The effect of citrulline and arginine supplementation on lactic acidemia in MELAS syndrome

Blood biomarkers for assessment of mitochondrial dysfunction: An expert review

Although mitochondrial dysfunction is the known cause of primary mitochondrial disease, mitochondrial dysfunction is often difficult to measure and prove, especially when biopsies of affected tissue are not available. In order to identify blood biomarkers of mitochondrial dysfunction, we reviewed studies that measured blood biomarkers in genetically, clinically or biochemically confirmed primary mitochondrial disease patients. In this way, we were certain that there was an underlying mitochondrial dysfunction which could validate the biomarker. We found biomarkers of three classes: 1) functional markers measured in blood cells, 2) biochemical markers of serum/plasma and 3) DNA markers. While none of the reviewed single biomarkers may perfectly reveal all underlying mitochondrial dysfunction, combining biomarkers that cover different aspects of mitochondrial impairment probably is a good strategy. This biomarker panel may assist in the diagnosis of primary mitochondrial disease patients. As mitochondrial dysfunction may also play a significant role in the pathophysiology of multifactorial disorders such as Alzheimer's disease and glaucoma, the panel may serve to assess mitochondrial dysfunction in complex multifactorial diseases as well and enable selection of patients who could benefit from therapies targeting mitochondria.

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.

L-Arginine Reduces Nitro-Oxidative Stress in Cultured Cells with Mitochondrial Deficiency

L-Arginine (L-ARG) supplementation has been suggested as a therapeutic option in several diseases, including Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like syndrome (MELAS), arguably the most common mitochondrial disease. It is suggested that L-ARG, a nitric oxide (NO) precursor, can restore NO levels in blood vessels, improving cerebral blood flow. However, NO also participates in mitochondrial processes, such as mitochondrial biogenesis, the regulation of the respiratory chain, and oxidative stress. This study investigated the effects of L-ARG on mitochondrial function, nitric oxide synthesis, and nitro-oxidative stress in cell lines harboring the MELAS mitochondrial DNA (mtDNA) mutation (m.3243A>G). We evaluated mitochondrial enzyme activity, mitochondrial mass, NO concentration, and nitro-oxidative stress. Our results showed that m.3243A>G cells had increased NO levels and protein nitration at basal conditions. Treatment with L-ARG did not affect the mitochondrial function and mass but reduced the intracellular NO concentration and nitrated proteins in m.3243A>G cells. The same treatment led to opposite effects in control cells. In conclusion, we showed that the main effect of L-ARG was on protein nitration. Lowering protein nitration is probably involved in the mechanism related to L-ARG supplementation benefits in MELAS patients.

Therapeutic Approaches to Treat Mitochondrial Diseases: "One-Size-Fits-All" and "Precision Medicine" Strategies

Primary mitochondrial diseases (PMD) refer to a group of severe, often inherited genetic conditions due to mutations in the mitochondrial genome or in the nuclear genes encoding for proteins involved in oxidative phosphorylation (OXPHOS). The mutations hamper the last step of aerobic metabolism, affecting the primary source of cellular ATP synthesis. Mitochondrial diseases are characterized by extremely heterogeneous symptoms, ranging from organ-specific to multisystemic dysfunction with different clinical courses. The limited information of the natural history, the limitations of currently available preclinical models, coupled with the large variability of phenotypical presentations of PMD patients, have strongly penalized the development of effective therapies. However, new therapeutic strategies have been emerging, often with promising preclinical and clinical results. Here we review the state of the art on experimental treatments for mitochondrial diseases, presenting "one-size-fits-all" approaches and precision medicine strategies. Finally, we propose novel perspective therapeutic plans, either based on preclinical studies or currently used for other genetic or metabolic diseases that could be transferred to PMD.

Cardiovascular Manifestations of Mitochondrial Disease

Genetic mitochondrial cardiomyopathies are uncommon causes of heart failure that may not be seen by most physicians. However, the prevalence of mitochondrial DNA mutations and somatic mutations affecting mitochondrial function are more common than previously thought. In this review, the pathogenesis of genetic mitochondrial disorders causing cardiovascular disease is reviewed. Treatment options are presently limited to mostly symptomatic support, but preclinical research is starting to reveal novel approaches that may lead to better and more targeted therapies in the future. With better understanding and clinician education, we hope to improve clinician recognition and diagnosis of these rare disorders in order to improve ongoing care of patients with these diseases and advance research towards discovering new therapeutic strategies to help treat these diseases.

