Inhalation of toluene diisocyanate is associated with increased production of nitric oxide by rat bronchoalveolar lavage cells

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.

A common fungal volatile organic compound induces a nitric oxide mediated inflammatory response in Drosophila melanogaster

Using a Drosophila model, we previously demonstrated truncated life span and neurotoxicity with exposure to 1-octen-3-ol, the volatile organic compound (VOC) responsible for much of the musty odor found in mold-contaminated indoor spaces. In this report, using biochemical and immunological assays, we show that exposure to 0.5 ppm 1-octen-3-ol induces a nitric oxide (NO) mediated inflammatory response in hemocytes, Drosophila innate immune cells. Moreover, exposed Drosophila brains show increased peroxynitrite expression. An increase in nitrite levels is observed with toluene and 1-octen-3-ol but not with 1-butanol. Pharmacological inhibitors of nitric oxide synthase (NOS) namely, L-NAME, D-NAME and minocycline, and NOS mutants show improvements of life span among 1-octen-3-ol exposed flies. Exposure to 1-octen-3-ol also induces NOS expression in larval tracheal tissues and remodels tracheal epithelial lining. These findings suggest a possible mechanistic basis for some of the reported adverse health effects attributed to mold exposure and demonstrates the utility of this in vivo Drosophila model to complement existing model systems for understanding the role of inflammation in VOC-mediated toxicity.

Thymoquinone attenuates lung injury induced by chronic toluene exposure in rats

The aim of this study was designed to evaluate the possible protective effects of thymoquinone (TQ) on the lung injury in rats after chronic toluene exposure. The rats were randomly allotted into one of three experimental groups: control, toluene-treated and toluene-treated with TQ; each group contain 10 animals. Control group received 1 mL serum physiologic and toluene treatment was performed by inhalation of 3000 parts per million (ppm) toluene, in an 8-hr/day and 6 day/week order for 12 weeks. The rats in TQ treated group was given TQ (50 mg/kg body weight) once a day orally for 12 weeks starting just after toluene exposure. Tissue samples were obtained for histopathological investigation. To date, no histopathological changes of lung in rats after chronic toluene exposure by TQ treatment have been reported. Our study showed that TQ treatment inhibits the inflammatory pulmonary responses reducing significantly peribronchial inflammatory cell infiltration, alveolar septal infiltration, alveolar edema, alveolar exudate, interstitial fibrosis and necrosis formation in toluene-treated rats. Our data indicate a significant reduction in the activity of in situ identification of apoptosis using terminal dUTP nick end-labeling (TUNEL), inducible nitric oxide synthase (iNOS) and a rise in the expression of surfactant protein D in lung tissue of toluene-treated with TQ therapy. We believe that further preclinical research into the utility of TQ may indicate its usefulness as a potential treatment on lung injury after chronic toluene exposure in rats.

Respiratory hypersensitivity to trimellitic anhydride in Brown Norway rats: a comparison of endpoints

A rat bioassay has been developed to provide an objective approach for the identification and classification of respiratory allergy using trimellitic anhydride (TMA), which is a known respiratory tract irritant and asthmagen. Particular emphasis was placed on the study of route-of-induction-dependent effects and their progression upon inhalation challenge with TMA (approximately 23 mg m(-3) for a duration of 30 min), which included analysis of specific and non-specific airway hyperreactivity and pulmonary inflammation initiated and sustained by immunological processes. Refinement of the bioassay focused on procedures to probe changes occurring upon challenge with TMA or methacholine aerosols using physiological, biochemical and immunological procedures. Following challenge with TMA, the rats sensitized to TMA showed marked changes in peak inspiratory and expiratory air flows and respiratory minute volume. In these animals, a sustained pulmonary inflammation occurred, characterized by specific endpoints determined in bronchoalveolar lavage (lactate dehydrogenase, protein, nitrite, eosinophil peroxidase, myeloperoxidase). When compared with the naive controls, lung weights were increased significantly, as were the weights of lung-associated lymph nodes following inhalation induction and auricular lymph nodes following topical induction. The extent of changes observed was equal or more pronounced in animals sensitized epicutaneously (day 0:150 microl vehicle/50% TMA on each flank, day 7; booster administration to the skin of the dorsum of both ears using half the concentration and volume used on day 0) when compared with rats sensitized by 5 x 3 h day(-1) inhalation exposures (low dose: 25 mg TMA m(-3), high dose: 120 mg TMA m(-3)). In summary, the findings support the conclusion that the Brown Norway rat model is suitable for identifying TMA as an agent that causes both an immediate-type change of breathing patterns and a delayed-type sustained pulmonary inflammatory response. However, it remains unresolved whether the marked effects observed in the topically sensitized rats are more related to a route-of-induction or dose-dependent phenomenon.

