Pharmacological therapeutics in Friedreich ataxia: the present state

Pharmacotherapeutic strategies for Friedreich Ataxia: a review of the available data

INTRODUCTION

Friedreich ataxia (FRDA) is a rare autosomal recessive disease, marked by loss of coordination as well as impaired neurological, endocrine, orthopedic, and cardiac function. There are many symptomatic medications for FRDA, and many clinical trials have been performed, but only one FDA-approved medication exists.

AREAS COVERED

The relative absence of the frataxin protein (FXN) in FRDA causes mitochondrial dysfunction, resulting in clinical manifestations. Currently, the only approved treatment for FRDA is an Nrf2 activator called omaveloxolone (Skyclarys). Patients with FRDA also rely on various symptomatic medications for treatment. Because there is only one approved medication for FRDA, clinical trials continue to advance in FRDA. Although some trials have not met their endpoints, many current and upcoming clinical trials provide exciting possibilities for the treatment of FRDA.

EXPERT OPINION

The approval of omaveloxolone provides a major advance in FRDA therapeutics. Although well tolerated, it is not curative. Reversal of deficient frataxin levels with gene therapy, protein replacement, or epigenetic approaches provides the most likely prospect for enduring, disease-modifying therapy in the future.

A peptide derived from TID1S rescues frataxin deficiency and mitochondrial defects in FRDA cellular models

Friedreich's ataxia (FRDA), the most common recessive inherited ataxia, results from homozygous guanine-adenine-adenine (GAA) repeat expansions in intron 1 of the FXN gene, which leads to the deficiency of frataxin, a mitochondrial protein essential for iron-sulphur cluster synthesis. The study of frataxin protein regulation might yield new approaches for FRDA treatment. Here, we report tumorous imaginal disc 1 (TID1), a mitochondrial J-protein cochaperone, as a binding partner of frataxin that negatively controls frataxin protein levels. TID1 interacts with frataxin both in vivo in mouse cortex and in vitro in cortical neurons. Acute and subacute depletion of frataxin using RNA interference markedly increases TID1 protein levels in multiple cell types. In addition, TID1 overexpression significantly increases frataxin precursor but decreases intermediate and mature frataxin levels in HEK293 cells. In primary cultured human skin fibroblasts, overexpression of TID1S results in decreased levels of mature frataxin and increased fragmentation of mitochondria. This effect is mediated by the last 6 amino acids of TID1S as a peptide made from this sequence rescues frataxin deficiency and mitochondrial defects in FRDA patient-derived cells. Our findings show that TID1 negatively modulates frataxin levels, and thereby suggests a novel therapeutic target for treating FRDA.

Omaveloxolone for the treatment of Friedreich ataxia: clinical trial results and practical considerations

INTRODUCTION

Omavaloxolone, an NRF2 activator, recently became the first drug approved specifically for the treatment of Friedreich ataxia (FRDA). This landmark achievement provides a background for a review of the detailed data leading to the approval.

AREAS COVERED

The authors review the data from the 4 major articles on FRDA in the context of the authors' considerable (>1000 patients) experience in treating individuals with FRDA. The data is presented in the context not only of its scientific meaning but also in the practical context of therapy in FRDA.

EXPERT OPINION

Omaveloxolone provides a significant advance in the treatment of FRDA that is likely to be beneficial in a majority of the FRDA population. The data suggesting a benefit is consistent, and adverse issues are relatively modest. The major remaining questions are the subgroups that are most responsive and how long the beneficial effects will remain significant in FRDA patients.

Hereditary Ataxias: From Bench to Clinic, Where Do We Stand?

Cerebellar ataxias are a wide heterogeneous group of movement disorders. Within this broad umbrella of diseases, there are both genetics and sporadic forms. The clinical presentation of these conditions can exhibit a diverse range of symptoms across different age groups, spanning from pure cerebellar manifestations to sensory ataxia and multisystemic diseases. Over the last few decades, advancements in our understanding of genetics and molecular pathophysiology related to both dominant and recessive ataxias have propelled the field forward, paving the way for innovative therapeutic strategies aimed at preventing and arresting the progression of these diseases. Nevertheless, the rarity of certain forms of ataxia continues to pose challenges, leading to limited insights into the etiology of the disease and the identification of target pathways. Additionally, the lack of suitable models hampers efforts to comprehensively understand the molecular foundations of disease's pathophysiology and test novel therapeutic interventions. In the following review, we describe the epidemiology, symptomatology, and pathological progression of hereditary ataxia, including both the prevalent and less common forms of these diseases. Furthermore, we illustrate the diverse molecular pathways and therapeutic approaches currently undergoing investigation in both pre-clinical studies and clinical trials. Finally, we address the existing and anticipated challenges within this field, encompassing both basic research and clinical endeavors.

Continuous, but not intermittent, regimens of hypoxia prevent and reverse ataxia in a murine model of Friedreich's ataxia

Friedreich's ataxia (FA) is a devastating, multi-systemic neurodegenerative disease affecting thousands of people worldwide. We previously reported that oxygen is a key environmental variable that can modify FA pathogenesis. In particular, we showed that chronic, continuous normobaric hypoxia (11% FIO2) prevents ataxia and neurological disease in a murine model of FA, although it did not improve cardiovascular pathology or lifespan. Here, we report the pre-clinical evaluation of seven 'hypoxia-inspired' regimens in the shFxn mouse model of FA, with the long-term goal of designing a safe, practical and effective regimen for clinical translation. We report three chief results. First, a daily, intermittent hypoxia regimen (16 h 11% O2/8 h 21% O2) conferred no benefit and was in fact harmful, resulting in elevated cardiac stress and accelerated mortality. The detrimental effect of this regimen is likely owing to transient tissue hyperoxia that results when daily exposure to 21% O2 combines with chronic polycythemia, as we could blunt this toxicity by pharmacologically inhibiting polycythemia. Second, we report that more mild regimens of chronic hypoxia (17% O2) confer a modest benefit by delaying the onset of ataxia. Third, excitingly, we show that initiating chronic, continuous 11% O2 breathing once advanced neurological disease has already started can rapidly reverse ataxia. Our studies showcase both the promise and limitations of candidate hypoxia-inspired regimens for FA and underscore the need for additional pre-clinical optimization before future translation into humans.

Anodal Cerebellar Transcranial Direct Current Stimulation Reduces Motor and Cognitive Symptoms in Friedreich's Ataxia: A Randomized, Sham-Controlled Trial

BACKGROUND

Friedreich Ataxia is the most common recessive ataxia with only one therapeutic drug approved solely in the United States.

OBJECTIVE

The aim of this work was to investigate whether anodal cerebellar transcranial direct current stimulation (ctDCS) reduces ataxic and cognitive symptoms in individuals with Friedreich's ataxia (FRDA) and to assess the effects of ctDCS on the activity of the secondary somatosensory (SII) cortex.

