Copper and zinc isotopic excursions in the human brain affected by Alzheimer's disease

Novel Insights Into DLAT's Role in Alzheimer's Disease-Related Copper Toxicity Through Microglial Exosome Dynamics

BACKGROUND

Alzheimer's disease (AD) is a complex neurodegenerative disorder, with recent research emphasizing the roles of microglia and their secreted extracellular vesicles in AD pathology. However, the involvement of specific molecular pathways contributing to neuronal death in the context of copper toxicity remains largely unexplored.

OBJECTIVE

This study investigates the interaction between pyruvate kinase M2 (PKM2) and dihydrolipoamide S-acetyltransferase (DLAT), particularly focusing on copper-induced neuronal death in Alzheimer's disease.

METHODS

Gene expression datasets were analyzed to identify key factors involved in AD-related copper toxicity. The role of DLAT was validated using 5xFAD transgenic mice, while in vitro experiments were conducted to assess the impact of microglial exosomes on neuronal PKM2 transfer and DLAT expression. The effects of inhibiting the PKM2 transfer via microglial exosomes on DLAT expression and copper-induced neuronal death were also evaluated.

RESULTS

DLAT was identified as a critical factor in the pathology of AD, particularly in copper toxicity. In 5xFAD mice, increased DLAT expression was linked to hippocampal damage and cognitive decline. In vitro, microglial exosomes were shown to facilitate the transfer of PKM2 to neurons, leading to upregulation of DLAT expression and increased copper-induced neuronal death. Inhibition of PKM2 transfer via exosomes resulted in a significant reduction in DLAT expression, mitigating neuronal death and slowing AD progression.

CONCLUSION

This study uncovers a novel pathway involving microglial exosomes and the PKM2-DLAT interaction in copper-induced neuronal death, providing potential therapeutic targets for Alzheimer's disease. Blocking PKM2 transfer could offer new strategies for reducing neuronal damage and slowing disease progression in AD.

Stable potassium isotope ratios in human blood serum towards biomarker development in Alzheimer's disease

The Alzheimer's disease (AD)-affected brain purges K with concurrently increasing serum K, suggesting brain-blood K transferal. Here, natural stable K isotope ratios-δ41K-of human serum samples were characterized in an AD biomarker pilot study (plus two paired Li-heparin and potassium ethylenediaminetetraacetic acid [K-EDTA] plasma samples). AD serum was found to have a significantly lower mean δ41K relative to controls. To mechanistically explore this change, novel ab initio calculations (density functional theory) of relative K isotope compositions between hydrated K+ and organically bound K were performed, identifying hydrated K+ as isotopically light (lower δ41K) compared to organically bound K. Taken together with literature, serum δ41K and density functional theory results are consistent with efflux of hydrated K+ from the brain to the bloodstream, manifesting a measurable decrease in serum δ41K. These data introduce serum δ41K for further investigation as a minimally invasive AD biomarker, with cost, scalability, and stability advantages over current techniques.

Transcriptomic Analysis of Lipid Metabolism Genes in Alzheimer's Disease: Highlighting Pathological Outcomes and Compartmentalized Immune Status

The dysregulation of lipid metabolism has been strongly associated with Alzheimer's disease (AD) and has intricate connections with various aspects of disease progression, such as amyloidogenesis, bioenergetic deficit, oxidative stress, neuroinflammation, and myelin degeneration. Here, a comprehensive bioinformatic assessment was conducted on lipid metabolism genes in the brains and peripheral blood of AD-derived transcriptome datasets, characterizing the correlation between differentially expressed genes (DEGs) of lipid metabolism and disease pathologies, as well as immune cell preferences. Through the application of weighted gene co-expression network analysis (WGCNA), modules eigengenes related to lipid metabolism were pinpointed, and the examination of their molecular functions within biological processes, molecular pathways, and their associations with pathological phenotypes and molecular networks has been characterized. Analysis of biological networks indicates notable discrepancies in the expression patterns of the DEGs between neuronal and immune cells, as well as variations in cell type enrichments within both brain tissue and peripheral blood. Additionally, drugs targeting the DEGs from central and peripheral and a diagnostic model for hub genes from the blood were retrieved and assessed, some of which were shown to be useful for therapeutic and diagnostic. These results revealed the distinctive pattern of transcriptionally abnormal lipid metabolism in central, peripheral, and immune cell activation, providing valuable insight into lipid metabolism for diagnosing and guiding more effective treatment for AD.

