Effect of Sex Differences in Silicotic Mice

Activation of Sirt1 by acetate alleviates silicofibrosis: Contribution of the gut microbiota

Silicosis is a prevalent occupational disease marked by progressive pulmonary fibrosis. Despite its significant health burden, the pathogenesis of silicosis remains unclear, and no specific therapeutic drugs are available. In this study, we developed a novel intervention strategy targeting gut microbiota and investigated its underlying mechanisms. Using 16S rRNA gene sequencing, we observed significant gut microbiota dysbiosis in silicosis rats at different times (1-8 weeks), notably characterized by altered relative abundance of Ruminococcus and Lactobacillus. Fecal microbiota transplantation altered the gut microbiota structure of silicosis rats, alleviated silica-induced lung histopathological injury, with LEfSe analysis identifying Bifidobacterium as a potential biomarker. Treatment with Bifidobacterium reduced the level of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α) and fibrosis markers (collagen III, α-SMA and vimentin) in the lungs of silicosis rats, accompanied with increased serum acetic acid levels. Acetate, a major metabolite of Bifidobacterium, demonstrated similar protective effects against silicosis in this study, suggesting its role as a key mediator of Bifidobacterium action in the lungs. Both Bifidobacterium and acetate significantly upregulated Sirt1 in intestinal and lung tissues, while Sirt1 inhibition diminished their benefits to silicosis. As a widely studied histone deacetylase, Sirt1 was proven to be markedly reduced in the lungs of silicosis rats in this study. EX-527, a potent Sirt1 inhibitor, could worsen silicosis damage by upregulating the level of TGF-β1 and the degree of Smad2/3 acetylation. Our study highlights the efficacy of postbiotics, such as Bifidobacterium and acetate, and identifies Sirt1 as a promising target for silicosis treatment.

Repeated Silica exposures lead to Silicosis severity via PINK1/PARKIN mediated mitochondrial dysfunction in mice model

BACKGROUND AND OBJECTIVES

Silicosis, one of the occupational health illnesses is caused by inhalation of crystalline silica. Deposition of extracellular matrix and fibroblast proliferation in lungs are linked to silicosis development. Mitochondrial dysfunction plays critical role in some diseases, but how these processes progress and regulated in silicosis, remains limited. Detailed study of silica induced pulmonary fibrosis in mouse model, its progression and severity may be helpful in designing future therapeutic strategies.

METHODS

In present study, mice model of silicosis has been developed after repeated silica exposures which may closely resemble clinical symptoms of silicosis in human. In addition to efficiently mimicking the acute/chronic transformation processes of silicosis, this is practical and efficient in terms of time and output, which avoids mechanical injury to the upper respiratory tract due to surgical interventions. Sonicated sterile silica suspension (120 mg/kg) was administered through intranasal route thrice a week at regular intervals (21, 28 and 35 days).

RESULTS

Presence of minute to larger silicotic nodules in H&E-stained lung sections were observed in all silica induced model groups. Enhanced ECM deposition was noted in MT stained lung sections of silica exposure groups as compared to control which were confirmed by significantly higher MMP9 expression levels and hydroxyproline content in silica 35 days group. Increase in Reactive oxygen species (ROS), inflammatory cell recruitment mainly, neutrophils and macrophage were observed in all three silica exposure groups. Transmission electron microscopic analysis has confirmed presence of many aberrant shaped mitochondria (swollen, round shape) in 35 days model where autophagosomes were minimum. Western blot analysis of mitophagy and autophagy markers such as Pink1, Parkin, Cytochrome c, SQSTM1/p62, the ratio of light chain LC3B II/LC3B I was found higher in 21 and 28 days which were significantly reduced in 35 days silica model.

CONCLUSIONS

Higher MMP9 activity and MMP9 /TIMP1 ratio demonstrate excessive extracellular matrix damage and deposition in 35 days model. Significantly reduced expressions of autophagy and mitophagy markers have also confirmed progression in fibrosis severity and its association with repeated silica exposures in 35 days model group.

Crystalline silica-induced pulmonary inflammation and autoimmunity in mature adult NZBW/f1 mice: age-related sensitivity and impact of omega-3 fatty acid intervention

OBJECTIVE

Occupational exposure to respirable crystalline silica (cSiO2) has been linked to lupus development. Previous studies in young lupus-prone mice revealed that intranasal cSiO2 exposure triggered autoimmunity, preventable with docosahexaenoic acid (DHA). This study explores cSiO2 and DHA effects in mature lupus-prone adult mice, more representative of cSiO2-exposed worker age.

METHODS

Female NZBWF1 mice (14-week old) were fed control (CON) or DHA-supplemented diets. After two weeks, mice were intranasally instilled saline (VEH) or 1 mg cSiO2 weekly for four weeks. Cohorts were then analyzed 1- and 5-weeks postinstillation for lung inflammation, cell counts, chemokines, histopathology, B- and T-cell infiltration, autoantibodies, and gene signatures, with results correlated to autoimmune glomerulonephritis onset.

RESULTS

VEH/CON mice showed no pathology. cSiO2/CON mice displayed significant ectopic lymphoid tissue formation in lungs at 1 week, increasing by 5 weeks. cSiO2/CON lungs exhibited elevated cellularity, chemokines, CD3+ T-cells, CD45R + B-cells, IgG + plasma cells, gene expression, IgG autoantibodies, and glomerular hypertrophy. DHA supplementation mitigated all these effects.

DISCUSSION

The mature adult NZBWF1 mouse used here represents a life-stage coincident with immunological tolerance breach and one that more appropriately represents the age (20-30 yr) of cSiO2-exposed workers. cSiO2-induced robust pulmonary inflammation, autoantibody responses, and glomerulonephritis in mature adult mice, surpassing effects observed previously in young adults. DHA at a human-equivalent dosage effectively countered cSiO2-induced inflammation/autoimmunity in mature mice, mirroring protective effects in young mice.

CONCLUSION

These results highlight life-stage significance in this preclinical lupus model and underscore omega-3 fatty acids' therapeutic potential against toxicant-triggered autoimmune responses.

From Basic Research to Clinical Practice: Considerations for Treatment Drugs for Silicosis

Silicosis, characterized by irreversible pulmonary fibrosis, remains a major global public health problem. Nowadays, cumulative studies are focusing on elucidating the pathogenesis of silicosis in order to identify preventive or therapeutic antifibrotic agents. However, the existing research on the mechanism of silica-dust-induced pulmonary fibrosis is only the tip of the iceberg and lags far behind clinical needs. Idiopathic pulmonary fibrosis (IPF), as a pulmonary fibrosis disease, also has the same problem. In this study, we examined the relationship between silicosis and IPF from the perspective of their pathogenesis and fibrotic characteristics, further discussing current drug research and limitations of clinical application in silicosis. Overall, this review provided novel insights for clinical treatment of silicosis with the hope of bridging the gap between research and practice in silicosis.

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

Background

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

Methods

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

Results

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

Conclusions

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