Decreased skeletal muscle mitochondrial DNA in patients with statin-induced myopathy

The Role of Mitochondria in Statin-Induced Myopathy

Statins represent the primary therapy for combatting hypercholesterolemia and reducing mortality from cardiovascular events. Despite their pleiotropic effects in lowering cholesterol synthesis, circulating cholesterol, as well as reducing the risk of other systemic diseases, statins have adverse events in a small, but significant, population of treated patients. The most prominent of these adverse effects is statin-induced myopathy, which lacks precise definition but is characterised by elevations in the muscle enzyme creatine kinase alongside musculoskeletal complaints, including pain, weakness and fatigue. The exact aetiology of statin-induced myopathy remains to be elucidated, although impaired mitochondrial function is thought to be an important underlying cause. This may result from or be the consequence of several factors including statin-induced inhibition of coenzyme Q10 (CoQ10) biosynthesis, impaired Ca2+ signalling and modified reactive oxygen species (ROS) generation. The purpose of this review article is to provide an update on the information available linking statin therapy with mitochondrial dysfunction and to outline any mechanistic insights, which may be beneficial in the future treatment of myopathic adverse events.

Fluvastatin-induced myofibrillar damage is associated with elevated ROS, and impaired fatty acid oxidation, and is preceded by mitochondrial morphological changes

Previously, we showed that fluvastatin treatment induces myofibrillar damage and mitochondrial phenotypes in the skeletal muscles of Drosophila. However, the sequential occurrence of mitochondrial phenotypes and myofibril damage remains elusive. To address this, we treated flies with fluvastatin for two and five days and examined their thorax flight muscles using confocal microscopy. In the two-day fluvastatin group, compared to the control, thorax flight muscles exhibited mitochondrial morphological changes, including fragmentation, rounding up and reduced content, while myofibrils remained organized in parallel. In the five-day fluvastatin treatment, not only did mitochondrial morphological changes become more pronounced, but myofibrils became severely disorganized with significantly increased thickness and spacing, along with myofilament abnormalities, suggesting myofibril damage. These findings suggest that fluvastatin-induced mitochondrial changes precede myofibril damage. Moreover, in the five-day fluvastatin group, the mitochondria demonstrated elevated H2O2 and impaired fatty acid oxidation compared to the control group, indicating potential mitochondrial dysfunction. Surprisingly, knocking down Hmgcr (Drosophila homolog of HMGCR) showed normal mitochondrial respiration in all parameters compared to controls or five-day fluvastatin treatment, which suggests that fluvastatin-induced mitochondrial dysfunction might be independent of Hmgcr inhibition. These results provide insights into the sequential occurrence of mitochondria and myofibril damage in statin-induced myopathy for future studies.

Differential effects of OATP2B1 on statin accumulation and toxicity in a beta cell model

An increased risk of new-onset diabetes mellitus has been recently reported for statin therapy, and experimental studies have shown reduced glucose-stimulated insulin secretion (GSIS) and mitochondrial dysfunction in beta cells with effects differing among agents. Organic anion transporting polypeptide (OATP) 2B1 contributes to hepatic uptake of rosuvastatin, atorvastatin and pravastatin, three known substrates. Since OATP2B1 is present in beta cells of the human pancreas, we investigated if OATP2B1 facilitates the local accumulation of statins in a rat beta cell model INS-1 832/13 (INS-1) thereby amplifying statin-induced toxicity. OATP2B1 overexpression in INS-1 cells via adenoviral transduction showed 2.5-, 1.8- and 1.4-fold higher cellular retention of rosuvastatin, atorvastatin and pravastatin, respectively, relative to LacZ control, while absolute intracellular concentration was about twice as high for the lipophilic atorvastatin compared to the more hydrophilic rosuvastatin and pravastatin. After 24 h statin treatment at high concentrations, OATP2B1 enhanced statin toxicity involving activation of intrinsic apoptosis (caspase 3/7 activation) and mitochondrial dysfunction (NADH dehydrogenase activity) following rosuvastatin and atorvastatin, which was partly reversed by isoprenoids. OATP2B1 had no effect on statin-induced reduction in GSIS, mitochondrial electron transport chain complex expression or caspase 9 activation. We confirmed a dose-dependent reduction in insulin secretion by rosuvastatin and atorvastatin in native INS-1 with a modest change in cellular ATP. Collectively, our results indicate a role of OATP2B1, which is abundant in human beta cells, in statin accumulation and statin-induced toxicity but not insulin secretion of rosuvastatin and atorvastatin in INS-1 cells.

Structural and functional impairments of skeletal muscle in patients with postacute sequelae of SARS-CoV-2 infection

Following acute coronavirus disease 2019 (COVID-19), a substantial proportion of patients showed symptoms and sequelae for several months, namely the postacute sequelae of COVID-19 (PASC) syndrome. Major phenomena are exercise intolerance, muscle weakness, and fatigue. We aimed to investigate the physiopathology of exercise intolerance in patients with PASC syndrome by structural and functional analyses of skeletal muscle. At least 3 mo after infection, nonhospitalized patients with PASC (n = 11, age: 54 ± 11 yr; PASC) and patients without long-term symptoms (n = 12, age: 49 ± 9 yr; CTRL) visited the laboratory on four nonconsecutive days. Spirometry, lung diffusion capacity, and quality of life were assessed at rest. A cardiopulmonary incremental exercise test was performed. Oxygen consumption (V̇o2) kinetics were determined by moderate-intensity exercises. Muscle oxidative capacity (k) was assessed by near-infrared spectroscopy. Histochemical analysis, O2 flux (JO2) by high-resolution respirometry, and quantification of key molecular markers of mitochondrial biogenesis and dynamics were performed in vastus lateralis biopsies. Pulmonary and cardiac functions were within normal range in all patients. V̇o2peak was lower in PASC than CTRL (24.7 ± 5.0 vs. 32.9 ± 7.4 mL·min-1·kg-1, respectively, P < 0.05). V̇o2 kinetics was slower in PASC than CTRL (41 ± 12 vs. 30 ± 9 s-1, P < 0.05). k was lower in PASC than CTRL (1.54 ± 0.49 vs. 2.07 ± 0.51 min-1, P < 0.05). Citrate synthase, peroxisome proliferator-activated receptor-γ coactivator (PGC)1α, and JO2 for mitochondrial complex II were significantly lower in PASC vs. CTRL (all P values <0.05). In our cohort of patients with PASC, we showed limited exercise tolerance mainly due to "peripheral" determinants. Substantial reductions were observed for biomarkers of mitochondrial function, content, and biogenesis. PASC syndrome, therefore, appears to negatively impact skeletal muscle function, although the disease is a heterogeneous condition.NEW & NOTEWORTHY Several months after mild acute SARS-CoV-2 infection, a substantial proportion of patients present persisting, and often debilitating, symptoms and sequelae. These patients show reduced quality of life due to exercise intolerance, muscle weakness, and fatigue. The present study supports the hypothesis that "peripheral" impairments at skeletal muscle level, namely, reduced mitochondrial function and markers of mitochondrial biogenesis, are major determinants of exercise intolerance and fatigue, "central" phenomena at respiratory, and cardiac level being less relevant.

TOMM40 and TOMM22 of the Translocase Outer Mitochondrial Membrane Complex rescue statin-impaired mitochondrial dynamics, morphology, and mitophagy in skeletal myotubes

Background

Statins are the drugs most commonly used for lowering plasma low-density lipoprotein (LDL) cholesterol levels and reducing cardiovascular disease risk. Although generally well tolerated, statins can induce myopathy, a major cause of non-adherence to treatment. Impaired mitochondrial function has been implicated as a cause of statin-induced myopathy, but the underlying mechanism remains unclear. We have shown that simvastatin downregulates transcription of TOMM40 and TOMM22 , genes that encode major subunits of the translocase of outer mitochondrial membrane (TOM) complex which is responsible for importing nuclear-encoded proteins and maintaining mitochondrial function. We therefore investigated the role of TOMM40 and TOMM22 in mediating statin effects on mitochondrial function, dynamics, and mitophagy.

