Nonoccupational and occupational exposure to isocyanates

The genetics of occupational asthma development among workers exposed to diisocyanates: A systematic literature review with meta-analysis

Diisocyanates are widely used compounds that pose a safety concern for workers in occupations within the spray-paint, spray-foam insulation, and furniture varnish industries. Epidemiological studies show that only a subset of workers exposed to diisocyanates develop diisocyanate-induced occupational asthma (diisocyanate asthma, DA), indicating that genetic susceptibility may play a role. The purpose of this systematic literature review was to compile and meta-analyze the reported data on genetic susceptibility markers for DA. Three databases (Embase, Pubmed, and Scopus) were searched and 169 non-duplicate publications were identified, of which 22 relevant occupational studies were included in this review. Researchers reported prevalence odds ratios (PORs) for 943 comparisons in 82 different genes/serotypes. Protein network functions for the DA-associated genes from this review include: antigen processing, lymphocyte activation, cytokine production regulation, and response to oxidative stress. Meta-analysis of comparisons between workers with DA and controls was conducted for 23 genetic markers within: CTNNA3, GSTM1, GSTP1, GSTT1, HLA-C, HLA-DQB1, HLA-DR1, HLA-DR3, HLA-DR4, HLA-DR7, and HLA-DR8. These genes code for proteins that are involved in cell-cell adhesions (CTNNA3), glutathione conjugation for xenobiotic metabolism (GST gene family), and immune system response (HLA gene family). The most compelling pooled PORs were for two studies on CTNNA3 (increased DA risk: rs10762058 GG, rs7088181 GG, rs4378283 TT; PORs 4.38–4.97) and three studies on HLA-DR1 (decreased DA risk, POR 0.24). Bioinformatics of the predicted protein pathways for DA shows overlap with biomarker-associated pathways in workers before development of asthma, suggesting overlap in toxicokinetic and toxicodynamic pathways of diisocyanates. The control groups were also compared against each other and differences were negligible. Suggestions for improving future research are also presented. Of the highest importance, the literature was found to be profoundly publication-biased, in which researchers need to report the data for all studied markers regardless of the statistical significance level. We demonstrate the utility of evaluating the overlap in predicted protein pathway functions for identifying more consistency across the reported literature including for asthma research, biomarker research, and in vitro studies. This will serve as an important resource for researchers to use when generating new hypothesis-driven research about diisocyanate toxicology.

Risk Assessment for Toluene Diisocyanate and Respiratory Disease Human Studies

BACKGROUND

Toluene diisocyanate (TDI) is a highly reactive chemical that causes sensitization and has also been associated with increased lung cancer. A risk assessment was conducted based on occupational epidemiologic estimates for several health outcomes.

METHODS

Exposure and outcome details were extracted from published studies and a NIOSH Health Hazard Evaluation for new onset asthma, pulmonary function measurements, symptom prevalence, and mortality from lung cancer and respiratory disease. Summary exposure-response estimates were calculated taking into account relative precision and possible survivor selection effects. Attributable incidence of sensitization was estimated as were annual proportional losses of pulmonary function. Excess lifetime risks and benchmark doses were calculated.

RESULTS

Respiratory outcomes exhibited strong survivor bias. Asthma/sensitization exposure response decreased with increasing facility-average TDI air concentration as did TDI-associated pulmonary impairment. In a mortality cohort where mean employment duration was less than 1 year, survivor bias pre-empted estimation of lung cancer and respiratory disease exposure response.

CONCLUSION

Controlling for survivor bias and assuming a linear dose-response with facility-average TDI concentrations, excess lifetime risks exceeding one per thousand occurred at about 2 ppt TDI for sensitization and respiratory impairment. Under alternate assumptions regarding stationary and cumulative effects, one per thousand excess risks were estimated at TDI concentrations of 10 - 30 ppt. The unexplained reported excess mortality from lung cancer and other lung diseases, if attributable to TDI or associated emissions, could represent a lifetime risk comparable to that of sensitization.

Development of a method for quantification of toluene diisocyanate and methylenediphenyl diisocyanate migration from polyurethane foam sample surface to artificial sweat by HPLC-UV-MS

