Diisocyanate-induced Occupational Asthma Research Articles

Andrographolide prevented toluene diisocyanate-induced occupational asthma and aberrant airway E-cadherin distribution via p38 MAPK-dependent Nrf2 induction

Toluene diisocyanate (TDI) is a major cause of chemical-induced occupational asthma, which contributes about 15% of global asthma burden. Resistance and compounded side effects associated with the use of corticosteroid in asthma necessitate the search for alternative drugs. Andrographolide (AGP), a naturally occurring diterpene lactone is known to exhibit various bioactivities. Its ability to ameliorate cardinal features of allergic asthma was previously suggested in an eosinophilic asthma endotype. However, its potential antiasthma activity and mechanism of action in a neutrophilic occupational asthma model, as well as its effect on epithelial dysfunction remain unknown. BALB/c mice were dermally sensitised with 0.3% TDI or acetone olive oil (AOO) vehicle on day 1 and 8, followed by 0.1% TDI intranasal challenge on days 15, 18 and 21. Endpoints were evaluated via bronchoalveolar lavage fluid (BALF) cell analysis, 2′,7′-dichlorofluorescein diacetate (DCFDA) assays, immunoblotting, immunohistochemistry and methacholine challenge test. Decreases in total and differential leukocyte counts of BALF were recorded in AGP-treated animals. The compound dose-dependently reduced intracellular de-esterification of DCFDA, thus suggesting AGP's potential to inhibit intracellular reactive oxygen species (ROS). Mechanistically, the treatment prevented TDI-induced aberrant E-cadherin distribution and restored airway epithelial β-catenin at cell to cell contact site. Furthermore, AGP ameliorated TDI induced pulmonary collagen deposition. In addition, the treatment significantly upregulated pulmonary HO-1, Nrf2 and phospho-p38 levels. Airway hyperresponsiveness was markedly suppressed among AGP-treated animals. Collectively, these findings suggest AGP's protective function against TDI-induced airway epithelial barrier dysfunction and oxidative lung damage possibly through the upregulation of adherence junction proteins and the activation of p38/Nrf2 signalling. This study elucidates the therapeutic potential of AGP in the control and management of chemical-induced allergic asthma. To the best of our knowledge, the potential anti-asthma activity of AGP in TDI-induced occupational asthma has not been reported previously.

Genome-Wide Association Study Identifies Novel Loci Associated With Diisocyanate-Induced Occupational Asthma.

Diisocyanates, reactive chemicals used to produce polyurethane products, are the most common causes of occupational asthma. The aim of this study is to identify susceptibility gene variants that could contribute to the pathogenesis of diisocyanate asthma (DA) using a Genome-Wide Association Study (GWAS) approach. Genome-wide single nucleotide polymorphism (SNP) genotyping was performed in 74 diisocyanate-exposed workers with DA and 824 healthy controls using Omni-2.5 and Omni-5 SNP microarrays. We identified 11 SNPs that exceeded genome-wide significance; the strongest association was for the rs12913832 SNP located on chromosome 15, which has been mapped to the HERC2 gene (p = 6.94 × 10(-14)). Strong associations were also found for SNPs near the ODZ3 and CDH17 genes on chromosomes 4 and 8 (rs908084, p = 8.59 × 10(-9) and rs2514805, p = 1.22 × 10(-8), respectively). We also prioritized 38 SNPs with suggestive genome-wide significance (p < 1 × 10(-6)). Among them, 17 SNPs map to the PITPNC1, ACMSD, ZBTB16, ODZ3, and CDH17 gene loci. Functional genomics data indicate that 2 of the suggestive SNPs (rs2446823 and rs2446824) are located within putative binding sites for the CCAAT/Enhancer Binding Protein (CEBP) and Hepatocyte Nuclear Factor 4, Alpha transcription factors (TFs), respectively. This study identified SNPs mapping to the HERC2, CDH17, and ODZ3 genes as potential susceptibility loci for DA. Pathway analysis indicated that these genes are associated with antigen processing and presentation, and other immune pathways. Overlap of 2 suggestive SNPs with likely TF binding sites suggests possible roles in disruption of gene regulation. These results provide new insights into the genetic architecture of DA and serve as a basis for future functional and mechanistic studies.