Methods

Cellular and biochemical assays and transmission electron microscopy were used to investigate effects of simvastatin and TOMM40 and TOMM22 expression on measures of mitochondrial function and dynamics in C2C12 and primary human skeletal cell myotubes.

Results

Knockdown of TOMM40 and TOMM22 in skeletal cell myotubes impaired mitochondrial oxidative function, increased production of mitochondrial superoxide, reduced mitochondrial cholesterol and CoQ levels, disrupted mitochondrial dynamics and morphology, and increased mitophagy, with similar effects resulting from simvastatin treatment. Overexpression of TOMM40 and TOMM22 in simvastatin-treated muscle cells rescued statin effects on mitochondrial dynamics, but not on mitochondrial function or cholesterol and CoQ levels. Moreover, overexpression of these genes resulted in an increase in number and density of cellular mitochondria.

Conclusion

These results confirm that TOMM40 and TOMM22 are central in regulating mitochondrial homeostasis and demonstrate that downregulation of these genes by statin treatment mediates disruption of mitochondrial dynamics, morphology, and mitophagy, effects that may contribute to statin-induced myopathy.

GRAPHICAL ABSTRACT

Mitochondrial Genetic Background May Impact Statins Side Effects and Atherosclerosis Development in Familial Hypercholesterolemia

Heredity of familial hypercholesterolemia (FH) can present as a dominant monogenic disorder of polygenic origin or with no known genetic cause. In addition, the variability of the symptoms among individuals or within the same families evidence the potential contribution of additional factors than monogenic mutations that could modulate the development and severity of the disease. In addition, statins, the lipid-lowering drugs which constitute the first-line therapy for the disease, cause associated muscular symptoms in a certain number of individuals. Here, we analyze the evidence of the mitochondrial genetic variation with a special emphasis on the role of CoQ₁₀ to explain this variability found in both disease symptoms and statins side effects. We propose to use mtDNA variants and copy numbers as markers for the cardiovascular disease development of FH patients and to predict potential statin secondary effects and explore new mechanisms to identify new markers of disease or implement personalized medicine strategies for FH therapy.

Cholesterol Management in Neurology: Time for Revised Strategies?

Statin therapy has been extensively evaluated and shown to reduce the incidence of new or recurrent vascular events, ischemic stroke included. As a consequence, each published guideline pushes for lower low-density cholesterol levels in the population at large, recommending increased statin doses and/or adding new cholesterol-lowering molecules. Neurologists find it sometimes difficult to apply these guidelines, having to confront situations such as (1) ischemic strokes, mainly cardioembolic ones, in patients with already low LDL-cholesterol levels; (2) myasthenic patients, whose lifespan has been extended by available treatment, and whose age and cholesterol levels put them at risk for ischemic stroke; (3) patients with myotonic dystrophy, whose disease often associates diabetes mellitus and heart conduction defects, and in whom blood cholesterol management is also not settled. As such, further trials are needed to address these issues.

Coenzyme Q10 Supplementation in Statin Treated Patients: A Double-Blinded Randomized Placebo-Controlled Trial

Myalgia and new-onset of type 2 diabetes have been associated with statin treatment, which both could be linked to reduced coenzyme Q10 (CoQ10) in skeletal muscle and impaired mitochondrial function. Supplementation with CoQ10 focusing on levels of CoQ10 in skeletal muscle and mitochondrial function has not been investigated in patients treated with statins. To investigate whether concomitant administration of CoQ10 with statins increases the muscle CoQ10 levels and improves the mitochondrial function, and if changes in muscle CoQ10 levels correlate with changes in the intensity of myalgia. 37 men and women in simvastatin therapy with and without myalgia were randomized to receive 400 mg CoQ10 daily or matched placebo tablets for eight weeks. Muscle CoQ10 levels, mitochondrial respiratory capacity, mitochondrial content (using citrate synthase activity as a biomarker), and production of reactive oxygen species were measured before and after CoQ10 supplementation, and intensity of myalgia was determined using the 10 cm visual analogue scale. Muscle CoQ10 content and mitochondrial function were unaltered by CoQ10 supplementation. Individual changes in muscle CoQ10 levels were not correlated with changes in intensity of myalgia. CoQ10 supplementation had no effect on muscle CoQ10 levels or mitochondrial function and did not affect symptoms of myalgia.

Mitochondrial DNA: Consensuses and Controversies

In the course of its short history, mitochondrial DNA (mtDNA) has made a long journey from obscurity to the forefront of research on major biological processes. mtDNA alterations have been found in all major disease groups, and their significance remains the subject of intense research. Despite remarkable progress, our understanding of the major aspects of mtDNA biology, such as its replication, damage, repair, transcription, maintenance, etc., is frustratingly limited. The path to better understanding mtDNA and its role in cells, however, remains torturous and not without errors, which sometimes leave a long trail of controversy behind them. This review aims to provide a brief summary of our current knowledge of mtDNA and highlight some of the controversies that require attention from the mitochondrial research community.

Quantification of mtDNA content in cultured cells by direct droplet digital PCR

Although alterations in cellular mitochondrial DNA (mtDNA) content have been linked to various pathological conditions, the mechanisms that govern mtDNA copy number (mtCN) control remain poorly understood. Moreover, techniques for mtDNA quantification do not allow for direct comparisons of absolute mtCNs between labs. Here we report the development of a direct droplet digital PCR technique for the determination of mtCNs in whole-cell lysates. Using this technique, we demonstrate that cellular mtDNA content can fluctuate in culture by as much as 50% and provide evidence for both cell proliferation-coupled and uncoupled mtDNA replication.

Effects of statins on mitochondrial pathways

Statins are a family of drugs that are used for treating hyperlipidaemia with a recognized capacity to prevent cardiovascular disease events. They inhibit β-hydroxy β-methylglutaryl-coenzyme A reductase, i.e. the rate-limiting enzyme in mevalonate pathway, reduce endogenous cholesterol synthesis, and increase low-density lipoprotein clearance by promoting low-density lipoprotein receptor expression mainly in the hepatocytes. Statins have pleiotropic effects including stabilization of atherosclerotic plaques, immunomodulation, anti-inflammatory properties, improvement of endothelial function, antioxidant, and anti-thrombotic action. Despite all beneficial effects, statins may elicit adverse reactions such as myopathy. Studies have shown that mitochondria play an important role in statin-induced myopathies. In this review, we aim to report the mechanisms of action of statins on mitochondrial function. Results have shown that statins have several effects on mitochondria including reduction of coenzyme Q10 level, inhibition of respiratory chain complexes, induction of mitochondrial apoptosis, dysregulation of Ca2+ metabolism, and carnitine palmitoyltransferase-2 expression. The use of statins has been associated with the onset of additional pathological conditions like diabetes and dementia as a result of interference with mitochondrial pathways by various mechanisms, such as reduction in mitochondrial oxidative phosphorylation, increase in oxidative stress, decrease in uncoupling protein 3 concentration, and interference in amyloid-β metabolism. Overall, data reported in this review suggest that statins may have major effects on mitochondrial function, and some of their adverse effects might be mediated through mitochondrial pathways.

Statins interfere with the attachment of S. cerevisiae mtDNA to the inner mitochondrial membrane

The 3-hydroxy-3-methylglutaryl-CoA reductase, a key enzyme of the mevalonate pathway for the synthesis of cholesterol in mammals (ergosterol in fungi), is inhibited by statins, a class of cholesterol lowering drugs. Indeed, statins are in a wide medical use, yet statins treatment could induce side effects as hepatotoxicity and myopathy in patients. We used Saccharomyces cerevisiae as a model to investigate the effects of statins on mitochondria. We demonstrate that statins are active in S.cerevisiae by lowering the ergosterol content in cells and interfering with the attachment of mitochondrial DNA to the inner mitochondrial membrane. Experiments on murine myoblasts confirmed these results in mammals. We propose that the instability of mitochondrial DNA is an early indirect target of statins.

