Functional Diagnostics in Mitochondrial Diseases

Biomolecules of Muscle Fatigue in Metabolic Myopathies

Metabolic myopathies are a group of genetic disorders that affect the normal functioning of muscles due to abnormalities in metabolic pathways. These conditions result in impaired energy production and utilization within muscle cells, leading to limitations in muscle function with concomitant occurrence of related signs and symptoms, among which fatigue is one of the most frequently reported. Understanding the underlying molecular mechanisms of muscle fatigue in these conditions is challenging for the development of an effective diagnostic and prognostic approach to test targeted therapeutic interventions. This paper outlines the key biomolecules involved in muscle fatigue in metabolic myopathies, including energy substrates, enzymes, ion channels, and signaling molecules. Potential future research directions in this field are also discussed.

Mitochondrial impairment but not peripheral inflammation predicts greater Gulf War illness severity

Gulf War illness (GWI) is an important exemplar of environmentally-triggered chronic multisymptom illness, and a potential model for accelerated aging. Inflammation is the main hypothesized mechanism for GWI, with mitochondrial impairment also proposed. No study has directly assessed mitochondrial respiratory chain function (MRCF) on muscle biopsy in veterans with GWI (VGWI). We recruited 42 participants, half VGWI, with biopsy material successfully secured in 36. Impaired MRCF indexed by complex I and II oxidative phosphorylation with glucose as a fuel source (CI&CIIOXPHOS) related significantly or borderline significantly in the predicted direction to 17 of 20 symptoms in the combined sample. Lower CI&CIIOXPHOS significantly predicted GWI severity in the combined sample and in VGWI separately, with or without adjustment for hsCRP. Higher-hsCRP (peripheral inflammation) related strongly to lower-MRCF (particularly fatty acid oxidation (FAO) indices) in VGWI, but not in controls. Despite this, whereas greater MRCF-impairment predicted greater GWI symptoms and severity, greater inflammation did not. Surprisingly, adjusted for MRCF, higher hsCRP significantly predicted lesser symptom severity in VGWI selectively. Findings comport with a hypothesis in which the increased inflammation observed in GWI is driven by FAO-defect-induced mitochondrial apoptosis. In conclusion, impaired mitochondrial function-but not peripheral inflammation-predicts greater GWI symptoms and severity.

The effect of coenzyme Q10 as a part of standard therapy on plasma concentrations of ubiquinol, ubiquinone, total CoQ10 and its redox state in patients with ischemic heart disease

BACKGROUND

Despite CoQ10 being a powerful antioxidant and its redox state that may characterize the body's antioxidant system, the latter remains unstudied in patients with cardiovascular diseases.

OBJECTIVE

This prospective case-control study aimed to investigate the concentrations of ubiquinol, ubiquinone, total CoQ10 and its redox state in patients with ischemic heart disease (IHD) and arterial hypertension (AH) during standard therapy and with the additional prescription of CoQ10.

METHODS

The study included 54 healthy individuals and 26 patients, who were divided into a control group receiving standard therapy and a test group receiving CoQ10 in addition to standard therapy. Quantitative determination of COQ10, ubiquinone and ubiquinol was carried out by HPLC-MS/MS.

RESULTS

It was found that the CoQ10 level in patients was significantly lower than in healthy individuals (on average -32Δ%). In the test group, after treatment, the concentrations of ubiquinol (+53 Δ%), ubiquinone (-28 Δ%), total CoQ10 (+27 Δ%) and redox state (+112 Δ%) were significantly different from the baseline, while in the control group no significant differences were noticed. In the test group after treatment, the levels of total CoQ10 (+25 Δ%), ubiquinol (+43 Δ%), and redox state (+86 Δ%) were statistically significantly higher than in the control group and total CoQ10 concentration did not significantly differ from that in healthy individuals (-12 Δ%).

CONCLUSION

The additional prescription of CoQ10 for patients with IHD significantly increases the level of total CoQ10, which leads to the increase of body antioxidant potential .

