Occupational asthma: a valid model for adult asthma?

Dermal exposure determines the outcome of repeated airway exposure in a long-term chemical-induced asthma-like mouse model

BACKGROUND

Exposure to diisocyanates is an important cause of occupational asthma (OA) in the industrialized world. Since OA occurs after long-term exposure to diisocyanates, we developed a chronic mouse model of chemical-induced asthma where toluene diisocyanate (TDI) was administered at two different exposure sites.

OBJECTIVES

Evaluating the effect of long-term respiratory isocyanate exposure - with or without prior dermal exposure- on sensitization, inflammatory responses and airway hyperreactivity (AHR).

METHODS

On days 1 and 8, BALB/c mice were dermally treated (20 μl/ear) with 0.5% 2,4-toluene diisocyanate TDI or the vehicle acetone olive oil (AOO) (3:2). Starting from day 15, mice received intranasal instillations with 0.1% TDI of vehicle five times in a week, for five successive weeks. One day after the last instillation airway hyperreactivity (AHR) to methacholine was assessed, followed by an evaluation of pulmonary inflammation and structural lung changes. Immune-related parameters were assessed in the lungs (BAL and tissue), blood, cervical- and auricular lymph nodes.

RESULTS

Mice repeatedly intranasally exposed to TDI showed systemic sensitization and a mixed Th1/Th2 type immune response, without the presence of AHR. However, when mice are first dermally sensitized with TDI, followed by repeated intranasal TDI challenges, this results in a pronounced Th2 response and AHR.

CONCLUSION

Dermal exposure to TDI determines airway hyperreactivity after repeated airway exposure to TDI.

Effect of inhaled toluene diisocyanate on local immune response based on murine model for occupational asthma

Highly reactive, low-molecular-weight diisocyanates (DIC) are the most commonly identified cause of occupational asthma (OA). Animal/clinical studies of DIC asthma have been more limited compared with atopic asthma, and an understanding of DIC pathogenesis is less clear. The aim of this study was to investigate in a mouse model, toluene diisocyanate (TDI, as 2,4-TDI isomer)-induced inflammatory reactions/cytokine profile changes in the lungs and accompanying changes in lymph node lymphocyte sub-populations. The study used female BALB/cJ/Han/IMP mice that were exposed first intra-nasally and then in an inhalation chamber to TDI or air. After the final exposure, bronchoalveolar lavage fluid (BALF) was collected and changes induced in inflammatory cell composition, levels of key cytokines (i.e. IL-4, TNFα, IFNγ), and lymphocyte sub-population profiles within auricular lymph nodes, were evaluated. Total number of cells in the BALF of treated mice was significantly higher than in control mice BALF. There was also a significant increase in BALF neutrophil and eosinophil levels with TDI mice compared to in controls; lymphocyte and macrophage numbers did not significantly differ. A significant increase in BALF levels of TNFα and IFNγ was also noted in mice exposed to TDI relative to levels in controls. BALF IL-4 levels were also increased, but the change from control was not significant. Lastly, the levels/percentages of CD3(+)CD4(+) (T-helper [TH]) lymphocytes significantly increased in the lymph nodes of TDI-exposed groups while those of the CD3(+)CD8(+) cells decreased as compared to in control mice. These studies, the first to assess TDI-induced changes in levels of three key cytokines in BALF in conjunction with changes in local lymph nodes following first an intra-nasal and then a general inhalation exposure to a low-level of TDI, confirm that TDI inhalation induces a pathology manifested by airway inflammation, TH cell-derived cytokine production, and shifts in lymph node lymphocytes sub-populations toward increases in TH cells.

Comparative studies of lymph node cell subpopulations and cytokine expression in murine model for testing the potentials of chemicals to induce respiratory sensitization

OBJECTIVES

To investigate immunological changes in lymph nodes based on expression of cell-specific receptors and cytokine expression profile and accompanying inflammatory reactions in lungs of mice treated with chemicals of known potentials to induce respiratory sensitization and those in which activity in this regard is unclear.

