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

Geranylgeranyl pyrophosphate depletion by statins compromises skeletal muscle insulin sensitivity

BACKGROUND

Statins are widely prescribed cholesterol-lowering drugs but have been shown to increase the risk of type 2 diabetes mellitus. However, the molecular mechanisms underlying the diabetogenic effect of statins are still not fully understood.

METHODS

The effects of geranylgeranyl transferase I and II (GGTase I and II) inhibition on insulin-stimulated glucose uptake and GLUT4 translocation, and the dependence of these effects on insulin signalling were investigated in skeletal muscle cells. The protective effects of geranylgeranyl pyrophosphate (GGPP) and its precursor geranylgeraniol (GGOH) on simvastatin-induced insulin resistance were evaluated in vitro and in vivo. The effect of GGTase II inhibition in skeletal muscle on insulin sensitivity in vivo was confirmed by adeno-associated virus serotype 9 (AAV9)-mediated knockdown of the specific subunit of GGTase II, RABGGTA. The regulatory mechanisms of GGTase I on insulin signalling and GGTase II on insulin-stimulated GLUT4 translocation were investigated by knockdown of RhoA, TAZ, IRS1, geranylgeranylation site mutation of RhoA, RAB8A, and RAB13.

RESULTS

Both inhibition of GGTase I and II mimicked simvastatin-induced insulin resistance in skeletal muscle cells. GGPP and GGOH were able to prevent simvastatin-induced skeletal muscle insulin resistance in vitro and in vivo. GGTase I inhibition suppressed the phosphorylation of AKT (Ser473) (-51.3%, P < 0.01), while GGTase II inhibition had no effect on it. AAV9-mediated knockdown of RABGGTA in skeletal muscle impaired glucose disposal without disrupting insulin signalling in vivo (-46.2% for gastrocnemius glucose uptake, P < 0.001; -52.5% for tibialis anterior glucose uptake, P < 0.001; -17.8% for soleus glucose uptake, P < 0.05; -31.4% for extensor digitorum longus glucose uptake, P < 0.01). Inhibition of RhoA, TAZ, IRS1, or geranylgeranylation deficiency of RhoA attenuated the beneficial effect of GGPP on insulin signalling in skeletal muscle cells. Geranylgeranylation deficiency of RAB8A inhibited insulin-stimulated GLUT4 translocation and concomitant glucose uptake in skeletal muscle cells (-42.8% for GLUT4 translocation, P < 0.01; -50.6% for glucose uptake, P < 0.001).

CONCLUSIONS

Geranylgeranyl pyrophosphate regulates glucose uptake via GGTase I-mediated insulin signalling-dependent way and GGTase II-mediated insulin signalling-independent way in skeletal muscle. Supplementation of GGPP/GGOH could be a potential therapeutic strategy for statin-induced insulin resistance.

A Narrative Review of Statin-Induced Rhabdomyolysis: Molecular Mechanism, Risk Factors, and Management

Although statins are effective for treating hypercholesterolemia, they can have various side effects, including rhabdomyolysis, a potentially fatal condition. This review evaluated the incidence and underlying molecular mechanism of statin-induced rhabdomyolysis and analyzed its risk factors, prevention, and management. We focused on the clinical and randomized clinical trials of statin monotherapies and combinations with other drugs. The primary mechanism of statin therapy-induced rhabdomyolysis is believed to be a decrease in ubiquinone (coenzyme Q) produced by the HMG-CoA pathway. Additionally, different types of lipophilic and hydrophilic statins play a role in causing rhabdomyolysis. Although statin-induced rhabdomyolysis has a low incidence, there is no guarantee that patients will be free of this side effect. Rhabdomyolysis can be prevented by reducing the risk factors, such as using CYP3A4 inhibitors, using high-dose statins, and strenuous physical activities.

Flavonoid-statin interactions causing myopathy and the possible significance of OATP transport, CYP450 metabolism and mevalonate synthesis

3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors, statins, are a primary treatment for hyperlipidemic cardiovascular diseases which are a leading global cause of death. Statin therapy is life saving and discontinuation due to adverse events such as myotoxicity may lead to unfavourable outcomes. There is no known mechanism for statin-induced myotoxicity although it is theorized that it is due to inhibition of downstream products of the HMG-CoA pathway. It is known that drug-drug interactions with conventional medicines exacerbate the risk of statin-induced myotoxicity, though little attention has been paid to herb-drug interactions with complementary medicines. Flavonoids are a class of phytochemicals which can be purchased as high dose supplements. There is evidence that flavonoids can raise statin plasma levels, increasing the risk of statin-induced myopathy. This could be due to pharmacokinetic interactions involving hepatic cytochrome 450 (CYP450) metabolism and organic anion transporter (OATP) absorption. There is also the potential for flavonoids to directly and indirectly inhibit HMG-CoA reductase which could contraindicate statin-therapy. This review aims to discuss what is currently known about the potential for high dose flavonoids to interact with the hepatic CYP450 metabolism, OATP uptake of statins or their ability to interact with HMG-CoA reductase. Flavonoids of particular interest will be covered and the difficulties of examining herbal products will be discussed throughout.

The glucocorticoid-induced leucine zipper mediates statin-induced muscle damage

Statins, the most prescribed class of drugs for the treatment of hypercholesterolemia, can cause muscle-related adverse effects. It has been shown that the glucocorticoid-induced leucine zipper (GILZ) plays a key role in the anti-myogenic action of dexamethasone. In the present study, we aimed to evaluate the role of GILZ in statin-induced myopathy. Statins induced GILZ expression in C2C12 cells, primary murine myoblasts/myotubes, primary human myoblasts, and in vivo in zebrafish embryos and human quadriceps femoris muscle. Gilz induction was mediated by FOXO3 activation and binding to the Gilz promoter, and could be reversed by the addition of geranylgeranyl, but not farnesyl, pyrophosphate. Atorvastatin decreased Akt phosphorylation and increased cleaved caspase-3 levels in myoblasts. This effect was reversed in myoblasts from GILZ knockout mice. Similarly, myofibers isolated from knockout animals were more resistant toward statin-induced cell death than their wild-type counterparts. Statins also impaired myoblast differentiation, and this effect was accompanied by GILZ induction. The in vivo relevance of our findings was supported by the observation that gilz overexpression in zebrafish embryos led to impaired embryonic muscle development. Taken together, our data point toward GILZ as an essential mediator of the molecular mechanisms leading to statin-induced muscle damage.

