Pharmacologic approaches to the treatment of Huntington's disease

Experiences of young people growing up in a family with Huntington's disease: A meta-ethnography of qualitative research

Huntington's disease is a genetic neurodegenerative condition with wide physical and psychological impacts. Children of a parent with the condition have a 50% chance of carrying the gene expansion and developing the condition themselves. This systematic review and meta-ethnography presents a synthesis of the qualitative research on the experiences of young people growing up in a family with Huntington's disease. The MEDLINE, PsycINFO, and CINAHL databases were systematically searched, and 13 papers met the inclusion criteria. Through the process of meta-ethnography, four themes were identified highlighting aspects of childhood that were stolen and fought for: thief of relationships, thief of self, thief of transparency, and search for reclamation. Within the themes, the complex challenges young people faced when growing up in a HD family were explored such as the impact of adverse childhood experiences and the possible effects of HD on attachment and social relationships. Clinical implications are considered, and recommendations are made for future research.

Translational Approach using Advanced Therapy Medicinal Products for Huntington's Disease

Current therapeutic approaches for Huntington's disease (HD) focus on symptomatic treatment. Therefore, the unavailability of efficient disease-modifying medicines is a significant challenge. Regarding the molecular etiology, targeting the mutant gene or advanced translational steps could be considered promising strategies. The evidence in gene therapy suggests various molecular techniques, including knocking down mHTT expression using antisense oligonucleotides and small interfering RNAs and gene editing with zinc finger proteins and CRISPR-Cas9-based techniques. Several post-transcriptional and post-translational modifications have also been proposed. However, the efficacy and long-term side effects of these modalities have yet to be verified. Currently, cell therapy can be employed in combination with conventional treatment and could be used for HD in which the structural and functional restoration of degenerated neurons can occur. Several animal models have been established recently to develop cell-based therapies using renewable cell sources such as embryonic stem cells, induced pluripotent stem cells, mesenchymal stromal cells, and neural stem cells. These models face numerous challenges in translation into clinics. Nevertheless, investigations in Advanced Therapy Medicinal Products (ATMPs) open a promising window for HD research and their clinical application. In this study, the ATMPs entry pathway in HD management was highlighted, and their advantages and disadvantages were discussed.

Green synthesis of nanoparticles using medicinal plants as an eco-friendly and therapeutic potential approach for neurodegenerative diseases: a comprehensive review

Central nervous system disorders impact over 1.5 billion individuals globally, with neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's diseases being particularly prominent. These conditions, often associated with aging, present debilitating symptoms including memory loss and movement difficulties. The growing incidence of neurological disorders, alongside a scarcity of effective anti-amyloidogenic therapies, highlights an urgent need for innovative treatment methodologies. Nanoparticles (NPs), derived from medicinal plants and characterized by their favorable pharmacological properties and minimal side effects, offer a promising solution. Their inherent attributes allow for successful traversal of the blood-brain barrier (BBB), enabling targeted delivery to the brain and the modulation of specific molecular pathways involved in neurodegeneration. NPs are crucial in managing oxidative stress, apoptosis, and neuroinflammation in ND. This study reviews the efficacy of green-synthesized nanoparticles in conjunction with various medicinal plants for treating neurodegenerative diseases, advocating for further research to refine these formulations for enhanced clinical applicability and improved patient outcomes.

Real-world experience with Deutetrabenazine management in patients with Huntington's disease using video-based telemedicine

BACKGROUND

Huntington's disease (HD) is a rare progressive neurological disorder, and telemedicine has the potential to improve the quality of care for patients with HD. Deutetrabenazine (DTBZ) can reduce chorea symptoms in HD; however, there is limited experience with this medication in Asian countries.

METHODS

Retrospective and prospective studies were employed to explore the feasibility and reliability of a video-based telemedicine system for HD patient care. Reliability was demonstrated through consistency between selected-item scores (SIS) and total motor scores (TMS) and the agreement of scores obtained from hospital and home videos. Finally, a single-centre real-world DTBZ management study was conducted based on the telemedicine system to explore the efficacy of DTBZ in patients with HD.

