Chronic endotoxin exposure produces airflow obstruction and lung dendritic cell expansion

The risk factors and threshold level of subchronic inhalation exposure of reclaimed water

Inhalation of reclaimed water is known to cause lung inflammation, and free endotoxins have been shown to be a major risk factor for acute exposure. Subchronic exposure has also been shown to induce inflammatory responses with visible tissue damage. However, subchronic risk factors have yet to be identified, and a threshold for the protection of occupational populations during urban reuse is necessary. In this study, potential risk factors in reclaimed water were examined by subchronic exposure with fractionated reclaimed water, and the health risk threshold was tested with a series of diluted reclaimed water. Accordingly, following a 12-week exposure, macromolecules and microorganisms were found to be two major risk factors in reclaimed water that could cause pulmonary inflammation, including increased proportion of polymorphonuclear leukocytes in bronchoalveolar fluid, formation of inducible bronchus-associated lymphoid tissue, and elevation of Immunoglobulin A levels. Moreover, inflammation persisted after a 4-week recovery period. The calculated threshold of reclaimed water exposure for mice was 31.8 Endotoxin Unit (EU)/(kg·day) under when exposed to 50% additional relative humidity from reclaimed water at 25°C for 2 hr/day. Meanwhile, the subchronic threshold estimate for humans under the same exposure conditions was found to be 12.2 EU/(kg·day), corresponding to endotoxin levels of 61.7 EU/mL in reclaimed water. The threshold level of endotoxin was lower than that in most non-potable reclaimed water. The findings of this study suggest that occupational exposure of reclaimed water can serve as a potential risk to workers.

Assessment of airborne endotoxin in sandstorm dust and indoor environments using a novel passive sampling device in Al Zulfi city, Saudi Arabia - Establishing threshold exposure levels

The impact of sandstorm dust events affects local air quality and public health. These issues are becoming of greater concern in Saudi Arabia. There is a significant lack of research on airborne endotoxin exposure and analysis in the Middle East countries and no coherent body of research exists focusing on sandstorm dust in worldwide. In this study, we used a novel design of an aluminum foil plate (AFP) electrostatic dust cloth (EDC) for the passive air sampling of sandstorm dust. A total of 38 sandstorm dust samples were collected during sandstorm episodes occurring between January and April 2020 in both indoor (7 days, n = 20) and outdoor environments (24 h, n = 18). After exposure, and following an extraction procedure, bacterial endotoxin levels were measured using the Limulus Amoebocyte Lysate (LAL) gel clot method. The study highlights that the airborne endotoxin level observed was between 10 and 200 EU/m² in both indoor and outdoor environments, during a sandstorm event. Agricultural activities and farmhouses observed higher airborne endotoxin levels. In general, increased endotoxin levels were related to the severity of the sandstorms. Given that the observed values were high as per existing guidelines for respiratory health, we recommend the setting an occupational airborne exposure limit for bacterial endotoxin. This is the first report and further studies across various sandstorm-hit regions will need to be undertaken, together with various sampling methods, in order to assess for seasonal and geographic trends.

CFTR regulates B cell activation and lymphoid follicle development

Background

Cystic fibrosis (CF) is an inherited disorder caused by mutations in the CF transmembrane conductance regulator (CFTR) gene that promotes persistent lung infection and inflammation and progressive loss of lung function. Patients with CF have increased lung lymphoid follicles (LFs) and B cell-activating factor of tumor necrosis factor family (BAFF) that regulates B cell survival and maturation. A direct role for CFTR in B cell activation and disease pathogenesis in CF remains unclear.

Methods

The number of LFs, BAFF⁺, TLR4⁺ and proliferation marker Ki67⁺ B cells in lung explants or resections from subjects with CF and normal controls was quantified by immunostaining. The role of CFTR in B cell activation and LF development was then examined in two independent cohorts of uninfected CFTR-deficient mice (Cftr^−/−) and wild type controls. The number of lung LFs, B cells and BAFF⁺, CXCR4⁺, immunoglobulin G⁺ B cells was examined by immunostaining. Lung and splenocyte B cell activation marker and major histocompatibility complex class II (MHC class II) expression was quantified by flow cytometry. Inflammatory cytokine levels were measured in supernatants from isolated B cells from Cftr^−/− and wild type mice stimulated in vitro with Pseudomonas aeruginosa lipopolysaccharide (LPS).

