Beneficial effect of L-arginine for stroke-like episode in MELAS

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.

L-arginine in Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes: A Systematic Review

Background and Objectives

Stroke management in the context of primary mitochondrial disease is clinically challenging, and the best treatment options for patients with stroke-like episodes remain uncertain. We sought to perform a systematic review of the safety and efficacy of l-arginine use in the acute and prophylactic management of stroke-like episodes in patients with mitochondrial disease.

Methods

The systematic review was registered in PROSPERO (CRD42020181230). We searched 6 databases from inception to January 15, 2021: MEDLINE, Embase, Scopus, Web of Science, CINAHL, and ClinicalTrials.gov. Original articles and registered trials available, in English, reporting l-arginine use in the acute or prophylactic management of stroke-like episodes in patients with genetically confirmed mitochondrial disease were eligible for inclusion. Data on safety and treatment response were extracted and summarized by multiple observers. Risk of bias was assessed by the methodologic quality of case reports, case series, and a risk-of-bias checklist for nonrandomized studies. Quality of evidence was synthesized with the Oxford Centre for Evidence-Based Medicine Levels of Evidence and Grade of Recommendations. The predetermined main outcome measures were clinical response to l-arginine treatment, adverse events, withdrawals, and deaths (on treatment and/or during follow-up), as defined by the author.

Results

Thirty-seven articles met inclusion criteria (0 randomized controlled trials; 3 open-label; 1 retrospective cohort; 33 case reports/case series) (N = 91 patients; 86% m.3243A>G). In the case reports, 54% of patients reported a positive clinical response to acute l-arginine, of which 40% were concomitantly treated with antiepileptic drugs. Improved headache at 24 hours was the greatest reported benefit in response to IV l-arginine in the open-label trials (31 of 39, 79%). In 15 of 48 patients (31%) who positively responded to prophylactic l-arginine, antiepileptic drugs were either used (7 of 15) or unreported (8 of 15). Moderate adverse events were reported in the follow-up of both IV and oral l-arginine treatment, and 11 patients (12%) died during follow-up or while on prophylactic treatment.

Discussion

The available evidence is of poor methodologic quality and classified as Level 5. IV and oral l-arginine confers no demonstrable clinical benefit in either the acute or prophylactic treatment of mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes, with more robust controlled trials required to assess its efficacy and safety profile.

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.

Neurovascular Syndromes

Patients with cerebrovascular syndromes are at risk for additional concerns associated with their syndrome. A wide variety of syndromes are associated with cerebrovascular diseases. Multidisciplinary care is helpful to ensure comprehensive evaluation and management. Precise diagnosis and appreciation for the underlying syndrome is critical for effective cerebrovascular and broader care. This text focuses on these conditions with a focus on underlying pathophysiology and associated genetics, presentation, diagnosis, and management of each disease.

Pearls & Oy-sters: Symmetric Numbness and Paresthesia Due to Stroke-like Episode in an Adolescent Male With MELAS

Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes (MELAS) syndrome is a mitochondrial condition with a wide range of neurologic complications including migraines, seizures, and stroke-like episodes. This case report highlights a rare presentation of bilateral sensory changes related to MELAS and offers an opportunity to consider how a differential diagnosis may need to be modified in patients with underlying mitochondrial disorders. Neurologic symptoms in MELAS may defy classic localization patterns, and early neuroimaging is warranted.

Dynamic derangement in amino acid profile during and after a stroke-like episode in adult-onset mitochondrial disease: a case report

Background

Maternally inherited diabetes and deafness, and mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes are examples of mitochondrial diseases that are relatively common in the adult population. Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes are assumed to be associated with decreases in arginine and citrulline. Biomarkers, such as growth differentiation factor-15, were developed to assist in the diagnosis of mitochondrial diseases.

Case presentation

A 55-year-old Japanese man, an insulin user, presented after a loss of consciousness. A laboratory test showed diabetic ketoacidosis. He and his mother had severe hearing difficulty. Bilateral lesions on magnetic resonance imaging, the presence of seizure, and an elevated ratio of lactate to pyruvate, altogether suggested a diagnosis of mitochondrial disease. Mitochondrial DNA in our patient’s peripheral blood was positive with a 3243A>G mutation, which is the most frequent cause of maternally inherited diabetes and deafness, and mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes. As a result, maternally inherited diabetes and deafness/mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes was diagnosed. We measured growth differentiation factor-15 and multiple amino acids in his blood, longitudinally during and after the stroke-like episode. Growth differentiation factor-15 was increased to an immeasurably high level on the day of the stroke-like episode. Although his diabetes improved with an increased dose of insulin, the growth differentiation factor-15 level gradually increased, suggesting that his mitochondrial insufficiency did not improve. Multiple amino acid species, including arginine, citrulline, and taurine, showed a decreased level on the day of the episode and a sharp increase the next day. In contrast, the level of aspartic acid increased to an extremely high level on the day of the episode, and decreased gradually thereafter.

