Cerebral metabolic abnormalities in A3243G mitochondrial DNA mutation carriers

Imaging brain glucose metabolism in vivo reveals propionate as a major anaplerotic substrate in pyruvate dehydrogenase deficiency

A vexing problem in mitochondrial medicine is our limited capacity to evaluate the extent of brain disease in vivo. This limitation has hindered our understanding of the mechanisms that underlie the imaging phenotype in the brain of patients with mitochondrial diseases and our capacity to identify new biomarkers and therapeutic targets. Using comprehensive imaging, we analyzed the metabolic network that drives the brain structural and metabolic features of a mouse model of pyruvate dehydrogenase deficiency (PDHD). As the disease progressed in this animal, in vivo brain glucose uptake and glycolysis increased. Propionate served as a major anaplerotic substrate, predominantly metabolized by glial cells. A combination of propionate and a ketogenic diet extended lifespan, improved neuropathology, and ameliorated motor deficits in these animals. Together, intermediary metabolism is quite distinct in the PDHD brain-it plays a key role in the imaging phenotype, and it may uncover new treatments for this condition.

Magnetic resonance spectroscopy in MELAS syndrome: correlation with CSF and plasma metabolite levels and change after glutamine supplementation

PURPOSE

MELAS syndrome is a genetic disorder caused by mitochondrial DNA mutations. We previously described that MELAS patients had increased CSF glutamate and decreased CSF glutamine levels and that oral glutamine supplementation restores these values. Proton magnetic resonance spectroscopy (1H-MRS) allows the in vivo evaluation of brain metabolism. We aimed to compare 1H-MRS of MELAS patients with controls, the 1H-MRS after glutamine supplementation in the MELAS group, and investigate the association between 1H-MRS and CSF lactate, glutamate, and glutamine levels.

METHODS

We conducted an observational case-control study and an open-label, single-cohort study with single-voxel MRS (TE 144/35 ms). We assessed the brain metabolism changes in the prefrontal (PFC) and parieto-occipital) cortex (POC) after oral glutamine supplementation in MELAS patients. MR spectra were analyzed with jMRUI software.

RESULTS

Nine patients with MELAS syndrome (35.8 ± 3.2 years) and nine sex- and age-matched controls were recruited. Lactate/creatine levels were increased in MELAS patients in both PFC and POC (0.40 ± 0.05 vs. 0, p < 0.001; 0.32 ± 0.03 vs. 0, p < 0.001, respectively). No differences were observed between groups in glutamate and glutamine (Glx/creatine), either in PFC (p = 0.930) or POC (p = 0.310). No differences were observed after glutamine supplementation. A positive correlation was found between CSF lactate and lactate/creatine only in POC (0.85, p = 0.003).

CONCLUSION

No significant metabolite changes were observed in the brains of MELAS patients after glutamine supplementation. While we found a positive correlation between lactate levels in CSF and 1H-MRS in MELAS patients, we could not monitor treatment response over short periods with this tool.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04948138; initial release 24/06/2021; first patient enrolled on 1/07/2021. https://clinicaltrials.gov/ct2/show/NCT04948138.

Mitochondrial Chronic Progressive External Ophthalmoplegia

BACKGROUND

Chronic progressive external ophthalmoplegia (CPEO) is a rare disorder that can be at the forefront of several mitochondrial diseases. This review overviews mitochondrial CPEO encephalomyopathies to enhance accurate recognition and diagnosis for proper management.

METHODS

This study is conducted based on publications and guidelines obtained by selective review in PubMed. Randomized, double-blind, placebo-controlled trials, Cochrane reviews, and literature meta-analyses were particularly sought.

DISCUSSION

CPEO is a common presentation of mitochondrial encephalomyopathies, which can result from alterations in mitochondrial or nuclear DNA. Genetic sequencing is the gold standard for diagnosing mitochondrial encephalomyopathies, preceded by non-invasive tests such as fibroblast growth factor-21 and growth differentiation factor-15. More invasive options include a muscle biopsy, which can be carried out after uncertain diagnostic testing. No definitive treatment option is available for mitochondrial diseases, and management is mainly focused on lifestyle risk modification and supplementation to reduce mitochondrial load and symptomatic relief, such as ptosis repair in the case of CPEO. Nevertheless, various clinical trials and endeavors are still at large for achieving beneficial therapeutic outcomes for mitochondrial encephalomyopathies.

KEY MESSAGES

Understanding the varying presentations and genetic aspects of mitochondrial CPEO is crucial for accurate diagnosis and management.

Mitochondrial heterogeneity in diseases

As key organelles involved in cellular metabolism, mitochondria frequently undergo adaptive changes in morphology, components and functions in response to various environmental stresses and cellular demands. Previous studies of mitochondria research have gradually evolved, from focusing on morphological change analysis to systematic multiomics, thereby revealing the mitochondrial variation between cells or within the mitochondrial population within a single cell. The phenomenon of mitochondrial variation features is defined as mitochondrial heterogeneity. Moreover, mitochondrial heterogeneity has been reported to influence a variety of physiological processes, including tissue homeostasis, tissue repair, immunoregulation, and tumor progression. Here, we comprehensively review the mitochondrial heterogeneity in different tissues under pathological states, involving variant features of mitochondrial DNA, RNA, protein and lipid components. Then, the mechanisms that contribute to mitochondrial heterogeneity are also summarized, such as the mutation of the mitochondrial genome and the import of mitochondrial proteins that result in the heterogeneity of mitochondrial DNA and protein components. Additionally, multiple perspectives are investigated to better comprehend the mysteries of mitochondrial heterogeneity between cells. Finally, we summarize the prospective mitochondrial heterogeneity-targeting therapies in terms of alleviating mitochondrial oxidative damage, reducing mitochondrial carbon stress and enhancing mitochondrial biogenesis to relieve various pathological conditions. The possibility of recent technological advances in targeted mitochondrial gene editing is also discussed.

