Statin myopathy as a metabolic muscle disease

Impaired muscle stem cell function and abnormal myogenesis in acquired myopathies

Skeletal muscle possesses a high plasticity and a remarkable regenerative capacity that relies mainly on muscle stem cells (MuSCs). Molecular and cellular components of the MuSC niche, such as immune cells, play key roles to coordinate MuSC function and to orchestrate muscle regeneration. An abnormal infiltration of immune cells and/or imbalance of pro- and anti-inflammatory cytokines could lead to MuSC dysfunctions that could have long lasting effects on muscle function. Different genetic variants were shown to cause muscular dystrophies that intrinsically compromise MuSC function and/or disturb their microenvironment leading to impaired muscle regeneration that contributes to disease progression. Alternatively, many acquired myopathies caused by comorbidities (e.g., cardiopulmonary or kidney diseases), chronic inflammation/infection, or side effects of different drugs can also perturb MuSC function and their microenvironment. The goal of this review is to comprehensively summarize the current knowledge on acquired myopathies and their impact on MuSC function. We further describe potential therapeutic strategies to restore MuSC regenerative capacity.

Effects of statins on fat oxidation improvements after aerobic exercise training

BACKGROUND

Statin blunts cardiorespiratory fitness improvements after exercise training and may affect fat oxidation adaptations to training.

METHODS

One hundred and six metabolic syndrome individuals either chronically medicated with statins (i.e., STATIN group; n = 46) or statin naïve (i.e., CONTROL group; n = 60) completed a 16-week supervised high-intensity interval training (HIIT) program. Maximal rates of oxygen consumption (V̇O2MAX), fat oxidation (FOMAX), and the shape of the workload-fat oxidation curve were assessed before and 48 h after training in an overnight fasted state.

RESULTS

Starting from a similar value at baseline, both groups increased V̇O2MAX after training, but the increase was larger in the CONTROL than in the STATIN group (19.4% vs. 12.6%; P = 0.013). Before training, FOMAX in the STATIN group was lower (0.19 ± 0.08 vs. 0.23 ± 0.07 g·min-1; P = 0.023) and took place at a lower workload (33 ± 21 vs. 37 ± 19 W; P = 0.015) than in CONTROL. After training, FOMAX improved similarly in both groups (0.06 ± 0.08; 95% CI, 0.03 to 0.08 g·min-1 and 0.05 ± 0.09; 95% CI, 0.03 to 0.07 g·min-1, for STATIN and CONTROL respectively; P < 0.001). Still, after training, FOMAX occurred at a 28% lower workload in the STATIN group (38 ± 26 vs. 53 ± 32 W, P = 0.048).V̇O2 -workload slope decreased after training in both groups (both P < 0.001) along with reductions in the respiratory exchange ratio - workload slope. Fat oxidation increased at all workloads after training regardless of the use of statins.

CONCLUSION

Long-term statin treatment is associated with blunted exercise fat oxidation before exercise training. However, statin use does not blunt the improvements in exercise fat oxidation (FOMAX) derived from intense aerobic exercise training. This finding should encourage statin users to exercise-train to benefit from increased fat oxidation once their fitness level improves.

Statin-Associated Myopathy: Emphasis on Mechanisms and Targeted Therapy

Hyperlipidemia is a major risk factor for cardiovascular morbidity and mortality. Statins are the first-choice therapy for dyslipidemias and are considered the cornerstone of atherosclerotic cardiovascular disease (ASCVD) in both primary and secondary prevention. Despite the statin-therapy-mediated positive effects on cardiovascular events, patient compliance is often poor. Statin-associated muscle symptoms (SAMS) are the most common side effect associated with treatment discontinuation. SAMS, which range from mild-to-moderate muscle pain, weakness, or fatigue to potentially life-threatening rhabdomyolysis, are reported by 10% to 25% of patients receiving statin therapy. There are many risk factors associated with patient features and hypolipidemic agents that seem to increase the risk of developing SAMS. Due to the lack of a "gold standard", the diagnostic test for SAMS is based on a clinical criteria score, which is independent of creatine kinase (CK) elevation. Mechanisms that underlie the pathogenesis of SAMS remain almost unclear, though a high number of risk factors may increase the probability of myotoxicity induced by statin therapy. Some of these, related to pharmacokinetic properties of statins and to concomitant therapies or patient characteristics, may affect statin bioavailability and increase vulnerability to high-dose statins.

