Electrical myotonia of rabbit skeletal muscles by HMG-CoA reductase inhibitors

Non-dystrophic myotonia: 2-year clinical and patient reported outcomes

INTRODUCTION/AIMS

Consistency of differences between non-dystrophic myotonias over time measured by standardized clinical/patient-reported outcomes is lacking. Evaluation of longitudinal data could establish clinically relevant endpoints for future research.

METHODS

Data from prospective observational study of 95 definite/clinically suspected non-dystrophic myotonia participants (six sites in the United States, United Kingdom, and Canada) between March 2006 and March 2009 were analyzed. Outcomes included: standardized symptom interview/exam, Short Form-36, Individualized Neuromuscular Quality of Life (INQoL), electrophysiological short/prolonged exercise tests, manual muscle testing, quantitative grip strength, modified get-up-and-go test. Patterns were assigned as described by Fournier et al. Comparisons were restricted to confirmed sodium channelopathies (SCN4A, baseline, year 1, year 2: n = 34, 19, 13), chloride channelopathies (CLCN1, n = 32, 26, 18), and myotonic dystrophy type 2 (DM2, n = 9, 6, 2).

RESULTS

Muscle stiffness was the most frequent symptom over time (54.7%-64.7%). Eyelid myotonia and paradoxical handgrip/eyelid myotonia were more frequent in SCN4A. Grip strength and combined manual muscle testing remained stable. Modified get-up-and-go showed less warm up in SCN4A but remained stable. Median post short exercise decrement was stable, except for SCN4A (baseline to year 2 decrement difference 16.6% [Q1, Q3: 9.5, 39.2]). Fournier patterns type 2 (CLCN1) and 1 (SCN4A) were most specific; 40.4% of participants had a change in pattern over time. INQoL showed higher impact for SCN4A and DM2 with scores stable over time.

DISCUSSION

Symptom frequency and clinical outcome assessments were stable with defined variability in myotonia measures supporting trial designs like cross over or combined n-of-1 as important for rare disorders.

Cholesterol in myasthenia gravis

The cholinergic neuromuscular junction is the paradigm peripheral synapse between a motor neuron nerve ending and a skeletal muscle fiber. In vertebrates, acetylcholine is released from the presynaptic site and binds to the nicotinic acetylcholine receptor at the postsynaptic membrane. A variety of pathologies among which myasthenia gravis stands out can impact on this rapid and efficient signaling mechanism, including autoimmune diseases affecting the nicotinic receptor or other synaptic proteins. Cholesterol is an essential component of biomembranes and is particularly rich at the postsynaptic membrane, where it interacts with and modulates many properties of the nicotinic receptor. The profound changes inflicted by myasthenia gravis on the postsynaptic membrane necessarily involve cholesterol. This review analyzes some aspects of myasthenia gravis pathophysiology and associated postsynaptic membrane dysfunction, including dysregulation of cholesterol metabolism in the myocyte brought about by antibody-receptor interactions. In addition, given the extensive therapeutic use of statins as the typical cholesterol-lowering drugs, we discuss their effects on skeletal muscle and the possible implications for MG patients under chronic treatment with this type of compound.

Diagnostic modelling and therapeutic monitoring of immune-mediated necrotizing myopathy: role of electrical myotonia

Delayed diagnosis of immune-mediated necrotizing myopathy leads to increased morbidity. Patients with the chronic course without 3-hydroxy-3-methylglutaryl-coenzyme-A reductase-IgG or signal recognition particle-IgG are often challenging to diagnose. Immunotherapy response can also be difficult to assess. We created a statistical model to assist immune-mediated necrotizing myopathy diagnosis. Electrical myotonia versus fibrillations were reviewed as biomarkers for immunotherapy treatment response. Identified were 119 immune-mediated necrotizing myopathy cases and 938 other myopathy patients. Inclusion criteria included all having electrophysiological evaluations, muscle biopsies showing inflammatory/necrotizing myopathies, comprehensively recorded neurological examinations, and creatine kinase values. Electrical myotonia was recorded in 56% (67/119) of retrospective and 67% (20/30) of our validation immune-mediated necrotizing myopathy cohorts, and significantly (P < 0.001) favoured immune-mediated necrotizing myopathy over other myopathies: sporadic inclusion body myositis (odds ratio = 4.78); dermatomyositis (odds ratio = 10.61); non-specific inflammatory myopathies (odds ratio = 8.46); limb-girdle muscular dystrophies (odds ratio = 5.34) or mitochondrial myopathies (odds ratio = 14.17). Electrical myotonia occurred in immune-mediated necrotizing myopathy seropositive (3-hydroxy-3-methylglutaryl-coenzyme-A reductase-IgG 70%, 37/53; signal recognition particle-IgG 29%, 5/17) and seronegative (51%, 25/49). Multivariate regression analysis of 20 variables identified 8 (including electrical myotonia) in combination accurately predicted immune-mediated necrotizing myopathy (97.1% area-under-curve). The model was validated in a separate cohort of 30 immune-mediated necrotizing myopathy cases. Delayed diagnosis of cases with electrical myotonia occurred in 24% (16/67, mean 8 months; range 0–194). Half (8/19) had a chronic course and were seronegative, with high model prediction (>86%) at the first visit. Inherited myopathies were commonly first suspected in them. Follow-up evaluation in patients with electrical myotonia on immunotherapy was available in 19 (median 21 months, range 2–124) which reduced from 36% (58/162) of muscles to 7% (8/121; P < 0.001). Reduced myotonia correlated with immunotherapy response in 64% (9/14) as well as with median creatine kinase reduction of 1779 U/l (range 401–9238, P < 0.001). Modelling clinical features with electrical myotonia is especially helpful in immune-mediated necrotizing myopathy diagnostic suspicion among chronic indolent and seronegative cases. Electrical myotonia favours immune-mediated necrotizing myopathy diagnosis and can serve as an adjuvant immunotherapy biomarker.