METHODS

We performed a single-blind, randomized, sham-controlled, crossover trial with anodal ctDCS (5 days/week for 1 week, 20 min/day, density current: 0.057 mA/cm2 ) in 24 patients with FRDA. Each patient underwent a clinical evaluation (Scale for the Assessment and Rating of Ataxia, composite cerebellar functional severity score, cerebellar cognitive affective syndrome scale) before and after anodal and sham ctDCS. Activity of the SII cortex contralateral to a tactile oddball stimulation of the right index finger was evaluated with brain functional magnetic resonance imaging at baseline and after anodal/sham ctDCS.

RESULTS

Anodal ctDCS led to a significant improvement in the Scale for the Assessment and Rating of Ataxia (-6.5%) and in the cerebellar cognitive affective syndrome scale (+11%) compared with sham ctDCS. It also led to a significant reduction in functional magnetic resonance imaging signal at the SII cortex contralateral to tactile stimulation (-26%) compared with sham ctDCS.

CONCLUSIONS

One week of treatment with anodal ctDCS reduces motor and cognitive symptoms in individuals with FRDA, likely by restoring the neocortical inhibition normally exerted by cerebellar structures. This study provides class I evidence that ctDCS stimulation is effective and safe in FRDA. © 2023 International Parkinson and Movement Disorder Society.

Double blind trial of a deuterated form of linoleic acid (RT001) in Friedreich ataxia

OBJECTIVES

Friedreich ataxia is (FRDA) an autosomal recessive neurodegenerative disorder associated with intrinsic oxidative damage, suggesting that decreasing lipid peroxidation (LPO) might ameliorate disease progression. The present study tested the ability of RT001, a deuterated form of linoleic acid (D2-LA), to alter disease severity in patients with FRDA in a double-blind placebo-controlled trial.

METHODS

Sixty-five subjects were recruited across six sites and received either placebo or active drug for an 11-month study. Subjects were evaluated at 0, 4, 9, and 11 months, with the primary outcome measure being maximum oxygen consumption (MVO2) during cardiopulmonary exercise testing (CPET). A key secondary outcome measure was a composite statistical test using results from the timed 1-min walk (T1MW), peak workload, and MVO2.

RESULTS

Forty-five subjects completed the protocol. RT001 was well tolerated, with no serious adverse events related to drug. Plasma and red blood cell (RBC) membrane levels of D2-LA and its primary metabolite deuterated arachidonic acid (D2-AA) achieved steady-state concentrations by 4 months. No significant changes in MVO2 were observed for RT001 compared to placebo. Similarly, no differences between the groups were found in secondary or exploratory outcome measures. Post hoc evaluations also suggested minimal effects of RT001 at the dosages used in this study.

INTERPRETATIONS

The results of this study provide no evidence for a significant benefit of RT001 at the dosages tested in this Friedreich ataxia patient population.

Ataxias: Hereditary, Acquired, and Reversible Etiologies

A variety of etiologies can cause cerebellar dysfunction, leading to ataxia symptoms. Therefore, the accurate diagnosis of the cause for cerebellar ataxia can be challenging. A step-wise investigation will reveal underlying causes, including nutritional, toxin, immune-mediated, genetic, and degenerative disorders. Recent advances in genetics have identified new genes for both autosomal dominant and autosomal recessive ataxias, and new therapies are on the horizon for targeting specific biological pathways. New diagnostic criteria for degenerative ataxias have been proposed, specifically for multiple system atrophy, which will have a broad impact on the future clinical research in ataxia. In this article, we aim to provide a review focus on symptoms, laboratory testing, neuroimaging, and genetic testing for the diagnosis of cerebellar ataxia causes, with a special emphasis on recent advances. Strategies for the management of cerebellar ataxia is also discussed.

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.

Designing phase II clinical trials in Friedreich ataxia

INTRODUCTION

Friedreich ataxia (FRDA) is an autosomal recessive disorder caused by deficiency of frataxin, an essential mitochondrial protein involved in iron sulfur cluster biogenesis, oxidative phosphorylation and other processes. FRDA most notably affects the heart, sensory neurons, spinal cord, cerebellum, and other brain regions, and manifests clinically as ataxia, sensory loss, dysarthria, spasticity, and hypertrophic cardiomyopathy. Therapeutic approaches in FRDA have consisted of two different approaches: (1) augmenting or restoring frataxin production and (2) modulating a variety of downstream processes related to mitochondrial dysfunction, including reactive oxygen species production, ferroptosis, or Nrf2 activation.

AREAS COVERED

In this review, we summarize data from major phase II clinical trials in FRDA published between 2015 and 2020, which includes A0001/EPI743, Omaveloxolone, RT001, and Actimmune.

EXPERT OPINION

A growing number of drug candidates are being tested in phase II clinical trials for FRDA; however, most have not met their primary endpoints, and none have received FDA approval. In this review, we aim to summarize completed phase II clinical trials in FRDA, outlining critical lessons that have been learned and that should be incorporated into future trial design to ultimately optimize drug development in FRDA.

Plasma idebenone monitoring in Friedreich's ataxia patients during a long-term follow-up

INTRODUCTION AND OBJECTIVES

Despite the growing interest and the potential benefits of idebenone as a repurposed drug for different orphan conditions, data regarding its monitoring are scarce. Our main goal was to report plasma idebenone values in a cohort of Friedreich's ataxia (FRDA) patients during a long-term follow-up. Taking advantage of this, we also assessed cardiological and neurological status together with idebenone values and genetic background.

METHODS

Long-term follow-up retrospective study in 27 FRDA patients with a disease onset at the paediatric age treated with idebenone by compassionate use. Plasma idebenone was measured by HPLC with electrochemical detection.

RESULTS

Median plasma idebenone values increased when doses were increased, but apparently linearity was lost in the highest dose group. Marked intraindividual and interindividual differences were observed among patients. We did not find a consistent positive effect after analysis of paired data at the beginning and the end of the study. We only found a correlation between some cardiological measures and the duration of idebenone therapy at high doses, but with uncertain significance.

CONCLUSIONS

The large variations observed among the different individuals involved in this study should be considered for optimization of individual dosage regimens.

Correlation of Visual Quality of Life With Clinical and Visual Status in Friedreich Ataxia

BACKGROUND

The primary objective was to determine the association of patient-reported vision-specific quality of life to disease status and visual function in patients with Friedreich's ataxia (FRDA).

METHODS

Patients with FRDA were assessed with the 25-Item National Eye Institute Visual Functioning Questionnaire (NEI-VFQ-25) along with measures of disease status (ataxia stage) and visual function (low- and high-contrast letter acuity scores). The relations of NEI-VFQ-25 scores to those for disease status and visual function were examined.

