Cytotoxicity and lamellar body induction potential of a racemic benzamide antiarrhythmic compound and enantiomers in cultured rat hepatocytes.
A wide variety of cationic amphiphilic compounds induce cytoplasmic lamellar bodies, accompanied by phospholipidosis and often coincidental with toxicity. The in vitro cytotoxic and lamellar body-inducing potentials of a racemic cationic amphiphilic benzamide antiarrhythmic compound and its trans-enantiomers were examined. Cultured rat hepatocytes were treated for 24 hr with the racemate and (+) and (-) trans-enantiomers in increasing concentrations to 1.0 mm. All compounds produced significant cytotoxicity at concentrations of 250 mum and greater, as assessed by lactate dehydrogenase release, but the (-) enantiomer was less cytotoxic than the racemate and (+) enantiomer at 500 mum. Electron microscopy revealed significant formation of lamellar bodies in all treated cultures at concentrations of 100 mum and higher for all compounds, with the (-) enantiomer producing significantly fewer lamellar bodies than the (+) enantiomer or racemic mixture. Acid phosphatase cytochemistry indicated that most, but not all, lamellar bodies were lysosomes. Fluorescence distributional studies with a phospholipid analogue, 1-acyl-2-[12-(7-nitro-2-1-,3-benzoxadiazol-4-yl)amino]dodecanoyl phosphatidylcholine, in living cells confirmed drug-induced cytoplasmic vacuoles to be formed from labelled plasma membrane at racemate drug concentrations as low as 10 mum, and suggested that lamellar body formation proceeds by a dynamic process involving the plasma membrane. These data indicate stereo-selective lamellar body-and cytotoxicity-inducing potentials between enantiomers, and that these are dissociable processes.
Cramer
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Investigative Toxicology Research, Upjohn Laboratories, 301 Henrietta St, Kalamazoo, MI 49007, USA.
Ulrich
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