Muscle Toxicity of Drugs: When Drugs Turn Physiology into Pathophysiology

Drugs are prescribed to manage or prevent symptoms and diseases, but may sometimes cause unexpected toxicity to muscles. The symptomatology and clinical manifestations of the myotoxic reaction can vary significantly between drugs and between patients on the same drug. This poses a challenge on how to recognize and prevent the occurrence of drug-induced muscle toxicity. The key to appropriate management of myotoxicity is prompt recognition that symptoms of patients may be drug related and to be aware that inter-individual differences in susceptibility to drug-induced toxicity exist. The most prevalent and well-documented drug class with unintended myotoxicity are the statins, but even today new classes of drugs with unintended myotoxicity are being discovered. This review will start off by explaining the principles of drug-induced myotoxicity and the different terminologies used to distinguish between grades of toxicity. The main part of the review will focus on the most important pathogenic mechanisms by which drugs can cause muscle toxicity, which will be exemplified by drugs with high risk of muscle toxicity. This will be done by providing information on key clinical and laboratory aspects, muscle electromyography patterns and biopsy results, and pathological mechanism and management for a specific drug from each pathogenic classification. In addition, rather new classes of drugs with unintended myotoxicity will be highlighted. Furthermore, we will explain why it is so difficult to diagnose drug-induced myotoxicity, and which tests can be used as a diagnostic aid. Lastly, a brief description will be given of how to manage and treat drug-induced myotoxicity.

Mitophagy protects against statin-mediated skeletal muscle toxicity

The deleterious effects of statins on skeletal muscle are well known, but the mechanism associated with these effects remains unresolved. Statins are associated with mitochondrial damage, which may contribute to muscle myopathy. Here we demonstrate that simvastatin induces mitophagy in skeletal muscle cells and hypothesized that attenuating this process by silencing the mitophagy adapter p62/sequestosome-1 (SQSTM1) might mitigate myotoxicity. Surprisingly, silencing p62/SQSTM1 in differentiated C2C12 muscle cells exacerbated rather than attenuated myotoxicity. This inhibition of mitophagy in the face of statin challenge correlated with increased release of cytochrome c to the cytosol, activation of caspase-3, and lactate dehydrogenase (LDH) release. Correspondingly, targeted knockdown of Parkin, a canonical E3 ubiquitin ligase important for mitophagy, mirrored the effects of p62/SQSTM1 silencing. To corroborate these findings in vivo, we treated Parkin knockout mice with simvastatin for 2 wk. In line with our findings in vitro, these mitophagy-compromised mice displayed reduced spontaneous activity, loss of grip strength, and increased circulating levels of muscle damage marker LDH. Our findings demonstrate that mitophagy is an important mechanism to resist statin-induced skeletal muscle damage.-Ramesh, M., Campos, J. C., Lee, P., Song, Y., Hernandez, G., Sin, J., Tucker, K. C., Saadaeijahromi, H., Gurney, M., Ferreira, J. C. B., Andres, A. M. Mitophagy protects against statin-mediated skeletal muscle toxicity.

Novel Phenotypes and Cardiac Involvement Associated With DNA2 Genetic Variants

Objectives: To report two novel DNA2 gene mutations causing early onset myopathy with cardiac involvement and late onset mitochondriopathy with rhabdomyolysis.

Methods: We performed detailed clinical, muscle histopathology and molecular studies including mitochondrial gene NGS analysis in two patients (Patient 1 and 2), a mother and her son, belonging to a Mexican family, and a third sporadic French patient.

Results: Patient 1 and 2 presented with an early onset myopathy associated with ptosis, velopharyngeal weakness, and cardiac involvement. Patient 3 presented rhabdomyolysis unmasking a mitochondrial disease characterized by a sensorineural hearing loss, ptosis, and lipomas. Muscle biopsies performed in all patients showed variable mitochondrial alterations. Patient 3 had multiple mtDNA deletion in his muscle. Genetic studies revealed a novel heterozygous frameshift mutation in DNA2 gene (c.2346delT p.Phe782Leufs^*3) in P1 and P2, and a novel heterozygous missense mutation in DNA2 gene (c.578T>C p.Leu193Ser) in the P3.

Conclusions: To date only few AD cases presenting either missense or truncating DNA2 variants have been reported. None of them presented with a cardiac involvement or rhabdomyolysis. Here we enlarge the genetic and phenotypic spectrum of DNA2-related mitochondrial disorders.

Statin Treatment Decreases Mitochondrial Respiration But Muscle Coenzyme Q10 Levels Are Unaltered: The LIFESTAT Study

BACKGROUND

Myalgia is a common adverse effect of statin therapy, but the underlying mechanism is unknown. Statins may reduce levels of coenzyme Q10 (CoQ10), which is an essential electron carrier in the mitochondrial electron transport system, thereby impairing mitochondrial respiratory function, potentially leading to myalgia.

OBJECTIVES

To investigate whether statin-induced myalgia is coupled to reduced intramuscular CoQ10 concentration and impaired mitochondrial respiratory function.

METHODS

Patients receiving simvastatin (i.e., statin) therapy (n = 64) were recruited, of whom 25 experienced myalgia (myalgic group) and 39 had no symptoms of myalgia (NS group). Another 20 had untreated high blood cholesterol levels (control group). Blood and muscle samples were obtained. Intramuscular CoQ10 concentration was measured, and mitochondrial respiratory function and reactive oxygen species (ROS) production were measured. Citrate synthase (CS) activity was used as a biomarker of mitochondrial content in skeletal muscle.

RESULTS

Intramuscular CoQ10 concentration was comparable among groups. Mitochondrial complex II-linked respiration was reduced in the statin-myalgic and -NS groups compared with the control group. When mitochondrial respiration was normalized to CS activity, respiration rate was higher in the myalgic group compared with the NS and control groups. Maximal ROS production was similar among groups.

CONCLUSION

Statin therapy appeared to impair mitochondrial complex-II-linked respiration, but the mitochondrial capacity for complex I+II-linked respiration remained intact. Myalgia was not coupled to reduced intramuscular CoQ10 levels. Intrinsic mitochondrial respiratory capacity was increased with statin-induced myalgia but not accompanied by increased ROS production.

Toxic myopathy with multiple deletions in mitochondrial DNA associated with long-term use of oral anti-viral drugs for hepatitis B: A case study

Oral nucleoside analogs (NAs) reduce hepatitis B virus (HBV) replication by inhibiting HBV DNA polymerase. However, NAs can also affect human mitochondrial DNA (mtDNA) polymerase, which can lead to mtDNA depletion (quantitative abnormality). Indeed, several mitochondrial myopathy cases have been reported in which a reduced mtDNA copy number was induced by oral NAs for hepatitis B. Herein, we report a case of toxic myopathy with multiple mtDNA deletions (qualitative abnormality) associated with long-term use of NAs for hepatitis B. A 68-year-old woman, who underwent long-term treatment with lamivudine and adefovir for chronic hepatitis B, developed proximal muscle weakness in the four extremities. Neurological examination showed mild proximal muscle weakness and atrophy in the four extremities. Upon admission to our hospital, her blood lactate/pyruvate ratio during an aerobic exercise test was elevated. Myogenic patterns were observed in lower limb muscles on electromyographic examination. Muscle magnetic resonance imaging revealed diffuse atrophy of proximal muscles in the four extremities with no signal changes. A biopsy from the biceps brachii muscle showed an abnormally large variation in fiber size, scattered muscle fibers with decreased cytochrome c oxidase activity, and ragged-red fibers. Analysis of mtDNA from skeletal muscle revealed no decrease in copy number but increased incidence of multiple deletions, including a deletion of 4977 base pairs (known as the common deletion) reflecting oxidative stress-induced mtDNA damage. This case study indicates that long-term oral antiviral therapy for hepatitis B can induce chronic oxidative damage to mtDNA resulting in qualitative mtDNA abnormalities and toxic myopathy.