Diagnosis of primary mitochondrial disorders -Emphasis on myopathological aspects

Mitochondrial disorders are one of the most common neurometabolic disorders affecting all age groups. The phenotype-genotype heterogeneity in these disorders can be attributed to the dual genetic control on mitochondrial functions, posing a challenge for diagnosis. Though the advancement in the high-throughput sequencing and other omics platforms resulted in a "genetics-first" approach, the muscle biopsy remains the benchmark in most of the mitochondrial disorders. This review focuses on the myopathological aspects of primary mitochondrial disorders. The utility of muscle biopsy is not limited to analyse the structural abnormalities; rather it also proves to be a potential tool to understand the deranged sub-cellular functions.

Oxidative Stress and the Pathophysiology and Symptom Profile of Schizophrenia Spectrum Disorders

Schizophrenia is associated with increased levels of oxidative stress, as reflected by an increase in the concentrations of damaging reactive species and a reduction in anti-oxidant defences to combat them. Evidence has suggested that whilst not the likely primary cause of schizophrenia, increased oxidative stress may contribute to declining course and poor outcomes associated with schizophrenia. Here we discuss how oxidative stress may be implicated in the aetiology of schizophrenia and examine how current understanding relates associations with symptoms, potentially via lipid peroxidation induced neuronal damage. We argue that oxidative stress may be a good target for future pharmacotherapy in schizophrenia and suggest a multi-step model of illness progression with oxidative stress involved at each stage.

The particulars of certain drugs' effect on the endogenous coenzyme Q10 plasma level in patients with cardiovascular diseases

Objectives Coenzyme Q10 (CoQ10) has many vital functions in human body and its endogenous level can be affected either by various diseases or by administrated drugs. This study reveals the effect of atorvastatin, amlodipine and ethoxidol on the endogenous CoQ10 plasma concentration. Methods It was determined the total plasma concentration of endogenous CoQ10 in the plasma of 54 healthy individuals and 62 patients with cardiovascular diseases during treatment with various drugs using high performance liquid chromatography with mass spectrometric detection (HPLC-MS/MS). Results It was found that CoQ10 plasma concentration in patients is statistically significantly lower (on average -49.0 Δ%) than in practically healthy individuals. The total CoQ10 plasma level in patients receiving atorvastatin in the complex therapy is statistically significantly lower (-15.2 Δ%), and in patients taking amlodipine or ethoxidol is statistically significantly higher (+18.2 and +20.2 Δ%, respectively) than in patients of control groups (a group of patients who receive the same drugs, except for the studied one). Conclusions The study showed that in patients with CVDs treated with various drugs the CoQ10 plasma level is statistically significantly lower than in practically healthy individuals. So, to avoid the adverse reactions connected with low CoQ10 plasma levels, it is recommended to adjust the therapy to maintain its constant level.

The Mechanism of Action of Ethoxidol on Oxidative Stress Indices in Heart Failure and Hypotension

The aim of the investigation was to study the effect of 2-ethyl-6-methyl-3-hydroxypyridine malate (Ethoxidol) on the concentration of oxidative stress metabolites in patients with chronic heart failure (CHF) and hypertension.

Materials and Methods

126 patients with FC I-III CHF have been examined. In addition to their individual therapy these patients received intravenous infusions of Ethoxidol. Blood content of 2,3-diphosphoglycerate (2,3-DPG), oxygen tension (рО₂), pH, concentration of total peroxides, lactate, and aldosterone were identified. 2,3-DPG levels (g/L erythrocytes) in whole blood samples were determined by an enzyme assay using the reagent kit (Rosh, Germany), values of рО₂, рСО₂, рН, lactate in the venous blood were measured using gas analyzer Stat Profil pHOx Ultra (Nova Biomedical, USA). Indices of oxidative stress, i.e. the concentration of plasma total peroxides, were investigated by ELISA using OxyStat kit (Biomedica, Austria). Peripheral venous blood samples were collected from all patients before and 6 days after the daily intravenous Ethoxidol infusion.

Results

In patients with FC I, II, III CHF, on day 7 after intravenous Ethoxidol infusion at a dose of 100 mg/day, statistically significant growth (p=0.0002) of PaO₂ level by 15.7, 17.4, and 22.8%, respectively, was noted. In patients with FC I, II, III CHF in the group receiving standard therapy, statistically significant (p=0.002) reduction of 2,3-DPG level by 2.7, 2.4, and 4.0%, respectively, was registered. On day 7 after the infusion of Ethoxidol at a dose of 100 mg/day, its decrease by 5.7, 10.5, and 26.2%, respectively (p<0.0001), was also observed.

