Occupational exposure to silica dust and risk of lung cancer: an updated meta-analysis of epidemiological studies

Risk Analysis Implications of Dose-Response Thresholds for NLRP3 Inflammasome-Mediated Diseases: Respirable Crystalline Silica and Lung Cancer as an Example

Chronic inflammation mediates an extraordinarily wide range of diseases. Recent progress in understanding intracellular inflammasome assembly, priming, activation, cytokine signaling, and interactions with mitochondrial reactive oxygen species, lysosome disruption, cell death, and prion-like polymerization and spread of inflammasomes among cells, has potentially profound implications for dose-response modeling. This article discusses mechanisms of exposure concentration and duration thresholds for NOD-like receptor protein 3 (NLRP3)-mediated inflammatory responses and develops a simple biomathematical model of the onset of exposure-related tissue-level chronic inflammation and resulting disease risks, focusing on respirable crystalline silica (RCS) and lung cancer risk as an example. An inflammation-mediated 2-stage clonal expansion model of RCS-induced lung cancer is proposed that explains why relatively low estimated concentrations of RCS (eg, <1 mg/m³) do not increase lung cancer risk and why even high occupational concentrations increase risk only modestly (typically relative risk <2). The model of chronic inflammation implies a dose-response threshold for excess cancer risk, in contrast to traditional linear-no-threshold assumptions. If this implication is correct, then concentrations of crystalline silica (or amphibole asbestos fibers, or other environmental challenges that act via the NLRP3 inflammasome) below the threshold do not cause chronic inflammation and resulting elevated risks of inflammation-mediated diseases.

The health equity measurement framework: a comprehensive model to measure social inequities in health

BACKGROUND

Despite the wealth of frameworks on social determinants of health (SDOH), two current limitations include the relative superficial description of factors affecting health and a lack of focus on measuring health equity. The Health Equity Measurement Framework (HEMF) addresses these gaps by providing a more encompassing view of the multitude of SDOH and drivers of health service utilisation and by guiding quantitative analysis for public health surveillance and policy development. The objective of this paper is to present the HEMF, which was specifically designed to measure the direct and indirect effects of SDOH to support improved statistical modelling and measurement of health equity.

METHODS

Based on a framework synthesis, the HEMF development involved initially integrating theoretical components from existing SDOH and health system utilisation frameworks. To further develop the framework, relevant publications on SDOH and health equity were identified through a literature review in major electronic databases. White and grey literatures were critically reviewed to identify strengths and gaps in the existing frameworks in order to inform the development of a unique health equity measurement framework. Finally, over a two-year period of consultation, scholars, health practitioners, and local policy influencers from municipal and provincial governments provided critical feedback on the framework regarding its components and causal relationships.

RESULTS

This unified framework includes the socioeconomic, cultural, and political context, health policy context, social stratification, social location, material and social circumstances, environment, biological factors, health-related behaviours and beliefs, stress, quality of care, and healthcare utilisation. Alongside the HEMF's self-exploratory diagram showing the causal pathways in-depth, a number of examples are provided to illustrate the framework's usefulness in measuring and monitoring health equity as well as informing policy-making.

CONCLUSIONS

The HEMF highlights intervention areas to be influenced by strategic public policy for any organisation whose purview has an effect on health, including helping non-health sectors (such as education and labour) to better understand how their policies influence population health and perceive their role in health equity promotion. The HEMF recognises the complexity surrounding the SDOH and provides a clear, overarching direction for empirical work on health equity.

Artificial Stone Associated Silicosis: A Systematic Review

Silicosis is a progressive fibrotic lung disease that is caused by the inhalation of respirable crystalline silica. Due to its high silica content, artificial stone (AS) can become a possible source of hazardous dust exposure for workers that are employed in the manufacturing, finishing, and installing of AS countertops. Therefore, the aim of this review was to verify the association between AS derived silica exposure and silicosis development, and also then define the pathological characteristics of the disease in relation to specific work practices and preventive and protective measures that were adopted in the workplace. A systematic review of articles available on Pubmed, Scopus, and Isi Web of Knowledge databases was performed. Although the characteristics of AS-associated silicosis were comparable to those that were reported for the disease in traditional silica exposure settings, some critical issues emerged concerning the general lack of suitable strategies for assessing/managing silica risks in these innovative occupational fields. Further research that is designed to assess the hazardous properties of AS dusts, levels of exposure in workplaces, and the effectiveness of protective equipment appears to be needed to increase awareness concerning AS risks and induce employers, employees, and all factory figures that are engaged in prevention to take action to define/adopt proper measures to protect the health of exposed workers.

Epidemiology of lung cancer in China

The incidence and mortality rates of lung cancer, the leading cause of cancer death in China, have significantly increased in recent years, and present geographic and gender differences as a result of diversity in lifestyles and socioeconomic development. A series of attribute risk analyses have shown that factors such as smoking, air pollution, and occupational factors are all related to lung cancer. Behavioral intervention, such as smoking cessation and screening, could effectively reduce lung cancer incidence and mortality.

Subradiological silicosis

The purpose of this commentary is to bring the neglected phenomenon of subradiological silicosis and its implications to the attention of readers. We define subradiological silicosis as silicosis detectable on pathological examination of lung tissue but not visible radiologically. For extent of the phenomenon, we draw on a study using a large South African autopsy database of deceased miners and chest radiographs taken in life. At an International Labour Organization threshold of >1/0 only 43% of all pathologically detected cases were detected on chest radiograph, and only 62% of those classified on pathology as "moderate or marked" silicosis. Subradiological silicosis has a number of implications for research and practice: for dose-response studies of silicosis; for studies of the relationship between silica and conditions such as tuberculosis, lung cancer, and autoimmune disease, including the mechanistic role of fibrogenesis; for prognostication in silica exposed workers; and for workers' compensation criteria.

