Chemistry and biology of mammalian metallothioneins

The paradoxical role of zinc on microglia

Zinc is an essential trace element for humans, and its homeostasis is essential for the health of the central nervous system. Microglia, the resident immune cells in the central nervous system, play the roles of sustaining, nourishing, and immune surveillance. Microglia are sensitive to microenvironment changes and are easily activated to M1 phenotype to enhance disease progression or the M2 phenotype to improve peripheral nerves injury repair. Zinc is requisite for microglial activation, However, the cytotoxicity outcome of zinc against microglia, the activated microglia phenotype, and activated microglia function are ambiguous. Herein, we have reviewed the neurological function of zinc and microglia, particularly the ambiguous role of zinc on microglia. We also pay attention to the role of zinc homeostasis on microglial function within the central nervous system disease. Finally, we observe the relationship between zinc and microglia, attempting to design new therapeutic measures against major nervous system disorders.

Biochemical Markers of Zinc Nutrition

Zinc is an important trace element involved in the biochemical and physiological functions of the organism and is essential in the human body. It has been reported that 17.3% of people around the world are at risk of many diseases due to zinc deficiency, which has already affected people's healthy lives. Currently, mild zinc deficiency is difficult to diagnose early due to the lack of typical clinical manifestations, so finding zinc biomarkers is crucial for people's health. The present article reviews the main representative zinc biomarkers, such as body fluid zinc levels, zinc-dependent proteins, tissue zinc, and zinc-containing enzymes, to provide a reference for actively promoting the study of zinc nutritional status and early clinical diagnosis.

Macrophage metallothioneins participate in the antileishmanial activity of antimonials

Host cell functions that participate in the pharmacokinetics and pharmacodynamics (PK/PD) of drugs against intracellular pathogen infections are critical for drug efficacy. In this study, we investigated whether macrophage mechanisms of xenobiotic detoxification contribute to the elimination of intracellular Leishmania upon exposure to pentavalent antimonials (SbV). Primary macrophages from patients with cutaneous leishmaniasis (CL) (n=6) were exposed ex vivo to L. V. panamensis infection and SbV, and transcriptomes were generated. Seven metallothionein (MT) genes, potent scavengers of heavy metals and central elements of the mammalian cell machinery for xenobiotic detoxification, were within the top 20 up-regulated genes. To functionally validate the participation of MTs in drug-mediated killing of intracellular Leishmania, tandem knockdown (KD) of MT2-A and MT1-E, MT1-F, and MT1-X was performed using a pan-MT shRNA approach in THP-1 cells. Parasite survival was unaffected in tandem-KD cells, as a consequence of strong transcriptional upregulation of MTs by infection and SbV, overcoming the KD effect. Gene silencing of the metal transcription factor-1 (MTF-1) abrogated expression of MT1 and MT2-A genes, but not ZnT-1. Upon exposure to SbV, intracellular survival of Leishmania in MTF-1KD cells was significantly enhanced. Results from this study highlight the participation of macrophage MTs in Sb-dependent parasite killing.

Cu(I) binds to Zn7-MT2 via two parallel pathways

Metallothionein proteins are essential for Cu(I) and Zn(II) homeostasis as well as heavy metal detoxification. The metallation properties of MT2 are of great interest due to their wide patterns of expression and correlation with multiple diseases including cancers, neurological disorders, and respiratory diseases. Use of isotopically pure 63Cu(I) and 68Zn(II) eliminates the complexity of the Cu, Zn-MT2 mass spectral peaks due to significant overlap of naturally abundant isotopes. This allows for the resolution of the precise Cu(I) and Zn(II) stoichiometries when both Cu(I) and Zn(II) are bound to MT2 at physiological pH as expected in vivo. Exact Cu: Zn ratios were determined from mass spectral simulations carried out for every point in the titration. We report that Cu(I) metallation of Zn7-MT2 can only be understood in terms of two pathways occurring in parallel with pathway ① resulting in Cu5Zn5-MT2 and Cu9Zn3-MT2. Pathway ② results in Cu6Zn4-MT2 and Cu10Zn2-MT2, which are the major products of the reaction. From the electrospray ionization (ESI)-mass spectral data we report a series of formation constants (KF) for species starting from Zn7-MT2 up to Cu11Zn2-MT2. Room temperature phosphorescence and circular dichroism (CD) spectra were measured in parallel with the ESI-mass spectrometry data allowing for the assignment of specific species to specific spectral bands. Through analysis of the CD spectral bands, we propose that Cu(I) binds to the β domain first to form a Cu5Zn1 cluster or Cu6 cluster with emission at 670 and 750 nm, respectively, leaving the Zn4 cluster in the α domain.

Xenobiotic Bi3+ Coordination by Cysteine-Rich Metallothionein-3 Reveals a Cooperatively Formed Thiolate-Sharing Bi2S5 Cluster

The field of designing artificial metalloproteins has yet to effectively tackle the incorporation of multimetal clusters, which is a key component of natural metalloproteins, such as metallothioneins (MTs) and calmodulin. MT is a physiological, essential, cysteine-rich metalloprotein that binds to a variety of metals but is only known to form metal-thiolate clusters with Cd2+, Zn2+, and Cu+. Bismuth is a xenobiotic metal and a component of metallodrugs used to treat gastric ulcers and cancer, as well as an emerging metal used in industrial practices. Electrospray ionization mass spectrometry, UV-visible spectroscopy, and extended X-ray absorption fine structure spectroscopy were used to probe the Bi3+ binding site structures in apo-MT3 (brain-located MT) at pH 7.4 and 2 and provide the complete set of binding affinities. We discovered the highly cooperative formation of a novel Bi3+ species, Bi2MT3, under physiological conditions, where each Bi3+ ion is coordinated by three cysteinyl thiolates, with one of the thiolates bridging between the two Bi3+ ions. This cluster structure was associated with a strong visible region absorption band, which was disrupted by the addition of Zn2+ and reversibly disrupted by acidification and increased temperature. This is the first reported presence of bridging cysteines for a xenobiotic metal in MT3 and the Bi2MT structure is the first Bi cluster found in a metalloprotein.

Structural Characterization of Zinc-Sucrose Complex and Its Ability to Promote Zinc Absorption in Caco-2 Monolayer Cells and Mice

Sucrose emerges as a metal-ion chelating agent with excellent stability that may increase metal-ion absorption. This study aimed to characterize the structure of zinc-sucrose complex and investigate its ability to promote zinc absorption in Caco-2 monolayer cells and mice. Based on the results of the inductively coupled plasma emission spectrometer (ICP-ES), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), and Fourier transform infrared spectroscopy (FT-IR), it can be inferred that zinc and sucrose were chelated at a 1:1 ratio, with the hydroxyl groups playing a significant role. The Caco-2 monolayer cell model revealed that zinc-sucrose complex increased the amount of zinc uptake, retention, and transport in a dose- and time-dependent manner. Through the upregulation of genes and proteins for ZIP4, MT1, and DMT1, treatment with zinc-sucrose complex improved the proportion of absorbed zinc utilized for transport compared to ZnCl2 (26.21 ± 4.96 versus 8.50 ± 1.51%). Pharmacokinetic analysis of mice confirmed the zinc absorption-promoting effect of zinc-sucrose complex, as indicated by the considerably higher serum zinc level (4.16 ± 0.53 versus 2.56 ± 0.45 mg/L) and intestinal ZIP4, MT1, and DMT1 gene expression than ZnCl2. Further treatment of different zinc channel inhibitors and CETSA demonstrated the direct interaction of zinc-sucrose complex with ZIP4 protein and ZIP4-mediated cellular transport of zinc-sucrose complex. These findings provide a novel insight into the zinc absorption-promoting mechanism of zinc-sucrose complex, which could be used as an ingredient in functional foods to treat zinc deficiency.

