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Effect of gentamicin on phospholipid metabolism in cultured rabbit proximal tubular cells
L S Ramsammy1, C Josepovitz, B Lane
1Department of Medicine, State University of New York, Stony Brook 11794.
Abstract:
We examined the hypothesis that the accumulation of phospholipid in cells exposed to gentamicin is due to impaired degradation. Experiments were performed in rabbit proximal tubular cells grown in primary culture. Cells exposed to 10(-3) M gentamicin manifested myeloid body formation and a progressive increase in total phospholipid that by day 6 was 44% higher than that of control cells and reflected increases of phosphatidylinositol of 235%, phosphatidylcholine of 60%, phosphatidylethanolamine of 90%, and phosphatidylserine of 55% above control values. Gentamicin impaired the degradation of these phospholipids. The t1/2 of the phospholipid pool labeled with [3H]myoinositol increased 146% from 1.17 (control) to 2.88 days (gentamicin); the t1/2 of the [3H]choline pool increased 34% from 1.77 to 2.38 days; the t1/2 of the [3H]ethanolamine pool increased 57% from 3.14 to 4.93 days; the t1/2 of the [3H] serine pool increased 37% from 6.30 to 8.63 days. Exposure of cells to gentamicin for 2 days also stimulated increased incorporation of [3H]myoinositol (68%) and [3H]ethanolamine (59%) into phospholipid. The data are consistent with the hypothesis that gentamicin inhibits the activity of lysosomal phospholipases that results in the accumulation of phospholipid within the lysosome in the form of myeloid bodies. Increased phospholipid synthesis may represent a compensatory response to the impaired lysosomal degradation of phospholipid. We postulate that the preferential increase of phosphatidylinositol reflects the capacity of the polycationic gentamicin to interact electrostatically with the anionic phosphoinositides and inhibit their turnover.
Insights
Gentamicin causes phospholipid accumulation in kidney cells by impairing their breakdown. This leads to myeloid body formation and suggests gentamicin inhibits lysosomal phospholipases, potentially increasing phospholipid synthesis as a response.
Area of Science:
- Nephrology
- Cell Biology
- Pharmacology
Background:
- Gentamicin is an antibiotic known to cause nephrotoxicity.
- Cellular mechanisms underlying gentamicin-induced kidney damage are not fully understood.
- Phospholipid accumulation, particularly in lysosomes, has been observed in gentamicin-exposed cells.
Purpose of the Study:
- To investigate the hypothesis that gentamicin causes phospholipid accumulation due to impaired degradation.
- To elucidate the specific phospholipids affected and the impact on their turnover.
- To explore the role of lysosomal phospholipases in gentamicin nephrotoxicity.
Main Methods:
- Primary rabbit proximal tubular cells were cultured and exposed to gentamicin (10(-3) M).
- Quantification of total phospholipid and specific phospholipid classes (phosphatidylinositol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine) was performed.
- Degradation rates of labeled phospholipids were assessed by measuring half-lives (t1/2).
- Incorporation of radiolabeled precursors into phospholipids was measured.
Main Results:
- Gentamicin exposure led to myeloid body formation and a 44% increase in total phospholipid after 6 days.
- Significant increases in phosphatidylinositol (235%), phosphatidylethanolamine (90%), phosphatidylcholine (60%), and phosphatidylserine (55%) were observed.
- Degradation of phospholipids was impaired, with increased half-lives for labeled myoinositol, choline, ethanolamine, and serine pools.
- Short-term gentamicin exposure stimulated phospholipid synthesis, particularly for myoinositol and ethanolamine.
Conclusions:
- Gentamicin impairs phospholipid degradation in proximal tubular cells, leading to accumulation within lysosomes as myeloid bodies.
- The data support the hypothesis that gentamicin inhibits lysosomal phospholipase activity.
- Increased phospholipid synthesis may be a compensatory mechanism, with preferential effects on phosphatidylinositol due to gentamicin's polycationic nature.
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