Metal dyshomeostasis and oxidative stress in Alzheimer’s disease

Assessment of metal concentrations in the SOD1G93A mouse model of amyotrophic lateral sclerosis and its potential role in muscular denervation, with particular focus on muscle tissue

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is among the most common of the motor neuron diseases, and arguably the most devastating. During the course of this fatal neurodegenerative disorder, motor neurons undergo progressive degeneration. The currently best-understood animal models of ALS are based on the over-expression of mutant isoforms of Cu/Zn superoxide dismutase 1 (SOD1); these indicate that there is a perturbation in metal homeostasis with disease progression. Copper metabolism in particular is affected in the central nervous system (CNS) and muscle tissue.

METHODS

This present study assessed previously published and newly gathered concentrations of transition metals (Cu, Zn, Fe and Se) in CNS (brain and spinal cord) and non-CNS (liver, intestine, heart and muscle) tissues from transgenic mice over-expressing the G93A mutant SOD1 isoform (SOD1^G93A), transgenic mice over-expressing wildtype SOD1 (SOD1^WT) and non-transgenic controls.

RESULTS

Cu accumulates in non-CNS tissues at pre-symptomatic stages in SOD1^G93A tissues. This accumulation represents a potentially pathological feature that cannot solely be explained by the over-expression of mSOD1. As a result of the lack of Cu uptake into the CNS there may be a deficiency of Cu for the over-expressed mutant SOD1 in these tissues. Elevated Cu concentrations in muscle tissue also preceded the onset of symptoms and were found to be pathological and not be the result of SOD1 over-expression.

CONCLUSIONS

It is hypothesized that the observed Cu accumulations may represent a pathologic feature of ALS, which may actively contribute to axonal retraction leading to muscular denervation, and possibly significantly contributing to disease pathology. Therefore, it is proposed that the toxic-gain-of-function and dying-back hypotheses to explain the molecular drivers of ALS may not be separate, individual processes; rather our data suggests that they are parallel processes.

Iron in neurodegenerative disorders: being in the wrong place at the wrong time?

Brain iron deposits have been reported consistently in imaging and histologic examinations of patients with neurodegenerative disorders. While the origins of this finding have not been clarified yet, it is speculated that impaired iron homeostasis or deficient transport mechanisms result in the accumulation of this highly toxic metal ultimately leading to formation of reactive oxygen species and cell death. On the other hand, there are also those who support that iron is just an incidental finding, a by product of neuronal loss. A literature review has been performed in order to present the key findings in support of the iron hypothesis of neurodegeneration, as well as to identify conditions causing or resulting from iron overload and compare and contrast their features with the most prominent neurodegenerative disorders. There is an abundance of experimental and observational findings in support of the hypothesis in question; however, as neurodegeneration is a rare incident of commonly encountered iron-associated disorders of the nervous system, and this metal is found in non-neurodegenerative disorders as well, it is possible that iron is the result or even an incidental finding in neurodegeneration. Understanding the underlying processes of iron metabolism in the brain and particularly its release during cell damage is expected to provide a deeper understanding of the origins of neurodegeneration in the years to come.

Alzheimer's disease: as it was in the beginning

Since Alzheimer's disease was first described in 1907, many attempts have been made to reveal its main cause. Nowadays, two forms of the disease are known, and while the hereditary form of the disease is clearly caused by mutations in one of several genes, the etiology of the sporadic form remains a mystery. Both forms share similar sets of neuropathological and molecular manifestations, including extracellular deposition of amyloid-beta, intracellular accumulation of hyperphosphorylated tau protein, disturbances in both the structure and functions of mitochondria, oxidative stress, metal ion metabolism disorders, impairment of N-methyl-D-aspartate receptor-related signaling pathways, abnormalities of lipid metabolism, and aberrant cell cycle reentry in some neurons. Such a diversity of symptoms led to proposition of various hypotheses for explaining the development of Alzheimer's disease, the amyloid hypothesis, which postulates the key role of amyloid-beta in Alzheimer's disease development, being the most prominent. However, this hypothesis does not fully explain all of the molecular abnormalities and is therefore heavily criticized. In this review, we propose a hypothetical model of Alzheimer's disease progression, assuming a key role of age-related mitochondrial dysfunction, as was postulated in the mitochondrial cascade hypothesis. Our model explains the connections between all the symptoms of Alzheimer's disease, with particular attention to autophagy, metal metabolism disorders, and aberrant cell cycle re-entry in neurons. Progression of the Alzheimer's disease appears to be a complex process involving aging and too many protective mechanisms affecting one another, thereby leading to even greater deleterious effects.

Tetrathiomolybdate Treatment Leads to the Suppression of Inflammatory Responses through the TRAF6/NFκB Pathway in LPS-Stimulated BV-2 Microglia

Although the positive relationship between copper and Alzheimer's disease (AD) was reported by a lot of epidemiological data, the mechanism is not completely known. Copper is a redox metal and serves as a mediator of inflammation. Because the homeostasis of copper is altered in Aβ precursor protein (APP) and presenilin 1 (PS1) transgenic (Tg) mice, the using of copper chelators is a potential therapeutic strategy for AD. Here we report that a copper chelator, tetrathiomolybdate (TM), is a potential therapeutic drug of AD. We investigated whether TM treatment led to a decrease of pro-inflammatory cytokines in vivo and in vitro, and found that TM treatment reduced the expression of iNOS and TNF-α in APP/PS1 Tg mice through up-regulating superoxide dismutase 1 (SOD1) activity. In vitro, once stimulated, microglia secretes a variety of proinflammatory cytokines, so we utilized LPS-stimulated BV-2 cells as the inflammatory cell model to detect the anti-inflammatory effects of TM. Our results indicated that TM-pretreatment suppressed the ubiquitination of TRAF6 and the activation of NFκB without affecting the expression of TLR4 and Myd88 in vitro. By detecting the activity of SOD1 and the production of reactive oxygen species (ROS), we found that the anti-inflammatory effects of TM could be attributed to its ability to reduce the amount of intracellular bioavailable copper, and the production of ROS which is an activator of the TRAF6 auto-ubiquitination. Hence, our results revealed that TM-treatment could reduce the production of inflammatory cytokines by the suppression of ROS/TRAF6/AKT/NFκB signaling pathway.

