Time course of the increase in airway responsiveness associated with late asthmatic reactions to toluene diisocyanate in sensitized subjects

To understand better the mechanism of the increase in airway responsiveness associated with late asthmatic reactions, we determined the time course of toluene diisocyanate (TDI) effect on airway responsiveness in six sensitized subjects who exhibited a late asthmatic response after TDI exposure (0.018 +/- 0.005 ppm, 30 min) in the laboratory. Airway responsiveness was assessed before TDI exposure and then at 8 hr, 1 day, 1 wk, and 1 mo after TDI exposure. To assess responsiveness we determined the provocative dose of methacholine causing a decrease in FEV1 of 20% (PD20FEV1). The methacholine PD20 decreased from 0.50 mg geometric standard error of the mean (GSEM = 1.54) to 0.06 mg (GSEM = 1.55) (p less than 0.001) at 8 hr after exposure to TDI, was still decreased to 0.15 mg (GSEM = 1.93) (p less than 0.05) at 1 day, returned to 0.26 mg (GSEM = 1.91) (p greater than 0.05) at 1 wk, and returned to 0.43 mg (GSEM = 1.71) at 1 mo, indicating that full recovery occurred within 1 to 4 wk. These results demonstrate that TDI-induced late asthmatic response is associated with a reversible increase in airway responsiveness to methacholine and suggest that the TDI effect is linked to an acute inflammatory response in the airways.     

Dexamethasone isonicotinate inhibits dual and late asthmatic reactions but not the increase of airway responsiveness induced by toluene diisocyanate in sensitized subjects

To determine whether treatment with aerosolized dexamethasone isonicotinate inhibits asthmatic reactions and the associated increase in airway responsiveness induced by toluene diisocyanate (TDI), we studied six sensitized subjects with previously demonstrated dual or late asthmatic reaction after inhalation challenge with TDI. Dexamethasone isonicotinate (four puffs bid for seven days, ie, 0.5 mg bid for seven days; last four puffs 30 minutes before TDI) was administered for seven days before the inhalation challenge with TDI (0.010 to 0.015 ppm for 10 to 30 minutes) to each subject, according to a single-blind study design. When the subjects received no treatment, FEV1 markedly decreased and airway responsiveness increased after exposure to TDI. By contrast, when the subjects were treated with dexamethasone-isonicotinate, FEV1 decreased significantly less, but airway responsiveness still significantly increased after exposure to TDI. These results suggest that aerosolized dexamethasone isonicotinate may be used in the prophylaxis of TDI-induced late asthmatic reactions.     

Influence of natural exposure to pollens and domestic animals on airway responsiveness and inflammation in sensitized non-asthmatic subjects

BACKGROUND: Atopy may be a risk factor in the development of asthma. Indoor allergens are considered to be more potent asthma inducers than outdoor ones such as pollens. Lower airway inflammation may be present in non-asthmatic subjects during natural exposure to relevant allergens and may eventually lead to the development of asthma. AIMS: To document seasonal variation in lower airway responsiveness and inflammation in sensitized non-asthmatic subjects, during natural exposure to allergens, and to determine whether it is more marked in those exposed to animals to which they are sensitized. METHODS: Twenty-two atopic subjects were seen during and out of the pollen season. All (but the controls) were sensitized to domestic animals, and to trees, grasses or ragweed. Eleven were not exposed to animals at home and 8 were exposed. They were compared with 3 normal controls. A respiratory questionnaire was administered, allergy skin prick tests, spirometry, methacholine challenge, blood and induced sputum with differential cell counts were obtained during the pollen season for all subjects. These tests were repeated out of the pollen season. RESULTS: Throughout the study, none of the subjects had asthma symptoms. Mean PC(20) was significantly lower in subjects exposed to animals compared with unexposed subjects or controls, both during and out of the pollen season. In season, subjects exposed to animals had significantly higher sputum eosinophil numbers than unexposed or normal control subjects. CONCLUSIONS: Non-asthmatic atopic subjects show variable degrees of airway responsiveness and inflammation. However, subjects exposed to animals show higher airway eosinophilia, which may suggest they are at increased risk of developing airway hyperresponsiveness and asthma.     

