Hog barn dust extract stimulates IL-8 and IL-6 release in human bronchial epithelial cells via PKC activation

Respiratory exposure to agricultural dust extract promotes increased intestinal Tnfα expression, gut barrier dysfunction, and endotoxemia in mice

Concentrated animal feeding operations (CAFOs) are responsible for the production of global greenhouse gases and harmful environmental pollutants including hydrogen sulfide, ammonia, and particulate matter. Swine farmers are frequently exposed to organic dust that is proinflammatory in the lung and are thus at greater risk of developing pneumonia, asthma, and other respiratory conditions. In addition to respiratory disease, air pollutants are directly associated with altered gastrointestinal (GI) physiology and the development of GI diseases, thereby highlighting the gut-lung axis in disease progression. Instillation of hog dust extract (HDE) for 3 wk has been reported to promote the development of chronic airway inflammation in mice, however, the impact of HDE exposure on intestinal homeostasis is poorly understood. We report that 3-wk intranasal exposure of HDE is associated with increased intestinal macromolecule permeability and elevated serum endotoxin concentrations in C57BL/6J mice. In vivo studies also indicated mislocalization of the epithelial cell adhesion protein, E-cadherin, in the colon as well as an increase in the proinflammatory cytokine, Tnfα, in the proximal colon. Moreover, mRNA expression of the Paneth cell-associated marker, Lyz1, was increased the proximal colon, whereas the expression of the goblet cell marker, Muc2, was unchanged in the epithelial cells of the ileum, cecum, and distal colon. These results demonstrate that airway exposure to CAFOs dusts promote airway inflammation and modify the gastrointestinal tract to increase intestinal permeability, induce systemic endotoxemia, and promote intestinal inflammation. Therefore, this study identifies complex physiological consequences of chronic exposure to organic dusts derived from CAFOs on the gut-lung axis.NEW & NOTEWORTHY Agricultural workers have a higher prevalence of occupational respiratory symptoms and are at greater risk of developing respiratory diseases. However, gastrointestinal complications have also been reported, yet the intestinal pathophysiology is understudied. This work is novel because it emphasizes the role of an inhaled environmental pollutant on the development of intestinal pathophysiological outcomes. This work will provide foundation for other studies evaluating how agricultural dusts disrupts host physiology and promotes debilitating gastrointestinal and systemic disorders.

Purification and characterization of a serine protease from organic dust and elucidation of its inductive effects on lung inflammatory mediators

Organic dust inhalation is associated with the development of respiratory diseases. Serine protease activities in organic dusts were previously reported to contribute to the induction of lung inflammatory mediators however, the identities of the proteases and the mechanisms by which they induce inflammatory mediators are unknown. The goal of this study was to purify and characterize serine protease(s) from organic dust and elucidate mechanisms by which they induce lung inflammatory mediators. A serine protease was purified from poultry organic dust by benzamidine-agarose affinity chromatography. Mass spectrometry and amino-terminal sequence analysis identified the purified protease as chicken trypsin II-P29. Purified protease induced proinflammatory cytokine levels in Beas2B and NHBE epithelial and THP-1 macrophage cells. Treatment with the purified protease increased cellular and mitochondrial reactive oxygen species (ROS) generation. Induction of inflammatory mediators and ROS were suppressed by serine protease inhibitors and antioxidants. Purified protease activated protein kinase C (PKC), mitogen-activated protein kinase (MAPK)1/3 and MAPK14 signaling, and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and signal transducer and activator of transcription 3 (Stat-3), and chemical inhibitors targeting these pathways suppressed induction of inflammatory mediators. Calcium mobilization studies showed that the purified protease activated protease-activated receptors (PAR) F2R, F2RL1, F2RL2, F2RL3, and F2R and F2RL1 knockdown suppressed the induction of inflammatory mediators. Intranasal instillation of purified protease increased lung chemokine (C-X-C motif) ligand (CXCL)1, interleukin (IL)-6, and tumor necrosis factor (TNF) levels in mice. Our studies have shown that chicken trypsin is a proinflammatory constituent of poultry organic dust, and induces lung inflammatory mediators via increased ROS and PAR activation in a cell signaling pathway involving PKC, MAPK1/3 and MAPK14, and NF-κB and Stat-3.NEW & NOTEWORTHY Inhalation of dust in industrial agricultural operations is linked to the development of lung diseases. Our studies have isolated for the first time a trypsin protease from poultry farm dust and have shown that it stimulates lung inflammation. The protease stimulates the production of oxidants and cell signaling pathways to increase inflammatory mediator production. Targeting trypsin protease in poultry farm environment may be a useful strategy to counter the harmful effects of dust.

Lipid-Sensing Receptor FFAR4 Modulates Pulmonary Epithelial Homeostasis following Immunogenic Exposures Independently of the FFAR4 Ligand Docosahexaenoic Acid (DHA)

The role of pulmonary free fatty acid receptor 4 (FFAR4) is not fully elucidated and we aimed to clarify the impact of FFAR4 on the pulmonary immune response and return to homeostasis. We employed a known high-risk human pulmonary immunogenic exposure to extracts of dust from swine confinement facilities (DE). WT and Ffar4-null mice were repetitively exposed to DE via intranasal instillation and supplemented with docosahexaenoic acid (DHA) by oral gavage. We sought to understand if previous findings of DHA-mediated attenuation of the DE-induced inflammatory response are FFAR4-dependent. We identified that DHA mediates anti-inflammatory effects independent of FFAR4 expression, and that DE-exposed mice lacking FFAR4 had reduced immune cells in the airways, epithelial dysplasia, and impaired pulmonary barrier integrity. Analysis of transcripts using an immunology gene expression panel revealed a role for FFAR4 in lungs related to innate immune initiation of inflammation, cytoprotection, and immune cell migration. Ultimately, the presence of FFAR4 in the lung may regulate cell survival and repair following immune injury, suggestive of potential therapeutic directions for pulmonary disease.

IL-22 regulates inflammatory responses to agricultural dust-induced airway inflammation

IL-22 is a unique cytokine that is upregulated in many chronic inflammatory diseases, including asthma, and modulates tissue responses during inflammation. However, the role of IL-22 in the resolution of inflammation and how this contributes to lung repair processes are largely unknown. Here, we tested the hypothesis that IL-22 signaling is critical in inflammation resolution after repetitive exposure to agricultural dust. Using an established mouse model of organic dust extract-induced lung inflammation, we found that IL-22 knockout mice have an enhanced response to agricultural dust as evidenced by an exacerbated increase in infiltrating immune cells and lung pathology as compared to wild-type controls. We further identified that, in response to dust, IL-22 is expressed in airway epithelium and in Ym1+ macrophages found within the parenchyma in response to dust. The increase in IL-22 expression was accompanied by increases in IL-22 receptor IL-22R1 within the lung epithelium. In addition, we found that alveolar macrophages in vivo as well as THP-1 cells in vitro express IL-22, and this expression is modulated by dust exposure. Furthermore, subcellular localization of IL-22 appears to be in the Golgi of resting THP1 human monocytes, and treatment with dust extracts is associated with IL-22 release into the cytosolic compartment from the Golgi reservoirs during dust extract exposure. Taken together, we have identified a significant role for macrophage-mediated IL-22 signaling that is activated in dust-induced lung inflammation in mice.

NADPH and xanthine oxidases control induction of inflammatory mediator expression by organic dust in the lung

Exposure to organic dust in animal and agricultural farms and the ensuing lung inflammation are linked to the development of respiratory diseases. We found previously that elevated production of reactive oxygen species (ROS) by aqueous poultry organic dust extract (hereafter referred to as dust extract) mediates induction of proinflammatory mediators in airway epithelial cells. In the present study, we investigated whether ROS generated by NADPH oxidases (NOX) and xanthine oxidase (XO) controls induction of inflammatory mediators by dust extract and the underlying mechanisms in bronchial epithelial cells. Using chemical inhibitors and siRNA targeted knockdown, we found that NOX1, NOX2, NOX4, and XO-derived ROS regulates induction of proinflammatory mediator levels. Like airway epithelial cells in vitro, NOX inhibitor VAS2870 reduced keratinocyte chemoattractant (KC), IL-6, and TNF-α production and 4-hydroxynonenal (4-HNE) staining induced by dust extract in mouse lungs. VAS2870 inhibition of proinflammatory mediators was associated with reduced NFκB and Stat3 activation indicating that NOX generated ROS activates NFκB and Stat3 to induce proinflammatory gene expression. Dust extract increased the membrane association of p47^phox in airway epithelial cells indicating NOX2 activation but had no effect on NOX2 protein levels. In summary, our studies have shown that NOX and XO generated ROS control organic dust induction of proinflammatory mediators in airway epithelial cells via NFκB and Stat3 activation.

Transcriptomic and ultrastructural evidence indicate that anti-HMGB1 antibodies rescue organic dust-induced mitochondrial dysfunction

Exposure to organic dust (OD) in agriculture is known to cause respiratory symptoms including loss of lung function. OD exposure activates multiple signaling pathways since it contains a variety of microbial products and particulate matter. Previously, we have shown how OD exposure leads to the secretion of HMGB1 and HMGB1-RAGE signaling, and how this can be a possible therapeutic target to reduce inflammation. Cellular mitochondria are indispensable for homeostasis and are emerging targets to curtail inflammation. Recently, we have also observed that OD exposure induces mitochondrial dysfunction characterized by loss of structural integrity and deficits in bioenergetics. However, the role of HMGB1 in OD-induced mitochondrial dysfunction in human bronchial epithelial (NHBE) cells remains elusive. Therefore, we aimed to study whether decreased levels of intracellular HMGB1 or antibody-mediated neutralization of secreted HMGB1 would rescue mitochondrial dysfunction. Single and repeated ODE exposure showed an elongated mitochondrial network and cristolysis whereas HMGB1 neutralization or the lack thereof promotes mitochondrial biogenesis evidenced by increased mitochondrial fragmentation, increased DRP1 expression, decreased MFN2 expression, and increased PGC1α expression. Repeated 5-day ODE exposure significantly downregulated transcripts encoding mitochondrial respiration and metabolism (ATP synthase, NADUF, and UQCR) as well as glucose uptake. This was reversed by the antibody-mediated neutralization of HMGB1. Our results support our hypothesis that, in NHBE cells, neutralization of ODE-induced HMGB1 secretion rescues OD-induced mitochondrial dysfunction.