Can Exercise-Induced Muscle Damage Be a Good Model for the Investigation of the Anti-Inflammatory Properties of Diet in Humans?

Subclinical, low-grade, inflammation is one of the main pathophysiological mechanisms underlying the majority of chronic and non-communicable diseases. Several methodological approaches have been applied for the assessment of the anti-inflammatory properties of nutrition, however, their impact in human body remains uncertain, because of the fact that the majority of the studies reporting anti-inflammatory effect of dietary patterns, have been performed under laboratory settings and/or in animal models. Thus, the extrapolation of these results to humans is risky. It is therefore obvious that the development of an inflammatory model in humans, by which we could induce inflammatory responses to humans in a regulated, specific, and non-harmful way, could greatly facilitate the estimation of the anti-inflammatory properties of diet in a more physiological way and mechanistically relevant way. We believe that exercise-induced muscle damage (EIMD) could serve as such a model, either in studies investigating the homeostatic responses of individuals under inflammatory stimuli or for the estimation of the anti-inflammatory or pro-inflammatory potential of dietary patterns, foods, supplements, nutrients, or phytochemicals. Thus, in this review we discuss the possibility of exercise-induced muscle damage being an inflammation model suitable for the assessment of the anti-inflammatory properties of diet in humans.

The effects of statins with a high hepatoselectivity rank on the extra-hepatic tissues; New functions for statins

Statins, as the most common treatment for hyperlipidemia, exert effects beyond their lipid-lowering role which are known as pleiotropic effects. These effects are mainly due to the inhibition of isoprenoids synthesis and consequently blocking prenylation of proteins involved in the cellular signaling pathways regulating cell development, growth, and apoptosis. Statins target cholesterol synthesis in the liver as the major source of cholesterol in the body and so reduce whole-body cholesterol. The reduced level of cholesterol forces other organs to an adaptive homeostatic reaction to increase their cholesterol synthesis capacity, however, this only occurs when statins have unremarkable access to the extra-hepatic tissues. In order to reduce the adverse effects of statin on the skeletal muscle, most recent efforts have been towards formulating new statins with the highest level of hepatoselectivity rank and the least level of access to the extra-hepatic tissues; however, the inaccessibility of statins for the extra-hepatic tissues may induce several biological reactions. In this review, we aim to evaluate the effects of statins on the extra-hepatic tissues when statins have unremarkable access to these tissues.

Atherosclerosis and Coenzyme Q10

Atherosclerosis is the most common cause of cardiac deaths worldwide. Classically, atherosclerosis has been explained as a simple arterial lipid deposition with concomitant loss of vascular elasticity. Eventually, this condition can lead to consequent blood flow reduction through the affected vessel. However, numerous studies have demonstrated that more factors than lipid accumulation are involved in arterial damage at the cellular level, such as inflammation, autophagy impairment, mitochondrial dysfunction, and/or free-radical overproduction. In order to consider the correction of all of these pathological changes, new approaches in atherosclerosis treatment are necessary. Ubiquinone or coenzyme Q₁₀ is a multifunctional molecule that could theoretically revert most of the cellular alterations found in atherosclerosis, such as cholesterol biosynthesis dysregulation, impaired autophagy flux and mitochondrial dysfunction thanks to its redox and signaling properties. In this review, we will show the latest advances in the knowledge of the relationships between coenzyme Q₁₀ and atherosclerosis. In addition, as atherosclerosis phenotype is closely related to aging, it is reasonable to believe that coenzyme Q₁₀ supplementation could be beneficial for both conditions.