Geranylgeraniol prevents statin-induced skeletal muscle fatigue without causing adverse effects in cardiac or vascular smooth muscle performance

The administration of geranylgeranyl pyrophosphate (GGPP) (or its precursor, geranylgeraniol [GGOH]) has been shown by several in vitro studies to be capable of abrogating statin-induced myotoxicity. Nonetheless, the potential of GGPP repletion to prevent statin-associated muscle symptoms (SAMS) in vivo is yet to be investigated. Therefore, this study aimed to evaluate the ability of GGOH to prevent SAMS in rodents. Female Wistar rats (12 weeks of age) were randomised to 1 of 4 treatment groups: control, control with GGOH, simvastatin or simvastatin with GGOH. Ex vivo assessment of force production was conducted in skeletal muscles of varying fiber composition. Ex vivo left ventricular performance and blood vessel function was also assessed to determine if the administration of GGOH caused adverse changes in these parameters. Statin administration was associated with reduced force production in fast-twitch glycolytic muscle, but coadministration with GGOH completely abrogated this effect. Additionally, GGOH improved the performance of muscles not adversely affected by simvastatin (ie, those with a greater proportion of slow-twitch oxidative fibers), and increased force production in the control animals. Neither control nor statin-treated rodents given GGOH exhibited adverse changes in cardiac function. Vascular relaxation was also maintained following treatment with GGOH. The findings of this study demonstrate that GGOH can prevent statin-induced skeletal muscle fatigue in rodents without causing adverse changes in cardiovascular function. Further studies to elucidate the exact mechanisms underlying the effects observed in this investigation are warranted.

Statin-Related Myotoxicity: A Comprehensive Review of Pharmacokinetic, Pharmacogenomic and Muscle Components

Statins are a cornerstone in the pharmacological prevention of cardiovascular disease. Although generally well tolerated, a small subset of patients experience statin-related myotoxicity (SRM). SRM is heterogeneous in presentation; phenotypes include the relatively more common myalgias, infrequent myopathies, and rare rhabdomyolysis. Very rarely, statins induce an anti-HMGCR positive immune-mediated necrotizing myopathy. Diagnosing SRM in clinical practice can be challenging, particularly for mild SRM that is frequently due to alternative aetiologies and the nocebo effect. Nevertheless, SRM can directly harm patients and lead to statin discontinuation/non-adherence, which increases the risk of cardiovascular events. Several factors increase systemic statin exposure and predispose to SRM, including advanced age, concomitant medications, and the nonsynonymous variant, rs4149056, in SLCO1B1, which encodes the hepatic sinusoidal transporter, OATP1B1. Increased exposure of skeletal muscle to statins increases the risk of mitochondrial dysfunction, calcium signalling disruption, reduced prenylation, atrogin-1 mediated atrophy and pro-apoptotic signalling. Rare variants in several metabolic myopathy genes including CACNA1S, CPT2, LPIN1, PYGM and RYR1 increase myopathy/rhabdomyolysis risk following statin exposure. The immune system is implicated in both conventional statin intolerance/myotoxicity via LILRB5 rs12975366, and a strong association exists between HLA-DRB1*11:01 and anti-HMGCR positive myopathy. Epigenetic factors (miR-499-5p, miR-145) have also been implicated in statin myotoxicity. SRM remains a challenge to the safe and effective use of statins, although consensus strategies to manage SRM have been proposed. Further research is required, including stringent phenotyping of mild SRM through N-of-1 trials coupled to systems pharmacology omics- approaches to identify novel risk factors and provide mechanistic insight.

Statins in ophthalmology

Statins, 3-hydroxy-3-methyl-gutaryl coenzyme A reductase inhibitors, are a class of lipid-lowering drugs with anti-inflammatory, immunomodulatory, and vascular effects. Statins are increasingly being used in the treatment of a variety of medical conditions. We examine the actions of statins on the eye and its associated ophthalmic disorders. Statins can be synthetic or nonsynthetic, and their differentiating derivations may contribute to their varying cholesterol-lowering and pleiotropic effects. There is conflicting evidence on the ocular therapeutic and adverse effects of the statins. Statins may play a role in reducing the burden of dry eye, corneal ulcer scarring, thyroid-associated orbitopathy, glaucoma, uveitis and other associated ocular inflammatory states, cataract, proliferative vitreoretinopathy, diabetic retinopathy, macular degeneration, and choroidal melanoma. Topical preparations of statins can be formulated, thereby extending the range of ocular diseases that may be amenable to treatment. Statins have a relatively safe side effect profile, but rare and serious adverse reactions have been reported with their usage in ophthalmology, including myopathies and rhabdomyolysis with acute renal failure.

[A Cellular Pharmacological Approach to the Development of Drugs to Treat Muscle Wasting]

　Skeletal muscle atrophy reduces quality of life and increases mortality. However, there are few available drugs for the treatment of muscle atrophy. Recently, cell signaling pathways involved in skeletal muscle atrophy or hypertrophy have been determined. To develop drugs for skeletal muscle atrophy, we have studied compounds which modulate pathways of myogenic differentiation, a pivotal step for the maintenance of skeletal muscle mass. First, we examined a K⁺ channel opener on myogenic differentiation, since hyperpolarization is a trigger for skeletal muscle differentiation. 5,6-Dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one (DCEBIO), an opener of the small/intermediate conductance Ca²⁺ activated K⁺ (SK_Ca/IK_Ca) channels, increases myogenic differentiation in C2C12 mouse skeletal myoblasts. This effect was inhibited by TRAM-34, an IK_Ca channel blocker. This suggests that K⁺ channels in skeletal muscle stem cells are potential targets for an anti-muscle atrophy drug. Next, we searched for drugs which prevent sepsis-induced muscle atrophy. Lipopolysaccharide (LPS), an inducer of sepsis, attenuates myogenic differentiation in C2C12 myoblasts. LPS also increases the protein expression of myostatin and activates NFκB during differentiation. The TLR4 signal inhibitor TAK-242, and an anti-TNFα neutralizing antibody, reduce these inflammatory responses. Our data suggest that LPS inhibits myogenic differentiation via the NFκB/TNFα pathway. This pathway may be involved in the development of muscle wasting caused by sepsis.

Effects of mulberry leaf on experimental hyperlipidemia rats induced by high-fat diet

Hypercholesterolemia is a major risk factor for cardiovascular disease. Mulberry leaf (ML) is a Traditional Chinese Medicine used to treat hyperlipidemia in clinical settings. The aim of the present study was to identify the potential effect and possible target of ML in anti-hypercholesterolemia. Male Sprague-Dawley rats were fed with a high-fat diet and treated with ML for 5 weeks. Blood lipid levels, total cholesterol (TC) and total bile acid (TBA) in the liver and feces were measured to assess the effects of ML on hypercholesterolemia. Harris's hematoxylin staining and oil red O staining was applied to observe the pathological change and lipid accumulation in the liver. Immunohistochemical assay was performed to observe the location of expressions of scavenger receptor class B type I and low-density lipoprotein (LDL) receptor (-R), and western blotting was applied to determine the protein expression of ATP-binding cassette transporter G5/G8 (ABCG5/8), nuclear transcription factor peroxisome proliferator-activated receptor-α (PPARα), farnesoid-X receptor (FXR) and cholesterol 7α-hydroxylase 1 (CYP7A1). The results demonstrated that ML treatment reduced serum TC and LDL-cholesterol levels, and liver TC and TBA contents; increased serum HDL-C levels, and fecal TC and TBA contents; and alleviated hepatocyte lipid degeneration. In addition, ML treatment inhibited liver LDL-R, PPARα and FXR protein expression, promoted protein expression of CYP7A1, and maintained the ratio of ABCG5/ABCG8. The findings of the present study provide a positive role of ML on cholesterol clearance via promoting cholesterol and TBA execration via FXR- and CYP7A1-mediated pathways; RCT regulation may be a potential mechanism of ML on anti-hypercholesterolemia.

