Involvement of SAPK/JNK Signaling Pathway in Copper Enhanced Zinc-Induced Neuronal Cell Death

Zinc, Copper, and Calcium: A Triangle in the Synapse for the Pathogenesis of Vascular-Type Senile Dementia

Zinc (Zn) and copper (Cu) are essential for normal brain functions. In particular, Zn and Cu are released to synaptic clefts during neuronal excitation. Synaptic Zn and Cu regulate neuronal excitability, maintain calcium (Ca) homeostasis, and play central roles in memory formation. However, in pathological conditions such as transient global ischemia, excess Zn is secreted to synaptic clefts, which causes neuronal death and can eventually trigger the pathogenesis of a vascular type of senile dementia. We have previously investigated the characteristics of Zn-induced neurotoxicity and have demonstrated that low concentrations of Cu can exacerbate Zn neurotoxicity. Furthermore, during our pharmacological approaches to clarify the molecular pathways of Cu-enhanced Zn-induced neurotoxicity, we have revealed the involvement of Ca homeostasis disruption. In the present review, we discuss the roles of Zn and Cu in the synapse, as well as the crosstalk between Zn, Cu, and Ca, which our study along with other recent studies suggest may underlie the pathogenesis of vascular-type senile dementia.

The Role of Zinc in the Development of Vascular Dementia and Parkinson's Disease and the Potential of Carnosine as Their Therapeutic Agent

Synaptic zinc ions (Zn2+) play an important role in the development of vascular dementia (VD) and Parkinson's disease (PD). In this article, we reviewed the current comprehension of the Zn2+-induced neurotoxicity that leads to the pathogenesis of these neuronal diseases. Zn2+-induced neurotoxicity was investigated by using immortalised hypothalamic neurons (GT1-7 cells). This cell line is useful for the development of a rapid and convenient screening system for investigating Zn2+-induced neurotoxicity. GT1-7 cells were also used to search for substances that prevent Zn2+-induced neurotoxicity. Among the tested substances was a protective substance in the extract of Japanese eel (Anguilla japonica), and we determined its structure to be like carnosine (β-alanylhistidine). Carnosine may be a therapeutic drug for VD and PD. Furthermore, we reviewed the molecular mechanisms that involve the role of carnosine as an endogenous protector and its protective effect against Zn2+-induced cytotoxicity and discussed the prospects for the future therapeutic applications of this dipeptide for neurodegenerative diseases and dementia.

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.

Heavy Metal Mediated Progressive Degeneration and Its Noxious Effects on Brain Microenvironment

Heavy metals, including lead (Pb), cadmium (Cd), arsenic (As), cobalt (Co), copper (Cu), manganese (Mn), zinc (Zn), and others, have a significant impact on the development and progression of neurodegenerative diseases in the human brain. This comprehensive review aims to consolidate the recent research on the harmful effects of different metals on specific brain cells such as neurons, microglia, astrocytes, and oligodendrocytes. Understanding the potential influence of these metals in neurodegeneration is crucial for effectively combating the ongoing advancement of these diseases. Metal-induced neurodegeneration involves molecular mechanisms such as apoptosis induction, dysregulation of metabolic and signaling pathways, metal imbalance, oxidative stress, loss of synaptic transmission, pathogenic peptide aggregation, and neuroinflammation. This review provides valuable insights by compiling the supportive evidence from recent research findings. Additionally, we briefly discuss the modes of action of natural neuroprotective compounds. While this comprehensive review aims to consolidate the recent research on the harmful effects of various metals on specific brain cells, it may not cover all studies and findings related to metal-induced neurodegeneration. Studies that are done using bioinformatics tools, microRNAs, long non-coding RNAs, emerging disease models, and studies based on the modes of exposure to toxic metals are a future prospect to be explored.

