title: Acid contact in the rodent pulmonary alveolus causes proinflammatory signaling by membrane pore formation.
abstract: Although gastric acid aspiration causes rapid lung inflammation and acute lung injury, the initiating mechanisms are not known. To determine alveolar epithelial responses to acid, we viewed live alveoli of the isolated lung by fluorescence microscopy, then we microinjected the alveoli with HCl at pH of 1.5. The microinjection caused an immediate but transient formation of molecule-scale pores in the apical alveolar membrane, resulting in loss of cytosolic dye. However, the membrane rapidly resealed. There was no cell damage and no further dye loss despite continuous HCl injection. Concomitantly, reactive oxygen species (ROS) increased in the adjacent perialveolar microvascular endothelium in a Ca(2+)-dependent manner. By contrast, ROS did not increase in wild-type mice in which we gave intra-alveolar injections of polyethylene glycol (PEG)-catalase, in mice overexpressing alveolar catalase, or in mice lacking functional NADPH oxidase (Nox2). Together, our findings indicate the presence of an unusual proinflammatory mechanism in which alveolar contact with acid caused membrane pore formation. The effect, although transient, was nevertheless sufficient to induce Ca(2+) entry and Nox2-dependent H(2)O(2) release from the alveolar epithelium. These responses identify alveolar H(2)O(2) release as the signaling mechanism responsible for lung inflammation induced by acid and suggest that intra-alveolar PEG-catalase might be therapeutic in acid-induced lung injury.
authors.affiliation: Lung Biology Laboratory, Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York, USA.
authors.forename: Kristin
authors.initials: K
authors.lastname: Westphalen
authors.forename: Eiji
authors.initials: E
authors.lastname: Monma
authors.forename: Mohammad N
authors.initials: MN
authors.lastname: Islam
authors.forename: Jahar
authors.initials: J
authors.lastname: Bhattacharya
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D002462:Cell Membrane / Q000378:metabolism* / Q000473:pathology; D004487:Edema / Q000378:metabolism; D004848:Epithelium / Q000201:enzymology / Q000276:immunology / Q000473:pathology; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D016257:Fura-2 / Q000378:metabolism; D005744:Gastric Acid; D006851:Hydrochloric Acid; D006861:Hydrogen Peroxide / Q000378:metabolism; D066298:In Vitro Techniques; D018836:Inflammation Mediators / Q000378:metabolism*; D008264:Macrophages / Q000473:pathology / Q000502:physiology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D055806:Microvessels / Q000378:metabolism; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011015:Pneumonia, Aspiration / Q000139:chemically induced / Q000276:immunology / Q000378:metabolism; D016062:Porosity; D011650:Pulmonary Alveoli / Q000098:blood supply / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; D018836:Inflammation Mediators; D008562:Membrane Glycoproteins; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D006861:Hydrogen Peroxide; C488842:Cybb protein, mouse; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D006851:Hydrochloric Acid; D016257:Fura-2