Distinct metabolic features in the plasma of patients with silicosis and dust-exposed workers in China: a case-control study

Silica aggravates pulmonary fibrosis through disrupting lung microbiota and amino acid metabolites

Silicosis, recognized as a severe global public health issue, is an irreversible pulmonary fibrosis caused by the long-term inhalation of silica particles. Given the intricate pathogenesis of silicosis, there is no effective intervention measure, which poses a severe threat to public health. Our previous study reported that dysbiosis of lung microbiota is associated with the development of pulmonary fibrosis, potentially involving the lipopolysaccharides/toll-like receptor 4 pathway. Similarly, the process of pulmonary fibrosis is accompanied by alterations in metabolic pathways. This study employed a combined approach of 16S rDNA sequencing and metabolomic analysis to investigate further the role of lung microbiota in silicosis delving deeper into the potential pathogenesis of silicosis. Silica exposure can lead to dysbiosis of the lung microbiota and the occurrence of pulmonary fibrosis, which was alleviated by a combination antibiotic intervention. Additionally, significant metabolic disturbances were found in silicosis, involving 85 differential metabolites among the three groups, which are mainly focused on amino acid metabolic pathways. The changed lung metabolites showed a substantial correlation with lung microbiota. The relative abundance of Pseudomonas negatively correlated with L-Aspartic acid, L-Glutamic acid, and L-Threonine levels. These results indicate that dysbiosis in pulmonary microbiota exacerbates silica-induced fibrosis through impacts on amino acid metabolism, providing new insights into the potential mechanisms and interventions of silicosis.

Research progress on the pathogenesis and prediction of pneumoconiosis among coal miners

Pneumoconiosis is the most common occupational disease among coal miners, which is a lung disease caused by long-term inhalation of coal dust and retention in the lungs. The early stage of this disease is highly insidious, and pulmonary fibrosis may occur in the middle and late stages, leading to an increase in patient pain index and mortality rate. Currently, there is a lack of effective treatment methods. The pathogenesis of pneumoconiosis is complex and has many influencing factors. Although the characteristics of coal dust have been considered the main cause of different mechanisms of pneumoconiosis, the effects of coal dust composition, particle size and shape, and coal dust concentration on the pathogenesis of pneumoconiosis have not been systematically elucidated. Meanwhile, considering the irreversibility of pneumoconiosis progression, early prediction for pneumoconiosis patients is particularly important. However, there is no early prediction standard for pneumoconiosis among coal miners. This review summarizes the relevant research on the pathogenesis and prediction of pneumoconiosis in coal miners in recent years. Firstly, the pathogenesis of coal worker pneumoconiosis and silicosis was discussed, and the impact of coal dust characteristics on pneumoconiosis was analyzed. Then, the early diagnostic methods for pneumoconiosis have been systematically introduced, with a focus on image collaborative computer-aided diagnosis analysis and biomarker detection. Finally, the challenge of early screening technology for miners with pneumoconiosis was proposed.

3D printer emissions elicit filament-specific and dose-dependent metabolic and genotoxic effects in human airway epithelial cells

Three-dimensional (3D) printers have become popular educational tools in secondary and post-secondary STEM curriculum; however, concerns have emerged regarding inhalation exposures and associated health risks. Current evidence suggests that filament materials and site conditions may cause differences in the chemical profiles and toxicological properties of 3D printer emissions; however, few studies have evaluated exposures directly in the classroom. In this study, we monitored and sampled particulate matter (PM) emitted from acrylonitrile-butadiene-styrene (ABS) and polylactic acid (PLA) filaments during a 3-hour 3D printing session in a high school classroom using aerosol monitoring instrumentation and collection media. To evaluate potential inhalation risks, Multiple Path Particle Dosimetry (MPPD) modeling was used to estimate inhaled doses and calculate in vitro concentrations based on the observed aerosol data and specific lung and breathing characteristics. Dynamic light scattering was used to evaluate the hydrodynamic diameter, zeta potential, and polydispersity index (PDI) of extracted PM emissions dispersed in cell culture media. Small airway epithelial cells (SAEC) were employed to determine cellular viability, genotoxic, inflammatory, and metabolic responses to each emission exposure using MTS, ELISA, and high-performance liquid chromatography-mass spectrometry (HPLC-MS), respectively. Aerosol monitoring data revealed that emissions from ABS and PLA filaments generated similar PM concentrations within the ultrafine and fine ranges. However, DLS analysis showed differences in the physicochemical properties of ABS and PLA PM, where the hydrodynamic diameter of PLA PM was greater than ABS PM, which may have influenced particle deposition rates and cellular outcomes. While exposure to both ABS and PLA PM reduced cell viability and induced MDM2, an indicator of genomic instability, PLA PM alone increased gamma-H2AX, a marker of double-stranded DNA breaks. ABS and PLA emissions also increased the release of pro-inflammatory cytokines, although this did not reach significance. Furthermore, metabolic profiling via high performance liquid chromatography-mass spectrometry (HPLC-MS) and subsequent pathway analysis revealed filament and dose dependent cellular metabolic alterations. Notably, our metabolomic analysis also revealed key metabolites and pathways implicated in PM-induced oxidative stress, DNA damage, and respiratory disease that were perturbed across both tested doses for a given filament. Taken together, these findings suggest that use of ABS and PLA filaments in 3D printers within school settings may potentially contribute to adverse respiratory responses especially in vulnerable populations.