Contribution of zinc accumulation to ischemic brain injury and its mechanisms about oxidative stress, inflammation, and autophagy: an update

Ischemic stroke is a leading cause of death and disability worldwide, and presently, there is no effective neuroprotective therapy. Zinc is an essential trace element that plays important physiological roles in the central nervous system. Free zinc concentration is tightly regulated by zinc-related proteins in the brain under normal conditions. Disruption of zinc homeostasis, however, has been found to play an important role in the mechanism of brain injury following ischemic stroke. A large of free zinc releases from storage sites after cerebral ischemia, which affects the functions and survival of nerve cells, including neurons, astrocytes, and microglia, resulting in cell death. Ischemia-triggered intracellular zinc accumulation also disrupts the function of blood-brain barrier via increasing its permeability, impairing endothelial cell function, and altering tight junction levels. Oxidative stress and neuroinflammation have been reported to be as major pathological mechanisms in cerebral ischemia/reperfusion injury. Studies have showed that the accumulation of intracellular free zinc could impair mitochondrial function to result in oxidative stress, and form a positive feedback loop between zinc accumulation and reactive oxygen species production, which leads to a series of harmful reactions. Meanwhile, elevated intracellular zinc leads to neuroinflammation. Recent studies also showed that autophagy is one of the important mechanisms of zinc toxicity after ischemic injury. Interrupting the accumulation of zinc will reduce cerebral ischemia injury and improve neurological outcomes. This review summarizes the role of zinc toxicity in cellular and tissue damage following cerebral ischemia, focusing on the mechanisms about oxidative stress, inflammation, and autophagy.

Eucalyptol antagonized the apoptosis and immune dysfunction of grass carp hepatocytes induced by tetrabromobisphenol A by regulating ROS/ASK1/JNK pathway

Tetrabromobisphenol A (TBBPA) is a common environmental pollutant which has multi-organ toxicity to mammals. Eucalyptol (EUC) has super antioxidant biological activity. However, in this experimental study, we probed into the mechanism of toxic of TBBPA exposure on Grass carp hepatocytes (L8824 cells) and the antagonistic impact of EUC on TBBPA. We treated L8824 cells with 8 μg/ml TBBPA and/or 20 μM EUC for 24 h in this test research. The experiment results suggested that TBBPA exposure induced elevated levels of reactive oxygen species (ROS), led to oxidative stress, decreased SOD and CAT activities, decreased GSH and T-AOC contents, exacerbated MDA accumulation, activated ASK1/JNK signaling pathway, and further increased the contents of mitochondrial dependent apoptosis pathway related indicators (Cyt-C, Bax, Caspase 9, Caspase 3), while Bcl-2 expression decreased. In addition, TBBPA exposure induced increased expression of TNF-α, IL-6, IL-1β, and decreased expression of IL-2, IFN-γ, Hepcidin, β-defensin, LEAP2. The oxidative stress level, ASK1/JNK signal pathway expression level, apoptosis ratio and cellular immune function of cells exposed to EUC alone did not change significantly. Combined exposure of TBBPA and EUC significantly reduced the proportion of apoptosis and restored cellular immune function. Therefore, these results suggest that EUC can effectively antagonize TBBPA-induced apoptosis and immune dysfunction of L8824 cells by regulating ROS/ASK1/JNK signaling pathway.

Spatiotemporal Dynamics of the Molecular Expression Pattern and Intercellular Interactions in the Glial Scar Response to Spinal Cord Injury

Nerve regeneration in adult mammalian spinal cord is poor because of the lack of intrinsic regeneration of neurons and extrinsic factors - the glial scar is triggered by injury and inhibits or promotes regeneration. Recent technological advances in spatial transcriptomics (ST) provide a unique opportunity to decipher most genes systematically throughout scar formation, which remains poorly understood. Here, we first constructed the tissue-wide gene expression patterns of mouse spinal cords over the course of scar formation using ST after spinal cord injury from 32 samples. Locally, we profiled gene expression gradients from the leading edge to the core of the scar areas to further understand the scar microenvironment, such as neurotransmitter disorders, activation of the pro-inflammatory response, neurotoxic saturated lipids, angiogenesis, obstructed axon extension, and extracellular structure re-organization. In addition, we described 21 cell transcriptional states during scar formation and delineated the origins, functional diversity, and possible trajectories of subpopulations of fibroblasts, glia, and immune cells. Specifically, we found some regulators in special cell types, such as Thbs1 and Col1a2 in macrophages, CD36 and Postn in fibroblasts, Plxnb2 and Nxpe3 in microglia, Clu in astrocytes, and CD74 in oligodendrocytes. Furthermore, salvianolic acid B, a blood-brain barrier permeation and CD36 inhibitor, was administered after surgery and found to remedy fibrosis. Subsequently, we described the extent of the scar boundary and profiled the bidirectional ligand-receptor interactions at the neighboring cluster boundary, contributing to maintain scar architecture during gliosis and fibrosis, and found that GPR37L1_PSAP, and GPR37_PSAP were the most significant gene-pairs among microglia, fibroblasts, and astrocytes. Last, we quantified the fraction of scar-resident cells and proposed four possible phases of scar formation: macrophage infiltration, proliferation and differentiation of scar-resident cells, scar emergence, and scar stationary. Together, these profiles delineated the spatial heterogeneity of the scar, confirmed the previous concepts about scar architecture, provided some new clues for scar formation, and served as a valuable resource for the treatment of central nervous system injury.