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.

Serum magnesium levels and lung cancer risk: a meta-analysis

Background

Whether serum magnesium levels were lower in patients with lung cancer than that in healthy controls is controversial. The aim of this study was to identify and synthesize all citations evaluating the relationship between serum magnesium levels and lung cancer.

Methods

We searched PubMed, WanFang, China National Knowledge Internet (CNKI), and SinoMed databases for relevant studies before December 31, 2017. Two authors independently selected studies, extracted data, and assessed risk of bias.

Results

Eleven citations comprising 707 cases with lung cancer and 7595 healthy controls were included in our study. Serum magnesium levels were not significantly lower in patients with lung cancer [summary SMD = 0.193, 95%CI = − 1.504 to 1.890] when compared to health controls, with significant heterogeneity (I² = 99.6%, P < 0.001) found. Negative associations were found among Asian populations [summary SMD = 0.229, 95%CI = − 1.637 to 2.094] and European populations [summary SMD = − 0.168, 95%CI = − 0.482 to 0.147]. No publication bias was found using the test of Egger and funnel plot.

Conclusions

Our study suggested that serum magnesium levels had no significant association on lung cancer risk.

Comparative RNA-Seq transcriptome analysis on silica induced pulmonary inflammation and fibrosis in mice silicosis model

Silicosis is a long-established public health issue in developing countries due to increasingly serious air pollution and poorly implemented occupational safety regulation. Inhalation of silica triggers cytotoxicity, oxidative stress, pulmonary inflammation and eventually silicosis. Current understanding in the pathogenesis and mechanism of silicosis is limited, and no effective cure is clinically available once silicosis is developed. A number of studies were conducted to investigate silica-induced alternate gene expressions in pulmonary cells. However, transcriptome analysis in a silicosis animal model is needed. This study was performed to evaluate the transcriptional alternations in silicotic mice using comparative RNA-Seq. A silicosis mice model was established by intratracheal instillation of silica suspensions, and validated by histological examinations. High-throughput sequencing and differential gene expression analysis revealed 749 upregulated genes and 70 downregulated genes in the silicosis model. Genes related to immune cell interactions, immune cell responses and inflammation were significantly enriched. Cytokine-cytokine receptor interaction and downstream JAK-STAT signaling pathways were the most significantly enriched KEGG pathways. Reverse transcription-polymerase chain reaction analysis and immunohistochemistry were performed to validate further the differential expression patterns of representative genes. The reported results in this study provide the basis for elucidating the molecular mechanisms for silica-induced pulmonary inflammation and fibrosis, and support the prevention and treatment of silicosis.

Up-regulation of exosomal miR-125a in pneumoconiosis inhibits lung cancer development by suppressing expressions of EZH2 and hnRNPK

Exposure to nanoparticles may lead to pneumoconiosis and lung cancer; however, whether patients suffering from pneumoconiosis also face a high risk of lung cancer has been under debate for decades. Recently, exosomes have been found to play critical roles in many diseases via intercellular cargo transportation, which has provided a new insight into the mechanistic investigation of nanoparticle-induced respiratory disorders. Herein, we isolated exosomes from the venous blood of patients with pneumoconiosis and healthy controls and then, we profiled the expression signatures of exosomal miRNAs using high-throughput sequencing technology. A total of 14 aberrantly expressed miRNAs were identified and used to process target gene prediction and functional annotation. Specially, miR-125a along with its target genes EZH2 and hnRNPK was found to play a significant role in the development of lung cancer. We then adopted a series of cellular experiments to validate the role of miR-125a in lung cancer. From the results obtained, we found that the suppression of EZH2 and hnRNPK by high levels of miR-125a inhibited the development of nanoparticle-induced lung adenocarcinoma, which contributed to the clarification of the relation between pneumoconiosis and lung cancer.

Exosomal miR-125a may act as a bridge between pneumoconiosis and lung cancer.

Profiling of the silica-induced molecular events in lung epithelial cells using the RNA-Seq approach

Silicosis is a prolonged, irreversible and incurable occupational disease, and there is a significant number of newly diagnosed cases every year in Hong Kong. Due to the long latency of the disease, the diagnosis can be missed until detailed clinical examination at a later stage. For a better control of this deadly disease, detailing the pro-inflammatory and fibrotic events in the macrophage would be instrumental in understanding the pathogenesis of the disease and essential for the significant biomarkers discovery. In this in vitro study, human cell line model A549 lung epithelial cells were used. The immediate molecular events underneath the activation of quartz silica polymorphs were followed in a time course of 0, 0.5, 2, 8, 16 and 24 h. The transcriptome library was prepared and subjected to RNA-Seq analysis. Data analysis was performed by pathway analysis tools and verified by real-time PCR. The results showed that triggered genes were mainly found in the immune response and inflammatory pathways. An interesting finding was the association of the DNA-binding protein inhibitor (ID) family in the silica exposure to lung cells. The linkage of ID1, ID2 and ID3 to cancer may rationalize themselves to be the markers indicating an early response of silicosis. However, further studies are required to consolidate the roles of these genes in silicosis. Copyright © 2017 John Wiley & Sons, Ltd.