Diseases caused by silica: mechanisms of injury and disease development

Consideration of Occupational Lung Disease and Pneumoconiosis in Forensic Pathology

Reports of workers stricken with lung disease sustained during the course of their employment date to antiquity. Despite stringent regulations to mitigate all manners of work place hazards, and the emergence of agencies and physicians engaged in the advancement of occupational health, occupational lung disease remains a significant problem within modern society. Inhalation of dusts and fumes sustained in the course of one's occupation may lead to significant morbidity and mortality, and lead to a huge cost to society in terms of lost productivity, medical care for the worker, and litigation. In certain circumstances, the identification of an underlying occupational lung disease may constitute a significant finding in medicolegal death investigation. This article will present an overview of common occupational diseases likely to be encountered in the practice of forensic pathology, based on the particular etiologic agent and occupational means of exposure.

Role of the aryl hydrocarbon receptor (AhR) in lung inflammation

Millions of individuals worldwide are afflicted with acute and chronic respiratory diseases, causing temporary and permanent disabilities and even death. Oftentimes, these diseases occur as a result of altered immune responses. The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, acts as a regulator of mucosal barrier function and may influence immune responsiveness in the lungs through changes in gene expression, cell-cell adhesion, mucin production, and cytokine expression. This review updates the basic immunobiology of the AhR signaling pathway with regards to inflammatory lung diseases such as asthma, chronic obstructive pulmonary disease, and silicosis following data in rodent models and humans. Finally, we address the therapeutic potential of targeting the AhR in regulating inflammation during acute and chronic respiratory diseases.

Baccharis trimera (Less.) DC as genotoxicity indicator of exposure to coal and emissions from a thermal power plant

During coal combustion, hazardous elements are discharged that impair environmental quality. Plant cover is the first available surface for the atmospheric pollutants in terrestrial ecosystems. The aim of this study was to evaluate genotoxicity in the aqueous extract of the native plant, Baccharis trimera, exposed to coal and emissions from a thermal power plant (coal-fired power plant in Candiota, Brazil), correlating seasonality, wind tunnel predominance, and presence of inorganic elements. The presence of inorganic elements in the aerial parts of B. trimera was analyzed by particle-induced X-ray emission (PIXE) spectrometry, and genotoxicity was evaluated by ex vivo comet assay. The genotoxic effects of aqueous extracts of B. trimera from four sites located in the area around power plant were analyzed by comet assay in peripheral human lymphocytes. Winter samples showed greater levels of metals than summer samples. Genotoxicity was detected in B. trimera extracts collected from the region exposed to extraction and burning coal. Extracts from the site impacted by the dominant wind induced more damage to DNA than those from other sites. Based on our data, we can suggest that in winter the inorganic elements from extraction and burning of coal and carried through the wind tunnel were responsible for the genotoxicity observed in aqueous extract of B. trimera.

Biomembrane disruption by silica-core nanoparticles: effect of surface functional group measured using a tethered bilayer lipid membrane

Engineered nanomaterials (ENM) have desirable properties that make them well suited for many commercial applications. However, a limited understanding of how ENM's properties influence their molecular interactions with biomembranes hampers efforts to design ENM that are both safe and effective. This paper describes the use of a tethered bilayer lipid membrane (tBLM) to characterize biomembrane disruption by functionalized silica-core nanoparticles. Electrochemical impedance spectroscopy was used to measure the time trajectory of tBLM resistance following nanoparticle exposure. Statistical analysis of parameters from an exponential resistance decay model was then used to quantify and analyze differences between the impedance profiles of nanoparticles that were unfunctionalized, amine-functionalized, or carboxyl-functionalized. All of the nanoparticles triggered a decrease in membrane resistance, indicating nanoparticle-induced disruption of the tBLM. Hierarchical clustering allowed the potency of nanoparticles for reducing tBLM resistance to be ranked in the order amine>carboxyl~bare silica. Dynamic light scattering analysis revealed that tBLM exposure triggered minor coalescence for bare and amine-functionalized silica nanoparticles but not for carboxyl-functionalized silica nanoparticles. These results indicate that the tBLM method can reproducibly characterize ENM-induced biomembrane disruption and can distinguish the BLM-disruption patterns of nanoparticles that are identical except for their surface functional groups. The method provides insight into mechanisms of molecular interaction involving biomembranes and is suitable for miniaturization and automation for high-throughput applications to help assess the health risk of nanomaterial exposure or identify ENM having a desired mode of interaction with biomembranes.

Engineered silica nanoparticles act as adjuvants to enhance allergic airway disease in mice

Background

With the increase in production and use of engineered nanoparticles (NP; ≤ 100 nm), safety concerns have risen about the potential health effects of occupational or environmental NP exposure. Results of animal toxicology studies suggest that inhalation of NP may cause pulmonary injury with subsequent acute or chronic inflammation. People with chronic respiratory diseases like asthma or allergic rhinitis may be even more susceptible to toxic effects of inhaled NP. Few studies, however, have investigated adverse effects of inhaled NP that may enhance the development of allergic airway disease.

Methods

We investigated the potential of polyethylene glycol coated amorphous silica NP (SNP; 90 nm diameter) to promote allergic airway disease when co-exposed during sensitization with an allergen. BALB/c mice were sensitized by intranasal instillation with 0.02% ovalbumin (OVA; allergen) or saline (control), and co-exposed to 0, 10, 100, or 400 μg of SNP. OVA-sensitized mice were then challenged intranasally with 0.5% OVA 14 and 15 days after sensitization, and all animals were sacrificed a day after the last OVA challenge. Blood and bronchoalveolar lavage fluid (BALF) were collected, and pulmonary tissue was processed for histopathology and biochemical and molecular analyses.

Results

Co-exposure to SNP during OVA sensitization caused a dose-dependent enhancement of allergic airway disease upon challenge with OVA alone. This adjuvant-like effect was manifested by significantly greater OVA-specific serum IgE, airway eosinophil infiltration, mucous cell metaplasia, and Th2 and Th17 cytokine gene and protein expression, as compared to mice that were sensitized to OVA without SNP. In saline controls, SNP exposure did cause a moderate increase in airway neutrophils at the highest doses.

Conclusions

These results suggest that airway exposure to engineered SNP could enhance allergen sensitization and foster greater manifestation of allergic airway disease upon secondary allergen exposures. Whereas SNP caused innate immune responses at high doses in non-allergic mice, the adjuvant effects of SNP were found at lower doses in allergic mice and were Th2/Th17 related. In conclusion, these findings in mice suggest that individuals exposed to SNP might be more prone to manifest allergic airway disease, due to adjuvant-like properties of SNP.