Guidelines on clinical presentation and management of nondystrophic myotonias

The nondystrophic myotonias are rare muscle hyperexcitability disorders caused by gain-of-function mutations in the SCN4A gene or loss-of-function mutations in the CLCN1 gene. Clinically, they are characterized by myotonia, defined as delayed muscle relaxation after voluntary contraction, which leads to symptoms of muscle stiffness, pain, fatigue, and weakness. Diagnosis is based on history and examination findings, the presence of electrical myotonia on electromyography, and genetic confirmation. In the absence of genetic confirmation, the diagnosis is supported by detailed electrophysiological testing, exclusion of other related disorders, and analysis of a variant of uncertain significance if present. Symptomatic treatment with a sodium channel blocker, such as mexiletine, is usually the first step in management, as well as educating patients about potential anesthetic complications.

Statin-Induced Muscle Necrosis in the Rat: Distribution, Development, and Fibre Selectivity

Simvastatin and cerivastatin have been used to investigate the development of statin-induced muscle necrosis in the rat. This was similar for both statins and was treatment-duration dependent, only occurring after 10 days had elapsed even if the dose was increased, and still occurring after this time when dosing was terminated earlier as a result of morbidity. It was then widespread and affected all areas of the muscular system. However, even when myotoxicity was severe, particular individual muscles and some types of fibres within affected muscles were spared consistently. Fibre typing of spared muscles and of acutely necrotic fibres within affected muscles indicated a differential fibre sensitivity to statin-induced muscle necrosis. The fibres showed a necrotic response to statin administration that matched their oxidative/glycolytic metabolic nature: Least sensitive →I ↔ IIA ↔ IID ↔ IIB ← most sensitive. Type I and IIB fibres represent metabolic extremes of a continuum of metabolic properties through the fibre types with type I fibres most oxidative in metabolism and type IIB fibres most glycolytic. In addition, in some (nonnecrotic) glycolytic fibres from muscles showing early multifocal single fibre necrosis the only subcellular alterations present in isolation of any other changes were mitochondrial. These changes were characterised by an increased incidence of vacuolation and the formation of myelinoid vesicular bodies that accumulated in the subsarcolemmal areas. These findings suggest an important early involvement of mitochondria in selective glycolytic muscle fibre necrosis following inhibition of the enzyme HMG-CoA reductase.

Case Records of the Massachusetts General Hospital. Case 30-2015: A 50-Year-Old Man with Cardiogenic Shock

A 50-year-old man with a history of cardiomyopathy and progressive muscle weakness was admitted with cardiogenic shock. Electroencephalography showed total suppression of cerebral activity; ventilator support was withdrawn, and he died. An autopsy was performed.

A Neuromuscular Approach to Statin-Related Myotoxicity

Approximately 95% of statin-treated patients tolerate this form of cholesterol management without any adverse effects. However, given their efficacy in reducing low density lipoproteins and cardiovascular events large numbers of patients are selected for statin therapy. Therefore muscle complications are, in fact, quite common. Limited understanding of the underlying pathophysiology has hampered physicians' ability to identify patients at risk for developing statin myotoxicity. A growing number of published case reports/series have implicated statins in the exacerbation of both acquired and genetic myopathies. A clinical management algorithm is presented which outlines a variety of co-morbidities which can potentiate the adverse effects of statins on muscle. In addition, a rational approach to the selection of those patients most likely to benefit from skeletal muscle biopsy is discussed. Ongoing work will define the extent to which statin-intolerant patients represent carriers of recessive metabolic myopathies or pre-symptomatic acquired myopathies. The expanding importance of pharmacogenomics will undoubtedly be realized in the field of statin myopathy research within the next few years. Such critical information is needed to establish more definitive management and diagnostic strategies.

Non-dystrophic myotonia: prospective study of objective and patient reported outcomes

