Iron overload and nitric oxide-derived oxidative stress following lung transplantation

Abstract

Background: Reactive oxygen species (ROS) may contribute to airway injury and the development of the bronchiolitis obliterans syndrome (BOS) following lung transplantation (LT). Chemically active iron released from ferritin stores and nitric oxide (NO)-derived radicals may add to the oxidative burden. Methods: We determined the concentrations of ferritin and the aqueous NO derivative nitrite (NO 2 −) within bronchoalveolar lavage fluid (BALF) of 14 stable LT recipients (ST) and 7 subjects with BOS and 21 normal controls. We also assessed the relationship between BALF ferritin and hemosiderin-laden macrophages (HLMs) using a hemosiderin score (HS) and determined BALF albumin concentration as a marker of microvascular leakage. Results: BALF ferritin concentrations and HSs were significantly elevated in LT recipients overall compared with normal controls ( p < 0.05). BALF NO 2 − levels were elevated in BOS subjects and STs compared with normal controls ( p = 0.002 and p = 0.09, respectively), but there was no difference between transplant groups. BALF albumin concentrations were elevated in BOS patients compared with normal controls ( p = 0.02) and ST ( p = 0.05), but there was no difference between STs and controls. There was a significant relationship between BALF ferritin concentration and HS in LT recipients overall ( r (s) = 0.7, p < 0.001). In BOS subjects, but not ST, BALF ferritin was significantly related to BALF albumin ( r (s) = 0.8, p = 0.05) and there was a weak relationship with NO 2 − concentration ( r (s) = 0.6, p = 0.1). BALF NO 2 − was strongly related to BAL %neutrophils in BOS subjects ( r (s) = 0.9, p < 0.01), but there was no such relationship in STs. Conclusions: Our findings suggest that the allograft could be subject to significant iron-generated oxidative stress, which may be exacerbated by NO and neutrophil-derived ROS, particularly in BOS. Microvascular leakage may be a feature of established chronic rejection, which potentiates the iron overload and contributes to further airway damage and remodeling.