Cell reactivity to different silica

The interaction between mineral structures and living beings is increasingly attracting the interest of research. The formation of skeletons, geomicrobiology, the study of the origin of life, soil biology, benthos biology, human and mammalian diseases generated by the inhalation of dust and biomaterials are some examples of scientific areas where the topic has a relevance. In this chapter we focus on cell reactivity to siliceous rocks and to the various forms of silicon dioxide, in particular. The examples here reported carefully review how such minerals may strongly affect different living beings, from simple ones to humans. The biomineralogy concept is explained, focusing on the effects of rocks on cell growth and development. The toxic action of silicon dioxide in mammalian lungs is the oldest evidence of crystalline silica bioactivity. More recently, we could demonstrate that crystalline silica has a deep impact on cell biology throughout the whole animal kingdom. One of the most illustrative case studies is the marine sponge Chondrosia reniformis, which has the amazing ability to incorporate and etch crystalline silica releasing dissolved silicates in the medium. This specific and selective action is due to the chemical reaction of ascorbic acid with quartz surfaces. One consequence of this is an increased production of collagen. The discovery of this mechanism opened the door to a new understanding of silica toxicity for animal cells and mammalian cells in particular. The presence of silica in sea water and substrates also affects processes like the settlement of larvae and the growth of diatoms. The following sections review all such aspects.

Biocompatibility assessment of Si-based nano- and micro-particles

Silicon is one of the most abundant chemical elements found on the Earth. Due to its unique chemical and physical properties, silicon based materials and their oxides (e.g. silica) have been used in several industries such as building and construction, electronics, food industry, consumer products and biomedical engineering/medicine. This review summarizes studies on effects of silicon and silica nano- and micro-particles on cells and organs following four main exposure routes, namely, intravenous, pulmonary, dermal and oral. Further, possible genotoxic effects of silica based nanoparticles are discussed. The review concludes with an outlook on improving and standardizing biocompatibility assessment for nano- and micro-particles.

Metabolomics in lung inflammation:a high-resolution (1)h NMR study of mice exposedto silica dust

ABSTRACT Here we report the first (1)H NMR metabolomics studies on excised lungs and bronchoalveolar lavage fluid (BALF) from mice exposed to crystalline silica. High-resolution (1)H NMR metabolic profiling on intact excised lungs was performed using slow magic angle sample spinning (slow-MAS) (1)H PASS (phase-altered spinning sidebands) at a sample spinning rate of 80 Hz. Metabolic profiling on BALF was completed using fast magic angle spinning at 2 kHz. Major findings are that the relative concentrations of choline, phosphocholine (PC), and glycerophosphocholine (GPC) were statistically significantly increased in silica-exposed mice compared to sham controls, indicating an altered membrane choline phospholipids metabolism (MCPM). The relative concentrations of glycogen/glucose, lactate, and creatine were also statistically significantly increased in mice exposed to silica dust, suggesting that cellular energy pathways were affected by silica dust. Elevated levels of glycine, lysine, glutamate, proline, and 4-hydroxyproline were also increased in exposed mice, suggesting the activation of a collagen pathway. Furthermore, metabolic profiles in mice exposed to silica dust were found to be spatially heterogeneous, consistent with regional inflammation revealed by in vivo magnetic resonance imaging (MRI).

Autocrine abscisic acid plays a key role in quartz-induced macrophage activation

Inhalation of quartz induces silicosis, a lung disease where alveolar macrophages release inflammatory mediators, including prostaglandin-E(2) (PGE(2)) and tumor necrosis factor α (TNF-α). Here we report the pivotal role of abscisic acid (ABA), a recently discovered human inflammatory hormone, in silica-induced activation of murine RAW264.7 macrophages and of rat alveolar macrophages (AMs). Stimulation of both RAW264.7 cells and AMs with quartz induced a significant increase of ABA release (5- and 10-fold, respectively), compared to untreated cells. In RAW264.7 cells, autocrine ABA released after quartz stimulation sequentially activates the plasma membrane receptor LANCL2 and NADPH oxidase, generating a Ca(2+) influx resulting in NFκ B nuclear translocation and PGE(2) and TNF-α release (3-, 2-, and 3.5-fold increase, respectively, compared to control, unstimulated cells). Quartz-stimulated RAW264.7 cells silenced for LANCL2 or preincubated with a monoclonal antibody against ABA show an almost complete inhibition of NFκ B nuclear translocation and PGE(2) and TNF-α release compared to controls electroporated with a scramble oligonucleotide or preincubated with an unrelated antibody. AMs showed similar early and late ABA-induced responses as RAW264.7 cells. These findings identify ABA and LANCL2 as key mediators in quartz-induced inflammation, providing possible new targets for antisilicotic therapy.

Aryl hydrocarbon receptor (AhR) regulates silica-induced inflammation but not fibrosis

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is responsible for mediating a variety of pharmacological and toxicological effects caused by halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, recent evidence has revealed that the AhR also has numerous physiological roles aside from xenobiotic metabolism, including regulation of immune and inflammatory signaling as well as normal development and homeostasis of several organs. To investigate the role of the AhR in crystalline silica (SiO(2))-induced inflammation and fibrosis, C57Bl/6 and AhR(-/)(-) mice were exposed to SiO(2) or vehicle. Similarly, C57Bl/6 mice were exposed to SiO(2) and TCDD either simultaneously or sequentially to assess whether AhR activation alters inflammation and fibrosis. SiO(2)-induced acute lung inflammation was more severe in AhR(-)(/-) mice; however, the fibrotic response of AhR(-)(/-) mice was attenuated compared with C57Bl/6 mice. In a model of chronic SiO(2) exposure, AhR activation by TCDD in C57Bl/6 mice resulted in reduced inflammation; however, the fibrotic response was not affected. Bone marrow-derived macrophages (BMM) from AhR(-)(/-) mice also produced higher levels of cytokines and chemokines in response to SiO(2). Analysis of gene expression revealed that BMM derived from AhR(-)(/-) mice exhibit increased levels of pro-interleukin (IL)-1β, IL-6, and Bcl-2, yet decreased levels of signal transducers and activators of transcription (STAT)2, STAT5a, and serpin B2 (Pai-2) in response to SiO(2).

Nanoexposure, unusual diseases, and new health and safety concerns

Accumulating studies in animals have shown that nanoparticles could cause unusual rapid lung injury and extrapulmonary toxicity. Whether exposure of workers to nanoparticles may result in some unexpected damage as seen in animals is still a big concern. We previously reported findings regarding a group of patients exposed to nanoparticles and presenting with an unusual disease. The reported disease was characterized by bilateral chest fluid, pulmonary fibrosis, pleural granuloma, and multiorgan damage and was highly associated with the nanoparticle exposure. To strengthen this association, further information on exposure and the disease was collected and discussed. Our studies show that some kinds of nanomaterials, such as silica nanoparticles and nanosilicates, may be very toxic and even fatal to occupational workers exposed to them without any effective personal protective equipment. More research and collaborative efforts on nanosafety are required in order to prevent and minimize the potential hazards of nanomaterials to humans and the environment.