Effects of MBL2 polymorphisms in patients with diisocyanate-induced occupational asthma.

Diisocyanate (DI) is the most common cause of occupational asthma (OA) in Korea. Mannose-binding lectin (MBL) initiates the lectin complement activation pathway following oxidative stress and plays an important role in the regulation of inflammatory processes. To determine whether there is a genetic association between MBL2 polymorphisms and DI-OA, 99 patients with DI-OA, 99 asymptomatic exposed controls (AECs) and 144 unexposed normal controls were enrolled in this study. Three polymorphisms (-554 G>C, -431A>C and -225 G>C) in the MBL2 promoter were genotyped, and serum MBL levels were determined by enzyme-linked immunosorbent assay. Functional variabilities in the promoter polymorphisms were analyzed by a luciferase reporter assay and electrophoretic mobility shift assay (EMSA). A significantly higher frequency of haplotype (ht) 2 [CAG] was noted in the DI-OA group compared with the AEC group (P=0.044). The patients with DI-OA carrying ht2 [CAG] had significantly lower PC20 methacholine levels (P<0.001) than the non-carriers. The serum MBL levels were significantly higher in the DI-exposed subjects (both the DI-OA patients and AECs) carrying ht1 [GAG] (P=0.028). Luciferase activity was significantly enhanced in ht1 [GAG] compared with ht2 [CAG] in human hepatocarcinoma cells (Hep3B) (P=0.002). The EMSA showed that a -554G probe produced a specific shifted band compared with the -554C probe. These findings suggest that decreased serum MBL levels due to polymorphisms of the MBL2 gene may increase susceptibility to the development of DI-OA in DI-exposed individuals.

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.

Interferon-γ Promoter Is Hypermethylated in Blood DNA from Workers with Confirmed Diisocyanate Asthma

Risk factors have not been identified that determine susceptibility for development of diisocyanate-induced occupational asthma (DA). We hypothesized that diisocyanate (DI) exposure could modify gene promoter regions regulating transcription of cytokine mediators and thereby influence expression of DA. A cross-sectional study was designed to investigate the promoter methylation status of candidate genes in DI-exposed workers. Subjects consisted of 131 workers in three groups: 40 cases with DA confirmed by a positive specific inhalation challenge (SIC) (DA+), 41 exposed workers with lower respiratory symptoms and negative SIC (DA-), and 50 asymptomatic exposed workers (AWs). We studied four candidate genes (GSTM1, DUSP22, IFN-γ, and IL-4) for which altered promoter methylation has been previously investigated for relationships with a variety of other environmental exposures. Methylation status was determined using methylation-specific quantitative PCR performed on genomic DNA extracted from whole blood. Results showed that relative methylation of IFN-γ promoter was significantly increased in DA+ in comparison with both comparator groups (DA- and AW), and it exhibited good sensitivity (77.5%) and specificity (80%) for identifying DA workers in a multivariate predictive model after adjusting for type of DI exposure, smoking status, methacholine PC₂₀, and gender. IL-4 promoter was slightly less methylated only in DA+ compared with AW among nonsmoking workers. Both GSTM1 and DUSP22 promoter methylations were found not associated with DA. Our finding suggests that exposure to occupational chemicals could play a heretofore undefined mechanistic role via epigenetic modification of specific genes in the promoter region.

Mild Improvement in Symptoms and Pulmonary Function in a Long-Term Follow-Up of Patients with Toluene Diisocyanate-Induced Asthma

