Silica exposure, smoking, silicosis and lung cancer--complex interactions

Essential principles for blood centrifugation

Currently, autologous platelet concentrates (APCs) are frequently used for soft- and hard-tissue regeneration, not only within the oral cavity, but also extra-orally including chronic wounds, burns, joints, dermatological conditions, among others. The benefits of APCs are largely influenced by the treatment strategy but also their preparation. This paper therefore discusses in detail: the physical properties of blood cells, the basic principles of blood centrifugation, the impact of the centrifugation protocol (rotations/revolutions per minute, g-force, variation between centrifuges), the importance of timing during the preparation of APCs, the impact of the inner surface of the blood tubes, the use/nonuse of anticoagulants within APC tubes, the impact of the patient's hematocrit, age, and gender, as well as the important requirements for an optimal centrifugation protocol. All these variables indeed have a significant impact on the clinical outcome of APCs.

Potential Effect of Combined Exposure of Crystalline Silica Dust and Cigarette Smoking on the Incidence of Silicosis among Chinese Male Stone Processing Workers: A Cross-Sectional Study

Background: Silicosis is a progressive and irreversible disease primarily caused by exposure to crystalline silica dust and, to a lesser extent, cigarette smoking. However, further research is needed to validate the potential combined effect of these risk factors on the increased incidence of the disease. Methods: A total of 1688 male workers employed at a Chinese stone processing plant between 1 January 1999 and 31 December 2019, were included in the study. Cumulative exposure to industrial crystalline silica dust and packyears of smoking were collected through health surveillance, and odds ratios (ORs) with 95% confidence intervals (CIs) for silicotic changes due to industrial silica exposure and cigarette smoking were estimated using logistic regression models. Results: Among all participants, a significant exposure-response relationship was observed between long-term exposure to industrial silica dust and radiographic findings resembling silicosis (OR 1.74, 95% CI 1.25 to 2.41). However, among middle-aged workers, a weak and statistically insignificant relationship was found between prolonged cigarette smoking and X-ray evidence of lung silicosis (OR 1.59, 95% CI 1.00 to 2.53). Furthermore, significant combined effects, exceeding the additive models, were identified in each age group and employment sector (relative risk due to interaction 0.51, 95% CI 0.08 to 3.42). Conclusions: It is critically important to implement effective dust removal measures and tobacco control strategies in order to enhance respiratory health among employees across all age groups in the stone processing industry.

Underdiagnosis of silicosis revealed by reinterpretation of chest radiographs in Thai ceramic workers

Background

In Thailand, epidemiological data on silicosis in the ceramic sector is lacking and the underdiagnosis of silicosis remains an extensive concern. Therefore, this study aimed to determine the prevalence of silicosis and the extent of underdiagnosis among Thai ceramic workers by reinterpreting chest radiographs previously taken by a health check-up unit.

Methods

This retrospective cross-sectional study was conducted on ceramic workers undergoing health surveillance using chest radiographs in one ceramic factory in September 2018. All chest radiographs were done retrospectively, then were reinterpreted by professional readers specially trained in using the ILO International Classification of Radiograph of Pneumoconioses (ILO/ICRP). Chest radiographs with a profusion of 1/1 or greater were suggestive of silicosis.

Results

Out of the 244 participants undergoing chest radiography, the prevalence of silicosis was 2.9%. Overall, the mean age of the participants was 41 years, and 72.1% were female. Among individuals with silicosis, the median age was 43 years; 71.4% were male; the average employment duration was 26.9 years; while the male sex was the significant variable associated with silicosis with an odds ratio of 7.01 (95% confidence interval 1.31 to 37.4). Regarding the underdiagnosis, the health check-up unit failed to recognize all individuals with silicosis, and could not detect any radiographic chest abnormalities in 57.1% of those with silicosis.

Conclusions

Despite the low prevalence of silicosis among Thai ceramic workers, this finding indicates ongoing exposure to silica in the ceramic industry. In addition, a significant proportion of the silicosis cases were underrecognized. Future efforts to prevent underdiagnosis and improve an occupational health surveillance service in Thailand are needed.

Reducing Construction Dust Pollution by Planning Construction Site Layout

Many construction activities generate fine particles and severely threaten the physical health of construction workers. Although many dust control measures are implemented in the industry, the occupational health risks still exist. In order to improve the occupational health level, this study proposes a new method of reducing the construction dust pollution through a reasonable site layout plan. This method is based on the field measurement and dust diffusion law. The dust diffusion law can be fitted based on the field monitoring data. With diffusion law, the average dust concentration exposed to workers of different site layouts can be simulated. In addition, the cost of the dust control method is a concern for site managers. Therefore, the total transportation cost reduction is another optimization objective. Finally, the multi-objective particle swarm optimization (MOPSO) algorithm is used to search for an optimized site layout that can reduce dust pollution and transportation cost simultaneously. The result shows that average dust concentration exposed to workers and total transportation cost are significantly reduced by 60.62% and 44.3%, respectively. This paper quantifies the construction dust pollution and provides site managers with a practical solution to reduce the construction dust pollution at low cost.

Silica-associated systemic lupus erythematosus with lupus nephritis and lupus pneumonitis: A case report and a systematic review of the literature

INTRODUCTION

Several epidemiological studies have shown that silica exposure triggers the onset of systemic lupus erythematosus (SLE); however, the clinical characteristics of silica-associated SLE have not been well studied.

PATIENT CONCERNS

A 67-year-old man with silicosis visited a primary hospital because of a fever and cough. His respiratory condition worsened, regardless of antibiotic medication, and he was referred to our hospital.

DIAGNOSIS

The patient showed leukopenia, lymphopenia, serum creatinine elevation with proteinuria and hematuria, decreased serum C3 level, and was positive for anti-double stranded DNA antibody, anti-nuclear antibody, and direct Coombs test. He was diagnosed with SLE. Renal biopsy was performed, and the patient was diagnosed with lupus nephritis (class IV-G(A/C) + V defined by the International Society of Nephrology/Renal Pathology Society classification). Computed tomography revealed acute interstitial pneumonitis, bronchoalveolar lavage fluid showed elevation of the lymphocyte fraction, and he was diagnosed with lupus pneumonitis.

