Glutathione reaction products with a chemical allergen, methylene-diphenyl diisocyanate, stimulate alternative macrophage activation and eosinophilic airway inflammation

"Isocyanates and isocyanides - life-threatening toxins or essential compounds?"

Isocyanides and isocyanates are some of the most reactive compounds in organic chemistry, making them perceived as compounds with high potential for use in both the laboratory and industry. With their high reactivity also comes several disadvantages, most notably their potentially high toxicity. The following article is a collection of information on the toxic effects of the isocyanide group on the human body and the environment. Information on the mechanism of how these harmful substances affect living tissues and the environment, worldwide information on how to protect against these chemicals, current regulations, and exposure limits for specific countries is compiled. The latest research on the application uses of isocyanates and isocyanides is also outlined, as well as the latest safer and greener methods and techniques to work with these compounds. Additionally, the presented article can serve as a brief guide to the organic toxicity of a group of isocyanates and isocyanates.

MicroRNA-mediated Krüppel-like factor 4 upregulation induces alternatively activated macrophage-associated marker and chemokine transcription in 4,4'-methylene diphenyl diisocyanate exposed macrophages

1. Occupational exposure to 4,4'-methylene diphenyl diisocyanate (MDI) is associated with occupational asthma (OA) development. Alveolar macrophage-induced recruitment of immune cells to the lung microenvironment plays an important role during asthma pathogenesis. Previous studies identified that MDI/MDI-glutathione (GSH)-exposure downregulates endogenous hsa-miR-206-3p/hsa-miR-381-3p. Our prior report shows that alternatively activated (M2) macrophage-associated markers/chemokines are induced by MDI/MDI-GSH-mediated Krüppel-Like Factor 4 (KLF4) upregulation in macrophages and stimulates immune cell chemotaxis. However, the underlying molecular mechanism(s) by which MDI/MDI-GSH upregulates KLF4 remain unclear.

2. Following MDI-GSH exposure, microRNA(miR)-inhibitors/mimics or plasmid transfection, endogenous hsa-miR-206-3p/hsa-miR-381-3p, KLF4, or M2 macrophage-associated markers (CD206, TGM2), and chemokines (CCL17, CCL22, CCL24) were measured by either RT-qPCR, western blot, or luciferase assay.

3. MDI-GSH exposure downregulates hsa-miR-206-3p/hsa-miR-381-3p by 1.46- to 9.75-fold whereas upregulates KLF4 by 1.68- to 1.99-fold, respectively. In silico analysis predicts binding between hsa-miR-206-3p/hsa-miR-381-3p and KLF4. Gain- and loss-of-function, luciferase reporter assays and RNA-induced silencing complex-immunoprecipitation (RISC-IP) studies confirm the posttranscriptional regulatory roles of hsa-miR-206-3p/hsa-miR-381-3p and KLF4 in macrophages. Furthermore, hsa-miR-206-3p/hsa-miR-381-3p regulate the expression of M2 macrophage-associated markers and chemokines via KLF4.

4. In conclusion, hsa-miR-206-3p/hsa-miR-381-3p play a major role in regulation of MDI/MDI-GSH-induced M2 macrophage-associated markers and chemokines by targeting the KLF4 transcript, and KLF4-mediated regulation in macrophages.

Lung Gene Expression Suggests Roles for Interferon-Stimulated Genes and Adenosine Deaminase Acting against RNA-1 in Pathologic Responses to Diisocyanate

