Accumulation of oxidative stress around the stroke-like lesions of MELAS patients

Arginine Supplementation in MELAS Syndrome: What Do We Know about the Mechanisms?

MELAS syndrome, characterized by mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes, represents a devastating mitochondrial disease, with the stroke-like episodes being its primary manifestation. Arginine supplementation has been used and recommended as a treatment for these acute attacks; however, insufficient evidence exists to support this treatment for MELAS. The mechanisms underlying the effect of arginine on MELAS pathophysiology remain unclear, although it is hypothesized that arginine could increase nitric oxide availability and, consequently, enhance blood supply to the brain. A more comprehensive understanding of these mechanisms is necessary to improve treatment strategies, such as dose and regimen adjustments; identify which patients could benefit the most; and establish potential markers for follow-up. This review aims to analyze the existing evidence concerning the mechanisms through which arginine supplementation impacts MELAS pathophysiology and provide the current scenario and perspectives for future investigations.

Mitochondrial Properties in Skeletal Muscle Fiber

Mitochondria are the primary source of energy production and are implicated in a wide range of biological processes in most eukaryotic cells. Skeletal muscle heavily relies on mitochondria for energy supplements. In addition to being a powerhouse, mitochondria evoke many functions in skeletal muscle, including regulating calcium and reactive oxygen species levels. A healthy mitochondria population is necessary for the preservation of skeletal muscle homeostasis, while mitochondria dysregulation is linked to numerous myopathies. In this review, we summarize the recent studies on mitochondria function and quality control in skeletal muscle, focusing mainly on in vivo studies of rodents and human subjects. With an emphasis on the interplay between mitochondrial functions concerning the muscle fiber type-specific phenotypes, we also discuss the effect of aging and exercise on the remodeling of skeletal muscle and mitochondria properties.

Humanin and diabetes mellitus: A review of in vitro and in vivo studies

Humanin (HN) is a 24-amino acid mitochondrial-derived polypeptide with cyto-protective and anti-apoptotic effects that regulates the mitochondrial functions under stress conditions. Accumulating evidence suggests the role of HN against age-related diseases, such as Alzheimer’s disease. The decline in insulin action is a metabolic feature of aging and thus, type 2 diabetes mellitus is considered an age-related disease, as well. It has been suggested that HN increases insulin sensitivity, improves the survival of pancreatic beta cells, and delays the onset of diabetes, actions that could be deployed in the treatment of diabetes. The aim of this review is to present the in vitro and in vivo studies that examined the role of HN in insulin resistance and diabetes and to discuss its newly emerging role as a therapeutic option against those conditions.

Sonlicromanol improves neuronal network dysfunction and transcriptome changes linked to m.3243A>G heteroplasmy in iPSC-derived neurons

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is often caused by an adenine to guanine variant at m.3243 (m.3243A>G) of the MT-TL1 gene. To understand how this pathogenic variant affects the nervous system, we differentiated human induced pluripotent stem cells (iPSCs) into excitatory neurons with normal (low heteroplasmy) and impaired (high heteroplasmy) mitochondrial function from MELAS patients with the m.3243A>G pathogenic variant. We combined micro-electrode array (MEA) measurements with RNA sequencing (MEA-seq) and found reduced expression of genes involved in mitochondrial respiration and presynaptic function, as well as non-cell autonomous processes in co-cultured astrocytes. Finally, we show that the clinical phase II drug sonlicromanol can improve neuronal network activity when treatment is initiated early in development. This was intricately linked with changes in the neuronal transcriptome. Overall, we provide insight in transcriptomic changes in iPSC-derived neurons with high m.3243A>G heteroplasmy, and show the pathology is partially reversible by sonlicromanol.

Molecular imaging for mitochondrial metabolism and oxidative stress in mitochondrial diseases and neurodegenerative disorders

BACKGROUND

Increasing evidence from pathological and biochemical investigations suggests that mitochondrial metabolic impairment and oxidative stress play a crucial role in the pathogenesis of mitochondrial diseases, such as mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, and various neurodegenerative disorders. Recent advances in molecular imaging technology with positron emission tomography (PET) and functional magnetic resonance imaging (MRI) have accomplished a direct and non-invasive evaluation of the pathophysiological changes in living patients.

