A new role for an old drug: Ambroxol triggers lysosomal exocytosis via pH-dependent Ca2+ release from acidic Ca2+ stores

Fois, G; Hobi, N; Felder, E; Ziegler, A; Miklavc, P; Walther, P; Radermacher, P; Haller, T; Dietl, P

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 Ca2+ stores. Ax lead to a significant neutralization of LB pH, followed by intracellular Ca2+ release, and to a dose-dependent surfactant exocytosis. Ax-induced Ca2+ 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 Ca2+ 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 – Ca2+ 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.

Citation

Fois, G., Hobi, N., Felder, E., Ziegler, A., Miklavc, P., Walther, P., …Dietl, P. (2015). A new role for an old drug: Ambroxol triggers lysosomal exocytosis via pH-dependent Ca2+ release from acidic Ca2+ stores. Cell Calcium, 58(6), 628-637. https://doi.org/10.1016/j.ceca.2015.10.002

• Journal Article Type: Article
• Acceptance Date: Oct 22, 2015
• Online Publication Date: Oct 27, 2015
• Publication Date: Dec 1, 2015
• Deposit Date: Oct 4, 2016
• Journal: Cell Calcium
• Print ISSN: 0143-4160
• Publisher: Elsevier
• Volume: 58
• Issue: 6
• Pages: 628-637
• DOI: https://doi.org/10.1016/j.ceca.2015.10.002
• Publisher URL: http://dx.doi.org/10.1016/j.ceca.2015.10.002
• Additional Information: Funders : Deutsche Forschungsgemeinschaft, DFG grant DI 1402 (to P.D.);Margarete von Wrangell scholarship from the Ministry of Science, Research and the Arts Baden-Württemberg (to P.M.);Carl Zeiss foundation, Germany (to N.H.)