Kynurenine acts as a signaling molecule to attenuate pulmonary fibrosis by enhancing the AHR-PTEN axis

INTRODUCTION

Pulmonary fibrosis (PF) is a fatal fibrotic lung disease without any options to halt disease progression. Feasible evidence suggests that aberrant metabolism of amino acids may play a role in the pathoetiology of PF. However, the exact impact of kynurenine (Kyn), a metabolite derived from tryptophan (Trp) on PF is yet to be addressed.

OBJECTIVES

This study aims to elucidate the role of kynurenine in both the onset and advancement of PF.

METHODS

Liquid chromatography-tandem mass spectrometry was employed to assess Kyn levels in patients with idiopathic PF and PF associated with Sjögren's syndrome. Additionally, a mouse model of PF induced by bleomycin was utilized to study the impact of Kyn administration. Furthermore, cell models treated with TGF-β1 were used to explore the mechanism by which Kyn inhibits fibroblast functions.

RESULTS

We demonstrated that high levels of Kyn are a clinical feature in both idiopathic PF patients and primary Sjögren syndrome associated PF patients. Further studies illustrated that Kyn served as a braking molecule to suppress fibroblast functionality, thereby protecting mice from bleomycin-induced lung fibrosis. The protective effects depend on AHR, in which Kyn induces AHR nuclear translocation, where it upregulates PTEN expression to blunt TGF-β mediated AKT/mTOR signaling in fibroblasts. However, in fibrotic microenviroment, the expression of AHR is repressed by methyl-CpG-binding domain 2 (MBD2), a reader interpreting the effect of DNA methylation, which results in a significantly reduced sensitivity of Kyn to fibroblasts. Therefore, exogenous administration of Kyn substantially reversed established PF.

CONCLUSION

Our studies not only highlighted a critical role of Trp metabolism in PF pathogenesis, but also provided compelling evidence suggesting that Kyn could serve as a promising metabolite against PF.

Urine LMs quantitative analysis strategy development and LMs CWP biomarkers discovery

Coal workers' pneumoconiosis (CWP) is one of the most common inhalation occupational diseases. It is no effective treatment methods. Early diagnosis of CWP could reduce mortality. Lipid mediators (LMs) as key mediators in the generation and resolution of inflammation, are natural biomarkers for diagnosis inflammatory disease, such as CWP. The UHPLC-MRM technique was used to detect LMs in urine. The metabolic network of LMs in CWP and CT group samples was comprehensively analyzed. Screening for major difference compounds between the two groups. Aimed to contribute to the early diagnosis and treatment of CWP. Urinary levels of 13-OxoODE, 9-OxoODE, and 9,10-EpOME were significantly higher in the CWP group compared with the CT group (P < 0.05). In the model group, the area under the receiver operating characteristic (ROC) for 9-OxoODE,13-OxoODE,9,10-EpOME was 84.4%, 73.3%, and 80.9%, respectively. In the validation group, the area under the ROC was 87.0%, 88.8%, and 68.8% for 9-OxoODE,13-OxoODE,9,10-EpOME, respectively. According to the logistic regression model, the area under the ROC was 80.4% in the model group and 86.7% in the validation group. 13-OxoODE,9-OxoODE,9,10-EpOME could be used as biomarkers for early diagnosis. Significant abnormalities of LOX and CYP450 enzyme pathways were seen in CWP organisms. Changes in the CYP450 enzyme pathway may be associated with PAHs.

