OXIDANT STRESS STIMULATES MUCIN SECRETION AND PLG IN AIRWAY EPITHELIUM VIA A NITRIC OXIDE-DEPENDENT MECHANISM

Reactive oxygen species (ROS) have been implicated in the pathogenesis of a wide variety of respiratory diseases. We investigated mechanisms of ROS-induced mucin secretion by guinea pig tracheal epithelial (GPT E) cells in primary culture, and ROS-induced activation of the second messenger-producing enzyme phospholipase C (PLC), in GPTE cells and in a virally transformed cell line (BEAS-2B) derived from human bronchia l epithelium. Mucin secretion was measured by a monoclonal antibody-ba sed enzyme-linked immunosorbent assay, and PLC activation was assessed by anion exchange chromatography. ROS generated enzymatically by xant hine oxidase (XO, 500 mu M) in the presence of purine (500 mu M) enhan ced release of mucin by GPTE cells and activated PLC in GPTE and BEAS cells. Hypersecretion of mucin and activation of PLC in response to pu rine + XO appeared to occur via an intracellular pathway(s) dependent on endogenously produced nitric oxide and possibly intracellularly gen erated oxidants. Both responses could be blocked or attenuated by prei ncubation of the cells with N-G-monomethyl-L-arginine, an inhibitor of the enzyme nitric oxide synthase, or with dimethylthiourea, a compoun d that can react with a variety of intracellular oxidant species. Reac tive nitrogen species generated chemically also stimulated secretion o f mucin and activated PLC via a mechanism dependent (at least in part) on intracellular oxidant-mediated process(es). The results suggest th at intracellularly generated radical species of nitrogen and oxygen ma y be important modulators of the response of airway epithelial cells t o external oxidant stress.