RESULTS

There were 77 patients included in the retrospective study, and a strong correlation was found between SIS and TMS (r = 0.911, P < 0.0001), indicating good representativeness. There were 32 patients enrolled in the prospective study. The reliability was further confirmed, indicated by correlations between SIS and TMS (r = 0.964, P < 0.0001) and consistency of SIS derived from the in-person and virtual visits (r = 0.969, P < 0.0001). There were 17 patients included in the DTBZ study with a mean 1.41 (95% confidence interval, 0.37-2.46) improvement in chorea score and reported treatment success.

CONCLUSIONS

A video-based telemedicine system is a feasible and reliable option for HD patient care. It may also be used for drug management as a supplementary tool for clinical visits.

Locomotor Behavior and Memory Dysfunction Induced by 3-Nitropropionic Acid in Adult Zebrafish: Modulation of Dopaminergic Signaling

Huntington's disease (HD) is a progressive neurodegenerative disease characterized by neuropsychiatric disturbance, cognitive impairment, and locomotor dysfunction. In the early stage (chorea) of HD, expression of dopamine D2 receptors (D2R) is reduced, whereas dopamine (DA) levels are increased. Contrary, in the late stage (bradykinesia), DA levels and the expression of D2R and dopamine D1 receptors (D1R) are reduced. 3-Nitropropionic acid (3-NPA) is a toxin that may replicate HD behavioral phenotypes and biochemical aspects. This study assessed the neurotransmitter levels, dopamine receptor gene expression, and the effect of acute exposure to quinpirole (D2R agonist) and eticlopride (D2R antagonist) in an HD model induced by 3-NPA in adult zebrafish. Quinpirole and eticlopride were acutely applied by i.p. injection in adult zebrafish after chronic treatment of 3-NPA (60 mg/kg). 3-NPA treatment caused a reduction in DA, glutamate, and serotonin levels. Quinpirole reversed the bradykinesia and memory loss induced by 3-NPA. Together, these data showed that 3-NPA acts on the dopaminergic system and causes biochemical alterations similar to late-stage HD. These data reinforce the hypothesis that DA levels are linked with locomotor and memory deficits. Thus, these findings may suggest that the use of DA agonists could be a pharmacological strategy to improve the bradykinesia and memory deficits in the late-stage HD.

Gut microbiota dysbiosis and Huntington's disease: Exploring the gut-brain axis and novel microbiota-based interventions

Huntington's disease (HD) is a complex progressive neurodegenerative disorder affected by genetic, environmental, and metabolic factors contributing to its pathogenesis. Gut dysbiosis is termed as the alterations of intestinal microbial profile. Emerging research has highlighted the pivotal role of gut dysbiosis in HD, focusing on the gut-brain axis as a novel research parameter in science. This review article provides a comprehensive overview of gut microbiota dysbiosis and its relationship with HD and its pathogenesis along with the future challenges and opportunities. The focuses on the essential mechanisms which link gut dysbiosis to HD pathophysiology including neuroinflammation, immune system dysregulation, altered metabolites composition, and neurotransmitter imbalances. We also explored the impacts of gut dysbiosis on HD onset, severity, and symptoms such as cognitive decline, motor dysfunction, and psychiatric symptoms. Furthermore, we highlight recent advances in therapeutics including microbiota-based therapeutic approaches, including dietary interventions, prebiotics, probiotics, fecal microbiota transplantation, and combination therapies with conventional HD treatments and their applications in managing HD. The future challenges are also highlighted as the heterogeneity of gut microbiota, interindividual variability, establishing causality between gut dysbiosis and HD, identifying optimal therapeutic targets and strategies, and ensuring the long-term safety and efficacy of microbiota-based interventions. This review provides a better understanding of the potential role of gut microbiota in HD pathogenesis and guides the development of novel therapeutic approaches.

