Aminoglycoside Antibiotics Prevent The Formation Of Non-Bilayer Structures In Negatively-Charged Membranes. Comparative Studies Using Fusogenic (Bis(Beta-Diethylaminoethylether)Hexestrol) And Aggregating (Spermine) Agents

Aminoglycoside antibiotics cause aggregation but not fusion of negatively-charged
liposomes at an extent proportional to their capacity to interact with acidic
phospholipids (Van Bambeke et al., 1995, Eur. J. Pharmacol., 289, 321-333). To
understand why aggregation is not followed by fusion, we have examined here the
influence of two aminoglycosides with markedly different toxic potential
(gentamicin > isepamicin) on lipid phase transition in negatively-charged
liposomes using 31P-NMR spectroscopy, in comparison with spermine (an aggregating
agent) and bis(beta-diethylaminoethylether)hexestrol or DEH (a fusogenic cationic
amphiphile). Gentamicin, spermine, and, to a lesser extent, isepamicin inhibit
the appearance of the isotropic signal seen upon warming of control liposomes and
denoting the presence of mobile structures. This non-bilayer signal appeared most
prominently when liposomes were incubated with DEH, a strong fusogenic agent. We
conclude that aminoglycosides, like spermine, have the potential to prevent
membrane fusion, by inhibiting the development of a critical change in membrane
organization, which is associated with fusion. We suggest that this capacity
could be a determinant in aminoglycoside toxicity.