Matrix metalloproteinase induction in fibrosis and fibrotic nodule formation due to silica inhalation

A study of inflammatory biomarkers in crystalline silica exposed rock drillers

BACKGROUND

Crystalline silica (CS) exposure can cause serious lung disease in humans, but mechanisms of pulmonary toxicity have not been completely elucidated.

AIMS

To assess pro-inflammatory and anti-inflammatory biomarkers and biomarkers related to the development of chronic obstructive pulmonary disease and fibrosis in serum of rock drillers exposed to CS.

METHODS

Rock drillers (N = 123) exposed to CS and non-specified particulate matter (PM) were compared to 48 referents without current or past exposure to PM in a cross-sectional study.

RESULTS

The rock drillers had been exposed to CS for 10.7 years on average. Geometric mean (GM) current exposure was estimated to 36 µg/m3. Their GM concentration of matrix metalloproteinase 12 (MMP-12) was significantly higher (16 vs. 13 ng/L; p = 0.04), while interleukin (IL) 6 and IL-8 were significantly lower compared to the referents. Also pentraxin 3 was significantly lower (3558 vs. 4592 ng/L; p = 0.01) in the rock drillers. A dose-response relationship was observed between cumulative exposure to CS and MMP-12, the highest exposed subgroup having significantly higher MMP-12 concentrations than the referents.

CONCLUSION

Exposure to CS may increase circulating MMP-12 concentrations in a dose-response related fashion. The results may also suggest a down-regulation of pro-inflammatory pathways.

Unraveling the mechanism of tetrandrine combined with Buyang Huanwu Decoction against silicosis using network pharmacology and molecular docking analyses

Silicosis is an incurable chronic disease characterized by lung fibrosis and inflammation. The combination of tetrandrine and Buyang Huanwu Decoction (BYHWD) has a curative effect on silicosis. However, the mechanism of action and the key active constituent in BYHWD are still unclear. The present study employed network pharmacology and molecular docking to determine the mechanism of action and the key active components of BYHWD of Tetrandrine in combination with BYHWD for silicosis. The primary elements and targets of BYHWD were obtained from the Traditional Chinese Medicine Systems Pharmacology and analysis platform. The targets associated with tetrandrine and silicosis were identified and extracted from the Comparative Toxicogenomics Database and GeneCards database. The potential targets for the treatment of silicosis using a combination of Tetrandrine and BYHWD were identified by considering the overlapping targets between compound drugs and silicosis. These targets were then utilized to construct protein-protein interaction networks, compound drug-ingredient-target networks, and perform enrichment analyses. The top 5 active ingredients present in the compound drug-ingredient-target network are tetrandrine, quercetin, luteolin, kaempferol, and beta-carotene. Similarly, the top 6 hub genes in the protein-protein interaction network are FGF2, MMP-9, MMP-1, IL-10, IL-17A, and IL-6. The molecular docking suggested that the active components may easily access the active pocket of the hub gene. The in-silico investigation suggested that quercetin might be the active component in BYHWD responsible for therapeutic effectiveness against silicosis. This study identified the active compound and potential molecular mechanism underlying the therapeutic effects of BYHWD in combination with tetrandrine for treating silicosis. Notably, we found that quercetin may serve as the key compound in BYHWD for the treatment of silicosis.

Integrated mRNA and microRNA profiling in lung tissue and blood from human silicosis

BACKGROUND

The overwhelming majority of subjects in the current silicosis mRNA and microRNA (miRNA) expression profile are of human blood, lung cells or a rat model, which puts limits on the understanding of silicosis pathogenesis and therapy. To address the limitations, our investigation was focused on differentially expressed mRNA and miRNA profiles in lung tissue from silicosis patients to explore potential biomarker for early detection of silicosis.

METHODS

A transcriptome study was conducted based on lung tissue from 15 silicosis patients and eight normal people, and blood samples from 404 silicosis patients and 177 normal people. Three early stage silicosis, five advanced silicosis and four normal lung tissues were randomly selected for microarray processing and analyze. The differentially expressed mRNAs were further used to conduct Gene Ontology and pathway analyses. Series test of cluster was performed to explore possible changes in differentially expressed mRNA and miRNA expression patterns during the process of silicosis. The blood samples and remaining lung tissues were used in a quantitative real-time PCR (RT-qPCR) (RT-qPCR).

RESULTS

In total, 1417 and 241 differentially expressed mRNAs and miRNAs were identified between lung tissue from silicosis patients and normal people (p < 0.05). However, there was no significant difference in most mRNA or miRNA expression between early stage and advanced stage silicosis lung tissues. RT-qPCR validation results in lung tissues showed expression of four mRNAs (HIF1A, SOCS3, GNAI3 and PTEN) and seven miRNAs was significantly down-regulated compared to those of control group. Nevertheless, PTEN and GNAI3 expression was significantly up-regulated (p < 0.001) in blood samples. The bisulfite sequencing PCR demonstrated that PTEN had significantly decreased the methylation rate in blood samples of silicosis patients.

CONCLUSIONS

PTEN might be a potential biomarker for silicosis as a result of low methylation in the blood.

Combined intervention with N-acetylcysteine and desipramine alleviated silicosis development by regulating the Nrf2/HO-1 and ASMase/ceramide signaling pathways

Silicosis is a systemic disease characterized by diffuse fibrosis of the lung tissue caused by long-term inhalation of large amounts of free silica (SiO₂) dust. The pathogenesis of silicosis has not been fully elucidated, and there is a lack of effective treatment methods. N-acetylcysteine (NAC) can potentially treat pulmonary fibrosis by exerting antioxidant effects. Desipramine (DMI) can influence pulmonary fibrosis development by inhibiting acid sphingomyelinase (ASMase) activity and regulating ceramide concentrations. Both can interfere with pulmonary fibrosis through different mechanisms, but the intervention effects of NAC combined with DMI on silicosis fibrosis have not been reported. Therefore, this study established a rat silicosis model using a single tracheal drip of SiO₂ dust suspension in Wistar rats to investigate the effect of NAC combined with DMI on SiO₂ dust-induced silicosis and its related molecular mechanisms. The histopathological examination of the SiO₂ dust-induced silicosis rats suggested that NAC and DMI alone or in combination could decrease the severity of pulmonary fibrosis in rats. The combined intervention had a better effect on reducing fibrosis than the individual interventions. NAC and DMI, alone or in combination, decreased the levels of markers related to pulmonary fibrosis in rats (smooth muscle α-actin (α-SMA), collagen (Col) I, Col III, hydroxyproline (HYP), inflammatory factors (transforming growth factor-β1 (TGF-β1) and tumor necrosis factor-α (TNF-α)), and lipid peroxidase malondialdehyde (MDA)). The nuclear factor-erythroid 2-related factor 2 (Nrf2)/heme-oxygenase-1 (HO-1) and ASMase/ceramide pathways were inhibited to some extent by increasing the superoxide dismutase (SOD) levels of antioxidant enzymes and 8-iso-prostaglandin F2α (8-iso-PGF2α) levels of lipid peroxides. The combined intervention and NAC alone inhibited the SiO₂ dust-induced elevation of matrix metalloproteinase 1 (MMP-1) and tissue inhibitor matrix metalloproteinase 1 (TIMP-1), but the effect was not significant in the DMI-treated group. Combining DMI and NAC inhibited Col I deposition and reduced HO-1, TIMP-1, and ASMase levels in lung tissues compared to individual treatments. In summary, the SiO₂ dust could induce oxidative stress and inflammation in rats, resulting in an imbalance in extracellular matrix (ECM) synthesis/catabolism and ASMase/ceramide signaling pathway activation, leading to silicosis development.The combined intervention of DMI and NAC may synergistically regulate the Nrf2/HO-1 pathway, maintain the anabolic balance of the ECM, inhibit ASMase/ceramide signaling pathway activation by suppressing the inflammatory response and effectively delay silicosis fibrosis progression.