RESULTS

Scores for the NEI-VFQ-25 were lower in patients with FRDA (n = 99) compared with published disease-free controls, particularly reduced in a subgroup of FRDA patients with features of early onset, older age, and abnormal visual function.

CONCLUSIONS

The NEI-VFQ-25 captures the subjective component of visual function in patients with FRDA.

Friedreich Ataxia: Multidisciplinary Clinical Care

Friedreich ataxia (FRDA) is a multisystem disorder affecting 1 in 50,000-100,000 person in the United States. Traditionally viewed as a neurodegenerative disease, FRDA patients also develop cardiomyopathy, scoliosis, diabetes and other manifestation. Although it usually presents in childhood, it continues throughout life, thus requiring expertise from both pediatric and adult subspecialist in order to provide optimal management. The phenotype of FRDA is unique, giving rise to specific loss of neuronal pathways, a unique form of cardiomyopathy with early hypertrophy and later fibrosis, and diabetes incorporating components of both type I and type II disease. Vision loss, hearing loss, urinary dysfunction and depression also occur in FRDA. Many agents are reaching Phase III trials; if successful, these will provide a variety of new treatments for FRDA that will require many specialists who are not familiar with FRDA to provide clinical therapy. This review provides a summary of the diverse manifestation of FRDA, existing symptomatic therapies, and approaches for integrative care for future therapy in FRDA.

In vivo survival and differentiation of Friedreich ataxia iPSC-derived sensory neurons transplanted in the adult dorsal root ganglia

Friedreich ataxia (FRDA) is an autosomal recessive disease characterized by degeneration of dorsal root ganglia (DRG) sensory neurons, which is due to low levels of the mitochondrial protein Frataxin. To explore cell replacement therapies as a possible approach to treat FRDA, we examined transplantation of sensory neural progenitors derived from human embryonic stem cells (hESC) and FRDA induced pluripotent stem cells (iPSC) into adult rodent DRG regions. Our data showed survival and differentiation of hESC and FRDA iPSC-derived progenitors in the DRG 2 and 8 weeks post-transplantation, respectively. Donor cells expressed neuronal markers, including sensory and glial markers, demonstrating differentiation to these lineages. These results are novel and a highly significant first step in showing the possibility of using stem cells as a cell replacement therapy to treat DRG neurodegeneration in FRDA as well as other peripheral neuropathies.

Friedreich Ataxia: current state-of-the-art, and future prospects for mitochondrial-focused therapies

Friedreich's Ataxia is an autosomal recessive genetic disease causing the defective gene product, frataxin. A body of literature has been focused on the attempts to counteract frataxin deficiency and the consequent iron imbalance, in order to mitigate the disease-associated pro-oxidant state and clinical course. The present mini review is aimed at evaluating the basic and clinical reports on the roles and the use of a set of iron chelators, antioxidants and some cofactors involved in the key mitochondrial functions. Extensive literature has focused on the protective roles of iron chelators, coenzyme Q10 and analogs, and vitamin E, altogether with varying outcomes in clinical studies. Other studies have suggested mitoprotective roles for other mitochondrial cofactors, involved in Krebs cycle, such as alpha-lipoic acid and carnitine, involved in acyl transport across the mitochondrial membrane. A body of evidence points to the strong antioxidant properties of these cofactors, and to their potential contribution in mitoprotective strategies in Friedreich's Ataxia clinical evolution. Thus, we suggest the rationale for planning combination strategies based on the 3 mitochondrial cofactors and of some antioxidants and iron binders as mitoprotective cocktails in Friedreich Ataxia patients, calling attention to clinical practitioners of the importance to implement clinical trials.

Safety and Efficacy of Omaveloxolone in Friedreich Ataxia (MOXIe Study)

OBJECTIVE

Friedreich ataxia (FA) is a progressive genetic neurodegenerative disorder with no approved treatment. Omaveloxolone, an Nrf2 activator, improves mitochondrial function, restores redox balance, and reduces inflammation in models of FA. We investigated the safety and efficacy of omaveloxolone in patients with FA.

METHODS

We conducted an international, double-blind, randomized, placebo-controlled, parallel-group, registrational phase 2 trial at 11 institutions in the United States, Europe, and Australia (NCT02255435, EudraCT2015-002762-23). Eligible patients, 16 to 40 years of age with genetically confirmed FA and baseline modified Friedreich's Ataxia Rating Scale (mFARS) scores between 20 and 80, were randomized 1:1 to placebo or 150mg per day of omaveloxolone. The primary outcome was change from baseline in the mFARS score in those treated with omaveloxolone compared with those on placebo at 48 weeks.

RESULTS

One hundred fifty-five patients were screened, and 103 were randomly assigned to receive omaveloxolone (n = 51) or placebo (n = 52), with 40 omaveloxolone patients and 42 placebo patients analyzed in the full analysis set. Changes from baseline in mFARS scores in omaveloxolone (-1.55 ± 0.69) and placebo (0.85 ± 0.64) patients showed a difference between treatment groups of -2.40 ± 0.96 (p = 0.014). Transient reversible increases in aminotransferase levels were observed with omaveloxolone without increases in total bilirubin or other signs of liver injury. Headache, nausea, and fatigue were also more common among patients receiving omaveloxolone.

INTERPRETATION

In the MOXIe trial, omaveloxolone significantly improved neurological function compared to placebo and was generally safe and well tolerated. It represents a potential therapeutic agent in FA. ANN NEUROL 2021;89:212-225.

Omaveloxolone: potential new agent for Friedreich ataxia

Friedreich ataxia is a slowly progressive neurodegenerative disorder leading to ataxia, dyscoordination, dysarthria and in many individuals vision and hearing loss. It is associated with cardiomyopathy, the leading cause of death in Friedreich ataxia (FRDA), diabetes and scoliosis. There are no approved therapies, but elucidation of the pathophysiology of FRDA suggest that agents that increase the activity of the transcription factor Nrf2 may provide a mechanism for ameliorating disease progression or severity. In this work, we review the evidence for use of omaveloxolone in FRDA from recent clinical trials. Though not at present approved for any indication, the present data suggest that this agent acting though increases in Nrf2 activity may provide a novel therapy for FRDA.

