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Interaction of the macrolide azithromycin with phospholipids. I. Inhibition of lysosomal phospholipase A1 activity
F Van Bambeke1, J P Montenez, J Piret
1Unité de Pharmacologie Cellulaire et Moléculaire, UCL 73.70, Bruxelles, Belgium. vanbambeke@facm.ucl.ac.be
Abstract:
Azithromycin, the first clinically developed dicationic macrolide antibiotic, displays an exceptional accumulation in lysosomes of cultured cells. In fibroblasts incubated with 50 mg/l (66.6 microM), it induces a distinct phospholipidosis as evidenced by biochemical and ultrastructural criteria, which strikingly resembles alterations described previously with gentamicin, a pentacationic aminoglycoside antibiotic which inhibits the lysosomal catabolism of phospholipids. We show that both drugs inhibit, in an equimolar manner, the activity of phospholipase A1 (assayed for phosphatidylcholine, included in negatively charged liposomes), in a way consistent with the model of 'charge neutralization' proposed already for gentamicin (Mingeot-Leclercq et al., 1988, Biochem. Pharmacol. 37, 591). Both drugs bind to negatively charged liposomes. Yet, in spite of this binding, azithromycin does not induce aggregation or fusion of negatively charged vesicles, under conditions in which gentamicin (or spermine, a fully hydrophilic polycation) causes a massive aggregation, and bis(beta-diethylaminoethylether)hexestrol (a dicationic amphiphile) causes fusion. The molecular interactions of azithromycin with acidic phospholipids are further examined in a companion paper.
Insights
Azithromycin causes phospholipidosis in cells by accumulating in lysosomes, similar to gentamicin. Both antibiotics inhibit phospholipase A1 activity through charge neutralization, affecting phospholipid metabolism.
Area of Science:
- Pharmacology
- Cell Biology
- Biochemistry
Background:
- Azithromycin, a dicationic macrolide antibiotic, accumulates in cell lysosomes.
- This accumulation leads to phospholipidosis, a condition resembling changes caused by gentamicin.
Purpose of the Study:
- To investigate the mechanism of azithromycin-induced phospholipidosis.
- To compare the effects of azithromycin and gentamicin on lysosomal phospholipid metabolism.
Main Methods:
- Biochemical and ultrastructural analysis of fibroblasts treated with azithromycin.
- Assay of phospholipase A1 activity using phosphatidylcholine in liposomes.
- Investigation of drug binding and effects on liposome aggregation and fusion.
Main Results:
- Azithromycin induces phospholipidosis in fibroblasts, similar to gentamicin.
- Both azithromycin and gentamicin inhibit phospholipase A1 activity via charge neutralization.
- Azithromycin binds to negatively charged liposomes but does not cause aggregation or fusion, unlike gentamicin.
Conclusions:
- Azithromycin's lysosomal accumulation and phospholipidosis are linked to phospholipase A1 inhibition.
- The mechanism of action for azithromycin differs from gentamicin regarding liposome interactions.
- Further studies are needed to fully elucidate azithromycin's molecular interactions with acidic phospholipids.