Matrix Metalloproteinases and Their Inhibitors in Pulmonary Fibrosis: EMMPRIN/CD147 Comes into Play

Pulmonary fibrosis (PF) is characterized by aberrant extracellular matrix (ECM) deposition, activation of fibroblasts to myofibroblasts and parenchymal disorganization, which have an impact on the biomechanical traits of the lung. In this context, the balance between matrix metalloproteinases (MMPs) and their tissue inhibitors of metalloproteinases (TIMPs) is lost. Interestingly, several MMPs are overexpressed during PF and exhibit a clear profibrotic role (MMP-2, -3, -8, -11, -12 and -28), but a few are antifibrotic (MMP-19), have both profibrotic and antifibrotic capacity (MMP7), or execute an unclear (MMP-1, -9, -10, -13, -14) or unknown function. TIMPs are also overexpressed in PF; hence, the modulation and function of MMPs and TIMP are more complex than expected. EMMPRIN/CD147 (also known as basigin) is a transmembrane glycoprotein from the immunoglobulin superfamily (IgSF) that was first described to induce MMP activity in fibroblasts. It also interacts with other molecules to execute non-related MMP aactions well-described in cancer progression, migration, and invasion. Emerging evidence strongly suggests that CD147 plays a key role in PF not only by MMP induction but also by stimulating fibroblast myofibroblast transition. In this review, we study the structure and function of MMPs, TIMPs and CD147 in PF and their complex crosstalk between them.

Retinal nerve fiber layer thickness and retinal vascular caliber alterations in coal miners in northern China: a community-based observational study

AIM

To evaluate retinal nerve fiber layer thickness and retinal vascular caliber alterations in coal mine workers.

METHODS

The community-based observational cross-sectional study included 4004 participants of a sub-population of the Kailuan Study. All the study participants underwent structured interviews with a standardized questionnaire, fundus photography and spectral-domain optical coherence tomography (OCT) examinations performed by trained doctors.

RESULTS

The retinal nerve fiber layer thickness was significantly higher (P=0.006) and the central macular thickness was lower in coal miners (n=659, 51.0±7.8y) as compared to the control (working above the ground; n=477, 51.8±7.5y; P=0.032). Additionally, the downhole workers showed a significantly thicker retinal artery (P=0.012) and vein diameters (P<0.001). In multivariable regression, a thicker retinal nerve fiber layer was associated with a higher cumulative silica dust exposure (P=0.005) after adjusting for younger age and larger spherical equivalent. In a reverse pattern, a higher cumulative silica dust exposure (P=0.004) was significantly associated with a thicker retinal nerve fiber layer after adjusting for age, high-density lipoproteins and uric acid. Wider retinal vein diameters were associated with higher cumulative silica dust exposure (P=0.036) after adjusting for younger age and larger spherical equivalent.

CONCLUSION

The retinal vessels diameters and retinal nerve fiber layer thickness are significantly thicker in long term of coal mining. The results of our study indicate that underground working environment may lead to retinal vessel dilation and inflammation. Thus, ocular examination might be needed within coal miners in order to monitor the occupational eye health as well as the incidence and progression of eye diseases.

Regulation of the Proteolytic Activity of Cysteine Cathepsins by Oxidants

Besides their primary involvement in the recycling and degradation of proteins in endo-lysosomal compartments and also in specialized biological functions, cysteine cathepsins are pivotal proteolytic contributors of various deleterious diseases. While the molecular mechanisms of regulation via their natural inhibitors have been exhaustively studied, less is currently known about how their enzymatic activity is modulated during the redox imbalance associated with oxidative stress and their exposure resistance to oxidants. More specifically, there is only patchy information on the regulation of lung cysteine cathepsins, while the respiratory system is directly exposed to countless exogenous oxidants contained in dust, tobacco, combustion fumes, and industrial or domestic particles. Papain-like enzymes (clan CA, family C1, subfamily C1A) encompass a conserved catalytic thiolate-imidazolium pair (Cys25-His159) in their active site. Although the sulfhydryl group (with a low acidic pKa) is a potent nucleophile highly susceptible to chemical modifications, some cysteine cathepsins reveal an unanticipated resistance to oxidative stress. Besides an introductory chapter and peculiar attention to lung cysteine cathepsins, the purpose of this review is to afford a concise update of the current knowledge on molecular mechanisms associated with the regulation of cysteine cathepsins by redox balance and by oxidants (e.g., Michael acceptors, reactive oxygen, and nitrogen species).

Mouse pulmonary response to dust from sawing Corian®, a solid-surface composite material

