Peptide SS-31 upregulates frataxin expression and improves the quality of mitochondria: implications in the treatment of Friedreich ataxia

Design and validation of cell-based potency assays for frataxin supplementation treatments

Friedreich's ataxia (FRDA) is a multisystem, autosomal recessive disorder caused by mutations in the frataxin (FXN) gene. As FRDA is considered an FXN deficiency disorder, numerous therapeutic approaches in development or clinical trials aim to supplement FXN or restore endogenous FXN expression. These include gene therapy, protein supplementation, genome editing or upregulation of FXN transcription. To evaluate efficacy of these therapies, potency assays capable of quantitative determination of FXN biological activity are needed. Herein, we evaluate the suitability of mouse embryonic fibroblasts derived from Fxn G127V knockin mice (MUT MEFs) as a candidate for cell-based potency assays. We demonstrate that these cells, when immortalized, continue to express minute amounts of Fxn and exhibit a broad range of phenotypes that result from severe Fxn deficiency. Exogenous FXN supplementation reverses these phenotypes. Thus, immortalized MUT MEFs are an excellent tool for developing potency assays to validate novel FRDA therapies. Care needs to be exercised while utilizing these cell lines, as extended passaging results in molecular changes that spontaneously reverse FRDA-like phenotypes without increasing Fxn expression. Based on transcriptome analyses, we identified the Warburg effect as the mechanism allowing cells expressing a minimal level of Fxn to thrive under standard cell culture conditions.

Genotype-specific effects of elamipretide in patients with primary mitochondrial myopathy: a post hoc analysis of the MMPOWER-3 trial

BACKGROUND

As previously published, the MMPOWER-3 clinical trial did not demonstrate a significant benefit of elamipretide treatment in a genotypically diverse population of adults with primary mitochondrial myopathy (PMM). However, the prespecified subgroup of subjects with disease-causing nuclear DNA (nDNA) pathogenic variants receiving elamipretide experienced an improvement in the six-minute walk test (6MWT), while the cohort of subjects with mitochondrial DNA (mtDNA) pathogenic variants showed no difference versus placebo. These published findings prompted additional genotype-specific post hoc analyses of the MMPOWER-3 trial. Here, we present these analyses to further investigate the findings and to seek trends and commonalities among those subjects who responded to treatment, to build a more precise Phase 3 trial design for further investigation in likely responders.

RESULTS

Subjects with mtDNA pathogenic variants or single large-scale mtDNA deletions represented 74% of the MMPOWER-3 population, with 70% in the mtDNA cohort having either single large-scale mtDNA deletions or MT-TL1 pathogenic variants. Most subjects in the nDNA cohort had pathogenic variants in genes required for mtDNA maintenance (mtDNA replisome), the majority of which were in POLG and TWNK. The mtDNA replisome post-hoc cohort displayed an improvement on the 6MWT, trending towards significant, in the elamipretide group when compared with placebo (25.2 ± 8.7 m versus 2.0 ± 8.6 m for placebo group; p = 0.06). The 6MWT results at week 24 in subjects with replisome variants showed a significant change in the elamipretide group subjects who had chronic progressive external ophthalmoplegia (CPEO) (37.3 ± 9.5 m versus - 8.0 ± 10.7 m for the placebo group; p = 0.0024). Pharmacokinetic (exposure-response) analyses in the nDNA cohort showed a weak positive correlation between plasma elamipretide concentration and 6MWT improvement.

CONCLUSIONS

Post hoc analyses indicated that elamipretide had a beneficial effect in PMM patients with mtDNA replisome disorders, underscoring the importance of considering specific genetic subtypes in PMM clinical trials. These data serve as the foundation for a follow-up Phase 3 clinical trial (NuPOWER) which has been designed as described in this paper to determine the efficacy of elamipretide in patients with mtDNA maintenance-related disorders.

CLASSIFICATION OF EVIDENCE

Class I CLINICALTRIALS.

GOV IDENTIFIER

NCT03323749.

The mitochondrial-targeted peptide therapeutic elamipretide improves cardiac and skeletal muscle function during aging without detectable changes in tissue epigenetic or transcriptomic age

Aging-related decreases in cardiac and skeletal muscle function are strongly associated with various comorbidities. Elamipretide (ELAM), a novel mitochondrial-targeted peptide, has demonstrated broad therapeutic efficacy in ameliorating disease conditions associated with mitochondrial dysfunction across both clinical and pre-clinical models. ELAM is proposed to restore mitochondrial bioenergetic function by stabilizing inner membrane structure and increasing oxidative phosphorylation coupling and efficiency. Although ELAM treatment effectively attenuates physiological declines in multiple tissues in rodent aging models, it remains unclear whether these functional improvements correlate with favorable changes in molecular biomarkers of aging. Herein, we investigated the impact of 8-week ELAM treatment on pre- and post- measures of C57BL/6J mice frailty, skeletal muscle, and cardiac muscle function, coupled with post-treatment assessments of biological age and affected molecular pathways. We found that health status, as measured by frailty index, cardiac strain, diastolic function, and skeletal muscle force are significantly diminished with age, with skeletal muscle force changing in a sex-dependent manner. Conversely, ELAM mitigated frailty accumulation and was able to partially reverse these declines, as evidenced by treatment-induced increases in cardiac strain and muscle fatigue resistance. Despite these improvements, we did not detect statistically significant changes in gene expression or DNA methylation profiles indicative of molecular reorganization or reduced biological age in most ELAM-treated groups. However, pathway analyses revealed that ELAM treatment showed pro-longevity shifts in gene expression such as upregulation of genes involved in fatty acid metabolism, mitochondrial translation and oxidative phosphorylation, and downregulation of inflammation. Together, these results indicate that ELAM treatment is effective at mitigating signs of sarcopenia and heart failure in an aging mouse model, but that these functional improvements occur independently of detectable changes in epigenetic and transcriptomic age. Thus, some age-related changes in function may be uncoupled from changes in molecular biological age.

The importance of synthetic pharmacotherapy for recessive cerebellar ataxias

INTRODUCTION

The last decade has witnessed major breakthroughs in identifying novel genetic causes of hereditary ataxias, deepening our understanding of disease mechanisms, and developing therapies for these debilitating disorders.

AREAS COVERED

This article reviews the currently approved and most promising candidate pharmacotherapies in relation to the known disease mechanisms of the most prevalent autosomal recessive ataxias. Omaveloxolone is an Nrf2 activator that increases antioxidant defense and was recently approved for treatment of Friedreich ataxia. Its therapeutic effect is modest, and further research is needed to find synergistic treatments that would halt or reverse disease progression. Promising approaches include upregulation of frataxin expression by epigenetic mechanisms, direct protein replacement, and gene replacement therapy. For ataxia-telangiectasia, promising approaches include splice-switching antisense oligonucleotides and small molecules targeting oxidative stress, inflammation, and mitochondrial function. Rare recessive ataxias for which disease-modifying therapies exist are also reviewed, emphasizing recently approved therapies. Evidence supporting the use of riluzole and acetyl-leucine in recessive ataxias is discussed.

EXPERT OPINION

Advances in genetic therapies for other neurogenetic conditions have paved the way to implement feasible approaches with potential dramatic benefits. Particularly, as we develop effective treatments for these conditions, we may need to combine therapies, consider newborn testing for pre-symptomatic treatment, and optimize non-pharmacological approaches.

Interplay of FXN expression and lipolysis in white adipocytes plays a critical role in insulin sensitivity in Friedreich's ataxia mouse model

Frataxin (FXN) is required for iron-sulfur cluster biogenesis, and its loss causes the early-onset neurodegenerative disease Friedreich ataxia (FRDA). Loss of FXN is a susceptibility factor in the development of diabetes, a common metabolic complication after myocardial hypertrophy in patients with FRDA. The underlying mechanism of FXN deficient-induced hyperglycemia in FRDA is, however, poorly understood. In this study, we confirmed that the FXN deficiency mouse model YG8R develops insulin resistance in elder individuals by disturbing lipid metabolic homeostasis in adipose tissues. Evaluation of lipolysis, lipogenesis, and fatty acid β-oxidation showed that lipolysis is most severely affected in white adipose tissues. Consistently, FXN deficiency significantly decreased expression of lipolytic genes encoding adipose triglyceride lipase (Atgl) and hormone-sensitive lipase (Hsl) resulting in adipocyte enlargement and inflammation. Lipolysis induction by fasting or cold exposure remarkably upregulated FXN expression, though FXN deficiency lessened the competency of lipolysis compared with the control or wild type mice. Moreover, we found that the impairment of lipolysis was present at a young age, a few months earlier than hyperglycemia and insulin resistance. Forskolin, an activator of lipolysis, or pioglitazone, an agonist of PPARγ, improved insulin sensitivity in FXN-deficient adipocytes or mice. We uncovered the interplay between FXN expression and lipolysis and found that impairment of lipolysis, particularly the white adipocytes, is an early event, likely, as a primary cause for insulin resistance in FRDA patients at later age.

