The epidermal growth factor receptor at the crossroads of airway remodeling

TGF-α/EGFR signaling promotes lipopolysaccharide-induced abnormal elastin deposition and alveolar simplification

Bronchopulmonary dysplasia (BPD) is characterized by shortened secondary septa and fewer, larger alveoli. Elastin deposition to the distal tips of the secondary septa is critical for elongation of the secondary septa. Alveolar myofibroblasts, which are thought to migrate to the septal tips during alveolarization, are mainly responsible for elastin production and deposition. Antenatal exposure to inflammation induces abnormal elastin deposition, thereby increasing the risk of developing BPD. Here, we found that lipopolysaccharide (LPS) significantly increased the expression of transforming growth factor-α (TGF-α) in an LPS-induced rat model of BPD and in LPS-treated human pulmonary epithelial cells (BEAS-2B). In addition, in vitro experiments suggested that LPS upregulated TGF-α expression via toll-like receptor 4 (TLR4)/tumor necrosis factor α-converting enzyme (TACE) signaling. Increased TGF-α levels via its receptor epidermal growth factor receptor (EGFR)-induced lysyl oxidase (LOX) overactivation and cell division cycle 42 (Cdc42) activity inhibition of myofibroblasts. Similarly, in vivo LOX overactivation and inhibition of Cdc42 activity were observed in the lungs of LPS-exposed pups. LOX overactivation led to abnormal elastin deposition, and inhibition of Cdc42 activity disturbed the directional migration of myofibroblasts and disrupted elastin localization. Most importantly, the EGFR inhibitor erlotinib partially rescued LOX overactivation and Cdc42 activity inhibition, and improved elastin deposition and alveolar development in antenatal LPS-treated rats. Taken together, our data suggest that TGF-α/EGFR signaling is critically involved in the regulation of elastin deposition and represents a novel therapeutic target.

Characterization of dental dust particles and their pathogenicity to respiratory system: a narrative review

OBJECTIVES

Dental professionals are exposed to large amounts of dust particles during routine treatment and denture processing. This article provides a narrative review to investigate the most prevalent dust-related respiratory diseases among dental professionals and to discuss the effects of dental dust on human respiratory health.

MATERIALS AND METHODS

A literature search was performed in PubMed/Medline, Web of Science, and Embase for articles published between 1990 and 2022. Any articles on the occupational respiratory health effects of dental dust were included.

RESULTS

The characterization and toxicity evaluation of dental dust show a correlation between dust exposure and respiratory system injury, and the possible pathogenic mechanism of dust is to cause lung injury and abnormal repair processes. The combination use of personal protective equipment and particle removal devices can effectively reduce the adverse health effects of dust exposure.

CONCLUSIONS

Dental dust should be considered an additional occupational hazard in dental practice. However, clinical data and scientific evidence on this topic are still scarce. Further research is required to quantify dust in the dental work environment and clarify its pathogenicity and potential toxicological pathways. Nonetheless, the prevention of dust exposure should become a consensus among dental practitioners.

CLINICAL RELEVANCE

This review provides dental practitioners with a comprehensive understanding and preventive advice on respiratory health problems associated with dust exposure.

The effect of nanoparticles on pulmonary fibrosis: a systematic review and Meta-analysis of preclinical studies