Mitochondrial dysfunction, AMPK activation and peroxisomal metabolism: A coherent scenario for non-canonical 3-methylglutaconic acidurias

The occurrence of 3-methylglutaconic aciduria (3-MGA) is a well understood phenomenon in leucine oxidation and ketogenesis disorders (primary 3-MGAs). In contrast, its genesis in non-canonical (secondary) 3-MGAs, a growing-up group of disorders encompassing more than a dozen of inherited metabolic diseases, is a mystery still remaining unresolved for three decades. To puzzle out this anthologic problem of metabolism, three clues were considered: (i) the variety of disorders suggests a common cellular target at the cross-road of metabolic and signaling pathways, (ii) the response to leucine loading test only discriminative for primary but not secondary 3-MGAs suggests these latter are disorders of extramitochondrial HMG-CoA metabolism as also attested by their failure to increase 3-hydroxyisovalerate, a mitochondrial metabolite accumulating only in primary 3-MGAs, (iii) the peroxisome is an extramitochondrial site possessing its own pool and displaying metabolism of HMG-CoA, suggesting its possible involvement in producing extramitochondrial 3-methylglutaconate (3-MG). Following these clues provides a unifying common basis to non-canonical 3-MGAs: constitutive mitochondrial dysfunction induces AMPK activation which, by inhibiting early steps in cholesterol and fatty acid syntheses, pipelines cytoplasmic acetyl-CoA to peroxisomes where a rise in HMG-CoA followed by local dehydration and hydrolysis may lead to 3-MGA yield. Additional contributors are considered, notably for 3-MGAs associated with hyperammonemia, and to a lesser extent in CLPB deficiency. Metabolic and signaling itineraries followed by the proposed scenario are essentially sketched, being provided with compelling evidence from the literature coming in their support.

Amyotrophic Lateral Sclerosis Associated with Statin Use: A Disproportionality Analysis of the FDA's Adverse Event Reporting System

INTRODUCTION

Apparent elevations in reporting of amyotrophic lateral sclerosis (ALS)-like conditions associated with statin use have been previously described from data obtained via US and European databases.

OBJECTIVE

The aim of this study was to examine US FDA Adverse Event Reporting System (FAERS) data to compare reporting odds ratios (RORs) of ALS and ALS-like conditions between statins and other drugs, for each statin agent.

METHODS

We assessed for disproportional rates of reported ALS and ALS-related conditions for each statin agent separately by using the ROR formula. FAERS data were analyzed through September 2015.

RESULTS

RORs for ALS were elevated for all statins, with elevations possibly stronger for lipophilic statins. RORs ranged from 9.09 (6.57-12.6) and 16.2 (9.56-27.5) for rosuvastatin and pravastatin (hydrophilic) to 17.0 (14.1-20.4), 23.0 (18.3-29.1), and 107 (68.5-167) for atorvastatin, simvastatin, and lovastatin (lipophilic), respectively. For simvastatin, an ROR of 57.1 (39.5-82.7) was separately present for motor neuron disease.

CONCLUSION

These findings extend previous evidence showing that significantly elevated ALS reporting extends to individual statin agents, and add to concerns about potential elevated occurrence of ALS-like conditions in association with statin usage.

An Observational Epidemiological Study of Exercise-induced Rhabdomyolysis Causing Acute Kidney Injury: A Single-center Experience

Exercise-induced rhabdomyolysis (EIR) is an uncommon cause of severe rhabdomyolysis and a very rare cause of acute kidney injury (AKI). A prospective observational study of 25 patients diagnosed with EIR was conducted in a multispecialty hospital in Dubai, from 2009 to 2015. Five out of 25 patients experienced AKI necessitating temporary renal replacement therapy. The initial presentation, biochemical parameters, and clinical course of patients were monitored, to understand epidemiology and risk factors for the development of AKI. There was male preponderance (4 out of 5 patients), higher rate of systemic symptoms (all 5 patients) versus 60% in NRAKI), oligo-anuria (all 5 patients), compartment syndrome (3 out \of 5) and severe dehydration seen in patients with RAKI group. On laboratory evaluation, there was higher rise in creatinine kinase (CK) enzyme, serum and urine myoglobin levels impaired renal function on presentation, hyperuricemia, high D-dimer level, PCV of more than 55%, found to be associated with RAKI as compared to NRAKI group. Hematuria by positive urine dipstick with absent red blood cells on urinalysis, is an insensitive tool as was present in only 62% and 43% of RAKI and NRAKI groups, respectively. It was also observed that delayed pesentation for medical care, metabolic acidosis, were commonly associated with AKI. All patients with RAKI required RRT for a comparable period of time (3-4 weeks). In all of them, no deterioration or relapse reported on follow-up of 3 months.