Kaempferol, a potential neuroprotective agent in neurodegenerative diseases: From chemistry to medicine

Neurodegenerative diseases (NDDs) encompass a range of conditions that involve progressive deterioration and dysfunction of the nervous system. Some of the common NDDs include Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). Although significant progress has been made in understanding the pathological mechanisms of NDDs in recent years, the development of targeted and effective drugs for their treatment remains challenging. Kaempferol is a flavonoid whose derivatives include kaempferol-O-rhamnoside, 3-O-β-rutinoside/6-hydroxykaempferol 3,6-di-O-β-d-glucoside, and kaempferide. Emerging studies have suggested that kaempferol and its derivatives possess neuroprotective properties and may have potential therapeutic benefits in NDDs. Here, we aimed to provide a theoretical basis for the use of kaempferol and its derivatives in the clinical treatment of NDDs. We systematically reviewed the literature in the PubMed, Web of Science, and Science Direct databases until June 2022 using the search terms "kaempferol," "kaempferol derivatives," "NDDs," "pharmacokinetics," and "biosynthesis" according to the reporting items for systematic review (PRISMA) standard. Based on combined results of in vivo and in vitro studies, we summarize the basic mechanisms and targets of kaempferol and its derivatives in the management of AD, PD, HD, and ALS. Kaempferol and its derivatives exert a neuroprotective role mainly by preventing the deposition of amyloid fibrils (such as Aβ, tau, and α-synuclein), inhibiting microglia activation, reducing the release of inflammatory factors, restoring the mitochondrial membrane to prevent oxidative stress, protecting the blood-brain barrier, and inhibiting specific enzyme activities (such as cholinesterase). Kaempferol and its derivatives are promising natural neuroprotective agents. By determining their pharmacological mechanism, kaempferol and its derivatives may be new candidate drugs for the treatment of NDDs.

Nanoparticle-Guided Brain Drug Delivery: Expanding the Therapeutic Approach to Neurodegenerative Diseases

Neurodegenerative diseases (NDs) represent a heterogeneous group of aging-related disorders featured by progressive impairment of motor and/or cognitive functions, often accompanied by psychiatric disorders. NDs are denoted as 'protein misfolding' diseases or proteinopathies, and are classified according to their known genetic mechanisms and/or the main protein involved in disease onset and progression. Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD) are included under this nosographic umbrella, sharing histopathologically salient features, including deposition of insoluble proteins, activation of glial cells, loss of neuronal cells and synaptic connectivity. To date, there are no effective cures or disease-modifying therapies for these NDs. Several compounds have not shown efficacy in clinical trials, since they generally fail to cross the blood-brain barrier (BBB), a tightly packed layer of endothelial cells that greatly limits the brain internalization of endogenous substances. By engineering materials of a size usually within 1-100 nm, nanotechnology offers an alternative approach for promising and innovative therapeutic solutions in NDs. Nanoparticles can cross the BBB and release active molecules at target sites in the brain, minimizing side effects. This review focuses on the state-of-the-art of nanoengineered delivery systems for brain targeting in the treatment of AD, PD and HD.

Pridopidine for the Improvement of Motor Function in Patients With Huntington's Disease: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Huntington's disease (HD) is a progressive neurodegenerative disorder. Generally, it is characterized by deficits in cognition, behavior, and movement. Recent studies have shown that pridopidine is a potential and effective drug candidate for the treatment of HD. In the present study, we performed a meta-analysis to evaluate the efficacy and safety of pridopidine in HD.

Methods: The MEDLINE, EMBASE, CENTRAL, and Clinicaltrials.gov databases were searched for randomized controlled trials (RCTs) which had that evaluated pridopidine therapy in HD patients.