Thioredoxin and Glutaredoxin Systems as Potential Targets for the Development of New Treatments in Friedreich's Ataxia

The thioredoxin family consists of a small group of redox proteins present in all organisms and composed of thioredoxins (TRXs), glutaredoxins (GLRXs) and peroxiredoxins (PRDXs) which are found in the extracellular fluid, the cytoplasm, the mitochondria and in the nucleus with functions that include antioxidation, signaling and transcriptional control, among others. The importance of thioredoxin family proteins in neurodegenerative diseases is gaining relevance because some of these proteins have demonstrated an important role in the central nervous system by mediating neuroprotection against oxidative stress, contributing to mitochondrial function and regulating gene expression. Specifically, in the context of Friedreich’s ataxia (FRDA), thioredoxin family proteins may have a special role in the regulation of Nrf2 expression and function, in Fe-S cluster metabolism, controlling the expression of genes located at the iron-response element (IRE) and probably regulating ferroptosis. Therefore, comprehension of the mechanisms that closely link thioredoxin family proteins with cellular processes affected in FRDA will serve as a cornerstone to design improved therapeutic strategies.

Molecular Defects in Friedreich's Ataxia: Convergence of Oxidative Stress and Cytoskeletal Abnormalities

Friedreich’s ataxia (FRDA) is a multi-faceted disease characterized by progressive sensory–motor loss, neurodegeneration, brain iron accumulation, and eventual death by hypertrophic cardiomyopathy. FRDA follows loss of frataxin (FXN), a mitochondrial chaperone protein required for incorporation of iron into iron–sulfur cluster and heme precursors. After the discovery of the molecular basis of FRDA in 1996, over two decades of research have been dedicated to understanding the temporal manifestations of disease both at the whole body and molecular level. Early research indicated strong cellular iron dysregulation in both human and yeast models followed by onset of oxidative stress. Since then, the pathophysiology due to dysregulation of intracellular iron chaperoning has become central in FRDA relative to antioxidant defense and run-down in energy metabolism. At the same time, limited consideration has been given to changes in cytoskeletal organization, which was one of the first molecular defects noted. These alterations include both post-translational oxidative glutathionylation of actin monomers and differential DNA processing of a cytoskeletal regulator PIP5K1β. Currently unknown in respect to FRDA but well understood in the context of FXN-deficient cell physiology is the resulting impact on the cytoskeleton; this disassembly of actin filaments has a particularly profound effect on cell–cell junctions characteristic of barrier cells. With respect to a neurodegenerative disorder such as FRDA, this cytoskeletal and tight junction breakdown in the brain microvascular endothelial cells of the blood–brain barrier is likely a component of disease etiology. This review serves to outline a brief history of this research and hones in on pathway dysregulation downstream of iron-related pathology in FRDA related to actin dynamics. The review presented here was not written with the intent of being exhaustive, but to instead urge the reader to consider the essentiality of the cytoskeleton and appreciate the limited knowledge on FRDA-related cytoskeletal dysfunction as a result of oxidative stress. The review examines previous hypotheses of neurodegeneration with brain iron accumulation (NBIA) in FRDA with a specific biochemical focus.

Molecular and Cellular Substrates for the Friedreich Ataxia. Significance of Contactin Expression and of Antioxidant Administration

In this study, the neural phenotype is explored in rodent models of the spinocerebellar disorder known as the Friedreich Ataxia (FA), which results from mutations within the gene encoding the Frataxin mitochondrial protein. For this, the M12 line, bearing a targeted mutation, which disrupts the Frataxin gene exon 4 was used, together with the M02 line, which, in addition, is hemizygous for the human Frataxin gene mutation (Pook transgene), implying the occurrence of 82-190 GAA repeats within its first intron. The mutant mice phenotype was compared to the one of wild type littermates in regions undergoing differential profiles of neurogenesis, including the cerebellar cortex and the spinal cord by using neuronal (β-tubulin) and glial (Glial Fibrillary Acidic Protein) markers as well as the Contactin 1 axonal glycoprotein, involved in neurite growth control. Morphological/morphometric analyses revealed that while in Frataxin mutant mice the neuronal phenotype was significantly counteracted, a glial upregulation occurred at the same time. Furthermore, Contactin 1 downregulation suggested that changes in the underlying gene contributed to the disorder pathogenesis. Therefore, the FA phenotype implies an alteration of the developmental profile of neuronal and glial precursors. Finally, epigallocatechin gallate polyphenol administration counteracted the disorder, indicating protective effects of antioxidant administration.

A Comprehensive Transcriptome Analysis Identifies FXN and BDNF as Novel Targets of miRNAs in Friedreich's Ataxia Patients

Friedreich's ataxia (FRDA) is a genetic neurodegenerative disease that is caused by guanine-adenine-adenine (GAA) nucleotide repeat expansions in the first intron of the frataxin (FXN) gene. Although present in the intron, this mutation leads to a substantial decrease in protein expression. Currently, no effective treatment is available for FRDA, and, in addition to FXN, other targets with therapeutic potential are continuously sought. As miRNAs can regulate the expression of a broad spectrum of genes, are used as biomarkers, and can serve as therapeutic tools, we decided to identify and characterize differentially expressed miRNAs and their targets in FRDA cells compared to unaffected control (CTRL) cells. In this study, we performed an integrated miRNAseq and RNAseq analysis using the same cohort of primary FRDA and CTRL cells. The results of the transcriptome studies were supported by bioinformatic analyses and validated by qRT-PCR. miRNA interactions with target genes were assessed by luciferase assays, qRT-PCR, and immunoblotting. In silico analysis identified the FXN transcript as a target of five miRNAs upregulated in FRDA cells. Further studies confirmed that miRNA-224-5p indeed targets FXN, resulting in decreases in mRNA and protein levels. We also validated the ability of miRNA-10a-5p to bind and regulate the levels of brain-derived neurotrophic factor (BDNF), an important modulator of neuronal growth. We observed a significant decrease in the levels of miRNA-10a-5p and increase in the levels of BDNF upon correction of FRDA cells via zinc-finger nuclease (ZFN)-mediated excision of expanded GAA repeats. Our comprehensive transcriptome analyses identified miRNA-224-5p and miRNA-10a-5p as negative regulators of the FXN and BDNF expression, respectively. These results emphasize not only the importance of miRNAs in the pathogenesis of FRDA but also their potential as therapeutic targets for this disease.

A systematic comparison of triterpenoid biosynthetic enzymes for the production of oleanolic acid in Saccharomyces cerevisiae

Triterpenoids are high-value plant metabolites with numerous applications in medicine, agriculture, food, and home and personal care products. However, plants produce triterpenoids in low abundance, and their complex structures make their chemical synthesis prohibitively expensive and often impossible. As such, the yeast Saccharomyces cerevisiae has been explored as an alternative means of production. An important triterpenoid is oleanolic acid because it is the precursor to many bioactive triterpenoids of commercial interest, such as QS-21 which is being evaluated as a vaccine adjuvant in clinical trials against HIV and malaria. Oleanolic acid is derived from 2,3-oxidosqualene (natively produced by yeast) via a cyclisation and a multi-step oxidation reaction, catalysed by a β-amyrin synthase and a cytochrome P450 of the CYP716A subfamily, respectively. Although many homologues have been characterised, previous studies have used arbitrarily chosen β-amyrin synthases and CYP716As to produce oleanolic acid and its derivatives in yeast. This study presents the first comprehensive comparison of β-amyrin synthase and CYP716A enzyme activities in yeast. Strains expressing different homologues are compared for production, revealing 6.3- and 4.5-fold differences in β-amyrin and oleanolic acid productivities and varying CYP716A product profiles, which are important to consider when engineering strains for the production of bioactive oleanolic acid derivatives.