Mitochondria-targeting peptide SS-31 attenuates ferroptosis via inhibition of the p38 MAPK signaling pathway in the hippocampus of epileptic rats

Ferroptosis is a newly identified form of non-apoptotic regulated cell death (RCD) andplaysanimportantrole in epileptogenesis. The p38 mitogen-activated protein kinase (p38 MAPK) pathway has been confirmed to be involved in ferroptosis. The mitochondria-targeting antioxidant Elamipretide (SS-31) can reduce the generation of lipid peroxidation and the buildup of reactive oxygen species (ROS). Collectively, our present study was to decipher whether SS-31 inhibits ferroptosis via the p38 MAPK signaling pathway in the rat epilepsy model induced by pilocarpine (PILO).Adult male Wistar rats were randomly divided into four groups: control group (CON group), epilepsy group (EP group), SS-31 treatment group (SS group), and p38 MAPK inhibitor (SB203580) treatment group (SB group). Our results demonstrated that the rat hippocampal neurons after epilepsy were followed by accumulated iron and malondialdehyde (MDA) content, upregulated phosphorylated p38 MAPK protein (P-p38) and nuclear factor erythroid 2-related factor 2 (Nrf2) levels, reduced glutathione peroxidase 4 (Gpx4) content, and depleted glutathione (GSH) activity. Morphologically, mitochondrial ultrastructural damage under electron microscopy was manifested by a partial increase in outer membrane density, disappearance of mitochondrial cristae, and mitochondrial shrinkage. SS-31 and SB203580 treatment blocked the initiation and progression of ferroptosis in the hippocampus of epileptic rats via reducing the severity of epileptic seizures, reversing the expression of Gpx4, P-p38 , decreasing the levels of iron and MDA, as well as increasing the activity of GSH and Nrf2. To summarize, our findings proved that ferroptosis was coupled with the pathology of epilepsy, and SS-31 can inhibit PILO-induced seizures by preventing ferroptosis, which may be connected to the inhibition of p38 MAPK phosphorylation, highlighting the potential therapeutic value for targeting ferroptosis process in individuals with seizure-related diseases.

SS-31 inhibits the inflammatory response by increasing ATG5 and promoting autophagy in lipopolysaccharide-stimulated HepG2 cells

SS-31 is a mitochondria-targeting short peptide. Recent studies have indicated its hepatoprotective effects. In our study, we investigated the impact of SS-31 on LPS-induced autophagy in HepG2 cells. The results obtained from a dual-fluorescence autophagy detection system revealed that SS-31 promotes the formation of autolysosomes and autophagosomes, thereby facilitating autophagic flux to a certain degree. Additionally, both ELISA and qPCR analyses provided further evidence that SS-31 safeguards HepG2 cells against inflammatory responses triggered by LPS through ATG5-dependent autophagy. In summary, our study demonstrates that SS-31 inhibits LPS-stimulated inflammation in HepG2 cells by upregulating ATG5-dependent autophagy.

Role of CD36 in central nervous system diseases

CD36 is a highly glycosylated integral membrane protein that belongs to the scavenger receptor class B family and regulates the pathological progress of metabolic diseases. CD36 was recently found to be widely expressed in various cell types in the nervous system, including endothelial cells, pericytes, astrocytes, and microglia. CD36 mediates a number of regulatory processes, such as endothelial dysfunction, oxidative stress, mitochondrial dysfunction, and inflammatory responses, which are involved in many central nervous system diseases, such as stroke, Alzheimer's disease, Parkinson's disease, and spinal cord injury. CD36 antagonists can suppress CD36 expression or prevent CD36 binding to its ligand, thereby achieving inhibition of CD36-mediated pathways or functions. Here, we reviewed the mechanisms of action of CD36 antagonists, such as Salvianolic acid B, tanshinone IIA, curcumin, sulfosuccinimidyl oleate, antioxidants, and small-molecule compounds. Moreover, we predicted the structures of binding sites between CD36 and antagonists. These sites can provide targets for more efficient and safer CD36 antagonists for the treatment of central nervous system diseases.

Application research of novel peptide mitochondrial-targeted antioxidant SS-31 in mitigating mitochondrial dysfunction

Due to the pivotal role of mitochondria in the generation of adenosine triphosphate (ATP) and the regulation of cellular homeostasis, mitochondrial dysfunction may exert a profound impact on various physiological systems, potentially precipitating a spectrum of distinct diseases. Consequently, research pertaining to mitochondrial therapeutics has assumed increasing significance, warranting heightened scrutiny. In recent years, the field of mitochondrial therapy has witnessed noteworthy advancements, with active exploration into diverse pharmacological agents aimed at ameliorating mitochondrial function. Elamipretide (SS-31), a novel synthetic mitochondrial-targeted antioxidant, has emerged as a promising candidate with extensive therapeutic potential. Its notable attributes encompass the mitigation of oxidative stress, the suppression of inflammatory processes, the maintenance of mitochondrial dynamics, and the prevention of cellular apoptosis. As such, SS-31 may emerge as a viable choice for the treatment of mitochondrial dysfunction-related ailments in the foreseeable future. This article extensively expounds upon the superiority of SS-31 over natural antioxidants and traditional mitochondrial-targeted antioxidants, delves into its mechanisms of modulating mitochondrial function, and comprehensively summarizes its applications in alleviating mitochondrial dysfunction-associated disorders. Furthermore, we offer a comprehensive outlook on the expansive prospects of SS-31's future development and application.

NCOA4 requires a [3Fe-4S] to sense and maintain the iron homeostasis

NCOA4 is a selective cargo receptor for ferritinophagy, the autophagic turnover of ferritin (FTH), a process critical for regulating intracellular iron bioavailability. However, how ferritinophagy flux is controlled through NCOA4 in iron-dependent processes needs to be better understood. Here, we show that the C-terminal FTH-binding domain of NCOA4 harbors a [3Fe-4S]-binding site with a stoichiometry of approximately one labile [3Fe-4S] cluster per NCOA4 monomer. By analyzing the interaction between NCOA4 and HERC2 ubiquitin ligase or NCOA4 and FTH, we demonstrate that NCOA4 regulates ferritinophagy by sensing the intracellular iron-sulfur cluster levels. Under iron-repletion conditions, HERC2 recognizes and recruits holo-NCOA4 as a substrate for polyubiquitination and degradation, favoring ferritin iron storage. Under iron-depletion conditions, NCOA4 exists in the form of apo-protein and binds ferritin to promote the occurrence of ferritinophagy and release iron. Thus, we identify an iron-sulfur cluster [3Fe-4S] as a critical cofactor in determining the fate of NCOA4 in favoring iron storage in ferritin or iron release via ferritinophagy and provide a dual mechanism for selective interaction between HERC2 and [3Fe-4S]-NCOA4 for proteasomal degradation or between ferritin and apo-NCOA4 for ferritinophagy in the control of iron homeostasis.

Real-time imaging of mitochondrial redox reveals increased mitochondrial oxidative stress associated with amyloid β aggregates in vivo in a mouse model of Alzheimer's disease

BACKGROUND

Reactive oxidative stress is a critical player in the amyloid beta (Aβ) toxicity that contributes to neurodegeneration in Alzheimer's disease (AD). Damaged mitochondria are one of the main sources of reactive oxygen species and accumulate in Aβ plaque-associated dystrophic neurites in the AD brain. Although Aβ causes neuronal mitochondria reactive oxidative stress in vitro, this has never been directly observed in vivo in the living mouse brain. Here, we tested for the first time whether Aβ plaques and soluble Aβ oligomers induce mitochondrial oxidative stress in surrounding neurons in vivo, and whether this neurotoxic effect can be abrogated using mitochondrial-targeted antioxidants.

METHODS

We expressed a genetically encoded fluorescent ratiometric mitochondria-targeted reporter of oxidative stress in mouse models of the disease and performed intravital multiphoton microscopy of neuronal mitochondria and Aβ plaques.

RESULTS

For the first time, we demonstrated by direct observation in the living mouse brain exacerbated mitochondrial oxidative stress in neurons after both Aβ plaque deposition and direct application of soluble oligomeric Aβ onto the brain, and determined the most likely pathological sequence of events leading to oxidative stress in vivo. Oxidative stress could be inhibited by both blocking calcium influx into mitochondria and treating with the mitochondria-targeted antioxidant SS31. Remarkably, the latter ameliorated plaque-associated dystrophic neurites without impacting Aβ plaque burden.

CONCLUSIONS

Considering these results, combination of mitochondria-targeted compounds with other anti-amyloid beta or anti-tau therapies hold promise as neuroprotective drugs for the prevention and/or treatment of AD.

Recent Advances in the Treatment Strategies of Friedreich's Ataxia: A Review of Potential Drug Candidates and their Underlying Mechanisms

BACKGROUND

Friedreich's Ataxia (FRDA) is a rare hereditary neurodegenerative disorder characterized by progressive ataxia, cardiomyopathy, and diabetes. The disease is caused by a deficiency of frataxin, a mitochondrial protein involved in iron-sulfur cluster synthesis and iron metabolism.

OBJECTIVE

This review aims to summarize recent advances in the development of treatment strategies for FRDA, with a focus on potential drug candidates and their mechanisms of action.

