A mechanism for zinc toxicity in neuroblastoma cells

Oxidative stress modulating nanomaterials and their biochemical roles in nanomedicine

Many pathological conditions are predominantly associated with oxidative stress, arising from reactive oxygen species (ROS); therefore, the modulation of redox activities has been a key strategy to restore normal tissue functions. Current approaches involve establishing a favorable cellular redox environment through the administration of therapeutic drugs and redox-active nanomaterials (RANs). In particular, RANs not only provide a stable and reliable means of therapeutic delivery but also possess the capacity to finely tune various interconnected components, including radicals, enzymes, proteins, transcription factors, and metabolites. Here, we discuss the roles that engineered RANs play in a spectrum of pathological conditions, such as cancer, neurodegenerative diseases, infections, and inflammation. We visualize the dual functions of RANs as both generator and scavenger of ROS, emphasizing their profound impact on diverse cellular functions. The focus of this review is solely on inorganic redox-active nanomaterials (inorganic RANs). Additionally, we deliberate on the challenges associated with current RANs-based approaches and propose potential research directions for their future clinical translation.

Zinc dynamics regulate early ovarian follicle development

Zinc fluctuations regulate key steps in late oocyte and preimplantation embryo development; however, roles for zinc in preceding stages in early ovarian follicle development, when cooperative interactions exist between the oocyte and somatic cells, are unknown. To understand the roles of zinc during early follicle development, we applied single cell X-ray fluorescence microscopy, a radioactive zinc tracer, and a labile zinc probe to measure zinc in individual mouse oocytes and associated somatic cells within early follicles. Here, we report a significant stage-specific increase and compartmental redistribution in oocyte zinc content upon the initiation of early follicle growth. The increase in zinc correlates with the increased expression of specific zinc transporters, including two that are essential in oocyte maturation. While oocytes in follicles exhibit high tolerance to pronounced changes in zinc availability, somatic survival and proliferation are significantly more sensitive to zinc chelation or supplementation. Finally, transcriptomic, proteomic, and zinc loading analyses reveal enrichment of zinc targets in the ubiquitination pathway. Overall, these results demonstrate that distinct cell type-specific zinc regulations are required for follicle growth and indicate that physiological fluctuation in the localization and availability of this inorganic cofactor has fundamental functions in early gamete development.

In vitro osteogenic performance of two novel strontium and zinc-containing glass polyalkenoate cements

Glass polyalkenoate cements (GPCs) are under investigation as potential bone adhesives, as they may provide an alternative to polymethylmethacrylate-based cements. GPCs containing strontium (Sr) and zinc (Zn) in place of aluminium (Al) are of particular interest because these ions are known stimulators of osteoprogenitor differentiation. GPCs have been manufactured from a novel bioactive glass (SiO2 :0.48, ZnO:0.36, CaO:0.12, SrO:0.04) in the past, but, while such materials have been assessed for their influence on viability, their influence on osteogenic function has not been investigated until now. For this study, two GPCs were formulated from the same glass precursor evaluated in previous studies. These GPCs were named GPC A and GPC B, and they differed in glass particle size, polyacrylic acid molecular weight, and their powder: liquid ratios. The effect of these two GPCs on osteogenic differentiation of primary rat osteoblasts were evaluated using three culture systems: culture with dissolution extracts, indirect contact with transwell-inserts and direct contact. Additionally, the degradation characteristics of GPCs were assessed, including their interfacial pH and surrounding pH. The experimental outcomes revealed that collagen deposition, alkaline phosphatase expression, and mineralization were largely dependent on GPC composition as well as the mode of interaction with cells. These markers were found to be significantly elevated in response to GPC A's dissolution products. However, osteogenic differentiation was inhibited when osteoblasts were cultured indirectly and directly with GPCs, with, overall, GPC B significantly outperforming GPC A. These results suggest that GPC degradation products effect osteogenic differentiation in a dose-dependent manner.