Nrf2 Activation Protects Against Organic Dust and Hydrogen Sulfide Exposure Induced Epithelial Barrier Loss and K. pneumoniae Invasion

Agriculture workers report various respiratory symptoms owing to occupational exposure to organic dust (OD) and various gases. Previously, we demonstrated that pre-exposure to hydrogen sulfide (H₂S) alters the host response to OD and induces oxidative stress. Nrf2 is a master-regulator of host antioxidant response and exposures to toxicants is known to reduce Nrf2 activity. The OD exposure-induced lung inflammation is known to increase susceptibility to a secondary microbial infection. We tested the hypothesis that repeated exposure to OD or H₂S leads to loss of Nrf2, loss of epithelial cell integrity and that activation of Nrf2 rescues this epithelial barrier dysfunction. Primary normal human bronchial epithelial (NHBE) cells or mouse precision cut-lung slices (PCLS) were treated with media, swine confinement facility organic dust extract (ODE) or H₂S or ODE+H₂S for one or five days. Cells were also pretreated with vehicle control (DMSO) or RTA-408, a Nrf2 activator. Acute exposure to H₂S and ODE+H₂S altered the cell morphology, decreased the viability as per the MTT assay, and reduced the Nrf2 expression as well as increased the keap1 levels in NHBE cells. Repeated exposure to ODE or H₂S or ODE+H₂S induced oxidative stress and cytokine production, decreased tight junction protein occludin and cytoskeletal protein ezrin expression, disrupted epithelial integrity and resulted in increased Klebsiella pneumoniae invasion. RTA-408 (pharmacological activator of Nrf2) activated Nrf2 by decreasing keap1 levels and reduced ODE+H₂S-induced changes including reversing loss of barrier integrity, inflammatory cytokine production and microbial invasion in PCLS but not in NHBE cell model. We conclude that Nrf2 activation has a partial protective function against ODE and H₂S.

Aspirin-Triggered Resolvin D1 Reduces Chronic Dust-Induced Lung Pathology without Altering Susceptibility to Dust-Enhanced Carcinogenesis

Lung cancer is the leading cause of cancer-related deaths worldwide, with increased risk being associated with unresolved or chronic inflammation. Agricultural and livestock workers endure significant exposure to agricultural dusts on a routine basis; however, the chronic inflammatory and carcinogenic effects of these dust exposure is unclear. We have developed a chronic dust exposure model of lung carcinogenesis in which mice were intranasally challenged three times a week for 24 weeks, using an aqueous dust extract (HDE) made from dust collected in swine confinement facilities. We also treated mice with the omega-3-fatty acid lipid mediator, aspirin-triggered resolvin D1 (AT-RvD1) to provide a novel therapeutic strategy for mitigating the inflammatory and carcinogenic effects of HDE. Exposure to HDE resulted in significant immune cell influx into the lungs, enhanced lung tumorigenesis, severe tissue pathogenesis, and a pro-inflammatory and carcinogenic gene signature, relative to saline-exposed mice. AT-RvD1 treatment mitigated the dust-induced inflammatory response but did not protect against HDE + NNK-enhanced tumorigenesis. Our data suggest that chronic HDE exposure induces a significant inflammatory and pro-carcinogenic response, whereas treatment with AT-RvD1 dampens the inflammatory responses, providing a strong argument for the therapeutic use of AT-RvD1 to mitigate chronic inflammation.

Sex-Specific Differences in Resolution of Airway Inflammation in Fat-1 Transgenic Mice Following Repetitive Agricultural Dust Exposure

In agriculture industries, workers are at increased risk for developing pulmonary diseases due to inhalation of agricultural dusts, particularly when working in enclosed confinement facilities. Agricultural dusts inhalation leads to unresolved airway inflammation that precedes the development and progression of lung disease. We have previously shown beneficial effects of the omega-3 polyunsaturated fatty acid (ω-3 PUFA) DHA in protecting against the negative inflammatory effects of repetitive dust exposure in the lung. Dietary manipulation of pulmonary disease risk is an attractive and timely approach given the contribution of an increased ω-6 to ω-3 PUFA ratio to low grade inflammation and chronic disease in the Western diet. To prevent any confounding factors that comes with dietary supplementation of ω-3 PUFA (different sources, purity, dose, and duration), we employed a Fat-1 transgenic mouse model that convert ω-6 PUFA to ω-3 PUFA, leading to a tissue ω-6 to ω-3 PUFA ratio of approximately 1:1. Building on our initial findings, we hypothesized that attaining elevated tissue levels of ω-3 PUFA would attenuate agricultural dust-induced lung inflammation and its resolution. To test this hypothesis, we compared wild-type (WT) and Fat-1 transgenic mice in their response to aqueous extracts of agricultural dust (DE). We also used a soluble epoxide hydrolase inhibitor (sEH) to potentiate the effects of ω-3 PUFA, since sEH inhibitors have been shown to stabilize the anti-inflammatory P450 metabolites derived from both ω-3 and ω-6 PUFA and promote generation of specialized pro-resolving lipid mediators from ω-3 PUFA. Over a three-week period, mice were exposed to a total of 15 intranasal instillations of DE obtained from swine confinement buildings in the Midwest. We observed genotype and sex-specific differences between the WT vs. Fat-1 transgenic mice in response to repetitive dust exposure, where three-way ANOVA revealed significant main effects of treatment, genotype, and sex. Also, Fat-1 transgenic mice displayed reduced lymphoid aggregates in the lung following DE exposure as compared to WT animals exposed to DE, suggesting improved resilience to the DE-induced inflammatory effects. Overall, our data implicate a protective role of ω-3 FA in the lung following repetitive dust exposure.

Lung inflammation from repeated exposure to LPS and glyphosate

Agricultural workplaces consist of multiple airborne contaminants and inhalation exposures induce respiratory effects in workers. Endotoxin (LPS) and glyphosate are two common airborne contaminants in agricultural environments. We have previously shown that exposure to a combination of LPS and glyphosate synergistically modulates immune reactions as compared to individual exposures. The immunopathogenesis of acute and chronic exposure to complex agricultural exposures including LPS and glyphosate is not known; therefore, we further investigated the lung cellular inflammatory differences in mice exposed to either a combination, or individual, LPS, and glyphosate for 1 day, 5 days, and 10 days. Exposure to a combination of LPS and glyphosate resulted in greater cellular inflammatory effects in lungs as compared to individual exposures to LPS or glyphosate. Repeated exposures to the combination of LPS and glyphosate resulted in robust infiltration of inflammatory cells in the perivascular, peribronchiolar, and alveolar regions, and increases of alveolar septal thicknesses and perivascular spaces in the lungs with intense intercellular adhesion molecule (ICAM) - 1 staining in the perivascular region, but minimal staining in the pulmonary artery endothelium.

A high docosahexaenoic acid diet alters lung inflammation and recovery following repetitive exposure to aqueous organic dust extracts

Agricultural workers, especially those who work in swine confinement facilities, are at increased risk for developing pulmonary diseases including asthma, chronic obstructive pulmonary disease, and chronic bronchitis due to exposures to fumes, vapors, and organic dust. Repetitive exposure to agricultural dust leads to unresolved inflammation, a common underlying mechanism that worsens lung disease. Besides occupational exposure to dusts, diet also significantly contributes to inflammation and disease progression. Since DHA (docosahexaenoic acid), a polyunsaturated omega-3 fatty acid and its bioactive metabolites have key roles in inflammation resolution, we rationalized that individuals chronically exposed to organic dusts can benefit from dietary modifications. Here, we evaluated the role of DHA in modifying airway inflammation in a murine model of repetitive exposure to an aqueous extract of agricultural dust (three-week exposure to swine confinement dust extract, HDE) and after a one-week resolution/recovery period. We found that mice fed a high DHA diet had significantly increased bronchoalveolar lavage fluid (BALF) levels of DHA-derived resolvins and lower TNFα along with altered plasma levels of endocannabinoids and related lipid mediators. Following the one-week recovery we identified significantly reduced BALF cellularity and cytokine/chemokine release along with increased BALF amphiregulin and resolvins in DHA diet-fed versus control diet-fed mice challenged with HDE. We further report observations on the effects of repetitive HDE exposure on lung Ym1+ and Arg-1+ macrophages. Overall, our findings support a protective role for DHA and identify DHA-derived resolvins and endocannabinoids among the potential mediators of DHA in altering airway inflammation in chronic agricultural dust exposure.

