Low molecular weight pollutants and asthma: pathogenetic mechanisms and genetic factors

Determination of albumin adducts of 4,4'-methylenediphenyl diisocyanate after specific inhalative challenge tests in workers

4,4'-Methylenediphenyl diisocyanate (MDI) is the most important isocyanate used in the industry. Lung sensitization with bronchial asthma is the main disorder in exposed workers. Albumin adducts of MDI might be involved in specific immunological reactions. MDI adducts with lysine (MDI-Lys) of albumin have been found in MDI-workers and construction workers. MDI-Lys is an isocyanate-specific adduct of MDI with albumin. In the present study, we report MDI-adducts in workers undergoing diagnostic MDI challenge tests. The workers were exposed for 2h to 5ppb of MDI. The adduct levels increase significantly after the exposure to MDI in the challenge chamber. About 0.6% of the dose was bound to albumin. So far, only urinary metabolites of MDI were measured to monitor isocyanate workers. However, such urinary metabolites are not isocyanate specific. Therefore, we propose to measure albumin adducts for monitoring MDI exposed subjects.

Determination of albumin adducts of 4,4'-methylenediphenyl diisocyanate in workers of a 4,4'-methylenedianiline factory

Lung sensitization and asthma are the main health effects of 4,4'-methylenediphenyl diisocyanate (MDI). Albumin adducts (isocyanate specific adducts) of MDI might be involved in the etiology of sensitization reactions. Albumin adducts of MDI have been found in subjects classified as 4,4'-methylenedianiline (MDA) workers. The mean adduct levels in these MDA-workers were 1.5 times higher than in MDI-workers of the same company. MDA-specific hemoglobin adducts, were present ten times more in the MDA-workers than in the MDI-workers. MDA-workers with specific work task had significantly higher albumin adduct levels.

Expression of lymphocyte cell surface markers in workers exposed to different respiratory hazards: biomarkers of occupational respiratory disease

This study was designed to evaluate the potential of flow cytometry to measure biomarkers of airways inflammation in the peripheral blood of two cohorts of workers reporting work related respiratory symptoms, who were exposed to different respiratory hazards. Nine bakers exposed to wheat flour and 10 glass bottle manufacturers exposed to a range of irritant chemicals were selected for study. Phenotypic and inducible cell surface markers were measured by flow cytometry. Results were compared with a control population of 58 volunteers reporting no respiratory problems. The bakers showed a significant increase above control values for cell types associated with inflammation; in particular CD3 CD4 cells p 0.005 and CD4 CD25 cells p 0.01 . In contrast, the workers reporting work related respiratory symptoms who were exposed to a range of irritant chemicals showed a different pattern of cell surface lymphocyte markers, with a significant decrease in the total T cell population p 0.05 . Comparison of results from a subset of smoking controls with the population of bakers who were all heavy smokers confirmed that the increase in CD3 CD4 cells and CD4 CD25 cells could not be ascribed to the effects of smoking alone. We have shown activation of helper T cells in the peripheral blood of bakers reporting work related respiratory symptoms consistent with the changes observed in mild to severe asthmatics. However, workers with similar symptoms who were exposed to irritant chemicals did not show this pattern of phenotypic or inducible cell surface markers, reflecting an absence of airways inflammation in these individuals. Our results suggest that flow cytometry may be of use as an objective test for detecting workers with airways inflammation to allow the identification of workers at risk of developing occupational asthma.

Synthetic approaches to obtain amino acid adducts of 4,4'-methylenediphenyl diisocyanate