Geranylgeraniol Prevents Statin-Dependent Myotoxicity in C2C12 Muscle Cells through RAP1 GTPase Prenylation and Cytoprotective Autophagy

The present study investigated the cytotoxic effects of statins (atorvastatin (ATR) and simvastatin (SIM), resp.) and methyl-beta-cyclodextrin (MβCD), at their respective IC₅₀ concentrations, on muscle regeneration in the in vitro model of murine C2C12 myoblasts. Cotreatment with mevalonate (MEV), farnesol (FOH), geranylgeraniol (GGOH), or water-soluble cholesterol (Chol-PEG) was employed to determine whether the statin-dependent myotoxicity resulted from the lower cholesterol levels or the attenuated synthesis of intermediates of mevalonate pathway. Our findings demonstrated that while GGOH fully reverted the statin-mediated cell viability in proliferating myoblasts, Chol-PEG exclusively rescued MβCD-induced toxicity in myocytes. Statins caused loss of prenylated RAP1, whereas the GGOH-dependent positive effect was accompanied by loss of nonprenylated RAP1. Geranylgeranyltransferases are essential for muscle cell survival as inhibition with GGTI-286 could not be reversed by GGOH cotreatment. The increase in cell viability correlated with elevated AKT 1(S463) and GSK-3β(S9) phosphorylations. Slight increase in the levels of autophagy markers (Beclin 1, MAP LC-3IIb) was found in response to GGOH cotreatment. Autophagy rose time-dependently during myogenesis and was inhibited by statins and MβCD. Statins and MβCD also suppressed myogenesis and neither nonsterol isoprenoids nor Chol-PEG could reverse this effect. These results point to GGOH as the principal target of statin-dependent myotoxicity, whereas plasma membrane cholesterol deposit is ultimately essential to restore viability of MβCD-treated myocytes. Overall, this study unveils for the first time a link found between the GGOH- and Chol-PEG-dependent reversal of statin- or MβCD-mediated myotoxicity and cytoprotective autophagy, respectively.

[Direct mechanism of action in toxic myopathies]

Toxic myopathies are a large group of disorders generated by surrounding agents and characterized by structural and/or functional disturbances of muscles. The most recurrent are those induced by commonly used medications. Illicit drugs, environmental toxins from animals, vegetables, or produced by micro-organisms as well as chemical products commonly used are significant causes of such disorders. The muscle toxicity results from multiple mechanisms at different biological levels. Many agents can induce myotoxicity through a direct mechanism in which statins, glucocorticoids and ethyl alcohol are the most representative. Diverse mechanisms were highlighted as interaction with macromolecules and induction of metabolic and cellular dysfunctions. Muscle damage can be related to amphiphilic properties of some drugs (chloroquine, hydroxychloroquine, etc.) leading to specific lysosomal disruptions and autophagic dysfunctions. Some agents affect the whole muscle fiber by inducing oxidative stress (ethyl alcohol and some statins) or triggering cell death pathways (apoptosis or necrosis) resulting in extensive alterations. More studies on these mechanisms are needed. They would allow a better knowledge of the intracellular mediators involved in these pathologies in order to develop targeted therapies of high efficiency.

Cholesterol depletion impairs contractile machinery in neonatal rat cardiomyocytes

Cholesterol regulates numerous cellular processes. Depleting its synthesis in skeletal myofibers induces vacuolization and contraction impairment. However, little is known about how cholesterol reduction affects cardiomyocyte behavior. Here, we deplete cholesterol by incubating neonatal cardiomyocytes with methyl-beta-cyclodextrin. Traction force microscopy shows that lowering cholesterol increases the rate of cell contraction and generates defects in cell relaxation. Cholesterol depletion also increases membrane tension, Ca2+ spikes frequency and intracellular Ca2+ concentration. These changes can be correlated with modifications in caveolin-3 and L-Type Ca2+ channel distributions across the sarcolemma. Channel regulation is also compromised since cAMP-dependent PKA activity is enhanced, increasing the probability of L-Type Ca2+ channel opening events. Immunofluorescence reveals that cholesterol depletion abrogates sarcomeric organization, changing spacing and alignment of α-actinin bands due to increase in proteolytic activity of calpain. We propose a mechanism in which cholesterol depletion triggers a signaling cascade, culminating with contraction impairment and myofibril disruption in cardiomyocytes.

Severity of statin-induced adverse effects on muscle and associated conditions: data from the DAMA study

BACKGROUND

Statins are generally well tolerated, but muscular adverse effects appear to be the most common obstacle limiting their use. Our objective was to describe the severity of muscle injury (myalgia, myositis and rhabdomyolysis) and associated conditions related to statin therapy that may be clinically significant.

METHODS

A cross-sectional one-visit, non-interventional, national multicenter study including patients of both sexes over 18 years of age referred for past or present muscle symptoms associated with statin therapy was conducted. Clinical, biochemical and drug therapy characteristics were obtained at the initial evaluation.

RESULTS

3,845 patients were recruited from a one-day record from 2,001 physicians. Myalgia was present in 78.2% of patients, myositis in 19.3% and rhabdomyolysis in 2.5%. The prevalence of different comorbidities such as diabetes, hypertension, atrial fibrillation, and coronary heart disease increased as the severity of myopathy rose. High-intensity statin therapy was used in 33.4% of patients. Concomitant drugs metabolized by the CYP450 3A4 pathway were taken by 9.3% of patients, and statins with this metabolic route by 75%. Independent variables associated with myositis or rhabdomyolysis compared with myalgia alone in the multivariate model were excessive alcohol consumption and pravastatin therapy.

CONCLUSION

Myalgia was the most common muscle adverse effect associated with statin therapy. Excessive alcohol consumption and pravastatin were independently associated with myositis or rhabdomyolysis.

Pregabalin- and azithromycin-induced rhabdomyolysis with purpura: An unrecognized interaction: A case report

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Pregabalin and azithromycin therapy is associated with a potentially fatal occurrence of rhabdomyolysis.

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We report an extremely rare case of rhabdomyolysis with purpura caused by a drug interaction between pregabalin and azithromycin.

