Effects of ozone on epithelium and sensory nerves in the bronchial mucosa of healthy humans

Abstract

Neuropeptides released from sensory nerves during inflammation have potent effects on bronchomotor tone, airway secretion, and inflammatory cells. We investigated the effects of ozone on sensory nerves by exposing 12 healthy, nonsmoking subjects to 0.2 ppm ozone and filtered air (FA) for 2 h on separate occasions, with intermittent exercise and rest. Spirometry was performed at baseline and 15 min after exposures, and bronchoscopy (bronchial biopsy and bronchoalveolar lavage [BAL]) was done 6 h after exposure. Frozen sections were immunostained for the anatomic neural marker protein gene peptide (PGP) 9.5 and the sensory neutropeptides substance P (SP) and calcitonin-gene-related peptide (CGRP). Nerves in the submucosa were quantified by image analysis. A trend toward an increase in the levels of polymorphonuclear leukocytes (PMNs) (air versus ozone, median [interquartile range]: 3.5 [2 to 5.3%] versus 9.8 [4.2 to 16.3%], p = 0.07) and ciliated epithelial cells (median [interquartile range]: 1.6 [1.3 to 3.4%] versus 5 [2.2 to 9.8%], p = 0.05) was observed in the BAL fluid (BALF). There was a significant decrease in SP immunoreactivity following ozone exposure (median [interquartile range]: 0.6 [0.05 to 1.2] versus 0.15 [0.08 to 0.18], p < 0.05). A significant inverse correlation was observed between SP immunoreactivity and: (1) percent PMNs and ciliated epithelial cells in the BALF; and (2) percent change in FEV1 following exposure to ozone. These findings indicate that short-term exposure to 0.2 ppm ozone causes epithelial shedding and stimulates subepithelial sensory nerves to release SP into the airways. The release of SP could contribute to bronchoconstriction and subsequent neutrophil infiltration into the airways.