IN-VITRO MYOTOXICITY OF THE 3-HYDROXY-3-METHYLGLUTARYL COENZYME-A REDUCTASE INHIBITORS, PRAVASTATIN, LOVASTATIN, AND SIMVASTATIN, USING NEONATAL RAT SKELETAL MYOCYTES

Pravastatin, lovastatin, and simvastatin, drugs which lower cholesterol by inhibiting 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, have been linked to skeletal myopathies in humans and rats. The myotoxicity of these three drugs was compared, after 48 hr exposure, in cultures of primary neonatal rat skeletal myotubes. Measurements included HMG CoA reductase activity ([C-14]acetate incorporation into cholesterol), indicators of membrane damage (CPK, LDH, and AST), cell viability (mitochondrial dehydrogenase metabolism of MTT), protein synthesis ([H-3]leucine incorporation), and energy status (ATP). All three drugs inhibited cholesterol synthesis to the same extent in rat hepatocytes (IC50s approximately 0.07 mu M). Lovastatin- and simvastatin-induced inhibition of cholesterol synthesis in myotubes was unchanged compared to that of hepatocytes, but pravastatin was 85-fold less potent (IC50 = 5.9 mu M) Protein synthesis and ATP levels were the most sensitive indicators of toxicity. Pravastatin (IC50 = 759 mu M) was > 100-fold less inhibitory of protein synthesis than lovastatin (IC50 = 5.4 mu M) or simvastatin (IC50 = 1.9 mu M). Addition of mevalonic acid (the immediate product of the HMG CoA reductase reaction), as 100 mu M mevalonic acid lactone, reversed the toxicity of all three drugs. Removal of serum for 24-72 hr did not alter the toxicity of any of the drugs compared to cultures containing 10% serum, suggesting that differences in protein binding did not account for the differences in toxicity of the drugs. These results indicate that pravastatin is less myotoxic than lovastatin or simvastatin in this in vitro system using neonatal rat skeletal muscle cells, and this differential toxicity is correlated with the selective decrease in inhibition of HMG CoA reductase by pravastatin in nonhepatic tissues. (C) 1995 Academic Press, Inc.