Therapeutic potential of pyruvate therapy for mitochondrial diseases

Citrin-deficient patient-derived induced pluripotent stem cells as a pathological liver model for congenital urea cycle disorders

Citrin deficiency is a congenital secondary urea cycle disorder lacking useful disease models for effective treatment development. In this study, human induced pluripotent stem cells (iPSCs) were generated from two patients with citrin deficiency and differentiated into hepatocyte-like cells (HLCs). Citrin-deficient HLCs produced albumin and liver-specific markers but completely lacked citrin protein and expressed argininosuccinate synthase only weakly. In addition, ammonia concentrations in a medium cultured with citrin-deficient HLCs were higher than with control HLCs. Sodium pyruvate administration significantly reduced ammonia concentrations in the medium of citrin-deficient HLCs and slightly reduced ammonia in HLCs differentiated from control iPSCs, though this change was not significant. Our results suggest that sodium pyruvate may be an efficient treatment for patients with citrin deficiency. Citrin-deficient iPSCs are a pathological liver model for congenital urea cycle disorders to clarify pathogenesis and develop novel therapies.

Near-Physiological Concentrations of Extracellular Pyruvate Stimulated Glucose Utilization along with Triglyceride Accumulation and Mitochondrial Activity in HepG2 Cells

Pyruvate, a key intermediate in energy and nutrient metabolism, probably plays important roles in these regulations. In previous reports using cell lines, extracellular pyruvate of supraphysiological concentrations inhibited the glucose uptake by myotubes while being stimulated by adipocytes. As the effect of pyruvate on the glucose utilization is unclear in cultured hepatocytes. We have investigated the effects of extracellular pyruvate on the glucose utilization and the subsequent metabolic changes using the cell line HepG2. In a 24 h culture, pyruvate enhanced the glucose consumption more potently than 1 μM insulin, and this enhancement was detectable at a near-physiological concentrations of ≤1 mM. For metabolic changes following glucose consumption, the conversion ratio of glucose and pyruvate to extracellular lactate was approximately 1.0 without extracellular pyruvate. The addition of pyruvate decreased the conversion ratio to approximately 0.7, indicating that the glycolytic reaction switched from being an anaerobic to a partially aerobic feature. Consistent with this finding, pyruvate increased the accumulation of intracellular triglycerides which are produced through substrate supply from the mitochondria. Furthermore, pyruvate stimulated mitochondria activity as evidenced by increases in ATP content, mitochondrial DNA copy number, enhanced mitochondria-specific functional imaging and oxygen consumption. Interestingly, 1 mM pyruvate increased oxygen consumption immediately after addition. In this study, we found that near-physiological concentrations of extracellular pyruvate exerted various changes in metabolic events, including glucose influx, lactate conversion rations, TG accumulation, and mitochondrial activity in HepG2 cells.

Outcomes of liver transplantation for mitochondrial respiratory chain disorder in children

AIM

Mitochondrial respiratory chain disorder (MRCD) can cause acute liver failure (ALF), which may necessitate liver transplantation (LT). However, MRCD is often difficult to diagnose before LT and the indications of LT are controversial due to the likelihood of progressive neurological disease. The present study further characterized the patient population and described the outcomes.

METHODS

Thirteen patients who underwent LT for MRCD from November 2005 to May 2020 were enrolled in this study.

RESULTS

Six of 13 MRCD patients were diagnosed with a mitochondrial inner membrane protein 17-related mitochondrial DNA depletion syndrome (MTDPS). Overall, nine survived with a median follow-up of 1.8 years (IQR, 1.3-5.1 years); four died within 2 years. In the long-term, seven survivors showed no progression of hypotonia after LT and attended a normal kindergarten or primary school. Neurological abnormalities were observed in two survivors, including vison loss related to Leber's hereditary optic neuropathy in one patient and psychomotor retardation related to Leigh syndrome in the other. Three non-survivors after LT were diagnosed with MTDPS and died of severe pulmonary hypertension, which had developed at 8, 9, and 18 months after LT (n=1 each). The remaining patient died of postoperative respiratory infection with respiratory syncytial virus.

CONCLUSION

The long-term results support the performance of LT in patients with MRCD, although a genetic diagnosis is preferable for determining the accurate indications for LT in these patients. Furthermore, care should be taken to avoid complications due to mitochondrial dysfunction during the long-term follow-up.

Clinical Insights into Mitochondrial Neurodevelopmental and Neurodegenerative Disorders: Their Biosignatures from Mass Spectrometry-Based Metabolomics

Mitochondria are dynamic multitask organelles that function as hubs for many metabolic pathways. They produce most ATP via the oxidative phosphorylation pathway, a critical pathway that the brain relies on its energy need associated with its numerous functions, such as synaptic homeostasis and plasticity. Therefore, mitochondrial dysfunction is a prevalent pathological hallmark of many neurodevelopmental and neurodegenerative disorders resulting in altered neurometabolic coupling. With the advent of mass spectrometry (MS) technology, MS-based metabolomics provides an emerging mechanistic understanding of their global and dynamic metabolic signatures. In this review, we discuss the pathogenetic causes of mitochondrial metabolic disorders and the recent MS-based metabolomic advances on their metabolomic remodeling. We conclude by exploring the MS-based metabolomic functional insights into their biosignatures to improve diagnostic platforms, stratify patients, and design novel targeted therapeutic strategies.

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

BACKGROUND

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

SCOPE OF REVIEW

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

MAJOR CONCLUSIONS

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

GENERAL SIGNIFICANCE

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

Mitochondrial medicine therapies: rationale, evidence, and dosing guidelines

PURPOSE OF REVIEW

Primary mitochondrial disease is a highly heterogeneous but collectively common inherited metabolic disorder, affecting at least one in 4300 individuals. Therapeutic management of mitochondrial disease typically involves empiric prescription of enzymatic cofactors, antioxidants, and amino acid and other nutrient supplements, based on biochemical reasoning, historical experience, and consensus expert opinion. As the field continues to rapidly advance, we review here the preclinical and clinical evidence, and specific dosing guidelines, for common mitochondrial medicine therapies to guide practitioners in their prescribing practices.

