Experimental lung research
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Apoptosis, or programmed cell death, has been reported to play an important role in the resolution of pulmonary inflammation. This study was undertaken to investigate the role of apoptosis in resolving particle-induced lung inflammatory responses in exposed rats, using a dose-response / time course experimental design. Groups of rats were exposed via intratracheal instillation to 0, 0.5, 1, 5, 10, or 50 mg/kg body weight of quartz (i.e., crystalline silica) particles or to 0, 0.5, 1, 5, 10, 20, or 50 mg/kg of pigment-grade titanium dioxide (TiO(2)) particles and evaluated for lung inflammation parameters and evidence of apoptosis of inflammatory cells at 24, 48, 72, or 168 hours post exposure. ⋯ Alternatively, it seems unlikely that apoptosis served to promote silica-induced lung inflammatory responses because the initial increase of apoptosis in inflammatory cells was subsequently correlated with a reduction of the pulmonary inflammatory response in silica-exposed rats. The findings from this in vivo study demonstrate that the neutrophil, and not the alveolar macrophage, is the primary inflammatory cell-type that undergoes apoptosis in response to particles. Furthermore, at doses causing similar degrees of inflammation at 24 hours post exposure, the magnitude of apoptosis induced by silica is significantly larger than that induced by TiO(2), indicating that there are potency differences in lung inflammation as well as apoptotic responses among different particle-types.
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Urban air consists of a combination of environmental pollutants. Recent studies have suggested that normally innocuous doses of a particular pollutant may be rendered more toxic to the lung if primed by earlier events. Pulmonary inflammation has been observed in humans and in many animal species after endotoxin and ozone exposures. ⋯ After 24 hours of recovery, significant increases were measured in bronchoalveolar lavage (BAL) fluid levels of protein and lavageable polymorphonuclear neutrophils (PMNs) after coexposure to ozone followed immediately by endotoxin inhalation as compared to exposures individually. Messages encoding macrophage inflammatory protein (MIP)-1beta, MIP-1alpha, MIP-2, monocyte chemoattractant protein (MCP)-1, interleukin (IL)-1alpha, IL-1beta, IL-1Ra, IL-6, and Macrophage Migration Inhibitory Factor (MIF) were significantly elevated 24 hours post ozone followed by endotoxin as compared to exposure to ozone or endotoxin individually. These results demonstrate that preexposure to ozone, which primarily attacks the epithelium, can cause sensitization to a secondary stimulus through a mechanism that culminates in a greater and prolonged onset of inflammatory cell recruitment, pulmonary edema, and increased expression of chemokine and cytokine messages.
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In a rat model of lung injury induced by the antineoplastic antibiotic, bleomycin, there is loss of type I alveolar epithelial cells (AECs) followed by infiltration of activated inflammatory cells, type II AEC proliferation, and fibrosis. At 4 and 7 days after bleomycin administration alveolar macrophages have increased production and release of active transforming growth factor (TGF)-beta1, an inhibitor of epithelial cell proliferation. Paradoxically at these same time intervals there is a concomitant induction of type II AEC proliferation. ⋯ Because both TbetaR-I and TbetaR-II are required for signal transduction, the reduction of TbetaR-I levels on the alveolar epithelium may alter the sensitivity of AECs to the antiproliferative effects of TGF-beta1 present in increased quantities following bleomycin injury. The loss of an antiproliferative response to TGF-beta1 may be important for the regeneration of the alveolar epithelium by proliferation while the expression of both receptors onfibroblasts would result in TGF-1 signaling for the synthesis of connective tissue proteins. Ourfindings suggest that during bleomycin-induced pulmonary fibrosis, the effects of TGF-beta1 on cells may be regulated by the expression of TbetaRs.
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The objective of this study was to determine if exogenous surfactant therapy could prevent the harmful effects of ventilation at high tidal volumes without positive end-expiratory pressure (PEEP). Rats were randomized to either a nontreated control group (8 mL/kg 4 cm H2O PEEP), a nontreated injuriously ventilated group (20 mL/kg 0 cm H2O PEEP) or a treatment group of either 50 mg/kg, 50 mg/kg + 5% surfactant-associated protein A, 100 mg/kg exogenous surfactant followed by injurious ventilation. Isolated lungs from animals in all 5 groups were ventilated in a humidified box at 37 degrees C for 2 hours. ⋯ Inflammatory cytokines (tumor necrosis factor-alpha [TNFalpha], interleukin [IL]-1beta, and IL-6) in the lavage were significantly higher in injuriously ventilated lungs compared to the control group. However the 3 treatment groups had cytokine concentrations that were similar to the injuriously ventilated group. We conclude that surfactant treatment is beneficial in preventing VILI; however, it does not prevent the release of inrflammatory cytokines during mechanical ventilation.
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Ozone (O3) is a highly reactive and toxic oxidant pollutant. The objective of this study is to compare cytokine, chemokine, and metallothionein (Mt) changes elicited by lethal and sublethal exposure to ozone in a genetically sensitive strain of mice. Eight-week-old C57BL/6J mice were exposed to 0.3 ppm ozone for 0, 24, or 96 hours; 1.0 ppm ozone for 0, 1, 2, or 4 hours; or 2.5 ppm ozone for 0, 2, 4, or 24 hours. ⋯ Increased mRNAs for eotaxin, MIP-1 alpha, MIP-2, and Mt were to a higher magnitude than were detected after 2 and 4 hours of exposure. Messages encoding IL-12, IL-10, interferon (IFN)-gamma, IL-1 alpha, IL-1 beta, and IL-1Ra were unaltered at all time points and doses examined. Our results demonstrate dose- and time-dependent changes in chemokine, cytokine, and Mt mRNA abundance and that early acute changes may be predictive of subacute and chronic responses to ozone.