An Observational Epidemiological Study of Exercise-induced Rhabdomyolysis Causing Acute Kidney Injury: A Single-center Experience

Exercise-induced rhabdomyolysis (EIR) is an uncommon cause of severe rhabdomyolysis and a very rare cause of acute kidney injury (AKI). A prospective observational study of 25 patients diagnosed with EIR was conducted in a multispecialty hospital in Dubai, from 2009 to 2015. Five out of 25 patients experienced AKI necessitating temporary renal replacement therapy. The initial presentation, biochemical parameters, and clinical course of patients were monitored, to understand epidemiology and risk factors for the development of AKI. There was male preponderance (4 out of 5 patients), higher rate of systemic symptoms (all 5 patients) versus 60% in NRAKI), oligo-anuria (all 5 patients), compartment syndrome (3 out \of 5) and severe dehydration seen in patients with RAKI group. On laboratory evaluation, there was higher rise in creatinine kinase (CK) enzyme, serum and urine myoglobin levels impaired renal function on presentation, hyperuricemia, high D-dimer level, PCV of more than 55%, found to be associated with RAKI as compared to NRAKI group. Hematuria by positive urine dipstick with absent red blood cells on urinalysis, is an insensitive tool as was present in only 62% and 43% of RAKI and NRAKI groups, respectively. It was also observed that delayed pesentation for medical care, metabolic acidosis, were commonly associated with AKI. All patients with RAKI required RRT for a comparable period of time (3-4 weeks). In all of them, no deterioration or relapse reported on follow-up of 3 months.

Plasma 2-hydroxyglutarate and hexanoylcarnitine levels are potential biomarkers for skeletal muscle toxicity in male Fischer 344 rats

To identify new candidate biomarkers for skeletal muscle toxicity, an unbiased metabolomic analysis was performed in rats treated with two distinct myotoxicants, cerivastatin (CER) and tetramethyl-p-phenylenediamine (TMPD). Skeletal muscle toxicity was induced in male Fischer 344 rats by administering CER or TMPD and monitored using established endpoints, such as increased plasma creatine kinase (CK) activity and histopathology, and a metabolomic analysis of skeletal muscle and plasma samples. Plasma CK levels in CER-treated rats were markedly elevated at Day 11; however, those in TMPD-treated rats showed a statistically significant decrease at 24 hr after dosing. Light microscopy revealed that vacuolated or necrotic fibers were evident in all CER-treated rats on Day 11, and slightly vacuolated fibers were observed in TMPD-treated rats at 6 and 24 hr after dosing. Metabolomic analysis of the rectus femoris indicated increases in 2-hydroxyglutarate (2HG) in CER-treated rats and hexanoylcarnitine in CER- and TMPD-treated rats. There were also increases in plasma 2HG in CER-treated rats on Days 8 and 11 and in TMPD-treated rats at 24 hr after dosing and increases in plasma hexanoylcarnitine in CER-treated rats on Day 11 and in TMPD-treated rats at 6 and 24 hr after dosing. These experiments demonstrated the potential of plasma 2HG and hexanoylcarnitine as specific and easily detectable biomarkers for skeletal muscle toxicity in rats and demonstrated the value of metabolomics for biomarker detection and identification in toxicological studies.

Statin-associated myopathy and the quest for biomarkers: can we effectively predict statin-associated muscle symptoms?