Iron-mediated lipid peroxidation and lipid raft disruption in low-dose silica-induced macrophage cytokine production

Silica inhalation can induce respiratory disease. Iron is suspected of playing an important role in silica-mediated respiratory toxicity, but unambiguously determining its role has been hampered by incomplete characterization, use of high particle doses, and lack of understanding of proinflammatory mechanisms. In this study, we investigated a novel hypothesis for the mechanism of silica particle-induced increase in cytokine production. We studied the role of iron in lipid peroxidation-dependent transcription of cytokines in macrophages by ground natural silica particles at low sublethal doses. Particle size, size distribution, surface area, and structure were determined using electron microscopy, nitrogen adsorption, and X-ray diffraction. Iron impurity concentrations before and after acid treatment were determined by energy-dispersive X-ray and inductively coupled plasma mass spectroscopy. At a low noncytotoxic dose (1 μg/ml) of 2-μm silica, the presence of iron significantly increased superoxide (O(2)(•-)), lipid peroxidation, lipid raft disruption, and cytokine production in macrophages. The iron chelators deferoxamine mesylate and diethylenetriaminepentaacetic acid were found to abrogate O(2)(•-) production and inhibit lipid peroxidation, raft disruption, and cytokine induction. Tricyclodecan-9-yl xanthate, a competitive inhibitor of phosphatidylcholine-specific phospholipase C (PC-PLC), which is an upstream participant in NF-κB activation, and manganese(III) tetrakis(N-ethylpyridinium-2-yl) porphyrin, a superoxide dismutase and catalase mimic, blocked silica-stimulated cytokine production. We propose a pathway of iron-induced lipid peroxidation disrupting lipid rafts and signaling for the production of cytokines through PC-PLC in silica-exposed macrophages.

Effect of mesoporous silica under Neisseria meningitidis transformation process: environmental effects under meningococci transformation

Background

This study aimed the use of mesoporous silica under the naturally transformable Neisseria meningitidis, an important pathogen implicated in the genetic horizontal transfer of DNA causing a escape of the principal vaccination measures worldwide by the capsular switching process. This study verified the effects of mesoporous silica under N. meningitidis transformation specifically under the capsular replacement.

Methods

we used three different mesoporous silica particles to verify their action in N. meningitis transformation frequency.

Results

we verified the increase in the capsular gene replacement of this bacterium with the three mesoporous silica nanoparticles.

Conclusion

the mesouporous silica particles were capable of increasing the capsule replacement frequency in N. meningitidis.

Nanomaterials in humans: identification, characteristics, and potential damage

Nanomaterials are increasingly being used for commercial purposes. However, concerns about the potential risks of exposure to humans have been raised. We previously reported unusual pulmonary disease and death in a group of patients with occupational exposure to spray paint. However, the nanoparticle and chemical composition of the exposure was not fully described. The present study aimed to isolate and identify the nanoparticles observed in the patients' biopsies and report the potential deleterious effects to human lungs using electron microscopy. Using electron microscopy and energy dispersive x-ray analysis, silica nanoparticles were identified and characterized mainly in macrophages, pulmonary microvessels, vascular endothelial cells, microlymphatic vessels, pleural effusions, and a few in alveolar epithelial cells and pulmonary interstitial tissue (with no microscale particles present). Notably, damage to alveolar epithelial cells, macrophages, vascular endothelial cells, and the blood-gas barrier was observed. Given the well-documented toxicity of microscale silica, it is possible that these silica nanoparticles may have contributed in part to the illness reported in these workers. Such a possibility supports the adoption of controls and prevention strategies to minimize inhalation of nanoparticles by workers, and it highlights the urgent need and the importance of the nanosafety study in humans.

Occupational exposure to dusts and risk of renal cell carcinoma

BACKGROUND

Occupational exposures to dusts have generally been examined in relation to cancers of the respiratory system and have rarely been examined in relation to other cancers, such as renal cell carcinoma (RCC). Although previous epidemiological studies, though few, have shown certain dusts, such as asbestos, to increase renal cancer risk, the potential for other occupational dust exposures to cause kidney damage and/or cancer may exist. We investigated whether asbestos, as well as 20 other occupational dust exposures, were associated with RCC risk in a large European, multi-center, hospital-based renal case-control study.

METHODS

General occupational histories and job-specific questionnaires were reviewed by occupational hygienists for subject-specific information. Odds ratios (ORs) and 95% confidence intervals (95% CIs) between RCC risk and exposures were calculated using unconditional logistic regression.

RESULTS

Among participants ever exposed to dusts, significant associations were observed for glass fibres (OR: 2.1; 95% CI: 1.1-3.9), mineral wool fibres (OR: 2.5; 95% CI: 1.2-5.1), and brick dust (OR: 1.5; 95% CI: 1.0-2.4). Significant trends were also observed with exposure duration and cumulative exposure. No association between RCC risk and asbestos exposure was observed.

CONCLUSION

Results suggest that increased RCC risk may be associated with occupational exposure to specific types of dusts. Additional studies are needed to replicate and extend findings.

Adverse effect of nano-silicon dioxide on lung function of rats with or without ovalbumin immunization

BACKGROUND

The great advances of nanomaterials have brought out broad important applications, but their possible nanotoxicity and risks have not been fully understood. It is confirmed that exposure of environmental particulate matter (PM), especially ultrafine PM, are responsible for many lung function impairment and exacerbation of pre-existing lung diseases. However, the adverse effect of nanoparticles on allergic asthma is seldom investigated and the mechanism remains undefined. For the first time, this work investigates the relationship between allergic asthma and nanosized silicon dioxide (nano-SiO₂).

METHODOLOGY/PRINCIPAL FINDINGS

Ovalbumin (OVA)-treated and saline-treated control rats were daily intratracheally administered 0.1 ml of 0, 40 and 80 µg/ml nano-SiO₂ solutions, respectively for 30 days. Increased nano-SiO₂ exposure results in adverse changes on inspiratory and expiratory resistance (Ri and Re), but shows insignificant effect on rat lung dynamic compliance (Cldyn). Lung histological observation reveals obvious airway remodeling in 80 µg/ml nano-SiO₂-introduced saline and OVA groups, but the latter is worse. Additionally, increased nano-SiO₂ exposure also leads to more severe inflammation. With increasing nano-SiO₂ exposure, IL-4 in lung homogenate increases and IFN-γ shows a reverse but insignificant change. Moreover, at a same nano-SiO₂ exposure concentration, OVA-treated rats exhibit higher (significant) IL-4 and lower (not significant) IFN-γ compared with the saline-treated rats. The percentages of eosinophil display an unexpected result, in which higher exposure results lower eosinophil percentages.