Conclusion

The increased concentrations of active oxygen forms have been established to negatively affect various bodily functions and adversely influence the pathophysiology of numerous diseases. Application of antioxidants, including Ethoxidol presented by us in this article, may become a clue to the development of preventive measures for many serious diseases.

Analytical Method Development for Coq10 Determination in Human Plasma Using HPLC-UV and HPLC/MS/MS

Background:

CoQ10 is a very important compound which is found in every tissue of our organism. It participates in the processes of cellular respiration and ATP production. Also, it acts as a strong antioxidant. In an organism, it is represented in two forms: oxidized (ubiquinone) and reduced (ubiquinol). Its low blood level may be a signal for a list of diseases.

Materials and Methods:

This study developed and compared two methods of CoQ10 determination in order to find the fastest and the most convenient one. The first one involved HPLC-UV with the wavelength of ubiquinone determination equivalent to 290 nm and 275 nm for ubiquinol, respectively. The second one was carried out on an HPLC/MS/MS system utilizing Electrospray Ionization (ESI) and triple quadrupole mass analyzer for quantification in MRM positive mode.

Results:

Two methods of ubiquinol and ubiquinone determination were developed and validated. HPLC-UV included sample preparation based on liquid-liquid extraction. The LLOQ was 0.50 µg/ml. HPLC-MS/MS method sample preparation was based on protein precipitation. The LLOQ was 0.10 µg/ml.

Conclusion:

During the investigation, a conclusion was drawn that the HPLC-UV method is too insensitive for simultaneous determination of ubiquinol and ubiquinone. Furthermore, ubiquinol is very unstable and during exogenous factors’ exposure, it rapidly turns into ubiquinone. While, the HPLCMS/ MS method turned out to be sensitive, selective, rapid as it provides an accurate determination of both forms of CoQ10 in spiked human plasma.

Coenzyme Q10 protects against hyperlipidemia-induced cardiac damage in apolipoprotein E-deficient mice

BACKGROUND

Hyperlipidemia is a well-established risk factor for cardiac damage, which can lead to cardiovascular diseases. Many studies have shown that Coenzyme Q10(CoQ10) protects against cardiac damage in vivo. The aim of this study was to investigate the possible protective effects of CoQ10 against cardiac damage in apolipoprotein E-deficient (ApoE^-/-) mice.

METHODS

Eight-week-old male C57BL/6 and ApoE^-/- mice were randomly divided into four groups: C57BL/6 mice fed a normal diet (C57BL/6 group); C57BL/6 mice fed a normal diet + CoQ10 (C57BL/6 + CoQ10 group); ApoE^-/- mice fed a high-fat diet (ApoE^-/- HD group), and ApoE^-/- mice fed a high-fat diet + CoQ10 (ApoE^-/- HD + CoQ10 group). All groups were fed the different diets for 16 weeks. Blood samples were obtained from the inferior vena cava and collected in serum tubes. The samples were then stored at - 80 °C until used. Coronal sections of heart tissues were fixed in 10% formalin and then embedded in paraffin for histological evaluation. The remainder of the heart tissues was snap-frozen in liquid nitrogen for mRNA or immunohistochemical analysis.

RESULTS

The metabolic parameters such as total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-c), and triglycerides (TG) levels were lower in ApoE^-/-HD + CoQ10 mice than in ApoE^-/- HD mice. There were significant pathophysiological changes (H&E, PAS, Masson and CD68 staining) in ApoE^-/- mice in the HD group compared with those in the HD + CoQ10 group. CoQ10 reduced HD-induced cardiac tissue damage via autophagy (p62 and LC3), as evidenced by immunoblotting, immunohistochemistry, and RT-qPCR. CoQ10 also inhibited inflammation (IL-6 and TNF-α) gene expression in ApoE^-/- mice.

CONCLUSIONS

These results indicate that CoQ10 is a potential therapeutic target for cardiac damage caused by hyperlipidemia.

