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

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.

Multi-dose enteral L-citrulline administration in premature infants at risk of developing pulmonary hypertension associated with bronchopulmonary dysplasia

OBJECTIVE

Information is needed to guide the design of randomized controlled trials (RCTs) evaluating L-citrulline therapy for premature infants with pulmonary hypertension associated with bronchopulmonary dysplasia (BPD-PH). Based on our single-dose pharmacokinetic study, we evaluated the ability of a multi-dose enteral L-citrulline strategy to achieve a target trough steady-state L-citrulline plasma concentration and its tolerability in premature infants.

STUDY DESIGN

Plasma L-citrulline concentrations were measured in six premature infants receiving 60 mg/kg L-citrulline every 6 h for 72 h before the first and last L-citrulline doses. L-citrulline concentrations were compared to concentration-time profiles from our previous study.

RESULTS

Target trough plasma L-citrulline concentrations were achieved in 2/6 subjects. No serious adverse events occurred.

CONCLUSIONS

Multi-dose L-citrulline was well tolerated. These results will assist in the design of phase II RCTs evaluating L-citrulline dosage strategies to achieve target plasma L-citrulline concentrations in infants at risk for BPD-PH.

CLINICAL TRIALS

gov ID: NCT03542812.

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.

Biomarkers of mitochondrial disorders

Mitochondrial diseases encompass a heterogeneous group of disorders with a wide range of clinical manifestations, most classically resulting in neurological, muscular, and metabolic abnormalities, but having the potential to affect any organ system. Over the years, substantial progress has been made in identifying and characterizing various biomarkers associated with mitochondrial diseases. This review summarizes the current knowledge of mitochondrial biomarkers based on a literature review and discusses the evidence behind their use in clinical practice. A total of 13 biomarkers were thoroughly reviewed including lactate, pyruvate, lactate:pyruvate ratio, creatine kinase, creatine, amino acid profiles, glutathione, malondialdehyde, GDF-15, FGF-21, gelsolin, neurofilament light-chain, and circulating cell-free mtDNA. Most biomarkers had mixed findings depending on the study, especially when considering their utility for specific mitochondrial diseases versus mitochondrial conditions in general. However, in large biomarker comparison studies, GDF-15 followed by FGF-21, seem to have the greatest value though they are still not perfect. As such, additional studies are needed, especially in light of newer biomarkers that have not yet been thoroughly investigated. Understanding the landscape of biomarkers in mitochondrial diseases is crucial for advancing early detection, improving patient management, and developing targeted therapies.

Challenges and opportunities to bridge translational to clinical research for personalized mitochondrial medicine

Mitochondrial disorders are a group of rare and heterogeneous genetic diseases characterized by dysfunctional mitochondria leading to deficient adenosine triphosphate synthesis and chronic energy deficit in patients. The majority of these patients exhibit a wide range of phenotypic manifestations targeting several organ systems, making their clinical diagnosis and management challenging. Bridging translational to clinical research is crucial for improving the early diagnosis and prognosis of these intractable mitochondrial disorders and for discovering novel therapeutic drug candidates and modalities. This review provides the current state of clinical testing in mitochondrial disorders, discusses the challenges and opportunities for converting basic discoveries into clinical settings, explores the most suited patient-centric approaches to harness the extraordinary heterogeneity among patients affected by the same primary mitochondrial disorder, and describes the current outlook of clinical trials.

Randomized placebo-controlled crossover study to assess tolerability and pharmacodynamics of zagociguat, a soluble guanylyl cyclase stimulator, in healthy elderly

AIMS

Dysfunction of nitric oxide-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate signalling is implicated in the pathophysiology of cognitive impairment. Zagociguat is a central nervous system (CNS) penetrant sGC stimulator designed to amplify nitric oxide-cyclic guanosine monophosphate signalling in the CNS. This article describes a phase 1b study evaluating the safety and pharmacodynamic effects of zagociguat.

METHODS

In this randomized crossover study, 24 healthy participants aged ≥65 years were planned to receive 15 mg zagociguat or placebo once daily for 2 15-day periods separated by a 27-day washout. Adverse events, vital signs, electrocardiograms and laboratory tests were conducted to assess safety. Pharmacokinetics of zagociguat were evaluated in blood and cerebrospinal fluid (CSF). Pharmacodynamic assessments included evaluation of cerebral blood flow, CNS tests, pharmaco-electroencephalography, passive leg movement and biomarkers in blood, CSF and brain.

RESULTS

Twenty-four participants were enrolled; 12 participants completed both treatment periods, while the other 12 participants completed only 1 treatment period. Zagociguat was well-tolerated and penetrated the blood-brain barrier, with a CSF/free plasma concentration ratio of 0.45 (standard deviation 0.092) measured 5 h after the last dose of zagociguat on Day 15. Zagociguat induced modest decreases in blood pressure. No consistent effects of zagociguat on other pharmacodynamic parameters were detected.