Recent Progress in Alzheimer's Disease Research, Part 1: Pathology

The field of Alzheimer's disease (AD) research has grown exponentially over the past few decades, especially since the isolation and identification of amyloid-β from postmortem examination of the brains of AD patients. Recently, the Journal of Alzheimer's Disease (JAD) put forth approximately 300 research reports which were deemed to be the most influential research reports in the field of AD since 2010. JAD readers were asked to vote on these most influential reports. In this 3-part review, we review the results of the 300 most influential AD research reports to provide JAD readers with a readily accessible, yet comprehensive review of the state of contemporary research. Notably, this multi-part review identifies the "hottest" fields of AD research providing guidance for both senior investigators as well as investigators new to the field on what is the most pressing fields within AD research. Part 1 of this review covers pathogenesis, both on a molecular and macro scale. Part 2 review genetics and epidemiology, and part 3 covers diagnosis and treatment. This part of the review, pathology, reviews amyloid-β, tau, prions, brain structure, and functional changes with AD and the neuroimmune response of AD.

Oxidative Stress, Synaptic Dysfunction, and Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder without a cure. Most AD cases are sporadic where age represents the greatest risk factor. Lack of understanding of the disease mechanism hinders the development of efficacious therapeutic approaches. The loss of synapses in the affected brain regions correlates best with cognitive impairment in AD patients and has been considered as the early mechanism that precedes neuronal loss. Oxidative stress has been recognized as a contributing factor in aging and in the progression of multiple neurodegenerative diseases including AD. Increased production of reactive oxygen species (ROS) associated with age- and disease-dependent loss of mitochondrial function, altered metal homeostasis, and reduced antioxidant defense directly affect synaptic activity and neurotransmission in neurons leading to cognitive dysfunction. In addition, molecular targets affected by ROS include nuclear and mitochondrial DNA, lipids, proteins, calcium homeostasis, mitochondrial dynamics and function, cellular architecture, receptor trafficking and endocytosis, and energy homeostasis. Abnormal cellular metabolism in turn could affect the production and accumulation of amyloid-β (Aβ) and hyperphosphorylated Tau protein, which independently could exacerbate mitochondrial dysfunction and ROS production, thereby contributing to a vicious cycle. While mounting evidence implicates ROS in the AD etiology, clinical trials with antioxidant therapies have not produced consistent results. In this review, we will discuss the role of oxidative stress in synaptic dysfunction in AD, innovative therapeutic strategies evolved based on a better understanding of the complexity of molecular mechanisms of AD, and the dual role ROS play in health and disease.

A Bacterial Component to Alzheimer's-Type Dementia Seen via a Systems Biology Approach that Links Iron Dysregulation and Inflammagen Shedding to Disease

The progression of Alzheimer's disease (AD) is accompanied by a great many observable changes, both molecular and physiological. These include oxidative stress, neuroinflammation, and (more proximal to cognitive decline) the death of neuronal and other cells. A systems biology approach seeks to organize these observed variables into pathways that discriminate those that are highly involved (i.e., causative) from those that are more usefully recognized as bystander effects. We review the evidence that iron dysregulation is one of the central causative pathway elements here, as this can cause each of the above effects. In addition, we review the evidence that dormant, non-growing bacteria are a crucial feature of AD, that their growth in vivo is normally limited by a lack of free iron, and that it is this iron dysregulation that is an important factor in their resuscitation. Indeed, bacterial cells can be observed by ultrastructural microscopy in the blood of AD patients. A consequence of this is that the growing cells can shed highly inflammatory components such as lipopolysaccharides (LPS). These too are known to be able to induce (apoptotic and pyroptotic) neuronal cell death. There is also evidence that these systems interact with elements of vitamin D metabolism. This integrative systems approach has strong predictive power, indicating (as has indeed been shown) that both natural and pharmaceutical iron chelators might have useful protective roles in arresting cognitive decline, and that a further assessment of the role of microbes in AD development is more than highly warranted.

Role of Copper in the Onset of Alzheimer's Disease Compared to Other Metals

Alzheimer's disease (AD) is a neurodegenerative disorder that is characterized by amyloid plaques in patients' brain tissue. The plaques are mainly made of β-amyloid peptides and trace elements including Zn2+, Cu2+, and Fe2+. Some studies have shown that AD can be considered a type of metal dyshomeostasis. Among metal ions involved in plaques, numerous studies have focused on copper ions, which seem to be one of the main cationic elements in plaque formation. The involvement of copper in AD is controversial, as some studies show a copper deficiency in AD, and consequently a need to enhance copper levels, while other data point to copper overload and therefore a need to reduce copper levels. In this paper, the role of copper ions in AD and some contradictory reports are reviewed and discussed.

Synthesis and structure-activity relationship study of multi-target triazine derivatives as innovative candidates for treatment of Alzheimer's disease

The complex pathogenesis of Alzheimer's disease (AD) requires using multi-target ligands (MTLs) for disease management. We synthesized, characterized and evaluated a series of novel triazine analogues as MTLs for AD. The biological screening results indicated that most of our compounds displayed potent inhibitory activities against β-site APP-cleaving enzyme 1 (BACE1) using a FRET-based assay. Compounds 6c and 6m were found to possess significant BACE1 inhibitory properties with IC₅₀ values of 0.91 (±0.25) µM and 0.69 (±0.20) µM, respectively. DPPH radical scavenging activity evaluation showed that compounds with hydroxyl and pyrrole moieties had antioxidant effects. Docking evaluations provided insight into enzyme inhibitory interactions of novel synthesized compounds with the BACE1 active site involving a critical role for Gln73 and/or Phe108 alongside of Asp32. Metal chelation tests confirmed that compound 6m is a chelator for Fe²⁺, Fe³⁺, Zn²⁺, Cu²⁺. Moreover 6m as the most potent BACE1 inhibitor did not show any toxicity against PC12 neuronal cells. These findings demonstrate the high potential of triazine scaffolds in the design of MTLs for treatment of AD.