Over the past three decades, statins have become the cornerstone of prevention and treatment of atherosclerotic cardiovascular and metabolic diseases. Albeit generally well tolerated, these drugs can elicit a variety of muscle-associated symptoms that represent the most important reason for treatment discontinuation. Statin-associated myopathy has been systematically underestimated by randomized controlled trials as compared with the incidence observed in clinical practice and obtained from patient registries. There are several reasons for this discrepancy, among which the lack of reliable diagnostic tests and a validated questionnaire to assess muscle symptoms are recognized as unmet needs. Here, we review the cellular and molecular mechanisms underlying statin-associated myopathy and discuss the experimental and clinical data on various biomarkers to diagnose and predict muscle-related complaints.

Exercise-induced rhabdomyolysis mechanisms and prevention: A literature review

Exercise-induced rhabdomyolysis (exRML), a pathophysiological condition of skeletal muscle cell damage that may cause acute renal failure and in some cases death. Increased Ca²⁺ level in cells along with functional degradation of cell signaling system and cell matrix have been suggested as the major pathological mechanisms associated with exRML. The onset of exRML may be exhibited in athletes as well as in general population. Previous studies have reported that possible causes of exRML were associated with excessive eccentric contractions in high temperature, abnormal electrolytes balance, and nutritional deficiencies possible genetic defects. However, the underlying mechanisms of exRML have not been clearly established among health professionals or sports medicine personnel. Therefore, we reviewed the possible mechanisms and correlated prevention of exRML, while providing useful and practical information for the athlete and general exercising population.

Laboratory Medicine in the Clinical Decision Support for Treatment of Hypercholesterolemia: Pharmacogenetics of Statins

Statin responsiveness is an area of great research interest given the success of the drug class in the treatment of hypercholesterolemia and in primary and secondary prevention of cardiovascular disease. Interrogation of the patient's genome for gene variants will eventually guide anti-hyperlipidemic intervention. In this review, we discuss methodological approaches to discover genetic markers predictive of class-wide and drug-specific statin efficacy and safety. Notable pharmacogenetic findings are summarized from hypothesis-free genome wide and hypothesis-led candidate gene association studies. Physiogenomic models and clinical decision support systems will be required for DNA-guided statin therapy to reach practical use in medicine.

Molecular mechanisms of statin intolerance

Statins reduce cardiovascular morbidity and mortality in primary and secondary prevention. Despite their efficacy, many persons are unable to tolerate statins due to adverse events such as hepatotoxicity and myalgia/myopathy. In the case of most patients, it seems that mild-to-moderate abnormalities in liver and muscle enzymes are not serious adverse effects and do not outweigh the benefits of coronary heart disease risk reduction. The risk for mortality or permanent organ damage ascribed to statin use is very small and limited to cases of myopathy and rhabdomyolysis. Statin-induced muscle-related adverse events comprise a highly heterogeneous clinical disorder with numerous, complex etiologies and a variety of genetic backgrounds. Every patient who presents with statin-related side effects cannot undergo the type of exhaustive molecular characterization that would include all of these mechanisms. Frequently the only solution is to either discontinue statin therapy/reduce the dose or attempt intermittent dosing strategies at a low dose.

Risk identification and possible countermeasures for muscle adverse effects during statin therapy

The use of statins for cardiovascular disease prevention is clearly supported by clinical evidence. However, in January 2014 the U.S. Food and Drug Administration released an advice on statin risk reporting that "statin benefit is indisputable, but they need to be taken with care and knowledge of their side effects". Among them the by far most common complication is myopathy, ranging from common but clinically benign myalgia to rare but life-threatening rhabdomyolysis. This class side effect appears to be dose dependent, with more lipophilic statin (i.e., simvastatin) carrying a higher overall risk. Hence, to minimize statin-associated myopathy, clinicians should take into consideration a series of factors that potentially increase this risk (i.e., drug-drug interactions, female gender, advanced age, diabetes mellitus, hypothyroidism and vitamin D deficiency). Whenever it is appropriate to stop statin treatment, the recommendations are to stay off statin until resolution of symptoms or normalization of creatine kinase values. Afterwards, clinicians have several options to treat dyslipidemia, including the use of a lower dose of the same statin, intermittent non-daily dosing of statin, initiation of a different statin, alone or in combination with nonstatin lipid-lowering agents, and substitution with red yeast rice.