The US Environmental protection agency (EPA) has published guidance that includes test procedures for evaluating indoor exposure to chemicals from products. One of the test procedures represents the migration test for evaluating potential dermal exposure from home furniture. Such an evaluation involves the chemical measurement of the sweat which is currently unavailable in the literature. The objective of this project was to develop and validate an analytical method for quantification of migration of 4,4'-methylenediphenyl diisocyanate (MDI), 2,6-toluene diisocyanate (2,6-TDI) and 2,4-toluene diisocyanate (2,4-TDI) from a polyurethane (PU) flexible foam to artificial sweat that meets the recommendations of the EPA test protocol. Following the EPA protocol, six synthetic sweat solutions were prepared and used in evaluation of isocyanate recovery performance. The migration tests were conducted using five foam types that were chosen and supplied by PU foam manufacturers to represent the types most commonly found in commercial products, and with formulations anticipated to have the highest potential residual TDI or MDI. Migration tests were conducted using glass fiber filters (GFF) coated with 1-(2-methoxyphenyl)piperazine (1,2-MP) and analyzed using HPLC equipped with a UV detector for quantification and a MS detector to qualify peaks. The detection limits of the method were 0.002 µg/mL for 2,6-TDI, 0.011 µg/mL for 2,4-TDI, and 0.003 µg/mL for MDI. Quantification limits were 0.006 µg/mL, 0.037 µg/mL, and 0.010 µg/mL, respectively. The recovery tests on a Teflon surface for 5 of the 6 EPA-recommended synthetic sweat solutions indicate the recovery percentage was approximately 80% for diisocyanates. Recovery for the sixth sweat solution was low, approximately 30%. TDI and MDI migration was not observed when testing was conducted on foam samples.

Costs of isocyanate-related occupational diseases: A systematic review

Although isocyanates are increasingly used in manufacturing and workplace exposure to isocyanates is widely recognized as one of the most frequent causes for occupational lung and skin diseases, little is known about the economic burden on the affected individual and the society. This study provides an overview on costs of occupational diseases related to isocyanates. We performed a systematic literature search of studies in the electronic databases of the German Institute of Medical Documentation and Information, and the Canadian Centre for Occupational Health and Safety. We extracted the key characteristics of the studies and performed a study quality assessment. We identified eight studies on the costs of illness, of which five focused on occupational lung diseases and three on occupational skin diseases. Further, eight studies calculated loss of income/compensation payments. Out of the 16 identified articles, only two reported costs directly attributable to isocyanate-induced diseases (asthma). Studies were hardly comparable because they differed substantially in their methodological approaches. Moreover, the quality assessment of the studies revealed substantial limitations. While a wide range of isocyanate-related costs was identified, consequences of isocyanate-related occupational diseases were considerable in terms of societal costs and loss of income. In most studies, indirect costs were the main cost driver. There is a need for high-quality cost of illness studies on isocyanate-induced diseases stratified by degree of severity and sex. Such studies provide valuable information to develop preventive strategies and set priorities for measures to lower the burden of professional health risks.

Sensitizing Capacities and Cross-Reactivity Patterns of Some Diisocyanates and Amines Using the Guinea-Pig Maximization Test. Can p-phenylenediamine be Used as a Marker for Diisocyanate Contact Allergy?

Background:

Isocyanates are mainly considered respiratory allergens but can also cause contact allergy. Diphenylmethane-4,4′-diamine (4,4′-MDA) has been considered a marker for diphenylmethane-4,4′-diisocyanate (4,4′-MDI) contact allergy. Furthermore, overrepresentation of positive patch-test reactions top-phenylenediamine (PPD) in 4,4′-MDA positive patients have been reported.

Objectives:

To investigate the sensitizing capacities of toluene-2,4-diisocyanate (2,4-TDI) and PPD and the cross-reactivity of 4,4′-MDA, 2,4-TDI, dicyclohexylmethane-4,4′-diamine (4,4′-DMDA), dicyclohexylmethane-4,4′-diisocyanate (4,4′-DMDI), 4,4′-MDI and PPD.

Methods:

The Guinea Pig Maximization Test (GPMT) was used.

Results:

PPD was shown to be a strong sensitizer (p<0.001). Animals sensitized to PPD showed cross-reactivity to 4,4′-MDA (p<0.001). Animals sensitized to 4,4′-MDA did not show cross-reactivity to PPD. 8 animals sensitized to 2,4-TDI were sacrificed due to toxic reactions at the induction site and could thus not be fully evaluated.

Conclusion:

PPD was shown to be a strong sensitizer. However, it cannot be used as a marker for isocyanate contact allergy. On the other hand, positive reactions to 4,4′-MDA could indicate a PPD allergy. The intradermal induction concentration of 2,4-TDI (0.70% w/v) can induce strong local toxic reactions in guinea-pigs and should be lowered.

Vitamin E effect in a rat model of toluene diisocyanate-induced asthma

Background and aim

The aim of the study was to evaluate vitamin E effect upon oxidative stress associated with toluene −2, 4-diisocyanate (TDI)-induced asthma in rats.

Methods

The five study groups were: control, vehicle, TDI, vehicle+E, TDI+E. TDI animals were sensitized by nasal administration of TDI 10% (5μl/nostril) between days 1–7 and 15–21. Between days 22–28 groups TDI+E and vehicle+E rats received vitamin E (50 mg/kg, i. v.), and control, vehicle and TDI groups received saline solution. On day 29 the rats were challenged by intranasal application of 5% TDI (5 μl/nostril). On day 30 blood, BALF and lung biopsy were harvested. Oxidative stress tests were malondialdehyde (MDA), protein carbonyls (PC), total thiols (tSH), 1,1-diphenyl-2-picryl hydrazyl (DPPH) and reduced glutathione (GSH).