Conclusions

Growth differentiation factor-15 can be used not only for the diagnosis of mitochondrial disease, but as an indicator of its acute exacerbation. A stroke-like episode of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes reflects a drastic derangement of multiple amino acids. The involvement of aspartic acid in the episodes should be explored in future studies.

Mitochondrial metabolic stroke: Phenotype and genetics of stroke-like episodes

Stroke-like episodes (SLEs) are the hallmark of mitochondrial encephalopathy with lactic acidosis and stroke-like episode (MELAS) syndrome but rarely occur also in other specific or nonspecific mitochondrial disorders. Pathophysiologically, SLLs are most likely due to a regional disruption of the blood-brain barrier triggered by the underlying metabolic defect, epileptic activity, drugs, or other factors. SLEs manifest clinically with a plethora of cerebral manifestations, which not only include features typically seen in ischemic stroke, but also headache, epilepsy, ataxia, visual impairment, vomiting, and psychiatric abnormalities. The morphological correlate of a SLE is the stroke-like lesion (SLL), best visualised on multimodal MRI. In the acute stages, a SLL presents as vasogenic edema but may be mixed up with cytotoxic components. Additionally, SLLs are characterized by hyperperfusion on perfusion studies. In the chronic stage, SLLs present with a colorful picture before they completely disappear, or end up as white matter lesion, cyst, laminar cortical necrosis, focal atrophy, or as toenail sign. Treatment of SLLs is symptomatic and relies on recommendations by experts. Beneficial effects have been reported with nitric-oxide precursors, antiepileptic drugs, antioxidants, the ketogenic diet, and steroids. Lot of research is still needed to uncover the enigma SLE/SLL.

Controlled Delivery of Nitric Oxide for Cancer Therapy

Nitric oxide (NO) is a short-lived, endogenously produced, signaling molecule which plays multiple roles in mammalian physiology. Underproduction of NO is associated with several pathological processes; hence a broad range of NO donors have emerged as potential therapeutics for cardiovascular and respiratory disorders, wound healing, the immune response to infection, and cancer. However, short half-lives, chemical reactivity, rapid systemic clearance, and cytotoxicity have hindered the clinical development of most low molecular weight NO donors. Hence, for controlled NO delivery, there has been extensive effort to design novel NO-releasing biomaterials for tumor targeting. This review covers the effects of NO in cancer biology, NO releasing moieties which can be used for NO delivery, and current advances in the design of NO releasing biomaterials focusing on their applications for tumor therapy.

MELAS: Monitoring treatment with magnetic resonance spectroscopy

BACKGROUND

To assess the utility of Magnetic Resonance Spectroscopy (MRS) as a biomarker of response to L-arginine in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS).

AIMS

To describe a case of MELAS treated with L-arginine that showed improvement clinically and on serial MRS METHODS: MRS was performed on a 1.5-Tesla scanner to evaluate a MELAS patient before, during, and after intravenous (IV) L-arginine therapy for the treatment of stroke-like episodes. L-arginine was infused at a dose of 500 mg/kg daily for 7 days followed by oral arginine therapy.

RESULTS

The patient had clinical improvement after treatment with IV L-arginine. MRS performed before, during, and after treatment with IV L-arginine showed significant improvement in brain lactate and increase in the N-acetylaspartate/Choline (NAA/Cho) ratio compared to pre-treatment baseline.

CONCLUSION

Serial MRS imaging showed significant improvement in lactate peaks and NAA/Cho ratios that corresponded with clinical improvement after L-arginine therapy. Given this correlation between radiologic and clinical improvement, MRS may be a useful biomarker assessing response to treatment in MELAS.

