The addition of ketone bodies alleviates mitochondrial dysfunction by restoring complex I assembly in a MELAS cellular model

Ketogenic diet enhances the anti-cancer effects of PD-L1 blockade in renal cell carcinoma

Introduction

Clear cell renal cell carcinoma (ccRCC) is characterized by a predominant metabolic reprogramming triggering energy production by anaerobic glycolysis at the expense of oxydative phosphorylation. Ketogenic diet (KD), which consists of high fat and low carbohydrate intake, could bring required energy substrates to healthy cells while depriving tumor cells of glucose. Our objective was to evaluate the effect of KD on renal cancer cell tumor metabolism and growth proliferation.

Methods

Growth cell proliferation and mitochondrial metabolism of ACHN and Renca renal carcinoma cells were evaluated under ketone bodies (KB) exposure. In vivo studies were performed with mice (nude or Balb/c) receiving a xenograft of ACHN cells or Renca cells, respectively, and were then split into 2 feeding groups, fed either with standard diet or a 2:1 KD ad libitum. To test the effect of KD associated to immunotherapy, Balb/c mice were treated with anti-PDL1 mAb. Tumor growth was monitored.

Results

In vitro, KB exposure was associated with a significant reduction of ACHN and Renca cell proliferation and viability, while increasing mitochondrial metabolism. In mice, KD was associated with tumor growth reduction and PDL-1 gene expression up-regulation. In Balb/c mice adjuvant KD was associated to a better response to anti-PDL-1 mAb treatment.

Conclusion

KB reduced the renal tumor cell growth proliferation and improved mitochondrial respiration and biogenesis. KD also slowed down tumor growth of ACHN and Renca in vivo. We observed that PDL-1 was significantly overexpressed in tumor in mice under KD. Response to anti-PDL-1 mAb was improved in mice under KD. Further studies are needed to confirm the therapeutic benefit of adjuvant KD combined with immunotherapy in patients with kidney cancer.

Mitochondrial dysfunction: mechanisms and advances in therapy

Mitochondria, with their intricate networks of functions and information processing, are pivotal in both health regulation and disease progression. Particularly, mitochondrial dysfunctions are identified in many common pathologies, including cardiovascular diseases, neurodegeneration, metabolic syndrome, and cancer. However, the multifaceted nature and elusive phenotypic threshold of mitochondrial dysfunction complicate our understanding of their contributions to diseases. Nonetheless, these complexities do not prevent mitochondria from being among the most important therapeutic targets. In recent years, strategies targeting mitochondrial dysfunction have continuously emerged and transitioned to clinical trials. Advanced intervention such as using healthy mitochondria to replenish or replace damaged mitochondria, has shown promise in preclinical trials of various diseases. Mitochondrial components, including mtDNA, mitochondria-located microRNA, and associated proteins can be potential therapeutic agents to augment mitochondrial function in immunometabolic diseases and tissue injuries. Here, we review current knowledge of mitochondrial pathophysiology in concrete examples of common diseases. We also summarize current strategies to treat mitochondrial dysfunction from the perspective of dietary supplements and targeted therapies, as well as the clinical translational situation of related pharmacology agents. Finally, this review discusses the innovations and potential applications of mitochondrial transplantation as an advanced and promising treatment.

Molecular Mechanisms of Neuroprotection by Ketone Bodies and Ketogenic Diet in Cerebral Ischemia and Neurodegenerative Diseases

Ketone bodies (KBs), such as acetoacetate and β-hydroxybutyrate, serve as crucial alternative energy sources during glucose deficiency. KBs, generated through ketogenesis in the liver, are metabolized into acetyl-CoA in extrahepatic tissues, entering the tricarboxylic acid cycle and electron transport chain for ATP production. Reduced glucose metabolism and mitochondrial dysfunction correlate with increased neuronal death and brain damage during cerebral ischemia and neurodegeneration. Both KBs and the ketogenic diet (KD) demonstrate neuroprotective effects by orchestrating various cellular processes through metabolic and signaling functions. They enhance mitochondrial function, mitigate oxidative stress and apoptosis, and regulate epigenetic and post-translational modifications of histones and non-histone proteins. Additionally, KBs and KD contribute to reducing neuroinflammation and modulating autophagy, neurotransmission systems, and gut microbiome. This review aims to explore the current understanding of the molecular mechanisms underpinning the neuroprotective effects of KBs and KD against brain damage in cerebral ischemia and neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease.

The Mitochondrial m.3243A>G Mutation on the Dish, Lessons from In Vitro Models

The m.3243A>G mutation in the tRNA Leu(UUR) gene (MT-TL1) is one of the most common pathogenic point mutations in human mtDNA. Patient symptoms vary widely and the severity of the disease ranges from asymptomatic to lethal. The reason for the high heterogeneity of m.3243A>G-associated disease is still unknown, and the treatment options are limited, with only supportive interventions available. Furthermore, the heteroplasmic nature of the m.3243A>G mutation and lack of specific animal models of mtDNA mutations have challenged the study of m.3243A>G, and, besides patient data, only cell models have been available for studies. The most commonly used cell models are patient derived, such as fibroblasts and induced pluripotent stem cell (iPSC)-derived models, and cybrid models where the mutant DNA is transferred to an acceptor cell. Studies on cell models have revealed cell-type-specific effects of the m.3243A>G mutation and that the tolerance for this mutation varies between cell types and between patients. In this review, we summarize the literature on the effects of m.3243A>G in cell models.