RECENT FINDINGS

Since publication of Mitochondrial Medicine Society guidelines for mitochondrial medicine therapies management in 2009, data has emerged to support consideration for using additional therapeutic agents and discontinuation of several previously used agents. Preclinical animal modeling data have indicated a lack of efficacy for vitamin C as an antioxidant for primary mitochondrial disease, but provided strong evidence for vitamin E and N-acetylcysteine. Clinical data have suggested L-carnitine may accelerate atherosclerotic disease. Long-term follow up on L-arginine use as prophylaxis against or acute treatment for metabolic strokes has provided more data supporting its clinical use in individuals with mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome and Leigh syndrome. Further, several precision therapies have been developed for specific molecular causes and/or shared clinical phenotypes of primary mitochondrial disease.

SUMMARY

We provide a comprehensive update on mitochondrial medicine therapies based on current evidence and our single-center clinical experience to support or refute their use, and provide detailed dosing guidelines, for the clinical management of mitochondrial disease. The overarching goal of empiric mitochondrial medicines is to utilize therapies with favorable benefit-to-risk profiles that may stabilize and enhance residual metabolic function to improve cellular resiliency and slow clinical disease progression and/or prevent acute decompensation.

Understanding the role of OXPHOS dysfunction in the pathogenesis of ECHS1 deficiency

Mitochondria provide the main source of energy for eukaryotic cells, oxidizing fatty acids and sugars to generate ATP. Mitochondrial fatty acid β-oxidation (FAO) and oxidative phosphorylation (OXPHOS) are two key pathways involved in this process. Disruption of FAO can cause human disease, with patients commonly presenting with liver failure, hypoketotic glycaemia and rhabdomyolysis. However, patients with deficiencies in the FAO enzyme short-chain enoyl-CoA hydratase 1 (ECHS1) are typically diagnosed with Leigh syndrome, a lethal form of subacute necrotizing encephalomyelopathy that is normally associated with OXPHOS dysfunction. Furthermore, some ECHS1-deficient patients also exhibit secondary OXPHOS defects. This sequela of FAO disorders has long been thought to be caused by the accumulation of inhibitory fatty acid intermediates. However, new evidence suggests that the mechanisms involved are more complex, and that disruption of OXPHOS protein complex biogenesis and/or stability is also involved. In this review, we examine the clinical, biochemical and genetic features of all ECHS1-deficient patients described to date. In particular, we consider the secondary OXPHOS defects associated with ECHS1 deficiency and discuss their possible contribution to disease pathogenesis.

Therapeutic potential of pyruvate therapy for patients with mitochondrial diseases: a systematic review

BACKGROUND

Mitochondrial disease is a term used to describe a set of heterogeneous genetic diseases caused by impaired structure or function of mitochondria. Pyruvate therapy for mitochondrial disease is promising from a clinical point of view.

METHODS

According to PRISMA guidelines, the following databases were searched to identify studies regarding pyruvate therapy for mitochondrial disease: PubMed, EMBASE, Cochrane Library, and Clinicaltrials. The search was up to April 2019. The endpoints were specific biomarkers (plasma level of lactate, plasma level of pyruvate, L/P ratio) and clinical rating scales [Japanese mitochondrial disease-rating scale (JMDRS), Newcastle Mitochondrial Disease Adult Scale (NMDAS), and others]. Two researchers independently screened articles, extracted data, and assessed the quality of the studies.

RESULTS

A total of six studies were included. Considerable differences were noted between studies in terms of study design, patient information, and outcome measures. The collected evidence may indicate an effective potential of pyruvate therapy on the improvement of mitochondrial disease. The majority of the common adverse events of pyruvate therapy were diarrhea and short irritation of the stomach.

CONCLUSION

Pyruvate therapy with no serious adverse events may be a potential therapeutic candidate for patients with incurable mitochondrial diseases, such as Leigh syndrome. However, recent evidence taken from case series and case reports, and theoretical supports of basic research are not sufficient. The use of global registries to collect patient data and more adaptive trial designs with larger numbers of participants are necessary to clarify the efficacy of pyruvate therapy.

Successful treatment of infantile-onset ACAD9-related cardiomyopathy with a combination of sodium pyruvate, beta-blocker, and coenzyme Q10

Mitochondrial acyl-CoA dehydrogenase 9 (ACAD9) deficiency is one of the common causes of respiratory chain complex I deficiency, which is characterized by cardiomyopathy, lactic acidemia, and muscle weakness. Infantile cardiomyopathy is the most common phenotype and is usually lethal by the age of 5 years. Riboflavin treatment is known to be effective in ~65% of the patients; however, the remaining are unresponsive to riboflavin and are in need of additional treatment measures. In this report, we describe a patient with ACAD9 deficiency who developed progressive cardiomyopathy at 8 months of age. As the patient's left ventricular ejection fraction (LVEF) kept decreasing to 45.4% at 1 year 8 months, sodium pyruvate treatment was introduced together with a beta-blocker and coenzyme Q10. This resulted in a steady improvement, with full and sustained normalization of cardiac function without riboflavin. The therapy, therefore, might be a useful addition for the treatment of ACAD9 deficiency.