Corian®, a solid-surface composite (SSC), is composed of alumina trihydrate and acrylic polymer. The aim of the present study was to examine the pulmonary toxicity attributed to exposure to SSC sawing dust. Male mice were exposed to either phosphate buffer saline (PBS, control), 62.5, 125, 250, 500, or 1000 µg of SSC dust, or 1000 µg silica (positive control) via oropharyngeal aspiration. Body weights were measured for the duration of the study. Bronchoalveolar lavage fluid (BALF) and tissues were collected for analysis at 1 and 14 days post-exposure. Enhanced-darkfield and histopathologic analysis was performed to assess particle distribution and inflammatory responses. BALF cells and inflammatory cytokines were measured. The geometric mean diameter of SSC sawing dust following suspension in PBS was 1.25 µm. BALF analysis indicated that lactate dehydrogenase (LDH) activity, inflammatory cells, and pro-inflammatory cytokines were significantly elevated in the 500 and 1000 µg SSC exposure groups at days 1 and 14, suggesting that exposure to these concentrations of SSC induced inflammatory responses, in some cases to a greater degree than the silica positive control. Histopathology indicated the presence of acute alveolitis at all doses at day 1, which was largely resolved by day 14. Alveolar particle deposition and granulomatous mass formation were observed in all exposure groups at day 14. The SSC particles were poorly cleared, with 81% remaining at the end of the observation period. These findings demonstrate that SSC sawing dust exposure induces pulmonary inflammation and damage that warrants further investigation. Abbreviations: ANOVA: Analysis of Variance; ATH: Alumina Trihydrate; BALF: Bronchoalveolar Lavage Fluid; D_pg: Geometric Mean Diameter; FE-SEM: Field Emission Scanning Electron Microscopy; IACUC: Institutional Animal Care and Use Committee; IFN-γ: Interferon Gamma; IL-1 Β: Interleukin-1 Beta; IL-10: Interleukin-10; IL-12: Interleukin-12; IL-2: Interleukin-2; IL-4: Interleukin-4; IL-5: Interleukin-5; IL-6: Interleukin-6; KC/GRO: Neutrophil-Activating Protein 3; MMAD: Mass Median Aerodynamic Diameter; PBS: Phosphate-Buffered Saline; PEL: Permissible Exposure Limit; PM: Polymorphonuclear Leukocytes; PNOR: Particles Not Otherwise Regulated; SEM/EDX: Scanning Electron Microscope/Energy-Dispersive X-Ray; SSA: Specific Surface Area; SSC: Solid Surface Composite; TNFα: Tumor Necrosis Factor-Alpha; VOC: Volatile Organic Compounds; σ_g: Geometric Standard Deviation.

Dioscin Alleviates Crystalline Silica-Induced Pulmonary Inflammation and Fibrosis through Promoting Alveolar Macrophage Autophagy

Occupational exposure to crystalline silica (CS) particles leads to silicosis, which is characterized by chronic inflammation and abnormal tissue repair. Alveolar macrophages (AMs) play a crucial role in the process of silicosis. Previously, we demonstrated positive effect of dioscin on silicosis through modulating macrophage-elicited innate immune response. However, the concrete molecular mechanism remains to be discovered.

Methods: We established experimental model of silicosis with wildtype and Atg5^flox/floxDppa3^Cre/+ mice and oral administrated dioscin daily to explore the effects of dioscin on macrophages and pulmonary fibrosis. AM cell line MH-S with Atg5 silence was used to explore specific function of dioscin on macrophage-derived inflammation and the underlying molecular mechanism.

Results: Dioscin could promote autophagy in macrophages. Dioscin-triggered AMs autophagy limited mitochondrial reactive oxygen species (mtROS) mass stimulated by CS, reduced mitochondria-dependent apoptosis pathway activation and facilitated cell survival. Relieved oxidative stress resulted in decreased secretion of inflammatory factors and chemokines. Dioscin treatment alleviated macrophage-derived inflammation and subsequent abnormal collagen repair. All the dioscin's protective effects were diminished in Atg5^flox/floxDppa3^Cre/+ mice.

Conclusion: Dioscin promoting autophagy leads to reduced CS-induced mitochondria-dependent apoptosis and cytokine production in AMs, which may provide concrete molecular mechanism for the therapy of silicosis.

Retracted: Pulmonary fibrosis of mice and its molecular mechanism following chronic inhaled exposure to TiO2 nanoparticles

Nanoparticulate titanium dioxide (nano-TiO2 ) has been widely used in industry, medicine and daily life. However, assessment of nano-TiO2 toxicity on health is an important occupational safety issue. Numerous studies have demonstrated that nano-TiO2 can induced sustained pulmonary inflammation, but whether chronic exposure to nano-TiO2 results in pulmonary fibrosis is unclear. In this study, therefore, nano-TiO2 was administered to the male mice by nasal administration for six consecutive months, the inflammatory and/or fibrogenic responses induced by nano-TiO2 were investigated. The results showed that chronic inhaled nano-TiO2 induced pulmonary inflammation and firosis, increased expression of inflammatory cytokines and fibrotic cytokines including nuclear factor-κB, interleukin-1β, tumor necrosis factor-α, monocyte chemotactic protein 1, macrophage inflammatory protein-2, intercellular adhesion molecule 1, vascular cell adhesion molecule 1, transform growth factor -β1, osteopontin, matrix metalloproteinase-1, -2, -3, and -9, tissue inhibitors of metalloproteinase-1, collagen, platelet derived growth factor, and connective tissue growth factor in mouse lung. Taken together, nano-TiO2 -induced pulmonary inflammation and fibrosis are closely associated with increased expression of inflammatory and/or fibrotic cytokines, an imbalanced production of MMPs and TIMP-1 that favors fibrosis in mice, implying that nano-TiO2 may lead to potential health effects.

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.

Therapeutic effects of bone marrow-derived mononuclear cells from healthy or silicotic donors on recipient silicosis mice

Background

Administration of bone marrow mononuclear cells (BMMCs) modulates lung inflammation and fibrosis in experimental silicosis. However, no studies have evaluated whether silicosis affects the efficacy of autologous BMMCs treatment. We hypothesized that BMMCs obtained from healthy or silicotic mice may improve lung function, but they might affect the inflammatory and fibrotic processes differently in experimental silicosis.

Methods

C57BL/6 mice were randomly divided into control (C) and silicosis (SIL) groups. Mice in the SIL group were instilled with silica particles intratracheally; the C animals received saline using the same protocol. On day 15, the animals were treated with saline (Sal) or BMMCs (2 × 10⁶ cells) from healthy (BMMC-healthy) and silicotic (BMMC-sil) donors. Lung mechanics were measured, and lungs were collected for histology and molecular biology analysis.

Results

BMMCs obtained from healthy and silicotic donors presented similar percentages of cell populations. ^99mTc-BMMCs tracking revealed preferential migration of cells to the liver, and only a few GFP⁺ BMMCs were observed in lung tissue 24 h after treatment, regardless of donor type. Both the SIL-BMMC-healthy and SIL-BMMC-sil groups showed improvement in lung function, a reduction in the fractional area of granuloma, and a decrease in the number of mononuclear and apoptotic cells in lung parenchyma. In addition, the number of F4/80⁺ macrophages, the levels of interleukin-1 beta and transforming growth factor beta, and collagen fiber content in granuloma were reduced in SIL-BMMC-healthy mice, whereas mRNA expression of MMP-9 and procollagen I and III was reduced in the SIL-BMMC-sil group.

Conclusions

Administration of BMMCs from healthy and silicotic donors reduced lung inflammation and fibrosis, thus improving lung function. In addition, BMMC-healthy exhibited a greater improvement in lung morpho-functional changes in murine model of silicosis.

