Irritant-induced asthma to hypochlorite in mice due to impairment of the airway barrier

Allergic Airway Inflammation Emerges from Gut Inflammation and Leakage in Mouse Model of Asthma

Asthma is an allergic airway inflammatory disease characterized by type 2 immune responses. Growing evidence suggests an association between allergic airways and intestinal diseases. However, the primary site of disease origin and initial mechanisms involved in the development of allergic airway inflammation (AAI) is not yet understood. Therefore, the initial contributing organs and mechanisms involved in the development of AAI are investigated using a mouse model of asthma. This study, without a local allergen challenge into the lungs, demonstrates a significant increase in intestinal inflammation with signature type-2 mediators including IL-4, IL-13, STAT6, eosinophils, and Th2 cells. In addition, gut leakage and mRNA expressions of gut leakage markers significantly increase in the intestine. Moreover, reduced mRNA expressions of tight junction proteins are observed in gut and interestingly, in lung tissues. Furthermore, in lung tissues, an increased pulmonary barrier permeability and IL-4 and IL-13 levels associated with significant increase of lipopolysaccharide-binding protein (LBP-gut leakage marker) and eosinophils are observed. However, with local allergen challenges into the lungs, these mechanisms are further enhanced in both gut and lungs. In conclusion, the primary gut originated inflammatory responses translocates into the lungs to orchestrate AAI in a mouse model of asthma.

Update on irritant-induced occupational asthma

PURPOSE OF REVIEW

In this narrative review, we aim to highlight novel research findings on both acute/subacute irritant-induced asthma (IIA) and chronic exposure IIA (also called 'low dose' IIA).

RECENT FINDINGS

Novel case series showed that acute and subacute IIA cases had similar causal agents (e.g., acid or base aerosols/fumes, dusts, mixtures) but had occurred in different circumstances (accidents vs. regular work). Acute and subacute IIA cases had similar clinical characteristics but poorer short-term outcomes than sensitizer-induced occupational asthma patients. Novel large epidemiological studies reported associations between chronic occupational exposure to irritants and current adult-onset asthma and poor asthma control, and with a specific asthma endotype characterized by neutrophilic inflammation and oxidative stress. Recent studies reconfirmed the association of the use of disinfectants and cleaning products (especially sprays) with IIA. A role for genetic susceptibility has been suggested.

SUMMARY

Recent literature provided further understanding of both acute/subacute and chronic exposure IIA, in terms of causes, possible mechanisms, and consequences such as poor asthma control. Research is needed to clarify several aspects of IIA, including its frequency (still likely underestimated), modulating factors, and mechanisms. Research aiming at improving irritant exposure assessment, including intensity/duration, and determining relevant exposure windows would be welcome.

Microcomputed Tomography to Visualize and Quantify Fungal Infection Burden and Inflammation in the Mouse Lung Over Time

Pulmonary mycoses are an important threat for immunocompromised patients, and although current treatments are effective, they suffer from multiple limitations and fail to further reduce mortality. With the increasing immunocompromised population and increased antifungal resistance, fungal infection research is more relevant than ever. In preclinical respiratory fungal infection research, animal models are indispensable. However, too often researchers still rely on endpoint measurements to assess fungal burden while the dynamics of disease progression are left undiscovered. To open up this "black box", microcomputed tomography (μCT) can be implemented to longitudinally visualize lung pathology in a noninvasive way and to quantify μCT-image derived biomarkers. That way, disease onset, progression, and responsiveness to treatment can be followed up with high resolution spatially and temporally in individual mice, increasing statistical power. Here, we describe a general method for the use of low-dose high-resolution μCT to longitudinally visualize and quantify lung pathology in mouse models of respiratory fungal infections, applied to mouse models of aspergillosis and cryptococcosis.

Irritant-Induced Asthma

Irritant-induced asthma (IIA) is a phenotype of asthma caused by the inhalation of irritant agents. Definite, probable, or possible IIA have been described, depending on the concentration of the inhaled irritants and the onset of respiratory symptoms respective to the time of exposure. Definite IIA represents approximately 4% to 14% of all cases of new-onset work-related asthma. Agents responsible for IIA can be encountered as fumes, gases, aerosols, or dusts. The most frequent are chlorine, nitrogen oxides, sulfur dioxide, ammonia, acetic acid, solvents, and cleaning materials. Although the diagnosis of definite IIA is based on a suggestive clinical history along with evidence of reversible airflow limitation and/or nonspecific bronchial hyperresponsiveness, possible IIA cannot be diagnosed with certainty because the relationship between exposure and the onset of symptoms is difficult to establish. This article reviews the epidemiology, pathophysiology, diagnostic approach, and management of IIA.