Enhancement of ATP production ameliorates motor and cognitive impairments in a mouse model of MPTP-induced Parkinson's disease

Approximately 30-40% of patients with Parkinson's disease (PD) exhibit cognitive impairments. However, there are currently no clinically effective drugs for the treatment of cognitive impairment in patients with PD. Previous studies have suggested that mitochondrial dysfunction such as decreased adenosine triphosphate (ATP) production triggers dopaminergic neurodegeneration in patients with PD and that mitochondria represent a potential target for the development of novel treatments for preventing PD. Therefore, in the present study, we investigated the cognition-enhancing effects of ethyl pyruvate (EP) and 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl) piperazine dihydrochloride (SA4503) in mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinsonism. PD model mice were generated via treatment with MPTP (25 mg/kg, i.p.) once a day for 5 consecutive days. Twenty-four hours after the final injection of MPTP, mice were intraperitoneally injected with EP (25, 50, 100 mg/kg) or SA4503 (1 mg/kg) once a day for 4 weeks. Chronic administration of EP (100 mg/kg i.p.) or SA4503 (1 mg/kg, i.p.) improved both motor deficits and cognitive impairments in MPTP-treated mice. Furthermore, treatment with EP or SA4503 attenuated decreases in the levels of ATP and tyrosine hydroxylase (TH) in the substantia nigra pars compacta (SNpc)/ventral tegmental area (VTA), striatum, and hippocampal CA1 region. Administration of EP or SA4503 protected the dopaminergic neurons from MPTP-induce toxicity and restored the dopamine levels in the striatum. Elevated 4-hydroxy-2-nonenal- (4-HNE-) and nitrotyrosine-reactive protein levels induced by MPTP-treatment were suppressed by EP or SA4503 treatment in the SNpc-VTA, striatum, and hippocampal CA1 region. These observations suggest that EP and SA4503 attenuate cognitive impairments and motor dysfunction in mice with MPTP-induced PD.

Biomarkers and clinical rating scales for sodium pyruvate therapy in patients with mitochondrial disease

Biomarkers and two clinical rating scales-the Japanese mitochondrial disease-rating scale (JMDRS) and Newcastle mitochondrial disease adult scale (NMDAS)-are clinically used when treating patients with mitochondrial disease. We explored the biomarker(s) and clinical rating scale(s) that are appropriate in preparing the protocol for a future clinical trial of sodium pyruvate (SP) therapy. A 48-week, prospective, single-centre, exploratory, clinical study enrolled 11 Japanese adult patients with genetically, biochemically, and clinically confirmed mitochondrial disease; they had intractable lactic acidosis and received SP (0.5 g/kg t.i.d. PO). Plasma concentrations of lactate and pyruvate, lateral ventricular levels of lactate, and serum concentrations of growth differentiation factor 15 (GDF15) and fibroblast growth factor 21 were measured at baseline and at weeks 12 and 48 of SP therapy. At week 48, plasma lactate (P = .004), the lactate/pyruvate ratio (P = .012), serum GDF15 (P = .020), and lateral ventricular lactate (P = .038) decreased significantly from the baseline values; the JMDRS and NMDAS scores did not decrease significantly, although the NMDAS overall score showed a strong tendency (P = .059). Two patients with end-stage MELAS at baseline died during SP therapy. The present study showed significant decreases in plasma and lateral ventricular lactate, the L/P ratio, and serum GDF15. Therefore, the protocol for a future clinical study of SP therapy in this patient population needs to include plasma and lateral ventricular lactate, the L/P ratio, and serum GDF15 as diagnostic indicators, and exclude patients with end-stage mitochondrial disease.

Recent topics: the diagnosis, molecular genesis, and treatment of mitochondrial diseases

Mitochondrial diseases are inherited metabolic diseases based on disorders of energy production. The expansion of exome analyses has led to the discovery of many pathogenic nuclear genes associated with these diseases, and research into the pathogenesis of metabolic diseases has progressed. In cases of Leigh syndrome, it is desirable to perform both biochemical and genetic analyses, and pathogenic gene mutations have been identified in over half of the cases analyzed this way. Tandem mass screening and organic acid analyses of urine can sometimes provide important information that leads to the identification of pathogenic genes. Our comprehensive gene analyses have led to the discovery of several novel genes for mitochondrial diseases. Indeed, we reported that GTPBP3 and QRSL1 are involved in mitochondrial DNA maturation. In 2017, as a result of international collaboration, we also identified that mutations in ATAD3 and C1QBP cause mitochondrial disease. Given the varied pathogeneses, treatments for mitochondrial diseases should be specifically tailored to the mutated gene. Clinical trials of sodium pyruvate, 5-aminolevulinic acid with sodium ferrous citrate, and taurine as a treatment for mitochondrial disease have begun in Japan. Given that some mitochondrial diseases may respond well to certain treatments if the pathogenic gene can be identified, an early genetic diagnosis is crucial. Additionally, in Japan, prenatal diagnoses for mitochondrial diseases caused by nuclear genes have been achieved for genes shown to be pathogenic. Treatment and management approaches, including prenatal diagnoses, specifically tailored to the various phenotypes and pathologies of mitochondrial diseases are expected to become increasingly available.

Efficacy of exogenous pyruvate in TremblerJ mouse model of Charcot-Marie-Tooth neuropathy

INTRODUCTION

Classic Charcot-Marie-Tooth (CMT) neuropathies including those with Schwann cell genetic defects exhibit a length-dependent process affecting the distal axon. Energy deprivation in the distal axon has been the proposed mechanism accounting for length-dependent distal axonal degeneration. We hypothesized that pyruvate, an intermediate glycolytic product, could restore nerve function, supplying lost energy to the distal axon.

METHODS

To test this possibility, we supplied pyruvate to the drinking water of the Trembler-J (TrJ ) mouse and assessed efficacy based on histology, electrophysiology, and functional outcomes. Pyruvate outcomes were compared with untreated TrJ controls alone or adeno-associated virus mediated NT-3 gene therapy (AAV1.NT-3)/pyruvate combinatorial approach.

RESULTS

Pyruvate supplementation resulted increased myelinated fiber (MF) densities and myelin thickness in sciatic nerves. Combining pyruvate with proven efficacy from AAV1.tMCK.NT-3 gene therapy provided additional benefits showing improved compound muscle action potential amplitudes and nerve conduction velocities compared to pyruvate alone cohort. The end point motor performance of both the pyruvate and the combinatorial therapy cohorts was better than untreated TrJ controls. In a unilateral sciatic nerve crush paradigm, pyruvate supplementation improved myelin-based outcomes in both regenerating and the contralateral uncrushed nerves.

CONCLUSIONS

This proof of principle study demonstrates that exogenous pyruvate alone or as adjunct therapy in TrJ may have clinical implications and is a candidate therapy for CMT neuropathies without known treatment.

