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Polyaspartic acid inhibits gentamicin-induced perturbations of phospholipid metabolism
L Ramsammy1, C Josepovitz, B Lane
1Department of Medicine, State University of New York, Stony Brook 11794.
Abstract:
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.
Insights
Polyaspartic acid (PAA) prevents kidney cell damage from gentamicin by binding to the antibiotic. This interaction stops gentamicin from disrupting essential cell membrane phospholipid metabolism, protecting kidney cells.
Area of Science:
- Nephrology
- Cell Biology
- Pharmacology
Background:
- Aminoglycoside antibiotics like gentamicin can cause kidney cell damage by disrupting phospholipid metabolism.
- The exact mechanism of this cellular toxicity is not fully understood.
- Phosphatidylinositol (PI) cascade disruption is implicated in aminoglycoside-induced renal cell injury.
Purpose of the Study:
- To investigate if polyaspartic acid (PAA) can inhibit aminoglycoside-induced phospholipid metabolism disturbances in cultured renal cells.
- To elucidate the mechanism by which PAA exerts its protective effects.
Main Methods:
- Cultured opossum and rabbit renal cells were treated with gentamicin alone or in combination with PAA.
- Phospholipid metabolism, including PI cascade response to bradykinin, was assessed.
- In vitro liposome studies were conducted to examine interactions between gentamicin, PAA, and phospholipids.
- Methylene blue binding assays were used to study electrostatic interactions.
Main Results:
- Gentamicin induced time-dependent increases in total phospholipid, lysosomal myeloid bodies, and impaired phospholipid degradation.
- Gentamicin disrupted the PI cascade response to bradykinin.
- PAA completely or almost completely prevented these gentamicin-induced alterations.
- PAA did not inhibit gentamicin accumulation within cells.
- In vitro, gentamicin decreased liposome permeability and promoted aggregation, effects blocked by PAA.
- PAA electrostatically binds gentamicin, preventing its interaction with anionic phospholipids.
Conclusions:
- PAA effectively protects renal cells from gentamicin-induced phospholipid metabolism perturbations.
- PAA's protective mechanism involves electrostatic binding of aminoglycoside antibiotics.
- This binding prevents polycationic drugs from interacting with anionic phospholipids in cell membranes.