Chlorine exposure and intensive exercise induces airway hyperreactivity in a 3-week murine exercise model

RATIONALE

Exercise-induced bronchoconstriction (EIB) is defined as acute narrowing of the airways during or immediately after exercise. EIB has a high prevalence in elite swimmers probably due to the high ventilation rate and exposure to the chlorine by-products. It is still puzzling which pathophysiological mechanisms drive EIB.

OBJECTIVE

In this study, we evaluated airway hyperreactivity, permeability, integrity and inflammation in a murine swimmers EIB model with and without chlorine exposure.

METHODS

Mice performed a 3-week swimming protocol in a swimming pool with counter current. Three hours after the last swimming session, airway hyperreactivity to methacholine was assessed. Cytokine levels and cellular differential analysis was performed in BAL fluid. Airway permeability and tight junction expression was measured in serum and lung tissue. T-, B-, dendritic and innate lymphoid cells were determined in lung tissue via flow cytometry.

RESULTS

A significant higher airway resistance (Rn; P < 0.0001) was observed in mice swimming in chlorinated water (mean Rn = 1.26 cmH₂O.s/ml) compared to mice swimming in tap water (mean Rn = 0.76 cmH₂O.s/ml) and both inhalation groups in the absence of cellular inflammation. No significant differences were found in lung immune cell populations or in lung tight junction mRNA expression. Experiments in SCID, Rag2^-/-γc^-/- or Cpa3^cre/+ mice showed a limited involvement of the innate, adaptive immune system or the mast cells.

CONCLUSION

Our 3-week swimming murine model mimics intensive swimming in chlorinated water with the presence of airway hyperreactivity in mice swimming in chlorinated water in the absence of airway inflammation and airway epithelial damage.

Epithelial barrier hypothesis: Effect of the external exposome on the microbiome and epithelial barriers in allergic disease

Environmental exposure plays a major role in the development of allergic diseases. The exposome can be classified into internal (e.g., aging, hormones, and metabolic processes), specific external (e.g., chemical pollutants or lifestyle factors), and general external (e.g., broader socioeconomic and psychological contexts) domains, all of which are interrelated. All the factors we are exposed to, from the moment of conception to death, are part of the external exposome. Several hundreds of thousands of new chemicals have been introduced in modern life without our having a full understanding of their toxic health effects and ways to mitigate these effects. Climate change, air pollution, microplastics, tobacco smoke, changes and loss of biodiversity, alterations in dietary habits, and the microbiome due to modernization, urbanization, and globalization constitute our surrounding environment and external exposome. Some of these factors disrupt the epithelial barriers of the skin and mucosal surfaces, and these disruptions have been linked in the last few decades to the increasing prevalence and severity of allergic and inflammatory diseases such as atopic dermatitis, food allergy, allergic rhinitis, chronic rhinosinusitis, eosinophilic esophagitis, and asthma. The epithelial barrier hypothesis provides a mechanistic explanation of how these factors can explain the rapid increase in allergic and autoimmune diseases. In this review, we discuss factors affecting the planet's health in the context of the 'epithelial barrier hypothesis,' including climate change, pollution, changes and loss of biodiversity, and emphasize the changes in the external exposome in the last few decades and their effects on allergic diseases. In addition, the roles of increased dietary fatty acid consumption and environmental substances (detergents, airborne pollen, ozone, microplastics, nanoparticles, and tobacco) affecting epithelial barriers are discussed. Considering the emerging data from recent studies, we suggest stringent governmental regulations, global policy adjustments, patient education, and the establishment of individualized control measures to mitigate environmental threats and decrease allergic disease.

Hypochlorous Acid: From Innate Immune Factor and Environmental Toxicant to Chemopreventive Agent Targeting Solar UV-Induced Skin Cancer