CONCLUSIONS/SIGNIFICANCE

This was a preliminary study which for the first time involved the effect of nano-SiO₂ to OVA induced rat asthma model. The results suggested that intratracheal administration of nano-SiO₂ could lead to the airway hyperresponsiveness (AHR) and the airway remolding with or without OVA immunization. This occurrence may be due to the Th1/Th2 cytokine imbalance accelerated by the nano-SiO₂ through increasing the tissue IL-4 production.

Genotoxicity of carbon nanofibers: are they potentially more or less dangerous than carbon nanotubes or asbestos?

The production of carbon nanofibers and nanotubes (CNF/CNT) and their composite products is increasing globally. CNF are generating great interest in industrial sectors such as energy production and electronics, where alternative materials may have limited performance or are produced at a much higher cost. However, despite the increasing industrial use of carbon nanofibers, information on their potential adverse health effects is limited. In the current study, we examine the cytotoxic and genotoxic potential of carbon-based nanofibers (Pyrograf®-III) and compare this material with the effects of asbestos fibers (crocidolite) or single-walled carbon nanotubes (SWCNT). The genotoxic effects in the lung fibroblast (V79) cell line were examined using two complementary assays: the comet assay and micronucleus (MN) test. In addition, we utilized fluorescence in situ hybridization to detect the chromatin pan-centromeric signals within the MN indicating their origin by aneugenic (chromosomal malsegregation) or clastogenic (chromosome breakage) mechanisms. Cytotoxicity tests revealed a concentration- and time-dependent loss of V79 cell viability after exposure to all tested materials in the following sequence: asbestos>CNF>SWCNT. Additionally, cellular uptake and generation of oxygen radicals was seen in the murine RAW264.7 macrophages following exposure to CNF or asbestos but not after administration of SWCNT. DNA damage and MN induction were found after exposure to all tested materials with the strongest effect seen for CNF. Finally, we demonstrated that CNF induced predominantly centromere-positive MN in primary human small airway epithelial cells (SAEC) indicating aneugenic events. Further investigations are warranted to elucidate the possible mechanisms involved in CNF-induced genotoxicity.

Evidence from Chile that arsenic in drinking water may increase mortality from pulmonary tuberculosis

Arsenic in drinking water causes increased mortality from several cancers, ischemic heart disease, bronchiectasis, and other diseases. This paper presents the first evidence relating arsenic exposure to pulmonary tuberculosis, by estimating mortality rate ratios for Region II of Chile compared with Region V for the years 1958-2000. The authors compared mortality rate ratios with time patterns of arsenic exposure, which increased abruptly in 1958 in Region II and then declined starting in 1971. Tuberculosis mortality rate ratios in men started increasing in 1968, 10 years after high arsenic exposure commenced. The peak male 5-year mortality rate ratio occurred during 1982-1986 (rate ratio = 2.1, 95% confidence interval: 1.7, 2.6; P < 0.001) and subsequently declined. Mortality rates in women were also elevated but with fewer excess pulmonary tuberculosis deaths (359 among men and 95 among women). The clear rise and fall of tuberculosis mortality rate ratios in men following high arsenic exposure are consistent with a causal relation. The findings are biologically plausible in view of evidence that arsenic is an immunosuppressant and also a cause of chronic lung disease. Finding weaker associations in women is unsurprising, because this is true of most arsenic-caused health effects. Confirmatory evidence is needed from other arsenic-exposed populations.

Role of TNFR1 in lung injury and altered lung function induced by the model sulfur mustard vesicant, 2-chloroethyl ethyl sulfide

Lung toxicity induced by sulfur mustard is associated with inflammation and oxidative stress. To elucidate mechanisms mediating pulmonary damage, we used 2-chloroethyl ethyl sulfide (CEES), a model sulfur mustard vesicant. Male mice (B6129) were treated intratracheally with CEES (3 or 6 mg/kg) or control. Animals were sacrificed 3, 7 or 14 days later and bronchoalveolar lavage (BAL) fluid and lung tissue collected. Treatment of mice with CEES resulted in an increase in BAL protein, an indication of alveolar epithelial damage, within 3 days. Expression of Ym1, an oxidative stress marker also increased in the lung, along with inducible nitric oxide synthase, and at 14 days, cyclooxygenase-2 and monocyte chemotactic protein-1, inflammatory proteins implicated in tissue injury. These responses were attenuated in mice lacking the p55 receptor for TNFα (TNFR1-/-), demonstrating that signaling via TNFR1 is key to CEES-induced injury, oxidative stress, and inflammation. CEES-induced upregulation of CuZn-superoxide dismutase (SOD) and MnSOD was delayed or absent in TNFR1-/- mice, relative to WT mice, suggesting that TNFα mediates early antioxidant responses to lung toxicants. Treatment of WT mice with CEES also resulted in functional alterations in the lung including decreases in compliance and increases in elastance. Additionally, methacholine-induced alterations in total lung resistance and central airway resistance were dampened by CEES. Loss of TNFR1 resulted in blunted functional responses to CEES. These effects were most notable in the airways. These data suggest that targeting TNFα signaling may be useful in mitigating lung injury, inflammation and functional alterations induced by vesicants.

Silica induces cell cycle changes through PI-3K/AP-1 pathway in human embryo lung fibroblast cells

Exposure to silica is associated with progressive pulmonary inflammation and fibrosis. Our previous study had demonstrated silica exposure could cause cell cycle alternation and activator protein-1 (AP-1) activation. This study showed that silica exposure induced phosphorylation of p70S6 kinase (p70S6K) and Akt in human embryo lung fibroblasts (HELFs). These changes were blocked by overexpression of dominant-negative mutants of phosphatidylinositol-3 kinase (Δp85) or Akt (DN-Akt), respectively. Moreover, pretreatment of cells with rapamycin, a specific p70S6K inhibitor, could inhibit silica-induced cell cycle alteration, AP-1 activation, and phosphorylation of p70S6K, but had no effect on Akt phosphorylation. This suggested that phosphatidylinositol-3 kinase (PI-3K)/AP-1 pathway was likely responsible for cell cycle changes. Furthermore, we observed the effect of the pathway on cell cycle regulatory proteins. Our results indicated that inactivation of PI-3K, Akt, or p70S6K could inhibit silica-induced overexpression of cyclin D1 and cyclin-dependent kinase 4 (CDK4) and decreased expression of E2F-4. Taken together, silica could induce cell cycle changes through PI-3K/ AP-1 pathway in HELFs.

Fouling of nanostructured insect cuticle: adhesion of natural and artificial contaminants

The adhesional properties of contaminating particles of scales of various lengths were investigated for a wide range of micro- and nanostructured insect wing cuticles. The contaminating particles consisted of artificial hydrophilic (silica) and spherical hydrophobic (C(18)) particles, and natural pollen grains. Insect wing cuticle architectures with an open micro-/nanostructure framework demonstrated topographies for minimising solid-solid and solid-liquid contact areas. Such structuring of the wing membranes allows for a variety of removal mechanisms to contend with particle contact, such as wind and self-cleaning droplet interactions. Cuticles exhibiting high contact angles showed considerably lower particle adhesional forces than more hydrophilic insect surfaces. Values as low as 3 nN were recorded in air for silica of ~28 nm in diameter and <25 nN for silica particles 30 μm in diameter. A similar adhesional trend was also observed for contact with pollen particles.