CONCLUSION

Zagociguat was well-tolerated and induced modest blood pressure reductions consistent with other sGC stimulators. No clear pharmacodynamic effects of zagociguat were detected. Studies in participants with proven reduced cerebral blood flow or CNS function may be an avenue for further evaluation of the compound.

The Effect of Photobiomodulation on the Treatment of Hereditary Mitochondrial Diseases

Introduction: Despite a wide variety of clinical presentations in hereditary Mitochondrial Diseases, muscle fatigue is a common theme and impairs a patient's quality of life and ability to function. Current treatments are only supportive and include nutritional supplementation and physical therapy. Photobiomodulation therapy (PBMT) using low-intensity, narrow spectrum light in the red/near infrared (NIR) range, from a low-level laser or light-emitting diode sources, enhances mitochondrial function in preclinical and clinical studies on a range of conditions. However, little research has been done on the effectiveness of photobiomodulation in hereditary mitochondrial disorders. Methods: We performed a scoping review of the evidence of the beneficial effects of photobiomodulation for treating the muscle-related symptoms of hereditary mitochondrial disease. Results: No studies regarding photobiomodulation in hereditary mitochondrial disease were identified. However, in other clinical conditions featuring acquired mitochondrial impairment, we identified studies that suggested improved function, although sample sizes were small in number and statistical power. Conclusion: There is emerging evidence of efficacy for PBMT for diseases involving acquired mitochondrial insufficiency. We identified no published research on PBMT in hereditary mitochondrial disease, but this review confirms a theoretical rationale for a positive effect and suggests further research.

Recent advances in small molecules for improving mitochondrial disorders

Mitochondrial disorders are observed in various human diseases, including rare genetic disorders and complex acquired pathologies. Recent advances in molecular biological techniques have dramatically expanded the understanding of multiple pathomechanisms involving mitochondrial disorders. However, the therapeutic methods for mitochondrial disorders are limited. For this reason, there is increasing interest in identifying safe and effective strategies to mitigate mitochondrial impairments. Small-molecule therapies hold promise for improving mitochondrial performance. This review focuses on the latest advances in developing bioactive compounds for treating mitochondrial disease, aiming to provide a broader perspective of fundamental studies that have been carried out to evaluate the effects of small molecules in regulating mitochondrial function. Novel-designed small molecules ameliorating mitochondrial functions are urgent for further research.

Multi-dose enteral L-citrulline administration in premature infants at risk of developing pulmonary hypertension associated with bronchopulmonary dysplasia

Objective

Information is needed to guide the design of randomized controlled trials (RCTs) evaluating L-citrulline as a therapy for premature infants with pulmonary hypertension associated with bronchopulmonary dysplasia (BPD-PH). Our goal was to evaluate the tolerability and ability to achieve a target steady-state L-citrulline plasma concentration in prematures treated enterally with a multi-dose L-citrulline strategy based on our single-dose pharmacokinetic study.

Study Design

Six prematures received 60 mg/kg of L-citrulline every 6 hours for 72 hours. Plasma L-citrulline concentrations were measured before the first and last L-citrulline doses. L-citrulline concentrations were compared to concentration-time profiles from our previous study.

Results

Plasma L-citrulline concentrations agreed with the simulated concentration-time profiles. No serious adverse events occurred.

Conclusions

Simulations based on single-doses can be used to predict target multi-dose plasma L-citrulline concentrations. These results assist the design of RCTs evaluating the safety and effectiveness of L-citrulline therapy for BPD-PH. Clinical trials.gov ID: NCT03542812.

Pharmacotherapy for Pulmonary Hypertension in Infants with Bronchopulmonary Dysplasia: Past, Present, and Future

Approximately 8-42% of premature infants with chronic lung disease of prematurity, bronchopulmonary dysplasia (BPD), develop pulmonary hypertension (PH). Infants with BPD-PH carry alarmingly high mortality rates of up to 47%. Effective PH-targeted pharmacotherapies are desperately needed for these infants. Although many PH-targeted pharmacotherapies are commonly used to treat BPD-PH, all current use is off-label. Moreover, all current recommendations for the use of any PH-targeted therapy in infants with BPD-PH are based on expert opinion and consensus statements. Randomized Control Trials (RCTs) are needed to determine the efficacy of PH-targeted treatments in premature infants with or at risk of BPD-PH. Prior to performing efficacy RCTs, studies need to be conducted to obtain pharmacokinetic, pharmacodynamic, and safety data for any pharmacotherapy used in this understudied and fragile patient population. This review will discuss current and needed treatment strategies, identify knowledge deficits, and delineate both challenges to be overcome and approaches to be taken to develop effective PH-targeted pharmacotherapies that will improve outcomes for premature infants with or at risk of developing BPD-PH.

