Occupational asthma caused by isocyanates: patterns of asthmatic reactions to increasing day-to-day doses

Serial fractional exhaled nitric oxide measurements off and at work in the diagnosis of occupational asthma

BACKGROUND

Fractional exhaled nitric oxide (FeNO) before and after specific inhalation challenge has been postulated as an additional tool in the diagnosis of occupational asthma (OA), but little is known about serial FeNO measurements at home and at work. The aim of the present study was to assess the contribution of serial measurements of FeNO off and at work toward the diagnosis of OA.

METHODS

Forty-one subjects with suspected (n = 35) or diagnosed (n = 6) OA performed FeNO measurements once daily during a 2-week holiday and a subsequent 2-week work period. A work-related increase in FeNO by 20 ppb (parts per billion) or more was considered positive. Subjects with negative or doubtful specific inhalation challenge but a FeNO increase of 20 ppb or more were evaluated individually by an overall expert rating taking into account all available information.

RESULTS

Seven of 35 subjects (20%) with suspected and three of six subjects (50%) with diagnosed OA showed a work-related FeNO increase of 20 ppb or more. Six of the seven with suspected OA were reclassified as having an OA diagnosis by the overall expert rating which also considered these FeNO changes.

CONCLUSIONS

Serial FeNO measurements off and at work provide complementary information in the diagnosis in about one-fifth of cases with suspected OA, especially if specific inhalation challenges are negative or cannot be performed.

N-Acetyltransferase 2 Genotypes Are Associated With Diisocyanate-Induced Asthma

OBJECTIVE

To investigate whether genetic variants of N-acetyltransferase (NAT) genes are associated with diisocyanate asthma (DA).

METHODS

The study population consisted of 354 diisocyanate-exposed workers. Genotyping was performed using a 5'-nuclease polymerase chain reaction assay.

RESULTS

The NAT2 rs2410556 and NAT2 rs4271002 variants were significantly associated with DA in the univariate analysis. In the first logistic regression model comparing DA+ and asymptomatic worker groups, the rs2410556 (P = 0.004) and rs4271002 (P < 0.001) single nucleotide polymorphisms and the genotype combination, NAT2 rs4271002*NAT1 rs11777998, showed associations with DA risk (P = 0.014). In the second model comparing DA+ and DA- groups, NAT2 rs4271002 variant and the combined genotype, NAT1 rs8190845*NAT2 rs13277605, were significantly associated with DA risk (P = 0.022, P = 0.036, respectively).

CONCLUSIONS

These findings suggest that variations in the NAT2 gene and their interactions contribute to DA susceptibility.

Genetic variants in TNFα, TGFB1, PTGS1 and PTGS2 genes are associated with diisocyanate-induced asthma

Diisocyanates are the most common cause of occupational asthma, but risk factors are not well defined. A case-control study was conducted to investigate whether genetic variants in inflammatory response genes (TNFα, IL1α, IL1β, IL1RN, IL10, TGFB1, ADAM33, ALOX-5, PTGS1, PTGS2 and NAG-1/GDF15) are associated with increased susceptibility to diisocyanate asthma (DA). These genes were selected based on their role in asthmatic inflammatory processes and previously reported associations with asthma phenotypes. The main study population consisted of 237 Caucasian French Canadians from among a larger sample of 280 diisocyanate-exposed workers in two groups: workers with specific inhalation challenge (SIC) confirmed DA (DA(+), n = 95) and asymptomatic exposed workers (AW, n = 142). Genotyping was performed on genomic DNA, using a 5' nuclease PCR assay. After adjusting for potentially confounding variables of age, smoking status and duration of exposure, the PTGS1 rs5788 and TGFB1 rs1800469 single nucleotide polymorphisms (SNP) showed a protective effect under a dominant model (OR = 0.38; 95% CI = 0.17, 0.89 and OR = 0.38; 95% CI = 0.18, 0.74, respectively) while the TNFα rs1800629 SNP was associated with an increased risk of DA (OR = 2.08; 95% CI = 1.03, 4.17). Additionally, the PTGS2 rs20417 variant showed an association with increased risk of DA in a recessive genetic model (OR = 6.40; 95% CI = 1.06, 38.75). These results suggest that genetic variations in TNFα, TGFB1, PTGS1 and PTGS2 genes contribute to DA susceptibility.