Results

There was a significant increase in well-formed LFs in subjects with CF compared to normal controls. Increased B cell activation and proliferation was observed in lung LFs from CF subjects as was quantified by a significant increase in B cell BAFF, TLR4 and Ki67 expression. Uninfected Cftr^−/− mice had increased lung LFs and BAFF⁺ and CXCR4⁺ B cells compared to wild type controls. Lung B cells isolated from uninfected Cftr^−/− mice demonstrated increased MHC class II expression. In vitro, isolated B cells from Cftr^−/− mice produced increased IL-6 when stimulated with LPS compared to wild type controls.

Conclusions

These data support a direct role for CFTR in B cell activation, proliferation and inflammatory cytokine production that promotes lung LF follicle development in cystic fibrosis.

Effects of ozonation on the activity of endotoxin and its inhalation toxicity in reclaimed water

Aerosolized reclaimed water can cause inflammatory responses in lung after inhalation, and endotoxin has been identified as the main inducer. Since the effects of disinfection treatments on endotoxins had conflicting results, this study explored the changes of endotoxin activity and inflammation inducing ability of reference endotoxin, gram-negative bacteria solutions and reclaimed water after ozonation respectively, and found that LAL assay based endotoxin activity and mouse inhalation exposure based inflammation examination had inconsistent results. The excessive ozone could not remove the endotoxin activity, but was able to reduce the inflammation inducing ability of free endotoxin. When treating on gram-negative strains, ozone first released the cell-bound endotoxin and caused the dramatic increase of endotoxin activity. But for the inflammatory response, despite the rapid increase at the very beginning, it immediately dropped back with further ozonation. The endotoxin aggregate size was proposed as a key regulator of the toxicity of endotoxin, which was modified by ozone oxidation. In real reclaimed water, insufficient ozone significantly enhanced the inflammatory response, but when the ozone dosages were large enough, the inflammation could be drawn back to the original level, which was consistent with the observations from pure endotoxin and bacteria. This work demonstrates that the endotoxin activity cannot predict the endotoxin-induced toxicity of ozone treated water, and low dosage of ozone treatment may even increase the health risk of reclaimed water.

Endotoxin and [Formula: see text] Contamination in Electronic Cigarette Products Sold in the United States

BACKGROUND

Cigarette smoke contains microbes and microbial toxins, such as endotoxin and [Formula: see text], that may have adverse respiratory effects. To our knowledge, the potential for contamination of electronic cigarette (EC) products sold in the United States has not been investigated.

OBJECTIVES

We aimed to determine whether popular cartridge and e-liquid EC products were contaminated with endotoxin or glucan and to examine differences according to the type and flavor of products.

METHODS

We selected 37 cartridges and 38 e-liquid products with the highest nicotine content from the ten top-selling U.S. brands. Flavors were classified into four groups: tobacco, menthol, fruit, and other. Endotoxin and glucan were measured using an endotoxin-specific kinetic turbidimetric assay and a Glucatell® Kinetic Assay (Associates of Cape Cod, Inc.), respectively.

RESULTS

Endotoxin concentrations were over the limit of detection (LOD) in 17 of 75 products tested (23%), and glucan concentrations were greater than LOD in 61 of 75 products (81%). After adjusting for brand and flavor, the mean glucan concentration was 3.2 times higher [95% confidence interval (CI): [Formula: see text], 18.4] in cartridge vs. e-liquid samples. After adjusting for brand and type of product, glucan concentrations in tobacco- and menthol-flavored ECs were 10.4 (95% CI: 1.8, 44.9) and 3.5 (95% CI: 0.1, 17.3) times higher than concentrations found in fruit-flavored products.

CONCLUSIONS

EC products may be contaminated with microbial toxins. Further studies with large representative samples of products are needed to confirm our findings, identify sources and routes of contamination, and evaluate health effects associated with the use of contaminated products. https://doi.org/10.1289/EHP3469.

Sputum from chronic obstructive pulmonary disease patients inhibits T cell migration in a microfluidic device

Chronic obstructive pulmonary disease (COPD) is a common lung disease characterized by narrowed airways, resulting in serious breathing difficulty. Previous studies have demonstrated that inflammatory infiltration of leukocytes in the airway is associated with the pathogenesis of COPD. In the present study, we employed a microfluidic approach to assess the effect of COPD sputum on activated human peripheral blood T cell migration and chemotaxis under well-controlled gradient conditions. Our results showed considerable basal migration of T cells derived from peripheral blood of COPD patients and healthy controls in the medium control groups. By contrast, the migration of T cells from COPD patients and healthy controls was significantly inhibited in the presence of a gradient of sputum supernatant from COPD patients. Furthermore, chemotaxis of T cells from COPD patients or healthy subjects toward an SDF-1α gradient was clearly inhibited by sputum samples from the COPD patients. The inhibition effect revealed by the microfluidic cell migration experiments provides new information about the complex involvement of T cell trafficking in COPD.