MATERIALS AND METHODS

On day 1 and 7, Balb/c mice received toluene-2,4-diisocyanate (TDI), trimellitic anhydride (TMA), 1-chloro-2,4-dinitrobenzene (DNCB), glutaraldehyde (GA), formaldehyde (FA), benzalkonium chloride (ChB) or vehicle. On day 14, they received a single intranasal instillation with the same chemical or vehicle. On day 15, auricular lymph nodes (LN) were excised and used for analyzes of T-, B-cells, expression of CD44 and for the estimation of IL-4 and IFN-gamma production after in vitro stimulation with concanavalin A (ConA) and also for IL-4 and IFN-gamma mRNA expression analyses using Real-Time PCR. Inflammatory changes in lungs were observed by estimation of TNF-alpha and MIP-2 concentrations and cell numbers and their type in BAL.

RESULTS

There were no significant changes in cell subpopulations of T helper cells in LN. The percent of B cells was significantly increased after treatment with DNCB, TDI, and GA. Increased expression of CD44 on T cells was also observed. Both IL-4 and IFN-gamma were found increased in TDI- and FA-treated mice, while only IL-4 was increased in TMA-treated mice. Real-Time PCR analyses, however, showed increased IL-4 mRNA expression for TDI- and TMA-, and IFN-gamma mRNA expression for DNCB-treated mice. We haven't observed significant changes in inflammatory reactions in the lungs of exposed animals.

CONCLUSIONS

Studying immunological changes with first determining the activation status of T cells followed by analyzes of expression of mRNA for Th1 and Th2 cytokines in murine model could be a useful method for assessment of the potentials of chemicals to induce respiratory sensitization but is not sufficient. Addition of ventilatory measurements, but not necessarily inflammatory reactions, could complete the model.

Occupational exposures and adult asthma

Occupational exposures can cause a new onset of asthma in a subset of susceptible workers on the basis of sensitization to a specific work agent or a high-level irritant exposure. Epidemiologic studies give insight into the natural history of occupational asthma, including host factors and environmental factors leading to the development of occupational asthma, the progression, and the potential role of preventive measures. Work-exacerbated asthma has been a focus of studies only recently but is recognized as common among asthmatic workers and is a potential cause of significant morbidity and socioeconomic impact.

Airway inflammation and bronchial remodelling in toluene diisocyanate-exposed BALB/c mouse model

Toluene diisocyanate (TDI), a highly reactive industrial chemical, is one of the leading causes of occupation-related asthma in industrialized countries. The pathogenesis of TDI-induced asthma, however, remains not fully understood, in part due to lack of appropriate animal models. Twenty five female BALB/c mice (age: 8 weeks) were randomly divided into 5 groups: Ovabumin (OVA); OVA peptide amino acid residues No. 323-339 (Pep); TDI; alum and physiological saline. Mice were intraperitoneally injected with 25 microg OVA or pep absorbed on 300 microg alum, 300 microg alum or saline on days 0, 7 and 14. For the TDI group, mice were sensitized subcutaneously with 20 microl neat TDI on day 0; 20 microl of TDI in olive oil (1:10) on days 7 and 14; on days 21-23. Then each group was challenged intranasally with 20 microl of 1% OVA, 1% Pep, 1% TDI, 10% alum and saline respectively. On day 28, mice were killed under pentothal anesthesia. The results demonstrated that neutrophil-dominant inflammation with a few eosinophil infiltration occurred in the peri-bronchial and peri-vascular regions of the lungs. This was accompanied by hyperplasia/hypertrophy of cells lining the airways and mucus production as shown by HE staining. Positive immunohistochemical MBP staining in parenchyma was also shown. Th2 cytokine IL-4 and IgE production were significant increased 5 days after last challenge while IFN-gamma level was below the detection limit.

CONCLUSION

the clear elevation of IL-4 and IgE could allow to conclude a possible Th2-like dominated allergic response in TDI-exposed BALB/c mouse model.

Airway hyperresponsiveness and risk of chest symptoms in an occupational model

BACKGROUND

The clinical outcome of asymptomatic airway hyperresponsiveness (AHR) remains unclear. A study was undertaken to evaluate the incidence of respiratory symptoms in a cohort of asymptomatic subjects with AHR at baseline.

METHODS

A 3 year prospective study involving methacholine challenge tests and serially administered questionnaires was undertaken in 769 apprentices exposed to high molecular weight allergens. Analyses were performed on 428 initially asymptomatic subjects.

