Macrophage solubilization and cytotoxicity of indium-containing particles in vitro

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

The Cytotoxicity of Tungsten Ions Derived from Nanoparticles Correlates with Pulmonary Toxicity

Tungsten carbide nanoparticles (nano-WC) are prevalent in composite materials, and are attributed to their physical and chemical properties. Due to their small size, nano-WC particles can readily infiltrate biological organisms via the respiratory tract, thereby posing potential health hazards. Despite this, the studies addressing the cytotoxicity of nano-WC remain notably limited. To this purpose, the BEAS-2B and U937 cells were cultured in the presence of nano-WC. The significant cytotoxicity of nano-WC suspension was evaluated using a cellular LDH assay. To investigate the cytotoxic impact of tungsten ions (W⁶⁺) on cells, the ion chelator (EDTA-2Na) was used to adsorb W⁶⁺ from nano-WC suspension. Subsequent to this treatment, the modified nano-WC suspension was subjected to flow cytometry analysis to evaluate the rates of cellular apoptosis. According to the results, a decrease in W⁶⁺ could mitigate the cellular damage and enhance cell viability, which indicated that W⁶⁺ indeed exerted a significant cytotoxic influence on the cells. Overall, the present study provides valuable insight into the toxicological mechanisms underlying the exposure of lung cells to nano-WC, thereby reducing the environmental toxicant risk to human health.

Pulmonary effects of exposure to indium and its compounds: cross-sectional survey of exposed workers and experimental findings in rodents

BACKGROUND

Many studies have shown that occupational exposure to indium and its compounds could induce lung disease. Although animal toxicological studies and human epidemiological studies suggest indium exposure may cause lung injury, inflammation, pulmonary fibrosis, emphysema, pulmonary alveolar proteinosis, and even lung cancer, related data collected from humans is currently limited and confined to single workplaces, and the early effects of exposure on the lungs are not well understood.

OBJECTIVES

This study combined population studies and animal experiments to examine the links of indium with pulmonary injury, as well as its mechanism of action. A cross-sectional epidemiological study of indium-exposed workers from China was conducted to evaluate associations between occupational indium exposure and serum biomarkers of early effect. This study also compares and analyzes the causal perspectives of changes in human serum biomarkers induced by indium compound exposure and indium exposure-related rat lung pathobiology, and discusses possible avenues for their recognition and prevention.

METHODS

This is a study of 57 exposed (at least 6 h per day for one year) workers from an indium ingot production plant, and 63 controls. Indium concentration in serum, urine, and airborne as exposure indices were measured by inductively coupled plasma-mass spectrometry. Sixteen serum biomarkers of pulmonary injury, inflammation, and oxidative stress were measured using ELISA. The associations between serum indium and 16 serum biomarkers were analyzed to explore the mechanism of action of indium on pulmonary injury in indium-exposed workers. Animal experiments were conducted to measure inflammatory factors levels in bronchoalveolar lavage fluid (BALF) and lung tissue protein expressions in rats. Four different forms of indium compound-exposed rat models were established (intratracheal instillation twice per week, 8 week exposure, 8 week recovery). Model I: 0, 1.2, 3, and 6 mg/kg bw indium tin oxide group; Model II: 0, 1.2, 3, and 6 mg/kg bw indium oxide (In₂O₃) group; Model III: 0, 0.523, 1.046, and 2.614 mg/kg bw indium sulfate (In₂(SO₄)₃) group; Model IV: 0, 0.065, 0.65, and 1.3 mg/kg bw indium trichloride (InCl₃) group. Lung pathological changes were assessed by hematoxylin & eosin, periodic acid Schiff, and Masson's staining, transmission electron microscopy, and the protein changes were determined by immunohistochemistry.

RESULTS

In the production workshop, the airborne indium concentration was 78.4 μg/m³. The levels of serum indium and urine indium in indium-exposed workers were 39.3 μg/L and 11.0 ng/g creatinine. Increased lung damage markers, oxidative stress markers, and inflammation markers were found in indium-exposed workers. Serum indium levels were statistically and positively associated with the serum levels of SP-A, IL-1β, IL-6 in indium-exposed workers. Among them, SP-A showed a duration-response pattern. The results of animal experiments showed that, with an increase in dosage, indium exposure significantly increased the levels of serum indium and lung indium, as well as the BALF levels of IL‑1β, IL‑6, IL‑10, and TNF‑α and up-regulated the protein expression of SP-A, SP-D, KL-6, GM-CSF, NF-κB p65, and HO-1 in all rat models groups. TEM revealed that In₂(SO₄)₃ and InCl₃ are soluble and that no particles were found in lung tissue, in contrast to the non-soluble compounds (ITO and In₂O₃). No PAS-staining positive substance was found in the lung tissue of In₂(SO₄)₃ and InCl₃ exposure groups, whereas ITO and In₂O₃ rat models supported findings of pulmonary alveolar proteinosis and interstitial fibrosis seen in human indium lung disease. ITO and InCl₃ can accelerate interstitial fibrosis. Findings from our in vivo studies demonstrated that intra-alveolar accumulation of surfactant (immunohistochemistry) and characteristic cholesterol clefts granulomas of indium lung disease (PAS staining) were triggered by a specific form of indium (ITO and In₂O₃).