Sirtuin 2 enhances allergic asthmatic inflammation

Allergic eosinophilic asthma is a chronic condition causing airway remodeling resulting in lung dysfunction. We observed that expression of sirtuin 2 (Sirt2), a histone deacetylase, regulates the recruitment of eosinophils after sensitization and challenge with a triple antigen: dust mite, ragweed, and Aspergillus fumigatus (DRA). Our data demonstrate that IL-4 regulates the expression of Sirt2 isoform 3/5. Pharmacological inhibition of Sirt2 by AGK2 resulted in diminished cellular recruitment, decreased CCL17/TARC, and reduced goblet cell hyperplasia. YM1 and Fizz1 expression was reduced in AGK2-treated, IL-4-stimulated lung macrophages in vitro as well as in lung macrophages from AGK2-DRA-challenged mice. Conversely, overexpression of Sirt2 resulted in increased cellular recruitment, CCL17 production, and goblet cell hyperplasia following DRA challenge. Sirt2 isoform 3/5 was upregulated in primary human alveolar macrophages following IL-4 and AGK2 treatment, which resulted in reduced CCL17 and markers of alternative activation. These gain-of-function and loss-of-function studies indicate that Sirt2 could be developed as a treatment for eosinophilic asthma.

Sub-chronic inhalation of reclaimed water-induced fibrotic lesion in a mouse model

When reclaimed water is used as municipal miscellaneous water, acute exposure of the generated aerosol with high levels of endotoxins can cause severe inflammation in the lungs. However, the potential risks of long-term inhalation of reclaimed water remains unclear. To identify the adverse effects of sub-chronic reclaimed water inhalation and explain the underlying mechanisms, a mouse model of 12-week sub-chronic exposure was established, and wastewater before a membrane bioreactor (MBR, positive control) and the MBR effluent (reclaimed water, which met the quality standard of urban use and was currently used for landscape irrigation) were tested in this study. The exposure dose was set to approach the real working scenarios. Lung lavage and histology were analyzed. Obvious epithelial cell apoptosis in the bronchi was observed, along with the accumulation of myofibroblasts and the collagen deposition both in main bronchi and terminal bronchioles. All these symptoms were persistent after 4 weeks of recovery. Inflammation and induced bronchus-associated lymphoid tissues (iBALT) were also observed but diminished after recovery indicating inflammation may not be the direct cause of the symptom. Furthermore, two fibrogenic cytokines (TNF-α and TGF-β) were constantly high in the lung during the study. They might be the biomarkers of lung damage after the inhalation of reclaimed water. Adaptive immune responses were also detected as elevated levels of IgG and IgA, but not for IgE. Inhalation of reclaimed water causes sustained fibrotic lesions in the lungs, which suggests potential health risks during urban application where aerosols generated.

Imaging Phenotype of Occupational Endotoxin-Related Lung Function Decline

BACKGROUND

Although occupational exposures contribute to a significant proportion of obstructive lung disease, the phenotype of obstructive lung disease associated with work-related organic dust exposure independent of smoking remains poorly defined.

OBJECTIVE

We identified the relative contributions of smoking and occupational endotoxin exposure to parenchymal and airway remodeling as defined by quantitative computed tomography (CT).

METHODS

The Shanghai Textile Worker Study is a longitudinal study of endotoxin-exposed cotton workers and endotoxin-unexposed silk workers that was initiated in 1981. Spirometry, occupational endotoxin exposure, and smoking habits were assessed at 5-year intervals. High-resolution computed tomography (CT) was performed in 464 retired workers in 2011, along with quantitative lung densitometric and airway analysis.

RESULTS

Significant differences in all CT measures were noted across exposure groups. Occupational endotoxin exposure was associated with a decrease (-1.3%) in percent emphysema (LAAI-950), a 3.3-Hounsfield unit increase in 15th percentile density, an 18.1-g increase in lung mass, and a 2.3% increase in wall area percent. Current but not former smoking was associated with a similar CT phenotype. Changes in LAAI-950 were highly correlated with 15th percentile density (correlation -1.0). Lung mass was the only measure associated with forced expiratory volume in 1 sec (FEV1) decline, with each 10-g increase in lung mass associated with an additional loss (-6.1 mL) of FEV1 (p = 0.001) between 1981 and 2011.