Liver Transplantation for Mitochondrial Respiratory Chain Disorder: A Single-Center Experience and Excellent Marker of Differential Diagnosis

Mitochondrial respiratory chain disorder (MRCD) can cause liver failure requiring liver transplantation (LT), although it is often difficult to diagnose before LT. From 2005 to 2016, 9 MRCD patients with the median age at LT of 6 months underwent LT in our institute. Their clinical courses were retrospectively reviewed and the laboratory parameters were compared between the MRCD patients and 10 patients with acute liver failure unrelated to MRCD (non-MRCD). Five patients had extrahepatic manifestations, including developmental disorders in 3 and failure to thrive in 3, before LT. Only 3 patients (33.3%) were diagnosed before LT. Between MRCD and non-MRCD, lactate was significantly high and lactate-to-pyruvate ratio (L/P ratio) tended to be higher in MRCD. From the receiver operating characteristic curve, the optimal cutoff value of lactate was 50.0 mg/dL and that of L/P ratio was 23.2. Patient survival rate of MRCD was 77.8%, although 2 patients with mitochondrial depletion syndrome suffered from de novo pulmonary hypertension after LT. Our experiences showed the difficulty of preoperative diagnosis, and preoperative extrahepatic manifestations did not always mean poor outcome. Our study showed that lactate value and L/P ratio can be excellent predictors of MRCD.

Role of inflammation and oxidative stress in the etiology of primary ovarian insufficiency

Objective:

The aim of this study was to elucidate the etiology and treatment of primary ovarian insufficiency, which is of unknown cause in 95% of the cases.

Materials and Methods:

Thirty patients aged 18-40 years who presented to Dicle University Faculty of Medicine Clinic of Obstetrics and Gynecology between June 2012 and January 2014 and were diagnosed as having primary ovarian insufficiency based on their clinical and endocrinologic data, and 30 healthy controls were included in this study.

Results:

No significant differences were found between patients with primary ovarian insufficiency and control subjects in demographic data and lipid profile levels, thyroid- stimulating hormone, prolactin, and glucose. However, the neutrophil to lymphocyte ratio and levels of follicle-stimulating hormone, luteinizing hormone, total antioxidant status, total oxidant status, and oxidative stress index were significantly higher in patients with primary ovarian insufficiency than in control subjects. In the correlation analysis, follicle-stimulating hormone exhibited a positive correlation with total oxidant status, oxidative stress index, and the neutrophil to lymphocyte ratio (r=0.573** p<0.001, r=0.584** p<0.001, r=0.541 p<0.001, respectively) and correlated negatively with total antioxidant status (r=-0.437** p<0.001).

Conclusion:

The neutrophil to lymphocyte ratio, total oxidant status, and oxidative stress index levels are elevated in primary ovarian insufficiency. Therefore, anti-oxidative and anti-inflammatory treatment might be administered to patients in the early stage of primary ovarian insufficiency. However, larger studies are needed to clarify whether these elevated levels are a cause or a consequence of primary ovarian insufficiency.

CV Protection in the EMPA-REG OUTCOME Trial: A "Thrifty Substrate" Hypothesis

The striking and unexpected relative risk reductions in cardiovascular (CV) mortality (38%), hospitalization for heart failure (35%), and death from any cause (32%) observed in the EMPA-REG OUTCOME trial using an inhibitor of sodium-glucose cotransporter 2 (SGLT2) in patients with type 2 diabetes and high CV risk have raised the possibility that mechanisms other than those observed in the trial-modest improvement in glycemic control, small decrease in body weight, and persistent reductions in blood pressure and uric acid level-may be at play. We hypothesize that under conditions of mild, persistent hyperketonemia, such as those that prevail during treatment with SGLT2 inhibitors, β-hydroxybutyrate is freely taken up by the heart (among other organs) and oxidized in preference to fatty acids. This fuel selection improves the transduction of oxygen consumption into work efficiency at the mitochondrial level. In addition, the hemoconcentration that typically follows SGLT2 inhibition enhances oxygen release to the tissues, thereby establishing a powerful synergy with the metabolic substrate shift. These mechanisms would cooperate with other SGLT2 inhibition-induced changes (chiefly, enhanced diuresis and reduced blood pressure) to achieve the degree of cardioprotection revealed in the EMPA-REG OUTCOME trial. This hypothesis opens up new lines of investigation into the pathogenesis and treatment of diabetic and nondiabetic heart disease.

Haloperidol aggravates transverse aortic constriction-induced heart failure via mitochondrial dysfunction

Haloperidol is an antipsychotic drug that inhibits the dopamine D2 receptor among others. Haloperidol also binds the sigma-1 receptor (σ1R) and inhibits it irreversibly. A serious outcome of haloperidol treatment of schizophrenia patients is death due to sudden cardiac failure. Although the cause remains unclear, we hypothesized that these effects were mediated by chronic haloperidol inhibition of cardiac σ1R. To test this, we treated neonatal rat cardiomyocytes with haloperidol, exposed them to angiotensin II and assessed hypertrophy, σ1R expression, mitochondrial Ca(2+) transport and ATP levels. In this context, haloperidol treatment altered mitochondrial Ca(2+) transport resulting in decreased ATP content by inactivating cardiac σ1R and/or reducing its expression. We also performed transverse aortic constriction (TAC) and then treated mice with haloperidol. After two weeks, haloperidol-treated mice showed enhanced heart failure marked by deteriorated cardiac function, reduced ATP production and increasing mortality relative to TAC only mice. ATP supplementation via sodium pyruvate rescued phenotypes seen in haloperidol-treated TAC mice. We conclude that σ1R inactivation or downregulation in response to haloperidol treatment impairs mitochondrial Ca(2+) mobilization, depleting ATP depletion from cardiomyocytes. These findings suggest a novel approach to mitigate haloperidol-related adverse effects in schizophrenia patients by ATP supplementation.