CONCLUSIONS

In indium-exposed workers, biomarker findings indicated lung damage, oxidative stress and an inflammatory response. In rat models of the four forms of indium encountered in a workplace, the biomarkers response to all compounds overall corresponded to that in humans. In addition, pulmonary alveolar proteinosis was found following exposure to indium tin oxide and indium oxide in the rat models, and interstitial fibrosis was found following exposure to indium tin oxide and indium trichloride, supporting previous report of human disease. Serum SP-A levels were positively associated with indium exposure and may be considered a potential biomarker of exposure and effect in exposed workers.

N-acetylcysteine alleviates pulmonary alveolar proteinosis induced by indium-tin oxide nanoparticles in male rats: involvement of the NF-κB signaling pathway

Indium-tin oxide (ITO) was previously found to have a toxic effect on lung tissues, and oxidative stress and the inflammatory response are two important mechanisms of ITO‑induced lung injury. N-acetylcysteine (NAC) has been found to exhibit antioxidant and anti‑inflammatory properties. The current study aimed to evaluate the possible protective effects of NAC against ITO nanoparticle (Nano-ITO)-induced pulmonary alveolar proteinosis (PAP) in adult male Sprague-Dawley rats, especially via modulation of nuclear factor-kappa B (NF-κB) signaling. For this purpose, 50 rats were randomly allocated into five groups (10 rats each) as follows: (1) control group; (2) saline group; (3) NAC (200 mg/kg) group; (4) PAP model group receiving a repeated intratracheal dose of Nano-ITO (6 mg/kg); and (5) PAP model+NF-κB inhibitor (NAC) group pre-treated intraperitoneally with NAC (200 mg/kg) twice per week before the administration of an intratracheal dose of Nano-ITO (6 mg/kg). Rats were then euthanized under anesthesia, and their lungs were removed for histopathological and biochemical investigations. A 6 mg/kg dose of Nano-ITO markedly altered the levels of some oxidative stress biomarkers. The histological examination of Nano-ITO-exposed rats demonstrated diffused alveolar damage that involved PAP, cholesterol crystals, alveolar fibrosis, pulmonary fibrosis, and alveolar emphysema. The immunohistochemical results of Nano-ITO-exposed rats revealed strongly positive NF-κB p65 and inhibitory kappa B kinase (IKK)-β and weakly positive inhibitor of kappa-B subunit alpha (IκB-α) staining reactivity in the nuclei of cells lining the epithelium of the bronchioles and alveoli. Moreover, Nano-ITO activated the NF-κB pathway. However, pre-treatment with NAC significantly attenuated Nano-ITO-evoked alterations in the previously mentioned parameters, highlighting their antioxidant, anti-inflammatory, and anti-apoptotic potential. The results indicated that the degree of pulmonary fibrosis and proteinosis in the NAC‑treated group was improved compared with that in the Nano-ITO-induced PAP model group. The level of malondialdehyde was also decreased overall in the NAC-treated group compared with that in the Nano-ITO-induced model group, indicating that the pulmonary fibrosis degree and oxidation levels were decreased. The present study also demonstrated that NAC increased the activity of antioxidant enzyme superoxide dismutase and total antioxidant capacity, indicating that it could alleviate oxidative stress in the lung tissue of Nano-ITO‑exposed rats. In addition, NAC reduced the production of pro‑inflammatory cytokines interleukin (IL)‑1β, IL‑6, and tumor necrosis factor (TNF)‑α, and increased the levels of anti‑inflammatory factor IL‑10. The current study demonstrated that NAC can effectively attenuate Nano-ITO‑induced lung injury by reducing oxidative damage and the inflammatory response.