CONCLUSIONS

There are many similarities between the effects of occupational endotoxin exposure and those of tobacco smoke exposure on lung parenchyma and airway remodeling. The effects of occupational endotoxin exposure appear to persist even after the cessation of exposure. LAAI-950 may not be a reliable indicator of emphysema in subjects without spirometric impairment. Lung mass is a CT-based biomarker of accelerated lung function decline.

CITATION

Lai PS, Hang J, Zhang F, Sun J, Zheng BY, Su L, Washko GR, Christiani DC. 2016. Imaging phenotype of occupational endotoxin-related lung function decline. Environ Health Perspect 124:1436-1442; http://dx.doi.org/10.1289/EHP195.

Respiratory problems among cotton textile workers

Background:

Long term occupational exposure to cotton dust is associated with respiratory symptoms and loss of pulmonary function.

Aim:

This study was conducted to explore respiratory symptoms, pulmonary function tests and chest radiography of workers, and to evaluate the findings of high resolution computed tomographyand its correlation with pulmonary function tests (PFT).

Material and Methods:

The study was conducted on 100 cotton workers as exposed group and 100 unexposed subjects. Smokers were excluded from the study. All workers were interviewed and examined by the pulmonologist. PFT and chest radiography were conducted for all subjects. HRCT was performed for those with abnormal PFT or chest radiography.

Results:

A total of 51% and 31% of the cotton textile workers had one or more respiratory symptoms and respiratory signs respectively. 28% of subjects in the exposed group and 5% of subjects in unexposed group had obstructive pattern. Bronchia wall thickening and air trapping were the most frequent chest radiography and HRCT abnormalities respectively. There was a significant correlation between HRCT and the results of PFT.

Conclusion:

We conclude that long term exposure to cotton dust is associated with obstructive disease that increase with duration of exposure (history of working years), also use of HRCT as a sensitive tool in the assessment of pathologic changes and it's correlation with PFT, confirms the expected pathophysiology of airway obstruction in cotton workers.

Murine models of cardiovascular comorbidity in chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) have an increased risk for cardiovascular disease (CVD). Currently, COPD patients with atherosclerosis (i.e., the most important underlying cause of CVD) receive COPD therapy complemented with standard CVD therapy. This may, however, not be the most optimal treatment. To investigate the link between COPD and atherosclerosis and to develop specific therapeutic strategies for COPD patients with atherosclerosis, a substantial number of preclinical studies using murine models have been performed. In this review, we summarize the currently used murine models of COPD and atherosclerosis, both individually and combined, and discuss the relevance of these models for studying the pathogenesis and development of new treatments for COPD patients with atherosclerosis. Murine and clinical studies have provided complementary information showing a prominent role for systemic inflammation and oxidative stress in the link between COPD and atherosclerosis. These and other studies showed that murine models for COPD and atherosclerosis are useful tools and can provide important insights relevant to understanding the link between COPD and CVD. More importantly, murine studies provide good platforms for studying the potential of promising (new) therapeutic strategies for COPD patients with CVD.

Risks associated with endotoxins in feed additives produced by fermentation

Increasingly, feed additives for livestock, such as amino acids and vitamins, are being produced by Gram-negative bacteria, particularly Escherichia coli. The potential therefore exists for animals, consumers and workers to be exposed to possibly harmful amounts of endotoxin from these products. The aim of this review was to assess the extent of the risk from endotoxins in feed additives and to calculate how such risk can be assessed from the properties of the additive. Livestock are frequently exposed to a relatively high content of endotoxin in the diet: no additional hazard to livestock would be anticipated if the endotoxin concentration of the feed additive falls in the same range as feedstuffs. Consumer exposure will be unaffected by the consumption of food derived from animals receiving endotoxin-containing feed, because the small concentrations of endotoxin absorbed do not accumulate in edible tissues. In contrast, workers processing a dusty additive may be exposed to hazardous amounts of endotoxin even if the endotoxin concentration of the product is low. A calculation method is proposed to compare the potential risk to the worker, based on the dusting potential, the endotoxin concentration and technical guidance of the European Food Safety Authority, with national exposure limits.