METHODS

A comprehensive literature search was conducted using various authentic scientific databases to identify studies published in the last decade that investigated potential treatment strategies for FRDA. The search terms used included "Friedreich's ataxia", "treatment", "drug candidates", and "mechanisms of action".

RESULTS

To date, only one drug got approval from US-FDA in the year 2023; however, significant developments were achieved in FRDA-related research focusing on diverse therapeutic interventions that could potentially alleviate the symptoms of this disease. Several promising drug candidates have been identified for the treatment of FRDA, which target various aspects of frataxin deficiency and aim to restore frataxin levels, reduce oxidative stress, and improve mitochondrial function. Clinical trials have shown varying degrees of success, with some drugs demonstrating significant improvements in neurological function and quality of life in FRDA patients.

CONCLUSION

While there has been significant progress in the development of treatment strategies for FRDA, further research is needed to optimize these approaches and identify the most effective and safe treatment options for patients. The integration of multiple therapeutic strategies may be necessary to achieve the best outcomes in FRDA management.

Peptide Power: Mechanistic Insights into the Effect of Mitochondria-Targeted Tetrapeptides on Membrane Electrostatics from Molecular Simulations

Mitochondrial dysfunction is implicated in nine of the ten leading causes of death in the US, yet there are no FDA-approved therapeutics to treat it. Synthetic mitochondria-targeted peptides (MTPs), including the lead compound SS-31, offer promise, as they have been shown to restore healthy mitochondrial function and treat a variety of common diseases. At the cellular level, research has shown that MTPs accumulate strongly at the inner mitochondrial membrane (IMM), slow energy sinks (e.g., proton leaks), and improve ATP production. Modulation of electrostatic fields around the IMM has been implicated as a key aspect in the mechanism of action (MoA) of these peptides; however, molecular and mechanistic details have remained elusive. In this study, we employed all-atom molecular dynamics simulations (MD) to investigate the interactions of four MTPs with lipid bilayers and calculate their effect on structural and electrostatic properties. In agreement with previous experimental findings, we observed the modulation of the membrane surface and dipole potentials by MTPs. The simulations reveal that the MTPs achieve a reduction in the dipole potential by acting to disorder both lipid head groups and water layers proximal to the bilayer surface. We also find that MTPs decrease the bilayer thickness and increase the membrane's capacitance. These changes suggest that MTPs may enhance how much potential energy can be stored across the IMM at a given transmembrane potential difference. The MTPs also displace cations away from the bilayer surface, modulating the surface potential and offering an alternative mechanism for how these MTPs reduce mitochondrial energy sinks like proton leaks and mitigate Ca2+ accumulation stress. In conclusion, this study highlights the therapeutic potential of MTPs and underlines how interactions of MTPs with lipid bilayers serve as a fundamental component of their MoA.

Mitochondrial dysfunction in neurodegenerative disorders: Potential therapeutic application of mitochondrial transfer to central nervous system-residing cells

Mitochondrial dysfunction is reiteratively involved in the pathogenesis of diverse neurodegenerative diseases. Current in vitro and in vivo approaches support that mitochondrial dysfunction is branded by several molecular and cellular defects, whose impact at different levels including the calcium and iron homeostasis, energetic balance and/or oxidative stress, makes it difficult to resolve them collectively given their multifactorial nature. Mitochondrial transfer offers an overall solution since it contains the replacement of damage mitochondria by healthy units. Therefore, this review provides an introducing view on the structure and energy-related functions of mitochondria as well as their dynamics. In turn, we summarize current knowledge on how these features are deregulated in different neurodegenerative diseases, including frontotemporal dementia, multiple sclerosis, amyotrophic lateral sclerosis, Friedreich ataxia, Alzheimer´s disease, Parkinson´s disease, and Huntington's disease. Finally, we analyzed current advances in mitochondrial transfer between diverse cell types that actively participate in neurodegenerative processes, and how they might be projected toward developing novel therapeutic strategies.

Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial

BACKGROUND AND OBJECTIVES

Primary mitochondrial myopathies (PMMs) encompass a group of genetic disorders that impair mitochondrial oxidative phosphorylation, adversely affecting physical function, exercise capacity, and quality of life (QoL). Current PMM standards of care address symptoms, with limited clinical impact, constituting a significant therapeutic unmet need. We present data from MMPOWER-3, a pivotal, phase-3, randomized, double-blind, placebo-controlled clinical trial that evaluated the efficacy and safety of elamipretide in participants with genetically confirmed PMM.

METHODS

After screening, eligible participants were randomized 1:1 to receive either 24 weeks of elamipretide at a dose of 40 mg/d or placebo subcutaneously. Primary efficacy endpoints included change from baseline to week 24 on the distance walked on the 6-minute walk test (6MWT) and total fatigue on the Primary Mitochondrial Myopathy Symptom Assessment (PMMSA). Secondary endpoints included most bothersome symptom score on the PMMSA, NeuroQoL Fatigue Short-Form scores, and the patient global impression and clinician global impression of PMM symptoms.

RESULTS

Participants (N = 218) were randomized (n = 109 elamipretide; n = 109 placebo). The m0ean age was 45.6 years (64% women; 94% White). Most of the participants (n = 162 [74%]) had mitochondrial DNA (mtDNA) alteration, with the remainder having nuclear DNA (nDNA) defects. At screening, the most frequent bothersome PMM symptom on the PMMSA was tiredness during activities (28.9%). At baseline, the mean distance walked on the 6MWT was 336.7 ± 81.2 meters, the mean score for total fatigue on the PMMSA was 10.6 ± 2.5, and the mean T score for the Neuro-QoL Fatigue Short-Form was 54.7 ± 7.5. The study did not meet its primary endpoints assessing changes in the 6MWT and PMMSA total fatigue score (TFS). Between the participants receiving elamipretide and those receiving placebo, the difference in the least squares mean (SE) from baseline to week 24 on distance walked on the 6MWT was -3.2 (95% CI -18.7 to 12.3; p = 0.69) meters, and on the PMMSA, the total fatigue score was -0.07 (95% CI -0.10 to 0.26; p = 0.37). Elamipretide treatment was well-tolerated with most adverse events being mild to moderate in severity.

DISCUSSION

Subcutaneous elamipretide treatment did not improve outcomes in the 6MWT and PMMSA TFS in patients with PMM. However, this phase-3 study demonstrated that subcutaneous elamipretide is well-tolerated.

TRIAL REGISTRATION INFORMATION

Trial registered with clinicaltrials.gov, Clinical Trials Identifier: NCT03323749; submitted on October 12, 2017; first patient enrolled October 9, 2017.

CLINICALTRIALS

gov/ct2/show/NCT03323749?term = elamipretide&draw = 2&rank = 9.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that elamipretide does not improve the 6MWT or fatigue at 24 weeks compared with placebo in patients with primary mitochondrial myopathy.

Improving mitochondrial function in preclinical models of heart failure: therapeutic targets for future clinical therapies?

INTRODUCTION

Heart failure is a complex clinical syndrome resulting from the unsuccessful compensation of symptoms of myocardial damage. Mitochondrial dysfunction is a process that occurs because of an attempt to adapt to the disruption of metabolic and energetic pathways occurring in the myocardium. This, in turn, leads to further dysfunction in cardiomyocyte processes. Currently, many therapeutic strategies have been implemented to improve mitochondrial function, but their effectiveness varies widely.

AREAS COVERED

This review focuses on new models of therapeutic strategies targeting mitochondrial function in the treatment of heart failure.

EXPERT OPINION

Therapeutic strategies targeting mitochondria appear to be a valuable option for treating heart failure. Currently, the greatest challenge is to develop new research models that could restore the disrupted metabolic processes in mitochondria as comprehensively as possible. Only the development of therapies that focus on improving as many dysregulated mitochondrial processes as possible in patients with heart failure will be able to bring the expected clinical improvement, along with inhibition of disease progression. Combined strategies involving the reduction of the effects of oxidative stress and mitochondrial dysfunction, appear to be a promising possibility for developing new therapies for a complex and multifactorial disease such as heart failure.

Hinokitiol-iron complex is a ferroptosis inducer to inhibit triple-negative breast tumor growth

BACKGROUND

Ferroptosis is a unique cell death, dependent on iron and phospholipid peroxidation, involved in massive processes of physiopathology. Tremendous attention has been caught in oncology, particularly for those therapy-resistant cancers in the mesenchymal state prone to metastasis due to their exquisite vulnerability to ferroptosis. Therefore, a therapeutical ferroptosis inducer is now underway to be exploited.

RESULTS

A natural compound, hinokitiol (hino), has been considered to be an iron chelator. We have a novel finding that hino complexed with iron to form Fe(hino)3 can function as a ferroptosis inducer in vitro. The efficiency, compared with the same concentration of iron, increases nearly 1000 folds. Other iron chelators, ferroptosis inhibitors, or antioxidants can inhibit Fe(hino)3-induced ferroptosis. The complex Fe(hino)3 efficacy is further confirmed in orthotopic triple-negative breast cancer (TNBC) tumor models that Fe(hino)3 significantly boosted lipid peroxidation to induce ferroptosis and significantly reduced the sizes of TNBC cell-derived tumors. The drug's safety was also evaluated, and no detrimental side effects were found with the tested dosage.