Effects of elevated CO2 levels on lung immune response to organic dust and lipopolysaccharide

Workplaces with elevated organic dust levels such as animal feed barns also commonly have elevated levels of gasses, such as CO₂. Workers exposed to such complex environments often experience respiratory effects that may be due to a combination of respirable factors. We examined the effects of CO₂ on lung innate immune responses in mice co-exposed to the inflammatory agents lipopolysaccharide (LPS) and organic dust. We evaluated CO₂ levels at the building recommended limit (1000 ppm) as well as the exposure limit (5000 ppm). Mice were nasally instilled with dust extracts or LPS and immediately put into chambers with a constant flow of room air (avg. 430 ppm CO₂), 1000 ppm, or 5000 ppm CO₂ enriched air. Results reveal that organic dust exposures tended to show decreased inflammatory responses with 1000 ppm CO₂ and increased responses at 5000 ppm CO₂. Conversely, LPS with addition of CO₂ as low as 1000 ppm tended to inhibit several inflammatory markers. In most cases saline treated animals showed few changes with CO₂ exposure, though some changes in mRNA levels were present. This shows that CO₂ as low as 1000 ppm CO₂ was capable of altering innate immune responses to both LPS and organic dust extracts, but each response was altered in a different fashion.

Every breath you take: Impacts of environmental dust exposure on intestinal barrier function-from the gut-lung axis to COVID-19

As countries continue to industrialize, major cities experience diminished air quality, whereas rural populations also experience poor air quality from sources such as agricultural operations. These exposures to environmental pollution from both rural and populated/industrialized sources have adverse effects on human health. Although respiratory diseases (e.g., asthma and chronic obstructive pulmonary disease) are the most commonly reported following long-term exposure to particulate matter and hazardous chemicals, gastrointestinal complications have also been associated with the increased risk of lung disease from inhalation of polluted air. The interconnectedness of these organ systems has offered valuable insights into the roles of the immune system and the micro/mycobiota as mediators of communication between the lung and the gut during disease states. A topical example of this relationship is provided by reports of multiple gastrointestinal symptoms in patients with coronavirus disease 2019 (COVID-19), whereas the rapid transmission and increased risk of COVID-19 has been linked to poor air quality and high levels of particulate matter. In this review, we focus on the mechanistic effects of environmental pollution on disease progression with special emphasis on the gut-lung axis.

Organic dust exposure induces stress response and mitochondrial dysfunction in monocytic cells

Exposure to airborne organic dust (OD), rich in microbial pathogen-associated molecular patterns (PAMPs), is shown to induce lung inflammation. A common manifestation in lung inflammation is altered mitochondrial structure and bioenergetics that regulate mitochondrial ROS (mROS) and feed a vicious cycle of mitochondrial dysfunction. The role of mitochondrial dysfunction in other airway diseases is well known. However, whether OD exposure induces mitochondrial dysfunction remains elusive. Therefore, we tested a hypothesis that organic dust extract (ODE) exposure induces mitochondrial stress using a human monocytic cell line (THP1). We examined whether co-exposure to ethyl pyruvate (EP) or mitoapocynin (MA) could rescue ODE exposure induced mitochondrial changes. Transmission electron micrographs showed significant differences in cellular and organelle morphology upon ODE exposure. ODE exposure with and without EP co-treatment increased the mtDNA leakage into the cytosol. Next, ODE exposure increased PINK1, Parkin, cytoplasmic cytochrome c levels, and reduced mitochondrial mass and cell viability, indicating mitophagy. MA treatment was partially protective by decreasing Parkin expression, mtDNA and cytochrome c release and increasing cell viability.

Organic dust-induced mitochondrial dysfunction could be targeted via cGAS-STING or cytoplasmic NOX-2 inhibition using microglial cells and brain slice culture models

Organic dust (OD) exposure in animal production industries poses serious respiratory and other health risks. OD consisting of microbial products and particulate matter and OD exposure-induced respiratory inflammation are under investigation. However, the effect of OD exposure on brain remains elusive. We show that OD exposure of microglial cells induces an inflammatory phenotype with the release of mitochondrial DNA (mt-DNA). Therefore, we tested a hypothesis that OD exposure-induced secreted mt-DNA signaling drives the inflammation. A mouse microglial cell line was treated with medium or organic dust extract (ODE, 1% v/v) along with either phosphate-buffered saline (PBS) or mitoapocynin (MA, 10 µmol). Microglia treated with control or anti-STING siRNA were exposed to medium or ODE. Mouse organotypic brain slice cultures (BSCs) were exposed to medium or ODE with or without MA. Various samples were processed to quantify mitochondrial reactive oxygen species (mt-ROS), mt-DNA, cytochrome c, TFAM, mitochondrial stress markers and mt-DNA-induced signaling via cGAS-STING and TLR9. Data were analyzed and a p value of ≤ 0.05 was considered significant. MA treatment decreased the ODE-induced mt-DNA release into the cytosol. ODE increased MFN1/2 and PINK1 but not DRP1 and MA treatment decreased the MFN2 expression. MA treatment decreased the ODE exposure-induced mt-DNA signaling via cGAS-STING and TLR9. Anti-STING siRNA decreased the ODE-induced increase in IRF3, IFN-β and IBA-1 expression. In BSCs, MA treatment decreased the ODE-induced TNF-α, IL-6 and MFN1. Therefore, OD exposure-induced mt-DNA signaling was curtailed through cytoplasmic NOX-2 inhibition or STING suppression to reduce brain microglial inflammatory response.

Pre-exposure to hydrogen sulfide modulates the innate inflammatory response to organic dust

Animal production units produce and store many contaminants on-site, including organic dust (OD) and hydrogen sulfide (H₂S). Workers in these settings report various respiratory disease symptoms. Both OD and H₂S have shown to induce lung inflammation. However, impact of co-exposure to both H₂S and OD has not been investigated. Therefore, we tested a hypothesis that pre-exposure to H₂S modulates the innate inflammatory response of the lungs to organic dust. In a mouse model of H₂S and organic dust extract (ODE) exposure, we assessed lung inflammation quantitatively. We exposed human airway epithelial and monocytic cells to medium or H₂S alone or H₂S followed by ODE and measured cell viability, oxidative stress, and other markers of inflammation. Exposure to 10 ppm H₂S followed by ODE increased the lavage fluid leukocytes. However, exposure to 10 ppm H₂S alone resulted in changes in tight junction proteins, an increase in mRNA levels of tlr2 and tlr4 as well as ncf1, ncf4, hif1α, and nrf2. H₂S alone or H₂S and ODE exposure decreased cell viability and increased reactive nitrogen species production. ODE exposure increased the transcripts of tlr2 and tlr4 in both in vitro and in vivo models, whereas increased nfkbp65 transcripts following exposure to ODE and H₂S was seen only in in vitro model. H₂S alone and H₂S followed by ODE exposure increased the levels of IL-1β. We conclude that pre-exposure to H₂S modulates lung innate inflammatory response to ODE.

Organic dust-induced lung injury and repair: Bi-directional regulation by TNFα and IL-10

Exposure to organic dust increases chronic airway inflammatory disorders. Effective treatment strategies are lacking. It has been reported that hog barn dust extracts (HDE) induce TNFα through protein kinase C (PKC) activation and that lung inflammation is enhanced in scavenger receptor A (SRA/CD204) knockout (KO) mice following HDE. Because interleukin (IL)-10 production can limit excessive inflammation, it was hypothesized here that HDE-induced IL-10 would require CD204 to effect inflammatory responses. C57BL/6 wild-type (WT), SRA KO, and IL-10 KO mice were intranasally challenged daily for 8 days with HDE and subsequently rested for 3 days with/without recombinant IL-10 (rIL-10) treatment. Primary peritoneal macrophages (PM) and murine alveolar macrophages (MH-S cells) were treated in vitro with HDE, SRA ligand (fucoidan), rIL-10, and/or PKC isoform inhibitors. HDE induced in vivo lung IL-10 in WT, but not SRA KO mice, and similar trends were demonstrated in isolated PM from same treated mice. Lung lymphocyte aggregates and neutrophils were elevated in in vivo HDE-treated SRA and IL-10 KO mice after a 3-d recovery, and treatment during recovery with rIL-10 abrogated these responses. In vitro rIL-10 treatment reduced HDE-stimulated TNFα release in MH-S and WT PM. In SRA KO macrophages, there was reduced IL-10 and PKC zeta (ζ) activity and increased TNFα following in vitro HDE stimulation. Similarly, blocking SRA (24 hr fucoidan pre-treatment) resulted in enhanced HDE-stimulated macrophage TNFα and decreased IL-10 and PKCζ activation. PKCζ inhibitors blocked HDE-stimulated IL-10, but not TNFα. Collectively, HDE stimulates IL-10 by an SRA- and PKCζ-dependent mechanism to regulate TNFα. Enhancing resolution of dust-mediated lung inflammation through targeting IL-10 and/or SRA may represent new approaches to therapeutic interventions.

Bacterial extracellular vesicles isolated from organic dust induce neutrophilic inflammation in the lung

Inhalation of organic dust is an occupational hazard leading to the development of respiratory symptoms and respiratory diseases. Bioaerosols from concentrated animal feeding operations are rich in bacteria and could carry bacterial extracellular vesicles (EVs) that could induce lung inflammation. It is not known if organic dust contains bacterial EVs and whether they modulate lung inflammation. Herein, we show that poultry organic dust contains bacterial EVs (dust EVs) that induce lung inflammation. Treatment of airway epithelial cells, THP-1-monocytes and -macrophages with dust EVs rapidly induced IL-8, IL-6, ICAM-1, proIL-1β, and TNF-α levels. In airway epithelial cells, induction of inflammatory mediators was due to increased mRNA levels and NF-κB activation. Induction of inflammatory mediators by dust EVs was not inhibited by polymyxin B. Single and repeated treatments of mice with dust EVs increased lung KC, IL-6, and TNF-α levels without significantly altering IL-17A levels. Increases in cytokines were associated with enhanced neutrophil infiltration into the lung. Repeated treatments of mice with dust EVs increased lung mean linear intercept and increased collagen deposition around airways indicating lung remodeling. Peribronchial cell infiltrates and airway epithelial thickening were also observed in treated mice. Because bacterial EVs are nanometer-sized particles, they can reach and accumulate in the bronchiolar and alveolar regions causing lung injury leading to the development of respiratory diseases. Our studies have provided new evidence for the presence of bacterial EVs in organic dust and for their role as one of the causative agents of organic dust-induced lung inflammation and lung injury.

