Omega-3 fatty acid intake suppresses induction of diverse autoantibody repertoire by crystalline silica in lupus-prone mice

Inhalation of crystalline silica (cSiO2) in the workplace is etiologically linked to lupus and other autoimmune diseases. Exposing lupus-prone NZBWF1 mice to respirable cSiO2 unleashes a vicious cycle of inflammation and cell death in the lung that triggers interferon-regulated gene expression, ectopic lymphoid structure (ELS) development, elevation of local and systemic autoantibodies (AAbs), and glomerulonephritis. However, cSiO2-induced inflammation and onset of autoimmunity can be prevented by inclusion of the ω-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) into the diet of these mice. Since cSiO2 both causes cell death and interferes with efferocytosis, secondary necrosis of residual cell corpses might provide a rich and varied autoantigen (AAg) source in the lung. While it is known that the particle induces anti-nuclear and anti-dsDNA AAbs in NZBWF1 mice, the full extent of the cSiO2-induced AAb response relative to specificity and isotype is not yet understood. The purpose of this study was to test the hypotheses that cSiO2 exposure induces a wide spectrum of AAbs in the pulmonary and systemic compartments, and that dietary DHA intervention prevents these changes. Archived tissue fluid samples were obtained from a prior study in which NZBWF1 mice were fed purified isocaloric diets containing no DHA (control) or DHA corresponding calorically to human doses of 2 and 5 g/day. Mice were intranasally instilled with 1 mg cSiO2 or saline vehicle weekly for 4 weeks, then groups euthanized 1, 5, 9, or 13 weeks post-instillation (PI) of the last cSiO2 dose. Bronchoalveolar lavage fluid (BALF) and plasma from each time point were subjected to AAb profiling using a microarray containing 122 AAgs. cSiO2 triggered robust IgG and IgM AAb responses against lupus-associated AAgs, including DNA, histones, ribonucleoprotein, Smith antigen, Ro/SSA, La/SSB, and complement as early as 1 week PI in BALF and 5 weeks PI in plasma, peaking at 9 and 13 weeks PI, respectively. Importantly, cSiO2 also induced AAbs to AAgs associated with rheumatoid arthritis (collagen II, fibrinogen IV, fibrinogen S, fibronectin, and vimentin), Sjögren's syndrome (α-fodrin), systemic sclerosis (topoisomerase I), vasculitis (MPO and PR3), myositis (Mi-2, TIF1-γ, MDA5), autoimmune hepatitis (LC-1), and celiac disease (TTG). cSiO2 elicited comparable but more modest IgA AAb responses in BALF and plasma. cSiO2-induced AAb production was strongly associated with time dependent inflammatory/autoimmune gene expression, ELS development, and glomerulonephritis. AAb responses were dose-dependently suppressed by DHA supplementation and negatively correlated with the ω-3 index, an erythrocyte biomarker of ω-3 content in tissue phospholipids. Taken together, these findings suggest that cSiO2 exposure elicits a diverse multi-isotype repertoire of AAbs, many of which have been reported in individuals with lupus and other autoimmune diseases. Furthermore, induction of this broad AAb spectrum could be impeded by increasing ω-3 tissue content via dietary DHA supplementation.

Respiratory surveillance for coal mine dust and artificial stone exposed workers in Australia and New Zealand: A position statement from the Thoracic Society of Australia and New Zealand

Coal mine lung dust disease (CMDLD) and artificial stone (AS) silicosis are preventable diseases which have occurred in serious outbreaks in Australia recently. This has prompted a TSANZ review of Australia's approach to respiratory periodic health surveillance. While regulating respirable dust exposure remains the foundation of primary and secondary prevention, identification of workers with early disease assists with control of further exposure, and with the aims of preserving lung function and decreasing respiratory morbidity in those affected. Prompt detection of an abnormality also allows for ongoing respiratory specialist clinical management. This review outlines a medical framework for improvements in respiratory surveillance to detect CMDLD and AS silicosis in Australia. This includes appropriate referral, improved data collection and interpretation, enhanced surveillance, the establishment of a nationwide Occupational Lung Disease Registry and an independent advisory group. These measures are designed to improve health outcomes for workers in the coal mining, AS and other dust-exposed and mining industries.

p62/SQSTM1 accumulation due to degradation inhibition and transcriptional activation plays a critical role in silica nanoparticle-induced airway inflammation via NF-κB activation

BACKGROUND

Most nanoparticles (NPs) reportedly block autophagic flux, thereby upregulating p62/SQSTM1 through degradation inhibition. p62 also acts as a multifunctional scaffold protein with multiple domains, and is involved in various cellular processes. However, the autophagy substrate-independent role of p62 and its regulation at the transcriptional level upon NPs exposure remain unclear.