SCOPE OF REVIEW

In this review, we focus on the latest achievements of molecular imaging for mitochondrial metabolism and oxidative stress in mitochondrial diseases and neurodegenerative disorders.

MAJOR CONCLUSIONS

Molecular imaging with PET and MRI exhibited mitochondrial metabolic changes, such as enhanced glucose utilization with lactic acid fermentation, suppressed fatty acid metabolism, decreased TCA-cycle metabolism, impaired respiratory chain activity, and increased oxidative stress, in patients with MELAS syndrome. In addition, PET imaging clearly demonstrated enhanced cerebral oxidative stress in patients with Parkinson's disease or amyotrophic lateral sclerosis. The magnitude of oxidative stress correlated well with clinical severity in patients, indicating that oxidative stress based on mitochondrial dysfunction is associated with the neurodegenerative changes in these diseases.

GENERAL SIGNIFICANCE

Molecular imaging is a promising tool to improve our knowledge regarding the pathogenesis of diseases associated with mitochondrial dysfunction and oxidative stress, and this would facilitate the development of potential antioxidants and mitochondrial therapies.

Chemical reversal of abnormalities in cells carrying mitochondrial DNA mutations

Mitochondrial DNA (mtDNA) mutations are the major cause of mitochondrial diseases. Cells harboring disease-related mtDNA mutations exhibit various phenotypic abnormalities, such as reduced respiration and elevated lactic acid production. Induced pluripotent stem cell (iPSC) lines derived from patients with mitochondrial disease, with high proportions of mutated mtDNA, exhibit defects in maturation into neurons or cardiomyocytes. In this study, we have discovered a small-molecule compound, which we name tryptolinamide (TLAM), that activates mitochondrial respiration in cybrids generated from patient-derived mitochondria and fibroblasts from patient-derived iPSCs. We found that TLAM inhibits phosphofructokinase-1 (PFK1), which in turn activates AMPK-mediated fatty-acid oxidation to promote oxidative phosphorylation, and redirects carbon flow from glycolysis toward the pentose phosphate pathway to reinforce anti-oxidative potential. Finally, we found that TLAM rescued the defect in neuronal differentiation of iPSCs carrying a high ratio of mutant mtDNA, suggesting that PFK1 represents a potential therapeutic target for mitochondrial diseases.

PET Imaging for Oxidative Stress in Neurodegenerative Disorders Associated with Mitochondrial Dysfunction

Oxidative stress based on mitochondrial dysfunction is assumed to be the principal molecular mechanism for the pathogenesis of many neurodegenerative disorders. However, the effects of oxidative stress on the neurodegeneration process in living patients remain to be elucidated. Molecular imaging with positron emission tomography (PET) can directly evaluate subtle biological changes, including the redox status. The present review focuses on recent advances in PET imaging for oxidative stress, in particular the use of the Cu-ATSM radioligand, in neurodegenerative disorders associated with mitochondrial dysfunction. Since reactive oxygen species are mostly generated by leakage of excess electrons from an over-reductive state due to mitochondrial respiratory chain impairment, PET with ⁶²Cu-ATSM, the accumulation of which depends on an over-reductive state, is able to image oxidative stress. ⁶²Cu-ATSM PET studies demonstrated enhanced oxidative stress in the disease-related brain regions of patients with mitochondrial disease, Parkinson’s disease, and amyotrophic lateral sclerosis. Furthermore, the magnitude of oxidative stress increased with disease severity, indicating that oxidative stress based on mitochondrial dysfunction contributes to promoting neurodegeneration in these diseases. Oxidative stress imaging has improved our insights into the pathological mechanisms of neurodegenerative disorders, and is a promising tool for monitoring further antioxidant therapies.