Background: Long-term follow-up of diisocyanate-induced occupational asthma has been occasionally reported. Methods: We studied the outcome of toluene diisocyanate (TDI)-induced asthma in 46 patients at diagnosis and after a follow-up of 11 ± 3.6 years. Symptoms, anti-asthma therapy, forced expiratory volume in 1 s (FEV₁) and bronchial hyperresponsiveness to methacholine were assessed. Results: A significant improvement in FEV₁ (% predicted) and PD20FEV₁ methacholine was observed at follow-up in comparison with diagnosis. Anti-asthma treatment was performed by 42% of patients at diagnosis and by 70% at follow-up. At the time of follow-up, 32 subjects had been removed from exposure for 6.0 ± 6.9 years, whereas 14 subjects continued to work with reduced exposure to TDI. There was a significant reduction in the prevalence of attacks of shortness of breath and dyspnoea at follow-up, but only in unexposed patients. PD20FEV₁ was significantly improved only in patients with a lower FEV₁ at diagnosis and in those who have ceased work. Logistic regression analysis, using different models with some independent variables, showed that there were no significant determinants of improvement in FEV₁ at follow-up, while a shorter duration of symptoms before diagnosis was a significant predictor of improvement in PD20FEV₁ at follow-up. Conclusions: Asthma-like symptoms, bronchial hyperresponsiveness and airway obstruction improved, but did not normalize, after a long-term follow-up with cessation or reduction in TDI exposure, mainly in subjects with an early diagnosis of occupational asthma and in patients with a lower baseline FEV₁ no longer exposed to TDI.

CTNNA3 (α-Catenin) Gene Variants Are Associated With Diisocyanate Asthma: A Replication Study in a Caucasian Worker Population

Recently, a genome-wide association study (GWAS) conducted in Korean subjects identified four CTNNA3 (alpha-T catenin) single nucleotide polymorphisms (SNPs) (rs10762058, rs7088181, rs1786929, and rs4378283) associated with diisocyanate-induced occupational asthma (DA). The CTNNA3 gene codes for a cadherin involved in formation of stretch-resistant cell-cell adhesions. We conducted a candidate gene association study to replicate these findings in Caucasian workers. Genotyping was performed on DNA using a 5' nuclease PCR assay collected from 410 diisocyanate-exposed and predominantly Canadian workers including 132 workers with DA confirmed by a specific inhalation challenge (DA+); 131 symptomatic workers in whom DA was excluded by a negative challenge (DA-); and 147 hexamethylene diisocyanate-exposed asymptomatic workers (AWs). As in the Korean study, highly linked CTNNA3 rs7088181 and rs10762058 SNPs (but not rs4378283 and rs1786929) were significantly associated with DA+ when compared with AWs but not in comparison with DA- workers (p ≤ 0.05). After adjusting for potentially confounding variables of age, smoking status, and duration of exposure, minor allele homozygotes of rs7088181 and rs10762058 SNPs were at increased risk for DA compared with AWs (OR = 9.05 [95% CI: 1.69, 48.54] and OR = 6.82 [95% CI: 1.65, 28.24], respectively). In conclusion, we replicated results from the only reported GWAS study of DA demonstrating an association between two closely linked CTNNA3 gene SNPs and DA. These findings lend further support to the clinical relevance of these genotypes in predicting susceptibility to DA and the potential importance of catenins in the disease process.

Is specific IgE antibody analysis feasible for the diagnosis of methylenediphenyl diisocyanate-induced occupational asthma?

PurposeEarly recognition improves the prognosis of isocyanate asthma. A major unanswered question is whether IgE-dependent mechanisms are of diagnostic value? Our objective was to appraise serological methods using various methylenediphenyl diisocyanate (MDI)-albumin conjugates and weigh up the data versus the outcome of standardized comprehensive clinical diagnostics to evaluate the viability of immunological analysis in supportive MDI-asthma diagnosis (OAI).MethodsSpecific IgE (sIgE) and IgG (sIgG) binding was measured with fluorescence enzyme immunoassay in 43 study subjects (using conjugates prepared in-vapor, in-solution and commercial preparations). The differential clinical diagnosis included standardized measurement of pulmonary function, non-specific bronchial hyper-responsiveness, specific MDI-prick test (MDI-SPT) and specific inhalation challenge (MDI-SIC).ResultsDetailed diagnostic scheme allows the differential OAI and MDI-induced hypersensitivity pneumonitis (PI). The presumed OAI diagnoses were confirmed in 84 % (45 % cases having demonstrable sIgE antibodies) with RR 5.7, P > 0.001, when OAI diagnosis is correlated with MDI-SIC/MDI-SPT (RR 1.28 for MDI-SIC alone); sIgG antibodies were clinically relevant for PI and not for the OA diagnosis. MDI-specific IgE data generated with commercial ImmunoCAP preparations show high correlation with our in-vapor generated MDI conjugates.ConclusionsIsocyanate-specific IgE antibodies are not always detectable but their presence is strongly predictive of OAI and supportive for the diagnosis. MDI-SPT can be a valuable parameter differentiating OAI and PI. We have confirmed and extended published data showing that isocyanate-albumin conjugates perform better in specific antibody assays when prepared with volatile phase formulations and would like to stress additionally the necessity for further refinements and standardization in clinical diagnostics procedures.Electronic supplementary materialThe online version of this article (doi:10.1007/s00420-012-0772-6) contains supplementary material, which is available to authorized users.