RESULTS

In this work, we exposed BEAS-2b cells and mice to silica nanoparticles (SiNPs), and found that SiNPs increased p62 protein levels in vivo and vitro. Then, we further explored the role and mechanism of SiNPs-stimulated p62 in vitro, and found that p62 degradation was inhibited due to autophagic flux blockade. Mechanistically, SiNPs blocked autophagic flux through impairment of lysosomal capacity rather than defective autophagosome fusion with lysosomes. Moreover, SiNPs stimulated translocation of NF-E2-related factor 2 (Nrf2) to the nucleus from the cytoplasm, which upregulated p62 transcriptional activation through direct binding of Nrf2 to the p62 promoter. Nrf2 siRNA dramatically reduced both the mRNA and protein levels of p62. These two mechanisms led to p62 protein accumulation, thus increasing interleukin (IL)-1 and IL-6 expression. SiNPs activated nuclear factor kappa B (NF-κB), and this effect could be alleviated by p62 knockdown.

CONCLUSION

SiNPs caused accumulation of p62 through both pre- and post-translational mechanisms, resulting in airway inflammation. These findings improve our understanding of SiNP-induced pulmonary damage and the molecular targets available to mitigate it.

Silico-tuberculosis, silicosis and other respiratory morbidities among sandstone mine workers in Rajasthan- a cross-sectional study

BACKGROUND

Exposures to respirable crystalline silica causes silicosis, pulmonary tuberculosis, chronic obstructive pulmonary disease, lung cancer, autoimmune disorders and chronic renal disease. The aim of this study was to find out the prevalence of silico-tuberculosis, silicosis and other respiratory morbidities in sandstone mine workers in Jodhpur district of Rajasthan.

METHODS

It was a cross-sectional study done in sandstone mines in Jodhpur. A total of 15 mines were selected. The sample size was calculated and fixed to 174 mine workers. Chi-square and t-test were applied to draw inferences.

RESULTS

The mean age of the mine workers was 39.13 ± 11.09 years. Three fourth (75.3%) of the workers were working for more than ten years in mines. Around 30.0% had a history of tuberculosis. Abnormal spirometry was found in 89.2% of workers. Around 42% of mine workers were found with abnormal chest x-rays. Prevalence of silicosis was 37.3%, silico-tuberculosis was 7.4%, tuberculosis was 10.0%, and other respiratory diseases like emphysema and pleural effusion were diagnosed among 4.3% workers.

CONCLUSION

Prevalence of silico-tuberculosis, silicosis and other respiratory morbidities are high among sandstone mine workers.

Association of Silica Dust Exposure and Cigarette Smoking With Mortality Among Mine and Pottery Workers in China

IMPORTANCE

The joint association of long-term silica dust exposure and cigarette smoking with mortality has not been well established.

OBJECTIVE

To evaluate the joint association of silica dust exposure and cigarette smoking with mortality in a large cohort of workers at mines and factories in China.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study included 44 708 adults who were employed in 20 metal mines and 9 pottery factories in central and southern China for at least 1 year between January 1, 1960, and December 31, 1974. Participants were retrospectively followed up to January 1, 1960, and prospectively followed up to December 31, 2003. Data analysis was conducted from April 5, 2019, to October 26, 2019.

EXPOSURES

Cumulative respirable silica dust exposure was estimated by linking a job-exposure matrix to participants' personal work histories. Cigarette smoking data were collected through participant questionnaires.

MAIN OUTCOMES AND MEASURES

The main outcome was mortality, with codes from the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) used to categorize diseases associated with mortality.

RESULTS

Among 44 708 participants, 38 221 (85.49%) were men, with a mean (SD) age at cohort entrance of 26.9 (8.1) years. A total of 13 700 deaths were observed during 1 534 005 person-years of follow-up, with a median follow-up period of 34.9 years (range, 4.8-43.9 years). Silica exposure was associated with a higher risk of mortality among individuals with all diseases, lung cancer, respiratory tuberculosis, cardiovascular diseases, and diseases of the respiratory system; cigarette smoking was associated with an increased risk of mortality among individuals with all diseases, lung cancer, respiratory tuberculosis, cerebrovascular diseases, and diseases of the respiratory tract. The hazard ratios for the joint association of silica dust exposure and cigarette smoking with mortality were 4.51 (95% CI, 3.23-6.29) for lung cancer, 3.21 (95% CI, 2.53-4.08) for certain infectious and parasitic diseases, 3.93 (95% CI, 2.99-5.15) for respiratory tuberculosis, 6.27 (95% CI, 4.83-8.15) for diseases of the respiratory system, and 12.52 (95% CI, 7.92-19.80) for pneumoconiosis, with a significant additive interaction (P < .001). The proportions of the joint association for the additive interaction of silica dust exposure and cigarette smoking were 21.63% for lung cancer, 42.12% for certain infectious and parasitic diseases, 42.25% for respiratory tuberculosis, 29.55% for diseases of the respiratory system, and 36.46% for pneumoconiosis.

