Physicochemical mechanism of the interaction between cobalt metal and carbide particles to generate toxic activated oxygen species

Reactive Oxygen Species Formed by Metal and Metal Oxide Nanoparticles in Physiological Media—A Review of Reactions of Importance to Nanotoxicity and Proposal for Categorization

Diffusely dispersed metal and metal oxide nanoparticles (NPs) can adversely affect living organisms through various mechanisms and exposure routes. One mechanism behind their toxic potency is their ability to generate reactive oxygen species (ROS) directly or indirectly to an extent that depends on the dose, metal speciation, and exposure route. This review provides an overview of the mechanisms of ROS formation associated with metal and metal oxide NPs and proposes a possible way forward for their future categorization. Metal and metal oxide NPs can form ROS via processes related to corrosion, photochemistry, and surface defects, as well as via Fenton, Fenton-like, and Haber–Weiss reactions. Regular ligands such as biomolecules can interact with metallic NP surfaces and influence their properties and thus their capabilities of generating ROS by changing characteristics such as surface charge, surface composition, dissolution behavior, and colloidal stability. Interactions between metallic NPs and cells and their organelles can indirectly induce ROS formation via different biological responses. H₂O₂ can also be generated by a cell due to inflammation, induced by interactions with metallic NPs or released metal species that can initiate Fenton(-like) and Haber–Weiss reactions forming various radicals. This review discusses these different pathways and, in addition, nano-specific aspects such as shifts in the band gaps of metal oxides and how these shifts at biologically relevant energies (similar to activation energies of biological reactions) can be linked to ROS production and indicate which radical species forms. The influences of kinetic aspects, interactions with biomolecules, solution chemistry (e.g., Cl⁻ and pH), and NP characteristics (e.g., size and surface defects) on ROS mechanisms and formation are discussed. Categorization via four tiers is suggested as a way forward to group metal and metal oxide NPs based on the ROS reaction pathways that they may undergo, an approach that does not include kinetics or environmental variations. The criteria for the four tiers are based on the ability of the metallic NPs to induce Fenton(-like) and Haber–Weiss reactions, corrode, and interact with biomolecules and their surface catalytic properties. The importance of considering kinetic data to improve the proposed categorization is highlighted.

Inhalation of tungsten metal particulates alters the lung and bone microenvironments following acute exposure

Inhalation of tungsten particulates is a relevant route of exposure in occupational and military settings. Exposure to tungsten alloys is associated with increased incidence of lung pathologies, including interstitial lung disease and cancer. We have demonstrated, oral exposure to soluble tungsten enhances breast cancer metastasis to the lungs through changes in the surrounding microenvironment. However, more research is required to investigate if changes in the lung microenvironment, following tungsten particulate exposure, can drive tumorigenesis or metastasis to the lung niche. This study examined if inhalation to environmentally relevant concentrations of tungsten particulates caused acute damage to the microenvironment in the lungs and/or systemically using a whole-body inhalation system. Twenty-four female BALB/c mice were exposed to Filtered Air, 0.60 mg/m3, or 1.7 mg/m3 tungsten particulates (< 1 µm) for 4 h. Tissue samples were collected at day 1 and 7 post-exposure. Tungsten accumulation in the lungs persisted up to 7 days post-exposure and produced acute changes to the lung microenvironment including increased macrophage and neutrophil infiltration, increased levels of pro-inflammatory cytokines IL-1β and CXCL1, and an increased percentage of activated fibroblasts (α-SMA+). Exposure to tungsten also resulted in systemic effects on the bone, including tungsten deposition and transient increases in gene expression of pro-inflammatory cytokines. Taken together, acute whole-body inhalation of tungsten particulates, at levels commonly observed in occupational and military settings, resulted in changes to the lung and bone microenvironments that may promote tumorigenesis or metastasis and be important molecular drivers of other tungsten-associated lung pathologies such as interstitial lung disease.

Adsorption of bio-organic eco-corona molecules reduces the toxic response to metallic nanoparticles in Daphnia magna

As the use of engineered nanomaterials increases, so does the risk of them spreading to natural ecosystems. Hitherto, knowledge regarding the toxic properties of nanoparticles (NP’s) and their potential interactions with natural bio-organic molecules adsorbed to them, and thereby forming surface coronas, is limited. However, we show here that the toxic effect of NPs of tungsten carbide cobalt (WC–Co) and cobalt (Co) on the crustacean Daphnia magna is postponed in the presence of natural biological degradation products (eco-corona biomolecules). For Daphnia exposed to WC–Co NPs the survival time increased with 20–25% and for Co NPs with 30–47% after mixing the particles with a solution of eco-corona biomolecules before exposure. This suggests that an eco-corona, composed of biomolecules always present in natural ecosystems, reduces the toxic potency of both studied NPs. Further, the eco-coronas did not affect the particle uptake, suggesting that the reduction in toxicity was related to the particle-organism interaction after eco-corona formation. In a broader context, this implies that although the increasing use and production of NPs may constitute a novel, global environmental threat, the acute toxicity and long-term effects of some NPs will, at least under certain conditions, be reduced as they enter natural ecosystems.

Amelioration of butylated hydroxytoluene against inorganic mercury induced cytotoxicity and mitochondrial apoptosis in PC12 cells via antioxidant effects

Mercury (Hg) is a toxic metal, well-known for its dangerous health effects on human. Butylated hydroxytoluene (BHT) is a phenolic component generally consumed as a food additive as an antioxidant. However, BHT induced antioxidant properties against heavy metals-influenced toxicity are little studied. We hypothesized that BHT has a regulatory effect on Hg-induced cytotoxicity. The objective of this research was to assess the protecting effects of BHT against inorganic Hg (iHg)-toxicity in PC12 cells, where cells were treated with/without HgCl₂ (Hg²⁺) (5 μM) and BHT (100 μM) for 48 h and analyzed further. Cells treated by Hg caused a significant cell viability reduction, membrane damage, glutathione reduction, DNA fragmentation, ROS generation, with suppressed expressions of akt, mTOR, ERK1, Nrf2 and HO1; and elevated apoptotic expressions of p53, Bax, cytochrome c and active caspase 3. However, BHT and Hg²⁺ co-exposure showed prevention against Hg²⁺-toxicity by improving GSH content and inhibiting ROS generation and oxidative stress mediated damages. Additionally, BHT co-treatment inverted the pro-apoptotic proteins by augmenting pro-survival regulatory proteins akt, mTOR, ERK1, Nrf2 and HO1. These findings proved that BHT inhibits Hg²⁺-toxicity, hindering ROS generation and intrinsic apoptosis, via enhancing glutathione and antioxidants; and suggested BHT implications as therapeutic.