Medical surveillance programme for diisocyanate exposure

ObjectivesSurveillance programmes for occupational asthma should reduce the severity of asthma both at the time of diagnosis and after removal from exposure as well as costs related to functional impairment....

Serum Cytokine Levels as Serologic Markers of Toluene Diisocyanate-induced Occupational Asthma

Serum Cytokine Levels as Serologic Markers of Toluene Diisocyanate-induced Occupational Asthma

Tissue Transglutaminase Can Be Involved in Airway Inflammation of Toluene Diisocyanate-Induced Occupational Asthma

This study was conducted to evaluate whether tissue transglutaminase (tTG) may be involved in airway inflammation of toluene diisocyanate-induced occupational asthma (TDI-OA). We enrolled 93 patients with TDI-OA, 177 asymptomatic exposed subjects, 43 patients with allergic asthma, and 70 unexposed normal controls. The prevalence of serum immunoglobulin G (IgG) to tTG in the TDI-OA group (20.2%) was significantly higher than that in the three other groups (P < 0.001). TDI-OA patients with serum IgG to tTG had significantly lower methacholine PC(20) values (P < 0.02) and significantly higher prevalence of specific immunoglobulin E to vapor type TDI-human serum albumin conjugate (P < 0.01; r(2) = 0.411, P < 0.05). TDI exposure could increase tTG activity via reactive oxygen species (ROS) production, which was found to cross-link with cytokeratin 19 on immunoblot analysis. Therefore, TDI exposure may activate tTG via ROS-mediated mechanism in the airway epithelium leading to persistent airway inflammation in TDI-OA patients.

Association of HLA Allele and Sensitization to Specific IgG Antibody to MDI-HSA Conjugate in Exposed Workers

RATIONALE: We previously reported a possible involvement of specific IgG in the pathogenic mechanism of methylene diphenyl diisocyanate-induced occupational asthma (MDI-OA). Since there has been no published data to suggest HLA allele association with MDI-OA, this is the first study to investigate HLA alleles associated with the phenotype of MDI-OA.

Diisocyanate-induced asthma: diagnosis, prognosis, and effects of medical surveillance measures.

Diisocyanates have been the most commonly identified cause for occupational asthma (OA) in industrialized areas. Asthma among diisocyanate workers may be true occupational asthma, caused by a high level of irritant exposure at work or by sensitization to diisocyanates. Alternatively, asthma may be coincidental to or may be aggravated by work exposures. A clear diagnosis usually requires a combination of investigations (serial peak expiratory flow recordings, methacholine challenges, and/or diisocyanate challenges), but it is important to provide the best management by identifying whether workplace changes are needed for the worker. Preventive measures to reduce the risk of occupational asthma from diisocyanates have not been prospectively evaluated. The introduction of a medical surveillance program (in Ontario, Canada) in 1983 was followed by retrospective assessments to determine benefits. Between 1980 and 1993, the proportion of all accepted compensation claims for OA that were attributed to diisocyanates, classified by year of symptom onset in the province with the program, rose to 64 percent by 1988, then fell significantly down to 29 percent in 1992 and 35 percent in 1993. Besides the medical surveillance program for diisocyanates, possible factors contributing to this reduction may include reduced diisocyanates exposures and better awareness of diisocyanate-induced asthma, both by workers and physicians. Compared with OA caused by other agents, those with OA due to diisocyanates had a significantly earlier onset of asthma after the start of the exposure (mean 5 yr vs. 7 yr), were younger and less likely to be atopic and to have smoked. The mean duration of asthma before the main medical assessment for compensation was significantly shorter among those with diisocyanate-induced asthma (mean 2 yr vs. 3 yr), and the severity was milder as assessed by medication use and pulmonary function. Those with diisocyanate-induced asthma were significantly less likely to be hospitalized for asthma. Among the subset whose outcome was determined at a mean of 2.1 years after the main medical assessment, the outcome severity was less for those with diisocyanate-induced OA. Among those with diisocyanate-induced OA, an earlier diagnosis and a trend to better outcome was found in workers from companies that were identified to be in compliance with surveillance measures.