CONCLUSIONS AND RELEVANCE

These findings suggest that cigarette smoking is associated with an increased risk of mortality in individuals exposed to silica dust. Smoking cessation and the control of silica dust concentrations may be important for reducing the risk of mortality among individuals exposed to silica.

Occupational exposure to silica and risk of heart disease: a systematic review with meta-analysis

OBJECTIVE

To search for evidence of the relationship between occupational silica exposure and heart disease.

DESIGN

A systematic review and meta-analysis.

BACKGROUND

Growing evidence suggests a relationship between occupational silica exposure and heart disease; however, the link between them is less clear.

DATA SOURCES

PubMed, ScienceDirect, Springer and EMBASE were searched for articles published between 1 January 1995 and 20 June 2019. Articles that investigated the effects of occupational silica exposure on the risk of heart disease were considered.

STUDY SELECTION

We included cohort studies, including prospective, retrospective and retroprospective studies.

DATA EXTRACTION AND SYNTHESIS

We extracted data using a piloted data collection form and conducted random-effects meta-analysis and exposure-response analysis. The meta-relative risk (meta-RR), a measure of the average ratio of heart disease rates in those with and without silica exposure, was used as an inverse variance-weighted average of relative risks from the individual studies. The Newcastle-Ottawa Quality Assessment Scale for cohort studies was used for study quality assessment.

OUTCOME MEASURE

We calculated the risk of heart diseases such as pulmonary heart disease, ischaemic heart disease and others.

RESULTS

Twenty cohort studies were included. The results suggest a significant increase in the risk of overall heart disease (meta-RR=1.08, 95% CI 1.03 to 1.13). Stronger evidence of association with pulmonary heart disease was found in the risk estimate of both categories of heart disease (meta-RR=1.24, 95% CI 1.08 to 1.43) and in the exposure-response analysis (meta-RR=1.39, 95% CI 1.19 to 1.62). Our subgroup analyses also revealed that the statistical heterogeneity among studies could be attributed mainly to the diversity in reference group, occupation and study quality score.

CONCLUSIONS

Silica-exposed workers are at an increased risk for overall heart disease, especially pulmonary heart disease. Further research is needed to better clarify the relationship between occupational silica exposure and ischaemic heart disease.

PROSPERO REGISTRATION NUMBER

CRD42019124673.

Trehalose Alleviates Crystalline Silica-Induced Pulmonary Fibrosis via Activation of the TFEB-Mediated Autophagy-Lysosomal System in Alveolar Macrophages

Silicosis is an occupational lung disease characterized by persistent inflammation and irreversible fibrosis. Crystalline silica (CS) particles are mainly phagocytized by alveolar macrophages (AMs), which trigger apoptosis, inflammation, and pulmonary fibrosis. Previously, we found that autophagy-lysosomal system dysfunction in AMs was involved in CS-induced inflammation and fibrosis. Induction of autophagy and lysosomal biogenesis by transcription factor EB (TFEB) nuclear translocation can rescue fibrotic diseases. However, the role of TFEB in silicosis is unknown. In this study, we found that CS induced TFEB nuclear localization and increased TFEB expression in macrophages both in vivo and in vitro. However, TFEB overexpression or treatment with the TFEB activator trehalose (Tre) alleviated lysosomal dysfunction and enhanced autophagic flux. It also reduced apoptosis, inflammatory cytokine levels, and fibrosis. Both pharmacologically inhibition of autophagy and TFEB knockdown in macrophages significantly abolished the antiapoptotic and anti-inflammatory effects elicited by either TFEB overexpression or Tre treatment. In conclusion, these results uncover a protective role of TFEB-mediated autophagy in silicosis. Our study suggests that restoration of autophagy-lysosomal function by Tre-induced TFEB activation may be a novel strategy for the treatment of silicosis.