Modelling of chemical species of Al, Mn, Zn, and Pb in river body waters of industrial areas of West Rhodope Mountain, Bulgaria

The assessment of the ecological status of natural surface water, in terms of dominant trace metals, within an area subject to various sources of pollution including a non-ferrous metal ore mining, such as the West Rhodope Mountain, Bulgaria, is significant. The present study estimates the ecological status of river body waters at industrial areas of the West Rhodope Mountain, Bulgaria, simultaneously evaluating the possibility of state forecasting, together with assessing the potential risks, through the study of scenarios focusing on (i) possible variations of physicochemical parameters such as pH, concentration levels of trace metals, sulphates, and dissolved organic carbon (DOC) of surface water and (ii) consideration of potential spontaneous precipitation reactions in the studied waters. The ecological status of river body waters was assessed through a combination of experimental field, laboratory, and computational techniques. Al, Mn, Zn, and Pb were found to be the dominant pollutants with a variety of chemical species and distribution. The most significant difference characterizing the chemical species distribution in light of total spontaneous crystallization in the systems was found for Pb, followed by Zn and Mn, with the differences being more significant at lower trace metal levels. The calculated species were discussed on the basis of HSAB (hard and soft acids and bases) principle.

Comparative Utilization of Dead and Live Fungal Biomass for the Removal of Heavy Metal: A Concise Review

Human and industrial activities produce and discharge wastes containing heavy metals into the water resources making them polluted, threatening human health and the ecosystem. Biosorption, the process of passive cation binding by dead or living biomass, represents a potentially cost-effective way of eliminating toxic heavy metals from industrial wastewater. The abilities of microorganisms to remove metal ions in solution have been extensively studied; in particular, live and dead fungi have been recognized as a promising class of low-cost adsorbents for the removal of heavy metal ions. The biosorption behavior of fungal biomass is getting attention due to its several advantages; hence, it needs to be explored further to take its maximum advantage on wastewater treatment. This review discusses the live and dead fungi characteristics of sorption, factors influencing heavy metal removal, and the biosorption capacities for heavy metal ions removal and also discusses the biosorption mechanisms.

Defect-Mediated Reactive Oxygen Species Generation in Mg-Substituted ZnO Nanoparticles: Efficient Nanomaterials for Bacterial Inhibition and Cancer Therapy

Mg-substituted ZnO nanoparticles (MgZnO NPs) were synthesized by a soft chemical approach and were well-characterized by X-ray diffraction, transmission electron microscopy, UV-visible spectroscopy, and photoluminescence spectroscopy. The absorption and photoluminescence spectra show that substitution of Mg ions results in the widening of the band gap and a significant enhancement in the concentration of defects in ZnO NPs. A systemic study of generation of reactive oxygen species (ROS) under dark, daylight, and visible light conditions suggests that the aqueous suspension of MgZnO NPs generates a higher level of ROS because of the surface defects (oxygen vacancies). This capability of MgZnO NPs makes them a more promising candidate for the inhibition of bacterial growth and for killing of cancer cells as compared to pure ZnO NPs, possibly because of the enhanced interaction and accumulation of MgZnO NPs in the cytoplasm or cell membrane in the presence of both Zn2+ and Mg2+ ions. Further, MgZnO NPs exhibit excellent selective killing of nasopharyngeal carcinoma cells (KB) and cervical cancer cells (HeLa) with minimal toxicity to normal fibroblast cells (L929). The results suggest that the generation of ROS and Zn2+ ions are possibly responsible for the higher activity toward the depolarization of cell membrane potential, the lipid peroxidation in bacterial cells, depolarization of the mitochondrial membrane, and cell cycle arrest in the S phase in cancer cells.

Zinc carnosine protects against hydrogen peroxide-induced DNA damage in WIL2-NS lymphoblastoid cell line independent of poly (ADP-Ribose) polymerase expression

The aim of this study is to investigate the ability of zinc carnosine to protect the human lymphoblastoid (WIL2-NS) cell line from hydrogen peroxide-induced DNA damage. Cells were cultured with medium containing zinc carnosine at the concentrations of 0.4, 4, 16 and 32 μM for 9 days prior to treatment with 30 μM of hydrogen peroxide (30 min). Zinc carnosine at the concentration 16 μM was optimal in protecting cells from hydrogen peroxide-induced cytotoxicity and gave the lowest percentage of apoptotic and necrotic cells. Results showed that zinc carnosine was able to induce glutathione production and protect cells from hydrogen peroxide-induced oxidative stress at all concentration and the highest protection was observed at 32-μM zinc carnosine culture. Cytokinesis-block micronucleus cytome assay showed that cells cultured with 4-32 μM of zinc carnosine showed significant reduction in micronuclei formation, nucleoplasmic bridges and nuclear bud frequencies (p < 0.05), suggesting that these concentrations maybe optimal in protecting cells from hydrogen peroxide-induced DNA damage. However, after being challenged with hydrogen peroxide, no increase in poly(ADP-ribose) polymerase expression was observed. Thus, results from this study demonstrate that zinc carnosines possess antioxidant properties and are able to reduce hydrogen peroxide-induced DNA damage in vitro independent of poly(ADP-ribose) polymerase. Further studies are warranted to understand the mechanism of protection of zinc carnosine against hydrogen peroxide-induced damage.

