Is interaction of amyloid β-peptides with metals involved in cognitive activity?

Associations Between Mild Cognitive Impairment and Whole Blood Zinc and Selenium in the Elderly Cohort

Some studies have shown that an imbalance in trace element homeostasis can lead to cognitive dysfunction, but data are lacking. The purpose of this study was to investigate the association between whole blood zinc (Zn), selenium (Se), copper-zinc ratio (Cu/Zn), copper-selenium ratio (Cu/Se), and zinc-selenium ratio (Zn/Se) and mild cognitive impairment (MCI) in elderly Chinese individuals. The study was based on the Elderly Health and Controlled Environmental Factors Cohort in Lu'an, Anhui Province, China, from June to September 2016. The cognitive function of the elderly was determined by the Mini-Mental State Examination (MMSE) and activities of daily living (ADL) scales. The concentrations of Zn, Cu, and Se in the whole blood were measured by inductively coupled plasma-mass spectrometry (ICP-MS). Binary logistic regression was used to analyze the associations between trace elements and MCI. A total of 1006 participants with an average age of 71.70 years old were included in this study. Compared with healthy people, MCI patients had higher whole blood Zn levels and lower Se levels, and Cu/Zn, Cu/Se, and Zn/Se were also significantly different. Binary logistic regression analysis showed that Zn, Cu/Se, and Zn/Se exposure in the third tertile was associated with an increased risk of MCI, while Se exposure in the third tertile was associated with a reduced risk of MCI. After adjustment for sex, age, marital status, BMI, and living status, whole blood Zn, Se, Cu/Zn, Cu/Se, and Zn/Se were significantly associated with MCI risk, especially in elderly women.

Big dynorphin is a neuroprotector scaffold against amyloid β-peptide aggregation and cell toxicity

Amyloid β-peptide (Aβ) misfolding into β-sheet structures triggers neurotoxicity inducing Alzheimer’s disease (AD). Molecules able to reduce or to impair Aβ aggregation are highly relevant as possible AD treatments since they should protect against Aβ neurotoxicity. We have studied the effects of the interaction of dynorphins, a family of opioid neuropeptides, with Aβ₄₀ the most abundant species of Aβ. Biophysical measurements indicate that Aβ₄₀ interacts with Big Dynorphin (BigDyn), lowering the amount of hydrophobic aggregates, and slowing down the aggregation kinetics. As expected, we found that BigDyn protects against Aβ₄₀ aggregates when studied in human neuroblastoma cells by cell survival assays. The cross-interaction between BigDyn and Aβ₄₀ provides insight into the mechanism of amyloid pathophysiology and may open up new therapy possibilities.

Structure and mechanism behind the inhibitory effect of water soluble metalloporphyrins on Aβ1-42 aggregation

Although the exact molecular mechanism of the pathogenesis of Alzheimer’s disease (AD) is still unclear, compounds that can inhibit the aggregation of amyloid-β peptide (Aβ1-42) or scavenge the highly toxic...

The Function of Transthyretin Complexes with Metallothionein in Alzheimer's Disease

Alzheimer’s disease (AD) is one of the most frequently diagnosed types of dementia in the elderly. An important pathological feature in AD is the aggregation and deposition of the β-amyloid (Aβ) in extracellular plaques. Transthyretin (TTR) can cleave Aβ, resulting in the formation of short peptides with less activity of amyloid plaques formation, as well as being able to degrade Aβ peptides that have already been aggregated. In the presence of TTR, Aβ aggregation decreases and toxicity of Aβ is abolished. This may prevent amyloidosis but the malfunction of this process leads to the development of AD. In the context of Aβplaque formation in AD, we discuss metallothionein (MT) interaction with TTR, the effects of which depend on the type of MT isoform. In the brains of patients with AD, the loss of MT-3 occurs. On the contrary, MT-1/2 level has been consistently reported to be increased. Through interaction with TTR, MT-2 reduces the ability of TTR to bind to Aβ, while MT-3 causes the opposite effect. It increases TTR-Aβ binding, providing inhibition of Aβ aggregation. The protective effect, assigned to MT-3 against the deposition of Aβ, relies also on this mechanism. Additionally, both Zn₇MT-2 and Zn₇MT-3, decrease Aβ neurotoxicity in cultured cortical neurons probably because of a metal swap between Zn₇MT and Cu(II)Aβ. Understanding the molecular mechanism of metals transfer between MT and other proteins as well as cognition of the significance of TTR interaction with different MT isoforms can help in AD treatment and prevention.