Metallothionein I/II Expression and Metal Ion Levels in Correlation with Amyloid Beta Deposits in the Aged Feline Brain

Brain aging has been correlated with high metallothionein I-II (MT-I/II) expression, iron and zinc dyshomeostasis, and Aβ deposition in humans and experimental animals. In the present study, iron and zinc accumulation, the expression of MT-I/II and Aβ42, and their potential association with aging in the feline brain were assessed. Tissue sections from the temporal and frontal grey (GM) and white (WM) matter, hippocampus, thalamus, striatum, cerebellum, and dentate nucleus were examined histochemically for the presence of age-related histopathological lesions and iron deposits and distribution. We found, using a modified Perl's/DAB method, two types of iron plaques that showed age-dependent accumulation in the temporal GM and WM and the thalamus, along with the age-dependent increment in cerebellar-myelin-associated iron. We also demonstrated an age-dependent increase in MT-I/II immunoreactivity in the feline brain. In cats over 7 years old, Aβ immunoreactivity was detected in vessel walls and neuronal somata; extracellular Aβ deposits were also evident. Interestingly, Aβ-positive astrocytes were also observed in certain cases. ICP-MS analysis of brain content regarding iron and zinc concentrations showed no statistically significant association with age, but a mild increase in iron with age was noticed, while zinc levels were found to be higher in the Mature and Senior groups. Our findings reinforce the suggestion that cats could serve as a dependable natural animal model for brain aging and neurodegeneration; thus, they should be further investigated on the basis of metal ion concentration changes and their effects on aging.

Arsenic binding to human metallothionein-3

Arsenic poisoning is of great concern with respect to its neurological toxicity, which is especially significant for young children. Human exposure to arsenic occurs worldwide from contaminated drinking water. In human physiology, one response to toxic metals is through coordination with the metallochaperone metallothionein (MT). Central nervous system expression of MT isoform 3 (MT3) is thought to be neuroprotective. We report for the first time on the metalation pathways of As3+ binding to apo-MT3 under physiological conditions, yielding the absolute binding constants (log Kn, n = 1-6) for each sequential As3+ binding event: 10.20, 10.02, 9.79, 9.48, 9.06, and 8.31 M-1. We report on the rate of the reaction of As3+ with apo-MT3 at pH 3.5 with rate constants (kn, n = 1-6) determined for each sequential As3+ binding event: 116.9, 101.2, 85.6, 64.0, 43.9, and 21.0 M-1 s-1. We further characterize the As3+ binding pathway to fully metalated Zn7MT3 and partially metalated Zn-MT3. As3+ binds rapidly with high binding constants under physiological conditions in a noncooperative manner, but is unable to replace the Zn2+ in fully-metalated Zn-MT3. As3+ binding to partially metalated Zn-MT3 takes place with a rearrangement of the Zn-binding profile. Our work shows that As 3+ rapidly and efficiently binds to both apo-MT3 and partially metalated Zn-MT3 at physiological pH.

Assessment of Knowledge on Metal Trace Element Concentrations and Metallothionein Biomarkers in Cetaceans

Cetaceans are recognized as bioindicators of pollution in oceans. These marine mammals are final trophic chain consumers and easily accumulate pollutants. For example, metals are abundant in oceans and commonly found in the cetacean tissues. Metallothioneins (MTs) are small non-enzyme proteins involved in metal cell regulation and are essential in many cellular processes (cell proliferation, redox balance, etc.). Thus, the MT levels and the concentrations of metals in cetacean tissue are positively correlated. Four types of metallothioneins (MT1, 2, 3, and 4) are found in mammals, which may have a distinct expression in tissues. Surprisingly, only a few genes or mRNA-encoding metallothioneins are characterized in cetaceans; molecular studies are focused on MT quantification, using biochemical methods. Thus, we characterized, in transcriptomic and genomic data, more than 200 complete sequences of metallothioneins (mt1, 2, 3, and 4) in cetacean species to study their structural variability and to propose to the scientific research community Mt genes dataset to develop in future molecular approaches which will study the four types of metallothioneins in diversified organs (brain, gonad, intestine, kidney, stomach, etc.).

Moonlighting enzymes: when cellular context defines specificity

It is not often realized that the absolute protein specificity is an exception rather than a rule. Two major kinds of protein multi-specificities are promiscuity and moonlighting. This review discusses the idea of enzyme specificity and then focusses on moonlighting. Some important examples of protein moonlighting, such as crystallins, ceruloplasmin, metallothioniens, macrophage migration inhibitory factor, and enzymes of carbohydrate metabolism are discussed. How protein plasticity and intrinsic disorder enable the removing the distinction between enzymes and other biologically active proteins are outlined. Finally, information on important roles of moonlighting in human diseases is updated.

Overnight Corticosterone and Gene Expression in Mouse Hippocampus: Time Course during Resting Period

The aim of the experiment was to test the effect of an elevated level of glucocorticoids on the mouse hippocampal transcriptome after 12 h of treatment with corticosterone that was administered during an active phase of the circadian cycle. Additionally, we also tested the circadian changes in gene expression and the decay time of transcriptomic response to corticosterone. Gene expression was analyzed using microarrays. Obtained results show that transcriptomic responses to glucocorticoids are heterogeneous in terms of the decay time with some genes displaying persistent changes in expression during 9 h of rest. We have also found a considerable overlap between genes regulated by corticosterone and genes implicated previously in stress response. The examples of such genes are Acer2, Agt, Apod, Aqp4, Etnppl, Fabp7, Fam107a, Fjx1, Fmo2, Galnt15, Gjc2, Heph, Hes5, Htra1, Jdp2, Kif5a, Lfng, Lrg1, Mgp, Mt1, Pglyrp1, Pla2g3, Plin4, Pllp, Ptgds, Ptn, Slc2a1, Slco1c1, Sult1a1, Thbd and Txnip. This indicates that the applied model is a useful tool for the investigation of mechanisms underlying the stress response.

Cadmium inhibits differentiation of human trophoblast stem cells into extravillous trophoblasts and disrupts epigenetic changes within the promoter region of the HLA-G gene

Cadmium (Cd) is a toxic heavy metal widely distributed in the environment. Maternal whole-blood Cd levels during pregnancy are positively associated with the risk of early preterm birth. We hypothesized that Cd inhibits trophoblast differentiation, resulting in the development of hypertensive disorders of pregnancy and a high risk of early preterm birth. Using the CT27 human trophoblast stem cell line, we found that exposing these cells to 0.1-0.4 µM Cd inhibited their differentiation into extravillous cytotrophoblasts (EVTs). Supporting this finding, we found that expression of the metal-binding protein metallothionein, which suppresses the toxicity of Cd, is low in EVTs. We also found that Cd exposure changes the methylation status of the promoter region of the HLA-G gene, which is specifically expressed in EVTs. Together, these results suggest that Cd inhibits placental formation by suppressing trophoblast differentiation into EVTs. This suppression may underlie the increased risk of gestational hypertension in women with high whole-blood Cd levels.

The Difference in Zinc Concentrations Required for Induction among Metallothionein Isoforms Can Be Explained by the Different MTF1 Affinities to MREs in Its Promoter

Metallothioneins (MTs) are cysteine-rich low-molecular-weight proteins that protect cells from heavy metal toxicity. MT1 and MT2 are considered ubiquitously expressed among the MT isoforms ranging from 1 to 4. These MT1 and MT2 transcriptions are regulated by metal regulatory transcription factor 1 (MTF1) binding to the metal response element (MRE) of the promoter, which is upregulated in response to zinc. The functional MT isoforms are MT1A, MT1B, MT1E, MT1F, MT1G, MT1H, MT1M, MT1X, and MT2A in humans, but these expressions were differently regulated. Here, MT1A was shown to be significantly less upregulated by zinc than MT1E, MT1G, MT1X, and MT2A. The poor responsiveness of the MT1A zinc was suggested to be due to the MRE sequence in the MT1A promoter region having a lower MTF1 binding affinity compared to the other isoforms. MT1A may be induced via pathways other than the MTF1-MRE binding pathway. These findings may help elucidate the differential regulation of MT isoform expression.

