Nitric oxide and interleukin-8 as inflammatory components of cystic fibrosis

Abstract

We examined the production of reactive nitrogen intermediates in the tracheo-bronchial tree of patients with cystic fibrosis (CF). Examination of the soluble phase of sputa from 17 CF patients revealed the presence of high levels of NO2-/NO3- assayed by the Greiss reaction. We also examined the presence of the chemotactic cytokine interleukin-8 (IL-8) in these samples so as to assess another important inflammatory marker; high levels of IL-8 were present in the sputa of cystic fibrosis subjects. The elevated nitrite was not produced by the presence of Pseudomonas bacteria in the sputa, inasmuch as bacteria in culture released undetectable amounts of nitrite in culture media. Neutrophils from the sputa of CF patients with disease exacerbation released higher amounts of nitrite and IL-8. Neutrophils from the sputa were also shown to spontaneously release substantial amounts of nitrite in the supernatants, and this release was partly blocked by the antagonist NG-mono-methyl-L-arginine (L-NMMA). Blood neutrophils were shown to release nitrite only in response to challenge with CF-associated strains of Pseudomonas, and not exposure to cytokines. There was no significant differences in nitrite release between normal and CF blood polymorphonuclear leucocytes (PMNs). A study of upper airway epithelial cell lines showed that these cells released low amounts of nitrite after infection with CF-associated strains of Pseudomonas but not after cytokine exposure. Epithelial cell lines with CF or normal phenotypes were shown to release similar quantities of nitrite, upon stimulation with Pseudomonas. These data demonstrate that elevated levels of reactive nitrogen intermediates and IL-8 are produced in the tracheo-bronchial tree of subjects with CF. Levels of IL-8 and nitrite were higher in the secretions of CF subjects with disease exacerbation. The involvement of nitric oxide and other reactive nitrogen intermediates produced by neutrophils and other cells in the tissue damaging processes in CF deserves further investigation.