The nanosilica hazard: another variable entity

Silica nanoparticles (SNPs) are produced on an industrial scale and are an addition to a growing number of commercial products. SNPs also have great potential for a variety of diagnostic and therapeutic applications in medicine. Contrary to the well-studied crystalline micron-sized silica, relatively little information exists on the toxicity of its amorphous and nano-size forms. Because nanoparticles possess novel properties, kinetics and unusual bioactivity, their potential biological effects may differ greatly from those of micron-size bulk materials. In this review, we summarize the physico-chemical properties of the different nano-sized silica materials that can affect their interaction with biological systems, with a specific emphasis on inhalation exposure. We discuss recent in vitro and in vivo investigations into the toxicity of nanosilica, both crystalline and amorphous. Most of the in vitro studies of SNPs report results of cellular uptake, size- and dose-dependent cytotoxicity, increased reactive oxygen species levels and pro-inflammatory stimulation. Evidence from a limited number of in vivo studies demonstrates largely reversible lung inflammation, granuloma formation and focal emphysema, with no progressive lung fibrosis. Clearly, more research with standardized materials is needed to enable comparison of experimental data for the different forms of nanosilicas and to establish which physico-chemical properties are responsible for the observed toxicity of SNPs.

Innate immune processes are sufficient for driving silicosis in mice

The lung is constantly exposed to potentially pathogenic particles and microorganisms. It has become evident recently that not only innate but also adaptive immune responses to particulates, such as SiO(2) entering the respiratory tract, are complex and dynamic events. Although the cellular mechanisms and anatomical consequences involved in the development of silicosis have been studied extensively, they still remain poorly understood. Based on their capacity for immune regulation, lymphocytes may play a key role in the respiratory response to environmental challenge by SiO(2). The objective of this study was to characterize the impact of SiO(2) exposure on respiratory immune processes, with particular emphasis on evaluating the importance of lymphocytes in the murine silicosis model. Therefore, lymphopenic mice, including NK-deficient, Rag1(-/-), or a combination (Rag1(-/-) NK-depleted), were used and demonstrated that SiO(2)-induced fibrosis and inflammation can occur independently of T, B, NK T, and NK cells. Studies in Rag1(-/-) mice suggest further that lymphocytes may participate in the regulation of SiO(2)-induced inflammation through modulation of the Nalp3 inflammasome. This observation may have clinical relevance in the treatment of inflammatory and fibrotic lung diseases that are refractory or respond suboptimally to current therapeutics.

Assessment of Serum Antioxidant Status in Patients with Silicosis

Prolonged exposure to silica dust causes an imbalance in the generation of free radicals and in the antioxidant system, thereby inducing oxidative stress. The antioxidant status of 113 silicosis patients and 116 control subjects without silicosis was examined. Serum superoxide dismutase (SOD) activity and serum levels of malondialdehyde (MDA) and glutathione (GSH) were significantly higher in silicosis patients than in controls. The GSH level in patients with stage I silicosis was higher than that in patients with other stages, but there was no difference in serum MDA level and SOD activity between disease stages. The GSH level of patients who worked with air drills was significantly lower than that of patients in other occupations, whereas the MDA level was significantly elevated in patients who used air drills. Serum SOD activity did not differ significantly according to the occupational group. It is concluded that the measurement of serum SOD, GSH and MDA levels could be beneficial in the clinical evaluation of serum antioxidant status in silicosis patients.

Increased micronucleus frequencies in surrogate and target cells from workers exposed to crystalline silica-containing dust

Mining, crushing, grinding, sandblasting and construction are high-risk activities with regard to crystalline silica exposure, especially in developing countries. Respirable crystalline silica (quartz and cristobalite) inhaled from occupational sources has been reclassified as a human carcinogen in 1997 by the International Agency for Research on Cancer. However, the biological activity of crystalline silica has been found to be variable among different industries, and this has formed the basis for further in vivo/in vitro mechanistic research and epidemiologic studies. This study was conducted for genotoxicity evaluation in a population of workers (e.g. glass industry workers, sandblasters, and stone grinders) mainly exposed to crystalline silica in four different workplaces in Turkey. The micronucleus (MN) assay was applied both in peripheral blood lymphocytes (PBL) as a surrogate tissue and in nasal epithelial cells (NEC) as a target tissue of the respiratory tract. Our study revealed significantly higher MN frequencies in the workers (n = 50) versus the control group (n = 29) (P < 0.001) and indicated a significant effect of occupational exposure on MN induction in both of the tissues. For the NEC target tissue, the difference in MN frequencies between the workers and control group was 3-fold, whereas in peripheral tissue, it was 2-fold. Respirable dust and crystalline silica levels exceeding limit values and mineralogical/elemental dust composition of the dust of at least 70% SiO(2) were used as markers of crystalline silica exposure in each of the workplaces. Moreover, 24% of the current workers were found to have early radiographical changes (profusion category of 1). In conclusion, although the PBL are not primary target cells for respiratory particulate toxicants, an evident increase in MN frequencies in this surrogate tissue was observed, alongside with a significant increase in NEC and may be an indicator of the accumulated genetic damage associated with crystalline silica exposure.

Ascorbic acid pre-treated quartz stimulates TNF-alpha release in RAW 264.7 murine macrophages through ROS production and membrane lipid peroxidation

BACKGROUND

Inhalation of crystalline silica induces a pulmonary fibrotic degeneration called silicosis caused by the inability of alveolar macrophages to dissolve the crystalline structure of phagocytosed quartz particles. Ascorbic acid is capable of partially dissolving quartz crystals, leading to an increase of soluble silica concentration and to the generation of new radical sites on the quartz surface. The reaction is specific for the crystalline forms of silica. It has been already demonstrated an increased cytotoxicity and stronger induction of pro-inflammatory cyclooxygenase-2 (COX-2) by ascorbic acid pre-treated quartz (QA) compared to untreated quartz (Q) in the murine macrophage cell line RAW 264.7.

METHODS

Taking advantage of the enhanced macrophage response to QA as compared to Q particles, we investigated the first steps of cell activation and the contribution of early signals generated directly from the plasma membrane to the production of TNF-alpha, a cytokine that activates both inflammatory and fibrogenic pathways.

RESULTS

Here we demonstrate that TNF-alpha mRNA synthesis and protein secretion are significantly increased in RAW 264.7 macrophages challenged with QA as compared to Q particles, and that the enhanced response is due to an increase of intracellular ROS. Plasma membrane-particle contact, in the absence of phagocytosis, is sufficient to trigger TNF-alpha production through a mechanism involving membrane lipid peroxidation and this appears to be even more detrimental to macrophage survival than particle phagocytosis itself.