Indium oxide nanoparticles induce lung intercellular toxicity between bronchial epithelial cells and macrophages

Concerns have been raised over the safety and health of industrial workers exposed to indium oxide nanoparticles (IO-NPs) when working. IO-NPs were previously shown in vitro and in vivo to be cytotoxic, but the mechanism of pathogenesis was unclear. In this study, the effects of IO-NPs on lung cells associated with respiratory and immune barriers and the toxic effects of intercellular cascades were studied. Here IO-NPs had acute toxicity to Wistar rats over a time course (5 days post-intratracheal instillation). Following treatment epithelial cells (16HBE) or macrophages (RAW264.7) with IO-NPs or IO fine particles (IO-FPs), the damage of 16HBE cells caused by IO-NPs was serious, mainly in the mitochondrial and rough endoplasmic reticulum. The lactate dehydrogenase level also showed that cytotoxicity in vitro was more serious for IO-NPs compared with IO-FPs. The level of In³⁺ (examined by inductively coupled plasma mass spectrometry) in 16HBE cells was 10 times higher than that in RAW cells. In³⁺ , releasing from IO-NPs absorbed by 16HBE cells, could not only significantly inhibit the phagocytosis and migration of macrophages (P < .0001), but also stimulate RAW cells to secrete high levels of inflammatory cytokines. IO-NPs can directly damage pulmonary epithelial cells. The In³⁺ released by epithelial cells affect the phagocytosis and migration of macrophages, which may be a new point for the decrease in the clearance of alveolar surfactants and the development of IO-related pulmonary alveolar proteinosis.

Nitrative DNA damage in lung epithelial cells exposed to indium nanoparticles and indium ions

Indium compounds have been widely used in manufacturing displays of mobile phones, computers and televisions. However, inhalation exposure to indium compounds causes interstitial pneumonia in exposed workers and lung cancer in experimental animals. 8-Nitroguanine (8-nitroG) is a mutagenic DNA lesion formed under inflammatory conditions and may participate in indium-induced carcinogenesis. In this study, we examined 8-nitroG formation in A549 cultured human lung epithelial cells treated with indium compounds, including nanoparticles of indium oxide (In₂O₃) and indium-tin oxide (ITO), and indium chloride (InCl₃). We performed fluorescent immunocytochemistry to examine 8-nitroG formation in indium-exposed A549 cells. All indium compounds significantly increased 8-nitroG formation in A549 cells at 5 ng/ml after 4 h incubation. 8-NitroG formation was largely reduced by 1400 W, methyl-β-cyclodextrin (MBCD) and monodansylcadaverine (MDC), suggesting the involvement of nitric oxide synthase and endocytosis. 8-NitroG formation in A549 cells was also largely suppressed by small interfering RNA (siRNA) for high-mobility group box-1 (HMGB1), receptor for advanced glycation and end products (AGER, RAGE) and Toll-like receptor 9 (TLR9). These results suggest that indium compounds induce inflammation-mediated DNA damage in lung epithelial cells via the HMGB1-RAGE-TLR9 pathway. This mechanism may contribute to indium-induced genotoxicity in the respiratory system.

Evaluation of cytotoxicity, apoptosis, and genotoxicity induced by indium chloride in macrophages through mitochondrial dysfunction and reactive oxygen species generation

Due to rapid advances in the era of electronic technologies, indium has played the important material for the production of liquid crystal display screens in the semiconductor and optoelectronic industries. The present study focuses on evaluating the toxic effects and related mechanisms of indium chloride (InCl₃) on RAW264.7 macrophages. Cytotoxicity was induced by InCl₃ in a concentration- and time-dependent manner. InCl₃ had the ability to induce macrophage death through apoptosis rather than through necrosis. According to the cytokinesis-block micronucleus assay and alkaline single-cell gel electrophoresis assay, InCl₃ induced DNA damage, also called genotoxicity, in a concentration-dependent manner. Cysteine-dependent aspartate-directed protease (caspase)-3, -8, and -9 were activated by InCl₃ in a concentration-dependent manner. Mitochondria dysfunction and cytochrome c release from the mitochondria were induced by InCl₃ in a concentration-dependent manner. Downregulation of BCL2 and upregulation of BAD were induced by InCl₃ in a concentration-dependent manner. More, we proposed that InCl₃ treatment generated reactive oxygen species (ROS) in a concentration-dependent manner. In conclusion, the current study revealed that InCl₃ induced macrophage cytotoxicity, apoptosis, and genotoxicity via a mitochondria-dependent apoptotic pathway and ROS generation.