Insights into the Impact of a Membrane-Anchoring Moiety on the Biological Activities of Bivalent Compounds As Potential Neuroprotectants for Alzheimer's Disease

Bivalent compounds anchoring in different manners to the membrane were designed and biologically characterized to understand the contribution of the anchor moiety to their biological activity as neuroprotectants for Alzheimer's disease. Our results established that the anchor moiety is essential, and we identified a preference for diosgenin, as evidenced by 17MD. Studies in primary neurons and mouse brain mitochondria also identified 17MD as exhibiting activity on neuritic outgrowth and the state 3 oxidative rate of glutamate while preserving the coupling capacity of the mitochondria. Significantly, our studies demonstrated that the integrated bivalent structure is essential to the observed biological activities. Further studies employing bivalent compounds as probes in a model membrane also revealed the influence of the anchor moiety on how they interact with the membrane. Collectively, our results suggest diosgenin to be an optimal anchor moiety, providing bivalent compounds with promising pharmacology that have potential applications for Alzheimer's disease.

A small bifunctional chelator that modulates Aβ42 aggregation

Multifunctional compounds that can modulate amyloid-β (Aβ) aggregation and interact with metal ions hold considerable promise as therapeutic agents for Alzheimer’s disease (AD). Using the copper-catalyzed azide-alkyne cycloaddition reaction, a novel bifunctional chelator 2-(1-(4-(dimethylamino)benzyl)-1H-1,2,3-triazol-4-yl)phenol (L1) was synthesized. L1 contains a bidentate metal-binding unit and a pendant dimethylamino moiety. The product was characterized by 1H NMR, 13C NMR, and MS. The metal-binding properties of L1 were probed by UV–vis spectroscopy to determine Cu:L stoichiometry. L1 was determined to limit Aβ aggregation at 48 h via a ThT assay. In addition, L1 complies with Lipinski’s rules and calculated logBB values for potential drug likeness and BBB permeability. These results suggest that L1 is a suitable candidate for further study as a multifunctional compound to treat AD.

Minor Structural Variations of Small Molecules Tune Regulatory Activities toward Pathological Factors in Alzheimer's Disease

Chemical tools have been valuable for establishing a better understanding of the relationships between metal ion dyshomeostasis, the abnormal aggregation and accumulation of amyloid-β (Aβ), and oxidative stress in Alzheimer's disease (AD). Still, very little information is available to correlate the structures of chemical tools with specific reactivities used to uncover such relationships. Recently, slight structural variations to the framework of a chemical tool were found to drastically determine the tool's reactivities toward multiple pathological facets to various extents. Herein, we report our rational design and characterization of a structural series to illustrate the extent to which the reactivities of small molecules vary toward different targets as a result of minor structural modifications. These compounds were rationally and systematically modified based on consideration of properties, including ionization potentials and metal binding, to afford their desired reactivities with metal-free or metal-bound Aβ, reactive oxygen species (ROS), and free organic radicals. Our results show that although small molecules are structurally similar, they can interact with multiple factors associated with AD pathogenesis and alleviate their reactivities to different degrees. Together, our studies demonstrate the rational structure-directed design that can be used to develop chemical tools capable of regulating individual or interrelated pathological features in AD.

Effect of the Biphenyl Neolignan Honokiol on Aβ42-Induced Toxicity in Caenorhabditis elegans, Aβ42 Fibrillation, Cholinesterase Activity, DPPH Radicals, and Iron(II) Chelation

The biphenyl neolignan honokiol is a neuroprotectant which has been proposed as a treatment for central nervous system disorders such as Alzheimer's disease (AD). The death of cholinergic neurons in AD is attributed to multiple factors, including accumulation and fibrillation of amyloid beta peptide (Aβ) within the brain; metal ion toxicity; and oxidative stress. In this study, we used a transgenic Caenorhabditis elegans model expressing full length Aβ₄₂ as a convenient in vivo system for examining the effect of honokiol against Aβ-induced toxicity. Furthermore, honokiol was evaluated for its ability to inhibit Aβ₄₂ oligomerization and fibrillation; inhibit acetylcholinesterase and butyrylcholinesterase; scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals; and chelate iron(II). Honokiol displayed activity similar to that of resveratrol and (-)-epigallocatechin gallate (EGCG) in delaying Aβ₄₂-induced paralysis in C. elegans, and it exhibited moderate-to-weak ability to inhibit Aβ₄₂ on-pathway aggregation, inhibit cholinesterases, scavenge DPPH radicals, and chelate iron(II). Moreover, honokiol was found to be chemically stable relative to EGCG, which was highly unstable. Together with its good drug-likeness and brain availability, these results suggest that honokiol may be amenable to drug development and that the synthesis of honokiol analogues to optimize these properties should be considered.