Effects of a common pharmaceutical, atorvastatin, on energy metabolism and detoxification mechanisms of a marine bivalve Mytilus edulis

Biologically active compounds from pharmaceuticals cause concern due to their common occurrence in water and sediments of urbanized coasts and potential threat to marine organisms. Atorvastatin (ATO), a globally prescribed drug, is environmentally stable and bioavailable to marine organisms; however, the physiological and toxic effects of this drug on ecologically important coastal species are yet to be elucidated. We studied the effect of ATO (˜1.2 μg L^-1) on bioenergetics (including whole-organism and mitochondrial respiration, as well as tissue energy reserves and mRNA expression of genes involved in mitochondrial biogenesis and fatty acid metabolism in the gills and the digestive gland) of a keystone bivalve Mytulis edulis (the blue mussel) from the Baltic Sea. Xenobiotic detoxification systems including activity and mRNA expression of P-glycoprotein, and Phase I and II biotransformation enzymes (cytochrome P450 monooxygenase CYP1A and glutathione transferase, GST) were also assessed in the gill and digestive gland of the mussels. Exposure to ATO caused rapid uptake and biotransformation of the drug by the mussels. Standard metabolic rate of ATO-exposed mussels increased by 56% indicating higher maintenance costs, yet no changes were detected in the respiratory capacity of isolated mitochondria. ATO exposure led to ˜60% decrease in the lysosomal membrane stability of hemocytes and ˜3-fold decrease in the whole-organism P-glycoprotein-driven and diffusional efflux of xenobiotics indicating altered membrane properties. The digestive gland was a major target of ATO toxicity in the mussels. Exposure of mussels to ATO led to depletion of lipid, carbohydrate and protein pools, and suppressed transcription of key enzymes involved in mitochondrial biogenesis (peroxisome proliferator-activated receptor gamma coactivator 1-alpha PGC-1α) and fatty acid metabolism (acetyl-CoA carboxylase and CYP4Y1) in the digestive gland. No bioenergetic disturbances were observed in the gills of ATO-exposed mussels, and elevated GST activity indicated enhanced ATO detoxification in this tissue. These data demonstrate that ATO can act as a metabolic disruptor and chemosensitizer in keystone marine bivalves and warrant further investigations of statins as emerging pollutants of concern in coastal marine ecosystems.

Sporadic Inclusion Body Myositis: An Acquired Mitochondrial Disease with Extras

The sporadic form of inclusion body myositis (IBM) is the most common late-onset myopathy. Its complex pathogenesis includes degenerative, inflammatory and mitochondrial aspects. However, which of those mechanisms are cause and which effect, as well as their interrelations, remain partly obscured to this day. In this review the nature of the mitochondrial dysregulation in IBM muscle is explored and comparison is made with other muscle disorders. Mitochondrial alterations in IBM are evidenced by histological and serum biomarkers. Muscular mitochondrial dynamics is disturbed, with deregulated organelle fusion leading to subsequent morphological alterations and muscle displays abnormal mitophagy. The tissue increases mitochondrial content in an attempt to compensate dysfunction, yet mitochondrial DNA (mtDNA) alterations and mild mtDNA depletion are also present. Oxidative phosphorylation defects have repeatedly been shown, most notably a reduction in complex IV activities and levels of mitokines and regulatory RNAs are perturbed. Based on the cumulating evidence of mitochondrial abnormality as a disease contributor, it is therefore warranted to regard IBM as a mitochondrial disease, offering a feasible therapeutic target to be developed for this yet untreatable condition.

Mitochondrial DNA degradation: A quality control measure for mitochondrial genome maintenance and stress response

Mitochondria play a central role in bioenergetics, and fulfill a plethora of functions in cell signaling, programmed cell death, and biosynthesis of key protein cofactors. Mitochondria harbor their own genomic DNA, which encodes protein subunits of the electron transport chain and a full set of transfer and ribosomal RNAs. Mitochondrial DNA (mtDNA) is essential for cellular and organismal functions, and defects in mitochondrial genome maintenance have been implicated in common human diseases and mitochondrial disorders. mtDNA repair and degradation are known pathways to cope with mtDNA damage; however, molecular factors involved in this process have remained unclear. Such knowledge is fundamental to the understanding of mitochondrial genomic maintenance and pathology, because mtDNA degradation may contribute to the etiology of mtDNA depletion syndromes and to the activation of the innate immune response by fragmented mtDNA. This article reviews the current literature regarding the importance of mitochondrial DNA degradation in mtDNA maintenance and stress response, and the recent progress in uncovering molecular factors involved in mtDNA degradation. These factors include key components of the mtDNA replication machinery, such as DNA polymerase γ, helicase Twinkle, and exonuclease MGME1, as well as a major DNA-packaging protein, mitochondrial transcription factor A (TFAM).

PGC-1β modulates statin-associated myotoxicity in mice

Statins inhibit cholesterol biosynthesis and lower serum LDL-cholesterol levels. Statins are generally well tolerated, but can be associated with potentially life-threatening myopathy of unknown mechanism. We have shown previously that statins impair PGC-1β expression in human and rat skeletal muscle, suggesting that PGC-1β may play a role in statin-induced myopathy. PGC-1β is a transcriptional co-regulator controlling the expression of important genes in mitochondrial biogenesis, antioxidative capacity and energy metabolism. The principle aim of the current study was to investigate the interaction between atorvastatin and PGC-1β in more detail. We therefore treated wild-type mice and mice with selective skeletal muscle knockout of PGC-1β (PGC-1β^(i)skm-/- mice) with oral atorvastatin (5 mg/kg/day) for 2 weeks. At the end of treatment, we determined body parameters, muscle function, structure, and composition as well as the function of muscle mitochondria, mitochondrial biogenesis and activation of apoptotic pathways. In wild-type mice, atorvastatin selectively impaired mitochondrial function in glycolytic muscle and caused a conversion of oxidative type IIA to glycolytic type IIB myofibers. Conversely, in oxidative muscle of wild-type mice, atorvastatin enhanced mitochondrial function via activation of mitochondrial biogenesis pathways and decreased apoptosis. In PGC-1β^(i)skm-/- mice, atorvastatin induced a switch towards glycolytic fibers, caused mitochondrial dysfunction, increased mitochondrial ROS production, impaired mitochondrial proliferation and induced apoptosis in both glycolytic and oxidative skeletal muscle. Our work reveals that atorvastatin mainly affects glycolytic muscle in wild-type mice and demonstrates the importance of PGC-1β for oxidative muscle integrity during long-term exposure to a myotoxic agent.

A Monochrome Multiplex Real-Time Quantitative PCR Assay for the Measurement of Mitochondrial DNA Content

Mitochondrial DNA copies per cell (mtDNA content) can fluctuate with cellular aging, oxidative stress, and mitochondrial dysfunction, and has been investigated in cancer, diabetes, HIV, and metabolic disease. mtDNA content testing in both clinical and basic settings is expected to increase as research uncovers its biological relevance. Herein, we present a novel mtDNA content assay developed on monochrome multiplex real-time quantitative PCR (MMqPCR) principles. This assay offers a greater than twofold improvement on time effectiveness and cost-effectiveness over conventional (monoplex) qPCR, as well as improved reproducibility given the reduced effects of human pipetting errors. The new MMqPCR method was compared with the gold standard monoplex qPCR assay on DNA from a variety of sources, including human whole blood, skeletal muscle, and commercial cell lines. The MMqPCR assay is reproducible (n = 98, r = 0.99, P < 0.0001) and highly correlated to the monoplex qPCR assay (n = 160, r > 0.98, P < 0.0001). Intra-assay and interassay variabilities, as established independently by multiple operators, range between 4.3% and 7.9% and between 2.9% and 9.2%, respectively. This robust assay can quantify >82 pg of template DNA per reaction, with a minimum mtDNA/nuclear DNA ratio of 20, and is especially suitable for studies that require high throughput.

