title: A new role for an old drug: Ambroxol triggers lysosomal exocytosis via pH-dependent Ca²⁺ release from acidic Ca²⁺ stores.
abstract: Ambroxol (Ax) is a frequently prescribed drug used to facilitate mucociliary clearance, but its mode of action is yet poorly understood. Here we show by X-ray spectroscopy that Ax accumulates in lamellar bodies (LBs), the surfactant storing, secretory lysosomes of type II pneumocytes. Using lyso- and acidotropic substances in combination with fluorescence imaging we confirm that these vesicles belong to the class of acidic Ca(2+) stores. Ax lead to a significant neutralization of LB pH, followed by intracellular Ca(2+) release, and to a dose-dependent surfactant exocytosis. Ax-induced Ca(2+) release was significantly reduced and slowed down by pretreatment of the cells with bafilomycin A1 (Baf A1), an inhibitor of the vesicular H(+) ATPase. These results could be nearly reproduced with NH3/NH4(+). The findings suggest that Ax accumulates within LBs and severely affects their H(+) and Ca(2+) homeostasis. This is further supported by an Ax-induced change of nanostructural assembly of surfactant layers. We conclude that Ax profoundly affects LBs presumably by disordering lipid bilayers and by acting as a weak base. The pH change triggers - at least in part - Ca(2+) release from stores and secretion of surfactant from type II cells. This novel mechanism of Ax as a lysosomal secretagogue may also play a role for its recently discussed use for lysosomal storage and other degenerative diseases.
authors.affiliation: Institute of General Physiology, University of Ulm, Albert-Einstein Allee 11, 89081 Ulm, Germany. Electronic address: giorgio.fois@uni-ulm.de.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Fois
authors.affiliation: Institute of General Physiology, University of Ulm, Albert-Einstein Allee 11, 89081 Ulm, Germany; Department of Physiology and Medical Physics, Division of Physiology, Medical University of Innsbruck, Fritz-Pregl-Str. 3, A-6020 Innsbruck, Austria. Electronic address: nina.hobi@uni-ulm.de.
authors.forename: Nina
authors.initials: N
authors.lastname: Hobi
authors.affiliation: Institute of General Physiology, University of Ulm, Albert-Einstein Allee 11, 89081 Ulm, Germany. Electronic address: edward.felder@uni-ulm.de.
authors.forename: Edward
authors.initials: E
authors.lastname: Felder
authors.affiliation: Z. E. Elektronenmikroskopie, Universität Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany. Electronic address: andreas.ziegler@uni-ulm.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Ziegler
authors.affiliation: Institute of General Physiology, University of Ulm, Albert-Einstein Allee 11, 89081 Ulm, Germany. Electronic address: pika.miklavc@uni-ulm.de.
authors.forename: Pika
authors.initials: P
authors.lastname: Miklavc
authors.affiliation: Z. E. Elektronenmikroskopie, Universität Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany. Electronic address: paul.walther@uni-ulm.de.
authors.forename: Paul
authors.initials: P
authors.lastname: Walther
authors.affiliation: Institut für Anästhesiologische Pathophysiologie und Verfahrensentwicklung, University of Ulm, Albert-Einstein Allee 11, 89081 Ulm, Germany. Electronic address: peter.radermacher@uni-ulm.de.
authors.forename: Peter
authors.initials: P
authors.lastname: Radermacher
authors.affiliation: Department of Physiology and Medical Physics, Division of Physiology, Medical University of Innsbruck, Fritz-Pregl-Str. 3, A-6020 Innsbruck, Austria. Electronic address: thomas.haller@i-med.ac.at.
authors.forename: Thomas
authors.initials: T
authors.lastname: Haller
authors.affiliation: Institute of General Physiology, University of Ulm, Albert-Einstein Allee 11, 89081 Ulm, Germany. Electronic address: paul.dietl@uni-ulm.de.
authors.forename: Paul
authors.initials: P
authors.lastname: Dietl
mesh_terms: D056809:Alveolar Epithelial Cells; D000551:Ambroxol / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002469:Cell Separation / Q000379:methods; D005089:Exocytosis / Q000187:drug effects* / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000187:drug effects*; D017207:Rats, Sprague-Dawley; D022142:Secretory Vesicles / Q000187:drug effects*
chemical_list: D000551:Ambroxol; D002118:Calcium
keywords: Alzheimer's disease; Autophagy; Host defense; Inflammation; Lysosomal storage disease; Mucus; Neurodegeneration; Parkinson's disease; Secretory lysosome