Nutritional Interventions for Mitochondrial OXPHOS Deficiencies: Mechanisms and Model Systems

Multisystem metabolic disorders caused by defects in oxidative phosphorylation (OXPHOS) are severe, often lethal, conditions. Inborn errors of OXPHOS function are termed primary mitochondrial disorders (PMDs), and the use of nutritional interventions is routine in their supportive management. However, detailed mechanistic understanding and evidence for efficacy and safety of these interventions are limited. Preclinical cellular and animal model systems are important tools to investigate PMD metabolic mechanisms and therapeutic strategies. This review assesses the mechanistic rationale and experimental evidence for nutritional interventions commonly used in PMDs, including micronutrients, metabolic agents, signaling modifiers, and dietary regulation, while highlighting important knowledge gaps and impediments for randomized controlled trials. Cellular and animal model systems that recapitulate mutations and clinical manifestations of specific PMDs are evaluated for their potential in determining pathological mechanisms, elucidating therapeutic health outcomes, and investigating the value of nutritional interventions for mitochondrial disease conditions.

Therapies for mitochondrial diseases and current clinical trials

Mitochondrial diseases are a clinically and genetically heterogeneous group of disorders that result from dysfunction of the mitochondrial oxidative phosphorylation due to molecular defects in genes encoding mitochondrial proteins. Despite the advances in molecular and biochemical methodologies leading to better understanding of the etiology and mechanism of these diseases, there are still no satisfactory therapies available for mitochondrial disorders. Treatment for mitochondrial diseases remains largely symptomatic and does not significantly alter the course of the disease. Based on limited number of clinical trials, several agents aiming at enhancing mitochondrial function or treating the consequences of mitochondrial dysfunction have been used. Several agents are currently being evaluated for mitochondrial diseases. Therapeutic strategies for mitochondrial diseases include the use of agents enhancing electron transfer chain function (coenzyme Q₁₀, idebenone, riboflavin, dichloroacetate, and thiamine), agents acting as energy buffer (creatine), antioxidants (vitamin C, vitamin E, lipoic acid, cysteine donors, and EPI-743), amino acids restoring nitric oxide production (arginine and citrulline), cardiolipin protector (elamipretide), agents enhancing mitochondrial biogenesis (bezafibrate, epicatechin, and RTA 408), nucleotide bypass therapy, liver transplantation, and gene therapy. Although, there is a lack of curative therapies for mitochondrial disorders at the current time, the increased number of clinical research evaluating agents that target different aspects of mitochondrial dysfunction is promising and is expected to generate more therapeutic options for these diseases in the future.

Anesthetic Management of Mitochondrial Encephalopathy With Lactic Acidosis and Stroke-Like Episodes (MELAS Syndrome) in a High-Risk Pregnancy: A Case Report

MELAS syndrome (mitochondrial encephalopathy, lactic acidosis, and stroke-like symptoms) is a rare and complex mitochondrial disorder. We present the in-hospital course of a 36-year-old gravida 2, para 0 with MELAS syndrome and severe preeclampsia, complicated by hyponatremia, hyperkalemia, and diabetes. A retained placenta with postpartum hemorrhage required urgent instrumental delivery under spinal anesthesia, transfusion, and intensive care unit admission for pulmonary edema, effusions, and atelectasis. Postpartum endometritis and sepsis also were encountered. This is to our knowledge the first case report of obstetric complications in MELAS syndrome and highlights the salient metabolic sequelae of this syndrome.

Arginine and citrulline for the treatment of MELAS syndrome

MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome is a maternally inherited mitochondrial disease with a broad spectrum of manifestations. In addition to impaired energy production, nitric oxide (NO) deficiency occurs in MELAS syndrome and leads to impaired blood perfusion in microvasculature that can contribute to several complications including stroke-like episodes, myopathy, and lactic acidosis. The supplementation of NO precursors, L-arginine and L-citrulline, increases NO production and hence can potentially have therapeutic utility in MELAS syndrome. L-citrulline raises NO production to a greater extent than L-arginine; therefore, L-citrulline may have a better therapeutic effect. The clinical effect of L-citrulline has not yet been studied and clinical studies on L-arginine, which are limited, only evaluated the stroke-like episodes aspect of the disease. Controlled studies are still needed to assess the clinical effects of L-arginine and L-citrulline on different aspects of MELAS syndrome.