Non-dystrophic myotonias are rare diseases caused by mutations in skeletal muscle chloride and sodium ion channels with considerable phenotypic overlap between diseases. Few prospective studies have evaluated the sensitivity of symptoms and signs of myotonia in a large cohort of patients. We performed a prospective observational study of 95 participants with definite or clinically suspected non-dystrophic myotonia recruited from six sites in the USA, UK and Canada between March 2006 and March 2009. We used the common infrastructure and data elements provided by the NIH-funded Rare Disease Clinical Research Network. Outcomes included a standardized symptom interview and physical exam; the Short Form-36 and the Individualized Neuromuscular Quality of Life instruments; electrophysiological short and prolonged exercise tests; manual muscle testing; and a modified get-up-and-go test. Thirty-two participants had chloride channel mutations, 34 had sodium channel mutations, nine had myotonic dystrophy type 2, one had myotonic dystrophy type 1, and 17 had no identified mutation. Phenotype comparisons were restricted to those with sodium channel mutations, chloride channel mutations, and myotonic dystrophy type 2. Muscle stiffness was the most prominent symptom overall, seen in 66.7% to 100% of participants. In comparison with chloride channel mutations, participants with sodium mutations had an earlier age of onset of stiffness (5 years versus 10 years), frequent eye closure myotonia (73.5% versus 25%), more impairment on the Individualized Neuromuscular Quality of Life summary score (20.0 versus 9.44), and paradoxical eye closure myotonia (50% versus 0%). Handgrip myotonia was seen in three-quarters of participants, with warm up of myotonia in 75% chloride channel mutations, but also 35.3% of sodium channel mutations. The short exercise test showed ≥10% decrement in the compound muscle action potential amplitude in 59.3% of chloride channel participants compared with 27.6% of sodium channel participants, which increased post-cooling to 57.6% in sodium channel mutations. In evaluation of patients with clinical and electrical myotonia, despite considerable phenotypic overlap, the presence of eye closure myotonia, paradoxical myotonia, and an increase in short exercise test sensitivity post-cooling suggest sodium channel mutations. Outcomes designed to measure stiffness or the electrophysiological correlates of stiffness may prove useful for future clinical trials, regardless of underlying mutation, and include patient-reported stiffness, bedside manoeuvres to evaluate myotonia, muscle specific quality of life instruments and short exercise testing.

Myotoxicity of gemfibrozil in cynomolgus monkey model and its relationship to pharmacokinetic properties

Fibrate drugs are PPARalpha agonists prescribed for the treatment of dyslipidemia. Severe myotoxicity has been reportedly associated with their use albeit at a low frequency, especially for gemfibrozil. Few studies have investigated the mechanism of fibrate-induced myotoxicity in vivo. Considering the apparent species-related differences in PPARalpha agonist-induced hepatotoxicity, we studied the myotoxicity of gemfibrozil in a Cynomolgus monkey model and explored the relationship between myotoxicity and pharmacokinetics. Six Cynomolgus monkeys were dosed with gemfibrozil twice daily at 600 mg/kg/day for the first two periods (P1 and P2, 8 days and 9 days respectively) and 300 mg/kg/day for the third period (P3, 14 days). Creatine kinase and myoglobin were measured, together with hepatotoxicity and nephrotoxicity markers. Behavioral responses were recorded for indication of toxicity. Pharmacokinetics was carried out following the 16th dosage of P1 and 17th dosage of P2 when myotoxicity was identified. Multivariable data analysis was employed to explore the relationship between pharmacokinetic parameters and myotoxicity markers. Consequently, myotoxicity occurred in monkey #2 (M2) and M6 in P1, M3 and M4 in P2, M3 and M6 in P3. Data analysis showed T80-150 (sustained time above the given concentration) contributed for myotoxicity discriminance and correlated with myotoxicity risk. This study revealed Cynomolgus monkey may be a good animal model for myotoxicity evaluation with sensitivity, reproducibility and similarities to humans. More interestingly, they exhibited a much higher incidence of myotoxicity than that of humans. Sustained high drug concentration plays an important role for the occurrence of myotoxicity. This may suggest an influence of drug transport and metabolism on myotoxicity.

Statins may aggravate myasthenia gravis

Statin-induced myopathy is well-known, but the effect of cholesterol-lowering agents on myasthenia gravis (MG) has not been studied in detail. We investigated statin use and its effects on MG among patients with this disease. Statin information was systemically obtained from 170 patients being treated at the Neuromuscular Disease Clinic at the University of Alabama at Birmingham. When a new myalgic syndrome or worsening of MG developed within 4 months after statin treatment, no other likely cause was found, and clinical improvement occurred either with or without discontinuation of the statin, we considered these symptoms to be statin-induced. Fifty-four patients (31%) were on statins. The statin group had proportionally more males, and older patients compared with the non-statin group. A myalgic syndrome was noted in 7 (13%) patients, but it resolved without any sequelae after withdrawal of the statin. MG worsening occurred in 6 (11%) patients without regard to type of MG or brand of statin. MG worsening occurred independently of myalgic syndrome and involved predominantly oculobulbar symptoms within 1-16 weeks of statin treatment. In 4 patients, additional treatment was needed to reverse MG worsening. Statins are safe in the majority of MG patients, but their use must be accompanied by close observation for possible MG worsening.

Myotonia congenita

Myotonia is a symptom of many different acquired and genetic muscular conditions that impair the relaxation phase of muscular contraction. Myotonia congenita is a specific inherited disorder of muscle membrane hyperexcitability caused by reduced sarcolemmal chloride conductance due to mutations in CLCN1, the gene coding for the main skeletal muscle chloride channel ClC-1. The disorder may be transmitted as either an autosomal-dominant or recessive trait with close to 130 currently known mutations. Although this is a rare disorder, elucidation of the pathophysiology underlying myotonia congenita established the importance of sarcolemmal chloride conductance in the control of muscle excitability and demonstrated the first example of human disease associated with the ClC family of chloride transporting proteins.

Diffusely Increased Insertional Activity: “EMG Disease” or Asymptomatic Myotonia Congenita? A Report of 2 Cases

The term "EMG disease" is used by some to describe the unexpected finding of diffusely increased insertional activity on needle electromyography in an otherwise asymptomatic person. The cause is unknown, but it has been hypothesized that these patients actually have a subclinical myotonic disorder. We describe 2 patients with diffusely increased insertional activity on electromyography who had mutations of the CLCN1 gene associated with myotonia congenita. Neither patient had symptoms or reproducible signs of this disorder. We propose that asymptomatic patients with CLCN1 mutations may at least partially account for the EMG disease phenotype.