Liquid-Phase Cyclic Chemiluminescence for the Identification of Cobalt Speciation

Accurate discrimination of metal species is a significant analytical challenge. Herein, we propose a novel methodology based on liquid-phase cyclic chemiluminescence (CCL) for the identification of cobalt speciation. The CCL multistage signals (In) of the luminol-H2O2 reaction catalyzed by different cobalt species have different decay coefficients k. Thereby, we can facilely identify various cobalt species according to the distinguishable k values, including the complicated and structurally similar cobalt complexes, such as analogues of [Co(NH3)5X]n+ (X = Cl-, H2O, and NH3), Co(II) porphyrins, and bis(2,4-pentanedione) cobalt(II) derivatives. Especially, the number of substituent atoms also influences the k value greatly, which allows excellent discrimination between complexes that only have a subtle difference in the substituent group. In addition, linear discriminant analysis based on In provides a complementary solution to improve the differentiating ability. We performed density functional theory calculations to investigate the interaction mode of H2O2 over cobalt species. A close negative correlation between the adsorption energy and the k value is observed. Moreover, the calculation of energy evolutions of H2O2 decomposition into a double hydroxide radical shows that a high level of consistency exists between the activation energy barrier and the k value. The results further demonstrate that the decay coefficient of the CCL multistage signal is associated with the catalytic reactivity of the cobalt species. Our work not only broadens the application of chemiluminescence but also provides a complementary technology for speciation analysis.

Copper Isotope Compositions Measured Using a Sapphire Dual Path MC-ICPMS with a Collision/Reaction Cell

We present a new approach to Cu isotopic measurements using a state-of-the-art Nu Sapphire multicollector inductively coupled plasma source mass spectrometer equipped with a collision/reaction cell (CRC-MC-ICPMS). We investigate the effects of Na doping and Cu concentration mismatch between bracketing standard and unknown samples and demonstrate the efficacy of introducing a He-H2 gas mix into the CRC to efficiently eliminate the sample matrix-based 40Ar23Na+ isobaric interference on 63Cu+. This capability is crucial when measuring samples with high Na/Cu ratios, such as some biological samples, which have significantly different chemical compositions compared to most geological samples. Moreover, considering the necessity of obtaining large data sets for biological samples to ensure reliable interpretations, the implementation of a CRC for mitigating the 40Ar23Na+ interference offers the advantage of minimizing the requirement for extensive Cu chemical separation procedure prior to Cu isotopic measurements. Our results demonstrate that the accurate determination of the δ65Cu values is achievable for samples with Na/Cu concentration ratios of up to ∼65, even when measuring 100 ppb Cu solutions (equivalent to a signal of ∼3.5-4 V total Cu). Furthermore, our results showcase a good short-term repeatability on δ65Cu for pure Cu standard solutions (NIST SRM 976 and Cu-IPGP), typically of 0.05‰ (2 SD) when measuring >50 ppb Cu solutions. Our long-term external reproducibility stands at approximately 0.07‰ (2 SD). This value accounts for the variable Cu concentrations analyzed across the different analytical sequences (from 10 to 100 ppb Cu solutions). To validate the robustness of our analytical method, we first conduct a comparison between data sets from mice brains processed twice through column chemistry using a Thermo Finnigan Neptune MC-ICPMS and a Nu Sapphire CRC-MC-ICPMS in CRC mode. This comparison serves to verify the reliability of our method for measuring Cu isotopic composition using the CRC on samples with a low Na/Cu ratio after traditional chemical processing. Then, we compare the data sets obtained for biological standards (tuna fish ERM-CE 464 (IRMM) and human serum Seronorm Trace Elements Serum L-1) processed either once, or twice, through column chemistry and demonstrate that the CRC allows accurate Cu isotopic measurements of the samples processed only once and therefore with a higher Na/Cu ratio.

