title: Azithromycin, a lysosomotropic antibiotic, impairs fluid-phase pinocytosis in cultured fibroblasts.
abstract: The dicationic macrolide antibiotic azithromycin inhibits the uptake of horseradish peroxidase (HRP) by fluid-phase pinocytosis in fibroblasts in a time- and concentration-dependent fashion without affecting its decay (regurgitation and/or degradation). The azithromycin effect is additive to that of nocodazole, known to impair endocytic uptake and transport of solutes along the endocytic pathway. Cytochemistry (light and electron microscopy) shows a major reduction by azithromycin in the number of HRP-labeled endocytic vesicles at 5 min (endosomes) and 2 h (lysosomes). Within 3 h of exposure, azithromycin also causes the appearance of large and light-lucentlelectron-lucent vacuoles, most of which can be labeled by lucifer yellow when this tracer is added to culture prior to azithromycin exposure. Three days of treatment with azithromycin result in the accumulation of very large vesicles filled with pleiomorphic content, consistent with phospholipidosis. These vesicles are accessible to fluorescein-labeled bovine serum albumin (FITC-BSA) and intensively stained with filipin, indicating a mixed storage with cholesterol. The impairment of HRP pinocytosis directly correlates with the amount of azithromycin accumulated by the cells, but not with the phospholipidosis induced by the drug. The proton ionophore monensin, which completely suppresses azithromycin accumulation, also prevents inhibition of HRP uptake. Erythromycylamine, another dicationic macrolide, also inhibits HRP pinocytosis in direct correlation with its cellular accumulation and is as potent as azithromycin at equimolar cellular concentrations. We suggest that dicationic macrolides inhibit fluid-phase pinocytosis by impairing the formation of pinocytic vacuoles and endosomes.
authors.affiliation: Unité de Pharmacologie Cellulaire et Moléculaire, Université Catholique de Louvain, Brussels, Belgium. tyteca@facm.ucl.ac.be
authors.forename: D
authors.initials: D
authors.lastname: Tyteca
authors.forename: P
authors.initials: P
authors.lastname: Van Der Smissen
authors.forename: F
authors.initials: F
authors.lastname: Van Bambeke
authors.forename: K
authors.initials: K
authors.lastname: Leys
authors.forename: P M
authors.initials: PM
authors.lastname: Tulkens
authors.forename: P J
authors.initials: PJ
authors.lastname: Courtoy
authors.forename: M P
authors.initials: MP
authors.lastname: Mingeot-Leclercq
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology; D017963:Azithromycin / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D004396:Coloring Agents; D004247:DNA / Q000096:biosynthesis; D004917:Erythromycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D005333:Fetus / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology; D006735:Horseradish Peroxidase / Q000493:pharmacokinetics; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008985:Monensin / Q000494:pharmacology; D015739:Nocodazole / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism; D010873:Pinocytosis / Q000187:drug effects*; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D014048:Tolonium Chloride; D014168:Transferrin / Q000378:metabolism; D022161:Transport Vesicles / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D000900:Anti-Bacterial Agents; D000970:Antineoplastic Agents; D004396:Coloring Agents; D007476:Ionophores; D010743:Phospholipids; D014168:Transferrin; C007626:erythromyclamine; D014048:Tolonium Chloride; D004917:Erythromycin; D017963:Azithromycin; D000255:Adenosine Triphosphate; D004247:DNA; D008985:Monensin; D006735:Horseradish Peroxidase; D015739:Nocodazole