Myopathology of Adult and Paediatric Mitochondrial Diseases

Mitochondria are dynamic organelles ubiquitously present in nucleated eukaryotic cells, subserving multiple metabolic functions, including cellular ATP generation by oxidative phosphorylation (OXPHOS). The OXPHOS machinery comprises five transmembrane respiratory chain enzyme complexes (RC). Defective OXPHOS gives rise to mitochondrial diseases (mtD). The incredible phenotypic and genetic diversity of mtD can be attributed at least in part to the RC dual genetic control (nuclear DNA (nDNA) and mitochondrial DNA (mtDNA)) and the complex interaction between the two genomes. Despite the increasing use of next-generation-sequencing (NGS) and various omics platforms in unravelling novel mtD genes and pathomechanisms, current clinical practice for investigating mtD essentially involves a multipronged approach including clinical assessment, metabolic screening, imaging, pathological, biochemical and functional testing to guide molecular genetic analysis. This review addresses the broad muscle pathology landscape including genotype–phenotype correlations in adult and paediatric mtD, the role of immunodiagnostics in understanding some of the pathomechanisms underpinning the canonical features of mtD, and recent diagnostic advances in the field.

Supplementation action with ascorbic acid in the morphology of the muscular layer and reactive acetylcholinesterase neurons of ileum of mdx mice

The Duchenne Muscular Dystrophy (DMD) is a genetic disorder characterized by the absence of dystrophin protein, causing severe myopathy from increases of oxidative stress. Injuries of intestinal muscle can compromise the myenteric plexus. This study aimed to evaluate the disorders occurred in the muscular layer and in the acetylcholinesterase myenteric neurons (ACHE-r) of ileum of mdx mice, and the effects of supplementation with ascorbic acid (AA) in both components. 30 male mice C57BL/10, and 30 male mice C57BL/10Mdx were separated according to the age and treatment (n=10/group): 30-days-old control group (C30); 30-days-old dystrophic group (D30); 60-days-old control group (C60); 60-days-old dystrophic group (D60); 60-days-old control group supplemented with AA (CS60); and 60-days-old dystrophic group supplemented with AA (DS60). The animals were euthanized and the ileum was collected and processed. Semi-serial sections were stained by Masson's trichrome, and acetylcholinesterase histochemical technique in whole-mounts preparations to identify the myenteric neurons. The muscular layer thickness and the area of smooth muscle of ileum were lower in dystrophic groups, especially in D30 group. The DS60 group showed the muscular layer thickness similar to C60. The density of ACHE-r neurons of myenteric plexus of ileum was lower in D30 animals; however, it was similar in animals of 60-days-old without treatment (C60 and D60) and, higher in DS60. The cell body profile area of ACHE-r neurons was similar in C30-D30 and C60-D60; however, it was higher in DS60. DMD caused damage to the ileum's musculature and myenteric plexus, and the AA prevented the ACHE-r neuronal loss.

Effect of Coenzyme Q10 Supplementation in Statin-Treated Obese Rats

Statins, HMG-CoA reductase inhibitors, are known to cause serious muscle injuries (e.g. myopathy, myositis and rhabdomyolysis), and these adverse effects can be rescued by co-administration of coenzyme Q₁₀ (CoQ₁₀) with statins. The goal of the current research is to assess the efficacy of combined treatment of CoQ₁₀ with Atorvastatin for hyperlipidemia induced by high-fat diet in SD rats. 4-week-old Sprague-Dawley male rats were fed normal diet or high-fat diet for 6 weeks. Then, rats were treated with either Statin or Statin with various dosages of CoQ₁₀ (30, 90 or 270 mg/kg/day, p.o.) for another 6 weeks. Compared to Statin only-treatment, CoQ₁₀ supplementation significantly reduced creatine kinase and aspartate aminotransferase levels in serum which are markers for myopathy. Moreover, CoQ₁₀ supplementation with Statin further reduced total fat, triglycerides, total cholesterol, and low-density lipoprotein-cholesterol. In contrast, the levels of high-density lipoprotein-cholesterol and CoQ₁₀ were increased in the CoQ₁₀ co-treated group. These results indicate that CoQ₁₀ treatment not only reduces the side effects of Statin, but also has an anti-obesity effect. Therefore an intake of supplementary CoQ₁₀ is helpful for solving problem of obese metabolism, so the multiple prescription of CoQ₁₀ makes us think a possibility that can be solved in being contiguous to the obesity problem, a sort of disease of the obese metabolism.