The use of simvastatin in rabbit posterolateral lumbar intertransverse process spine fusion

BACKGROUND CONTEXT

There has been recent enthusiasm regarding the potential positive effects of statins on bone. Statins vary in their ability to influence bone activity. Simvastatin has been shown in experimental models to stimulate bone acting growth factors and enhance bone formation.

PURPOSE

The potential efficacy of Simvastatin in enhancing spinal fusion was evaluated in a rabbit posterolateral intertransverse process fusion model.

STUDY DESIGN/SETTING

Posterior lumbar intertransverse process spinal fusion performed on New Zealand White rabbits. PATIENT/STUDY SAMPLE: 44 New Zealand White rabbits.

OUTCOME MEASURES

Spinal fusion as determined by manual palpation testing and fine detail radiography. Bone fusion mass volume and density as determined by CT scan imaging.

METHODS

Forty-four New Zealand White rabbits underwent posterolateral intertransverse process spine fusion using autogenous iliac crest bone graft. Simvastatin was administered orally in 20 animals and the serum lipid profile quantified in test and control animals. The animals were euthanized 9 weeks following index surgery and the lumbar spine was harvested. Spinal fusion was determined by manual palpation testing and fine detail radiography. The volume and density of the bone fusion mass was quantified by computed tomography.

RESULTS

Drug treatment for 9 weeks caused a reduction in serum lipid biochemical markers when compared with controls. The spinal fusion rate, as judged by manual palpation testing (13.0% control group, 16.6% Simvastatin group) and fine detail radiography, was not significantly different comparing treatment with control animals. Accordant with the assessment of spinal fusion, there was no statistically significant effect on the volume of the fusion mass (1,224.7+/-98.7 mm(3) in the control group and 1,075.9+/-66.3 mm(3) in the Simvastatin group), the density of bone in the lumbar spine or that in the formed fusion mass.

CONCLUSIONS

Systemic use of Simvastatin caused a reduction in lipid biochemical parameters in treated animals. Successful spinal fusion as judged by manual palpation testing and fine detail radiography was not significantly different in treated versus untreated animals. The bone volume density of the formed fusion mass was not significantly different in treated versus untreated animals. There did not appear to be a significant advantage or disadvantage to the use of Simvastatin rabbit posterolateral spinal fusion. The potential positive effects of statins on bone require further study.

Complications of anaesthesia in neuromuscular disorders

The purpose of this review is to alert non-anaesthesiologists to the various complications from which patients with neuromuscular disorders and those susceptible to malignant hyperthermia can suffer during anaesthesia. The patient's outcome correlates with the quality of consultation between anaesthesiologists, surgeons, neurologists and cardiologists. Special precautions must be taken, since many anaesthetics and muscle relaxants can aggravate the clinical features or trigger life-threatening reactions. Complications frequently occur in these patients, although anaesthetic procedures have become safer by the reduced administration of suxamethonium and the use of total intravenous anaesthesia, new volatile anaesthetics and non-depolarising relaxants. This review provides a synopsis of pre-operative anaesthetic considerations and adverse drug effects on skeletal, cardiac and smooth muscle tissue. It describes the pathogenetic aspects of typical complications and introduces anaesthetic procedures for the various neuromuscular disorders, including regional anaesthesia for patients in whom a restriction of respiratory and/or cardiac function is predicted.

Statins activate the mitochondrial pathway of apoptosis in human lymphoblasts and myeloma cells

Although statins are lipid-lowering drugs that block cholesterol biosynthesis, they exert immunomodulatory, anti-inflammatory, anti-angiogenic and anti-proliferative functions by reducing the isoprenylation of proteins involved in cell signal transduction such as Ras and RhoA. In this study, we provide evidence that several natural (lovastatin, simvastatin and pravastatin) and synthetic (cerivastatin and atorvastatin) statins exert a cytotoxic effect on human T, B and myeloma tumor cells by promoting their apoptosis. Dissimilar susceptibility to apoptosis has been detected in these lines, presumably in relation to the altered expression of proteins involved in the regulation of cellular signals. Cerivastatin promptly activated the cell death even in doxorubicin resistant cell lines such as MCC-2, whereas pravastatin, a hydrophilic compound, failed to induce any effect on either proliferation or apoptosis. The statin-induced apoptotic pathway in these cell lines was presumably regulated by altered prenylation of either Ras or RhoA, as measured by the defective membrane localization of these small GTPases. In addition the cell proliferation was rescued by both farnesylpyrophosphate (FPP) and geranyl-geranylpyrophosphate (GGPP), whereas no effect was obtained with squalene, a direct precursor of cholesterol. Statins primed apoptosis through its intrinsic pathway involving the mitochondria. In fact, we observed the reduction of mitochondrial membrane potential and the cytosolic release of the second mitochondria-derived activator of caspases (Smac/DIABLO). The apoptotic pathway was caspase-dependent since caspases 9, 3 and 8 were efficiently activated. These results support the potential use of statins in association with conventional treatment as apoptosis-triggering agents in these tumors.