Visual memory failure presages conversion to MELAS phenotype

OBJECTIVE

To examine the correlation between verbal and visual memory function and correlation with brain metabolites (lactate and N-Acetylaspartate, NAA) in individuals with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS).

METHODS

Memory performance and brain metabolites (ventricular lactate, occipital lactate, and occipital NAA) were examined in 18 MELAS, 58 m.3243A > G carriers, and 20 familial controls. Measures included the Selective Reminding Test (verbal memory), Benton Visuospatial Retention Test (visual memory), and MR Spectroscopy (NAA, Lactate). ANOVA, chi-squared/Fisher's exact tests, paired t-tests, Pearson correlations, and Spearman correlations were used.

RESULTS

When compared to carriers and controls, MELAS patients had the: (1) most impaired memory functions (Visual: p = 0.0003; Verbal: p = 0.02), (2) greatest visual than verbal memory impairment, (3) highest brain lactate levels (p < 0.0001), and (4) lowest brain NAA levels (p = 0.0003). Occipital and ventricular lactate to NAA ratios correlated significantly with visual memory performance (p ≤ 0.001). Higher lactate levels (p ≤ 0.01) and lower NAA levels (p = 0.0009) correlated specifically with greater visual memory dysfunction in MELAS. There was little or no correlation with verbal memory.

INTERPRETATION

Individuals with MELAS are at increased risk for impaired memory. Although verbal and visual memory are both affected, visual memory is preferentially affected and more clearly associated with brain metabolite levels. Preferential involvement of posterior brain regions is a distinctive clinical signature of MELAS. We now report a distinctive cognitive phenotype that targets visual memory more prominently and earlier than verbal memory. We speculate that this finding in carriers presages a conversion to the MELAS phenotype.

MRI Features of Stroke-Like Episodes in Mitochondrial Encephalomyopathy With Lactic Acidosis and Stroke-Like Episodes

Mitochondrial myopathy encephalopathy lactic acidosis and stroke-like episodes (MELAS) is an important cause of stroke-mimicking diseases that predominantly affect patients before 40 years of age. MELAS results from gene mutations in either mitochondrial DNA (mtDNA) or nuclear DNA (nDNA) responsible for the wide spectrum of clinical symptoms and imaging findings. Neurological manifestations can present with stroke-like episodes (the cardinal features of MELAS), epilepsy, cognitive and mental disorders, or recurrent headaches. Magnetic resonance imaging (MRI) is an important tool for detecting stroke-like lesions, accurate recognition of imaging findings is important in guiding clinical decision making in MELAS patients. With the development of neuroimaging technologies, MRI plays an increasingly important role in course monitoring and efficacy assessment of the disease. In this article, we provide an overview of the neuroimaging features and the application of novel MRI techniques in MELAS syndrome.

Sexual Dysfunctions in Parkinson’s Disease and Their Influence on Partnership—Data of the PRISM Study

Background: Sexual dysfunctions (SD) are common but underreported in Parkinson’s disease (PD) and have negative impacts on the quality of life (QoL) and partnership. Methods: We analyzed the data set from the PRISM study for demographics of SD and their influence on quality of life and partnership. Results: 449/861 (52.1%) PD patients reported SD, with male patients being affected more often and having a longer course of disease. The most common SD in men was erectile dysfunction (ED) (n = 152), while women’s most frequent complaints were orgasm dysfunction (n = 84) and reduced libido (n = 81). Hypersexual SDs were reported significantly more often by men. Spousal caregivers of patients reporting inability to relax and enjoy sex and reduced libido indicated a negative influence on the relationship in general. Negative effects on the sexual relationship were reported significantly more often for patients with ED, difficulties with sexual arousal, inability to relax and enjoy sex, and reduced libido. Hypersexual dysfunctions showed no effect on the relationship. Conclusion: SD is a common but underreported problem in the treatment of patients with PD. Due to the negative influence on the relationship and QoL of patients and caregivers, SD should be assessed routinely.

Stroke and stroke-like episodes in inborn errors of metabolism: Pathophysiological and clinical implications

Inborn errors of metabolism causing stroke (ischemic or haemorrhagic) or stroke-like episodes (e.g., that are also called "metabolic strokes" and include acute brain lesions not related with alterations of blood flow) cover a wide range of diseases in which acute metabolic decompensations after trigger events (e.g., fever, dehydration, sepsis etc.) may have a variable frequency. The early diagnosis of these conditions is essential because, despite their rarity, effective symptomatic treatments may be available for acute settings (e.g., arginine for Mitochondrial myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like episodes- MELAS) while in other cases disease modifying therapies may be useful to prevent stroke occurrence, recurrence, or relapse (e.g., Fabry disease). The detection of a non-vascular distribution of lesions and the diffuse use of ¹HMRS are often diriment in the differential of ischemic and metabolic strokes. This review summarized the main clinical features and the pathophysiological mechanisms of stroke and stroke-like episodes in inborn errors of metabolism presenting with stroke as part of natural history of the disease. These conditions belong to different etiological groups, such as organic acidurias, mitochondrial encephalopathies, homocystinuria and remethylation disorders, urea cycle disorders, lysosomal diseases (e.g. Fabry disease, glycogen storage disease), congenital disorders of glycosylation, neurotransmitter disorders, adenosine deaminase 2 deficiency and few other neurometabolic disorders.