Complex I deficiency in m.3243A>G fibroblasts is alleviated by reducing NADH accumulation

Introduction: Mitochondrial disease is a spectrum of debilitating disorders caused by mutations in the mitochondrial DNA (mtDNA) or nuclear DNA that compromises the respiratory chain. Mitochondrial 3243A>G (m.3243 A>G) is the most common mutation showing great heterogeneity in phenotype. Previous studies have indicated that NADH: ubiquinone oxidoreductase (complex I) deficiency accompanied by a decreased nicotinamide adenine dinucleotide (NAD+)/reduced NAD+ (NADH) ratio may play a pivotal role in the pathogenesis of m.3243A>G mutation. Methods: To evaluate the potential effects of strategies targeting the imbalanced NAD+/NADH ratio in m.3243A>G mutation, we treated fibroblasts derived from patients with the m.3243 A>G mutation using nicotinamide riboside (NR) or mitochondria-targeted H2O-forming NADH oxidase (mitoLbNOX). Results: M.3243 A>G fibroblasts showed a significant reduction in complex I core subunit 6, complex I enzymatic activity, complex I-dependent oxygen consumption rate (OCR), and adenosine triphosphate (ATP) production compared to the controls. The NAD+/NADH ratio was also significantly reduced in m.3243 A>G fibroblasts, and, using fluorescence lifetime imaging microscopy, we also found that the NADH level was elevated in m.3243 A>G fibroblasts. After NR treatment, the NAD+/NADH ratio, complex I-dependent OCR, and ATP levels increased, whereas NADH levels remained unchanged. More excitingly, after treatment with mitoLbNOX, the NAD+/NADH ratio, complex I-independent OCR, and ATP levels increased more pronouncedly compared with the NR treatment group, accompanied by significantly reduced NADH levels. Discussion: The present study suggests that compared with repletion of NAD+ alone, the combination of this therapeutic modality with alleviation of NADH overload may amplify the treatment effect of restoring NAD+/NADH balance in m.3243A>G fibroblasts.

Ketogenic Diet: An Effective Treatment Approach for Neurodegenerative Diseases

This review discusses the effects and mechanisms of a ketogenic diet on neurodegenerative diseases on the basis of available evidence. A ketogenic diet refers to a high-fat, mediumprotein, and low-carbohydrate diet that leads to a metabolic shift to ketosis. This review systematically summarizes the scientific literature supporting this effective treatment approach for neurodegenerative diseases, including effects on mitochondrial function, oxidative stress, neuronal apoptosis, neuroinflammation, and the microbiota-gut-brain axis. It also highlights the clinical evidence for the effects of the ketogenic diet in the treatment of Alzheimer's disease, Parkinson's disease, and motor neuron disease. Finally, it discusses the common adverse effects of ketogenic therapy. Although the complete mechanism of the ketogenic diet in the treatment of neurodegenerative diseases remains to be elucidated, its clinical efficacy has attracted many new followers. The ketogenic diet is a good candidate for adjuvant therapy, but its specific applicability depends on the type and the degree of the disease.

Efficacy and Safety of the Ketogenic Diet for Mitochondrial Disease With Epilepsy: A Prospective, Open-labeled, Controlled Study

Background

The ketogenic diet (KD) is increasingly used to treat drug-resistant epilepsy because of its favorable effect on seizure reduction. Patients with mitochondrial diseases tend to experience seizures. Therefore, this study aimed to test the efficacy of the KD on participants with mitochondrial diseases in a controlled trial.

Methods

Participants from fourteen clinical centers who were diagnosed with mitochondrial disease were semi-randomized to either the intervention (KD) or control group. The KD group followed a 3-month KD intervention, while the control group received a 1-month normal diet initially and then a 3-month KD intervention. The primary outcome measure was seizure reduction. Biomarker changes, cognitive impairments, and side effects were also recorded, if available.

Result

A total of 33 participants were assigned to the KD (n = 22) and control groups (n = 11). In the KD group, 31.8% (7/22) of participants achieved ≥50% seizure reduction after 1 month of diet intervention, which increased to 40.9% (9/22) at 3 months. In the control group, only 18.2% (2/11) of the participants had ≥50% seizure reduction during the normal diet period. After the control group was transferred to the KD, 63.6% (7/11) of participants had >50% seizure reduction, and this rate increased to 72.7% (8/11) at 3 months. The KD also showed high efficacy in participants with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) or pathogenic variants in mitochondrial DNA (mtDNA) (90% and 93.3% response rates, respectively). The most frequent side effects reported at the 3-month review were vomiting, cold, hyperlipidemia, and bloating.

Conclusion

The KD is a safe and effective therapy for seizure control in mitochondrial diseases, especially MELAS and pathogenic variants of mtDNA. KD intervention can be considered in the management of these patients.

