The interaction of asbestos and neutrophils injures cultured human pulmonary epithelial cells: Role of hydrogen peroxide

Asbestos exposure causes diffuse interstitial pulmonary fibrosis. Since alveolar epithelial cell injury is hypothesized to precede the fibrotic response in asbestosis, we investigated whether asbestos, either alone or in conjunction with neutrophils (PMNs), injured cultured human pulmonary epithelial cells (HPECs). HPEC cytotoxicity was assessed with a standard ⁵¹chromium release assay after a 16-hour incubation with asbestos and PMNs. Negligible HPEC cytotoxicity was observed after incubation with either amosite asbestos (500 μg/ml) or PMNs alone in serum-free media. However, incubation with both asbestos and PMNs caused significant HPEC injury, which was asbestos dose-dependent; causing 25% ± 4% detachment and 52% ± 8% ⁵¹chromium relese with 500 μg/ml asbestos. The cytotoxic effects of asbestos plus PMNs were nearly completely attenuated with serum (20%) or catalase (100 μg/ml) but were not prevented with scavengers of superoxide anion, hydroxyl radical, or hypochlorous acid. A role for hydrogen peroxide (H₂O₂) in mediating HPEC injury was also suggested by the demonstration of asbestos-induced generation of H₂O₂ by PMNs. Furthermore, H₂O₂ alone (10^-4mol/L) caused significant HPEC damage. Intimate contact between asbestos-activated PMNs and HPECs was a necessary requirement for PMN-medicated HPEC cytotoxicity. These data suggest that pulmonary epithelial cell injury is mediated in part by H₂O₂ release from asbestos-activated PMNs as well as intimate contact between the epithelial cell, PMNs, and asbestos.