Airway injury in an in vitro human epithelium-fibroblast model of diacetyl vapor exposure: diacetyl-induced basal/suprabasal spongiosis

Inhalation exposure to diacetyl (DA) is associated with obliterative bronchiolitis (OB) in workers and induces OB-like fibrotic airway lesions in rats. The pathogenesis of OB is poorly understood in part due to complex interactions between airway epithelial, mesenchymal and blood-derived inflammatory cells. DA-induced airway toxicity in the absence of recruited-inflammatory/immune cells was characterized using an air-liquid interface (ALI) model consisting of human airway epithelium with (Epi/FT) and without (Epi) a mesenchymal component. ALI cultures were exposed to 25 mM DA-derived vapors (using vapor cups) for 1 h on day 0, 2 and 4. In some experiments, the tissues were exposed to 2,3-hexanedione (Hex) which is structurally-similar, but much less fibrogenic than DA. Lactate dehydrogenase activity and day 6 histopathologic changes associated with epithelial injury, including basal/suprabasal spongiosis, were increased following exposure of Epi/FT tissues to DA but not control or Hex vapors. IL-1a, IL-6, IL-8, sIL-1Ra, TGFa, MCP-3 and TNFa proteins were increased following DA exposure of Epi/FT tissues; only IL-1a, IL-8, sIL-1Ra and TGFa were increased following exposure of Epi tissues. MMP-1, MMP-3 and TIMP-1 proteins were increased following DA exposure of Epi/FT tissues; whereas MMP-2, MMP-7 and TIMP-2 were decreased, and production was largely dependent upon the presence of sub-epithelial stromal matrix/fibroblasts. Hex-induced protein changes were minimal. This in vitro study demonstrated that exposure of human airways to DA vapors induced epithelial injury (with the histopathologic feature of basal/suprabasal spongiosis) and increased release of pro-inflammatory and pro-fibrotic cytokines/chemokines as well as MMPs/TIMPs in the absence of recruited-inflammatory cells.

Characterization and toxicity of nanoscale fragments in wastewater treatment plant effluent

Much attention has been paid to extracting and isolating specific and well-known nanoparticles (especially for engineered nanomaterials) from complex environmental matrices. However, such research may not provide global information on actual contamination because nanoscale fragments exist as mixtures of various elements and matrices in the real environment. The present work first isolated and characterized nanoscale fragments in effluents from municipal wastewater treatment plants (WWTPs). The nanoscale fragments were found to be composed of 70-85% carbon and low amounts of oxygen, heavy metals and other elements and exhibited nanosheet topographies (approximately 0.87-1.31 nm thickness and 68-187 nm lateral length). Because the isolated nanoscale fragments were mixtures rather than one specific type of nanoparticle, they were present at high concentrations ranging from 0.07 to 0.55 mg/L. It was also found that the accumulation of nanoscale fragments in rice reached 0.59 mg/g under exposure to environmentally relevant concentrations, leading to marked phytotoxicity (e.g., ultrastructural damage to chloroplasts and mitochondria). Metabolic analysis revealed the toxicological mechanisms to be related to disorders of carbohydrate, amino acid and fatty acid metabolism. This study is the first to characterize the properties and analyze the toxicity of nanoscale fragments in the effluents of WWTPs. Given that WWTP effluents containing nanoscale fragments are continuously discharged to the soil, surface water and seas, nanoscale fragment materials deserve considerable attention in future work compared with the few widely studied engineered nanoparticles.

The impact of nanomaterial characteristics on inhalation toxicity

During the last few decades, nanotechnology has evolved into a success story, apparent from a steadily increasing number of scientific publications as well as a large number of applications based on engineered nanomaterials (ENMs). Its widespread uses suggest a high relevance for consumers, workers and the environment, hence justifying intensive investigations into ENM-related adverse effects as a prerequisite for nano-specific regulations. In particular, the inhalation of airborne ENMs, being assumed to represent the most hazardous type of human exposure to these kinds of particles, needs to be scrutinized. Due to an increased awareness of possible health effects, which have already been seen in the case of ultrafine particles (UFPs), research and regulatory measures have set in to identify and address toxic implications following their almost ubiquitous occurrence. Although ENM properties differ from those of the respective bulk materials, the available assessment protocols are often designed for the latter. Despite the large benefit ensuing from the application of nanotechnology, many issues related to ENM behavior and adverse effects are not fully understood or should be examined anew. The traditional hypothesis that ENMs exhibit different or additional hazards due to their "nano" size has been challenged in recent years and ENM categorization according to their properties and toxicity mechanisms has been proposed instead. This review summarizes the toxicological effects of inhaled ENMs identified to date, elucidating the modes of action which provoke different mechanisms in the respiratory tract and their resulting effects. By linking particular mechanisms and adverse effects to ENM properties, grouping of ENMs based on toxicity-related properties is supposed to facilitate toxicological risk assessment. As intensive studies are still required to identify these "ENM classes", the need for alternatives to animal studies is evident and advances in cell-based test systems for pulmonary research are presented here. We hope to encourage the ongoing discussion about ENM risks and to advocate the further development and practice of suitable testing and grouping methods.