Glutamate-Induced Deregulation of Krebs Cycle in Mitochondrial Encephalopathy Lactic Acidosis Syndrome Stroke-Like Episodes (MELAS) Syndrome Is Alleviated by Ketone Body Exposure

(1) Background: The development of mitochondrial medicine has been severely impeded by a lack of effective therapies. (2) Methods: To better understand Mitochondrial Encephalopathy Lactic Acidosis Syndrome Stroke-like episodes (MELAS) syndrome, neuronal cybrid cells carrying different mutation loads of the m.3243A > G mitochondrial DNA variant were analysed using a multi-omic approach. (3) Results: Specific metabolomic signatures revealed that the glutamate pathway was significantly increased in MELAS cells with a direct correlation between glutamate concentration and the m.3243A > G heteroplasmy level. Transcriptomic analysis in mutant cells further revealed alterations in specific gene clusters, including those of the glutamate, gamma-aminobutyric acid pathways, and tricarboxylic acid (TCA) cycle. These results were supported by post-mortem brain tissue analysis from a MELAS patient, confirming the glutamate dysregulation. Exposure of MELAS cells to ketone bodies significantly reduced the glutamate level and improved mitochondrial functions, reducing the accumulation of several intermediate metabolites of the TCA cycle and alleviating the NADH-redox imbalance. (4) Conclusions: Thus, a multi-omic integrated approach to MELAS cells revealed glutamate as a promising disease biomarker, while also indicating that a ketogenic diet should be tested in MELAS patients.

Characterization of histone lysine β-hydroxybutyrylation in bovine tissues, cells, and cumulus-oocyte complexes

Besides their canonical roles as energy sources, short-chain fatty acids act as metabolic regulators of gene expression through histone posttranslational modifications. Ketone body β-hydroxybutyrate (BHB) causes a novel epigenetic modification, histone lysine β-hydroxybutyrylation (Kbhb), which is associated with genes upregulated in starvation-responsive metabolic pathways. Dairy cows increase BHB in early lactation, and the effects of this increase on cellular epigenomes are unknown. We searched for and identified that Kbhb is present in bovine tissues in vivo and confirmed that this epigenetic mark is responsive to BHB in bovine and human fibroblasts cultured in vitro in a dose-dependent manner. Maturation of cumulus-oocyte complexes with high concentrations of BHB did not affect the competence to complete meiotic maturation or to develop until the blastocyst stage. BHB treatment strongly induced H3K9bhb in cumulus cells, but faintly in oocytes. RNA-seq analysis in cumulus cells indicated that BHB treatment altered the expression of 345 genes. The downregulated genes were mainly involved in glycolysis and ribosome assembly pathways, while the upregulated genes were involved in mitochondrial metabolism and oocyte development. The genes and pathways altered by BHB will provide entry points to carry out functional experiments aiming to mitigate metabolic disorders and improve fertility in cattle.

USE OF KETOGENIC DIET THERAPY IN EPILEPSY WITH MITOCHONDRIAL DYSFUNCTION: A SYSTEMATIC AND CRITICAL REVIEW

With the development of molecular techniques over time more than %60 of epilepsy has associated with mitochondrial (mt) dysfunction. Ketogenic diet (KD) has been used in the treatment of epilepsy since the 1920s. Aim. To evaluate the evidence behind KD in mt dysfunction in epilepsy. Methods. Databases PubMed, Google Scholar and MEDLINE were searched in an umbrella approach to 12 March 2021 in English. To identify relevant studies specific search strategies were devised for the following topics: (1) mitochondrial dysfunction (2) epilepsy (3) KD treatment. Results. From 1794 papers, 36 articles were included in analysis: 16 (%44.44) preclinical studies, 11 (%30.55) case reports, 9 (%25) clinical studies. In all the preclinic studies, KD regulated the number of mt profiles, transcripts of metabolic enzymes and encoding mt proteins, protected the mice against to seizures and had an anticonvulsant mechanism. Case reports and clinical trials have reported patients with good results in seizure control and mt functions, although not all of them give good results as well as preclinical. Conclusion. Healthcare institutions, researchers, neurologists, health promotion organizations, and dietitians should consider these results to improve KD programs and disease outcomes for mt dysfunction in epilepsy.

Ketogenic Diet for KARS-Related Mitochondrial Dysfunction and Progressive Leukodystrophy

KARS encodes lysyl-tRNA synthetase, which is essential for protein translation. KARS mutations sometimes cause impairment of cytoplasmic and mitochondrial protein synthesis, and sometimes lead to progressive leukodystrophies with mitochondrial signature and psychomotor regression, and follow a rapid regressive course to premature death. There has been no disease-modifying therapy beyond supportive treatment. We present a 5-year-old male patient with an asymmetrical leukodystrophy who showed overt evidence of mitochondrial dysfunction, including elevation of lactate on brain MR spectroscopy and low oxygen consumption rate in fibroblasts. We diagnosed this patient's condition as KARS-related leukodystrophy with cerebral calcification, congenital deafness, and evidence of mitochondrial dysfunction. We employed a ketogenic diet as well as multiple vitamin supplementation with the intention to alleviate mitochondrial dysfunction. The patient showed alleviation of his psychomotor regression and even partial restoration of his abilities within 4 months. This is an early report of a potential disease-modifying therapy for KARS-related progressive leukodystrophy without appreciable adverse effects.

Ketogenesis controls mitochondrial gene expression and rescues mitochondrial bioenergetics after cervical spinal cord injury in rats

A better understanding of the secondary injury mechanisms that occur after traumatic spinal cord injury (SCI) is essential for the development of novel neuroprotective strategies linked to the restoration of metabolic deficits. We and others have shown that Ketogenic diet (KD), a high fat, moderate in proteins and low in carbohydrates is neuroprotective and improves behavioural outcomes in rats with acute SCI. Ketones are alternative fuels for mitochondrial ATP generation, and can modulate signaling pathways via targeting specific receptors. Here, we demonstrate that ad libitum administration of KD for 7 days after SCI rescued mitochondrial respiratory capacity, increased parameters of mitochondrial biogenesis, affected the regulation of mitochondrial-related genes, and activated the NRF2-dependent antioxidant pathway. This study demonstrates that KD improves post-SCI metabolism by rescuing mitochondrial function and supports the potential of KD for treatment of acute SCI in humans.