Retinopathy of prematurity: A review of pathophysiology and signaling pathways

Retinopathy of prematurity (ROP) is a vasoproliferative disorder of the retina and a leading cause of visual impairment and childhood blindness worldwide. The disease is characterized by an early stage of retinal microvascular degeneration, followed by neovascularization that can lead to subsequent retinal detachment and permanent visual loss. Several factors play a key role during the different pathological stages of the disease. Oxidative and nitrosative stress and inflammatory processes are important contributors to the early stage of ROP. Nitric oxide synthase and arginase play important roles in ischemia/reperfusion-induced neurovascular degeneration. Destructive neovascularization is driven by mediators of the hypoxia-inducible factor pathway, such as vascular endothelial growth factor and metabolic factors (succinate). The extracellular matrix is involved in hypoxia-induced retinal neovascularization. Vasorepulsive molecules (semaphorin 3A) intervene preventing the revascularization of the avascular zone. This review focuses on current concepts about signaling pathways and their mediators, involved in the pathogenesis of ROP, highlighting new potentially preventive and therapeutic modalities. A better understanding of the intricate molecular mechanisms underlying the pathogenesis of ROP should allow the development of more effective and targeted therapeutic agents to reduce aberrant vasoproliferation and facilitate physiological retinal vascular development.

Clinical trials in mitochondrial diseases

Primary mitochondrial diseases are some of the most common and complex inherited inborn errors of metabolism. Their molecular and phenotypic diversity has led to difficulties in finding disease-modifying therapies and clinical trial efforts have been slow due to multiple significant challenges. Lack of robust natural history data, difficulties in finding specific biomarkers, absence of well-validated outcome measures, and small patient numbers have made clinical trial design and conduct difficult. Encouragingly, new interest in treating mitochondrial dysfunction in common diseases and regulatory incentives to develop therapies for rare conditions have led to significant interest and efforts to develop drugs for primary mitochondrial diseases. Here, we review past and present clinical trials and future strategies of drug development in primary mitochondrial diseases.

Clinical score for early diagnosis and treatment of stroke-like episodes in MELAS syndrome

BACKGROUND AND OBJECTIVES

Stroke-like episodes (SLEs) in patients with MELAS syndrome are often initially misdiagnosed as acute ischemic stroke (AIS), resulting in treatment delay. We aimed to determine clinical features that may distinguish SLEs from AISs and explore the benefit of early L-arginine treatment on patient outcomes.

METHODS

We looked retrospectively for MELAS patients admitted between January 2005 and January 2022 and compared them to an AIS cohort with similar lesion topography. MELAS patients who received L-arginine within 40 days of their first SLE were defined as the early treatment group and the remaining as late or no treatment group.

RESULTS

Twenty-three SLEs in 10 MELAS patients and 21 AISs were included. SLE patients had significantly different features: they were younger, more commonly reported hearing loss, lower body mass index, had more commonly a combination of headache and/or seizures at presentation, serum lactate was higher, and hemiparesis was less common. An SLE Early Clinical Score (SLEECS) was constructed by designating one point to each above features. SLEECS ≥ 4 had 80% sensitivity and 100% specificity for SLE diagnosis. Compared to late or no treatment, early treatment group patients (n = 5) had less recurrent SLEs (total 2 vs. 11), less seizures (14% vs. 25%, p = 0.048), lower degree of disability at first and last follow-up (modified ranking scale, mRS 2 ± 0.7 vs. 4.2 ± 1, p = 0.005; 2 ± 0.7 vs. 5.8 ± 0.5, p < 0.001, respectively), and a lower mortality (0% vs. 80% p = 0.048).

CONCLUSIONS

The SLEECS model may aid in the early diagnosis and treatment of SLEs and lead to improved clinical outcomes.

Adult-onset MELAS syndrome in a 51-year-old woman without typical clinical manifestations: a case report

Background

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome is a multi-organ disorder resulting from mitochondrial DNA (mtDNA) mutations. We report a case of suspected MELAS syndrome that progressed to left ventricular dysfunction 24 years after an initial diagnosis of atrioventricular block (AVB).

Case summary

A 51-year-old woman was referred to heart failure clinic because of dyspnoea on exertion and progressive cardiomegaly. She had a dual-chamber pacemaker implanted for 24 years because of a high-degree AVB. She was treated for diabetes mellitus for 23 years and used hearing aids for 12 years because of sensorineural hearing loss. Transthoracic echocardiography revealed reduced left ventricular ejection fraction (26%), with increased thickness and unusual texture of the myocardium. The absence of abnormal findings on serum and urine protein electrophoresis suggested that light-chain amyloidosis was unlikely. In addition, ^99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid scintigraphy revealed no definite uptake in the myocardium. Endomyocardial biopsy revealed a hypertrophy of myocytes in haematoxylin-eosin staining, and electron microscopy revealed a disarrangement of mitochondrial cristae, which were suggestive of mitochondrial cardiomyopathy. A mtDNA test detected the m.3243A > G mutation in the MT-TL1 gene. According to these findings, MELAS syndrome was the most probable diagnosis despite the absence of common symptoms such as stroke-like episodes or lactic acidosis.