Nanotechnology for angiogenesis: opportunities and challenges

Angiogenesis plays a critical role within the human body, from the early stages of life (i.e., embryonic development) to life-threatening diseases (e.g., cancer, heart attack, stroke, wound healing). Many pharmaceutical companies have expended huge efforts on both stimulation and inhibition of angiogenesis. During the last decade, the nanotechnology revolution has made a great impact in medicine, and regulatory approvals are starting to be achieved for nanomedicines to treat a wide range of diseases. Angiogenesis therapies involve the inhibition of angiogenesis in oncology and ophthalmology, and stimulation of angiogenesis in wound healing and tissue engineering. This review aims to summarize nanotechnology-based strategies that have been explored in the broad area of angiogenesis. Lipid-based, carbon-based and polymeric nanoparticles, and a wide range of inorganic and metallic nanoparticles are covered in detail. Theranostic and imaging approaches can be facilitated by nanoparticles. Many preparations have been reported to have a bimodal effect where they stimulate angiogenesis at low dose and inhibit it at higher doses.

Multigenerational Exposure to WCCo Nanomaterials-Epigenetics in the Soil Invertebrate Enchytraeus crypticus

It has become clear how important it is to assess longer term effects of (nano) materials in the environment given the current evidence showing how epigenetics drives response mechanisms. Here we studied global DNA methylation in standard soil invertebrate Enchytraeus crypticus over 224 days when exposed to nanostructured tungsten carbide cobalt (WCCo nanomaterials (NMs)) and to cobalt (CoCl₂) in a multigenerational experiment. In order to assess the transgenerational effect, we used a multigenerational (MG) test design consisting of four generations in spiked soil followed by two generations in clean soil. Results showed that MG exposure to WCCo NMs caused global DNA methylation to increase, which continued in unexposed generations and was associated with an increase in reproduction (phenotypic effect). In general, WCCo NMs caused more (and more consistent) methylation than CoCl₂.

Cobalt nanoparticles trigger ferroptosis-like cell death (oxytosis) in neuronal cells: Potential implications for neurodegenerative disease

The neurotoxicity of hard metal-based nanoparticles (NPs) remains poorly understood. Here, we deployed the human neuroblastoma cell line SH-SY5Y differentiated or not into dopaminergic- and cholinergic-like neurons to study the impact of tungsten carbide (WC) NPs, WC NPs sintered with cobalt (Co), or Co NPs versus soluble CoCl₂ . Co NPs and Co salt triggered a dose-dependent cytotoxicity with an increase in cytosolic calcium, lipid peroxidation, and depletion of glutathione (GSH). Co NPs and Co salt also suppressed glutathione peroxidase 4 (GPX4) mRNA and protein expression. Co-exposed cells were rescued by N-acetylcysteine (NAC), a precursor of GSH, and partially by liproxstatin-1, an inhibitor of lipid peroxidation. Furthermore, in silico analyses predicted a significant correlation, based on similarities in gene expression profiles, between Co-containing NPs and Parkinson's disease, and changes in the expression of selected genes were validated by RT-PCR. Finally, experiments using primary human dopaminergic neurons demonstrated cytotoxicity and GSH depletion in response to Co NPs and CoCl₂ with loss of axonal integrity. Overall, these data point to a marked neurotoxic potential of Co-based but not WC NPs and show that neuronal cell death may occur through a ferroptosis-like mechanism.

LiCoO2 particles used in Li-ion batteries induce primary mutagenicity in lung cells via their capacity to generate hydroxyl radicals

BACKGROUND

Li-ion batteries (LIB) are used in most portable electronics. Among a wide variety of materials, LiCoO₂ (LCO) is one of the most used for the cathode of LIB. LCO particles induce oxidative stress in mouse lungs due to their Co content, and have a strong inflammatory potential. In this study, we assessed the mutagenic potential of LCO particles in lung cells in comparison to another particulate material used in LIB, LTO (Li₄Ti₅O₁₂), which has a low inflammatory potential compared to LCO particles.

RESULTS

We assessed the mutagenic potential of LCO and LTO particles in vitro by performing a cytokinesis-block micronucleus (MN) assay with rat lung epithelial cells (RLE), as well as in vivo in alveolar type II epithelial (AT-II) cells. LCO particles induced MN in vitro at non-cytotoxic concentrations and in vivo at non-inflammatory doses, indicating a primary genotoxic mechanism. LTO particles did not induce MN. Electron paramagnetic resonance and terephthalate assays showed that LCO particles produce hydroxyl radicals (•OH). Catalase inhibits this •OH production. In an alkaline comet assay with the oxidative DNA damage repair enzyme human 8-oxoguanine DNA glycosylase 1, LCO particles induced DNA strand breaks and oxidative lesions. The addition of catalase reduced the frequency of MN induced by LCO particles in vitro.

CONCLUSIONS

We report the mutagenic activity of LCO particles used in LIB in vitro and in vivo. Our data support the role of Co(II) ions released from these particles in their primary genotoxic activity which includes the formation of •OH by a Fenton-like reaction, oxidative DNA lesions and strand breaks, thus leading to chromosomal breaks and the formation of MN. Documenting the genotoxic potential of the other LIB particles, especially those containing Co and/or Ni, is therefore needed to guarantee a safe and sustainable development of LIB.

Are Fe-Based Stenting Materials Biocompatible? A Critical Review of In Vitro and In Vivo Studies

Fe-based materials have increasingly been considered for the development of biodegradable cardiovascular stents. A wide range of in vitro and in vivo studies should be done to fully evaluate their biocompatibility. In this review, we summarized and analyzed the findings and the methodologies used to assess the biocompatibility of Fe materials. The majority of investigators drew conclusions about in vitro Fe toxicity based on indirect contact results. The setup applied in these tests seems to overlook the possible effects of Fe corrosion and does not allow for understanding of the complexity of released chemical forms and their possible impact on tissue. It is in particular important to ensure that test setups or interpretations of in vitro results do not hide some important mechanisms, leading to inappropriate subsequent in vivo experiments. On the other hand, the sample size of existing in vivo implantations is often limited, and effects such as local toxicity or endothelial function are not deeply scrutinized. The main advantages and limitations of in vitro design strategies applied in the development of Fe-based alloys and the correlation with in vivo studies are discussed. It is evident from this literature review that we are not yet ready to define an Fe-based material as safe or biocompatible.