Air pollution is a big ecumenical problem associated with public health around the world. The rapid development of nanotechnology worldwide resulted in a significant increase in human exposure with unknown particles, and ultimately leading to an increase in acute and chronic diseases. The effect of nanoparticles on pulmonary fibrosis has been reported in vivo and in vitro studies; however, the results are inconsistent. The present systematic review and meta-analysis of animal preclinical studies was conducted to assess the effect of nanoparticles on pulmonary fibrosis. A systematic search of online databases and gray literature as well as reference lists of retrieved studies was performed up to February 2019 to identify preclinical animal studies. Studies were assessed for methodological quality using the SYstematic Review Center for Laboratory animal Experimentation bias risk tool (SYRCLE's ROB tool). Pooled standardized mean difference (SMD) estimate with corresponding 95% CI was calculated using inverse-variance weights method while random effects meta-analysis was used, taking into account conceptual heterogeneity. To assess the robustness of pooled estimates as well as heterogeneity across studies, sensitivity analysis and Cochran Q statistic (with I² statistic) was carried out using Stata 11.0. Of 6494 retrieved studies, 85 were reviewed in depth for eligibility. 16 studies met the criteria for inclusion in this systematic review. The meta-analysis was conducted on 10 studies which had reported the mean of TGF-β in 7 days after exposure by nanoparticles jointly (exposure compared to no exposure). Findings showed that exposure to nanoparticles significantly induced pulmonary fibrosis (SMD: 4.12, 95% CI: 2.57-5.67). A statistical heterogeneity was found [P < 0.001 (Q statistics), I² = 83.0%] across studies. Nanoparticles were the most influencing in inducing pulmonary fibrosis in animal models. Sensitivity analysis demonstrated consistency of the results, indicating that the meta-analysis model was robust. Publication bias (using visual inspection and statistical tests) was unlikely in the association between nanoparticles and pulmonary fibrosis. We found that the nanoparticles significantly induce pulmonary fibrosis through increasing proinflammatory cytokine TGF-β and histopathological changes.

Mechanisms of nanoparticle-induced oxidative stress and toxicity

The rapidly emerging field of nanotechnology has offered innovative discoveries in the medical, industrial, and consumer sectors. The unique physicochemical and electrical properties of engineered nanoparticles (NP) make them highly desirable in a variety of applications. However, these novel properties of NP are fraught with concerns for environmental and occupational exposure. Changes in structural and physicochemical properties of NP can lead to changes in biological activities including ROS generation, one of the most frequently reported NP-associated toxicities. Oxidative stress induced by engineered NP is due to acellular factors such as particle surface, size, composition, and presence of metals, while cellular responses such as mitochondrial respiration, NP-cell interaction, and immune cell activation are responsible for ROS-mediated damage. NP-induced oxidative stress responses are torch bearers for further pathophysiological effects including genotoxicity, inflammation, and fibrosis as demonstrated by activation of associated cell signaling pathways. Since oxidative stress is a key determinant of NP-induced injury, it is necessary to characterize the ROS response resulting from NP. Through physicochemical characterization and understanding of the multiple signaling cascades activated by NP-induced ROS, a systemic toxicity screen with oxidative stress as a predictive model for NP-induced injury can be developed.

Bronchial epithelium as a target for innovative treatments in asthma

Increasing evidence of a critical role played by the bronchial epithelium in airway homeostasis is opening new therapeutic avenues. Its unique situation at the interface with the environment suggests that the subtle regulation orchestrated by the epithelium between tolerance and specific immune response might be impaired in asthma. Airway mucus is acting as a physical and a biological fluid between the environment and the epithelium, synergistically moved by the cilia. In asthma, excessive mucus production is a hallmark of airway remodeling. Since many years we tried to therapeutically target mucus hypersecretion, but actually this option is still not achieved. The present review discusses the dynamic processes regulating airway mucus production. Airway inflammation is central in current asthma management. Understanding of how the airway epithelium influences the TH2 paradigm in response to deleterious agents is improving. The multiple receptors expressed by the airway epithelium are the transducers of the biological signals induced by various invasive agents to develop the most adapted response. Airway remodeling is observed in severe chronic airway diseases and may result from ongoing disturbance of signal transduction and epithelial renewal. Chronic airway diseases such as asthma will require assessment of these epithelial abnormalities to identify phenotypic characteristics associated with predicting a clinical benefit for epithelial-directed therapies.