INTERVENTIONS

Prednisolone (50 mg/day) with intravenous cyclophosphamide (500 mg/body) were initiated.

OUTCOMES

The patient showed a favorable response to these therapies. He was discharged from our hospital and received outpatient care with prednisolone slowly tapered off. He had cytomegalovirus and herpes zoster virus infections during treatment, which healed with antiviral therapy.

REVIEW

We searched for the literature on sSLE, and selected 11 case reports and 2 population-based studies. The prevalence of SLE manifestations in sSLE patients were comparative to that of general SLE, particularly that of elderly-onset SLE. Our renal biopsy report and previous reports indicate that lupus nephritis of sSLE patients show as various histological patterns as those of general SLE patients. Among the twenty sSLE patients reported in the case articles, three patients developed lupus pneumonitis and two of them died of it. Moreover, two patients died of bacterial pneumonia, one developed aspergillus abscesses, one got pulmonary tuberculosis, and one developed lung cancer.

CONCLUSION

Close attention is needed, particularly for respiratory system events and infectious diseases, when treating patients with silica-associated SLE using immunosuppressive therapies.

The bioinformatics analysis of RIOX2 gene in lung adenocarcinoma and squamous cell carcinoma

Lung cancer is characterized by high morbidity and mortality rates, and it has become an important public health issue worldwide. The occurrence and development of tumors is a multi-gene and multi-stage complex process. As an oncogene, ribosomal oxygenase 2 (RIOX2) has been associated with a variety of cancers. In this article, we analyzed the correlation between RIOX2 expression and methylation in lung cancer based on the databases including the cancer genome atlas (TCGA) (https://portal.gdc.cancer.gov/) and the gene expression omnibus (GEO) (https://www.ncbi.nlm.nih.gov/geo/). It was found that RIOX2 is highly expressed in lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) tissues, whose expression is negatively correlated with its methylation level. In this regard, methylation at cg09716038, cg14773523, cg14941179, and cg22299097 had a significant negative correlation with RIOX2 expression in LUAD, whereas in LUSC, methylation at cg09716038, cg14773523, cg14941179, cg22299097, cg05451573, cg10779801, and cg23629183 is negatively correlated with RIOX2 expression. According to the analysis based on the databases, RIOX2 gene could not be considered as the independent prognostic biomarker in lung adenocarcinoma or squamous cell lung cancer. However, the molecular mechanism of RIOX2 gene in the development of lung cancer may be helpful in improving lung cancer therapy.

Crystalline silica induces macrophage necrosis and causes subsequent acute pulmonary neutrophilic inflammation

Crystalline silica (CS), an airborne particulate, is a major global occupational health hazard. While it is known as an important pathogenic factor in many severe lung diseases, the underlying mechanisms of its toxicity are still unclear. In the present study, we found that intra-tracheal instillation of CS caused rapid emergence of necrotic alveolar macrophages. Cell necrosis was a consequence of the release of cathepsin B in CS-treated macrophages, which caused dysfunction of the mitochondrial membrane. Damage to mitochondria disrupted Na⁺/K⁺ ATPase activity in macrophages, leading to intracellular sodium overload and the subsequent cell necrosis. Further studies indicate that CS-induced macrophage necrosis and the subsequent release of mitochondrial DNA could trigger the recruitment of neutrophils in the lung, which was regulated by the TLR9 signaling pathway. In conclusion, our results suggest a novel mechanism whereby CS leads to rapid macrophage necrosis through cathepsin B release, following the leakage of mitochondrial DNA as a key event in the induction of pulmonary neutrophilic inflammation. This study has important implications for the early prevention and treatment of diseases induced by CS.

Association of silica dust exposure with mortality among never smokers: A 44-year cohort study

The association of silica dust exposure with mortality among never smokers has not been well established. We aimed to evaluate the association of silica dust exposure with mortality among never smokers. We studied 17,130 workers employed for at least 1 year between January 1, 1960 and December 31, 1974, with follow-up until the end of 2013. Cumulative respirable silica dust exposure (CDE) was estimated by linking a job-exposure matrix to personal work history. We observed 3937 deaths during 589,357.26 person-years of follow-up. Significant positive exposure-response relationships were found between CDE and mortality from all cause (HR = 1.01, 95%CI = 1.01-1.02), respiratory tuberculosis (HR = 1.04, 95%CI = 1.02-1.06), CVDs (HR = 1.03, 95%CI = 1.02-1.04), and diseases of the respiratory system (HR = 1.06, 95%CI = 1.04-1.07). We found higher standardized mortality ratios for respiratory tuberculosis (2.62, 2.32-2.95), CVDs (1.43, 1.32-1.54), and pneumoconiosis (77.75, 68.21-88.25) among silica dust exposed workers. In addition, we estimated that 4.19%, 20.69%, 7.48% and 34.06% of deaths for all cause, respiratory tuberculosis, CVDs, and diseases of the respiratory system among Chinese workers were attributed to silica, after adjusting for other covariates. With regard to lung cancer, compared with unexposed group, the HRs and 95% CI were 0.94 (0.52-1.71), 1.86 (1.15-3.00), 1.65 (0.95-2.86) for low, medium, and high exposed workers, respectively. Long-term silica dust exposure is associated with increased mortality in the absence of cigarette smoking.

A Bayesian assessment of occupational health surveillance in workers exposed to silica in the energy and construction industry

Medical records generated during occupational health surveillance processes have large amounts of unexploited information that can help to reduce silica-related health risks and many occupational diseases. The methodology applied in this study consists in analyzing through machine learning techniques a database with 70,000 medical examinations from workers in the energy and construction industry in Spain. First, a general unsupervised Bayesian model is built and node force analysis is used to identify the factors with the greatest impact on the worker's health surveillance process. Second, a predictive Bayesian model is created and mutual information is employed to assess the more relevant factors affecting the medical capability of workers exposed to silica dust. The lung auscultation and the breathing exploration are the two factors that influence the most the medical capability of silica-exposed employees. Probabilistic inference shows a remarkable gender effect, where women present more resilience towards occupational diseases than men showing a higher proportion of normal results in certain key factors, such as body mass index (♀49.73%, ♂25.17%) or spirometry (♀53.73%, ♂48.91%). Finally, environmental conditions demonstrate to have a major influence on spatial variability of occupational diseases. The design of health prevention programs based on geographical variations can be crucial to the attainment of an ongoing and sustained healthier workforce with a reduction in the number of chronic workplace illnesses.