Transcriptomics in toxicology

Xenobiotics, of which many are toxic, may enter the human body through multiple routes. Excessive human exposure to xenobiotics may exceed the body's capacity to defend against the xenobiotic-induced toxicity and result in potentially fatal adverse health effects. Prevention of the adverse health effects, potentially associated with human exposure to the xenobiotics, may be achieved by detecting the toxic effects at an early, reversible and, therefore, preventable stage. Additionally, an understanding of the molecular mechanisms underlying the toxicity may be helpful in preventing and/or managing the ensuing adverse health effects. Human exposures to a large number of xenobiotics are associated with hepatotoxicity or pulmonary toxicity. Global gene expression changes taking place in biological systems, in response to exposure to xenobiotics, may represent the early and mechanistically relevant cellular events contributing to the onset and progression of xenobiotic-induced adverse health outcomes. Hepatotoxicity and pulmonary toxicity resulting from exposure to xenobiotics are discussed as specific examples to demonstrate the potential application of transcriptomics or global gene expression analysis in the prevention of adverse health effects associated with exposure to xenobiotics.

TAK1 inhibition attenuates both inflammation and fibrosis in experimental pneumoconiosis

Pneumoconiosis, caused by inhalation of mineral dusts, is a major occupational disease worldwide. Currently, there are no effective drugs owing to a lack of potential therapeutic targets during either the inflammation or fibrosis molecular events in pneumoconiosis. Here, we performed microarrays to identify aberrantly expressed genes in the above molecular events in vitro and found a hub gene transforming growth factor-β-activated kinase 1 (TAK1), which was highly expressed and activated in pneumoconiosis patients as well as silica-exposed rats with experimental pneumoconiosis. Genetic modulation of TAK1 by CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9, RNA interference and overexpression indicated the important role of TAK1 in both inflammation and fibrosis in experimental pneumoconiosis. To achieve pharmacological TAK1 inhibition, we virtually screened out a natural product resveratrol, which targeted TAK1 at both N161 and A107 residues, and significantly inhibited TAK1 activation to attenuate inflammation and fibrosis in vitro. Consistently, in vivo prevention and intervention studies showed that resveratrol could inhibit pulmonary inflammation and fibrosis in silica-exposed rats.

Role of Proteases in Lung Disease: A Brief Overview

Proteases play an important role in health and disease of the lung. In the normal lungs, proteases maintain their homeostatic functions that regulate processes like its regeneration and repair. Dysregulation of proteases–antiproteases balance is crucial in the manifestation of different types of lung diseases. Chronic inflammatory lung pathologies are associated with a marked increase in protease activities. Thus, in addition to protease activities, inhibition of anti-proteolytic control mechanisms are also important for effective microbial infection and inflammation in the lung. Herein, we briefly summarize the role of different proteases and to some extent antiproteases in regulating a variety of lung diseases.

The protective effects of bone morphogenetic protein-7 against epithelial injury and matrix metalloproteases upregulation induced by silica in vitro

OBJECTIVE

We investigate the effects of bone morphogenetic protein-7 (BMP-7) on models with silica-induced and macrophage-mediated fibrosis and its possible mechanisms in vitro.

METHODS

Rat alveolar II epithelial (RLE-6TN) cells were incubated with the supernatant of mouse macrophage-like cells (RAW264.7) and treated with 0, 25, 50, and 100 μg/mL silica. Using Western blotting, the epithelial markers (surfactant proteins-C and E-cadherin) and the mesenchymal markers (fibronectin (FN) and viminten (Vim)) were detected. After neutralizing the BMP-7, the progress of fibrosis was assessed by the content of hydroxyproline (Hyp) and collagen I, III protein levels as well as the Smad signaling pathway proteins, including phosphorylated Smad1/5(P-Smad1/5) and phosphorylated Smad2/3(P-Smad2/3). Collagen I was also identified by immunofluorescence and pretreated with SB-431542, LDN-193189, or anti-BMP-7-neutralizing antibody. In addition, the levels of matrix metalloproteinase-2 (MMP-2) and MMP-9 were detected using Western blotting.

RESULTS

The model of RLE-6TN cells was established successfully, the expressions of Vim, FN, MMP-2, and MMP-9 were upregulated, while the concentration of silica is increased. Neutralizing BMP-7 stimulated the decrease of P-Smad1/5 and the increase of P-Smad2/3, as well as the collagen I, collagen III, FN, and Hyp via Smad signaling pathway. Furthermore, pretreated with LDN-193189 or anti-BMP-7-neutralizing antibody, the expression of collagen I was increased, yet it was decreased with SB-431542 intervention.

CONCLUSION

The activated BMP/Smad and suppressed transforming growth factor-β/Smad pathways could suppress silica-induced fibrosis via a MMP-dependent mechanism. BMP-7 is expected to be the optimized strategy of delaying the interstitial changes.

Environmental, Inhaled and Ingested Causes of Pulmonary Fibrosis

Pulmonary fibrosis is a general term that refers to a collection of connective tissue around alveolar structures. There are over 200 disorders where the lungs may be involved in a fibrotic response. To determine the cause of pulmonary fibrosis requires an in depth understanding of the pathogenesis of pulmonary fibrosis and breadth of knowledge of the causative agents and associated disorders that may lead to pulmonary fibrosis. A comprehensive evaluation of the patient is absolutely essential, starting with detailed history that includes an occupational and environmental history because fibrogenic exposures can occur in many settings. Equally important is a history of ingestion of pharmaceutical or nonpharmaceutical substances. A physical examination and judicious investigations are always a part of any comprehensive clinical assessment but they are not commonly helpful in elucidating the cause of most pulmonary fibrotic disorders. Although, a chest film is invariably done, a logical and strongly recommended next step is a high-resolution computed tomography (HRCT). HRCT provides a better assessment of the radiological pattern, may suggest a diagnosis as well as direct the site, and type of lung biopsy. If the history and investigations do not lead to a diagnosis then a lung biopsy is required. Prevention or removal of the inciting agent is critical to the treatment of these disorders and in some instances corticosteroids may be of help.

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.

Matrix metalloproteinase-10: a novel biomarker for idiopathic pulmonary fibrosis

Background

Matrix metalloproteinases (MMPs) are believed to be involved in the pathogenesis of idiopathic pulmonary fibrosis (IPF), and MMP-7 has been described as a useful biomarker for IPF. However, little is known regarding the significance of MMP-10 as a biomarker for IPF.

Methods

This observational cohort study included 57 patients with IPF. Serum MMPs were comprehensively measured in all patients, and the relationships between these markers and both disease severity and prognosis were evaluated. Bronchoalveolar lavage fluid (BALF) MMP-7 and -10 levels were measured in 19 patients to investigate the correlation between these markers and their corresponding serum values. Immunohistochemical staining for MMP-10 was also performed in IPF lung tissue.