Mutational Analysis and mtDNA Haplogroup Characterization in Three Serbian Cases of Mitochondrial Encephalomyopathies and Literature Review

Mitochondrial encephalomyopathies (MEMP) are heterogeneous multisystem disorders frequently associated with mitochondrial DNA (mtDNA) mutations. Clinical presentation varies considerably in age of onset, course, and severity up to death in early childhood. In this study, we performed molecular genetic analysis for mtDNA pathogenic mutation detection in Serbian children, preliminary diagnosed clinically, biochemically and by brain imaging for mitochondrial encephalomyopathies disorders. Sanger sequencing analysis in three Serbian probands revealed two known pathogenic mutations. Two probands had a heteroplasmic point mutation m.3243A>G in the MT-TL1 gene, which confirmed mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode syndrome (MELAS), while a single case clinically manifested for Leigh syndrome had an almost homoplasmic (close to 100%) m.8993T>G mutation in the MT-ATP6 gene. After full mtDNA MITOMASTER analysis and PhyloTree build 17, we report MELAS' association with haplogroups U and H (U2e and H15 subclades); likewise, the mtDNA-associated Leigh syndrome proband shows a preference for haplogroup H (H34 subclade). Based on clinical-genetic correlation, we suggest that haplogroup H may contribute to the mitochondrial encephalomyopathies' phenotypic variability of the patients in our study. We conclude that genetic studies for the distinctive mitochondrial encephalomyopathies should be well-considered for realizing clinical severity and possible outcomes.

Clinical Characteristics of Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, a maternally inherited mitochondrial disorder, is characterized by its genetic, biochemical and clinical complexity. The most common mutation associated with MELAS syndrome is the mtDNA A3243G mutation in the MT-TL1 gene encoding the mitochondrial tRNA-leu(UUR), which results in impaired mitochondrial translation and protein synthesis involving the mitochondrial electron transport chain complex subunits, leading to impaired mitochondrial energy production. Angiopathy, either alone or in combination with nitric oxide (NO) deficiency, further contributes to multi-organ involvement in MELAS syndrome. Management for MELAS syndrome is amostly symptomatic multidisciplinary approach. In this article, we review the clinical presentations, pathogenic mechanisms and options for management of MELAS syndrome.

Metabolic abnormality in acute stroke-like lesion and its relationship with focal cerebral blood flow in patients with MELAS: Evidence from proton MR spectroscopy and arterial spin labeling

Our purpose is to detect the metabolic alterations in acute stroke-like lesions (SLLs) and further investigate the correlations between metabolic concentrations and focal cerebral blood flow in patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) using proton MR spectroscopy (¹H-MRS) and arterial spin labeling (ASL). A total of 23 patients with MELAS at acute stage of stroke-like episodes (SLEs) and 20 normal controls (NC) were recruited in this study, respectively. All subjects underwent conventional MRI and¹H-MRS. In addition, ASL was performed in each patient. The measurements of creatine (Cr), choline (Cho), N-acetyl aspartate (NAA), lactate (Lac), glutamine/glutamate (Glx) levels and the ratios of Cho/Cr, NAA/Cr, Lac/Cr and Glx/Cr in acute SLLs for MELAS patients and left parietal and occipital lobes for NC were measured using LC-model software. Furthermore, in MELAS group, the associations between relative cerebral blood flow (rCBF) and metabolite concentrations in acute SLLs were also assessed. In MELAS group, acute SLLs were identified with metabolic abnormalities and increased rCBF. Specifically, compared with controls, MELAS patients exhibited significantly higher Lac, Cho levels and Lac/Cr, Cho/Cr ratios, and lower NAA, Glx levels and NAA/Cr and Glx/Cr ratios. Moreover, for MELAS patients, Lac concentration in acute SLLs was positively correlated with focal rCBF. This study exhibited the neural injury with increasing lactate and cerebral blood flow in the acute SLEs. It might shed light on the underlying biochemical mechanism of mitochondrial cytopathy and angiopathy in MELAS.

Advanced magnetic resonance spectroscopic neuroimaging: Experts' consensus recommendations

Magnetic resonance spectroscopic imaging (MRSI) offers considerable promise for monitoring metabolic alterations associated with disease or injury; however, to date, these methods have not had a significant impact on clinical care, and their use remains largely confined to the research community and a limited number of clinical sites. The MRSI methods currently implemented on clinical MRI instruments have remained essentially unchanged for two decades, with only incremental improvements in sequence implementation. During this time, a number of technological developments have taken place that have already greatly benefited the quality of MRSI measurements within the research community and which promise to bring advanced MRSI studies to the point where the technique becomes a true imaging modality, while making the traditional review of individual spectra a secondary requirement. Furthermore, the increasing use of biomedical MR spectroscopy studies has indicated clinical areas where advanced MRSI methods can provide valuable information for clinical care. In light of this rapidly changing technological environment and growing understanding of the value of MRSI studies for biomedical studies, this article presents a consensus from a group of experts in the field that reviews the state-of-the-art for clinical proton MRSI studies of the human brain, recommends minimal standards for further development of vendor-provided MRSI implementations, and identifies areas which need further technical development.

Developing new treatments in partnership for primary mitochondrial disease: What does industry need from academics, and what do academics need from industry?

Developing novel therapeutics for primary mitochondrial disease is likely to require significant academia-industry collaboration. Translational assessments, a tool often used in industry at target validation stage, can highlight disease specific development challenges which requires focused collaborative effort. For PMD, definition of pivotal trial populations and primary endpoints is challenging given lack of clinical precedence, high numbers of subgroups with overlapping symptoms despite common genetics. Disease pathophysiology has not been systematically assessed simultaneously with outcomes in available natural history studies, resulting in a lack of pathophysiology biomarker utilization in clinical trials. Preclinical model systems are available to assist drug development efforts, although these may require better standardization and access. Multistakeholder precompetitive efforts have been used to progress disease pathophysiology biomarker and confirmatory clinical trial endpoint readiness in neurological disease with limited treatment options, such as rare familial Parkinson's disease. This type of approach may be beneficial for PMD therapeutic development, although requires significant funding and time, supported by industry and other funding bodies. Industry expertise on chemistry, data quality and drug development know-how is available to support academic drug development efforts. A combination of industry mindset-reduction of uncertainty to provide an indication statement supportable by evidence-together with academic approach-question-based studies to understand disease mechanisms and patients-has great potential to deliver novel PMD therapeutics.