8-year retrospective analysis of intravenous arginine therapy for acute metabolic strokes in pediatric mitochondrial disease

BACKGROUND

Intravenous (IV) arginine has been reported to ameliorate acute metabolic stroke symptoms in adult patients with Mitochondrial Encephalopathy with Lactic Acidosis and Stroke-like Episodes (MELAS) syndrome, where its therapeutic benefit is postulated to result from arginine acting as a nitric oxide donor to reverse vasospasm. Further, reduced plasma arginine may occur in mitochondrial disease since the biosynthesis of arginine's precursor, citrulline, requires ATP. Metabolic strokes occur across a wide array of primary mitochondrial diseases having diverse molecular etiologies that are likely to share similar pathophysiologic mechanisms. Therefore, IV arginine has been increasingly used for the acute clinical treatment of metabolic stroke across a broad mitochondrial disease population.

METHODS

We performed retrospective analysis of a large cohort of subjects who were under 18 years of age at IRB #08-6177 study enrollment and had molecularly-confirmed primary mitochondrial disease (n = 71, excluding the common MELAS m.3243A>G mutation). 9 unrelated subjects in this cohort received acute arginine IV treatment for one or more stroke-like episodes (n = 17 total episodes) between 2009 and 2016 at the Children's Hospital of Philadelphia. Retrospectively reviewed data included subject genotype, clinical symptoms, age, arginine dosing, neuroimaging (if performed), prophylactic therapies, and adverse events.

RESULTS

Genetic etiologies of subjects who presented with acute metabolic strokes included 4 mitochondrial DNA (mtDNA) pathogenic point mutations, 1 mtDNA deletion, and 4 nuclear gene disorders. Subject age ranged from 19 months to 23 years at the time of any metabolic stroke episode (median, 8 years). 3 subjects had recurrent stroke episodes. 70% of subjects were on prophylactic arginine or citrulline therapy at the time of a stroke-like episode. IV arginine was initiated on initial presentation in 65% of cases. IV arginine was given for 1-7 days (median, 1 day). A positive clinical response to IV arginine occurred in 47% of stroke-like episodes; an additional 6% of episodes showed clinical benefit from multiple simultaneous treatments that included arginine, confounding sole interpretation of arginine effect. All IV arginine-responsive stroke-like episodes (n = 8) received treatment immediately on presentation (p = .003). Interestingly, the presence of unilateral symptoms strongly predicted arginine response (p = .02, Chi-Square); however, almost all of these cases immediately received IV arginine, confounding interpretation of causality direction. Suggestive trends toward increased IV arginine response were seen in subjects with mtDNA relative to nDNA mutations and in older pediatric subjects, although statistical significance was not reached possibly due to small sample size. No adverse events, including hypotensive episodes, from IV arginine therapy were reported.

CONCLUSIONS

Single-center retrospective analysis suggests that IV arginine therapy yields significant therapeutic benefit with little risk in pediatric mitochondrial disease stroke subjects across a wide range of genetic etiologies beyond classical MELAS. Acute hemiplegic stroke, in particular, was highly responsive to IV arginine treatment. Prospective studies with consistent arginine dosing, and pre- and post-neuroimaging, will further inform the clinical utility of IV arginine therapy for acute metabolic stroke in pediatric mitochondrial disease.

Stroke-like episodes, peri-episodic seizures, and MELAS mutations

PURPOSE

Stroke-like episodes (SLEs) are a hallmark of various mitochondrial disorders, in particular MELAS syndrome. SLEs manifest with vasogenic oedema (DWI and ADC hyperintensity) or partial cytotoxic oedema (DWI hyperintensity, ADC hypointensity) in the acute and subacute stage, and with gyriform T1-hyperintensity (cortical necrosis) in the chronic stage.

PRINCIPAL RESULTS

SLEs must be clearly distinguished from ischaemic stroke, since management of these two entities is different. SLEs may go along with or without seizures or epileptiform discharges on EEG. However, in MELAS syndrome seizures may also occur in the absence of SLEs. Focal and generalised seizures have been reported but it is currently unknown if the one or the other prevail. SLEs with and without seizures may respond to NO-precursors l-arginine, succinate, or citrulline. As a supportive measure a ketogenic diet should be initiated. Seizures prior to or during a SLE or paroxysmal EEG-activity during a SLE should be initially treated with antiepileptic drugs (AEDs) with low mitochondrion-toxicity. Only in case these AEDs are ineffective, AEDs with higher mitochondrion-toxicity should be added.

MAJOR CONCLUSIONS

All patients with SLEs need to have an EEG recorded irrespective if they have manifesting seizures or not. There are no mtDNA or nDNA mutations which predispose for SLEs with seizures.

