1: Eur J Cell Biol  2001 Jul;80(7):466-78

Azithromycin, a lysosomotropic antibiotic, impairs fluid-phase pinocytosis in
cultured fibroblasts.

Tyteca D, Van Der Smissen P, Van Bambeke F, Leys K, Tulkens PM, Courtoy PJ,
Mingeot-Leclercq MP.

Unite de Pharmacologie Cellulaire et Moleculaire, Universite Catholique de
Louvain, Brussels, Belgium. tyteca@facm.ucl.ac.be

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.

PMID: 11499789 [PubMed - in process]