New interplay between interstitial and alveolar macrophages explains pulmonary alveolar proteinosis (PAP) induced by indium tin oxide particles

Occupational exposure to indium tin oxide (ITO) particles has been associated with the development of severe lung diseases, including pulmonary alveolar proteinosis (PAP). The mechanisms of this lung toxicity remain unknown. Here, we reveal the respective roles of resident alveolar (Siglec-F^high AM) and recruited interstitial (Siglec-F^low IM) macrophages contributing in concert to the development of PAP. In mice treated with ITO particles, PAP is specifically associated with IL-1α (not GM-CSF) deficiency and Siglec-F^high AM (not Siglec-F^low IM) depletion. Mechanistically, ITO particles are preferentially phagocytosed and dissolved to soluble In³⁺ by Siglec-F^low IM. In contrast, Siglec-F^high AM weakly phagocytose or dissolve ITO particles, but are sensitive to released In³⁺ through the expression of the transferrin receptor-1 (TfR1). Blocking pulmonary Siglec-F^low IM recruitment in CCR2-deficient mice reduces ITO particle dissolution, In³⁺ release, Siglec-F^high AM depletion, and PAP formation. Restoration of IL-1-related Siglec-F^high AM also prevented ITO-induced PAP. We identified a new mechanism of secondary PAP development according to which metal ions released from inhaled particles by phagocytic IM disturb IL-1α-dependent AM self-maintenance and, in turn, alveolar clearance.

Comparison of the toxicity of sintered and unsintered indium-tin oxide particles in murine macrophage and epidermal cells

Indium-tin oxide (ITO) is used to produce flat panel displays and several other technology products. Composed of 90% indium oxide (In₂O₃) and 10% tin oxide (SnO₂) by weight, ITO is synthesized under conditions of high heat via a process known as sintering. Indium lung disease, a recently recognized occupational illness, is characterized by pulmonary alveolar proteinosis, fibrosis, and emphysema. Murine macrophage (RAW 264.7) and epidermal (JB6) cells stably transfected with AP-1 to study tumor promoting potential, were used to differentiate between the toxicological profiles of sintered ITO (SITO) and unsintered mixture (UITO). We hypothesized that sintering would play a key role in free radical generation and cytotoxicity. Exposure of cells to both UITO and SITO caused a time and dose dependent decrease of the viability of cells. Intracellular ROS generation was inversely related to the dose of both UITO and SITO, a direct reflection of the decreased number of viable RAW 264.7 and JB6/AP-1 cells observed at higher concentrations. Electron spin resonance showed significantly increased hydroxyl radical (OH) generation in cells exposed to UITO compared to SITO. This is different from LDH release, which showed that SITO caused significantly increased damage to the cell membrane compared to UITO. Lastly, the JB6/AP-1 cell line did not show activation of the AP-1 pathway. Our results highlight both the differences in the mechanisms of cytotoxicity and the consistent adverse effects associated with UITO and SITO exposure.

Application of the ICRP respiratory tract model to estimate pulmonary retention of industrially sampled indium-containing dusts

Inhalation of indium-containing dusts is associated with the development of indium lung disease. Workers may be exposed to several different chemical forms of indium; however, their lung dosimetry is not fully understood. We characterized the physicochemical properties and measured the lung dissolution kinetics of eight indium-containing dusts. Indium dissolution rates in artificial lung fluids spanned two orders of magnitude. We used the International Commission on Radiological Protection (ICRP) human respiratory model (HRTM) to estimate pulmonary indium deposition, retention and biokinetic clearance to blood. For a two-year (median workforce tenure at facility) exposure to respirable-sized particles of the indium materials, modeled indium clearance (>99.99% removed) from the alveolar-interstitial compartment was slow for all dusts; salts would clear in 4 years, sintered indium-tin oxide (ITO) would clear in 9 years, and indium oxide would require 48 years. For this scenario, the ICRP HRTM predicted that indium translocated to blood would be present in that compartment for 3.5-18 years after cessation of exposure, depending on the chemical form. For a 40-year exposure (working lifetime), clearance from the alveolar-interstitial compartment would require 5, 10 and 60 years for indium salts, sintered ITO and indium oxide, respectively and indium would be present in blood for 5-53 years after exposure. Consideration of differences in chemical forms of indium, dissolution rates, alveolar clearance and residence time in blood should be included in exposure assessment and epidemiological studies that rely on measures of total indium in air or blood to derive risk estimates.