CONCLUSION

Taken together these data suggest that an impairment of pulmonary macrophage phagocytosis, i.e. in the case of alcoholic subjects, could potentiate lung disease in silica-exposed individuals.

Suppressive oligodeoxynucleotides inhibit silica-induced pulmonary inflammation

Inhalation of silica-containing dust particles induces silicosis, an inflammatory disease of the lungs characterized by the infiltration of macrophages and neutrophils into the lungs and the production of proinflammatory cytokines, chemokines, and reactive oxygen species (ROS). Synthetic oligodeoxynucleotides (ODN) expressing "immunosuppressive motifs" were recently shown to block pathologic inflammatory reactions in murine models of autoimmune disease. Based on those findings, the potential of suppressive ODN to prevent acute murine silicosis was examined. In vitro studies indicate that suppressive ODN blunt silica-induced macrophage toxicity. This effect was associated with a reduction in ROS production and p47phox expression (a subunit of NADPH oxidase key to ROS generation). In vivo studies show that pretreatment with suppressive (but not control) ODN reduces silica-dependent pulmonary inflammation, as manifest by fewer infiltrating cells, less cytokine/chemokine production, and lower levels of ROS (p < 0.01 for all parameters). Treatment with suppressive ODN also reduced disease severity and improved the survival (p < 0.05) of mice exposed to silica.

A comparative study of grape seed extract and vitamin E effects on silica-induced pulmonary fibrosis in rats

Due to the production of reactive oxygen species (ROS), oxidative stress has been implicated in the pathogenesis of silica-induced lung fibrosis. So it is hypothesized that grape seed extract (GSE) or vitamin E (Vit E) as antioxidants may ameliorate some symptoms of the disease. Male Wistar albino rats were divided into 7 groups: rats in group I instilled intratracheally (IT) with a single dose of silica suspension (50mg/rat) as positive control (PC). Treatment groups (II-IV) received Vit E (20 IU/kg/day), GSE (150 mg/kg/day), or Vit E+GSE simultaneously orally 1 day after instillation of silica. Groups V and VI were given oral GSE or Vit E after instillation of the equivalent volume of saline (IT) as controls for GSE or Vit E. Rats of group VII only instilled saline (IT) as negative control. After 90 days animals were sacrificed and plasma-malondialdehyde (p-MDA) and lung tissue hydroxyproline (HP) were quantified. The lungs were also investigated for histopathological changes. The mean concentrations of p-MDA and HP in studied groups (I-VII) were 1.95, 2.77, 0.72, 0.81, 0.64, 0.94, 1.02 micromolMDA/L(plasma) and 28.476, 27.85, 22.83, 22.64, 15.40, 18.31, 18.51 mgHP/g(tissue), respectively. Silica caused a significant increase in HP content of lungs and MDA levels in the plasma except in GSE-treated groups (III and IV). According to the results of this study GSE could reduce the fibrogenic effect of silica. However; no synergistic effect was observed after co-administration of GSE and Vit E.

Impact of the FcgammaII-receptor on quartz uptake and inflammatory response by alveolar macrophages

The inflammatory response following particle inhalation is described as a key event in the development of lung diseases, e.g., fibrosis and cancer. The essential role of alveolar macrophages (AM) in the pathogenicity of particles through their functions in lung clearance and mediation of inflammation is well known. However, the molecular mechanisms and direct consequences of particle uptake are still unclear. Inhibition of different classic phagocytosis receptors by flow cytometry shows a reduction of the dose-dependent quartz particle (DQ12) uptake in the rat AM cell line NR8383. Thereby the strongest inhibitory effect was observed by blocking the FcgammaII-receptor (FcgammaII-R). Fluorescence immunocytochemistry, demonstrating FcgammaII-R clustering at particle binding sites as well as transmission electron microscopy, visualizing zippering mechanism-like morphological changes, confirmed the role of the FcgammaII-R in DQ12 phagocytosis. FcgammaII-R participation in DQ12 uptake was further strengthened by the quartz-induced activation of the Src-kinase Lyn, the phospho-tyrosine kinases Syk (spleen tyrosine kinase) and PI3K (phosphatidylinositol 3-kinase), as shown by Western blotting. Activation of the small GTPases Rac1 and Cdc42, shown by immunoprecipitation, as well as inhibition of tyrosine kinases, GTPases, or Rac1 provided further support for the role of the FcgammaII-R. Consistent with the uptake results, FcgammaII-R activation with its specific ligand caused a similar generation of reactive oxygen species and TNF-alpha release as observed after treatment with DQ12. In conclusion, our results indicate a major role of FcgammaII-R and its downstream signaling cascade in the phagocytosis of quartz particles in AM as well as in the associated generation and release of inflammatory mediators.

Silica suppresses Toll-like receptor ligand-induced dendritic cell activation

Inhalation of silica, without evidence of silicosis, is believed to predispose individuals to bacterial infections and impair respiratory immune functions. Silica may alter the sensitivity of antigen-presenting cells (APCs), such as macrophages and dendritic cells (DCs), to other types of infection; however, the exact nature of these exchanges remains uncertain. The purpose of the present study is to characterize the effect of silica exposure on innate pulmonary defense mechanisms following Toll-like receptor (TLR) ligand-induced activation using DCs as a model APC and determine whether these signals act in synergy or opposition to one another. Using C57Bl/6 mice, pattern recognition receptor expression on DCs was examined in vitro and in vivo using flow cytometry, and the activation state of pulmonary and granulocyte-macrophage colony-stimulating factor-derived DCs was assessed in response to silica in combination with TLR ligands (lipopolysaccharide, cytosine-phosphate-guanine, or polyinosinic:polycytidylic acid) using flow cytometry and measurement of cytokine production. In this study, silica attenuated TLR ligand-dependent DC activation with regards to accessory molecule expression as well as nitric oxide and inflammatory cytokine production. Furthermore, silica's ability to modulate TLR ligand-dependent DC activation did not appear to be dependent on the class A scavenger receptors. Taken together, silica's ability to alter susceptibility to infection may be due to impaired inflammatory responses and reduced antibacterial activity.