Bioavailability and Pharmaco-therapeutic Potential of Luteolin in Overcoming Alzheimer's Disease

Luteolin is a naturally occurring, yellow crystalline flavonoid found in numerous dietary supplements we frequently have in our meals. Studies in the last 2 decades have revealed its therapeutic potential to reduce the Alzheimer's disease (AD) symptoms in various in vitro and in vivo models. The anti-Alzheimer's potential of luteolin is attributed to its ability to suppress Aβ as well as tau aggregation or promote their disaggregation, down-regulate the expression of COX-2, NOS, MMP-9, TNF-α, interleukins and chemokines, reduce oxidative stress by scavenging ROS, modulate the activities of transcription factors CREB, cJun, Nrf-1, NF-κB, p38, p53, AP-1 and β-catenine and inhibiting the activities of various protein kinases. In several systems, luteolin has been described as a potent antioxidant and anti-inflammatory agent. In addition, we have also discussed about the bio-availability of the luteolin in the plasma. After being metabolized luteolin persists in plasma as glucuronides and sulphate-conjugates. Human clinical trials indicated no dose limiting toxicity when administered at a dose of 100 mg/day. Improvements in the formulations and drug delivery systems may further enhance the bioavailability and potency of luteolin. The current review describes in detail the data supporting these studies.

Copper complexes of synthetic peptides mimicking neurotrophin-3 enhance neurite outgrowth and CREB phosphorylation

In this work we report on the synthesis and physiochemical/biological characterization of a peptide encompassing the first thirteen residues of neurotrophin-3 (NT-3). The protein capability to promote neurite outgrowth and axonal branching by a downstream mechanism that involves the increase of the cAMP response element-binding level (CREB) was found for the NT3(1-13) peptide, thus validating its protein mimetic behaviour. Since copper ions are also involved in neurotransmission and their internalization may be an essential step in neuron differentiation and CREB phosphorylation, the peptide and its copper complexes were characterized by potentiometric and spectroscopic techniques, including UV-visible, CD and EPR. To have a detailed picture of the coordination features of the copper complexes with NT3(1-13), we also scrutinized the two peptide fragments encompassing the shorter sequences 1-5 and 5-13, respectively, showing that the amino group is the main anchoring site for Cu(ii) at physiological pH. The peptide activity increased in the presence of copper ions. The effect of copper(ii) addition is more marked for NT3(1-13) than the other two peptide fragments, in agreement with its higher affinity for metal ions. Confocal microscopy measurements carried out on fluorescently labelled NT3(1-13) indicated that copper ions increase peptide internalization.

Silymarin's Inhibition and Treatment Effects for Alzheimer's Disease

As a longstanding problem, Alzheimer's disease (AD) has stymied researchers in the medical field with its increasing incidence and enormous treatment difficulty. Silymarin has always been valued by researchers for its good efficacy and safety in treating liver disease. Recent studies have shown that silymarin also has good pharmacological activity in the nervous system, especially for the treatment of AD. Silymarin can control the production of Aβ by inhibiting the precursor substance of Aβ (β-amyloid precursor protein), and it can inhibit the polymerization of Aβ. Silymarin can also increase the acetylcholine content in the nervous system by inhibiting cholinesterase activity. At the same time, it also has the effect of resisting oxidative stress and the inflammatory response of the nervous system. These pharmacological activities contribute to the inhibition of the onset of AD. The good efficacy of silymarin on AD and its high safety and availability give it huge potential for the treatment of AD.

A multifunctional bis-(-)-nor-meptazinol-oxalamide hybrid with metal-chelating property ameliorates Cu(II)-induced spatial learning and memory deficits via preventing neuroinflammation and oxido-nitrosative stress in mice

Excess copper exposure is a risk factor of neurodegeneration related to Alzheimer's disease (AD). Evidence indicates that, besides promoting amyloid β aggregation, activation of neuroinflammation and oxido-nitrosative stress (two key pathophysiological processes of AD) may also play important roles in Cu(II)-induced neuronal injury. Therefore, the copper-chelating strategy has gained attention in search for new anti-AD drugs. We previously reported a novel multifunctional compound N¹,N²-bis(3-(S)-meptazinol-propyl) oxalamide (ZLA), a bis-(-)-nor-meptazinol-oxalamide hybrid with properties of dual binding site acetylcholinesterase (AChE) inhibition and Cu(II)/Zn(II) chelation. The present study was aimed to explore its effect on cognitive deficits caused by intrahippocampal injection of Cu(II) in mice. Results showed that ZLA (2, 5 mg/kg; i.p.) treatment significantly ameliorated the Cu(II)-induced impairment of hippocampus-dependent learning and memory, whereas rivastigmine, an AChE inhibitor showing a similar potency of enzyme inhibition to ZLA, had no obvious effect. Immunohistochemical and Western blot analyses revealed that ZLA attenuated the decrease in hippocampal expression of microtubule-associated protein 2 (MAP2, a dendritic marker) in Cu(II)-challenged mice. Further analysis showed that ZLA suppressed the Cu(II)-evoked microglial activation. Moreover, it inhibited the Cu(II)-evoked production of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-1β and expression of inducible nitric oxide synthase in the hippocampus. The Cu(II)-induced oxidative and nitrosative stress in the hippocampus was also attenuated after ZLA treatment. Collectively, these results suggest that ZLA ameliorates the Cu(II)-caused cognitive deficits. Inhibition of neuroinflammation and oxido-nitrosative stress, and thus ameliorating neuronal injury, may be the potential mechanism for the anti-amnesic effect of ZLA.