Immunologic and respiratory responses to airway challenges of dogs with toluene diisocyanate

Dogs received biweekly or monthly aerosol immunization with single'doses of taluene diisocyanate (TDI) that were cumulative doses analogous to human chronic exposure at 0.02 ppm. The three dogs developed systemic immune responses to TDI-dog serum albumin (DSA). The immune responses included IgG, IgA, and IgM antibody, responses and development of lymphocyte reactivity. IgA titers approached IgG titers and both were persistent, whereas IgM titers were low and of f. short duration. IgE antibody titers demonstrated by endpoint cutaneous titration appeared but fluctuated and became negative in spite of continued aerosol exposure of TDI. Immediate-type airway responses occurred afier TDI aerosolization. Some limited responses that showed only abnormalities of selected pulmonury.function parameters were clearly not immunologically mediated because they occurred with initial exposure. Other immediate-type airway responses occurred that qualitatively simulated IgE-mediated, antigen-induced airway responses in dogs. There was a statistically significant correlation (p = 0.0268) between these latter airway responses and immediate-type skin reactivity. This study demonstrates that this dog model simulates the complexity of airway responses to TDI in man but may provide a laboratory system for evaluation of immunologic or other proposed mechanisms of TDI asthma.     

Eosinophil cationic protein (ECP), histamine and tryptase in peripheral blood before and during inhalation challenge with toluene diisocyanate (TDI) in sensitized subjects

To determine whether the measurement of specific markers of inflammatory cells in peripheral blood might be used to detect the inflammatory activity in the airways in asthma induced by toluene diisocyanate (TDI). we measured the levels of eosinophil cationic protein (ECP), histamine and tryplase in peripheral blood before and during inhalation challenge with TDI or methacholine in two groups of subjects who exhibited or did not exhibit an asthmatic reaction after exposure to toluene diisocyanate in the laboratory. When the subjects developed a late asthmatic reaction after exposure to TDI, the\ showed an increase in their ECP serum levels. By contrast, there were no signilicam changes in serum ECP levels after exposure to TDI in the control group or after methacholine challenge in either group. Tryptase levels in serum were not detectable before or during inhalation challenge with TDI or methacholinc. There was no significant increase in plasma histamine levels during inhalation challenge with TDJ or methacholine. These results suggest that eosinophils arc ‘activated’ in subjects who develop a late asthmatic reaction after exposure to TDI and that the measurement of ECP levels in peripheral blood may be a useful marker to monitor airway inflammation.     

Increase in the level of histidine decarboxylase mRNA expression in nasal mucosa of rats sensitized by toluene diisocyanate

Inflammation Research -     

Ketotifen does not inhibit asthmatic reactions induced by toluene di-isocyanate in sensitized subjects

In order to determine whether treatment with ketotifen inhibits asthmatic reactions induced by toluene di-isocyanate (TDI), we studied six sensitized subjects with previously demonstrated dual or late asthmatic reaction after inhalation challenge with TDI. Ketotifen (1 mg b.i.d., orally) or placebo was administered for 7 days to the examined subjects, according to a double-blind, cross-over, placebo-controlled study design. When the subjects were treated with either ketotifen or placebo, FEV1 markedly decreased after exposure to TDI. These results suggest that the anti-asthmatic agent ketotifen is not effective in TDI-induced asthma and suggest that it should not be used in the prophylaxis of asthmatic reactions induced by TDI in sensitized subjects.     

Bronchial responsiveness to methacholine during airway cooling in normal subjects

In order to investigate the effects of airway cooling on bronchial responsiveness in normal subjects, we measured bronchial responsiveness to inhaled methacholine with and without the inhalation of cold air. Two out of seven subjects showed an increase in baseline respiratory resistance (Rrs) during cooling of the airway but the other five subjects showed little change in their baseline Rrs. All subjects increased bronchial responsiveness to methacholine. Additionally, the threshold dose of methacholine decreased to one-third of the control dose with cooling of the airway. We speculate that airway cooling increased bronchial responsiveness to methacholine in normal subjects presumably due to increased vagal tone, increased alpha-adrenergic activity and/or a release of chemical mediators.     