Physico-chemical characterization of African urban aerosols (Bamako in Mali and Dakar in Senegal) and their toxic effects in human bronchial epithelial cells: description of a worrying situation

Background

The involvement of particulate matter (PM) in cardiorespiratory diseases is now established in developed countries whereas in developing areas such as Africa with a high level of specific pollution, PM pollution and its effects are poorly studied. Our objective was to characterize the biological reactivity of urban African aerosols on human bronchial epithelial cells in relation to PM physico-chemical properties to identify toxic sources.

Methods

Size-speciated aerosol chemical composition was analyzed in Bamako (BK, Mali, 2 samples with one having desert dust event BK1) and Dakar (DK; Senegal) for Ultrafine UF, Fine F and Coarse C PM. PM reactivity was studied in human bronchial epithelial cells investigating six biomarkers (oxidative stress responsive genes and pro-inflammatory cytokines).

Results

PM mass concentrations were mainly distributed in coarse mode (60%) and were impressive in BK1 due to the desert dust event. BK2 and DK samples showed a high content of total carbon characteristic of urban areas. The DK sample had huge PAH quantities in bulk aerosol compared with BK that had more water soluble organic carbon and metals. Whatever the site, UF and F PM triggered the mRNA expression of the different biomarkers whereas coarse PM had little or no effect. The GM-CSF biomarker was the most discriminating and showed the strongest pro-inflammatory effect of BK2 PM. The analysis of gene expression signature and of their correlation with main PM compounds revealed that PM-induced responses are mainly related to organic compounds. The toxicity of African aerosols is carried by the finest PM as with Parisian aerosols, but when considering PM mass concentrations, the African population is more highly exposed to toxic particulate pollution than French population. Regarding the prevailing sources in each site, aerosol biological impacts are higher for incomplete combustion sources resulting from two-wheel vehicles and domestic fires than from diesel vehicles (Dakar). Desert dust events seem to produce fewer biological impacts than anthropogenic sources.

Discussion

Our study shows that combustion sources contribute to the high toxicity of F and UF PM of African urban aerosols, and underlines the importance of emission mitigation and the imperative need to evaluate and to regulate particulate pollution in Africa.

Pulmonary toxicity and fibrogenic response of carbon nanotubes

Carbon nanotubes (CNTs) have been a subject of intensive research for a wide range of applications. However, because of their extremely small size and light weight, CNTs are readily inhaled into human lungs resulting in increased rates of pulmonary disorders, most notably fibrosis. Several studies have demonstrated the fibrogenic effects of CNTs given their ability to translocate into the surrounding areas in the lung causing granulomatous lesions and interstitial and sub-pleural fibrosis. However, the mechanisms underlying the disease process remain obscure due to the lack of understanding of the cellular interactions and molecular targets involved. Interestingly, certain physicochemical properties of CNTs have been shown to affect their respiratory toxicity, thereby becoming significant determinants of fibrogenesis. CNT-induced fibrosis involves a multitude of cell types and is characterized by the early onset of inflammation, oxidative stress and accumulation of extracellular matrix. Increased reactive oxygen species activate various cytokine/growth factor signaling cascades resulting in increased expression of inflammatory and fibrotic genes. Profibrotic growth factors and cytokines contribute directly to fibroblast proliferation and collagen production. Given the role of multiple players during the pathogenesis of CNT-induced fibrosis, the objective of this review is to summarize the key findings and discuss major cellular and molecular events governing pulmonary fibrosis. We also discuss the physicochemical properties of CNTs and their effects on pulmonary toxicities as well as various biological factors contributing to the development of fibrosis.