Development and validation of TOF-SIMS and CLSM imaging method for cytotoxicity study of ZnO nanoparticles in HaCaT cells

Zinc oxide nanoparticles (ZnO NPs) exhibit novel physiochemical properties and have found increasing use in sunscreen products and cosmetics. The potential toxicity is of increasing concern due to their close association with human skin. A time-of-flight secondary ion mass spectrometry (TOF-SIMS) and confocal laser scanning microscopy (CLSM) imaging method was developed and validated for rapid and sensitive cytotoxicity study of ZnO NPs using human skin equivalent HaCaT cells as a model system. Assorted material, chemical, and toxicological analysis methods were used to confirm their shape, size, crystalline structure, and aggregation properties as well as dissolution behavior and effect on HaCaT cell viability in the presence of various concentrations of ZnO NPs in aqueous media. Comparative and correlative analyses of aforementioned results with TOF-SIMS and CLSM imaging results exhibit reasonable and acceptable outcome. A marked drop in survival rate was observed with 50μg/ml ZnO NPs. The CLSM images reveal the absorption and localization of ZnO NPs in cytoplasm and nuclei. The TOF-SIMS images demonstrate elevated levels of intracellular ZnO concentration and associated Zn concentration-dependent (40)Ca/(39)K ratio, presumably caused by the dissolution behavior of ZnO NPs. Additional validation by using stable isotope-labeled (68)ZnO NPs as tracers under the same experimental conditions yields similar cytotoxicity effect. The imaging results demonstrate spatially-resolved cytotoxicity relationship between intracellular ZnO NPs, (40)Ca/(39)K ratio, phosphocholine fragments, and glutathione fragments. The trend of change in TOF-SIMS spectra and images of ZnO NPs treated HaCaT cells demonstrate the possible mode of actions by ZnO NP involves cell membrane disruption, cytotoxic response, and ROS mediated apoptosis.

Red light represses the photophysiology of the scleractinian coral Stylophora pistillata

Light spectrum plays a key role in the biology of symbiotic corals, with blue light resulting in higher coral growth, zooxanthellae density, chlorophyll a content and photosynthesis rates as compared to red light. However, it is still unclear whether these physiological processes are blue-enhanced or red-repressed. This study investigated the individual and combined effects of blue and red light on the health, zooxanthellae density, photophysiology and colouration of the scleractinian coral Stylophora pistillata over 6 weeks. Coral fragments were exposed to blue, red, and combined 50/50% blue red light, at two irradiance levels (128 and 256 μmol m⁻² s⁻¹). Light spectrum affected the health/survival, zooxanthellae density, and NDVI (a proxy for chlorophyll a content) of S. pistillata. Blue light resulted in highest survival rates, whereas red light resulted in low survival at 256 μmol m⁻² s⁻¹. Blue light also resulted in higher zooxanthellae densities compared to red light at 256 μmol m⁻² s⁻¹, and a higher NDVI compared to red and combined blue red light. Overall, our results suggest that red light negatively affects the health, survival, symbiont density and NDVI of S. pistillata, with a dominance of red over blue light for NDVI.