Importance of inflammatory and immune components in a mouse model of airway reactivity to toluene diisocyanate (TDI)

BACKGROUND: Nearly 9 million individuals are exposed to agents in the workplace associated with asthma, and isocyanates represent the most common cause of occupationally induced asthma. OBJECTIVES: Nonetheless, the immunological mechanisms responsible for isocyanate-induced asthma are not clear. A murine model for toluene diisocyanate (TDI) asthma is described and employed to examine inflammatory and immune components that may be involved in the disease. METHODS: Groups (n = 6) of C57BL/6J and athymic mice were sensitized by subcutaneous injection (20 microl on day 1, 5 microl on days 4 and 11), and 7 days later challenged by inhalation (100 p.p.b., days 20, 22 and 24) with TDI. Twenty-four hours following the last challenge the tracheae and lungs were examined for histological changes as well as for the expression of Th1, Th2 and pro-inflammatory cytokines. Mice were also examined for airway reactivity to methacholine challenge and for specific and total IgE and IgG antibodies. RESULTS: TDI sensitization resulted in increased reactivity to methacholine challenge as well as a significant inflammatory response in the trachea and nares of wild-type mice, but not in the athymic mice nor in the lungs of the C57BL/6J mice. Airway inflammation was characterized by inflammatory cell influx, goblet cell metaplasia and epithelial damage. Histological changes in the trachea were accompanied by increased mRNA expression of interleukin (IL)-4, tumour necrosis factor alpha, lymphotoxin beta, lymphotactin and Rantes, as well as TDI-specific IgG antibodies and elevated levels of total IgE. IgE-specific antibodies were not detected with this exposure regimen but were produced when the TDI concentrations were increased. CONCLUSIONS: These studies provide a unique murine model for occupational asthma that generates both inflammatory and immune mediators similar to those occurring in TDI-induced asthma in humans.     

Role of tumor necrosis factor in toluene diisocyanate asthma

Nearly 9 million workers are exposed to chemical agents associated with occupational asthma, with isocyanates representing the chemical class most responsible. Isocyanate-induced asthma has been difficult to diagnose and control, in part because the biologic mechanisms responsible for the disease and the determinants of exposure have not been well defined. Isocyanate-induced asthma is characterized by airway inflammation, and we hypothesized that inflammation is a prerequisite of isocyanate-induced asthma, with tumor necrosis factor (TNF)-alpha being critical to this process. To explore this hypothesis, wild-type mice, athymic mice, TNF-alpha receptor knockout (TNFR), and anti-TNF-alpha antibody-treated mice were sensitized by subcutaneous injection (20 micro l on Day 1; 5 micro l, Days 4 and 11), and challenged 7 d later by inhalation (100 ppb; Days 20, 22, and 24) with toluene diisocyanate (TDI). Airway inflammation, goblet cell metaplasia, epithelial cell damage, and nonspecific airway reactivity to methacholine challenge, measured 24 h following the last challenge, were reduced to baseline levels in TNF-alpha null mice and athymic mice. TNF-alpha deficiency also markedly abrogated TDI-induced Th2 cytokines in airway tissues, indicating a role in the development of Th2 responses. Despite abrogation of all indicators of asthma pathology, TNF-alpha neutralization had no effect on serum IgE levels or IgG-specific TDI antibodies, suggesting the lack of importance of a humoral response in the manifestation of TDI-induced asthma. Instillation studies with fluorescein-conjugated isothiocyanate and TDI suggested that TNF-alpha deficiency also resulted in a significant reduction in the migration of airway dendritic cells to the draining lymph nodes. Taken together, these results suggest that, unlike protein antigens, TNF-alpha has multiple and central roles in TDI-induced asthma, influencing both nonspecific inflammatory processes and specific immune events.     

Radioallergosorbent testing with p-tolyl monoisocyanate in toluene diisocyanate workers

Sera from 149 occupationally exposed toluene diisocyanate (TDI) workers were tested by RAST with p-tolyl monoisocyanate human serum albumin (TMI-HSA). Of the seven positives, one had a history suggestive of TDI asthma and one had a rash which may have been TDI related. These results indicate that false positive RAST with TMI-HSA may occur in asymptomatic workers.     

Allergen-induced changes in airway responsiveness are related to baseline airway responsiveness

In the literature, bronchial allergen challenge is usually reported to result in an increase in histamine-induced airway responsiveness (AR). The present study investigated the relation between baseline AR and allergen-induced changes in AR. The effect of allergen challenge on AR was investigated in 21 atopic asthmatic patients. Allergen challenge resulted in a significant decrease in PC₂₀ histamine after 24 h. When the group was divided into three subgroups according to baseline PC₂₀ histamine, a significant decrease in PC₂₀ histamine was found only in patients with relatively high baseline PC₂₀ histamine (groups 1 and 2). A significant inverse correlation was found between baseline PC₂₀ and allergen-induced PC₂₀ histamine. The effect of repeated allergen challenge on AR was studied in eight patients. The first allergen challenge resulted in a significant decrease in PC₂₀ histamine; no further decrease in mean PC₂₀ histamine was seen after the second allergen challenge. These results suggest that allergen-induced changes in AR occur mainly in patients with relatively high baseline PC₂₀ values. Once an increase in AR is induced, further allergen challenge does not always result in further increase in AR.     