Results

Serum MMP-7 and -10 levels correlated significantly with both the percentage of predicted forced vital capacity (ρ = −0.31, p = 0.02 and ρ = −0.34, p < 0.01, respectively) and the percentage of predicted diffusing capacity of the lung for carbon monoxide (ρ = −0.32, p = 0.02 and ρ = −0.43, p < 0.01, respectively). BALF MMP-7 and -10 levels correlated with their corresponding serum concentrations. Only serum MMP-10 predicted clinical deterioration within 6 months and overall survival. In IPF lungs, the expression of MMP-10 was enhanced and localized to the alveolar epithelial cells, macrophages, and peripheral bronchiolar epithelial cells.

Conclusions

MMP-10 may be a novel biomarker reflecting both disease severity and prognosis in patients with IPF.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0280-9) contains supplementary material, which is available to authorized users.

Indications for distinct pathogenic mechanisms of asbestos and silica through gene expression profiling of the response of lung epithelial cells

Occupational and environmental exposures to airborne asbestos and silica are associated with the development of lung fibrosis in the forms of asbestosis and silicosis, respectively. However, both diseases display distinct pathologic presentations, likely associated with differences in gene expression induced by different mineral structures, composition and bio-persistent properties. We hypothesized that effects of mineral exposure in the airway epithelium may dictate deviating molecular events that may explain the different pathologies of asbestosis versus silicosis. Using robust gene expression-profiling in conjunction with in-depth pathway analysis, we assessed early (24 h) alterations in gene expression associated with crocidolite asbestos or cristobalite silica exposures in primary human bronchial epithelial cells (NHBEs). Observations were confirmed in an immortalized line (BEAS-2B) by QRT-PCR and protein assays. Utilization of overall gene expression, unsupervised hierarchical cluster analysis and integrated pathway analysis revealed gene alterations that were common to both minerals or unique to either mineral. Our findings reveal that both minerals had potent effects on genes governing cell adhesion/migration, inflammation, and cellular stress, key features of fibrosis. Asbestos exposure was most specifically associated with aberrant cell proliferation and carcinogenesis, whereas silica exposure was highly associated with additional inflammatory responses, as well as pattern recognition, and fibrogenesis. These findings illustrate the use of gene-profiling as a means to determine early molecular events that may dictate pathological processes induced by exogenous cellular insults. In addition, it is a useful approach for predicting the pathogenicity of potentially harmful materials.

Asbestos-associated mesothelial cell autoantibodies promote collagen deposition in vitro

Fibrosis, characterized by excessive collagen protein deposition, is a progressive disease that can fatally inhibit organ function. Prolonged exposure to pathogens or environmental toxicants such as asbestos can lead to chronic inflammatory responses associated with fibrosis. Significant exposure to amphibole asbestos has been reported in and around Libby, Montana due to local mining of asbestos-contaminated vermiculite. These exposures have been implicated in a unique disease etiology characterized predominantly by pleural disorders, including fibrosis. We recently reported the discovery of mesothelial cell autoantibodies (MCAAs) in the sera of Libby residents and demonstrated a positive and significant correlation with pleural disease; however, a mechanistic link was not determined. Here we demonstrate that MCAAs induce pleural mesothelial cells to produce a collagen matrix but do not affect production of the pro-inflammatory cytokine tumor growth factor-β. While autoantibodies commonly induce a pro-fibrotic state by inducing epithelial-mesenchymal transition (EMT) of target cells, we found no evidence supporting EMT in cells exposed to MCAA positive human sera. Although implicated in other models of pulmonary fibrosis, activity of the protein SPARC (secreted protein, acidic and rich in cysteine) did not affect MCAA-induced collagen deposition. However, matrix formation was dependent on matrix metalloproteinase (MMP) activity, and we noted increased expression of MMP-8 and -9 in supernatants of mesothelial cells incubated with MCAA positive sera compared to control. These data suggest a mechanism by which MCAA binding leads to increased collagen deposition through altering MMP expression and provides an important mechanistic link between MCAAs and asbestos-related, autoimmune-induced pleural fibrosis.

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.

Extrapulmonary transport of MWCNT following inhalation exposure

Background

Inhalation exposure studies of mice were conducted to determine if multi-walled carbon nanotubes (MWCNT) distribute to the tracheobronchial lymphatics, parietal pleura, respiratory musculature and/or extrapulmonary organs. Male C57BL/6 J mice were exposed in a whole-body inhalation system to a 5 mg/m³ MWCNT aerosol for 5 hours/day for 12 days (4 times/week for 3 weeks, lung burden 28.1 ug/lung). At 1 day and 336 days after the 12 day exposure period, mice were anesthetized and lungs, lymph nodes and extrapulmonary tissues were preserved by whole body vascular perfusion of paraformaldehyde while the lungs were inflated with air. Separate, clean-air control groups were studied at 1 day and 336 days post-exposure. Sirius Red stained sections from lung, tracheobronchial lymph nodes, diaphragm, chest wall, heart, brain, kidney and liver were analyzed. Enhanced darkfield microscopy and morphometric methods were used to detect and count MWCNT in tissue sections. Counts in tissue sections were expressed as number of MWCNT per g of tissue and as a percentage of total lung burden (Mean ± S.E., N = 8 mice per group). MWCNT burden in tracheobronchial lymph nodes was determined separately based on the volume density in the lymph nodes relative to the volume density in the lungs. Field emission scanning electron microscopy (FESEM) was used to examine MWCNT structure in the various tissues.

Results

Tracheobronchial lymph nodes were found to contain 1.08 and 7.34 percent of the lung burden at 1 day and 336 days post-exposure, respectively. Although agglomerates account for approximately 54% of lung burden, only singlet MWCNT were observed in the diaphragm, chest wall, liver, kidney, heart and brain. At one day post exposure, the average length of singlet MWCNT in liver and kidney, was comparable to that of singlet MWCNT in the lungs 8.2 ± 0.3 versus 7.5 ± 0.4 um, respectively. On average, there were 15,371 and 109,885 fibers per gram in liver, kidney, heart and brain at 1 day and 336 days post-exposure, respectively. The burden of singlet MWCNT in the lymph nodes, diaphragm, chest wall and extrapulmonary organs at 336 days post-exposure was significantly higher than at 1 day post-exposure.

Conclusions

Inhaled MWCNT, which deposit in the lungs, are transported to the parietal pleura, the respiratory musculature, liver, kidney, heart and brain in a singlet form and accumulate with time following exposure. The tracheobronchial lymph nodes contain high levels of MWCNT following exposure and further accumulate over nearly a year to levels that are a significant fraction of the lung burden 1 day post-exposure.

