Silicate pneumoconiosis in camels (Camelus dromedarius L.)

Saharan dust induces the lung disease-related cytokines granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor

Desert dust exposure is associated with adverse respiratory health effects. Desert dust is a complex pollutant mixtures that includes respirable crystalline and amorphous particles, metals, and microbial constituents. Given the health effects of desert dust and its heterogeneity, as yet unidentified harmful biological pathways may be triggered. Therefore, we exposed human in vitro air-liquid interface co-cultures of alveolar epithelial A549 cells and THP-1 macrophages to Saharan dust (SD). For comparison, we used the known pulmonary toxicant DQ12 quartz dust. Via RNA sequencing, we identified that SD but not DQ12 increased the gene expression of granulocyte-macrophage colony-stimulating factor (GMCSF) and granulocyte colony-stimulating factor (GCSF). These findings were confirmed by quantitative reverse transcriptase PCR. SD dose-dependently upregulated GMCSF and GCSF expression with significant 7 and 9-fold changes, respectively, at the highest tested concentration of 31 µg/cm2. Furthermore, we observed that SD significantly enhanced the secretion of GM-CSF and G-CSF by 2-fold. Both cytokines have previously been associated with lung diseases such as asthma and fibrosis. Hence, we present two molecular messengers that may contribute to the adverse health effects of desert dust and might serve as drug targets for this globally relevant non-anthropogenic air pollutant.

Saharan dust induces NLRP3-dependent inflammatory cytokines in an alveolar air-liquid interface co-culture model

BACKGROUND

Epidemiological studies have related desert dust events to increased respiratory morbidity and mortality. Although the Sahara is the largest source of desert dust, Saharan dust (SD) has been barely examined in toxicological studies. Here, we aimed to assess the NLRP3 inflammasome-caspase-1-pathway-dependent pro-inflammatory potency of SD in comparison to crystalline silica (DQ12 quartz) in an advanced air-liquid interface (ALI) co-culture model. Therefore, we exposed ALI co-cultures of alveolar epithelial A549 cells and macrophage-like differentiated THP-1 cells to 10, 21, and 31 µg/cm² SD and DQ12 for 24 h using a Vitrocell Cloud system. Additionally, we exposed ALI co-cultures containing caspase (CASP)1-/- and NLRP3-/- THP-1 cells to SD.

RESULTS

Characterization of nebulized DQ12 and SD revealed that over 90% of agglomerates of both dusts were smaller than 2.5 μm. Characterization of the ALI co-culture model revealed that it produced surfactant protein C and that THP-1 cells remained viable at the ALI. Moreover, wild type, CASP1-/-, and NLRP3-/- THP-1 cells had comparable levels of the surface receptors cluster of differentiation 14 (CD14), toll-like receptor 2 (TLR2), and TLR4. Exposing ALI co-cultures to non-cytotoxic doses of DQ12 and SD did not induce oxidative stress marker gene expression. SD but not DQ12 upregulated gene expressions of interleukin 1 Beta (IL1B), IL6, and IL8 as well as releases of IL-1β, IL-6, IL-8, and tumor necrosis factor α (TNFα). Exposing wild type, CASP1-/-, and NLRP3-/- co-cultures to SD induced IL1B gene expression in all co-cultures whereas IL-1β release was only induced in wild type co-cultures. In CASP1-/- and NLRP3-/- co-cultures, IL-6, IL-8, and TNFα releases were also reduced.

CONCLUSIONS

Since surfactants can decrease the toxicity of poorly soluble particles, the higher potency of SD than DQ12 in this surfactant-producing ALI model emphasizes the importance of readily soluble SD components such as microbial compounds. The higher potency of SD than DQ12 also renders SD a potential alternative particulate positive control for studies addressing acute inflammatory effects. The high pro-inflammatory potency depending on NLRP3, CASP-1, and IL-1β suggests that SD causes acute lung injury which may explain desert dust event-related increased respiratory morbidity and mortality.