Are high copper levels related to Alzheimer's and Parkinson's diseases? A systematic review and meta-analysis of articles published between 2011 and 2022

Copper performs an important role in the brain, but in high levels it can be neurotoxic. Further, some authors have described that copper dyshomeostasis could be related with neurodegenerative diseases. Thus, this review was performed to observe whether high copper levels are related to Alzheimer's and Parkinson's diseases (AD and PD), using the literature published recently. Articles that measured copper levels in AD or PD patients was included, as well as they that measured copper levels in models used to mimic these diseases. Also, results about high copper levels effects and its relationship with AD and PD observed in laboratory animals are considered. In summary, 38 and 24 articles with AD and PD patients were included, respectively. Despite of the heterogeneity between the studies in humans, meta-analysis has demonstrated that there is an increase in free and total copper levels in the blood of AD patients compared to controls, and a decrease in copper levels in PD patients. A decrease in the metal content in postmortem brain tissue was observed in AD and PD. In manuscripts using animal models that mimic AD and PD, it was included seven and three articles, respectively. Two of them have reported an increase in copper concentrations in AD model, and one in PD model. Finally, studies with laboratory animals have concluded that high copper levels are related to oxidative stress, neuroinflammation, mitochondrial dysfunction, changes in neurotransmitter levels, cell death, and reduced both cognitive and locomotor activity, which are also described in AD or PD.

Microglial Activation in Metal Neurotoxicity: Impact in Neurodegenerative Diseases

Neurodegenerative processes encompass a large variety of diseases with different pathological patterns and clinical features, such as Alzheimer's and Parkinson's diseases. Exposure to metals has been hypothesized to increase oxidative stress in brain cells leading to cell death and neurodegeneration. Neurotoxicity of metals has been demonstrated by several in vitro and in vivo experimental studies, and most probably, each metal has its specific pathway to trigger cell death. As a result, exposure to essential metals, such as manganese, iron, copper, zinc, and cobalt, and nonessential metals, including lead, aluminum, and cadmium, perturbs metal homeostasis at the cellular and organism levels leading to neurodegeneration. In this contribution, a comprehensive review of the molecular mechanisms by which metals affect microglia physiology and signaling properties is presented. Furthermore, studies that validate the disruption of microglia activation pathways as an essential mechanism of metal toxicity that can contribute to neurodegenerative disease are also presented and discussed.

Isotopic composition of serum zinc and copper in healthy children and children with autism spectrum disorder in North America

To better understand zinc and copper regulation and their involvement in various biochemical pathways as it relates to autism spectrum disorder (ASD), isotopic composition of serum zinc and copper were evaluated in both healthy children and children with ASD in North America. No significant difference in isotopic composition of serum zinc or copper with respect to healthy controls and ASD children were identified. However, the isotopic composition of serum copper in boys was found to be enriched in ⁶⁵Cu in comparison to previously published healthy adult copper isotopic composition. Furthermore, in both boys and girls, the average isotopic composition of serum zinc is heavier than previously published healthy adult isotopic zinc composition. There was also a negative association between total zinc concentrations in serum and the zinc isotopic composition of serum in boys. Finally, children with heavier isotopic composition of copper also showed a high degree of variability in their zinc isotopic composition. While numerous studies have measured the isotopic composition of serum zinc and copper in adults, this is one of the first studies which measured the isotopic composition of serum copper and zinc in children, specifically those diagnosed with ASD. The results of this study showed that age and gender specific normal ranges of isotopic composition must be established to effectively use isotopic composition analysis in studying various diseases including ASD.