Rapid and Sensitive Differentiating Ischemic and Hemorrhagic Strokes by Dried Blood Spot Based Direct Injection Mass Spectrometry Metabolomics Analysis

Cerebral infarction (CI) and intracerebral hemorrhage are lethal cerebrovascular diseases, sometimes sharing similar clinical manifestations but with distinct therapeutic strategies. Delayed treatment usually resulted in poor prognosis. A timely diagnosis report is highly warranted especially in emergency. One hundred twenty-nine CI patients, 73 intracerebral hemorrhage (ICH) patients, and 98 controls were enrolled in this study. A direct injection mass spectrometry metabolomics approach was adopted using dried blood spot samples. This targeted metabolomics analysis focused on absolute quantitation of 23 amino acids, 26 carnitine/carnitine esters, and 22 calculated ratios parameters. Compared to the normal control group, CI and ICH showed distinct metabolite changes, respectively. For stroke differentiation, Tyr, C5-OH/C0, Cit, Asn, Pro, Val, Arg/Orn, Leu, and Val/Phe were elevated in the CI group. On the contrary, C5:1, Phe/Tyr, (C0 + C2 + C3 + C16 + C18:1)/Cit, and Met/Leu were of lower levels in the CI group. Using regression model based on some of the above-mentioned parameters, 79.07% of stroke patients from a new set could be definitely confirmed. This study proved the targeted metabolomics analysis was a promising tool for rapid and timely stroke differentiation.

Impaired nitric oxide production in children with MELAS syndrome and the effect of arginine and citrulline supplementation

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is one of the most frequent maternally inherited mitochondrial disorders. The pathogenesis of this syndrome is not fully understood and believed to result from several interacting mechanisms including impaired mitochondrial energy production, microvasculature angiopathy, and nitric oxide (NO) deficiency. NO deficiency in MELAS syndrome is likely to be multifactorial in origin with the decreased availability of the NO precursors, arginine and citrulline, playing a major role. In this study we used stable isotope infusion techniques to assess NO production in children with MELAS syndrome and healthy pediatric controls. We also assessed the effect of oral arginine and citrulline supplementations on NO production in children with MELAS syndrome. When compared to control subjects, children with MELAS syndrome were found to have lower NO production, arginine flux, plasma arginine, and citrulline flux. In children with MELAS syndrome, arginine supplementation resulted in increased NO production, arginine flux, and arginine concentration. Citrulline supplementation resulted in a greater increase of these parameters. Additionally, citrulline supplementation was associated with a robust increase in citrulline concentration and flux and de novo arginine synthesis rate. The greater effect of citrulline in increasing NO production is due to its greater ability to increase arginine availability particularly in the intracellular compartment in which NO synthesis takes place. This study, which is the first one to assess NO metabolism in children with mitochondrial diseases, adds more evidence to the notion that NO deficiency occurs in MELAS syndrome, suggests a better effect for citrulline because of its greater role as NO precursor, and indicates that impaired NO production occurs in children as well as adults with MELAS syndrome. Thus, the initiation of treatment with NO precursors may be beneficial earlier in life. Controlled clinical trials to assess the therapeutic effects of arginine and citrulline on clinical complications of MELAS syndrome are needed.

MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is one of the most frequent maternally inherited mitochondrial disorders. MELAS syndrome is a multi-organ disease with broad manifestations including stroke-like episodes, dementia, epilepsy, lactic acidemia, myopathy, recurrent headaches, hearing impairment, diabetes, and short stature. The most common mutation associated with MELAS syndrome is the m.3243A>G mutation in the MT-TL1 gene encoding the mitochondrial tRNA(Leu(UUR)). The m.3243A>G mutation results in impaired mitochondrial translation and protein synthesis including the mitochondrial electron transport chain complex subunits leading to impaired mitochondrial energy production. The inability of dysfunctional mitochondria to generate sufficient energy to meet the needs of various organs results in the multi-organ dysfunction observed in MELAS syndrome. Energy deficiency can also stimulate mitochondrial proliferation in the smooth muscle and endothelial cells of small blood vessels leading to angiopathy and impaired blood perfusion in the microvasculature of several organs. These events will contribute to the complications observed in MELAS syndrome particularly the stroke-like episodes. In addition, nitric oxide deficiency occurs in MELAS syndrome and can contribute to its complications. There is no specific consensus approach for treating MELAS syndrome. Management is largely symptomatic and should involve a multidisciplinary team. Unblinded studies showed that l-arginine therapy improves stroke-like episode symptoms and decreases the frequency and severity of these episodes. Additionally, carnitine and coenzyme Q10 are commonly used in MELAS syndrome without proven efficacy.