Mechanisms underlying methylene diphenyl diisocyanate (MDI) and other low molecular weight chemical-induced asthma are unclear and appear distinct from those of high molecular weight (HMW) allergen-induced asthma. We sought to elucidate molecular pathways that differentiate asthma-like pathogenic vs nonpathogenic responses to respiratory tract MDI exposure in a murine model. Lung gene expression differences in MDI exposed immune-sensitized and nonsensitized mice vs unexposed controls were measured by microarrays, and associated molecular pathways were identified through bioinformatic analyses and further compared with published studies of a prototypic HMW asthmagen (ovalbumin). Respiratory tract MDI exposure significantly altered lung gene expression in both nonsensitized and immune-sensitized mice, vs controls. Fifty-three gene transcripts were altered in all MDI exposed lung tissue vs controls, with levels up to 10-fold higher in immune-sensitized vs nonsensitized mice. Gene transcripts selectively increased in MDI exposed immune-sensitized animals were dominated by chitinases and chemokines and showed substantial overlap with those increased in ovalbumin-induced asthma. In contrast, MDI exposure of nonsensitized mice increased type I interferon stimulated genes (ISGs) in a pattern reflecting deficiency in adenosine deaminase acting against RNA (ADAR-1), an important regulator of innate, as well as "sterile" or autoimmunity triggered by tissue damage. Thus, MDI-induced changes in lung gene expression were identified that differentiate nonpathogenic innate responses in nonsensitized hosts from pathologic adaptive responses in immune-sensitized hosts. The data suggest that MDI alters unique biological pathways involving ISGs and ADAR-1, potentially explaining its unique immunogenicity/allergenicity.

4,4'-Methylene diphenyl diisocyanate exposure induces expression of alternatively activated macrophage-associated markers and chemokines partially through Krüppel-like factor 4 mediated signaling in macrophages

Occupational exposure to the most widely used monomeric diisocyanate (dNCO), 4,4'-methylene diphenyl diisocyanate (MDI), may lead to the development of occupational asthma (OA). Alveolar macrophages with alternatively activated (M2) phenotype have been implicated in allergic airway responses and the pathogenesis of asthma. Recent in vivo studies demonstrate that M2 macrophage-associated markers and chemokines are induced by MDI-exposure, however, the underlying molecular mechanism(s) by which this proceeds is unclear.Following MDI exposure (in vivo and in vitro) M2 macrophage-associated transcription factors (TFs), markers, and chemokines were determined by RT-qPCR, western blots, and ELISA.Expression of M2 macrophage-associated TFs and markers including Klf4/KLF4, Cd206/CD206, Tgm2/TGM2, Ccl17/CCL17, Ccl22/CCL22, and CCL24 were induced by MDI/MDI-GSH exposure in bronchoalveolar lavage cells (BALCs)/THP-1 macrophages. The expression of CD206, TGM2, CCL17, CCL22, and CCL24 are upregulated by 3.83-, 7.69-, 6.22-, 6.08-, and 1.90-fold in KLF4-overexpressed macrophages, respectively. Endogenous CD206 and TGM2 were downregulated by 1.65-5.17-fold, and 1.15-1.78-fold, whereas CCL17, CCL22, and CCL24 remain unchanged in KLF4-knockdown macrophages. Finally, MDI-glutathione (GSH) conjugate-treated macrophages show increased chemotactic ability to T-cells and eosinophils, which may be attenuated by KLF4 knockdown.Our data suggest that MDI exposure may induce M2 macrophage-associated markers partially through induction of KLF4.

Fast and Bioorthogonal Release of Isocyanates in Living Cells from Iminosydnones and Cycloalkynes

Bioorthogonal click-and-release reactions are powerful tools for chemical biology, allowing, for example, the selective release of drugs in biological media, including inside animals. Here, we developed two new families of iminosydnone mesoionic reactants that allow a bioorthogonal release of electrophilic species under physiological conditions. Their synthesis and reactivities as dipoles in cycloaddition reactions with strained alkynes have been studied in detail. Whereas the impact of the pH on the reaction kinetics was demonstrated experimentally, theoretical calculations suggest that the newly designed dipoles display reduced resonance stabilization energies compared to previously described iminosydnones, explaining their higher reactivity. These mesoionic compounds react smoothly with cycloalkynes under physiological, copper-free reaction conditions to form a click pyrazole product together with a released alkyl- or aryl-isocyanate. With rate constants up to 1000 M^-1 s^-1, this click-and-release reaction is among the fastest described to date and represents the first bioorthogonal process allowing the release of isocyanate electrophiles inside living cells, offering interesting perspectives in chemical biology.

