Scientific Publications by FDA Staff

Am J Respir Cell Mol Biol 2016 Aug;55(2):288-98

Oxidized Ferric And Ferryl Forms Of Hemoglobin Trigger Mitochondrial Dysfunction And Injury In Alveolar Type I Cells.

Chintagari NR, Jana S, Alayash AI

Lung alveoli are lined by alveolar type I cells (AT1) and cuboidal type II (AT2) cells. The AT1 cells are likely to be exposed to cell-free hemoglobin (Hb) in multiple lung diseases; however, the role of Hb redox (reduction-oxidation) reactions and their precise contributions to AT1 cell injury are not well understood. Using mouse E10 cells as an AT1 cell model, we demonstrated here that higher Hb oxidation states ferric (HbFe3+) and ferryl Hb (HbFe4+) and subsequent heme loss play a central role in the genesis of injury. Exposures to HbFe2+ and HbFe3+ for 24 hours induced expression of heme oxygenase-1 (HO-1) protein in E10 cells and HO-1 translocation in the purified mitochondrial fractions. Both of these effects were intensified with increasing oxidation states of Hb. Next, we examined the effects of Hb oxidation and free heme on mitochondrial bioenergetic function by measuring changes in the mitochondrial transmembrane potential (¿¿m) and oxygen consumption rate (OCR). In contrast to HbFe2+, HbFe3+ reduced basal OCR indicating a compromised mitochondrial activity. However, HbFe4+ exposure not only induced an early expression of HO-1 but also caused mitochondrial dysfunction within 12h when compared to HbFe2+ and HbFe3+. HbFe4+ exposure for 24h also caused mitochondrial depolarization in E10 cells. The deleterious effects of HbFe3+ and HbFe4+ were reversed by the addition of scavenger proteins, haptoglobin (Hp) and hemopexin (Hpx). Collectively, these data establish for the first time a central role for cell-free Hb in lung epithelial injury and that these effects are mediated through the redox transition of Hb to higher oxidation states.