Long-term voluntary running prevents the onset of symptomatic Friedreich's ataxia in mice

The common clinical symptoms of Friedreich's ataxia (FRDA) include ataxia, muscle weakness, type 2 diabetes and heart failure, which are caused by impaired mitochondrial function due to the loss of frataxin (FXN) expression. Endurance exercise is the most powerful intervention for promoting mitochondrial function; however, its impact on FRDA has not been studied. Here we found that mice with genetic knockout and knock-in of the Fxn gene (KIKO mice) developed exercise intolerance, glucose intolerance and moderate cardiac dysfunction at 6 months of age. These abnormalities were associated with impaired mitochondrial respiratory function concurrent with reduced iron regulatory protein 1 (Irp1) expression as well as increased oxidative stress, which were not due to loss of mitochondrial content and antioxidant enzyme expression. Importantly, long-term (4 months) voluntary running in KIKO mice starting at a young age (2 months) completely prevented the functional abnormalities along with restored Irp1 expression, improved mitochondrial function and reduced oxidative stress in skeletal muscle without restoring Fxn expression. We conclude that endurance exercise training prevents symptomatic onset of FRDA in mice associated with improved mitochondrial function and reduced oxidative stress. These preclinical findings may pave the way for clinical studies of the impact of endurance exercise in FRDA patients.

The NRF2 Signaling Network Defines Clinical Biomarkers and Therapeutic Opportunity in Friedreich's Ataxia

Friedreich’s ataxia (FA) is a trinucleotide repeats expansion neurodegenerative disorder, for which no cure or approved therapies are present. In most cases, GAA trinucleotide repetitions in the first intron of the FXN gene are the genetic trigger of FA, determining a strong reduction of frataxin, a mitochondrial protein involved in iron homeostasis. Frataxin depletion impairs iron–sulfur cluster biosynthesis and determines iron accumulation in the mitochondria. Mounting evidence suggests that these defects increase oxidative stress susceptibility and reactive oxygen species production in FA, where the pathologic picture is worsened by a defective regulation of the expression and signaling pathway modulation of the transcription factor NF-E2 p45-related factor 2 (NRF2), one of the fundamental mediators of the cellular antioxidant response. NRF2 protein downregulation and impairment of its nuclear translocation can compromise the adequate cellular response to the frataxin depletion-dependent redox imbalance. As NRF2 stability, expression, and activation can be modulated by diverse natural and synthetic compounds, efforts have been made in recent years to understand if regulating NRF2 signaling might ameliorate the pathologic defects in FA. Here we provide an analysis of the pharmaceutical interventions aimed at restoring the NRF2 signaling network in FA, elucidating specific biomarkers useful for monitoring therapeutic effectiveness, and developing new therapeutic tools.

Frameless Stereotactic Targeting of the Cerebellar Dentate Nucleus in Nonhuman Primates: Translatable Model for the Surgical Delivery of Gene Therapy

BACKGROUND

Stereotactic targeting techniques in nonhuman primate (NHP) models are often utilized in the preclinical investigation of new drug therapies with the goal of demonstrating accurate and reliable delivery of a therapy to the target tissue. However, targeting certain neuroanatomical structures can be challenging. The deep cerebellar nuclei, specifically the dentate nucleus, are potential stereotactic targets for the treatment of certain ataxias. Currently, there are no detailed techniques describing frameless targeting of these structures in a NHP model. A well-defined, accurate, and reliable stereotactic surgical approach to the dentate in these animal models is critical to prove the feasibility and safety of drug delivery in order to develop clinical protocols.

METHODS

Frameless stereotactic neuronavigation was employed to target the bilateral dentate nuclei of the cerebellum in four healthy juvenile Cynomolgus monkeys via a suboccipital, transcerebellar approach. The precision and accuracy of the targeting were evaluated radiologically and histologically.

RESULTS

Using the described surgical methodology, we were successful in hitting the target deep cerebellar nuclei seven out of eight times.

CONCLUSION

Frameless stereotactic targeting of the cerebellar dentate nuclei in NHPs for future investigational drug delivery is feasible, safe, and accurate as described by this report. Potential areas for improving the technique are discussed.

SINEUP non-coding RNAs rescue defective frataxin expression and activity in a cellular model of Friedreich's Ataxia

Friedreich's ataxia (FRDA) is an untreatable disorder with neuro- and cardio-degenerative progression. This monogenic disease is caused by the hyper-expansion of naturally occurring GAA repeats in the first intron of the FXN gene, encoding for frataxin, a protein implicated in the biogenesis of iron-sulfur clusters. As the genetic defect interferes with FXN transcription, FRDA patients express a normal frataxin protein but at insufficient levels. Thus, current therapeutic strategies are mostly aimed to restore physiological FXN expression. We have previously described SINEUPs, natural and synthetic antisense long non-coding RNAs, which promote translation of partially overlapping mRNAs through the activity of an embedded SINEB2 domain. Here, by in vitro screening, we have identified a number of SINEUPs targeting human FXN mRNA and capable to up-regulate frataxin protein to physiological amounts acting at the post-transcriptional level. Furthermore, FXN-specific SINEUPs promote the recovery of disease-associated mitochondrial aconitase defects in FRDA-derived cells. In summary, we provide evidence that SINEUPs may be the first gene-specific therapeutic approach to activate FXN translation in FRDA and, more broadly, a novel scalable platform to develop new RNA-based therapies for haploinsufficient diseases.

Orphan Drugs In Development For The Treatment Of Friedreich's Ataxia: Focus On Omaveloxolone

Friedreich’s Ataxia (FRDA) is a devastating and progressive ataxia, marked by mitochondrial dysfunction and oxidative stress. Nrf2 activators such as omaveloxolone (Omav) modulate antioxidative mechanisms, and thus may be viable therapeutic agents in FRDA.