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.

Setting Occupational Exposure Limits for Chemical Allergens--Understanding the Challenges

Chemical allergens represent a significant health burden in the workplace. Exposures to such chemicals can cause the onset of a diverse group of adverse health effects triggered by immune-mediated responses. Common responses associated with workplace exposures to low molecular weight (LMW) chemical allergens range from allergic contact dermatitis to life-threatening cases of asthma. Establishing occupational exposure limits (OELs) for chemical allergens presents numerous difficulties for occupational hygiene professionals. Few OELs have been developed for LMW allergens because of the unique biological mechanisms that govern the immune-mediated responses. The purpose of this article is to explore the primary challenges confronting the establishment of OELs for LMW allergens. Specific topics include: (1) understanding the biology of LMW chemical allergies as it applies to setting OELs; (2) selecting the appropriate immune-mediated response (i.e., sensitization versus elicitation); (3) characterizing the dose (concentration)-response relationship of immune-mediated responses; (4) determining the impact of temporal exposure patterns (i.e., cumulative versus acute exposures); and (5) understanding the role of individual susceptibility and exposure route. Additional information is presented on the importance of using alternative exposure recommendations and risk management practices, including medical surveillance, to aid in protecting workers from exposures to LMW allergens when OELs cannot be established.

Genetic variants in the major histocompatibility complex class I and class II genes are associated with diisocyanate-induced Asthma

OBJECTIVE

To investigate the association between single nucleotide polymorphisms (SNPs) located across the major histocompatibility complex and susceptibility to diisocyanate-induced asthma (DA).

METHODS

The study population consisted of 140 diisocyanate-exposed workers. Genotyping was performed using the Illumina GoldenGate major histocompatibility complex panels.

RESULTS

The HLA-E rs1573294 and HLA-DPB1 rs928976 SNPs were associated with an increased risk of DA under dominant (odds ratio [OR], 6.27; 95% confidence interval [CI], 2.37 to 16.6; OR, 2.79, 95% CI, 0.99 to 7.81, respectively) and recessive genetic models (OR, 6.27, 95% CI, 1.63 to 24.13; OR, 10.10, 95% CI, 3.16 to 32.33, respectively). The HLA-B rs1811197, HLA-DOA rs3128935, and HLA-DQA2 rs7773955 SNPs conferred an increased risk of DA in a dominant model (OR, 7.64, 95% CI, 2.25 to 26.00; OR, 19.69, 95% CI, 2.89 to 135.25; OR, 8.43, 95% CI, 3.03 to 23.48, respectively).

CONCLUSION

These results suggest that genetic variations within HLA genes play a role in DA risk.

Occupational rhinitis due to steel welding fumes

Exposure to welding fumes is a recognized respiratory hazard. Occupational asthma but not occupational rhinitis has been documented in workers exposed to steel welding fumes. We report a 26-year-old male with work-related rhinitis symptoms as well as lower airways symptoms suggestive of occupational asthma and metal fume fever associated with exposure to steel welding fumes. The diagnosis of occupational rhinitis was confirmed by specific inhalation challenge.