Molecular clues into the pathogenesis of statin-mediated muscle toxicity

The pathophysiology of statin-mediated muscle dysfunction is poorly defined. Reductions in skeletal muscle membrane cholesterol were initially thought to account for the range of myopathic reactions, e.g., myalgia, elevated serum creatine kinase, or rhabdomyolysis. This assumption however, does not consider a potential role of the isoprenoids in the pathophysiology of statin myopathy. The observation that derangements in mevalonate kinase (MK), but not more distal enzymes of cholesterologenesis, are associated with a skeletal myopathy suggests a critical role for the isoprenoids in the maintenance of muscle. Statins also deplete the isoprenoid pool by inhibiting the enzyme, beta-hydroxy-beta-methylglutaryl coenzyme A reductase, which is upstream of MK. Identifying candidate proteins that are both dependent on isoprenoid-mediated modification and associated with muscle disease, when genetically mutated, offers further insight into potential mechanisms of statin myopathy. For example, lamin A/C, selenoprotein N, alpha- and beta-dystroglycan, and cytoskeletal G-proteins all require isoprenylation for optimal function. Understanding the pleiotropic effects of protein prenylation, and the potential consequences of a generalized insufficiency of this form of protein modification, may help clarify the molecular pathogenesis of statin myopathy.

Current overview of statin-induced myopathy

Statins are an efficacious and well-tolerated class of lipid-altering agents that have been shown to reduce the risk of initial and recurrent cardiovascular events. However, cerivastatin was withdrawn from the world market because of its potential for severe myotoxic effects. Since the benefits of statin treatment outweigh the small risk of adverse events, statins remain the first-line therapy for lipid lowering and preventing atherosclerotic cardiovascular diseases. The risk of myopathy may be minimized with the appropriate choice of agent and by identifying patients at risk of myotoxic effects. Elderly or female patients, or those with concomitant medications or impaired metabolic processes, may be at increased risk and should be monitored closely. The risk of myopathy may also be inferred from the pharmacologic and pharmacokinetic properties of the statin used. Since myotoxic events are more frequent at higher doses, statins that are effective in reducing cholesterol levels and helping patients to reach target levels at start doses may be useful. The lipophilicity of a statin and its potential for drug-drug interactions may also help to determine the likelihood of muscular effects. Drug-drug interactions may be avoided by selecting a statin that does not share the same metabolic pathway.

Effects of HMG-CoA reductase inhibitors on skeletal muscle: are all statins the same?

The 3-hydroxy-3-methyl coenzyme A (HMG-CoA) reductase inhibitors or statins, specifically inhibit the enzyme HMG-CoA in the liver, thereby inhibiting the rate limiting step in cholesterol biosynthesis and so reducing plasma cholesterol levels. Numerous studies have consistently demonstrated that cholesterol lowering with statin therapy reduces morbidity and mortality from coronary heart disease, whilst recent evidence has demonstrated that benefits of statin therapy may also extend into stroke prevention. Since hypercholesterolaemia is a chronic condition, the long-term safety and tolerability of these agents is an important issue. Numerous large-scale clinical trials have consistently demonstrated a positive safety and tolerability profile for statins. Hepatic, renal and muscular systems are rarely affected during statin therapy, with adverse reactions involving skeletal muscle being the most common, ranging from mild myopathy to myositis and occasionally to rhabdomyolysis and death. Postmarketing data supports the positive safety and tolerability profile of statins, with an overall adverse event frequency of less than 0.5% and a myotoxicity event rate of less than 0.1%. The recent withdrawal of cerivastatin from the world market due to deaths from rhabdomyolysis has, however, focused attention on the risk of adverse events and in particular myotoxicity associated with statins. Indeed, initial clinical trial data supports postmarketing data, demonstrating a higher incidence of myotoxicity associated with cerivastatin, particularly when used in combination with fibrates. The potential mechanisms underlying statin-induced myotoxicity are complex with no clear consensus of opinion. Candidate mechanisms include intracellular depletion of essential metabolites and destabilisation of cell membranes, resulting in increased cytotoxicity. Cytochrome P450 3A4 is the main isoenzyme involved in statin metabolism. Reduced activity of this enzyme due to either reduced expression or inhibition by other drugs prescribed concomitantly such as cyclosporin or itraconazole may increase drug bioavailability and the risk of myotoxicity. Such factors may partly account for the interindividual variability in susceptibility to statin-induced myotoxicity, although other as of yet unclarified, genetic factors may also be involved. The risk of rhabdomyolysis is increased with combination fibrate-statin therapy, with initial evidence suggesting that gemfibrozil-statin combination may particularly increase the risk of myotoxicity, with pharmacodynamic as well as pharmacokinetic mechanisms being involved.

Colchicine-induced acute myopathy in a patient with concomitant use of simvastatin

Colchicine and 3-hydroxy-3-methy-glutaryl coenzyme A (HMG-CoA) reductase inhibitors are well known to cause myopathy. Myotoxicity is dose-dependent in both drugs; therefore, the onset of symptoms usually takes months or years. We report the case of a patient with chronic renal failure who had been taking simvastatin for 2 years and developed acute weakness 2 weeks after the start of treatment with colchicines for recurrent gout. The electromyography and elevated muscle enzymes indicated that his symptoms were caused by myopathy. When this patient stopped taking both drugs, his weakness resolved rapidly. Acute myopathy induced by combination therapy with colchicines and simvastatin is rare. In patients with chronic renal failure, co-administration of colchicine with simvastatin may accelerate the onset of myopathy because CYP3A4 (part of cytochrome P450) is crucial in the breakdown of both drugs. When adding colchicine to a medication regimen that includes a HMG-CoA reductase inhibitor for patients with renal insufficiency, drugs that are metabolized outside the CYP3A4 system (e.g., fluvastatin and pravastatin) should be selected instead.