Oxidative Stress Markers and Metal Ions are Correlated With Cognitive Function in Alzheimer's Disease

We investigated oxidative stress markers and metal ions in patients with Alzheimer's disease (AD). The serum levels of ceruloplasmin (CER), C-reactive protein (CRP), uric acid (UA), homocysteine (Hcy), copper, iron, and zinc were determined in 125 patients with AD (mild, n = 2 8; moderate, n = 42; and severe, n = 55) and 40 healthy control (HC) participants. Compared to HC, CER and UA levels were significantly lower in moderate and severe AD groups, whereas CRP and Hcy levels were significantly higher in the severe AD group. Copper level was significantly higher in moderate and severe AD groups than the other groups. Compared to HC, iron level was significantly higher in patients with AD, whereas zinc level was significantly lower in patients with AD. In patients with AD, the severity of cognitive impairment was positively correlated with CER, UA, and zinc levels, whereas it was negatively correlated with copper level. Taken together, our findings provide a novel approach to assess AD progression.

Glutathione peroxidases as oncotargets

Oxidative stress is a disturbance in the equilibrium among free radicals, reactive oxygen species, and endogenous antioxidant defense mechanisms. Oxidative stress is a result of imbalance between the production of reactive oxygen and the biological system's ability to detoxify the reactive intermediates or to repair the resulting damage. Mounting evidence has implicated oxidative stress in various physiological and pathological processes, including DNA damage, proliferation, cell adhesion, and survival of cancer cells. Glutathione peroxidases (GPxs) (EC 1.11.1.9) are an enzyme family with peroxidase activity whose main biological roles are to protect organisms from oxidative damage by reducing lipid hydroperoxides as well as free hydrogen peroxide. Currently, 8 sub-members of GPxs have been identified in humans, all capable of reducing H₂O₂ and soluble fatty acid hydroperoxides. A large number of publications has demonstrated that GPxs have significant roles in different stages of carcinogenesis. In this review, we will update recent progress in the study of the roles of GPxs in cancer. Better mechanistic understanding of GPxs will potentially contribute to the development and advancement of improved cancer treatment models.

Investigation of Exhaled Breath Samples from Patients with Alzheimer's Disease Using Gas Chromatography-Mass Spectrometry and an Exhaled Breath Sensor System

Exhaled breath is a body secretion, and the sampling process of this is simple and cost effective. It can be non-invasively collected for diagnostic procedures. Variations in the chemical composition of exhaled breath resulting from gaseous exchange in the extensive capillary network of the body are proposed to be associated with pathophysiological changes. In light of the foreseeable potential of exhaled breath as a diagnostic specimen, we used gas chromatography and mass spectrometry (GC-MS) to study the chemical compounds present in exhaled breath samples from patients with Alzheimer’s disease (AD), Parkinson’s disease (PD), and from healthy individuals as a control group. In addition, we also designed and developed a chemical-based exhaled breath sensor system to examine the distribution pattern in the patient and control groups. The results of our study showed that several chemical compounds, such as 1-phenantherol and ethyl 3-cyano-2,3-bis (2,5,-dimethyl-3-thienyl)-acrylate, had a higher percentage area in the AD group than in the PD and control groups. These results may indicate an association of these chemical components in exhaled breath with the progression of disease. In addition, in-house fabricated exhaled breath sensor systems, containing several types of gas sensors, showed significant differences in terms of the normalized response of the sensitivity characteristics between the patient and control groups. A subsequent clustering analysis was able to distinguish between the AD patients, PD patients, and healthy individuals using principal component analysis, Sammon’s mapping, and a combination of both methods, in particular when using the exhaled breath sensor array system A consisting of eight sensors. With this in mind, the exhaled breath sensor system could provide alternative option for diagnosis and be applied as a useful, effective tool for the screening and diagnosis of AD in the near future.

3-Hydroxykynurenine and 3-Hydroxyanthranilic Acid Enhance the Toxicity Induced by Copper in Rat Astrocyte Culture

Copper is an integral component of various enzymes, necessary for mitochondrial respiration and other biological functions. Excess copper is related with neurodegenerative diseases as Alzheimer and is able to modify cellular redox environment, influencing its functions, signaling, and catabolic pathways. Tryptophan degradation through kynurenine pathway produces some metabolites with redox properties as 3-hydroxykynurenine (3-HK) and 3-hydroxyanthranilic acid (3-HANA). The imbalance in their production is related with some neuropathologies, where the common factors are oxidative stress, inflammation, and cell death. This study evaluated the effect of these kynurenines on the copper toxicity in astrocyte cultures. It assessed the CuSO₄ effect, alone and in combination with 3-HK or 3-HANA on MTT reduction, ROS production, mitochondrial membrane potential (MMP), GHS levels, and cell viability in primary cultured astrocytes. Also, the chelating copper effect of 3-HK and 3-HANA was evaluated. The results showed that CuSO4 decreased MTT reduction, MMP, and GSH levels while ROS production and cell death are increasing. Coincubation with 3-HK and 3-HANA enhances the toxic effect of copper in all the markers tested except in ROS production, which was abolished by these kynurenines. Data suggest that 3-HK and 3-HANA increased copper toxicity in an independent manner to ROS production.

Targeting Free Radicals in Oxidative Stress-Related Human Diseases

Cancer and Alzheimer's disease (AD) are characterized by (i) opposing biological mechanisms, (ii) an inverse correlation between their incidences, and (iii) oxidative stress being a common denominator of both diseases. Increased formation of reactive oxygen species (ROS) in cancer cells from oncogenic signaling and/or metabolic disturbances leads to upregulation of cellular antioxidant capacity to maintain ROS levels below a toxic threshold. Combining drugs that induce high levels of ROS with compounds that suppress cellular antioxidant capacity by depleting antioxidant systems [glutathione (GSH), superoxide dismutase (SOD), and thioredoxin (TRX)] and/or targeting glucose metabolism represents a potential anticancer strategy. In AD, free metals and/or Aβ:metal complexes may cause damage to biomolecules in the brain (via Fenton reaction), including DNA. Metal chelation, based on the application of selective metal chelators or metal delivery, may induce neuroprotective signaling and represents a promising therapeutic strategy. This review examines therapeutic strategies based on the modulation of oxidative stress in cancer and AD.