Pharmacology of manipulating lean body mass

Dysfunction and wasting of skeletal muscle as a consequence of illness decreases the length and quality of life. Currently, there are few, if any, effective treatments available to address these conditions. Hence, the existence of this unmet medical need has fuelled large scientific efforts. Fortunately, these efforts have shown many of the underlying mechanisms adversely affecting skeletal muscle health. With increased understanding have come breakthrough disease-specific and broad spectrum interventions, some progressing through clinical development. The present review focuses its attention on the role of the antagonistic process regulating skeletal muscle mass before branching into prospective promising therapeutic targets and interventions. Special attention is given to therapies in development against cancer cachexia and Duchenne muscular dystrophy before closing remarks on design and conceptualization of future therapies are presented to the reader.

Statin therapy depresses fat metabolism in older individuals

OBJECTIVE

Statins (3-hydroxy-3-methylglutaryl coenzyme A [HMG CoA] reductase inhibitors) reduce blood lipoproteins and reduce the risk of cardiovascular events. However, they may reduce fat metabolism. This study tested the hypothesis that total body fat oxidation is reduced by statins in older subjects and the reduction is not due to substrate availability.

METHODS

A total of 14 elderly patients (71 ± 6 years) on statin therapy were compared with 14 matched elderly controls (75 ± 7 years). Subjects were tested for respiratory exchange ratio (RER) during both maximal and submaximal sustained (70% Vo(2max)) exercise to voluntary exhaustion. Blood samples were drawn for lipoprotein analysis and substrate availability.

RESULTS

RER was significantly higher in subjects taking statins during both the max and submax tests, indicating reduced fat oxidation. Blood lipoprotein levels after a fast were not different between the statin and control groups. Levels of glucose, lactate, or triglyceride were not different between groups; however, free fatty acid levels were elevated by exercise in the statin group. Fat oxidation was significantly reduced in older subjects taking statin drugs that were not associated with diet, exercise, and fitness, which were matched between groups, nor availability of fat from the blood, which was higher in the statin group.

CONCLUSION

Although statin therapy normalizes blood lipoproteins, it reduced fat metabolism in older individuals, which cannot be a result of lower availability from blood.

The relationship of vitamin D deficiency to statin myopathy

OBJECTIVE

Our goal was to examine the interaction between vitamin D and statins and the possible role of vitamin D deficiency in statin myopathy.

BACKGROUND

The vitamin D receptor is present in skeletal muscle and vitamin D deficiency can cause myopathy. Statins (3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors) are generally well tolerated, but have been associated with a spectrum of skeletal muscle complaints, ranging from myalgia and asymptomatic mild elevations of creatine kinase (CK) to rhabdomyolysis. There has been recent interest in the possible interaction between statin myopathy and vitamin D deficiency. We performed a systematic medical literature review to examine this possible relationship.

METHODS

We identified English language articles relating statins, vitamin D and statin myopathy via a PubMed search through July 2010. Articles pertinent to the topic were reviewed in detail.

RESULTS/CONCLUSIONS

Our review suggests that some but not all statins increase 25(OH) D levels. Two cross sectional studies have associated vitamin D deficiency with statin-associated myalgias, and suggested that that increasing vitamin D levels can reverse the myalgia. Nevertheless, given the quality and paucity of studies examining this possibility, additional studies are needed to examine the potential role of vitamin D deficiency in statin myopathy. It is presently premature to recommend vitamin D supplementation as treatment for statin associated muscle complaints in the absence of low vitamin D levels although such supplementation could be tried in patients with deficient or reduced vitamin D levels.