The myotoxicity of statins

PURPOSE OF REVIEW

Since hypercholesterolaemia is a chronic condition, the long-term safety of statins is important. Adverse reactions involving skeletal muscle are the most common (reported incidence 1-7%). The recent withdrawal of cerivastatin because of deaths from rhabdomyolysis, of which 25% were related to gemfibrozil-cerivastatin combination therapy, has focused attention on myotoxicity associated with statins and in particular with statin-fibrate combinations. We review the safety profiles of the individual statins, and discuss the mechanisms that may account for myotoxicity associated with statins and these agents and how these may relate to the different myotoxic potential of individual agents.

RECENT FINDINGS

The statins, particularly the first-generation agents, have been well evaluated from the perspective of safety and efficacy. Cerivastatin was associated with a 10-fold higher incidence of myotoxicity than any other statin, suggesting that there may be differences in myotoxic potential between agents. Statin-associated myotoxicity is complex, involving effects on cell membrane structure and function, mitochondrial dysfunction and impaired myocyte duplication. Potential differences in myotoxicity between agents may relate to the physicochemical, pharmacokinetic and pharmacodynamic properties of individual drugs. The aetiology of myotoxicity associated with statin-fibrate combination therapy is complex and multifactorial, with recent studies suggesting that there may be differences in myotoxic potential between individual fibrates.

SUMMARY

Recent evidence suggests that there may be differences in myotoxic potential between individual agents. Thus, the choice of hypolipidaemic therapy needs to be based not only on outcome evidence and cost-effectiveness analysis, but also on safety considerations for individual agents.

Myopathy Associated With HMG-CoA Reductase Inhibitors (Statins): A Series of 10 Patients and Review of the Literature

OBJECTIVE

To examine the clinical profile of patients with myotoxicity due to HMG-CoA reductase inhibitors and the pathological features in the biopsies.

DESIGN

All patients receiving HMG-CoA reductase inhibitors who underwent muscle biopsy at the State Neuropathology Service, Melbourne, from October 2000 to September 2001 were identified, and clinical questionnaires were completed by the referring doctor.

RESULTS

Ten patients, including 4 males and 6 females, aged 50 to 76 years (median, 69.5 y), were identified. Six patients were diabetic and one was severely hypothyroid. Statins included simvastatin in 5, atorvastatin in 4, and cerivastatin in 1. Six patients had either a recent doubling in dosage of statin or change to another statin. Six patients were also taking one or more drugs with known interaction with HMG-CoA reductase inhibitors (gemfibrozil, ketoconazole, calcium channel antagonists, dothiepin, celecoxib, amiodarone). All patients had weakness, 8 had myalgias, and 3 had myoglobinuria. Peak creatine kinase (CK) elevation ranged from 1100 to 160,000 U/L (median, 16,000 U/L). Following cessation of statins, resolution of symptoms and normalization of CK levels were noted in all within a few months. All muscle biopsies showed necrotizing myopathy with minimal inflammation in 4 (40%). Histochemical studies did not suggest mitochondrial cytopathy.

CONCLUSION

Myotoxicity due to HMG-CoA reductase inhibitors commonly occurs in patients taking concomitant medication known to interact with metabolism of these agents, such as gemfibrozil or ketoconazole, or with an increase in dose. In addition, elderly patients with obesity, diabetes mellitus, and hypothyroidism appear to be at increased risk of developing myotoxicity.

Inherited muscle and brain channelopathies

In the past 5 years, advances in the complementary fields of neurogenetics and cellular electrophysiology have resulted in an explosion of knowledge about a group of disorders now known as the neurological channelopathies. These advances have resulted in more accurate DNA-based diagnosis and have increased our understanding of cellular pathophysiology. This is leading to more tailored therapies for patients with these disorders.

HMG-CoA reductase inhibitors and myotoxicity

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors specifically inhibit HMG-CoA reductase in the liver, thereby inhibiting the biosynthesis of cholesterol. These drugs significantly reduce plasma cholesterol level and long term treatment reduces morbidity and mortality associated with coronary heart disease. The tolerability of these drugs during long term administration is an important issue. Adverse reactions involving skeletal muscle are not uncommon, and sometimes serious adverse reactions involving skeletal muscle such as myopathy and rhabdomyolysis may occur, requiring discontinuation of the drug. Occasionally, arthralgia, alone or in association with myalgia, has been reported. In this article we review scientific data provided via Medline, adverse drug reaction case reports from the Swedish Drug Information System (SWEDIS) and the World Health Organization's International Drug Information System (INTDIS) database, focusing on HMG-CoA reductase inhibitor-related musculoskeletal system events. Cytochrome P450 (CYP) 3A4 is the main isoenzyme involved in the metabolic transformation of HMG-CoA reductase inhibitors. Individuals with both low hepatic and low gastrointestinal tract levels of CYP3A4 expression may be at in increased risk of myotoxicity due to potentially higher HMG-CoA reductase inhibitor plasma concentrations. The reported incidence of myotoxic reactions in patients treated with this drug class varies from 1 to 7% and varies between different agents. The risk of these serious adverse reactions is dose-dependent and may increase when HMG-CoA reductase inhibitors are prescribed concomitantly with drugs that inhibit their metabolism, such as itraconazole, cyclosporin, erythromycin and nefazodone. Electrolyte disturbances, infections, major trauma, hypoxia as well as drugs of abuse may increase the risk of myotoxicity. It is important that the potentially serious adverse reactions are recognised and correctly diagnosed so that the HMG-CoA reductase inhibitor may at once be withdrawn to prevent further muscular damage.