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The details of the interaction between azithromycin and the pregabalin are still unknown.

Introduction

Rhabdomyolysis associated with the use of pregabalin or azithromycin has been demonstrated to be a rare but potentially life-threatening adverse event. Here, we report an extremely rare case of rhabdomyolysis with purpura in a patient who had used pregabalin and azithromycin.

Presentation of case

We present the case of a 75-year-old woman with a history of fibromyalgia who was admitted with mild limb weakness and lower abdominal purpura. She was prescribed pregabalin (75 mg, twice daily) for almost 3 months to treat chronic back pain. Her medical history revealed that 3 days before admission, she began experiencing acute bronchitis and was treated with a single dose of azithromycin (500 mg). She had developed rapid onset severe myalgia, mild whole body edema, muscle weakness leading to gait instability, abdominal purpura and tender purpura on the lower extremities. Laboratory values included a white blood cell count of 25,400/mL and a creatinine phosphokinase (CPK) concentration of 1250 IU/L. Based on these findings and the patient’s clinical history, a diagnosis of pregabalin- and azithromycin-induced rhabdomyolysis was made.

Discussion

The long-term use of pregabalin and the initiation azithromycin therapy followed by a rapid onset of rhabdomyolysis is indicative of a drug interaction between pregabalin and azithromycin.

Conclusion

We report an extremely rare case of rhabdomyolysis with purpura caused by a drug interaction between pregabalin and azithromycin. However, the mechanisms of the interactions between azithromycin on the pregabalin are still unknown.

Fluvastatin delays propagation of viral infection in isolated rat FDB myofibers but does not affect exocytic membrane trafficking

We have utilized the enveloped viral model to study the effect of fluvastatin on membrane trafficking in isolated rat myofibers. Our immunofluorescence studies constantly showed that infections in myofibers, which were treated with fluvastatin prior and during the infection with either vesicular stomatitis virus (VSV) or influenza A virus, propagated more slowly than in control myofibers without drug treatment. Experiments with a virus expressing Dad1 tagged with green fluorescent protein (GFP-Dad1) showed that fluvastatin did not affect its distribution within the ER/SR network and immunofluorescence staining for GM130 did not show any marked effect on the structure of the Golgi components. Furthermore, fluvastatin did not inhibit trafficking of the chimeric transport marker VSV temperature sensitive G protein (tsG-GFP) from the ER to the Golgi. We next subjected VSV infected myofibers for pulse-chase labeling experiments and found that fluvastatin did not slow down the ER-to-Golgi trafficking or Golgi to plasma membrane trafficking of the viral glycoprotein. These studies show that fluvastatin inhibited the propagation of viral infection in skeletal myofibers but no adverse effect on the exocytic trafficking could be demonstrated. These results suggest that other effects of statins rather than inhibition of ER-to-Golgi trafficking might be behind the myotoxic effects of the statins.

Pathogenic mechanisms and the prospect of gene therapy for choroideremia

INTRODUCTION

Choroideremia is a rare, X-linked disorder recognized by its specific ocular phenotype as a progressive degenerative retinopathy resulting in blindness. New therapeutic approaches, primarily based on genetic mechanisms, have emerged that aim to prevent the progressive vision loss.

AREAS COVERED

This article will review the research that has progressed incrementally over the past two decades from mapping to gene discovery, uncovering the presumed mechanisms triggering the retinopathy to preclinical testing of potential therapies.

EXPERT OPINION

While still in an evaluative phase, the introduction of gene replacement as a potential therapy has been greeted with great enthusiasm by patients, advocacy groups and the medical community.

The causes of drug-induced muscle toxicity

PURPOSE OF REVIEW

Clinically identified myopathies are frequently a consequence of medication toxicities. However, recognizing drug-induced myopathies is sometimes difficult. Developing a greater understanding of the underlying mechanisms of drug-induced muscle toxicity will promote enhanced awareness and recognition, and improved management of these syndromes.

RECENT FINDINGS

The adverse impact of certain drugs on muscle metabolism, muscle cell atrophy, and myocyte apoptosis is increasingly clear. Glucocorticoids impair glucose handling and directly promote protein catabolism. Statins impair mitochondrial function and alter intracellular signaling proteins, which can lead to myocyte apoptosis. Alternatively, statins can induce an autoimmune necrotizing myositis. Several medications impair autophagy, thus limiting access to the needed glycogen stores.

SUMMARY

This review provides an overview of the main underlying mechanisms of drug-induced myopathies. These myopathies will most often be related to a drug's ability to alter metabolism and protein balance, induce necrosis, or impair autophagy.

Pravastatin-induced rhabdomyolysis and purpura fulminans in a patient with chronic renal failure

INTRODUCTION

Rhabdomyolysis associated with the use of pravastatin has been demonstrated to be a rare but potentially life-threatening adverse effect of statins. Here, we report a rare case of rhabdomyolysis and purpura fulminans in a patient who had used pravastatin and developed chronic renal failure (CRF) necessitating the initiation of dialysis.

PRESENTATION OF CASE

We present the case of an 86-year-old man with chronic kidney disease (CKD) treated with dialysis who was admitted with back pain. He was prescribed and took pravastatin for almost 3 years to treat hyperlipidemia. He received hemodialysis therapy 7 times prior to presentation. Laboratory values included a serum creatine concentration of 6.6mg/dl and a creatinine phosphokinase (CPK) concentration of 2350IU/L. An abdominal computed tomography scan showed swollen muscles with reduced muscle density and air density in the multifidus muscle. Two days after admission, he had large, tender ecchymotic lesions and purpuric progressive skin necrosis over the back, abdomen, and upper and lower extremities. The patient died 6 days after the initial admission due to disseminated intravascular coagulation (DIC). Based on these findings and the clinical history, a diagnosis of pravastatin-induced rhabdomyolysis and purpura fulminans was made.

DISCUSSION

The long-term use of statin therapy and the initiation of dialysis therapy due to ESRD, followed by a rapid onset of rhabdomyolysis within 6 days, is indicative of an elevated statin concentration.

CONCLUSION

We report an extremely rare case of pravastatin-induced rhabdomyolysis and purpura fulminans with DIC in a patient with CRF.