Leigh syndrome: Resolving the clinical and genetic heterogeneity paves the way for treatment options

Leigh syndrome is a progressive neurodegenerative disorder, affecting 1 in 40,000 live births. Most patients present with symptoms between the ages of three and twelve months, but adult onset Leigh syndrome has also been described. The disease course is characterized by a rapid deterioration of cognitive and motor functions, in most cases resulting in death due to respiratory failure. Despite the high genetic heterogeneity of Leigh syndrome, patients present with identical, symmetrical lesions in the basal ganglia or brainstem on MRI, while additional clinical manifestations and age of onset varies from case to case. To date, mutations in over 60 genes, both nuclear and mitochondrial DNA encoded, have been shown to cause Leigh syndrome, still explaining only half of all cases. In most patients, these mutations directly or indirectly affect the activity of the mitochondrial respiratory chain or pyruvate dehydrogenase complex. Exome sequencing has accelerated the discovery of new genes and pathways involved in Leigh syndrome, providing novel insights into the pathophysiological mechanisms. This is particularly important as no general curative treatment is available for this devastating disorder, although several recent studies imply that early treatment might be beneficial for some patients depending on the gene or process affected. Timely, gene-based personalized treatment may become an important strategy in rare, genetically heterogeneous disorders like Leigh syndrome, stressing the importance of early genetic diagnosis and identification of new genes/pathways. In this review, we provide a comprehensive overview of the most important clinical manifestations and genes/pathways involved in Leigh syndrome, and discuss the current state of therapeutic interventions in patients.

Dysfunctional mitochondrial bioenergetics and the pathogenesis of hepatic disorders

The liver is involved in a variety of critical biological functions including the homeostasis of glucose, fatty acids, amino acids, and the synthesis of proteins that are secreted in the blood. It is also at the forefront in the detoxification of noxious metabolites that would otherwise upset the functioning of the body. As such, this vital component of the mammalian system is exposed to a notable quantity of toxicants on a regular basis. It therefore comes as no surprise that there are over a hundred disparate hepatic disorders, encompassing such afflictions as fatty liver disease, hepatitis, and liver cancer. Most if not all of liver functions are dependent on energy, an ingredient that is primarily generated by the mitochondrion, the power house of all cells. This organelle is indispensable in providing adenosine triphosphate (ATP), a key effector of most biological processes. Dysfunctional mitochondria lead to a shortage in ATP, the leakage of deleterious reactive oxygen species (ROS), and the excessive storage of fats. Here we examine how incapacitated mitochondrial bioenergetics triggers the pathogenesis of various hepatic diseases. Exposure of liver cells to detrimental environmental hazards such as oxidative stress, metal toxicity, and various xenobiotics results in the inactivation of crucial mitochondrial enzymes and decreased ATP levels. The contribution of the latter to hepatic disorders and potential therapeutic cues to remedy these conditions are elaborated.

[Effect of sodium pyruvate on exercise intolerance and muscle weakness due to mitochondrial myopathy: a case report]

We report the case of a 19-year-old woman who had been suffering from general fatigue and exercise intolerance since 15 years old. At 18 years old, she experienced muscle weakness and myalgia of the calves. Six months later, she was admitted to our hospital. She showed muscle weakness of the neck and proximal limbs, and myalgia of the calves was prominent. Serum levels of creatine kinase (CK) and lactic acid were elevated, as was the level of lactic acid in cerebrospinal fluid. T2-weighted and short-inversion-time inversion recovery (STIR) imaging of the lower limbs showed hyperintensity on bilateral gastrocnemius muscles, and the region revealed Gd enhancement. Based on histopathological findings from muscle and identification of a m.3271T>C point mutation, mitochondrial myopathy was diagnosed. Rest and administration of vitamins B1 and B2, coenzyme Q10, and L-carnitine improved serum CK levels; however, exercise intolerance, myalgia, and lactic acidemia remained. Sodium pyruvate was then administered, and lactic acid levels, exercise intolerance, and findings on magnetic resonance imaging improved. Sodium pyruvate could prove effective in addressing both elevated serum lactic acid levels and exercise intolerance in mitochondrial disease.

Methyl pyruvate rescues mitochondrial damage caused by SIGMAR1 mutation related to amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a disease caused by motor neuron degeneration. Recently, a novel SIGMAR1 gene variant (p.E102Q) was discovered in some familial ALS patients.

METHODS

We address mechanisms underlying neurodegeneration caused by the mutation using Neuro2A cells overexpressing σ1R(E102Q), a protein of a SIGMAR1 gene variant (p.E102Q) and evaluate potential amelioration by ATP production via methyl pyruvate (MP) treatment.

RESULTS

σ1R(E102Q) overexpression promoted dissociation of the protein from the endoplasmic reticulum (ER) membrane and cytoplasmic aggregation, which in turn impaired mitochondrial ATP production and proteasome activity. Under ER stress conditions, overexpression of wild-type σ1R suppressed ER stress-induced mitochondrial injury, whereas σ1R(E102Q) overexpression aggravated mitochondrial damage and induced autophagic cell death. Moreover, σ1R(E102Q)-overexpressing cells showed aberrant extra-nuclear localization of the TAR DNA-binding protein (TDP-43), a condition exacerbated by ER stress. Treatment of cells with the mitochondrial Ca(2+) transporter inhibitor Ru360 mimicked the effects of σ1R(E102Q) overexpression, indicating that aberrant σ1R-mediated mitochondrial Ca(2+) transport likely underlies TDP-43 extra-nuclear localization, segregation in inclusion bodies, and ubiquitination. Finally, enhanced ATP production promoted by methyl pyruvate (MP) treatment rescued proteasome impairment and TDP-43 extra-nuclear localization caused by σ1R(E102Q) overexpression.

CONCLUSIONS

Our observations suggest that neurodegeneration seen in some forms of ALS are due in part to aberrant mitochondrial ATP production and proteasome activity as well as TDP-43 mislocalization resulting from the SIGMAR1 mutation.