Mitochondrial 3243A > G mutation confers pro-atherogenic and pro-inflammatory properties in MELAS iPS derived endothelial cells

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a mitochondrial disorder that is commonly caused by the m.3243A > G mutation in the MT-TL1 gene encoding for mitochondrial tRNA(Leu(UUR)). While clinical studies reported cerebral infarcts, atherosclerotic lesions, and altered vasculature and stroke-like episodes (SLE) in MELAS patients, it remains unclear how this mutation causes the onset and subsequent progression of the disease. Here, we report that in addition to endothelial dysfunction, diseased endothelial cells (ECs) were found to be pro-atherogenic and pro-inflammation due to high levels of ROS and Ox-LDLs, and high basal expressions of VCAM-1, in particular isoform b, respectively. Consistently, more monocytes were found to adhere to MELAS ECs as compared to the isogenic control, suggesting the presence of an atherosclerosis-like pathology in MELAS. Notably, these disease phenotypes in endothelial cells can be effectively reversed by anti-oxidant treatment suggesting that the lowering of ROS is critical for treating patients with MELAS syndrome.

Humanin: a mitochondrial signaling peptide as a biomarker for impaired fasting glucose-related oxidative stress

Mitochondrial RNR-2 (mt-RNR2, humanin) has been shown to play a role in protecting several types of cells and tissues from the effects of oxidative stress. Humanin (HN) functions through extracellular and intracellular pathways adjusting mitochondrial oxidative phosphorylation and ATP production. Addition of HN improved insulin sensitivity in animal models of diabetes mellitus but no clinical studies have been carried out to measure HN levels in humans associated with hyperglycemia. The plasma levels of HN in participants attending a diabetes complications screening clinic were measured. Clinical history and anthropometric data were obtained from all participants. Plasma levels of HN were measured by a commercial ELISA kit. All data were analyzed applying nonparametric statistics and general linear modeling to correct for age and gender. A significant decrease (P = 0.0001) in HN was observed in the impaired fasting glucose (IFG) group (n = 23; 204.84 ± 92.87 pg mL(-1)) compared to control (n = 58; 124.3 ± 83.91 pg mL(-1)) consistent with an adaptive cellular response by HN to a slight increase in BGL.

Oxidative stress in inherited mitochondrial diseases

Mitochondria are a source of reactive oxygen species (ROS). Mitochondrial diseases are the result of inherited defects in mitochondrially expressed genes. One potential pathomechanism for mitochondrial disease is oxidative stress. Oxidative stress can occur as the result of increased ROS production or decreased ROS protection. The role of oxidative stress in the five most common inherited mitochondrial diseases, Friedreich ataxia, LHON, MELAS, MERRF, and Leigh syndrome (LS), is discussed. Published reports of oxidative stress involvement in the pathomechanisms of these five mitochondrial diseases are reviewed. The strongest evidence for an oxidative stress pathomechanism among the five diseases was for Friedreich ataxia. In addition, a meta-analysis was carried out to provide an unbiased evaluation of the role of oxidative stress in the five diseases, by searching for "oxidative stress" citation count frequency for each disease. Of the five most common mitochondrial diseases, the strongest support for oxidative stress is for Friedreich ataxia (6.42%), followed by LHON (2.45%), MELAS (2.18%), MERRF (1.71%), and LS (1.03%). The increased frequency of oxidative stress citations was significant relative to the mean of the total pool of five diseases (p<0.01) and the mean of the four non-Friedreich diseases (p<0.0001). Thus there is support for oxidative stress in all five most common mitochondrial diseases, but the strongest, significant support is for Friedreich ataxia.

The ROS-sensitive microRNA-9/9* controls the expression of mitochondrial tRNA-modifying enzymes and is involved in the molecular mechanism of MELAS syndrome