New discoveries of mdig in the epigenetic regulation of cancers

Mineral dust-induced gene (mdig) encodes a member of the evolutionarily conserved JmjC family proteins that play fundamental roles in regulating chromatin-based processes as well as transcription of the genes in eukaryotic cells. This gene is also named as myc-induced nuclear antigen 53 (MINA), nucleolar protein 52 (NO52) and ribosomal oxygenase 2 (RIOX2). Increased expression of mdig had been noted in a number of human cancers, esp. lung cancer. Emerging evidence suggests that the oncogenic activity of mdig is most likely achieved through its regulation on the demethylation of histone proteins, despite it lacks the structural identities of the demethylases. Here, we discuss the latest discoveries on the characteristics of the mdig protein and its roles in a wide variety of normal and carcinogenic processes. We will also provide perspectives on how mdig is involved in the maintenance and differentiation of the embryonic stem cells, somatic stem cells and cancer stem cells.

Evidence for Contamination of Silica Microparticles in Advanced Platelet-Rich Fibrin Matrices Prepared Using Silica-Coated Plastic Tubes

Platelet-rich fibrin (PRF) therapy has been widely applied in regenerative dentistry, and PRF preparation has been optimized to efficiently form fibrin clots using plain glass tubes. Currently, a shortage of commercially available glass tubes has forced PRF users to utilize silica-coated plastic tubes. However, most plastic tubes are approved by regulatory authorities only for diagnostic use and remain to be approved for PRF therapy. To clarify this issue, we quantified silica microparticles incorporated into the PRF matrix. Blood samples were collected into three different brands of silica-containing plastic tubes and were immediately centrifuged following the protocol for advanced-PRF (A-PRF). Advanced-PRF-like matrices were examined using a scanning electron microscope (SEM), and silica microparticles were quantified using a spectrophotometer. Each brand used silica microparticles of specific size and appearance. Regardless of tube brands and individual donors, significant, but not accidental, levels of silica microparticles were found to be incorporated into the A-PRF-like matrix, which will be consequently incorporated into the implantation sites. Presently, from the increasing data for cytotoxicity of amorphous silica, we cannot exclude the possibility that such A-PRF-like matrices negatively influence tissue regeneration through induction of inflammation. Further investigation should be performed to clarify such potential risks.

Pseudogene CHIAP2 inhibits proliferation and invasion of lung adenocarcinoma cells by means of the WNT pathway

Recently, pseudogenes have emerged as critical regulators in the onset of human neoplasia. Here, we present a comprehensive analysis of pseudogene alterations at transcriptional levels in lung adenocarcinoma (LUAD) from The Cancer Genome Atlas. By combinations of differential expression analysis, survival analysis, and univariate and multivariable Cox proportional hazards regression models, we identified four dysregulated pseudogenes, whose expression level was closely related to LUAD patients' prognosis and the four pseudogene signature could act as an independent prognostic indicator for LUAD patients. We further characterized CHIAP2, one of those four pseudogenes, whose expression level was the most closely linked to LUAD patients' prognosis. Consistent with our analysis, the expression of CHIAP2 was abnormally downregulated in LUAD tissues compared with that in normal tissues in our 50 pairs of clinical samples. Functional assays demonstrated that upregulation of CHIAP2 significantly impaired cell proliferation and invasion. After performing RNA sequencing (RNA-seq) and small RNA-seq between CHIAP2 overexpression and negative control LUAD cell lines, we identified differentially expressed messenger RNAs and microRNAs (miRNAs), among which six miRNAs were downregulated. Target genes of six downregulated miRNAs were predicted with online miRNA target prediction tools and significant pathways including the WNT signal pathway were identified with Gene Set Enrichment Analysis. By combining predictor genes of six downregulated miRNAs and dysregulated genes of the WNT pathway, we inferred that overexpression of CHAP2 may inhibit LUAD cell proliferation and invasion via modulation of NFATC2 or GSK3B (WNT signal pathway) targeted by miR-3614-5p or miR-873-3p.

Silicosis and lung cancer: current perspectives

"Silica" refers to crystalline particles formed by the combination of silicon with oxygen. Inhalation of silica particles promotes the development of pulmonary fibrosis that over prolonged periods increases the risk of lung cancer. The International Agency for Research on Cancer (IARC) classified crystalline silica as a human carcinogen in 1997. This categorization was questioned due to 1) the absence of dose-response findings, 2) the presence of confounding variables that complicated interpretation of the data and 3) potential selection bias for compensated silicosis. Yet, recent epidemiologic studies strongly support the conclusion that silica exposure increases the risk of lung cancer in humans independent of confounding factors including cigarette smoke. Based on this evidence, the US Occupational Safety and Health Administration (OSHA) lowered the occupational exposure limit for crystalline silica from 0.1 to 0.05 mg/m³ in 2013. Further supporting the human epidemiologic data, murine models show that chronic silicosis is associated with an increased risk of lung cancer. In animals, the initial inflammation induced by silica exposure is followed by the development of an immunosuppressive microenvironment that supports the growth of lung tumors. This work will review our current knowledge of silica-associated lung cancers, highlighting how recent mechanistic insights support the use of cutting-edge approaches to diagnose and treat silica-related lung cancer.

Estimating the Impact of Changes to Occupational Standards for Silica Exposure on Lung Cancer Mortality

BACKGROUND

Respiratory exposure to silica is associated with the risk of death owing to malignant and nonmalignant disease. 2.3 million US workers are exposed to silica. Occupational exposure limits for silica are derived from a number of lines of evidence, including observational studies. Observational studies may be subject to healthy worker survivor bias, which could result in underestimates of silica's impact on worker mortality and, in turn, bias risk estimates for occupational exposure limits.

METHODS

Using data on 65,999 workers pooled across multiple industries, we estimate the impacts of several hypothetical occupational exposure limits on silica exposure on lung cancer and all-cause mortality. We use the parametric g-formula, which can account for healthy worker survivor bias.