The ketogenic diet as a therapeutic intervention strategy in mitochondrial disease

Classical mitochondrial disease (MD) represents a group of complex metabolic syndromes primarily linked to dysfunction of the mitochondrial ATP-generating oxidative phosphorylation (OXPHOS) system. To date, effective therapies for these diseases are lacking. Here we discuss the ketogenic diet (KD), being a high-fat, moderate protein, and low carbohydrate diet, as a potential intervention strategy. We concisely review the impact of the KD on bioenergetics, ROS/redox metabolism, mitochondrial dynamics and mitophagy. Next, the consequences of the KD in (models of) MD, as well as KD adverse effects, are described. It is concluded that the current experimental evidence suggests that the KD can positively impact on mitochondrial bioenergetics, mitochondrial ROS/redox metabolism and mitochondrial dynamics. However, more information is required on the bioenergetic consequences and mechanistic mode-of-action aspects of the KD at the cellular level and in MD patients.

Applications of Ketogenic Diets in Patients with Headache: Clinical Recommendations

Headaches are among the most prevalent and disabling neurologic disorders and there are several unmet needs as current pharmacological options are inadequate in treating patients with chronic headache, and a growing interest focuses on nutritional approaches as non-pharmacological treatments. Among these, the largest body of evidence supports the use of the ketogenic diet (KD). Exactly 100 years ago, KD was first used to treat drug-resistant epilepsy, but subsequent applications of this diet also involved other neurological disorders. Evidence of KD effectiveness in migraine emerged in 1928, but in the last several year's different groups of researchers and clinicians began utilizing this therapeutic option to treat patients with drug-resistant migraine, cluster headache, and/or headache comorbid with metabolic syndrome. Here we describe the existing evidence supporting the potential benefits of KDs in the management of headaches, explore the potential mechanisms of action involved in the efficacy in-depth, and synthesize results of working meetings of an Italian panel of experts on this topic. The aim of the working group was to create a clinical recommendation on indications and optimal clinical practice to treat patients with headaches using KDs. The results we present here are designed to advance the knowledge and application of KDs in the treatment of headaches.

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.

Clinical Therapeutic Management of Human Mitochondrial Disorders

Despite recent advances in the elucidation of etiology and pathogenesis of mitochondrial disorders, their therapeutic management remains challenging. This review focuses on currently available therapeutic options for human mitochondrial disorders. Current treatment of mitochondrial disorders relies on symptomatic, multidisciplinary therapies of various manifestations in organs such as the brain, muscle, nerves, eyes, ears, endocrine organs, heart, intestines, kidneys, lungs, bones, bone marrow, cartilage, immune system, and skin. If respiratory chain functions are primarily or secondarily impaired, antioxidants or cofactors should be additionally given one by one. All patients with mitochondrial disorders should be offered an individually tailored diet and physical training program. Irrespective of the pathogenesis, all patients with mitochondrial disorders should avoid exposure to mitochondrion-toxic agents and environments. Specific treatment can be offered for stroke-like episodes, mitochondrial epilepsy, mitochondrial neurogastrointestinal encephalopathy, Leber hereditary optic neuropathy, thiamine-responsive Leigh syndrome, primary coenzyme Q deficiency, primary carnitine deficiency, Friedreich ataxia, ethylmalonic encephalopathy, acyl-CoA dehydrogenase deficiency, pyruvate dehydrogenase deficiency, and hereditary vitamin E deficiency. Preventing the transmission of mitochondrial DNA-related mitochondrial disorders can be achieved by mitochondrion replacement therapy (spindle transfer, pronuclear transfer). In conclusion, specific and nonspecific therapies for human mitochondrial disorders are available, and beneficial effects have been anecdotally reported. However, double-blind, placebo-controlled studies to confirm effectiveness are lacking for the majority of the measures applied to mitochondrial disorders. Transmission of certain mitochondrial disorders can be prevented by mitochondrion replacement therapy. A multidisciplinary approach is required to meet the therapeutic challenges of patients with mitochondrial disorders.

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.

Ketones Elicit Distinct Alterations in Adipose Mitochondrial Bioenergetics

Objective: The rampant growth of obesity worldwide has stimulated explosive research into human metabolism. Energy expenditure has been shown to be altered by diets differing in macronutrient composition, with low-carbohydrate, ketogenic diets eliciting a significant increase over other interventions. The central aim of this study was to explore the effects of the ketone β-hydroxybutyrate (βHB) on mitochondrial bioenergetics in adipose tissue. Methods: We employed three distinct systems—namely, cell, rodent, and human models. Following exposure to elevated βHB, we obtained adipose tissue to quantify mitochondrial function. Results: In every model, βHB robustly increased mitochondrial respiration, including an increase of roughly 91% in cultured adipocytes, 113% in rodent subcutaneous adipose tissue (SAT), and 128% in human SAT. However, this occurred without a commensurate increase in adipose ATP production. Furthermore, in cultured adipocytes and rodent adipose, we quantified and observed an increase in the gene expression involved in mitochondrial biogenesis and uncoupling status following βHB exposure. Conclusions: In conclusion, βHB increases mitochondrial respiration, but not ATP production, in mammalian adipocytes, indicating altered mitochondrial coupling. These findings may partly explain the increased metabolic rate evident in states of elevated ketones, and may facilitate the development of novel anti-obesity interventions.