Inflammatory cells and eicosanoid mediators in subjects with late asthmatic responses and increases in airway responsiveness

To determine the relationship of inflammatory cells and eicosanoid mediators to the pathogenesis of the late asthmatic response (LAR) and increases in nonspecific airway responsiveness, we studied bronchoalveolar lavage (BAL) cells and fluid in 27 subjects 12 hours after inhaled antigen challenge. Methacholine challenge was performed before antigen challenge and 24 hours later (12 hours after BAL). Eight subjects had no LAR (-LAR, less than or equal to 10% fall in FEV1), nine subjects had an equivocal LAR (+/- LAR, 11% 25% fall in FEV1), and 10 subjects had a definite LAR (+LAR, greater than 25% fall in FEV1). Subjects developing +LAR had increased airway responsiveness at baseline compared with that of subjects developing an +/- LAR, but not with subjects having -LAR. If airway responsiveness was markedly increased at baseline, further increases after antigen challenge were often not observed. We found that both percent neutrophils and eosinophils increased in BAL as the severity of the LAR increased, but significant differences between the groups with -LAR and +LAR were only observed when both cell types were considered together. In addition, there was a significant correlation between the combined cell percentages and the severity of the LAR as determined by fall in FEV1. Likewise, increases in airway responsiveness were associated with significant increases in both neutrophil and eosinophil numbers, but only neutrophils correlated with the change in airway responsiveness after antigen challenge. However, despite the significant physiologic and cellular differences that we found between our groups, no significant differences could be found in BAL eicosanoid-mediator concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Eosinophilic inflammation, remodeling of lower airway, bronchial responsiveness and cough reflex sensitivity in non-asthmatic subjects with nasal allergy

BACKGROUND: It has been reported that nasal allergy influences the lower airway inflammation and functions. We elucidated whether nasal allergy would contribute to lower airway inflammation and functions. METHODS: 266 subjects aged 21-39 years were interviewed with special emphasis on history of asthma and nasal allergies (perennial allergic rhinitis (PAR) and seasonal allergic rhinitis (Japanese cedar pollinosis; PO)). Symptomatic subject was defined when nasal symptoms were present during a 3-week study period. Pulmonary function, provocative concentration of methacholine causing a 20% fall in forced expiratory volume in 1 s (PC20), capsaicin cough threshold defined as capsaicin concentration eliciting 5 or more coughs (C5) and eosinophil percentage in hypertonic saline-induced sputum were measured. RESULTS: Based on the interview, 232 subjects without asthma were divided into symptomatic (n = 25) and asymptomatic (n = 22) PAR, PO on-season (n = 15) and off-season (n = 36), and non-nasal allergy subjects (control) (n = 134). Sputum eosinophils were significantly greater in symptomatic PAR than another four groups (p < 0.01). FEV1/FVC ratio was significantly lower in PAR than control (p < 0.05). Maximum mean expiratory flow was lower in PAR than control (asymptomatic: p < 0.05, symptomatic: p = 0.06). C5 was not different among groups. PAR tended to have a lower PC20 compared to control (symptomatic: p = 0.078; asymptomatic: p = 0.086). CONCLUSIONS: These results suggest that eosinophilic inflammation occurred in symptomatic period of PAR may contribute to development of lower airway remodeling and bronchial hyperresponsiveness. Reversely, PO may not be associated with lower airway eosinophilic inflammation or abnormal bronchial functions. Nasal allergy dose not influence the cough reflex sensitivity.     