Toxicological Assessment of ITER-Like Tungsten Nanoparticles Using an In Vitro 3D Human Airway Epithelium Model

The International Thermonuclear Experimental Reactor (ITER) is an international project aimed at the production of carbon-free energy through the use of thermonuclear fusion. During ITER operation, in case of a loss-of-vacuum-accident, tungsten nanoparticles (W-NPs) could potentially be released into the environment and induce occupational exposure via inhalation. W-NPs toxicity was evaluated on MucilAir™, a 3D in vitro cell model of the human airway epithelium. MucilAir™ was exposed for 24 h to metallic ITER-like milled W-NPs, tungstate (WO₄²⁻) and tungsten carbide cobalt particles alloy (WC-Co). Cytotoxicity and its reversibility were assessed using a kinetic mode up to 28 days after exposure. Epithelial tightness, metabolic activity and interleukin-8 release were also evaluated. Electron microscopy was performed to determine any morphological modification, while mass spectrometry allowed the quantification of W-NPs internalization and of W transfer through the MucilAir™. Our results underlined a decrease in barrier integrity, no effect on metabolic activity or cell viability and a transient increase in IL-8 secretion after exposure to ITER-like milled W-NPs. These effects were associated with W-transfer through the epithelium, but not with intracellular accumulation. We have shown that, under our experimental conditions, ITER-like milled W-NPs have a minor impact on the MucilAir™ in vitro model.

In Vitro Analysis of the Effects of ITER-Like Tungsten Nanoparticles: Cytotoxicity and Epigenotoxicity in BEAS-2B Cells

Tungsten was chosen as a wall component to interact with the plasma generated by the International Thermonuclear Experimental fusion Reactor (ITER). Nevertheless, during plasma operation tritiated tungsten nanoparticles (W-NPs) will be formed and potentially released into the environment following a Loss-Of-Vacuum-Accident, causing occupational or accidental exposure. We therefore investigated, in the bronchial human-derived BEAS-2B cell line, the cytotoxic and epigenotoxic effects of two types of ITER-like W-NPs (plasma sputtering or laser ablation), in their pristine, hydrogenated, and tritiated forms. Long exposures (24 h) induced significant cytotoxicity, especially for the hydrogenated ones. Plasma W-NPs impaired cytostasis more severely than the laser ones and both types and forms of W-NPs induced significant micronuclei formation, as shown by cytokinesis-block micronucleus assay. Single DNA strand breaks, potentially triggered by oxidative stress, occurred upon exposure to W-NPs and independently of their form, as observed by alkaline comet assay. After 24 h it was shown that more than 50% of W was dissolved via oxidative dissolution. Overall, our results indicate that W-NPs can affect the in vitro viability of BEAS-2B cells and induce epigenotoxic alterations. We could not observe significant differences between plasma and laser W-NPs so their toxicity might not be triggered by the synthesis method.

Comparative Assessment of Tungsten Toxicity in the Absence or Presence of Other Metals

Tungsten is a refractory metal that is used in a wide range of applications. It was initially perceived that tungsten was immobile in the environment, supporting tungsten as an alternative for lead and uranium in munition and military applications. Recent studies report movement and detection of tungsten in soil and potable water sources, increasing the risk of human exposure. In addition, experimental research studies observed adverse health effects associated with exposure to tungsten alloys, raising concerns on tungsten toxicity with questions surrounding the safety of exposure to tungsten alone or in mixtures with other metals. Tungsten is commonly used as an alloy with nickel and cobalt in many applications to adjust hardness and thermal and electrical conductivity. This review addresses the current state of knowledge in regard to the mechanisms of toxicity of tungsten in the absence or presence of other metals with a specific focus on mixtures containing nickel and cobalt, the most common components of tungsten alloy.

Fate and Effect of Nano Tungsten Carbide Cobalt (WCCo) in the Soil Environment: Observing a Nanoparticle Specific Toxicity in Enchytraeus crypticus

Tungsten carbide cobalt (WCCo) nanoparticles (NPs) are widely used in hard metal industries. Pulmonary diseases and risk of cancer are associated with occupational exposure, but knowledge about the environmental fate and effects is virtually absent. In this study, the fate and effects of crystalline WCCo NPs, WC, and Co²⁺ were assessed in the soil model Enchytraeus crypticus, following the standard Enchytraeid Reproduction Test (ERT). An additional 28 day exposure period compared to the ERT (i.e., a total of 56 days) was performed to assess longer-term effects. WCCo NPs affected reproduction at a concentration higher than the corresponding Co based (EC50 = 1500 mg WCCo/kg, equivalent to 128 mg Co/kg). WC showed no negative effect up to 1000 mg W/kg. Maximum uptake of Co was 10-fold higher for CoCl₂ compared to WCCo exposed organisms. Overall toxicity seems to be due to a combined effect between WC and Co. This is supported by the soil bioavailable fraction and biological tissue measurements. Last, results highlight the need to consider longer exposure period of NPs for comparable methods standardized for conventional chemicals.

Cobalt and its compounds: update on genotoxic and carcinogenic activities

This article summarizes recent experimental and epidemiological data on the genotoxic and carcinogenic activities of cobalt compounds. Emphasis is on the respiratory system, but endogenous exposure from Co-containing alloys used in endoprostheses, and limited data on nanomaterials and oral exposures are also considered. Two groups of cobalt compounds are differentiated on the basis of their mechanisms of toxicity: (1) those essentially involving the solubilization of Co(II) ions, and (2) metallic materials for which both surface corrosion and release of Co(II) ions act in concert. For both groups, identified genotoxic and carcinogenic mechanisms are non-stochastic and thus expected to exhibit a threshold. Cobalt compounds should, therefore, be considered as genotoxic carcinogens with a practical threshold. Accumulating evidence indicates that chronic inhalation of cobalt compounds can induce respiratory tumors locally. No evidence of systemic carcinogenicity upon inhalation, oral or endogenous exposure is available. The scarce data available for Co-based nanosized materials does not allow deriving a specific mode of action or assessment for these species.