Gender Differences and Quality of Life in Parkinson's Disease

Parkinson's disease has been found to significantly affect health-related quality of life. The gender differences of the health-related quality of life of subjects with Parkinson's disease have been observed in a number of studies. These differences have been reported in terms of the age at onset, clinical manifestations, and response to therapy. In general, women with Parkinson's disease showed more positive disease outcomes with regard to emotion processing, non-motor symptoms, and cognitive functions, although women report more Parkinson's disease-related clinical manifestations. Female gender predicted poor physical functioning and socioemotional health-related quality of life, while male gender predicted the cognitive domain of health-related quality of life. Some studies reported gender differences in the association between health-related quality of life and non-motor symptoms. Depression and fatigue were the main causes of poorer health-related quality of life in women, even in the early stages of Parkinson's disease. The aim of this review was to collect the best available evidence on gender differences in the development of Parkinson's disease symptoms and health-related quality of life.

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.

Molecular Biomarkers in Multiple Sclerosis and Its Related Disorders: A Critical Review

Multiple sclerosis (MS) is a chronic autoimmune disease affecting the central nervous system (CNS) which can lead to severe disability. Several diseases can mimic the clinical manifestations of MS. This can often lead to a prolonged period that involves numerous tests and investigations before a definitive diagnosis is reached. As well as the possibility of misdiagnosis. Molecular biomarkers can play a unique role in this regard. Molecular biomarkers offer a unique view into the CNS disorders. They help us understand the pathophysiology of disease as well as guiding our diagnostic, therapeutic, and prognostic approaches in CNS disorders. This review highlights the most prominent molecular biomarkers found in the literature with respect to MS and its related disorders. Based on numerous recent clinical and experimental studies, we demonstrate that several molecular biomarkers could very well aid us in differentiating MS from its related disorders. The implications of this work will hopefully serve clinicians and researchers alike, who regularly deal with MS and its related disorders.

The metabolic hypothesis is more likely than the epileptogenic hypothesis to explain stroke-like lesions

Stroke-like episodes (SLEs) are a hallmark of mitochondrial encephalopathy, lactic acidosis, and stroke-like episode (MELAS) syndrome but occur in other mitochondrial disorders (MIDs) as well. The morphological equivalent of the SLE is the stroke-like lesion (SLL) on magnetic resonance imaging (MRI). The pathophysiology of SLLs is under debate, but several hypotheses have been raised to explain the phenomenon. Of these, the metabolic, epileptogenic, and vascular hypotheses are the most frequently discussed. There are several arguments for and against these hypotheses, but a consensus has not been reached which of them provides the correct explanation. A recent consensus statement generated by a panel of experts applying the Delphi method, favoured the epileptogenic hypothesis and recommended treatment of SLEs with antiepileptic drugs, irrespective if the patient presented with a seizure or epileptiform discharges on electroencephalography (EEG) or not. We disagree with this general procedure and provide the following arguments against the epileptogenic hypothesis: 1. not each SLE is associated with seizures. 2. epileptiform discharges may be absent on EEG during a SLE. 3. SLLs are not restricted to the cortex. 4. antiseizure-drugs (ASDs) may not prevent the progression or recurrence of a SLL. 5. ASDs may terminate seizures but no other phenotypic feature of a SLE. 6. patients already under ASDs are not immune from developing a SLL. 7. SLLs usually last longer than seizures. 8. no animal model supports the epileptogenic hypothesis. The strongest arguments for the metabolic hypothesis are that SLLs are not confined to a vascular territory, that the oxygen-extraction fraction within a SLL is reduced, and that there is hypometabolism within a SLL on FDG-PET. SLLs may respond to antioxidants, NO-precursors, steroids, or the ketogenic diet. ASDs should be applied only if there is clinical or electrophysiological evidence of seizure-activity.

The metabolic hypothesis is more likely than the epileptogenic hypothesis to explain stroke-like lesions

Stroke-like episodes (SLEs) are a hallmark of mitochondrial encephalopathy, lactic acidosis, and stroke-like episode (MELAS) syndrome but occur in other mitochondrial disorders (MIDs) as well. The morphological equivalent of the SLE is the stroke-like lesion (SLL) on magnetic resonance imaging (MRI). The pathophysiology of SLLs is under debate, but several hypotheses have been raised to explain the phenomenon. Of these, the metabolic, epileptogenic, and vascular hypotheses are the most frequently discussed. There are several arguments for and against these hypotheses, but a consensus has not been reached which of them provides the correct explanation. A recent consensus statement generated by a panel of experts applying the Delphi method, favoured the epileptogenic hypothesis and recommended treatment of SLEs with antiepileptic drugs, irrespective if the patient presented with a seizure or epileptiform discharges on electroencephalography (EEG) or not. We disagree with this general procedure and provide the following arguments against the epileptogenic hypothesis: 1. not each SLE is associated with seizures. 2. epileptiform discharges may be absent on EEG during a SLE. 3. SLLs are not restricted to the cortex. 4. antiseizure-drugs (ASDs) may not prevent the progression or recurrence of a SLL. 5. ASDs may terminate seizures but no other phenotypic feature of a SLE. 6. patients already under ASDs are not immune from developing a SLL. 7. SLLs usually last longer than seizures. 8. no animal model supports the epileptogenic hypothesis. The strongest arguments for the metabolic hypothesis are that SLLs are not confined to a vascular territory, that the oxygen-extraction fraction within a SLL is reduced, and that there is hypometabolism within a SLL on FDG-PET. SLLs may respond to antioxidants, NO-precursors, steroids, or the ketogenic diet. ASDs should be applied only if there is clinical or electrophysiological evidence of seizure-activity.