Statins for primary prevention and rhabdomyolysis: A nationwide cohort study in France

AIMS

The purpose of this study was to investigate the risk of rhabdomyolysis in subjects initiating statin therapy for primary prevention of cardiovascular disease, focusing on the type of statin, dose and time since initiation.

METHODS AND RESULTS

A nationwide cohort study using French hospital discharge and claims databases was performed, studying subjects from the general population 40-75 years in 2009, with no history of cardiovascular disease and no lipid-lowering drugs during the preceding three-year period, followed for up to seven years. The primary outcome was hospitalization for rhabdomyolysis. Event-free survival analysis and case-time-control analysis were both performed, separately by gender. The cohort included 8,236,667 subjects, 969,460 of whom initiated a lipid-lowering drug for cardiovascular disease primary prevention. During 18,407,391 person-months exposed to statins, 168 events were observed, corresponding to an incidence of rhabdomyolysis of 1.10 per 10,000 person-years (1.54 in men vs 0.81 in women); 10/168 cases were fatal, and 18/168 and 57/168 cases occurred during the first month and first trimester of treatment, respectively. Survival analysis did not reveal any increased overall risk (hazard ratio = 1.02 (0.83-1.25) in men and 0.76 (0.60-0.96) in women). However, exposure to high-potency statins was associated with an increased risk in men (hazard ratio = 1.93 (1.27-2.94)). Rosuvastatin 20 mg (in men and women) and simvastatin 40 mg (in men) were associated with hazard ratios > 5. Case-time-control analyses showed similar patterns of risk. Drug interactions did not appear to significantly contribute to rhabdomyolysis events in this study.

CONCLUSION

Although the overall risk of statin-associated rhabdomyolysis in the context of primary prevention was not increased, the first months of treatment and the use of high-potency statins represent at-risk situations, which require appropriate monitoring, especially in men.

Histopathologic and Biochemical Evidence for Mitochondrial Disease Among 279 Patients with Severe Statin Myopathy

BACKGROUND

Statins have well-known benefits in the prevention of cardiovascular disease, however, 7-29% of patients develop muscle side effects and up to 0.5% develop severe symptoms. Mitochondrial dysfunction has been associated with severe statin-induced myopathy (SM); however, there is a paucity of systematic studies in affected individuals.

OBJECTIVES

The goal of this study was to combine clinical and laboratory features with quantitative biochemical and histopathologic studies of skeletal muscle biopsies from SM cases to determine what proportion could be attributed to mitochondrial dysfunction and how many of these had primary respiratory chain defects.

METHODS

A retrospective analysis was performed on patient records derived from 279 SM patients whose muscle biopsies were referred to our clinical diagnostic laboratory for analysis. Clinical, histopathologic and biochemical features were compared with two myopathic control groups unexposed to statins: individuals with idiopathic mitochondrial myopathy (MMP; n = 94) and with unknown metabolic myopathy (UMP; n = 86); normal controls were unavailable for this record review study.

RESULTS

More SM patients had significantly elevated plasma CK than in the other two groups (p < 0.01). A subset of SM patients (67 of 279; 24%) had histopathologic and/or electron microscopic (EM) evidence for mitochondrial dysfunction in skeletal muscle; more cases were identified by EM than by histochemical analysis. Of 279 cases, 29 (10%) were confirmed to have respiratory chain defects by biochemical analysis; 4 of these had mitochondrial abnormalities by EM. An additional 20 cases had mitochondrial abnormalities by EM without a biochemical diagnosis.

CONCLUSIONS

Both primary and secondary mitochondrial dysfunction was found in subsets of SM patients. The fact that respiratory chain defects were not found in most cases with histopathologic mitochondrial abnormalities does not rule out primary mitochondrial disease in these cases, however, it is more likely that secondary effects on mitochondrial structure and function have occurred; molecular analysis may be helpful only in a small number of cases.

Trimetazidine restores the positive adaptation to exercise training by mitigating statin-induced skeletal muscle injury

BACKGROUND

Exercise rehabilitation is demonstrated to improve the prognosis of patients with coronary heart disease (CHD). Statins, as the key medicine to lower cholesterol in CHD, result in skeletal muscle injury and impair exercise training adaptation. Energy metabolism dysfunction is identified as the potential mechanism underlying statin-induced skeletal muscle injury. In this study, we investigated the effects of the metabolic modulator trimetazidine on skeletal muscle energy metabolism and statin-associated exercise intolerance.

METHODS

High-fat fed apolipoprotein E knockout (ApoE-/- ) mice were given aerobic exercise and administrated simvastatin, trimetazidine, or simvastatin plus trimetazidine by gavage. Exercise capacity was evaluated at the end of the treatment by hanging grid test, forelimb grip strength, and running tolerance test. Plasma glucose, lipid, and creatine kinase concentrations were measured at the end of the treatment. After sacrifice, gastrocnemii were stored for assessment of muscle morphology and fibre type. Energy metabolism was estimated by plasma lactic acid concentration, ragged red fibres, and glycogen stores. Activities of mitochondrial complex III, citrate synthase activity, and membrane potential were measured to assess mitochondrial function. Oxidative stress was also evaluated by superoxide in mitochondria, superoxide dismutase activity, and glutathione redox state.

RESULTS

In high-fat fed ApoE-/- mice, exercise training had no effect on lipid concentrations. Lower lipid concentrations with increased creatine kinase were observed with additional simvastatin treatment. Exercise capacity increased significantly in response to exercise training alone but was blunted by the addition of simvastatin. Similarly, cross-sectional area of muscle fibres and the proportion of slow-twitch fibres increased in the exercise group but decreased in the simvastatin plus exercise group. Additionally, simvastatin increased centronucleated fibres and induced energy metabolism dysfunction by inhibiting complex III activity and thus promoted oxidative stress in gastrocnemius. We demonstrated that trimetazidine could reverse simvastatin-induced exercise intolerance and muscle damages. We also found the ability of trimetazidine in restoration of muscle fibre hypertrophy and facilitating fast-to-slow type shift. The energy metabolism dysfunction and oxidative stress in gastrocnemii were rescued by trimetazidine.

CONCLUSIONS

Trimetazidine alleviated statin-related skeletal muscle injury by restoration of oxidative phenotype and increasing fibre cross-sectional areas in response to exercise training. Correspondingly, the exercise training adaptation were improved in high-fat fed ApoE-/- mice. Moreover, trimetazidine is able to exert its positive effects without affecting the beneficial lipid-lowering properties of the statins. Thus, trimetazidine could be prescribed to remedy the undesirable statins-induced exercise intolerance during cardiac rehabilitation in patients with CHD.

Statins Affect Skeletal Muscle Performance: Evidence for Disturbances in Energy Metabolism

CONTEXT

Statin myopathy is linked to disturbances in mitochondrial function and exercise intolerance.

OBJECTIVES

To determine whether differences exist in exercise performance, muscle function, and muscle mitochondrial oxidative capacity and content between symptomatic and asymptomatic statin users, and control subjects.

DESIGN

Cross-sectional study.

SETTING

Department of Physiology, Radboud University Medical Center.

PARTICIPANTS

Long-term symptomatic and asymptomatic statin users, and control subjects (n = 10 per group).