RESULTS

Assuming we could eliminate occupational exposure, we estimate that there would be 20.7 fewer deaths per 1,000 workers in our pooled study by age 80 (95% confidence interval = 14.5, 26.8), including 3.91 fewer deaths owing to lung cancer (95% CI = 1.53, 6.30). Less restrictive interventions demonstrated smaller but still substantial risk reductions.

CONCLUSIONS

Our results suggest that occupational exposure limits for silica can be further strengthened to reduce silica-associated mortality and illustrate how current risk analysis for occupational limits can be improved.

EBUS-TBNA Cytology Specimens are Predictive of Occupational Dust Exposure in Patients With Bilateral Mediastinal and Hilar Lymphadenopathy

OBJECTIVES

The aim of this study was to describe the cytological features of patients with significant occupational dust exposure presenting with benign bilateral mediastinal and hilar lymphadenopathy (BHL).

METHODS

A retrospective cohort study including patients undergoing EBUS-TBNA for investigation of benign BHL. Patient characteristics, dust exposure history, radiology, and cytology samples from EBUS-TBNA were assessed.

RESULTS

EBUS-TBNA cytology in patients with exposure showed a significant increase in the presence of birefringent fibers (60.7% vs 19.2%, P = 0.001) and intracellular carbon pigment (75.0% vs 28.9%, P = 0.001) compared with patients without exposure. The presence of these two features together yielded a sensitivity of 53.6% and a specificity of 88.5%.

CONCLUSION

In patients with BHL and a history of occupational dust exposure, the presence of birefringent fibers and intracellular carbon pigment in EBUS-TBNA cytology samples may assist in a diagnosis of lymphadenopathy due to occupational dust exposure.

Transcription Factor and lncRNA Regulatory Networks Identify Key Elements in Lung Adenocarcinoma

Lung cancer is the second most commonly diagnosed carcinoma and is the leading cause of cancer death. Although significant progress has been made towards its understanding and treatment, unraveling the complexities of lung cancer is still hampered by a lack of comprehensive knowledge on the mechanisms underlying the disease. High-throughput and multidimensional genomic data have shed new light on cancer biology. In this study, we developed a network-based approach integrating somatic mutations, the transcriptome, DNA methylation, and protein-DNA interactions to reveal the key regulators in lung adenocarcinoma (LUAD). By combining Bayesian network analysis with tissue-specific transcription factor (TF) and targeted gene interactions, we inferred 15 disease-related core regulatory networks in co-expression gene modules associated with LUAD. Through target gene set enrichment analysis, we identified a set of key TFs, including known cancer genes that potentially regulate the disease networks. These TFs were significantly enriched in multiple cancer-related pathways. Specifically, our results suggest that hepatitis viruses may contribute to lung carcinogenesis, highlighting the need for further investigations into the roles that viruses play in treating lung cancer. Additionally, 13 putative regulatory long non-coding RNAs (lncRNAs), including three that are known to be associated with lung cancer, and nine novel lncRNAs were revealed by our study. These lncRNAs and their target genes exhibited high interaction potentials and demonstrated significant expression correlations between normal lung and LUAD tissues. We further extended our study to include 16 solid-tissue tumor types and determined that the majority of these lncRNAs have putative regulatory roles in multiple cancers, with a few showing lung-cancer specific regulations. Our study provides a comprehensive investigation of transcription factor and lncRNA regulation in the context of LUAD regulatory networks and yields new insights into the regulatory mechanisms underlying LUAD. The novel key regulatory elements discovered by our research offer new targets for rational drug design and accompanying therapeutic strategies.

Safety of Nonporous Silica Nanoparticles in Human Corneal Endothelial Cells

Nonporous silica nanoparticles (SiNPs) are promising drug carrier platforms for intraocular drug delivery. In this study, we investigated the safety of three different sizes of SiNPs (50, 100, and 150 nm) in a human corneal endothelial cell (HCEC) line, B4G12. The HCECs were exposed to different concentrations (0, 25, 50, and 100 µg/ml) of three sizes of SiNPs for up to 48 h. Cellular viability, autophagy, lactate dehydrogenase (LDH) assay, and mammalian target of rapamycin (mTOR) pathway activation were evaluated. Intracellular distribution of the SiNPs was evaluated with transmission electron microscopy (TEM). TEM revealed that the SiNPs were up-taken by the HCECs inside cytoplasmic vacuoles. No mitochondrial structural damage was observed. Both cellular viability and LDH level remained unchanged with up to 100 µg/mL of SiNP treatment. Autophagy showed a significant dose-dependent activation with 50, 100, and 150 nm SiNPs. However, the mTOR activation remained unchanged. Human corneal tissue culture with 100 µg/ml concentrations of SiNPs for 72 h revealed no significant endothelial toxicity. In vivo corneal safety of the SiNPs (0.05 ml intracameral injection, 200 mg/ml concentration) was also verified in rabbit models. These findings suggested that 50, 100, and 150 nm SiNPs did not induce acute significant cytotoxicity in corneal endothelial cells at concentrations up to 100 µg/mL. However, long-term toxicity of SiNPs remains unknown.

Drillers and mill operators in an open-pit gold mine are at risk for impaired lung function

BACKGROUND

Occupational studies of associations of exposures with impaired lung function in mining settings are built on exposure assessment and far less often on workplace approach, so the aim of this study was to identify vulnerable occupational groups for early lung function reduction in a cohort of healthy young miners.

METHODS

Data from annual screening lung function tests in gold mining company in Kyrgyzstan were linked to occupations. We compared per cent predicted forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and FEV1/FVC between occupational groups and tested selected occupations in multivariate regression adjusted for smoking and work duration for the following outcomes: FEV1 < 80 %, FEV1/FVC < 70 % and both.