Impaired hypoxic tolerance in APP23 mice: a dysregulation of neuroprotective globin levels

Although neuroglobin confers neuroprotection against Alzheimer's disease (AD) pathology, its expression becomes downregulated in late-stage AD. Here, we provide evidence that indicates that this decrease is associated with the AD-linked angiopathy. While wild-type mice of different ages show upregulated cerebral neuroglobin expression upon whole-body hypoxia, APP23 mice exhibit decreased cerebral transcription of neuroglobin. Interestingly, transcription of cytoglobin, whose involvement in amyloid pathology still needs to be elucidated, follows a similar pattern. To further unravel the underlying mechanism, we examined the expression levels of the RE-1-silencing transcription factor (REST/NRSF) after identifying a recognition site for it in the regulatory region of both globins. Neuroglobin-cytoglobin-REST/NRSF expression correlations are detected mainly in the cortex. This raises the possibility of REST/NRSF being an upstream regulator of these globins.

Metal ions influx is a double edged sword for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a common form of dementia in aged people, which is defined by two pathological characteristics: β-amyloid protein (Aβ) deposition and tau hyperphosphorylation. Although the mechanisms of AD development are still being debated, a series of evidence supports the idea that metals, such as copper, iron, zinc, magnesium and aluminium, are involved in the pathogenesis of the disease. In particular, the processes of Aβ deposition in senile plaques (SP) and the inclusion of phosphorylated tau in neurofibrillary tangles (NFTs) are markedly influenced by alterations in the homeostasis of the aforementioned metal ions. Moreover, the mechanisms of oxidative stress, synaptic plasticity, neurotoxicity, autophagy and apoptosis mediate the effects of metal ions-induced the aggregation state of Aβ and phosphorylated tau on AD development. More importantly, imbalance of these mechanisms finally caused cognitive decline in different experiment models. Collectively, reconstructing the signaling network that regulates AD progression by metal ions may provide novel insights for developing chelators specific for metal ions to combat AD.

Is heart disease a risk factor for low dementia test battery scores in older persons with Down syndrome? Exploratory, pilot study, and commentary

OBJECTIVES

Certain heart conditions and diseases are common in Down syndrome (DS; trisomy 21), but their role in early onset dementia that is prevalent in older adults with DS has not been evaluated. To address this knowledge gap, we conducted a study of risk factors for low neurocognitive/behavioral scores obtained with a published dementia test battery (DTB). Participants were adults with DS living in New York (N = 29; average age 46 years). We asked three questions. 1. Does having any type of heart disease affect the association between DTB scores and chronological age? 2. Does thyroid status affect the association between heart disease and DTB scores? 3. Are the E4 or E2 alleles of apolipoprotein E (APOE) associated with DTB scores or with heart disease?

METHOD

The study was retrospective, pilot, and exploratory. It involved analysis of information in a database previously established for the study of aging in DS. Participants had moderate intellectual disability on average. Information for each person included: gender, age, a single DTB score obtained by combining results from individual subscales of the DTB, the presence or absence of heart disease, thyroid status (treated hypothyroidism or normal), and APOE genotype. Trends were visualized by inspection of graphs and contingency tables. Statistical methods used to evaluate associations included Pearson correlation analysis, Fisher's exact tests (2-tailed), and odds ratio analysis. P values were interpreted at the 95% confidence level without Bonferroni correction. P values >.05<.1 were considered trends.

RESULTS

The negative correlation between DTB scores and age was significant in those with heart disease but not in those without. Heart disease was significantly associated with DTB scores >1 SD below the sample mean; there was a strong association between heart disease and low DTB scores in those with treated hypothyroidism but not in those with normal thyroid status. The APOE genotype was weakly associated with heart disease (E4, predisposing; E2, protective) in males.

CONCLUSIONS

On the basis of the potentially important findings from the present study, large prospective studies are warranted to confirm and extend the observations. In these, particular heart conditions or diseases and other medical comorbidities in individuals should be documented.

Serum Hepcidin Levels, Iron Dyshomeostasis and Cognitive Loss in Alzheimer's Disease

This pilot study examined the status of the master iron regulatory peptide, hepcidin, and peripheral related iron parameters in Alzheimer's disease (AD) and mild cognitive impairment patients, and evaluated the relationship between iron dyshomeostasis and amyloid-beta (Aβ), cognitive assessment tests, neuroimaging and clinical data. Frozen serum samples from the Oregon Tissue Bank were used to measure serum levels of hepcidin, ferritin, Aβ40, Aβ42 using enzyme-linked immunosorbent assay. Serum transferrin levels were determined indirectly as total iron binding capacity, serum iron was measured and the percent saturation of transferrin calculated. The study variables were correlated with the patients' existing cognitive assessment tests, neuroimaging, and clinical data. Hepcidin, and iron-related proteins tended to be higher in AD patients than controls, reaching statistical significance for ferritin, whereas Aβ40, Aβ42 serum levels tended to be lower. Patients with pure AD had three times higher serum hepcidin levels than controls; gender differences in hepcidin and iron-related proteins were observed. Patient stratification based on clinical dementia rating-sum of boxes revealed significantly higher levels of iron and iron-related proteins in AD patients in the upper 50% as compared to controls, suggesting that iron dyshomeostasis worsens as cognitive impairment increases. Unlike Aβ peptides, iron and iron-related proteins showed significant association with cognitive assessment tests, neuroimaging, and clinical data. Hepcidin and iron-related proteins comprise a group of serum biomarkers that relate to AD diagnosis and AD disease progression. Future studies should determine whether strategies targeted to diminishing hepcidin synthesis/secretion and improving iron homeostasis could have a beneficial impact on AD progression.