Blood metabolite data in response to maximal exercise in healthy subjects

Maximal exercise test with gas exchange measurement evaluates exercise capacities with maximal oxygen uptake (VO(2) max) measurement. Measurements of lactate (L), lactate/pyruvate ratio (L/P) and ammonium (A) during rest, exercise and recovery enhance interpretative power of maximal exercise by incorporating muscular metabolism exploration. Maximal exercise test with gas exchange measurement is standardized in cardiopulmonary evaluations but, no reference data of blood muscular metabolites are available to evaluate the muscular metabolism. We determined normal values of L, L/P and A during a standardized maximal exercise and recovery in 48 healthy sedentary volunteers and compared with results obtained in four patients with exercise intolerance and a mitochondrial disease. In healthy subjects, L, L/P and A rose during exercise. In 98% of them L, L/P or A decreased between the fifth and the fifteenth minutes of recovery. In mitochondrial patients, VO(2) max was normal or low, and L, L/P and A had the same evolution as normal subjects or showed no decrease during recovery. We gave normal L, L/P and A values, which establish references for a maximal exercise test with muscular metabolism exploration. This test is helpful for clinicians in functional evaluation, management and treatment of metabolic myopathy and would be a useful tool in diagnosis of metabolic myopathy.

Scurvy: past, present and future

This study outlines the major landmarks in the research on scurvy and its relationship to vitamin C. A thorough search including original manuscripts, books and contemporary reviews published in PubMed was conducted using as keywords "scurvy", "vitamin C", and "history of medicine". Observations on scurvy first appear in Egyptian medical scrolls 3500 years ago, and continue through to the discovery of vitamin C and the modern research on the physiological role of ascorbic acid. The observations of great navigators during the 15th and 16th centuries, when scurvy plagued ships' crews, played an important role in clarifying scurvy's etiology. Among the personalities in the history of the disease, James Lind and Albert Szent-Györgyi are most noteworthy, the first for conducting the first clinical trial on the treatment of scurvy with lemon and orange juices, and the second for discovering and identifying vitamin C.

Metabolic myopathies: functional evaluation by different exercise testing approaches

Metabolic myopathies are a clinically and etiologically heterogeneous group of disorders due to defects in muscular energy metabolism. They include glycogen storage diseases, fatty acid oxidation defects, and mitochondrial disorders. The typical manifestations of a metabolic myopathy are exercise-induced myalgias, exercise intolerance, and cramps. Evaluating subjects with such symptoms is not easy because of the frequent lack of clinical features. Exercise tests are, therefore, reliable screening tools. Here, we discuss the possible role of such exercise testing techniques in the diagnostic approach of a patient with suspected metabolic myopathy.

Cardiopulmonary exercise testing: relevant but underused

Cardiopulmonary exercise testing (CPX) is a relatively old technology, but has sustained relevance for many primary care clinical scenarios in which it is, ironically, rarely considered. Advancing computer technology has made CPX easier to administer and interpret at a time when our aging population is more prone to comorbidities and higher prevalence of nonspecific symptoms of exercise intolerance and dyspnea, for which CPX is particularly useful diagnostically and prognostically. These discrepancies in application are compounded by patterns in which CPX is often administered and interpreted by cardiology, pulmonary, or exercise specialists who limit their assessments to the priorities of their own discipline, thereby missing opportunities to distinguish symptom origins. When used properly, CPX enables the physician to assess fitness and uncover cardiopulmonary issues at earlier phases of work-up, which would therefore be especially useful for primary care physicians. In this article, we provide an overview of CPX principles and testing logistics, as well as some of the clinical contexts in which it can enhance patient care.

mtDNA disease for the neurologist

Inherited and acquired mutations of mtDNA cause an extraordinary group of diseases that are associated with a diverse panoply of neurological and non-neurological features. These diseases are surprisingly common and are often severely debilitating and readily transmitted through families. Remarkable advances in understanding molecular mechanisms have been made since the first pathogenic mtDNA mutations were identified in 1988, and while widely available genetic techniques have facilitated diagnosis, the complexities of mitochondrial genetics leave the neurologist facing important challenges in recognizing, managing and counseling patients with mtDNA mutations. In this article, we will discuss the clinical phenotypes associated with mtDNA disease, current diagnostic strategies, disease management and genetic counseling, as well as presenting new developments in preventing disease transmission and secondary complications.