A novel mutation in the mitochondrial DNA cytochrome b gene (MTCYB) in a patient with mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes syndrome

Mutations in the mitochondrial DNA cytochrome b gene (MTCYB) have been commonly associated with isolated mitochondrial myopathy and exercise intolerance, rarely with multisystem disorders, and only once with a parkinsonism/mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) overlap syndrome. Here, we describe a novel mutation (m.14864 T>C) in MTCYB in a 15-year-old girl with a clinical history of migraines, epilepsy, sensorimotor neuropathy, and strokelike episodes, a clinical picture reminiscent of MELAS.  The mutation, which changes a highly conserved cysteine to arginine at amino acid position 40 of cytochrome b, was heteroplasmic in muscle, blood, fibroblasts, and urinary sediment from the patient but absent in accessible tissues from her asymptomatic mother. This case demonstrates that MTCYB must be included in the already long list of mitochondrial DNA genes that have been associated with the MELAS phenotype.

Nitric oxide synthesis is increased in cybrid cells with m.3243A>G mutation

Nitric oxide (NO) is a free radical and a signaling molecule in several pathways, produced by nitric oxide synthase (NOS) from the conversion of l-arginine to citrulline. Supplementation of l-arginine has been used to treat MELAS (mitochondrial encephalopathy with lactic acidosis and stroke like syndrome), a mitochondrial disease caused by the m.3243A>G mutation. Low levels of serum arginine and endothelium dysfunction have been reported in MELAS and this treatment may increase NO in endothelial cells and promote vasodilation, decreasing cerebral ischemia and strokes. Although clinical benefits have been reported, little is known about NO synthesis in MELAS. In this study we found that osteosarcoma derived cybrid cells with high levels of m.3243A>G had increased nitrite, an NO metabolite, and increased intracellular NO, demonstrated by an NO fluorescent probe (DAF-FM). Muscle vessels from patients with the same mutation had increased staining in NADPH diaphorase, suggestive of increased NOS. These results indicate increased production of NO in cells harboring the m.3243A>G, however no nitrated protein was detected by Western blotting. Further studies are necessary to clarify the exact mechanisms of l-arginine effect to determine the appropriate clinical use of this drug therapy.

Stroke and Stroke-like Episodes in Muscle Disease

Background:

Though not obvious at a first glance, myopathies may be associated with ischemic stroke. Stroke-like episodes resemble ischemic stroke only to some extent but are a unique feature of certain mitochondrial disorders with a pathogenesis at variance from that of ischemic stroke. Only limited data are available about ischemic stroke in pri-mary myopathies and the management of stroke-like episodes in mitochondrial disorders. This review aims to summarize and discuss current knowledge about stroke in myopathies and to delineate stroke-like episodes from ischemic stroke.

Methods:

Literature review via PubMED using the search terms “stroke”, “cerebrovascular”, “ischemic event”, “stroke-like episode”, “stroke-mimic”, “mitochondrial disorder”.

Results:

Stroke in myopathies is most frequently cardioembolic due to atrial fibrillation or atrial flutter, dilated cardio-myopathy, or left-ventricular hypertrabeculation (noncompaction). The second most frequent cause of stroke in myopathies is angiopathy from atherosclerosis or vasculitis, which may be a feature of inflammatory myopathies. Athero-sclerosis may either result from classical risk factors, such as diabetes, arterial hypertension, hyperlpidemia, or smoking, associated with muscle disease, or may be an inherent feature of a mitochondrial disorder. In case of severe heart failure from cardiomyopathy as a manifestation of muscle disease low flow infarcts may occur. Thrombophilic stroke has been described in polymyositis and dermatomyositis in association with anti-phospholipid syndrome. Stroke-like episodes occur particularly in mitochondrial encephalopathy, lactacidosis and stroke-likeepisode syndrome but rarely also in Leigh-syndrome and other mitochondrial disorders. Stroke-like episodes are at variance from ischemic stroke, pathogenically, clinically and on imaging. They may be the manifestation of a vascular, metabolic or epileptic process and present with predominantly vasogenic but also cytotoxic edema on MRI. Differentiation between ischemic stroke and stroke-like episodes is essential in terms of management and prognosis. Management of ischemic stroke in patients with myopathy is not at variance from the treatment of ischemic stroke in non-myopathic patients. There is no standardized treatment of stroke-like episodes but there is increasing evidence that these patients profit from the administration of L-arginine and conse-quent antiepileptic treatment if associated with seizure activity.