GENERAL SIGNIFICANCE

ATP supplementation by MP represents a potential therapeutic strategy to treat ALS caused by SIGMAR1 mutation.

Efficacy of pyruvate therapy in patients with mitochondrial disease: a semi-quantitative clinical evaluation study

BACKGROUND

Disorders of oxidative phosphorylation (OXPHOS) cause an increase in the NADH/NAD(+) ratio, which impairs the glycolysis pathway. Treatment with pyruvate is expected to decrease the ratio and thereby restore glycolysis. There are some case reports on the efficacy of pyruvate treatment for mitochondrial diseases. However, few of these reports assessed their results using a standardized scale.

METHODS

We monitored 4 bedridden patients with OXPHOS disorders who continued therapies of 0.5-1.0 g/kg/day of sodium pyruvate for more than 12 months. The efficacies of these treatments were evaluated with the Newcastle Pediatric Mitochondrial Disease Scale and the Gross Motor Function Measure with 88 items.

RESULTS

The ages of the patients at the treatment initiation ranged from 8-100 months. Of the 4 patients, 3 exhibited improvements within 1-3 months from the initiation of treatment. Among these 3 patients, one maintained the improvement for over 2 years. The remaining 2 regressed 3-6 months after the initiation of treatment. The blood lactate/pyruvate ratios did not correlate with the efficacy of treatment.

CONCLUSION

Pyruvate was effective even in bedridden patients with OXPHOS disorders, at least in the short term. Clinical trials with more patients and less severe disabilities are necessary to evaluate the long-term efficacy of this treatment. Biomarkers other than lactate and pyruvate need to be identified to biochemically monitor the efficacy of this treatment.

Tumor necrosis factor-α impairs oligodendroglial differentiation through a mitochondria-dependent process

Mitochondrial defects, affecting parameters such as mitochondrial number and shape, levels of respiratory chain complex components and markers of oxidative stress, have been associated with the appearance and progression of multiple sclerosis. Nevertheless, mitochondrial physiology has never been monitored during oligodendrocyte progenitor cell (OPC) differentiation, especially in OPCs challenged with proinflammatory cytokines. Here, we show that tumor necrosis factor alpha (TNF-α) inhibits OPC differentiation, accompanied by altered mitochondrial calcium uptake, mitochondrial membrane potential, and respiratory complex I activity as well as increased reactive oxygen species production. Treatment with a mitochondrial uncoupler (FCCP) to mimic mitochondrial impairment also causes cells to accumulate at the progenitor stage. Interestingly, AMP-activated protein kinase (AMPK) levels increase during TNF-α exposure and inhibit OPC differentiation. Overall, our data indicate that TNF-α induces metabolic changes, driven by mitochondrial impairment and AMPK activation, leading to the inhibition of OPC differentiation.

Phenylbutyrate therapy for pyruvate dehydrogenase complex deficiency and lactic acidosis

Lactic acidosis is a buildup of lactic acid in the blood and tissues, which can be due to several inborn errors of metabolism as well as nongenetic conditions. Deficiency of pyruvate dehydrogenase complex (PDHC) is the most common genetic disorder leading to lactic acidosis. Phosphorylation of specific serine residues of the E1α subunit of PDHC by pyruvate dehydrogenase kinase (PDK) inactivates the enzyme, whereas dephosphorylation restores PDHC activity. We found that phenylbutyrate enhances PDHC enzymatic activity in vitro and in vivo by increasing the proportion of unphosphorylated enzyme through inhibition of PDK. Phenylbutyrate given to C57BL/6 wild-type mice results in a significant increase in PDHC enzyme activity and a reduction of phosphorylated E1α in brain, muscle, and liver compared to saline-treated mice. By means of recombinant enzymes, we showed that phenylbutyrate prevents phosphorylation of E1α through binding and inhibition of PDK, providing a molecular explanation for the effect of phenylbutyrate on PDHC activity. Phenylbutyrate increases PDHC activity in fibroblasts from PDHC-deficient patients harboring various molecular defects and corrects the morphological, locomotor, and biochemical abnormalities in the noa(m631) zebrafish model of PDHC deficiency. In mice, phenylbutyrate prevents systemic lactic acidosis induced by partial hepatectomy. Because phenylbutyrate is already approved for human use in other diseases, the findings of this study have the potential to be rapidly translated for treatment of patients with PDHC deficiency and other forms of primary and secondary lactic acidosis.

Metabolomic profiling rationalized pyruvate efficacy in cybrid cells harboring MELAS mitochondrial DNA mutations

Pyruvate treatment was found to alleviate clinical symptoms of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome and is highly promising therapeutic. Using capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS), we measured time-changes of 161 intracellular and 85 medium metabolites to elucidate metabolic effects of pyruvate treatment on cybrid human 143B osteosarcoma cells harboring normal (2SA) and MELAS mutant (2SD) mitochondria. The results demonstrated dramatic and sustainable effects of pyruvate administration on the energy metabolism of 2SD cells, corroborating pyruvate as a metabolically rational treatment regimen for improving symptoms associated with MELAS and possibly other mitochondrial diseases.

Beneficial effect of pyruvate therapy on Leigh syndrome due to a novel mutation in PDH E1α gene

Leigh syndrome (LS) is a progressive untreatable degenerating mitochondrial disorder caused by either mitochondrial or nuclear DNA mutations. A patient was a second child of unconsanguineous parents. On the third day of birth, he was transferred to neonatal intensive care units because of severe lactic acidosis. Since he was showing continuous lactic acidosis, the oral supplementation of dichloroacetate (DCA) was introduced on 31st day of birth at initial dose of 50 mg/kg, followed by maintenance dose of 25 mg/kg/every 12 h. The patient was diagnosed with LS due to a point mutation of an A-C at nucleotide 599 in exon 6 in the pyruvate dehydrogenase E1α gene, resulting in the substitution of aspartate for threonine at position 200 (N200T). Although the concentrations of lactate and pyruvate in blood were slightly decreased, his clinical conditions were deteriorating progressively. In order to overcome the mitochondrial or cytosolic energy crisis indicated by lactic acidosis as well as clinical symptoms, we terminated the DCA and administered 0.5 g/kg/day TID of sodium pyruvate orally. We analyzed the therapeutic effects of DCA or sodium pyruvate in the patient, and found that pyruvate therapy significantly decreased lactate, pyruvate and alanine levels, showed no adverse effects such as severe neuropathy seen in DCA, and had better clinical response on development and epilepsy. Though the efficacy of pyruvate on LS will be evaluated by randomized double-blind placebo-controlled study design in future, pyruvate therapy is a possible candidate for therapeutic choice for currently incurable mitochondrial disorders such as LS.