An advanced case of indium lung disease with progressive emphysema

Objectives:

To report the occurrence of an advanced case of indium lung disease with severely progressive emphysema in an indium-exposed worker.

Case report:

A healthy 42-year-old male smoker was employed to primarily grind indium-tin oxide (ITO) target plates, exposing him to indium for 9 years (1998-2008). In 2004, an epidemiological study was conducted on indium-exposed workers at the factory in which he worked. The subject's serum indium concentration (In-S) was 99.7 μg/l, while his serum Krebs von den Lungen-6 level was 2,350 U/ml. Pulmonary function tests showed forced vital capacity (FVC) of 4.17 l (91.5% of the JRS predicted value), forced expiratory volume in 1 s (FEV₁) of 3.19 l (80.8% of predicted), and an FEV₁-to-FVC ratio of 76.5%. A high-resolution chest computed tomography (HRCT) scan showed mild interlobular septal thickening and mild emphysematous changes. In 2008, he was transferred from the ITO grinding workplace to an inspection work section, where indium concentrations in total dusts had a range of 0.001-0.002 mg/m³. In 2009, the subject's In-S had increased to 132.1 μg/l, and pulmonary function tests revealed obstructive changes. In addition, HRCT scan showed clear evidence of progressive lung destruction with accompanying severe centrilobular emphysema and interlobular septal thickening in both lung fields. The subject's condition gradually worsened, and in 2015, he was registered with the Japan Organ Transplant Network for lung transplantation (LTx).

Conclusions:

Heavy indium exposure is a risk factor for emphysema, which can lead to a severity level that requires LTx as the final therapeutic option.

The toxicology of indium tin oxide

Indium tin oxide (ITO) is a technologically important semiconductor. An increasing number of cases of severe lung effects (characterized by pulmonary alveolar proteinosis and/or interstitial fibrosis) in ITO-exposed workers warrants a review of the toxicological hazards. Short- and long-term inhalation studies in rats and mice revealed persistent alveolar proteinosis, inflammation and fibrosis in the lungs down to concentrations as low as 0.01mg/m(3). In rats, the incidences of bronchiolo-alveolar adenomas and carcinomas were significantly increased at all concentrations. In mice, ITO was not carcinogenic. A few bronchiolo-alveolar adenomas occurring after repeated intratracheal instillation of ITO to hamsters have to be interpreted as treatment-related. In vitro and in vivo studies on the formation of reactive oxygen species suggest epigenetic effects as cause of the lung tumor development. Repeated intratracheal instillation of ITO to hamsters slightly affected the male sexual organs, which might be interpreted as a secondary effect of the lung damage. Epidemiological and medical surveillance studies, serum/blood indium levels in workers as well as data on the exposure to airborne indium concentrations indicate a need for measures to reduce exposure at ITO workplaces.

Pulmonary toxicity of indium-tin oxide production facility particles in rats

Indium-tin oxide (ITO) is used to make transparent conductive coatings for touch-screen and liquid crystal display electronics. Occupational exposures to potentially toxic particles generated during ITO production have increased in recent years as the demand for consumer electronics continues to rise. Previous studies have demonstrated cytotoxicity in vitro and animal models have shown pulmonary inflammation and injury in response to various indium-containing particles. In humans, pulmonary alveolar proteinosis (PAP) and fibrotic interstitial lung disease have been observed in ITO facility workers. However, which indium materials or specific processes in the workplace may be the most toxic to workers is unknown. Here we examined the pulmonary toxicity of three different particle samples that represent real-life worker exposures, as they were collected at various production stages throughout an ITO facility. Indium oxide (In2O3), sintered ITO (SITO) and ventilation dust (VD) particles each caused pulmonary inflammation and damage in rats over a time course (1, 7 and 90 days post-intratracheal instillation), but SITO and VD appeared to induce greater toxicity in rat lungs than In2O3 at a dose of 1 mg per rat. Downstream pathological changes such as PAP and fibrosis were observed in response to all three particles 90 days after treatment, with a trend towards greatest severity in animals exposed to VD when comparing animals that received the same dose. These findings may inform workplace exposure reduction efforts and provide a better understanding of the pathogenesis of an emerging occupational health issue.

