IN-VITRO AND IN-VIVO ULTRASTRUCTURAL-CHANGES INDUCED BY MACROLIDE ANTIBIOTIC LY281389

High doses of LY281389 (9-N-(12-propyl)-erythromycylamine) cause cytop lasmic vacuolar changes in striated and smooth muscle characteristic o f drug-induced phospholipidosis. This study characterized phospholipid osis in striated and smooth muscle of rats and dogs, compared in vivo observations with those in a cultured rat myoblast model, and attempte d to confirm the lysosomal origin of the drug-induced vacuoles. Standa rd transmission electron microscopy and acid phosphatase cytochemistry techniques were used to evaluate ultrastructural changes in vivo and in vitro. Rats and dogs exposed to LY281389 had a time- and dose-relat ed increase in number and size of vacuoles containing concentric lamel lar figures in cardiac and skeletal muscle. Cytochemical staining of d og stomach smooth muscle for acid phosphatase, a lysosomal enzyme, sta ined the periphery of vacuoles that contained concen tric lamellar fig ures. Cultured rat L6 myoblast cells were exposed to 0.25 mg LY281389/ ml for 2.5, 5, 10, 20, 30, or 90 min and 2, 6, 12, 24, or 48 hr. Cell cultures exposed for 2 hr had several predominantly large, clear, memb rane-bound vacuoles, and at 6 and 12 hr there were greater numbers of large vacuoles that contained increased amounts of membranous figures. Following 24- or 48-hr exposures, vacuoles occupied most of the cytop lasmic volume, and were engorged predominantly with amorphous or granu lar material. These findings indicate that LY281389 can induce similar phospholipidosis-like vacuolar changes in rat and dog muscle and in a cultured rat muscle cell line. Further, positive acid phosphatase sta ining of drug-induced vacuolar structures, in conjunction with standar d transmission electron microscopy techniques, strongly suggests that vacuoles seen in vitro and in vivo are lysosomal in origin. (C) 1996 S ociety of Toxicology