Lipopolysaccharide disrupts the directional persistence of alveolar myofibroblast migration through EGF receptor

Bronchopulmonary dysplasia (BPD) is characterized by alveolar simplification with decreased alveolar number and increased airspace size. Formation of alveoli involves a process known as secondary septation triggered by myofibroblasts. This study investigated the underlying mechanisms of altered lung morphogenesis in a rat model of BPD induced by intra-amniotic injection of lipopolysaccharide (LPS). Results showed that LPS disrupted alveolar morphology and led to abnormal localization of myofibroblasts in the lung of newborn rats, mostly in primary septa with few in secondary septa. To identify potential mechanisms, in vitro experiments were carried out to observe the migration behavior of myofibroblasts. The migration speed of lung myofibroblasts increased with LPS treatment, whereas the directional persistence decreased. We found that LPS induced activation of EGFR and overexpression of its ligand, TGF-α in myofibroblasts. AG1478, an EGFR inhibitor, abrogated the enhanced locomotivity of myofibroblasts by LPS and also increased the directional persistence of myofibroblast migration. Myofibroblasts showed a high asymmetry of phospho-EGFR localization, which was absent after LPS treatment. Application of rhTGF-α to myofibroblasts decreased the directional persistence. Our findings indicated that asymmetry of phospho-EGFR localization in myofibroblasts was important for cell migration and its directional persistence. We speculate that LPS exposure disrupts the asymmetric localization of phospho-EGFR, leading to decreased stability of cell polarity and final abnormal location of myofibroblasts in vivo, which is critical to secondary septation and may contribute to the arrested alveolar development in BPD.

Activation of epidermal growth factor receptor is required for NTHi-induced NF-κB-dependent inflammation

BACKGROUND

Inflammation is a hallmark of many serious human diseases. Nontypeable Haemophilus influenzae (NTHi) is an important human pathogen causing respiratory tract infections in both adults and children. NTHi infections are characterized by inflammation, which is mainly mediated by nuclear transcription factor-kappa B (NF-κB)-dependent production of proinflammatory mediators. Epidermal growth factor receptor (EGFR) has been shown to play important roles in regulating diverse biological processes, including cell growth, differentiation, apoptosis, adhesion, and migration. Its role in regulating NF-κB activation and inflammation, however, remains largely unknown.

METHODOLOGY/PRINCIPAL FINDINGS

In the present study, we demonstrate that EGFR plays a vital role in NTHi-induced NF-κB activation and the subsequent induction of proinflammatory mediators in human middle ear epithelial cells and other cell types. Importantly, we found that AG1478, a specific tyrosine kinase inhibitor of EGFR potently inhibited NTHi-induced inflammatory responses in the middle ears and lungs of mice in vivo. Moreover, we found that MKK3/6-p38 and PI3K/Akt signaling pathways are required for mediating EGFR-dependent NF-κB activation and inflammatory responses by NTHi.

CONCLUSIONS/SIGNIFICANCE

Here, we provide direct evidence that EGFR plays a critical role in mediating NTHi-induced NF-κB activation and inflammation in vitro and in vivo. Given that EGFR inhibitors have been approved in clinical use for the treatment of cancers, current studies will not only provide novel insights into the molecular mechanisms underlying the regulation of inflammation, but may also lead to the development of novel therapeutic strategies for the treatment of respiratory inflammatory diseases and other inflammatory diseases.

Nanoparticle-induced pulmonary toxicity

In recent decades, advances in nanotechnology engineering have given rise to the rapid development of many novel applications in the biomedical field. However, studies into the health and safety of these nanomaterials are still lacking. The main concerns are the adverse effects to health caused by acute or chronic exposure to nanoparticles (NPs), especially in the workplace environment. The lung is one of the main routes of entry for NPs into the body and, hence, a likely site for accumulation of NPs. Once NPs enter the interstitial air spaces and are quickly taken up by alveolar cells, they are likely to induce toxic effects. In this review, we highlight the different aspects of lung toxicity resulting from NP exposure, such as generation of oxidative stress, DNA damage and inflammation leading to fibrosis and pneumoconiosis, and the underlying mechanisms causing pulmonary toxicity.