RESULTS

Thirty eight subjects (8.9%) were airway hyperresponsive (PC(20) < or =8 mg/ml) and asymptomatic at the start of the study. Forty four apprentices (10.3%) developed two or more respiratory symptoms unrelated to work, 13 (34.2%) in the AHR group and 31 (7.9%) in the non-AHR group (risk ratio (RR) 7.88 (95% CI 2.53 to 24.55) among subjects with AHR). The RR of developing two or more respiratory symptoms increased as the degree of PC(20) decreased with a significant trend (p<0.001). In a multivariate analysis, AHR (RR 8.33, 95% CI 2.65 to 26.16) and self-reported rhinitis on exposure to pollen through an interaction with a family history of asthma (RR 6.3, 95% CI 1.29 to 31.89) were associated with the incidence of two or more respiratory symptoms; atopy was not a significant covariate.

CONCLUSION

AHR in asymptomatic subjects is an important determinant for the development of respiratory symptoms outside the workplace among apprentices exposed to high molecular weight allergens in their training environment.

Animal models to test respiratory allergy of low molecular weight chemicals: a guidance

At present, there are no widely applied or fully validated test methods to identify respiratory LMW allergens, i.e. compounds that are considered capable of inducing allergic asthma. Most tests have been investigated using strong respiratory allergens. Moreover, they are meant to detect the potential of a chemical to induce respiratory sensitisation at relatively high doses. Consequently, the sensitivity of the tests is not well-known, and they do not provide information on low doses such as generally found in occupational situations, and on threshold levels to be used in risk assessment. In addition, the various test methods use different application routes, i.e. intradermal, topical or inhalation exposure, and different parameters. Therefore standardised and validated dose-response test methods are urgently required in order to be able to identify respiratory allergens and to recommend safe exposure levels for consumers and workers. In the present paper, methods or testing strategies are described to detect respiratory sensitisation and/or allergy. Overall, assays that utilize only an induction phase may serve as indicators of respiratory sensitisation potential whereas assays that use both an induction and an elicitation or challenge phase may provide information on potency and presence of thresholds. The dermal route as sensitisation route has the advantage of the respiratory tract not being exposed to the allergen prior to challenge which facilitates the distinction between irritant and allergic effects.

Control chart for monitoring occupational asthma

INTRODUCTION

Work-related asthma has become the most prevalent occupational respiratory disease in the developed world. Occupational asthma is thought to affect 5%-10% of people worldwide. The first step in the diagnosis of occupational asthma is to establish work-relatedness. Although considerable research has been conducted in the area of occupational asthma, no simple, effective, and statistically sound method has been developed that can be used as an initial step to effectively identify the workers at risk for occupational asthma. The purpose of this research was to investigate whether Shewhart control chart method can be used as an effective method to detect occupational asthma.

METHOD

Forty-five workers who completed the study and provided usable peak expiratory flow (a lung function marker) recordings while at work and away from work were included in this study. Control charts were developed using Shewhart's Method. The lower control limit of at work control chart (LCL(W)) was compared to each subject's Personal Best (PB) value.

RESULTS

Reviewing the results of this comparison showed LCL(W)<60% PB to have a sensitivity of 85.71%, specificity of 87.50%, and an error rate of 13.33%. When the subjects suspected for false positive and false negative diagnoses were identified, the test produced a sensitivity of 95.24%, a specificity of 95.83% and an error rate of 4.44%.

CONCLUSIONS

Our results were as good as, and in some cases better than, published clinical guidelines.

IMPACT ON INDUSTRY

Our research showed that the control chart method is an effective, simple, and inexpensive tool for early intervention in workers suspected for occupational asthma.

Occupational asthma

Substantial epidemiologic and clinical evidence indicates that agents inhaled at work can induce asthma. In industrialized countries, occupational factors have been implicated in 9 to 15% of all cases of adult asthma. Work-related asthma includes (1) immunologic occupational asthma (OA), characterized by a latency period before the onset of symptoms; (2) nonimmunologic OA, which occurs after single or multiple exposures to high concentrations of irritant materials; (3) work-aggravated asthma, which is preexisting or concurrent asthma exacerbated by workplace exposures; and (4) variant syndromes. Assessment of the work environment has improved, making it possible to measure concentrations of several high- and low-molecular-weight agents in the workplace. The identification of host factors, polymorphisms, and candidate genes associated with OA is in progress and may improve our understanding of mechanisms involved in OA. A reliable diagnosis of OA should be confirmed by objective testing early after its onset. Removal of the worker from exposure to the causal agent and treatment with inhaled glucocorticoids lead to a better outcome. Finally, strategies for preventing OA should be implemented and their cost-effectiveness examined.