Discussion

The patient had progressed to heart failure with reduced ejection fraction 24 years after the first cardiac manifestation. An identification of the mutation in the MT-TL1 gene, indicative of MELAS syndrome, enabled the diagnosis of MELAS syndrome without typical manifestations.

Comparative plasma and urine metabolomics analysis of juvenile and adult canines

Background and aims

The metabolomic profile of a biofluid can be affected by age, and thus provides detailed information about the metabolic alterations in biological processes and reflects the in trinsic rule regulating the growth and developmental processes.

Methods

To systemically investigate the characteristics of multiple metabolic profiles associated with canine growth, we analyzed the metabolomics in the plasma and urine samples from 15 young and 15 adult beagle dogs via UHPLC-Q-TOFMS-based metabolomics. Blood routine and serum biochemical analyses were also performed on fasting blood samples.

Results

The metabolomics results showed remarkable differences in metabolite fingerprints both in plasma and urine between the young and adult groups. The most obvious age-related metabolite alterations include decreased serumlevels of oxoglutaric acid and essential amino acids and derivatives but increased levels of urine levels of O-acetylserine. These changes primarily involved in amino acid metabolism and bile secretion pathways. We also found that the levels of glutamine were consistently higher in both serum and urine of adults, while N-acetylhistamine and uracil concentrations were much lower in the adult group compared to younger ones.

Conclusion

Our study provides a whole metabolic profile of serum and urine characteristics of young and adult canines, identifying several metabolites that were significantly associated with age change, which provides theoretical support for the nutrition-related research and age-related homeostasis maintenance in dogs.

Pharmacokinetics of L-Citrulline in Neonates at Risk of Developing Bronchopulmonary Dysplasia-Associated Pulmonary Hypertension

BACKGROUND

Options to treat pulmonary hypertension (PH) in neonates with bronchopulmonary dysplasia (BPD) are few and largely ineffective. Improving the bioavailability of nitric oxide (NO) might be an efficacious treatment for BPD-PH. When administered orally, the NO-L-arginine precursor, L-citrulline, increases NO production in children and adults, however, pharmacokinetic (PK) studies of oral L-citrulline have not been performed in infants and children.

OBJECTIVES

This study characterized the PK of enterally administered L-citrulline in neonates at risk of developing BPD-PH to devise a model-informed dosing strategy.

METHODS AND RESULTS

Ten premature neonates (≤ 28 weeks gestation) were administered a single dose of 150 mg/kg (powder form solubilized in sterile water) oral L-citrulline at 32 ± 1 weeks postmenstrual age. Due to the need to limit blood draws, time windows were used to maximize the sampling over the dosing interval by assigning neonates to one of two groups (ii) samples collected pre-dose and at 1- and 2.5-h post-dose, and (ii) pre-dose and 0.25- and 3-h post-dose. The L-arginine concentrations (µmol/L) and the L-citrulline (µmol/L) plasma concentration-time data were evaluated using non-compartmental analysis (Phoenix WinNonlin version 8.1). Optimal dosage strategies were derived using a simulation-based methodology. Simulated doses of 51.5 mg or 37.5 mg/kg given four times a day produced steady-state concentrations close to a target of 50 µmol/L. The volume of distribution (V/F) and clearance (CL/F) were 302.89 ml and 774.96 ml/h, respectively, with the drug exhibiting a half-life of 16 minutes. The AUC from the time of dosing to the time of last concentration was 1473.3 h*μmol/L, with Cmax and Tmax of 799 μmol/L and 1.55 h, respectively.

CONCLUSION

This is the first PK study in neonates presenting data that can be used to inform dosing strategies in future randomized controlled trials evaluating enteral L-citrulline as a potential treatment to reduce PH associated with BPD in premature neonates.

REGISTRATION

Clinical trials.gov Identifier: NCT03542812.

Mitochondrial Unfolded Protein Response and Integrated Stress Response as Promising Therapeutic Targets for Mitochondrial Diseases

The development and application of high-throughput omics technologies have enabled a more in-depth understanding of mitochondrial biosynthesis metabolism and the pathogenesis of mitochondrial diseases. In accordance with this, a host of new treatments for mitochondrial disease are emerging. As an essential pathway in maintaining mitochondrial proteostasis, the mitochondrial unfolded protein response (UPR^mt) is not only of considerable significance for mitochondrial substance metabolism but also plays a fundamental role in the development of mitochondrial diseases. Furthermore, in mammals, the integrated stress response (ISR) and UPR^mt are strongly coupled, functioning together to maintain mitochondrial function. Therefore, ISR and UPR^mt show great application prospects in the treatment of mitochondrial diseases. In this review, we provide an overview of the molecular mechanisms of ISR and UPR^mt and focus on them as potential targets for mitochondrial disease therapy.