Mitochondrial dysfunction activates mitochondria-to-nucleus signaling pathways whose components are mostly unknown. Identification of these components is important to understand the molecular mechanisms underlying mitochondrial diseases and to discover putative therapeutic targets. MELAS syndrome is a rare neurodegenerative disease caused by mutations in mitochondrial (mt) DNA affecting mt-tRNA(Leu(UUR)). Patient and cybrid cells exhibit elevated oxidative stress. Moreover, mutant mt-tRNAs(Leu(UUR)) lack the taurine-containing modification normally present at the wobble uridine (U34) of wild-type mt-tRNA(Leu(UUR)), which is considered an etiology of MELAS. However, the molecular mechanism is still unclear. We found that MELAS cybrids exhibit a significant decrease in the steady-state levels of several mt-tRNA-modification enzymes, which is not due to transcriptional regulation. We demonstrated that oxidative stress mediates an NFkB-dependent induction of microRNA-9/9*, which acts as a post-transcriptional negative regulator of the mt-tRNA-modification enzymes GTPBP3, MTO1 and TRMU. Down-regulation of these enzymes by microRNA-9/9* affects the U34 modification status of non-mutant tRNAs and contributes to the MELAS phenotype. Anti-microRNA-9 treatments of MELAS cybrids reverse the phenotype, whereas miR-9 transfection of wild-type cells mimics the effects of siRNA-mediated down-regulation of GTPBP3, MTO1 and TRMU. Our data represent the first evidence that an mt-DNA disease can directly affect microRNA expression. Moreover, we demonstrate that the modification status of mt-tRNAs is dynamic and that cells respond to stress by modulating the expression of mt-tRNA-modifying enzymes. microRNA-9/9* is a crucial player in mitochondria-to-nucleus signaling as it regulates expression of nuclear genes in response to changes in the functional state of mitochondria.

Occasional seizures, epilepsy, and inborn errors of metabolism

Seizures are a common paediatric problem, with inborn errors of metabolism being a rare underlying aetiology. The clinical presentation of inborn errors of metabolism is often associated with other neurological symptoms, such as hypotonia, movement disorders, and cognitive disturbances. However, the occurrence of epilepsy associated with inborn errors of metabolism represents a major challenge that needs to be identified quickly; for some cases, specific treatments are available, metabolic decompensation might be avoided, and accurate counselling can be given about recurrence risk. Some clinical presentations are more likely than others to point to an inborn error of metabolism as the cause of seizures. Knowledge of important findings at examination, and appropriate biochemical investigation of children with seizures of uncertain cause, can aid the diagnosis of an inborn error of metabolism and ascertain whether or not the seizures are amenable to specific metabolic treatment.

Oxidative stress and mitochondrial dysfunction across broad-ranging pathologies: toward mitochondria-targeted clinical strategies

Beyond the disorders recognized as mitochondrial diseases, abnormalities in function and/or ultrastructure of mitochondria have been reported in several unrelated pathologies. These encompass ageing, malformations, and a number of genetic or acquired diseases, as diabetes and cardiologic, haematologic, organ-specific (e.g., eye or liver), neurologic and psychiatric, autoimmune, and dermatologic disorders. The mechanistic grounds for mitochondrial dysfunction (MDF) along with the occurrence of oxidative stress (OS) have been investigated within the pathogenesis of individual disorders or in groups of interrelated disorders. We attempt to review broad-ranging pathologies that involve mitochondrial-specific deficiencies or rely on cytosol-derived prooxidant states or on autoimmune-induced mitochondrial damage. The established knowledge in these subjects warrants studies aimed at elucidating several open questions that are highlighted in the present review. The relevance of OS and MDF in different pathologies may establish the grounds for chemoprevention trials aimed at compensating OS/MDF by means of antioxidants and mitochondrial nutrients.

Quantitative measurement of cerebral oxygen extraction fraction using MRI in patients with MELAS

OBJECTIVE

To quantify the cerebral OEF at different phases of stroke-like episodes in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) by using MRI.

METHODS

We recruited 32 patients with MELAS confirmed by gene analysis. Conventional MRI scanning, as well as functional MRI including arterial spin labeling and oxygen extraction fraction imaging, was undertaken to obtain the pathological and metabolic information of the brains at different stages of stroke-like episodes in patients. A total of 16 MRI examinations at the acute and subacute phase and 19 examinations at the interictal phase were performed. In addition, 24 healthy volunteers were recruited for control subjects. Six regions of interest were placed in the anterior, middle, and posterior parts of the bilateral hemispheres to measure the OEF of the brain or the lesions.

RESULTS

OEF was reduced significantly in brains of patients at both the acute and subacute phase (0.266 ± 0.026) and at the interictal phase (0.295 ± 0.009), compared with normal controls (0.316 ± 0.025). In the brains at the acute and subacute phase of the episode, 13 ROIs were prescribed on the stroke-like lesions, which showed decreased OEF compared with the contralateral spared brain regions. Increased blood flow was revealed in the stroke-like lesions at the acute and subacute phase, which was confined to the lesions.