Homoplasmic deleterious MT-ATP6/8 mutations in adult patients

To address the frequency of complex V defects, we systematically sequenced MT-ATP6/8 genes in 512 consecutive patients. We performed functional analysis in muscle or fibroblasts for 12 out of 27 putative homoplasmic mutations and in cybrids for four. Fibroblasts, muscle and cybrids with known deleterious mutations underwent parallel analysis. It included oxidative phosphorylation spectrophotometric assays, western blots, structural analysis, ATP production, glycolysis and cell proliferation evaluation. We demonstrated the deleterious nature of three original mutations. Striking gradation in severity of the mutations consequences and differences between muscle, fibroblasts and cybrids implied a likely under-diagnosis of human complex V defects.

Comparative In Vitro Toxicology of Novel Cytoprotective Short-Chain Naphthoquinones

Short-chain quinones (SCQs) have been identified as potential drug candidates against mitochondrial dysfunction, which largely depends on the reversible redox characteristics of the active quinone core. We recently identified 11 naphthoquinone derivatives, 1–11, from a library of SCQs that demonstrated enhanced cytoprotection and improved metabolic stability compared to the clinically used benzoquinone idebenone. Since the toxicity properties of our promising SCQs were unknown, this study developed multiplex methods and generated detailed toxicity profiles from 11 endpoint measurements using the human hepatocarcinoma cell line HepG2. Overall, the toxicity profiles were largely comparable across different assays, with simple standard assays showing increased sensitivity compared to commercial toxicity assays. Within the 11 naphthoquinones tested, the L-phenylalanine derivative 4 consistently demonstrated the lowest toxicity across all assays. The results of this study not only provide useful information about the toxicity features of SCQs but will also enable the progression of the most promising drug candidates towards their clinical use.

Induced Ketosis as a Treatment for Neuroprogressive Disorders: Food for Thought?

Induced ketosis (or ketone body ingestion) can ameliorate several changes associated with neuroprogressive disorders, including schizophrenia, bipolar disorder, and major depressive disorder. Thus, the effects of glucose hypometabolism can be bypassed through the entry of beta-hydroxybutyrate, providing an alternative source of energy to glucose. The weight of evidence suggests that induced ketosis reduces levels of oxidative stress, mitochondrial dysfunction, and inflammation-core features of the above disorders. There are also data to suggest that induced ketosis may be able to target other molecules and signaling pathways whose levels and/or activity are also known to be abnormal in at least some patients suffering from these illnesses such as peroxisome proliferator-activated receptors, increased activity of the Kelch-like ECH-associated protein/nuclear factor erythroid 2-related factor 2, Sirtuin-1 nuclear factor-κB p65, and nicotinamide adenine dinucleotide (NAD). This review explains the mechanisms by which induced ketosis might reduce mitochondrial dysfunction, inflammation, and oxidative stress in neuropsychiatric disorders and ameliorate abnormal levels of molecules and signaling pathways that also appear to contribute to the pathophysiology of these illnesses. This review also examines safety data relating to induced ketosis over the long term and discusses the design of future studies.

More Than One HMG-CoA Lyase: The Classical Mitochondrial Enzyme Plus the Peroxisomal and the Cytosolic Ones

There are three human enzymes with HMG-CoA lyase activity that are able to synthesize ketone bodies in different subcellular compartments. The mitochondrial HMG-CoA lyase was the first to be described, and catalyzes the cleavage of 3-hydroxy-3-methylglutaryl CoA to acetoacetate and acetyl-CoA, the common final step in ketogenesis and leucine catabolism. This protein is mainly expressed in the liver and its function is metabolic, since it produces ketone bodies as energetic fuels when glucose levels are low. Another isoform is encoded by the same gene for the mitochondrial HMG-CoA lyase (HMGCL), but it is located in peroxisomes. The last HMG-CoA lyase to be described is encoded by a different gene, HMGCLL1, and is located in the cytosolic side of the endoplasmic reticulum membrane. Some activity assays and tissue distribution of this enzyme have shown the brain and lung as key tissues for studying its function. Although the roles of the peroxisomal and cytosolic HMG-CoA lyases remain unknown, recent studies highlight the role of ketone bodies in metabolic remodeling, homeostasis, and signaling, providing new insights into the molecular and cellular function of these enzymes.

Ketogenic treatment reduces the percentage of a LHON heteroplasmic mutation and increases mtDNA amount of a LHON homoplasmic mutation

BACKGROUND

The vision loss in Leber hereditary optic neuropathy patients is due to mitochondrial DNA mutations. No treatment has shown a clear-cut benefit on a clinically meaningful end-point. However, clinical evidences suggest two therapeutic approaches: the reduction of the mutation load in heteroplasmic patients or the elevation of mitochondrial DNA amount in homoplasmic patients.

RESULTS

Here we show that ketogenic treatment, in cybrid cell lines, reduces the percentage of the m.13094 T > C heteroplasmic mutation and also increases the mitochondrial DNA levels of the m.11778G > A mitochondrial genotype.