Independent origin for m.3243A>G mitochondrial mutation in three Venezuelan cases of MELAS syndrome

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a multisystem and progressive neurodegenerative mitochondrial disease, caused by point nucleotide changes in the mtDNA where 80 % of cases have the mutation m.3243A>G in the MT-TL1 gene. In this work, we described the clinical, biochemical and molecular analysis of three Venezuelan patients affected with MELAS syndrome. All cases showed lactic acidosis, cortical cerebral atrophy on magnetic resonance imaging and muscular system deficit, and in two of the cases alteration of urine organic acid levels was also registered. A screening for the mutation m.3243A>G in different patients' body samples confirmed the presence of this mutation with variable degrees of heteroplasmy (blood = 7-41 %, buccal mucosa = 14-53 %, urine = 58-94 %). The mitochondrial haplogroups for the three patients were different (H, C1b, and A2), indicating an independent origin for the mutation.

Delay in diagnosing a patient with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome who presented with status epilepticus and lactic acidosis: a case report

Background

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episode syndrome is a rare mitochondrial genetic disorder that can present with a variety of clinical manifestations, including stroke, hearing loss, seizures, and lactic acidosis. The most common genetic mutation associated with this syndrome is M.3243A>G. The main underlying mechanism of the disease relates to protein synthesis, energy depletion, and nitric oxide deficiency. Controlling disease complications and improving patient quality of life are the primary aims of treatment options.

Case presentation

A 28-year-old Arabic female visited Al-Amiri Hospital in Kuwait. The patient was newly diagnosed with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episode syndrome following her admission as a case of status epilepticus requiring further investigation. The patient’s seizures were controlled, and she was evaluated to rule out the most serious complications by carrying out appropriate clinical, laboratory, and radiological imaging. The patient was discharged from the hospital after 2 weeks with a follow-up plan.

Conclusion

This case report emphasizes the importance of considering mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episode syndrome as a potential cause of status epilepticus with lactic acidosis in a young female patient with a past history of stroke-like episodes. It also stresses the most important workup to rule out every possible life-threatening complication to improve patients’ lives.

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.

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.

Effects of L-Citrulline Supplementation and Aerobic Training on Vascular Function in Individuals with Obesity across the Lifespan

Children with obesity are at higher risk for developing cardiometabolic diseases that once were considered health conditions of adults. Obesity is commonly associated with cardiometabolic risk factors such as dyslipidemia, hyperglycemia, hyperinsulinemia and hypertension that contribute to the development of endothelial dysfunction. Endothelial dysfunction, characterized by reduced nitric oxide (NO) production, precedes vascular abnormalities including atherosclerosis and arterial stiffness. Thus, early detection and treatment of cardiometabolic risk factors are necessary to prevent deleterious vascular consequences of obesity at an early age. Non-pharmacological interventions including L-Citrulline (L-Cit) supplementation and aerobic training stimulate endothelial NO mediated vasodilation, leading to improvements in organ perfusion, blood pressure, arterial stiffness, atherosclerosis and metabolic health (glucose control and lipid profile). Few studies suggest that the combination of L-Cit supplementation and exercise training can be an effective strategy to counteract the adverse effects of obesity on vascular function in older adults. Therefore, this review examined the efficacy of L-Cit supplementation and aerobic training interventions on vascular and metabolic parameters in obese individuals.

Nitric Oxide Deficiency in Mitochondrial Disorders: The Utility of Arginine and Citrulline

Mitochondrial diseases represent a growing list of clinically heterogeneous disorders that are associated with dysfunctional mitochondria and multisystemic manifestations. In spite of a better understanding of the underlying pathophysiological basis of mitochondrial disorders, treatment options remain limited. Over the past two decades, there is growing evidence that patients with mitochondrial disorders have nitric oxide (NO) deficiency due to the limited availability of NO substrates, arginine and citrulline; decreased activity of nitric oxide synthase (NOS); and NO sequestration. Studies evaluating the use of arginine in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) presenting with stroke-like episodes showed symptomatic improvement after acute administration as well as a reduction in the frequency and severity of stroke-like episodes following chronic use. Citrulline, another NO precursor, was shown through stable isotope studies to result in a greater increase in NO synthesis. Recent studies showed a positive response of arginine and citrulline in other mitochondrial disorders besides MELAS. Randomized-controlled studies with a larger number of patients are warranted to better understand the role of NO deficiency in mitochondrial disorders and the efficacy of NO precursors as treatment modalities in these disorders.