A High Docosahexaenoic Acid Diet Alters the Lung Inflammatory Response to Acute Dust Exposure

Agricultural workers are at risk for the development of acute and chronic lung diseases due to their exposure to organic agricultural dusts. A diet intervention using the omega-3 fatty acid docosahexaenoic acid (DHA) has been shown to be an effective therapeutic approach for alleviating a dust-induced inflammatory response. We thus hypothesized a high-DHA diet would alter the dust-induced inflammatory response through the increased production of specialized pro-resolving mediators (SPMs). Mice were pre-treated with a DHA-rich diet 4 weeks before being intranasally challenged with a single dose of an extract made from dust collected from a concentrated swine feeding operation (HDE). This omega-3-fatty-acid-rich diet led to reduced arachidonic acid levels in the blood, enhanced macrophage recruitment, and increased the production of the DHA-derived SPM Resolvin D1 (RvD1) in the lung following HDE exposure. An assessment of transcript-level changes in the immune response demonstrated significant differences in immune pathway activation and alterations of numerous macrophage-associated genes among HDE-challenged mice fed a high DHA diet. Our data indicate that consuming a DHA-rich diet leads to the enhanced production of SPMs during an acute inflammatory challenge to dust, supporting a role for dietary DHA supplementation as a potential therapeutic strategy for reducing dust-induced lung inflammation.

HMGB1-RAGE Signaling Plays a Role in Organic Dust-Induced Microglial Activation and Neuroinflammation

Occupational exposure to contaminants in agriculture and other industries is known to cause significant respiratory ailments. The effect of organic dust on lung inflammation and tissue remodeling has been actively investigated over many years but the adverse effect of organic dust-exposure on the central vital organ brain is beginning to emerge. Brain microglial cells are a major driver of neuroinflammation upon exposure to danger signals. Therefore, we tested a hypothesis that organic dust-exposure of microglial cells induces microglial cell activation and inflammation through HMGB1-RAGE signaling. Mouse microglial cells were exposed to organic dust extract showed a time-dependent increase in cytoplasmic translocation of high-mobility group box 1 (HMGB1) from the nucleus, increased expression of receptor for advanced glycation end products (RAGE) and activation of Iba1 as compared to control cells. Organic dust also induced reactive oxygen species generation, NF-κB activation, and proinflammatory cytokine release. To establish a functional relevance of HMGB1-RAGE activation in microglia-mediated neuroinflammation, we used both pharmacological and genetic approaches involving HMGB1 translocation inhibitor ethyl pyruvate (EP), anti-HMGB1 siRNA, and NOX-inhibitor mitoapocynin. Interestingly, EP effectively reduced HMGB1 nucleocytoplasmic translocation and RAGE expression along with reactive oxygen species (ROS) generation and TNF-α and IL-6 production but not NF-κB activation. HMGB1 knockdown by siRNA also reduced both ROS and reactive nitrogen species (RNS) and IL-6 levels but not TNF-α. NOX2 inhibitor mitoapocynin significantly reduced RNS levels. Collectively, our results demonstrate that organic dust activates HMGB1-RAGE signaling axis to induce a neuroinflammatory response in microglia and that attenuation of HMGB1-RAGE activation by EP and mitoapocynin treatments or genetic knockdown can dampen the neuroinflammation.

Organic dust inhibits surfactant protein expression by reducing thyroid transcription factor-1 levels in human lung epithelial cells

Exposure to organic dust is a risk factor for the development of respiratory diseases. Surfactant proteins (SP) reduce alveolar surface tension and modulate innate immune responses to control lung inflammation. Therefore, changes in SP levels could contribute to the development of organic-dust-induced respiratory diseases. Because information on the effects of organic dust on SP levels is lacking, we studied the effects of dust from a poultry farm on SP expression. We found that dust extract reduced SP-A and SP-B mRNA and protein levels in H441 human lung epithelial cells by inhibiting their promoter activities, but did not have any effect on SP-D protein levels. Dust extract also reduced SP-A and SP-C levels in primary human alveolar epithelial cells. The inhibitory effects were not due to LPS or protease activities present in dust extract or mediated via oxidative stress, but were dependent on a heat-labile factor(s). Thyroid transcription factor-1, a key transcriptional activator of SP expression, was reduced in dust-extract-treated cells, indicating that its down-regulation mediates inhibition of SP levels. Our study implies that down-regulation of SP levels by organic dust could contribute to the development of lung inflammation and respiratory diseases in humans.

Insufficient zinc intake enhances lung inflammation in response to agricultural organic dust exposure

Organic dust exposure particularly within hog confinement facilities is a significant cause of airway inflammation and lung disease. In a cohort of Midwestern veterans with COPD and agricultural work exposure we observed reduced zinc intakes which were associated with decreased lung function. Because insufficient zinc intake is common within the U.S. and a potent modulator of innate immune function, we sought to determine whether deficits in zinc intake would impact the airway inflammatory response to hog confinement facility dust extract (HDE). Adult male C57BL/6 mice were randomized to zinc deficient or matched zinc sufficient diets for 3 weeks and subsequently treated with intranasal HDE inhalation or saline once or daily for 3 weeks while maintained on specific diets. Lavage fluid and lung tissue was collected. Conditions of zinc deficiency were also studied in macrophages exposed to HDE. Single and repetitive HDE inhalation exposure resulted in increased influx of total cells and neutrophils, increased mediator hyper-responsiveness (TNFα, IL-6, CXCL1, and amphiregulin), and enhanced tissue pathology that was more pronounced in zinc deficient mice compared to normal dietary counterparts. Airway inflammation was most pronounced in zinc deficient mice treated with repetitive HDE for 3 weeks. Similarly, macrophages maintained in a zinc deficient environment exhibited increased CXCL1 and IL-23 production as a result of increased NF-κB activation. Conclusion: Given the relatively high incidence of dietary deficiencies in agriculture workers, we anticipate that zinc intake, or a lack thereof, may play an important role in modulating the host response to organic dust exposure.

Organic dust induces inflammatory gene expression in lung epithelial cells via ROS-dependent STAT-3 activation

Exposure to dust in agricultural and animal environments, known as organic dust, is associated with the development of respiratory symptoms and respiratory diseases. Inflammation is a key feature of lung pathologies associated with organic dust exposure, and exposure to organic dust induces the expression of several immune and inflammatory mediators. However, information on transcription factors and cellular and molecular mechanisms controlling the production of immune and inflammatory mediators induced by organic dust is limited. In this study, we have identified STAT-3 as an important transcription factor controlling the induction of expression of immune and inflammatory mediators by poultry dust extracts in airway epithelial cells and in mouse lungs and delineated the cellular pathway for STAT-3 activation. Poultry dust extract activated STAT-3 phosphorylation in Beas2B and normal human bronchial epithelial cells and in mouse lungs. Chemical inhibition and siRNA knockdown of STAT-3 suppressed induction of immune and inflammatory mediator expression. Antioxidants suppressed the increase of STAT-3 phosphorylation induced by poultry dust extract indicating that oxidative stress [elevated reactive oxygen species (ROS) levels] is important for the activation. Chemical inhibition and siRNA knockdown experiments demonstrated that STAT-3 activation is dependent on the activation of nonreceptor tyrosine-protein kinase 2 (TYK2) and epidermal growth factor receptor (EGFR) tyrosine kinases. Our studies show that poultry dust extract controls the induction of immune and inflammatory mediator expression via a cellular pathway involving oxidative stress-mediated STAT-3 activation by TYK2 and EGFR tyrosine kinases.

Biphasic changes in airway epithelial cell EGF receptor binding and phosphorylation induced by components of hogbarn dust

PURPOSE OF THE STUDY

Workers in enclosed hogbarns experience an increased incidence of airway inflammation and obstructive lung disease, and an aqueous hogbarn dust extract (HDE) induces multiple inflammation-related responses in cultured airway epithelial cells. Epidermal growth factor receptor (EGFR) phosphorylation and activation has been identified as one important mediator of inflammatory cytokine release from these cells. The studies here investigated both early and late phase adaptive changes in EGFR binding properties and subcellular localization induced by exposure of cells to HDE.

MATERIALS AND METHODS

Cell surface EGFRs were quantified as binding to intact cells on ice. EGFR phosphorylation, expression, and localization were assessed with anti-EGFR antibodies and either blotting or confocal microscopy.

RESULTS

In BEAS-2B and primary human bronchial epithelial cells, HDE induced decreases in cell surface EGFR binding following both 15-min and 18-h exposures. In contrast, H292 cells exhibited only the 15-min decrease, with binding near the control level at 18 hr. Confocal microscopy showed that the 15-min decrease in binding is due to EGFR endocytosis. Although total EGFR immunoreactivity decreased markedly at 18 hr in confocal microscopy with BEAS-2B cells, immunoblots showed no loss of EGFR protein. HDE stimulated EGFR phosphorylation at both 15 min and 18 hr in BEAS-2B cells and primary cells, but only at 15 min in H292 cells, indicating that the different EGFR binding changes among these cell types is likely related to their different time-dependent changes in phosphorylation.

CONCLUSIONS

These studies extend the evidence for EGFRs as important cellular targets for components of HDE and they reveal novel patterns of EGFR phosphorylation and binding changes that vary among airway epithelial cell types. The results provide both impetus and convenient assays for identifying the EGFR-activating components and pathways that likely contribute to hogbarn dust-induced lung disease in agricultural workers.