Mitochondrial dysfunction and biogenesis: do ICU patients die from mitochondrial failure?

Mitochondrial functions include production of energy, activation of programmed cell death, and a number of cell specific tasks, e.g., cell signaling, control of Ca²⁺ metabolism, and synthesis of a number of important biomolecules. As proper mitochondrial function is critical for normal performance and survival of cells, mitochondrial dysfunction often leads to pathological conditions resulting in various human diseases. Recently mitochondrial dysfunction has been linked to multiple organ failure (MOF) often leading to the death of critical care patients. However, there are two main reasons why this insight did not generate an adequate resonance in clinical settings. First, most data regarding mitochondrial dysfunction in organs susceptible to failure in critical care diseases (liver, kidney, heart, lung, intestine, brain) were collected using animal models. Second, there is no clear therapeutic strategy how acquired mitochondrial dysfunction can be improved. Only the benefit of such therapies will confirm the critical role of mitochondrial dysfunction in clinical settings. Here we summarized data on mitochondrial dysfunction obtained in diverse experimental systems, which are related to conditions seen in intensive care unit (ICU) patients. Particular attention is given to mechanisms that cause cell death and organ dysfunction and to prospective therapeutic strategies, directed to recover mitochondrial function. Collectively the data discussed in this review suggest that appropriate diagnosis and specific treatment of mitochondrial dysfunction in ICU patients may significantly improve the clinical outcome.

Pyruvate therapy for mitochondrial DNA depletion syndrome

BACKGROUND

Mitochondrial DNA depletion syndromes are a group of heterogeneous autosomal recessive disorders associated with a severe reduction in mitochondrial DNA in the affected tissues. Sodium pyruvate has been reported to have a therapeutic effect in mitochondrial diseases.

METHODS

We analyzed the effects of 0.5g/kg of sodium pyruvate administered through a nasogastric tube in a one-year-old patient with myopathic mitochondrial DNA depletion syndrome. To evaluate the improvement, we used the Newcastle Paediatric Mitochondrial Disease Scale (NPMDS) and manual muscle testing. As the improvement of motor functions in this severely disabled infant could not be comprehensively detected by NPMDS, we also observed the infant's ability to perform several tasks such as pouting, winking, and number of times she could tap a toy xylophone with a stick. Blood lactate and pyruvate levels were also monitored.

RESULTS

After one month's treatment, the NPMDS score in section IV, the domain for the quality of life, improved from 17 to13. The infant became capable of raising her forearm, lower leg and wrist against gravity. The maximum number of times she could repeat each task increased and the movements became brisker and stronger. No significant change of the blood lactate level or lactate-to-pyruvate ratio, both of which were mildly increased at the initiation of the therapy, was observed despite the clinical improvement.

CONCLUSION

Sodium pyruvate administered at 0.5g/kg improved the muscle strength and the NPMDS score of an infant with myopathic mitochondrial DNA depletion syndrome.

GENERAL SIGNIFICANCE

Sodium pyruvate may be effective for ameliorating the clinical manifestations of mitochondrial diseases. This article is part of a Special Issue entitled: Biochemistry of Mitochondria.

Sirt3 promotes the urea cycle and fatty acid oxidation during dietary restriction

Emerging evidence suggests that protein acetylation is a broad-ranging regulatory mechanism. Here we utilize acetyl-peptide arrays and metabolomic analyses to identify substrates of mitochondrial deacetylase Sirt3. We identified ornithine transcarbamoylase (OTC) from the urea cycle, and enzymes involved in β-oxidation. Metabolomic analyses of fasted mice lacking Sirt3 (sirt3(-/-)) revealed alterations in β-oxidation and the urea cycle. Biochemical analysis demonstrated that Sirt3 directly deacetylates OTC and stimulates its activity. Mice under caloric restriction (CR) increased Sirt3 protein levels, leading to deacetylation and stimulation of OTC activity. In contrast, sirt3(-/-) mice failed to deacetylate OTC in response to CR. Inability to stimulate OTC under CR led to a failure to reduce orotic acid levels, a known outcome of OTC deficiency. Thus, Sirt3 directly regulates OTC activity and promotes the urea cycle during CR, and the results suggest that under low energy input, Sirt3 modulates mitochondria by promoting amino acid catabolism and β-oxidation.

Slc25a12 disruption alters myelination and neurofilaments: a model for a hypomyelination syndrome and childhood neurodevelopmental disorders

BACKGROUND

SLC25A12, a susceptibility gene for autism spectrum disorders that is mutated in a neurodevelopmental syndrome, encodes a mitochondrial aspartate-glutamate carrier (aspartate-glutamate carrier isoform 1 [AGC1]). AGC1 is an important component of the malate/aspartate shuttle, a crucial system supporting oxidative phosphorylation and adenosine triphosphate production.

METHODS

We characterized mice with a disruption of the Slc25a12 gene, followed by confirmatory in vitro studies.

RESULTS

Slc25a12-knockout mice, which showed no AGC1 by immunoblotting, were born normally but displayed delayed development and died around 3 weeks after birth. In postnatal day 13 to 14 knockout brains, the brains were smaller with no obvious alteration in gross structure. However, we found a reduction in myelin basic protein (MBP)-positive fibers, consistent with a previous report. Furthermore, the neocortex of knockout mice contained abnormal neurofilamentous accumulations in neurons, suggesting defective axonal transport and/or neurodegeneration. Slice cultures prepared from knockout mice also showed a myelination defect, and reduction of Slc25a12 in rat primary oligodendrocytes led to a cell-autonomous reduction in MBP expression. Myelin deficits in slice cultures from knockout mice could be reversed by administration of pyruvate, indicating that reduction in AGC1 activity leads to reduced production of aspartate/N-acetylaspartate and/or alterations in the dihydronicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide(+) ratio, resulting in myelin defects.