Primary Mitochondrial Disorders of the Pediatric Central Nervous System: Neuroimaging Findings

Primary mitochondrial disorders (PMDs) constitute the most common cause of inborn errors of metabolism in children, and they frequently affect the central nervous system. Neuroimaging findings of PMDs are variable, ranging from unremarkable and nonspecific to florid and highly suggestive. An overview of PMDs, including a synopsis of the basic genetic concepts, main clinical symptoms, and neuropathologic features, is presented. In addition, eight of the most common PMDs that have a characteristic imaging phenotype in children are reviewed in detail. Online supplemental material is available for this article. ^©RSNA, 2020.

Impact of arginine therapy on mitochondrial function in children with sickle cell disease during vaso-occlusive pain

Altered mitochondrial function occurs in sickle cell disease (SCD), due in part to low nitric oxide (NO) bioavailability. Arginine, the substrate for NO production, becomes acutely deficient in SCD patients with vaso-occlusive pain episodes (VOE). To determine if arginine improves mitochondrial function, 12 children with SCD-VOE (13.6 ± 3 years; 67% male; 75% hemoglobin-SS) were randomized to 1 of 3 arginine doses: (1) 100 mg/kg IV 3 times/day (TID); (2) loading dose (200 mg/kg) then 100 mg/kg TID; or (3) loading dose (200 mg/kg) followed by continuous infusion (300 mg/kg per day) until discharge. Platelet-rich plasma mitochondrial activity, protein expression, and protein-carbonyls were measured from emergency department (ED) presentation vs discharge. All VOE subjects at ED presentation had significantly decreased complex-V activity compared to a steady-state cohort. Notably, complex-V activity was increased at discharge in subjects from all 3 arginine-dosing schemes; greatest increase occurred with a loading dose (P < .001). Although complex-IV and citrate synthase activities were similar in VOE platelets vs steady state, enzyme activities were significantly increased in VOE subjects after arginine-loading dose treatment. Arginine also decreased protein-carbonyl levels across all treatment doses (P < .01), suggesting a decrease in oxidative stress. Arginine therapy increases mitochondrial activity and reduces oxidative stress in children with SCD/VOE. This trial was registered at www.clinicaltrials.gov as #NCT02536170.

Current and Emerging Clinical Treatment in Mitochondrial Disease

Primary mitochondrial disease (PMD) is a group of complex genetic disorders that arise due to pathogenic variants in nuclear or mitochondrial genomes. Although PMD is one of the most prevalent inborn errors of metabolism, it often exhibits marked phenotypic variation and can therefore be difficult to recognise. Current treatment for PMD revolves around supportive and preventive approaches, with few disease-specific therapies available. However, over the last decade there has been considerable progress in our understanding of both the genetics and pathophysiology of PMD. This has resulted in the development of a plethora of new pharmacological and non-pharmacological therapies at varying stages of development. Many of these therapies are currently undergoing clinical trials. This review summarises the latest emerging therapies that may become mainstream treatment in the coming years. It is distinct from other recent reviews in the field by comprehensively addressing both pharmacological non-pharmacological therapy from both a bench and a bedside perspective. We highlight the current and developing therapeutic landscape in novel pharmacological treatment, dietary supplementation, exercise training, device use, mitochondrial donation, tissue replacement gene therapy, hypoxic therapy and mitochondrial base editing.

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.

Clinical trials in mitochondrial disorders, an update

Mitochondrial disorders comprise a molecular and clinically diverse group of diseases that are associated with mitochondrial dysfunction leading to multi-organ disease. With recent advances in molecular technologies, the understanding of the pathomechanisms of a growing list of mitochondrial disorders has been greatly expanded. However, the therapeutic approaches for mitochondrial disorders have lagged behind with treatment options limited mainly to symptom specific therapies and supportive measures. There is an increasing number of clinical trials in mitochondrial disorders aiming for more specific and effective therapies. This review will cover different treatment modalities currently used in mitochondrial disorders, focusing on recent and ongoing clinical trials.

Therapeutic Potential of Citrulline as an Arginine Supplement: A Clinical Pharmacology Review

Supplemental arginine has shown promise as a safe therapeutic option to improve endogenous nitric oxide (NO) regulation in cardiovascular diseases associated with endothelial dysfunction. In clinical studies in adults, L-arginine, an endogenous amino acid, was reported to improve cardiovascular function in hypertension, pulmonary hypertension, preeclampsia, angina, and MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome. L-citrulline, a natural precursor of L-arginine, is more bioavailable than L-arginine because it avoids hepatic first-pass metabolism and has a longer circulation time. Although not yet well-studied, arginine/citrulline has immense therapeutic potential in some life-threatening diseases in children. However, the optimal clinical development of arginine or citrulline in children requires more information about pharmacokinetics and exposure-response relationships at appropriate ages and under relevant disease states. This article summarizes the preclinical and clinical studies of arginine/citrulline in both adults and children, including currently available pharmacokinetic information. The pharmacology of arginine/citrulline is confounded by several patient-specific factors such as variations in baseline arginine/citrulline due to developmental ages and disease states. Currently available pharmacokinetic studies are insufficient to inform the optimal design of clinical studies, especially in children. Successful bench-to-bedside clinical translation of arginine supplementation awaits information from well-designed pharmacokinetic/pharmacodynamic studies, along with pharmacometric approaches.