Inhibition of prenyltransferase activity by statins in both liver and muscle cell lines is not causative of cytotoxicity

As inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, statins are an important first-line treatment for hypercholesterolemia. However, a recognized side-effect of statin therapy is myopathy, which in severe cases can present as potentially fatal rhabdomyolysis. This represents an important impediment to successful statin therapy, and despite decades of research the molecular mechanisms underlying this side-effect remain unclear. Current evidence supports a role for reduced levels of mevalonate pathway intermediates, with the most accepted hypothesis being a reduction in isoprenoids formation, leading to faulty post-translational modifications of membrane-associated proteins. We have undertaken a comprehensive analysis of the impact of nine statins on two human cell lines; Huh7 hepatoma and RD rhabdomyosarcoma. In both cell lines, concentration-dependent inhibition of prenylation was observed for cerivastatin and simvastatin, which could be rescued with the pathway intermediate mevalonate; in general, muscle cells were more sensitive to this effect, as measured by the levels of unprenylated Rap1A, a marker for prenylation by geranylgeranyl transferase I. Concentration-dependent toxicity was observed in both cell lines, with muscle cells again being more sensitive. Importantly, there was no correlation between inhibition of prenylation and cell toxicity, suggesting they are not causally linked. The lack of a causal relationship was confirmed by the absence of cytotoxicity in all cell lines following exposure to specific inhibitors of geranylgeranyl transferases I and II, and farnesyl transferase. As such, we provide strong evidence against the commonly accepted hypothesis linking inhibition of prenylation and statin-mediated toxicity, with the two processes likely to be simultaneous but independent.

Translational insight into statin-induced muscle toxicity: from cell culture to clinical studies

Statins are lipid-lowering drugs used widely to prevent and treat cardiovascular and coronary heart diseases. These drugs are among the most commonly prescribed medicines intended for long-term use. In general, statins are well tolerated. However, muscular adverse effects appear to be the most common obstacle that limits their use, resulting in poor patient compliance or even drug discontinuation. In addition, rare but potentially fatal cases of rhabdomyolysis have been reported with the use of these drugs, especially in the presence of certain risk factors. Previous reports have investigated statin-induced myotoxicity in vivo and in vitro using a number of cell lines, muscle tissues, and laboratory animals, in addition to randomized clinical trials, observational studies, and case reports. None of them have compared directly results from laboratory investigations with clinical observations of statin-related muscular adverse effects. To the best of our knowledge this is the first review article that combines laboratory investigation with clinical aspects of statin-induced myotoxicity. By reviewing published literature of in vivo, in vitro, and clinically relevant studies of statin myotoxicity, we aim to translate this important drug-related problem to establish a clear picture of proposed mechanisms that explain the risk factors and describe the diagnostic approaches currently used for evaluating the degree of muscle damage induced by these agents. This review provides baseline novel translational insight that can be used to enhance the safety profile, to minimize the chance of progression of these adverse effects to more severe and potentially fatal rhabdomyolysis, and to improve the overall patient compliance and adherence to long-term statin therapy.

Statins and skeletal muscles toxicity: from clinical trials to everyday practice

The mechanism(s) underlying the occurrence of statin-induced myopathy are ill defined, but the results of observational studies and clinical trials provide compelling evidence that skeletal muscle toxicity is a frequent, dose-dependent, adverse event associated with all statins. It has been suggested that reduced availability of metabolites produced by the mevalonate pathway rather than intracellular cholesterol lowering per se might be the primary trigger of toxicity, however other alternative explanations have gained credibility in recent years. Aim of this review is: (i) to describe the molecular mechanisms associated to statin induced myopathy including defects in isoprenoids synthesis followed by altered prenylation of small GTPase, such as Ras and Rab proteins; (ii) to present the emerging aspects on pharmacogenetics, including CYP3A4, OATP1B1 and glycine amidinotransferase (GATM) polymorphisms impacting either statin bioavailability or creatine synthesis; (iii) to summarize the available epidemiological evidences; and (iii) to discuss the concepts that would be of interest to the clinicians for the daily management of patients with statin induced myopathy. The interplay between drug-environment and drug-drug interaction in the context of different genetic settings contribute to statins and skeletal muscles toxicity. Until specific assays/algorithms able to combine genetic scores with drug-drug-environment interaction to identify patients at risk of myopathies will become available, clinicians should continue to monitor carefully patients on polytherapy which include statins and be ready to reconsider dose, statin or switching to alternative treatments. The beneficial effects of adding agents to provide the muscle with the metabolites, such as CoQ10, affected by statin treatment will also be addressed.

Simvastatin inhibits glucose metabolism and legumain activity in human myotubes

Simvastatin, a HMG-CoA reductase inhibitor, is prescribed worldwide to patients with hypercholesterolemia. Although simvastatin is well tolerated, side effects like myotoxicity are reported. The mechanism for statin-induced myotoxicity is still poorly understood. Reports have suggested impaired mitochondrial dysfunction as a contributor to the observed myotoxicity. In this regard, we wanted to study the effects of simvastatin on glucose metabolism and the activity of legumain, a cysteine protease. Legumain, being the only known asparaginyl endopeptidase, has caspase-like properties and is described to be involved in apoptosis. Recent evidences indicate a regulatory role of both glucose and statins on cysteine proteases in monocytes. Satellite cells were isolated from the Musculus obliquus internus abdominis of healthy human donors, proliferated and differentiated into polynuclear myotubes. Simvastatin with or without mevalonolactone, farnesyl pyrophosphate or geranylgeranyl pyrophosphate were introduced on day 5 of differentiation. After 48 h, cells were either harvested for immunoblotting, ELISA, cell viability assay, confocal imaging or enzyme activity analysis, or placed in a fuel handling system with [¹⁴C]glucose or [³H]deoxyglucose for uptake and oxidation studies. A dose-dependent decrease in both glucose uptake and oxidation were observed in mature myotubes after exposure to simvastatin in concentrations not influencing cell viability. In addition, simvastatin caused a decrease in maturation and activity of legumain. Dysregulation of glucose metabolism and decreased legumain activity by simvastatin points out new knowledge about the effects of statins on skeletal muscle, and may contribute to the understanding of the myotoxicity observed by statins.

Mechanism of statin-induced rhabdomyolysis

Statins, a group of drugs used for the treatment of hypercholesterolemia, have adverse effects on skeletal muscle. The symptoms of these effects range from slight myalgia to severe rhabdomyolysis. The number of patients currently taking statins is estimated to be several millions worldwide. However, the mechanism of statins' myotoxic effects is unclear. Statins inhibit biosynthesis of mevalonate, a rate-limiting step of cholesterol synthesis, by inhibiting HMG-CoA reductase. Mevalonate is also an essential precursor for producing isoprenoids such as farnesylpyrophosphate and geranylgeranylpyrophosphate. These isoprenoids are especially important for anchoring small GTPases to the membrane before they function; e.g., Ras GTPases modulate proliferation and apoptosis, Rho GTPases control cytoskeleton formation, and Rab GTPases are essential for intracellular vesicle trafficking. Inactivation of these small GTPases alters cellular functions. Recently, we successfully reproduced statin-induced myotoxicity in culture dishes using in vitro skeletal muscle systems (e.g., skeletal myotubes and myofibers). This review summarizes our findings that statins induce depletion of isoprenoids and inactivation of small GTPases, especially Rab, which are critical for statin-induced myotoxicity. Although further study is required, our findings may contribute to the prevention and treatment of statins' adverse effects on skeletal muscle and development of safer anti-hypercholesterolemia drugs.