Glutathione reactivity with aliphatic polyisocyanates

Isocyanate chemicals known to cause adverse health effects when inhaled are essential to making important products and are used in multiple industries. Glutathione (GSH), a major antioxidant of the lower airways with a well described role in xenobiotic metabolism, is a primary reaction target for di-isocyantes. However, GSHs reactivity with poly-isocyanates which have largely replaced diisocyanates (particularly aliphatic) in most end-user settings remains uncertain. We hypothesized aliphatic polyisocyanates would readily react with glutathione under physiologic conditions and the products could be identified using liquid chromatography (LC) coupled-mass spectrometry (MS) and tandem MS/MS. The data identified (tris)GSH-isocyanate adducts as the major reaction product of GSH with the most commonly used contemporary polymeric (tri-isocyanate) formulations of hexamethylene diisocyanate (HDI), the isocyanurate and biuret, as [M+H]⁺ ions of 1426.53 and 1400.55 m/z respectively in reverse phase LC-MS using electrospray in positive ion mode. The uretdione form of HDI, a stabilized dimer, formed two reaction products with GSH, a tris(GSH)-isocyanate reaction product recognized as a 1258.44 m/z [M+H]⁺ ion, and a bis(GSH)-isocyanate product identified as a 951.36 m/z [M+H]⁺ ion. Predicted structures for the newly described GSH-polyisocyanate reaction products, modeled based on collision induced dissociation (CID) fragmentation patterns in tandem MS/MS, support S-linkage of the GSH to N = C = O groups. In summary, industrially-used aliphatic polyisocyanates readily react with GSH to form primarily S-linked tris(GSH)-conjugates, a process that may play an important role in response to respiratory tract exposure.

Absorption, distribution, metabolism, and excretion of methylene diphenyl diisocyanate and toluene diisocyanate: Many similarities and few differences

Methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) are high production volume chemicals used for the manufacture of polyurethanes. For both substances, the most relevant adverse health effects after overexposure in the workplace are isocyanate-induced asthma, lung function decrement and, to a much lesser extent, skin effects. Over the last two decades many articles have addressed the reactivity of MDI and TDI in biological media and the associated biochemistry, which increased the understanding of their biochemical and physiological behavior. In this review, these new insights with respect to similarities and differences concerning the adsorption, distribution, metabolism, and excretion (ADME) of these two diisocyanates and the implications on their toxicities are summarized. Both TDI and MDI show very similar behavior in reactivity to biological macromolecules, distribution, metabolism, and excretion. Evidence suggests that the isocyanate (NCO) group is scavenged at the portal-of-entry and is not systemically available in unbound reactive form. This explains the lack of other than portal-of-entry toxicity observed in repeated-dose inhalation tests.

MicroRNA-mediated calcineurin signaling activation induces CCL2, CCL3, CCL5, IL8, and chemotactic activities in 4,4'-methylene diphenyl diisocyanate exposed macrophages