Development of a respiratory sensitization/elicitation protocol of toluene diisocyanate (TDI) in Brown Norway rats to derive an elicitation-based occupational exposure level

Toluene diisocyanate (TDI), a known human asthmagen, was investigated in skin-sensitized Brown Norway rats for its concentration×time (C×t)-response relationship on elicitation-based endpoints. The major goal of study was to determine the elicitation inhalation threshold dose in sensitized, re-challenged Brown Norway rats, including the associated variables affecting the dosimetry of inhaled TDI-vapor in rats and as to how these differences can be translated to humans. Attempts were made to duplicate at least some traits of human asthma by using skin-sensitized rats which were subjected to single or multiple inhalation-escalation challenge exposures. Two types of dose-escalation protocols were used to determine the elicitation-threshold C×t; one used a variable C (Cvar) and constant t (tconst), the other a constant C (Cconst) and variable t (tvar). The selection of the "minimal irritant" C was based an ancillary pre-studies. Neutrophilic granulocytes (PMNs) in bronchoalveolar lavage fluid (BAL) were considered as the endpoint of choice to integrate the allergic pulmonary inflammation. These were supplemented by physiological measurements characterizing nocturnal asthma-like responses and increased nitric oxide in exhaled breath (eNO). The Cconst×tvar regimen yielded the most conclusive dose-response relationship as long C was high enough to overcome the scrubbing capacity of the upper airways. Based on ancillary pre-studies in naïve rats, the related human-equivalent respiratory tract irritant threshold concentration was estimated to be 0.09ppm. The respective 8-h time-adjusted asthma-related human-equivalent threshold C×t-product (dose), in 'asthmatic' rats, was estimated to be 0.003ppm. Both thresholds are in agreement of the current ACGIH TLV(®) of TDI and published human evidence. In summary, the findings from this animal model suggest that TDI-induced respiratory allergy is likely to be contingent on two interlinked, sequentially occurring mechanisms: first, dermal sensitizing encounters high enough to cause systemic sensitization. Second, when followed by inhalation exposure(s) high enough to initiate and amplify an allergic airway inflammation, then a progression into asthma may occur. This bioassay requires an in-depth knowledge on respiratory tract dosimetry and irritation of the involved test substance to clearly understand the dosimetry causing C- and/or C×t-dependent respiratory tract irritation and eventually asthma.

Evaluation of a 4-steps-1-day whole body challenge protocol for the diagnosis of occupational asthma due to diisocyanates

Inhalative challenges are important in the diagnosis of occupational asthma due to diisocyanates. As existing protocols are time-consuming and costly, it was the aim of this study to develop a short duration whole body exposure protocol. Ninety three subjects with suspected occupational diisocyanate-induced asthma and verified current or previous occupational exposure to diisocyanates and ten control subjects without diisocyanate exposure but with bronchial hyperresponsiveness were investigated. After baseline examination on the first day, subjects underwent a standardized whole body multiple-steps-1-day challenge with exposures of up to four times 30 min to concentrations of 5, 10, 20, and 30 ppb of the dominant diisocyanate used at work on the second day. Common spirometric and body plethysmographic parameters were used as positivity criteria. Overall, 14 subjects demonstrated a positive diisocyanate challenge, 19 were considered doubtful, and 60 were negative. All controls had negative challenges. Positive reactions occurred during the challenge (n = 10) or during follow-up (n = 4). Eight subjects showed >40 % fall of FEV1. These severe reactions occurred after 5 ppb (n = 2) or 10 ppb (n = 3), while isolated late reactions after 2 h of follow-up were not observed. Multivariate analysis showed an association between a positive challenge and both the degree of previous occupational exposure and the presence of baseline bronchial hyperresponsiveness. In summary, the proposed 4-steps-1-day diisocyanate challenge protocol induced pronounced bronchial reactions in a small number of subjects. As these reactions were more likely to occur after low concentrations, it is recommended to shift the initial concentration/dose step to lower exposures.

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.