Contribution of Ryugu-like material to Earth's volatile inventory by Cu and Zn isotopic analysis

Initial analyses showed that asteroid Ryugu's composition is close to CI (Ivuna-like) carbonaceous chondrites -the chemically most primitive meteorites, characterized by near-solar abundances for most elements. However, some isotopic signatures (e.g., Ti, Cr) overlap with other carbonaceous chondrite (CC) groups, so the details of the link between Ryugu and the CI chondrites are not fully clear yet. Here we show that Ryugu and CI chondrites have the same zinc and copper isotopic composition. As the various chondrite groups have very distinct Zn and Cu isotopic signatures, our results point at a common genetic heritage between Ryugu and CI chondrites, ruling out any affinity with other CC groups. Since Ryugu's pristine samples match the solar elemental composition for many elements, their Zn and Cu isotopic compositions likely represent the best estimates of the solar composition. Earth's mass-independent Zn isotopic composition is intermediate between Ryugu/CC and non-carbonaceous chondrites, suggesting a contribution of Ryugu-like material to Earth's budgets of Zn and other moderately volatile elements.

Exploring the K isotope composition of Göttingen minipig brain regions, and implications for Alzheimer's disease

Natural stable metal isotopes have shown utility in differentiation between healthy and diseased brain states (e.g. Alzheimer's disease, AD). While the AD brain accumulates some metals, it purges others, namely K (accompanied by increased serum K, suggesting brain-blood transferal). Here, K isotope compositions of Göttingen minipig brain regions for two AD models at midlife are reported. Results indicate heavy K isotope enrichment where amyloid beta (Aβ) accumulation is observed, and this enrichment correlates with relative K depletion. These results suggest preferential efflux of isotopically light K+ from the brain, a linkage between brain K concentrations and isotope compositions, and linkage to Aβ (previously shown to purge cellular brain K+). Brain K isotope compositions differ from that for serum and brain K is much more abundant than in serum, suggesting that changes in brain K may transfer a measurable K isotope excursion to serum, thereby generating an early AD biomarker.

Role of micronutrients in Alzheimer's disease: Review of available evidence

Alzheimer's disease (AD) is one of the most common age-related neurodegenerative disorders that have been studied for more than 100 years. Although an increased level of amyloid precursor protein is considered a key contributor to the development of AD, the exact pathogenic mechanism remains known. Multiple factors are related to AD, such as genetic factors, aging, lifestyle, and nutrients. Both epidemiological and clinical evidence has shown that the levels of micronutrients, such as copper, zinc, and iron, are closely related to the development of AD. In this review, we summarize the roles of eight micronutrients, including copper, zinc, iron, selenium, silicon, manganese, arsenic, and vitamin D in AD based on recently published studies.

The position of geochemical variables as causal co-factors of diseases of unknown aetiology

Abstract

The term diseases of unknown aetiology (DUA) or idiopathic diseases is used to describe diseases that are of uncertain or unknown cause or origin. Among plausible geoenvironmental co-factors in causation of DUA, this article focusses on the entry of trace elements, including metals and metalloids into humans, and their involvement in humoral and cellular immune responses, representing potentially toxic agents with implications as co-factors for certain DUA. Several trace elements/metals/metalloids (micronutrients) play vital roles as co-factors for essential enzymes and antioxidant molecules, thus, conferring protection against disease. However, inborn errors of trace element/metal/metalloid metabolisms can occur to produce toxicity, such as when there are basic defects in the element transport mechanism. Ultimately, it is the amount of trace element, metal or metalloid that is taken up, its mode of accumulation in human tissues, and related geomedical attributes such as the chemical form and bioavailability that decisively determine whether the exerted effects are toxic or beneficial. Several case descriptions of DUA that are common worldwide are given to illustrate our knowledge so far of how trace element/metal/metalloid interactions in the immune system may engender its dysregulation and be implicated as causal co-factors of DUA.

Article highlights

The importance of a proper understanding of geochemical perturbations in human metabolisms is emphasisedIt is proferred that such an understanding would aid greatly in the decipherment of diseases of unknown aetiology (DUA)The thesis presented may pave the way towards better diagnosis and therapy of DUA.