CONCLUSIONS

These results suggest that ketogenic diet could be a therapeutic strategy for Leber hereditary optic neuropathy.

Early Motor-Behavioral Outcome of Ischemic Stroke with Ketogenic Diet Preconditioning: Interventional Animal Study

BACKGROUND

Cerebral stroke, with ischemic stroke being its most common type, is the leading cause of chronic disability. The ketogenic diet has been used for treating seizures for centuries and has been considered to be a treatment for other neurologic diseases in recent years. The goal of this study is to evaluate the effects of ketogenic diet preconditioning on the early motor-behavior outcome of rats with induced cerebral ischemic stroke.

METHODS

Twenty-four rats were surveyed in 3 groups of Main, Control, and Sham. The Main group received a ketogenic diet plus medium chain triglyceride oil starting 3 days prior to stroke induction, while the other 2 groups took a normal diet. Subsequently, Endothelin-1 was injected stereotactically near the middle cerebral artery to induce an ischemic stroke in the Main and Control group. Normal saline was injected to the members of the Sham group with the same technique. The motor-behavior functions of the rats were compared between 3 groups using adjusting step, beam, and cylinder tests.

RESULTS

After stroke induction, rats on ketogenic diet were able to adjust their steps more efficiently, moved faster on the beam, and used their hands more symmetrically in the transparent cylinder in relation to the rats in the Control group.

CONCLUSION

It seems that ketogenic diet preconditioning improves the early motor-behavioral outcome of ischemic stroke.

Bioinformatics Tools and Databases to Assess the Pathogenicity of Mitochondrial DNA Variants in the Field of Next Generation Sequencing

The development of next generation sequencing (NGS) has greatly enhanced the diagnosis of mitochondrial disorders, with a systematic analysis of the whole mitochondrial DNA (mtDNA) sequence and better detection sensitivity. However, the exponential growth of sequencing data renders complex the interpretation of the identified variants, thereby posing new challenges for the molecular diagnosis of mitochondrial diseases. Indeed, mtDNA sequencing by NGS requires specific bioinformatics tools and the adaptation of those developed for nuclear DNA, for the detection and quantification of mtDNA variants from sequence alignment to the calling steps, in order to manage the specific features of the mitochondrial genome including heteroplasmy, i.e., coexistence of mutant and wildtype mtDNA copies. The prioritization of mtDNA variants remains difficult, relying on a limited number of specific resources: population and clinical databases, and in silico tools providing a prediction of the variant pathogenicity. An evaluation of the most prominent bioinformatics tools showed that their ability to predict the pathogenicity was highly variable indicating that special efforts should be directed at developing new bioinformatics tools dedicated to the mitochondrial genome. In addition, massive parallel sequencing raised several issues related to the interpretation of very low mtDNA mutational loads, discovery of variants of unknown significance, and mutations unrelated to patient phenotype or the co-occurrence of mtDNA variants. This review provides an overview of the current strategies and bioinformatics tools for accurate annotation, prioritization and reporting of mtDNA variations from NGS data, in order to carry out accurate genetic counseling in individuals with primary mitochondrial diseases.

Clinical syndromes associated with mtDNA mutations: where we stand after 30 years

The landmark year 1988 can be considered as the birthdate of mitochondrial medicine, when the first pathogenic mutations affecting mtDNA were associated with human diseases. Three decades later, the field still expands and we are not ‘scraping the bottom of the barrel’ yet. Despite the tremendous progress in terms of molecular characterization and genotype/phenotype correlations, for the vast majority of cases we still lack a deep understanding of the pathogenesis, good models to study, and effective therapeutic options. However, recent technological advances including somatic cell reprogramming to induced pluripotent stem cells (iPSCs), organoid technology, and tailored endonucleases provide unprecedented opportunities to fill these gaps, casting hope to soon cure the major primary mitochondrial phenotypes reviewed here. This group of rare diseases represents a key model for tackling the pathogenic mechanisms involving mitochondrial biology relevant to much more common disorders that affect our currently ageing population, such as diabetes and metabolic syndrome, neurodegenerative and inflammatory disorders, and cancer.

Anti-replicative recombinant 5S rRNA molecules can modulate the mtDNA heteroplasmy in a glucose-dependent manner

Mutations in mitochondrial DNA are an important source of severe and incurable human diseases. The vast majority of these mutations are heteroplasmic, meaning that mutant and wild-type genomes are present simultaneously in the same cell. Only a very high proportion of mutant mitochondrial DNA (heteroplasmy level) leads to pathological consequences. We previously demonstrated that mitochondrial targeting of small RNAs designed to anneal with mutant mtDNA can decrease the heteroplasmy level by specific inhibition of mutant mtDNA replication, thus representing a potential therapy. We have also shown that 5S ribosomal RNA, partially imported into human mitochondria, can be used as a vector to deliver anti-replicative oligoribonucleotides into human mitochondria. So far, the efficiency of cellular expression of recombinant 5S rRNA molecules bearing therapeutic insertions remained very low. In the present study, we designed new versions of anti-replicative recombinant 5S rRNA targeting a large deletion in mitochondrial DNA which causes the KSS syndrome, analyzed their specific annealing to KSS mitochondrial DNA and demonstrated their import into mitochondria of cultured human cells. To obtain an increased level of the recombinant 5S rRNA stable expression, we created transmitochondrial cybrid cell line bearing a site for Flp-recombinase and used this system for the recombinase-mediated integration of genes coding for the anti-replicative recombinant 5S rRNAs into nuclear genome. We demonstrated that stable expression of anti-replicative 5S rRNA versions in human transmitochondrial cybrid cells can induce a shift in heteroplasmy level of KSS mutation in mtDNA. This shift was directly dependent on the level of the recombinant 5S rRNA expression and the sequence of the anti-replicative insertion. Quantification of mtDNA copy number in transfected cells revealed the absence of a non-specific effect on wild type mtDNA replication, indicating that the decreased proportion between mutant and wild type mtDNA molecules is not a consequence of a random repopulation of depleted pool of mtDNA genomes. The heteroplasmy change could be also modulated by cell growth conditions, namely increased by cells culturing in a carbohydrate-free medium, thus forcing them to use oxidative phosphorylation and providing a selective advantage for cells with improved respiration capacities. We discuss the advantages and limitations of this approach and propose further development of the anti-replicative strategy based on the RNA import into human mitochondria.