Cobalt related interstitial lung disease

Cobalt exposure in the hard metal and bonded diamond tool industry is a well-established cause of ILD. The primary theories regarding the underlying mechanism of cobalt related ILD include an immunologic mechanism and an oxidant injury mechanism. Cobalt related ILD may present in subacute and chronic forms and often has associated upper respiratory symptoms. The evaluation begins with a thorough occupational history and includes PFTs, HRCT, and bronchoalveolar lavage. HRCT findings are nonspecific and may resemble NSIP, UIP, sarcoidosis, or HP. The finding of cannibalistic multinucleated giant cells is diagnostic provided there is a history of exposure and appropriate changes on imaging; however, when these cells are not found on lavage, lung biopsy is required for diagnosis. Giant cell interstitial pneumonia is the classic pathologic pattern, but cobalt related ILD may also present with pathologic findings of UIP, DIP, or HP. When cobalt related ILD is suspected, removal from exposure is the most important step in treatment. Case reports suggest that treatment with steroids results in symptomatic, physiologic, and radiographic improvement.

Nanoparticles of WC-Co, WC, Co and Cu of relevance for traffic wear particles - Particle stability and reactivity in synthetic surface water and influence of humic matter

Studded tyres made of tungsten carbide cobalt (WC-Co) are in the Northern countries commonly used during the winter time. Tungsten (W)-containing nano- and micron-sized particles have been detected close to busy roads in several European countries. Other typical traffic wear particles consist of copper (Cu). The aims of this study were to investigate particle stability and transformation/dissolution properties of nanoparticles (NPs) of WC-Co compared with NPs of tungsten carbide (WC), cobalt (Co), and Cu. Their physicochemical characteristics (primarily surface oxide and charge) are compared with their extent of sedimentation and metal release in synthetic surface water (SW) with and without two different model organic molecules, 2,3- and 3,4-dihydroxybenzoic acid (DHBA) mimicking certain sorption sites of humic substances, for time periods up to 22 days. The WC-Co NPs possessed a higher electrochemical and chemical reactivity in SW with and without DHBA molecules as compared with NPs of WC, Co, and Cu. Co was completely released from the WC-Co NPs within a few hours of exposure, although it remained adsorbed/bonded to the particle surface and enabled the adsorption of negatively charged DHBA molecules, in contrast with the WC NPs (no adsorption of DHBA). The DHBA molecules were found to rapidly adsorb on the Co and Cu NPs. The sedimentation of the WC and WC-Co NPs was not influenced by the presence of the 2,3- or 3,4-DHBA molecules. A slight influence (slower sedimentation) was observed for the Co NPs, and a strong influence (slower sedimentation) was observed for the Cu NPs in SW with 2,3-DHBA compared with SW alone. The extent of metal release increased in the order: WC < Cu < Co < WC-Co NPs. All NPs released more than 1 wt-% of their metal total mass. The release from the Cu NPs was most influenced by the presence of DHBA molecules.

Nanotoxicity: emerging concerns regarding nanomaterial safety and occupational hard metal (WC-Co) nanoparticle exposure

As the number of commercial and consumer products containing engineered nanomaterials (ENMs) continually rises, the increased use and production of these ENMs presents an important toxicological concern. Although ENMs offer a number of advantages over traditional materials, their extremely small size and associated characteristics may also greatly enhance their toxic potentials. ENM exposure can occur in various consumer and industrial settings through inhalation, ingestion, or dermal routes. Although the importance of accurate ENM characterization, effective dosage metrics, and selection of appropriate cell or animal-based models are universally agreed upon as important factors in ENM research, at present, there is no “standardized” approach used to assess ENM toxicity in the research community. Of particular interest is occupational exposure to tungsten carbide cobalt (WC-Co) “dusts,” composed of nano- and micro-sized particles, in hard metal manufacturing facilities and mining and drilling industries. Inhalation of WC-Co dust is known to cause “hard metal lung disease” and an increased risk of lung cancer; however, the mechanisms underlying WC-Co toxicity, the inflammatory disease state and progression to cancer are poorly understood. Herein, a discussion of ENM toxicity is followed by a review of the known literature regarding the effects of WC-Co particle exposure. The risk of WC-Co exposure in occupational settings and the updates of in vitro and in vivo studies of both micro- and nano-WC-Co particles are discussed.

Krüppel-like Factor 13 Is a Major Mediator of Glucocorticoid Receptor Signaling in Cardiomyocytes and Protects These Cells from DNA Damage and Death

Glucocorticoid receptor (GR) signaling has recently been shown to play a direct role in the regulation of cardiomyocyte function. In this study, we investigated the potential role of KLF13 as a downstream effector of GR action utilizing both in vivo and in vitro approaches. Our data show that KLF13 mRNA and protein levels are significantly diminished in the hearts of mice lacking GR in cardiomyocytes. Glucocorticoid administration up-regulated Klf13 mRNA in the mouse heart, in isolated primary cardiomyocytes, and in immortal cardiomyocyte cell lines. Glucocorticoid Klf13 gene expression was abolished by treatment with a GR antagonist (RU486) or by knockdown of GR in cardiomyocytes. Moreover, glucocorticoid induction of Klf13 mRNA was resistant to de novo protein synthesis inhibition, demonstrating that Klf13 is a direct glucocorticoid receptor gene target. A glucocorticoid responsive element (GRE) was identified in the Klf13 gene and its function was verified by chromatin immunoprecipitation in HL-1 cells and mouse hearts. Functional studies showed that GR regulation of Klf13 is critical to protect cardiomyocytes from DNA damage and cell death induced by cobalt(II) chloride hexahydrate (CoCl2·6H2O) and the antineoplastic drug doxorubicin. These results established a novel role for GR and KLF13 signaling in adult cardiomyocytes with potential clinical implications for the prevention of cardiotoxicity induced heart failure.