4,4'-Methylenediphenyl diisocyanate (MDI) is the most important isocyanate used in the chemical industry. Lung sensitization and asthma are the main types of damage after exposure to MDI. Albumin adducts of MDI might be involved in the etiology of sensitization reactions. It is therefore necessary to have sensitive and specific biomarkers such as blood protein adducts to monitor people exposed to isocyanates. For the discovery of new isocyanate adducts with blood proteins present in vivo, new synthetic standards are needed. To achieve this, we developed five methods to obtain amino acid adducts of MDI. We synthesized and isolated MDI adducts of aspartic acid, glutamic acid, cysteine, and valine. The new adducts were characterized by LC-MS/MS and NMR. We synthesized the corresponding isotope-labeled MDI adducts to develop analytical methods using LC-MS/MS. Glutathione adducts of isocyanates are an important way of transportation of the reactive isocyanates to distant sites from the original site of exposure. Therefore, we used N-acetyl-cysteine adducts of MDI as reactants: N-acetyl-S-[[4-(4-aminobenzyl)phenyl]carbamoyl]-cysteine (MDI-AcCys) and N-acetyl-S-[[4-(4-acetylaminobenzyl)phenyl]carbamoyl]-cysteine (AcMDI-AcCys). MDI-AcCys or AcMDI-AcCys formed adducts with albumin, N(α)-acetyl lysine, and valine. Isotope-labeled albumin adducts (= d(4)-MDI-albumin) were synthesized from d(4)-MDI-AcCys and albumin. d(4)-MDI-albumin can be used as an internal standard to analyze biological samples. Such an internal standard will not correct only for the extraction recovery of the adducts but also for the potential variation of the enzymatic digestions used in the procedure to analyze albumin adducts of MDI. The synthetic procedures described in this manuscript will be applicable to the synthesis of amino acid adducts from other isocyanates.

The epidemiology of work-related asthma

Much has been learned from epidemiologic studies conducted in the past 4 decades that can be directly applied to the management of workers affected with occupational asthma. Studies have provided information about host factors, environmental exposure, and occupational agents posing the highest risks for development of severe irreversible airway obstruction and asthma disability. Investigators have developed methods for screening workers at risk and novel interventions that may prevent new cases among exposed worker populations. Less is known about the natural history and chronic morbidity associated with work-aggravated asthma and irritant-induced asthma syndromes; more studies are needed in at-risk worker populations.

Determination of a new biomarker in subjects exposed to 4,4'-methylenediphenyl diisocyanate

4,4'-Methylenediphenyl diisocyanate (MDI) is the most important of the isocyanates used as intermediates in the chemical industry. Among the main types of damage after exposure to low levels of MDI are lung sensitization and asthma. Albumin adducts of MDI might be involved in the etiology of sensitization reactions. This work presents a liquid chromatography (LC)-mass spectrometry (MS/MS) procedure for determination of isocyanate-specific albumin adducts in humans. MDI formed adducts with lysine of albumin: MDI-Lys and AcMDI-Lys. The MDI-Lys levels, 25th, 50th, 75th, 90th percentile, were 0, 65.2, 134, 244 fmol mg(-1) and 0, 30.5, 57.4, 95.8 fmol mg(-1) in the exposed construction and factory workers, respectively. This new biomonitoring procedure will allow assessment of suspected exposure sources and may contribute to the identification of individuals who are particularly vulnerable for developing bronchial asthma and other respiratory diseases after exposure to isocyanates.

New isocyanate-specific albumin adducts of 4,4'-methylenediphenyl diisocyanate (MDI) in rats

4,4'-Methylenediphenyl diisocyanate (MDI) is the most important of the isocyanates used as intermediates in the chemical industry. Among the main types of damage after exposure to low levels of MDI are lung sensitization and asthma. Albumin adducts of MDI might be involved in the etiology of sensitization reactions. It is, therefore, necessary to have sensitive and specific methods for monitoring the isocyanate exposure of workers. To date, urinary metabolites or protein adducts have been used as biomarkers in workers exposed to MDI. However, with these methods it is not possible to determine whether the biomarkers result from exposure to MDI or to the parent aromatic amine 4,4'-methylenedianiline (MDA). This work presents a procedure for the determination of isocyanate-specific albumin adducts. In a long-term experiment, designed to determine the carcinogenic and toxic effects of MDI, rats were exposed chronically for 3 months, to 0.0 (control), 0.26, 0.70, and 2.06 mg MDI/m(3) as aerosols. Albumin was isolated from plasma, digested with Pronase E, and analyzed by LC-MS/MS. MDI formed adducts with lysine: N(6)-[({4-[4-aminobenzyl]phenyl}amino)carbonyl]lysine (MDI-Lys) and N(6)-[({4-[4-(acetylamino)benzyl]phenyl}amino)carbonyl] lysine (AcMDI-Lys). For the quantitation of the adducts in vivo, isotope dilution mass spectrometry was used to measure the adducts in 2 mg of albumin. The adducts found in vivo (MDI-Lys and AcMDI-Lys) and the corresponding isotope labeled compounds (MDI-[(13)C(6)(15)N(2)]Lys and Ac[(2)H(4)]MDI-Lys) were synthesized and used for quantitation. The MDI-Lys levels increased from 0-24.8 pmol/mg albumin, and the AcMDI-Lys levels increased from 0-1.85 pmol/mg albumin. The mean ratio of MDI-Lys/AcMDI-Lys for each dose level was greater than >20. The albumin adducts correlate with other biomarkers measured in the same rats in the past: urinary metabolites and hemoglobin adducts released after mild base hydrolysis. This method will enable one to measure isocyanate-specific albumin adducts in workers. This new biomonitoring procedure will allow for the assessment of suspected exposure sources and may contribute to the identification of individuals who are particularly vulnerable for developing bronchial asthma and other respiratory diseases after exposure to isocyanates. In addition, it will help to improve the production of antigens for the analysis of antibodies in exposed workers.