Neuronal cytotoxicity and genotoxicity induced by zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnO NPs) are one of the most abundantly used nanomaterials in consumer products and biomedical applications. As a result, human exposure to these NPs is highly frequent and they have become an issue of concern to public health. Although toxicity of ZnO NPs has been extensively studied and they have been shown to affect many different cell types and animal systems, there is a significant lack of toxicological data for ZnO NPs on the nervous system, especially for human neuronal cells and tissues. In this study, the cytotoxic and genotoxic effects of ZnO NPs on human SHSY5Y neuronal cells were investigated under different exposure conditions. Results obtained by flow cytometry showed that ZnO NPs do not enter the neuronal cells, but their presence in the medium induced cytotoxicity, including viability decrease, apoptosis and cell cycle alterations, and genotoxicity, including micronuclei production, H2AX phosphorylation and DNA damage, both primary and oxidative, on human neuronal cells in a dose- and time-dependent manner. Free Zn(2+) ions released from the ZnO NPs were not responsible for the viability decrease, but their role on other types of cell damage cannot be ruled out. The results obtained in this work contribute to increase the knowledge on the genotoxic and cytotoxic potential of ZnO NPs in general, and specifically on human neuronal cells, but further investigations are required to understand the action mechanism underlying the cytotoxic and genotoxic effects observed.

Effects of serum on cytotoxicity of nano- and micro-sized ZnO particles

Although an increasing number of in vitro studies are being published regarding the cytotoxicity of nanomaterials, the components of the media for toxicity assays have often varied according to the needs of the scientists. Our aim for this study was to evaluate the influence of serum-in this case, fetal bovine serum-in a cell culture medium on the toxicity of nano-sized (50-70 nm) and micro-sized (<1 μm) ZnO on human lung epithelial cells (A549). The nano- and micro-sized ZnO both exhibited their highest toxicity when exposed to serum-free media, in contrast to exposure in media containing 5 or 10 % serum. This mainly comes not only from the fact that ZnO particles in the serum-free media have a higher dosage-per-cell ratio, which results from large aggregates of particles, rapid sedimentation, absence of protein protection, and lower cell growth rate, but also that extracellular Zn²⁺ release contributes to cytotoxicity. Although more extracellular Zn²⁺ release was observed in serum-containing media, it did not contribute to nano-ZnO cytotoxicity. Furthermore, non-dissolved particles underwent size-dependent particle agglomeration, resulting in size-dependent toxicity in both serum-containing and serum-free media. A low correlation between cytotoxicity and inflammation endpoints in the serum-free medium suggested that some signaling pathways were changed or induced. Since cell growth, transcription behavior for protein production, and physicochemical properties of ZnO particles all were altered in serum-free media, we recommend the use of a serum-containing medium when evaluating the cytotoxicity of NPs.

Toxic effect of different ZnO particles on mouse alveolar macrophages

To study the toxicity mechanism of ZnO nanoparticles on mouse macrophages, the toxic effect of different ZnO nanoparticles on mouse alveolar macrophages (MH-S) was investigated in this study. The results showed that the 24h IC(50) of four ZnO particles were 48.53, 47.37, 45.43 and 26.74 μg/ml for bulk ZnO, 100 nm, 30 nm and 10-30 nm ZnO particles, respectively. At the concentration of 10 μg/ml and below, dissolved zinc ions induced metallothionein synthesis, enhanced cellular resistance to oxidative stress. ZnO particles mainly induced cell apoptosis. When the concentration of ZnO particles was 20 μg/ml and above, excessive zinc destroyed mitochondrial function and cell membrane, caused cell necrosis. Dissolved zinc ions first cause toxicity in MH-S cells. However, the toxic effect of dissolved zinc ions may exist a threshold on mouse macrophages, inducing about 50% cell death. The toxic difference of different ZnO particles mainly depended on the effect of nondissolved ZnO particles.

Luteolin protects against reactive oxygen species-mediated cell death induced by zinc toxicity via the PI3K-Akt-NF-κB-ERK-dependent pathway

Zinc ion elevation contributes to acute excitotoxic brain injury and correlates with the severity of dementia in chronic neurodegenerative diseases. Downstream control of zinc-triggered signals is believed to be an efficient countermeasure. In the current study, we examined whether the flavonoid luteolin (Lu) could protect human neuroblastoma SH-SY5Y cells against zinc toxicity. We found that Lu suppressed overproduction of reactive oxygen species and protected against apoptotic cell death induced by zinc. By using specific inhibitors, we found that zinc strongly triggered Akt and ERK1/2 activation via a PI3K-Akt-NF-κB-ERK1/2-dependent pathway. Furthermore, Lu completely blocked this activation. Our study strongly supports the hypothesis that Lu might protect SH-SY5Y cells against ROS-mediated apoptotic cell death induced by zinc in part by inhibiting the PI3K-Akt-NF-κB-ERKs pathway.