Results

TDI sensitization increased oxidative stress systemically, but also locally in the respiratory airways and lung tissue. There was an increase of MDA and PC formation associated with a deficiency of the antioxidant defense reflected by DPPH decreases. There were no differences between systemic and local lung concentrations of oxidized molecules.

After vitamin E treatment oxidative stress was reduced mostly due to serum, BALF and lung tissue GSH and DPPH increase.

Conclusion

The study showed that in rat TDI-induced asthma there was oxidative stress caused by increased ROS production and antioxidants deficiency, and vitamin E reduced ROS production and improved antioxidant defense.

Residual Isocyanates in Medical Devices and Products: A Qualitative and Quantitative Assessment

We conducted a pilot qualitative and quantitative assessment of residual isocyanates and their potential initial exposures in neonates, as little is known about their contact effect. After a neonatal intensive care unit (NICU) stockroom inventory, polyurethane (PU) and PU foam (PUF) devices and products were qualitatively evaluated for residual isocyanates using Surface SWYPE™. Those containing isocyanates were quantitatively tested for methylene diphenyl diisocyanate (MDI) species, using UPLC-UV-MS/MS method. Ten of 37 products and devices tested, indicated both free and bound residual surface isocyanates; PU/PUF pieces contained aromatic isocyanates; one product contained aliphatic isocyanates. Overall, quantified mean MDI concentrations were low (4,4'-MDI = 0.52 to 140.1 pg/mg) and (2,4'-MDI = 0.01 to 4.48 pg/mg). The 4,4'-MDI species had the highest measured concentration (280 pg/mg). Commonly used medical devices/products contain low, but measurable concentrations of residual isocyanates. Quantifying other isocyanate species and neonatal skin exposure to isocyanates from these devices and products requires further investigation.

Toluene diisocyanate: Induction of the autotaxin-lysophosphatidic acid axis and its association with airways symptoms

Diisocyanates are industrial chemicals which have a wide range of applications in developed and developing countries. They are notorious lung toxicants and respiratory sensitizers. However, the mechanisms behind their adverse effects are not adequately characterized. Autotaxin (ATX) is an enzyme producing lysophosphatidic acid (LPA), and the ATX-LPA axis has been implicated in lung related inflammatory conditions and diseases, including allergic asthma, but not to toxicity of environmental low-molecular-weight chemicals. We investigated effects of toluene diisocyanate (TDI) on ATX induction in human lung epithelial cell models, and we correlated LPA-levels in plasma to biomarkers of TDI exposure in urine collected from workers exposed to <5ppb (parts per billion). Information on workers' symptoms was collected through interviews. One nanomolar TDI robustly induced ATX release within 10min in vitro. A P2X7- and P2X4-dependent microvesicle formation was implicated in a rapid ATX release and a subsequent protein synthesis. Co-localization between purinergic receptors and ATX was documented by immunofluorescence and confocal microscopy. The release was modulated by monocyte chemoattractant protein-1 (MCP-1) and by extracellular ATP. In workers, we found a dose-response relationship between TDI exposure biomarkers in urine and LPA levels in plasma. Among symptomatic workers reporting "sneezing", the LPA levels were higher than among non-symptomatic workers. This is the first report indicating induction of the ATX-LPA axis by an environmental low-molecular-weight chemical, and our data suggest a role for the ATX-LPA axis in TDI toxicity.

Is the analysis of histamine and/or interleukin-4 release after isocyanate challenge useful in the identification of patients with IgE-mediated isocyanate asthma?

Isocyanates are a well-known and frequent cause of occupational asthma. The implementation of specific inhalation challenges (SICs) is the gold standard in asthma diagnosis supporting occupational case history, lung function testing, specific skin prick tests and the detection of specific IgE. However, the diagnosis is not always definitive. An interesting new approach, analyses of individual genetic susceptibilities, requires discrimination between a positive SIC reaction arising from IgE-mediated immune responses and one from other pathophysiological mechanisms. Hence, additional refinement tools would be helpful in defining sub-classes of occupational asthma and diagnosis. We used total IgE levels, specific IgE and SIC results for sub-classification of 27 symptomatic isocyanate workers studied. Some mutations in glutathione S-transferases (GSTs) are suspected either to enhance or to decrease the individual risk in the development of isocyanate asthma. Our patient groups were assessed for the point mutations GSTP1*I105V and GSTP1*A114V as well as deletions (null mutations) of GSTM1 and GSTT1. There seems to be a higher risk in developing IgE-mediated reactions when GSTM1 is deleted, while GSTT1 deletions were found more frequently in the SIC positive group. Blood samples taken before SIC, 30-60 min and 24h after SIC, were analyzed for histamine and IL-4, classical markers for the IgE-mediated antigen-specific activation of basophils or mast cells. We suggest that the utility of histamine measurements might provide an additional useful marker reflecting isocyanate-induced cellular reactions (although the sampling times require optimization). The promising measurement of IL-4 is not feasible at present due to the lack of a reliable, validated assay.