CONCLUSIONS

Our data implicate AGC1 activity in myelination and in neuronal structure and indicate that while loss of AGC1 leads to hypomyelination and neuronal changes, subtle alterations in AGC1 expression could affect brain development, contributing to increased autism susceptibility.

Pathophysiology of stroke-like episodes in MELAS: neuron–astrocyte uncoupling in neuronal hyperexcitability

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) is a distinct clinical syndrome characterized by fluctuated encephalopathy, migraineous headache, seizure and stroke-like episodes. The molecular mechanism of MELAS mutations has been elucidated; however, the pathogenesis of stroke-like episodes remains largely unknown. Three main hypotheses include ischemic, metabolic and neuronal hyperexcitability hypotheses. Recently, emerging hypotheses include alterations in nitric oxide homeostasis and over-reduction/oxidative stress mechanisms. Although neuron–astrocyte communication is crucial in various physiological functions, it has not been seriously considered in the pathophysiology of stroke-like episodes. This review summarizes what is known about the molecular mechanisms of gene mutation, clinico-radiological, clinico-physiological and pathological features of stroke-like episodes, as well as its pathogenesis. We finally discuss potential mechanisms involved in the pathogenesis of stroke-like episodes based on currently available clinical data and the current understanding of the mechanisms of neuron–astrocyte communications. We propose that neuron–astrocyte uncoupling is a new target of research in mitochondrial disorders.

Progesterone stimulates mitochondrial activity with subsequent inhibition of apoptosis in MCF-10A benign breast epithelial cells

The effects of progesterone on breast epithelial cells remain poorly defined with observations showing both proliferative and antiproliferative effects. As an example, progesterone levels correlate with increased epithelial cell proliferation, but there is discordance between the dividing cells and the cells with nuclear progesterone receptor expression. The release of paracrine growth factors from nuclear receptor-positive cells has been postulated as a mechanism, since in vitro studies show a lack of growth effect by progesterone in breast epithelial cells lacking nuclear receptors. This study examined possible nongenomic effects of progesterone in breast epithelia by using MCF-10A cells known to lack nuclear progesterone receptor expression. Treatment for 30-60 min with progesterone or the progestin, R5020, increased mitochondrial activity as shown by an increase in mitochondrial membrane potential (hyperpolarization) with a concordant increase in total cellular ATP. The reaction was inhibited by a specific progesterone receptor antagonist and not affected by the translation inhibitor cycloheximide. Progestin treatment inhibited apoptosis induced by activation of the FasL pathway, as shown by a decrease in sub-G(1) cell fraction during fluorescence-activated cell sorting and a decrease in caspase 3/7 levels. Progestin treatment did not alter the cell cycle over 48 h. Our study demonstrates a nongenomic action of progesterone on benign breast epithelial cells, resulting in enhanced cellular respiration and protection from apoptosis.

Pyruvate therapy for Leigh syndrome due to cytochrome c oxidase deficiency

BACKGROUND

Recently we proposed the therapeutic potential of pyruvate therapy for mitochondrial diseases. Leigh syndrome is a progressive neurodegenerative disorder ascribed to either mitochondrial or nuclear DNA mutations.

METHODS

In an attempt to circumvent the mitochondrial dysfunction, we orally applied sodium pyruvate and analyzed its effect on an 11-year-old female with Leigh syndrome due to cytochrome c oxidase deficiency accompanied by cardiomyopathy. The patient was administered sodium pyruvate at a maintenance dose of 0.5 g/kg/day and followed up for 1 year.

RESULTS

The exercise intolerance was remarkably improved so that she became capable of running. Echocardiography indicated improvements both in the left ventricle ejection fraction and in the fractional shortening. Electrocardiography demonstrated amelioration of the inverted T waves. When the pyruvate administration was interrupted because of a gastrointestinal infection, the serum lactate level became elevated and the serum pyruvate level, decreased, suggesting that the pyruvate administration was effective in decreasing the lactate-to-pyruvate ratio.

CONCLUSIONS

These data indicate that pyruvate therapy was effective in improving exercise intolerance at least in a patient with cytochrome c oxidase deficiency.

GENERAL SIGNIFICANCE

Administration of sodium pyruvate may prove effective for other patients with cytochrome c oxidase deficiency due to mitochondrial or nuclear DNA mutations.

Treatment of a citrin-deficient patient at the early stage of adult-onset type II citrullinaemia with arginine and sodium pyruvate

Citrin deficiency is a common congenital metabolic defect not only in East Asian populations but also in other populations around the world. It has been shown that although liver transplantation is ultimately required in many patients to prevent neurological decompensation associated with hyperammonaemia, arginine is effective in lowering ammonia in hyperammonaemic patients, and a high-protein low-carbohydrate diet may provide some benefit to infants in improving failure to thrive. In the present study, the clinical symptoms and laboratory findings are reported for a 13-year-old citrin-deficient girl in the early stage of adult-onset type II citrullinaemia (CTLN2), and the therapeutic effect of orally administered arginine and sodium pyruvate was investigated. The patient complained of anorexia, lethargy, fatigue and poor growth, and showed laboratory findings typical of CTLN2; elevated levels of plasma citrulline, threonine-to-serine ratio, and serum pancreatic secretory trypsin inhibitor. Oral administration of arginine and sodium pyruvate for over 3 years improved her clinical symptoms and has almost completely normalized her laboratory findings. It is suggested that the administration of arginine and sodium pyruvate with low-carbohydrate meals may be an effective therapy in patients with citrin deficiency in order either to prolong metabolic normalcy or to provide a safer and more affordable alternative to liver transplantation.