Metabolic stroke or stroke-like lesion: Peculiarities of a phenomenon

OBJECTIVES

One of the most frequent cerebral lesions in mitochondrial disorders(MIDs) on imaging is the stroke-like lesion(SLL) clinically manifesting as stroke-like episode (SLE, metabolic stroke). This review aims at discussing recent advances concerning the presentation, diagnosis, and treatment of SLLs.

METHODS

Systematic literature review using appropriate search terms.

RESULTS

SLLs are the hallmark of MELAS but occasionally occur in other MIDs. SLLs are best identified on multimodal, cerebral MRI. SLLs may present as uni-/multilocular, symmetric/asymmetric, cortical/subcortical, supra-/infratentorial condition, initially resembling a cytotoxic edema and later a vasogenic edema, or a variable mix between them. SLLs run through an acute and a chronic stage. The acute stage is characterised by a progressively expanding lesion over days, weeks, or months, showing up as increasing hyperintensity on T2/FLAIR, DWI, and PWI and by hyperperfusion, that does not conform to a vascular territory. ADC maps are initially hypointens to become hyperintens during the course. More rarely, a variable mixture of hyper- and hypointensities may be found. The chronic stage is characterised by hypoperfusion, gadolinium enhancement, and regression of hyperintensities to various endpoints. SLLs originate from an initial cortical lesion due to focal metabolic breakdown, which either remains stable or expands within the cortex or to subcortical areas. Some SLLs show spontaneous reversibility (fleeing cortical lesions) suggesting that neuronal/glial damage does not reach the threshold of irreversible cell death.

CONCLUSIONS

SLLs are a unique feature of various MIDs in particular MELAS. SLLs are dynamic and change their appearance over time. SLLs are accessible to treatment.

Cerebrospinal fluid ATP as a potential biomarker in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke like episodes (MELAS)

Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is caused by defective oxidative phosphorylation in the cerebral parenchyma, cerebral blood vessels, and leptomeningeal tissue. Although increased blood and cerebrospinal fluid (CSF) lactate level has been used as a diagnostic biomarker in patients with MELAS, no biomarkers reflecting disease activity exist. Since we have developed a highly sensitive ATP assay system using luciferase luminous reaction, we examined CSF ATP in patients with MELAS and found that it negatively correlates with disease activity and that it reflects the efficacy of the treatment. CSF ATP might be a novel disease monitoring marker for MELAS.

mtDNA heteroplasmy level and copy number indicate disease burden in m.3243A>G mitochondrial disease

Mitochondrial disease associated with the pathogenic m.3243A>G variant is a common, clinically heterogeneous, neurogenetic disorder. Using multiple linear regression and linear mixed modelling, we evaluated which commonly assayed tissue (blood N = 231, urine N = 235, skeletal muscle N = 77) represents the m.3243A>G mutation load and mitochondrial DNA (mtDNA) copy number most strongly associated with disease burden and progression. m.3243A>G levels are correlated in blood, muscle and urine (R² = 0.61–0.73). Blood heteroplasmy declines by ~2.3%/year; we have extended previously published methodology to adjust for age. In urine, males have higher mtDNA copy number and ~20% higher m.3243A>G mutation load; we present formulas to adjust for this. Blood is the most highly correlated mutation measure for disease burden and progression in m.3243A>G‐harbouring individuals; increasing age and heteroplasmy contribute (R² = 0.27, P < 0.001). In muscle, heteroplasmy, age and mtDNA copy number explain a higher proportion of variability in disease burden (R² = 0.40, P < 0.001), although activity level and disease severity are likely to affect copy number. Whilst our data indicate that age‐corrected blood m.3243A>G heteroplasmy is the most convenient and reliable measure for routine clinical assessment, additional factors such as mtDNA copy number may also influence disease severity.

Correlation of Serum Biomarkers and Magnetic Resonance Spectroscopy in Monitoring Disease Progression in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes Due to mtDNA A3243G Mutation

Background: Analysis of serum biomarkers and magnetic resonance spectroscopy (MRS) are useful for monitoring disease progression in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). We evaluated the correlation of serum biomarkers and MRS parameters during changes associated with stroke-like episodes. Methods: In 13 symptomatic MELAS patients carrying the A3243G mutation, we retrospectively obtained 207 voxels from 41 MRS studies, which were divided into three groups according to the temporal association with stroke-like episodes. The MRS NAA/Cr, Cho/Cr, NAA/Cho ratios, the presence of a lactate peak, serum biomarkers, serum lactate level and the pyruvate (Lac/Pyr) ratio were determined. Results: In regions with acute infarcts, the severity of serum Lac/Pyr and that of the MRS lactate peak (P = 0.0007) correlated; serum lactate (P = 0.02), severity of elevated serum lactate (P = 0.04), and serum Lac/Pyr (P = 0.02) correlated weakly. In previously infarcted regions, the severity of the MRS lactate peak and serum Lac/Pyr (P = 0.03), as well as the severity of serum Lac/Pyr (P = 0.02) were weakly correlated. In structurally normal regions, we found a weak to moderate negative correlation between serum lactate and MRS NAA/Cr (P = 0.008), and between the severity of elevated serum lactate and MRS NAA/Cr (P = 0.002) as well as MRS NAA/Cho (P = 0.02). Conclusions: MRS parameters correlate with specific serum biomarkers, and are useful for monitoring changes in brain metabolites, particularly as related to stroke-like episodes.