Bioreactivity of the crystalline silica polymorphs, quartz and cristobalite, and implications for occupational exposure limits (OELs)

Silica or silicon dioxides (SiO₂) are naturally occurring substances that comprise the vast majority of the earth's crust. Because of their prevalence and commercial applications, they have been widely studied for their potential to induce pulmonary fibrosis and other disorders. Historically, the focus in the workplace has been on the development of inflammation and fibrotic lung disease, the basis for promulgating workplace standards to protect workers. Crystalline silica (CS) polymorphs, predominantly quartz and cristobalite, are used in industry but are different in their mineralogy, chemistry, surface features, size dimensions and association with other elements naturally and during industrial applications. Epidemiologic, clinical and experimental studies in the literature historically have predominantly focused on quartz polymorphs. Thus, in this review, we summarize past scientific evaluations and recent peer-reviewed literature with an emphasis on cristobalite, in an attempt to determine whether quartz and cristobalite polymorphs differ in their health effects, toxicity and other properties that may dictate the need for various standards of protection in the workplace. In addition to current epidemiological and clinical reports, we review in vivo studies in rodents as well as cell culture studies that shed light on mechanisms intrinsic to the toxicity, altered cell responses and protective or defense mechanisms in response to these minerals. The medical and scientific literature indicates that the mechanisms of injury and potential causation of inflammation and fibrotic lung disease are similar for quartz and cristobalite. Our analysis of these data suggests similar occupational exposure limits (OELs) for these minerals in the workplace.

Matrix metalloproteinase induction of Rac1b, a key effector of lung cancer progression

Lung cancer is more deadly than colon, breast, and prostate cancers combined, and treatment improvements have failed to improve prognosis significantly. Here, we identify a critical mediator of lung cancer progression, Rac1b, a tumor-associated protein with cell-transforming properties that are linked to the matrix metalloproteinase (MMP)-induced epithelial-mesenchymal transition (EMT) in lung epithelial cells. We show that expression of mouse Rac1b in lung epithelial cells of transgenic mice stimulated EMT and spontaneous tumor development and that activation of EMT by MMP-induced expression of Rac1b gave rise to lung adenocarcinoma in the transgenic mice through bypassing oncogene-induced senescence. Rac1b is expressed abundantly in stages 1 and 2 of human lung adenocarcinomas and, hence, is an attractive molecular target for the development of new therapies that prevent progression to later-stage lung cancers.

Bone marrow-derived matrix metalloproteinase-9 is associated with fibrous adhesion formation after murine flexor tendon injury

The pathogenesis of adhesions following primary tendon repair is poorly understood, but is thought to involve dysregulation of matrix metalloproteinases (Mmps). We have previously demonstrated that Mmp9 gene expression is increased during the inflammatory phase following murine flexor digitorum (FDL) tendon repair in association with increased adhesions. To further investigate the role of Mmp9, the cellular, molecular, and biomechanical features of healing were examined in WT and Mmp9^−/− mice using the FDL tendon repair model. Adhesions persisted in WT, but were reduced in Mmp9^−/− mice by 21 days without any decrease in strength. Deletion of Mmp9 resulted in accelerated expression of neo-tendon associated genes, Gdf5 and Smad8, and delayed expression of collagen I and collagen III. Furthermore, WT bone marrow cells (GFP⁺) migrated specifically to the tendon repair site. Transplanting myeloablated Mmp9^−/− mice with WT marrow cells resulted in greater adhesions than observed in Mmp9^−/− mice and similar to those seen in WT mice. These studies show that Mmp9 is primarily derived from bone marrow cells that migrate to the repair site, and mediates adhesion formation in injured tendons. Mmp9 is a potential target to limit adhesion formation in tendon healing.

Induction of pulmonary fibrosis by cerium oxide nanoparticles

Cerium compounds have been used as a diesel engine catalyst to lower the mass of diesel exhaust particles, but are emitted as cerium oxide (CeO(2)) nanoparticles in the diesel exhaust. In a previous study, we have demonstrated a wide range of CeO(2)-induced lung responses including sustained pulmonary inflammation and cellular signaling that could lead to pulmonary fibrosis. In this study, we investigated the fibrogenic responses induced by CeO(2) in a rat model at various time points up to 84 days post-exposure. Male Sprague Dawley rats were exposed to CeO(2) by a single intratracheal instillation. Alveolar macrophages (AM) were isolated by bronchial alveolar lavage (BAL). AM-mediated cellular responses, osteopontin (OPN) and transform growth factor (TGF)-β1 in the fibrotic process were investigated. The results showed that CeO(2) exposure significantly increased fibrotic cytokine TGF-β1 and OPN production by AM above controls. The collagen degradation enzymes, matrix metalloproteinase (MMP)-2 and -9 and the tissue inhibitor of MMP were markedly increased in the BAL fluid at 1 day- and subsequently declined at 28 days after exposure, but remained much higher than the controls. CeO(2) induced elevated phospholipids in BAL fluid and increased hydroxyproline content in lung tissue in a dose- and time-dependent manner. Immunohistochemical analysis showed MMP-2, MMP-9 and MMP-10 expressions in fibrotic regions. Morphological analysis noted increased collagen fibers in the lungs exposed to a single dose of 3.5mg/kg CeO(2) and euthanized at 28 days post-exposure. Collectively, our studies show that CeO(2) induced fibrotic lung injury in rats, suggesting it may cause potential health effects.

Blood gene expression profiling detects silica exposure and toxicity

Blood gene expression profiling was investigated as a minimally invasive surrogate approach to detect silica exposure and resulting pulmonary toxicity. Rats were exposed by inhalation to crystalline silica (15 mg/m³, 6 h/day, 5 days), and pulmonary damage and blood gene expression profiles were determined after latency periods (0-16 weeks). Silica exposure resulted in pulmonary toxicity as evidenced by histological and biochemical changes in the lungs. The number of significantly differentially expressed genes in the blood, identified by microarray analysis, correlated with the severity of silica-induced pulmonary toxicity. Functional analysis of the differentially expressed genes identified activation of inflammatory response as the major biological signal. Induction of pulmonary inflammation, as suggested by the blood gene expression data, was supported by significant increases in the number of macrophages and infiltrating neutrophils as well as the activity of pro-inflammatory chemokines observed in the lungs of the silica-exposed rats. A gene expression signature developed using the blood gene expression data predicted the exposure of rats to lower, minimally toxic and nontoxic concentrations of silica. Taken together, our findings suggest the potential application of peripheral blood gene expression profiling as a minimally invasive surrogate approach to detect pulmonary toxicity induced by silica in the rat. However, further research is required to determine the potential application of our findings specifically to monitor human exposure to silica and the resulting pulmonary effects.