The accumulation of assembly intermediates of the mitochondrial complex I matrix arm is reduced by limiting glucose uptake in a neuronal-like model of MELAS syndrome

Ketogenic diet (KD) which combined carbohydrate restriction and the addition of ketone bodies has emerged as an alternative metabolic intervention used as an anticonvulsant therapy or to treat different types of neurological or mitochondrial disorders including MELAS syndrome. MELAS syndrome is a severe mitochondrial disease mainly due to the m.3243A > G mitochondrial DNA mutation. The broad success of KD is due to multiple beneficial mechanisms with distinct effects of very low carbohydrates and ketones. To evaluate the metabolic part of carbohydrate restriction, transmitochondrial neuronal-like cybrid cells carrying the m.3243A > G mutation, shown to be associated with a severe complex I deficiency was exposed during 3 weeks to glucose restriction. Mitochondrial enzyme defects were combined with an accumulation of complex I (CI) matrix intermediates in the untreated mutant cells, leading to a drastic reduction in CI driven respiration. The severe reduction of CI was also paralleled in post-mortem brain tissue of a MELAS patient carrying high mutant load. Importantly, lowering significantly glucose concentration in cell culture improved CI assembly with a significant reduction of matrix assembly intermediates and respiration capacities were restored in a sequential manner. In addition, OXPHOS protein expression and mitochondrial DNA copy number were significantly increased in mutant cells exposed to glucose restriction. The accumulation of CI matrix intermediates appeared as a hallmark of MELAS pathophysiology highlighting a critical pathophysiological mechanism involving CI disassembly, which can be alleviated by lowering glucose fuelling and the induction of mitochondrial biogenesis, emphasizing the usefulness of metabolic interventions in MELAS syndrome.

Nutritional Ketosis and Mitohormesis: Potential Implications for Mitochondrial Function and Human Health

Impaired mitochondrial function often results in excessive production of reactive oxygen species (ROS) and is involved in the etiology of many chronic diseases, including cardiovascular disease, diabetes, neurodegenerative disorders, and cancer. Moderate levels of mitochondrial ROS, however, can protect against chronic disease by inducing upregulation of mitochondrial capacity and endogenous antioxidant defense. This phenomenon, referred to as mitohormesis, is induced through increased reliance on mitochondrial respiration, which can occur through diet or exercise. Nutritional ketosis is a safe and physiological metabolic state induced through a ketogenic diet low in carbohydrate and moderate in protein. Such a diet increases reliance on mitochondrial respiration and may, therefore, induce mitohormesis. Furthermore, the ketone β-hydroxybutyrate (BHB), which is elevated during nutritional ketosis to levels no greater than those resulting from fasting, acts as a signaling molecule in addition to its traditionally known role as an energy substrate. BHB signaling induces adaptations similar to mitohormesis, thereby expanding the potential benefit of nutritional ketosis beyond carbohydrate restriction. This review describes the evidence supporting enhancement of mitochondrial function and endogenous antioxidant defense in response to nutritional ketosis, as well as the potential mechanisms leading to these adaptations.

Selection and Characterization of Palmitic Acid Responsive Patients with an OXPHOS Complex I Defect

Mitochondrial disorders are genetically and clinically heterogeneous, mainly affecting high energy-demanding organs due to impaired oxidative phosphorylation (OXPHOS). Currently, effective treatments for OXPHOS defects, with complex I deficiency being the most prevalent, are not available. Yet, clinical practice has shown that some complex I deficient patients benefit from a high-fat or ketogenic diet, but it is unclear how these therapeutic diets influence mitochondrial function and more importantly, which complex I patients could benefit from such treatment. Dietary studies in a complex I deficient patient with exercise intolerance showed increased muscle endurance on a high-fat diet compared to a high-carbohydrate diet. We performed whole-exome sequencing to characterize the genetic defect. A pathogenic homozygous p.G212V missense mutation was identified in the TMEM126B gene, encoding an early assembly factor of complex I. A complementation study in fibroblasts confirmed that the p.G212V mutation caused the complex I deficiency. The mechanism turned out to be an incomplete assembly of the peripheral arm of complex I, leading to a decrease in the amount of mature complex I. The patient clinically improved on a high-fat diet, which was supported by the 25% increase in maximal OXPHOS capacity in TMEM126B defective fibroblast by the saturated fatty acid palmitic acid, whereas oleic acid did not have any effect in those fibroblasts. Fibroblasts of other patients with a characterized complex I gene defect were tested in the same way. Patient fibroblasts with complex I defects in NDUFS7 and NDUFAF5 responded to palmitic acid, whereas ACAD9, NDUFA12, and NDUFV2 defects were non-responding. Although the data are too limited to draw a definite conclusion on the mechanism, there is a tendency that protein defects involved in early assembly complexes, improve with palmitic acid, whereas proteins defects involved in late assembly, do not. Our data show at a clinical and biochemical level that a high fat diet can be beneficial for complex I patients and that our cell line assay will be an easy tool for the selection of patients, who might potentially benefit from this therapeutic diet.