A multitude of extrinsic environmental factors (referred to in their entirety as the 'skin exposome') impact structure and function of skin and its corresponding cellular components. The complex (i.e. additive, antagonistic, or synergistic) interactions between multiple extrinsic (exposome) and intrinsic (biological) factors are important determinants of skin health outcomes. Here, we review the role of hypochlorous acid (HOCl) as an emerging component of the skin exposome serving molecular functions as an innate immune factor, environmental toxicant, and topical chemopreventive agent targeting solar UV-induced skin cancer. HOCl [and its corresponding anion (OCl-; hypochlorite)], a weak halogen-based acid and powerful oxidant, serves two seemingly unrelated molecular roles: (i) as an innate immune factor [acting as a myeloperoxidase (MPO)-derived microbicidal factor] and (ii) as a chemical disinfectant used in freshwater processing on a global scale, both in the context of drinking water safety and recreational freshwater use. Physicochemical properties (including redox potential and photon absorptivity) determine chemical reactivity of HOCl towards select biochemical targets [i.e. proteins (e.g. IKK, GRP78, HSA, Keap1/NRF2), lipids, and nucleic acids], essential to its role in innate immunity, antimicrobial disinfection, and therapeutic anti-inflammatory use. Recent studies have explored the interaction between solar UV and HOCl-related environmental co-exposures identifying a heretofore unrecognized photo-chemopreventive activity of topical HOCl and chlorination stress that blocks tumorigenic inflammatory progression in UV-induced high-risk SKH-1 mouse skin, a finding with potential implications for the prevention of human nonmelanoma skin photocarcinogenesis.

Asthma-inducing potential of 28 substances in spray cleaning products-Assessed by quantitative structure activity relationship (QSAR) testing and literature review

Exposure to spray cleaning products constitutes a potential risk for asthma induction. We set out to review whether substances in such products are potential inducers of asthma. We identified 101 spray cleaning products for professional use. Twenty‐eight of their chemical substances were selected. We based the selection on (a) positive prediction for respiratory sensitisation in humans based on quantitative structure activity relationship (QSAR) in the Danish (Q)SAR Database, (b) positive QSAR prediction for severe skin irritation in rabbits and (c) knowledge on the substances' physico‐chemical characteristics and toxicity. Combining the findings in the literature and QSAR predictions, we could group substances into four classes: (1) some indication in humans for asthma induction: chloramine, benzalkonium chloride; (2) some indication in animals for asthma induction: ethylenediaminetetraacetic acid (EDTA), citric acid; (3) equivocal data: hypochlorite; (4) few or lacking data: nitriloacetic acid, monoethanolamine, 2‐(2‐aminoethoxy)ethanol, 2‐diethylaminoethanol, alkyldimethylamin oxide, 1‐aminopropan‐2‐ol, methylisothiazolinone, benzisothiazolinone and chlormethylisothiazolinone; three specific sulphonates and sulfamic acid, salicylic acid and its analogue sodium benzoate, propane‐1,2‐diol, glycerol, propylidynetrimethanol, lactic acid, disodium malate, morpholine, bronopol and benzyl alcohol. In conclusion, we identified an asthma induction potential for some of the substances. In addition, we identified major knowledge gaps for most substances. Thus, more data are needed to feed into a strategy of safe‐by‐design, where substances with potential for induction of asthma are avoided in future (spray) cleaning products. Moreover, we suggest that QSAR predictions can serve to prioritise substances that need further testing in various areas of toxicology.

We reviewed whether substances in spray cleaning products constitute a potential risk for asthma induction. For this, we identified 101 spray cleaning products for professional use and prioritised their ingredient substances by use of quantitative structure activity relationship (QSAR). We provide a review of 28 selected substances: we give conclusions on their asthma induction potential, as well as a discussion on the use of QSAR for prioritisation of substances, and the major knowledge gaps we encountered.

Household Cleaning and Poor Asthma Control Among Elderly Women

BACKGROUND

Asthma control is suboptimal in nearly half of adults with asthma. Household exposure to disinfectants and cleaning products (DCP) has been associated with adverse respiratory effects, but data on their association with asthma control are scant.

OBJECTIVES

To investigate the association between household use of DCP and asthma control in a large cohort of French elderly women.

METHODS

We used data from a case-control study on asthma (2011-2013) nested in the E3N cohort. Among 3023 women with current asthma, asthma control was defined by the Asthma Control Test (ACT). We used a standardized questionnaire to assess the frequency of cleaning tasks and DCP use. We also identified household cleaning patterns using a clustering approach. Associations between DCP and ACT were adjusted for age, smoking status, body mass index, and education.

RESULTS

Data on ACT and DCP use were available for 2223 women (70 ± 6 years old). Asthma was controlled (ACT = 25), partly controlled (ACT = 20-24), and poorly controlled (ACT ≤ 19) in 29%, 46%, and 25% of the participants, respectively. Weekly use of sprays and chemicals was associated with poorly controlled asthma (odds ratio [95% confidence interval]: 1 spray: 1.31 [0.94-1.84], ≥2 sprays: 1.65 [1.07-2.53], P trend: .01; 1 chemical: 1.24 [0.94-1.64], ≥2 chemicals: 1.47 [1.03-2.09], P trend: .02). Risk for poor asthma control increased with the patterns "very frequent use of products" (1.74 [1.13-2.70]) and "infrequent cleaning tasks and intermediate use of products" (1.62 [1.05-2.51]).