Perinatal increases in TGF-α disrupt the saccular phase of lung morphogenesis and cause remodeling: microarray analysis

Transforming growth factor-α (TGF-α) and its receptor, the epithelial growth factor receptor (EGFR), have been associated with lung remodeling in premature infants with bronchopulmonary dysplasia (BPD). The goal of this study was to target TGF-α overexpression to the saccular phase of lung morphogenesis and determine early alterations in gene expression. Conditional lung-specific TGF-α bitransgenic mice and single-transgene control mice were generated. TGF-α overexpression was induced by doxycycline (Dox) treatment from embryonic day 16.5 (E16.5) to E18.5. After birth, all bitransgenic pups died by postnatal day 7 (P7). Lung histology at E18.5 and P1 showed abnormal lung morphogenesis in bitransgenic mice, characterized by mesenchymal thickening, vascular remodeling, and poor apposition of capillaries to distal air spaces. Surfactant levels (saturated phosphatidylcholine) were not reduced in bitransgenic mice. Microarray analysis was performed after 1 or 2 days of Dox treatment during the saccular (E17.5, E18.5) and alveolar phases (P4, P5) to identify genes induced by EGFR signaling that were shared or unique to each phase. We found 196 genes to be altered (>1.5-fold change; P < 0.01 for at least 2 time points), with only 32% similarly altered in both saccular and alveolar phases. Western blot analysis and immunostaining showed that five genes selected from the microarrays (egr-1, SP-B, SP-D, S100A4, and pleiotrophin) were also increased at the protein level. Pathological changes in TGF-α-overexpressing mice bore similarities to premature infants born in the saccular phase who develop BPD, including remodeling of the distal lung septae and arteries.

Pollution atmosphérique et maladies respiratoires

Epidemiological studies have clearly shown a relationship between respiratory diseases and air pollution. Ozone and ambient particles are the main pollutants contributing to the exacerbation of these pathologies. Their toxicity resides in their ability to generate an oxidative stress. The level of oxidative stress and the specificity of the cellular responses result from complex interactions between pro- and anti-oxidants, leading to differentiated cellular strategies. Hierarchical biological responses: adaptation, inflammation, lesions, can be determined according to the oxidative insult and individual anti-oxidant capacities. A better health risk assessment could be achieved by taking into account the oxidative properties of air pollution especially those of ultrafine particles.

Susceptibility of signal transducer and activator of transcription-1-deficient mice to pulmonary fibrogenesis

The signal transducer and activator of transcription (Stat)-1 mediates growth arrest and apoptosis. We postulated that lung fibrosis characterized by excessive proliferation of lung fibroblasts would be enhanced in Stat1-deficient (Stat1-/-) mice. Two weeks after bleomycin aspiration (3 U/kg), Stat1-/- mice exhibited a more severe fibroproliferative response and significantly elevated total lung collagen compared to wild-type mice. Growth factors [epidermal growth factor (EGF) or platelet-derived growth factor (PDGF)] enhanced [3H]thymidine uptake in lung fibroblasts isolated from Stat1-/- mice compared to wild-type mice. Interferon (IFN)-gamma, which signals growth arrest via Stat1, inhibited EGF- or PDGF-stimulated mitogenesis in wild-type fibroblasts but enhanced [3H]thymidine uptake in Stat1-/- fibroblasts. Moreover, IFN-gamma treatment in the absence of growth factors induced a concentration-dependent increase in [3H]thymidine uptake in Stat1-/- but not wild-type fibroblasts. Mitogen-activated protein kinase (ERK-1/2) phosphorylation in response to PDGF or EGF did not differ among Stat1-/- and wild-type fibroblasts. However, Stat3 phosphorylation induced by PDGF, EGF, or IFN-gamma increased twofold in Stat1-/- fibroblasts compared to wild-type fibroblasts. Our findings indicate that Stat1-/- mice are more susceptible to bleomycin-induced lung fibrosis than wild-type mice due to 1) enhanced fibroblast proliferation in response to growth factors (EGF and PDGF), 2) stimulation of fibroblast growth by a Stat1-independent IFN-gamma signaling pathway, and 3) increased activation of Stat3.