Isoflurane Ameliorates Acute Lung Injury by Preserving Epithelial Tight Junction Integrity

BACKGROUND

Isoflurane may be protective in preclinical models of lung injury, but its use in patients with lung injury remains controversial and the mechanism of its protective effects remains unclear. The authors hypothesized that this protection is mediated at the level of alveolar tight junctions and investigated the possibility in a two-hit model of lung injury that mirrors human acute respiratory distress syndrome.

METHODS

Wild-type mice were treated with isoflurane 1 h after exposure to nebulized endotoxin (n = 8) or saline control (n = 9) and then allowed to recover for 24 h before mechanical ventilation (MV; tidal volume, 15 ml/kg, 2 h) producing ventilator-induced lung injury. Mouse lung epithelial cells were similarly treated with isoflurane 1 h after exposure to lipopolysaccharide. Cells were cyclically stretched the following day to mirror the MV protocol used in vivo.

RESULTS

Mice treated with isoflurane following exposure to inhaled endotoxin and before MV exhibited significantly less physiologic lung dysfunction. These effects appeared to be mediated by decreased vascular leak, but not altered inflammatory indices. Mouse lung epithelial cells treated with lipopolysaccharide and cyclic stretch and lungs harvested from mice after treatment with lipopolysaccharide and MV had decreased levels of a key tight junction protein (i.e., zona occludens 1) that was rescued by isoflurane treatment.

CONCLUSIONS

Isoflurane rescued lung injury induced by a two-hit model of endotoxin exposure followed by MV by maintaining the integrity of the alveolar-capillary barrier possibly by modulating the expression of a key tight junction protein.

Dendritic cell-bound IgE functions to restrain allergic inflammation at mucosal sites

Antigen-mediated cross-linking of Immunoglobulin E (IgE) bound to mast cells/basophils via FcɛRI, the high affinity IgE Fc-receptor, is a well-known trigger of allergy. In humans, but not mice, dendritic cells (DCs) also express FcɛRI that is constitutively occupied with IgE. In contrast to mast cells/basophils, the consequences of IgE/FcɛRI signals for DC function remain poorly understood. We show that humanized mice that express FcɛRI on DCs carry IgE like non-allergic humans and do not develop spontaneous allergies. Antigen-specific IgE/FcɛRI cross-linking fails to induce maturation or production of inflammatory mediators in human DCs and FcɛRI-humanized DCs. Furthermore, conferring expression of FcɛRI to DCs decreases the severity of food allergy and asthma in disease-relevant models suggesting anti-inflammatory IgE/FcɛRI signals. Consistent with the improved clinical parameters in vivo, antigen-specific IgE/FcɛRI cross-linking on papain or lipopolysaccharide-stimulated DCs inhibits the production of pro-inflammatory cytokines and chemokines. Migration assays confirm that the IgE-dependent decrease in cytokine production results in diminished recruitment of mast cell progenitors; providing a mechanistic explanation for the reduced mast cell-dependent allergic phenotype observed in FcɛRI-humanized mice. Our study demonstrates a novel immune regulatory function of IgE and proposes that DC-intrinsic IgE signals serve as a feedback mechanism to restrain allergic tissue inflammation.

Endotoxin and gender modify lung function recovery after occupational organic dust exposure: a 30-year study

OBJECTIVES

The purpose of this study is to determine the trajectory of lung function change after exposure cessation to occupational organic dust exposure, and to identify factors that modify improvement.

METHODS

The Shanghai Textile Worker Study is a longitudinal study of 447 cotton workers exposed to endotoxin-containing dust and 472 silk workers exposed to non-endotoxin-containing dust. Spirometry was performed at 5-year intervals. Air sampling was performed to estimate individual cumulative exposures. The effect of work cessation on forced expiratory volume in 1 s (FEV1) was modelled using generalised additive mixed effects models to identify the trajectory of FEV1 recovery. Linear mixed effects models incorporating interaction terms were used to identify modifiers of FEV1 recovery. Loss to follow-up was accounted for with inverse probability of censoring weights.

RESULTS

74.2% of the original cohort still alive participated in 2011. Generalised additive mixed models identified a non-linear improvement in FEV1 for all workers after exposure cessation, with no plateau noted 25 years after retirement. Linear mixed effects models incorporating interaction terms identified prior endotoxin exposure (p=0.01) and male gender (p=0.002) as risk factors for impaired FEV1 improvement after exposure cessation. After adjusting for gender, smoking delayed the onset of FEV1 gain but did not affect the overall magnitude of change.

CONCLUSIONS

Lung function improvement after cessation of exposure to organic dust is sustained. Endotoxin exposure and male gender are risk factors for less FEV1 improvement.