Intracellular S-glutathionyl adducts in murine lung and human bronchoepithelial cells after exposure to diisocyanatotoluene

Diisocyanatotoluene (toluene diisocyanate, TDI), a 4:1 mixture of 2, 4- and 2,6-isomers used in the preparation of polyurethanes, causes occupational asthma by an as yet unknown mechanism. We previously showed that it forms adducts with the apical surface of the bronchoepithelium in vivo, and with ciliary microtubules in cultured human bronchoepithelial (HBE) cells. These results suggested that TDI may not enter HBE cells. In vitro studies, however, showed that TDI avidly forms bis adducts with glutathione (GSH) and that these adducts transfer monoisocyanato-monoglutathionyl-TDI to a sulfhydryl-containing peptide. This study sought to elucidate intracellular reactions of TDI. Using an electron paramagnetic resonance spectrometric (EPR) method, we established that the level of thiol-dependent quenching of phenoxyl radicals of etoposide was decreased >40% in pulmonary tissue of mice that received TDI intrabronchially. Similarly, HBE cells exposed to 100 ppb TDI vapor experienced a >30% reduction in thiol levels as determined with a thiol-specific fluorescent probe (ThioGlo 1). HPLC/UV analysis of lysates from HBE cells exposed to 200 and 500 ppb TDI vapor suggested a dose-related formation of S-glutathionyl adducts. Data from the 500 ppb TDI-treated HBE cells verified the identity of the 2-monoglutathionyl-4-monoisocyanato adduct. The results provide firm evidence that TDI enters pulmonary cells and reacts with GSH. This rapid reaction leading to formation of S-glutathionyl adducts of TDI suggests the importance of cellular thiols in TDI-induced pulmonary disease.

Enhancement of nitric oxide production by pulmonary cells following silica exposure

In vivo exposure of rat lungs to crystalline silica either by intratracheal instillation or by inhalation results in an increase in mRNA levels for inducible nitric oxide synthase (iNOS) in bronchoalveolar lavage cells (BALC), elevated nitric oxide (.NO) production by BALC, and an increase in .NO-dependent chemiluminescence (CL) from alveolar macrophages (AM). Induction of iNOS message occurs in both AM and polymorphonuclear leukocytes (PMN) harvested from silica-exposed lungs but is not significantly elevated in lavaged lung tissue. In vitro exposure of AM to silica does not stimulate .NO production or enhance iNOS message. However, treatment of naive AM with conditioned media from BALC harvested from silica-exposed rats does increase iNOS message and .NO production by these AM. The potency of this conditioned medium is dependent on interaction between AM and PMN. In the rat model, a relationship exists between the ability of various dusts to cause PMN recruitment or protein leakage into the alveolar space and the induction of iNOS message in BALC, i.e., silica > coal mine dust > carbonyl iron > titanium dioxide. Similarly, a comparison of BALC from a healthy volunteer, a silica-exposed coal miner with a normal chest radiograph, and a silica-exposed coal miner with an abnormal chest radiograph shows a correlation between pathology and both the level of iNOS message in BALC and the magnitude of .NO-dependent CL from AM. These data suggest that .NO may play a role in silicosis and that human pulmonary phagocytes exhibit enhanced .NO production in response to an inflammatory insult.