A Clinical Review of Statin-Associated Myopathy

Objective: To review the epidemiology, clinical features, proposed mechanisms, risk factors, and management of statin-associated myopathy. Data Sources: Literature searches were conducted in PubMed (1948 to April 2013), TOXLINE, International Pharmaceutical Abstracts (1970 to April 2013), and Google Scholar using the terms statin, hydroxymethylglutaryl-coenzyme A reductase inhibitors, myopathy, myalgia, safety, and rhabdomyolysis. Results were limited to English publications. Study Selection and Data Extraction: All relevant original studies, guidelines, meta-analyses, and reviews of statin-associated myopathy and safety of statins were assessed for inclusion. References from selected articles were reviewed to identify additional citations. Data Synthesis: The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors remain one of the most effective medications for reducing low-density-lipoprotein cholesterol. Statins are well tolerated by most patients; however, it is estimated that 10% to 15% of patients develop statin-related muscle adverse effects known as statin-associated myopathy. Although clinicians may be aware of statin-associated myopathy, they may not be aware of its clinical presentation. Providers should assess individual patient risk factors before choosing the appropriate statin. A variety of skeletal muscle aches that may not present as a danger to the patient, may affect patient adherence and quality of life. There are several steps that providers can take to properly treat and manage patients with myalgia complaints. Conclusions: Statin-associated myopathy is a clinical problem that contributes to statin therapy discontinuation. Patients who are statin intolerant may be treated with alternative treatment options such as low-dose statins, switching statins, using alternative dosing strategies in statins with longer half-lives, non-statin lipid-lowering agents, and complementary therapies.

Individualized risk for statin-induced myopathy: current knowledge, emerging challenges and potential solutions

Skeletal muscle toxicity is the primary adverse effect of statins. In this review, we summarize current knowledge regarding the genetic and nongenetic determinants of risk for statin induced myopathy. Many genetic factors were initially identified through candidate gene association studies limited to pharmacokinetic (PK) targets. Through genome-wide association studies, it has become clear that SLCO1B1 is among the strongest PK predictors of myopathy risk. Genome-wide association studies have also expanded our understanding of pharmacodynamic candidate genes, including RYR2. It is anticipated that deep resequencing efforts will define new loci with rare variants that also contribute, and sophisticated computational approaches will be needed to characterize gene-gene and gene-environment interactions. Beyond environment, race is a critical covariate, and its influence is only partly explained by geographic differences in the frequency of known pharmacodynamic and PK variants. As such, admixture analyses will be essential for a full understanding of statin-induced myopathy.

A small-molecule screening strategy to identify suppressors of statin myopathy

The reduction of plasma low-density lipoprotein levels by HMG-CoA reductase inhibitors, or statins, has had a revolutionary impact in medicine, but muscle-related side effects remain a dose-limiting toxicity in many patients. We describe a chemical epistasis approach that can be useful in refining the mechanism of statin muscle toxicity, as well as in screening for agents that suppress muscle toxicity while preserving the ability of statins to increase the expression of the low-density lipoprotein receptor. Using this approach, we identified one compound that attenuates the muscle side effects in both cellular and animal models of statin toxicity, likely by influencing Rab prenylation. Our proof-of-concept screen lays the foundation for truly high-throughput screens that could help lead to the development of clinically useful adjuvants that can one day be co-administered with statins.

The gunmetal mouse reveals Rab geranylgeranyl transferase to be the major molecular target of phosphonocarboxylate analogues of bisphosphonates

The described ability of phosphonocarboxylate analogues of bisphosphonates (BPs) to inhibit Rab geranylgeranyl transferase (RGGT) is thought to be the mechanism underlying their cellular effects, including their ability to reduce macrophage cell viability and to inhibit osteoclast-mediated resorption. However, until now the possibility that at least some of the effects of these drugs may be mediated through other targets has not been excluded. Since RGGT is the most distal enzyme in the process of Rab prenylation, it has not proved possible to confirm the mechanism underlying the effects of these drugs by adding back downstream intermediates of the mevalonate pathway, the approach used to demonstrate that bisphosphonates act through this pathway. We now confirm that RGGT is the major pharmacological target of phosphonocarboxylates by using several alternative approaches. Firstly, analysis of several different phosphonocarboxylate drugs demonstrates a very good correlation between the ability of these drugs to inhibit RGGT with their ability to: (a) reduce macrophage cell viability; (b) induce apoptosis; and (c) induce vacuolation in rabbit osteoclasts. Secondly, we have found that cells from the gunmetal (gm/gm) mouse, which bear a homozygous mutation in RGGT that results in ~80% reduced activity of this enzyme compared to wild-type or heterozygous mice, are more sensitive to the effects of active phosphonocarboxylates (including reducing macrophage cell viability, inhibiting osteoclast formation and inhibiting fluid-phase endocytosis), confirming that these effects are mediated through inhibition of RGGT. In conclusion, these data demonstrate that all of the pharmacological effects of phosphonocarboxylates found thus far appear to be mediated through the specific inhibition of RGGT, highlighting the potential therapeutic value of this class of drugs.

Inhibition of Rab1 GTPase and endoplasmic reticulum-to-Golgi trafficking underlies statin's toxicity in rat skeletal myofibers

HMG-CoA reductase inhibitor statins are used for the treatment of hypercholesterolemia. However, statins have adverse effects on skeletal muscles with unknown mechanism. We have reported previously that fluvastatin induced vacuolation and cell death in rat skeletal myofibers by depleting geranylgeranylpyrophosphate (GGPP) and suppressing small GTPases, particularly Rab (FASEB J 21:4087-4094, 2007). Rab1 is one of the most susceptible Rab isoforms to GGPP depletion and is essential for endoplasmic reticulum (ER)-to-Golgi trafficking. Here, we explored whether Rab1 and ER-to-Golgi vesicle trafficking were affected by statins in cultured single myofibers isolated from flexor digitorum brevis muscles of adult rats. Western blot analysis revealed that Rab1A protein resided predominantly in membrane but not in cytosol in control myofibers, whereas it was opposite in fluvastatin-treated myofibers, indicating that fluvastatin inhibited Rab1A translocation from cytosol to membrane. GGPP supplementation prevented the effect of fluvastatin on Rab1A translocation. Brefeldin A, a specific suppressor of ER-to-Golgi trafficking, induced vacuolation and cell death in myofibers in a manner similar to that of fluvastatin. Although ER-to-Golgi traffic suppression induces unfolded protein response (UPR) and cell death in some cell types, neither fluvastatin nor brefeldin A up-regulated UPR in myofibers. Immunofluorescence study revealed that the distribution of an ER marker, calnexin, was restricted to the region around nucleus with fluvastatin, suggesting the inhibition of ER membrane traffic by fluvastatin. We conclude that suppression of Rab1 GTPase and the subsequent inhibition of ER-to-Golgi traffic are involved in statin-induced skeletal myotoxicity.