Diagnosis and prevention of diseases induced by isocyanate

Isocyanates are among the most frequent causes of occupational asthma in industrialized countries. Early diagnosis of diisocyanate asthma followed by prompt termination of chemical exposure can prevent chronic morbidity due to persistent asthma. Chronic exposure to isocyanates also induces hypersensitivity pneumonitis (HP). The accurate diagnosis of diisocynate asthma requires a systematic approach that combines information obtained from the occupational history, immunologic tests and physiologic studies. The prevention of health problems from toluene diisocyanate (TDI), 4,4'-methylenediphenyl diisocyanate (MDI) and 1,6'-hexamethylene diisocyanate (HDI) is essential for all those handling the chemicals. Regulatory exposure limits should be observed. However, wheezing, coughing or even asthmatic attacks may occur after exposure much below the regulatory exposure limits especially in sensitive individuals. Preventing or minimizing exposure is of prime importance and should be supported by the installation of engineering controls, by education of the workforce, by regular monitoring of the workplace exposure and by medical surveillance. To prevent such asthma it is suggested that workers should be tested airway sensitivity and should avoid working in areas that have dust containing specific-IgE. Such tests must be periodically performed after working. Symptoms induced by isocyanate need earlier discover and early isolation of the associated individuals.

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.

Genetic variants in antioxidant genes are associated with diisocyanate-induced asthma

Diisocyanates are a common cause of occupational asthma, but risk factors are not well defined. A case-control study was conducted to investigate whether genetic variants of antioxidant defense genes, glutathione S-transferases (GSTM1, GSTT1, GSTM3, GSTP1), manganese superoxide dismutase (SOD2), and microsomal epoxide hydrolase (EPHX1) are associated with increased susceptibility to diisocyanate-induced asthma (DA). The main study population consisted of 353 Caucasian French-Canadians from among a larger sample of 410 diisocyanate-exposed workers in three groups: workers with specific inhalation challenge (SIC) confirmed DA (DA(+), n = 95); symptomatic diisocyanate workers with a negative SIC (DA(-), n = 116); and asymptomatic exposed workers (AW, n = 142). Genotyping was performed on genomic DNA, using a 5'-nuclease PCR assay. The SOD2 rs4880, GSTP1 rs1695, and EPHX1 rs2740171 variants were significantly associated with DA in both univariate and multivariate analyses. In the first logistic regression model comparing DA(+) and DA(-) groups, SOD2 rs4880, GSTM1 (null), GSTP1 rs762803, and EPHX1 rs2854450 variants were associated with DA (p = 0.004, p = 0.047, p = 0.021, p <0.001, respectively). Genotype combinations GSTT1*GSTP1 rs762803, GSTM1*EPHX1 rs2854450, EPHX1 rs2740168*EPHX1 rs1051741, and GSTP1 rs762803*EPHX1 rs2740168 were also associated with DA in this model (p = 0.027, p = 0.002, p = 0.045, p = 0.044, respectively). The GSTP1 rs1695 and EPHX1 rs1051741 and rs2740171 variants showed an association with DA in the second model comparing DA(+) and AW groups (p = 0.040, p = 0.019, p = 0.002, respectively). The GSTM3 rs110913*EPHX1 rs1051741 genotype combination was also associated with DA under this model (p = 0.042). The results suggest that variations in SOD2, GST, and EPHX1 genes and their interactions contribute to DA susceptibility.

Elimination kinetics of diisocyanates after specific inhalative challenges in humans: mass spectrometry analysis, as a basis for biomonitoring strategies

Background

Isocyanates are some of the leading occupational causes of respiratory disorders, predominantly asthma. Adequate exposure monitoring may recognize risk factors and help to prevent the onset or aggravation of these aliments. Though, the biomonitoring appears to be most suitable for exposure assessment, the sampling time is critical, however. In order to settle the optimal time point for the sample collection in a practical biomonitoring approach, we aimed to measure the elimination of isocyanate urine metabolites.

Methods

A simple biomonitoring method enabling detection of all major diamine metabolites, from mono-, poly- and diisocyanates in one analytical step, has been established. Urine samples from 121 patients undergoing inhalative challenge tests with diisocyanates for diagnostic reasons were separated by gas chromatography and analyzed with mass spectrometry (GC-MS) at various time points (0-24 h) after the onset of exposure.

