Correction to: Copper signalling: causes and consequences

Mechanism of Cu entry into the brain: many unanswered questions

Brain tissue requires high amounts of copper (Cu) for its key physiological processes, such as energy production, neurotransmitter synthesis, maturation of neuropeptides, myelination, synaptic plasticity, and radical scavenging. The requirements for Cu in the brain vary depending on specific brain regions, cell types, organism age, and nutritional status. Cu imbalances cause or contribute to several life-threatening neurologic disorders including Menkes disease, Wilson disease, Alzheimer's disease, Parkinson's disease, and others. Despite the well-established role of Cu homeostasis in brain development and function, the mechanisms that govern Cu delivery to the brain are not well defined. This review summarizes available information on Cu transfer through the brain barriers and discusses issues that require further research.

Induction of mitophagy via ROS-dependent pathway protects copper-induced hypothalamic nerve cell injury

Copper (Cu) is one of the essential trace elements in the body, but excessive amounts of Cu harm multiple organs and tissues such as liver, kidneys, testis, ovaries, and brain. However, the mechanism of hypothalamic neurotoxicity induced by Cu is still unknown. This study examined the relationship between reactive oxygen species (ROS) and mitophagy in mouse hypothalamus treated with high Cu. The results demonstrated that high levels of copper sulfate (CuSO4) could cause histopathological and neuronal changes in the mouse hypothalamus, produce a large amount of ROS, induce mitophagy, and lead to an imbalance of mitochondrial fusion/fission. The main manifestations are an increase in the expression levels of LC3-II/LC3-I, p62, DRP1, and FIS1, and a decrease in the expression levels of MFN1 and MFN2. Cu can induce mitophagy also was confirmed by LC3 co-localization with TOMM20 (mitochondrial marker). Next, the effect of oxidative stress on CuSO4-induced mitophagy was demonstrated. The results showed that ROS inhibitor N-acetylcysteine (NAC) diminished CuSO4-induced mitophagy and reversed the disturbance of mitochondrial dynamics. Additionally, a study was carried out to evaluate the role of mitophagy in CuSO4-induced hypothalamic injury. The inhibition of mitophagy using mitophagy inhibitor (Mdivi-1) decreased cell viability and promoted CuSO4-inhibited mitochondrial fusion. The aforementioned results suggested that CuSO4 induced mitophagy via oxidative stress in N38 cells and mouse hypothalamus, and that the activation of mitophagy might generate protective mechanisms by alleviating Cu-induced mitochondrial dynamics disorder. This study provided a novel approach and theoretical basis for studying and preventing Cu neurotoxicity.

The Bioinorganic Chemistry of Mammalian Metallothioneins

The functions, purposes, and roles of metallothioneins have been the subject of speculations since the discovery of the protein over 60 years ago. This article guides through the history of investigations and resolves multiple contentions by providing new interpretations of the structure-stability-function relationship. It challenges the dogma that the biologically relevant structure of the mammalian proteins is only the one determined by X-ray diffraction and NMR spectroscopy. The terms metallothionein and thionein are ambiguous and insufficient to understand biological function. The proteins need to be seen in their biological context, which limits and defines the chemistry possible. They exist in multiple forms with different degrees of metalation and types of metal ions. The homoleptic thiolate coordination of mammalian metallothioneins is important for their molecular mechanism. It endows the proteins with redox activity and a specific pH dependence of their metal affinities. The proteins, therefore, also exist in different redox states of the sulfur donor ligands. Their coordination dynamics allows a vast conformational landscape for interactions with other proteins and ligands. Many fundamental signal transduction pathways regulate the expression of the dozen of human metallothionein genes. Recent advances in understanding the control of cellular zinc and copper homeostasis are the foundation for suggesting that mammalian metallothioneins provide a highly dynamic, regulated, and uniquely biological metal buffer to control the availability, fluctuations, and signaling transients of the most competitive Zn(II) and Cu(I) ions in cellular space and time.

Simultaneous Quantification and Speciation of Trace Metals in Paired Serum and CSF Samples by Size Exclusion Chromatography-Inductively Coupled Plasma-Dynamic Reaction Cell-Mass Spectrometry (SEC-DRC-ICP-MS)

BACKGROUND

Transition metals play a crucial role in brain metabolism: since they exist in different oxidation states they are involved in ROS generation, but they are also co-factors of enzymes in cellular energy metabolism or oxidative defense.

