Pathogenesis Of Occupational Asthma Research Articles

Neutrophil activation in occupational asthma.

The aim of this review is to emphasize the role of neutrophils in patients with occupational asthma. This review facilitates a better understanding, accurate diagnosis, and proper management of asthmatic reactions provoked at the workplace. Increased recruitment and infiltration of neutrophils are found in patients with occupational asthma. Activated neutrophils release several mediators including pro-inflammatory cytokines and extracellular traps, leading to stimulation of airway epithelium and other inflammatory cells. New insights into neutrophils in the pathogenesis of occupational asthma may provide a novel approach to the individual patient with occupational asthma.

Toluene diisocyanate exposure induces airway inflammation of bronchial epithelial cells via the activation of transient receptor potential melastatin 8

Toluene diisocyanate (TDI) is the most important cause of occupational asthma (OA), and various pathogenic mechanisms have been suggested. Of these mechanisms, neurogenic inflammation is an important inducer of airway inflammation. Transient receptor potential melastatin 8 (TRPM8) is a well-established cold-sensing cation channel that is expressed in both neuronal cells and bronchial epithelial cells. A recent genome-wide association study of TDI-exposed workers found a significant association between the phenotype of TDI-induced OA and the single-nucleotide polymorphism rs10803666, which has been mapped to the TRPM8 gene. We hypothesized that TRPM8 located in airway epithelial cells may be involved in the pathogenic mechanisms of TDI-induced OA and investigated its role. Bronchial epithelial cells were treated with TDI in a dose- and time-dependent manner. The expression levels of TRPM8 mRNA and protein were determined by quantitative real-time polymerase chain reaction and western blotting. TDI-induced morphological changes in the cells were evaluated by immunocytochemistry. Alterations in the transcripts of inflammatory cytokines were examined in accordance with TRPM8 activation by TDI. TRPM8 expression at both the mRNA and protein levels was enhanced by TDI in airway epithelial cells. TRPM8 activation by TDI led to significant increases in the mRNA of interleukin (IL)-4, IL-13, IL-25 and IL-33. The increased expression of the cytokine genes by TDI was partly attenuated after treatment with a TRPM8 antagonist. TDI exposure induces increased expression of TRPM8 mRNA in airway epithelial cells coupled with enhanced expression of inflammatory cytokines, suggesting a novel role of TRPM8 in the pathogenesis of TDI-induced OA.

The Cardiac Protein Alpha-T-Catenin Contributes to the Pathogenesis of Occupational Asthma

The Cardiac Protein Alpha-T-Catenin Contributes to the Pathogenesis of Occupational Asthma

Cells and mediators in diisocyanate-induced occupational asthma

Diisocyanates are the most common cause of occupational asthma in many industrialized countries, and various pathogenic mechanisms have been suggested to be involved. Occupational asthma causes airway remodeling unless diagnosed and treated within a proper time frame. However, treatment modalities are limited because of an insufficient understanding regarding underlying pathogenic mechanisms. Several immunological and nonimmunological mechanisms have been suggested, indicating that the pathogenesis of occupational asthma may be more complex than other types of asthma. Airway epithelial cells are the first to encounter diisocyanates and orchestrate various responses, such as cytokine release, oxidative stress generation, and autoantibody formation. Some evidence supports the involvement of adaptive immune responses. Additional evidence suggests that other mechanisms are involved in diisocyanate-induced occupational asthma. One such candidate mechanism is oxidative stress. Oxidative stress has been shown to trigger and aid in the development of diisocyanate-induced occupational asthma in human samples and genetic studies, and some therapeutic trials were performed based on this finding. Diisocyanate-induced occupational asthma may be caused by a complex interaction of innate and adaptive immune responses. The knowledge presented in this review may help lead to the development of new treatment modalities through an increased understanding of occupational asthma pathogenesis.