Heterologous Expression of Human Metallothionein Gene HsMT1L Can Enhance the Tolerance of Tobacco (Nicotiana nudicaulis Watson) to Zinc and Cadmium

Metallothionein (MT) is a multifunctional inducible protein in animals, plants, and microorganisms. MT is rich in cysteine residues (10-30%), can combine with metal ions, has a low molecular weight, and plays an essential biological role in various stages of the growth and development of organisms. Due to its strong ability to bind metal ions and scavenge free radicals, metallothionein has been used in medicine, health care, and other areas. Zinc is essential for plant growth, but excessive zinc (Zn) is bound to poison plants, and cadmium (Cd) is a significant environmental pollutant. A high concentration of cadmium can significantly affect the growth and development of plants and even lead to plant death. In this study, the human metallothionein gene HsMT1L under the control of the CaMV 35S constitutive promoter was transformed into tobacco, and the tolerance and accumulation capacity of transgenic tobacco plants to Zn and Cd were explored. The results showed that the high-level expression of HsMT1L in tobacco could significantly enhance the accumulation of Zn²⁺ and Cd²⁺ in both the aboveground parts and the roots compared to wild-type tobacco plants and conferred a greater tolerance to Zn and Cd in transgenic tobacco. Subcellular localization showed that HsMT1L was localized to the nucleus and cytoplasm in the tobacco. Our study suggests that HsMT1L can be used for the phytoremediation of soil for heavy metal removal.

The Modular Architecture of Metallothioneins Facilitates Domain Rearrangements and Contributes to Their Evolvability in Metal-Accumulating Mollusks

Protein domains are independent structural and functional modules that can rearrange to create new proteins. While the evolution of multidomain proteins through the shuffling of different preexisting domains has been well documented, the evolution of domain repeat proteins and the origin of new domains are less understood. Metallothioneins (MTs) provide a good case study considering that they consist of metal-binding domain repeats, some of them with a likely de novo origin. In mollusks, for instance, most MTs are bidomain proteins that arose by lineage-specific rearrangements between six putative domains: α, β1, β2, β3, γ and δ. Some domains have been characterized in bivalves and gastropods, but nothing is known about the MTs and their domains of other Mollusca classes. To fill this gap, we investigated the metal-binding features of NpoMT1 of Nautilus pompilius (Cephalopoda class) and FcaMT1 of Falcidens caudatus (Caudofoveata class). Interestingly, whereas NpoMT1 consists of α and β1 domains and has a prototypical Cd²⁺ preference, FcaMT1 has a singular preference for Zn²⁺ ions and a distinct domain composition, including a new Caudofoveata-specific δ domain. Overall, our results suggest that the modular architecture of MTs has contributed to MT evolution during mollusk diversification, and exemplify how modularity increases MT evolvability.

Molecular Background of Toxic-Substances-Induced Morphological Alterations in the Umbilical Cord Vessels and Fetal Red Blood Cells

The relationship between smoking and human health has been investigated mostly in adults, despite the fact that the chemicals originating from sustained maternal smoking disrupt the carefully orchestrated regulatory cascades in the developing fetus. In this study, we followed molecular alterations in the umbilical cord (UC) vessels and fetal red blood cells (RBCs), which faithfully reflect the in vivo status of the fetus. We showed evidence for the decreased level of DNA-PKcs-positive nuclei in samples with smoking origin, which is associated with the impaired DNA repair system. Furthermore, we pointed out the altered ratio of MMP-9 metalloproteinase and its endogenous inhibitor TIMP-1, which might be a possible explanation for the morphological abnormalities in the UC vessels. The presented in vivo dataset emphasizes the higher vulnerability of the veins, as the primary target for the toxic materials unfiltered by the placenta. All these events become amplified by the functionally impaired fetal RBC population via a crosstalk mechanism between the vessel endothelium and the circulating RBCs. In our ex vivo approach, we looked for the molecular explanation of metal-exposure-induced alterations, where expressions of the selected genes were upregulated in the control group, while samples with smoking origin showed a lack of response, indicative of prior long-term in utero exposure.

Comparative cisplatin reactivity towards human Zn7-metallothionein-2 and MTF-1 zinc fingers: potential implications in anticancer drug resistance

Cis-diamminedichloroplatinum(II) (cisplatin) is a widely used metal-based chemotherapeutic drug for the treatment of cancers. However, intrinsic and acquired drug resistance limit the efficacy of cisplatin-based treatments. Increased production of intracellular thiol-rich molecules, in particular metallothioneins (MTs), which form stable coordination complexes with the electrophilic cisplatin, results in cisplatin sequestration leading to pre-target resistance. MT-1/-2 are overexpressed in cancer cells, and their expression is controlled by the metal response element (MRE)-binding transcription factor-1 (MTF-1), featuring six Cys2His2-type zinc fingers which, upon zinc metalation, recognize specific MRE sequences in the promoter region of MT genes triggering their expression. Cisplatin can efficiently react with protein metal binding sites featuring nucleophilic cysteine and/or histidine residues, including MTs and zinc fingers proteins, but the preferential reactivity towards specific targets with competing binding sites cannot be easily predicted. In this work, by in vitro competition reactions, we investigated the thermodynamic and kinetic preferential reactivity of cisplatin towards human Zn7MT-2, each of the six MTF-1 zinc fingers, and the entire human MTF-1 zinc finger domain. By spectroscopic, spectrometric, and electrophoretic mobility shift assays (EMSA), we demonstrated that cisplatin preferentially reacts with Zn7MT-2 to form Cys4-Pt(II) complexes, resulting in zinc release from MT-2. Zinc transfer from MT-2 to the MTF-1 triggers MTF-1 metalation, activation, and binding to target MRE sequences, as demonstrated by EMSA with DNA oligonucleotides. The cisplatin-dependent MT-mediated MTF-1 activation leading to apo-MT overexpression potentially establishes one of the molecular mechanisms underlying the development and potentiation of MT-mediated pre-target resistance.

ptk2 and mt2a Genes Expression in Gastritis and Gastric Cancer Patients with Helicobacter pylori Infection

BACKGROUND

ptk2 and mt2a genes contribute to the cell cycle during proliferation and apoptosis, respectively. Designing a case-control study including gastric adenocarcinoma and gastritis patients with and without Helicobacter pylori infection would lead to determinate of the correlations between ptk2 and mt2a genes expression with H. pylori infection in gastric antral epithelial cells.

METHODS

Overall, 50 and 30 gastric antral biopsy samples of gastric cancer (case group) and gastritis (control group) patients were included into study, respectively. All biopsy samples were collected considering the exclusion criteria including patients with a history of consumption of tobacco, alcohol, and anti-H. pylori drugs. Each patient group is divided into with and without H. pylori infection to detect cDNA fold changes of ptk2 and mt2a genes by using Real Time RT PCR. Furthermore, the presence of H. pylori virulence genes was detected directly by using specific primers and simple PCR on cDNA synthesized from total RNA of gastric antral biopsy samples.

RESULTS

A negative correlation was revealed between age and clinical manifestations with the ΔCt value of the ptk2 gene (P < 0.05). The H. pylori iceA1/2 and cagE genes revealed positive and negative correlations with the ΔCt value of the ptk2 gene (P < 0.05), respectively. Furthermore, a weak correlation was detectable between H. pylori babA2/B, oipA, and cagY genes and the ΔCt value of the mt2a gene in gastric antral epithelial cells of patients (P < 0.1).

CONCLUSIONS

The results of the current study opened a view for more investigation on the stunning roles of H. pylori infection in clinical outcomes through mt2a and ptk2 gene expression in gastric antral epithelial cells.