Genetic Variations as Modifying Factors to Dietary Zinc Requirements-A Systematic Review

Due to reduced cost and accessibility, the use of genetic testing has appealed to health professionals for personalising nutrition advice. However, translation of the evidence linking polymorphisms, dietary requirements, and pathology risk proves to be challenging for nutrition and dietetic practitioners. Zinc status and polymorphisms of genes coding for zinc-transporters have been associated with chronic diseases. The present study aimed to systematically review the literature to assess whether recommendations for zinc intake could be made according to genotype. Eighteen studies investigating 31 Single Nucleotide Polymorphisms (SNPs) in relation to zinc intake and/or status were identified. Five studies examined type 2 diabetes; zinc intake was found to interact independently with two polymorphisms in the zinc-transporter gene SLC30A8 to affect glucose metabolism indicators. While the outcomes were statistically significant, the small size of the effect and lack of replication raises issues regarding translation into nutrition and dietetic practice. Two studies assessed the relationship of polymorphisms and cognitive performance; seven studies assessed the association between a range of outcomes linked to chronic conditions in aging population; two papers described the analysis of the genetic contribution in determining zinc concentration in human milk; and two papers assessed zinc concentration in plasma without linking to clinical outcomes. The data extracted confirmed a connection between genetics and zinc requirements, although the direction and magnitude of the dietary modification for carriers of specific genotypes could not be defined. This study highlights the need to summarise nutrigenetics studies to enable health professionals to translate scientific evidence into dietary recommendations.

Neurotoxicity of Zinc

Zinc-induced neurotoxicity has been shown to play a role in neuronal damage and death associated with traumatic brain injury, stroke, seizures, and neurodegenerative diseases. During normal firing of "zinc-ergic" neurons, vesicular free zinc is released into the synaptic cleft where it modulates a number of postsynaptic neuronal receptors. However, excess zinc, released after injury or disease, leads to excitotoxic neuronal death. The mechanisms of zinc-mediated neurotoxicity appear to include not only neuronal signaling but also regulation of mitochondrial function and energy production, as well as other mechanisms such as aggregation of amyloid beta peptides in Alzheimer's disease. However, recent data have raised questions about some of our long-standing assumptions about the mechanisms of zinc in neurotoxicity. Thus, this review explores the most recent published findings and highlights the current mechanistic controversies.

Two decades of new drug discovery and development for Alzheimer's disease

Alzheimer's disease is a progressive and irreversible neurodegenerative disease, associated with a decreased cognitive function and severe behavioral abnormalities.

Alzheimer's Disease as the Product of a Progressive Energy Deficiency Syndrome in the Central Nervous System: The Neuroenergetic Hypothesis

The decreased availability of metabolizable energy resources in the central nervous system is hypothesized to be a key factor in the pathogenesis of Alzheimer's disease. More specifically, the age-related decline in the ability of glucose to cross the blood-brain barrier creates a metabolic stress that shifts the normal, benign processing of amyloid-β protein precursor toward pathways associated with the production of amyloid-β plaques and tau-containing neurofibrillary tangles that are characteristic of the disease. The neuroenergetic hypothesis provides insight into the etiology of Alzheimer's disease and illuminates new approaches for diagnosis, monitoring, and treatment.

Sodium selenate regulates the brain ionome in a transgenic mouse model of Alzheimer's disease

Many studies have shown that imbalance of mineral metabolism may play an important role in Alzheimer's disease (AD) progression. It was recently reported that selenium could reverse memory deficits in AD mouse model. We carried out multi-time-point ionome analysis to investigate the interactions among 15 elements in the brain by using a triple-transgenic mouse model of AD with/without high-dose sodium selenate supplementation. Except selenium, the majority of significantly changed elements showed a reduced level after 6-month selenate supplementation, especially iron whose levels were completely reversed to normal state at almost all examined time points. We then built the elemental correlation network for each time point. Significant and specific elemental correlations and correlation changes were identified, implying a highly complex and dynamic crosstalk between selenium and other elements during long-term supplementation with selenate. Finally, we measured the activities of two important anti-oxidative selenoenzymes, glutathione peroxidase and thioredoxin reductase, and found that they were remarkably increased in the cerebrum of selenate-treated mice, suggesting that selenoenzyme-mediated protection against oxidative stress might also be involved in the therapeutic effect of selenate in AD. Overall, this study should contribute to our understanding of the mechanism related to the potential use of selenate in AD treatment.

Therapeutic targeting of oxygen-sensing prolyl hydroxylases abrogates ATF4-dependent neuronal death and improves outcomes after brain hemorrhage in several rodent models

Disability or death due to intracerebral hemorrhage (ICH) is attributed to blood lysis, liberation of iron, and consequent oxidative stress. Iron chelators bind to free iron and prevent neuronal death induced by oxidative stress and disability due to ICH, but the mechanisms for this effect remain unclear. We show that the hypoxia-inducible factor prolyl hydroxylase domain (HIF-PHD) family of iron-dependent, oxygen-sensing enzymes are effectors of iron chelation. Molecular reduction of the three HIF-PHD enzyme isoforms in the mouse striatum improved functional recovery after ICH. A low-molecular-weight hydroxyquinoline inhibitor of the HIF-PHD enzymes, adaptaquin, reduced neuronal death and behavioral deficits after ICH in several rodent models without affecting total iron or zinc distribution in the brain. Unexpectedly, protection from oxidative death in vitro or from ICH in vivo by adaptaquin was associated with suppression of activity of the prodeath factor ATF4 rather than activation of an HIF-dependent prosurvival pathway. Together, these findings demonstrate that brain-specific inactivation of the HIF-PHD metalloenzymes with the blood-brain barrier-permeable inhibitor adaptaquin can improve functional outcomes after ICH in several rodent models.