Occupational exposure to 4,4'-methylene diphenyl diisocyanate (MDI), the most widely used monomeric diisocyanate, is one of the leading causes of occupational asthma (OA). Previously, we identified microRNA (miR)-206-3p/miR-381-3p-mediated PPP3CA/calcineurin signalling regulated iNOS transcription in macrophages and bronchoalveolar lavage cells (BALCs) after acute MDI exposure; however, whether PPP3CA/calcineurin signalling participates in regulation of other asthma-associated mediators secreted by macrophages/BALCs after MDI exposure is unknown.Several asthma-associated, macrophage-secreted mediator mRNAs from MDI exposed murine BALCs and MDI-glutathione (GSH) conjugate treated differentiated THP-1 macrophages were analysed using RT-qPCR.Endogenous IL1B, TNF, CCL2, CCL3, CCL5, and TGFB1 were upregulated in MDI or MDI-GSH conjugate exposed BALCs and macrophages, respectively. Calcineurin inhibitor tacrolimus (FK506) attenuated the MDI-GSH conjugate-mediated induction of CCL2, CCL3, CCL5, and CXCL8/IL8 but not others. Transfection of either miR-inhibitor-206-3p or miR-inhibitor-381-3p in macrophages induced chemokine CCL2, CCL3, CCL5, and CXCL8 transcription, whereas FK506 attenuated the miR-inhibitor-206-3p or miR-inhibitor-381-3p-mediated effects. Finally, MDI-GSH conjugate treated macrophages showed increased chemotactic ability to various immune cells, which may be attenuated by FK506.In conclusion, these results indicate that MDI exposure to macrophages/BALCs may recruit immune cells into the airway via induction of chemokines by miR-206-3p and miR-381-3p-mediated calcineurin signalling activation.

Acute 4,4'-Methylene Diphenyl Diisocyanate Exposure-Mediated Downregulation of miR-206-3p and miR-381-3p Activates Inducible Nitric Oxide Synthase Transcription by Targeting Calcineurin/NFAT Signaling in Macrophages

Exposure to 4,4'-methylene diphenyl diisocyanate (MDI) in the occupational setting may lead to development of occupational asthma (OA), and the underlying molecular mechanisms of MDI-induced disease pathogenesis remain an active area of research. Using a nose-only mouse inhalation model, we find that circulating microRNA (miR)-206-3p and miR-381-3p are downregulated after MDI exposure; however, cellular miR-206-3p and miR-381-3p responses after MDI aerosol exposure and their pathophysiological roles in MDI-OA are unknown. We hypothesize that miR-206-3p and miR-381-3p-regulated mechanisms cause increased expression of the inducible nitric oxide synthase (iNOS) after MDI aerosol exposure. We examined cellular miR-206-3p and miR-381-3p, calcineurins, nuclear factors of activated T cells (NFATs), and iNOS levels from both nose-only exposed murine bronchoalveolar lavage cells (BALCs) and differentiated THP-1 macrophages treated with MDI-glutathione (GSH) conjugates. Both in vivo murine MDI aerosol exposure and in vitro MDI-GSH exposures in THP-1 macrophages result in downregulation of endogenous miR-206-3p and miR-381-3p and upregulation of PPP3CA and iNOS expression. Transfection of THP-1 macrophages with miR-inhibitor-206-3p and miR-inhibitor-381-3p resulted in the upregulation of PPP3CA and iNOS. Using RNA-induced silencing complex immunoprecipitation and translational reporter assays, we verified that PPP3CA, but not iNOS, is directly targeted by both miR-206-3p and miR-381-3p. Downregulation of miR-206-3p and miR-381-3p following by MDI exposure induces calcineurin/NFAT signaling-mediated iNOS transcription in macrophages and BALCs.

Analysis of Lung Gene Expression Reveals a Role for Cl- Channels in Diisocyanate-induced Airway Eosinophilia in a Mouse Model of Asthma Pathology

Diisocyanates are well-recognized causes of asthma. However, sensitized workers frequently lack diisocyanate-specific IgE, which complicates diagnosis and suggests the disease involves IgE-independent mechanisms. We used a mouse model of methylene diphenyl diisocyanate (MDI) asthma to identify biological pathways that may contribute to asthma pathogenesis. MDI sensitization and respiratory tract exposure were performed in Balb/c, transgenic B-cell (e.g., IgE)-deficient mice and a genetic background (C57BL/6)-matched strain. Eosinophils in airway fluid were quantitated by flow cytometry. Lung tissue gene expression was assessed using whole-genome mRNA microarrays. Informatic software was used to identify biological pathways affected by respiratory tract exposure and potential targets for disease intervention. Airway eosinophilia and changes (>1.5-fold; P value < 0.05) in expression of 192 genes occurred in all three mouse strains tested, with enrichment in chemokines and a pattern associated with alternatively activated monocytes/macrophages. CLCA1 (calcium-activated chloride channel regulator 1) was the most upregulated gene transcript (>100-fold) in all exposed mouse lungs versus controls, followed closely by SLC26A4, another transcript involved in Cl- conductance. Crofelemer, a U.S. Food and Drug Administration-approved Cl- channel inhibitor, reduced MDI exposure induction of airway eosinophilia, mucus, CLCA1, and other asthma-associated gene transcripts. Expression changes in a core set of genes occurs independent of IgE in a mouse model of chemical-induced airway eosinophilia. In addition to chemokines and alternatively activated monocytes/macrophages, the data suggest a crucial role for Cl- channels in diisocyanate asthma pathology and as a possible target for intervention.