The symptoms of chronic fatigue syndrome are related to abnormal ion channel function

The pathogenesis of chronic fatigue syndrome (CFS) is unknown but one of the most characteristic features of the illness is fluctuation in symptoms which can be induced by physical and/or mental stress. Other conditions in which fluctuating fatigue occurs are caused by abnormal ion channels in the cell membrane. These include genetically determined channelopathies, e.g. hypokalemic periodic paralysis, episodic ataxia type 2 and acquired conditions such as neuromyotonia, myasthenic syndromes, multiple sclerosis and inflammatory demyelinating polyneuropathies. Our hypothesis is that abnormal ion channel function underlies the symptoms of CFS and this is supported also by the finding of abnormal cardiac-thallium201 SPECT scans in CFS, similar to that found in syndrome X, another disorder of ion channels. CFS and syndrome X can have identical clinical symptoms. CFS may begin after exposure to specific toxins which are known to produce abnormal sodium ion channels. Finally, in CFS, increased resting energy expenditure (REE) occurs, a state influenced by transmembrane ion transport. The hypothesis that ion channels are abnormal in CFS may help to explain the fluctuating fatigue and other symptoms.

Role of tyrosine phosphorylation of phospholipase C gamma1 in the signaling pathway of HMG-CoA reductase inhibitor-induced cell death of L6 myoblasts

Our previous studies have shown that the HMG-CoA reductase (HCR) inhibitor (HCRI), simvastatin, kills L6 myoblasts by involving Ca2+ mobilization from the Ca2+ pool in the cells but not by influx from extracellular space. More recently, we found that HCRI induced tyrosine phosphorylation of several cellular proteins, followed by apoptotic cell death of L6 myoblasts. The present study was aimed to elucidate the molecular target(s) of these tyrosine phosphorylations induced by HCRI and demonstrated that simvastatin induces tyrosine phosphorylation of phospholipase C (PLC) gamma1. This tyrosine phosphorylation of PLC-gamma1 caused the increment of the intracellular inositol triphosphate (IP3) levels in L6 myoblasts. Pretreatment of the cells with herbimycin A, a specific inhibitor of protein tyrosine kinase, inhibited a simvastatin-induced increase in IP3 level in the cells as well as tyrosine phosphorylation of PLC-gamma1. Interestingly, pretreatment of the cells with U-73122, a specific inhibitor of PLC, prevented simvastatin-induced cell death. Thus, these results strongly suggest that simvastatin-induced tyrosine phosphorylation of PLC-gamma1 plays, at least in part, an important role for the development of simvastatin-induced cell death.

Involvement of tyrosine phosphorylation in HMG-CoA reductase inhibitor-induced cell death in L6 myoblasts

Our previous studies have shown that the HMG-CoA reductase (HCR) inhibitor (HCRI), simvastatin, causes myopathy in rabbits and kills L6 myoblasts. The present study was designed to elucidate the molecular mechanism of HCRI-induced cell death. We have demonstrated that simvastatin induces the tyrosine phosphorylation of several cellular proteins within 10 min. These phosphorylations were followed by apoptosis, as evidenced by the occurrence of internucleosomal DNA fragmentation and by morphological changes detected with Nomarski optics. Simvastatin-induced cell death was prevented by tyrosine kinase inhibitors. The MTT assay revealed that the addition of mevalonic acid into the culture medium partially inhibited simvastatin-induced cell death. Thus, these results suggested that protein tyrosine phosphorylation might play an important role in the intracellular signal transduction pathway mediating the HCRI-induced death of myoblasts.

Myopathy induced by HMG-CoA reductase inhibitors in rabbits: a pathological, electrophysiological, and biochemical study

A combination of electrophysiological, pathological, and biochemical studies were performed in myopathy induced by 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors. Simvastatin (a lipophilic inhibitor) or pravastatin (a hydrophilic inhibitor) were administered by gavage to rabbits. In Group I (simvastatin-treated group, 50 mg/kg/day for 4 weeks), four rabbits showed muscle necrosis and high serum creatine kinase (CK) levels, and all six rabbits showed electrical myotonia. In Group II (pravastatin-treated group, 100 mg/kg/day for 4 weeks), no rabbit showed either condition. In Group III (pravastatin-treated group, 200 mg/kg/day for 3 weeks plus 300 mg/kg/day for 3 weeks), one rabbit showed muscle necrosis and high serum CK level and two rabbits showed electrical myotonia. The pathological findings were muscle fiber necrosis and degeneration with increased acid phosphatase activity by light microscopy, autophagic vacuoles and mitochondrial swelling, and disruption and hypercontraction of myofibrils by electron microscopy. Ubiquinone content decreased in skeletal muscle by 22 to 36% in Group I, by 18 to 52% in Group II, and by 49 to 72% in Group III. However, mitochondrial enzyme activities of respiratory chain were normal in all groups. These results indicate that myopathy was not induced by a secondary dysfunction of mitochondrial respiration due to low ubiquinone levels.

