MECHANISMS OF POLLUTANT-INDUCED AIRWAYS TOXICITY

Respiratory Effects of Short-Term, High-Intensity Toxic Inhalations: Smoke, Gases, and Fumes

Respiratory insufficiency resulting from inhalation of hot air, smoke, or toxic gas is a common cause of death in fire victims. Toxic gas inhalation in settings other than fires is a less common but still important cause of death and disability. Pulmonary inhalation injury and systemic intoxication from exposure to a variety of agents are discussed with regard to their pathogenesis, pathophysi ology, diagnosis, and treatment. Upper airway obstruc tion and noncardiogenic pulmonary edema are the life- threatening respiratory complications in the immediate postinhalation period. Carbon monoxide and hydrogen cyanide intoxication are frequently associated with in halation injury in fire victims. Early recognition and treatment of inhalation injury and systemic intoxication in victims of fires and industrial and environmental acci dents could well result in improved survival.

Abnormal surface liquid pH regulation by cultured cystic fibrosis bronchial epithelium

Cystic fibrosis (CF) transmembrane conductance regulator (CFTR)-dependent airway epithelial bicarbonate transport is hypothesized to participate in airway surface liquid pH regulation and contribute to lung defense. We measured pH and ionic composition in apical surface liquid (ASL) on polarized normal (NL) and CF primary bronchial epithelial cell cultures under basal conditions, after cAMP stimulation, and after challenge with luminal acid loads. Under basal conditions, CF epithelia acidified ASL more rapidly than NL epithelia. Two ASL pH regulatory paths that contributed to basal pH were identified in the apical membrane of airway epithelia, and their activities were measured. We detected a ouabain-sensitive (nongastric) H+,K+-ATPase that acidified ASL, but its activity was not different in NL and CF cultures. We also detected the following evidence for a CFTR-dependent HCO3- secretory pathway that was defective in CF: (i). ASL [HCO3-] was higher in NL than CF ASL; (ii). activating CFTR with forskolin/3-isobutyl-1-methylxanthine alkalinized NL ASL but acidified CF ASL; and (iii). NL airway epithelia more rapidly and effectively alkalinized ASL in response to a luminal acid challenge than CF epithelia. We conclude that cultured human CF bronchial epithelial pHASL is abnormally regulated under basal conditions because of absent CFTR-dependent HCO3- secretion and that this defect can lead to an impaired capacity to respond to airway conditions associated with acidification of ASL.

The role of airway mucus in pulmonary toxicology

Airway mucus is a complex airway secretion whose primary function as part of the mucociliary transport mechanism is to to serve as renewable and transportable barrier against inhaled particulates and toxic agents. The rheologic properties necessary for this function are imparted by glycoproteins, or mucins. Some respiratory disease states, e.g., asthma, cystic fibrosis, and bronchitis, are characterized by quantitative and qualitative changes in mucus biosynthesis that contribute to pulmonary pathology. Similar alterations in various aspects of mucin biochemistry and biophysics, leading to mucus hypersecretion and altered mucus rheology, result from inhalation of certain air pollutants, such as ozone, sulfur dioxide, nitrogen dioxide, and cigarette smoke. The consequences of these pollutant-induced alterations in mucus biology are discussed in the context of pulmonary pathophysiology and toxicology.

Enzyme histochemistry of the rat nasal mucosa embedded in cold glycol methacrylate

The nasal passages are anatomically complex, and while there have been a number of descriptions of nasal structure in many species, there is very little information available on the distribution of enzymes in the nasal mucosa. In rodents, this delicate mucosa is the first site within the respiratory tract to be exposed during inhalation toxicology studies designed to assess human risks from such exposures. However, the nasal mucosa presents problems for histologic preparation because it is encased in brittle bones. Because of recent interest in the nose as a target site, and findings from biochemical studies which indicate that the nose is very active metabolically, studies were carried out to determine the value of cold glycol methacrylate (GMA) processing for localization of nasal enzymes. For these studies, liver and kidney were used as positive controls. Published histochemical procedures for acid and alkaline phosphatase, adenosine triphosphatase, glucose-6-phosphatase, gamma-glutamyl transpeptidase, and naphthyl butyrate esterase were applied, with modifications, to undecalcified nasal passages of Fisher-344 rats. Frozen sections exhibited excellent enzyme preservation but very poor morphology, while GMA gave good enzyme preservation and excellent morphology. For GMA, acetone fixation generally resulted in the best preservation of enzyme activity. It was concluded that cold GMA processing provides a useful approach to studies of nasal enzyme distribution and that this technique of value for inhalation toxicology studies. Details of enzyme distribution in the squamous, respiratory, and olfactory epithelia, associated glands, and other structures of the nose of the rat are described and discussed.