Zinc in Cognitive Impairment and Aging

Zinc, an essential micronutrient for life, was first discovered in 1869 and later found to be indispensable for the normal development of plants and for the normal growth of rats and birds. Zinc plays an important role in many physiological and pathological processes in normal mammalian brain development, especially in the development of the central nervous system. Zinc deficiency can lead to neurodegenerative diseases, mental abnormalities, sleep disorders, tumors, vascular diseases, and other pathological conditions, which can cause cognitive impairment and premature aging. This study aimed to review the important effects of zinc and zinc-associated proteins in cognitive impairment and aging, to reveal its molecular mechanism, and to highlight potential interventions for zinc-associated aging and cognitive impairments.

Reducing Endogenous Labile Zn May Help to Reduce Smooth Muscle Cell Injury around Vascular Stents

Vascular stent service involves complex service environments and performance requirements, among which the histocompatibility of the stent could seriously affect the therapeutic effect. In the pathology of vascular disease, the thin fiber cap is easily ruptured, exposing the necrotic core below, and triggering a series of dangerous biochemical reactions. In contrast, the thin neointima, considered an essential structure growing on the stent, may evolve into vulnerable plaque structures due to lesions induced by the stent. Therefore, the reduction of necrosis around the stent below the thin neointima is indispensable. In this work, different cell model experiments suggested that the content of endogenous labile Zn positively correlated with cell injury. Zinquin-Zn fluorescence experiments and zinc ion channels research suggested that the change in the content of endogenous labile Zn in smooth muscle cells is affected by different stent coatings. The content of endogenous labile Zn in cells negatively correlated with cell viability. Animal experiments indirectly verified the increase in endogenous labile Zn by detecting the expression of Zn regulatory protein (metallothionein) in the necrotic tissues. Reducing the content of endogenous labile Zn may favor a reduction in smooth muscle cell injury and necrosis. This biochemical mechanism is effective in improving the therapeutic effect of vascular stents.

Protein interactions with metallothionein-3 promote vectorial active transport in human proximal tubular cells

Metallothionein 3 (MT-3) is a small, cysteine-rich protein that binds to essential metals required for homeostasis, as well as to heavy metals that have the potential to exert toxic effects on cells. MT-3 is expressed by epithelial cells of the human kidney, including the cells of the proximal tubule. Our laboratory has previously shown that mortal cultures of human proximal tubular (HPT) cells express MT-3 and form domes in the cell monolayer, a morphological feature indicative of vectorial active transport, an essential function of the proximal tubule. However, an immortalized proximal tubular cell line HK-2 lacks the expression of MT-3 and fails to form domes in the monolayer. Transfection of HK-2 cells with the MT-3 gene restores dome formation in these cells suggesting that MT-3 is required for vectorial active transport. In order to determine how MT-3 imparts this essential feature to the proximal tubule, we sought to identify proteins that interact either directly or indirectly with MT-3. Using a combination of pulldowns, co-immunoprecipitations, and mass spectrometry analysis, putative protein interactants were identified and subsequently confirmed by Western analysis and confocal microscopy, following which proteins with direct physical interactions were investigated through molecular docking. Our data shows that MT-3 interacts with myosin-9, aldolase A, enolase 1, β-actin, and tropomyosin 3 and that these interactions are maximized at the periphery of the apical membrane of doming proximal tubule cells. Together these observations reveal that MT-3 interacts with proteins involved in cytoskeletal organization and energy metabolism, and these interactions at the apical membrane support vectorial active transport and cell differentiation in proximal tubule cultures.

The Oxidative Balance Orchestrates the Main Keystones of the Functional Activity of Cardiomyocytes

This review is aimed at providing an overview of the key hallmarks of cardiomyocytes in physiological and pathological conditions. The main feature of cardiac tissue is the force generation through contraction. This process requires a conspicuous energy demand and therefore an active metabolism. The cardiac tissue is rich of mitochondria, the powerhouses in cells. These organelles, producing ATP, are also the main sources of ROS whose altered handling can cause their accumulation and therefore triggers detrimental effects on mitochondria themselves and other cell components thus leading to apoptosis and cardiac diseases. This review highlights the metabolic aspects of cardiomyocytes and wanders through the main systems of these cells: (a) the unique structural organization (such as different protein complexes represented by contractile, regulatory, and structural proteins); (b) the homeostasis of intracellular Ca²⁺ that represents a crucial ion for cardiac functions and E-C coupling; and (c) the balance of Zn²⁺, an ion with a crucial impact on the cardiovascular system. Although each system seems to be independent and finely controlled, the contractile proteins, intracellular Ca²⁺ homeostasis, and intracellular Zn²⁺ signals are strongly linked to each other by the intracellular ROS management in a fascinating way to form a "functional tetrad" which ensures the proper functioning of the myocardium. Nevertheless, if ROS balance is not properly handled, one or more of these components could be altered resulting in deleterious effects leading to an unbalance of this "tetrad" and promoting cardiovascular diseases. In conclusion, this "functional tetrad" is proposed as a complex network that communicates continuously in the cardiomyocytes and can drive the switch from physiological to pathological conditions in the heart.

Transcriptomic and functional analysis of Aβ1-42 oligomer-stimulated human monocyte-derived microglia-like cells

Dysregulation of microglial function contributes to Alzheimer's disease (AD) pathogenesis. Several genetic and transcriptome studies have revealed microglia specific genetic risk factors, and changes in microglia expression profiles in AD pathogenesis, viz. the human-Alzheimer's microglia/myeloid (HAM) profile in AD patients and the disease-associated microglia profile (DAM) in AD mouse models. The transcriptional changes involve genes in immune and inflammatory pathways, and in pathways associated with Aβ clearance. Aβ oligomers have been suggested to be the initial trigger of microglia activation in AD. To study the direct response to Aβ oligomers exposure, we assessed changes in gene expression in an in vitro model for microglia, the human monocyte-derived microglial-like (MDMi) cells. We confirmed the initiation of an inflammatory profile following LPS stimulation, based on increased expression of IL1B, IL6, and TNFα. In contrast, the Aβ_1-42 oligomers did not induce an inflammatory profile or a classical HAM profile. Interestingly, we observed a specific increase in the expression of metallothioneins in the Aβ_1-42 oligomer treated MDMi cells. Metallothioneins are involved in metal ion regulation, protection against reactive oxygen species, and have anti-inflammatory properties. In conclusion, our data suggests that exposure to Aβ_1-42 oligomers may initially trigger a protective response in vitro.

Combined effects of copper and microplastics on physiological parameters of Tubastrea aurea corals

Microplastics (MPs) have been a serious environmental problem because it can carry pollution like heavy metals and organic pollutants. However, the combined effect of MPs and bivalent copper ion (Cu(II)) on the coral azooxanthellate has been rarely studied. In the present study, the combined effects of PVC and Cu(II) on the physiological responses of Tubastrea aurea were studied. Our results showed that MPs alone enhanced the activity of catalase (CAT), superoxide dismutase (SOD), and reduced glutathione (GSH). The mixture groups had the same effects on the CAT and GSH, which enhanced CAT and GSH activity by 97% and 53% respectively. MPs alone and the combined treatment groups decreased the activity of lipid peroxide (LPO) and the content of metallothionein (MT) by 45% and 20% of the coral Tubastrea aurea. Cu(II) exposure always had negative effect on the physiological parameters of coral, and MPs decreased the toxicity of Cu(II) in the combined groups. This work is the first time to report the combined effects of Cu(II) and microplastics on azooxanthellate coral, which will provide important preliminary data for the following research.