Establishment and characterization of a multi-purpose large animal exposure chamber for investigating health effects

Air pollution poses a significant threat to the environment and human health. Most in vivo health studies conducted regarding air pollutants, including particulate matter (PM) and gas phase pollutants, have been either through traditional medical intranasal treatment or using a tiny chamber, which limit animal activities. In this study, we designed and tested a large, whole-body, multiple animal exposure chamber with uniform dispersion and exposure stability for animal studies. The chamber simultaneously controls particle size distribution and PM mass concentration. Two different methods were used to generate aerosol suspension through either soluble material (Alternaria extract), liquid particle suspension (nanosilica solution), or dry powder (silica powder). We demonstrate that the chamber system provides well controlled and characterized whole animal exposures, where dosage is by inhalation of particulate matter.

Effects of Agricultural Organic Dusts on Human Lung-Resident Mesenchymal Stem (Stromal) Cell Function

Agricultural organic dust exposures trigger harmful airway inflammation, and workers experiencing repetitive dust exposures are at increased risk for lung disease. Mesenchymal stem/stromal cells (MSCs) regulate wound repair processes in the lung, and may contribute to either proresolution or -fibrotic lung responses. It is unknown how organic dust exposures alter lung-resident MSC activation and proinflammatory versus prorepair programs in the lung. To address this gap in knowledge, we isolated human lung-resident MSC from lung tissue. Cells were stimulated with aqueous extracts of organic dusts (DE) derived from swine confinement facilities and were assessed for changes in proliferative and migratory capacities, and production of proinflammatory and prorepair mediators. Through these investigations, we found that DE induces significant release of proinflammatory mediators TNF-α, IL-6, IL-8, and matrix metalloproteases, while also inducing the production of prorepair mediators amphiregulin, FGF-10, and resolvin D1. In addition, DE significantly reduced the growth and migratory capacities of lung-resident MSC. Together, these investigations indicate lung-resident MSC activation and wound repair activities are altered by organic dust exposures. These findings warrant future investigations to assess how organic dusts affect lung-resident mesenchymal stem/stromal cell function and impact airway inflammation, injury, and repair during agricultural aerosol exposures.

Ethyl pyruvate reduces organic dust-induced airway inflammation by targeting HMGB1-RAGE signaling

BACKGROUND

Animal production workers are persistently exposed to organic dust and can suffer from a variety of respiratory disease symptoms and annual decline in lung function. The role of high mobility group box-1 (HMGB1) in inflammatory airway diseases is emerging. Hence, we tested a hypothesis that organic dust exposure of airway epithelial cells induces nucleocytoplasmic translocation of HMGB1 and blocking this translocation dampens organic dust-induced lung inflammation.

METHODS

Rats were exposed to either ambient air or swine barn (8 h/day for either 1, 5, or 20 days) and lung tissues were processed for immunohistochemistry. Swine barn dust was collected and organic dust extract (ODE) was prepared and sterilized. Human airway epithelial cell line (BEAS-2B) was exposed to either media or organic dust extract followed by treatment with media or ethyl pyruvate (EP) or anti-HMGB1 antibody. Immunoblotting, ELISA and other assays were performed at 0 (control), 6, 24 and 48 h. Data (as mean ± SEM) was analyzed using one or two-way ANOVA followed by Bonferroni's post hoc comparison test. A p value of less than 0.05 was considered significant.

RESULTS

Compared to controls, barn exposed rats showed an increase in the expression of HMGB1 in the lungs. Compared to controls, ODE exposed BEAS-2B cells showed nucleocytoplasmic translocation of HMGB1, co-localization of HMGB1 and RAGE, reactive species and pro-inflammatory cytokine production. EP treatment reduced the ODE induced nucleocytoplasmic translocation of HMGB1, HMGB1 expression in the cytoplasmic fraction, GM-CSF and IL-1β production and augmented the production of TGF-β1 and IL-10. Anti-HMGB1 treatment reduced ODE-induced NF-κB p65 expression, IL-6, ROS and RNS but augmented TGF-β1 and IL-10 levels.

CONCLUSIONS

HMGB1-RAGE signaling is an attractive target to abrogate OD-induced lung inflammation.

Organic barn dust inhibits surfactant protein D production through protein kinase-c alpha dependent increase of GPR116

Prolonged exposure to organic barn dusts can lead to chronic inflammation and a broad range of lung problems over time, mediated by innate immune mechanisms. The immune surfactant or collectin surfactant protein D (SP-D) is a crucial multifunctional innate immune receptor. Little work to date has examined the effect of such collectins in response to organic dusts. We provide evidence here that agricultural organic dusts can inhibit mRNA and protein expression of SP-D in a human alveolar epithelial cell line, and an in vivo mouse model. This inhibition was not a result of lipopolysaccharide (LPS) or peptidoglycans, the two most commonly cited immune active components of these dusts. We further show that inhibition of the signaling molecule protein kinase C alpha (PKCα) can reverse this inhibition implicating it as a mechanism of SP-D inhibition. Examination of the SP-D regulatory receptor GPR116 showed that its mRNA expression was increased in response to dust and inhibited by blocking PKCα, implicating it as a means of inhibiting SP-D in the lungs in response to organic dusts. This reduction shows that organic barn dust can reduce lung SP-D, thus leaving workers potentially at risk for a host of pathogens.

Bovine milk-derived extracellular vesicles enhance inflammation and promote M1 polarization following agricultural dust exposure in mice

Occupational agricultural dust exposure can cause severe lung injury, including COPD and asthma exacerbations. Cell-derived extracellular vesicles can mediate inflammatory responses and immune activation, but the contribution of diet-derived extracellular vesicles to these processes is poorly understood. We investigated whether bovine milk-derived extracellular vesicles modulate inflammatory responses to agricultural dust exposures in a murine model. C57BL/6 mice were fed either an extracellular vesicle-enriched modification of the AIN-93G diet with lyophilized bovine milk (EV) or a control diet wherein the milk was presonicated, disrupting the milk extracellular vesicles and thereby leading to RNA degradation (DEV). Mice were maintained on the diets for 5-7 weeks and challenged with a single (acute) intranasal instillation of a 12.5% organic dust extract (DE) or with 15 instillations over 3 weeks (repetitive exposure model). Through these investigations, we identified significant interactions between diet and DE when considering numerous inflammatory outcomes, including lavage inflammatory cytokine levels and cellular infiltration into the lung airways. DE-treated peritoneal macrophages also demonstrated altered polarization, with EV-fed mouse macrophages exhibiting an M1 shift compared to an M2 phenotype in DEV-fed mice (IL-6, TNF, IL-12/23 all significantly elevated, and IL-10 and arginase decreased in EV macrophages, ex vivo). In complementary in vitro studies, mouse macrophages treated with purified milk-derived EV were found to express similar polarization phenotypes upon DE stimulation. These results suggest a role for dietary extracellular vesicles in the modulation of lung inflammation in response to organic dust which may involve macrophage phenotype polarization.

Agriculture Occupational Exposures and Factors Affecting Health Effects

PURPOSE OF REVIEW

Agriculture environments contain a variety of inflammatory aerosols that may increase risk for lung inflammation and disease in exposed individuals. In addition, epidemiological studies have also identified protective effects of rural environments and farming exposures.

RECENT FINDINGS

In this review, we will discuss recent literature published since 2016 that investigates the impact of differing agricultural exposures on respiratory health. Discussions include the impact of farming modernization, education, and personal protective equipment usage among workers, timing and duration in mediating lung health outcomes, and population studies investigating the association between exposure and risk for numerous lung diseases.

Relationship of systemic IL-10 levels with proinflammatory cytokine responsiveness and lung function in agriculture workers

BACKGROUND

Agriculture workers are exposed to microbial component- and particulate matter-enriched organic dust aerosols. Whereas it is clear that exposure to these aerosols can lead to lung inflammation, it is not known how inflammatory responses are resolved in some individuals while others develop chronic lung disease. Interleukin (IL)-10 is an immunomodulatory cytokine that is recognized as a potent anti-inflammatory and pro-resolving factor. The objective of this study was to determine whether there is a relationship of systemic IL-10 and proinflammatory responses and/or respiratory health effects in humans with prior agriculture exposure.

METHODS

This is a cross sectional study of 625 veterans with > 2 years of farming experience. Whole blood was stimulated with or without organic dust and measured for IL-6, TNFα and IL-10. Participants underwent spirometry and respiratory symptoms were assessed by questionnaire.

RESULTS

We found that baseline IL-10 concentration from the whole blood assay was inversely associated with ΔTNF-α (r = - 0.63) and ΔIL-6 (r = - 0.37) levels. Results remained highly significant in the linear regression model after adjusting for age, sex, BMI, race, education, smoking status, and white blood cell count (ΔTNF-α, p < 0.0001; ΔIL-6, p < 0.0001). We found no association between chronic cough (p = 0.18), chronic phlegm (p = 0.31) and chronic bronchitis (p = 0.06) and baseline IL-10 levels using univariate logistic regression models. However, we did find that higher FEV1/FVC was significantly associated with increased baseline IL-10 concentration.

CONCLUSIONS

Collectively, these studies support a potential role for IL-10 in modulating an inflammatory response and lung function in agriculture-exposed persons.

