title: Methemoglobin-induced signaling and chemokine responses in human alveolar epithelial cells.
abstract: Diffuse alveolar hemorrhage is characterized by the presence of red blood cells and free hemoglobin in the alveoli and complicates a number of serious medical and surgical lung conditions including the pulmonary vasculitides and acute respiratory distress syndrome. In this study we investigated the hypothesis that exposure of human alveolar epithelial cells to hemoglobin and its breakdown products regulates chemokine release via iron- and oxidant-mediated activation of the transcription factor NF-κB. Methemoglobin alone stimulated the release of IL-8 and MCP-1 from A549 cells via activation of the NF-κB pathway; additionally, IL-8 required ERK activation and MCP-1 required JNK activation. Neither antioxidants nor iron chelators and knockdown of ferritin heavy and light chains affected these responses, indicating that iron and reactive oxygen species are not involved in the response of alveolar epithelial cells to methemoglobin. Incubation of primary cultures of human alveolar type 2 cells with methemoglobin resulted in a similar pattern of chemokine release and signaling pathway activation. In summary, we have shown for the first time that methemoglobin induced chemokine release from human lung epithelial cells independent of iron- and redox-mediated signaling involving the activation of the NF-κB and MAPK pathways. Decompartmentalization of hemoglobin may be a significant proinflammatory stimulus in a variety of lung diseases.
authors.affiliation: Unit of Critical Care, Royal Brompton and Harefield NHS Foundation Trust Hospital, Sydney St., London SW3 6NP, UK. g.quinlan@imperial.ac.uk.
authors.forename: Sharon
authors.initials: S
authors.lastname: Mumby
authors.forename: Latha
authors.initials: L
authors.lastname: Ramakrishnan
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Evans
authors.forename: Mark J D
authors.initials: MJ
authors.lastname: Griffiths
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Quinlan
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D056809:Alveolar Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D000975:Antioxidants / Q000494:pharmacology; D045744:Cell Line, Tumor; D018932:Chemokine CCL2 / Q000378:metabolism*; D018925:Chemokines / Q000378:metabolism; D003676:Deferoxamine / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism*; D007502:Iron Chelating Agents / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D008706:Methemoglobin / Q000494:pharmacology / Q000502:physiology*; D016328:NF-kappa B / Q000378:metabolism; D018384:Oxidative Stress; D010618:Phenanthrolines / Q000494:pharmacology; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D011650:Pulmonary Alveoli / Q000166:cytology; D034622:RNA Interference
chemical_list: D000975:Antioxidants; C111835:CCL2 protein, human; D018932:Chemokine CCL2; D018925:Chemokines; D016209:Interleukin-8; D007502:Iron Chelating Agents; D016328:NF-kappa B; D010618:Phenanthrolines; D008706:Methemoglobin; D051550:I-kappa B Kinase; D003676:Deferoxamine; D000111:Acetylcysteine
keywords: alveolar epithelial cells; cytokines; methemoglobin