Crosstalk of copper and zinc in the pathogenesis of vascular dementia

Copper and zinc are essential for normal brain functions. Both are localized in presynaptic vesicles and are secreted into synaptic clefts during neuronal excitation. Despite their significance, excesses of copper and zinc are neurotoxic. In particular, excess zinc after transient global ischemia plays a central role in the ischemia-induced neurodegeneration and pathogenesis of vascular type senile dementia. We previously found that sub-lethal concentrations of copper remarkably exacerbated zinc-induced neurotoxicity, and we investigated the molecular pathways of copper-enhanced zinc-induced neurotoxicity. The endoplasmic reticulum stress pathway, the stress-activated protein kinases/c-‍Jun amino-terminal kinases pathway, and mitochondrial energy production failure were revealed to be involved in the neurodegenerative processes. Regarding the upstream factors of these pathways, we focused on copper-derived reactive oxygen species and the disruption of calcium homeostasis. Because excess copper and zinc may be present in the synaptic clefts during ischemia, it is possible that secreted copper and copper-induced reactive oxygen species may enhance zinc neurotoxicity and eventually contribute to the pathogenesis of vascular type senile dementia.

Copper as a Collaborative Partner of Zinc-Induced Neurotoxicity in the Pathogenesis of Vascular Dementia

Copper is an essential trace element and possesses critical roles in various brain functions. A considerable amount of copper accumulates in the synapse and is secreted in neuronal firings in a manner similar to zinc. Synaptic copper and zinc modulate neuronal transmission and contribute to information processing. It has been established that excess zinc secreted during transient global ischemia plays central roles in ischemia-induced neuronal death and the pathogenesis of vascular dementia. We found that a low concentration of copper exacerbates zinc-induced neurotoxicity, and we have demonstrated the involvement of the endoplasmic reticulum (ER) stress pathway, the stress-activated protein kinases/c-Jun amino-terminal kinases (SAPK/JNK) signaling pathway, and copper-induced reactive oxygen species (ROS) production. On the basis of our results and other studies, we discuss the collaborative roles of copper in zinc-induced neurotoxicity in the synapse and the contribution of copper to the pathogenesis of vascular dementia.

Silver nanoparticles protect against arsenic induced genotoxicity via attenuating arsenic bioaccumulation and elevating antioxidation in mammalian cells

Arsenic (As) and its compounds have been classified as Group I carcinogenic agents by the International Agency for Research on Cancer (IARC); however, there is few specific and efficient antidotes used for As detoxification. The present study aimed to investigate the protective effects of silver nanoparticles (AgNPs) at non-toxic concentrations on As(Ⅲ) induced genotoxicity and the underlying mechanism. Our data showed that AgNPs pretreatment significantly inhibited the generation of phosphorylated histone H2AX (γ-H2AX, marker of nuclear DNA double strand breaks) and the mutation frequencies induced by As(Ⅲ) exposure. Atomic fluorescence spectrometer (AFS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis revealed that the intracellular accumulation of As(Ⅲ) in human-hamster hybrid A_L cells was declined by AgNPs via suppressing the expression of specific As(Ⅲ)-binding protein (Gal-1). Moreover, the activities of antioxidant enzymes were greatly up-regulated by AgNPs, which eventually inhibited the generation of reactive oxygen species (ROS) induced by As(Ⅲ) and the downstream stress-activated protein kinases/c-Jun amino-terminal kinases (SAPK/JNK) signaling pathway. These results provided clear evidence that AgNPs dramatically suppressed the genotoxic response of As(Ⅲ) in mammalian cells via decreasing As(Ⅲ) bioaccumulation and elevating intracellular antioxidation, which might provide a new clue for AgNPs applications in As(Ⅲ) detoxification.