Conclusions:

Ischemic stroke may be a complication of myopathy and needs to be delineated from stroke-like episodes, which are unique to mitochondrial disorders, particularly mitochondrial encephalopathy, lactacidosis and stroke-likeepisode syndrome. Ischemic stroke in myopathies is most frequently cardioembolic and treatment is not at variance from non-myopathic ischemic stroke. Treatment of stroke-like episodes is not standardized but seems to respond to L-arginine and adequate antiepileptic treatment.

L-arginine is effective in stroke-like episodes of MELAS associated with the G13513A mutation

We report a case involving a 15-year-old boy with MELAS (G13513A mutation) who developed several stroke-like episodes in a short period of time. Intravenous administration of l-arginine during the acute phase of the stroke-like episodes reduced symptoms immediately, and oral supplementation of l-arginine successfully prevented further stroke-like episodes. This is the first report on effective l-arginine therapy in MELAS associated with the G13513A mutation.

Neuroimaging of stroke-like episodes in MELAS

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) shows sudden neurological deficits that are called 'stroke-like episodes'. With regard to the pathophysiology of stroke-like episodes, so-called mitochondrial angiopathy and cytopathy theories have been proposed, but the subject is still controversial. To clarify this matter and to contribute to the development of a treatment for MELAS, we review here current neuroimaging research and consider the pathophysiology of stroke-like lesions. With regard to diffusion-weighted imaging findings, early reports often showed an elevated apparent diffusion coefficient (ADC) in stroke-like lesions; this was considered to be mainly vasogenic edema in the acute phase and is a different pattern than that in stroke. However, there has recently been an increase in the number of reports of a decrease in ADC; these cases are considered to be cytotoxic edema in the acute phase, which is compatible with stroke. With regard to (1)H-magnetic resonance spectroscopy findings in stroke-like lesions, a decrease in N-acetylaspartate and an increase in lactate have been reported. With regard to single photon emission computed tomography findings for stroke-like lesions in MELAS, an overall trend is hyperperfusion in the acute stage (within 1 month) of stroke-like episodes and hypoperfusion in the chronic stage (several months later). With regard to positron emission tomography, nearly all of these reports are consistent with the mitochondrial cytopathy theory. With regard to neuropathology in MELAS, the most common findings during the chronic stage of stroke-like episodes include foci of necrosis and peculiar vascular changes (abnormalities of mitochondria in small arteries). Concerning the pathology of the acute stage of stroke-like episodes, extensive petechial hemorrhage along the gyri of the cortex corresponding to acute stroke-like lesions has been reported. To clarify the true pathophysiology of stroke-like episodes, we offer three suggestions. First, we must define the precise onset of stroke-like episodes. Second, current studies are limited by the difficulty of imaging just before and just after (within a few minutes) the onset of stroke-like episodes. Third, we hope to establish an experimental animal model. We should conduct a simultaneous multimodal imaging and histological study just before and just after (within a few minutes) the onset of stroke-like episodes in an experimental animal model.

Mitochondrial response to controlled nutrition in health and disease

Mitochondria exert crucial physiological functions that create complex links among nutrition, health, and disease. While mitochondrial dysfunction with subsequent impairment of oxidative phosphorylation (OXPHOS) is the hallmark of the rare inherited OXPHOS diseases, OXPHOS dysfunction also plays a central role in the pathophysiology of common conditions such as type 2 diabetes and various neurodegenerative disorders. Dietary interventions, especially calorie restriction, have been shown to improve the course of these diseases and to extend the lifespan. Few data are available on the impact of nutraceuticals (macronutrients, vitamins, and cofactors) on primary inherited OXPHOS diseases. This review presents recent knowledge about the impact of nutritional modulation on mitochondria and lifespan regulation and about the development of potential treatments for mitochondrial dysfunction diseases.

The neurologic manifestations of mitochondrial disease

The nervous system contains some of the body's most metabolically demanding cells that are highly dependent on ATP produced via mitochondrial oxidative phosphorylation. Thus, the neurological system is consistently involved in patients with mitochondrial disease. Symptoms differ depending on the part of the nervous system affected. Although almost any neurological symptom can be due to mitochondrial disease, there are select symptoms that are more suggestive of a mitochondrial problem. Certain symptoms that have become sine qua non with underlying mitochondrial cytopathies can serve as diagnostic "red-flags." Here, the typical and atypical presentations of mitochondrial disease in the nervous system are reviewed, focusing on "red flag" neurological symptoms as well as associated symptoms that can occur in, but are not specific to, mitochondrial disease. The multitudes of mitochondrial syndromes are not reviewed in-depth, though a select few are discussed in some detail.

