1: J Membr Biol. 2003 Apr 1;192(3):203-15.  

The macrolide antibiotic azithromycin interacts with lipids and affects membrane
organization and fluidity: studies on Langmuir-Blodgett monolayers, liposomes
and J774 macrophages.

Tyteca D, Schanck A, Dufrene YF, Deleu M, Courtoy PJ, Tulkens PM,
Mingeot-Leclercq MP.

Unite de Pharmacologie Cellulaire et Moleculaire, Universite Catholique de
Louvain, Brussels, Belgium.

The macrolide antibiotic azithromycin was shown to markedly inhibit endocytosis.
Here we investigate the interaction of azithromycin with biomembranes and its
effects on membrane biophysics in relation to endocytosis. Equilibrium dialysis
and 31P NMR revealed that azithromycin binds to lipidic model membranes and
decreases the mobility of phospholipid phosphate heads. In contrast,
azithromycin had no effect deeper in the bilayer, based on fluorescence
polarization of TMA-DPH and DPH, compounds that, respectively, explore the
interfacial and hydrophobic domains of bilayers, and it did not induce membrane
fusion, a key event of vesicular trafficking. Atomic force microscopy showed
that azithromycin perturbed lateral phase separation in Langmuir-Blodgett
monolayers, indicating a perturbation of membrane organization in lateral
domains. The consequence of azithromycin/ phospholipid interaction on membrane
endocytosis was next evaluated in J774 macrophages by using three tracers with
different insertion preferences inside the biological membranes and
intracellular trafficking: C6-NBD-SM, TMA-DPH and N-Rh-PE. Azithromycin
differentially altered their insertion into the plasma membrane, slowed down
membrane trafficking towards lysosomes, as evaluated by the rate of N-Rh-PE
self-quenching relief, but did not affect bulk membrane internalization of
C6-NBD-SM and TMA-DPH. Azithromycin also decreased plasma membrane fluidity, as
shown by TMA-DPH fluorescence polarization and confocal microscopy after
labeling by fluorescent concanavalin A. We conclude that azithromycin directly
interacts with phospholipids, modifies biophysical properties of membrane and
affects membrane dynamics in living cells. This antibiotic may therefore help to
elucidate the physico-chemical properties underlying endocytosis.

PMID: 12820665 [PubMed - in process]