Intracellular accumulation of indium ions released from nanoparticles induces oxidative stress, proinflammatory response and DNA damage

Due to the widespread use of indium tin oxide (ITO), it is important to investigate its effect on human health. In this study, we evaluated the cellular effects of ITO nanoparticles (NPs), indium chloride (InCl3) and tin chloride (SnCl3) using human lung epithelial A549 cells. Transmission electron microscopy and inductively coupled plasma mass spectrometry were employed to study cellular ITO NP uptake. Interestingly, greater uptake of ITO NPs was observed, as compared with soluble salts. ITO NP species released could be divided into two types: 'indium release ITO' or 'tin release ITO'. We incubated A549 cells with indium release ITO, tin release ITO, InCl3 or SnCl2 and investigated oxidative stress, proinflammatory response, cytotoxicity and DNA damage. We found that intracellular reactive oxygen species were increased in cells incubated with indium release ITO, but not tin release ITO, InCl3 or SnCl2. Messenger RNA and protein levels of the inflammatory marker, interleukin-8, also increased following exposure to indium release ITO. Furthermore, the alkaline comet assay revealed that intracellular accumulation of indium ions induced DNA damage. Our results demonstrate that the accumulation of ionic indium, but not ionic tin, from ITO NPs in the intracellular matrix has extensive cellular effects.

Sintered indium-tin oxide particles induce pro-inflammatory responses in vitro, in part through inflammasome activation

Indium-tin oxide (ITO) is used to make transparent conductive coatings for touch-screen and liquid crystal display electronics. As the demand for consumer electronics continues to increase, so does the concern for occupational exposures to particles containing these potentially toxic metal oxides. Indium-containing particles have been shown to be cytotoxic in cultured cells and pro-inflammatory in pulmonary animal models. In humans, pulmonary alveolar proteinosis and fibrotic interstitial lung disease have been observed in ITO facility workers. However, which ITO production materials may be the most toxic to workers and how they initiate pulmonary inflammation remain poorly understood. Here we examined four different particle samples collected from an ITO production facility for their ability to induce pro-inflammatory responses in vitro. Tin oxide, sintered ITO (SITO), and ventilation dust particles activated nuclear factor kappa B (NFκB) within 3 h of treatment. However, only SITO induced robust cytokine production (IL-1β, IL-6, TNFα, and IL-8) within 24 h in both RAW 264.7 mouse macrophages and BEAS-2B human bronchial epithelial cells. Our lab and others have previously demonstrated SITO-induced cytotoxicity as well. These findings suggest that SITO particles activate the NLRP3 inflammasome, which has been implicated in several immune-mediated diseases via its ability to induce IL-1β release and cause subsequent cell death. Inflammasome activation by SITO was confirmed, but it required the presence of endotoxin. Further, a phagocytosis assay revealed that pre-uptake of SITO or ventilation dust impaired proper macrophage phagocytosis of E. coli. Our results suggest that adverse inflammatory responses to SITO particles by both macrophage and epithelial cells may initiate and propagate indium lung disease. These findings will provide a better understanding of the molecular mechanisms behind an emerging occupational health issue.

In vitro evaluation of the cellular effect of indium tin oxide nanoparticles using the human lung adenocarcinoma A549 cells

Indium tin oxide (ITO) nanoparticles are taken up by human lung adenocarcinoma cells and the nanoparticles induce oxidative stress and DNA damage.

Macrophage solubilization and cytotoxicity of indium-containing particles as in vitro correlates to pulmonary toxicity in vivo

Macrophage-solubilized indium-containing particles (ICPs) were previously shown in vitro to be cytotoxic. In this study, we compared macrophage solubilization and cytotoxicity of indium phosphide (InP) and indium-tin oxide (ITO) with similar particle diameters (∼ 1.5 µm) and then determined if relative differences in these in vitro parameters correlated with pulmonary toxicity in vivo. RAW 264.7 macrophages were treated with InP or ITO particles and cytotoxicity was assayed at 24 h. Ionic indium was measured in 24 h culture supernatants. Macrophage cytotoxicity and particle solubilization in vitro were much greater for InP compared with ITO. To correlate changes in vivo, B6C3F1 mice were treated with InP or ITO by oropharyngeal aspiration. On Days 14 and 28, bronchoalveolar lavage (BAL) and pleural lavage (PL) fluids were collected and assayed for total leukocytes. Cell differentials, lactate dehydrogenase activity, and protein levels were also measured in BAL. All lavage parameters were greatly increased in mice treated with InP compared with ITO. These data suggest that macrophage solubilization and cytotoxicity of some ICPs in vitro are capable of predicting pulmonary toxicity in vivo. In addition, these differences in toxicity were observed despite the two particulate compounds containing similar amounts of indium suggesting that solubilization, not total indium content, better reflects the toxic potential of some ICPs. Soluble InCl3 was shown to be more cytotoxic than InP to macrophages and lung epithelial cells in vitro further suggesting that ionic indium is the primary cytotoxic component of InP.