Crotoxin Conjugated to SBA-15 Nanostructured Mesoporous Silica Induces Long-Last Analgesic Effect in the Neuropathic Pain Model in Mice

Neuropathic pain is a disease caused by structural and functional plasticity in central and peripheral sensory pathways that produce alterations in nociceptive processing. Currently, pharmacological treatment for this condition remains a challenge. Crotoxin (CTX), the main neurotoxin of Crotalus durissus terrificus rattlesnake venom, has well described prolonged anti-inflammatory and antinociceptive activities. In spite of its potential benefits, the toxicity of CTX remains a limiting factor for its use. SBA-15 is an inert nanostructured mesoporous silica that, when used as a vehicle, may reduce toxicity and potentiate the activity of different compounds. Based on this, we propose to conjugate crotoxin with SBA-15 (CTX:SBA-15) in order to investigate if when adsorbed to silica, CTX would have its toxicity reduced and its analgesic effect enhanced in neuropathic pain induced by the partial sciatic nerve ligation (PSNL) model. SBA-15 enabled an increase of 35% of CTX dosage. Treatment with CTX:SBA-15 induced a long-lasting reduction of mechanical hypernociception, without modifying the previously known pathways involved in antinociception. Moreover, CTX:SBA-15 reduced IL-6 and increased IL-10 levels in the spinal cord. Surprisingly, the antinociceptive effect of CTX:SBA-15 was also observed after oral administration. These data indicate the potential use of the CTX:SBA-15 complex for neuropathic pain control and corroborates the protective potential of SBA-15.

Mesoporous Silica Nanoparticles Trigger Liver and Kidney Injury and Fibrosis Via Altering TLR4/NF-κB, JAK2/STAT3 and Nrf2/HO-1 Signaling in Rats

Mesoporous silica nanoparticles (MSNs) represent a promising inorganic platform for multiple biomedical applications. Previous studies have reported MSNs-induced hepatic and renal toxicity; however, the toxic mechanism remains unclear. This study aimed to investigate MSNs-induced hepatic and nephrotoxicity and test the hypothesis that altered TLR4/MyD88/NF-κB, JAK2/STAT3, and Nrf2/ARE/HO-1 signaling pathways mediate oxidative stress, inflammation, and fibrosis induced by MSNs. Rats were administered 25, 50, 100, and 200 mg/kg MSNs for 30 days, and samples were collected for analyses. MSNs induced functional and histologic alterations, increased the levels of reactive oxygen species (ROS), lipid peroxidation and nitric oxide, suppressed antioxidants, and Nrf2/HO-1 signaling in the liver and kidney of rats. MSNs up-regulated the expression of liver and kidney TLR4, MyD88, NF-κB p65, and caspase-3 and increased serum pro-inflammatory cytokines. In addition, MSNs activated the JAK2/STAT3 signaling pathway, down-regulated peroxisome proliferator activated receptor gamma (PPARγ), and promoted fibrosis evidenced by the increased collagen expression and deposition. In conclusion, this study conferred novel information on the role of ROS and deregulated TLR4/MyD88/NF-κB, JAK2/STAT3, PPARγ, and Nrf2/ARE/HO-1 signaling pathways in MSNs hepatic and nephrotoxicity. These findings provide experimental evidence for further studies employing genetic and pharmacological strategies to evaluate the safety of MSNs for their use in nanomedicine.

Association of wheat chaff derived silica fiber and esophageal cancer in north China

BACKGROUND

Despite decades of research and intervention programs, the epidemic of esophageal squamous cell carcinoma (ESCC) in the Taihang Mountain area of north China has not seen convincing explanation by any risk factor yet and the incidence has not seen a substantial decrease. Based on recently disclosed association of aridity and wheat consumption with esophageal cancer, we revisited the hypothesis of biogenic silica in esophageal cancer development.

METHODS

From the archives of the Pathology Department of Heping Hospital, Changzhi Medical College, we selected three pairs of formalin-fixed samples, tumor tissues and distant normal tissues, of three patients operated for ESCC who had no history of workplace exposure to silica dust. Two pairs of dried tissue samples were used for phytolith (silica body) analysis and another pair for microanalysis with Transmission Electron Microscope (TEM).

RESULTS

One of the phytoliths in ESCC tumor tissue was similar to the prickle hair on the surface of wheat bract. In the mineral particles detected in the tumor tissue the predominant elements were Si, Ca, and P, whereas Si signals were not obvious in the distant normal tissue.

CONCLUSIONS

The preliminary findings on the detection of phytoliths and the higher than normal Si concentration in ESCC tumor tissue warrants further testing the role of biogenic silica in esophageal cancer.