Myotonia in colchicine myoneuropathy

Colchicine may induce a myoneuropathy in patients with renal insufficiency. To date, myotonia has not been described in this disorder. We recently studied 4 patients treated with routine doses of colchicine who, in the setting of renal insufficiency, developed a severe myoneuropathy characterized by prominent myotonic discharges on electromyography. In addition, 1 of the 4 patients had profound clinical myotonia. In the 3 patients in whom biopsies were performed, marked myopathic change with intracytoplasmic vacuolization was identified. All 4 patients improved rapidly with discontinuation of the medication. The patient in whom electrophysiologic studies were repeated had a complete resolution of the myotonic discharges. Colchicine myoneuropathy can present with prominent clinical and electrophysiologic myotonia that resolves completely with discontinuation of the medication.

Subchronic toxicity of atorvastatin, a hydroxymethylglutaryl-coenzyme A reductase inhibitor, in beagle dogs

The toxicity of atorvastatin (AT), an inhibitor of hydroxymethylglutaryl-coenzyme A reductase (HMG), was evaluated in beagle dogs. In 4 studies [2-wk rising dose (daily increasing doses for 1 wk; maintenance for 1 wk), 12-wk rising dose (daily dosing with weekly increases in dose), 2-wk toxicity (daily dosing for 2 wk; 3 dose levels), 13-wk toxicity (daily dosing for 13 wk; 3 dose levels)], dogs received up to 400 mg/kg orally. Doses of 180 mg/kg induced moribundity, necessitating euthanasia. Weight losses up to 26% were seen at doses > or = 150 mg/kg. Decreases in cholesterol levels were dose-related. Alanine and/or aspartate aminotransferase were increased at doses > or = 80 mg/kg; alkaline phosphatase was increased at doses > or = 150 mg/kg. Histopathologic findings were seen at > or = 150 mg/kg and included hepatocellular eosinophilia related to increased smooth endoplasmic reticulum and cholangiohepatitis and cholecystitis at 150 mg/kg in the 2-wk toxicity study; hepatocellular degeneration, centrilobular bridging, cholecystitis, hemorrhage in gallbladder and brain, demyelination of optic nerve, and skeletal muscle necrosis at > or = 280 mg/kg in the 12-wk rising dose study; and erosion and hemorrhage in large intestine, hepatocellular degeneration and necrosis, and inflammation and necrosis of gallbladder epithelium at 320 mg/kg in the 2-wk rising dose study. Doses up to 80 mg/kg for 13 wk did not induce histopathologic lesions in examined organs. AT effectively lowered serum cholesterol in normal lipidemic dogs. Toxicity at AT in dogs was similar to that with other inhibitors of HMG except that lenticular changes were not seen, significant hepatic, testicular, or neurological toxicity was associated only with high doses at AT, and skeletal muscle changes similar to those described in rats and rabbits were identified.

Effects of HMG-CoA reductase inhibitors on growth and differentiation of cultured rat skeletal muscle cells

HMG-CoA reductase inhibitors have been associated with skeletal muscle myopathy, ranging from asymptomatic elevations of serum creatine kinase (CK) activity to rhabdomyolysis. In this study, we assessed the effects of addition of different concentrations of simvastatin and pravastatin on growth and differentiation of cultured primary rat skeletal muscle cells. Protein concentrations, CK activity and percentage CK-MM, which is a parameter for maturation, were determined. Effects were generally stronger if inhibitors were added to both growth and differentiation medium rather than only to differentiation medium. Addition of 25 microM pravastatin caused only a decrease of CK activity. Addition of 1-5 microM simvastatin resulted in a decrease of protein concentration, CK activity and percentage CK-MM, whereas 25 microM simvastatin resulted in cell death. Addition of mevalonic acid or cholesterol could not prevent the effects of 1 microM simvastatin. In addition, 1 microM simvastatin did not influence the cholesterol and phospholipid content of the cells. Superfusion of cultured cells with simvastatin concentrations of 10 microM and higher caused a transient increase of the cytoplasmic calcium concentration followed by an apparent second rise and cell puncture. The results indicate that HMG-CoA reductase inhibitors may affect skeletal muscle cell regeneration in vivo by a direct toxic effect on growth and differentiation.

Cholesterol synthesis inhibitors in cholesterol gallstone disease

Cholesterol synthesis inhibitors (HMG-CoA Reductase Inhibitors) are reported to decrease cholesterol saturation index of duodenal bile in hypercholesterolaemic subjects. The dissolution of gallstones in animals on treatment with these drugs created expectations of a therapeutical role for these drugs in cholesterol gallstone disease. However, in prospective studies with these drugs in humans, no effect on number and size of cholesterol gallstones was observed. This is likely the result of the fact that not just biliary secretion of cholesterol is decreased during treatment with these drugs in cholesterol gallstone disease, but phospholipids and bile salts as well. As a consequence, nucleation time of cholesterol crystals in gallbladder bile is not influenced by these drugs. Another important determinant in cholesterol gallstone disease, e.g. gallbladder motility, is not influenced by HMG-CoA reductase inhibitors. Although these drugs and their metabolites are secreted into the bile, they do not influence biliary lithogenicity. In conclusion, there seems to be no therapeutic role for HMG-CoA reductase inhibitors in the treatment of cholesterol gallstone disease, although no negative effects on determinants of cholesterol gallstone formation during treatment with these drugs are observed either.