Animal models of silicosis: fishing for new therapeutic targets and treatments

Silicosis as an occupational lung disease has been present in our lives for centuries. Research studies have already developed and implemented many animal models to study the pathogenesis and molecular basis of the disease and enabled the search for treatments. As all experimental animal models used to date have their advantages and disadvantages, there is a continuous search for a better model, which will not only accelerate basic research, but also contribute to clinical aspects and drug development. We review here, for the first time, the main animal models developed to date to study silicosis and the unique advantages of the zebrafish model that make it an optimal complement to other models. Among the main advantages of zebrafish for modelling human diseases are its ease of husbandry, low maintenance cost, external fertilisation and development, its transparency from early life, and its amenability to chemical and genetic screening. We discuss the use of zebrafish as a model of silicosis, its similarities to other animal models and the characteristics of patients at molecular and clinical levels, and show the current state of the art of inflammatory and fibrotic zebrafish models that could be used in silicosis research.

Histology, prevalence, and environmental sources for pulmonary silicates depositions in domestic and wild animals

The source and significance of pulmonary silicate crystals in animals and people are poorly understood. To estimate the prevalence and characterize the pulmonary crystalline material in animals from St. Kitts, tissue samples from dogs, horses, cattle, sheep, goats, pigs, chickens, mongooses, and monkeys were examined by light microscopy, scanning electron microscopy with energy-dispersive x-ray analysis (SEM/EDXA), and x-ray diffraction. Crystalline material was seen in 201 of 259 (77.6%) lung samples as perivascular and interstitial accumulations of heterogeneous crystalline particulate material, free or within macrophages (silicate-laden macrophages [SLMs]), mostly lacking evidence of chronic inflammation or fibrosis. The crystalline material was birefringent, basophilic on acid-fast, and composed of silicas on SEM/EDXA. Mongooses (100%) and monkeys (98%) had the highest prevalence of SLM, followed by cattle and chickens. Lesions were graded on a 3-point scale based on the histologic location and extent of silicates and SLM and were significantly more severe in mongooses (median = 3) than in monkeys (median = 2), dogs (median = 2), and chickens (median = 1). On EDXA, the crystalline material from lungs, air, and topsoil was composed of silicon, oxygen, aluminum, and iron, with a particulate matter size between 2.5 and 10 µm. We hypothesize Saharan dust, volcanic ash, topsoil, and rock quarry dust are potential sources of siliceous dust inhalation and SLM accumulations lacking chronic inflammation (silicosis); dust generation may be potentiated by road vehicle or wind suspension. Future investigations are warranted on the role of silicate inhalation and respiratory comorbidities in people, with monkeys, mongooses, or chickens serving as possible sentinels for exposure.

Pulmonary silicosis in 2 rock hyraxes, and literature review

Two rock hyraxes (Procavia capensis), from the Chattanooga Zoo, were submitted separately for autopsy at the University of Tennessee Veterinary Medical Center. The first was a 4-y-old intact female that died without premonitory signs and the second was a 10-y-old intact male that was euthanized because of severe renal disease. Microscopically, the lungs of both hyraxes had multifocal-to-coalescing, <1-mm diameter aggregates of epithelioid macrophages separated by streams of fibrous tissue. Macrophages contained intracytoplasmic, clear, acicular, birefringent crystals. Transmission electron microscopy and energy-dispersive x-ray spectroscopy findings on the lung samples were consistent with silica crystal deposition. The hyraxes had been housed together on commercially sourced play sand composed of 99-99.5% quartz, a crystalline silica polymorph. The microscopic findings, transmission electron microscopy, and energy-dispersive x-ray spectroscopy of the intrahistiocytic crystals, in addition to the history of exposure to crystalline silica, were consistent with pulmonary silicosis. Pulmonary silicosis has not been reported previously in rock hyraxes, to our knowledge.