Evaluation of antibodies for western blot analysis of frataxin protein isoforms

Frataxin is the protein that is down-regulated in Friedreich ataxia (FRDA), an autosomal recessive genetic disease caused by an intronic GAA repeat expansion in intron-1 of the FXN gene. The GAA repeats result in epigenetic silencing of the FXN gene and reduced expression of the cytosolic full-length frataxin (1-210) protein. Full length frataxin translocates to the mitochondria, leading to formation of mature frataxin (81-210) formed by cleavage of the mitochondrial targeting sequence at K-80 of the full-length protein. There are currently no approved treatments for FRDA, although experimental approaches involving up-regulation or replacement of mature frataxin protein through numerous approaches are being tested. Many of the pre-clinical studies of these experimental approaches are conducted in mouse and monkey models as well as in human cell lines. Consequently, well-validated antibodies are required for use in western blot analysis to determine whether levels of various forms of frataxin have been increased. Here we examined the specificity of five commercially available anti-frataxin antibodies and determined whether they detect mature frataxin in mouse heart tissue. Four protein standards of monkey, human, and mouse frataxin as well as mouse heart tissue were examined using polyacrylamide gel electrophoresis (PAGE) in combination with western blot analysis. One antibody failed to detect any of the frataxin standards or endogenous frataxin in mouse heart tissue. Three of the antibodies detected a protein in mouse heart tissue that ran slightly faster on PAGE (at 23.4 kDa) to that predicted for full-length frataxin (23.9 kDa). One antibody detected all four frataxin standards as well as endogenous mouse mature frataxin in mouse tissue. Significantly, this antibody, which will be useful for monitoring mature frataxin levels in monkey, human, and mouse tissues, did not detect a protein in mouse heart tissue at 23.4 kDa. Therefore, antibodies detecting the immunoreactive protein at 23.4 kDa could be misleading when testing for the up-regulation of frataxin in animal models.

Targeting NRF2 for the Treatment of Friedreich's Ataxia: A Comparison among Drugs

NRF2 (Nuclear factor Erythroid 2-related Factor 2) signaling is impaired in Friedreich's Ataxia (FRDA), an autosomal recessive disease characterized by progressive nervous system damage and degeneration of nerve fibers in the spinal cord and peripheral nerves. The loss of frataxin in patients results in iron sulfur cluster deficiency and iron accumulation in the mitochondria, making FRDA a fatal and debilitating condition. There are no currently approved therapies for the treatment of FRDA and molecules able to activate NRF2 have the potential to induce clinical benefits in patients. In this study, we compared the efficacy of six redox-active drugs, some already adopted in clinical trials, targeting NRF2 activation and frataxin expression in fibroblasts obtained from skin biopsies of FRDA patients. All of these drugs consistently increased NRF2 expression, but differential profiles of NRF2 downstream genes were activated. The Sulforaphane and N-acetylcysteine were particularly effective on genes involved in preventing inflammation and maintaining glutathione homeostasis, the dimethyl fumarate, omaxevolone, and EPI-743 in counteracting toxic products accumulation, the idebenone in mitochondrial protection. This study may contribute to develop synergic therapies, based on a combination of treatment molecules.

Health-related quality of life and depressive symptoms in Friedreich ataxia

PURPOSE

Friedreich ataxia (FRDA) is a chronic, progressive and highly disabling cerebellar degenerative disease. Despite this, little attention has been paid to the health-related quality of life (HRQOL) in this disease. The aim of the present study was to assess FRDA patients' perception of HRQOL and to determine the influence of depression, and demographic and clinical variables.

METHOD

The sample consisted of 62 patients with genetically confirmed FRDA. The SF-36 Health Survey was used to assess HRQOL. Depressive symptoms were evaluated with the Beck Depression Inventory-II.

RESULTS

FRDA patients' mean scores were significantly lower than the values for the Spanish population in all SF36 dimensions. Average z scores ranged from - 5.5 in physical functioning to - 0.48 in mental health. Age and clinical variables were significant predictors of HRQOL in only several dimensions, whereas BDI scores were able to predict a significant percentage of variance in all SF36 dimensions, except physical functioning.

CONCLUSIONS

Our study demonstrates the high impact of Friedreich ataxia on quality of life. This impact does not only occur in those aspects most related to motor disability but it is also present in non-motor dimensions. Depressive symptomatology is the most relevant variable for predicting quality of life.

New developments in pharmacotherapy for Friedreich ataxia

Introduction: Friedreich ataxia (FRDA), a rare disease caused by the deficiency of the mitochondrial matrix protein frataxin, affects roughly 1 in 50,000 individuals worldwide. Current and emerging therapies focus on reversing the deleterious effects of such deficiency including mitochondrial augmentation and increasing frataxin levels, providing the possibility of treatment options for this physiologically complex, multisystem disorder. Areas covered: In this review article, the authors discuss the current and prior in vivo and in vitro research studies related to the treatment of FRDA, with a particular interest in future implications of each therapy. Expert opinion: Since the discovery of FXN in 1996, multiple clinical trials have occurred or are currently occurring; at a rapid pace for a rare disease. These trials have been directed at the augmentation of mitochondrial function and/or alleviation of symptoms and are not regarded as potential cures in FRDA. Either a combination of therapies or a drug that replaces or increases the pathologically low levels of frataxin better represent potential cures in FRDA.

The current state of biomarker research for Friedreich's ataxia: a report from the 2018 FARA biomarker meeting

The 2018 FARA Biomarker Meeting highlighted the current state of development of biomarkers for Friedreich’s ataxia. A mass spectroscopy assay to sensitively measure mature frataxin (reduction of which is the root cause of disease) is being developed. Biomarkers to monitor neurological disease progression include imaging, electrophysiological measures and measures of nerve function, which may be measured either in serum and/or through imaging-based technologies. Potential pharmacodynamic biomarkers include metabolic and protein biomarkers and markers of nerve damage. Cardiac imaging and serum biomarkers may reflect cardiac disease progression. Considerable progress has been made in the development of biomarkers for various contexts of use, but further work is needed in terms of larger longitudinal multisite studies, and identification of novel biomarkers for additional use cases

Biomarkers are characteristics that can be objectively measured, evaluated and used as indicators of disease progression or the effect of a therapy. Friedreich’s ataxia is a progressive multisystem neuromuscular disease with no treatment. Current clinical measures cannot robustly detect disease progression in less than a year, meaning that clinical trials are long and drug development is slow. The Friedreich’s Ataxia Research Alliance and the scientific community are looking for biomarkers that show change in shorter time frames that can accelerate drug development. The 2018 FARA Biomarker Meeting summarized the exciting findings that represent the current state of the field.