Dilysine-Methylene Diphenyl Diisocyanate (MDI), a Urine Biomarker of MDI Exposure?

Biomonitoring of methylene diphenyl diisocyanate (MDI) in urine may be useful in industrial hygiene and exposure surveillance approaches toward disease (occupational asthma) prevention and in understanding pathways by which the internalized chemical is excreted. We explored possible urine biomarkers of MDI exposure in mice after respiratory tract exposure to MDI, as glutathione (GSH) reaction products (MDI-GSH), and after skin exposure to MDI dissolved in acetone. LC-MS analyses of urine identified a unique m/ z 543.29 [M + H]+ ion from MDI-exposed mice but not from controls. The m/ z 543.29 [M + H]+ ion was detectable within 24 h of a single MDI skin exposure and following multiple respiratory tract exposures to MDI-GSH reaction products. The m/ z 543.29 [M + H]+ ion possessed properties of dilysine-MDI, including (a) an isotope distribution pattern for a molecule with the chemical formula C27H38N6O6, (b) the expected collision-induced dissociation (CID) fragmentation pattern upon MS/MS, and (c) a retention time in reversed-phase LC-MS identical to that of synthetic dilysine-MDI. Further MDI-specific Western blot studies suggested albumin (which contains multiple dilysine sites susceptible to MDI carbamylation) as a possible source for dilysine-MDI and the presence of MDI-conjugated albumin in urine up to 6 days after respiratory tract exposure. Two additional [M + H]+ ions ( m/ z 558.17 and 863.23) were found exclusively in urine of mice exposed to MDI-GSH via the respiratory tract and possessed characteristics of previously described cyclized MDI-GSH and oxidized glutathione (GSSG)-MDI conjugates, respectively. Together the data identify urinary biomarkers of MDI exposure in mice and possible guidance for future translational investigation.

LC-UV-MS and MS/MS Characterize Glutathione Reactivity with Different Isomers (2,2' and 2,4' vs. 4,4') of Methylene Diphenyl-Diisocyanate

Methylene diphenyl diisocyanate (MDI), the most abundantly produced diisocyanate worldwide, is among the best recognized chemical causes of occupational asthma. The bulk of synthesized MDI, the 4,4' isomer, has been the focus of most biochemical research to date. The biological reactivity of other MDI isomers (2,2' and 2,4'), present at concentrations approaching 50% in some commercial products, remains less clear. We hypothesized 2,2' and 2,4' MDI react with glutathione (GSH), a major anti-oxidant of the lower airways, similarly to 4,4' MDI, and that the products could be characterized using a combination of LC-UV-MS and MS/MS. Purified 2,2' and 2,4' MDI isomers were mixed with GSH in pH-buffered aqueous phase at 37°C and reaction products were analyzed at varying time points. Within minutes, S-linked bis(GSH)-MDI conjugates were detectable as the dominant [M+H]⁺ ion, with an 865.25 m/z and more intense [M+2H]²⁺ ions of the same nominal mass. Upon longer reaction, [M+H]+ ions with greater retention times and the 558.17 m/z expected for mono(GSH)-MDI reaction products were observed, and exhibited MS/MS collision-induced dissociation (CID)-fragmentation patterns consistent with cyclized structures. Compared with 4,4' MDI, 2,2' and 2,4' isomers exhibit similar rapid reactivity with GSH and formation of bis(GSH)-MDI conjugates, but greater formation of cyclized mono(GSH) conjugates following extended reaction times (10 minutes to 2 hours). Further translational studies will be required to determine if the present in vitro findings extend to the complex lower airway microenvironment in vivo.