RESULTS

1550 tests of permanent workers of 41 occupations (mean age 40.5 ± 9.2 years, 29.8 % never smokers) were included in the analysis. The mean overall VC was 103.0 ± 12.9 %; FVC 109.1 ± 13.0 % and FEV1 100.2 ± 25.9 %. Drillers and smoking food handlers had the lowest FEV1%. In non-smokers, the lowest FEV1 was in drillers (94.9 ± 11.3 % compared to 115.2 ± 17.7 % in engineers). Drillers (adjusted odds ratio (OR) 1.53 (95 % confidence interval (CI) 1.11-2.09)) and mill operators (OR 2.01 (1.13-3.57)) were at greater risk of obstructive ventilation pattern (FEV1/FVC < 70 %).

CONCLUSIONS

Drilling and mill operations are the highest risk jobs in an open-pit mine for reduced lung function. Occupational medical clinic at site should follow-up workers in these occupations with depth and strongly recommend smoking cessation.

Cell-Based Therapy for Silicosis

Silicosis is the most common pneumoconiosis globally, with higher prevalence and incidence in developing countries. To date, there is no effective treatment to halt or reverse the disease progression caused by silica-induced lung injury. Significant advances have to be made in order to reduce morbidity and mortality related to silicosis. In this review, we have highlighted the main mechanisms of action that cause lung damage by silica particles and summarized the data concerning the therapeutic promise of cell-based therapy for silicosis.

Structure, mechanism and therapeutic utility of immunosuppressive oligonucleotides

Synthetic oligodeoxynucleotides that can down-regulate cellular elements of the immune system have been developed and are being widely studied in preclinical models. These agents vary in sequence, mechanism of action, and cellular target(s) but share the ability to suppress a plethora of inflammatory responses. This work reviews the types of immunosuppressive oligodeoxynucleotide (Sup ODN) and compares their therapeutic activity against diseases characterized by pathologic levels of immune stimulation ranging from autoimmunity to septic shock to cancer (see graphical abstract). The mechanism(s) underlying the efficacy of Sup ODN and the influence size, sequence and nucleotide backbone on function are considered.

Risk Assessment of Exposure to Silica Dust in Building Demolition Sites

Background

Building demolition can lead to emission of dust into the environment. Exposure to silica dust may be considered as an important hazard in these sites. The objectives of this research were to determine the amount of workers' exposure to crystalline silica dust and assess the relative risk of silicosis and the excess lifetime risk of mortality from lung cancer in demolition workers.

Methods

Four sites in the Tehran megacity region were selected. Silica dust was collected using the National Institute for Occupational Safety and Health method 7601 and determined spectrophotometrically. The Mannetje et al and Rice et al models were chosen to examine the rate of silicosis-related mortality and the excess lifetime risk of mortality from lung cancer, respectively.

Results

The amount of demolition workers' exposure was in the range of 0.085–0.185 mg/m³. The range of relative risk of silicosis related mortality was increased from 1 in the workers with the lowest exposure level to 22.64/1,000 in the employees with high exposure level. The range of the excess lifetime risk of mortality from lung cancer was in the range of 32–60/1,000 exposed workers.

Conclusion

Geometric and arithmetic mean of exposure was higher than threshold limit value for silica dust in all demolition sites. The risk of silicosis mortality for many demolition workers was higher than 1/1,000 (unacceptable level of risk). Estimating the lifetime lung cancer mortality showed a higher risk of mortality from lung cancer in building demolition workers.

Process evaluation of an intervention program to reduce occupational quartz exposure among Dutch construction workers

OBJECTIVES

Evaluate the process of an intervention in the construction industry to reduce quartz exposure.

METHODS

In a cluster randomized controlled trial, data on seven process aspects (ie, recruitment, reach, dose delivered, dose received, fidelity, satisfaction, and context) were quantitatively collected on manager and worker levels.

RESULTS

Dose delivered was 95% for the plenary sessions and 20% for the worksite visit. Although the protocol was mostly implemented as intended, dose received was lower than expected. Both managers and workers appreciated the intervention and recommended the intervention for future implementation. Workers attending all intervention sessions were most satisfied about the intervention.

CONCLUSIONS

High rates for dose delivered and fidelity for the plenary sessions and relatively high satisfaction rates were achieved. Furthermore, continuous monitoring of contextual factors beforehand and alongside the implementation of interventions is recommended.

Crystalline silica-induced leukotriene B4-dependent inflammation promotes lung tumour growth

Chronic exposure to crystalline silica (CS) causes silicosis, an irreversible lung inflammatory disease that may eventually lead to lung cancer. In this study, we demonstrate that in K-ras(LA1) mice, CS exposure markedly enhances the lung tumour burden and genetic deletion of leukotriene B4 receptor-1 (BLT1(-/-)) attenuates this increase. Pulmonary neutrophilic inflammation induced by CS is significantly reduced in BLT1(-/-)K-ras(LA1) mice. CS exposure induces LTB4 production by mast cells and macrophages independent of inflammasome activation. In an air-pouch model, CS-induced neutrophil recruitment is dependent on LTB4 production by mast cells and BLT1 expression on neutrophils. In an implantable lung tumour model, CS exposure results in rapid tumour growth and decreased survival that is attenuated in the absence of BLT1. These results suggest that the LTB4/BLT1 axis sets the pace of CS-induced sterile inflammation that promotes lung cancer progression. This knowledge may facilitate development of immunotherapeutic strategies to fight silicosis and lung cancer.

Liver functions in silica-exposed workers in Egypt: possible role of matrix remodeling and immunological factors

BACKGROUND

Brick manufacturing constitutes an important industrial sector in Egypt with considerable exposure to silica.

OBJECTIVES

We aimed for evaluating hepatic functions in silica-exposed workers in the clay brick industry, and the possible role of matrix remodeling and immunological factors.

METHODS

A case-control study, 87 workers as exposed and 45 as control subjects. Questionnaire, clinical examination, and laboratory investigations: liver functions, matrix metalloproteinase-9, immunoglobulins G and E, and anti-liver kidney microsomal antibody.

RESULTS

In the exposed workers, mean levels of liver functions, matrix metalloproteinase-9 (MMP-9), and IgG and IgE were significantly higher. In the silicotic subgroup the mean level of GGT was almost twice the level in the non-silicotic subjects. Logistic regression showed that abnormal GGT and ALT were associated with production workers.

CONCLUSION

Workers in the clay brick industry showed evidence of liver disease that could be related to matrix remodeling.