The IL-4Ralpha pathway in macrophages and its potential role in silica-induced pulmonary fibrosis

Crystalline silica exposure can result in pulmonary fibrosis, where the pulmonary macrophage is key as a result of its ability to react to silica particles. In the mouse silicosis model, there is initial Th1-type inflammation, characterized by TNF-alpha and IFN-gamma. Previous studies determined that Th2 mediators (i.e., IL-13) are vital to development of pulmonary fibrosis. The present study, using in vivo and in vitro techniques, compares silica exposures between Balb/c and Th2-deficient mice in an effort to determine the link between Th2 immunity and silicosis. In long-term experiments, a significant increase in fibrosis and activated interstitial macrophages was observed in Balb/c but not IL-4Ralpha(-/-) mice. Additionally, a significant increase in Ym1 mRNA levels, a promoter of Th2 immunity, was determined in the interstitial leukocyte population of silica-exposed Balb/c mice. To elucidate the effects of silica on macrophage function, bone marrow-derived macrophages (BMdM) were exposed to particles and assayed for T cell (TC) stimulation activity. As a control, Ym1 mRNA expression in Balb/c BMdM was determined using IL-4 stimulation. In the in vitro assay, a significant increase in TC activation, as defined by surface markers and cytokines, was observed in the cultures containing the silica-exposed macrophages in wild-type and IL-4Ralpha(-/-) mice, with one exception: IL-4Ralpha(-/-) BMdM were unable to induce an increase in IL-13. These results suggest that crystalline silica alters cellular functions of macrophages, including activation of TC, and that the increase in Th2 immunity associated with silicosis is via the IL-4Ralpha-Ym1 pathway.

Antigen-presenting cell population dynamics during murine silicosis

Silicosis is an occupational lung disease resulting from the inhalation of silica particles over prolonged periods of time, which causes chronic inflammation and progressive pulmonary fibrosis. Alveolar macrophages (AM) are critical effector cells, while less is known about the role and function of pulmonary dendritic cells (DC) in silicosis. We hypothesize that a balance exists between the suppressive nature of AM and the stimulatory capacity of DC to regulate lung immunity, and that this equilibrium may be overcome by silica exposure in vivo. Our results demonstrate that in response to silica exposure, both the percent and absolute number of AM significantly decreased over time, with a concomitant significant increase in DC. Both AM and DC exhibited cellular activation in response to silica, indicated by increased expression of cell surface markers. In the absence of silica-induced AM apoptosis (TNFR 1/2-null and Gld mice), no change was observed in the percent or absolute number of either cell type. Furthermore, bone marrow-derived DC, but not bone marrow-derived macrophages, migrated from the alveoli into the lung parenchyma in response to silica, resulting in significantly increased numbers of activated T lymphocytes. Collectively, the results demonstrate that AM and DC are distinct antigen-presenting cells within the respiratory tract that respond to silica exposure in vivo in unique ways, with significant implications for immune reactivity of the lung in response to environmental pathogens.

Toxicity and carcinogenicity mechanisms of fibrous antigorite

We studied the effects of fibrous antigorite on mesothelial MeT-5A and monocyte-macrophage J774 cell lines to further understand cellular mechanisms induced by asbestos fibers leading to lung damage and cancer. Antigorite is a mineral with asbestiform properties, which tends to associate with chrysotile or tremolite, and frequently occurs as the predominant mineral in the veins of several serpentinite rocks found abundantly in the Western Alps. Particles containing antigorite are more abundant in the breathing air of this region than those typically found in urban ambient air. Exposure of MeT-5A and J774 cells to fibrous antigorite at concentrations of 5-100 microg/ml for 72 hr induced dose-dependent cytotoxicity. Antigorite also stimulated the ROS production, induced the generation of nitrite and PGE2. MeT-5A cells were more sensitive to antigorite than J774 cells. The results of this study revealed that the fibrous antigorite stimulates cyclooxygenase and formation of hydroxyl and nitric oxide radicals. These changes represent early cellular responses to antigorite fibers, which lead to a host of pathological and neoplastic conditions because free radicals and PGE2 play important roles as mediators of tumor pathogenesis. Understanding the mechanisms of the cellular responses to antigorite and other asbestos particles should be helpful in designing rational prevention and treatment approaches.

Genetic polymorphisms in alveolar macrophage response-related genes, and risk of silicosis and pulmonary tuberculosis in Chinese iron miners

Alveolar macrophages (AMs) play a prominent role in influencing the development of lung inflammation and injury. The aim of this study is to investigate the roles of AMs response-related genes TNF-alpha, iNOS, and NRAMP1 (SLC11A1) in susceptibility to silicosis and pulmonary tuberculosis (PTB), and to analyze the interaction of dust exposure and genetic susceptibility to silicosis, interactions of TNF-alpha-308 and Natural Resistance-associated Macrophage Protein 1 (NRAMP1) INT4, D543N polymorphisms to PTB. Several epidemiological designs were used: retrospective investigations on dust exposure, case-control studies of 184 silicosis cases and 111 miners occupationally exposed to silica dust, and 1:2 matched case-control studies of 61 PTB cases and 122 PTB-free miners. The miners and controls were recruited from an iron mining operation in Anhui province, China. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was applied to detect single nucleotide polymorphisms. Despite the recruitment of high dust exposure among the controls, silicosis patients still had significantly higher dust exposure than controls (242.6 +/- 98.8 vs. 217.6 +/- 100.7 mg a/m(3)). The mutation of iNOS Ser608Leu is associated with protection against silicosis and against severity of silicosis in the miners. There is a 0.47-fold (95% CI: 0.28-0.79) decrease in risk of silicosis for individuals with C/T, T/T genotype compared with the wild-type homozygous (C/C) individuals after adjustment for occupational exposure, smoking, and drinking. The protection effect of the iNOS polymorphism was particularly detected in the > or = 150 mg a/m(3) exposure group (OR: 0.44, 95% CI: 0.22-0.91). However, no interaction of dust exposure with the iNOS polymorphism was observed. Furthermore, the variant NRAMP1 INT4 genotype is significantly associated with PTB in miners. No association of other polymorphisms (NRAMP1 D543N, TNF-alpha-308) and susceptibility to silicosis or PTB in Chinese miners was found. Our data showed a 3.26-fold (95% CI: 1.47-7.23) increased risk of PTB for miners carrying both the NRAMP1 D543N G/G and NRAMP1 INT4 G/C+C/C genotypes. Additionally, in miners with TNF-alpha-308 G/G genotype, the risk of PTB increased 2.38-fold if they carry the NRAMP1 INT4 G/C+C/C genotype (95% CI: 1.14-4.98). In conclusion, the C>T mutation of iNOS Ser608Leu may be an important protective factor to miners. On the other hand, the variant NRAMP1 INT4 may play a role in the development of PTB in Chinese miners. Therefore, the novel information can be used as guideline for further mechanistic investigations and for strengthening specific protection protocols for workers.