Betacellulin overexpression in transgenic mice causes disproportionate growth, pulmonary hemorrhage syndrome, and complex eye pathology

The EGF family comprises a network of ligands and receptors that regulate proper development and elicit diverse functions in physiology and pathology. Betacellulin (BTC) is a rather poorly characterized member of the EGF family whose in vivo effects have been linked mainly to endocrine pancreas, intestine, and mammary gland function. In vitro studies revealed that this growth factor is a potent mitogen for diverse cell types and suggested unique receptor-binding properties. Genetic ablation of BTC in mice yielded a mild phenotype, probably because of opportunistic compensation by other EGF receptor ligands. To study the biological capabilities of BTC in vivo, we generated transgenic mice overexpressing BTC ubiquitously, with highest expression levels in heart, lung, brain, and pancreas. Mice overexpressing BTC exhibit high early postnatal mortality, reduced body weight gain, and impaired longitudinal growth. In addition, a variety of pathological alterations were observed. Cataract and abnormally shaped retinal layers as well as bone alterations leading to a dome-shaped, round head form were hallmarks of BTC transgenic mice. The most important finding and the cause of reduced life expectancy of BTC transgenic mice were severe alterations of the lung. Pulmonary pathology was primarily characterized by alveolar hemorrhage, thickening of the alveolar septa, intraalveolar accumulation of hemosiderin-containing macrophages, and nodular pulmonary remodeling. Thus, our model uncovers multiple consequences of BTC overexpression in vivo. These transgenic mice provide a useful model for examining the effects of BTC excess on different organs.

Transient induction of TGF-α disrupts lung morphogenesis, causing pulmonary disease in adulthood

Clinical studies have associated increased transforming growth factor (TGF)-α and EGF receptor with lung remodeling in diseases including bronchopulmonary dysplasia (BPD). BPD is characterized by disrupted alveolar and vascular morphogenesis, inflammation, and remodeling. To determine whether transient increases in TGF-α are sufficient to disrupt postnatal lung morphogenesis, we utilized neonatal transgenic mice conditionally expressing TGF-α. Expression of TGF-α from postnatal days 3 to 5 disrupted postnatal alveologenesis, causing permanent enlargement of distal air spaces in neonatal and adult mice. Lung volume-to-body weight ratios and lung compliance were increased in adult TGF-α transgenic mice, whereas tissue and airway elastance were reduced. Elastin fibers in the alveolar septae were fragmented and disorganized. Pulmonary vascular morphogenesis was abnormal in TGF-α mice, with attenuated and occasionally tortuous arterial branching. The ratios of right ventricle weight to left ventricle plus septal weight were increased in TGF-α mice, indicating pulmonary hypertension. Electron microscopy showed gaps in the capillary endothelium and extravasation of erythrocytes into the alveolar space of TGF-α mice. Hemorrhage and inflammatory cells were seen in distal air spaces at 1 mo of age. In adult TGF-α mice, alveolar remodeling, nodules, proteinaceous deposits, and inflammatory cells were seen. Immunostaining for pro-surfactant protein C showed that type II cells were abundant in the nodules, as well as neutrophils and macrophages. Trichrome staining showed that pulmonary fibrosis was minimal, apart from areas of nodular remodeling in adult TGF-α mice. Transient induction of TGF-α during early alveologenesis permanently disrupted lung structure and function and caused chronic lung disease.