CONCLUSIONS

When entering cells, the chelated iron by hinokitiol as a complex Fe(hino)3 is proposed to be redox-active to vigorously promote the production of free radicals via the Fenton reaction. Thus, Fe(hino)3 is a ferroptosis inducer and, therapeutically, exhibits anti-TNBC activity.

Omaveloxolone: an activator of Nrf2 for the treatment of Friedreich ataxia

INTRODUCTION

Friedreich ataxia (FRDA) is a rare autosomal recessive degenerative disorder characterized by ataxia, dysarthria, diabetes, cardiomyopathy, scoliosis, and occasionally vision loss in late-stage disease. The discovery of the abnormal gene in FRDA and its product frataxin has provided insight into the pathophysiology and mechanisms of treatment.

AREAS COVERED

Although the neurologic phenotype of FRDA is well defined, there are currently no established pharmacological treatments. Omaveloxolone, a nuclear factor erythroid 2-related factor 2 (Nrf2) activator, is currently under review by the Food and Drug Administration (FDA) and has the potential to be the first approved treatment for FRDA. In the present report, we have reviewed the basic and clinical literature on Nrf2 deficiency in FRDA, and evidence for the benefit of omaveloxolone.

EXPERT OPINION

The present perspective suggests that omaveloxolone is a rational and efficacious therapy that is possibly disease modifying in treatment of FRDA.

Beneficial effects of SS-31 peptide on cardiac mitochondrial dysfunction in tafazzin knockdown mice

Barth Syndrome (BTHS), a genetic disease associated with early-onset cardioskeletal myopathy, is caused by loss-of-function mutations of the TAFAZZIN gene, which is responsible for remodeling the mitochondrial phospholipid cardiolipin (CL). Deregulation of CL biosynthesis and maturation in BTHS mitochondria result in a dramatically increased monolysocardiolipin (MLCL)/CL ratio associated with bioenergetic dysfunction. One of the most promising therapeutic approaches for BTHS includes the mitochondria-targeted tetrapeptide SS-31, which interacts with CL. Here, we used TAFAZZIN knockdown (Taz^KD) mice to investigate for the first time whether in vivo administration of SS-31 could affect phospholipid profiles and mitochondrial dysfunction. The CL fingerprinting of Taz^KD cardiac mitochondria obtained by MALDI-TOF/MS revealed the typical lipid changes associated with BTHS. Taz^KD mitochondria showed lower respiratory rates in state 3 and 4 together with a decreased in maximal respiratory rates. Treatment of Taz^KD mice with SS-31 improved mitochondrial respiratory capacity and promoted supercomplex organization, without affecting the MLCL/CL ratio. We hypothesize that SS-31 exerts its effect by influencing the function of the respiratory chain rather than affecting CL directly. In conclusion, our results indicate that SS-31 have beneficial effects on improving cardiac mitochondrial dysfunction in a BTHS animal model, suggesting the peptide as future pharmacologic agent for therapy.

Evaluation of SS-31 as a Potential Strategy for Tendinopathy Treatment: An In Vitro Model

BACKGROUND

Studies in our laboratory have demonstrated mitochondrial dysfunction in human and animal models of supraspinatus tendinopathy. SS-31 (elamipretide) has been reported to improve mitochondrial function and to be effective in clinical trials for several diseases. The potential of SS-31 in treating tendinopathy has not been explored.

HYPOTHESIS

SS-31 would improve mitochondrial function in human tenocytes sampled from patients with tendinopathy.

STUDY DESIGN

Controlled laboratory study.

METHODS

Healthy tenocytes were obtained from normal hamstring tendon biopsy specimens in 9 patients undergoing anterior cruciate ligament reconstruction, and tenocytes were collected from degenerative supraspinatus tendon biopsy specimens in 9 patients undergoing rotator cuff repair. Tenocytes were cultured, used at passage 1, and assigned to 4 groups: healthy tenocytes, healthy tenocytes with 1μM SS-31 treatment for 72 hours, degenerative tenocytes, and degenerative tenocytes with 1μM SS-31 treatment for 72 hours. The outcomes included measurements of mitochondrial potential, mitochondrial morphology by transmission electron microscopy imaging, reactive oxygen species and superoxidative dismutase activity, gene expression, and cell viability.

RESULTS

An increase in the cell fraction with depolarized mitochondria was found in degenerative tenocytes (P = .014), followed by a decrease after SS-31 treatment (P = .018). Transmission electron microscopy images demonstrated morphological changes with a decreased number and size of mitochondria per cell in the degenerative tenocytes (P = .018) and with improvement after SS-31 treatment. There was no significant difference in the level of reactive oxygen species between healthy and degenerative tenocytes in culture, but superoxidative dismutase activity was significantly decreased in the degenerative group (P = .006), which then increased after SS-31 treatment (P = .012). These findings suggested that mitochondrial dysfunction may be reversed by SS-31 treatment. The gene expression of matrix metalloproteinase-1 (matrix remodeling, P = .029) and fatty acid-binding protein 4 (fatty infiltration, P = .046) was significantly upregulated in the degenerative tenocytes and reduced by SS-31 treatment (P = .048; P = .007). Gene expression for hypoxia-inducible factor1 α and the proapoptotic regulator Bcl-2-associated X protein was increased in the degenerative tenocytes. There was a significant decrease in cell viability in degenerative tenocytes as compared with the healthy tenocytes, with small improvement after treatment with SS-31.

CONCLUSION

There are changes in mitochondrial structure and function in tenocytes derived from degenerative tendons, and SS-31, as a mitochondrial protectant, could improve mitochondrial function and promote the healing of tendinopathy.

CLINICAL RELEVANCE

Mitochondrial dysfunction appears to play a role in the development of tendinopathy, and SS-31, as a mitochondrial protective agent, may be a therapeutic agent in the treatment of tendinopathy.

Structure-activity relationships of mitochondria-targeted tetrapeptide pharmacological compounds

Mitochondria play a central role in metabolic homeostasis, and dysfunction of this organelle underpins the etiology of many heritable and aging-related diseases. Tetrapeptides with alternating cationic and aromatic residues such as SS-31 (elamipretide) show promise as therapeutic compounds for mitochondrial disorders. In this study, we conducted a quantitative structure-activity analysis of three alternative tetrapeptide analogs, benchmarked against SS-31, that differ with respect to aromatic side chain composition and sequence register. We present the first structural models for this class of compounds, obtained with Nuclear Magnetic Resonance (NMR) and molecular dynamics approaches, showing that all analogs except for SS-31 form compact reverse turn conformations in the membrane-bound state. All peptide analogs bound cardiolipin-containing membranes, yet they had significant differences in equilibrium binding behavior and membrane interactions. Notably, analogs had markedly different effects on membrane surface charge, supporting a mechanism in which modulation of membrane electrostatics is a key feature of their mechanism of action. The peptides had no strict requirement for side chain composition or sequence register to permeate cells and target mitochondria in mammalian cell culture assays. All four peptides were pharmacologically active in serum withdrawal cell stress models yet showed significant differences in their abilities to restore mitochondrial membrane potential, preserve ATP content, and promote cell survival. Within our peptide set, the analog containing tryptophan side chains, SPN10, had the strongest impact on most membrane properties and showed greatest efficacy in cell culture studies. Taken together, these results show that side chain composition and register influence the activity of these mitochondria-targeted peptides, helping provide a framework for the rational design of next-generation therapeutics with enhanced potency.

Metabolomics analysis reveals dysregulation in one carbon metabolism in Friedreich Ataxia

Friedreich Ataxia (FA) is a rare and often fatal autosomal recessive disease in which a mitochondrial protein, frataxin (FXN), is severely reduced in all tissues. With loss of FXN, mitochondrial metabolism is severely disrupted. Multiple therapeutic approaches are in development, but a key limitation is the lack of biomarkers reflecting the activity of FXN in a timely fashion. We predicted this dysregulated metabolism would present a unique metabolite profile in blood of FA patients versus Controls (Con). Plasma from 10 FA and 11 age and sex matched Con subjects was analyzed by targeted mass spectrometry and untargeted NMR. This combined approach yielded quantitative measurements for 540 metabolites and found 59 unique metabolites (55 from MS and 4 from NMR) that were significantly different between cohorts. Correlation-based network analysis revealed several clusters of pathway related metabolites including a cluster associated with one‑carbon (1C) metabolism composed of formate, sarcosine, hypoxanthine, and homocysteine. Receiver operator characteristics analyses demonstrated an excellent ability to discriminate between Con and FA with AUC values >0.95. These results are the first reported metabolomic analyses of human patients with FA. The metabolic perturbations, especially those related to 1C metabolism, may serve as a valuable biomarker panel of disease progression and response to therapy. The identification of dysregulated 1C metabolism may also inform the search for new therapeutic targets related to this pathway.