Nanosized zinc oxide particles induce neural stem cell apoptosis

Given the intensive application of nanoscale zinc oxide (ZnO) materials in our life, growing concerns have arisen about its unintentional health and environmental impacts. In this study, the neurotoxicity of different sized ZnO nanoparticles in mouse neural stem cells (NSCs) was investigated. A cell viability assay indicated that ZnO nanoparticles manifested dose-dependent, but no size-dependent toxic effects on NSCs. Apoptotic cells were observed and analyzed by confocal microscopy, transmission electron microscopy examination, and flow cytometry. All the results support the viewpoint that the ZnO nanoparticle toxicity comes from the dissolved Zn(2+) in the culture medium or inside cells. Our results highlight the need for caution during the use and disposal of ZnO manufactured nanomaterials to prevent the unintended environmental and health impacts.

Impact of overexpression of metallothionein-1 on cell cycle progression and zinc toxicity

Metallothioneins (MTs) have an important role in zinc homeostasis and may counteract the impact of oversupply. Both intracellular zinc and MT expression have been implicated in proliferation control and resistance to cellular stress, although the interdependency is unclear. The study addresses the consequences of a steady-state overexpression of MT-1 for intracellular zinc levels, cell cycle progression, and protection from zinc toxicity using a panel of cell lines with differential expression of MT-1. The panel comprised parental Chinese hamster ovary-K1 cells with low endogenous expression of MT and transfectants with enhanced expression of mouse MT-1 on an autonomously replicating expression vector with a noninducible promoter. Cell cycle progression, determined by flow cytometry and time-lapse microscopy, revealed that enhanced cytoplasmic expression of MT-1 does not impact on normal cell cycle operation, suggesting that basal levels of MT-1 expression are not limiting for background levels of oxidative stress. MT-1 overexpression correlated with a steady-state increase in cytoplasmic free Zn(2+), assessed using the fluorescent zinc-sensor Zinquin, particularly at high levels of overexpression, further suggesting that zinc availability is normally not limiting for cell cycle progression. Enhanced MT-1 expression, over a 10-fold range, had a clear impact on resistance to Cd(2+) and Zn(2+) toxicity. In the case of Zn(2+), the degree of protection afforded was less, indicating that MT-1 has a limited range and saturable capacity for effecting resistance. The results have implications for the use of cellular stress responses to exogenously supplied zinc and zinc-based systemic therapies.

Effect of zinc upon human and murine cell viability and differentiation

Most zinc studies show its benefits or changes that coincide with its deficiency, but some have reported damages by supplements. In this work, the effects of zinc in different cell lines (U-937, human monocytes, and murine bone marrow cells) were analyzed. The cells were put in their specific culture medium either alone or with a stimulant [1-phorbol 12-myristate 13-acetate (PMA) for U-937 and monocytes, granulocyte macrophage colony stimulating factor (GM-CSF) for bone marrow cells]. These preparations, with or without zinc (0.05 to 1.0 mM), were incubated and microscopically analyzed on days 3, 9, and 11. The viability of all cells cultivated with 0.05 and 0.1 mM of zinc was similar to that of the controls without zinc (90%). With 1.0 mM of zinc, the viability diminished (p < 0.005) to 80% in U-937 and to 50% in monocytes and bone marrow cells; the number of cells increased in the three lines, but there was no differentiation. We conclude that the effects observed with different doses of zinc vary not only among the different species but also according to the time the cells were exposed to the metal. The same doses of zinc can have either a stimulatory or an inhibitory effect.

Metals on the brain

Current research suggests that imbalances in metal-ion homeostasis play a critical role in neurodegenerative disorders, such as Alzheimer's disease and transmissible spongiform encephalopathy, and in cancer. It is thus important to elucidate the mechanisms by which homeostasis is maintained and how metals function in cellular processes, including cell signaling, neurotransmission, and protein transport and storage. This summary of a meeting recently held in Barcelona, Spain, highlights some of the latest findings on intra- and extracellular zinc signaling, the consequences of zinc imbalances on cells and on the brain, the mechanisms of metal-ion influx and efflux, how metal ions are sequestered by metallothioneins, and the development of candidate drugs to treat brain injury due to metal-ion imbalances.