Mechanism of statin-induced contractile dysfunction in rat cultured skeletal myofibers

An adverse effect of statins, cholesterol-lowering drugs, is contractile dysfunction of skeletal muscles. We investigated the mechanism underlying this effect in cultured myofibers isolated from rats. Fluvastatin (Flv) for 72 h decreased caffeine- and ionomycin-induced contraction of myofibers and Ca(2+) release from sarcoplasmic reticulum (SR). Ca(2+)-shortening curves measured in skinned myofibers indicated that myofibrillar Ca(2+) sensitivity was unaffected by Flv. A luciferin-luciferase assay revealed less ATP contents in Flv-treated myofibers. Among mevalonate metabolites, including geranylgeranylpyrophosphate (GGPP), farnesylpyrophosphate (FPP), coenzyme Q9, and coenzyme Q10, only GGPP prevented Flv-induced ATP reduction. A selective Rab geranylgeranyltransferase (GG transferase) inhibitor, perillyl alcohol (POH), and a specific GG transferase-I inhibitor, GGTI-298, both mimicked Flv in decreasing ATP and contraction. Mitochondrial membrane potential was decreased by Flv, and this effect was rescued by GGPP and mimicked by POH and GGTI-298. An endoplasmic reticulum (ER)-to-Golgi traffic inhibitor, brefeldin A, and a Rho inhibitor, membrane permeable exoenzyme C3 transferase, both decreased ATP. We conclude that statin-induced contractile dysfunction is due to reduced Ca(2+) release from SR and reduced ATP levels in myofibers with damaged mitochondria. GGPP depletion and subsequent inactivation of Rab1, possibly along with Rho, may underlie the mitochondrial damage by Flv.

Membrane blebbing as an assessment of functional rescue of dysferlin-deficient human myotubes via nonsense suppression

Mutations that result in the loss of the protein dysferlin result in defective muscle membrane repair and cause either a form of limb girdle muscular dystrophy (type 2B) or Miyoshi myopathy. Most patients are compound heterozygotes, often carrying one allele with a nonsense mutation. Using dysferlin-deficient mouse and human myocytes, we demonstrated that membrane blebbing in skeletal muscle myotubes in response to hypotonic shock requires dysferlin. Based on this, we developed an in vitro assay to assess rescue of dysferlin function in skeletal muscle myotubes. This blebbing assay may be useful for drug discovery/validation for dysferlin deficiency. With this assay, we demonstrate that the nonsense suppression drug, ataluren (PTC124), is able to induce read-through of the premature stop codon in a patient with a R1905X mutation in dysferlin and produce sufficient functional dysferlin (approximately 15% of normal levels) to rescue myotube membrane blebbing. Thus ataluren is a potential therapeutic for dysferlin-deficient patients harboring nonsense mutations.

A novel geranylgeranyl transferase inhibitor in combination with lovastatin inhibits proliferation and induces autophagy in STS-26T MPNST cells

Prenylation inhibitors have gained increasing attention as potential therapeutics for cancer. Initial work focused on inhibitors of farnesylation, but more recently geranylgeranyl transferase inhibitors (GGTIs) have begun to be evaluated for their potential antitumor activity in vitro and in vivo. In this study, we have developed a nonpeptidomimetic GGTI, termed GGTI-2Z [(5-nitrofuran-2-yl)methyl-(2Z,6E,10E)-3,7,11,15-tetramethylhexadeca-2,6,10,14-tetraenyl 4-chlorobutyl(methyl)phosphoramidate], which in combination with lovastatin inhibits geranylgeranyl transferase I (GGTase I) and GGTase II/RabGGTase, without affecting farnesylation. The combination treatment results in a G(0)/G(1) arrest and synergistic inhibition of proliferation of cultured STS-26T malignant peripheral nerve sheath tumor cells. We also show that the antiproliferative activity of drugs in combination occurs in the context of autophagy. The combination treatment also induces autophagy in the MCF10.DCIS model of human breast ductal carcinoma in situ and in 1c1c7 murine hepatoma cells, where it also reduces proliferation. At the same time, there is no detectable toxicity in normal immortalized Schwann cells. These studies establish GGTI-2Z as a novel geranylgeranyl pyrophosphate derivative that may work through a new mechanism involving the induction of autophagy and, in combination with lovastatin, may serve as a valuable paradigm for developing more effective strategies in this class of antitumor therapeutics.

Human skeletal muscle drug transporters determine local exposure and toxicity of statins

RATIONALE

The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, are important drugs used in the treatment and prevention of cardiovascular disease. Although statins are well tolerated, many patients develop myopathy manifesting as muscle aches and pain. Rhabdomyolysis is a rare but severe toxicity of statins. Interindividual differences in the activities of hepatic membrane drug transporters and metabolic enzymes are known to influence statin plasma pharmacokinetics and risk for myopathy. Interestingly, little is known regarding the molecular determinants of statin distribution into skeletal muscle and its relevance to toxicity.

OBJECTIVE

We sought to identify statin transporters in human skeletal muscle and determine their impact on statin toxicity in vitro.

METHODS AND RESULTS

We demonstrate that the uptake transporter OATP2B1 (human organic anion transporting polypeptide 2B1) and the efflux transporters, multidrug resistance-associated protein (MRP)1, MRP4, and MRP5 are expressed on the sarcolemmal membrane of human skeletal muscle fibers and that atorvastatin and rosuvastatin are substrates of these transporters when assessed using a heterologous expression system. In an in vitro model of differentiated, primary human skeletal muscle myoblast cells, we demonstrate basal membrane expression and drug efflux activity of MRP1, which contributes to reducing intracellular statin accumulation. Furthermore, we show that expression of human OATP2B1 in human skeletal muscle myoblast cells by adenoviral vectors increases intracellular accumulation and toxicity of statins and such effects were abrogated when cells overexpressed MRP1.

CONCLUSIONS

These results identify key membrane transporters as modulators of skeletal muscle statin exposure and toxicity.

Statin-induced muscle damage and atrogin-1 induction is the result of a geranylgeranylation defect

Statins are widely used to treat hypercholesterolemia but can lead to a number of side effects in muscle, including rhabdomyolysis. Our recent findings implicated the induction of atrogin-1, a gene required for the development of muscle atrophy, in statin-induced muscle damage. Since statins inhibit many biochemical reactions besides cholesterol synthesis, we sought to define the statin-inhibited pathways responsible for atrogin-1 expression and muscle damage. We report here that lovastatin-induced atrogin-1 expression and muscle damage in cultured mouse myotubes and zebrafish can be prevented in the presence of geranylgeranol but not farnesol. Further, inhibitors of the transfer of geranylgeranyl isoprene units to protein targets cause statin muscle damage and atrogin-1 induction in cultured cells and in fish. These findings support the concept that dysfunction of small GTP-binding proteins lead to statin-induced muscle damage since these molecules require modification by geranylgeranyl moieties for their cellular localization and activity. Collectively, our animal and in vitro findings shed light on the molecular mechanism of statin-induced myopathy and suggest that atrogin-1 may be regulated by novel signaling pathways.