Reaction products of hexamethylene diisocyanate vapors with "self" molecules in the airways of rabbits exposed via tracheostomy

1. Hexamethylenediisocyanate (HDI) is a widely used aliphatic diisocyanate and a well-recognized cause of occupational asthma. 2. "Self" molecules (peptides/proteins) in the lower airways, susceptible to chemical reactivity with HDI, have been hypothesized to play a role in asthma pathogenesis and/or chemical metabolism, but remain poorly characterized. 3. This study employed unique approaches to identify and characterize "self" targets of HDI reactivity in the lower airways. Anesthetized rabbits free breathed through a tracheostomy tube connected to chambers containing either, O2, or O2 plus ∼200 ppb HDI vapors. Following 60 minutes of exposure, the airways were lavaged and the fluid was analyzed by LC-MS and LC-MS/MS. 4. The low-molecular weight (<3 kDa) fraction of HDI exposed, but not control rabbit bronchoalveolar lavage (BAL) fluid identified 783.26 and 476.18 m/z [M+H]+ ions with high energy collision-induced dissociation (HCD) fragmentation patterns consistent with bis glutathione (GSH)-HDI and mono(GSH)-HDI. Proteomic analyses of the high molecular weight (>3 kDa) fraction of exposed rabbit BAL fluid identified HDI modification of specific lysines in uteroglobin (aka clara cell protein) and albumin. 5. In summary, this study utilized a unique approach to chemical vapor exposure in rabbits, to identify HDI reaction products with "self" molecules in the lower airways.

Mass spectrometry-based analysis of murine bronchoalveolar lavage fluid following respiratory exposure to 4,4'-methylene diphenyl diisocyanate aerosol

1. Diisocyanates are highly reactive electrophiles utilized in the manufacture of a wide range of polyurethane products and have been identified as causative agents of occupational allergic respiratory disease. However, in spite of the significant occupational health burden associated with diisocyanate-induced asthma, the mechanism of disease pathogenesis remains largely unknown. 2. To better understand the fate of inhaled diisocyanates, a nose-only aerosol exposure system was constructed and utilized to expose a BALB/c mouse model to an aerosol generated from 4,4'-methylene diphenyl diisocyanate (MDI). Tissue and bronchoalveolar lavage samples were evaluated 4 and 24 h post-exposure for evidence of diisocyanate-protein haptenation, and a label-free quantitative proteomics strategy was employed to evaluate relative changes to the protein content of the cellular fraction of the lavage fluid. 3. Following MDI aerosol exposure, expression of the number of proteins with immunological or xenobiotic metabolism relevance is increased, including endoplasmin, cytochrome P450 and argininosuccinate synthase. Western blot analysis indicated MDI-conjugated protein in the lavage fluid, which was identified as serum albumin. 4. Tandem mass spectrometry analysis of MDI-albumin revealed MDI conjugation occurs at a dilysine motif at Lys525, as well as at a glutamine-lysine motif at Lys414, in good agreement with previously published in vitro data on diisocyanate-conjugated serum albumin.