Assessment of neurotoxicity induced by different-sized Stöber silica nanoparticles: induction of pyroptosis in microglia

With the wide application of Stöber silica nanoparticles and their ability to access the brain, it is crucial to evaluate their neurotoxicity. In this study, we used three in vitro model cells, i.e., N9, bEnd.3 and HT22 cells, representing microglia, microendothelial cells and neurons, respectively, to assess the neurotoxicity of Stöber silica nanoparticles with different sizes. We found that Stöber silica nanoparticles almost had no effect on the viability of bEnd.3 and HT22 cells. In contrast, they induced size-dependent toxicity in N9 cells, which represent the residential macrophages of the central nervous system. Further mechanistic study demonstrated that the toxicity in N9 cells was related to their surface silanol display. In addition, we demonstrated that Stöber silica nanoparticles induced the production of mitochondrial ROS, release of IL-1β, cleavage of GSDMD, and occurrence of pyroptosis in N9 cells. Features of pyroptosis were also observed in primary microglia and macrophage J774A.1. In conclusion, these findings were helpful for the safety consideration of Stöber silica nanoparticles considering their wide applications in our daily life.

Autoimmune Pulmonary Alveolar Proteinosis Diagnosed after Exposure to a Fire Extinguisher Containing Silica Powder

We herein report a case of autoimmune pulmonary alveolar proteinosis (PAP) diagnosed after one-time exposure to silica powder. Owing to the misuse of a silica-containing fire extinguisher and the inhalation of large amounts of its powder, the patient experienced prolonged cough and visited our hospital. The findings of chest computed tomography and surgical lung biopsy specimens led to the diagnosis of PAP. Interestingly, the presence of anti-GM-CSF antibody was detected; therefore, both autoimmune characteristics and exposure to large amounts of silica may have caused the development of PAP in this patient. This case provides important insight into the mechanisms leading to the onset of PAP.

SPIO nanoparticle-labeled bone marrow mesenchymal stem cells inhibit pulmonary EndoMT induced by SiO2

Endothelial-mesenchymal transition (EndoMT) is a key step during lung fibrosis. Studies have shown that bone marrow mesenchymal stem cells (BMSCs) may act as therapeutic candidates for lung fibrosis. However, the effects of BMSCs on EndoMT induced by SiO₂ have not been elucidated, and means to label and track grafted cells have been lacking. The current study explored whether BMSCs prevented pulmonary fibrosis by targeting EndoMT, as well as analyzed the distribution of BMSCs labeled with superparamagnetic iron oxide (SPIO) nanoparticles during treatment. TIE2-GFP mice, human umbilical vein endothelial cells (HUVECs), and BMSCs labeled with SPIO nanoparticles were used to explore the distributions and therapeutic effects of BMSCs in vivo and in vitro. We found that BMSCs reversed lung fibrosis by targeting EndoMT in vivo. Furthermore, we show that BMSCs labeled with SPIO nanoparticles could be used to track stem cells reliably in the lungs for 14 days. Conditioned medium from BMSCs attenuated the increased functional changes and reversed the SiO₂-induced upregulation of ER stress and autophagy markers irrespective of whether they were nanoparticle labeled or not. Our findings identify novel methods to track labeled BMSCs with therapeutic potential.

Complex to simple: In vitro exposure of particulate matter simulated at the air-liquid interface discloses the health impacts of major air pollutants

Particulate matter (PM) exposure poses many adverse effects on human health. However, it is challenging to clearly differentiate between the contributions of individual pollutants on toxicity from complex mixtures of ambient air pollutants. The aim of this study is to generate aerosols constituted by silica nanoparticles (NPs) and bisulfate to serve as simulators of particle-associated high-sulfur air pollution. Then, the health impacts of sulfur dioxide were evaluated at the cellular level using an air-liquid interface (ALI) exposure chamber. BEAS-2B cells were exposed to either nano-silica or bisulfite aerosol individually or bisulfate-coated silica (SiO₂-NH₂@HSO₃) for 3 h using the ALI. The cellular toxicities were carefully compared based on the exposure dosages. The ALI exposure of SiO₂ NPs alone did not produce any apparent cytotoxicity in cells, but the aerosol exposure of SiO₂-NH₂@HSO₃ significantly decreased the cell viability and enhanced the production of cellular reactive oxygen species in a dose-dependent manner. Consequently, the excessive oxidative stress resulted in mitochondrial damage as well as cellular apoptosis. ALI exposure can possibly reflect the realistic physiological exposure condition of the human respiratory system. As a derivative of the sulfur dioxide component of air pollution, sulfate exacerbates the toxic effects of inhalable PMs. This result may be due to the large surface area of the nanoparticles, with the possibility of carrying more sulfite to the target cells during aerosol exposure. The sulfate levels offer a meaningful complement to the present PM_2.5 index of air pollution for achieving better human health protection.

A possible role of biogenic silica in esophageal cancer in North China?