Kinome analyses of inflammatory responses to swine barn dust extract in human bronchial epithelial and monocyte cell lines

Exacerbated inflammation upon persistent barn organic dust exposure is a key contributor to the pathogenesis of lung inflammation and lung function decline. Barn dust constituents and the mechanisms contributing to the exacerbated inflammation are not clearly known. We set out to understand the inflammatory effects of Swine Barn Dust Extracts (SBDE) on human lung epithelial (BEAS2B) and macrophage (THP-1 monocyte derived) cell lines on a kinome array to determine phosphorylation events in the inflammatory signaling pathways. Upon identifying events unique to SBDE or those induced by innate immune ligands in each cell line, we validated the signaling pathway activation by transcriptional analyses of downstream inflammatory cytokines. Our findings indicate that SBDE-mediated pro-inflammatory effects are predominantly due to the induction of neutrophilic chemokine IL-8. Differentially phosphorylated peptides implicated in IL-8 induction in BEAS2B cell line include, TLR2, 4, 5, 7, 8, 9, PKC, MAP kinases (p38, JNK), inflammasomes (NLRP1, NLRP3), NF-κB and AP-1. In the THP-1 cell line, in addition to the aforementioned peptides, peptides corresponding to RIG-I-like receptors (RIG-I, MDA5) were found. This is the first report to demonstrate the application of a kinome array to delineate key inflammatory signaling pathways activated upon SBDE exposure in vitro.

The Effect of Inhalant Organic Dust on Bone Health

PURPOSE OF REVIEW

Agriculture remains a major economic sector globally, and workers experience high rates of chronic inflammatory lung and musculoskeletal diseases. Whereas obstructive pulmonary diseases are known risk factors for bone loss, the underlying relationship between lung inflammation and bone health is not well known.

RECENT FINDINGS

An agriculture organic dust extract inhalation animal model has recently linked lung injury-induced inflammation to systemic bone loss. This process is dependent upon lipopolysaccharide and the toll-like receptor 4 (TLR4) signaling pathway. Downstream systemic interleukin-6 is a key mediator that subsequently activates osteoclastogenesis. Age is a host factor that impacted bone disease with younger mice demonstrating increased susceptibility to bone loss following inhalant exposures as compared to older mice. Supplemental dietary vitamin D was shown to prevent organic dust-induced bone loss, but not lung disease, in animals. Recent animal studies provide new mechanistic insight into the lung-bone inflammatory axis. Host factors, diet, and lipopolysaccharide/TLR4 signaling pathways play a significant role in explaining how inhalant organic dust exposures impact bone health. These investigations might lead to specific targeted therapeutic approaches.

TRPC6 contributes to LPS-induced inflammation through ERK1/2 and p38 pathways in bronchial epithelial cells

receptor potential canonical (TRPC) channels are presently an emerging target for airway disorders. Recent evidence has indicated that TRPC6 as a member of the TRPC family plays an important role in airway inflammation, but its precise function in bronchial epithelial cells remains unclear. The aim of this study was to investigate the role of TRPC6 in Toll-like receptor 4 (TLR4)-mediated inflammation in human bronchial epithelial cells stimulated by endotoxin [lipopolysaccharide (LPS)]. Hyp9 is a simplified phloroglucinol derivative of hyperforin that highly selectively activates TRPC6 channels. The results show that the activation of TRPC6 by Hyp9 induced the production of interleukin (IL)-8 and IL-6. LPS was also able to induce the release of IL-8 and IL-6, which was significantly aggravated by Hyp9 and reduced by knockdown of TRPC6. Treatment with LPS not only chronically induced the expression of TRPC6 mRNA and protein in a TLR4-dependent manner but also acutely increased Ca²⁺ influx through TRPC6 channels. In addition, LPS-induced overexpression of TRPC6 and Ca²⁺ influx were associated with the phosphorylation of phosphatidylinositol 3-kinase (PI3K) and Akt. Importantly, TRPC6 was required for the activation of ERK1/2, p38, and NF-κB. In conclusion, these data reveal that LPS induced the overexpression of TRPC6 and TRPC6-dependent Ca²⁺ influx via the TLR4/PI3K/Akt pathway resulting in Ca²⁺ mobilization, which subsequently promoted the activation of ERK1/2, p38, and NF-κB and the inflammatory response in bronchial epithelial cells.

Docosahexaenoic acid enhances amphiregulin-mediated bronchial epithelial cell repair processes following organic dust exposure

Injurious dust exposures in the agricultural workplace involve the release of inflammatory mediators and activation of epidermal growth factor receptor (EGFR) in the respiratory epithelium. Amphiregulin (AREG), an EGFR ligand, mediates tissue repair and wound healing in the lung epithelium. Omega-3 fatty acids such as docosahexaenoic acid (DHA) are also known modulators of repair and resolution of inflammatory injury. This study investigated how AREG, DHA, and EGFR modulate lung repair processes following dust-induced injury. Primary human bronchial epithelial (BEC) and BEAS-2B cells were treated with an aqueous extract of swine confinement facility dust (DE) in the presence of DHA and AREG or EGFR inhibitors. Mice were exposed to DE intranasally with or without EGFR inhibition and DHA. Using a decellularized lung scaffolding tissue repair model, BEC recolonization of human lung scaffolds was analyzed in the context of DE, DHA, and AREG treatments. Through these investigations, we identified an important role for AREG in mediating BEC repair processes. DE-induced AREG release from BEC, and DHA treatment following DE exposure, enhanced this release. Both DHA and AREG also enhanced BEC repair capacities and rescued DE-induced recellularization deficits. In vivo, DHA treatment enhanced AREG production following DE exposure, whereas EGFR inhibitor-treated mice exhibited reduced AREG in their lung homogenates. These data indicate a role for AREG in the process of tissue repair after inflammatory lung injury caused by environmental dust exposure and implicate a role for DHA in regulating AREG-mediated repair signaling in BEC.

Effect of low-level CO2 on innate inflammatory protein response to organic dust from swine confinement barns

BACKGROUND

Organic hog barn dust (HDE) exposure induces lung inflammation and long-term decreases in lung function in agricultural workers. While concentrations of common gasses in confined animal facilities are well characterized, few studies have been done addressing if exposure to elevated barn gasses impacts the lung immune response to organic dusts. Given the well documented effects of hypercapnia at much higher levels we hypothesized that CO2 at 8 h exposure limit levels (5000 ppm) could alter innate immune responses to HDE.

METHODS

Using a mouse model, C57BL/6 mice were nasally instilled with defined barn dust extracts and then housed in an exposure box maintained at one of several CO2 levels for six hours. Bronchiolar lavage (BAL) was tested for several cytokines while lung tissue was saved for mRNA purification and immunohistochemistry.

RESULTS

Exposure to elevated CO2 significantly increased the expression of pro-inflammatory markers, IL-6 and KC, in BAL fluid as compared to dust exposure alone. Expression of other pro-inflammatory markers, such as ICAM-1 and matrix metalloproteinase-9 (MMP-9), were also tested and showed similar increased expression upon HDE + CO2 exposure. A chemokine array analysis of BAL fluid revealed that MIP-1γ (CCL9) shows a similar increased response to HDE + CO2. Further testing showed CCL9 was significantly elevated by barn dust and further enhanced by CO2 co-exposure in a dose-dependent manner that was noticeable at the protein and mRNA levels. In all cases, except for ICAM-1, increases in tested markers in the presence of elevated CO2 were only significant in the presence of HDE as well.

CONCLUSIONS

We show that even at mandated safe exposure limits, CO2 is capable of enhancing multiple markers of inflammation in response to HDE.

Alcohol Inhibits Organic Dust-induced ICAM-1 Expression on Bronchial Epithelial Cells

Aims: Exposure to dusts/bioaerosols in concentrated animal feeding operations (CAFOs) results in inflammatory lung diseases in workers. Hog CAFOs dust extract (HDE) increases expression of intercellular adhesion molecule-1 (ICAM-1), neutrophil adhesion, and TNFα release in bronchial epithelial cells. Alcohol consumption is increasingly recognized to impair lung immunity. We hypothesized that alcohol impairs HDE-induced TNFα, ICAM-1 expression and neutrophil adhesion by directly inhibiting TNFα converting enzyme (TACE) activity.

METHODS

Bronchial epithelial cells (BEAS-2B) and primary human bronchial epithelial cells were pretreated with ethanol (EtOH) or TACE inhibitor. ICAM-1 surface expression, TNFα release, and TACE activity were analyzed following HDE stimulation. The effect of alcohol and TACE inhibition on HDE-regulated epithelial cell/neutrophil adhesion interactions was investigated. Finally, utilizing an established animal model, C57BL/6 mice were fed ad libitum ethanol (20%) in drinking water for 8 wk followed by daily intranasal inhalation of HDE or saline during the final two weeks. Mice were sacrificed and lung sections immunostained for ICAM-1.

RESULTS

Pretreatment with alcohol or TACE inhibitor significantly decreased HDE-induced ICAM-1 expression and TNFα release. HDE augmented neutrophil adhesion to epithelial cells, which was decreased with alcohol (32% decrease) or TACE inhibitor (55% decrease) pretreatment. TACE activity increased following HDE exposure, but TACE activity was inhibited following alcohol pretreatment. Alcohol-fed mice demonstrated decreased HDE-induced airway epithelium ICAM-1 expression.

CONCLUSIONS

Alcohol diminishes HDE-induced ICAM-1 expression, TNFα release, and neutrophil adhesion via inhibition of TACE activity. These results suggest that alcohol may be an important modulator of lung innate immune responses following CAFO exposure.

Pulmonary innate inflammatory responses to agricultural occupational contaminants

Agricultural workers are exposed to many contaminants and suffer from respiratory and other symptoms. Dusts, gases, microbial products and pesticide residues from farms have been linked to effects on the health of agricultural workers. Growing sets of data from in vitro and in vivo models demonstrate the role of the innate immune system, especially Toll-like receptor 4 (TLR4) and TLR9, in lung inflammation induced following exposure to contaminants in agricultural environments. Interestingly, inflammation and lung function changes appear to be discordant indicating the complexity of inflammatory responses to exposures. Whereas the recent development of rodent models and exposure systems have yielded valuable data, we need new systems to examine the combined effects of multiple contaminants in order to increase our understanding of farm-exposure-induced negative health effects.