Case Report of Occupational Asthma Induced by Polyvinyl Chloride and Nickel

Polyvinyl chloride (PVC) is a widely used chemical for production of plastics. However occupational asthma (OA) caused by PVC has been reported only rarely. We report a 34-yr-old male wallpaper factory worker with OA due to PVC and nickel (Ni) whose job was mixing PVC with plasticizers. He visited the emergency room due to an asthma attack with moderate airflow obstruction and markedly increased sputum eosinophil numbers. A methacholine challenge test was positive (PC20 2.5 mg/mL). Bronchoprovocation tests with both PVC and Ni showed early and late asthmatic responses, respectively. Moreover, the fractional concentration of exhaled nitric oxide (FeNO) was increased after challenge with PVC. To our knowledge, this is the first case of OA in Korea induced by exposure to both PVC and Ni. We suggest that eosinophilic inflammation may be involved in the pathogenesis of PVC-induced OA and that FeNO monitoring can be used for its diagnosis.

AMPK activation reduces vascular permeability and airway inflammation by regulating HIF/VEGFA pathway in a murine model of toluene diisocyanate-induced asthma

Occupational asthma is characterized by airway inflammation and hyperresponsiveness associated with increased vascular permeability. AMP-activated protein kinase (AMPK) has been suggested to be a novel signaling molecule modulating inflammatory responses. We sought to evaluate the involvement of AMPK in pathogenesis of occupational asthma and more specifically investigate the effect and molecular mechanisms of AMPK activation in regulating vascular permeability. The mechanisms of action and therapeutic potential of an AMPK activator, 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) were tested in a murine model of toluene diisocyanate (TDI)-induced asthma. AICAR attenuated airway inflammation and hyperresponsiveness increased by TDI inhalation. Moreover, TDI-induced increases in levels of hypoxia-inducible factor (HIF)-1α, HIF-2α, vascular endothelial growth factor A (VEGFA), and plasma exudation were substantially decreased by treatment with AICAR. Our results also showed that VEGFA expression was remarkably reduced by inhibition of HIF-1α and HIF-2α with 2-methoxyestradiol (2ME2) and that an inhibitor of VEGFA activity, CBO-P11 as well as 2ME2 significantly suppressed vascular permeability, airway infiltration of inflammatory cells, and airway hyperresponsiveness induced by TDI. In addition, AICAR reduced reactive oxygen species (ROS) generation and levels of malondialdehyde and T-helper type 2 cytokines (IL-4, IL-5, and IL-13), while this agent enhanced expression of an anti-inflammatory cytokine, IL-10. These results suggest that AMPK activation ameliorates airway inflammatory responses by reducing vascular permeability via HIF/VEGFA pathway as well as by inhibiting ROS production and thus may be a possible therapeutic strategy for TDI-induced asthma and other airway inflammatory diseases.

Monoclonal Antibodies Against Toluene Diisocyanate Haptenated Proteins from Vapor-Exposed Mice

Toluene diisocyanate (TDI) is an industrially important polymer cross-linker used in the production of polyurethane. Workplace exposure to TDI and other diisocyanates is reported to be a leading cause of low molecular weight-induced occupational asthma (OA). Currently we have a limited understanding of the pathogenesis of OA. Monoclonal antibodies (MAbs) that recognize TDI bound proteins would be valuable tools/reagents, both in exposure monitoring and in TDI-induced asthma research. We sought to develop toluene diisocyanate (TDI)-specific MAbs for potential use in the development of standardized immunoassays for exposure and biomarker assessments. Mice were exposed 4 h/day for 12 consecutive weekdays to 50 ppb, 2,4;2,6 TDI vapor (80/20 mixture). Splenocytes were isolated 24 h after the last exposure for hybridoma production. Hybridomas were screened in a solid-phase indirect enzyme-linked immunosorbent assay (ELISA) against a 2,4 TDI-human serum albumin (2,4 TDI-HSA) protein conjugate. Three hybridomas producing 2,4 TDI-HSA reactive IgM MAbs were obtained. The properties of these MAbs (isotype and reactivity to various protein-isocyanate conjugate epitopes) were characterized using ELISA, dot blot, and Western blot analyses. Western blot analyses demonstrated that some TDI conjugates form inter- and intra-molecular links, resulting in multimers and a change in the electrophoretic mobility of the conjugate. These antibodies may be useful tools for the isolation of endogenous diisocyanate-modified proteins after natural or experimental exposures and for characterization of the toxicity of specific dNCOs.