Certain areas in North China have the highest incidence of esophageal squamous cell carcinoma (ESCC) in the world, which has not seen convincing explanation by any risk factor yet. Biogenic silica in millet bran was linked to ESCC in the early 1980s but the hypothesis was largely dismissed because of the lack of geographic correlation between millet consumption and ESCC. Later epidemiological studies disclosed the linkage of wheat consumption in North China to ESCC instead. Now, we hypothesize silica phytoliths (silicified bodies that have definite shapes) from wheat chaff are a major etiologic factor of ESCC in this region. This hypothesis is supported by the potentially high abundance of silica phytoliths on the bracts of wheat (Triticum aestivum) in North China due to favorable Si-accumulation genotype, arid climate, and siallitic soil with bioavailable Si. These silica phytoliths can contaminate wheat flour and cause repeated local injuries in the esophagus and stimulate proliferation by providing anchorage.

Initiation of Pulmonary Fibrosis after Silica Inhalation in Rats is linked with Dysfunctional Shelterin Complex and DNA Damage Response

Occupational exposure to silica has been observed to cause pulmonary fibrosis and lung cancer through complex mechanisms. Telomeres, the nucleoprotein structures with repetitive (TTAGGG) sequences at the end of chromosomes, are a molecular "clock of life", and alterations are associated with chronic disease. The shelterin complex (POT1, TRF1, TRF2, Tin2, Rap1, and POT1 and TPP1) plays an important role in maintaining telomere length and integrity, and any alteration in telomeres may activate DNA damage response (DDR) machinery resulting in telomere attrition. The goal of this study was to assess the effect of silica exposure on the regulation of the shelterin complex in an animal model. Male Fisher 344 rats were exposed by inhalation to Min-U-Sil 5 silica for 3, 6, or 12 wk at a concentration of 15 mg/m3 for 6 hr/d for 5 consecutive d/wk. Expression of shelterin complex genes was assessed in the lungs at 16 hr after the end of each exposure. Also, the relationship between increased DNA damage protein (γH2AX) and expression of silica-induced fibrotic marker, αSMA, was evaluated. Our findings reveal new information about the dysregulation of shelterin complex after silica inhalation in rats, and how this pathway may lead to the initiation of silica-induced pulmonary fibrosis.

iTRAQ-based secretome reveals that SiO2 induces the polarization of RAW264.7 macrophages by activation of the NOD-RIP2-NF-κB signaling pathway

Silicosis is characterized by inflammation and pulmonary fibrosis due to long-term inhalation of crystalline silica (SiO₂). To clarify the role of macrophage polarization in the inflammatory response of silicosis, we used iTRAQ-coupled 2D LC-MS/MS to study the change in the secretome in RAW264.7 macrophages. We successfully screened 330 differentially expressed proteins, including 120 proteins with upregulated expression and 210 proteins with down-regulated expression (p < 0.05). Bioinformatics analysis showed that the differentially expressed proteins were mainly involved in biological processes, such as oxidative stress, mitochondrial damage, apoptosis and acute inflammatory response. In particular, the expression levels of mitochondrial apoptosis-related proteins, such as AKT1, BAX, HSPD1, TNF, CASP8 and DAP, were increased after SiO₂ exposure. Taken together, our study indicated that SiO₂ could induce macrophage polarization by activation of the NOD-RIP2-NF-κB signaling pathway in RAW264.7 macrophages. This may represent a potential mechanism in the development of silicosis.

Combined effect of silica dust exposure and cigarette smoking on total and cause-specific mortality in iron miners: a cohort study

BACKGROUND

Both cigarette smoking and long-term exposure to crystalline silica dust were reported to be associated with increased mortality. However, the combined effect of both factors has not been well evaluated.

METHODS

We investigated a retro-prospective cohort of 7,665 workers from one Chinese iron mine with a median follow-up of 42.8 years. Cumulative silica exposure was estimated for each worker by linking work histories with a job-exposure matrix. Cigarette smoking information was collected through face-to-face questionnaires. Hazard ratios (HRs) for total and cause-specific mortality due to silica exposure and smoking were estimated using Cox proportional hazards models.

RESULTS

A total of 2,814 deaths occurred during 315,772.9 person-years of follow-up. Significantly elevated mortality from all causes, cardiovascular disease, non-malignant respiratory disease and lung cancer was observed among silica-exposed workers, while elevated mortality from non-malignant respiratory disease and lung cancer was observed among smokers. Combined exposure to silica dust and cigarette smoking elevated the proportion of mortality and accounted for 21.2, 76.0, 35.7 and 81.4% of all causes, non-malignant respiratory disease, cardiovascular disease, and lung cancer, respectively. Significant additive joint effects of silica exposure and cigarette smoking on mortality from lung cancer (HR 1.893, 95% CI 0.628 to 3.441) and pneumoconiosis (6.457, 0.725 to 39.114), together with a significant multiplicative joint effect from all causes (1.002, 1.000 to 1.004) were observed.