Results

After controlled exposures to different concentrations of diisocyanates (496 ± 102 ppb-min or 1560 ± 420 ppb-min) the elimination kinetics (of respective isocyanate diamine metabolites) revealed differences between aliphatic and aromatic isocyanates (the latter exhibiting a slower elimination) and a dose-response relationship. No significant differences were observed, however, when the elimination time patterns for individual isocyanates were compared, in respect of either low or high exposure or in relation to the presence or absence of prior immunological sensitization.

Conclusions

The detection of isocyanate metabolites in hydrolyzed urine with the help of gas chromatography combined with mass spectrometric detection system appears to be the most suitable, reliable and sensitive method to monitor possible isocyanate uptake by an individual. Additionally, the information on elimination kinetic patterns must be factored into estimates of isocyanate uptake before it is possible for biomonitoring to provide realistic assessments of isocyanate exposure. The pathophysiological elimination of 1,6-hexamethylene diamine, 2,4-diamine toluene, 2,6-diamine toluene, 1,5-naphthalene diamine, 4,4'-diphenylmethane diamine and isophorone diamines (as respective metabolites of: 1,6-hexamethylene diisocyanate, 2,4-toluene diisocyanate and 2,6 toluene diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate and isophorone diisocyanates) differs between individual isocyanates' diamines.

Clinical and immunologic findings of methylene diphenyl diisocyanate-induced occupational asthma in a car upholstery factory

BACKGROUND

Although methylene diphenyl diisocyanate (MDI) is widely used in many industries, there have been few immunological studies of MDI-induced occupational asthma.

OBJECTIVES

We investigated the effects of MDI exposure on the clinical and immunologic condition of workers in a single car upholstery factory.

METHODS

Fifty-eight MDI-exposed workers were studied. Work-related lower-respiratory symptoms (WRRS) were identified using a questionnaire. Serum-specific IgE and IgG antibodies to MDI-human serum albumin conjugate were detected by ELISA. Atopy was evaluated using a skin prick test. MDI-induced occupational asthma was confirmed in the symptomatic workers with a positive result on an MDI-specific inhalation test.

RESULTS

Thirteen (22.4%) of the subjects complained of WRRS. MDI-induced occupational asthma was confirmed in five (8.6%) of the workers, and occupational eosinophilic bronchitis was confirmed in two (3.5%). The prevalence of specific IgG antibodies (20.7%) was higher than that of specific IgE antibodies (8.6%). The prevalence of MDI-induced occupational asthma/eosinophilic bronchitis was strongly associated with the presence of both WRRS and serum-specific IgG antibodies to an MDI-human serum albumin conjugate (P<0.01, <0.05, respectively).

CONCLUSION

These findings suggest that MDI could be a causative agent of occupational asthma among MDI-exposed workers. The prevalence of MDI-induced occupational asthma was 8.6%, and MDI-induced eosinophilic bronchitis was confirmed in two workers. The presence of work-related lower-respiratory symptoms and serum-specific IgG antibodies to an MDI-human serum albumin conjugate may be used to predict MDI-induced occupational asthma/eosinophilic bronchitis in MDI-exposed workers.

Brown Norway rat asthma model of diphenylmethane-4,4'-diisocyanate (MDI): analysis of the elicitation dose-response relationship