The effects of inhaled leukotriene E4 on the airway responsiveness to histamine in subjects with asthma and normal subjects

Eight subjects with asthma inhaled on separate occasions leukotriene E4 (LTE4) (6.1 nmol, geometric mean), methacholine, and diluent, which produced an average 41.0%, 37.0%, and 3.3% decrease in specific airway conductance (SGaw), respectively. When the SGaw had recovered to baseline levels at 60 minutes after challenge, the provocative dose of inhaled histamine that produced a 35% decrease in SGaw (PD35) was determined. The histamine PD35 observed after inhalation of LTE4 was 0.46 mumol, and this was significantly less than the histamine PD35 observed after inhalation of methacholine (0.88 mumol; p less than 10(-4) and diluent (0.97 mumol; p less than 10(-5). Histamine responsiveness was also enhanced by a fiftyfold lower dose of LTE4 (p = 0.005), and the enhancement was less than that elicited by the higher dose of LTE4 in the same individuals (p = 0.02). The changes in histamine PD35 during a 1-week period after LTE4 and methacholine challenges were compared in four subjects with asthma. There was a time-dependent enhancement in histamine responsiveness that reached a maximal of 3.5-fold at 7 hours after LTE4. The enhancement had disappeared by 1 week. Similar changes were not observed after methacholine challenge, which elicited the same degree of bronchoconstriction as LTE4. Inhalation of LTE4 in five normal subjects that produced a mean 37.6% decrease in SGaw did not change histamine responsiveness for up to 7 hours. These findings suggest that LTE4 may play a role in the perpetuation of nonspecific airway hyperresponsiveness in bronchial asthma.     

Development and loss of toluene diisocyanate reactivity: immunologic,pharmacologic, and provocative challenge studies

Toluene diisocyanate (TDI) sensitivity accompanied by nonspecific bronchial hyperresponsiveness occurs in approximately 5% of occupationally exposed workers. We report the case of a 32-yr-old worker followed longitudinally after removal from isocyanate exposure. TDI reactivity was lost 11 mo after removal from exposure and nonspecific bronchial hyperresponsiveness resolved after 17 mo. Bronchial reactivity to radishes (Raphanus sativus), which developed concurrently with TDI reactivity, was lost 2 yr later. Immunopharmacologic results show that the worker's initial decreased ability of lymphocytes to produce cyclic AMP returned to near normal after 2 yr. IgE antibodies to a human serum albumin tolyl monoisocyanate conjugate were still present at this time.     

Significant changes of bronchial responsiveness to methacholine after early asthmatic reaction to toluene diisocyanate (TDI) in a TDI-sensitive asthmatic worker

Current asthma is often diagnostically excluded by the presence of normal bronchial responsiveness. We report on a TDI-induced occupational asthma patient with normal bronchial responsiveness. He had suffered from shortness of breath during and after TDI exposure for several months. His initial methacholine bronchial challenge test showed a negative response. The bronchoprovacation test with TDI showed an isolated immediate bronchoconstriction. The following methacholine bronchial challenge tests revealed that the bronchial hyperresponsiveness developed seven hours after the TDI challenge (methacholine PC20:5.1 mg/ml), progressed up until 24 hours, and returned to normal on the seventh day. This case provides evidence that the response of the airway to TDI may not always be accompanied by bronchial hyperresponsiveness to methacholine. Screening programs utilizing methacholine challenges may not always identify TDI-sensitized asthmatic workers.     

Allergen-induced increase in airway responsiveness, airway eosinophilia, and bone-marrow eosinophil progenitors in mice.

Increases in bone-marrow (BM) inflammatory cell progenitors are associated with allergen-induced airway hyperresponsiveness and inflammation in asthmatics and dogs. Here, for the first time, we compare the time course of airway hyperresponsiveness, inflammation, and marrow progenitor responses in a mouse model of airway allergen challenge. Sensitized BALB/c mice were studied at 2, 12, 24, 48, and 72 h after intranasal ovalbumin or saline challenges. Outcome measurements included airway responsiveness, airway inflammation as assessed via bronchoalveolar lavage (BAL) and lung tissue sections, and BM eosinophil colony-forming units (Eo-CFU) as enumerated using a semisolid culture assay with optimal concentrations of interleukin-5. We observed significant increases in BAL fluid eosinophils, neutrophils, lymphocytes, and macrophages by 2 h after the second of two intranasal allergen challenges (P < 0.05). Significant increases in airway responsiveness or BM Eo-CFU were observed at 24 h and persisted until 48 h after the second challenge (P < 0.05). Airway inflammation, including eosinophils, persisted until at least 72 h (P < 0.05). We observed that allergen-induced airway eosinophilia is accompanied by increases in BM eosinophil progenitors, indicating that in this model, increased eosinophil production involves an expansion of the relevant stem-cell population. These findings support the use of this model to explore the mechanisms of increased eosinopoiesis observed in human asthma.