of reactive oxygen species (ROS), which has been associated with oxidative stress and neuronal damages in Alzheimer disease. Despite intensive studies, it is still not conclusive how the interaction of Cu(+)/Cu(2+) with Aβ aggregates leads to ROS production even at the in vitro level. In this study, we examined the interaction between Cu(+)/Cu(2+) and Aβ fibrils by solid-state NMR (SSNMR) and other spectroscopic methods. Our photometric studies confirmed the production of ~60 μM hydrogen peroxide (H2O2) from a solution of 20 μM Cu(2+) ions in complex with Aβ(1-40) in fibrils ([Cu(2+)]/[Aβ] = 0.4) within 2 h of incubation after addition of biological reducing agent ascorbate at the physiological concentration (~1 mM). Furthermore, SSNMR (1)H T1 measurements demonstrated that during ROS production the conversion of paramagnetic Cu(2+) into diamagnetic Cu(+) occurs while the reactive Cu(+) ions remain bound to the amyloid fibrils. The results also suggest that O2 is required for rapid recycling of Cu(+) bound to Aβ back to Cu(2+), which allows for continuous production of H2O2. Both (13)C and (15)N SSNMR results show that Cu(+) coordinates to Aβ(1-40) fibrils primarily through the side chain Nδ of both His-13 and His-14, suggesting major rearrangements from the Cu(2+) coordination via Nε in the redox cycle. (13)C SSNMR chemical shift analysis suggests that the overall Aβ conformations are largely unaffected by Cu(+) binding. These results present crucial site-specific evidence of how the full-length Aβ in amyloid fibrils offers catalytic Cu(+) centers.

Low concentrations of copper in drinking water increase AP-1 binding in the brain

Copper (Cu) in trace amounts is essential for biological organisms. However, dysregulation of the redox-active metal has been implicated in different neurological disorders such as Wilson’s, Menkes’, Alzheimer’s, and Parkinson’s diseases. Since many households use Cu tubing in the plumbing system, and corrosion causes the metal to leach into the drinking water, there may be adverse effects on the central nervous system connected with low-level chronic exposure. The present study demonstrates that treatment with a biologically relevant concentration of Cu for 3 months significantly increases activation of the redox-modulated transcription factor AP-1 in mouse brains. This was independent of an upstream kinase indicated in AP-1 activation. Another redox-active transcription factor, NF-κB, was not significantly modified by the Cu exposure. These results indicate that the effect of Cu on AP-1 is unique and may involve direct modulation of DNA binding.

Ceruloplasmin (ferroxidase) oxidizes hydroxylamine probes: deceptive implications for free radical detection

Ceruloplasmin (ferroxidase) is a copper-binding protein known to promote Fe(2+) oxidation in plasma of mammals. In addition to its classical ferroxidase activity, ceruloplasmin is known to catalyze the oxidation of various substrates, such as amines and catechols. Assays based on cyclic hydroxylamine oxidation are used to quantify and detect free radicals in biological samples ex vivo and in vitro. We show here that human ceruloplasmin promotes the oxidation of the cyclic hydroxylamine 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine hydrochloride (CPH) and related probes in Chelex-treated phosphate buffer and rat serum. The reaction is suppressed by the metal chelators DTPA, EDTA, and desferal, whereas heparin and bathocuproine have no effect. Catalase or superoxide dismutase additions do not interfere with the CPH-oxidation yield, demonstrating that oxygen-derived free radicals are not involved in the CPH oxidation mediated by ceruloplasmin. Plasma samples immunodepleted of ceruloplasmin have lower levels of CPH oxidation, which confirms the role of ceruloplasmin (ferroxidase) as a biological oxidizing agent of cyclic hydroxylamines. In conclusion, we show that the ferroxidase activity of ceruloplasmin is a possible biological source of artifacts in the cyclic hydroxylamine-oxidation assay used for reactive oxygen species detection and quantification.

Role of amyloid-β–metal interactions in Alzheimer’s disease

There is an evolving field of metallobiology that has begun to describe a key role for bioavailable metals (particularly copper, zinc and iron) in the pathogenesis of Alzheimer’s disease (AD). In particular, there is an apparent failure in metal ion homeostasis, potentially caused by a pathological mislocalization of the metals in the brain, which appears to be an obligatory step in both the precipitation and potentiation of the disease. A number of both preclinical and clinical studies have also provided a strong burden of proof that normalizing metal ion homeostasis represents a valid therapeutic target, and may indeed represent the first disease-modifying strategy for AD. The role of metals in the pathophysiology of AD will be discussed in this article.