Unlocking the Recovery Potential: JMJD3 Inhibition-Mediated SAPK/JNK Signaling Inactivation Supports Endogenous Oligodendrocyte-Lineage Commitment Post Mammalian Spinal Cord Injury

Spinal cord injury (SCI) induced catastrophic neurological disability is often incurable at present. The injury triggered immediately oligodendrocytes loss and overwhelming demyelination are regarded as an insurmountable barrier to SCI recovery. To date, effective strategy to promote the endogenous oligodendrocytes replacement post SCI remains elusive. Epigenetic modifications are emerging as critical molecular switches of gene expression in CNS. However, the epigenetic mechanisms underlying oligodendrogenesis post SCI yet to be discovered. In this study, we report that H3K27me3 demethylase JMJD3 exists as a pivotal epigenetic regulator which manipulates the endogenous oligodendrogenesis post SCI. We found that JMJD3 inhibition promotes the oligodendrocyte linage commitment of neural stem/progenitor cells (NPCs) in vitro and in vivo. Moreover, we demonstrated that JMJD3 inhibition mediated SAPK/JNK signaling inactivation is functionally necessary for endogenous oligodendrocyte-lineage commitment post SCI. Our results also suggested that JMJD3 is downstream of SAPK/JNK pathway, and capable of translates SCI induced SAPK/JNK signaling into epigenetic codes readable by spinal cord endogenous NPCs. Taken together, our findings provide novel evidence of JMJD3 mediated oligodendrocyte-lineage commitment orchestration post SCI, which would be a potential epigenetic approach to induce the mature mammalian endogenous recovery.

A self-designed versatile and portable sensing device based on smart phone for colorimetric detection

A UV-vis spectrometer, as a sort of important analytical instrument, has been widely used to analyze various substances. However, expensive equipment and skilled operators are required, which limits its broad applications for out-of-lab and daily measurements. In this work, a self-designed sensing device based on smart phone was developed as a sensitive, cost-effective, facile, and portable testing tool. The sensing device fabricated by 3D printing was used to lodge a sample solution and produce a light signal, and the optical sensor on a smart phone worked as a transducer. The light source in the device generated wide-wavelength radiation, which passed through an inner filter and only light of a designated wavelength reached the testing solution. The intensity of transmitted light was then measured by an optical sensor internally installed in most smart phones, where the signals were processed as well. The feasibility of our device was verified by detecting four kinds of common heavy metal ions in actual water samples, and the testing results showed good agreement with those obtained from the UV-vis spectrometer. This work is expected to shed some light on the construction of smart phone-based sensors, featuring decent portability, simple operation, low cost, high sensitivity, and good accuracy.

Carnosine suppresses neuronal cell death and inflammation induced by 6-hydroxydopamine in an in vitro model of Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disease for which prevention and effective treatments are lacking. The pathogenesis of Parkinson's disease is not clearly understood. It is thought to be caused by oxidative stress-dependent loss of dopamine neurons in the substantia nigra and the promotion of inflammatory responses by microglia at the lesion site. In addition, cell loss occurs in the hypothalamus of Parkinson's disease patients. Carnosine is an endogenous dipeptide that can exert many beneficial effects, including an antioxidant action, metal ion chelation, proton buffering capacity, and inhibition of protein carbonylation and glycolysis. Previously, we found that carnosine inhibits trace metal-induced death of immortalized hypothalamic neuronal GT1-7 cells. In this study, we analyzed the efficacy of carnosine on 6-hydroxydopamine (6-OHDA)-dependent GT1-7 cell death and inflammatory responses. We found that carnosine significantly prevented 6-OHDA-dependent GT1-7 cell death in a dose-dependent manner. Moreover, carnosine significantly suppressed the expression of 6-OHDA-induced integrated stress response (ISR)-related factors and pro-inflammatory cytokines. Carnosine also significantly inhibited 6-OHDA-dependent reactive oxygen species (ROS) production and c-Jun amino-terminal kinase (JNK) pathway activation in GT1-7 cells. These results indicate that carnosine inhibits hypothalamic neuronal cell death and inflammatory responses by inhibiting the ROS-JNK pathway. We therefore suggest that carnosine may be effective in preventing the onset or the exacerbation of Parkinson's disease.