Treatment of mitochondrial disorders

Treatment of mitochondrial disorders (MIDs) is a challenge since there is only symptomatic therapy available and since only few randomized and controlled studies have been carried out, which demonstrate an effect of some of the symptomatic or supportive measures available. Symptomatic treatment of MIDs is based on mainstay drugs, blood transfusions, hemodialysis, invasive measures, surgery, dietary measures, and physiotherapy. Drug treatment may be classified as specific (treatment of epilepsy, headache, dementia, dystonia, extrapyramidal symptoms, Parkinson syndrome, stroke-like episodes, or non-neurological manifestations), non-specific (antioxidants, electron donors/acceptors, alternative energy sources, cofactors), or restrictive (avoidance of drugs known to be toxic for mitochondrial functions). Drugs which more frequently than in the general population cause side effects in MID patients include steroids, propofol, statins, fibrates, neuroleptics, and anti-retroviral agents. Invasive measures include implantation of a pacemaker, biventricular pacemaker, or implantable cardioverter defibrillator, or stent therapy. Dietary measures can be offered for diabetes, hyperlipidemia, or epilepsy (ketogenic diet, anaplerotic diet). Treatment should be individualized because of the peculiarities of mitochondrial genetics. Despite limited possibilities, symptomatic treatment should be offered to MID patients, since it can have a significant impact on the course and outcome.

Pathogenesis and treatment of mitochondrial disorders

In the past 50 years, our understanding of the biochemical and molecular causes of mitochondrial diseases, defined restrictively as disorders due to defects of the mitochondrial respiratory chain (RC), has made great strides. Mitochondrial diseases can be due to mutations in mitochondrial DNA (mtDNA) or in nuclear DNA (nDNA) and each group can be subdivided into more specific classes. Thus, mtDNA-related disorders can result from mutations in genes affecting protein synthesis in toto or mutations in protein-coding genes. Mendelian mitochondrial disorders can be attributed to mutations in genes that (i) encode subunits of the RC ("direct hits"); (ii) encode assembly proteins or RC complexes ("indirect hits"); (iii) encode factors needed for mtDNA maintenance, replication, or translation (intergenomic signaling); (iv) encode components of the mitochondrial protein import machinery; (v) control the synthesis and composition of mitochondrial membrane phospholipids; and (vi) encode proteins involved in mitochondrial dynamics.In contrast to this wealth of knowledge about etiology, our understanding of pathogenic mechanism is very limited. We discuss pathogenic factors that can influence clinical expression, especially ATP shortage and reactive oxygen radicals (ROS) excess. Therapeutic options are limited and fall into three modalities: (i) symptomatic interventions, which are palliative but crucial for day-to-day management; (ii) radical approaches aimed at correcting the biochemical or molecular error, which are interesting but still largely experimental; and (iii) pharmacological means of interfering with the pathogenic cascade of events (e.g. boosting ATP production or scavenging ROS), which are inconsistently and incompletely effective, but can be safe and helpful.

Mitochondrial encephalopathy, lactic acidosis, and strokelike episodes: basic concepts, clinical phenotype, and therapeutic management of MELAS syndrome

Since the initial description almost 25 years ago, the syndrome of mitochondrial encephalopathy, lactic acidosis, and strokelike episodes (MELAS) has been a useful model to study the complex interplay of factors that define mitochondrial disease. This syndrome, most commonly caused by an A-to-G transition mutation at position 3243 of the mitochondrial genome, is typified by characteristic neurological manifestations including seizures, encephalopathy, and strokelike episodes, as well as other frequent secondary manifestations including short stature, cognitive impairment, migraines, depression, cardiomyopathy, cardiac conduction defects, and diabetes mellitus. In this review, we discuss the history, pathogenesis, clinical features, and diagnostic and management strategies of mitochondrial disease in general and of MELAS in particular. We explore features of mitochondrial genetics, including the concepts of heteroplasmy, mitotic segregation, and threshold effect, as a basis for understanding the variability and complicated inheritance patterns seen with this group of diseases. We also describe systemic manifestations of MELAS-associated mutations, including cardiac, renal, endocrine, gastrointestinal, and endothelial abnormalities and pathology, as well as the hypothetical role of derangements to COX enzymatic function in driving the unique pathology and clinical manifestations of MELAS. Although therapeutic options for MELAS and other mitochondrial diseases remain limited, and recent trials have been disappointing, we also consider current and potential therapeutic modalities.