Dimethyl fumarate dosing in humans increases frataxin expression: A potential therapy for Friedreich's Ataxia

Friedreich's Ataxia (FA) is an inherited neurodegenerative disorder resulting from decreased expression of the mitochondrial protein frataxin, for which there is no approved therapy. High throughput screening of clinically used drugs identified Dimethyl fumarate (DMF) as protective in FA patient cells. Here we demonstrate that DMF significantly increases frataxin gene (FXN) expression in FA cell model, FA mouse model and in DMF treated humans. DMF also rescues mitochondrial biogenesis deficiency in FA-patient derived cell model. We further examined the mechanism of DMF's frataxin induction in FA patient cells. It has been shown that transcription-inhibitory R-loops form at GAA expansion mutations, thus decreasing FXN expression. In FA patient cells, we demonstrate that DMF significantly increases transcription initiation. As a potential consequence, we observe significant reduction in both R-loop formation and transcriptional pausing thereby significantly increasing FXN expression. Lastly, DMF dosed Multiple Sclerosis (MS) patients showed significant increase in FXN expression by ~85%. Since inherited deficiency in FXN is the primary cause of FA, and DMF is demonstrated to increase FXN expression in humans, DMF could be considered for Friedreich's therapy.

GRP75 overexpression rescues frataxin deficiency and mitochondrial phenotypes in Friedreich ataxia cellular models

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused by the deficiency of frataxin, a mitochondrial protein crucial for iron-sulfur cluster biogenesis and adenosine triphosphate (ATP) production. Currently, there is no therapy to slow down the progression of FRDA. Recent evidence indicates that posttranslational regulation of residual frataxin levels can rescue some of the functional deficit of FRDA, raising the possibility of enhancing levels of residual frataxin as a treatment for FRDA. Here, we present evidence that mitochondrial molecular chaperone GRP75, also known as mortalin/mthsp70/PBP74, directly interacts with frataxin both in vivo in mouse cortex and in vitro in cortical neurons. Overexpressing GRP75 increases the levels of both wild-type frataxin and clinically relevant missense frataxin variants in human embryonic kidney 293 cells, while clinical GRP75 variants such as R126W, A476T and P509S impair the binding of GRP75 with frataxin and the effect of GRP75 on frataxin levels. In addition, GRP75 overexpression rescues frataxin deficiency and abnormal cellular phenotypes such as the abnormal mitochondrial network and decreased ATP levels in FRDA patient-derived cells. The effect of GRP75 on frataxin might be in part mediated by the physical interaction between GRP75 and mitochondrial processing peptidase (MPP), which makes frataxin more accessible to MPP. As GRP75 levels are decreased in multiple cell types of FRDA patients, restoring GRP75 might be effective in treating both typical FRDA patients with two guanine-adenine-adenine repeat expansions and compound heterozygous patients with point mutations.

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.

Phosphodiesterase Inhibitors Revert Axonal Dystrophy in Friedreich's Ataxia Mouse Model

Friedreich's ataxia (FRDA) is a neurodegenerative disorder caused by an unstable GAA repeat expansion within intron 1 of the FXN gene and characterized by peripheral neuropathy. A major feature of FRDA is frataxin deficiency with the loss of large sensory neurons of the dorsal root ganglia (DRG), namely proprioceptive neurons, undergoing dying-back neurodegeneration with progression to posterior columns of the spinal cord and cerebellar ataxia. We used isolated DRGs from a YG8R FRDA mouse model and C57BL/6J control mice for a proteomic study and a primary culture of sensory neurons from DRG to test novel pharmacological strategies. We found a decreased expression of electron transport chain (ETC) proteins, the oxidative phosphorylation (OXPHOS) system and antioxidant enzymes, confirming a clear impairment in mitochondrial function and an oxidative stress-prone phenotype. The proteomic profile also showed a decreased expression in Ca2+ signaling related proteins and G protein-coupled receptors (GPCRs). These receptors modulate intracellular cAMP/cGMP and Ca2+ levels. Treatment of frataxin-deficient sensory neurons with phosphodiesterase (PDE) inhibitors was able to restore improper cytosolic Ca2+ levels and revert the axonal dystrophy found in DRG neurons of YG8R mice. In conclusion, the present study shows the effectiveness of PDE inhibitors against axonal degeneration of sensory neurons in YG8R mice. Our findings indicate that PDE inhibitors may become a future FRDA pharmacological treatment.

Targeted Oligonucleotides for Treating Neurodegenerative Tandem Repeat Diseases

Nucleotide repeat disorders encompass more than 30 diseases, most of which show dominant inheritance, such as Huntington's disease, spinocerebellar ataxias, and myotonic dystrophies. Yet others, including Friedreich's ataxia, are recessively inherited. A common feature is the presence of a DNA tandem repeat in the disease-associated gene and the propensity of the repeats to expand in germ and in somatic cells, with ensuing neurological and frequently also neuromuscular defects. Repeat expansion is the most frequent event in these diseases; however, sequence contractions, deletions, and mutations have also been reported. Nucleotide repeat sequences are predisposed to adopt non-B-DNA conformations, such as hairpins, cruciform, and intramolecular triple-helix structures (triplexes), also known as H-DNA. For gain-of-function disorders, oligonucleotides can be used to target either transcripts or duplex DNA and in diseases with recessive inheritance oligonucleotides may be used to alter repressive DNA or RNA conformations. Most current treatment strategies are aimed at altering transcript levels, but therapies directed against DNA are also emerging, and novel strategies targeting DNA, instead of RNA, are described. Different mechanisms using modified oligonucleotides are discussed along with the structural aspects of repeat sequences, which can influence binding modes and efficiencies.

Therapeutic Prospects for Friedreich's Ataxia

Friedreich's ataxia (FRDA) is a progressive disease affecting multiple organs that is caused by systemic insufficiency of the mitochondrial protein frataxin. Current therapeutic strategies aim to elevate frataxin levels and/or alleviate the consequences of frataxin deficiency. Recent significant advances in the FRDA therapeutic pipeline are bringing patients closer to a cure.

Drug repositioning screening identifies etravirine as a potential therapeutic for friedreich's ataxia

BACKGROUND

Friedreich's ataxia is an autosomal-recessive cerebellar ataxia caused by mutation of the frataxin gene, resulting in decreased frataxin expression, mitochondrial dysfunction, and oxidative stress. Currently, no treatment is available for Friedreich's ataxia patients. Given that levels of residual frataxin critically affect disease severity, the main goal of a specific therapy for Friedreich's ataxia is to increase frataxin levels.

OBJECTIVES

With the aim to accelerate the development of a new therapy for Friedreich's ataxia, we took a drug repositioning approach to identify market-available drugs able to increase frataxin levels.

METHODS

Using a cell-based reporter assay to monitor variation in frataxin amount, we performed a high-throughput screening of a library containing 853 U.S. Food and Drug Administration-approved drugs.