INTERVENTIONS

Maximal incremental cycling tests, involuntary electrically stimulated isometric quadriceps-muscle contractions, and biopsy of vastus lateralis muscle.

MAIN OUTCOMES MEASURED

Maximal exercise capacity, substrate use during exercise, muscle function, and mitochondrial energy metabolism.

RESULTS

Peak oxygen uptake, maximal work load, and ventilatory efficiency were comparable between groups, but both statin groups had a depressed anaerobic threshold compared with the control group (P = 0.01). Muscle relaxation time was prolonged in both statin groups compared with the control group and rate of maximal force rise was decreased (Ptime×group < 0.001 for both measures). Mitochondrial activity of complexes II and IV was lower in symptomatic statin users than control subjects and tended to be lower for complex (C) III (CII: P = 0.03; CIII: P = 0.05; CIV: P = 0.04). Mitochondrial content tended to be lower in both statin groups than in control subjects.

CONCLUSION

Statin use attenuated substrate use during maximal exercise performance, induced muscle fatigue during repeated muscle contractions, and decreased muscle mitochondrial oxidative capacity. This suggests disturbances in mitochondrial oxidative capacity occur with statin use even in patients without statin-induced muscle complaints.

Statins, Muscle Disease and Mitochondria

Cardiovascular disease (CVD) accounts for >17 million deaths globally every year, and this figure is predicted to rise to >23 million by 2030. Numerous studies have explored the relationship between cholesterol and CVD and there is now consensus that dyslipidaemia is a causal factor in the pathogenesis of atherosclerosis. Statins have become the cornerstone of the management of dyslipidaemia. Statins have proved to have a very good safety profile. The risk of adverse events is small compared to the benefits. Nevertheless, the potential risk of an adverse event occurring must be considered when prescribing and monitoring statin therapy to individual patients. Statin-associated muscle disease (SAMS) is by far the most studied and the most common reason for discontinuation of therapy. The reported incidence varies greatly, ranging between 5% and 29%. Milder disease is common and the more serious form, rhabdomyolysis is far rarer with an incidence of approximately 1 in 10,000. The pathophysiology of, and mechanisms leading to SAMS, are yet to be fully understood. Literature points towards statin-induced mitochondrial dysfunction as the most likely cause of SAMS. However, the exact processes leading to mitochondrial dysfunction are not yet fully understood. This paper details some of the different aetiological hypotheses put forward, focussing particularly on those related to mitochondrial dysfunction.

Polypharmacy and sun exposure: Implications for mitochondrial DNA deletions in skin

Most somatic cells contain many copies of mitochondrial DNA (mtDNA). Because of both the high copy number and the lack of repair mechanisms available to mtDNA, damage to it largely goes unrepaired, and can accumulate over time. Large scale deletions are a recognised type of damage sustained by mtDNA as a consequence of exposure to the ultraviolet light in sunlight. A group of patients were identified as having abnormally high levels of either a 4977 base pair deletion (mtDNA⁴⁹⁷⁷) or 3895 base pair deletion (mtDNA³⁸⁹⁵), in mtDNA from sun exposed skin or skin suspected to be a non-melanoma skin cancer, but not in their non-sun exposed skin biopsies. In three of the four cases, skin cancer was ruled out due to histological testing. Additional factors from these patients' medical histories were studied, and it was noted that they shared diagnoses for multiple pathologies common to an older population, and that they were being treated with the same or related pharmaceuticals, including some that had been known to cause dermal side effects. Investigation into the biochemistry underlying the symptoms, the effects of sun exposure and side effects of the prescribed pharmaceuticals revealed a possible synergistic relationship leading to the localised high levels of mtDNA deletions.

Cu@SnS/SnO2 nanoparticles as novel sorbent for dispersive micro solid phase extraction of atorvastatin in human plasma and urine samples by high-performance liquid chromatography with UV detection: Application of central composite design (CCD)

Separation and detection of residual drug in biological fluids has directly related to human health in term of their beneficial or side effects. In biological fluid samples (complex matrix which containing drug at very low level) conduction of preliminary efficient technique as good choice for pre-concentration and clean-up of real sample before their instrumental analysis is highly recommended. In this result technique, based on nano-structure material which poses higher available surface area and larger member of reactive sites led to significant improvement in characteristic performance of analytical method. This paper focused on the synthesis and application of novel nano-sorbent for pre-concentration and extraction of atorvastatin (AT) from different biological fluids. Influence of various variables including sorbent dosage, eluent volume and sonication time on present method response was studied and optimized by central composite design under response surface methodology and accordingly an acceptable calibration curves over wide linear ranges (0.3-2000μgL^-1) with high coefficient of determination higher than 0.999 strongly confirm high applicability of present method for quantification of analyte while limit of detection and quantification in plasma sample were 0.0608 and 0.2033μg L^-1, respectively.

Rosuvastatin safety: An experimental study of myotoxic effects and mitochondrial alterations in rats

Myopathy is the most commonly reported adverse effect of statins. All statins are associated with myopathy, though with different rates. Rosuvastatin is a potent statin reported to induce myopathy comparable to earlier statins. However, in clinical practice most patients could tolerate rosuvastatin over other statins. This study aimed to evaluate the myopathic pattern of rosuvastatin in rats using biochemical, functional and histopathological examinations. The possible deleterious effects of rosuvastatin on muscle mitochondria were also examined. The obtained results were compared to myopathy induced by atorvastatin in equimolar dose. Results showed that rosuvastatin induced a rise in CK, a slight increase in myoglobin level together with mild muscle necrosis. Motor activity, assessed by rotarod, showed that rosuvastatin decreased rats' performance. All these manifestations were obviously mild compared to the prominent effects of atorvastatin. Parallel results were obtained in mitochondrial dysfunction parameters. Rosuvastatin only induced a slight increase in LDH and a minor decrease in ATP (∼14%) and pAkt (∼12%). On the other hand, atorvastatin induced an increase in LDH, lactate/pyruvate ratio and a pronounced decline in ATP (∼80%) and pAkt (∼65%). These findings showed that rosuvastatin was associated with mild myotoxic effects in rats, especially when compared to atorvastatin.

A short-term statin treatment changes the contractile properties of fast-twitch skeletal muscles

Background

Cumulative evidence indicates that statins induce myotoxicity. However, the lack of understanding of how statins affect skeletal muscles at the structural, functional, and physiological levels hampers proper healthcare management. The purpose of the present study was to investigate the early after-effects of lovastatin on the slow-twitch soleus (Sol) and fast-twitch extensor digitorum longus (EDL) muscles.

Methods

Adult C57BL/6 mice were orally administrated with placebo or lovastatin [50 mg/kg/d] for 28 days. At the end of the treatment, the isometric ex vivo contractile properties of the Sol and EDL muscles were measured. Subtetanic and tetanic contractions were assessed and contraction kinetics were recorded. The muscles were then frozen for immunohistochemical analyses. Data were analyzed by two-way ANOVA followed by an a posteriori Tukey’s test.

Results

The short-term lovastatin treatment did not induce muscle mass loss, muscle fiber atrophy, or creatine kinase (CK) release. It had no functional impact on slow-twitch Sol muscles. However, subtetanic stimulations at 10 Hz provoked greater force production in fast-twitch EDL muscles. The treatment also decreased the maximal rate of force development (dP/dT) of twitch contractions and prolonged the half relaxation time (1/2RT) of tetanic contractions of EDL muscles.

Conclusions

An early short-term statin treatment induced subtle but significant changes in some parameters of the contractile profile of EDL muscles, providing new insights into the selective initiation of statin-induced myopathy in fast-twitch muscles.