A critical approach to the therapy of mitochondrial respiratory chain and oxidative phosphorylation diseases

Taking advantage of a series of questions raised by an association of patients with mitochondrial disease, this review, after a brief overview of basic concepts of mitochondrial bioenergetics and genetics, discusses the pros and cons of a number of practical options in the field of mitochondrial therapy. This makes it clear that, in contrast to the spectacular progress in our understanding of the biochemical and molecular bases of the mitochondrial diseases defined restrictively as disorders due to defects in the mitochondrial respiratory chain, we are still extremely limited in our ability to treat these conditions. We finally discussed the emerging genetic-based strategies that show some promise, even if much work remains to be done.

[L-arginine therapy on MELAS]

MELAS is the most dominant clinical features among mitochondrial disorders. However the natural course of MELAS has not been clarified yet. In order to elucidate the natural course of MELAS, we have done the Japanese Cohort study on MELAS. By the age of onset, we divided MELAS into two subgroups, a juvenile form (onset is less than 18 years of age) and an adult form (onset is more than 18 years of age). Juvenile form is significantly different from adult form not only in the mean age of onset, but the mean age of death and survival rate (juvenile has 3.2 times higher chance of death than adult). Our date indicate that juvenile form of MELAS is more severe and poor prognosis than those seen in adult form. Based on the hypothesis that MELAS is caused by impaired vasodilation in an intracerebral artery, we evaluated the effects of administering L-arginine, a nitric oxide precursor. Patients were administered L-arginine intravenously at acute phase, or per orally at interictal phase. L-arginine infusions significantly improved all stroke-like symptoms suggesting stroke within 30 min, and oral administration significantly decreased frequency and severity of stroke-like episodes. L-arginine therapy showed promise in treating stroke-like episodes in MELAS.

New indications and controversies in arginine therapy

Arginine is an important, versatile and a conditionally essential amino acid. Besides serving as a building block for tissue proteins, arginine plays a critical role in ammonia detoxification, and nitric oxide and creatine production. Arginine supplementation is an essential component for the treatment of urea cycle defects but recently some reservations have been raised with regards to the doses used in the treatment regimens of these disorders. In recent years, arginine supplementation or restriction has been proposed and trialled in several disorders, including vascular diseases and asthma, mitochondrial encephalopathy lactic acidosis and stroke-like episodes (MELAS), glutaric aciduria type I and disorders of creatine metabolism, both production and transportation into the central nervous system. Herein we present new therapeutic indications and controversies surrounding arginine supplementation or deprivation.

Effect of L-arginine on synaptosomal mitochondrial function

OBJECTIVE

Specific aim of this study is to elucidate the direct effects of L-arginine on the synaptosomal neurotransmission related to the mitochondrial respiratory function.

METHODS

Using isolated endbrains from wild-type mice (ICR), crude synaptosome was analyzed for their concentration of gamma-aminobutyric acid (GABA) and glutamate (Glu) with/without addition of L-arginine. We analyzed the contents of releasing amino acids evoked by high potassium condition and uptake of them in three separated fractions (cytosol, vesicles, and intact mitochondria). The oxygen consumption was also measured by oxygen electrode.

RESULTS

The entire uptakes of GABA and Glu were inhibited by rotenone (about 30 nmol/mg protein) with dose-dependent manner and showed a plateau at about 70% of total uptake. L-arginine inhibited the uptake of Glu logarithmically, however it showed no change in uptake of GABA. The contents of GABA and Glu in synaptosome were decreased in the presence of L-arginine. L-arginine enhanced the respiration of state II by succinate on synaptosomal respiration, although the respiration of synaptosomal mitochondrial fraction and the respiratory chains enzyme activities were almost unaffected by L-arginine. In the presence of rotenone, L-arginine decreased the uptake of Glu without changing the uptake of GABA, increased the releasing of GABA, and may modulate the excitability of neuronal state on the cytosol, cytomembrane, and/or organelles except for mitochondria.

CONCLUSIONS

L-arginine may modulate excitation by neurotransmitters at nerve endings, in relation to potentiated respiratory metabolism of succinate in synaptosomes. Such effects might contribute to alleviation of stroke-like symptoms in MELAS.

