Increased iron and ferritin content of sputum from patients with cystic fibrosis or chronic bronchitis

Purpose: Extracellular free iron, or iron bound to ferritin, may promote oxidative injury and bacterial growth in airways of patients with chronic airway inflammation due to cystic fibrosis (CF) or chronic bronchitis (CB). In this study, we assessed sputum content of total iron, ferritin, and transferrin in patients with CF or CB as well as sputum from normal subjects with acute airway inflammation caused by viral upper respiratory tract infections (URTIs). Methods: Spontaneously produced sputum was obtained from 33 subjects, including 10 subjects with CF, 18 subjects with CB (10 acute exacerbations, 8 with stable CB), and 5 subjects with URTIs (control subjects). After lysing and dilution, total iron concentrations were determined by controlled coulometry, ferritin was measured by radioimmunoassay, and transferrin was measured by enzyme-linked immunosorbent assay. Results: Iron was not present in detectable amounts in control sputums, but ferritin was present (6±2 ng/mg protein, mean±SE), as was transferrin (2.37±0.44 μg/mg). Compared with control subjects, concentrations of iron in sputum were increased in patient groups with higher amounts in CF patients (242±47 ng/mg, p<0.01) than CB patients with acute exacerbations or patients with stable CB (98±50 and 42±12 ng/mg, p <0.05 for both). Ferritin content of sputum was also increased in each group, with CF patients (113±22 ng/mg, p<0.001) higher than CB patients (acute, 45±10 ng/mg; stable, 87±24 ng/mg; p<0.01 for both). Compared with control subjects, sputum transferrin was decreased in CF patients (1.09±0.40 μg/mg, p<0.05), but not CB patients. Conclusions: These findings indicate there are increased airway concentrations of total iron and ferritin-bound iron in patients with CB and, to a greater extent, in patients with CF. Particularly in CF patients who also demonstrated decreased airway concentrations of transferrin, ferritin-bound iron in airways may promote oxidative injury and enhance bacterial growth.