Endothelial Dysfunction and the Effect of Arginine and Citrulline Supplementation in Children and Adolescents With Mitochondrial Diseases

BACKGROUND

In addition to the reduced energy production, characteristic of mitochondrial disorders, nitric oxide (NO) deficiency can occur as well. The NO produced by vascular endothelial cells relaxes vascular smooth muscles, resulting in vasodilation that maintains the patency of small blood vessels and promotes blood flow through microvasculature. Endothelial dysfunction due to inability of vascular endothelium to generate enough NO to maintain adequate vasodilation can result in decreased perfusion in the microvasculature of various tissues, contributing to many complications seen in individuals with mitochondrial diseases. The amino acids arginine and citrulline are NO precursors: increasing their concentrations could potentially restore NO production.

METHODS

In this study, we assessed endothelial dysfunction in children and adolescents with mitochondrial diseases. We also investigated the effect of arginine and citrulline supplementation on endothelial dysfunction in these individuals. We used peripheral arterial tonometry to measure the reactive hyperemic index (RHI), which is low when there is endothelial dysfunction.

RESULTS

The results demonstrated low RHI in individuals with mitochondrial diseases, indicating endothelial dysfunction. RHI increased with arginine or citrulline supplementation suggesting that supplementation with NO precursors can improve endothelial dysfunction by enhancing NO production.

CONCLUSIONS

This study is the first one to use peripheral arterial tonometry methodology in mitochondrial diseases. The results of this study provide evidence for endothelial dysfunction in mitochondrial diseases and demonstrate that arginine or citrulline supplementation can alleviate the endothelial dysfunction, providing more evidence for the potential therapeutic utility of these amino acids in mitochondrial diseases.

Advances in drug therapy for mitochondrial diseases

Mitochondrial diseases are a group of clinically and genetically heterogeneous disorders driven by oxidative phosphorylation dysfunction of the mitochondrial respiratory chain which due to pathogenic mutations of mitochondrial DNA (mtDNA) or nuclear DNA (nDNA). Recent progress in molecular genetics and biochemical methodologies has provided a better understanding of the etiology and pathogenesis of mitochondrial diseases, and this has expanded the clinical spectrum of this conditions. But the treatment of mitochondrial diseases is largely symptomatic and thus does not significantly change the course of the disease. Few clinical trials have led to the design of drugs aiming at enhancing mitochondrial function or reversing the consequences of mitochondrial dysfunction which are now used in the clinical treatment of mitochondrial diseases. Several other drugs are currently being evaluated for clinical management of patients with mitochondrial diseases. In this review, the current status of treatments for mitochondrial diseases is described systematically, and newer potential treatment strategies for mitochondrial diseases are also discussed.

Arginine therapy in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes

PURPOSE OF REVIEW

We would like to inform clinicians that the systematic administration of oral and intravenous L-arginine is therapeutically beneficial and clinically useful for patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), when they maintain plasma arginine concentration at least 168 μmol/l.

RECENT FINDINGS

MELAS is associated with endothelial dysfunction by decreased plasma L-arginine, nitric oxide (NO), and cyclic guanosine monophosphate. Endothelial dysfunction is also evident using flow-mediated vasodilation measurement by high-resolution Doppler echocardiography in the forearm artery in patients with MELAS. L-arginine is known to be an important precursor of NO to normalize the endothelial function in MELAS. In our clinical trial followed by 7 years follow-up study, the systematic administration of L-arginine to patients with MELAS significantly improved the survival curve of patients compared with natural history. Maintaining plasma arginine concentration at least 168 μmol/l may prevent the ictuses through the putative pathophysiologic mechanism and optimal normalization of endothelial dysfunction.

SUMMARY

Neither death nor bedriddenness occurred during the 2-year clinical trials, and the latter did not develop during the 7-year follow-up despite the progressively neurodegenerative and eventually life-threatening nature of MELAS. Therapeutic regimen of L-arginine on MELAS may be beneficial and clinically useful for patient care with MELAS.

Mitochondrial disorders and the eye

Mitochondria are cellular organelles that play a key role in energy metabolism and oxidative phosphorylation. Malfunctioning of mitochondria has been implicated as the cause of many disorders with variable inheritance, heterogeneity of systems involved, and varied phenotype. Metabolically active tissues are more likely to be affected, causing an anatomic and physiologic disconnect in the treating physicians' mind between presentation and underlying pathophysiology. We shall focus on disorders of mitochondrial metabolism relevant to an ophthalmologist. These disorders can affect all parts of the visual pathway (crystalline lens, extraocular muscles, retina, optic nerve, and retrochiasm). After the introduction reviewing mitochondrial structure and function, each disorder is reviewed in detail, including approaches to its diagnosis and most current management guidelines.