Serum CA125 and NSE: biomarkers of disease severity in patients with silicosis

BACKGROUND

We investigated the clinical significance of tumor markers in patients with silicosis.

METHODS

Eighty silicosis patients without malignancy and 50 healthy volunteers were compared for serum tumor marker concentrations. Pulmonary function and several routine laboratory tests were performed. Correlation between serum tumor marker concentrations and severity markers for silicosis was analyzed. Tumor marker concentrations were detected in both blood and BALF samples in silicosis patients. The pre- and post-lavage differences in the serum tumor marker concentrations were also investigated. Immunohistochemical staining for tumor markers was performed in a lung biopsy specimen from a silicosis patient.

RESULTS

Both serum NSE and CA125 concentrations were significantly higher in cases compared with controls. Significant positive correlations were found between values of NSE and CA125 and LDH concentration. Significant negative correlations were also observed between values of NSE and CA125 and spirometric parameters. Patients with silicosis had higher concentrations of NSE in BALF than that in serum. 11 of 14 patients experienced a decrease in NSE concentrations following whole lung lavage. Immunohistochemical studies showed positive NSE staining in lung biopsy specimen.

CONCLUSIONS

Serum NSE and CA125 concentrations would provide valuable clinical information to assess disease severity in silicosis.

Presence of nanosilica (E551) in commercial food products: TNF-mediated oxidative stress and altered cell cycle progression in human lung fibroblast cells

Silica (E551) is commonly used as an anti-caking agent in food products. The morphology and the dimension of the added silica particles are not, however, usually stated on the food product label. The food industry has adapted nanotechnology using engineered nanoparticles to improve the quality of their products. However, there has been increased debate regarding the health and safety concerns related to the use of engineered nanoparticles in consumer products. In this study, we investigated the morphology and dimensions of silica (E551) particles in food. The silica content of commercial food products was determined using inductively coupled plasma optical emission spectrometry. The result indicates that 2.74-14. 45 μg/g silica was found in commercial food products; however, the daily dietary intake in increase causes adverse effects on human health. E551 was isolated from food products and the morphology, particle size, crystalline nature, and purity of the silica particles were analyzed using XRD, FTIR, TEM, EDX and DLS. The results of these analyses confirmed the presence of spherical silica nanoparticles (of amorphous nature) in food, approximately 10-50 nm in size. The effects of E551 on human lung fibroblast cell viability, intracellular ROS levels, cell cycle phase, and the expression levels of metabolic stress-responsive genes (CAT, GSTA4, TNF, CYP1A, POR, SOD1, GSTM3, GPX1, and GSR1) were studied. The results suggest that E551 induces a dose-dependent cytotoxicity and changes in ROS levels and alters the gene expression and cell cycle. Treatment with a high concentration of E551 caused significant cytotoxic effects on WI-38 cells. These findings have implications for the use of these nanoparticles in the food industry.

Suppressive oligodeoxynucleotides reduce lung cancer susceptibility in mice with silicosis

Silicosis is an inflammatory lung disease induced by the inhalation of silica-containing dust particles. There is conflicting data on whether patients with silicosis are more susceptible to lung cancer induced by cigarette smoke. To examine this issue experimentally, a model was developed in which one of the most abundant and potent carcinogens present in cigarette smoke [4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK)] was administered to mice at the peak of silica-induced pulmonary inflammation. Results show that the incidence of lung tumors in silicotic mice treated with NNK was significantly increased compared with mice exposed to silica or NNK alone. Synthetic oligonucleotides (ODN) containing repetitive TTAGGG motifs can block pathologic inflammation. We therefore examined whether treatment with these suppressive (Sup) ODN could block silica-induced pulmonary inflammation and thereby reduce susceptibility to lung cancer. Results show that Sup (but not control) ODN inhibit pulmonary fibrosis and other inflammatory manifestations of chronic silicosis. Of greater import, Sup ODN reduced lung tumor incidence and multiplicity in silicotic mice exposed to NNK. These findings establish an experimental model for examining the role of silicotic inflammation in cancer susceptibility and demonstrate that Sup ODN represent a novel therapy for chronic silicosis.

Exposure-response analysis and risk assessment for lung cancer in relationship to silica exposure: a 44-year cohort study of 34,018 workers

Crystalline silica has been classified as a human carcinogen by the International Agency for Research on Cancer (Lyon, France); however, few previous studies have provided quantitative data on silica exposure, silicosis, and/or smoking. We investigated a cohort in China (in 1960-2003) of 34,018 workers without exposure to carcinogenic confounders. Cumulative silica exposure was estimated by linking a job-exposure matrix to work history. Cox proportional hazards model was used to conduct exposure-response analysis and risk assessment. During a mean 34.5-year follow-up, 546 lung cancer deaths were identified. Categorical analyses by quartiles of cumulative silica exposure (using a 25-year lag) yielded hazard ratios of 1.26, 1.54, 1.68, and 1.70, respectively, compared with the unexposed group. Monotonic exposure-response trends were observed among nonsilicotics (P for trend < 0.001). Analyses using splines showed similar trends. The joint effect of silica and smoking was more than additive and close to multiplicative. For workers exposed from ages 20 to 65 years at 0.1 mg/m(3) of silica exposure, the estimated excess lifetime risk (through age 75 years) was 0.51%. These findings confirm silica as a human carcinogen and suggest that current exposure limits in many countries might be insufficient to protect workers from lung cancer. They also indicate that smoking cessation could help reduce lung cancer risk for silica-exposed individuals.

Nanoparticles: toxicity, radicals, electron transfer, and antioxidants

In recent years, nanoparticles have received increasing attention in research and technology, including a variety of practical applications. The bioactivity appears to be related to the small particle size, in addition to inherent chemical activity as electron transfer (ET) agents, generators of reactive oxygen species (ROS) with subsequent oxidative stress (OS), and as antioxidants (AOs). The mechanism of toxicity, therapeutic action, and AO property is addressed based on the ET-ROS-OS approach. There are several main classes of ET functionalities, namely, quinones (or phenolic precursors), metal compounds, aromatic nitro compounds (or reduction products), and imine or iminium species. Most of the nanospecies fall within the metal category. Cell signaling is also discussed. This review discusses recent developments based on ET-ROS-OS-AO framework.