CONCLUSION

MRI can quantitatively show changes in OEF at different phases of stroke-like episodes. The utilization of oxygen in the brain seems to be reduced more severely after the onset of episodes in MELAS, especially for those brain tissues involved in the episodes.

Epilepsy in inborn errors of metabolism

Epilepsies associated with inborn errors of metabolism (IEM) represent a major challenge. Seizures rarely dominate the clinical presentation, which is more frequently associated with other neurological symptoms, such as hypotonia and/or cognitive disturbances. Although epilepsy in IEM can be classified in various ways according to pathogenesis, age of onset, or electroclinical presentation, the most pragmatic approach is determined by whether they are accessible to specific treatment or not. The main potentially treatable causes comprise vitamin B6 (pyridoxine deficiency), biotine, and GLUT1 deficiency (GLUT1DS) syndromes. Folinic acid-dependent seizures are allelic with pyridoxine dependency. Incompletely treatable IEMs include pyridoxal phosphate, serine, and creatine deficiencies. The main IEMs that present with epilepsy but offer no specific treatment are nonketotic hyperglycinemia, mitochondrial disorders, sulfite oxidase deficiency, ceroid-lipofuscinosis, Menkes disease, and peroxisomal disorders.

Patient-derived fibroblasts indicate oxidative stress status and may justify antioxidant therapy in OXPHOS disorders

Oxidative phosphorylation disorders are often associated with increased oxidative stress and antioxidant therapy is frequently given as treatment. However, the role of oxidative stress in oxidative phosphorylation disorders or patients is far from clear and consequently the preventive or therapeutic effect of antioxidants is highly anecdotic. Therefore, we performed a systematic study of a panel of oxidative stress parameters (reactive oxygen species levels, damage and defense) in fibroblasts of twelve well-characterized oxidative phosphorylation patients with a defect in the POLG1 gene, in the mitochondrial DNA-encoded tRNA-Leu gene (m.3243A>G or m.3302A>G) and in one of the mitochondrial DNA-encoded NADH dehydrogenase complex I (CI) subunits. All except two cell lines (one POLG1 and one tRNA-Leu) showed increased reactive oxygen species levels compared with controls, but only four (two CI and two tRNA-Leu) cell lines provided evidence for increased oxidative protein damage. The absence of a correlation between reactive oxygen species levels and oxidative protein damage implies differences in damage prevention or correction. This was investigated by gene expression studies, which showed adaptive and compensating changes involving antioxidants and the unfolded protein response, especially in the POLG1 group. This study indicated that patients display individual responses and that detailed analysis of fibroblasts enables the identification of patients that potentially benefit from antioxidant therapy. Furthermore, the fibroblast model can also be used to search for and test novel, more specific antioxidants or explore ways to stimulate compensatory mechanisms.

Evaluation of systemic redox states in patients carrying the MELAS A3243G mutation in mitochondrial DNA

BACKGROUND/AIMS

To clarify the change of systemic redox states in patients carrying the A3243G mutation in mitochondrial DNA (A3243G), we evaluated oxidative stress and antioxidant activity in the serum of patients.

METHODS

Oxidative stress and antioxidant activity in the serum samples obtained from 14 patients carrying A3243G and from 34 healthy controls were analyzed using the diacron-reactive oxygen metabolites (d-ROMs) and biological antioxidant potential (BAP) tests, respectively.

RESULTS

The mean d-ROMs level of all patients was significantly greater than that of the controls (p < 0.005), and the mean BAP/d-ROMs ratio of all patients was significantly lower than that of the controls (p < 0.02). In the patients with a history of stroke-like episodes (n = 10), both mean d-ROMs and BAP levels were increased compared with those of the controls (both p < 0.01). The mean BAP level of the patients without a history of stroke-like episodes (n = 4) was significantly decreased compared with that of the controls (p < 0.001), but the mean d-ROMs levels were not significantly different.

CONCLUSION

d-ROMs and BAP tests indicated that patients carrying A3243G are always exposed to underlying oxidative stress, even at a remission state of stroke-like episodes.

