HMG COA REDUCTASE INHIBITOR-INDUCED MYOTOXICITY - PRAVASTATIN AND LOVASTATIN INHIBIT THE GERANYLGERANYLATION OF LOW-MOLECULAR-WEIGHT PROTEINS IN NEONATAL RAT MUSCLE-CELL CULTURE

In previous studies, inhibition of cholesterol synthesis by HMG CoA re ductase inhibitors (HMGRI) was associated with myotoxicity in cultures of neonatal rat skeletal myotubes, and rhabdomyolysis in rats, rabbit s, and humans in vivo. In vitro myotoxicity was directly related to HM GRI-induced depletion of mevalonate, farnesol, and geranylgeraniol, si nce supplementation with these intermediate metabolites abrogated the toxicity. Both farnesol and geranylgeraniol are required for the postt ranslational modification, or isoprenylation, of essential regulatory proteins in mammalian cells. The objective of the present study was to measure changes in protein isoprenylation in cultured neonatal rat sk eletal muscle cells exposed for 24 hr to increasing concentrations of pravastatin or lovastatin. Proteins were labeled with [H-3]mevalonate, [H-3]farnesyl pyrophosphate (FPP), or [H-3]geranylgeranyl pyrophospha te (GGPP), and then separated by SDS-PAGE and quantitated by scintilla tion counting and densitometry of autoradiographs. Mevalonate and FPP labeling of the majority of proteins increased in a concentration-depe ndent manner, even at concentrations greater than 2 mu M lovastatin an d 25 mu M pravastatin that completely inhibited cholesterol synthesis. In contrast, mevalonate and FPP labeling of three protein bands with molecular weights of 26.6, 27.7, and 28.9 kDa was markedly inhibited a t concentrations higher than 1 mu M lovastatin and 400 iud pravastatin , which inhibited protein synthesis and disrupted myotube morphology a fter longer exposures in a previous study. In contrast, these proteins were equally well labeled by GGPP at al HMGRI concentrations tested, suggesting that isoprenylation of the 26.9-, 27.8-, and 28.9-kDa prote ins requires geranylgeraniol. The results of this study indicate that HMGRI-induced myotoxicity is most likely related to reduced posttransl ational modification of specific regulatory proteins by geranylgeranio l. (C) 1997 Academic Press.