Toluene diisocyanate pulmonary disease: immunopharmacologic and mecholyl challenge studies

Role of tachykinins and neutral endopeptidase in toluene diisocyanate-induced bronchial hyperresponsiveness in guinea pigs

The role of tachykinins in toluene diisocyanate (TDI)-induced non-specific bronchial hyperreactivity (NSBH) in guinea pigs was investigated, and it was determined whether or not the activity of airway neutral endopeptidase (NEP) was inhibited in conditions where a bronchial hyperreactivity to acetylcholine (ACh) was observed. Exposures to 3 ppm TDI for 1 h, or to 0.029 ppm for 8 weeks caused a significant bronchial hyperreactivity to ACh. The depletion of tachykinins by a pretreatment with capsaicin (140 mg/kg) eliminated the TDI-induced airway hyperresponsiveness in both patterns of exposure to TDI. Capsaicin treatment had no effect on the response to ACh in guinea-pigs exposed to air (controls). Bronchial NEP activity determined by histoenzymology was significantly less 4 and 24 h after the end of a 1-h exposure to 3 ppm TDI than after exposure to air. Bronchial NEP activity evaluated 24 h after the end of a 48-h exposure to 0.116 ppm TDI, or a 1-week exposure to 0.050 ppm TDI was not significantly different from those of controls exposed to air, whereas in the same conditions of exposure a NSBH is observed in guinea-pigs. These data suggest that tachykinins released from C-fibers upon acute or repeated exposures to high or low concentrations of TDI, respectively, play an essential role in the observed bronchial hyperreactivity, and that the inhibition of NEP by TDI cannot completely account for the observed airway hyperreactivity.

Bronchial responsiveness and inflammation in guinea-pigs exposed to toluene diisocyanate: a study on single and repeated exposure

The question of whether or not toluene diisocyanate (TDI)-induced airway hyperresponsiveness in the guinea-pig is accompanied by neutrophil influx into bronchoalveolar lavage fluid (BALF) was addressed. Two modes of exposure were studied; (1) acute exposures where animals were exposed to 3 ppm TDI for 1 h and experiments were carried out 30 min, 4 h, 24 h, 48 h and 1 week after the TDI exposures; (2) subacute exposures where animals were exposed to 0.080 and 0.046 ppm TDI for 48 h 1 week, respectively, and experiments were carried out 24 h after the TDI exposures. The changes in airway responsiveness to increasing doses of intravenous acetylcholine (ACh) in anaesthetized and tracheotomized spontaneously breathing guinea-pigs were examined. In order to elucidate the possible relationships of airway responsiveness to cellular infiltration, bronchoalveolar lavage was performed in additional group of guinea-pigs exposed to the same conditions. After acute exposure to 3 ppm TDI, increased bronchial responsiveness was evident within 30 min, lasted 48 h, but had vanished 1 week after the exposure. An influx of neutrophils occurred into the BALF within 1 h after exposure. The influx of neutrophil into BALF lasted 48 h and vanished 1 week after the end of exposure. After 48 h of exposure to TDI at 0.080 ppm, or 0.046 ppm for 1 week, increased bronchial responsiveness was evident 24 h after the end of the both modes of exposure, but no influx of neutrophils was observed into the BALF. It was concluded that even though the neutrophil influx and hyperresponsiveness evolve in the same way after acute exposure to a high concentration of TDI (3 ppm), this is not the case after subchronic exposure to low concentrations of TDI, where a bronchial hyperresponsiveness is observed without detectable neutrophil influx.

Setting acceptable exposure limits for toluene diisocyanate on the basis of different airway effects observed in animals

Little epidemiological data are available to enable the development of a dose-response relationship for the effects of isocyanates, powerful sensitizing agents in humans. Remarkably, most classes of effects have been reproduced in some animal models and parallels between animals and man are impressive. In this paper animal data concerning different effects of TDI on the respiratory system were used to calculate acceptable exposure levels for humans. Animal data on respiratory irritation, sensitization, airway hyperresponsiveness, and gradual loss of pulmonary function are discussed. Two different approaches for extrapolation to man were applied to these data. The two models used to extrapolate animal data to man gave similar results. The extrapolations lead to acceptable exposure varying from 6 to 46 ppb. Most international acceptable levels for occupational airborne TDI exposure are within this range. Interestingly, the lowest standard is obtained using the data on respiratory irritation. It is, however, concluded that there is no critical (adverse) effect to define acceptable toluene diisocyanate exposure since the data were obtained from different studies and the accuracy of the applied extrapolation approach might depend on the biological effect considered. We recommend prior testing of "alternative" diisocyanates in one of the animal models described and calibrated for TDI.

Peripheral eosinophilia and respiratory symptoms in rubber injection press operators: a case-control study

To evaluate a suspected association between an outbreak of acute respiratory illness and eosinophilia and employment as a rubber worker, we performed a retrospective review of medical records of rubber workers employed from September 1983 to July 1984 in a plant housing a thermoinjection process. Twenty-five workers met the case definition of a respiratory illness requiring a physician visit. The predominant respiratory illness was acute in onset with cough, chest tightness, and dyspnea. Peripheral eosinophilia, up to 40% of white blood cells in a peripheral smear, was seen in 10 of 18 (56%) cases. Twenty-one of 25 white males with respiratory symptoms were employed in the thermoinjection process (odds ratio = 22, p less than .001). Smoking and employment in this process contributed independently to an increased risk of being a case as determined by a logistic regression analysis. Return to the plant building caused recurrence of symptoms in most cases, and these workers have been transferred or left the company. We conclude that a strong previously unrecognized association exists between employment in this neoprene rubber thermoinjection process and the development of an acute respiratory illness.

