title: Effects of nitrogen dioxide on the expression of intercellular adhesion molecule-1, neutrophil adhesion, and cytotoxicity: studies in human bronchial epithelial cells.
abstract: Nitrogen Dioxide (NO2) is a product of high-temperature combustion and an environmental oxidant of concern. We have recently reported that early changes in NO2-exposed human bronchial epithelial cells are causally linked to increased generation of proinflammatory mediators, such as nitric oxide/nitrite and cytokines like interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha and IL-8. The objective of the present in vitro study was to further delineate the cellular mechanisms of NO2-mediated toxicity, and to define the nature of cell death that ensues upon exposure of normal human bronchial epithelial (NHBE) cells to a brief high dose of NO2. Our results demonstrate that the NHBE cells undergo apoptotic cell death during the early post-NO2 period, but this is independent of any significant increase in caspase-3 activity. However, necrotic cell death was more prevalent at later time intervals. Interestingly, an increased expression of HO-1, a redox-sensitive stress protein, was observed in NO2-exposed NHBE cells at 24 h. Since neutrophils (PMNs) play an active role in acute lung inflammation and resultant oxidative injury, we also investigated changes in human PMN-NHBE cell interactions. As compared to normal cells, increased adhesion of PMNs to NO2-exposed cells was observed, which resulted in an increased NHBE cell death. The latter was also increased in the presence of IL-8 and TNF-alpha + interferon (IFN)-gamma, which correlated with upregulation of intercellular adhesion molecule-1 (ICAM-1). Our results confirmed an involvement of nitric oxide (NO) in NO2-induced cytotoxicity. By using NO synthase inhibitors such as L-NAME and 3-aminoguanidine (AG), a significant decrease in cell death, PMN adhesion, and ICAM-1 expression was observed. These findings indicate a role for the L-arginine/NO synthase pathway in the observed NO2-mediated toxicity in NHBE cells. Therapeutic strategies aimed at controlling excess generation of NO and/or inflammatory cytokines may be useful in alleviating NO2-mediated adverse effects on the bronchial epithelium.
authors.affiliation: Department of Respiratory Research, Division of Military Casualty Research, Walter Reed Army Institute of Research, Silver Spring, Maryland 20910, USA.
authors.forename: Vijayalakshmi N
authors.initials: VN
authors.lastname: Ayyagari
authors.forename: Adolph
authors.initials: A
authors.lastname: Januszkiewicz
authors.forename: Jayasree
authors.initials: J
authors.lastname: Nath
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001980:Bronchi / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D053148:Caspase 3 / Q000378:metabolism; D002448:Cell Adhesion / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004336:Drug Antagonism; D004338:Drug Combinations; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D051547:Heme Oxygenase-1 / Q000378:metabolism; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology; D016209:Interleukin-8 / Q000494:pharmacology; D009336:Necrosis; D009504:Neutrophils / Q000187:drug effects* / Q000502:physiology; D009585:Nitrogen Dioxide / Q000633:toxicity*; D010083:Oxidants, Photochemical / Q000633:toxicity*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D004338:Drug Combinations; D004791:Enzyme Inhibitors; D016209:Interleukin-8; D010083:Oxidants, Photochemical; D014409:Tumor Necrosis Factor-alpha; D018799:Intercellular Adhesion Molecule-1; D007371:Interferon-gamma; C496541:HMOX1 protein, human; D051547:Heme Oxygenase-1; D053148:Caspase 3; D009585:Nitrogen Dioxide