Clioquinol inhibits dopamine-β-hydroxylase secretion and noradrenaline synthesis by affecting the redox status of ATOX1 and copper transport in human neuroblastoma SH-SY5Y cells

Clioquinol (5-chloro-7-indo-8-quinolinol), a chelator and ionophore of copper/zinc, was extensively used as an amebicide to treat indigestion and diarrhea in the mid-1900s. However, it was withdrawn from the market in Japan because its use was epidemiologically linked to an increase in the incidence of subacute myelo-optic neuropathy (SMON). SMON is characterized by the subacute onset of sensory and motor disturbances in the lower extremities with occasional visual impairments, which are preceded by abdominal symptoms. Although pathological studies demonstrated axonopathy of the spinal cord and optic nerves, the underlying mechanisms of clioquinol toxicity have not been elucidated in detail. In the present study, a reporter assay revealed that clioquinol (20-50 µM) activated metal response element-dependent transcription in human neuroblastoma SH-SY5Y cells. Clioquinol significantly increased the cellular level of zinc within 1 h, suggesting zinc influx due to its ionophore effects. On the other hand, clioquinol (20-50 µM) significantly increased the cellular level of copper within 24 h. Clioquinol (50 µM) induced the oxidation of the copper chaperone antioxidant 1 (ATOX1), suggesting its inactivation and inhibition of copper transport. The secretion of dopamine-β-hydroxylase (DBH) and lysyl oxidase, both of which are copper-dependent enzymes, was altered by clioquinol (20-50 µM). Noradrenaline levels were reduced by clioquinol (20-50 µM). Disruption of the ATOX1 gene suppressed the secretion of DBH. This study suggested that the disturbance of cellular copper transport by the inactivation of ATOX1 is one of the mechanisms involved in clioquinol-induced neurotoxicity in SMON.

Seleno-l-methionine suppresses copper-enhanced zinc-induced neuronal cell death via induction of glutathione peroxidase

Excessive zinc ion (Zn²⁺) release is induced in pathological situations and causes neuronal cell death. Previously, we have reported that copper ions (Cu²⁺) markedly exacerbated Zn²⁺-induced neuronal cell death by potentiating oxidative stress, the endoplasmic reticulum (ER) stress response, and the activation of the c-Jun amino-terminal kinase (JNK) signaling pathway. In contrast, selenium (Se), an essential trace element, and amino acids containing selenium (such as seleno-l-methionine) have been reported to inhibit stress-induced neuronal cell death and oxidative stress. Thus, we investigated the effect of seleno-l-methionine on Cu²⁺/Zn²⁺-induced neuronal cell death in GT1-7 cells. Seleno-l-methionine treatment clearly restored the Cu²⁺/Zn²⁺-induced decrease in the viable cell number and attenuated the Cu²⁺/Zn²⁺-induced cytotoxicity. Accordingly, the levels of ER stress-related factors (especially, CHOP and GADD34) and of phosphorylated JNK increased upon CuCl₂ and ZnCl₂ co-treatment, whereas pre-treatment with seleno-l-methionine significantly suppressed these upregulations. Analysis of reactive oxygen species (ROS) as upstream factors of these pathways revealed that Cu²⁺/Zn²⁺-induced ROS production was clearly suppressed by seleno-l-methionine treatment. Finally, we found that seleno-l-methionine induced the antioxidative protein, glutathione peroxidase. Taken together, our findings suggest that seleno-l-methionine suppresses Cu²⁺/Zn²⁺-induced neuronal cell death and oxidative stress via induction of glutathione peroxidase. Thus, we think that seleno-l-methionine may help prevent refractory neurological diseases.