RESULTS

Among the potentially interesting candidates isolated from the screening, we focused our attention on etravirine, an antiviral drug currently in use as an anti-human immunodeficiency virus therapy. Here, we show that etravirine can promote a significant increase in frataxin levels in cells derived from Friedreich's ataxia patients, by enhancing frataxin messenger RNA translation. Importantly, frataxin accumulation in treated patient cell lines is comparable to frataxin levels in unaffected carrier cells, suggesting that etravirine could be therapeutically relevant. Indeed, etravirine treatment restores the activity of the iron-sulphur cluster containing enzyme aconitase and confers resistance to oxidative stress in cells derived from Friedreich's ataxia patients.

CONCLUSIONS

Considering its excellent safety profile along with its ability to increase frataxin levels and correct some of the disease-related defects, etravirine represents a promising candidate as a therapeutic for Friedreich's ataxia. © 2019 International Parkinson and Movement Disorder Society.

Randomized, double-blind, placebo-controlled study of interferon-γ 1b in Friedreich Ataxia

Objective

In vitro, in vivo, and open-label studies suggest that interferon gamma (IFN-γ 1b) may improve clinical features in Friedreich Ataxia through an increase in frataxin levels. The present study evaluates the efficacy and safety of IFN-γ 1b in the treatment of Friedreich Ataxia through a double-blind, multicenter, placebo-controlled trial.

Methods

Ninety-two subjects with FRDA between 10 and 25 years of age were enrolled. Subjects received either IFN-γ 1b or placebo for 6 months. The primary outcome measure was the modified Friedreich Ataxia Rating Scale (mFARS).

Results

No difference was noted between the groups after 6 months of treatment in the mFARS or secondary outcome measures. No change was noted in buccal cell or whole blood frataxin levels. However, during an open-label extension period, subjects had a more stable course than expected based on natural history data.

Conclusions

This study provides no direct evidence for a beneficial effect of IFN-γ1b in FRDA. The modest stabilization compared to natural history data leaves open the possibility that longer studies may demonstrate benefit.

The Role of Iron in Friedreich's Ataxia: Insights From Studies in Human Tissues and Cellular and Animal Models

Friedreich’s ataxia (FRDA) is a rare early-onset degenerative disease that affects both the central and peripheral nervous systems, and other extraneural tissues, mainly the heart and endocrine pancreas. This disorder progresses as a mixed sensory and cerebellar ataxia, primarily disturbing the proprioceptive pathways in the spinal cord, peripheral nerves and nuclei of the cerebellum. FRDA is an inherited disease with an autosomal recessive pattern caused by an insufficient amount of the nuclear-encoded mitochondrial protein frataxin, which is an essential and highly evolutionary conserved protein whose deficit results in iron metabolism dysregulation and mitochondrial dysfunction. The first experimental evidence connecting frataxin with iron homeostasis came from Saccharomyces cerevisiae; iron accumulates in the mitochondria of yeast with deletion of the frataxin ortholog gene. This finding was soon linked to previous observations of iron deposits in the hearts of FRDA patients and was later reported in animal models of the disease. Despite advances made in the understanding of FRDA pathophysiology, the role of iron in this disease has not yet been completely clarified. Some of the questions still unresolved include the molecular mechanisms responsible for the iron accumulation and iron-mediated toxicity. Here, we review the contribution of the cellular and animal models of FRDA and relevance of the studies using FRDA patient samples to gain knowledge about these issues. Mechanisms of mitochondrial iron overload are discussed considering the potential roles of frataxin in the major mitochondrial metabolic pathways that use iron. We also analyzed the effect of iron toxicity on neuronal degeneration in FRDA by reactive oxygen species (ROS)-dependent and ROS-independent mechanisms. Finally, therapeutic strategies based on the control of iron toxicity are considered.

Mitochondrial Iron in Human Health and Disease

Mitochondria are an iconic distinguishing feature of eukaryotic cells. Mitochondria encompass an active organellar network that fuses, divides, and directs a myriad of vital biological functions, including energy metabolism, cell death regulation, and innate immune signaling in different tissues. Another crucial and often underappreciated function of these dynamic organelles is their central role in the metabolism of the most abundant and biologically versatile transition metals in mammalian cells, iron. In recent years, cellular and animal models of mitochondrial iron dysfunction have provided vital information in identifying new proteins that have elucidated the pathways involved in mitochondrial homeostasis and iron metabolism. Specific signatures of mitochondrial iron dysregulation that are associated with disease pathogenesis and/or progression are becoming increasingly important. Understanding the molecular mechanisms regulating mitochondrial iron pathways will help better define the role of this important metal in mitochondrial function and in human health and disease.

Impact of Drosophila Models in the Study and Treatment of Friedreich's Ataxia

Drosophila melanogaster has been for over a century the model of choice of several neurobiologists to decipher the formation and development of the nervous system as well as to mirror the pathophysiological conditions of many human neurodegenerative diseases. The rare disease Friedreich’s ataxia (FRDA) is not an exception. Since the isolation of the responsible gene more than two decades ago, the analysis of the fly orthologue has proven to be an excellent avenue to understand the development and progression of the disease, to unravel pivotal mechanisms underpinning the pathology and to identify genes and molecules that might well be either disease biomarkers or promising targets for therapeutic interventions. In this review, we aim to summarize the collection of findings provided by the Drosophila models but also to go one step beyond and propose the implications of these discoveries for the study and cure of this disorder. We will present the physiological, cellular and molecular phenotypes described in the fly, highlighting those that have given insight into the pathology and we will show how the ability of Drosophila to perform genetic and pharmacological screens has provided valuable information that is not easily within reach of other cellular or mammalian models.

Clinical and genetic aspects of defects in the mitochondrial iron-sulfur cluster synthesis pathway

Iron-sulfur clusters are evolutionarily conserved biological structures which play an important role as cofactor for multiple enzymes in eukaryotic cells. The biosynthesis pathways of the iron-sulfur clusters are located in the mitochondria and in the cytosol. The mitochondrial iron-sulfur cluster biosynthesis pathway (ISC) can be divided into at least twenty enzymatic steps. Since the description of frataxin deficiency as the cause of Friedreich's ataxia, multiple other deficiencies in ISC biosynthesis pathway have been reported. In this paper, an overview is given of the clinical, biochemical and genetic aspects reported in humans affected by a defect in iron-sulfur cluster biosynthesis.

Progress in the treatment of Friedreich ataxia

Friedreich ataxia (FRDA) is a progressive neurological disorder affecting approximately 1 in 29,000 individuals of European descent. At present, there is no approved pharmacological treatment for this condition however research into treatment of FRDA has advanced considerably over the last two decades since the genetic cause was identified. Current proposed treatment strategies include decreasing oxidative stress, increasing cellular frataxin, improving mitochondrial function as well as modulating frataxin controlled metabolic pathways. Genetic and cell based therapies also hold great promise. Finally, physical therapies are being explored as a means of maximising function in those affected by FRDA.