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

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

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.

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.

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.

[Genetic causes of stroke in young patients]

The paper addresses genetic causes of stroke: MELAS, antiphospholipid syndrome, CADASIL, Fabry disease. The etiology and pathogenesis, symptoms, diagnosis, treatment methods of these diseases are described.

Current and Emerging Therapies for Mitochondriopathies

Mitochondrial diseases are a clinically and genetically heterogeneous group of disorders. The underlying dysfunction of the mitochondrial electron transport chain and oxidative phosphorylation is caused by variants of genes encoding mitochondrial proteins. Despite substantial advances in the understanding of the mechanism of these diseases, there are still no satisfactory therapies available. Therapeutic strategies include the use of antioxidants, inducers of mitochondrial biogenesis, enhancers of electron transfer chain function, energy buffers, amino acids restoring NO production, nucleotide bypass therapy, liver transplantation, and gene therapy. Although there are some promising projects underway, to date satisfactory therapies are missing.

Different mitochondrial genetic defects exhibit the same protein signature of metabolism in skeletal muscle of PEO and MELAS patients: A role for oxidative stress

A major challenge in mitochondrial diseases (MDs) is the identification of biomarkers that could inform of the mechanisms involved in the phenotypic expression of genetic defects. Herein, we have investigated the protein signature of metabolism and of the antioxidant response in muscle biopsies of clinically and genetically diagnosed patients with Progressive External Ophthalmoplegia due to single large-scale (PEO-sD) or multiple (PEO-mD) deletions of mtDNA and Mitochondrial Encephalopathy Lactic Acidosis and Stroke-like episode (MELAS) syndrome, and healthy donors. A high-throughput immunoassay technique that quantitates the expression of relevant proteins of glycolysis, glycogenolysis, pentose phosphate pathway, oxidative phosphorylation, pyruvate and fatty acid oxidation, tricarboxylic acid cycle and the antioxidant response in two large independent and retrospectively collected cohorts of PEO-sD, PEO-mD and MELAS patients revealed that despite the heterogeneity of the genetic alterations, the three MDs showed the same metabolic signatures in both cohorts of patients, which were highly divergent from those of healthy individuals. Linear Discriminant Analysis and Support Vector Machine classifier provided a minimum of four biomarkers to discriminate healthy from pathological samples. Regardless of the induction of a large number of enzymes involved in ameliorating oxidative stress, the down-regulation of mitochondrial superoxide dismutase (SOD2) and catalase expression favored the accumulation of oxidative damage in patients' proteins. Down-regulation of SOD2 and catalase expression in MD patients is not due to relevant changes in the availability of their mRNAs, suggesting that oxidative stress regulates the expression of the two enzymes post-transcriptionally. We suggest that SOD2 and catalase could provide specific targets to improve the detoxification of reactive oxygen species that affects muscle proteins in these patients.

Emerging therapies for mitochondrial diseases

For the vast majority of patients with mitochondrial diseases, only supportive and symptomatic therapies are available. However, in the last decade, due to extraordinary advances in defining the causes and pathomechanisms of these diverse disorders, new therapies are being developed in the laboratory and are entering human clinical trials. In this review, we highlight the current use of dietary supplement and exercise therapies as well as emerging therapies that may be broadly applicable across multiple mitochondrial diseases or tailored for specific disorders. Examples of non-tailored therapeutic targets include: activation of mitochondrial biogenesis, regulation of mitophagy and mitochondrial dynamics, bypass of biochemical defects, mitochondrial replacement therapy, and hypoxia. In contrast, tailored therapies are: scavenging of toxic compounds, deoxynucleoside and deoxynucleotide treatments, cell replacement therapies, gene therapy, shifting mitochondrial DNA mutation heteroplasmy, and stabilization of mutant mitochondrial transfer RNAs.

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.

Pharmacological targeting of exercise adaptations in skeletal muscle: Benefits and pitfalls

Exercise exerts significant effects on the prevention and treatment of many diseases. However, even though some of the key regulators of training adaptation in skeletal muscle have been identified, this biological program is still poorly understood. Accordingly, exercise-based pharmacological interventions for many muscle wasting diseases and also for pathologies that are triggered by a sedentary lifestyle remain scarce. The most efficacious compounds that induce muscle hypertrophy or endurance are hampered by severe side effects and are classified as doping. In contrast, dietary supplements with a higher safety margin exert milder outcomes. In recent years, the design of pharmacological agents that activate the training program, so-called "exercise mimetics", has been proposed, although the feasibility of such an approach is highly debated. In this review, the most recent insights into key regulatory factors and therapeutic approaches aimed at leveraging exercise adaptations are discussed.

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.