How cellular Zn2+ signaling drives physiological functions

Zinc is an essential micronutrient affecting many aspects of human health. Cellular Zn²⁺ homeostasis is critical for cell function and survival. Zn²⁺, acting as a first or second messenger, triggers signaling pathways that mediate the physiological roles of Zn²⁺. Transient changes in Zn²⁺ concentrations within the cell or in the extracellular region occur following its release from Zn²⁺ binding metallothioneins, its transport across membranes by the ZnT or ZIP transporters, or release of vesicular Zn²⁺. These transients activate a distinct Zn²⁺ sensing receptor, ZnR/GPR39, or modulate numerous proteins and signaling pathways. Importantly, Zn²⁺ signaling regulates cellular physiological functions such as: proliferation, differentiation, ion transport and secretion. Indeed, novel therapeutic approaches aimed to maintain Zn²⁺ homeostasis and signaling are evolving. This review focuses on recent findings describing roles of Zn²⁺ and its transporters in regulating physiological or pathological processes.

Relevance of arginine residues in Cu(II)-induced DNA breakage and Proteinase K resistance of H1 histones

This work analyzes the involvement of arginines in copper/H₂O₂-induced DNA breakage. Copper is a highly redox active metal which has been demonstrated to form compounds with arginines. For this aim we used mixtures of pGEM3 DNA plasmid and two types of H1 histones which differ only in their arginine content. The sperm H1 histone from the annelid worm Chaetopterus variopedatus (arginine content 12.6 mol% K/R ratio 2) and the somatic H1 histone from calf thymus (arginine content 1.8 mol% and K/R ratio 15). Copper/H₂O₂-induced DNA breakage was observed only in presence of sperm H1 histones, but it was more relevant for the native molecule than for the deguanidinated derivative (K/R ratio 14), in which 80% of arginine residues were converted to ornithine. Further, copper induced proteinase K resistance and increase of DNA binding affinity on native sperm H1 histones. These observations are consistent with a copper induced reorganization of the side-chains of arginine residues. Copper, instead, did not affect DNA binding affinity of somatic and deguanidinated H1 histones, which show similar K/R ratio and DNA binding mode. These results indicate that arginine residues could affect these H1 histones properties and provide new insights into copper toxicity mechanisms.

Using on-line solid phase extraction for in vivo speciation of diffusible ferrous and ferric iron in living rat brain extracellular fluid

Exploration of brain extracellular non-protein-bound/diffusible iron species remains a critically important issue in investigations of free radical biology and neurodegenerative diseases. In this study, a facile sample pretreatment scheme, involving poly(vinyl chloride)-metal ion interactions as a selective extraction procedure, was optimized in conjunction with microdialysis (MD) sampling and inductively coupled plasma mass spectrometry (ICP-MS) in cool-plasma mode for in vivo online monitoring of rat brain extracellular Fe(II) and Fe(III) species. Optimization of the system provided detection limits in the range 0.9-6.9 μg Fe L^-1, based on a 12-μL microdialysate, for the tested iron species; relative standard deviations of the signal intensities during 7.8 h of continuous measurement were less than 9.4%-sufficient to determine the basal concentrations of rat brain extracellular Fe(II) and Fe(III) species and to describe their dynamic actions. The method's applicability was verified through (i) spike analyses of offline-collected rat brain microdialysates, (ii) determination of the basal Fe(II) and Fe(III) concentrations of living rat brain extracellular fluids, and (iii) monitoring of the dynamic changes in the Fe(II) and Fe(III) concentrations in response to perfusion of a high-K⁺ medium. This proposed sample pretreatment scheme, based on polymer-metal ion interactions and hyphenation to an MD sampling device and an ICP-MS system, appears to have great practicality for the online monitoring of rat brain extracellular diffusible iron species.