Respiratory effects of inhaled isocyanates

Numerous industrial chemicals are known to cause allergic reactions in the lung. Prominent among such chemicals are isocyanates, the starting material in the production of polyurethanes. In view of the extensive worldwide production of isocyanates (1.5 million metric tons per year), and the diversity of products manufactured from isocyanates (i.e., cars, airplanes, furniture, bedding, etc.) there is considerable potential for adverse health effects associated with exposure to isocyanates. Syndromes of immediate respiratory reactivity, delayed-onset sensitivity, and hypersensitivity pneumonitis have all been associated with isocyanate exposure. However, little is known concerning how sensitivity develops, which individuals are most likely to become sensitized, or how to best detect early sensitivity. Answers to such questions are beginning to emerge from the recent development of animal models of lung sensitivity. These models will be discussed together with their application to clinical situations.

A study of serum antibody activity in workers with occupational exposure to diphenylmethane diisocyanate

The prevalence of sensitization was studied in a group of 76 foundry workers with occupational exposure to diphenylmethane diisocyanate (MDI). Ten workers had clinical evidence of asthma, 40 had non-asthmatic respiratory symptoms, and 26 were asymptomatic. Specific IgE antibodies to MDI were found in two workers (2.6%) and specific IgG antibodies, in five workers (6.6%). The prevalence of IgE and IgG antibodies was higher in the 10 subjects with asthma than in the non-asthmatic group. The prevalence of anti-paratolyl-monoisocyanate antibodies was not significantly different from that of anti-MDI antibodies, and both haptenic determinants displayed a high degree of cross-reactivity in the RAST inhibition test. The role of humoral immunological mechanisms in MDI-induced asthma is unclear in view of the rather low prevalence of these serum antibodies in this group of workers.

Occupational asthma caused by a plastics blowing agent, azodicarbonamide

A prevalence study of occupational asthma was carried out by questionnaire in 1980 among a group of 151 workers who had been exposed to azodicarbonamide dust in the process of its manufacture. Twenty-eight (18.5%) people without previous asthma gave a history of episodes of late onset asthma after exposure to azodicarbonamide. Re-exposure caused repetition and worsening of symptoms. Immediate removal from further exposure resulted in rapid cessation of symptoms without further recurrence. Seven of 13 sensitised individuals who were still exposed three months after the onset of disease developed prolonged airways hyperreactivity to common environmental irritants. Azodicarbonamide should be excluded as a causative agent in plastics and rubber industry workers complaining of occupational asthma.

Toluene di-isocyanate-induced asthma. II. Inhalation challenge tests and bronchial reactivity studies

In sixty-three workers exposed to toluene di-isocyanate (TDI), no overall differences in bronchial reactivity to histamine inhalation and to exercise testing were found between the total groups of positive and negative TDI reactors to provocation tests. A subgroup of TDI highly sensitive subjects reacting to very low concentrations (less than or equal to 0.001 p.p.m.) were more sensitive to both histamine and exercise than the group who were less sensitive to TDI, and who reacted to higher concentrations (0.002--0.02 p.p.m.) than the group of non-reactors. There were, however, in the last group a number of subjects with high degrees of histamine reactivity who did not react to the TDI. These findings suggest that, on the one hand, the asthmatic reactions to TDI cannot be attributed solely to non-specific mechanisms and, on the other, that in subjects with high degrees of specific sensitivity non-specific mechanisms may also be playing a part.

Allergen-induced increase in non-allergic bronchial reactivity

Non-allergic bronchial hyper-reactivity is a feature of most patients with asthma. We have measured non-allergic bronchial reactivity to inhaled histamine and methacholine in thirteen asthmatic subjects before and after allergen inhalation in the laboratory. The allergen inhalation produced mild early asthmatic responses (19-40% FEV1 fall) in all thirteen, additional definite late asthmatic responses (17-29% FEV1 fall) in four, and equivocal late asthmatic responses (5-11% FEV1 fall) in five. Following allergen inhalation, non-allergic bronchial reactivity increased in seven for up to 7 days. The seven included all four with definite late asthmatic responses and three of the five with equivocal late asthmatic responses. We conclude that allergens make asthma worse, partly through non-allergic mechanisms, and that avoidance of allergens is important in reducing non-allergic bronchial hyper-reactivity.

The in vitro effect of toluene diisocyanate on lymphocyte cyclic adenosine monophosphate production by isoproterenol, prostaglandin, and histamine: a possible mode of action

Toluene diisocyanate (TDI) significantly inhibits the rise in intracellular cyclic 3',5'-adenosine monophosphate (cAMP) that follows in vitro incubation of human lymphocytes with 6.7 x 10(-3) M isoproterenol and 1 x 10(-6) M prostagladin E1 (p less than 0.05). TDI has no significant effect on th production of lymphocyte cAMP following incubation with histamine (1 x 10(-3) M). The inhibitory action of TDI is greatest at a concentration of 3.3 x 10(-4) M and diminishes as the TDI concentration is increased or decreased. TDI also caused four- to fivefold stimulation of lymphocyte cAMP, an effect that is maximal at 1 x 10(-3) M, a concentration which has no significant inhibitory effect on stimulation of cAMP by isoproterenol or prostagladin E1. Conversely, 3.3 x 10(-4) M TDI, which inhibits cAMP production by isoproterenol and prostaglandin, has little stimulatory effect itself on cAMP production. This evidence suggests that TDI might induce obstructive airways disease through pharmacologic mechanisms and that TDI may be acting as a partial agonist.