Na+ -Ca2+ exchanger expression and its modulation

Here we reviewed our recent work on the chronic effects of nicotine on the Na+ -Ca2+ exchanger (NCX) gene and protein expressions in various organs of rats treated with nicotine in the drinking water for 4-12 weeks. Microarray analysis and reverse transcriptase-polymerase chain reaction (RT-PCR) did not detect significant changes in NCX mRNA expression in cerebral cortex, hippocampus, heart and skeletal muscle. However, NCX1 protein was up-regulated by nicotine in cerebral cortex and hippocampus, but was down-regulated in the heart. NCX2 protein was up-regulated by nicotine in hippocampus. We suggest that although mRNA change was insignificant, NCX protein expression was altered by chronic nicotine administration in brain and heart in rats. We also reviewed our work on modulators of NCX gene expression and function in cardiac myocytes.

Statin-induced myopathy in the rat: relationship between systemic exposure, muscle exposure and myopathy

Rare instances of myopathy are associated with all statins, but cerivastatin was withdrawn from clinical use due to a greater incidence of myopathy. The mechanism of statin-induced myopathy with respect to tissue disposition was investigated by measuring the systemic, hepatic, and skeletal muscle exposure of cerivastatin, rosuvastatin, and simvastatin in rats before and after muscle damage. The development of myopathy was not associated with the accumulation of statins in skeletal muscle. For each statin exposure was equivalent in muscles irrespective of their fibre-type sensitivity to myopathy. The low amount of each statin in skeletal muscle relative to the liver does not support a significant role for transporters in the disposition of statins in skeletal muscle. Finally, the concentration of cerivastatin necessary to cause necrosis in skeletal muscle was considerably lower than rosuvastatin or simvastatin, supporting the concept cerivastatin is intrinsically more myotoxic than other statins.

Blunted Akt/FOXO signalling and activation of genes controlling atrophy and fuel use in statin myopathy

Statins are used clinically for cholesterol reduction, but statin therapy is associated with myopathic changes through a poorly defined mechanism. We used an in vivo model of statin myopathy to determine whether statins up-regulate genes associated with proteasomal- and lysosomal-mediated proteolysis and whether PDK gene expression is simultaneously up-regulated leading to the impairment of muscle carbohydrate oxidation. Animals were dosed daily with 80 mg kg(-1) day(-1) simvastatin for 4 (n = 6) and 12 days (n = 5), 88 mg kg(-1) day(-1) simvastatin for 12 days (n = 4), or vehicle (0.5% w/v hydroxypropyl-methylcellulose and 0.1% w/v polysorbate 80; Control, n = 6) for 12 days by oral gavage. We found, in biceps femoris muscle, decreased Akt(Ser473), FOXO1(Ser253) and FOXO3a(Ser253) phosphorylation in the cytosol (P < 0.05, P < 0.05, P < 0.001, respectively) and decreased phosphorylation of FOXO1 in the nucleus after 12 days simvastatin when compared to Control (P < 0.05). This was paralleled by a marked increase in the transcription of downstream targets of FOXO, i.e. MAFbx (P < 0.001), MuRF-1 (P < 0.001), cathepsin-L (P < 0.05), PDK2 (P < 0.05) and PDK4 (P < 0.05). These changes were accompanied by increased PPARalpha (P < 0.05), TNFalpha (P < 0.01), IL6 (P < 0.01), Mt1A (P < 0.01) mRNA and increased muscle glycogen (P < 0.05) compared to Control. RhoA activity decreased after 4 days simvastatin (P < 0.05); however, activity was no different from Control after 12 days. Simvastatin down-regulated PI3k/Akt signalling, independently of RhoA, and up-regulated FOXO transcription factors and downstream gene targets known to be implicated in proteasomal- and lysosomal-mediated muscle proteolysis, carbohydrate oxidation, oxidative stress and inflammation in an in vivo model of statin-induced myopathy. These changes occurred in the main before evidence of extensive myopathy or a decline in the muscle protein to DNA ratio.

Molecular basis for statin-induced muscle toxicity: implications and possibilities

Statins are widely used to treat hypercholesterolemia, a known risk factor for atherosclerosis. These drugs can lead to a number of side effects in muscle, including rhabdomyolysis; however, the mechanism of muscle injury is poorly defined. We review the clinical characteristics of this diverse syndrome, as well as the biochemical mechanisms that might provide an explanation for the toxicity of these agents. New findings implicating atrogin-1, a gene required for muscle atrophy, in the pathophysiology of statin-induced muscle injury are discussed, as well as implications of these novel discoveries.

Involvement of organic anion transporting polypeptides in the toxicity of hydrophilic pravastatin and lipophilic fluvastatin in rat skeletal myofibres

BACKGROUND AND PURPOSE

There is a discrepancy in the adverse effect of 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors, statins between the clinical reports and the studies using skeletal muscle cell models. In the clinical reports, both hydrophilic and lipophilic statins induce myotoxicity, whereas in in vitro experiments using cell lines of myoblasts, lipophilic, but not hydrophilic, statins exert myotoxicity. We investigated the cause of this discrepancy.

EXPERIMENTAL APPROACH

Skeletal myofibres, fibroblasts and satellite cells were isolated from rat flexor digitorum brevis (FDB) muscles. Using these primary cultured cells as well as the L6 myoblast cell line, we compared the toxicity of hydrophilic pravastatin and lipophilic fluvastatin. The mRNA expression levels of possible drug transporters for statins were also examined in these cells using reverse transcriptase-PCR.

KEY RESULTS

In the skeletal myofibres, both pravastatin and fluvastatin induced vacuolation and cell death, whereas in the mononuclear cells only fluvastatin, but not pravastatin, was toxic. mRNA of the organic anion transporting polypeptides (Oatp) 1a4 and Oatp2b1 were expressed in the skeletal myofibres, but not in mononucleate cells. Estrone-3-sulphate, a substrate for Oatps, attenuated the effects of pravastatin and fluvastatin in skeletal myofibres; p-aminohippuric acid, a substrate for the organic anion transporters (Oats), but not Oatps, failed to do so.

CONCLUSIONS AND IMPLICATIONS

The statin transporters Oatp1a4 and Oatp2b1 are expressed in rat skeletal myofibres, but not in satellite cells, fibroblasts or in L6 myoblasts. This is probably why hydrophilic pravastatin affects skeletal muscle, but not skeletal myoblasts.