Mitochondrial disorders of the retinal ganglion cells and the optic nerve

OBJECTIVES

To summarise and discuss recent findings and future perspectives concerning mitochondrial disorders (MIDs) affecting the retinal ganglion cells and the optic nerve (mitochondrial optic neuropathy. MON).

METHOD

Literature review.

RESULTS

MON in MIDs is more frequent than usually anticipated. MON may occur in specific as well as non-specific MIDs. In specific and non-specific MIDs, MON may be a prominent or non-prominent phenotypic feature and due to mutations in genes located either in the mitochondrial DNA (mtDNA) or the nuclear DNA (nDNA). Clinically, MON manifests with painless, bilateral or unilateral, slowly or rapidly progressive visual impairment and visual field defects. In some cases, visual impairment may spontaneously recover. The most frequent MIDs with MON include LHON due to mutations in mtDNA-located genes and autosomal dominant optic atrophy (ADOA) or autosomal recessive optic atrophy (AROA) due to mutations in nuclear genes. Instrumental investigations for diagnosing MON include fundoscopy, measurement of visual acuity, visual fields, and color vision, visually-evoked potentials, optical coherence tomography, fluorescein angiography, electroretinography, and MRI of the orbita and cerebrum. In non-prominent MON, work-up of the muscle biopsy with transmission electron microscopy may indicate mitochondrial destruction. Treatment is mostly supportive but idebenone has been approved for LHON and experimental approaches are promising.

CONCLUSIONS

MON needs to be appreciated, requires extensive diagnostic work-up, and supportive treatment should be applied although loss of vision, as the most severe outcome, can often not be prevented.

The therapeutic potential of a calorie-restricted ketogenic diet for the management of Leber hereditary optic neuropathy

Leber hereditary optic neuropathy (LHON) is a maternally inherited, bilateral, sequential optic neuropathy that usually affects young males. LHON arises from a defect in complex I of the oxidative phosphorylation chain that generates increased reactive oxygen species and causes a decline in cellular ATP production. There exists no cure at present for LHON. Asymptomatic LHON mutation carriers show signs of increased mitochondrial biogenesis that may compensate for the compromise in complex I activity. Partial recovery in LHON is associated with a wider optic disc diameter and a younger age at disease onset, which may allow for greater mitochondrial bioenergetic capacity. Rescuing a mitochondrial bioenergetic deficit soon after disease onset may improve the chances of recovery and reduce visual loss in the second eye. We here propose that a calorie-restricted ketogenic diet has the potential to enhance mitochondrial bioenergetic capacity and should be explored as a potential therapeutic option for treating LHON.

Ketogenic diet attenuates hepatopathy in mouse model of respiratory chain complex III deficiency caused by a Bcs1l mutation

Mitochondrial disorders are among the most prevalent inborn errors of metabolism but largely lack treatments and have poor outcomes. High-fat, low-carbohydrate ketogenic diets (KDs) have shown beneficial effects in mouse models of mitochondrial myopathies, with induction of mitochondrial biogenesis as the suggested main mechanism. We fed KD to mice with respiratory chain complex III (CIII) deficiency and progressive hepatopathy due to mutated BCS1L, a CIII assembly factor. The mutant mice became persistently ketotic and tolerated the KD for up to 11 weeks. Liver disease progression was attenuated by KD as shown by delayed fibrosis, reduced cell death, inhibition of hepatic progenitor cell response and stellate cell activation, and normalization of liver enzyme activities. Despite no clear signs of increased mitochondrial biogenesis in the liver, CIII assembly and activity were improved and mitochondrial morphology in hepatocytes normalized. Induction of hepatic glutathione transferase genes and elevated total glutathione level were normalized by KD. Histological findings and transcriptome changes indicated modulation of liver macrophage populations by the mutation and the diet. These results reveal a striking beneficial hepatic response to KD in mice with mitochondrial hepatopathy and warrant further investigations of dietary modification in the management of these conditions in patients.

Multi-dimensional Roles of Ketone Bodies in Fuel Metabolism, Signaling, and Therapeutics

Ketone body metabolism is a central node in physiological homeostasis. In this review, we discuss how ketones serve discrete fine-tuning metabolic roles that optimize organ and organism performance in varying nutrient states and protect from inflammation and injury in multiple organ systems. Traditionally viewed as metabolic substrates enlisted only in carbohydrate restriction, observations underscore the importance of ketone bodies as vital metabolic and signaling mediators when carbohydrates are abundant. Complementing a repertoire of known therapeutic options for diseases of the nervous system, prospective roles for ketone bodies in cancer have arisen, as have intriguing protective roles in heart and liver, opening therapeutic options in obesity-related and cardiovascular disease. Controversies in ketone metabolism and signaling are discussed to reconcile classical dogma with contemporary observations.