Evidence for a Long-Lived, Cu-Coupled and Oxygen-Inert Disulfide Radical Anion in the Assembly of Metallothionein-3 Cu(I)4-Thiolate Cluster

The human copper-binding protein metallothionein-3 (MT-3) can reduce Cu(II) to Cu(I) and form a polynuclear Cu(I)₄-Cys_5-6 cluster concomitant with intramolecular disulfide bonds formation, but the cluster is unusually inert toward O₂ and redox-cycling. We utilized a combined array of rapid-mixing spectroscopic techniques to identify and characterize the transient radical intermediates formed in the reaction between Zn₇MT-3 and Cu(II) to form Cu(I)₄Zn(II)₄MT-3. Stopped-flow electronic absorption spectroscopy reveals the rapid formation of transient species with absorption centered at 430-450 nm and consistent with the generation of disulfide radical anions (DRAs) upon reduction of Cu(II) by MT-3 cysteine thiolates. These DRAs are oxygen-stable and unusually long-lived, with lifetimes in the seconds regime. Subsequent DRAs reduction by Cu(II) leads to the formation of a redox-inert Cu(I)₄-Cys₅ cluster with short Cu-Cu distances (<2.8 Å), as revealed by low-temperature (77 K) luminescence spectroscopy. Rapid freeze-quench Raman and electron paramagnetic resonance (EPR) spectroscopy characterization of the intermediates confirmed the DRA nature of the sulfur-centered radicals and their subsequent oxidation to disulfide bonds upon Cu(II) reduction, generating the final Cu(I)₄-thiolate cluster. EPR simulation analysis of the radical g- and A-values indicate that the DRAs are directly coupled to Cu(I), potentially explaining the observed DRA stability in the presence of O₂. We thus provide evidence that the MT-3 Cu(I)₄-Cys₅ cluster assembly process involves the controlled formation of novel long-lived, copper-coupled, and oxygen-stable disulfide radical anion transient intermediates.

Cadmium Removal from Giant Squid (Dosidicus gigas) Hydrolysate in Fixed-Bed Columns Packed with Iminodiacetic Resin: Tools for Scaling up the Process

Giant squid hydrolysate (GSH) elaborated from different batches from a fishing company was evaluated for cadmium removal. Fixed-bed column packed with iminodiacetic resin as adsorbent was used. GSH solution at different cadmium concentrations were fed in the fixed-bed column and breakthrough curves were evaluated. A high degree of metal removal from the solution was achieved and the saturation point (C_e/C₀ ≤ 0.8) was achieved more quickly at higher concentrations of cadmium. The maximum capacity of adsorption (q₀) was obtained using the Thomas model, where 1137.4, 860.4, 557.4, and 203.1 mg g^-1 were achieved using GSH with concentrations of 48.37, 20.97, 12.13, and 3.26 mg L^-1, respectively. Five cycles of desorption of the resin with HCl (1 M) backflow and regeneration with NaOH (0.5 M) were also evaluated, where no significant differences (p-value > 0.05) were observed between each cycle, with an average of 935.9 mg g^-1 of q_max. The in-series columns evaluated reached a total efficiency of 90% on average after the third column in GSH with a cadmium concentration of 20.97 mg L^-1. This kind of configuration should be considered the best alternative for cadmium removal from GSH. Additionally, the chemical composition of GSH, which was considered a quality parameter, was not affected by cadmium adsorption.

Bioinorganic Chemistry of Zinc in Relation to the Immune System

Zinc is well-known to have a central role in human inflammation and immunity and is itself an anti-inflammatory and antiviral agent. Despite its massively documented role in such processes, the underlying chemistry of zinc in relation to specific proteins and pathways of the immune system has not received much focus. This short review provides an overview of this topic, with emphasis on the structures of key proteins, zinc coordination chemistry, and probable mechanisms involved in zinc-based immunity, with some focus points for future chemical and biological research.

Changes in Copper, Zinc, Arsenic, Mercury, and Lead Concentrations in Rat Biofluids and Tissues Induced by the "Renqing Changjue" Pill, a Traditional Tibetan Medicine

The "Renqing Changjue" pill (RQCJ), as an effective prescription of Traditional Tibetan Medicine (TTM), has been widely used in treating advanced gastroenteropathy diseases for over a thousand years. However, the toxicity and adverse effects of TTM have attracted increasing attention because heavy metals may be added as active ingredients. In this work, we introduced a robust model based on endogenous metabolism enabling the study of changes in copper (Cu), zinc (Zn), arsenic (As), mercury (Hg), and lead (Pb) concentrations and the mechanism between biofluids (blood and urine) and tissue (liver, kidney, spleen) samples from rats treated with RQCJ, along with metabolic changes after different treatment time points. Inductively coupled plasma-mass spectrometry was used to monitor the heavy metals. Slightly different trends of heavy metals were observed in rat metabolites. The levels of Hg, As, and Pb were clearly dose-dependent in the tissue and biofluid samples. Basic recovery of Hg and Pb was found after stopping treatment with RQCJ. The accumulation of As was more obvious in the blood, liver, kidney, and spleen; however, Hg was deposited in the kidney. Pb accumulated the most in the spleen. The concentrations of Cu and Zn were constant or accumulated to a certain extent, which could cause the body to have Cu and Zn metabolism disorders in the administration period. Our findings highlight how metal changes and effects on the mechanisms might contribute to the progression of understanding of the toxicity information for RQCJ. Therefore, precautions should be taken in the clinic to monitor the potential toxicity of RQCJ with long-term administration.

Crossroads between membrane trafficking machinery and copper homeostasis in the nerve system

Imbalanced copper homeostasis and perturbation of membrane trafficking are two common symptoms that have been associated with the pathogenesis of neurodegenerative and neurodevelopmental diseases. Accumulating evidence from biophysical, cellular and in vivo studies suggest that membrane trafficking orchestrates both copper homeostasis and neural functions-however, a systematic review of how copper homeostasis and membrane trafficking interplays in neurons remains lacking. Here, we summarize current knowledge of the general trafficking itineraries for copper transporters and highlight several critical membrane trafficking regulators in maintaining copper homeostasis. We discuss how membrane trafficking regulators may alter copper transporter distribution in different membrane compartments to regulate intracellular copper homeostasis. Using Parkinson's disease and MEDNIK as examples, we further elaborate how misregulated trafficking regulators may interplay parallelly or synergistically with copper dyshomeostasis in devastating pathogenesis in neurodegenerative diseases. Finally, we explore multiple unsolved questions and highlight the existing challenges to understand how copper homeostasis is modulated through membrane trafficking.

The effects of metallothionein in paraquat-induced Parkinson disease model of zebrafish

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disease caused by selective degeneration of dopaminergic neurons in the substantia nigra. Metallothionein has been shown to act as a neuroprotectant in various brain injury. Thus, this study aims to identify the effects of full-length human metallothionein 2 peptide (hMT2) in paraquat-induced brain injury in the zebrafish.

METHODOLOGY

A total of 80 adult zebrafish were divided into 4 groups namely control, paraquat-treated, pre-hMT2-treated, and post-hMT2-treated groups. Fish were treated with paraquat intraperitoneally every 3 days for 15 days. hMT2 were injected intracranially on day 0 (pre-treated group) and day 16 (post-treated group). Fish were sacrificed on day 22 and the brains were collected for qPCR, ELISA and immunohistochemistry analysis.

RESULTS

qPCR analysis showed that paraquat treatment down-regulated the expression of genes related to dopamine activity and biosynthesis (dat and th1) and neuroprotective agent (bdnf). Paraquat treatment also up-regulated the expression of the mt2, smtb and proinflammatory genes (il-1α, il-1β, tnf-α and cox-2). hMT2 treatment was able to reverse the effects of paraquat. Lipid peroxidation decreased in the paraquat and pre-hMT2-treated groups. However, lipid peroxidation increased in the post-hMT2-treated group. Paraquat treatment also led to a reduction of dopaminergic neurons while their numbers showed an increase following hMT2 treatment.

CONCLUSION

Paraquat has been identified as one of the pesticides that can cause the death of dopaminergic neurons and affect dopamine biosynthesis. Treatment with exogenous hMT2 could reverse the effects of paraquat in the zebrafish brain.