Tungsten Carbide-Cobalt Nanoparticles Induce Reactive Oxygen Species, AKT, ERK, AP-1, NF-κB, VEGF, and Angiogenesis

Powder mixtures of tungsten carbide and metallic cobalt (WC-Co) are widely used in various products. Nanoparticles are engineered structures with at least one dimension of 100 nm or smaller. WC-Co is known to be associated with lung injury and diseases. Angiogenesis is a key process during vasculature, carcinogenesis, recovery of injury, and inflammatory diseases. However, the cellular effects of WC-Co nanoparticles on angiogenesis remain to be elucidated. In this study, we investigated angiogenic response and relative mechanisms after exposure to WC-Co nanoparticles. Our results showed that WC-Co nanoparticles at 5 μg/cm(2) induced ROS production which activated AKT and ERK1/2 signaling pathways in lung epithelial cells by reactive oxygen species (ROS) staining and immunoblotting; WC-Co treatment also increased transcriptional activation of AP-1, NF-κB, and VEGF by reporter assay. Further studies demonstrated that ROS are upstream molecules of AKT and ERK signaling pathways; the activation of AP-1, NF-κB, and VEGF was through ROS generation, AKT and ERK1/2 activation. In addition, WC-Co nanoparticles affected the cells to induce angiogenesis by chicken chorioallantoic membrane (CAM) assay. These results illustrate that exposure to WC-Co nanoparticles induces angiogenic response by activating ROS, AKT, and ERK1/2 signaling pathways and the downstream molecules and elucidate the potential molecular mechanisms during this process. This information may be useful for preventing potential damage from nanoparticle exposure in the future.

Free-radical chemistry as a means to evaluate lunar dust health hazard in view of future missions to the moon

Lunar dust toxicity has to be evaluated in view of future manned missions to the Moon. Previous studies on lunar specimens and simulated dusts have revealed an oxidant activity assigned to HO· release. However, the mechanisms behind the reactivity of lunar dust are still quite unclear at the molecular level. In the present study, a complementary set of tests--including terephthalate (TA) hydroxylation, free radical release as measured by means of the spin-trapping/electron paramagnetic resonance (EPR) technique, and cell-free lipoperoxidation--is proposed to investigate the reactions induced by the fine fraction of a lunar dust analogue (JSC-1A-vf) in biologically relevant experimental environments. Our study proved that JSC-1A-vf is able to hydroxylate TA also in anaerobic conditions, which indicates that molecular oxygen is not involved in such a reaction. Spin-trapping/EPR measures showed that the HO· radical is not the reactive intermediate involved in the oxidative potential of JSC-1A-vf. A surface reactivity implying a redox cycle of phosphate-complexed iron via a Fe(IV) state is proposed. The role of this iron species was investigated by assessing the reactivity of JSC-1A-vf toward hydrogen peroxide (Fenton-like activity), formate ions (homolytic rupture of C-H bond), and linoleic acid (cell-free lipoperoxidation). JSC-1A-vf was active in all tests, confirming that redox centers of transition metal ions on the surface of the dust may be responsible for dust reactivity and that the TA assay may be a useful field probe to monitor the surface oxidative potential of lunar dust.

Genotoxicity of tungsten carbide-cobalt (WC-Co) nanoparticles in vitro: mechanisms-of-action studies

We showed previously that tungsten carbide-cobalt (WC-Co) nanoparticles (NP) can be used as a nanoparticulate positive control in some in vitro mammalian genotoxicity assays. Here, we investigate the mechanisms of action involved in WC-Co NP genotoxicity in L5178Y mouse lymphoma cells and primary human lymphocytes, in vitro. Data from the micronucleus assay coupled with centromere staining and from the chromosome-aberration assay show the involvement of both clastogenic and aneugenic events. Experiments with the formamidopyrimidine DNA glycosylase (FPG)-modified comet assay showed a slight (non-significant) increase in FPG-sensitive sites in the L5178Y mouse lymphoma cells but not in the human lymphocytes. Electron paramagnetic resonance spin-trapping results showed the presence of hydroxyl radicals (•OH) in WC-Co NP suspensions, with or without cells, but with time-dependent production in the presence of cells. However, a significant difference in •OH production was observed between human lymphocytes from two different donors. Using H2O2, we showed that WC-Co NP can participate in Fenton-like reactions. Thus, •OH might be produced either via intrinsic generation by WC-Co NP or through a Fenton-like reaction in the presence of cells.

Exploring the potential role of tungsten carbide cobalt (WC-Co) nanoparticle internalization in observed toxicity toward lung epithelial cells in vitro

Tungsten carbide cobalt (WC-Co) has been recognized as a workplace inhalation hazard in the manufacturing, mining and drilling industries by the National Institute of Occupational Safety and Health. Exposure to WC-Co is known to cause "hard metal lung disease" but the relationship between exposure, toxicity and development of disease remain poorly understood. To better understand this relationship, the present study examined the role of WC-Co particle size and internalization on toxicity using lung epithelial cells. We demonstrated that nano- and micro-WC-Co particles exerted toxicity in a dose- and time-dependent manner and that nano-WC-Co particles caused significantly greater toxicity at lower concentrations and shorter exposure times compared to micro-WC-Co particles. WC-Co particles in the nano-size range (not micron-sized) were internalized by lung epithelial cells, which suggested that internalization may play a key role in the enhanced toxicity of nano-WC-Co particles over micro-WC-Co particles. Further exploration of the internalization process indicated that there may be multiple mechanisms involved in WC-Co internalization such as actin and microtubule based cytoskeletal rearrangements. These findings support our hypothesis that WC-Co particle internalization contributes to cellular toxicity and suggest that therapeutic treatments inhibiting particle internalization may serve as prophylactic approaches for those at risk of WC-Co particle exposure.