Proteomic DIGE analysis of the mitochondria-enriched fraction from aged rat skeletal muscle

Skeletal muscle aging is associated with a loss in tissue mass and contractile strength, as well as fiber type shifting and bioenergetic adaptation processes. Since mitochondria represent the primary site for energy generation via oxidative phosphorylation, we investigated potential changes in the expression pattern of the mitochondrial proteome using the highly sensitive DIGE approach. The comparative analysis of the mitochondria-enriched fraction from young adult versus aged muscle revealed an age-related change in abundance for 39 protein species. MS technology identified the majority of altered proteins as constituents of muscle mitochondria. An age-dependent increase was observed for NADH dehydrogenase, the mitochondrial inner membrane protein mitofilin, peroxiredoxin isoform PRX-III, ATPase synthase, succinate dehydrogenase, mitochondrial fission protein Fis1, succinate-coenzyme A ligase, acyl-coenzyme A dehydrogenase, porin isoform VDAC2, ubiquinol-cytochrome c reductase core I protein and prohibitin. Immunoblotting, enzyme testing and confocal microscopy were used to validate proteomic findings. The DIGE-identified increase in key mitochondrial elements during aging agrees with the concept that sarcopenia is associated with a shift to a slower contractile phenotype and more pronounced aerobic-oxidative metabolism. This suggests that mitochondrial markers are reliable candidates that should be included in the future establishment of a biomarker signature of skeletal muscle aging.

Electron transfer mediators and other metabolites and cofactors in the treatment of mitochondrial dysfunction

Mitochondrial disorders (MDs) are caused by impairment of the mitochondrial electron transport chain (ETC). The ETC is needed for oxidative phosphorylation, which provides the cell with the most efficient energy outcome in terms of ATP production. One of the pathogenic mechanisms of MDs is the accumulation of reactive oxygen species. Mitochondrial dysfunction and oxidative stress appear to also have a strong impact on the pathogenesis of neurodegenerative diseases and cancer. The treatment of MDs is still inadequate. Therapies that have been attempted include ETC cofactors, other metabolites secondarily decreased in MDs, antioxidants, and agents acting on lactic acidosis. However, the role of these dietary supplements in the treatment of the majority of MDs remains unclear. This article reviews the rationale for their use and their role in clinical practice in the context of MDs and other disorders involving mitochondrial dysfunction.

Advances in molecular diagnostics for mitochondrial diseases

BACKGROUND

Mitochondrial disorders (MD) are diseases caused by impairment of the mitochondrial respiratory chain. Phenotypes are polymorphous and may range from pure myopathy to multisystemic disorders. The genetic defect can be located on mitochondrial or nuclear DNA. At present, diagnosis of MD requires a complex approach: measurement of serum lactate, electromyography, muscle histology and enzymology, and genetic analysis. Magnetic resonance spectroscopy allows the assessment of tissue metabolic alterations, thus providing useful information for the diagnosis and monitoring of MD. Molecular soluble markers of mitochondrial dysfunction, at rest and during exercise, can identify the impairment of the aerobic system in MD, but a reliable biomarker for the screening or diagnosis of MD is still needed.

OBJECTIVE

Molecular and genetic characterization of MD, together with other experimental approaches, contribute to add new insights to these diseases. Here, the role and advances of diagnostic techniques for MD are reviewed.

CONCLUSION

Possible applications of the results obtained by new molecular investigative approaches could in future guide therapeutic strategies.

Vitamin C: update on physiology and pharmacology

Although ascorbic acid is an important water-soluble antioxidant and enzyme cofactor in plants and animals, humans and some other species do not synthesize ascorbate due to the lack of the enzyme catalyzing the final step of the biosynthetic pathway, and for them it has become a vitamin. This review focuses on the role of ascorbate in various hydroxylation reactions and in the redox homeostasis of subcellular compartments including mitochondria and endoplasmic reticulum. Recently discovered functions of ascorbate in nucleic acid and histone dealkylation and proteoglycan deglycanation are also summarized. These new findings might delineate a role for ascorbate in the modulation of both pro- and anti-carcinogenic mechanisms. Recent advances and perspectives in therapeutic applications are also reviewed. On the basis of new and earlier observations, the advantages of the lost ability to synthesize ascorbate are pondered. The increasing knowledge of the functions of ascorbate and of its molecular sites of action can mechanistically substantiate a place for ascorbate in the treatment of various diseases.