CONCLUSION

Regular use of DCP may contribute to poor asthma control in elderly women. Limiting their use may help improve asthma management.

Respiratory Health Effects of Exposure to Cleaning Products

There is consistent and growing evidence of an epidemic of "asthma-like" symptoms among professional cleaners. Questions include how big is this problem worldwide, which cleaning agents are dangerous, how do they affect the lungs, and is it really asthma? This issue is important to public health because of the increasing number of professional cleaners, many from vulnerable categories. There are implications for anybody exposed to cleaning products during housekeeping, including children. This article uses available evidence to give a broad but concise overview on what we know so far and how we can prevent the cleaning-associated respiratory public health burden.

Cleaners and airway diseases

PURPOSE OF REVIEW

Evidence for adverse respiratory effects of occupational exposure to disinfectants and cleaning products (DCPs) has grown in the last two decades. The relationship between DCPs and asthma is well documented but questions remain regarding specific causal agents. Beyond asthma, associations between DCPs and COPD or chronic rhinitis are plausible and have been examined recently. The purpose of this review is to summarize recent advances on the effect of occupational exposure to DCP and chronic airway diseases.

RECENT FINDINGS

Recent epidemiological studies have often focused on healthcare workers and are characterized by efforts to improve assessment of exposure to specific DCPs. Despite increasing knowledge on the effect of DCPs on asthma, the burden of work-related asthma caused by DCPs has not decreased in the past decade, emphasizing the need to strengthen prevention efforts. Novel data suggest an association between occupational exposure to DCPs and other chronic airway diseases, such as rhinitis, COPD, and poor lung function.

SUMMARY

Epidemiological and experimental data showed that many chemicals contained in DCPs are likely to cause airway damage, indicating that prevention strategies should target multiple products. Further research is needed to evaluate the impact of DCP exposure on occupational airway diseases beyond asthma.

From Mouse to Man and Back: Closing the Correlation Gap between Imaging and Histopathology for Lung Diseases

Lung diseases such as fibrosis, asthma, cystic fibrosis, infection and cancer are life-threatening conditions that slowly deteriorate quality of life and for which our diagnostic power is high, but our knowledge on etiology and/or effective treatment options still contains important gaps. In the context of day-to-day practice, clinical and preclinical studies, clinicians and basic researchers team up and continuously strive to increase insights into lung disease progression, diagnostic and treatment options. To unravel disease processes and to test novel therapeutic approaches, investigators typically rely on end-stage procedures such as serum analysis, cyto-/chemokine profiles and selective tissue histology from animal models. These techniques are useful but provide only a snapshot of disease processes that are essentially dynamic in time and space. Technology allowing evaluation of live animals repeatedly is indispensable to gain a better insight into the dynamics of lung disease progression and treatment effects. Computed tomography (CT) is a clinical diagnostic imaging technique that can have enormous benefits in a research context too. Yet, the implementation of imaging techniques in laboratories lags behind. In this review we want to showcase the integrated approaches and novel developments in imaging, lung functional testing and pathological techniques that are used to assess, diagnose, quantify and treat lung disease and that may be employed in research on patients and animals. Imaging approaches result in often novel anatomical and functional biomarkers, resulting in many advantages, such as better insight in disease progression and a reduction in the numbers of animals necessary. We here showcase integrated assessment of lung disease with imaging and histopathological technologies, applied to the example of lung fibrosis. Better integration of clinical and preclinical imaging technologies with pathology will ultimately result in improved clinical translation of (therapy) study results.

Cobalt exposure via skin alters lung immune cells and enhances pulmonary responses to cobalt in mice