Discovery of Therapeutics Targeting Oxidative Stress in Autosomal Recessive Cerebellar Ataxia: A Systematic Review

Autosomal recessive cerebellar ataxias (ARCAs) are a heterogeneous group of rare neurodegenerative inherited disorders. The resulting motor incoordination and progressive functional disabilities lead to reduced lifespan. There is currently no cure for ARCAs, likely attributed to the lack of understanding of the multifaceted roles of antioxidant defense and the underlying mechanisms. This systematic review aims to evaluate the extant literature on the current developments of therapeutic strategies that target oxidative stress for the management of ARCAs. We searched PubMed, Web of Science, and Science Direct Scopus for relevant peer-reviewed articles published from 1 January 2016 onwards. A total of 28 preclinical studies fulfilled the eligibility criteria for inclusion in this systematic review. We first evaluated the altered cellular processes, abnormal signaling cascades, and disrupted protein quality control underlying the pathogenesis of ARCA. We then examined the current potential therapeutic strategies for ARCAs, including aromatic, organic and pharmacological compounds, gene therapy, natural products, and nanotechnology, as well as their associated antioxidant pathways and modes of action. We then discussed their potential as antioxidant therapeutics for ARCAs, with the long-term view toward their possible translation to clinical practice. In conclusion, our current understanding is that these antioxidant therapies show promise in improving or halting the progression of ARCAs. Tailoring the therapies to specific disease stages could greatly facilitate the management of ARCAs.

Frataxin deficiency lowers lean mass and triggers the integrated stress response in skeletal muscle

Friedreich's ataxia (FRDA) is an inherited disorder caused by reduced levels of frataxin (FXN), which is required for iron-sulfur cluster biogenesis. Neurological and cardiac comorbidities are prominent and have been a major focus of study. Skeletal muscle has received less attention despite indications that FXN loss affects it. Here, we show that lean mass is lower, whereas body mass index is unaltered, in separate cohorts of adults and children with FRDA. In adults, lower lean mass correlated with disease severity. To further investigate FXN loss in skeletal muscle, we used a transgenic mouse model of whole-body inducible and progressive FXN depletion. There was little impact of FXN loss when FXN was approximately 20% of control levels. When residual FXN was approximately 5% of control levels, muscle mass was lower along with absolute grip strength. When we examined mechanisms that can affect muscle mass, only global protein translation was lower, accompanied by integrated stress response (ISR) activation. Also in mice, aerobic exercise training, initiated prior to the muscle mass difference, improved running capacity, yet, muscle mass and the ISR remained as in untrained mice. Thus, FXN loss can lead to lower lean mass, with ISR activation, both of which are insensitive to exercise training.

Recessive cerebellar and afferent ataxias - clinical challenges and future directions

Cerebellar and afferent ataxias present with a characteristic gait disorder that reflects cerebellar motor dysfunction and sensory loss. These disorders are a diagnostic challenge for clinicians because of the large number of acquired and inherited diseases that cause cerebellar and sensory neuron damage. Among such conditions that are recessively inherited, Friedreich ataxia and RFC1-associated cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) include the characteristic clinical, neuropathological and imaging features of ganglionopathies, a distinctive non-length-dependent type of sensory involvement. In this Review, we discuss the typical and atypical phenotypes of Friedreich ataxia and CANVAS, along with the features of other recessive ataxias that present with a ganglionopathy or polyneuropathy, with an emphasis on recently described clinical features, natural history and genotype-phenotype correlations. We review the main developments in understanding the complex pathology that affects the sensory neurons and cerebellum, which seem to be most vulnerable to disorders that affect mitochondrial function and DNA repair mechanisms. Finally, we discuss disease-modifying therapeutic advances in Friedreich ataxia, highlighting the most promising candidate molecules and lessons learned from previous clinical trials.

Therapeutic Strategies Targeting Mitochondrial Calcium Signaling: A New Hope for Neurological Diseases?

Calcium (Ca²⁺) is a versatile secondary messenger involved in the regulation of a plethora of different signaling pathways for cell maintenance. Specifically, intracellular Ca²⁺ homeostasis is mainly regulated by the endoplasmic reticulum and the mitochondria, whose Ca²⁺ exchange is mediated by appositions, termed endoplasmic reticulum-mitochondria-associated membranes (MAMs), formed by proteins resident in both compartments. These tethers are essential to manage the mitochondrial Ca²⁺ influx that regulates the mitochondrial function of bioenergetics, mitochondrial dynamics, cell death, and oxidative stress. However, alterations of these pathways lead to the development of multiple human diseases, including neurological disorders, such as amyotrophic lateral sclerosis, Friedreich's ataxia, and Charcot-Marie-Tooth. A common hallmark in these disorders is mitochondrial dysfunction, associated with abnormal mitochondrial Ca²⁺ handling that contributes to neurodegeneration. In this work, we highlight the importance of Ca²⁺ signaling in mitochondria and how the mechanism of communication in MAMs is pivotal for mitochondrial maintenance and cell homeostasis. Lately, we outstand potential targets located in MAMs by addressing different therapeutic strategies focused on restoring mitochondrial Ca²⁺ uptake as an emergent approach for neurological diseases.

SS-31 efficacy in a mouse model of Friedreich ataxia by upregulation of frataxin expression

Friedreich ataxia (FRDA) is a serious hereditary neurodegenerative disease, mostly accompanied with hypertrophic cardiomyopathy, caused by the reduced expression of frataxin (FXN). However, there is still no effective treatment. Our previous studies have shown that SS-31, a mitochondrion-targeted peptide, is capable to upregulate the expression of FXN and improve the mitochondrial function in cells derived from FRDA patients. To further explore the potential of SS-31, we used the GAA expansion-based models, including Y47 and YG8R (Fxn KIKO) mice, primary neurons and macrophages from the mice and cells derived from FRDA patients. After once-daily intraperitoneal injection of 1 mg/kg SS-31 for 1 month, we observed the significant improvement of motor function. The vacuolation in dorsal root ganglia, lesions in dentate nuclei and the lost thickness of myelin sheath of spinal cord were all repaired after SS-31 treatment. In addition, the hypertrophic cardiomyocytes and disarrayed abnormal Purkinje cells were dramatically reduced. Interestingly, we found that SS-31 treatment upregulated FXN expression not only at the translational levels as observed in cell culture but also at mRNA levels in vivo. Consequently, mitochondrial morphology and function were greatly improved in all tested tissues. Importantly, our data provided additional evidence that the maintenance of the therapeutic benefits needed continuous drug administration. Taken together, our findings have demonstrated the effectiveness of SS-31 treatment through the upregulation of FXN in vivo and offer guidance of the potential usage in the clinical application for FRDA.

Mitochondrial and metabolic dysfunction in Friedreich ataxia: update on pathophysiological relevance and clinical interventions

Friedreich ataxia (FRDA) is a recessive disorder resulting from relative deficiency of the mitochondrial protein frataxin. Frataxin functions in the process of iron–sulfur (Fe–S) cluster synthesis. In this review, we update some of the processes downstream of frataxin deficiency that may mediate the pathophysiology. Based on cellular models, in vivo models and observations of patients, ferroptosis may play a major role in the pathogenesis of FRDA along with depletion of antioxidant reserves and abnormalities of mitochondrial biogenesis. Ongoing clinical trials with ferroptosis inhibitors and nuclear factor erythroid 2-related factor 2 (Nrf2) activators are now targeting each of the processes. In addition, better understanding of the mitochondrial events in FRDA may allow the development of improved imaging methodology for assessing the disorder. Though not technologically feasible at present, metabolic imaging approaches may provide a direct methodology to understand the mitochondrial changes occurring in FRDA and provide a methodology to monitor upcoming trials of frataxin restoration.

Drp1-dependent peptide reverse mitochondrial fragmentation, a homeostatic response in Friedreich ataxia

Friedreich ataxia is an autosomal recessive, neurodegenerative disease characterized by the deficiency of the iron-sulfur cluster assembly protein frataxin. Loss of this protein impairs mitochondrial function. Mitochondria alter their morphology in response to various stresses; however, such alterations to morphology may be homeostatic or maladaptive depending upon the tissue and disease state. Numerous neurodegenerative diseases exhibit excessive mitochondrial fragmentation, and reversing this phenotype improves bioenergetics for diseases in which mitochondrial dysfunction is a secondary feature of the disease. This paper demonstrates that frataxin deficiency causes excessive mitochondrial fragmentation that is dependent upon Drp1 activity in Friedreich ataxia cellular models. Drp1 inhibition by the small peptide TAT-P110 reverses mitochondrial fragmentation but also decreases ATP levels in frataxin-knockdown fibroblasts and FRDA patient fibroblasts, suggesting that fragmentation may provide a homeostatic pathway for maintaining cellular ATP levels. The cardiolipin-stabilizing compound SS-31 similarly reverses fragmentation through a Drp1-dependent mechanism, but it does not affect ATP levels. The combination of TAT-P110 and SS-31 does not affect FRDA patient fibroblasts differently from SS-31 alone, suggesting that the two drugs act through the same pathway but differ in their ability to alter mitochondrial homeostasis. In approaching potential therapeutic strategies for FRDA, an important criterion for compounds that improve bioenergetics should be to do so without impairing the homeostatic response of mitochondrial fragmentation.