Intracellular signal modulation by nanomaterials

A thorough understanding of the interactions of nanomaterials with biological systems and the resulting activation of signal transduction pathways is essential for the development of safe and consumer friendly nanotechnology. Here we present an overview of signaling pathways induced by nanomaterial exposures and describe the possible correlation of their physicochemical characteristics with biological outcomes. In addition to the hierarchical oxidative stress model and a review of the intrinsic and cell-mediated mechanisms of reactive oxygen species (ROS) generating capacities of nanomaterials, we also discuss other oxidative stress dependent and independent cellular signaling pathways. Induction of the inflammasome, calcium signaling, and endoplasmic reticulum stress are reviewed. Furthermore, the uptake mechanisms can be of crucial importance for the cytotoxicity of nanomaterials and membrane-dependent signaling pathways have also been shown to be responsible for cellular effects of nanomaterials. Epigenetic regulation by nanomaterials, effects of nanoparticle-protein interactions on cell signaling pathways, and the induction of various cell death modalities by nanomaterials are described. We describe the common trigger mechanisms shared by various nanomaterials to induce cell death pathways and describe the interplay of different modalities in orchestrating the final outcome after nanomaterial exposures. A better understanding of signal modulations induced by nanomaterials is not only essential for the synthesis and design of safer nanomaterials but will also help to discover potential nanomedical applications of these materials. Several biomedical applications based on the different signaling pathways induced by nanomaterials are already proposed and will certainly gain a great deal of attraction in the near future.

Oxidative stress contributes to cobalt oxide nanoparticles-induced cytotoxicity and DNA damage in human hepatocarcinoma cells

Background

Cobalt oxide nanoparticles (Co₃O₄NPs) are increasingly recognized for their utility in biological applications, magnetic resonance imaging, and drug delivery. However, little is known about the toxicity of Co₃O₄NPs in human cells.

Methods

We investigated the possible mechanisms of genotoxicity induced by Co₃O₄NPs in human hepatocarcinoma (HepG2) cells. Cell viability, reactive oxygen species (ROS), glutathione, thiobarbituric acid reactive substance, apoptosis, and DNA damage were assessed in HepG2 cells after Co₃O₄NPs and Co²⁺ exposure.

Results

Co₃O₄NPs elicited a significant (P < 0.01) reduction in glutathione with a concomitant increase in lipid hydroperoxide, ROS generation, superoxide dismutase, and catalase activity after 24- and 48-hour exposure. Co₃O₄NPs had a mild cytotoxic effect in HepG2 cells; however, it induced ROS and oxidative stress, leading to DNA damage, a probable mechanism of genotoxicity. The comet assay showed a statistically significant (P < 0.01) dose- and time-related increase in DNA damage for Co₃O₄NPs, whereas Co²⁺ induced less change than Co₃O₄NPs but significantly more than control.

Conclusion

Our results demonstrated that Co₃O₄NPs induced cytotoxicity and genotoxicity in HepG2 cells through ROS and oxidative stress.

How physico-chemical characteristics of nanoparticles cause their toxicity: complex and unresolved interrelations

The increased use of and interest in nanoparticles (NPs) have resulted in an enormous amount of NPs with different compositions and physico-chemical properties. These unique properties not only determine their utility for (bio-medical) applications, but also their toxicity. Recently, "nano-researchers" became aware of the importance of determining the characteristics since they might be predictors of their toxicity. Currently, we face a large set of (non-coordinated) experiments with miscellaneous objectives resulting in a large quantity of available (and often incomplete) data, which hamper the unraveling of the complex interrelated NP characteristics with experimental results. Here, we try to link different critical physico-chemical characteristics separately with toxicity observed in both in vitro and in vivo models.

Comparative evaluation of particle properties, formation of reactive oxygen species and genotoxic potential of tungsten carbide based nanoparticles in vitro

Tungsten carbide (WC) and cobalt (Co) are constituents of hard metals and are used for the production of extremely hard tools. Previous studies have identified greater cytotoxic potential of WC-based nanoparticles if particles contained Co. The aim of this study was to investigate whether the formation of reactive oxygen species (ROS) and micronuclei would help explain the impact on cultured mammalian cells by three different tungsten-based nanoparticles (WC(S), WC(L), WC(L)-Co (S: small; L: large)). The selection of particles allowed us to study the influence of particle properties, e.g. surface area, and the presence of Co on the toxicological results. WC(S) and WC(L)/WC(L)-Co differed in their crystalline structure and surface area, whereas WC(S)/WC(L) and WC(L)-Co differed in their cobalt content. WC(L) and WC(L)-Co showed neither a genotoxic potential nor ROS induction. Contrary to that, WC(S) nanoparticles induced the formation of both ROS and micronuclei. CoCl(2) was tested in relevant concentrations and induced no ROS formation, but increased the rate of micronuclei at concentrations exceeding those present in WC(L)-Co. In conclusion, ROS and micronuclei formation could not be associated with the presence of Co in the WC-based particles. The contrasting responses elicited by WC(S) vs. WC(L) appear to be due to large differences in crystalline structure.

Reactive oxygen species and oxidative DNA damage mediate the cytotoxicity of tungsten-nickel-cobalt alloys in vitro

Tungsten alloys (WA) have been introduced in an attempt to find safer alternatives to depleted uranium and lead munitions. However, it is known that at least one alloy, 91% tungsten-6% nickel-3% cobalt (WNC-91-6-3), causes rhabdomyosarcomas when fragments are implanted in rat muscle. This raises concerns that shrapnel, if not surgically removable, may result in similar tumours in humans. There is therefore a clear need to develop rapid and robust in vitro methods to characterise the toxicity of different WAs in order to identify those that are most likely to be harmful to human health and to guide development of new materials in the future. In the current study we have developed a rapid visual in vitro assay to detect toxicity mediated by individual WA particles in cultured L6-C11 rat muscle cells. Using a variety of techniques (histology, comet assay, caspase-3 activity, oxidation of 2'7'-dichlorofluorescin to measure the production of reactive oxygen species and whole-genome microarrays) we show that, in agreement with the in vivo rat carcinogenicity studies, WNC-91-6-3 was the most toxic of the alloys tested. On dissolution, it produces large amounts of reactive oxygen species, causes significant amounts of DNA damage, inhibits caspase-3, triggers a severe hypoxic response and kills the cells in the immediate vicinity of the alloy particles within 24h. By combining these in vitro data we offer a mechanistic explanation of the effect of this alloy in vivo and show that in vitro tests are a viable alternative for assessing new alloys in the future.