Toluene diisocyanate (TDI) regulates haem oxygenase-1/ferritin expression: implications for toluene diisocyanate-induced asthma

Diisocyanate is a leading cause of occupational asthma (OA). Diisocyanate-induced OA is an inflammatory disease of the airways that is associated with airway remodelling. Although the pathogenic mechanisms are unclear, oxidative stress may be related to the pathogenesis of diisocyanate-induced OA. In our previous report, we observed that the expression of ferritin light chain (FTL) was decreased in both of bronchoalveolar lavage fluid and serum of patients with diphenyl-methane diisocyanate (MDI)-induced OA compared to those of asymptomatic exposed controls and unexposed healthy controls. In this study of toluene diisocyanate (TDI)-OA, we found identical findings with increased transferrin and decreased ferritin levels in the serum of patients with TDI-OA. To elucidate whether diisocyanate suppresses FTL synthesis directly, we tested the effect of TDI on the FTL synthesis in A549 cells, a human airway epithelial cell line. We found that haem oxygenase-1 as well as FTL was suppressed by treatment with TDI in dose- and time-dependent manners. We also found that the synthesis of other anti-oxidant proteins such as thioredoxin-1, glutathione peroxidase, peroxiredoxin 1 and catalase were suppressed by TDI. Furthermore, TDI suppressed nuclear translocation of Nrf2 through suppressing the phosphorylation of mitogen-activated protein kinases (MAPKs); extracellular-regulated kinase 1/2 (ERK1/2); p38; and c-Jun N-terminal kinase (JNK). Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists, 15-deoxy-Delta(12,14)-PGJ2 and rosiglitazone rescued the effect of TDI on HO-1/FTL expression. Collectively, our findings suggest that TDI suppressed HO-1/FTL expression through the MAPK-Nrf2 signalling pathway, which may be involved in the pathogenesis of TDI-induced OA. Therefore, elucidating these observations further should help to develop the therapeutic strategies of diisocyanate-induced OA.

Animal models for diisocyanate asthma: answers for lingering questions.

Diisocyanates are the leading cause of occupational asthma, the most commonly reported lung disease associated with the workplace. Clinical studies have implicated the immune system in the pathogenesis of occupational asthma, but ethical and moral issues prevent mechanistic investigations in humans. For this reason, the development and characterization of animal models are germane to further understanding of diisocyanate occupational asthma and to identify avenues for therapeutic intervention. This review will highlight important features of existing experimental animal models with emphasis on new developments. Experimental animal models of diisocyanate occupational asthma have demonstrated an immunological basis for the disease. Mice can be sensitized by dermal or respiratory exposure, suggesting that either exposure route may be important in the workplace. Recent findings show that sensitized mice develop airway hyperreactivity and inflammation, reflective of human disease. The transfer of lymphocytes or serum from sensitized mice can cause clinical disease in naive mice. Transgenic animals have identified a role for specific immunity, including the involvement of T-helper type 1/2 responses as well as CD4 and CD8 T cells in diisocyanate occupational asthma. Recent animal models have shown that sensitization can occur through subchronic inhalation of vapor-phase diisocyanate at levels as low as 20 ppb. Recent progress using animal models has been instrumental in furthering current understanding of the involvement of the immune system in disease pathogenesis. The demonstration of diisocyanate occupational asthma in a murine model after sub-chronic inhalation exposure at relevant exposure levels should provide opportunities for more accurate risk assessment data.

Occupational asthma due to exposure to iroko wood dust

Occupational asthma (OA) from iroko wood has been reported primarily in case reports. To improve understanding of the pathogenesis of OA induced by iroko wood dust. Three groups of woodworkers were included in this study: 9 workers who had clinically proven OA from iroko; 10 asymptomatic woodworkers; and 10 woodworkers with asthma. All patients underwent the following tests: a skin test with an iroko aqueous extract, specific IgE determination, and an iroko bronchial provocation test (IBPT). An eosinophil count was determined before and after the IBPT, and a methacholine inhalation test was performed after avoidance of exposure to iroko. Patients were asked to monitor their peak expiratory flow rates during a week at work followed by a week's vacation. In all patients with a personal history predictive of OA from iroko, a reduction of the peak expiratory flow rate and positivity to the IBPT while working with iroko were present. The latter test result showed a dual response, with a decrease in forced expiratory volume in 1 second from 25% to 32% at 10 minutes and a further decrease from 35% to 43% at 8 hours; at 24 hours, the eosinophil count was higher (P = .046). In 4 patients, the intradermal test results with iroko extract were positive, whereas the skin prick test result and the specific IgE determination were negative in all patients. The methacholine test result was also positive. In the control groups, all the test results with iroko extract were negative. Our data suggest that OA due to iroko wood may be induced by immunologic mechanisms other than IgE-mediated immediate hypersensitivity reactions.