Drugs for preventing lung cancer in healthy people

BACKGROUND

This is an updated version of the original review published in Issue 2, 2003. Some studies have suggested a protective effect of antioxidant nutrients on lung cancer. Observational epidemiological studies suggest an association between higher dietary levels of fruits and vegetables containing beta-carotene and a lower risk of lung cancer.

OBJECTIVES

To determine whether vitamins, minerals and other potential agents, alone or in combination, reduce incidence and mortality from lung cancer in healthy people.

SEARCH METHODS

For this update we have used a search strategy adapted from the design in the original review. The following electronic databases have been searched up to December 2011: MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials (CENTRAL). References included in published studies and reviews were also screened.

SELECTION CRITERIA

Included studies were randomised controlled clinical trials comparing different vitamins, mineral supplements or supplements with placebo, administered to healthy people with the aim of preventing lung cancer.

DATA COLLECTION AND ANALYSIS

Two authors independently selected the trials to be included in the review, assessed the methodological quality of each trial and extracted data using a standardised form. For each study, relative risk and 95% confidence limits were calculated for dichotomous outcomes and pooled results were calculated using the random-effect model.

MAIN RESULTS

In the first version of this review four studies were included; in this review update, an additional five studies have been included. Four studies included only males and two only females; two studies included only participants considered at high risk, namely smokers or exposed to asbestos, and one study included people deficient in many micronutrients. Six studies analysed vitamin A, three vitamin C, four vitamin E, one selenium supplements, and six studied combinations of two or more products. All the RCTs included in this review were classified as being of low risk of bias.For people not at high risk of lung cancer and compared to placebo, none of the supplements of vitamins or minerals or their combinations resulted in a statistically significant difference in lung cancer incidence or mortality, except for a single study that included 7627 women and found a higher risk of lung cancer incidence for those taking vitamin C but not for total cancer incidence, but that effect was not seen in males or when the results for males and females were pooled.For people at high risk of lung cancer, such as smokers and those exposed to asbestos and compared to placebo, beta-carotene intake showed a small but statistically significant higher risk of lung cancer incidence, lung cancer mortality and for all-causes mortality.

AUTHORS' CONCLUSIONS

There is no evidence for recommending supplements of vitamins A, C, E, selenium, either alone or in different combinations, for the prevention of lung cancer and lung cancer mortality in healthy people. There is some evidence that the use of beta-carotene supplements could be associated with a small increase in lung cancer incidence and mortality in smokers or persons exposed to asbestos.

Quantitative relationship between silica exposure and lung cancer mortality in German uranium miners, 1946-2003

Background:

In 1996 and 2009, the International Agency for Research on Cancer classified silica as carcinogenic to humans. The exposure–response relationship between silica and lung cancer risk, however, is still debated. Data from the German uranium miner cohort study were used to further investigate this relationship.

Methods:

The cohort includes 58 677 workers with individual information on occupational exposure to crystalline silica in mg m⁻³-years and the potential confounders radon and arsenic based on a detailed job-exposure matrix. In the follow-up period 1946–2003, 2995 miners died from lung cancer. Internal Poisson regression with stratification by age and calendar year was used to estimate the excess relative risk (ERR) per dust-year. Several models including linear, linear quadratic and spline functions were applied. Detailed adjustment for cumulative radon and arsenic exposure was performed.

Results:

A piecewise linear spline function with a knot at 10 mg m⁻³-years provided the best model fit. After full adjustment for radon and arsenic no increase in risk <10 mg m⁻³-years was observed. Fixing the parameter estimate of the ERR in this range at 0 provided the best model fit with an ERR of 0.061 (95% confidence interval: 0.039, 0.083) >10 mg m⁻³-years.

Conclusion:

The study confirms a positive exposure–response relationship between silica and lung cancer, particularly for high exposures.

Silicosis

Silicosis is a fibrotic lung disease caused by inhalation of free crystalline silicon dioxide or silica. Occupational exposure to respirable crystalline silica dust particles occurs in many industries. Phagocytosis of crystalline silica in the lung causes lysosomal damage, activating the NALP3 inflammasome and triggering the inflammatory cascade with subsequent fibrosis. Impairment of lung function increases with disease progression, even after the patient is no longer exposed. Diagnosis of silicosis needs carefully documented records of occupational exposure and radiological features, with exclusion of other competing diagnoses. Mycobacterial diseases, airway obstruction, and lung cancer are associated with silica dust exposure. As yet, no curative treatment exists, but comprehensive management strategies help to improve quality of life and slow deterioration. Further efforts are needed for recognition and control of silica hazards, especially in developing countries.

Effect of oxidative stress on development of silicosis

AIM: To investigate the changes of oxidative stress indicators in the serum of silicosis patients and explore the mechanism of silicosis development.

METHODS: Two hundred workers who were exposed to silica dust for more than one year were recruited as dust-exposed group, 100 non-dust-exposed subjects served as control group, 32 patients with suspected 0⁺ silicosis as observation group, and 130 silicosis patients were taken as the silicosis group. Indicators of oxidative stress, including superoxide dismutase (SOD), nitric oxide (NO), serum glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), nitric oxide synthase (NOS), and lipid malondialdehyde (MDA), were determined in all the groups.

RESULTS: Compared with the control group, NO and GSH-Px in dust-exposed group and silicosis group increased, and SOD decreased significantly (81.162 ± 35.176, 270.469 ± 39.228 and 68.209 ± 21.528, respectively, P = 0.004, P = 0.002, P = 0.005). Compared with the control and dust-exposed group, T-AOC, NOS and MDA in silicosis group increased significantly (13.048 ± 4.153, 36.201 ± 7.782 and 5.054 ± 1.204, respectively, P = 0.018, P = 0.022, P = 0.011). Compared with dust-exposed group, GSH-Px in the silicosis group increased significantly (270.469 ± 39.228, P = 0.002). GSH-Px in phase III silicosis was significantly higher than in phase I silicosis (290.750 ± 39.129, P = 0.021). Pearson correlation analysis showed that serum GSH-Px was positively correlated with silicosis staging, length of dust exposure and type of occupation (47.109 ± 8.015, P = 0.001).

