Increased concentrations of iron and isoferritins in the lower respiratory tract of patients with stable cystic fibrosis

Abstract

Reactive oxygen species may contribute to airway injury in patients with cystic fibrosis (CF) and iron catalyzes oxidant injury by promoting generation of highly reactive hydroxyl radicals. Iron in the lower respiratory tract may be free, ferritin bound (from which iron can be reductively mobilized), or transferrin bound (which generally prevents iron mobilization). Ferritin is composed of subunits that are heavy (H) or light (L), and H-rich ferritins have additional biologic effects including inhibition of lymphocyte proliferation and cell growth. To assess concentrations of iron and iron-binding proteins in the lower respiratory tract of patients with CF, we measured iron (ferrozine), L-ferritin, H-ferritin, and transferrin (enzyme-linked immunosorbent assay [ELISA]) in bronchoalveolar lavage (BAL) fluid recovered from stable patients with CF (n = 8), healthy nonsmokers (NS; n = 8), or heavy cigarette smokers (HS; n = 8). Iron was detected in BAL fluid from patients with CF and HS, but not NS, with higher iron concentrations in patients with CF (42.0 +/- 11.6 microgram/dl) than in HS (9.9 +/- 2.6 microgram/dl, p < 0.05). Ferritin was present in all BAL fluids, with higher total ferritin (L + H) in patients with CF (647 +/- 84 ng/ml) than in HS (181 +/- 25 ng/ml, p < 0.005) or NS (9 +/- 3 ng/ml, p < 0.0005). Ferritin recovered from HS and NS lungs was < 2% H type, whereas ferritin in CF lungs was > 40% H-type ferritin. Transferrin concentrations in BAL fluid were not different in any group. Tumor necrosis factor (TNF)-alpha was present only in BAL samples from patients with CF. To assess whether TNF-alpha contributed to H-ferritin accumulation in CF lungs, we treated lung epithelial cells (A549) with iron alone (FeSO(4), 10-40 microM) or with iron and TNF-alpha (5-20 ng/ml). Iron-treated A549 cells synthesized almost entirely L-ferritin whereas exposure to TNF-alpha with iron caused a dose-dependent increase in accumulation of H-type ferritin. These findings suggest that oxidant injury could be promoted in lungs of patients with cystic fibrosis by iron mobilized from extracellular ferritin and, in addition, that TNF-alpha-promoted accumulation of H-type ferritin may impair local immune function and cell growth.