Concurrent pulmonary adenocarcinoma and silicate pneumoconiosis in a red-legged partridge (Alectoris rufa)

An adult red-legged partridge (Alectoris rufa) presented with concurrent pulmonary carcinoma and severe silicosis. The animal was submitted to the Veterinary Teaching Hospital of the University of Córdoba (Spain) because of respiratory signs, and it died during clinical examination. At postmortem examination, numerous firm, whitish to yellowish nodules involving the lungs, mainly the right lobe, were found. The histopathologic study revealed numerous peribronchiolar large granulomatous lesions composed of macrophages, which showed abundant cytoplasm containing numerous birefringent crystals identified as silicates by transmission electron microscopy. An epithelial neoplasm showing papillary, acinar, and solid patterns occupied large areas of the pulmonary parenchyma. The histopathologic and immunohistochemical features were consistent with a pulmonary carcinoma. Small tumor nests were often located close to the granulomatous lesions. This is the first report of concurrent pneumoconiosis and pulmonary carcinoma in a nonhuman species.

Silicate pneumoconiosis in hens

Thirteen cases of silicate pneumoconiosis in 3- to 4-year-old hens are described. Ten of the birds were raised in the suburbs of a city near several chalk quarries and two cement-works; the remaining three hens (aged 3 years) had lived in an environment with high particulate pollution from a nearby brick-works in which large amounts of clay were used daily. Silicotic granulomas composed of dust-laden macrophages were scattered over the lungs. They were located mainly in the infundibula and atria of tertiary bronchi and around vessels; more rarely they occurred in the lamina propria mucosae of primary and secondary bronchi. Energy dispersive x-ray microanalysis coupled with both transmission and scanning electron microscopy revealed that the dust was composed mainly of silicon, aluminium, calcium, iron and potassium. Titanium, sulphur, magnesium, zinc, copper and chlorine were also found. It is concluded that animals raised in polluted environmental conditions may serve as an important indicator of risks to human health and pathogenetic mechanisms. Thirteen cases of silicate pneumoconiosis in 3- to 4-year-old hens are described. Ten of the birds were raised in the suburbs of a city near several chalk quarries and two cement-works; the remaining three hens (aged 3 years) had lived in an environment with high particulate pollution from a nearby brick-works in which large amounts of clay were used daily. Silicotic granulomas composed of dust-laden macrophages were scattered over the lungs. They were located mainly in the infundibula and atria of tertiary bronchi and around vessels; more rarely they occurred in the lamina propria mucosae of primary and secondary bronchi. Energy dispersive x-ray microanalysis coupled with both transmission and scanning electron microscopy revealed that the dust was composed mainly of silicon, aluminium, calcium, iron and potassium. Titanium, sulphur, magnesium, zinc, copper and chlorine were also found. It is concluded that animals raised in polluted environmental conditions may serve as an important indicator of risks to human health and pathogenetic mechanisms.

Extrapulmonary silicosis in two water buffaloes

Two cases of extrathoracic silicosis in buffaloes raised near a quartz quarry and suffering from clinically severe silicosis are described. The extrapulmonary changes were characterized by silicoconiotic nodules in the tonsils, mesenteric lymph nodes and spleen. A combination of energy dispersive X-ray microanalysis and scanning electron microscopy revealed that the mineral component of these lesions consisted mainly of silicon, aluminium, iron, calcium, magnesium, zinc, sulphur and potassium. It is concluded that domestic animals raised in polluted environmental conditions represent an important biological source from which helpful data may be obtained for assessing risks to human health and gaining new insight into pathogenetic mechanisms.

Silicate pneumoconiosis in pigs: optical and scanning electron microscopical investigations with X-ray microanalysis

Four cases of silicate pneumoconiosis are described in pigs raised near several chalk quarries and two cement works. The pulmonary changes were characterized by thickened alveolar septa, resulting in distorted airspaces, and small foci of initial fibrosis. In the bronchiolar and alveolar sites, as in the interstitium, free and intracytoplasmic dust was detected. An energy dispersive X-ray microanalysis coupled with a scanning electron microscope revealed that this dust was composed mainly of silicon, calcium, potassium, sulphur, aluminium and iron. In lung-associated lymph nodes, severe lymphoid cell depletion and dilatation of peritrabecular and subcapsular sinuses were constant findings. The inorganic material found in the lymph nodes contained the elements listed above. Air samples from the same geographical area revealed particulate pollutants, the qualitative features of which were similar to those found in lung and lymph nodal tissue. It is concluded that domestic animals raised in polluted environmental conditions represent an important biological source from which helpful data may be obtained for assessing risks to human health.