AJP - Cell Physiology, Vol 258, Issue 6 C1141-C1149, Copyright © 1990 by American Physiological Society
Polyaspartic acid inhibits gentamicin-induced perturbations of phospholipid metabolism
L. Ramsammy, C. Josepovitz, B. Lane and G. J. Kaloyanides
Department of Medicine, State University of New York, Stony Brook 11794.
We investigated whether polyaspartic acid (PAA) can inhibit
aminoglycoside-induced perturbations of phospholipid metabolism in cultured
renal cells of opossum and rabbit and examined the mechanism involved.
Cells incubated in medium containing gentamicin (10(-3) M) manifested a
time-dependent increase in total phospholipid in association with the
appearance of lysosomal myeloid bodies, impaired degradation of
phospholipid, and disruption of the phosphatidylinositol (PI) cascade in
response to bradykinin stimulation. These alterations of phospholipid
metabolism were either completely or almost completely prevented in cells
grown in medium containing gentamicin (10(-3) M) and PAA (3 x 10(-4) M, mol
wt 11,000) even though PAA did not inhibit the cellular accumulation of
gentamicin (40 +/- 1 vs. 42 +/- 1 micrograms/mg protein). In other in vitro
studies, we demonstrated that gentamicin depressed the permeability of
phosphatidylcholine (PC)/PI liposomes to glycerol and promoted liposomal
aggregation. Both effects were blocked by prior addition of PAA. Methylene
blue, a cationic dye, was shown to form an electrostatic complex with PAA;
gentamicin competitively displaced methylene blue bound to PAA. Our results
support the conclusion that the protective effect of PAA is related to its
ability to serve as an anionic substrate that electrostatically binds
aminoglycoside antibiotics and, thereby, prevents these polycationic drugs
from interacting electrostatically with anionic phospholipid of cell
membranes.