Protective effect of polaprezinc on cadmium-induced injury of lung epithelium

Cadmium is a toxic metal contained in food, water and the atmosphere, and exposure to cadmium can cause respiratory diseases in humans. Various health problems caused by cadmium result from oxidative stress-dependent cellular injury. Metallothioneins are intracellular, cysteine-rich, metal-binding proteins that have a detoxifying action on heavy metals such as cadmium in various organs. In addition, expression of metallothioneins is induced by metals with low biological toxicity, such as zinc. Therefore, in this study we examined whether polaprezinc, a chelate compound consisting of carnosine and zinc, can suppress cadmium-induced lung epithelial cell death. We found that cell viability markers (intracellular ATP levels and mitochondrial activity) and cytotoxicity (lactate dehydrogenase release) were decreased and increased, respectively by cadmium treatment; however, polaprezinc significantly reversed these changes. Moreover, cadmium-dependent endoplasmic reticulum stress responses were suppressed by polaprezinc treatment. We then examined the protective mechanisms of polaprezinc, focusing on oxidative stress. Cadmium induced the production of reactive oxygen species (ROS) in A549 cells in a dose-dependent manner and polaprezinc significantly suppressed this cadmium-induced ROS production. Finally, we examined whether polaprezinc exerts an antioxidative action by inducing metallothioneins. We found that polaprezinc dose-dependently induced metallothioneins using real-time RT-PCR, ELISA, and western blotting analyses. These results indicate that polaprezinc can suppress cadmium-induced lung epithelial cell death and oxidative stress by inducing metallothioneins. We therefore suggest that polaprezinc may have therapeutic effects against respiratory diseases, such as chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis.

Carnosine as a Possible Drug for Zinc-Induced Neurotoxicity and Vascular Dementia

Increasing evidence suggests that the metal homeostasis is involved in the pathogenesis of various neurodegenerative diseases including senile type of dementia such as Alzheimer’s disease, dementia with Lewy bodies, and vascular dementia. In particular, synaptic Zn²⁺ is known to play critical roles in the pathogenesis of vascular dementia. In this article, we review the molecular pathways of Zn²⁺-induced neurotoxicity based on our and numerous other findings, and demonstrated the implications of the energy production pathway, the disruption of calcium homeostasis, the production of reactive oxygen species (ROS), the endoplasmic reticulum (ER)-stress pathway, and the stress-activated protein kinases/c-Jun amino-terminal kinases (SAPK/JNK) pathway. Furthermore, we have searched for substances that protect neurons from Zn²⁺-induced neurotoxicity among various agricultural products and determined carnosine (β-alanyl histidine) as a possible therapeutic agent for vascular dementia.

Silver Ions as a Tool for Understanding Different Aspects of Copper Metabolism

In humans, copper is an important micronutrient because it is a cofactor of ubiquitous and brain-specific cuproenzymes, as well as a secondary messenger. Failure of the mechanisms supporting copper balance leads to the development of neurodegenerative, oncological, and other severe disorders, whose treatment requires a detailed understanding of copper metabolism. In the body, bioavailable copper exists in two stable oxidation states, Cu(I) and Cu(II), both of which are highly toxic. The toxicity of copper ions is usually overcome by coordinating them with a wide range of ligands. These include the active cuproenzyme centers, copper-binding protein motifs to ensure the safe delivery of copper to its physiological location, and participants in the Cu(I) ↔ Cu(II) redox cycle, in which cellular copper is stored. The use of modern experimental approaches has allowed the overall picture of copper turnover in the cells and the organism to be clarified. However, many aspects of this process remain poorly understood. Some of them can be found out using abiogenic silver ions (Ag(I)), which are isoelectronic to Cu(I). This review covers the physicochemical principles of the ability of Ag(I) to substitute for copper ions in transport proteins and cuproenzyme active sites, the effectiveness of using Ag(I) to study copper routes in the cells and the body, and the limitations associated with Ag(I) remaining stable in only one oxidation state. The use of Ag(I) to restrict copper transport to tumors and the consequences of large-scale use of silver nanoparticles for human health are also discussed.