The displacement of frataxin from the mitochondrial cristae correlates with abnormal respiratory supercomplexes formation and bioenergetic defects in cells of Friedreich ataxia patients

Friedreich ataxia (FRDA) is a neurodegenerative disease resulting from a severe decrease of frataxin (FXN). Most patients carry a GAA repeat expansion in both alleles of the FXN gene, whereas a small fraction of them are compound heterozygous for the expansion and a point mutation in the other allele. FXN is involved in the mitochondrial biogenesis of the FeS-clusters. Distinctive feature of FRDA patient cells is an impaired cellular respiration, likely due to a deficit of key redox cofactors working as electrons shuttles through the respiratory chain. However, a definite relationship between FXN levels, FeS-clusters assembly dysregulation and bioenergetics failure has not been established. In this work, we performed a comparative analysis of the mitochondrial phenotype of cell lines from FRDA patients, either homozygous for the expansion or compound heterozygotes for the G130V mutation. We found that, in healthy cells, FXN and two key proteins of the FeS-cluster assembly machinery are enriched in mitochondrial cristae, the dynamic subcompartment housing the respiratory chain. On the contrary, FXN widely redistributes to the matrix in FRDA cells with defects in respiratory supercomplexes assembly and altered respiratory function. We propose that this could be relevant for the early mitochondrial defects afflicting FRDA cells and that perturbation of mitochondrial morphodynamics could in turn be critical in terms of disease mechanisms.

Mitochondria-Targeted Antioxidants: A Step towards Disease Treatment

Mitochondria are the main organelles that produce adenosine 5′-triphosphate (ATP) and reactive oxygen species (ROS) in eukaryotic cells and meanwhile susceptible to oxidative damage. The irreversible oxidative damage in mitochondria has been implicated in various human diseases. Increasing evidence indicates the therapeutic potential of mitochondria-targeted antioxidants (MTAs) for oxidative damage-associated diseases. In this article, we introduce the advantageous properties of MTAs compared with the conventional (nontargeted) ones, review different mitochondria-targeted delivery systems and antioxidants, and summarize their experimental results for various disease treatments in different animal models and clinical trials. The combined evidence demonstrates that mitochondrial redox homeostasis is a potential target for disease treatment. Meanwhile, the limitations and prospects for exploiting MTAs are discussed, which might pave ways for further trial design and drug development.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

The cardiolipin-binding peptide elamipretide mitigates fragmentation of cristae networks following cardiac ischemia reperfusion in rats

Mitochondrial dysfunction contributes to cardiac pathologies. Barriers to new therapies include an incomplete understanding of underlying molecular culprits and a lack of effective mitochondria-targeted medicines. Here, we test the hypothesis that the cardiolipin-binding peptide elamipretide, a clinical-stage compound under investigation for diseases of mitochondrial dysfunction, mitigates impairments in mitochondrial structure-function observed after rat cardiac ischemia-reperfusion. Respirometry with permeabilized ventricular fibers indicates that ischemia-reperfusion induced decrements in the activity of complexes I, II, and IV are alleviated with elamipretide. Serial block face scanning electron microscopy used to create 3D reconstructions of cristae ultrastructure reveals that disease-induced fragmentation of cristae networks are improved with elamipretide. Mass spectrometry shows elamipretide did not protect against the reduction of cardiolipin concentration after ischemia-reperfusion. Finally, elamipretide improves biophysical properties of biomimetic membranes by aggregating cardiolipin. The data suggest mitochondrial structure-function are interdependent and demonstrate elamipretide targets mitochondrial membranes to sustain cristae networks and improve bioenergetic function.

Identification of Frataxin as a regulator of ferroptosis

Ferroptosis is a newly discovered form of non-apoptotic regulated cell death and is characterized by iron-dependent and lipid peroxidation. Due to the enhanced dependence on iron in cancer cells, induction of ferroptosis is becoming a promising therapeutic strategy. However, the precise underlying molecular mechanism and regulation process of ferroptosis remains largely unknown. In the present study, we demonstrate that the protein Frataxin (FXN) is a key regulator of ferroptosis by modulating iron homeostasis and mitochondrial function. Suppression of FXN expression specifically repressed the proliferation, destroyed mitochondrial morphology, impeded Fe-S cluster assembly and activated iron starvation stress. Moreover, suppression of FXN expression significantly enhanced erastin-induced cell death through accelerating free iron accumulation, lipid peroxidation and resulted in dramatic mitochondria morphological damage including enhanced fragmentation and vanished cristae. In addition, this type of cell death was confirmed to be ferroptosis, since it could be pharmacologically restored by ferroptotic inhibitor Fer-1 or GSH, but not by inhibitors of apoptosis, necrosis. Vice versa, enforced expression of FXN blocked iron starvation response and erastin-induced ferroptosis. More importantly, pharmacological or genetic blocking the signal of iron starvation could completely restore the resistance to ferroptosis in FXN knockdown cells and xenograft graft in vivo. This paper suggests that FXN is a novel ferroptosis modulator, as well as a potential provided target to improve the antitumor activity based on ferroptosis.

Randomized controlled trial of N-acetylcysteine therapy for RYR1-related myopathies

Objective

To investigate the efficacy of N-acetylcysteine (NAC) for decreasing elevated oxidative stress and increasing physical endurance in individuals with ryanodine receptor 1-related myopathies (RYR1-RM).

Methods

In this 6-month natural history assessment (n = 37) followed by a randomized, double-blinded, placebo-controlled trial, 33 eligible participants were block-randomized (1:1) to receive NAC (n = 16) or placebo (n = 17), orally for 6 months (adult dose 2,700 mg/d; pediatric dose 30 mg/kg/d). The primary endpoint was urine 15-F2t isoprostane concentration and the clinically meaningful co-primary endpoint was 6-minute walk test (6MWT) distance.

Results

When compared to the general population, participants had elevated baseline 15-F2t isoprostane concentrations and most had a decreased 6MWT distance (mean ± SD 3.2 ± 1.5 vs 1.1 ± 1.7 ng/mg creatinine and 468 ± 134 vs 600 ± 58 m, respectively, both p < 0.001). 15-F2t isoprostane concentration and 6MWT distance did not change over the 6-month natural history assessment (p = 0.98 and p = 0.61, respectively). NAC treatment did not improve 15-F2t isoprostane concentration (least squares means difference 0.1 [95% confidence interval [CI] −1.4 to 1.6] ng/mg creatinine, p = 0.88) or 6MWT distance (least squares means difference 24 [95% CI −5.5 to 53.4] m, p = 0.11). NAC was safe and well-tolerated at the doses administered in this study.

Conclusion

In ambulatory RYR1-RM–affected individuals, we observed stable disease course, and corroborated preclinical reports of elevated oxidative stress and decreased physical endurance. NAC treatment did not decrease elevated oxidative stress, as measured by 15-F2t isoprostane.

Classification of evidence

This study provides Class I evidence that, for people with RYR1-RM, treatment with oral NAC does not decrease oxidative stress as measured by 15-F2t isoprostane.

Clinicaltrials.gov identifier

NCT02362425.

Mitochondrial dysfunction in neurons in Friedreich's ataxia

Friedreich's ataxia is a multisystemic genetic disorder within the family of mitochondrial diseases that is characterized by reduced levels of the essential mitochondrial protein frataxin. Based on clinical evidence, the peripheral nervous system is affected early, neuronal dysfunction progresses towards the central nervous system, and other organs (such as heart and pancreas) are affected later. However, little attention has been given to the specific aspects of mitochondria function altered by frataxin depletion in the nervous system. For years, commonly accepted views on mitochondria dysfunction in Friedreich's ataxia stemmed from studies using non-neuronal systems and may not apply to neurons, which have their own bioenergetic needs and present a unique, extensive neurite network. Moreover, the basis of the selective neuronal vulnerability, which primarily affects large sensory neurons in the dorsal root ganglia, large principal neurons in the dentate nuclei of the cerebellum, and pyramidal neurons in the cerebral cortex, remains elusive. In order to identify potential misbeliefs in the field and highlight controversies, we reviewed current knowledge on frataxin expression in different tissues, discussed the molecular function of frataxin, and the consequences of its deficiency for mitochondria structural and functional properties, with a focus on the nervous system.

Elamipretide (SS-31) improves mitochondrial dysfunction, synaptic and memory impairment induced by lipopolysaccharide in mice

Background

It is widely accepted that mitochondria have a direct impact on neuronal function and survival. Oxidative stress caused by mitochondrial abnormalities play an important role in the pathophysiology of lipopolysaccharide (LPS)-induced memory impairment. Elamipretide (SS-31) is a novel mitochondrion-targeted antioxidant. However, the impact of elamipretide on the cognitive sequelae of inflammatory and oxidative stress is unknown.

Methods

We utilized MWM and contextual fear conditioning test to assess hippocampus-related learning and memory performance. Molecular biology techniques and ELISA were used to examine mitochondrial function, oxidative stress, and the inflammatory response. TUNEL and Golgi-staining was used to detect neural cell apoptosis and the density of dendritic spines in the mouse hippocampus.

