© 1997 Oxford University Press
research-article |
Tetracycline-Induced Steatosis in Primary Canine Hepatocyte Cultures
Department of Drug Safety Evaluation Pfizer Central Research, Groton, Connecticut 06340 *Department of Neurosciences Pfizer Central Research, Groton, Connecticut 06340
Received July 1, 1997; accepted October 2, 1997
Primary hepatocyte cultures prepared from male beagle dog liver were used to determine susceptibility of the canine liver to tetracycline-induced steatosis. The effects of the drug on mitochondrial lipid metabolism and intracellular triglyceride accumulation were monitored at the same time that steatosis was detected by light microscopy and quantitated using lipid-specific stains. Exposure of primary canine hepatocyte cultures to tetracycline for 24–48 h resulted in concentration-dependent, significant increases in the Oil Red O-stained lipid inclusions. Microscopic examination of the total stained areas suggested that increases over control levels were due primarily to the increase in the size of the lipid inclusions rather than in the number. Biochemical analyses for triglyceride content and histological staining with Nile red, another neutral lipid-specific dye, confirmed a specific increase in intracellular triglyceride following a 24-h exposure to noncytotoxic levels of tetracycline. ß-oxidation studies based on the oxidation of [14]palmetic acid or [14]palmetoyl carnitine demonstrated a concentration-dependent inhibition of mitochondrial but not peroxisomal ß-oxidation in hepatocytes after a 24-h exposure to tetracycline. In vitro incubation of tetracycline with mitochondria isolated from dog liver showed similar, concentration-dependent inhibition. This study clearly indicates that the canine hepatocyte is susceptible to tetracycline-induced steatosis. Triglyceride accumulation was concomitant with the inhibition of mitochondrial lipid metabolism, indicating that this is a primary mechanism leading to steatosis in dog hepatocytes following tetracycline exposure.