Short- and long-term effects of endurance training in patients with mitochondrial myopathy

BACKGROUND AND PURPOSE

It is unknown whether prolonged training is a safe treatment to alleviate exercise intolerance in patients with mitochondrial DNA (mtDNA) mutations.

METHODS

The effect of 3 and 12 months training and 3-12 months deconditioning was studied in four patients carrying different mtDNA mutations.

RESULTS

Three-month moderate-intensity training increased oxidative capacity by 23%, which was sustained after 6-12 months of low-intensity training. Training and deconditioning did not induce adverse effects on clinical symptoms, muscle morphology and mtDNA mutation load in muscle.

CONCLUSION

Long-term training effectively improves exercise capacity in patients with mitochondrial myopathy, and appears to be safe.

Concerted action of two novel tRNA mtDNA point mutations in chronic progressive external ophthalmoplegia

CPEO (chronic progressive external ophthalmoplegia) is a common mitochondrial disease phenotype in adults which is due to mtDNA (mitochondrial DNA) point mutations in a subset of patients. Attributing pathogenicity to novel tRNA mtDNA mutations still poses a challenge, particularly when several mtDNA sequence variants are present. In the present study we report a CPEO patient for whom sequencing of the mitochondrial genome revealed three novel tRNA mtDNA mutations: G5835A, del4315A, T1658C in tRNATyr, tRNAIle and tRNAVal genes. In skeletal muscle, the tRNAVal and tRNAIle mutations were homoplasmic, whereas the tRNATyr mutation was heteroplasmic. To address the pathogenic relevance, we performed two types of functional tests: (i) single skeletal muscle fibre analysis comparing G5835A mutation loads and biochemical phenotypes of corresponding fibres, and (ii) Northern-blot analyses of mitochondrial tRNATyr, tRNAIle and tRNAVal. We demonstrated that both the G5835A tRNATyr and del4315A tRNAIle mutation have serious functional consequences. Single-fibre analyses displayed a high threshold of the tRNATyr mutation load for biochemical phenotypic expression at the single-cell level, indicating a rather mild pathogenic effect. In contrast, skeletal muscle tissue showed a severe decrease in respiratory-chain activities, a reduced overall COX (cytochrome c oxidase) staining intensity and abundant COX-negative fibres. Northern-blot analyses showed a dramatic reduction of tRNATyr and tRNAIle levels in muscle, with impaired charging of tRNAIle, whereas tRNAVal levels were only slightly decreased, with amino-acylation unaffected. Our findings suggest that the heteroplasmic tRNATyr and homoplasmic tRNAIle mutation act together, resulting in a concerted effect on the biochemical and histological phenotype. Thus homoplasmic mutations may influence the functional consequences of pathogenic heteroplasmic mtDNA mutations.

Genetic ablation of calcium-independent phospholipase A2gamma leads to alterations in mitochondrial lipid metabolism and function resulting in a deficient mitochondrial bioenergetic phenotype

Previously, we identified a novel calcium-independent phospholipase, designated calcium-independent phospholipase A(2) gamma (iPLA(2)gamma), which possesses dual mitochondrial and peroxisomal subcellular localization signals. To identify the roles of iPLA(2)gamma in cellular bioenergetics, we generated mice null for the iPLA(2)gamma gene by eliminating the active site of the enzyme through homologous recombination. Mice null for iPLA(2)gamma display multiple bioenergetic dysfunctional phenotypes, including 1) growth retardation, 2) cold intolerance, 3) reduced exercise endurance, 4) greatly increased mortality from cardiac stress after transverse aortic constriction, 5) abnormal mitochondrial function with a 65% decrease in ascorbate-induced Complex IV-mediated oxygen consumption, and 6) a reduction in myocardial cardiolipin content accompanied by an altered cardiolipin molecular species composition. We conclude that iPLA(2)gamma is essential for maintaining efficient bioenergetic mitochondrial function through tailoring mitochondrial membrane lipid metabolism and composition.