Kynurenine Pathway in Respiratory Diseases

The kynurenine pathway is the primary route for tryptophan catabolism and has received increasing attention as its association with inflammation and the immune system has become more apparent. This review provides a broad overview of the kynurenine pathway in respiratory diseases, from the initial observations to the characterization of the different cell types involved in the synthesis of kynurenine metabolites and the underlying immunoregulatory mechanisms. With a focus on respiratory infections, the various attempts to characterize the kynurenine/tryptophan (K/T) ratio as an inflammatory marker are reviewed. Its implication in chronic lung inflammation and its exacerbation by respiratory pathogens is also discussed. The emergence of preclinical interventional studies targeting the kynurenine pathway opens the way for the future development of new therapies.

Lipid characteristics of lung tissue in silicosis rat model were studied based on lipid metabolomics

Silicosis is a common occupational disease caused by the long-term inhalation of large amounts of silica dust. Lipid metabolism plays an important role in the progression of silicosis, but its contributing mechanism remains unclear. The aim of this study was to investigate the differential lipid metabolites and active metabolic pathways in silicosis rat lung tissue. We first constructed a silicosis rat model, and randomly divided 24 male SD rats into control group (C), silicosis group for 1 week (S1W), silicosis group for 2 weeks (S2W) and silicosis group for 4 weeks (S4W) with 6 rats in each group. 1 mL SiO2 suspension (50 mg/mL) or normal saline were injected into the trachea, and the rats were killed at 1 week, 2 weeks and 4 weeks, respectively. The lung tissue pathology of the rats was observed by HE staining and VG staining, and the plasma TC and FC levels were detected by the kit. Western blot was used to detect the expression of lipid-related factors CD36, PGC1α and LXR. In addition, lipidomics analysis of lung tissue samples was performed using UPLC-IMS-QTOF mass spectrometer to screen out potential differential metabolites in silicosis models and analyze lipid enrichment, and verified the expression of differential gene CHPT1 in the metabolic pathway. HE and VG staining showed that the number of nodules and fibrosis increased in a time-dependent manner in the silicosis model group, and the levels of TC, FC and CE in silicosis plasma increased. Western blot results showed that PGC1α and LXR decreased in the silicosis model group, while CD36 expression increased. In addition, metabolomics screened out 28 differential metabolites in the S1W group, 32 in the S2W group, and 22 in the S4W group, and found that the differential metabolites were mainly enriched in metabolic pathways such as glycerophospholipid metabolism and ether lipid metabolism, and the expression of differential gene CHPT1 in the metabolic pathway was decreased in the silicosis model group. These results suggest that there are significant changes in lipid metabolites in lung tissue in silicosis rat models, and glycerophospholipid metabolism was significantly enriched, suggesting that glycerophospholipids play an important role in the progression of silicosis. The differential metabolites and pathways reported in this study may provide new ideas for the pathogenesis of silicosis.

Longitudinal assessment of bleomycin-induced pulmonary fibrosis by evaluating TGF-β1/Smad2, Nrf2 signaling and metabolomic analysis in mice

INTRODUCTION

Pulmonary fibrosis (PF) is characterized by an increase in collagen synthesis and deposition of extracellular matrix. Several factors, including transforming growth factor-β1 (TGF-β1), mothers against decapentaplegic homolog family proteins (Smad), and alpha-smooth muscle actin (α-SMA) trigger extracellular matrix (ECM) accumulation, fibroblast to myofibroblasts conversion, and epithelial-to-mesenchymal-transition (EMT) leading to PF. However, the role of cellular defense mechanisms such as the role of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling during the onset and progression of PF is not understood completely.

AIM

The present study aims to analyze the involvement of TGF-β1/Smad signaling, and Nrf2 in the EMT and metabolic alterations that promote fibrosis in a time-dependent manner using bleomycin (BLM)-induced PF model in C57BL/6 mice.

KEY FINDINGS

Histopathological studies revealed loss of lung architecture and increased collagen deposition in BLM-exposed mice. BLM upregulated TGF-β1/Smad signaling and α-SMA at all time-points. The gradual increase in the accumulation of α-SMA and collagen implied the progression of PF. BLM exposure raises Nrf2 throughout each specified time-point, which suggests that Nrf2 activation might be responsible for TGF-β1-induced EMT and the development of PF. Further, metabolomic studies linked the development of PF to alterations in metabolic pathways. The pentose phosphate pathway (PPP) was consistently enriched across all the time-points. Additionally, alterations in 22 commonly enriched pathways, associated with fatty acid (FA) and amino acid metabolism were observed in 30- and 60-days.

SIGNIFICANCE

This study elucidates the association of TGF-β1/Smad and Nrf2 signaling in the EMT and metabolic alterations associated with the etiology and progression of PF.