Pathogenesis of occupational asthma.

The development of occupational asthma (OA) is likely to result from the complex interaction of environmental and host factors. This article addresses a series of issues relating to the multiple environmental factors that could affect the initiation of OA, including the intrinsic characteristics of causative agents, as well as the influence of the level, mode and route of exposure. Although the clinical and pathological features of OA caused by low molecular weight agents resemble those of immunoglobulin (Ig)E-mediated asthma, the failure to detect specific IgE antibodies against most of these agents and/or poor association with disease status have resulted in intense speculation about alternative or complementary physiopathological mechanisms leading to airway sensitisation. In this contribution, the roles of specific immunoglobulin E and G antibodies, cell-mediated immunity and inflammatory effector cells are critically reviewed. Recent advances in the characterisation of the molecular interactions between chemical sensitisers and human airway proteins provide promising avenues for elucidating the immunological basis of occupational asthma caused by low molecular weight agents.

Occupational Asthma Due to Persulfate Salts : Diagnosis and Follow-up

Persulfate salts have been identified as a cause of occupational asthma (OA). The aim of the present study was to describe the clinical characteristics, diagnostic testing results, and follow-up of eight patients with OA that was triggered by these chemical compounds. Eight patients with OA due to exposure to persulfate salts were studied. Immunologic, lung function, and specific bronchial challenge tests (SBCTs) were performed in all patients. Once their condition had been diagnosed, the patients were seen every 1, 3, and 6 months for a mean duration of 18 months. The mean time of exposure to persulfate salts up to diagnosis was 15 years (range, 3 to 27 years), and mean time that had elapsed between symptom onset and diagnosis was 38 months (range, 3 to 120 months). Three patients were smokers, six patients presented with rhinitis prior to asthma in relation to persulfate exposure, and three presented with dermatitis. The results of total IgE tests were positive in six patients, and the results of skin-prick tests for detection of persulfate salts were positive in five of these patients. The results of a SBCT was positive in the seven patients in whom it was performed. Symptoms persisted in all but one patient and required medical treatment. The results suggest that the reliable diagnosis of OA due to persulfate salts must be based on the specific challenge test until further experience has been acquired. Despite avoiding exposure, patients continued with symptoms and required treatment for the control of symptoms. Finally, a dependent IgE mechanism appears to be implicated in the pathogenesis of OA due to exposure to persulfate salts.

Pathogenesis of Occupational Asthma due to Chemical Sensitizers

Pathogenesis of Occupational Asthma due to Chemical Sensitizers

Evidence for neutrophil activation in occupational asthma.

In order to evaluate the role of neutrophils in the pathogenesis of occupational asthma (OA), 15 toluene diisocyanate (TDI)-asthma and six grain dust-asthma patients were recruited. Controls were the same number of subjects showing negative bronchoprovocation test (BPT) and six house dust mite-sensitive asthma. Bronchoscopic biopsy specimens were stained with monoclonal antibodies to mast cell (AA1), eosinophil (EG2), pan T cell (CD3) and neutrophil (NE). Serum neutrophil chemotactic activity (NCA) was measured before and 10-420 min after BPT. Sputum interleukin-8 (IL-8) and myeloperoxidase (MPO) were also measured. There was a significant increase of NE+ cells as well as AA1+ and EG2+ cells in grain dust- and TDI-asthma compared with house dust-sensitive asthma (P < 0.05). Neutrophil+ cells and AA1+ cells showed a significant correlation in TDI-asthma (r = 0.73, P = 0.02). Serum NCA was significantly increased at 10 min after BPT and decreased at 60 min in subjects with TDI-asthma. In grain dust-asthma, serum NCA increased at 30 min and decreased at 240 min after BPT (P < 0.05). Sputum IL-8 and MPO were significantly increased after BPT in both TDI- and grain dust-asthma (P < 0.05). These findings suggested that neutrophils in the lungs might contribute to bronchoconstriction induced by either TDI or grain dust. The possible involvement of IL-8 in activation of neutrophils was also suggested.