High-Precision Isotopic Analysis of Cu and Fe via Multi-Collector Inductively Coupled Plasma-Mass Spectrometry Reveals Lipopolysaccharide-Induced Inflammatory Effects in Blood Plasma and Brain Tissues

The concentration and the isotopic composition of the redox-active essential elements Cu and Fe were investigated in blood plasma and specific brain regions (hippocampus, cortex, brain stem and cerebellum) of mice to assess potential alterations associated with sepsis-associated encephalopathy induced by lipopolysaccharide (LPS) administration. Samples were collected from young (16-22 weeks) and aged (44-65 weeks) mice after intraperitoneal injection of the LPS, an endotoxin inducing neuroinflammation, and from age- and sex-matched controls, injected with phosphate-buffered saline solution. Sector-field single-collector inductively coupled plasma-mass spectrometry was relied upon for elemental analysis and multi-collector inductively coupled plasma-mass spectrometry for isotopic analysis. Significant variations were observed for the Cu concentration and for the Cu and Fe isotope ratios in the blood plasma. Concentrations and isotope ratios of Cu and Fe also varied across the brain tissues. An age- and an inflammatory-related effect was found affecting the isotopic compositions of blood plasma Cu and cerebellum Fe, whereas a regional Cu isotopic redistribution was found within the brain tissues. These findings demonstrate that isotopic analysis of essential mineral elements picks up metabolic changes not revealed by element quantification, making the two approaches complementary.

Rapamycin Attenuated Zinc-Induced Tau Phosphorylation and Oxidative Stress in Rats: Involvement of Dual mTOR/p70S6K and Nrf2/HO-1 Pathways

Alzheimer's disease is pathologically characterized by abnormal accumulation of amyloid-beta plaques, neurofibrillary tangles, oxidative stress, neuroinflammation, and neurodegeneration. Metal dysregulation, including excessive zinc released by presynaptic neurons, plays an important role in tau pathology and oxidase activation. The activities of mammalian target of rapamycin (mTOR)/ribosomal S6 protein kinase (p70S6K) are elevated in the brains of patients with Alzheimer's disease. Zinc induces tau hyperphosphorylation via mTOR/P70S6K activation in vitro. However, the involvement of the mTOR/P70S6K pathway in zinc-induced oxidative stress, tau degeneration, and synaptic and cognitive impairment has not been fully elucidated in vivo. Here, we assessed the effect of pathological zinc concentrations in SH-SY5Y cells by using biochemical assays and immunofluorescence staining. Rats (n = 18, male) were laterally ventricularly injected with zinc, treated with rapamycin (intraperitoneal injection) for 1 week, and assessed using the Morris water maze. Evaluation of oxidative stress, tau phosphorylation, and synaptic impairment was performed using the hippocampal tissue of the rats by biochemical assays and immunofluorescence staining. The results from the Morris water maze showed that the capacity of spatial memory was impaired in zinc-treated rats. Zinc sulfate significantly increased the levels of P-mTOR Ser2448, P-p70S6K Thr389, and P-tau Ser356 and decreased the levels of nuclear factor erythroid 2-related factor-2 (Nrf2) and heme oxygenase-1 (HO-1) in SH-SY5Y cells and in zinc-treated rats compared with the control groups. Increased expression of reactive oxygen species was observed in zinc sulfate-induced SH-SY5Y cells and in the hippocampus of zinc-injected rats. Rapamycin, an inhibitor of mTOR, rescued zinc-induced increases in mTOR/p70S6K activation, tau phosphorylation, and oxidative stress, and Nrf2/HO-1 inactivation, cognitive impairment, and synaptic impairment reduced the expression of synapse-related proteins in zinc-injected rats. In conclusion, our findings imply that rapamycin prevents zinc-induced cognitive impairment and protects neurons from tau pathology, oxidative stress, and synaptic impairment by decreasing mTOR/p70S6K hyperactivity and increasing Nrf2/HO-1 activity.