The known human asthmagen polymeric diphenylmethane-diisocyanate (MDI) was investigated in the Brown Norway rat skin asthma model. Two types of dose-response relationships are addressed with the following focus: (1) does sensitization dose and surface area influence the subsequent elicitation response and (2) is the elicitation response more dependent on previous elicitation doses or more on skin sensitizing dose? These two aims are investigated in two elaborated experiments, using inflammatory (bronchoalveolar lavage, BAL) and physiologic (Penh) endpoints to characterize asthma-like responses in rats. Postchallenge measurements of Penh focused on responses delayed in onset. Inflammatory endpoints in BAL were performed one day after the fourth challenge. Both protocols utilized a dermal sensitization phase with two administrations on days 0 and 7 followed by four inhalation challenges with approximately 38 mg MDI/m(3) in intervals of 2 weeks. In the first protocol three groups of rats were topically dosed with 40, 10, and 2.5 mul of MDI per rat. Each dose group consisted of three subgroups with dosed surface areas of 3.1-12.6 cm(2), 0.8-3.1 cm(2), and 0.4-0.8 cm(2), respectively. In the second protocol groups of rats were topically dosed with 40 microl of MDI per rat followed by three challenges with 37 mg MDI/m(3). At the fourth challenge subgroups of rats were either challenged with 8, 18, or 39 mg MDI/m(3). Independent of the protocol used, response was characterized by increased influx of neutrophilic granulocytes in BAL and delayed respiratory response. All groups from the first study sensitized to and challenged with MDI elicited a distinct response relative to similarly challenged naive rats. A sensitization dose dependence of the elicitation response was not found. The second protocol revealed that the elicitation dose correlates with increased neutrophils in BAL and delayed-onset respiratory responses. In summary, these data suggest that the vigor of asthma-like responses appear to be more dependent on the inhalation elicitation dose of previously challenged rats rather than the dermal induction dose.

Interpatient variability in rates of asthma progression: can genetics provide an answer?

Asthma is a heterogeneous disorder with a variable natural history. In children 3 patterns of the natural history of asthma have been described: early onset but transient, persistent, and later onset, with only the former leading to persistent asthma later in childhood. In adults a range of different asthma phenotypes differing in their environmental, inflammatory, and prognostic characteristics have also been described. These extend beyond allergic (extrinsic) and nonallergic (intrinsic) asthma to include persistent airflow obstruction and accelerated decrease in lung function over time. Asthma progression can be defined as the change in an individual's phenotype along a continuum ranging from nonasthmatic to asthmatic and subsequent development of severe chronic disease. It is clear that for prevention of asthma progression in patients, there is a need for both better understanding of the pathophysiology of asthma and identification of predictors of progression. Interpatient genetic variability has been shown to affect multiple facets of asthma progression, including increased susceptibility to atopy and subsequent asthma, progression to severe disease, and modification of the response to treatment. Thus genetic testing might provide a means for predicting the likely progression of an individual along the continuum, allowing targeting of preventative treatment. However, the prospect of the use of genetic information in clinical practice raises important social and ethical issues that will need to be addressed before genetic testing can be used to inform the preventative treatment of patients to prevent the development of progression of asthma in individuals.

Determination of airborne isocyanates

Isocyanates are important in industrial hygiene and workplace monitoring. Owing to their severe acute toxicity and sensitizing properties, analytical methods with high sampling efficiency and sensitivity in the low ppb to ppt range are required. The reactivity of isocyanates necessitates initial derivatization with nucleophilic agents--usually amines--for stabilization and enrichment; this is often followed by chromatographic separation with spectroscopic, electrochemical, or mass spectrometric detection. Sampling strategies for airborne isocyanates comprise active, i.e. pumped, or passive, i.e. diffusive, methods; the method selected depends on the application. Whereas active methods rely mainly on impingers, reagent-coated filters, or sampling tubes, passive samplers make use of reagent-coated filters, the surface of which is connected to the air sample by diffusion channels. Because airborne isocyanates are prone to occur in different forms, i.e. as vapors, as aerosols, or adsorbed on particulate matter, denuder sampling has been introduced, thus enabling simultaneous collection of gaseous and aerosol isocyanates. The first part of this review summarizes chemical methods and reagents which have been introduced for derivatization of airborne isocyanates. The advantages and drawbacks of the individual derivatization procedures and their combination with different detection principles are evaluated. In the second part, the most recent developments in air sampling for isocyanates, with special focus on diffusive sampling, are reviewed and critically discussed.

Polyisocyanates in occupational environments: a critical review of exposure limits and metrics

BACKGROUND

Determination of polyisocyanates is important because they are a major contributor of exposure to the isocyanate functional group in many workplace environments and are capable of inducing sensitization and asthma. However, with multiple different measurement metrics in use, comparison of isocyanate exposure data between studies and development of occupational exposure limits (OELs) for polyisocyanates is difficult.