Results

Mice treated with LPS exhibited mitochondrial dysfunction, oxidative stress, an inflammatory response, neural cell apoptosis, and loss of dendritic spines in the hippocampus, leading to impaired hippocampus-related learning and memory performance in the MWM and contextual fear conditioning test. Treatment with elamipretide significantly ameliorated LPS-induced learning and memory impairment during behavioral tests. Notably, elamipretide not only provided protective effects against mitochondrial dysfunction and oxidative stress but also facilitated the regulation of brain-derived neurotrophic factor (BDNF) signaling, including the reversal of important synaptic-signaling proteins and increased synaptic structural complexity.

Conclusion

These findings indicate that LPS-induced memory impairment can be attenuated by the mitochondrion-targeted antioxidant elamipretide. Consequently, elamipretide may have a therapeutic potential in preventing damage from the oxidative stress and neuroinflammation that contribute to perioperative neurocognitive disorders (PND), which makes mitochondria a potential target for treatment strategies for PND.

SS-31 Peptide Reverses the Mitochondrial Fragmentation Present in Fibroblasts From Patients With DCMA, a Mitochondrial Cardiomyopathy

We used patient dermal fibroblasts to characterize the mitochondrial abnormalities associated with the dilated cardiomyopathy with ataxia syndrome (DCMA) and to study the effect of the mitochondrially-targeted peptide SS-31 as a potential novel therapeutic. DCMA is a rare and understudied autosomal recessive disorder thought to be related to Barth syndrome but caused by mutations in DNAJC19, a protein of unknown function localized to the mitochondria. The clinical disease is characterized by 3-methylglutaconic aciduria, dilated cardiomyopathy, abnormal neurological development, and other heterogeneous features. Until recently no effective therapies had been identified and affected patients frequently died in early childhood from intractable heart failure. Skin fibroblasts from four pediatric patients with DCMA were used to establish parameters of mitochondrial dysfunction. Mitochondrial structure, reactive oxygen species (ROS) production, cardiolipin composition, and gene expression were evaluated. Immunocytochemistry with semi-automated quantification of mitochondrial structural metrics and transmission electron microscopy demonstrated mitochondria to be highly fragmented in DCMA fibroblasts compared to healthy control cells. Live-cell imaging demonstrated significantly increased ROS production in patient cells. These abnormalities were reversed by treating DCMA fibroblasts with SS-31, a synthetic peptide that localizes to the inner mitochondrial membrane. Levels of cardiolipin were not significantly different between control and DCMA cells and were unaffected by SS-31 treatment. Our results demonstrate the abnormal mitochondria in fibroblasts from patients with DCMA and suggest that SS-31 may represent a potential therapy for this devastating disease.

Differential Effects of the Mitochondria-Active Tetrapeptide SS-31 (D-Arg-dimethylTyr-Lys-Phe-NH2) and Its Peptidase-Targeted Prodrugs in Experimental Acute Kidney Injury

The mitochondria-active tetrapeptide SS-31 can control oxidative tissue damage in kidney diseases. To investigate other potential beneficial nephroprotective effects of SS-31, in vivo murine models of acute tubular injury and glomerular damage were developed. Reduction of acute kidney injury was demonstrated in mice treated with SS-31. The expression of mRNAs involved in acute inflammatory and oxidative stress responses in the diseased kidneys confirmed that SS-31 could regulate these pathways in our in vivo models. Furthermore, ex vivo histoenzymography of mouse kidneys showed that aminopeptidase A (APA), the enzyme involved in the processing of angiotensin (Ang) II to Ang III, was induced in the diseased kidneys, and its activity was inhibited by SS-31. As the renin–angiotensin system (RAS) is a main regulator of kidney functions, the modulation of Ang receptors (ATR) and APA by SS-31 was further investigated using mRNAs extracted from diseased kidneys. Following acute tubular and/or glomerular damage, the expression of the AT₁R mRNA was upregulated, which could be selectively downregulated upon SS-31 administration to the animals. At the same time, SS-31 was able to increase the expression of the AT₂R, which may contribute to limit renal damage. Consequently, SS-31-based prodrugs were developed as substrates and/or inhibitors for APA and were screened using cells expressing high levels of APA, showing its selective regulation by α-Glu-SS-31. Thus, a link between SS-31 and the RAS opens new therapeutic implications for SS-31 in kidney diseases.

Reversible Mitochondrial Fragmentation in iPSC-Derived Cardiomyocytes From Children With DCMA, a Mitochondrial Cardiomyopathy

BACKGROUND

Dilated cardiomyopathy with ataxia syndrome (DCMA) is an understudied autosomal recessive disease caused by loss-of-function mutations in the poorly characterized gene DNAJC19. Clinically, DCMA is commonly associated with heart failure and early death in affected children through an unknown mechanism. DCMA has been linked to Barth syndrome, a rare but well-studied disorder caused by deficient maturation of cardiolipin (CL), a key mitochondrial membrane phospholipid.

METHODS

Peripheral blood mononuclear cells from 2 children with DCMA and severe cardiac dysfunction were reprogrammed into induced pluripotent stem cells (iPSCs). Patient and control iPSCs were differentiated into beating cardiomyocytes (iPSC-CMs) using a metabolic selection strategy. Mitochondrial structure and CL content before and after incubation with the mitochondrially targeted peptide SS-31 were quantified.

RESULTS

Patient iPSCs carry the causative DNAJC19 mutation (rs137854888) found in the Hutterite population, and the iPSC-CMs demonstrated highly fragmented and abnormally shaped mitochondria associated with an imbalanced isoform ratio of the mitochondrial protein OPA1, an important regulator of mitochondrial fusion. These abnormalities were reversible by incubation with SS-31 for 24 hours. Differentiation of iPSCs into iPSC-CMs increased the number of CL species observed, but consistent, significant differences in CL content were not seen between patients and control.

CONCLUSIONS

We describe a unique and novel cellular model that provides insight into the mitochondrial abnormalities present in DCMA and identifies SS-31 as a potential therapeutic for this devastating disease.

Mitochondrial Dysfunction Underlies Cardiomyocyte Remodeling in Experimental and Clinical Atrial Fibrillation

Atrial fibrillation (AF), the most common progressive tachyarrhythmia, results in structural remodeling which impairs electrical activation of the atria, rendering them increasingly permissive to the arrhythmia. Previously, we reported on endoplasmic reticulum stress and NAD⁺ depletion in AF, suggesting a role for mitochondrial dysfunction in AF progression. Here, we examined mitochondrial function in experimental model systems for AF (tachypaced HL-1 atrial cardiomyocytes and Drosophila melanogaster) and validated findings in clinical AF. Tachypacing of HL-1 cardiomyocytes progressively induces mitochondrial dysfunction, evidenced by impairment of mitochondrial Ca²⁺-handling, upregulation of mitochondrial stress chaperones and a decrease in the mitochondrial membrane potential, respiration and ATP production. Atrial biopsies from AF patients display mitochondrial dysfunction, evidenced by aberrant ATP levels, upregulation of a mitochondrial stress chaperone and fragmentation of the mitochondrial network. The pathophysiological role of mitochondrial dysfunction is substantiated by the attenuation of AF remodeling by preventing an increased mitochondrial Ca²⁺-influx through partial blocking or downregulation of the mitochondrial calcium uniporter, and by SS31, a compound that improves bioenergetics in mitochondria. Together, these results show that conservation of the mitochondrial function protects against tachypacing-induced cardiomyocyte remodeling and identify this organelle as a potential novel therapeutic target.

In Vitro interaction between yeast frataxin and superoxide dismutases: Influence of mitochondrial metals

BACKGROUND

Friedreich's ataxia results from a decreased expression of the nuclear gene encoding the mitochondrial protein, frataxin. Frataxin participates in the biosynthesis of iron-sulfur clusters and heme cofactors, as well as in iron storage and protection against oxidative stress. How frataxin interacts with the antioxidant defence components is poorly understood.

METHODS

Therefore, we have investigated by kinetic, thermodynamic and modelling approaches the molecular interactions between yeast frataxin (Yfh1) and superoxide dismutases, Sod1 and Sod2, and the influence of Yfh1 on their enzymatic activities.

RESULTS

Yfh1 interacts with cytosolic Sod1 with a dissociation constant, Kd = 1.3 ± 0.3 μM, in two kinetic steps. The first step occurs in the 200 ms range and corresponds to the Yfh1-Sod1 interaction, whereas the second is slow and is assumed to be a change in the conformation of the protein-protein adduct. Furthermore, computational investigations confirm the stability of the Yfh1-Sod1 complex. Yfh1 forms two protein complexes with mitochondrial Sod2 with 1:1 and 2:1 Yfh1/Sod2 stoichiometry (Kd1 = 1.05 ± 0.05 and Kd2 = 6.6 ± 0.1 μM). Furthermore, Yfh1 increases the enzymatic activity of Sod1 while slightly affecting that of Sod2. Finally, the stabilities of the protein-protein adducts and the effect of Yfh1 on superoxide dismutase activities depend on the nature of the mitochondrial metal.

CONCLUSIONS

This work confirms the participation of Yfh1 in cellular defence against oxidative stress.