Epistatic effect of TLR-1, -6 and -10 polymorphisms on organic dust-mediated cytokine response

Exposure to organic dust from agricultural environments is associated with inflammatory respiratory conditions. The putative causal agents in organic dust include viral, microbial and fungal components, which are recognized by the family of toll-like receptors and drive host innate and adaptive responses. Our aim in this study was to determine whether responsiveness to organic dust among agricultural workers was dependent on polymorphisms in the TLR10-TLR1-TLR6 gene cluster. We stimulated whole blood from 509 agricultural workers with organic dust, triacyl lipopeptide N-palmitoyl-S-dipalmitoylglyceryl Cys-Ser-(Lys)₄ (Pam3CSK4) and the diacyl- lipopeptide peptidoglycan. Several of the tagging polymorphisms and haplotypes conferred hyper-responsiveness to organic dust with an increase in IL-6 (p < 0.005), but not TNF-α, secretion. We conclude that genetic variation in the TLR10-TLR1-TLR6 gene cluster mediates responsiveness to organic dust, but indicates different signaling pathways for IL-6 and TNF-α. These studies provide new insight into the role of the TLR10-TLR1-TLR6 gene cluster and the innate immune response to organic dust.

High throughput genomic sequencing of bioaerosols in broiler chicken production facilities

Chronic inhalation exposure to agricultural dust promotes the development of chronic respiratory diseases among poultry workers. Poultry dust is composed of dander, chicken feed, litter bedding and microbes. However, the microbial composition and abundance has not been fully elucidated. Genomic DNA was extracted from settled dust and personal inhalable dust collected while performing litter sampling or mortality collection tasks. DNA libraries were sequenced using a paired-end sequencing-by-synthesis approach on an Illumina HiSeq 2500. Sequencing data showed that poultry dust is predominantly composed of bacteria (64-67%) with a small quantity of avian, human and feed DNA (< 2% of total reads). Staphylococcus sp. AL1, Salinicoccus carnicancri and Lactobacillus crispatus were the most abundant bacterial species in personal exposure samples of inhalable dust. Settled dust had a moderate relative abundance of these species as well as Staphylococcus lentus and Lactobacillus salivarius. There was a statistical difference between the microbial composition of aerosolized and settled dust. Unlike settled dust composition, aerosolized dust composition had little variance between samples. These data provide an extensive analysis of the microbial composition and relative abundance in personal inhalable poultry dust and settled poultry dust.

Alcohol Decreases Organic Dust-Stimulated Airway Epithelial TNF-Alpha Through a Nitric Oxide and Protein Kinase-Mediated Inhibition of TACE

BACKGROUND

Farm workers in rural areas consume more alcohol than those who reside in urban areas. Occupational exposures such as agricultural work can pose hazards on the respiratory system. It is established that hog barn dust induces inflammation in the airway, including the release of cytokines such as tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), and IL-8. We have shown that alcohol alters airway epithelial innate defense through changes in both nitric oxide (NO) and cAMP-dependent protein kinase A (PKA). Simultaneous exposure to hog barn dust and alcohol decreases inflammatory mediators, TNF-α, IL-6, and IL-8, in mice. Previously, mice exposed to both alcohol and hog barn dust showed a depleted amount of lymphocytes compared to mice exposed only to hog barn dust. Weakening of the innate immune response could lead to enhanced susceptibility to disease. In addition, mice that were co-exposed to hog barn dust and alcohol also experienced increased mortality.

METHODS

Because we recently demonstrated that PKA activation inhibits the TNF-α sheddase, TNF-α-converting enzyme (TACE), we hypothesized that an alcohol-mediated PKA pathway blocks TACE activity and prevents the normative inflammatory response to hog barn dust exposure. To delineate these effects, we used PKA pathway inhibitors (adenylyl cyclase [AC], cAMP, and PKA) to modulate the effects of alcohol on dust-stimulated TNF-α release in the bronchial epithelial cell line, BEAS-2B. Alcohol pretreatment blocked TACE activity and TNF-α release in hog barn dust-treated cells.

RESULTS

Alcohol continued to block hog barn dust-mediated TNF-α release in the presence of the particulate AC inhibitor, SQ22,536. The soluble adenylyl cyclase inhibitor, KH7, however, significantly increased the inflammatory response to hog barn dust. phosphodiesterase 4 inhibitors significantly elevated cAMP and enhanced alcohol-mediated inhibition of dust-stimulated TNF-α release. In addition, the NO synthase inhibitor, l-NMMA, also reversed the alcohol-blocking effect on dust-stimulated TNF-α.

CONCLUSIONS

These data suggest that alcohol requires a soluble cyclase-generated cAMP-PKA pathway that is dependent upon the action of NO to inhibit TACE and TNF-α release. These findings support our observations that alcohol functions through a dual NO and PKA pathway in bronchial epithelial cells.

Proteases and oxidant stress control organic dust induction of inflammatory gene expression in lung epithelial cells

Background

Persistant inflammatory responses to infectious agents and other components in organic dust underlie lung injury and development of respiratory diseases. Organic dust components responsible for eliciting inflammation and the mechanisms by which they cause lung inflammation are not fully understood. We studied the mechanisms by which protease activities in poultry dust extracts and intracellular oxidant stress induce inflammatory gene expression in A549 and Beas2B lung epithelial cells.

Methods

The effects of dust extracts on inflammatory gene expression were analyzed by quantitative polymerase chain reaction (qPCR), enzyme linked immunosorbent (ELISA) and western blot assays. Oxidant stress was probed by dihydroethidium (DHE) labeling, and immunostaining for 4-hydroxynonenal (4-HNE). Effects on interleukin-8 (IL-8) promoter regulation were determined by transient transfection assay.

Results

Dust extracts contained trypsin and elastase activities, and activated protease activated receptor (PAR)-1 and -2. Serine protease inhibitors and PAR-1 or PAR-2 knockdown suppressed inflammatory gene induction. Dust extract induction of IL-8 gene expression was associated with increased DHE-fluorescence and 4-HNE staining, and antioxidants suppressed inflammatory gene induction. Protease inhibitors and antioxidants suppressed protein kinase C and NF-κB activation and induction of IL-8 promoter activity in cells exposed to dust extract.

Conclusions

Our studies demonstrate that proteases and intracellular oxidants control organic dust induction of inflammatory gene expression in lung epithelial cells. Targeting proteases and oxidant stress may serve as novel approaches for the treatment of organic dust induced lung diseases. This is the first report on the involvement of oxidant stress in the induction of inflammatory gene expression by organic dust.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0455-z) contains supplementary material, which is available to authorized users.

β2-Adrenergic agonists attenuate organic dust-induced lung inflammation

Agricultural dust exposure results in significant lung inflammation, and individuals working in concentrated animal feeding operations (CAFOs) are at risk for chronic airway inflammatory diseases. Exposure of bronchial epithelial cells to aqueous extracts of hog CAFO dusts (HDE) leads to inflammatory cytokine production that is driven by protein kinase C (PKC) activation. cAMP-dependent protein kinase (PKA)-activating agents can inhibit PKC activation in epithelial cells, leading to reduced inflammatory cytokine production following HDE exposure. β2-Adrenergic receptor agonists (β2-agonists) activate PKA, and we hypothesized that β2-agonists would beneficially impact HDE-induced adverse airway inflammatory consequences. Bronchial epithelial cells were cultured with the short-acting β2-agonist salbutamol or the long-acting β2-agonist salmeterol prior to stimulation with HDE. β2-Agonist treatment significantly increased PKA activation and significantly decreased HDE-stimulated IL-6 and IL-8 production in a concentration- and time-dependent manner. Salbutamol treatment significantly reduced HDE-induced intracellular adhesion molecule-1 expression and neutrophil adhesion to epithelial cells. Using an established intranasal inhalation exposure model, we found that salbutamol pretreatment reduced airway neutrophil influx and IL-6, TNF-α, CXCL1, and CXCL2 release in bronchoalveolar lavage fluid following a one-time exposure to HDE. Likewise, when mice were pretreated daily with salbutamol prior to HDE exposure for 3 wk, HDE-induced neutrophil influx and inflammatory mediator production were also reduced. The severity of HDE-induced lung pathology in mice repetitively exposed to HDE for 3 wk was also decreased with daily salbutamol pretreatment. Together, these results support the need for future clinical investigations to evaluate the utility of β2-agonist therapies in the treatment of airway inflammation associated with CAFO dust exposure.

Gene expression profiling of the effects of organic dust in lung epithelial and THP-1 cells reveals inductive effects on inflammatory and immune response genes

The intensification and concentration of animal production operations expose workers to high levels of organic dusts in the work environment. Exposure to organic dusts is a risk factor for the development of acute and chronic respiratory symptoms and diseases. Lung epithelium plays important roles in the control of immune and inflammatory responses to environmental agents to maintain lung health. To better understand the effects of organic dust on lung inflammatory responses, we characterized the gene expression profiles of A549 alveolar and Beas2B bronchial epithelial and THP-1 monocytic cells influenced by exposure to poultry dust extract by DNA microarray analysis using Illumina Human HT-12 v4 Expression BeadChip. We found that A549 alveolar and Beas2B bronchial epithelial and THP-1 cells responded with unique changes in the gene expression profiles with regulation of genes encoding inflammatory cytokines, chemokines, and other inflammatory proteins being common to all the three cells. Significantly induced genes included IL-8, IL-6, IL-1β, ICAM-1, CCL2, CCL5, TLR4, and PTGS2. Validation by real-time qRT-PCR, ELISA, Western immunoblotting, and immunohistochemical staining of lung sections from mice exposed to dust extract validated DNA microarray results. Pathway analysis indicated that dust extract induced changes in gene expression influenced functions related to cellular growth and proliferation, cell death and survival, and cellular development. These data show that a broad range of inflammatory mediators produced in response to poultry dust exposure can modulate lung immune and inflammatory responses. This is the first report on organic dust induced changes in expression profiles in lung epithelial and THP-1 monocytic cells.