Evolution of brain imaging abnormalities in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes

An 18-year-old man developed consecutive homonymous hemianopias that were eventually attributed to mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS). The diagnosis was initially suspected when brain CT scans showed bilateral dystrophic basal ganglia calcifications and MR spectroscopy later showed a prominent lactate peak. Diffusion-weighted MRI showed progressive evolution of restricted proton diffusion at the margins of the lesion from day 3 through 3 weeks. Genetic testing from peripheral blood confirmed an A3243G transition in the patient's MTTL1 gene encoding the transfer RNA for leucine. The patient's visual function improved, but severe atrophy of gray and white matter was visible on MRI.

Central nervous system manifestations of mitochondrial disorders

The central nervous system (CNS) is, after the peripheral nervous system, the second most frequently affected organ in mitochondrial disorders (MCDs). CNS involvement in MCDs is clinically heterogeneous, manifesting as epilepsy, stroke-like episodes, migraine, ataxia, spasticity, extrapyramidal abnormalities, bulbar dysfunction, psychiatric abnormalities, neuropsychological deficits, or hypophysial abnormalities. CNS involvement is found in syndromic and non-syndromic MCDs. Syndromic MCDs with CNS involvement include mitochondrial encephalomyopathy, lactacidosis, stroke-like episodes syndrome, myoclonic epilepsy and ragged red fibers syndrome, mitochondrial neuro-gastrointestinal encephalomyopathy syndrome, neurogenic muscle weakness, ataxia, and retinitis pigmentosa syndrome, mitochondrial depletion syndrome, Kearns-Sayre syndrome, and Leigh syndrome, Leber's hereditary optic neuropathy, Friedreich's ataxia, and multiple systemic lipomatosis. As CNS involvement is often subclinical, the CNS including the spinal cord should be investigated even in the absence of overt clinical CNS manifestations. CNS investigations comprise the history, clinical neurological examination, neuropsychological tests, electroencephalogram, cerebral computed tomography scan, and magnetic resonance imaging. A spinal tap is indicated if there is episodic or permanent impaired consciousness or in case of cognitive decline. More sophisticated methods are required if the CNS is solely affected. Treatment of CNS manifestations in MCDs is symptomatic and focused on epilepsy, headache, lactacidosis, impaired consciousness, confusion, spasticity, extrapyramidal abnormalities, or depression. Valproate, carbamazepine, corticosteroids, acetyl salicylic acid, local and volatile anesthetics should be applied with caution. Avoiding certain drugs is often more beneficial than application of established, apparently indicated drugs.

The mitochondrial myopathy encephalopathy, lactic acidosis with stroke-like episodes (MELAS) syndrome: a review of treatment options

Mitochondrial encephalomyopathies are a multisystemic group of disorders that are characterised by a wide range of biochemical and genetic mitochondrial defects and variable modes of inheritance. Among this group of disorders, the mitochondrial myopathy, encephalopathy, lactic acidosis with stroke-like episodes (MELAS) syndrome is one of the most frequently occurring, maternally inherited mitochondrial disorders. As the name implies, stroke-like episodes are the defining feature of the MELAS syndrome, often occurring before the age of 15 years. The clinical course of this disorder is highly variable, ranging from asymptomatic, with normal early development, to progressive muscle weakness, lactic acidosis, cognitive dysfunction, seizures, stroke-like episodes, encephalopathy and premature death. This syndrome is associated with a number of point mutations in the mitochondrial DNA, with over 80% of the mutations occurring in the dihydrouridine loop of the mitochondrial transfer RNA(Leu(UUR)) [tRNA(Leu)((UUR))] gene. The pathophysiology of the disease is not completely understood; however, several different mechanisms are proposed to contribute to this disease. These include decreased aminoacylation of mitochondrial tRNA, resulting in decreased mitochondrial protein synthesis; changes in calcium homeostasis; and alterations in nitric oxide metabolism. Currently, no consensus criteria exist for treating the MELAS syndrome or mitochondrial dysfunction in other diseases. Many of the therapeutic strategies used have been adopted as the result of isolated case reports or limited clinical studies that have included a heterogeneous population of patients with the MELAS syndrome, other defects in oxidative phosphorylation or lactic acidosis due to disorders of pyruvate metabolism. Current approaches to the treatment of the MELAS syndrome are based on the use of antioxidants, respiratory chain substrates and cofactors in the form of vitamins; however, no consistent benefits have been observed with these treatments.