METHODS

An analysis of existing problems in the measurement and regulation of isocyanates is presented based on the published analytical, toxicological, and regulatory literature, and the authors' own analytical data and experience with isocyanates.

RESULTS

This analysis supports a need for standardization of isocyanate measurement metrics and provides a framework for the development of an OEL for polyisocyanates.

CONCLUSIONS

The total isocyanate group (microg NCO/m(3)) is recommended as the most feasible and practical metric (unit) by which to express polyisocyanate exposures for research, control, and regulatory purposes. The establishment of a comprehensive isocyanate OEL that simplifies the current agent-by-agent approach and expands coverage to polyisocyanates is also recommended.

Spray-painting and chronic airways obstruction

BACKGROUND

The aim was to investigate the respiratory response of HDI-based paint aerosol within the context of the protection afforded by current exposure guidelines.

METHODS

A cross-sectional study of 240 painters spraying polyurethane enamels was undertaken at four aircraft maintenance plants. Questionnaire and spirometric data were related to gravimetric measures of cumulative total and respirable paint aerosol (TPA and RPA) and estimated isocyanate in total and respirable aerosols (TIA and RIA).

RESULTS

Average cumulative exposures in mg/m(3)-years +/- SD were 159.0 +/- 115.2 TPA, 19.1 +/- 13.8 RPA, 15.8 +/- 11.5 TIA, and 1.9 +/- 1.4 RIA. After adjusting for smoking and asthma symptoms, higher exposures were associated with statistically significant reduction in expiratory flowrates. Significant smoking-related reductions were also observed, without exposure interactions.

CONCLUSIONS

These results suggest important respiratory effects from exposures to spray paint aerosols at levels generally in compliance with existing standards for otherwise unregulated particulates and for the isocyanate component of the paint.

8. Occupational asthma and allergies

A diversity of airborne dusts, gases, fumes, and vapors can cause dose-related symptoms in individuals exposed in the workplace. More than 250 chemicals have been incriminated as a cause of occupational asthma (OA). The prevalence of OA ranges from 2% to 6% of the asthmatic population. Predisposing factors facilitating the development of OA include the work environment, climatic conditions, genetic proclivities, tobacco and recreational drug use, respiratory infection, and bronchial hyperresponsiveness. Pathogenetically, new-onset OA may be immunologic or nonimmunologic in origin. The immunologic variants are usually caused by high molecular-weight allergens such as grain dust and animal or fish protein. Symptoms ensue after a latent period of months to years. Nonimmunologic OA can be precipitated by a brief, high-level exposure to a potent irritant. Symptoms occur immediately or within a few hours of the exposure. In either instance, once the diagnosis is established, the worker should be removed from the workplace. If the diagnosis is made in a timely fashion, most workers experience improvement. Prevention is the best therapeutic intervention.

Occupational asthma, lung function decrement, and toluene diisocyanate (TDI) exposure: a critical review of exposure-response relationships

An extensive amount of clinical/epidemiological literature exists regarding the effects of toluene diisocyanate (TDI) exposure on respiratory health. This review presents an evaluation and synthesis of that literature with an emphasis on assessing exposure-response relationships in the workplace. The key respiratory disorders examined are bronchial asthma and an accelerated decline in lung function. In the early years of the industry, annual incidence rates of TDI-induced occupational asthma (OA) were as high as 5-6 percent. In settings where mean TDI concentrations have been maintained below 5 ppb based on 8-hr personal samples, OA incidence rates have declined to < 1 percent annually. Recent data also suggest that overexposure incidents may play an important role in inducing OA, particularly in work environments engineered to minimize routine ambient air concentrations. Fourteen studies were reviewed that examined lung function decrement. Early studies from the 1960s and 1970s provided evidence of transient or fixed lung function loss (measured as a decline in forced expiratory volume in one second [FEV1]) during periods of ongoing exposure among employees experiencing high rates of work-related symptoms of OA. Such findings would not be unexpected in that modest FEV1 declines have been demonstrated in general population studies of persons with bronchial hyperresponsiveness or persistent non-occupational asthma. More recent workplace studies have provided no consistent evidence of accelerated FEV1 loss among employees exposed up to 5 ppb TDI (8-hr TWA) even with documented routine short-term TDI concentrations exceeding 20 ppb TDI.