Investigations on Zinc Isotope Fractionation in Breast Cancer Tissue Using in vitro Cell Culture Uptake-Efflux Experiments

Zinc (Zn) accumulates in breast cancer tumors compared to adjacent healthy tissue. Clinical samples of breast cancer tissue show light Zn isotopic compositions (δ66Zn) relative to healthy tissue. The underlying mechanisms causing such effects are unknown. To investigate if the isotopic discrimination observed for in vivo breast cancer tissue samples can be reproduced in vitro, we report isotopic data for Zn uptake-efflux experiments using a human breast cancer cell line. MDA-MB-231 cell line was used as a model for triple receptor negative breast cancer. We determined Zn isotope fractionation for Zn cell uptake (Δ66Znuptake) and cell efflux (Δ66Znefflux) using a drip-flow reactor to enable comparison with the in vivo environment. The MDA-MB-231 cell line analyses show Zn isotopic fractionations in an opposite direction to those observed for in vivo breast cancer tissue. Uptake of isotopically heavy Zn (Δ66Znuptake = +0.23 ± 0.05‰) is consistent with transport via Zn transporters (ZIPs), which have histidine-rich binding sites. Zinc excreted during efflux is isotopically lighter than Zn taken up by the cells (Δ66Znefflux = -0.35 ± 0.06‰). The difference in Zn isotope fractionation observed between in vitro MDA-MB-231 cell line experiments and in vivo breast tissues might be due to differences in Zn transporter levels or intercellular Zn storage (endoplasmic reticulum and/or Zn specific vesicles); stromal cells, such as fibroblasts and immune cells. Although, additional experiments using other human breast cancer cell lines (e.g., MCF-7, BT-20) with varying Zn protein characteristics are required, the results highlight differences between in vitro and in vivo Zn isotope fractionation.

Iron Isotopic Composition of Biological Standards Relevant to Medical and Biological Applications

Iron isotopes are fractionated by multiple biological processes, which offers a novel opportunity to study iron homeostasis. The determination of Fe isotope composition in biological samples necessitates certified biological reference materials with known Fe isotopic signature in order to properly assess external reproducibility and data quality between laboratories. We report the most comprehensive study on the Fe isotopic composition for widely available international biological reference materials. They consist of different terrestrial and marine animal organs (bovine, porcine, tuna, and mussel) as well as apple leaves and human hair (ERC-CE464, NIST1515, ERM-DB001, ERM-BB186, ERM-BB184, ERM-CE196, BCR668, ERM-BB185, ERM-BB124). Previously measured Fe isotopic compositions were available for only two of these reference materials (ERC-CE464 tuna fish and ERM-BB186 pig kidney) and these literature data are in excellent agreement with our data. The Fe isotopic ratios are reported as the permil deviation of the ⁵⁶Fe/⁵⁴Fe ratio from the IRMM-014 standard. All reference materials present δ⁵⁶Fe ranging from −2.27 to −0.35%0. Combined with existing data, our results suggest that animal models could provide useful analogues of the human body regarding the metabolic pathways affecting Fe isotopes, with many potential applications to medicine.

Biogenic metallic elements in the human brain?

The chemistry of copper and iron plays a critical role in normal brain function. A variety of enzymes and proteins containing positively charged Cu+, Cu2+, Fe2+, and Fe3+ control key processes, catalyzing oxidative metabolism and neurotransmitter and neuropeptide production. Here, we report the discovery of elemental (zero-oxidation state) metallic Cu0 accompanying ferromagnetic elemental Fe0 in the human brain. These nanoscale biometal deposits were identified within amyloid plaque cores isolated from Alzheimer's disease subjects, using synchrotron x-ray spectromicroscopy. The surfaces of nanodeposits of metallic copper and iron are highly reactive, with distinctly different chemical and magnetic properties from their predominant oxide counterparts. The discovery of metals in their elemental form in the brain raises new questions regarding their generation and their role in neurochemistry, neurobiology, and the etiology of neurodegenerative disease.