Long-term respiratory health effects in textile workers

PURPOSE OF REVIEW

Over 60 million people worldwide work in the textile or clothing industry. Recent studies have recognized the contribution of workplace exposures to chronic lung diseases, in particular chronic obstructive pulmonary disease (COPD). Early studies in textile workers have focused on the relationship between hemp or cotton dust exposure and the development of a syndrome termed byssinosis. The purpose of this review is to evaluate the effect of long-term exposure to organic dust in textile workers on chronic respiratory disease in the broader context of disease classifications, such as reversible or irreversible obstructive lung disease (i.e. asthma or COPD), and restrictive lung disease.

RECENT FINDINGS

Cessation of exposure to cotton dust leads to improvement in lung function. Recent animal models have suggested a shift in the lung macrophage:dendritic cell population ratio as a potential mechanistic explanation for persistent inflammation in the lung due to repeated cotton dust-related endotoxin exposure. Other types of textile dust, such as silk, may contribute to COPD in textile workers.

SUMMARY

Textile dust-related obstructive lung disease has characteristics of both asthma and COPD. Significant progress has been made in the understanding of chronic lung disease due to organic dust exposure in textile workers.

Redox markers and inflammation are differentially affected by atorvastatin, pravastatin or simvastatin administered before endotoxin-induced acute lung injury

Statins are standard therapy for the treatment of lipid disorders, and the field of redox biology accepts that statins have antioxidant properties. Our aim in this report was to consider the pleiotropic effects of atorvastatin, pravastatin and simvastatin administered prior to endotoxin-induced acute lung injury. Male mice were divided into 5 groups and intraperitoneally injected with LPS (10 mg/kg), LPS plus atorvastatin (10 mg/kg/day; A + LPS group), LPS plus pravastatin (5 mg/kg/day; P + LPS group) or LPS plus simvastatin (20 mg/kg/day; S + LPS group). The control group received saline. All mice were sacrificed one day later. There were fewer leukocytes in the P + LPS and S + LPS groups than in the LPS group. MCP-1 cytokine levels were lower in the P + LPS group, while IL-6 levels were lower in the P + LPS and S + LPS groups. TNF-α was lower in all statin-treated groups. Levels of redox markers (superoxide dismutase and catalase) were lower in the A + LPS group (p < 0.01). The extent of lipid peroxidation (malondialdehyde and hydroperoxides) was reduced in all statin-treated groups (p < 0.05). Myeloperoxidase was lower in the P + LPS group (p < 0.01). Elastance levels were significantly greater in the LPS group compared to the statin groups. Our results suggest that atorvastatin and pravastatin but not simvastatin exhibit anti-inflammatory and antioxidant activity in endotoxin-induced acute lung injury.

Integrating murine gene expression studies to understand obstructive lung disease due to chronic inhaled endotoxin

RATIONALE

Endotoxin is a near ubiquitous environmental exposure that that has been associated with both asthma and chronic obstructive pulmonary disease (COPD). These obstructive lung diseases have a complex pathophysiology, making them difficult to study comprehensively in the context of endotoxin. Genome-wide gene expression studies have been used to identify a molecular snapshot of the response to environmental exposures. Identification of differentially expressed genes shared across all published murine models of chronic inhaled endotoxin will provide insight into the biology underlying endotoxin-associated lung disease.

METHODS

We identified three published murine models with gene expression profiling after repeated low-dose inhaled endotoxin. All array data from these experiments were re-analyzed, annotated consistently, and tested for shared genes found to be differentially expressed. Additional functional comparison was conducted by testing for significant enrichment of differentially expressed genes in known pathways. The importance of this gene signature in smoking-related lung disease was assessed using hierarchical clustering in an independent experiment where mice were exposed to endotoxin, smoke, and endotoxin plus smoke.

RESULTS

A 101-gene signature was detected in three murine models, more than expected by chance. The three model systems exhibit additional similarity beyond shared genes when compared at the pathway level, with increasing enrichment of inflammatory pathways associated with longer duration of endotoxin exposure. Genes and pathways important in both asthma and COPD were shared across all endotoxin models. Mice exposed to endotoxin, smoke, and smoke plus endotoxin were accurately classified with the endotoxin gene signature.

CONCLUSIONS

Despite the differences in laboratory, duration of exposure, and strain of mouse used in three experimental models of chronic inhaled endotoxin, surprising similarities in gene expression were observed. The endotoxin component of tobacco smoke may play an important role in disease development.