The amylin peptide implicated in type 2 diabetes stimulates copper-mediated carbonyl group and ascorbate radical formation

Human amylin (hA), which is toxic to islet β-cells, can self-generate H(2)O(2), and this process is greatly enhanced in the presence of Cu(II) ions. Here we show that carbonyl groups, a marker of oxidative modification, were formed in hA incubated in the presence of Cu(II) ions or Cu(II) ions plus H(2)O(2), but not in the presence of H(2)O(2) alone. Furthermore, under similar conditions (i.e., in the presence of both Cu(II) ions and H(2)O(2)), hA also stimulated ascorbate radical formation. The same observations concerning carbonyl group formation were made when the histidine residue (at position 18) in hA was replaced by alanine, indicating that this residue does not play a key role. In complete contrast to hA, rodent amylin, which is nontoxic, does not generate H(2)O(2), and binds Cu(II) ions only weakly, showed none of these properties. We conclude that the hA-Cu(II)/Cu(I) complex is redox active, with electron donation from the peptide reducing the oxidation state of the copper ions. The complex is capable of forming H(2)O(2) from O(2) and can also generate (•)OH via Fenton chemistry. These redox properties of hA can explain its ability to stimulate copper-mediated carbonyl group and ascorbate radical formation. The formation of reactive oxygen species from hA in this way could hold the key to a better understanding of the damaging consequences of amyloid formation within the pancreatic islets of patients with type 2 diabetes mellitus.

Respiration and ROS production in brain and spinal cord mitochondria of transgenic rats with mutant G93a Cu/Zn-superoxide dismutase gene

Mitochondrial dysfunction is involved in the pathogenesis of motor neuron degeneration in the G93A mutant transgenic (tgmSOD1) animal model of ALS. However, it is unknown whether mitochondriopathy is a primary or secondary event. We isolated brain (BM) and spinal cord (SCM) mitochondria from 2 month old presymptomatic tgmSOD1 rats and studied respiration and generation of reactive oxygen species (ROS) using a new metabolic paradigm (Panov et al., Am. J. Physiol., Regul. Integr. Comp. Physiol., 2011). The yields of BM and SCM from tgmSOD1 rats were 27% and 58% lower than normal rats (WT). The rates of the State 3 and State 3U respiration of tgBM and tgSCM were normal with glutamate+pyruvate+malate as substrates but were inhibited with pyruvate+malate in tgBM and glutamate+malate in tgSCM. In tgSCM the State 4 respiration with all substrates was significantly (1.5-2 fold) increased as compared with WT-SCM. Western blot analysis showed that tgSCM had lower contents of complexes III (-60%) and IV (-35%), and the presence of mutated SOD1 protein in both tgBM and tgSCM. With glutamate+pyruvate+malate or succinate+glutamate+pyruvate+malate as substrates, tgBM and tgSCM generated 5-7 fold more ROS than normal mitochondria, and tgSCM generated two times more ROS than tgBM. We show that the major damaging ROS species in tgmSOD1 animals is H(2)O(2). It is known that mutated SOD1, damaged by H(2)O(2), associates with mitochondria, and we suggest that this further increases production of H(2)O(2). We also show that the total tissue calcium content remained normal in the brain but was diminished by 26% in the spinal cord of presymptomatic tgmSOD1 rats.

CONCLUSION

In tgSCM abnormally high rates of ROS generation, associated with reverse electron transport, result in accelerated mitochondriopathy, and the Ca(2+)-dependent excitotoxic death of motor neurons. Thus mitochondrial dysfunction is a key early element in pathogenesis of motor neuron degeneration in tgmSOD1 rats.

Identification and characterization of a copper-binding site in αA-crystallin

Previous studies have shown that both αA- and αB-crystallins bind Cu2+, suppress the formation of Cu2+-mediated active oxygen species, and protect ascorbic acid from oxidation by Cu2+. αA- and αB-crystallins are small heat shock proteins with molecular chaperone activity. In this study we show that the mini-αA-crystallin, a peptide consisting of residues 71-88 of αA-crystallin, prevents copper-induced oxidation of ascorbic acid. Evaluation of binding of copper to mini-αA-crystallin showed that each molecule of mini-αA-crystallin binds one copper molecule. Isothermal titration calorimetry and nanospray mass spectrometry revealed dissociation constants of 10.72 and 9.9 μM, respectively. 1,1'-Bis(4-anilino)naphthalene-5,5'-disulfonic acid interaction with mini-αA-crystallin was reduced after binding of Cu2+, suggesting that the same amino acids interact with these two ligands. Circular dichroism spectrometry showed that copper binding to mini-αA-crystallin peptide affects its secondary structure. Substitution of the His residue in mini-αA-crystallin with Ala abolished the redox-suppression activity of the peptide. During the Cu2+-induced ascorbic acid oxidation assay, a deletion mutant, αAΔ70-77, showed about 75% loss of ascorbic acid protection compared to the wild-type αA-crystallin. This difference indicates that the 70-77 region is the primary Cu2+-binding site(s) in human native full-size αA-crystallin. The role of the chaperone site in Cu2+ binding in native αA-crystallin was confirmed by the significant loss of chaperone activity by the peptide after Cu2+ binding.