N-acetyl cysteine improves affinity of beta-tricalcium phosphate granules for cultured osteoblast-like cells

Enhancement of bone substitute's biocompatibility may accelerate healing of surrounding bone. Although widely used as a biodegradable alloplastic bone substitute for alveolar bone augmentation, the osteocompatibility of beta-tricalcium phosphate (β-TCP) remains to be proven. The adverse cellular response to biomaterials is associated with oxidative stress. We hypothesized that commercially available β-TCP granules for clinical use, caused oxidative stress and was not optimal in osteocompatibility and that application of antioxidant amino acid derivative N-acetyl cysteine (NAC) would improve osteoblastic responses to the material. Only 20% of rat calvarial osteoblasts cultured on β-TCP granules remained viable at 24 h after seeding as opposed to 90% on polystyrene. Cell death on β-TCP granules was characterized by necrosis. However, the percentage of viable osteoblasts cultured on β-TCP granules showed a 100% increase with pre-treatment with NAC. NAC restored suppressed alkaline phosphatase activity on β-TCP granules at day 5. Intracellular ROS level on β-TCP granules was 16-fold greater than that on polystyrene, but decreased by half with pre-treatment with NAC. Cell death and intracellular ROS elevation were also induced in polystyrene culture under β-TCP granules even when the osteoblasts were not in direct contact with the β-TCP granules. NAC, however, prevented induction of cell death and elevation of intracellular ROS under β-TCP granules. These results indicate that commercially available β-TCP granules negatively affect cultured osteoblastic viability and function via oxidative stress and that NAC improves these negative responses to the material. This implies enhanced bone regeneration around biodegradable calcium phosphate-based bone substitute by NAC.

Dissolution of cemented carbide powders in artificial sweat: implications for cobalt sensitization and contact dermatitis

Skin exposure to cobalt-containing materials can cause systemic immune sensitization and upon repeat contact, elicitation of allergic contact dermatitis (ACD). Data on cobalt dissolution rates are needed to calculate uptake through skin and for development of models to understand risk of sensitization or dermatitis. The purpose of this research was to measure the dissolution kinetics of feedstock and process-sampled powders encountered in the production of hard metal alloys using artificial sweat. The physicochemical properties of each material were characterized prior to evaluation of dissolution behavior. Variations in artificial sweat solvent pH and chemistry were used to understand critical factors in dissolution. Dissolution of cobalt, tungsten, and tungsten carbide was often biphasic with the initial rapid phase being up to three orders of magnitude faster than the latter long-term phase. Artificial sweat pH did not influence dissolution of cobalt or tungsten carbide. Solvent composition had little influence on observed dissolution rates; however, vitamin E suppressed the dissolution of cobalt and tungsten carbide from sintered particles obtained from a chamfer grinder. There was no effect of particle size on dissolution of feedstock cobalt, tungsten, tungsten carbide, and admixture powders. Particle physicochemical properties influenced observed dissolution rates with more cobalt and tungsten carbide dissolving from chamfer grinder particles compared to the feedstock powders or admixture powder. Calculations using the observed dissolution rates revealed that skin exposure concentrations were similar to concentrations known to induce cobalt sensitization and elicit ACD. Observed dissolution rates for cobalt in artificial sweat indicate that dermal uptake may be sufficient to induce cobalt sensitization and allergic dermatitis.

The role of oxidative stress in carcinogenesis induced by metals and xenobiotics

In addition to a wide range of adverse effects on human health, toxic metals such as cadmium, arsenic and nickel can also promote carcinogenesis. The toxicological properties of these metals are partly related to generation of reactive oxygen species (ROS) that can induce DNA damage and trigger redox-dependent transcription factors. The precise mechanisms that induce oxidative stress are not fully understood. Further, it is not yet known whether chronic exposures to low doses of arsenic, cadmium or other metals are sufficient to induce mutations in vivo, leading to DNA repair responses and/or tumorigenesis. Oxidative stress can also be induced by environmental xenobiotics, when certain metabolites are generated that lead to the continuous release of superoxide, as long as the capacity to reduce the resulting dions (quinones) into hydroquinones is maintained. However, the specific significance of superoxide-dependent pathways to carcinogenesis is often difficult to address, because formation of DNA adducts by mutagenic metabolites can occur in parallel. Here, we will review both mechanisms and toxicological consequences of oxidative stress triggered by metals and dietary or environmental pollutants in general. Besides causing DNA damage, ROS may further induce multiple intracellular signaling pathways, notably NF-kB, JNK/SAPK/p38, as well as Erk/MAPK. These signaling routes can lead to transcriptional induction of target genes that could promote proliferation or confer apoptosis resistance to exposed cells. The significance of these additional modes depends on tissue, cell-type and is often masked by alternate oncogenic mechanisms being activated in parallel.

Tungsten carbide cobalt nanoparticles exert hypoxia-like effects on the gene expression level in human keratinocytes

Background

Tungsten carbide (WC) and tungsten carbide cobalt (WC-Co) nanoparticles are of occupational health relevance because of the increasing usage in hard metal industries. Earlier studies showed an enhanced toxic potential for WC-Co compared to WC or cobalt ions alone. Therefore, we investigated the impact of these particles, compared to cobalt ions applied as CoCl₂, on the global gene expression level in human keratinocytes (HaCaT) in vitro.

Results

WC nanoparticles exerted very little effects on the transcriptomic level after 3 hours and 3 days of exposure. In contrast, WC-Co nanoparticles caused significant transcriptional changes that were similar to those provoked by CoCl₂. However, CoCl₂ exerted even more pronounced changes in the transcription patterns. Gene set enrichment analyses revealed that the differentially expressed genes were related to hypoxia response, carbohydrate metabolism, endocrine pathways, and targets of several transcription factors. The role of the transcription factor HIF1 (hypoxia inducible factor 1) is particularly highlighted and aspects of downstream events as well as the role of other transcription factors related to cobalt toxicity are considered.

Conclusions

This study provides extensive data useful for the understanding of nanoparticle and cobalt toxicity. It shows that WC nanoparticles caused low transcriptional responses while WC-Co nanoparticles are able to exert responses similar to that of free cobalt ions, particularly the induction of hypoxia-like effects via interactions with HIF1α in human keratinocytes. However, the enhanced toxicity of WC-Co particles compared to CoCl₂ could not be explained by differences in gene transcription.