Assessment of the short-term toxicity of TiO2 nanofiber in Sprague Dawley rats

Synthetic nanomaterials have many unique chemical and physical properties, mainly due to their high specific surface area and quantum confinement effect. Specifically, titanium dioxide (TiO₂ ) nanomaterial has high stability, anticorrosive, and photocatalytic properties. However, there are concerns over adverse biological effects resulting from bioeffects. This study was to investigate adverse effects associated with acute ingestion of TiO₂ nanofiber (TDNF). TDNF was fabricated via electrospinning method, followed by dissolution in water. Six- to seven-week-old male Sprague Dawley rats were exposed to a total of 0, 40, and 60 ppm of TDNF for 2 weeks via oral gavage. Serum total protein and weight gain during the course of this study displayed marginal concentration-dependent alterations. These findings were followed by a global gene expression analysis to identify which transcripts might be responsive to TNDF toxicity. Differentially expressed mRNA levels were dose-dependently higher in animals exposed to TNDF. The majority of the affected genes were biochemically involved in immune response and inflammation. We believe this is due to the fact that TNDF is unable to penetrate the cell and forms phagocytosis sites that trigger inflammatory and immune response. All results taken together, short-term ingestion of TNDF produced marginal effects indicative of inflammation. Finally, the broad gene expression data were validated through quantification of immunoglobulin heavy chain alpha (Igha). Igha gene was upregulated in treated groups, showing similar expression patterns to the global gene expression data.

Identification of novel reaction products of methylene-bis-phenylisocyanate ("MDI") with oxidized glutathione in aqueous solution and also during incubation of MDI with a murine hepatic S9 fraction

Methylene diphenyl diisocyanate (MDI) is an important industrial chemical and asthmagenic respiratory sensitizer, however its metabolism remains unclear. In this study we used LC-MS and LC-MS/MS to identify novel reaction products of MDI with oxidized glutathione (GSSG), including an 837m/z [M+H](+) ion corresponding to GSSG bound (via one of its N-termini) to partially hydrolyzed MDI, and an 863m/z [M+H](+) ion corresponding to GSSG cross-linked by MDI (via its two γ-glutamate N-termini) [corrected]. Further studies with heavy isotope labeled and native reduced glutathione (GSH) identified an [M+H](+) ion corresponding to previously described mono(GSH)-MDI, and evidence for "oligomeric" GSH-MDI conjugates. This study also investigated transformational changes in MDI after incubation with an S9 fraction prepared from murine liver. LC-MS analyses of the S9 reaction products revealed the formation of [M+H](+) ions with m/z's and retention times identical to the newly described GSSG-MDI (837 and 863) conjugates and the previously described mono(GSH)-MDI conjugate. Together the data identify novel biological transformations of MDI, which could have implications for exposure-related health effects, and may help target future in vivo studies of metabolism.

Immunochemical detection of the occupational allergen, methylene diphenyl diisocyanate (MDI), in situ

Diisocyanate chemicals essential to polyurethane production are a well-recognized cause of occupational asthma. The pathogenesis of diisocyanate-induced asthma, including the pathways by which the chemical is taken up and its distribution in exposed tissue, especially the lung, remains unclear. We developed an antiserum with specificity for methylene diphenyl diisocyanate (MDI) the most abundantly produced and utilized diisocyanate world-wide, and established its ability to detect MDI in situ. Polyclonal MDI-specific IgG was induced by immunizing rabbits with MDI-conjugated to keyhole limpet hemocyanin (KLH) emulsified in complete Freund's adjuvant, followed by two booster injections with incomplete Freund's adjuvant. The antiserum contains IgG that recognize a variety of different MDI conjugated proteins, but not unconjugated or mock exposed proteins by dot blot analysis. The antiserum further demonstrates specificity for proteins conjugated with MDI, but not other commonly used diisocyanates. Immunochemical studies with cytospun airway cells and formalin-fixed paraffin embedded lung tissue sections from mice intranasally exposed to MDI (as reversibly reactive glutathione conjugates, e.g. GSH-MDI) demonstrated the antiserum's ability to detect MDI in tissue samples. The data demonstrate penetration of MDI into the lower airways, localized deposition in the epithelial region surrounding airways, and uptake by alveolar macrophages. The new immunochemical reagent should be useful for further studies delineating the uptake and tissue distribution of MDI, especially as it relates to adverse health effects from exposure.

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.