Effect of oxidative stress on development of silicosis

Trimetazidine, a metabolic modulator, attenuates silica-induced pulmonary fibrosis and decreases lactate levels and LDH activity in rats

Pulmonary fibrosis has been recently linked to metabolic dysregulation. Silica-induced pulmonary fibrosis in rats was employed by the current study to explore the effects of trimetazidine (a metabolic modulator-antianginal drug; TMZ) on silica-induced pulmonary fibrosis. Pulmonary fibrosis was induced by intranasal instillation of silica (50 mg/100 µl/rat) in TMZ versus vehicle-treated rats. Body weights of rats, weights of lungs, and wet-to-dry lung weights were determined. Various parameters were also measured in serum, bronchoalveolar lavage fluid (BALF) in addition to lung tissue homogenates. Moreover, histopathological examination of sectioned lungs for lesion score and distribution and histochemical detection of myeloperoxidase (MPO) in lung tissues were also performed. No significant differences were observed in body weight gains, lung coefficients, lung weights, and wet-to-dry lung weight in silica versus control rats. Elevated lactate levels in serum and lung homogenates were significantly attenuated by TMZ. In addition, lactate dehydrogenase activity, transforming growth factor-β, and total proteins in BALF were significantly normalized with TMZ. Moreover, TMZ significantly increased reduced glutathione and adenosine triphosphate levels and decreased nitrate/nitrite and hydroxyproline content in lungs of silica-treated rats. Histopathological examination of lungs revealed more than 56% reduction in lesion score and distribution by TMZ. MPO expression in lungs of silica-treated rats was also significantly attenuated by TMZ. TMZ attenuates silica-induced pulmonary fibrosis, an effect that could be mediated by suppressing anaerobic glycolysis-induced excessive lactate production. Regulation of oxidative stress could also play a role in TMZ-promoted protective effects.

Occupational exposure to crystalline silica and peripheral biomarkers: An update

Peripheral biomarkers are important tools for detecting occupational exposures to prevent the onset and/or progression of diseases. Studies that reveal early peripheral biomarkers are highly important to preserve the health of workers and can potentially contribute to diagnosing and/or prognosing occupational pathologies. Exposure to crystalline silica is a problem in several workplaces because it increases the risk of chronic obstructive pulmonary disease (COPD), tuberculosis, cancer, and pulmonary fibrosis, clinically defined as silicosis. Silicosis is diagnosed by chest radiography and/or lung tomography in advanced stages when there is a severe loss of lung function. Peripheral biomarkers can help in diagnosing early changes prior to silicosis and represent a highly important technical-scientific advance that is minimally invasive. This review aimed to investigate the biomarkers studied for evaluating occupational exposure to crystalline silica and to understand the recent advances in this area. Potential oxidative, inflammatory, and immunological biomarkers were reviewed, as well as routine biomarkers such as biochemical parameters. It was found that biomarkers of effect such as serum CC16 and l-selectin levels could represent promising alternatives. Additionally, studies have shown that neopterin levels in urine and serum can be used to monitor worker exposure. However, further studies are needed that include a greater number of participants, different times of exposure to crystalline silica, and a combination of silicosis patients and healthy volunteers. Evaluating the concentration of crystalline silica in occupational environments, its impact on biomarkers of effect, and alterations in lung function could contribute to revealing early health alterations in workers in a more robust manner.

Club cell protein 16 as a biomarker for early detection of silicosis

Background & objectives

Clinically silicosis is diagnosed by chest X-ray showing specific opacities along with history of silica dust exposure. Diagnosis is invariably made at an advanced or end stage when it is irreversible. Moreover, silicosis patients are susceptible to develop tuberculosis. Therefore, a suitable biomarker for early detection of silicosis is needed. This study evaluated the suitability of club cell protein (CC16) as a biomarker for early detection of silicosis.

Methods

This pilot study included 121 individuals from X-ray-confirmed/advanced silicosis, moderate silica dust-exposed workers and healthy controls from western India. CC16 levels were quantified in serum samples through ELISA. Sensitivity and specificity of CC16 values at different cut-off points were calculated in both non-smokers and smokers.

Results

Serum CC16 level was significantly (P <0.01) decreased in X-ray confirmed advanced silicosis patients (4.7±3.07 ng/ml) followed by moderately exposed workers (10.2±1.77 ng/ml) as compared to healthy non-exposed individuals (16.7±3.81 ng/ml). Tobacco smoking also caused a significant decrease of serum CC16 concentration in both healthy (10.2±1.12 ng/ml) and advanced silicosis workers (2.6±2.28 ng/ml) compared to non-smokers. Sensitivity and specificity of CC16 values were also found to be ≥83 per cent for screening all categories of individuals.