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.

The spectrum of irritant-induced asthma: sudden and not-so-sudden onset and the role of allergy

A retrospective investigation of 86 asthmatic subjects defined clinical features of irritant-induced asthma and assessed the contributory role of an allergic predisposition. Three categories of asthma were evaluated: (1) occupational asthma due to a sensitizer (11 subjects, 13%); (2) irritant-induced asthma (54 persons, 63%); and (3) not occupational/environmental exposure-related asthma (21 subjects, 24%). Two distinct clinical presentations of irritant-induced asthma emerged: the first was sudden onset (29 subjects) and the second was not so sudden in onset (25 subjects). Sudden-onset, irritant-induced asthma was analogous to the reactive airways dysfunction syndrome. Clinical manifestations began immediately or within a few hours (always within 24 h) following an accidental, brief, and massive exposure. In contrast, for the not-so-sudden-onset asthma subjects, the causative irritant exposure was not brief, usually not massive, continued for > 24 h, and the initiation of asthma took longer to evolve. Eighty-eight percent of individuals with not-so-sudden irritant-induced asthma displayed an atopy/allergy status (p < 0.01). Some of the atopy/allergy subjects with presumed new-onset asthma were found to have suffered preexisting asthma that had been clinically quiescent for at least 1 year before the triggering exposure (16 persons). We conclude that preexisting allergic/atopy and/or preexisting asthma were significant contributors to the pathogenesis of not-so-sudden, irritant-induced asthma and emphasizes a critical interaction between environmental and host factors in the pathogenesis of asthma.

Study of employees with anhydride-induced respiratory disease after removal from exposure

The purpose of this study was to determine the clinical and immunologic status of hexahydrophthalic anhydride (HHPA)-exposed employees who had developed an immunologic respiratory disease and who have been removed from exposure for at least 1 year. In a surveillance study spanning 4 years, we identified 28 employees with HHPA-induced immunologic respiratory disease who had been removed from exposure for at least 1 year. Seven had asthma, nine had hemorrhagic rhinitis, four had both, and eight had allergic rhinitis alone. Respiratory symptoms were assessed by physician-administered questionnaires. For each employee, a physical examination, spirometry, and chest roentgenograph were performed. Antibody against HHPA conjugated to human serum albumin (HHP-HSA) was measured using an enzyme-linked immunosorbent assay. Symptoms, signs, and spirometry normalized in all but one employee. There were no chest-roentgenograph findings at follow-up that could be attributed to HHPA. There was a decline in antibody liter for both immunoglobulin E and G against HHP-HSA. In this group of 28 employees, there was only one employee with mild asthma after removal from exposure for at least I year. Although specific antibody was still present in many, the titers were generally lower at follow-up than at presentation.

Early reaction type allergies and diseases of the respiratory passages in employees from persulphate production

The prevalence of positive skin-prick test reactions ammonium persulphate and potassium persulphate (1% and 5% solutions) was tested in a cross-sectional study on 52 employees of a company producing persulphates after a case of "persulphate asthma" was observed. A random test of 13 persons without occupational exposure to persulphates served as controls; among them all the skin-prick test reactions were negative. Eight company employees showed a positive skin-prick test reaction to at least one of the persulphate solutions tested. Employees showed lower lung function results with a positive prick test reaction than did employees with a negative result. The positive skin-prick reactions correspond well to the anamnestic data and indicate a possible relationship to obstructive ventilation disorders. The results therefore suggest an IgE-induced, allergic pathomechanism of "persulphate asthma" triggered by persulphates.