Biomarkers for mitochondrial energy metabolism diseases

Biomarkers are an indicator of biologic or pathogenic processes, whose function is indicating the presence/absence of disease or monitoring disease course and its response to treatment. Since mitochondrial disorders (MDs) can represent a diagnostic challenge for clinicians, due to their clinical and genetic heterogeneity, the identification of easily measurable biomarkers becomes a high priority. Given the complexity of MD, in particular the primary mitochondrial respiratory chain (MRC) diseases due to oxidative phosphorylation (OXPHOS) dysfunction, a reliable single biomarker, relevant for the whole disease group, could be extremely difficult to find, most of times leading the physicians to better consider a 'biosignature' for the diagnosis, rather than a single biochemical marker. Serum biomarkers like lactate and pyruvate are largely determined in the diagnostic algorithm of MD, but they are not specific to this group of disorders. The concomitant determination of creatine (Cr), plasma amino acids, and urine organic acids might be helpful to reinforce the biosignature in some cases. In recent studies, serum fibroblast growth factor 21 (sFGF21) and serum growth differentiation factor 15 (sGDF15) appear to be promising molecules in identifying MD. Moreover, new different approaches have been developed to discover new MD biomarkers. This work discusses the most important biomarkers currently used in the diagnosis of MRC diseases, and some approaches under evaluation, discussing both their utility and weaknesses.

Biomarkers for Detecting Mitochondrial Disorders

(1) Objectives: Mitochondrial disorders (MIDs) are a genetically and phenotypically heterogeneous group of slowly or rapidly progressive disorders with onset from birth to senescence. Because of their variegated clinical presentation, MIDs are difficult to diagnose and are frequently missed in their early and late stages. This is why there is a need to provide biomarkers, which can be easily obtained in the case of suspecting a MID to initiate the further diagnostic work-up. (2) Methods: Literature review. (3) Results: Biomarkers for diagnostic purposes are used to confirm a suspected diagnosis and to facilitate and speed up the diagnostic work-up. For diagnosing MIDs, a number of dry and wet biomarkers have been proposed. Dry biomarkers for MIDs include the history and clinical neurological exam and structural and functional imaging studies of the brain, muscle, or myocardium by ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), MR-spectroscopy (MRS), positron emission tomography (PET), or functional MRI. Wet biomarkers from blood, urine, saliva, or cerebrospinal fluid (CSF) for diagnosing MIDs include lactate, creatine-kinase, pyruvate, organic acids, amino acids, carnitines, oxidative stress markers, and circulating cytokines. The role of microRNAs, cutaneous respirometry, biopsy, exercise tests, and small molecule reporters as possible biomarkers is unsolved. (4) Conclusions: The disadvantages of most putative biomarkers for MIDs are that they hardly meet the criteria for being acceptable as a biomarker (missing longitudinal studies, not validated, not easily feasible, not cheap, not ubiquitously available) and that not all MIDs manifest in the brain, muscle, or myocardium. There is currently a lack of validated biomarkers for diagnosing MIDs.

Monitoring clinical progression with mitochondrial disease biomarkers

Mitochondrial disorders are genetically determined metabolic diseases due to a biochemical deficiency of the respiratory chain. Given that multi-system involvement and disease progression are common features of mitochondrial disorders they carry substantial morbidity and mortality. Despite this, no disease-modifying treatments exist with clear clinical benefits, and the current best management of mitochondrial disease is supportive. Several therapeutic strategies for mitochondrial disorders are now at a mature preclinical stage. Some are making the transition into early-phase patient trials, but the lack of validated biomarkers of disease progression presents a challenge when developing new therapies for patients. This update discusses current biomarkers of mitochondrial disease progression including metabolomics, circulating serum markers, exercise physiology, and both structural and functional imaging. We discuss the advantages and disadvantages of each approach, and consider emerging techniques with a potential role in trials of new therapies.

Mitochondrial dysfunction and cerebral metabolic abnormalities in patients with mitochondrial encephalomyopathy subtypes: Evidence from proton MR spectroscopy and muscle biopsy

AIMS

Accumulated evidence indicates that cerebral metabolic features, evaluated by proton magnetic resonance spectroscopy (¹ H-MRS), are sensitive to early mitochondrion dysfunction associated with mitochondrial encephalomyopathy (ME). The metabolite ratios of lactate (lac)/Cr, N-acetyl aspartate (NAA)/creatine (Cr), total choline (tCho)/Cr, and myoinositol (mI)/Cr are measured in the infarct-like lesions by ¹ H-MRS and may reveal metabolic changes associated with ME. However, the application of this molecular imaging technique in the investigation of the pathology of ME subtypes is unknown.

METHODS

In this study, cerebral metabolic features of pathologically diagnosed ME cases, that is, 19 mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS); nine chronic progressive external ophthalmoplegia (CPEO); and 23 healthy controls, were investigated using ¹ H-MRS. Receiver operating characteristics (ROC) analysis was used to evaluate the diagnostic power of the cerebral metabolites. Histochemical evaluation was carried out on muscle tissues derived from biopsy to assess the abnormal mitochondrial proliferation. The association between cerebral metabolic and mitochondrial cytopathy was examined by correlation analysis.

RESULTS

Patients with MELAS or CPEO exhibited a significantly higher Lac/Cr ratio and a lower NAA/Cr ratio compared with controls. The ROC curve of Lac/Cr ratio indicated prominent discrimination between MELAS or CPEO and healthy control subjects, whereas the NAA/Cr ratio may present diagnostic power in the distinction of MELAS from CPEO. Lower NAA/Cr ratio was associated with higher Lac/Cr in MELAS, but not in CPEO. Furthermore, higher ragged-red fibers (RRFs) percentages were associated with elevated Lac/Cr and reduced NAA/Cr ratios, notably in MELAS. This association was not noted in the case of mI/Cr ratio.