Metabolically induced heteroplasmy shifting and l-arginine treatment reduce the energetic defect in a neuronal-like model of MELAS

The m.3243A>G variant in the mitochondrial tRNA(Leu(UUR)) gene is a common mitochondrial DNA (mtDNA) mutation. Phenotypic manifestations depend mainly on the heteroplasmy, i.e. the ratio of mutant to normal mtDNA copies. A high percentage of mutant mtDNA is associated with a severe, life-threatening neurological syndrome known as MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes). MELAS is described as a neurovascular disorder primarily affecting the brain and blood vessels, but the pathophysiology of the disease is poorly understood. We developed a series of cybrid cell lines at two different mutant loads: 70% and 100% in the nuclear background of a neuroblastoma cell line (SH-SY5Y). We investigated the impact of the mutation on the metabolism and mitochondrial respiratory chain activity of the cybrids. The m.3243A>G mitochondrial mutation induced a metabolic switch towards glycolysis in the neuronal cells and produced severe defects in respiratory chain assembly and activity. We used two strategies to compensate for the biochemical defects in the mutant cells: one consisted of lowering the glucose content in the culture medium, and the other involved the addition of l-arginine. The reduction of glucose significantly shifted the 100% mutant cells towards the wild-type, reaching a 90% mutant level and restoring respiratory chain complex assembly. The addition of l-arginine, a nitric oxide (NO) donor, improved complex I activity in the mutant cells in which the defective NO metabolism had led to a relative shortage of NO. Thus, metabolically induced heteroplasmy shifting and l-arginine therapy may constitute promising therapeutic strategies against MELAS.

Apparent diffusion coefficients of metabolites in patients with MELAS using diffusion-weighted MR spectroscopy

BACKGROUND AND PURPOSE

DW-MR spectroscopy can detect the diffusion coefficients of NAA, Cr, PCr, and Cho and can, therefore, provide some useful information. The aims of this study were to probe the mechanisms underlying the pathogenesis of MELAS and to see whether DW-MR spectroscopy is a useful technique for other diseases besides cerebral infarction.

MATERIALS AND METHODS

Fifteen healthy volunteers and 10 patients with MELAS were enrolled in the study. All were scanned on a 3T whole-body MR imaging scanner. Fifteen ADCs of the singlet metabolites in the gray matter of the healthy subjects, 10 ADCs of the singlet metabolites in the lesions, and 8 ADCs of the singlet metabolites in the nonaffected areas were used in the statistical analysis, respectively.

RESULTS

The metabolite ADCs of the nonaffected areas and the lesions in the patients were higher than those of the frontal gray matter in the healthy controls. There were significant differences between the metabolite ADCs of the nonaffected areas in patients and those in the healthy controls, and it was the same with the metabolite ADCs of the lesions and those of the healthy controls.

CONCLUSIONS

The increased ADC values of the metabolites reveal that MELAS is a mitochondrial neuronopathy and involves the entire brain. DW-MR spectroscopy is a very useful noninvasive technique, which can show some valuable information that conventional MR imaging cannot display. Thus, it can be applied to brain diseases besides cerebral infarction.

The appearance of ADCs in the non-affected areas of the patients with MELAS

INTRODUCTION

The exact mechanism of the mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) remain unclear. Diffusion-weighted imaging (DWI) is a magnetic resonance (MR) imaging technique for studying the pathophysiologic change of the MELAS. The purpose of the study is to see whether the apparent diffusion coefficient (ADC) of MELAS in the non-affected areas is different from the ADC of the normal subjects and to speculate the pathophysiological mechanisms of the MELAS.

METHODS

Sixteen cases of MELAS were retrospectively analyzed. Thirty healthy subjects were chosen to constitute the control group. All of them were performed on the 3.0T whole-body MR scanner with axial view T2 fluid attenuated inversion recovery (flair), T2-weighted imaging, T1flair, and DWI. An ADC map was reconstructed in the workstation. Two to five regions of interest were put in the non-affected frontal lobe and basal ganglia. All data took statistical analysis.

RESULTS

There were significant differences between the ADC of the patients with MELAS and the controls in the non-affected areas, including the superior frontal gyrus, precentral gyrus, corpus striatum, thalamus, and white matter of the semi-oval centrum.

CONCLUSION

ADCs in the non-affected areas of the patients with MELAS are higher than those of the normal subjects. Pathological changes take place in the non-affected areas of the patients with MELAS.