Tunicates Illuminate the Enigmatic Evolution of Chordate Metallothioneins by Gene Gains and Losses, Independent Modular Expansions, and Functional Convergences

To investigate novel patterns and processes of protein evolution, we have focused in the metallothioneins (MTs), a singular group of metal-binding, cysteine-rich proteins that, due to their high degree of sequence diversity, still represents a "black hole" in Evolutionary Biology. We have identified and analyzed more than 160 new MTs in nonvertebrate chordates (especially in 37 species of ascidians, 4 thaliaceans, and 3 appendicularians) showing that prototypic tunicate MTs are mono-modular proteins with a pervasive preference for cadmium ions, whereas vertebrate and cephalochordate MTs are bimodular proteins with diverse metal preferences. These structural and functional differences imply a complex evolutionary history of chordate MTs-including de novo emergence of genes and domains, processes of convergent evolution, events of gene gains and losses, and recurrent amplifications of functional domains-that would stand for an unprecedented case in the field of protein evolution.

Modular Evolution and Population Variability of Oikopleura dioica Metallothioneins

Chordate Oikopleura dioica probably is the fastest evolving metazoan reported so far, and thereby, a suitable system in which to explore the limits of evolutionary processes. For this reason, and in order to gain new insights on the evolution of protein modularity, we have investigated the organization, function and evolution of multi-modular metallothionein (MT) proteins in O. dioica. MTs are a heterogeneous group of modular proteins defined by their cysteine (C)-rich domains, which confer the capacity of coordinating different transition metal ions. O. dioica has two MTs, a bi-modular OdiMT1 consisting of two domains (t-12C and 12C), and a multi-modular OdiMT2 with six t-12C/12C repeats. By means of mass spectrometry and spectroscopy of metal-protein complexes, we have shown that the 12C domain is able to autonomously bind four divalent metal ions, although the t-12C/12C pair –as it is found in OdiMT1– is the optimized unit for divalent metal binding. We have also shown a direct relationship between the number of the t-12C/12C repeats and the metal-binding capacity of the MTs, which means a stepwise mode of functional and structural evolution for OdiMT2. Finally, after analyzing four different O. dioica populations worldwide distributed, we have detected several OdiMT2 variants with changes in their number of t-12C/12C domain repeats. This finding reveals that the number of repeats fluctuates between current O. dioica populations, which provides a new perspective on the evolution of domain repeat proteins.

The Enigmatic Metallothioneins: A Case of Upward-Looking Research

In the mid-1950s, Bert Lester Vallee and his colleague Marvin Margoshes discovered a molecule referred to today as metallothionein (MT). Meanwhile, MTs have been shown to be common in many biological organisms. Despite their prevalence, however, it remains unclear to date what exactly MTs do and how they contribute to the biological function of an organism or organ. We investigate why biochemical research has not yet been able to pinpoint the function(s) of MTs. We shall systematically examine both the discovery of and recent research on Dr. Vallee's beloved family of MT proteins utilizing tools from philosophy of science. Our analysis highlights that Vallee's initial work exhibited features prototypical of a developing research tradition: it was upward-looking, exploratory, and utilized mere interactions. Since the 1960s, MT research has increasingly become intervention- and hypothesis-based while it remained largely upward-looking in character. Whilst there is no reason to think that upward-looking research cannot successfully yield structure-function mappings, it has not yet been successful in the case of MTs. Thus, we suggest it might be time to change track and consider other research strategies looking into the evolution of MTs. Recent studies in mollusks render research in this direction worthy of pursuit.

The Evolving Role for Zinc and Zinc Transporters in Cadmium Tolerance and Urothelial Cancer

Cadmium (Cd) is an environmental toxicant with serious public health consequences due to its persistence within arable soils, and the ease with which it enters food chains and then, accumulates in human tissues to induce a broad range of adverse health effects. The present review focuses on the role of zinc (Zn), a nutritionally essential metal, to protect against the cytotoxicity and carcinogenicity of Cd in urinary bladder epithelial cells. The stress responses and defense mechanisms involving the low-molecular-weight metal binding protein, metallothionein (MT), are highlighted. The efflux and influx transporters of the ZnT and Zrt-/Irt-like protein (ZIP) gene families are discussed with respect to their putative role in retaining cellular Zn homeostasis. Among fourteen ZIP family members, ZIP8 and ZIP14 mediate Cd uptake by cells, while ZnT1 is among ten ZnT family members solely responsible for efflux of Zn (Cd), representing cellular defense against toxicity from excessively high Zn (Cd) intake. In theory, upregulation of the efflux transporter ZnT1 concomitant with the downregulation of influx transporters such as ZIP8 and ZIP14 can prevent Cd accumulation by cells, thereby increasing tolerance to Cd toxicity. To link the perturbation of Zn homeostasis, reflected by the aberrant expression of ZnT1, ZIP1, ZIP6, and ZIP10, with malignancy, tolerance to Cd toxicity acquired during Cd-induced transformation of a cell model of human urothelium, UROtsa, is discussed as a particular example.

Transcriptomic insights into the zinc homeostasis of MCF-7 breast cancer cells via next-generation RNA sequencing

A significant gap in the knowledge of zinc homeostasis exists for breast cancer cells. In this study, we investigated the transcriptomic response of the luminal breast cancer cells (MCF-7) to the exposure of extracellular zinc using next-generation RNA sequencing. The dataset was collected for three time points (T0, T30, and T120) in the time course of zinc treatment, which revealed the dramatic increase, up to 869-fold, of the gene expression for metallothioneins (MT1B, MT1F, MT1X, and MT2A) and the zinc exporter ZnT1 (SLC30A1) at T30, continuingly through to T120. The similar dynamic expression pattern was found for the autophagy-related gene (VMP1) and numerous genes for zinc finger proteins (e.g. RNF165, ZNF365, ZBTB2, SNAI1, ZNF442, ZNF547, ZNF563, and ZNF296). These findings point to the all-hands-on-deck strategy adopted by the cancer cells for maintaining zinc homeostasis. The stress responsive genes encoding heat shock proteins (HSPA1A, HSPA1B, HSPA1L, HSPA4L, HSPA6, HSPA8, HSPH1, HSP90AA1, and HSP90AB1) and the MTF-1 biomarker genes (AKR1C2, CLU, ATF3, GDF15, HMOX1, MAP1A, MAFG, SESN2, and UBC) were also differentially up-regulated at T120, suggesting a role of heat shock proteins and the MTF-1 related stress proteins in dealing with zinc exposure. It is for the first time that the gene encoding Polo-like kinase 2 (PLK2) was found to be involved in zinc-related response. The top differentially expressed genes were validated by qRT-PCR and further extended to the basal type breast cancer cells (MDA-MB-231). It was found that the expression level of SLC30A1 in MDA-MB-231 was higher than MCF-7 in response to zinc exposure. Taken together, the findings contribute to our knowledge and understanding of zinc homeostasis in breast cancer cells.

Structurally restricted Bi(III) metallation of apo-βMT1a: metal-induced tangling

Non-toxic bismuth salts are used in anti-ulcer medications and to protect against nephrotoxicity from anticancer drugs. Bismuth salts also induce metallothionein (MT), a metal-binding protein that lacks a formal secondary structure. We report the impact on the metallation properties of Bi(III) to the 9-cysteine β fragment of MT as a function of cysteine accessibility using electrospray ionization mass spectrometry. At pH 7.4, Bi2βMT formed cooperatively. Cysteine modification shows that each Bi(III) was terminally bound to three cysteinyl thiolates. Non-cooperative Bi(III) binding was observed at pH 2.3, where cysteine accessibility is increased. However, competition from H4EDTA inhibited Bi(III) binding. When GdmCl, a well-known denaturing agent, was used to increase cysteine accessibility of the apoβMT at pH 7.4, a greater fraction of Bi3βMT formed using all nine cysteines. The change in binding profile and equilibrium of Bi2βMT was determined as a function of acidification, which changed as a result of competition with H4EDTA. There was no Bi(III) transfer between Bi2βMT, Cd3βMT, and Zn3βMT. This lack of metal exchange and the resistance towards binding the third Bi(III) suggest a rigidity in the Bi2βMT binding sites that inhibits Bi(III) mobility. These experiments emphasize the conformational control of metallation that results in substantially different metallated products: at pH 7.4 (many cysteines buried) Bi2βMT, whereas at pH 7.4 (all cysteines accessible) enhanced formation of Bi3βMT. These data suggest that the addition of the first two Bi(III) crosslinks the protein, blocking access to the remaining three cysteines for the third Bi(III), as a result of tangle formation.