CONCLUSIONS

Mitochondrial cytopathy (lactic acidosis and RRFs on muscle biopsy) was associated with neuronal viability but not glial proliferation, notably in MELAS. Mitochondrial neuronopathy and neuronal vulnerability are considered significant causes in the pathogenesis of MELAS, particularly with regard to stroke-like episodes.

Elevations of Ventricular Lactate Levels Occur in Both Chronic Fatigue Syndrome and Fibromyalgia

Background

Chronic fatigue syndrome (CFS) and fibromyalgia (FM) frequently have overlapping symptoms, leading to the suggestion that the same disease processes may underpin the two disorders - the unitary hypothesis. However, studies investigating the two disorders have reported substantial clinical and/or biological differences between them, suggesting distinct pathophysiological underpinnings.

Purpose

The purpose of this study was to further add to the body of evidence favoring different disease processes in CFS and FM by comparing ventricular cerebrospinal fluid lactate levels among patients with CFS alone, FM alone, overlapping CFS and FM symptoms, and healthy control subjects.

Methods

Ventricular lactate was assessed in vivo with proton magnetic resonance spectroscopic imaging (¹H MRSI) with the results normed across the 2 studies in which the data were collected.

Results

Mean CSF lactate levels in CFS, FM and CFS+FM did not differ among the three groups, but were all significantly higher than the mean values for control subjects.

Conclusion

While patients with CFS, FM and comorbid CFS and FM can be differentiated from healthy subjects based on measures of CFS lactate, this neuroimaging outcome measure is not a viable biomarker for differentiating CFS from FM or from patients in whom symptoms of the two disorders overlap.

MELAS Syndrome with Cardiac Involvement: A Multimodality Imaging Approach

A 49-year-old man presented with chest pain, dyspnea, and lactic acidosis. Left ventricular hypertrophy and myocardial fibrosis were detected. The sequencing of mitochondrial genome (mtDNA) revealed the presence of A to G mtDNA point mutation at position 3243 (m.3243A>G) in tRNA^Leu(UUR) gene. Diagnosis of cardiac involvement in a patient with Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes syndrome (MELAS) was made. Due to increased risk of sudden cardiac death, cardioverter defibrillator was implanted.

Distinctive distribution of brain volume reductions in MELAS and mitochondrial DNA A3243G mutation carriers: A voxel-based morphometric study

OBJECTIVE

The aim of this study was to investigate the clinically latent brain atrophy of patients with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) harboring a mitochondrial DNA A3243G mutation (A3243G) and A3243G carriers without stroke-like episodes (SEs).

METHODS

We used voxel-based morphometry (VBM) with magnetic resonance imaging to investigate gray matter (GM) and white matter (WM) volume reductions in four MELAS patients and in five A3243G carriers compared to 16 healthy controls. In addition, we investigated the regions of previous SEs using conventional MRI.

RESULTS

All four MELAS patients showed significant GM volume reductions in the left superior parietal lobule (SPL), right precuneus, right middle temporal gyrus (MTG), and bilateral posterior lobes of the cerebellum. These areas of GM volume reduction were beyond the regions of previous SEs. As for A3243G carriers, GM volume reductions in the left SPL, right precuneus, right MTG, and bilateral posterior lobes of the cerebellum were detected in three, one, two, and five subjects, respectively. All four MELAS patients showed significant WM volume reductions in the bilateral or unilateral temporal sub-gyral regions, which were included in the regions of previous SEs. No A3243G carriers showed WM volume reductions.

CONCLUSION

The distribution patterns of GM volume reductions in VBM may reflect a common vulnerability of the brains among MELAS patients and A3243G carriers.

Progress in Diagnosing Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like Episodes

Objective:

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a progressive, multisystem affected mitochondrial disease associated with a number of disease-related defective genes. MELAS has unpredictable presentations and clinical course, and it can be commonly misdiagnosed as encephalitis, cerebral infarction, or brain neoplasms. This review aimed to update the diagnosis progress in MELAS, which may provide better understanding of the disease nature and help make the right diagnosis as well.

Data Sources:

The data used in this review came from published peer review articles from October 1984 to October 2014, which were obtained from PubMed. The search term is “MELAS”.

Study Selection:

Information selected from those reported studies is mainly based on the progress on clinical features, blood biochemistry, neuroimaging, muscle biopsy, and genetics in diagnosing MELAS.

Results:

MELAS has a wide heterogeneity in genetics and clinical manifestations. The relationship between mutations and phenotypes remains unclear. Advanced serial functional magnetic resonance imaging (MRI) can provide directional information on this disease. Muscle biopsy has meaningful value in diagnosing MELAS, which shows the presence of ragged red fibers and mosaic appearance of cytochrome oxidase negative fibers. Genetic studies have reported that approximately 80% of MELAS cases are caused by the mutation m.3243A>G of the mitochondrial transfer RNA (Leu (UUR)) gene (MT-TL1).

Conclusions:

MELAS involves multiple systems with variable clinical symptoms and recurrent episodes. The prognosis of MELAS patients depends on timely diagnosis. Therefore, overall diagnosis of MELAS should be based on the maternal inheritance family history, clinical manifestation, and findings from serial MRI, muscle biopsy, and genetics.

Mitochondrial Encephalomyopathy Lactic Acidosis and Stroke-Like Episodes (MELAS): A Case Report and Critical Reappraisal of Treatment Options

IMPORTANCE

Stroke-like episodes signal progression and significant disability in the mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes syndrome. Arginine is widely used as a treatment for stroke-like episode, although there is little evidence for this intervention. We discuss the management of a patient with mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes who presented with a stroke-like episode.

OBSERVATION

During a seizure, which triggers the stroke-like episode, neurons are forced to utilize glycolysis as a source of adenosine triphosphate. Glycolytic by-products are damaging to the neuron. Breakdown of the blood-brain barrier leads to vasogenic edema.

CONCLUSION

Treatment of stroke-like episode should include anticonvulsants interictally to prevent seizures and dexamethasone ictally to help repair the blood-brain barrier.