Nerolidol-loaded nanospheres prevent behavioral impairment via ameliorating Na+, K+-ATPase and AChE activities as well as reducing oxidative stress in the brain of Trypanosoma evansi-infected mice

The aim of this study was to investigate the effect of nerolidol-loaded nanospheres (N-NS) on the treatment of memory impairment caused by Trypanosoma evansi in mice, as well as oxidative stress, and Na⁺, K⁺-ATPase and acetylcholinesterase (AChE) activities in brain tissue. Animals were submitted to behavioral tasks (inhibitory avoidance task and open-field test) 4 days postinfection (PI). Reactive oxygen species (ROS) and thiobarbituric acid-reactive substance (TBARS) levels and catalase (CAT), superoxide dismutase (SOD), Na⁺, K⁺-ATPase and AChE activities were measured on the fifth-day PI. T. evansi-infected mice showed memory deficit, increased ROS and TBARS levels and SOD and AChE activities, and decreased CAT and Na⁺, K⁺-ATPase activities compared to uninfected mice. N-NS prevented memory impairment and oxidative stress parameters (except SOD activity), while free nerolidol (N-F) restored only CAT activity. Also, N-NS treatment was able to prevent alterations in Na⁺, K⁺-ATPase and AChE activities caused by T. evansi infection. A significantly negative correlation was observed between memory and ROS production (p < 0.001; r = -0.941), as well as between memory and AChE activity (p < 0.05; r = -0.774). On the contrary, a significantly positive correlation between memory and Na⁺, K⁺-ATPase activity was observed (p < 0.01; r = 0.844). In conclusion, N-NS was able to reverse memory impairment and to prevent increased ROS and TBARS levels due to amelioration of Na⁺, K⁺-ATPase and AChE activities and to activation of the antioxidant enzymes, respectively. These results suggest that N-NS treatment may be a useful strategy to treat memory dysfunction and oxidative stress caused by T. evansi infection.

One protein, multiple pathologies: multifaceted involvement of amyloid β in neurodegenerative disorders of the brain and retina

Accumulation of amyloid β (Aβ) and its aggregates in the ageing central nervous system is regarded synonymous to Alzheimer's disease (AD) pathology. Despite unquestionable advances in mechanistic and diagnostic aspects of the disease understanding, the primary cause of Aβ accumulation as well as its in vivo roles remains elusive; nonetheless, the majority of the efforts to address pathological mechanisms for therapeutic development are focused towards moderating Aβ accumulation in the brain. More recently, Aβ deposition has been identified in the eye and is linked with distinct age-related diseases including age-related macular degeneration, glaucoma as well as AD. Awareness of the Aβ accumulation in these markedly different degenerative disorders has led to an increasing body of work exploring overlapping mechanisms, a prospective biomarker role for Aβ and the potential to use retina as a model for brain related neurodegenerative disorders. Here, we present an integrated view of current understanding of the retinal Aβ deposition discussing the accumulation mechanisms, anticipated impacts and outlining ameliorative approaches that can be extrapolated to the retina for potential therapeutic benefits. Further longitudinal investigations in humans and animal models will determine retinal Aβ association as a potential pathognomonic, diagnostic or prognostic biomarker.

Structure-mechanism-based engineering of chemical regulators targeting distinct pathological factors in Alzheimer's disease

The absence of effective therapeutics against Alzheimer's disease (AD) is a result of the limited understanding of its multifaceted aetiology. Because of the lack of chemical tools to identify pathological factors, investigations into AD pathogenesis have also been insubstantial. Here we report chemical regulators that demonstrate distinct specificity towards targets linked to AD pathology, including metals, amyloid-β (Aβ), metal–Aβ, reactive oxygen species, and free organic radicals. We obtained these chemical regulators through a rational structure-mechanism-based design strategy. We performed structural variations of small molecules for fine-tuning their electronic properties, such as ionization potentials and mechanistic pathways for reactivity towards different targets. We established in vitro and/or in vivo efficacies of the regulators for modulating their targets' reactivities, ameliorating toxicity, reducing amyloid pathology, and improving cognitive deficits. Our chemical tools show promise for deciphering AD pathogenesis and discovering effective drugs.

To advance our understanding of pathological features associated with Alzheimer's disease (AD), chemical tools with distinct specificity towards AD targets would be valuable. Here the authors used a structure-mechanism-based design strategy to obtain small molecules as chemical regulators for distinct pathological factors linked to AD pathology.

Serum Copper and Zinc in a Representative Sample of Bulgarian Population

Copper (Cu) and zinc (Zn) are essential for life. Body Cu and Zn content depends on variety of factors - age, gender, and diet, type of drinking water, geographical location and genetic predisposition. Copper status becomes even more relevant not only in rare genetic disorders such as Wilson disease but in diseases such as cardiovascular ones, impaired glucose tolerance and neuro-degenerative and tumor diseases. The study aimed to examine the distribution of serum Cu and Zn in a representative group of the Bulgarian population and to describe factors which influence metal content. It also aimed to describe the link between serum Cu levels and the frequency of Alzheimer’s disease (AD) in Bulgarians. Cu and Zn in serum were measured in 379 individuals (172 males and 207 females) from 5 different regions in Bulgaria by flame atomic absorption using AAnalyst 400, Perkin Elmer. Statistical analyses were performed by SPSS, 19. Median and inert-quartile range (IQR) for blood Cu were 15.89 (13.87-7.89) μmol/L and for Zn - 13.00 (11.7-14.68) μmol/L in the examined group. Higher Cu levels in females than in males were found (p < 0.001). Decrease of Zn with aging was established (p > 0.05). Significant difference (p < 0.05) was found in serum Cu between young people (< 30 year old) and adults over 61 year old. Statistically significant difference in Cu and Zn was observed (p < 0.05) in respect of residences. Difference without significance was measured between serum lipids and serum Cu (p = 0.541) and Zn (p = 0.741).