Indium and indium tin oxide induce endoplasmic reticulum stress and oxidative stress in zebrafish (Danio rerio)

Indium and indium tin oxide (ITO) are extensively used in electronic technologies. They may be introduced into the environment during production, use, and leaching from electronic devices at the end of their life. At present, surprisingly little is known about potential ecotoxicological implications of indium contamination. Here, molecular effects of indium nitrate (In(NO3)3) and ITO nanoparticles were investigated in vitro in zebrafish liver cells (ZFL) cells and in zebrafish embryos and novel insights into their molecular effects are provided. In(NO3)3 led to induction of endoplasmic reticulum (ER) stress response, induction of reactive oxygen species (ROS) and induction of transcripts of pro-apoptotic genes and TNF-α in vitro at a concentration of 247 μg/L. In(NO3)3 induced the ER stress key gene BiP at mRNA and protein level, as well as atf6, which ultimately led to induction of the important pro-apoptotic marker gene chop. The activity of In(NO3)3 on ER stress induction was much stronger than that of ITO, which is explained by differences in soluble free indium ion concentrations. The effect was also stronger in ZFL cells than in zebrafish embryos. Our study provides first evidence of ER stress and oxidative stress induction by In(NO3)3 and ITO indicating a critical toxicological profile that needs further investigation.

Interferon-γ inhibits nonopsonized phagocytosis of macrophages via an mTORC1-c/EBPβ pathway

Bacterial infection often follows virus infection due to pulmonary interferon-γ (IFN-γ) production during virus infection, which down-regulates macrophage phagocytosis. The molecular mechanisms for this process are still poorly understood. In the present study, IFN-γ treatment significantly inhibited the ability of mouse macrophages to phagocytize nonopsonized chicken red blood cells (cRBCs), bacteria and beads in vitro, while it enhanced IgG- and complement-opsonized phagocytosis. IFN-γ treatment decreased the expression of MARCO (macrophage receptor with collagenous structure) in macrophages. Macrophages showed lower binding to and phagocytic ability of cRBCs when MARCO was blocked with antibody. In addition, IFN-γ induced high activity of mTOR (mammalian target of rapamycin) and decreased the expression of c/EBPβ (CCAAT enhancer-binding protein β) in macrophages. Rapamycin, a specific mTOR inhibitor, significantly reversed the inhibitory effect of IFN-γ on nonopsonized phagocytosis of macrophages and restored c/EBPβ and MARCO expression. Biochemical assays showed that c/EBPβ directly bound to the MARCO gene promoter. Rapamycin significantly hampered the viral-bacterial synergy and protected influenza-infected mice from subsequent bacterial infection. Thus, IFN-γ inhibited the nonopsonized phagocytosis of macrophages through the mTOR-c/EBPβ-MARCO pathway. The present study offered evidence indicating that mTOR may be one of the key target molecules for the prevention of secondary bacterial infection caused by primary virus infection.

Cytotoxicity and characterization of particles collected from an indium-tin oxide production facility

Occupational exposure to indium compound particles has recently been associated with lung disease among workers in the indium-tin oxide (ITO) industry. Previous studies suggested that excessive alveolar surfactant and reactive oxygen species (ROS) may play a role in the development of pulmonary lesions following exposure to indium compounds. However, toxicity at the cellular level has not been comprehensively evaluated. Thus, the aim of this study was to assess which, if any, compounds encountered during ITO production are toxic to cultured cells and ultimately contribute to the pathogenesis of indium lung disease. The compounds used in this study were collected from eight different processing stages at an ITO production facility. Enhanced dark field imaging showed 5 of the compounds significantly associated with cells within 1 h, suggesting that cellular reactions to the compound particles may be occurring rapidly. To examine the potential cytotoxic effects of these associations, ROS generation, cell viability, and apoptosis were evaluated following exposures in RAW 264.7 mouse monocyte macrophage and BEAS-2B human bronchial epithelial cell lines. Both exhibited reduced viability with exposures, while apoptosis only occurred in RAW 264.7 cells. Our results suggested that excessive ROS production is likely not the predominant mechanism underlying indium-induced lung disease. However, the effects on cell viability reveal that several of the compounds are cytotoxic, and therefore, exposures need to be carefully monitored in the industrial setting.