CONCLUSION: The imbalance of oxidative and anti-oxidation system is associated with the development of silicosis. The surveillance of oxidative stress indicators will benefit the prognosis of silicosis patients.

Inflammation and cancer: a comparative view

Rudolph Virchow first speculated on a relationship between inflammation and cancer more than 150 years ago. Subsequently, chronic inflammation and associated reactive free radical overload and some types of bacterial, viral, and parasite infections that cause inflammation were recognized as important risk factors for cancer development and account for one in four of all human cancers worldwide. Even viruses that do not directly cause inflammation can cause cancer when they act in conjunction with proinflammatory cofactors or when they initiate or promote cancer via the same signaling pathways utilized in inflammation. Whatever its origin, inflammation in the tumor microenvironment has many cancer-promoting effects and aids in the proliferation and survival of malignant cells and promotes angiogenesis and metastasis. Mediators of inflammation such as cytokines, free radicals, prostaglandins, and growth factors can induce DNA damage in tumor suppressor genes and post-translational modifications of proteins involved in essential cellular processes including apoptosis, DNA repair, and cell cycle checkpoints that can lead to initiation and progression of cancer.

An exposure-response threshold for lung diseases and lung cancer caused by crystalline silica

Whether crystalline silica (CS) exposure increases risk of lung cancer in humans without silicosis, and, if so, whether the exposure-response relation has a threshold, have been much debated. Epidemiological evidence is ambiguous and conflicting. Experimental data show that high levels of CS cause lung cancer in rats, although not in other species, including mice, guinea pigs, or hamsters; but the relevance of such animal data to humans has been uncertain. This article applies recent insights into the toxicology of lung diseases caused by poorly soluble particles (PSPs), and by CS in particular, to model the exposure-response relation between CS and risk of lung pathologies such as chronic inflammation, silicosis, fibrosis, and lung cancer. An inflammatory mode of action is described, having substantial empirical support, in which exposure increases alveolar macrophages and neutrophils in the alveolar epithelium, leading to increased reactive oxygen species (ROS) and nitrogen species (RNS), pro-inflammatory mediators such as TNF-alpha, and eventual damage to lung tissue and epithelial hyperplasia, resulting in fibrosis and increased lung cancer risk among silicotics. This mode of action involves several positive feedback loops. Exposures that increase the gain factors around such loops can create a disease state with elevated levels of ROS, TNF-alpha, TGF-beta, alveolar macrophages, and neutrophils. This mechanism implies a "tipping point" threshold for the exposure-response relation. Applying this new model to epidemiological data, we conclude that current permissible exposure levels, on the order of 0.1 mg/m³, are probably below the threshold for triggering lung diseases in humans.

Association between lymph node silicosis and lung silicosis in 4,384 German uranium miners with lung cancer

This study investigates the association between lymph node-only and lung silicosis in uranium miners with lung cancer and exposure to quartz dust. Tissue slides of 4,384 German uranium miners with lung cancer were retrieved from an autopsy archive and reviewed by 3 pathologists regarding silicosis in the lungs and lymph nodes. Cumulative exposure to quartz dust was assessed with a quantitative job-exposure matrix. The occurrence of silicosis by site was investigated with regression models for exposure to quartz dust. Miners with lung silicosis had highest cumulative quartz exposure, followed by lymph node-only silicosis and no silicosis. At a cumulative quartz exposure of 40 mg/m(3) × years, the probability of lung silicosis was above 90% and the likelihood of lymph node-only silicosis and no silicosis do not differ anymore. The results support that lymph node silicosis can precede lung silicosis, at least in a proportion of subjects developing silicosis, and that lung silicosis strongly depends on the cumulative quartz dose.

Decision tree of occupational lung cancer using classification and regression analysis

OBJECTIVES

Determining the work-relatedness of lung cancer developed through occupational exposures is very difficult. Aims of the present study are to develop a decision tree of occupational lung cancer.

METHODS

153 cases of lung cancer surveyed by the Occupational Safety and Health Research Institute (OSHRI) from 1992-2007 were included. The target variable was whether the case was approved as work-related lung cancer, and independent variables were age, sex, pack-years of smoking, histological type, type of industry, latency, working period and exposure material in the workplace. The Classification and Regression Test (CART) model was used in searching for predictors of occupational lung cancer.

RESULTS

In the CART model, the best predictor was exposure to known lung carcinogens. The second best predictor was 8.6 years or higher latency and the third best predictor was smoking history of less than 11.25 pack-years. The CART model must be used sparingly in deciding the work-relatedness of lung cancer because it is not absolute.

CONCLUSION

We found that exposure to lung carcinogens, latency and smoking history were predictive factors of approval for occupational lung cancer. Further studies for work-relatedness of occupational disease are needed.

Dysregulation of the immune system caused by silica and asbestos

Silica and asbestos cause pneumoconioses known as silicosis and asbestosis, respectively, that are each characterized by progressive pulmonary fibrosis. While local effects of inhaled silica particles alter the function of alveolar macrophages and sequential cellular and molecular biological events, general systemic immunological effects may also evolve. One well-known health outcome associated with silica exposure/silicosis is an increase in the incidence of autoimmune disorders. In addition, while exposure to silica--in the crystalline form--has also been seen to be associated with the development of lung cancers, it remains unclear as to whether or not silicosis is a necessary condition for the elevation of silica-associated lung cancer risks. Since asbestos is a mineral silicate, it would be expected to also possess generalized immunotoxicological effects similar to those associated with silica particles. However, asbestos-exposed patients are far better known than silicotic patients for development of malignant diseases such as lung cancer and mesothelioma, and less so for the development of autoimmune disorders. With both asbestos and crystalline silica, one important dysregulatory outcome that needs to be considered is an alteration in tumor immunity that allows for silica- or asbestos- (or asbestos-associated agent)-induced tumors to survive and thrive in situ. In this review, the immunotoxicological effects of both silica and asbestos are presented and contrasted in terms of their abilities to induce immune system dysregulation that then are manifest by the onset of autoimmunity or by alterations in host-tumor immunity.