Yangqing Chenfei formula alleviates silica-induced pulmonary inflammation in rats by inhibiting macrophage M1 polarization

BACKGROUND

Yangqing Chenfei formula (YCF) is a traditional Chinese medicine formula for early-stage silicosis. However, the therapeutic mechanism is unclear. The purpose of this study was to determine the mechanism for the effects of YCF on early-stage experimental silicosis.

METHODS

The anti-inflammatory and anti-fibrotic effects of YCF were determined in a silicosis rat model, which was established by intratracheal instillation of silica. The anti-inflammatory efficacy and molecular mechanisms of YCF were examined in a lipopolysaccharide (LPS)/interferon (IFN)-γ-induced macrophage inflammation model. Network pharmacology and transcriptomics were integrated to analyze the active components, corresponding targets, and anti-inflammatory mechanisms of YCF, and these mechanisms were validated in vitro.

RESULTS

Oral administration of YCF attenuated the pathological changes, reduced inflammatory cell infiltration, inhibited collagen deposition, decreased the levels of inflammatory factors, and reduced the number of M1 macrophages in the lung tissue of rats with silicosis. YCF5, the effective fraction of YCF, significantly attenuated the inflammatory factors induced by LPS and IFN-γ in M1 macrophages. Network pharmacology analysis showed that YCF contained 185 active components and 988 protein targets, which were mainly associated with inflammation-related signaling pathways. Transcriptomic analysis showed that YCF regulated 117 reversal genes mainly associated with the inflammatory response. Integrative analysis of network pharmacology and transcriptomics indicated that YCF suppressed M1 macrophage-mediated inflammation by regulating signaling networks, including the mTOR, mitogen-activated protein kinases (MAPK), PI3K-Akt, NF-κB, and JAK-STAT signaling pathways. In vitro studies confirmed that the active components of YCF significantly decreased the levels of p-mTORC1, p-P38, and p-P65 by suppressing the activation of related-pathways.

CONCLUSION

YCF significantly attenuated the inflammatory response in rats with silicosis via the suppression of macrophage M1 polarization by inhibiting a "multicomponent-multitarget-multipathway" network.

The temporal characteristics of the disruption of gut microbiota, serum metabolome, and cytokines by silica exposure in wistar rats

Silicosis is one of the most frequent, rapidly developing, and lethal types of pneumoconiosis. However, our understanding of the underlying mechanisms of its pathogenesis and progress remains unclear. We investigated the fundamental processes of silicosis incidence and progression using a combination of lung function testing, histopathology, 16 S rRNA, untargeted metabolomics, and cytokine chips at different exposure times (4 or 8 weeks). The results show that silica exposure damages lung tissue reduces lung function, and increases with time. Cytokines with time-specific properties were found in lung lavage fluid: IFN-γ (4 weeks; P＜0.05), TNF-α, M-CSF, GM-CSF (8 weeks; P＜0.01). In addition, silica exposure for different periods interferes to varying degrees with the metabolism of lipids. The composition of the intestinal microbiota changed with increasing exposure time and there were time-specific: Allobaculum, Turicibacter、Jeotgalicoccu、Coprococcus 1 (4 weeks; P＜0.05), Ruminococcaceae NK4A214 group、Ruminiclostridium 5 (8 weeks; P＜0.05). We found strong associations between cytokines, gut microbiota changes, and metabolic disturbances at different exposure times. These results suggest that time-specific changes in crosstalk among cytokines, the gut microbiota, and metabolites may be a potential mechanism for silica-induced lung injury.

Lipid dysregulation associated with progression of silica-induced pulmonary fibrosis

Silicosis is an irreversible, progressive, fibrotic lung disease caused by long-term exposure to dust-containing silica particles at the workplace. Despite the precautions enforced, the rising incidence of silicosis continues to occur globally, particularly in developing countries. A better understanding of the disease progression and potential metabolic reprogramming of silicosis is warranted. The low- or high-dose silica-induced pulmonary fibrosis in mice was constructed to mimic chronic or accelerated silicosis. Silica-induced mice lung fibrosis was analyzed by histology, lung function, and computed tomography scans. Non-targeted metabolomics of the lung tissues was conducted by ultra-high-performance liquid chromatography-mass spectrometry to show the temporal metabolic trajectory. The low-dose silica-induced silicosis characterized inflammation for up to 42 days, with the onset of cellular silicon nodules. Conversely, the high-dose silica-induced silicosis characterized inflammation for up to 14 days, after which the disease developed rapidly, with a large volume of collagen deposition, presenting progressive massive fibrosis. Both low- and high silica-induced fibrosis had aberrant lipid metabolism. Combined with the RNA-Seq data, this multiomics study demonstrated alterations in the enzymes involved in sphingolipid metabolism. Time-dependent metabolic reprogramming revealing abnormal glycerophospholipid metabolism was intimately associated with the process of inflammation, whereas sphingolipid metabolism was crucial during lung fibrosis. These findings suggest that lipid dysregulation, especially sphingolipid metabolism, was involved in the process of silicosis.