Correction of half the cardiomyocytes fully rescue Friedreich ataxia mitochondrial cardiomyopathy through cell-autonomous mechanisms

Friedreich ataxia (FA) is currently an incurable inherited mitochondrial neurodegenerative disease caused by reduced levels of frataxin. Cardiac failure constitutes the main cause of premature death in FA. While adeno-associated virus-mediated cardiac gene therapy was shown to fully reverse the cardiac and mitochondrial phenotype in mouse models, this was achieved at high dose of vector resulting in the transduction of almost all cardiomyocytes, a dose and biodistribution that is unlikely to be replicated in clinic. The purpose of this study was to define the minimum vector biodistribution corresponding to the therapeutic threshold, at different stages of the disease progression. Correlative analysis of vector cardiac biodistribution, survival, cardiac function and biochemical hallmarks of the disease revealed that full rescue of the cardiac function was achieved when only half of the cardiomyocytes were transduced. In addition, meaningful therapeutic effect was achieved with as little as 30% transduction coverage. This therapeutic effect was mediated through cell-autonomous mechanisms for mitochondria homeostasis, although a significant increase in survival of uncorrected neighboring cells was observed. Overall, this study identifies the biodistribution thresholds and the underlying mechanisms conditioning the success of cardiac gene therapy in Friedreich ataxia and provides guidelines for the development of the clinical administration paradigm.

Iron Pathophysiology in Friedreich's Ataxia

Friedreich's ataxia (FRDA) is a degenerative disease that affects both the central and the peripheral nervous systems and non-neural tissues including, mainly, heart, and endocrine pancreas. It is an autosomal recessive disease caused by a GAA triplet-repeat localized within an Alu sequence element in intron 1 of frataxin (FXN) gene, which encodes a mitochondrial protein FXN. This protein is essential for mitochondrial function by the involvement of iron-sulfur cluster biogenesis. The effects of its deficiency also include disruption of cellular, particularly mitochondrial, iron homeostasis, i.e., relatively more iron accumulated in mitochondria and less iron presented in cytosol. Though iron toxicity is commonly thought to be mediated via Fenton reaction, oxidative stress seems not to be the main problem to result in detrimental effects on cell survival, particularly neuron survival. Therefore, the basic research on FXN function is urgently demanded to understand the disease. This chapter focuses on the outcome of FXN expression, regulation, and function in cellular or animal models of FRDA and on iron pathophysiology in the affected tissues. Finally, therapeutic strategies based on the control of iron toxicity and iron cellular redistribution are considered. The combination of multiple therapeutic targets including iron, oxidative stress, mitochondrial function, and FXN regulation is also proposed.

Targeting mitochondrial dysfunction and oxidative stress in heart failure: Challenges and opportunities

Mitochondrial dysfunction characterized by impaired bioenergetics, oxidative stress and aldehydic load is a hallmark of heart failure. Recently, different research groups have provided evidence that selective activation of mitochondrial detoxifying systems that counteract excessive accumulation of ROS, RNS and reactive aldehydes is sufficient to stop cardiac degeneration upon chronic stress, such as heart failure. Therefore, pharmacological and non-pharmacological approaches targeting mitochondria detoxification may play a critical role in the prevention or treatment of heart failure. In this review we discuss the most recent findings on the central role of mitochondrial dysfunction, oxidative stress and aldehydic load in heart failure, highlighting the most recent preclinical and clinical studies using mitochondria-targeted molecules and exercise training as effective tools against heart failure.

SS-31 Provides Neuroprotection by Reversing Mitochondrial Dysfunction after Traumatic Brain Injury

SS-31, a novel mitochondria-targeted peptide, has been proven to provide neuroprotection in a variety of neurological diseases. Its role as a mitochondrial reactive oxygen species (ROS) scavenger and the underlying pathophysiological mechanisms in traumatic brain injury (TBI) are still not well understood. The aim of the designed study was to investigate the potential neuroprotective effects of SS-31 and fulfill our understanding of the process of the mitochondrial change in the modified Marmarou weight-drop model of TBI. Mice were randomly divided into sham, TBI, TBI + vehicle, and TBI + SS-31 groups in this study. Peptide SS-31 (5 mg/kg) or vehicle was intraperitoneally administrated 30 min after TBI with brain samples harvested 24 h later for further analysis. SS-31 treatment significantly reversed mitochondrial dysfunction and ameliorated secondary brain injury caused by TBI. SS-31 can directly decrease the ROS content, restore the activity of superoxide dismutase (SOD), and decrease the level of malondialdehyde (MDA) and the release of cytochrome c, thus attenuating neurological deficits, brain water content, DNA damage, and neural apoptosis. Moreover, SS-31 restored the expression of SIRT1 and upregulated the nuclear translocation of PGC-1α, which were proved by Western blot and immunohistochemistry. Taken together, these data demonstrate that SS-31 improves the mitochondrial function and provides neuroprotection in mice after TBI potentially through enhanced mitochondrial rebiogenesis. The present study gives us an implication for further clinical research.

Abnormalities of Mitochondrial Dynamics in the Failing Heart: Normalization Following Long-Term Therapy with Elamipretide

PURPOSE

Abnormalities of MITO dynamics occur in HF and have been implicated in disease progression. This study describes the broad range abnormalities of mitochondrial (MITO) dynamics in Heart Failure with reduced ejection fraction (HF) and evaluates the effects of long-term therapy with elamipretide (ELAM), a MITO-targeting peptide, on these abnormalities.

METHODS

Studies were performed in left ventricular tissue from dogs and humans with HF, and were compared with tissue from healthy dogs and healthy donor human hearts. Dogs with HF were randomized to 3 months therapy with ELAM or vehicle. The following were evaluated in dog and human hearts: (1) regulators of MITO biogenesis, including endothelial nitric oxide synthase (eNOS), cyclic guanosine monophosphate (cGMP), and peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α, a transcription factor that drives MITO biogenesis); (2) regulators of MITO fission and fusion, including fission-1, dynamin-related protein-1, mitofusion-2, dominant optic atrophy-1, and mitofilin; and (3) determinants of cardiolipin (CL) synthesis and remodeling, including CL synthase-1, tafazzin-1, and acyl-CoA:lysocardiolipin acyltransferase-1.

RESULTS

The study showed decreased levels of eNOS, cGMP, and PGC-1α in HF (dog and human). Increased levels of fission-associated proteins, decreased levels of fusion-associated proteins, decreased mitofilin, and abnormalities of CL synthesis and remodeling were also observed. In all instances, these maladaptations were normalized following long-term therapy with ELAM.

CONCLUSIONS

Critical abnormalities of MITO dynamics occur in HF and are normalized following long-term therapy with ELAM. The findings provide support for the continued development of ELAM for the treatment of HF.

Cis- and Trans-Modifiers of Repeat Expansions: Blending Model Systems with Human Genetics

Over 30 hereditary diseases are caused by the expansion of microsatellite repeats. The length of the expandable repeat is the main hereditary determinant of these disorders. They are also affected by numerous genomic variants that are either nearby (cis) or physically separated from (trans) the repetitive locus, which we review here. These genetic variants have largely been elucidated in model systems using gene knockouts, while a few have been directly observed as single-nucleotide polymorphisms (SNPs) in patients. There is a notable disconnect between these two bodies of knowledge: knockouts poorly approximate the SNP-level variation in human populations that gives rise to medically relevant cis- and trans-modifiers, while the rarity of these diseases limits the statistical power of SNP-based analysis in humans. We propose that high-throughput SNP-based screening in model systems could become a useful approach to quickly identify and characterize modifiers of clinical relevance for patients.

Protective effects of mitochondrion-targeted peptide SS-31 against hind limb ischemia-reperfusion injury

Hind limb ischemia-reperfusion injury is an important pathology in vascular surgery. Reactive oxygen species are thought to be involved in the pathogenesis of hind limb ischemia-reperfusion injury. SS-31, which belongs to a family of mitochondrion-targeted peptide antioxidants, was shown to reduce mitochondrial reactive oxygen species production. In this study, we investigated whether the treatment of SS-31 could protect hind limb from ischemia-reperfusion injury in a mouse model. The results showed that SS-31 treatment either before or after ischemia exhibited similar protective effects. Histopathologically, SS-31 treatment prevented the IR-induced histological deterioration compared with the corresponding vehicle control. SS-31 treatment diminished oxidative stress revealed by the reduced malondialdehyde level and increased activities and protein levels of Sod and catalase. Cellular ATP contents and mitochondrial membrane potential increased and the level of cytosolic cytC was decreased after SS-31 treatment in this IR model, demonstrating that mitochondria were protected. The IR-induced increase of levels of inflammatory factors, such as Tnf-α and Il-1β, was prevented by SS-31 treatment. In agreement with the reduced cytosolic cytC, cleaved-caspase 3 was kept at a very low level after SS-31 treatment. Overall, the effect of SS-31 treatment before ischemia is mildly more effective than that after ischemia. In conclusion, our results demonstrate that SS-31 confers a protective effect in the mouse model of hind limb ischemia-reperfusion injury preventatively and therapeutically.