CONCLUSIONS

The present findings indicated that silica exposure in combination with cigarette smoking accounted for a fraction of extra deaths in our cohort. Our research showed the urgent need for smoking cessation and silica control among iron miners.

Lupus Pleuritis with Silicotic Nodules in the Parietal Pleura

A 63-year-old man with occupational exposure to silica presented with cutaneous ulcer, pleuritic pain, and a fever. Laboratory data showed lymphopenia and positive serum antinuclear and anti-DNA antibodies. Computed tomography of the chest showed egg shell-like calcification of the hilar and mediastinal lymph nodes without pulmonary parenchymal involvement of silicosis. A surgical biopsy showed silicotic nodules with surrounding infiltration of lymphocytes and plasma cells in the parietal pleura. With a diagnosis of systemic lupus erythematosus (SLE), systemic corticosteroid therapy was given, which led to the resolution of symptoms and laboratory abnormalities. We discuss the relationship between silica exposure and the development of SLE.

A Cohort Study of Workers Employed in a Refractory Brick Plant

A mortality study was carried out on a cohort of workers who were exposed to silica dust in a refractory brick plant. The cohort was divided into two groups: workers with and without silicosis, and their mortality was contrasted with the death rate of Genova from 1960 to 1979. Results show an increased risk for laryngeal tumors (3 obs., 0.44 exp., SMR = 682), nonmalignant respiratory disease (16 obs., 3.2 exp., SMR = 500), and cardiovascular diseases (19 obs., 11 exp., SMR = 173) among silicotics. The mortality rate for lung cancer showed an increase for the cohort of workers as a whole (11 obs., 6 exp., SMR = 183). The almost double overall mortality observed in silicotic subjects raises some doubts about the validity of other proportional mortality studies that showed no excesses for workers in these industries.

A Pathological Study of Acute Pulmonary Toxicity Induced by Inhaled Kanto Loam Powder

The frequency and volume of Asian sand dust (ASD) (Kosa) are increasing in Japan, and it has been reported that ASD may cause adverse respiratory effects. The pulmonary toxicity of ASD has been previously analyzed in mice exposed to ASD particles by intratracheal instillation. To study the pulmonary toxicity induced by inhalation of ASD, ICR mice were exposed by inhalation to 50 or 200 mg/m³ Kanto loam powder, which resembles ASD in elemental composition and particle size, for 6 h a day over 1, 3, 6, 9, or 15 consecutive days. Histological examination revealed that Kanto loam powder induced acute inflammation in the whole lung at all the time points examined. The lesions were characterized by infiltration of neutrophils and macrophages. The intensity of the inflammatory changes in the lung and number of neutrophils in both histological lesions and bronchoalveolar lavage fluid (BALF) appeared to increase over time. Immunohistochemical staining showed interleukin (IL)-6- and tumor necrosis factor (TNF)-α-positive macrophages and a decrease in laminin positivity in the inflammatory lesions of the lung tissues. Electron microscopy revealed vacuolar degeneration in the alveolar epithelial cells close to the Kanto loam particles. The nitric oxide level in the BALF increased over time. These results suggest that inhaled Kanto loam powder may induce diffuse and acute pulmonary inflammation, which is associated with increased expression of inflammatory cytokines and oxidative stress.

Total and Cause-Specific Mortality Risk Associated With Low-Level Exposure to Crystalline Silica: A 44-Year Cohort Study From China

The association between low-level crystalline silica (silica) exposure and mortality risk is not well understood. We investigated a cohort of 44,807 Chinese workers who had worked in metal mines or pottery factories for at least 1 year from January 1, 1960, to December 31, 1974, and were followed through 2003. Low-level silica exposure was defined as having a lifetime highest annual mean silica exposure at or under a permissible exposure limit (PEL). We considered 3 widely used PELs, including 0.05 mg/m3, 0.10 mg/m3, and 0.35 mg/m3. Cumulative silica exposure was estimated by linking a job exposure matrix with each participant's work history. For the 0.10-mg/m3 exposure level, Cox proportional hazards models showed significantly increased risk of mortality from all diseases (for each 1-ln mg/m3-years increase in logged cumulative silica exposure, hazard ratio (HR) = 1.05, 95% confidence interval (CI): 1.03, 1.07), malignant neoplasms (HR = 1.06, 95% CI: 1.03, 1.09), lung cancer (HR = 1.08, 95% CI: 1.02, 1.14), ischemic heart disease (HR = 1.09, 95% CI: 1.02, 1.16), pulmonary heart disease (HR = 1.08, 95% CI: 1.00, 1.16), and respiratory disease (HR = 1.20, 95% CI: 1.14, 1.26). The 0.05-mg/m3 and 0.35-mg/m3 exposure levels yielded similar associations. Long-term exposure to low levels (PELs ≤0.05 mg/m3, ≤0.10 mg/m3, or ≤0.35 mg/m3) of silica is associated with increased total and certain cause-specific mortality risk. Control of ambient silica levels and use of personal protective equipment should be emphasized in practice.