Fibrogenic and redox-related but not proinflammatory genes are upregulated in Lewis rat model of chronic silicosis

Silicosis, a fibrotic granulomatous lung disease, may occur through accidental high-dose or occupational inhalation of silica, leading to acute/accelerated and chronic silicosis, respectively. While chronic silicosis has a long asymptomatic latency, lung inflammation and apoptosis are hallmarks of acute silicosis. In animal models, histiocytic granulomas develop within days after high-dose intratracheal (IT) silica instillation. However, following chronic inhalation of occupationally relevant doses of silica, discrete granulomas resembling human silicosis arise months after the final exposure without significant lung inflammation/apoptosis. To identify molecular events associated with chronic silicosis, lung RNA samples from controls or subchronic silica-exposed rats were analyzed by Affymetrix at 28 wk after silica exposures. Results suggested a significant upregulation of 144 genes and downregulation of 7 genes. The upregulated genes included complement cascade, chemokines/chemokine receptors, G-protein signaling components, metalloproteases, and genes associated with oxidative stress. To examine the kinetics of gene expression relevant to silicosis, quantitative polymerase chain reaction (qPCR), enzyme-linked immunosorbent assay (ELISA), Luminex-bead assays, Western blotting, and/or zymography were performed on lung tissues from 4 d, 28 wk, and intermediate times after subchronic silica exposure and compared with 14-d acute silicosis samples. Results indicated that genes regulating fibrosis (secreted phosphoprotein-1, Ccl2, and Ccl7), redox enzymes (superoxide dismutase-2 and arginase-1), and the enzymatic activities of matrix metalloproteinases 2 and 9 were upregulated in acute and chronic silicosis models. However, proinflammatory cytokines were strongly upregulated only in acute silicosis. Thus, inflammatory cytokines are associated with acute but not chronic silicosis. Data suggest that genes regulating fibrosis, oxidative stress, and metalloproteases may contribute to both acute and chronic silicosis.

Direct fibrogenic effects of dispersed single-walled carbon nanotubes on human lung fibroblasts

Nanomaterials, including single-walled carbon nanotubes (SWCNT), are being developed for a variety of commercial products. However, adverse health effects attributed to these new materials are not well understood. Recent reports showed that exposure of mice to dispersed SWCNT (DSWCNT) produced a rapid and progressive interstitial lung fibrosis without persistent inflammation. To understand the mechanism underlying this unusual fibrogenicity of DSWCNT, the present investigation focused on the direct bioactivity of DSWCNT using a cell culture of lung fibroblasts that represent a major cell type resident in the lung interstitium and responsible for the production of collagen matrix. At concentrations relevant to those used in vivo, in vitro exposure of lung fibroblasts to DSWCNT stimulated cell proliferation and induced collagen production without producing cell damage. One of the major matrix metalloproteinases (MMP), MMP-9, which is known to be involved in lung fibrosis, was also elevated by DSWCNT treatment both in vitro and in vivo. Taken together, these results suggest that direct stimulation of fibroblasts by DSWCNT translocated into the interstitium may play a significant role in DSWCNT-induced lung fibrosis. Our data also suggest that the dispersion status and/or size of the SWCNT structures is a critical factor in determining nanoparticle fibrogenicity and that MMP-9 may be involved in the fibrogenic process. The results obtained may aid in the development of in vitro models for rapid screening of the potential fibrogenicity of carbon nanotubes, which are lacking and urgently needed.

Spaceflight modulates expression of extracellular matrix, adhesion, and profibrotic molecules in mouse lung

NASA has reported pulmonary abnormalities in astronauts on space missions, but the molecular changes in lung tissue remain unknown. The goal of the present study was to explore the effects of spaceflight on expression of extracellular matrix (ECM), cell adhesion, and pro-fibrotic molecules in lungs of mice flown on Space Shuttle Endeavour (STS-118). C57BL/6Ntac mice housed in animal enclosure modules during a 13-day mission in space (FLT) were killed within hours after return; ground controls were treated similarly for comparison (GRD). Analysis of genes associated with ECM and adhesion molecules was performed according to quantitative RT-PCR. The data revealed that FLT lung samples had statistically significant transcriptional changes, i.e., at least 1.5-fold, in 25 out of 84 examined genes (P < 0.05); 15 genes were upregulated and 10 were downregulated. The genes that were upregulated by more than twofold were Ctgf, Mmp2, Ncam1, Sparc, Spock1, and Timp3, whereas the most downregulated genes were Lama1, Mmp3, Mmp7, vcam-1, and Sele. Histology showed profibrosis-like changes occurred in FLT mice, more abundant collagen accumulation around blood vessels, and thicker walls compared with lung samples from GRD mice. Immunohistochemistry was used to compare expression of six selected proteins associated with fibrosis. Immunoreactivity of four proteins (MMP-2, CTGF, TGF-beta1, and NCAM) was enhanced by spaceflight, whereas, no difference was detected in expression of MMP-7 and MMP-9 proteins between the FLT and GRD groups. Taken together, the data demonstrate that significant changes can be readily detected shortly after return from spaceflight in the expression of factors that can adversely influence lung function.

Response of extracellular matrix regulators in mouse lung after exposure to photons, protons and simulated solar particle event protons

This study compared the effects of photons (gamma rays), protons and simulated solar particle event protons (sSPE) on the expression of profibrotic factors/extracellular matrix (ECM) regulators in lung tissue after whole-body irradiation. TGF-beta1, matrix metalloproteinase 2 and 9 (MMP-2, -9), and tissue inhibitor of metalloproteinase 1 and 2 (TIMP-1, -2) were assessed on days 4 and 21 in lungs from C57BL/6 mice exposed to 0 Gy or 2 Gy photons (0.7 Gy/min), protons (0.9 Gy/min) and sSPE (0.056 Gy/h). RT-PCR, histological and immunohistochemical techniques were used. The most striking changes included (1) up-regulation of TGF-beta1 by photons and sSPE, but not protons, at both times, (2) MMP-2 enhancement by photons and sSPEs, (3) TIMP-1 up-regulation by photons at both times, and (4) more collagen accumulation after exposure to either photons or sSPE than after exposure to protons. The findings demonstrate that expression of important ECM regulators was highly dependent upon the radiation regimen as well as the time after exposure. The data further suggest that irradiation during an SPE may increase an astronaut's risk for pulmonary complications. The greater perturbations after photon exposure compared to proton exposure have clinical implications and warrant further investigation.