Towards a comprehensive view of 8-oxo-7,8-dihydro-2'-deoxyguanosine: Highlighting the intertwined roles of DNA damage and epigenetics in genomic instability

8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a major product of DNA oxidation, is a pre-mutagenic lesion which is prone to mispair, if left unrepaired, with 2'-deoxyadenosine during DNA replication. While unrepaired or incompletely repaired 8-oxodG has classically been associated with genome instability and cancer, it has recently been reported to have a role in the epigenetic regulation of gene expression. Despite the growing collection of genome-wide 8-oxodG mapping studies that have been used to provide new insight on the functional nature of 8-oxodG within the genome, a comprehensive view that brings together the epigenetic and the mutagenic nature of the 8-oxodG is still lacking. To help address this gap, this review aims to provide (i) a description of the state-of-the-art knowledge on both the mutagenic and epigenetic roles of 8-oxodG; (ii) putative molecular models through which the 8-oxodG can cause genome instability; (iii) a possible molecular model on how 8-oxodG, acting as an epigenetic signal, could cause the translocations and deletions which are associated with cancer.

Are granulins copper sequestering proteins?

Granulins (GRN 1-7) are short (~6 kDa), cysteine-rich proteins that are generated upon the proteolytic processing of progranulin (PGRN). These peptides, along with their precursor, have been implicated in multiple pathophysiological roles, especially in neurodegenerative diseases. Previously we showed that GRN-3 and GRN-5 are fully disordered in the reduced form implicating redox sensitive attributes to the proteins. Redox-based modulations are often carried out by metalloproteins in mitigating oxidative stress and maintaining metal-homeostasis within cells. To probe whether GRNs play a role in metal sequestration, we tested the metal binding propensity of the reduced forms of GRNs -3 and - 5 under neutral and acidic pH mimicking cytosolic and lysosomal conditions, respectively. We found, at neutral pH, both GRNs selectively bind Cu and no other divalent metal cations, with a greater specificity for Cu(I). Binding of Cu did not result in a disorder-to-order structural transition but partly triggered the multimerization of GRNs via uncoordinated cystines at both pH conditions. Overall, the results indicate that GRNs -3 and - 5 have surprisingly strong affinity for Cu in the pM range, comparable to other known copper sequestering proteins. The results also hint at a potential of GRNs to reduce Cu(II) to Cu(I), a process that has significance in mitigating Cu-induced ROS cytotoxicity in cells. Together, this report uncovers metal-coordinating property of GRNs for the first time, which may have profound significance in their structure and pathophysiological functions.

Ethyl maltol enhances copper mediated cytotoxicity in lung epithelial cells

Ethyl maltol (EM) is a flavoring agent commonly used in foods that falls under the generally recognized as safe category. It is added to many commercial e-cigarette vaping fluids and has been detected in the aerosols. Considering that EM facilitates heavy metal transport across plasma membranes, and that heavy metals have been detected in aerosols generated from e-cigarettes, this study examines whether EM enhances heavy metal mediated toxicity. A decrease in viability was observed in the Calu-6 and A549 lung epithelial cell lines co-exposed to EM and copper (Cu) but no decrease was observed after co-exposure to EM with iron (Fe). Interestingly, co-exposure to EM and Fe decreased viability of the HEK293 and IMR-90 fibroblast cell lines but co-exposure to EM and Cu did not. Increases in the apoptotic markers Annexin V staining and fragmented nuclei were observed in Calu-6 cells co-exposed to EM and Cu. Co-exposure to EM and Cu in Calu-6 cells resulted in DNA damage as indicated by activation of ATM and expression of γH2A.x foci. Finally, co-exposure to EM and Cu caused oxidative stress as indicated by increases in the generation of reactive oxygen species and the expression of ferritin light chain mRNA and hemeoxygenase-1 mRNA and protein. These data show that co-exposure to EM and Cu, at concentrations that are not toxic for either chemical individually, induce apoptosis and evoke oxidative stress and DNA damage in lung epithelial cells. We suggest that there is a greater risk of lung damage in users of c-cigarette who vape with vaping fluid containing EM.

Mirtazapine exerts astrocyte-mediated dopaminergic neuroprotection

Mirtazapine, a noradrenergic and specific serotonergic antidepressant (NaSSA), is known to activate serotonin (5-HT) 1A receptor. Our recent study demonstrated that stimulation of astrocytic 5-HT1A receptors promoted astrocyte proliferation and upregulated antioxidative property in astrocytes to protect dopaminergic neurons against oxidative stress. Here, we evaluated the neuroprotective effects of mirtazapine against dopaminergic neurodegeneration in models of Parkinson’s disease (PD). Mirtazapine administration attenuated the loss of dopaminergic neurons in the substantia nigra and increased the expression of the antioxidative molecule metallothionein (MT) in the striatal astrocytes of 6-hydroxydopamine (6-OHDA)-injected parkinsonian mice via 5-HT1A receptors. Mirtazapine protected dopaminergic neurons against 6-OHDA-induced neurotoxicity in mesencephalic neuron and striatal astrocyte cocultures, but not in enriched neuronal cultures. Mirtazapine-treated neuron-conditioned medium (Mir-NCM) induced astrocyte proliferation and upregulated MT expression via 5-HT1A receptors on astrocytes. Furthermore, treatment with medium from Mir-NCM-treated astrocytes protected dopaminergic neurons against 6-OHDA neurotoxicity, and these effects were attenuated by treatment with a MT-1/2-specific antibody or 5-HT1A antagonist. Our study suggests that mirtazapine could be an effective disease-modifying drug for PD and highlights that astrocytic 5-HT1A receptors may be a novel target for the treatment of PD.

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.

An alloy of zinc and innate immunity: Galvanising host defence against infection

Innate immune cells such as macrophages and neutrophils initiate protective inflammatory responses and engage antimicrobial responses to provide frontline defence against invading pathogens. These cells can both restrict the availability of certain transition metals that are essential for microbial growth and direct toxic concentrations of metals towards pathogens as antimicrobial responses. Zinc is important for the structure and function of many proteins, however excess zinc can be cytotoxic. In recent years, several studies have revealed that innate immune cells can deliver toxic concentrations of zinc to intracellular pathogens. In this review, we discuss the importance of zinc status during infectious disease and the evidence for zinc intoxication as an innate immune antimicrobial response. Evidence for pathogen subversion of this response is also examined. The likely mechanisms, including the involvement of specific zinc transporters that facilitate delivery of zinc by innate immune cells for metal ion poisoning of pathogens are also considered. Precise mechanisms by which excess levels of zinc can be toxic to microorganisms are then discussed, particularly in the context of synergy with other antimicrobial responses. Finally, we highlight key unanswered questions in this emerging field, which may offer new opportunities for exploiting innate immune responses for anti-infective development.

