Biochem Pharmacol 1990 Aug 1;40(3):499-506

Effect of acidic phospholipids on the activity of lysosomal phospholipases and
on their inhibition induced by aminoglycoside antibiotics--II. Conformational
analysis.

Mingeot-Leclercq MP, Piret J, Tulkens PM, Brasseur R

Laboratoire de Chimie Physiologique, Universite Catholique de Louvain,
Bruxelles, Belgium.

In a companion paper (Mingeot-Leclercq et al. Biochem Pharmacol 40: 489-497,
1990), we showed that the inhibitory potency of gentamicin on the activity of
lysosomal phospholipases, measured towards phosphatidylcholine included in
negatively-charged liposomes, is markedly influenced by the nature of the acidic
phospholipid used (phosphatidylinositol, phosphatidylserine, phosphatidic acid),
whereas the binding of the drug to the three types of liposomes is similar. This
result challenged previous conclusions pointing to a key role exerted by drug
binding to phospholipid membranes and presumably charge neutralization, for
phospholipases inhibition (Carlier et al. Antimicrob Agents Chemother, 23:
440-449, 1983; Mingeot-Leclercq et al., Biochem Pharmacol 37:591-599, 1988).
Conformational analysis of mixed monolayers of gentamicin and each of the three
acid phospholipids shows that gentamicin systematically adopts an orientation
largely parallel to the hydrophobic-hydrophilic interface, but that (i) the
energies of interaction are largely different (phosphatidylinositol greater than
phosphatidylserine greater than phosphatidic acid), and (ii) the apparent
accessibility of the bound drug to water varies in an inverse relation with the
energies of interaction. Amikacin, a semisynthetic derivative of kanamycin A
with a lower inhibitory potential towards phospholipases than gentamicin in the
three types of liposomes used, also showed similar differences in energies of
interaction and accessibility to water, but constantly exhibited an orientation
perpendicular to the hydrophobic-hydrophilic interface. We conclude that
impairment of lysosomal phospholipase activities towards phosphatidylcholine
included in negatively-charged membranes by aminoglycoside antibiotics is indeed
dependent upon drug binding to the bilayer, but is also modulated by (i) the
nature of the acidic phospholipid, which influences the energy of interaction
and the accessibility of the drug with respect to the hydrophilic phase, and
(ii) the orientation of the drug, which it itself related to its chemical
structure. Inasmuch as phospholipases inhibition is related to aminoglycoside
nephrotoxicity, these findings may help in better defining the molecular
determinants and mechanisms responsible for this adverse effect.

PMID: 2383283, UI: 90343840