Risk of sarcoidosis and seropositive rheumatoid arthritis from occupational silica exposure in Swedish iron foundries: a retrospective cohort study

OBJECTIVE

To study the impact of occupational silica exposure on the incidence rates of sarcoidosis and rheumatoid arthritis (RA) in a cohort of exposed workers in Swedish iron foundries.

DESIGN

The prevalence of sarcoidosis and RA in a cohort of silica exposed workers was compared with the prevalence in the general Swedish population in this register study. A mixed model was used to calculate silica exposure, and individual silica exposures were used to compute dose responses.

SETTING

Personnel records from 10 iron foundries were used to identify workers whose employment began before 2005 which was then linked to the national non-primary outpatient visits register.

PARTICIPANTS

The final cohort consisted of 2187 silica-exposed male workers who had been employed for at least 1 year and were still alive without having emigrated when the follow-up study began. The cohort's employment period covers 23 807 person-years at risk.

MAIN OUTCOME

The presented results indicate that moderate to high levels of silica exposure increase risks for sarcoidosis and seropositive RA.

RESULTS

Mean levels of airborne silica dust in the foundries decreased significantly between the 1970s and 2000s. Incidence rates of sarcoidosis (3.94; 95% CI 1.07 to 10.08) and seropositive RA (2.59; 95% CI 1.24 to 4.76) were significantly higher among highly exposed individuals.

CONCLUSION

Our results reveal increased risks for sarcoidosis and seropositive RA among individuals with high exposure to silica dust (>0.048 mg/m³) compared with non-exposed and less-exposed groups.

Effects of Occupational Silica Exposure on OXIDATIVE Stress and Immune System Parameters in Ceramic Workers in TURKEY

Silica is the second most common element after oxygen, and therefore, exposures to crystalline silica dust occur in a large variety of occupations such as metal foundries, constructions, and ceramic, quarry, and pottery industries. Since crystalline silica exposure has been linked with silicosis, lung cancer, and other pulmonary diseases, adverse effect attributed to this element has be a cause for concern worldwide. Silica dust exposure in workers is still considered to be important health problem especially in developing countries. The aim of the study was to investigate the effects of occupational silica exposure on oxidative stress parameters including the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx), and levels of total glutathione (GSH) and thiobarbituric acid reactive substance (TBARS) as well as immune system parameters such as interleukin (IL)-1α, IL-1β, IL-2, IL-4, IL-6, and IL-10 and tumor necrosis factor (TNF)-α in Turkish ceramic workers. In this study, nearly 50% of Turkish ceramic workers were diagnosed with silicosis. Eighty-four percent of these silicotic workers were found to present with profusion category 1 silicosis, whereas controls (n = 81) all displayed normal chest radiographs. Data demonstrated a significant decrease in levels of GSH and activities of CAT, SOD, and GPx, but a significant increase in MDA levels and activity of GR in all workers. Further, workers possessed significantly higher levels of IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-10, and TNF-α. These observations suggest that ceramic workers may have impaired antioxidant/oxidant status and activated immune system indicative of inflammatory responses.

Evaluation of Dynamic Disulphide/Thiol Homeostasis in Silica Exposed Workers

BACKGROUND

Oxidative stress is implicated as one of the main molecular mechanism underlying silicosis.

AIMS

In this study, our aim was to asses the redox status in occupationally silica-exposed workers, by evaluating the dynamic thiol-disulphide homeostasis.

STUDY DESIGN

Case-control study.

METHODS

Thirty-six male workers occupationally exposed to silica particles and 30 healthy volunteers, working as office workers were included to the study. Posteroanterior chest radiographs and pulmonary function tests of both groups were evaluated. Also serum thiol disulphide levels were measured using the spectrophotometric method described by Erel and Neşelioğlu.

RESULTS

Among the 36 workers that underwent pulmonary function tests 6 (17%) had obstructive, 7 (19%) had restrictive, 6 (17%) had obstructive and restrictive signs whereas 17 (47%) had no signs. The mean PFTs results of silica-exposed workers were significantly lower than control subjects. The serum disulphide levels of silica-exposed workers were significantly higher than control subjects (23.84±5.89 μmol/L and 21.18±3.44 μmol/L, respectively p=0.02).

CONCLUSION

The serum disulphide levels, a biomarker of oxidative stress, are found to be higher in silica-exposed workers.