Membrane insertion exacerbates the α-Synuclein-Cu(II) dopamine oxidase activity: Metallothionein-3 targets and silences all α-synuclein-Cu(II) complexes

Copper binding to α-synuclein (α-Syn), the major component of intracellular Lewy body inclusions in substantia nigra dopaminergic neurons, potentiate its toxic redox-reactivity and plays a detrimental role in the etiology of Parkinson disease (PD). Soluble α-synuclein-Cu(II) complexes possess dopamine oxidase activity and catalyze ROS production in the presence of biological reducing agents via Cu(II)/Cu(I) redox cycling. These metal-centered redox reactivities harmfully promote the oxidation and oligomerization of α-Syn. While this chemistry has been investigated on recombinantly expressed soluble α-Syn, in vivo, α-Syn is acetylated at its N-terminus and is present in equilibrium between soluble and membrane-bound forms. This post-translational modification and membrane-binding alter the Cu(II) coordination environment and binding modes and are expected to affect the α-Syn-Cu(II) reactivity. In this work, we first investigated the reactivity of acetylated and membrane-bound complexes, and subsequently addressed whether the brain metalloprotein Zn₇-metallothionein-3 (Zn₇MT-3) possesses a multifaceted-role in targeting these aberrant copper interactions and consequent reactivity. Through biochemical characterization of the reactivity of the non-acetylated/N-terminally acetylated soluble or membrane-bound α-Syn-Cu(II) complexes towards dopamine, oxygen, and ascorbate, we reveal that membrane insertion dramatically exacerbates the catechol oxidase-like reactivity of α-Syn-Cu(II) as a result of a change in the Cu(II) coordination environment, thereby potentiating its toxicity. Moreover, we show that Zn₇MT-3 can efficiently target all α-Syn-Cu(II) complexes through Cu(II) removal, preventing their deleterious redox activities. We demonstrate that the Cu(II) reduction by the thiolate ligands of Zn₇MT-3 and the formation of Cu(I)₄Zn₄MT-3 featuring an unusual redox-inert Cu(I)₄-thiolate cluster is the molecular mechanism responsible for the protective effect exerted by MT-3 towards α-Syn-Cu(II). This work provides the molecular basis for new therapeutic interventions to control the deleterious bioinorganic chemistry of α-Syn-Cu(II).

Zinc Deficiency Promoted Fibrosis via ROS and TIMP/MMPs in the Myocardium of Mice

Zinc (Zn) is an important trace element in the body that has antioxidant effects. It has been proven that Zn deficiency can cause oxidative stress. The purpose of the present study was to clarify the effect and mechanism of Zn deficiency on myocardial fibrosis. Mice were fed with different Zn levels dietary for 9 weeks: Zn-normal group (ZnN, 34 mg Zn/kg), Zn-deficient group (ZnD, 2 mg Zn/kg), and Zn-adequate group (ZnA, 100 mg Zn/kg). We found that the Zn-deficient diet reduced the Zn concentration in myocardial tissue. Moreover, the TUNEL results demonstrated that cardiomyocytes in the ZnD group died in large numbers. Furthermore, ROS levels were significantly increased, and metallothionein (MT) expression levels decreased in the ZnD group. The results of Sirius Red staining indicated an increase in collagen in the ZnD group. Moreover, the ELISA results showed that collagen I, III, and IV and fibronectin (FN) were increased. In addition, the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase (TIMPs) was detected by RT-qPCR. The results showed that the expression of TIMP-1 in the ZnD group was increased, while MMPs were decreased. Immunohistochemical results showed an increase in the content of α-smooth muscle actin (α-SMA), while H&E staining showed an increase in interstitial width and a decrease in the number of cardiac cells. All data suggest that Zn deficiency enhances the oxidative stress response of myocardial tissue and eventually triggers myocardial fibrosis.

Copper Sources for Sod1 Activation

Copper ions (i.e., copper) are a critical part of several cellular processes, but tight regulation of copper levels and trafficking are required to keep the cell protected from this highly reactive transition metal. Cu, Zn superoxide dismutase (Sod1) protects the cell from the accumulation of radical oxygen species by way of the redox cycling activity of copper in its catalytic center. Multiple posttranslational modification events, including copper incorporation, are reliant on the copper chaperone for Sod1 (Ccs). The high-affinity copper uptake protein (Ctr1) is the main entry point of copper into eukaryotic cells and can directly supply copper to Ccs along with other known intracellular chaperones and trafficking molecules. This review explores the routes of copper delivery that are utilized to activate Sod1 and the usefulness and necessity of each.

Trace Elements in Home-Processed Food Obtained from Unconventional Animals

Wild animals have been used as food since ancient times and, currently, the consumption of unconventional animals is increasing worldwide. The process of cooking meat using traditional recipes includes a variety of ingredients, which can influence the total metal intake from the diet. In this study, the concentrations of eight essential (Fe, Zn, Cu, Mn, Se, Ni, Mo, and Co) and six non-essential (Pb, Cd, Hg, Al, As, and Cr) trace elements were determined in home-processed food obtained from snails and from three common species of game animals (woodcock, pheasant, and hare), seasoned with anchovies, mushrooms, and different vegetables using inductively coupled plasma mass spectrometry (ICP-MS). In general, Fe was the most abundant trace element, ranging from 18 ± 8 µg/g in pheasant to 99 ± 76 µg/g in snail, and Co was the least abundant, ranging from 0.007 ± 0.003 µg/g in hare to 0.093 ± 0.048 µg/g in snail. Regarding the non-essential trace elements, Pb concentrations showed wide variations, reaching a concentration of 17.30 µg/g in hare, while Cd concentrations were higher in snail, ranging from 0.18 to 0.46 µg/g. These alternative food sources can offer an important contribution to the human nutritional requirements of essential trace elements, in particular of Fe. The high concentrations of Pb and Cd present in some samples should be considered as potentially dangerous for the consumers.

Zinc at the crossroads of exercise and proteostasis

Zinc is an essential element for all forms of life, and one in every ten human proteins is a zinc protein. Zinc has catalytic, structural and signalling functions and its correct homeostasis affects many cellular processes. Zinc deficiency leads to detrimental consequences, especially in tissues with high demand such as skeletal muscle. Zinc cellular homeostasis is tightly regulated by different transport and buffer protein systems. Specifically, in skeletal muscle, zinc has been found to affect myogenesis and muscle regeneration due to its effects on muscle cell activation, proliferation and differentiation. In relation to skeletal muscle, exercise has been shown to modulate zinc serum and urinary levels and could directly affect cellular zinc transport. The oxidative stress induced by exercise may provide the basis for the mild zinc deficiency observed in athletes and could have severe consequences on health and sport performance. Proteostasis is induced during exercise and zinc plays an essential role in several of the associated pathways.

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Zinc deficiency could be a crucial issue in sport performance for athletes.

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Exercise could modulate zinc serum and cellular homeostasis.

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Zinc is part of proteostatic systems critical during exercise.

Metal Exchange in the Interprotein ZnII -Binding Site of the Rad50 Hook Domain: Structural Insights into CdII -Induced DNA-Repair Inhibition

CdII is a major genotoxic agent that readily displaces ZnII in a multitude of zinc proteins, abrogates redox homeostasis, and deregulates cellular metalloproteome. To date, this displacement has been described mostly for cysteine(Cys)-rich intraprotein binding sites in certain zinc finger domains and metallothioneins. To visualize how a ZnII -to-CdII swap can affect the target protein's status and thus understand the molecular basis of CdII -induced genotoxicity an intermolecular ZnII -binding site from the crucial DNA repair protein Rad50 and its zinc hook domain were examined. By using a length-varied peptide base, ZnII -to-CdII displacement in Rad50's hook domain is demonstrated to alter it in a bimodal fashion: 1) CdII induces around a two-orders-of-magnitude stabilization effect (log  K 12 Zn II =20.8 vs. log  K 12 Cd II =22.7), which defines an extremely high affinity of a peptide towards a metal ion, and 2) the displacement disrupts the overall assembly of the domain, as shown by NMR spectroscopic and anisotropy decay data. Based on the results, a new model explaining the molecular mechanism of CdII genotoxicity that underlines CdII 's impact on Rad50's dimer stability and quaternary structure that could potentially result in abrogation of the major DNA damage response pathway is proposed.