Maresin-1 reduces airway inflammation associated with acute and repetitive exposures to organic dust

Agriculture industry workers are at a higher risk for chronic bronchitis and obstructive pulmonary diseases, and current therapeutics are not entirely effective. We previously found that the specialized proresolving lipid mediator maresin-1 (MaR1) reduced proinflammatory cytokine release and intracellular adhesion molecule-1 (ICAM-1) expression in bronchial epithelial cells exposed to extracts of organic dust (DE) derived from swine confinement facilities in vitro. The objective of this study was to determine whether MaR1 is effective at limiting lung inflammation associated with acute and repetitive exposures to DE in an established murine model of inhalant dust exposures. C57Bl/6 mice were treated with MaR1 or vehicle control and intranasally instilled with DE once or daily for 3 weeks. Bronchioalveolar lavage fluid was analyzed for total and differential cell counts and proinflammatory cytokine levels, and lung tissues were assessed for histopathology and ICAM-1 expression. In both single and repetitive DE exposure studies, MaR1 significantly decreased bronchoalveolar lavage neutrophil infiltration, interleukin 6, tumor necrosis factor α, and chemokine C-X-C motif ligand 1 levels without altering repetitive DE-induced bronchioalveolar inflammation or lymphoid aggregate formation. Lung tissue ICAM-1 expression was also reduced in both single and repetitive exposure studies. These data suggest that MaR1 might contribute to an effective strategy to reduce airway inflammatory diseases induced by agricultural-related organic dust environmental exposures.

Effect of elevated carbon dioxide on bronchial epithelial innate immune receptor response to organic dust from swine confinement barns

Hypercapnia is known to have immunoregulatory effects within the lung. Cell culture systems demonstrate this in both macrophages and alveolar cell lines, suggesting that the alveoli are affected by changes in CO2 levels. We hypothesized that hypercapnia would also modulate human bronchial epithelial cell immune responses. Innate immune responses to Pam3CSK4 (TLR2 ligand), LPS (TLR4 ligand) and a complex innate immune stimulus, an extract from the organic dust of swine confinement barns (barn dust extract or BDE), were tested in a human bronchial epithelial cell line, BEAS-2B. Both TLR ligands showed a decrease in IL-6 and IL-8 production, and an increase in MCP-1 in response to elevated CO2 indicating an enhancement in cytokine production to hypercapnia. This change was not reflected in expression levels of TLR receptor RNA which remained unchanged in response to elevated CO2. Interestingly, barn dust showed an increase in IL-6, IL-8 and MCP-1 response at 9% CO2, suggesting that elevated CO2 exerts different effects on different stimuli. Our results show that airway epithelial cell immune responses to barn dust respond differently to hypercapnic conditions than individual TLR ligands.

Proteases in agricultural dust induce lung inflammation through PAR-1 and PAR-2 activation

Workers exposed to aerosolized dust present in concentrated animal feeding operations (CAFOs) are susceptible to inflammatory lung diseases, such as chronic obstructive pulmonary disease. Extracts of dust collected from hog CAFOs [hog dust extract (HDE)] are potent stimulators of lung inflammatory responses in several model systems. The observation that HDE contains active proteases prompted the present study, which evaluated the role of CAFO dust proteases in lung inflammatory processes and tested whether protease-activated receptors (PARs) are involved in the signaling pathway for these events. We hypothesized that the damaging proinflammatory effect of HDE is due, in part, to the proteolytic activation of PARs, and inhibiting the proteases in HDE or disrupting PAR activation would attenuate HDE-mediated inflammatory indexes in bronchial epithelial cells (BECs), in mouse lung slices in vitro, and in a murine in vivo exposure model. Human BECs and mouse lung slice cultures stimulated with 5% HDE released significantly more of each of the cytokines measured (IL-6, IL-8, TNF-α, keratinocyte-derived chemokine/CXC chemokine ligand 1, and macrophage inflammatory protein-2/CXC chemokine ligand 2) than controls, and these effects were markedly diminished by protease inhibition. Inhibition of PARs also blunted the HDE-induced cytokine release from BECs. In addition, protease depletion inhibited HDE-induced BEC intracellular PKCα and PKCε activation. C57BL/6J mice administered 12.5% HDE intranasally, either once or daily for 3 wk, exhibited increased total cellular and neutrophil influx, bronchial alveolar fluid inflammatory cytokines, lung histopathology, and inflammatory scores compared with mice receiving protease-depleted HDE. These data suggest that proteases in dust from CAFOs are important mediators of lung inflammation, and these proteases and their receptors may provide novel targets for therapeutic intervention in CAFO dust-induced airways disease.

CXCR1/CXCR2 antagonist CXCL8(3-74)K11R/G31P blocks lung inflammation in swine barn dust-instilled mice

Inhalation of agricultural occupational dusts from swine confinement facilities can result in lung inflammation. The innate immune response to organic barn dusts results in production of a number of pro-inflammatory factors in the lungs of barn workers such as cytokines, chemokines, and an influx of neutrophils. Many of these inflammatory factors are influenced by the chemokine CXCL8/IL-8 (KC or MIP-2 in mice). Previously, we have demonstrated that an endotoxin-independent component of swine barn dust extract (SBE) elevates lung chemokines in a protein kinase C (PKC)-dependent manner resulting in the significant formation of lung inflammatory cell infiltrates in a mouse model of SBE injury. In this study we test the ability of a CXCR1/CXCR2 antagonist, CXCL8(3-74)K11R/G31P (G31P) to block many of the features of lung-inflammation in response to challenge with SBE in an established mouse exposure system. Injection of G31P concurrent with SBE nasal instillation over a course of 3 weeks significantly reduced neutrophil accumulation in the lungs of barn dust exposed animals compared to those given SBE alone. There was a similar reduction in pro-inflammatory cytokines and chemokines IL-6, KC, and MIP-2 in SBE plus G31P-treated mice. In addition to excreted products, the receptors ICAM-1, CXCR1, and CXCR2, which all were elevated with SBE exposure, were also decreased with G31P treatment. SBE activation of PKCα and PKCε was reduced as well with G31P treatment. Thus, G31P was found to be highly effective at reducing several features of lung inflammation in mice exposed to barn dust extracts.

Transcriptional mechanisms and protein kinase signaling mediate organic dust induction of IL-8 expression in lung epithelial and THP-1 cells

Exposure to the agricultural work environment is a risk factor for the development of respiratory symptoms and chronic lung diseases. Inflammation is an important contributor to the pathogenesis of tissue injury and disease. Cellular and molecular mechanisms mediating lung inflammatory responses to agricultural dust are not yet fully understood. We studied the effects of poultry dust extract on molecular regulation of interleukin-8 (IL-8), a proinflammatory cytokine, in A549 and Beas2B lung epithelial and THP-1 monocytic cells. Our findings indicate that poultry dust extract potently induces IL-8 levels by increasing IL-8 gene transcription without altering IL-8 mRNA stability. Increase in IL-8 promoter activity was due to enhanced binding of activator protein 1 and NF-κB. IL-8 induction was associated with protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) activation and inhibited by PKC and MAPK inhibitors. IL-8 increase was not inhibited by polymyxin B or l-nitroarginine methyl ester, indicating lack of involvement of lipopolysaccharide and nitric oxide in the induction. Lung epithelial and THP-1 cells share common mechanisms for induction of IL-8 levels. Our findings identify key roles for transcriptional mechanisms and protein kinase signaling pathways for IL-8 induction and provide insights into the mechanisms regulating lung inflammatory responses to organic dust exposure.

Differential response of human nasal and bronchial epithelial cells upon exposure to size-fractionated dairy dust

Exposure to organic dusts is associated with increased respiratory morbidity and mortality in agricultural workers. Organic dusts in dairy farm environments are complex, polydisperse mixtures of toxic and immunogenic compounds. Previous toxicological studies focused primarily on exposures to the respirable size fraction; however, organic dusts in dairy farm environments are known to contain larger particles. Given the size distribution of dusts from dairy farm environments, the nasal and bronchial epithelia represent targets of agricultural dust exposures. In this study, well-differentiated normal human bronchial epithelial cells and human nasal epithelial cells were exposed to two different size fractions (PM10 and PM>10) of dairy parlor dust using a novel aerosol-to-cell exposure system. Levels of proinflammatory transcripts (interleukin [IL]-8, IL-6, and tumor necrosis factor [TNF]-α) were measured 2 h after exposure. Lactate dehydrogenase (LDH) release was also measured as an indicator of cytotoxicity. Cell exposure to dust was measured in each size fraction as a function of mass, endotoxin, and muramic acid levels. To our knowledge, this is the first study to evaluate the effects of distinct size fractions of agricultural dust on human airway epithelial cells. Our results suggest that both PM10 and PM>10 size fractions elicit a proinflammatory response in airway epithelial cells and that the entire inhalable size fraction needs to be considered when assessing potential risks from exposure to agricultural dusts. Further, data suggest that human bronchial cells respond differently to these dusts than human nasal cells, and therefore that the two cell types need to be considered separately in airway cell models of agricultural dust toxicity.