Increased ventricular cerebrospinal fluid lactate in depressed adolescents

BACKGROUND

Mitochondrial dysfunction has been increasingly examined as a potential pathogenic event in psychiatric disorders, although its role early in the course of major depressive disorder (MDD) is unclear. Therefore, the purpose of this study was to investigate mitochondrial dysfunction in medication-free adolescents with MDD through in vivo measurements of neurometabolites using high-spatial resolution multislice/multivoxel proton magnetic resonance spectroscopy.

METHODS

Twenty-three adolescents with MDD and 29 healthy controls, ages 12-20, were scanned at 3T and concentrations of ventricular cerebrospinal fluid lactate, as well as N-acetyl-aspartate (NAA), total creatine (tCr), and total choline (tCho) in the bilateral caudate, putamen, and thalamus were reported.

RESULTS

Adolescents with MDD exhibited increased ventricular lactate compared to healthy controls [F(1,41)=6.98, P=0.01]. However, there were no group differences in the other neurometabolites. Dimensional analyses in the depressed group showed no relation between any of the neurometabolites and symptomatology, including anhedonia and fatigue.

CONCLUSIONS

Increased ventricular lactate in depressed adolescents suggests mitochondrial dysfunction may be present early in the course of MDD; however it is still not known whether the presence of mitochondrial dysfunction is a trait vulnerability of individuals predisposed to psychopathology or a state feature of the disorder. Therefore, there is a need for larger multimodal studies to clarify these chemical findings in the context of network function.

Lactate and its many faces

BACKGROUND

Lactate is traditionally seen as a marker of ischemia and a waste product of anaerobic glycolysis. In the last thirty years a more beneficial side of lactate as an alternative 'glucose sparing' fuel has been demonstrated. However, the translation of these growing insights to clinical practice seems to appear with great delay.

METHODS

A review of the literature was performed, focusing on glucose and lactate in relation to cerebral energy metabolism, in the context of four typical clinical situations, namely (transient states of) low glucose availability for the brain due to hypoglycemia, combined with high blood lactate concentrations; permanent neuroglycopenia; lactic acidosis in mitochondrial disorders; and ischemic as well as traumatic brain injury.

RESULTS

Lactate is thought to be an alternative fuel in the brain of patients with glucose transporter type 1 deficiency syndrome and glycogen storage disease, and it has been demonstrated that lactate might have a protective role in ischemic and traumatic brain injury.

CONCLUSION

Lactate has an apparently largely ignored, but potential beneficial role in the clinical management of several neurologic disorders.

Effect of Milnacipran Treatment on Ventricular Lactate in Fibromyalgia: A Randomized, Double-Blind, Placebo-Controlled Trial

Milnacipran, a serotonin/norepinephrine reuptake inhibitor, has been approved by the US Food and Drug Administration for the treatment of fibromyalgia (FM). This report presents the results of a randomized, double-blind, placebo-controlled trial of milnacipran conducted to test the hypotheses that a) similar to patients with chronic fatigue syndrome, patients with FM have increased ventricular lactate levels at baseline; b) 8 weeks of treatment with milnacipran will lower ventricular lactate levels compared with baseline levels and with ventricular lactate levels after placebo; and c) treatment with milnacipran will improve attention and executive function in the Attention Network Test compared with placebo. In addition, we examined the results for potential associations between ventricular lactate and pain. Baseline ventricular lactate measured by proton magnetic resonance spectroscopic imaging was found to be higher in patients with FM than in healthy controls (F1,37 = 22.11, P < .0001, partial η(2) = .37). Milnacipran reduced pain in patients with FM relative to placebo but had no effect on cognitive processing. At the end of the study, ventricular lactate levels in the milnacipran-treated group had decreased significantly compared with baseline and after placebo (F1,18 = 8.18, P = .01, partial η(2) = .31). A significantly larger proportion of patients treated with milnacipran showed decreases in both ventricular lactate and pain than those treated with placebo (P = .03). These results suggest that proton magnetic resonance spectroscopic imaging measurements of lactate may serve as a potential biomarker for a therapeutic response in FM and that milnacipran may act, at least in part, by targeting the brain response to glial activation and neuroinflammation.

PERSPECTIVE

Patients treated with milnacipran showed decreases in both pain and ventricular lactate levels compared with those treated with placebo, but, even after treatment, levels of ventricular lactate remained higher than in controls. The hypothesized mechanism for these decreases is via drug-induced reductions of a central inflammatory state.

Assessment of glutamate in striatal subregions in obsessive-compulsive disorder with proton magnetic resonance spectroscopy

Glutamatergic signaling abnormalities in cortico-striatal circuits are hypothesized to lead to the repetitive thoughts and behaviors of obsessive-compulsive disorder (OCD). To test this hypothesis, studies have used proton magnetic resonance spectroscopy (1H MRS) to measure glutamatergic compounds in the striatum of individuals with OCD. However, no studies have used methods that could measure glutamate minimally contaminated by glutamine and γ-aminobutyric acid (GABA) in striatal subregions. Therefore, in this study, a proton MRS imaging (1H MRSI) technique with relatively high spatial resolution at 3.0 T was used to measure minimally contaminated glutamate levels in three striatal subregions (i.e., dorsal caudate, dorsal putamen, and ventral striatum) in 15 unmedicated adults with OCD and 16 matched healthy control subjects. No significant group differences in glutamate levels were found in any of the three striatal subregions. In contrast, a study in unmedicated pediatric OCD patients that measured glutamatergic compounds in the dorsal caudate by MRS at 1.5 T found significant elevations. Further studies are warranted to assess whether these discrepant MRS findings are due to differences in subject age or MRS methodology, or potentially are associated with glutamatergic gene variants implicated in OCD.