Advances in metal-induced oxidative stress and human disease

Detailed studies in the past two decades have shown that redox active metals like iron (Fe), copper (Cu), chromium (Cr), cobalt (Co) and other metals undergo redox cycling reactions and possess the ability to produce reactive radicals such as superoxide anion radical and nitric oxide in biological systems. Disruption of metal ion homeostasis may lead to oxidative stress, a state where increased formation of reactive oxygen species (ROS) overwhelms body antioxidant protection and subsequently induces DNA damage, lipid peroxidation, protein modification and other effects, all symptomatic for numerous diseases, involving cancer, cardiovascular disease, diabetes, atherosclerosis, neurological disorders (Alzheimer's disease, Parkinson's disease), chronic inflammation and others. The underlying mechanism of action for all these metals involves formation of the superoxide radical, hydroxyl radical (mainly via Fenton reaction) and other ROS, finally producing mutagenic and carcinogenic malondialdehyde (MDA), 4-hydroxynonenal (HNE) and other exocyclic DNA adducts. On the other hand, the redox inactive metals, such as cadmium (Cd), arsenic (As) and lead (Pb) show their toxic effects via bonding to sulphydryl groups of proteins and depletion of glutathione. Interestingly, for arsenic an alternative mechanism of action based on the formation of hydrogen peroxide under physiological conditions has been proposed. A special position among metals is occupied by the redox inert metal zinc (Zn). Zn is an essential component of numerous proteins involved in the defense against oxidative stress. It has been shown, that depletion of Zn may enhance DNA damage via impairments of DNA repair mechanisms. In addition, Zn has an impact on the immune system and possesses neuroprotective properties. The mechanism of metal-induced formation of free radicals is tightly influenced by the action of cellular antioxidants. Many low-molecular weight antioxidants (ascorbic acid (vitamin C), alpha-tocopherol (vitamin E), glutathione (GSH), carotenoids, flavonoids, and other antioxidants) are capable of chelating metal ions reducing thus their catalytic activity to form ROS. A novel therapeutic approach to suppress oxidative stress is based on the development of dual function antioxidants comprising not only chelating, but also scavenging components. Parodoxically, two major antioxidant enzymes, superoxide dismutase (SOD) and catalase contain as an integral part of their active sites metal ions to battle against toxic effects of metal-induced free radicals. The aim of this review is to provide an overview of redox and non-redox metal-induced formation of free radicals and the role of oxidative stress in toxic action of metals.

Baicalin prevents the production of hydrogen peroxide and oxidative stress induced by Aβ aggregation in SH-SY5Y cells

Alzheimer's disease (AD) is a common form of neurodegenerative disease. Mounting evidence suggests that metal ions play a key role in the aggregation of amyloid β peptide (Aβ), which acts as a factor or cofactor in the etiopathogenesis of AD. Therefore, inhibition of Aβ aggregation emerges as a potential approach for the treatment of AD. We have found that baicalin can interact with copper directly and inhibits Aβ1-42 aggregation. In addition, baicalin protects SH-SY5Y cells from oxidative injuries induced by Aβ1-42 aggregation through decreasing H(2)O(2) production that is normally formed as a deleterious by-product of beta amyloid aggregation and the formation of plaques. Taken together, these data indicate that baicalin may be a potential agent to inhibit Aβ aggregation and thereby delay, mitigate or modify the progression of neurodegenerative diseases such as AD.

Screening assay for metal-catalyzed oxidation inhibitors using liquid chromatography-mass spectrometry with an N-terminal beta-amyloid peptide

Production of microregional catalytic reactive oxygen species (ROS) by metal-binding amyloid-beta (Abeta) peptides mediates the neurotoxicity of Alzheimer's disease, and inhibitors of this activity may be of therapeutic value. No current analytical methods target specific ROS inhibitors produced by metal-binding peptides. We report a screening assay for metal-catalyzed oxidation (MCO) inhibitors based on liquid chromatography-mass spectrometry (LC-MS) with a model N-terminal Abeta peptide (Abeta(1-6)). When subjected to MCO by Cu(II)/ascorbic acid, singly and doubly charged Abeta(1-6) molecules were observed at m/z 729.2 and 364.8 and m/z 685.3 and 343.3, respectively, corresponding to a decrease in mass of 45 and 89 Da compared with the model peptide. In contrast, H(2)O(2) did not modify the Abeta(1-6) peptide. Modified peptides were characterized by a specific MCO of Abeta(1-6), which contains both His and N-terminal Asp residues. LC-MS detection of the modified peptides allowed us to identify antioxidants that inhibit MCO of Abeta(1-6). MCO of the model peptide was inhibited by curcumin, but not dibutylhydroxytoluene, carotene, tocopherol, estradiol or nicotine, revealing a clear difference between curcumin and other antioxidants. This novel assay may allow for the identification of antioxidants that protect against MCO of peptides and proteins related to degenerative diseases.