Response of rat tracheal epithelium to ozone and oxygen exposure in vitro

Ozone-induced epithelial injury in the ferret is similar to nonhuman primates

Extrapolation to humans from rodent ozone exposure is limited by the anatomic differences between the species. Ferrets have similar pulmonary structures to humans, with well developed respiratory bronchioles and submucosal glands. We exposed adult ferrets, monkeys, and rats to 1 ppm ozone (O(3)) or filtered air for 8 h followed by 1 h in filtered air. Bronchoalveolar lavage (BAL) analysis, histopathology, and confocal microscopy were used to evaluate ozone-induced epithelial injury and inflammation. BAL showed significantly increased numbers of neutrophils in ozone-exposed as compared with filtered air ferrets, monkeys, and rats. However, there were 3- to 4-fold more neutrophils in monkeys and ferrets per milliliter of BAL than in rats. Ozone-exposed lungs showed a severe, acute infiltration of neutrophils in regions with necrotic epithelial cells, especially in the centriacinar region that was more severe in ferrets and monkeys than rats. We conclude that acute ozone exposure in ferrets induce severe epithelial necrosis and inflammation, results in similar epithelial injury compared with monkeys, and represents a better model of humans than rodents.

Interactions of oxygen radicals with airway epithelium

Reactive oxygen species (ROS) have been implicated in the pathogenesis of numerous disease processes. Epithelial cells lining the respiratory airways are uniquely vulnerable regarding potential for oxidative damage due to their potential for exposure to both endogenous (e.g., mitochondrial respiration, phagocytic respiratory burst, cellular oxidases) and exogenous (e.g., air pollutants, xenobiotics, catalase negative organisms) oxidants. Airway epithelial cells use several nonenzymatic and enzymatic antioxidant mechanisms to protect against oxidative insult. Nonenzymatic defenses include certain vitamins and low molecular weight compounds such as thiols. The enzymes superoxide dismutase, catalase, and glutatione peroxidase are major sources of antioxidant protection. Other materials associated with airway epithelium such as mucus, epithelial lining fluid, and even the basement membrane/extracellular matrix may have protective actions as well. When the normal balance between oxidants and antioxidants is upset, oxidant stress ensues and subsequent epithelial cell alterations or damage may be a critical component in the pathogenesis of several respiratory diseases. Oxidant stress may profoundly alter lung physiology including pulmonary function (e.g., forced expiratory volumes, flow rates, and maximal inspiratory capacity), mucociliary activity, and airway reactivity. ROS may induce airway inflammation; the inflammatory process may serve as an additional source of ROS in airways and provoke the pathophysiologic responses described. On a more fundamental level, cellular mechanisms in the pathogenesis of ROS may involve activation of intracellular signaling enzymes including phospholipases and protein kinases stimulating the release of inflammatory lipids and cytokines. Respiratory epithelium may be intimately involved in defense against, and pathophysiologic changes invoked by, ROS.

In vitro exposure of tracheobronchial epithelial cells and of tracheal explants to ozone

An in vitro system for exposing respiratory epithelial cells or explant tissues to ozone has been developed and characterized. This system is designed to generate and monitor consistent, reproducible levels of ozone, over a range of concentrations, in a humidified atmosphere, and to allow an exposure time of 24 h or longer. Based on chemical analysis, highly reproducible concentrations of ozone are delivered throughout the chamber, with a coefficient of variation of < 5% between five replicate vials exposed to 0.5 ppm of ozone for 50 min. The viability of cultured human tracheobronchial epithelial cells, as measured by the ability to oxidize a vital dye, and of rat tracheal epithelium, as measured by total numbers of necrotic cells in tracheal explants, after ozone exposure was examined in this system. Responses of cultured cells to ozone exposure as measured by bioassay were consistent with the observed low level of variability of ozone concentration between replicate incubation dishes or vials. Responses of cultured cells to ozone were proportional to duration of exposure and inversely proportional to the volume of medium covering the cells. We conclude that this newly developed in vitro exposure system will allow relatively simple and convenient exposure of cultured cells or organs to ozone or other gaseous agents under highly controlled and reproducible conditions.

In vitro studies of mechanisms of lung injury in the rodent

In order to better define the responses of lung cells to potentially pathogenic insults, primary cell cultures of dissociated respiratory epithelial cells have been established. These epithelial cells have been obtained from various areas of the respiratory tract ranging from the trachea to the alveolus and the cultures have been demonstrated to mimic the differnetiated state of these cell types as observed in situ. Several procedures which enhance the differentiated state have been evaluated, which include maintenance on more physiologically-relevant substrata, such as collagen gels, use of defined serum-free medium and use of air/liquid interface systems. These approaches have allowed intracellular responses of respiratory epithelium to toxic insult to be better defined.