Prognostic factors for toluene diisocyanate-induced occupational asthma after removal from exposure

Prognostic factors for toluene diisocyanate-induced occupational asthma after removal from exposure

Prognostic factors for toluene diisocyanate‐induced occupational asthma after removal from exposure

The outcome of isocyanate-induced occupational asthma remains to be further defined. There have been few studies on the role of specific antibodies in prognosis of toluene diisocyanate (TDI) induced occupational asthma. Moreover, to the best of our knowledge, there have been no studies on the improvement pattern of airway hyperresponsiveness (AH). We analysed the prognostic factors that affected the outcome of 35 toluene diisocyanate-induced occupational asthma. To define clinical and laboratory parameters predicting favourable prognosis for TDI-induced occupational asthma. After confirmation of bronchial sensitivity by TDI bronchoprovocation test (BPT), 35 patients were recommended to avoid exposure to TDI; they were also given anti-asthmatic medications including inhaled steroids and monitored for 2 years. Seventeen (49%) recovered completely with disappearance of airway hyperresponsiveness (AH) to methacholine during the follow-up period (mean duration: 12 months, range of 3-30 months). Eleven (31%) showed a significant improvement in AH for first year, which improvement stabilized in the next year with mild symptoms. Seven (20%) patients did not show any evidence of improvement in AH and had persistent symptoms. Favourable prognosis was associated with a short duration of asthmatic symptoms before diagnosis (P < 0.05), immediate cessation of exposure after diagnosis (P < 0.05), milder degree of AH at diagnosis (P < 0.05), and the presence of specific IgE antibodies to TDI-human serum albumin conjugate (0.05 < P < 0.1). No association was found with atopic and smoking status, age, exposure duration, or length of latent period (P > 0.05). These data suggest that early detection of TDI-induced asthma and immediate cessation of exposure are important factors for a favourable prognosis.

T-cell receptor Vβ gene segment expression in diisocyanate-induced occupational asthma

Background: Diisocyanates are the most common cause of occupational asthma induced by low-molecular-weight chemicals. The disease appears to be immunologically mediated but is independent of IgE antibody synthesis. An underlying genetic susceptibility is suggested by the fact that the disease only develops in approximately 5% to 10% of exposed workers. Objective: The study was designed to determine whether disease susceptibility is influenced by HLA and T-cell receptor Vβ gene segment usage. Methods: T-cell receptor Vβ gene repertoires were quantitated by using primer pairs specific for Vβ gene segments in conjunction with a common Cβ region primer. One group of workers with diisocyanate-induced occupational asthma produced diisocyanate-specific IgG and IgE antibodies, whereas the other group did not produce specific antibodies. Occupational asthma was previously confirmed by either workplace challenge or laboratory specific diisocyanate bronchoprovocation. Control groups consisted of diisocyanate-exposed workers who were free of symptoms, patients with nonoccupational asthma, and unexposed subjects who were free of symptoms. Results: Lymphocytes from workers with diisocyanate-induced occupational asthma had significantly decreased Vβ1 and Vβ5 gene segment expression before in vitro exposure to diisocyanates, compared with control groups. Percent Vβ1 and Vβ5 gene segment expression was selectively increased when peripheral blood mononuclear cells were stimulated in vitro with diisocyanate-conjugated proteins. Low-resolution HLA class II phenotyping revealed no significant differences in the distribution of HLA-DR or HLA-DQ alleles between diisocyanate-induced occupational asthma and control groups. Conclusions: These findings are consistent with a hypothesis that antigen-specific T-cell subpopulations may be sequestered in the lungs of workers with diisocyanate-induced occupational asthma and clonally expand after further exposure to diisocyanates. (J Allergy Clin Immunol 1997;99:245-50.)

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.