Heparin-binding epidermal growth factor cleavage mediates zinc-induced epidermal growth factor receptor phosphorylation

We have previously shown that exposure to zinc ions can activate epidermal growth factor (EGF) receptor (EGFR) signaling in murine fibroblasts and A431 cells through a mechanism involving Src kinase. While studying the effects of zinc ions in normal human bronchial epithelial cell, we uncovered evidence for an additional mechanism of Zn(2+)-induced EGFR activation. Exposure to Zn(2+) induced phosphorylation of EGFR at tyrosine 1068, a major autophosphorylation site, in a dose- and time-dependent fashion. This effect of Zn(2+) on EGFR was significantly blocked with an antibody against the ligand-binding domain of the receptor. Neutralizing antibodies against EGFR ligands revealed the involvement of heparin-binding EGF (HB-EGF) in Zn(2+)-induced EGFR phosphorylation. This observation was further supported by immunoblots showing elevated levels of HB-EGF released by Zn(2+)-exposed cells. Zymography showed the existence of matrix metalloproteinase-3 in Zn(2+)-challenged cells. Incubation with a specific matrix metalloproteinase-3 inhibitor suppressed Zn(2+)-induced EGFR phosphorylation as well as HB-EGF release. Therefore, these data support an autocrine or paracrine mechanism whereby Zn(2+) induces EGFR phosphorylation through the extracellular release of EGFR ligands, which may be mediated by metalloproteinases.

Fine particulate matter induces amphiregulin secretion by bronchial epithelial cells

Particulate matter (PM) is thought to be responsible for respiratory health problems. Epithelial cells exposed to particles release pro-inflammatory cytokines leading to inflammation of airways. However, the signaling cascades triggered by particles are poorly understood. We demonstrate that PM with an aerodynamic diameter < 2.5 microm (PM2.5) or diesel exhaust particles upregulate the expression of amphiregulin (AR), a ligand of the epidermal growth factor receptor (EGFR), in human bronchial epithelial cells. AR secretion was blocked by an inhibitor of the EGFR tyrosine kinase (AG1478), or a selective mitogen-activated protein (MAP) kinase/extracellular regulated kinase (Erk) inhibitor (PD98059), but not by the p38 MAP kinase inhibitor (SB203580). Thus, AR secretion is mediated through the activation of the EGFR and Erk MAP kinase pathway. In addition, AR secretion was inhibited by the antioxidant N-acetyl cysteine, but not by a neutralizing anti-EGFR, suggesting an EGFR transactivation via oxidative stress. AR may be involved in cytokine secretion, as AR can induce granulocyte macrophage-colony-stimulating factor (GM-CSF) release and a neutralizing anti-EGFR reduces the particle-induced GM-CSF release. This study indicates that PM2.5 induces the expression and secretion of AR, an EGFR ligand contributing to GM-CSF release, which may reflect an important mechanism for sustaining the proinflammatory response.

Leukotrienes mediate part of Ova-induced lung effects in mice via EGFR

Antigen induces murine bronchial hyperreactivity (BHR), inflammation, mucus accumulation, and airway remodeling. To investigate whether leukotrienes (LT) mediate the effects of antigen [ovalbumin (Ova)], we studied 5-lipoxygenase (5-LO) expression in immunized BP2 mice and blocked LT synthesis with the 5-LO inhibitor zileuton or antagonized their effects with receptor antagonists [cysteinyl leukotriene (Cys-LT)-ra MK-571, LY-171883; LTB4-ra PH-163]. Cys-LT content increased in the bronchoalveolar lavage fluid (BALF) as early as 15 min after the intratracheal instillation of Ova. Zileuton inhibited LT release in the BALF and eosinophil recruitment in the lungs, and dose dependently reduced BHR, mucus accumulation, and remodeling, as did the LT-ra. Thus LT, released just after antigen challenge, might constitute the first step in accounting for the effects of Ova. Because mucus accumulation is regulated via the EGF receptor (EGFR), which is also implicated in the effects of LT, we studied this pathway with AG-1478, an EGFR tyrosine kinase inhibitor given at 0.5, 4, and 20 mg/kg. AG-1478 inhibited BHR, inflammation, and lung remodeling induced by Ova or by molecules themselves generated by Ova, such as LT, IL-13, and monocyte chemoattractant protein-1, which promote identical effects, suggesting the involvement of the EGFR pathway in the asthma-like syndrome observed.