METHODS

Paired serum and cerebrospinal fluid (CSF) samples were analyzed for iron, zinc, copper and manganese as well as for speciation using SEC-ICP-DRC-MS. Brain extracts from Mn-exposed rats were additionally analyzed with SEC-ICP-DRC-MS.

RESULTS

The concentration patterns of transition metal size fractions were correlated between serum and CSF: Total element concentrations were significantly lower in CSF. Fe-ferritin was decreased in CSF whereas a LMW Fe fraction was relatively increased. The 400-600 kDa Zn fraction and the Cu-ceruloplasmin fraction were decreased in CSF, by contrast the 40-80 kDa fraction, containing Cu- and Zn-albumin, relatively increased. For manganese, the α-2-macroglobulin fraction showed significantly lower concentration in CSF, whereas the citrate Mn fraction was enriched. Results from the rat brain extracts supported the findings from human paired serum and CSF samples.

CONCLUSIONS

Transition metals are strictly controlled at neural barriers (NB) of neurologic healthy patients. High molecular weight species are down-concentrated along NB, however, the Mn-citrate fraction seems to be less controlled, which may be problematic under environmental load.

The Influence of Nutritional Factors on Immunological Outcomes

Through food intake, humans obtain a variety of nutrients that are essential for growth, cellular function, tissue development, energy, and immune defense. A special interaction between nutrients and gut-associated lymphoid tissue occurs in the intestinal tract. Enterocytes of the intestinal barrier act as sensors for antigens from nutrients and the intestinal microbiota, which they deliver to the underlying immune system of the lamina propria, triggering an immune response. Studies investigating the mechanism of influence of nutrition on immunological outcomes have highlighted an important role of macronutrients (proteins, carbohydrates, fatty acids) and micronutrients (vitamins, minerals, phytochemicals, antioxidants, probiotics) in modulating immune homeostasis. Nutrients exert their role in innate immunity and inflammation by regulating the expression of TLRs, pro- and anti-inflammatory cytokines, thus interfering with immune cell crosstalk and signaling. Chemical substrates derived from nutrient metabolism may act as cofactors or blockers of enzymatic activity, influencing molecular pathways and chemical reactions associated with microbial killing, inflammation, and oxidative stress. Immune cell function appears to be influenced by certain nutrients that form parts of the cell membrane structure and are involved in energy production and prevention of cytotoxicity. Nutrients also contribute to the initiation and regulation of adaptive immune responses by modulating B and T lymphocyte differentiation, proliferation and activation, and antibody production. The purpose of this review is to present the available data from the field of nutritional immunology to elucidate the complex and dynamic relationship between nutrients and the immune system, the delineation of which will lead to optimized nutritional regimens for disease prevention and patient care.

Biomarkers of Zinc and Copper Status and Associated Factors in Outpatients with Ischemic and Non-Ischemic Heart Failure

Background: Few studies have explored the impact of ischemic and non-ischemic etiologies of heart failure and other factors associated with heart failure on zinc and copper status. This study examined zinc and copper status in 80 outpatients with ischemic (n = 36) and non-ischemic (n = 44) heart failure and associations with biodemographic, clinical, biochemical, and nutritional parameters.Materials: Biomarkers of plasma zinc and copper, copper-zinc ratio, 24-h urinary zinc excretion, ceruloplasmin, and dietary intake of zinc and copper were assessed. Plasma zinc and copper and urinary zinc were measured by inductively coupled plasma mass spectrometry (ICP-MS).Results: Patients with ischemic heart failure showed lower dietary zinc intake and higher dietary copper intake (both p = 0.02). Zinc and copper in plasma, copper-zinc ratio, ceruloplasmin, and 24-h urinary zinc excretion showed no statistical differences between the groups (all p ≥ 0.05). An inverse association was found between age (β =-0.001; p = 0.005) and the use of diuretics (β = -0.047; p = 0.013) and plasma zinc. Copper levels in plasma (β = 0.001; p < 0.001), and albumin (β = 0.090; p<0.001) were directly associated with plasma zinc. A positive association was found between ceruloplasmin (β = 0.011; p < 0.001), gamma-glutamyl transferase (β = 0.001; p < 0.001), albumin (β = 0.077; p = 0.001), and high-sensitivity c-reactive protein (β = 0.001; p = 0.024) and plasma copper.Conclusion: Zinc and copper biomarkers in clinically stable patients with heart failure did not seem to be responsive to the differences in zinc and copper intake observed in this study, regardless of heart failure etiology. The predictors of plasma zinc and copper levels related to oxidative stress and inflammation should be monitored in heart failure clinical practice.