Biological monitoring of aromatic diisocyanates in workers exposed to thermal degradation products of polyurethanes

Exposure to diisocyanates was assessed by biological monitoring among workers exposed to the thermal degradation products of polyurethanes (PURs) in five PUR-processing environments. The processes included grinding and welding in car repair shops, milling and turning of PUR-coated metal cylinders, injection moulding of thermoplastic PUR, welding and cutting of PUR-insulated district heating pipes during installation and joint welding, and heat-flexing of PUR floor covering. Isocyanate-derived amines in acid-hydrolysed urine samples were analysed as perfluoroacylated derivatives by gas chromatography mass spectrometry in negative chemical ionisation mode. The limits of quantification (LOQs) for the aromatic diamines 2,4- and 2,6-toluenediamine (2,4- and 2,6-TDA) and 4,4'-methylenedianiline (4,4'-MDA) were 0.25 nmol l(-1), 0.25 nmol l(-1) and 0.15 nmol l(-1), respectively. The LOQ for the aliphatic diamines hexamethylenediamine (HDA), isophoronediamine (IpDA) and 4,4'-diaminodicyclohexyl methane (4,4'-DDHM) was 5 nmol l(-1). TDA and MDA were detected in urine samples from workers in car repair shops and MDA in samples from workers welding district heating pipes. The 2,4-TDA isomer accounted for about 80% of the total TDA detected. No 2.6-TDA was found in the urine of non-exposed workers. The highest measured urinary TDA and MDA concentrations were 0.79 nmol mmol(-1) creatinine and 3.1 nmol mmol(-1) creatinine, respectively. The concentrations found among non-exposed workers were 0.08 nmol mmol(-1) creatinine for TDA and 0.05 nmol mmol(-1) creatinine for MDA (arithmetic means). Exposure to diisocyanates originating from the thermal degradation of PURs are often intermittent and of short duration. Nevertheless, exposure to aromatic diisocyanates can be identified by monitoring diisocyanate-derived amines in acid-hydrolysed urine samples.

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.

Identification of human lung and skin proteins conjugated with hexamethylene diisocyanate in vitro and in vivo

Diisocyanates are asthma-causing chemicals used in the commercial production of polyurethane. We have previously shown that human lung epithelial cell proteins can become conjugated with hexamethylene diisocyanate (HDI) and may be biologically important in diisocyanate-induced asthma. The objective of this study was to identify specific human lung and skin proteins that become conjugated with diisocyanate after in vitro and in vivo exposure. Following in vitro exposure of human airway epithelial cells (A549), keratin 18, the 78-kD glucose-regulated protein, trans-1, 2-dihyrobenzene-1,2-diol dehydrogenase, and actin were identified as prominent diisocyanate-conjugated proteins through use of a combination of immunocytochemical and mass spectrometric techniques. Following in vivo inhalation of an HDI aerosol, keratin 18 was also identified as the predominant diisocyanate-conjugated protein in human endobronchial biopsy samples, whereas albumin was the predominant diisocyanate-conjugated protein in bronchoalveolar lavage fluid. Keratin was also identified as a predominant diisocyanate-conjugated protein in human skin biopsy samples after epicutaneous exposure to liquid-phase HDI, although the major skin diisocyanate-conjugated protein (56-kD) differed from the predominant lung diisocyanate-conjugated keratin (47-kD). The data from this study identify keratin and other proteins as potential "carriers" for diisocyanates in vivo, and suggest that HDI conjugation of these proteins may play a role in the pathogenesis of diisocyanate-induced asthma.