Immunotoxicity of Workplace Xenobiotics

National Institute Of Environmental Health Sciences

Investigators

Abstract

The goal of this interagency agreement is to provide support of National Toxicology Program (NTP) hazard identification (or hazard assessment) activities targeted toward the prevention of diseases or adverse effects caused by environmental exposure to chemical or physical agents. These cooperative studies continue to improve the risk assessment process by determining quantitatively what constitutes an adverse health effect on the immune system in humans. These studies evaluate unique cohorts of individuals from professions associated with immune-mediated occupational diseases including asthma, respiratory and contact allergy, chronic beryllium disease, rhinitis, and silicosis. Occupational cohorts are being studied for a number of endpoints including, impact of genetic polymorphisms on inflammatory disease development and clinical outcomes, the role that genetic variations play in environmental and workplace related diseases and identification of unique immunological biomarkers for disease. The NIOSH Laboratory for Occupational Genomics serves as a resource for obtaining samples from individuals with occupational and occupationally related diseases including chemical-induced contact dermatitis, musculoskeletal disease, chronic beryllium disease, pulmonary fibrosis, chronic obstructive pulmonary disease, HIV infection, occupationally related cancer, neurodegenerative disease, occupational asthma and rhinitis, and silicosis. A major emphasis has been placed on cytokine polymorphisms, especially within the MHC region, as a large number of occupational/environmental diseases are associated with chronic inflammatory responses and, thus, immune responses. This project has been expanded to study genetic variations in the major histocompatibility complex (MHC) region. Recruitment of subjects exposed to low- and high-molecular weight agents as well as work-matched controls has been completed (approximately 500 subjects). Genotyping of MHC region variations using high density SNP microarray platform has been completed. Preliminary analyses comparing workers with positive inhalation challenge to low molecular weight agents (majority isocyanates) and workplace controls showed that over 100 SNPs are statistically significantly associated with OA. Increased frequencies of specific alleles and 3 combined genotypes have been found in hexamethylene diisocyanate (HDI)-exposed spray workers with respiratory symptoms. Current activities involve additional genotyping and data analyses. These findings will be further investigated in a larger case control study of a homogeneous French Canadian worker population. In addition to HDI, genotype associations with exposure to other diisocyanates (TDI and MDI) will be explored to determine if there are common alleles or genotypes that predict diisocyanate-induced asthma. We are also investigating the contribution of genetic variability in the immune-inflammatory-antioxidant responses to the development and/or severity of irritant contact dermatitis (ICD) in health care workers. Subject recruitment, sample collection and follow-ups are completed for approximately 400 individuals and recruitment of additional subjects is ongoing. Preliminary results from questionnaire and patch test data indicate a trend toward increased dermatitis with increased hand washing frequency (more than 10 times a day). 77% of subjects who reacted to 2.5% SLS developed dermatitis suggesting that the 24-h irritant patch test may be useful for prediction of susceptibility to ICD. In addition, genetic variations that control expression level of several inflammatory mediators and antioxidants were differently represented in high and low irritant responders. To further current understanding of the pathobiology of respiratory disease induced by exposure to diisocyanates in the workplace we are using whole-genome techniques to identify major biological pathways that may serve as targets for biomarker development, disease diagnosis and/or treatment of disease. To fulfill this objective, we have initiated collaborations with extramural partners to investigate the mechanisms of occupational rhinitis in workers exposure to diisocyanates. Patient enrollment, clinical assessment and sample collection is ongoing. Nasal mucosal tissue will be obtained from workers that are confirmed as specific inhalation challenge positive to diisocyanate challenge. Nasal cytology will be performed on one sample to examine the cellular inflammation that characterizes this disease. Whole-genome microarrays will then be performed on a second sample to investigate the underlying biology and identify potential targets for biomarker development. Similar studies in diverse worker populations are required to develop biomarkers that may be useful for disease surveillance and diagnosis in geographically and ethnically distinct populations. In parallel studies in a murine model of diisocyanate-induced rhinitis we have conducted microarray gene expression analysis during the active stage of disease and the results strongly support an allergic etiology. Using this animal model, we are working to establish gene expression biomarker signatures that define the transition from TDI exposure to sensitization and active disease. Occupational rhinitis is a chronic inflammatory disease of the upper respiratory tract that is present in greater than 90% of workers with occupational asthma. A cohort of chronic rhinosinusitis patients is being evaluated for subjects with allergies to molds. One hundred sinusitis patients and 40 controls have been skin prick tested for a number of mold allergens and the sera have been analyzed for IgG and IgE to mold and other seasonal allergens. At this time additional control subjects are being recruited. As there is currently a lack of information on dry fungal aerosol exposures, a series of studies was undertaken utilizing aerosols from several organisms to investigate the consequences of dry fungal aerosol exposures in a rodent model. The insufflation technique that had been used to expose mice to dry preparations of spores and fragments has not yielded results that are reproducible and studies with Green Fluorescent Protein-labeled Aspergillus fumagatus suggest that the aerosolized materials were not reaching the alveoli . Work continues on an exposure chamber with an acoustical generator as a potential model of a more natural type of exposure and initial tests of the chamber and exposure characterization is currently underway. A related project includes work to characterize the role of terrelysin as a marker of Aspergillus terreus exposure. Terrelysin has been successfully cloned and produced as a functionally active (hemolytic) recombinant protein. Monoclonal antibodies have been developed for use in environmental and personal exposure assessment methodologies. Occupational exposure to flour and wheat dust may occur in non-bakery environments. A human health assessment was begun at a large (~500 employees) commercial facility that uses flour and wheat to bread the products before frying. In a preliminary visit to the plant, several employees had complaints consistent with occupational rhinitis and/or asthma and dust exposure levels were high (>50 mg/m3). Using a protocol developed to study commercial bakeries, antigen specific IgE and IgG to flour dust and wheat, garlic, onion, soybean and corn, total IgE (AlaTop) and environmental total dust, wheat, and soy flour will be evaluated. Medical histories as well as questions about health problems at work are being captured via questionnaires. Finally, ongoing studies are identifying and quantifying the volatile reaction products of gas-phase compounds present in the indoor environment, especially dicarbonyls, and investigating immunotoxic and hypersensitivity effects of these reaction products in both in vitro and in vivo models. Studies to characterize the effects of dicarbonyls on the respiratory tract have been conducted using an in vitro indoor air exposure system. Changes in inflammatory cytokine expression were evaluated in a pulmonary epithelial cell line (A549) after exposure to dicarbonyls (diacetyl, 4-OPA, glyoxal, methyl glyoxal and glutaraldehyde) individually and in a reaction mixture. Dicarbonyls stimulate the release of a number of pro-inflammatory mediators from lung epithelial cells. These studies suggest that oxygenated reaction products may be contributing to the adverse health effects associated with indoor air exposure. Consistent elevations in inflammatory cytokines obtained for the structurally similar compounds suggest that the effects may be caused by exposure to the combined exposures to small amounts of reaction products.