Characterization of histamine releasing factors in diisocyanate-induced occupational asthma

Immunologic mechanisms contributing to diisocyanate-induced occupational asthma (OA) are poorly defined. There is a relatively low incidence of diisocyanate-specific IgE antibody responses. The frequent occurrence of delayed onset asthmatic responses in workers with diisocyanate asthma suggests a role for cellular immune mechanisms. We have shown in vitro production of antigen-specific mononuclear cell-derived histamine releasing factors (HRF) by peripheral blood mononuclear cells (PBMCs) of workers with OA. Monocyte chemoattractant protein-1 (MCP-1) and RANTES (acronym for “regulated on activation normal T expressed and secreted”) are chemokines found in PBMC supernatants that express HRF activity. Diisocyanate-exposed workers were tested for diisocyanate antigen-stimulated enhancement of HRF, MCP-1, and RANTES production in supernatants of PBMCs and for serum specific IgE and IgG antibody levels to diisocyanate antigens bound to human serum albumin (HSA). PBMCs of workers with diisocyanate OA showed significantly increased production of antigen-specific HRF activity and MCP-1 ( >300 ng/ml) compared to diisocyanate-exposed asymptomatic workers ( P < 0.05). Antigen-stimulated enhancement of MCP-1 mRNA was demonstrated by reverse-transcription PCR. RANTES mRNA and chemokine secretion (< 1 ng/ ml) was also demonstrated in PBMCs, but did not show antigen enhancement in OA workers. Hapten specificity for the diisocyanate chemical to which a patient had been exposed was demonstrated for HRF enhancement and for IgG antibody reactions, but not for IgE reactions. HRF production was demonstrated in PBMC subpopulations, including lymphocytes and purified T cells. OA subjects showed increased CD8 + cells by immunofluorescence (mean CD4 +:CD8 + = 1.2 ± 0.2). The results suggest that diisocyanate antigen enhancement of HRF and MCP-1 production are stimulated by hapten-specific T cell reactions. Since a weak association has been found between IgE antibody synthesis and induction of diisocyanate OA, the role of T cell cytokines and chemokines in the pathogenesis of OA requires further investigation.

Immune responses to colophony, an agent causing occupational asthma.

Inhalation of fumes from heated colophony (pine resin) is a recognised cause of occupational asthma, although the mechanisms by which colophony produces symptoms are unclear and specific immune responses to colophony have not been reported in sensitised workers. A study was carried out to determine whether colophony is antigenic. The immune responses to colophony were studied in C57BL/6 mice and Dunkin Hartley guinea pigs after intraperitoneal injection of colophony conjugated to bovine serum albumin (BSA) or human IgG by a mixed anhydride procedure. Colophony and dinitrofluorobenzene were also compared in an assay of dermal sensitisation. Mice immunised with the colophony conjugates produced antibodies which recognised conjugates of both BSA and human IgG irrespective of which had been used as the immunogen. Solutions of unconjugated colophony inhibited the binding of antibodies to the BSA-colophony and BSA-abietic acid conjugates, confirming that the antibodies recognised one or more components in the colophony. Portuguese colophony also abrogated the antigen binding of serum from guinea pigs immunised with the BSA-colophony conjugate. Spleen cells from immunised mice proliferated in the presence of the conjugates. Although there was some cross reactivity in these responses, it was not as marked as in the antibody assays. Unconjugated colophony failed to induce an immune response when injected intraperitoneally with adjuvant. Skin sensitisation could not be induced in mice by topical application, or by subcutaneous or intradermal injection of unconjugated colophony. Colophony components have the potential to act as haptens and an immune component could be involved in the pathogenesis of occupational asthma in workers exposed to colophony. Colophony is not readily immunogenic unless conjugated ex vivo to proteins.