Copper toxicity of inflection point in human intestinal cell line Caco-2 dissected: influence of temporal expression patterns

We previously described a non-monotonic dose response curve at low copper concentrations where 3.125 μM CuSO₄ (the early inflection point) was more toxic than 25 μM CuSO₄ in Caco-2 cells. We employed global proteomics to investigate this observation. The altered expression levels of a small number of proteins displaying a temporal response may provide the best indication of the underlying mechanism; more well-known copper response proteins including the metal binding metallothioneins (MT1X, MT1F, MT2A) and antioxidant response proteins including Heme oxygenase were upregulated to a similar level in both copper concentrations and so are less likely to underpin this phenomenon.The temporal response proteins include Granulins, AN1-type zinc finger protein 2A (ZFAND2A), and the heat shock proteins (HSPA6 and HSPA1B). Granulins were decreased after 4 h only in 25 μM CuSO₄ but from 24 h, were decreased in both copper concentrations to a similar level. Induction of ZFAND2A and increases in HSPA6 and HSPA1B were observed at 24 h only in 25 μM CuSO₄ but were present at 48 h in both copper conditions. The early expression of ZFAND2A, HSPs, and higher levels of α-crystallin B (CRYAB) correlated with lower levels of misfolded proteins in 25 μM CuSO₄ compared to 3.125 μM CuSO₄ at 48 h. These results suggest that 3.125 μM CuSO₄ at early time points was unable to activate the plethora of stress responses invoked by the higher copper concentration, paradoxically exposing the Caco-2 cells to higher levels of misfolded proteins and greater proteotoxic stress.

The Role of Copper in Tau-Related Pathology in Alzheimer's Disease

All tauopathies, including Alzheimer's disease (AD), are characterized by the intracellular accumulation of abnormal forms of tau protein in neurons and glial cells, which negatively affect microtubule stability. Under physiological conditions, tubulin-associated unit (Tau) protein is intrinsically disordered, almost without secondary structure, and is not prone to aggregation. In AD, it assembles, and forms paired helical filaments (PHFs) that further build-up neurofibrillary tangles (NFTs). Aggregates are composed of hyperphosphorylated tau protein that is more prone to aggregation. The pathology of AD is also linked to disturbed copper homeostasis, which promotes oxidative stress (OS). Copper imbalance is widely observed in AD patients. Deregulated copper ions may initiate and exacerbate tau hyperphosphorylation and formation of β-sheet-rich tau fibrils that ultimately contribute to synaptic failure, neuronal death, and cognitive decline observed in AD patients. The present review summarizes factors affecting the process of tau aggregation, conformational changes of small peptide sequences in the microtubule-binding domain required for these motifs to act as seeding sites in aggregation, and the role of copper in OS induction, tau hyperphosphorylation and tau assembly. A better understanding of the various factors that affect tau aggregation under OS conditions may reveal new targets and novel pharmacological approaches for the therapy of AD.

Feedback adaptation of synaptic excitability via Glu:Na+ symport driven astrocytic GABA and Gln release

Glutamatergic transmission composed of the arriving of action potential at the axon terminal, fast vesicular Glu release, postsynaptic Glu receptor activation, astrocytic Glu clearance and Glu→Gln shuttle is an abundantly investigated phenomenon. Despite its essential role, however, much less is known about the consequences of the mechanistic connotations of Glu:Na⁺ symport. Due to the coupled Na⁺ transport, Glu uptake results in significantly elevated intracellular astrocytic [Na⁺] that markedly alters the driving force of other Na⁺-coupled astrocytic transporters. The resulting GABA and Gln release by reverse transport through the respective GAT-3 and SNAT3 transporters help to re-establish the physiological Na⁺ homeostasis without ATP dissipation and consequently leads to enhanced tonic inhibition and replenishment of axonal glutamate pool. Here, we place this emerging astrocytic adjustment of synaptic excitability into the centre of future perspectives. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.