Cyclodextrins 3-Functionalized with 8-Hydroxyquinolines: Copper-Binding Ability and Inhibition of Synuclein Aggregation

Neurodegenerative diseases such as Parkinson's and Alzheimer's diseases are multifactorial disorders related to protein aggregation, metal dyshomeostasis, and oxidative stress. To advance understanding in this area and to contribute to therapeutic development, many efforts have been directed at devising suitable agents that can target metal ions associated with relevant biomolecules such as α-synuclein. This paper presents a new cyclodextrin-8-hydroxyquinoline conjugate and discusses the properties of four cyclodextrins 3-functionalized with 8-hydroxyquinoline as copper(II) chelators and inhibitors of copper-induced synuclein aggregation. The encouraging results establish the potential of cyclodextrin-8-hydroxyquinoline conjugates as chelators for the control of copper toxicity.

The effect of copper from water and food: changes of serum nonceruloplasmin copper and brain's amyloid-beta in mice

Copper is an essential element and also produces adverse health consequences when overloaded. Food and water are the main sources of copper intake, however few studies have been conducted to investigate the difference between the ways of its intake in water and food in animals. In this study, copper was fed to mice with food as well as water (two groups: water and diet) for three months at concentrations of 6, 15 and 30 ppm. The copper concentration in water was adjusted for keeping the same amount during its intake in food. The experimental studies show a slow growth rate, lower hepatic reduced glutathione (GSH)/superoxide dismutase (SOD) activity and higher serum 'free' copper in the water group. The brain's soluble amyloid-beta 1-42 (Aβ42) of the water group was significantly higher than that of the diet group at the levels of 6 and 15 ppm. In conclusion, copper in the water group significantly increased the soluble Aβ42 in the brain and the 'free' copper in the serum, decreased the growth rate and hepatic GSH/SOD activity. The research studies carried out suggest that the copper in water is more 'toxic' than copper in diet and may increase the risk of Alzheimer's disease (AD).

Metallo-pathways to Alzheimer's disease: lessons from genetic disorders of copper trafficking

Copper is an essential metal ion that provides catalytic function to numerous enzymes and also regulates neurotransmission and intracellular signaling. Conversely, a deficiency or excess of copper can cause chronic disease in humans. Menkes and Wilson disease are two rare heritable disorders of copper transport that are characterized by copper deficiency and copper overload, respectively. Changes to copper status are also a common feature of several neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). In the case of AD, which is characterized by brain copper depletion, changes in the distribution of copper has been linked with various aspects of the disease process; protein aggregation, defective protein degradation, oxidative stress, inflammation and mitochondrial dysfunction. Although AD is a multifactorial disease that is likely caused by a breakdown in multiple cellular pathways, copper and other metal ions such as iron and zinc play a central role in many of these cellular processes. Pioneering work by researchers who have studied relatively rare copper transport diseases has shed light on potential metal ion related disease mechanisms in other forms of neurodegeneration such as AD.

Serum Iron, Zinc, and Copper Levels in Patients with Alzheimer's Disease: A Replication Study and Meta-Analyses

To evaluate whether iron, zinc, and copper levels in serum are disarranged in Alzheimer's disease (AD), we performed meta-analyses of all studies on the topic published from 1984 to 2014 and contextually carried out a replication study in serum as well. Our meta-analysis results showed that serum zinc was significantly lower in AD patients. Our replication and meta-analysis results showed that serum copper was significantly higher in AD patients than in healthy controls, so our findings were consistent with the conclusions of four previously published copper meta-analyses. Even if a possible role of iron in the pathophysiology of the disease could not be ruled out, the results of our meta-analysis showed no change of serum iron levels in AD patients, but this conclusion was not robust and requires further investigation. The meta-regression analyses revealed that in some studies, differences in serum iron levels could be due to the different mean ages, while differences in zinc levels appeared to be due to the different sex ratios. However, the effect of sex ratio on serum zinc levels in our meta-analysis is subtle and needs further confirmation. Also, diverse demographic terms and methodological approaches appeared not to explain the high heterogeneity of our copper meta-analysis. Therefore, when investigating trace elements, covariants such as age and sex have to be taken into account in the analyses. In the light of these findings, we suggest that the possible alteration of serum zinc and copper levels are involved in the pathogenesis of AD.

Copper Exposure Perturbs Brain Inflammatory Responses and Impairs Clearance of Amyloid-Beta

Copper promotes a toxic buildup of amyloid-beta (Aβ) and neurofibrillary tangle pathology in the brain, and its exposure may increase the risk for Alzheimer's disease (AD). However, underlying molecular mechanisms by which copper triggers such pathological changes remain largely unknown. We hypothesized that the copper exposure perturbs brain inflammatory responses, leading to impairment of Aβ clearance from the brain parenchyma. Here, we investigated whether copper attenuated Aβ clearance by microglial phagocytosis or by low-density lipoprotein-related receptor protein-1 (LRP1) dependent transcytosis in both in vitro and in vivo When murine monocyte BV2 cells were exposed to copper, their phagocytic activation induced by fibrillar Aβ or LPS was significantly reduced, while the secretion of pro-inflammatory cytokines, such as IL-1β, TNF-α, and IL-6, were increased. Interestingly, not only copper itself but also IL-1β, IL-6, or TNF-α were capable of markedly reducing the expression of LRP1 in human microvascular endothelial cells (MVECs) in a concentration-dependent manner. While copper-mediated downregulation of LRP1 was proteasome-dependent, the cytokine-induced loss of LRP1 was proteasome- or lysosome-independent. In the mouse model, copper exposure also significantly elevated neuroinflammation and downregulated LRP1 in the brain, consistent with our in vitro results. Taken together, our findings support the pathological impact of copper on inflammatory responses and Aβ clearance in the brain, which could serve as key mechanisms to explain, in part, the copper exposure as an environmental risk factor for AD.