Comparison of free radical generation by pre- and post-sintered cemented carbide particles

Rapid generation of reactive oxygen species (ROS) may occur in response to cellular contact with metal particles. Generation of ROS by cobalt and/or tungsten carbide is implicated in causing hard metal lung disease (HMD) and allergic contact dermatitis (ACD). In this study, ROS generation and particle properties that influence radical generation were assessed for three sizes of tungsten, tungsten carbide, cobalt, admixture (tungsten carbide and cobalt powders), spray dryer, and post-sintered chamfer grinder powders using chemical (H(2)O(2) plus phosphate buffered saline, artificial lung surfactant, or artificial sweat) and cellular (RAW 264.7 mouse peritoneal monocytes plus artificial lung surfactant) reaction systems. For a given material, on a mass basis, hydroxyl (.OH) generation generally increased as particle size decreased; however, on a surface area basis, radical generation levels were more, but not completely, similar. Chamfer grinder powder, polycrystalline aggregates of tungsten carbide in a metallic cobalt matrix, generated the highest levels of .OH radicals (p < 0.05). Radical generation was not dependent on the masses of metals, rather, it involved surface-chemistry-mediated reactions that were limited to a biologically active fraction of the total available surface area of each material. Improved understanding of particle surface chemistry elucidated the importance of biologically active surface area in generation of ROS by particle mixtures.

Size-dependent effects of tungsten carbide-cobalt particles on oxygen radical production and activation of cell signaling pathways in murine epidermal cells

Hard metal or cemented carbide consists of a mixture of tungsten carbide (WC) (85%) and metallic cobalt (Co) (5-15%). WC-Co is considered to be potentially carcinogenic to humans. However, no comparison of the adverse effects of nano-sized WC-Co particles is available to date. In the present study, we compared the ability of nano- and fine-sized WC-Co particles to form free radicals and propensity to activate the transcription factors, AP-1 and NF-kappaB, along with stimulation of mitogen-activated protein kinase (MAPK) signaling pathways in a mouse epidermal cell line (JB6 P(+)). Our results demonstrated that nano-WC-Co generated a higher level of hydroxyl radicals, induced greater oxidative stress, as evidenced by a decrease of GSH levels, and caused faster JB6 P(+) cell growth/proliferation than observed after exposure of cells to fine WC-Co. In addition, nano-WC-Co activated AP-1 and NF-kappaB more efficiently in JB6(+/+) cells as compared to fine WC-Co. Experiments using AP-1-luciferase reporter transgenic mice confirmed the activation of AP-1 by nano-WC-Co. Nano- and fine-sized WC-Co particles also stimulated MAPKs, including ERKs, p38, and JNKs with significantly higher potency of nano-WC-Co. Finally, co-incubation of the JB6(+/+) cells with N-acetyl-cysteine decreased AP-1 activation and phosphorylation of ERKs, p38 kinase, and JNKs, thus suggesting that oxidative stress is involved in WC-Co-induced toxicity and AP-1 activation.

Characterization of exposures among cemented tungsten carbide workers. Part I: Size-fractionated exposures to airborne cobalt and tungsten particles

As many as 30,000 workers in the United States of America are exposed to cemented tungsten carbides (CTC), alloys composed primarily of tungsten carbide and cobalt, which are used in cutting tools. Inhalation of cobalt-containing particles may be sufficient for the development of occupational asthma, whereas tungsten carbide particles in association with cobalt particles are associated with the development of hard metal disease (HMD) and lung cancer. Historical epidemiology and exposure studies of CTC workers often rely only on measures of total airborne cobalt mass concentration. In this study, we characterized cobalt- and tungsten-containing aerosols generated during the production of CTC with emphasis on (1) aerosol "total" mass (n=252 closed-face 37 mm cassette samples) and particle size-selective mass concentrations (n=108 eight-stage cascade impactor samples); (2) particle size distributions; and (3) comparison of exposures obtained using personal cassette and impactor samplers. Total cobalt and tungsten exposures were highest in work areas that handled powders (e.g., powder mixing) and lowest in areas that handled finished product (e.g., grinding). Inhalable, thoracic, and respirable cobalt and tungsten exposures were observed in all work areas, indicating potential for co-exposures to particles capable of getting deposited in the upper airways and alveolar region of the lung. Understanding the risk of CTC-induced adverse health effects may require two exposure regimes: one for asthma and the other for HMD and lung cancer. All sizes of cobalt-containing particles that deposit in the lung and airways have potential to cause asthma, thus a thoracic exposure metric is likely biologically appropriate. Cobalt-tungsten mixtures that deposit in the alveolar region of the lung may potentially cause HMD and lung cancer, thus a respirable exposure metric for both metals is likely biologically appropriate. By characterizing size-selective and co-exposures as well as multiple exposure pathways, this series of papers offer an approach for developing biologically meaningful exposure metrics for use in epidemiology.

Toxicity of tungsten carbide and cobalt-doped tungsten carbide nanoparticles in mammalian cells in vitro

BACKGROUND

Tungsten carbide nanoparticles are being explored for their use in the manufacture of hard metals. To develop nanoparticles for broad applications, potential risks to human health and the environment should be evaluated and taken into consideration.

OBJECTIVE

We aimed to assess the toxicity of well-characterized tungsten carbide (WC) and cobalt-doped tungsten carbide (WC-Co) nanoparticle suspensions in an array of mammalian cells.

METHODS

We examined acute toxicity of WC and of WC-Co (10% weight content Co) nanoparticles in different human cell lines (lung, skin, and colon) as well as in rat neuronal and glial cells (i.e., primary neuronal and astroglial cultures and the oligodendrocyte precursor cell line OLN-93). Furthermore, using electron microscopy, we assessed whether nanoparticles can be taken up by living cells. We chose these in vitro systems in order to evaluate for potential toxicity of the nanoparticles in different mammalian organs (i.e., lung, skin, intestine, and brain).

RESULTS

Chemical-physical characterization confirmed that WC as well as WC-Co nanoparticles with a mean particle size of 145 nm form stable suspensions in serum-containing cell culture media. WC nanoparticles were not acutely toxic to the studied cell lines. However, cytotoxicity became apparent when particles were doped with Co. The most sensitive were astrocytes and colon epithelial cells. Cytotoxicity of WC-Co nanoparticles was higher than expected based on the ionic Co content of the particles. Analysis by electron microscopy demonstrated presence of WC nanoparticles within mammalian cells.

CONCLUSIONS

Our findings demonstrate that doping of WC nanoparticles with Co markedly increases their cytotoxic effect and that the presence of WC-Co in particulate form is essential to elicit this combinatorial effect.