Serum metabolic profiling of coal worker's pneumoconiosis using untargeted lipidomics

In this work, untargeted lipidomics was employed to analyze the effects of coal dust exposure on serum metabolite profiles. Furthermore, the potential of differential metabolites as novel biomarkers for diagnosis was investigated by binary logistic classification model. Nineteen differential metabolites were found among the three groups. The compounds were enriched in pathways associated with linoleic acid metabolism and pyrimidine metabolism. Fifty-three differential metabolites were found in coal dust-exposed people and CWP patients, and they were mainly enriched in glycerophospholipid metabolism. Three differential metabolites were correlated with lung function values. The diagnostic model, composed of lysoPI (16:0/0:0), bilirubin, and lysoPC (24:1/0:0), showed strong discrimination ability between dust-exposed people and CWP patients. The sensitivity, specificity, and AUC values of the model were 0.869, 0.600, and 0.750, respectively. The results suggest that coal worker's pneumoconiosis causes abnormal lipid metabolism in the body. A diagnostic model may aid current CWP diagnostic methods, and lysoPI (16:0/0:0), bilirubin, and lysoPC (24:1/0:0) can be used as potential CWP biomarkers. Further study is warranted to validate the findings in larger populations.

Caveolin-1 and Its Functional Peptide CSP7 Affect Silica-Induced Pulmonary Fibrosis by Regulating Fibroblast Glutaminolysis

Exposure to silica is a cause of pulmonary fibrosis disease termed silicosis, which leads to respiratory failure and ultimately death. However, what drives fibrosis is not fully elucidated and therapeutic options remain limited. Our previous RNA-sequencing analysis showed that the expression of caveolin-1 (CAV1) was downregulated in silica-inhaled mouse lung tissues. Here, we not only verified that CAV1 was decreased in silica-induced fibrotic mouse lung tissues in both messenger RNA and protein levels, but also found that CSP7, a functional peptide of CAV1, could attenuate pulmonary fibrosis in vivo. Further in vitro experiments revealed that CAV1 reduced the expression of Yes-associated protein 1(YAP1) and affected its nuclear translocation in fibroblasts. In addition, Glutaminase 1 (GLS1), a key regulator of glutaminolysis, was identified to be a downstream effector of YAP1. CAV1 could suppress the activity of YAP1 to decrease the transcription of GLS1, thereby inhibiting fibroblast activation. Taken together, our results demonstrated that CAV1 and its functional peptide CSP7 may be potential molecules or drugs for the prevention and intervention of silicosis.

Exploration study on serum metabolic profiles of Chinese male patients with artificial stone silicosis, silicosis, and coal worker's pneumoconiosis

Long-term exposure to inhaled silica dust induces pneumoconiosis, which remains a heavy burden in developing countries. Modern industry provides new resources of occupational SiO₂ leading to artificial stone silicosis especially in developed countries. This study aimed to characterize the serum metabolic profile of pneumoconiosis and artificial stone silicosis patients. Our case-control study recruited 46 pairs of pneumoconiosis patients and dust-exposed workers. Nontargeted metabolomics and lipidomics by ultra-high-performance liquid chromatography-tandem mass spectrometry platform were conducted to characterize serum metabolic profile in propensity score-matched (PSM) pilot study. 54 differential metabolites were screened, 24 of which showed good screening efficiency through receiver operating characteristics (ROC) in pilot study and validation study (both AUC > 0.75). 4 of the 24 metabolites can predict pneumoconiosis stages, which are 1,2-dioctanoylthiophosphatidylcholine, phosphatidylcholine(O-18:1/20:1), indole-3-acetamide and l-homoarginine. Kynurenine, N-tetradecanoylsphingosine 1-phosphate, 5-methoxytryptophol and phosphatidylethanolamine(22:6/18:1) displayed the potential as specific biomarkers for artificial stone silicosis. Taken together, our results confirmed that tryptophan metabolism is closely related to pneumoconiosis and may be related to disease progression. Hopefully, our results could supplement the biomarkers of pneumoconiosis and provide evidence for the discovery of artificial stone silicosis-specific biomarkers.