Effects of statins on skeletal muscle: a perspective for physical therapists

Hyperlipidemia, also known as high blood cholesterol, is a cardiovascular health risk that affects more than one third of adults in the United States. Statins are commonly prescribed and successful lipid-lowering medications that reduce the risks associated with cardiovascular disease. The side effects most commonly associated with statin use involve muscle cramping, soreness, fatigue, weakness, and, in rare cases, rapid muscle breakdown that can lead to death. Often, these side effects can become apparent during or after strenuous bouts of exercise. Although the mechanisms by which statins affect muscle performance are not entirely understood, recent research has identified some common causative factors. As musculoskeletal and exercise specialists, physical therapists have a unique opportunity to identify adverse effects related to statin use. The purposes of this perspective article are: (1) to review the metabolism and mechanisms of actions of statins, (2) to discuss the effects of statins on skeletal muscle function, (3) to detail the clinical presentation of statin-induced myopathies, (4) to outline the testing used to diagnose statin-induced myopathies, and (5) to introduce a role for the physical therapist for the screening and detection of suspected statin-induced skeletal muscle myopathy.

Neurodevelopmental manifestations of mitochondrial disease

Mitochondrial disease is an increasingly recognized but widely heterogeneous group of multisystemic disorders that commonly involve severe neurodevelopmental manifestations in childhood. This review explores the presentation, genetic basis, and diagnostic evaluation of primary mitochondrial disease. Emphasis is placed on neurodevelopmental findings that may be encountered by a Developmental Pediatrician that should provoke consideration of a mitochondrial disorder. The inheritance patterns and mechanisms by which mutations in genes located in either the nuclear or mitochondrial genomes can cause mitochondrial diseases are discussed. A general overview of the current diagnostic evaluation that can be readily initiated by the Developmental Pediatrician is provided, along with a summary of currently available treatment options.

The effects of statins on skeletal muscle strength and exercise performance

PURPOSE OF REVIEW

HMG-CoA reductase inhibitors or statins are associated with a variety of muscle side-effects but little is known about the effect of statins on skeletal muscle strength and exercise performance. We performed a literature search to examine these issues.

RECENT FINDINGS

We identified six studies examining the effect of statins on muscle strength and nine studies examining their effect on exercise tolerance. In general, studies examining both issues were small and used crude measures of strength and exercise performance.

SUMMARY

There is insufficient data to determine if statins affect muscle strength and exercise performance. There is suggestive evidence that these drugs may reduce muscle strength in older patients and alter energy metabolism during aerobic exercise, both possibilities require further study.

The genetics of statin-induced myopathy

OBJECTIVE

Our goal was to use genetic variants to identify factors contributing to the muscular side effects of statins.

BACKGROUND

Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are usually well tolerated medications, but muscle symptoms, ranging from mild myalgia to clinically important rhabdomyolysis are an important side effect of these drugs and a leading cause of noncompliance. Recent results suggest that genetic factors increase the risk of statin-related muscle complaints. We performed a systematic review of the medical literature to determine genetic factors associated with statin myopathy.

METHODS

We identified English language articles relating statin myopathy and genetic diseases and gene variants via a PubMed search. Articles pertinent to the topic were reviewed in detail.

RESULTS/CONCLUSIONS

Our review suggests that some patients are susceptible to statin myopathy because of pre-existing subclinical inherited muscular disorders, or genetic variation in statin uptake proteins encoded by SLCO1B1 or the cytochrome P enzyme system. Variations in genes affecting pain perception and polymorphism in vascular receptors may also contribute to statin myopathy. None of the variants identified in this review suggested novel metabolic mechanisms leading to statin myopathy.

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.

Thyroid hormone mimetics: potential applications in atherosclerosis, obesity and type 2 diabetes

Thyroid hormones influence heart rate, serum lipids, metabolic rate, body weight and multiple aspects of lipid, carbohydrate, protein and mineral metabolism. Although increased thyroid hormone levels can improve serum lipid profiles and reduce fat, these positive effects are counterbalanced by harmful effects on the heart, muscle and bone. Thus, attempts to use thyroid hormones for cholesterol-lowering and weight loss purposes have so far been limited. However, over the past decade, thyroid hormone analogues that are capable of uncoupling beneficial effects from deleterious effects have been developed. Such drugs could serve as powerful new tools to address two of the largest medical problems in developed countries--atherosclerosis and obesity.

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.