Interpretation & conclusions

Because of high sensitivity and specificity, serum CC16 could be used as predictive biomarker for suspicion and early detection of silicosis, which would help in reducing/delaying premature deaths caused by silicosis. It would also control silicotuberculosis additionally.

Inflammatory and oxidative stress biomarkers at protein and molecular levels in workers occupationally exposed to crystalline silica

Workers chronically exposed to respirable crystalline silica (CS) are susceptible to adverse health effects like silicosis and lung cancer. This study aimed to investigate potential early peripheral biomarkers of inflammation and oxidative stress in miners. The subjects enrolled in this study were occupationally unexposed workers (OUW, n = 29) and workers exposed to crystalline silica (WECS), composed by miners, which were divided into two subgroups: workers without silicosis (WECS I, n = 39) and workers diagnosed with silicosis, retired from work (WECS II, n = 42). The following biomarkers were evaluated: gene expression of L-selectin, CXCL2, CXCL8 (IL-8), HO-1, and p53; malondialdehyde (MDA) plasma levels and non-protein thiol levels in erythrocytes. Additionally, protein expression of L-selectin was evaluated to confirm our previous findings. The results demonstrated that gene expression of L-selectin was decreased in the WECS I group when compared to the OUW group (p < 0.05). Regarding gene expression of CXCL2, CXCL8 (IL-8), HO-1, and p53, significant fold change decreases were observed in workers exposed to CS in relation to unexposed workers (p < 0.05). The results of L-selectin protein expression in lymphocyte surface corroborated with our previous findings; thus, significant downregulation in the WECS groups was observed compared to OUW group (p < 0.05). The MDA was negatively associated with the gene expression of CXCL-2, CXCL8 (IL-8), and p53 (p < 0.05). The participants with silicosis (WECS II) presented significant increased non-protein thiol levels in relation to other groups (p < 0.05). Taken together, our findings may contribute to help the knowledge about the complex mechanisms involved in the silicosis pathogenesis and in the risk of lung cancer development in workers chronically exposed to respirable CS.

Inflammatory and oxidative stress parameters as potential early biomarkers for silicosis

Workers involved in mining activities are exposed to crystalline silica, which leads to constant pulmonary inflammatory reactions and severe oxidative damage, resulting in silicosis. In this work, we aimed to evaluate inflammatory and oxidative stress parameters as potential early biomarkers of effect to assess crystalline silica toxicity in workers who had occupational exposure during mining. We enrolled 38 workers exposed to crystalline silica (WECS), 24 individuals with silicosis (IWS), and 30 occupationally unexposed workers (OUW), a total of 92 participants. The WECS were divided into 2 groups, according to the time of exposure: 19 workers with 1-15 years of occupational exposure (WECS I) and 19 workers with >16 years of occupational exposure (WECS II). The inflammatory parameters assessed were L-selectin, β-2 integrin, and intercellular adhesion molecule-1 (ICAM-1) surface protein expression in lymphocytes and monocytes, complement C3 and C4, high sensitivity C-reactive protein (hsCRP), and adenosine deaminase (ADA) in serum. Plasma levels of malondialdehyde (MDA) and serum levels of vitamin C were determined as biomarkers of oxidative stress. Biochemical and hematological parameters were also investigated. L-selectin surface protein expression was significantly decreased in the WECS II group (p < 0.05), indicating the importance of this immune system component as a potential marker of crystalline-silica-induced toxicity. The MDA levels were significantly increased in the WECS I, WECS II, and IWS groups compared to the OUW group (p < 0.05). Vitamin C levels were decreased, while C3, hsCRP, ADA, and aspartate aminotransferase (AST) levels were increased in the IWS group compared to the OUW group (p < 0.05). Glucose and urea levels were significantly higher in the WECS I, II, and IWS groups compared to the OUW group (p < 0.05). Negative partial association was found between L-selectin and time of exposure (p < 0.001), supporting the relevance of this biomarker evaluation in long-term exposure to crystalline silica. Significant associations were also observed among inflammatory and oxidative stress biomarkers. Therefore, our results demonstrated the relevance of L-selectin as a potential peripheral biomarker for monitoring crystalline silica-induced toxicity in miners after chronic exposure, before silicosis has developed. However, more studies are necessary for better understanding of the use L-selectin as an early biomarker in exposed workers.