Drug induced mitochondrial dysfunction: Mechanisms and adverse clinical consequences

Several commonly used medications impair mitochondrial function resulting in adverse effects or toxicities. Drug induced mitochondrial dysfunction may be a consequence of increased production of reactive oxygen species, altered mitochondrial permeability transition, impaired mitochondrial respiration, mitochondrial DNA damage or inhibition of beta-oxidation of fatty acids. The clinical manifestation depends on the specific drug and its effect on mitochondria. Given the ubiquitous presence of mitochondria and its central role in cellular metabolism, drug-mitochondrial interactions may manifest clinically as hepatotoxicity, enteropathy, myelosuppression, lipodystrophy syndrome or neuropsychiatric adverse effects, to name a few. The current review focuses on specific drug groups which adversely affect mitochondria, the mechanisms involved and the clinical consequences based on the data available from experimental and clinical studies. Knowledge of these adverse drug-mitochondrial interactions may help the clinicians foresee potential issues in individual patients, prevent adverse drug reactions or alter drug regimens to enhance patient safety.

Low-density lipoprotein cholesterol in a global cohort of 57,885 statin-treated patients

BACKGROUND AND AIMS

There is an inconsistency between international guidelines on lipid-lowering treatment regarding whether to pursue LDL-C treatment targets or to focus on the intensity of treatment. While either approach is attractive, there is no recent global data on actual LDL-C values, treatment targets attained, and the intensity of treatment in statin-treated patients. We aimed to determine and compare the extent of treatment target attainment globally using standardized data collection.

METHODS

Analyses were based on the Dyslipidemia International Study (DYSIS), a cross-sectional study documenting statin-treated outpatients throughout 30 countries worldwide (across Europe, the Middle East, Canada, Africa, and Asia). Patients were classified as being at very high, high, or non-high cardiovascular risk based on the 2011 European Society of Cardiology (ESC)/European Atherosclerosis Society (EAS) guidelines.

RESULTS

Data were available for a total of 57,885 patients with a median LDL-C value of 98.2 mg/dl (IQR: 76.6, 125.7 mg/dl). Overall, only 26.8% of patients were documented to have attained their risk-based target LDL-C level. Of the 76% of patients who were classified as being at very high risk, only 21.7% attained their LDL-C goal. Globally, the median distance to target was 33.0 mg/dl, ranging from 18.8 to 42.1 mg/dl across countries. We calculated that a further LDL-C reduction of just 10 mg/dl would result in an 11% increase in the proportion of very-high-risk and high-risk patients attaining their target level (9% for non-high risk patients).

CONCLUSIONS

In spite of statin therapy, LDL-C values were high, with a substantial distance to target that was even more pronounced in (very) high risk patients. These results call for the optimization of existing treatment strategies and a collaborative effort to improve the impact of treatment guidance on clinical practice.

Presequence-Independent Mitochondrial Import of DNA Ligase Facilitates Establishment of Cell Lines with Reduced mtDNA Copy Number

Due to the essential role played by mitochondrial DNA (mtDNA) in cellular physiology and bioenergetics, methods for establishing cell lines with altered mtDNA content are of considerable interest. Here, we report evidence for the existence in mammalian cells of a novel, low- efficiency, presequence-independent pathway for mitochondrial protein import, which facilitates mitochondrial uptake of such proteins as Chlorella virus ligase (ChVlig) and Escherichia coli LigA. Mouse cells engineered to depend on this pathway for mitochondrial import of the LigA protein for mtDNA maintenance had severely (up to >90%) reduced mtDNA content. These observations were used to establish a method for the generation of mouse cell lines with reduced mtDNA copy number by, first, transducing them with a retrovirus encoding LigA, and then inactivating in these transductants endogenous Lig3 with CRISPR-Cas9. Interestingly, mtDNA depletion to an average level of one copy per cell proceeds faster in cells engineered to maintain mtDNA at low copy number. This makes a low-mtDNA copy number phenotype resulting from dependence on mitochondrial import of DNA ligase through presequence-independent pathway potentially useful for rapidly shifting mtDNA heteroplasmy through partial mtDNA depletion.

Biochemistry of Statins

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide. Elevated blood lipids may be a major risk factor for CVD. Due to consistent and robust association of higher low-density lipoprotein (LDL)-cholesterol levels with CVD across experimental and epidemiologic studies, therapeutic strategies to decrease risk have focused on LDL-cholesterol reduction as the primary goal. Current medication options for lipid-lowering therapy include statins, bile acid sequestrants, a cholesterol-absorption inhibitor, fibrates, nicotinic acid, and omega-3 fatty acids, which all have various mechanisms of action and pharmacokinetic properties. The most widely prescribed lipid-lowering agents are the HMG-CoA reductase inhibitors, or statins. Since their introduction in the 1980s, statins have emerged as the one of the best-selling medication classes to date, with numerous trials demonstrating powerful efficacy in preventing cardiovascular outcomes (Kapur and Musunuru, 2008 [1]). The statins are commonly used in the treatment of hypercholesterolemia and mixed hyperlipidemia. This chapter focuses on the biochemistry of statins including their structures, pharmacokinetics, and mechanism of actions as well as the potential adverse reactions linked to their clinical uses.

Negative statin-related news stories decrease statin persistence and increase myocardial infarction and cardiovascular mortality: a nationwide prospective cohort study

AIM

We tested the hypothesis that statin-related news stories, cardiovascular disease, diabetes, statin dose, calendar year, and socio-demographic status are associated with early statin discontinuation. We also examined frequency and consequences of early statin discontinuation.

METHODS AND RESULTS

From the entire Danish population, we studied 674 900 individuals aged 40 or older who were initiated on statin therapy in 1995-2010, and followed them until 31 December 2011. Individuals on statins increased from <1% in 1995 to 11% in 2010, while early statin discontinuation increased from 6% in 1995 to 18% in 2010. The odds ratios for early statin discontinuation vs. continued use were 1.09 (95% confidence interval, 1.06-1.12) for negative statin-related news stories, 1.04 (1.02-1.07) per increasing calendar year, 1.04 (1.02-1.06) per increasing defined daily dose of statin, 1.05 (1.03-1.06) for male sex, 1.13 (1.11-1.15) for living in cities, 1.67 (1.63-1.71) for other ethnicity than Danish, 0.92 (0.90-0.94) for positive statin-related news stories, 0.73 (0.72-0.74) for baseline cardiovascular disease, and 0.91 (0.90-0.93) for baseline diabetes. During follow-up, the hazard ratios for individuals with vs. without early statin discontinuation were 1.26 (1.21-1.30) for myocardial infarction and 1.18 (1.14-1.23) for death from cardiovascular disease.

CONCLUSION

Early statin discontinuation increased with negative statin-related news stories, calendar year, statin dose, male sex, living in cities, and with other ethnicity than Danish, while the opposite was true for positive statin-related news stories and for baseline cardiovascular disease and diabetes. Early statin discontinuation was also associated with increased risk of myocardial infarction and death from cardiovascular disease.

Effects of Statin Therapy on Exercise Levels in Participants in the National Runners' and Walkers' Health Study

OBJECTIVES

To determine whether decreases in exercise 1) were greater in individuals who were diagnosed as having hypercholesterolemia than in those without the diagnosis during follow-up and 2) were greater in incident hypercholesterolemic participants starting statins than in those not treated with cholesterol-lowering medications.

PARTICIPANTS AND METHODS

Regression analyses of changes since baseline (Δ) in exercise vs diagnosis of hypercholesterolemia and its treatment in 66,377 runners and 12,031 walkers not using cholesterol medications at baseline who were resurveyed during the National Runners' and Walkers' Health Study follow-up (January 1, 1991, through December 31, 2006).

