SUBCELLULAR-DISTRIBUTION OF DAPTOMYCIN GIVEN ALONE OR WITH TOBRAMYCININ RENAL PROXIMAL TUBULAR CELLS

Previous studies in experimental animals showed that daptomycin, a lip opeptide antibiotic, protects against aminoglycoside nephrotoxicity (C . A. Wood, H. C. Finkbeiner, S. J. Kohlhepp, P. W. Kohnen, and D. N. G ilbert, Antimicrob. Agents Chemother. 33:1280-1285, 1989; D. Beauchamp , M. Pellerin, P. Gourde, M. Pettigrew, and M. G. Bergeron, Antimicrob . Agents Chemother. 34:139-147, 1990). In order to better understand t he mechanism involved in this protective effect, the subcellular distr ibution of daptomycin was investigated in the proximal tubular cells o f animals treated with daptomycin alone or in combination with tobramy cin. A first group of female Sprague-Dawley rats received a single int ravenous injection of daptomycin at a dose of 100 mg/kg of body weight and were killed at 10 min, 1 h, or 24 h after the injection. Other gr oups of rats were treated during 10 days with saline (NaCl, 0.9%), tob ramycin at dosages of 20 mg/kg/12 h, daptomycin at dosages of 10 mg/kg /12 h, or the combination tobramycin-daptomycin at the same dosages. A t the time of sacrifice, the renal cortex of the right kidney of each animal was dissected, and small blocks of tissue were fixed, dehydrate d, and embedded in Araldite 502 epoxy resin. The subcellular distribut ion of daptomycin and tobramycin was determined on ultrathin sections by immunogold labeling. Ten minutes after the injection of daptomycin alone, gold particles were seen over the brush border membrane and on the membranes of the endocytic vacuoles of proximal tubular cells. One hour after the injection, a similar distribution was seen and numerou s gold particles were found over the lysosomes of proximal tubular cel ls. After 24h, daptomycin was seen essentially inside the lysosomes of proximal tubular cells. Daptomycin was also found inside the lysosome s of proximal tubular cells in animals treated with daptomycin alone o r in combination with tobramycin. However, daptomycin was seen over th e myeloid bodies inside the lysosomes of proximal tubular cells in the renal cortexes of animals treated with the combination tobramycin-dap tomycin after 10 days of treatment. The double labeling showed daptomy cin and tobramycin inside the lysosomes of proximal tubular cells. The results suggest that daptomycin might protect against aminoglycoside nephrotoxicity by interfering with the interaction between the aminogl ycoside and phospholipids inside the lysosomes of proximal tubular cel ls.