Cobalt has been associated with allergic contact dermatitis and occupational asthma. However, the link between skin exposure and lung responses to cobalt is currently unknown. We investigated the effect of prior dermal sensitization to cobalt on pulmonary physiological and immunological responses after subsequent challenge with cobalt via the airways. BALB/c mice received epicutaneous applications (25 μL/ear) with 5% CoCl_2*6H₂O (Co) or the vehicle (Veh) dimethyl sulfoxide (DMSO) twice; they then received oropharyngeal challenges with 0.05% CoCl_2*6H₂O or saline five times, thereby obtaining four groups: Veh/Veh, Co/Veh, Veh/Co, and Co/Co. To detect early respiratory responses noninvasively, we performed sequential in vivo microcomputed tomography (µCT). One day after the last challenge, we assessed airway hyperreactivity (AHR) to methacholine, inflammation in bronchoalveolar lavage (BAL), innate lymphoid cells (ILCs) and dendritic cells (DCs) in the lungs, and serum IgE. Compared with the Veh/Veh group, the Co/Co group showed increased µCT-derived lung response, increased AHR to methacholine, mixed neutrophilic and eosinophilic inflammation, elevated monocyte chemoattractant protein-1 (MCP-1), and elevated keratinocyte chemoattractant (KC) in BAL. Flow cytometry in the Co/Co group demonstrated increased DC, type 1 and type 2 conventional DC (cDC1/cDC2), monocyte-derived DC, increased ILC group 2, and natural cytotoxicity receptor^-ILC group 3. The Veh/Co group showed only increased AHR to methacholine and elevated MCP-1 in BAL, whereas the Co/Veh group showed increased cDC1 and ILC2 in lung. We conclude that dermal sensitization to cobalt may increase the susceptibility of the lungs to inhaling cobalt. Mechanistically, this enhanced susceptibility involves changes in pulmonary DCs and ILCs.

Aggravation of asthmatic inflammation by chlorine exposure via innate lymphoid cells and CD11cintermediate macrophages

BACKGROUND

Chlorine is widely used in daily life as disinfectant. However, chronic exposure to chlorine products aggravates allergic T_H 2 inflammation and airway hyperresponsiveness (AHR). Innate lymphoid cells (ILCs) in airways contribute to the inception of asthma in association with virus infection, pollution, and excess of nutrient, but it is not known whether chronic chlorine exposure can activate innate immune cells. The aim of this study was to evaluate the impact of chlorine inhalation on the innate immunity such as ILCs and macrophages in relation with the development of asthma by using murine ovalbumin (OVA) sensitization/challenge model.

METHODS

Six-week-old female BALB/c mice were sensitized and challenged with OVA in the presence and absence of chronic low-dose chlorine exposure by inhalation of naturally vaporized gas of 5% sodium hypochlorite solution. AHR, airway inflammatory cells, from BALF and the population of ILCs and macrophages in the lung were evaluated.

RESULTS

The mice exposed to chlorine with OVA (Cl + OVA group) showed enhanced AHR and eosinophilic inflammation compared to OVA-treated mice (OVA group). The population of T_H 2 cells, ILC2s, and ILC3s increased in Cl + OVA group compared with OVA group. CD11c^int macrophages also remarkably increased in Cl + OVA group compared with OVA group. The deletion of macrophages by clodronate resulted in reduction of ILC2s and ILC3s population which was restored by adoptive transfer of CD11c^int macrophages.

CONCLUSIONS

Chronic chlorine inhalation contributes to the exacerbation of airway inflammation in asthmatic airway by mobilizing pro-inflammatory macrophage into the lung as well as stimulating group 2 and 3 ILCs.

Low-Dose Imaging in a New Preclinical Total-Body PET/CT Scanner

Ionizing radiation constitutes a health risk to imaging scientists and study animals. Both PET and CT produce ionizing radiation. CT doses in pre-clinical in vivo imaging typically range from 50 to 1,000 mGy and biological effects in mice at this dose range have been previously described. [¹⁸F]FDG body doses in mice have been estimated to be in the range of 100 mGy for [¹⁸F]FDG. Yearly, the average whole body doses due to handling of activity by PET technologists are reported to be 3–8 mSv. A preclinical PET/CT system is presented with design features which make it suitable for small animal low-dose imaging. The CT subsystem uses a X-source power that is optimized for small animal imaging. The system design incorporates a spatial beam shaper coupled with a highly sensitive flat-panel detector and very fast acquisition (<10 s) which allows for whole body scans with doses as low as 3 mGy. The mouse total-body PET subsystem uses a detector architecture based on continuous crystals, coupled to SiPM arrays and a readout based in rows and columns. The PET field of view is 150 mm axial and 80 mm transaxial. The high solid-angle coverage of the sample and the use of continuous crystals achieve a sensitivity of 9% (NEMA) that can be leveraged for use of low tracer doses and/or performing rapid scans. The low-dose imaging capabilities of the total-body PET subsystem were tested with NEMA phantoms, in tumor models, a mouse bone metabolism scan and a rat heart dynamic scan. The CT imaging capabilities were tested in mice and in a low contrast phantom. The PET low-dose phantom and animal experiments provide evidence that image quality suitable for preclinical PET studies is achieved. Furthermore, CT image contrast using low dose scan settings was suitable as a reference for PET scans. Total-body mouse PET/CT studies could be completed with total doses of <10 mGy.