RESULTS

A total of 3510 runners began statin treatment, 1779 began other or unspecified cholesterol-lowering drug treatment, and 2583 had untreated hypercholesterolemia; 58,505 runners remained nonhypercholesterolemic controls during the mean 7.2-year follow-up. Usual distance run decreased significantly more in hypercholesterolemic runners who began taking statins (mean ± SE: -0.47±0.06 km/d) than in runners who remained nonhypercholesterolemic during follow-up (-0.08±0.02 km/d) (P<.001). However, running distance also decreased significantly more in hypercholesterolemic runners who began unspecified/other (-0.52±0.08 km/d) or no (-0.47±0.07 km/d) cholesterol drugs than in nonhypercholesterolemic runners during follow-up. Moreover, Δrunning distance did not differ significantly between hypercholesterolemic runners who were statin treated vs those treated with other/unspecified (P=.64) or no (P=.94) cholesterol drugs. Initiating statin therapy was not associated with Δrunning pace in hypercholesterolemic runners or Δwalking distances in hypercholesterolemic walkers.

CONCLUSION

These results are consistent with the premise that a decrease in running distance is associated with hypercholesterolemia and do not suggest that statins reduce exercise level or intensity.

The role of mitochondria in statin-induced myopathy

BACKGROUND

Statins inhibit hydroxymethylglutaryl-coenzyme A reductase, decrease plasma low-density lipoprotein cholesterol and reduce cardiovascular morbidity and mortality. They can also exert adverse effects, mostly affecting skeletal muscle, ranging from mild myalgia to rhabdomyolysis.

MATERIALS AND METHODS

Based on a PubMed search until December 2014, this review summarizes studies on statin effects on muscle mitochondrial morphology and function in the context of myopathy.

RESULTS

Possible mechanisms of statin-induced myopathy include lower cholesterol synthesis and production of prenylated proteins, reduced dolichols and increased atrogin-1 expression. Statin-treated patients frequently feature decreased muscle coenzyme Q10 (CoQ10) contents, suggesting that statins might impair mitochondrial function. In cell cultures, statins diminish muscle oxygen consumption, promote mitochondrial permeability transient pore opening and generate apoptotic proteins. Animal models confirm the statin-induced decrease in muscle CoQ10, but reveal no changes in mitochondrial enzyme activities. Human studies yield contradictory results, with decreased CoQ10, elevated lipids, decreased enzyme activities in muscle and impaired maximal oxygen uptake in several but not all studies. Some patients are susceptible to statin-induced myopathy due to variations in genes encoding proteins involved in statin uptake and biotransformation such as the solute carrier organic anion transporter family member 1B1 (SLCO1B1) or cytochrome P450 (CYP2D6, CYP3A4, CYP3A5). Carriers for carnitine palmitoyltransferase II deficiency and McArdle disease also present with higher prevalence of statin-induced myopathy.

CONCLUSIONS

Despite the widespread use of statins, the pathogenesis of statin-induced myopathy remains unclear, requiring prospective randomized controlled trials with intensive phenotyping also for identifying strategies for its risk assessment, prevention and treatment.

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.

Mitochondrial DNA: A disposable genome?

In mammalian cells, mitochondria are the only organelles besides the nucleus that house genomic DNA. The mammalian mitochondrial genome is represented by prokaryotic-type, circular, highly compacted DNA molecules. Today, more than a half-century after their discovery, the biology of these small and redundant molecules remains much less understood than that of their nuclear counterparts. One peculiarity of the mitochondrial genome that emerged in recent years is its disposable nature, as evidenced by cells abandoning a fraction of their mitochondrial DNA (mtDNA) in response to various stimuli with little or no physiological consequence. Here, we review some recent developments in the field of mtDNA biology and discuss emerging questions on the disposability and indispensability of mtDNA.

Statin-Induced Increases in Atrophy Gene Expression Occur Independently of Changes in PGC1α Protein and Mitochondrial Content

One serious side effect of statin drugs is skeletal muscle myopathy. Although the mechanism(s) responsible for statin myopathy remains to be fully determined, an increase in muscle atrophy gene expression and changes in mitochondrial content and/or function have been proposed to play a role. In this study, we examined the relationship between statin-induced expression of muscle atrophy genes, regulators of mitochondrial biogenesis, and markers of mitochondrial content in slow- (ST) and fast-twitch (FT) rat skeletal muscles. Male Sprague Dawley rats were treated with simvastatin (60 or 80 mg·kg^-1·day^-1) or vehicle control via oral gavage for 14 days. In the absence of overt muscle damage, simvastatin treatment induced an increase in atrogin-1, MuRF1 and myostatin mRNA expression; however, these were not associated with changes in peroxisome proliferator gamma co-activator 1 alpha (PGC-1α) protein or markers of mitochondrial content. Simvastatin did, however, increase neuronal nitric oxide synthase (nNOS), endothelial NOS (eNOS) and AMPK α-subunit protein expression, and tended to increase total NOS activity, in FT but not ST muscles. Furthermore, simvastatin induced a decrease in β-hydroxyacyl CoA dehydrogenase (β-HAD) activity only in FT muscles. These findings suggest that the statin-induced activation of muscle atrophy genes occurs independent of changes in PGC-1α protein and mitochondrial content. Moreover, muscle-specific increases in NOS expression and possibly NO production, and decreases in fatty acid oxidation, could contribute to the previously reported development of overt statin-induced muscle damage in FT muscles.

Statin-associated muscle symptoms: impact on statin therapy-European Atherosclerosis Society Consensus Panel Statement on Assessment, Aetiology and Management

Statin-associated muscle symptoms (SAMS) are one of the principal reasons for statin non-adherence and/or discontinuation, contributing to adverse cardiovascular outcomes. This European Atherosclerosis Society (EAS) Consensus Panel overviews current understanding of the pathophysiology of statin-associated myopathy, and provides guidance for diagnosis and management of SAMS. Statin-associated myopathy, with significant elevation of serum creatine kinase (CK), is a rare but serious side effect of statins, affecting 1 per 1000 to 1 per 10 000 people on standard statin doses. Statin-associated muscle symptoms cover a broader range of clinical presentations, usually with normal or minimally elevated CK levels, with a prevalence of 7-29% in registries and observational studies. Preclinical studies show that statins decrease mitochondrial function, attenuate energy production, and alter muscle protein degradation, thereby providing a potential link between statins and muscle symptoms; controlled mechanistic and genetic studies in humans are necessary to further understanding. The Panel proposes to identify SAMS by symptoms typical of statin myalgia (i.e. muscle pain or aching) and their temporal association with discontinuation and response to repetitive statin re-challenge. In people with SAMS, the Panel recommends the use of a maximally tolerated statin dose combined with non-statin lipid-lowering therapies to attain recommended low-density lipoprotein cholesterol targets. The Panel recommends a structured work-up to identify individuals with clinically relevant SAMS generally to at least three different statins, so that they can be offered therapeutic regimens to satisfactorily address their cardiovascular risk. Further research into the underlying pathophysiological mechanisms may offer future therapeutic potential.

Treatment of dyslipidemia with statins and physical exercises: recent findings of skeletal muscle responses

Statin treatment in association with physical exercise practice can substantially reduce cardiovascular mortality risk of dyslipidemic individuals, but this practice is associated with myopathic event exacerbation. This study aimed to present the most recent results of specific literature about the effects of statins and its association with physical exercise on skeletal musculature. Thus, a literature review was performed using PubMed and SciELO databases, through the combination of the keywords "statin" AND "exercise" AND "muscle", restricting the selection to original studies published between January 1990 and November 2013. Sixteen studies evaluating the effects of statins in association with acute or chronic exercises on skeletal muscle were analyzed. Study results indicate that athletes using statins can experience deleterious effects on skeletal muscle, as the exacerbation of skeletal muscle injuries are more frequent with intense training or acute eccentric and strenuous exercises. Moderate physical training, in turn, when associated to statins does not increase creatine kinase levels or pain reports, but improves muscle and metabolic functions as a consequence of training. Therefore, it is suggested that dyslipidemic patients undergoing statin treatment should be exposed to moderate aerobic training in combination to resistance exercises three times a week, and the provision of physical training prior to drug administration is desirable, whenever possible.