Comparative in vitro toxicity of grape- and citrus-farm dusts

Agricultural workers are exposed to a variety of airborne dusts, including crystalline silica and other inorganic minerals. This study was designed to characterize the organic and inorganic components of agricultural dusts in California grape- and citrus-farm fields and to compare their cytotoxicity using in vitro toxicity bioassays as predictors of pathogenicity. Aerosolized dusts collected from farm fields were characterized by scanning-electron-microscopic energy-dispersive x-ray analysis, x-ray diffraction, trace metal analysis by plasma emission spectroscopy, and surface area measurements. As indicators of cytotoxicity, cell viability, release of alveolar enzymes activities (lactate dehydrogenase, N-acetyl glucosaminidase), production of reactive oxygen species (ROS), such as H2O2 and hydroxyl radical (OH), and lipid peroxidation were monitored after exposure of cells to grape- and citrus-farm dusts or inorganic components of these dusts. In addition, activation of nuclear factor kappa B and activator protein-1 were evaluated at the peak time for response of 36 h postexposure. All toxicity studies were done in comparison with crystalline silica of similar particle size and diameter using the same mass concentrations as farm dusts. The results showed that inorganic minerals in the aerosolized farm dust fractions were mostly composed of aluminum silicates, crystalline silica, and free iron. Crystalline silica used in these studies was more cytotoxic than grape- and citrus-farm dusts. However, in general, citrus farm dust exhibited the greatest ability to generate ROS and induce lipid peroxidation. These results support human epidemiologic studies, reporting an increased incidence of pulmonary fibrosis in farm workers, by documenting the potential of farm dusts to induce oxidative stress and initiate disease development.

Ascorbic acid-pretreated quartz enhances cyclo-oxygenase-2 expression in RAW 264.7 murine macrophages

Exposure to quartz particles induces a pathological process named silicosis. Alveolar macrophages initiate the disease through their activation, which is the origin of the later dysfunctions. Ascorbic acid is known to selectively dissolve the quartz surface. During the reaction, ascorbic acid progressively disappears and hydroxyl radicals are generated from the quartz surface. These observations may be relevant to mammalian quartz toxicity, as substantial amounts of ascorbic acid are present in the lung epithelium. We studied the inflammatory response of the murine macrophage cell line RAW 264.7 incubated with ascorbic acid-treated quartz, through the expression and activity of the enzyme cyclo-oxygenase-2 (COX-2). COX-2 expression and prostaglandin secretion were enhanced in cells incubated with ascorbic acid-treated quartz. In contrast, no changes were observed in cells incubated with Aerosil OX50, an amorphous form of silica. Quantification of COX-2 mRNA showed a threefold increase in cells incubated with ascorbic acid-treated quartz compared with controls. The transcription factors, NF-kappaB, pCREB and AP-1, were all implicated in the increased inflammatory response. Reactive oxygen species (H(2)O(2) and OH(*)) were involved in COX-2 expression in this experimental model. Parallel experiments performed on rat alveolar macrophages from bronchoalveolar lavage confirmed the enhanced COX-2 expression and activity in the cells incubated with ascorbic acid-treated quartz compared with untreated quartz. In conclusion, the selective interaction with, and modification of, quartz particles by ascorbic acid may be a crucial event determining the inflammatory response of macrophages, which may subsequently develop into acute inflammation, eventually leading to the chronic pulmonary disease silicosis.

Silica induces macrophage cytokines through phosphatidylcholine-specific phospholipase C with hydrogen peroxide

Silica particle-associated inflammation is implicated in the genesis of several pulmonary diseases, including silicosis and lung cancer. In this study we investigated the role of phosphatidylcholine-specific phospholipase C (PC-PLC) in silica-stimulated induction of TNF-alpha and IL-1beta and how PC-PLC activity is regulated by silica in a rat alveolar macrophage model. We demonstrated that inhibition of PC-PLC, which was achieved with tricychodecan-9-yl-xanthate (D609), blocked the silica-stimulated induction of TNF-alpha and IL-1beta in alveolar macrophage, suggesting that PC-PLC is involved in the silica-associated inflammatory response. PC-PLC activity was increased significantly by silica exposure, and this could be inhibited by MnTBAP, which catalyzes both the dismutation of O2.- to O2 and H2O2 and the dismutation of H2O2 to O2 and H2O, revealing that PC-PLC activity is regulated in a redox-dependent manner. This is further confirmed by the finding that PC-PLC activity was increased by exogenous H2O2. The intracellular calcium chelator BAPTA blocked the H2O2-increased PC-PLC activity, while the calcium ionophore, A23187, enhanced PC-PLC activity. The data indicate that PC-PLC plays critical roles in the silica-associated inflammatory response and that PC-PLC is regulated through redox- and calcium-dependent manners in alveolar macrophages.

Fibrose maciça progressiva em trabalhadores expostos à sílica: achados na tomografia computadorizada de alta resolução

OBJETIVO: Avaliar as características radiológicas das massas conglomeradas pela tomografia computadorizada de alta resolução de tórax. MÉTODOS: Foram selecionados 75 pacientes silicóticos, a maioria jateadores de areia, portadores de fibrose maciça progressiva, atendidos no Hospital Universitário Antônio Pedro entre 1986 e 2004. Os pacientes foram submetidos a avaliação clínica, radiografia simples de tórax e tomografia computadorizada de alta resolução. RESULTADOS: Mais da metade dos pacientes com silicose complicada mostrou na radiografia de tórax grandes opacidades dos tipos B e C, denotando a gravidade da doença nesses pacientes. Dos 75 casos, apenas um apresentou massa unilateral simulando câncer de pulmão. Quarenta e quatro pacientes realizaram tomografia computadorizada de alta resolução do tórax. As massas predominaram nos terços superiores e posteriores (88,6%). Broncograma aéreo e calcificações no interior das massas foram observados em 70,4% e 63,8% dos casos, respectivamente. História de tuberculose foi relatada em 52% dos pacientes estudados. CONCLUSÃO: Na grande maioria dos casos as massas eram bilaterais, predominando nas regiões póstero-superiores dos pulmões, com broncogramas aéreos e calcificações de permeio. Associação com calcificações linfonodais foi um achado freqüente. A exposição a elevadas concentrações de poeira e a tuberculose foram consideradas fatores de risco para o desenvolvimento da fibrose maciça progressiva.

Essential role of ROS-mediated NFAT activation in TNF-alpha induction by crystalline silica exposure

Occupational exposure to crystalline silica has been associated with progressive pulmonary silicosis and lung cancer, but the underlying molecular mechanisms are not well understood. Previous studies have shown that crystalline silica exposure can generate reactive oxygen species (ROS) and induce the expression of the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) in cells. TNF-alpha is believed to be critical in the development of silica-related diseases. Thus it will be of significance to understand the mechanisms of TNF-alpha induction by silica exposure. Given the fact that the transcription factor nuclear factor of activated T cells (NFAT) plays an important role in the regulation of TNF-alpha and can also be activated by ROS, in this study we investigated the potential role of ROS in silica-induced NFAT activity as well as TNF-alpha expression in Cl41 cells. The results showed that exposure of cells to silica led to NFAT transactivation and TNF-alpha induction, where superoxide anion radical (O(2)(-).), but not H(2)O(2), was involved. The knockdown of NFAT3 by its specific small interfering RNA significantly attenuated the silica-induced TNF-alpha transcription. This study demonstrated that silica was able to activate NFAT in an O(2)(-).-dependent manner, which was required for TNF-alpha induction.