8-isoprostane and leukotrienes in exhaled breath condensate in Czech subjects with silicosis

Silicosis has progressive, but unpredictable development. There are no markers routinely available to measure the activity and prognosis of silicosis. 8-isoprostane, a marker of oxidative stress and leukotrienes B4, C4, D4, and E4 were measured in exhaled breath condensate in patients with silicosis. Sixty subjects were examined, with mean age 66.7+/-2.0 yr and mean exposure to silica 23.6+/-2.5 yr. The control group had 25 subjects, with mean age 64.7+/-4.8 yr. Exhaled breath was collected using the EcoScreen (Jaeger, Germany); 8-isoprostane and leukotrienes were analyzed by high-performance liquid chromatography/mass spectrometry. Several lung functions parameters were impaired in silicotics in comparisons with the controls; ESR, alpha1-antitrypsin and proteinuria were higher in the silicotics. Antineutrophilic cytoplasmic antibodies were more frequent in the silicotics (39%) than in the controls (4%), (p=0.0017). The mean level of 8-isoprostane in the patients with silicosis was 73.6+/-9.9 vs. 43+/-10 pg/ml (p=0.0001) in the controls. Silica exposure category (high, medium, none) was positively associated with the level of 8-isoprostane. In the patients with complicated silicosis, a high level of 8-isoprostane was found more frequently (p=0.0194). Leukotriene D4 was also increased in the silicotics (21.1+/-2.7 pg/ml) vs. the controls (14.7+/-2.7 pg/ml), (p=0.001). No significant effect of smoking or alcohol consumption on the markers examined was seen. This is the first study using exhaled breath condensate analysis in patients with silicosis.

Differences in both matrix metalloproteinase 9 concentration and zymographic profile between plasma and serum with clot activators are due to the presence of amorphous silica or silicate salts in blood collection devices

Matrix metalloproteinases (MMPs) are promising diagnostic tools, and blood sampling/handling alters MMP concentrations between plasma and serum and between serum with and without clot activators. To explain the higher MMP-9 expression in serum collected with clot accelerators relative to serum with no additives and to plasma, we analyzed the effects of increasing amounts of silica and silicates (components of clot activators) in citrate plasma, serum, and buffy coats collected in both plastic and glass tubes from 50 healthy donors, and we analyzed the effects of silica and silicate on cultured leukemia cells. The levels of MMP-2 did not show significant changes between glass and plastic tubes, between serum and plasma, between serum with and without clot accelerators, or between silica and silicate treatments. No modification of MMP-9 expression was obtained by the addition of silica or silicate to previously separated plasma and serum. Increasing the amounts of nonsoluble silica and soluble silicate added to citrate and empty tubes prior to blood collection resulted in increasing levels of MMP-9 relative to citrate plasma and serum. Silica and silicate added to buffy coats and leukemia cells significantly induced MMP-9 release/secretion, demonstrating that both silica and silicate induce the release of pro- and complexed MMP-9 forms. We recommend limiting the misuse of serum and avoiding the interfering effects of clot activators.

Cysteine cathepsins and caspases in silicosis

Silicosis is an occupational pneumoconiosis caused by inhalation of crystalline silica. It leads to the formation of fibrohyalin nodes that result in progressive fibrosis. Alternatively, emphysema may occur, with abnormal destruction of collagen fibres in the advanced stages. Although the pathophysiological mechanisms remain unclear, it has been established that the lung responds to silica by massive enrollment of alveolar macrophages, triggering an inflammatory cascade of reactions. An imbalance in the expression of lung proteases and their inhibitors is implicated in extracellular matrix remodelling and basement membrane disruption. Moreover, exposure to silica can initiate apoptotic cell death of macrophages. This review summarises the current knowledge on cysteine cathepsins that have been ignored so far during silicosis and outlines the recent progress on cellular pathways leading to silica-induced caspase activation, which have been partly delineated.

Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs in the respiratory tract: potential implications in asthma and other lung diseases

In healthy lung, Matrix Metalloproteinases (MMPs) and their physiological inhibitors, tissue inhibitors of matrix metalloproteinases (TIMPs), are produced in the respiratory tract by a panel of different structural cells. These activities are mandatory for many physiological processes including development, wound healing and cell trafficking. Deregulation of proteolytic-antiproteolytic network and inappropriate secretion of various MMPs by stimulated structural or inflammatory cells is thought to take part to pathophysiology of numerous lung diseases including asthma, chronic obstructive pulmonary disease (COPD), lung fibrosis and lung cancer. Cytokines and growth factors are involved in these inflammatory processes and some of those mediators interact directly with MMPs and TIMPs leading either to a regulation of their expression or changes in their biological activities by proteolytic cleavage. In turn, cytokines and growth factors modulate secretion of MMPs establishing a complex network of reciprocal interactions. Every MMP seem to play a rather specific role and some variations of their expression are observed in different lung diseases. The precise role of these enzymes and their inhibitors is now studied in depth as they could represent relevant therapeutic targets for many diseases. Indeed, MMP inhibition can lead either to a decrease of the intensity of a pathological process or, in the contrary for some of them, to an increase of disease severity. In this review, we focus on the role played by MMPs and TIMPs in asthma and we provide an overview of their potential roles in COPD, lung fibrosis and lung cancer, with a special emphasis on loops including MMPs and cytokines and growth factors relevant in these diseases.

Nitric Oxide and Reactive Oxygen Species Production Causes Progressive Damage in Rats after Cessation of Silica Inhalation

Our laboratory has previously reported results from a rat silica inhalation study which determined that, even after silica exposure ended, pulmonary inflammation and damage progressed with subsequent fibrosis development. In the present study, the relationship between silica exposure, nitric oxide (NO) and reactive oxygen species (ROS) production, and the resultant pulmonary damage is investigated in this model. Rats were exposed to silica (15 mg/m3, 6 h/day) for either 20, 40, or 60 days. A portion of the rats from each exposure were sacrificed at 0 days postexposure, while another portion was maintained without further exposure for 36 days to examine recovery or progression. The major findings of this study are: (1) silica-exposed rat lungs were in a state of oxidative stress, the severity of which increased during the postexposure period, (2) silica-exposed rats had significant increase in lung NO production which increased in magnitude during the postexposure period, and (3) the presence of silica particle(s) in an alveolar macrophage (AM) was highly associated with inducible nitric oxide synthase (iNOS) protein. These data indicate that, even after silica exposure has ended, and despite declining silica lung burden, silica-induced pulmonary NO and ROS production increases, thus producing a more severe oxidative stress. A quantitative association between silica and expression of iNOS protein in AMs was also determined, which adds to our previous observation that iNOS and NO-mediated damage are associated anatomically with silica-induced pathological lesions. Future studies will be needed to determine whether the progressive oxidative stress, and iNOS activation and NO production, is a direct result of silica lung burden or a consequence of silica-induced biochemical mediators.