Rab‐small GTPases are involved in fluvastatin and pravastatin‐induced vacuolation in rat skeletal myofibers

Abstract

Three-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitors, known as statins, induce skeletal muscle injury including myalgia, myositis, and rhabdomyolysis. The mechanism of this myotoxicity remains unknown. This study examined the effect of statins on single skeletal myofibers enzymatically isolated from the rat flexor digitorum brevis muscles. Fluvastatin and pravastatin induced the formation of numerous vacuoles in the myofibers after 72 h of treatment. This effect progressed in a time- and concentration-dependent manner and, consequently, cell death occurred after 120 h. Electron micrographs revealed craters along the sarcolemma and swelling of the sarcoplasmic reticula and mitochondria, in addition to intracellular vacuoles. When caffeine was added after 72 h of fluvastatin treatment, contractile shortening of statin-treated myofibers was significantly attenuated and blebs formed on the surface of the myofibers. The coapplication of geranylgeranylpyrophosphate (GGPP) with fluvastatin prevented the morphological changes, while that of farnesylpyrophosphate (FPP) was ineffective. Furthermore, perillyl alcohol, an inhibitor of Rab geranylgeranyl transferase and geranylgeranyl transferase-I (GGTase-I), mimicked the effect of statins, while a specific GGTase-I inhibitor (GGTI-298) or a farnesyl transferase inhibitor (FTI-277) failed to do so. These results suggest that the inactivation of Rab GTPase, which involved in intracellular membrane transport, is a crucial factor in statin-induced-morphological abnormality in skeletal muscle fibers.

Mechanism of Statin-Induced Rhabdomyolysis

“…1). The statin treatment reduced the contractility of the cultured myofibers and made them vulnerable to caffeine-induced contraction, resulting in cell damage (15). These results were similar to those of previous reports of statin-induced muscle weakness (4) and myotoxicity exacerbated by exercise (18).…”

“…In the cultured rat FDB myofibers, application of 1 mM fluvastatin or 10 mM pravastatin for 3 -4 days induced vacuolation, which was similar to those reported in in vivo animal experiments (15,16). Longer (> 5 days) treatment of the statins caused death of myofibers with a release of cell contents (15,16) (Fig.…”

“…One group using rat immortalized L6 myoblasts reported that the depletion of FPP is critical for myotoxicity (22), but another laboratory using the same cell line suggested that GGPP was the critical isoprenoid (12). In our hands, it was not FPP (3 mM), but GGPP (3 mM) alone, because the addition of GGPP, not FPP, in the presence of fluvastatin completely canceled the toxic effects of statins in skeletal myofibers (15,17). FPP also failed to rescue myotoxicity in a study using myotubes differentiated from C2C12 myoblasts (23).…”

“…Longer (> 5 days) treatment of the statins caused death of myofibers with a release of cell contents (15,16) (Fig. 1).…”

“…L6 skeletal myoblasts were also damaged by statins due to the inactivation of the Rho/ROCK system (12). However, the inhibitors of either Rho or ROCK did not damage myofibers, unlike (in contrast to their effects on) myoblasts (15,17). Furthermore, we tested the effect of GGTase inhibitors to determine whether geranylgeranylated small GTPases were involved in statin's adverse actions on myofibers.…”