Results: We pooled data from 1,119 patients across four RCTs. Patients in the pridopidine group had a significantly lower Unified Huntington's Disease Rating Scale (UHDRS)-modified Motor Score (mMS) (MD −0.79, 95% CI = −1.46 to −0.11, p = 0.02) than those in the placebo group. Additionally, no differences were observed in the UHDRS-Total Motor Score (TMS) (MD −0.91. 95% CI = −2.03 to 0.21, p = 0.11) or adverse events (RR 1.06, 95% CI = 0.96 to 1.16, p = 0.24) in the pridopidine and placebo groups. In the subgroup analysis, the short-term (≤12 weeks) and long-term (>12 weeks) subgroups exhibited similar efficacy and safety with no statistical significance in TMS, mMS, or adverse events. However, TMS (MD −1.50, 95% CI = −2.87 to −0.12, p = 0.03) and mMS (MD −1.03, 95% CI = −1.87 to −0.19, p = 0.02) were observed to be improved significantly when the dosage of pridopidine ≥90 mg/day. Additionally, pridopidine (≥90 mg/day) increased total adverse events (RR 1.11, 95% CI = 1.00 to 1.22, p = 0.04) compared with placebo. On this basis, we analyzed the incidence of various adverse events when the dosage was ≥90 mg/day. Nonetheless, these results were within the acceptable threshold, although patients developed symptoms, such as nasopharyngitis and insomnia.

Conclusion: Pridopidine improved mMS and had no statistical significance in association with TMS or adverse events. Pridopidine (≥90 mg/day) improved TMS and mMS but increased adverse events, such as nasopharyngitis and insomnia. More RCTs were expected to assess pridopidine in HD.

Androgen Therapy in Neurodegenerative Diseases

Neurodegenerative diseases, including Alzheimer disease (AD), Parkinson disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), and Huntington disease, are characterized by the loss of neurons as well as neuronal function in multiple regions of the central and peripheral nervous systems. Several studies in animal models have shown that androgens have neuroprotective effects in the brain and stimulate axonal regeneration. The presence of neuronal androgen receptors in the peripheral and central nervous system suggests that androgen therapy might be useful in the treatment of neurodegenerative diseases. To illustrate, androgen therapy reduced inflammation, amyloid-β deposition, and cognitive impairment in patients with AD. As well, improvements in remyelination in MS have been reported; by comparison, only variable results are observed in androgen treatment of PD. In ALS, androgen administration stimulated motoneuron recovery from progressive damage and regenerated both axons and dendrites. Only a few clinical studies are available in human individuals despite the safety and low cost of androgen therapy. Clinical evaluations of the effects of androgen therapy on these devastating diseases using large populations of patients are strongly needed.

Dapagliflozin improves behavioral dysfunction of Huntington's disease in rats via inhibiting apoptosis-related glycolysis

AIMS

Huntington's disease is a rare neurodegenerative disorder which is associated with defected glucose metabolism with consequent behavioral disturbance including memory and locomotion. 3-nitropropionic acid (3-NP) can cause, in high single dose, an acute striatal injury/Huntington's disease. Dapagliflozin, which is one of the longest duration of action of SGLTIs family, may be able to diminish that injury and its resultant behavioral disturbances.

MATERIAL AND METHODS

Forty rats were divided into four groups (n = 10 in each group): normal control group (CTRL), dapagliflozin (CTRL + DAPA) group, 3-nitropropionic acid (3-NP) group, and dapagliflozin plus 3-nitropropionic acid (DAPA + 3-NP) group. Behavioral tests (beam walking test, hanging wire test, limb withdrawal test, Y-maze spontaneous alteration, elevated plus maze) were performed with evaluating neurological scoring. In striatum, neurotransmitters (glutamate, aspartate, GABA, ACh and AChE activity) were measured. In addition, apoptosis and glycolysis markers (NF-κB, Cyt-c, lactate, HK-II activity, P53, calpain, PEA15 and TIGAR) were determined. Inflammation (IL-1β, IL-6, IL-8 and TNF-α) and autophagy (beclin-1, LC3 and DRAM) indicators were measured. Additionally, histopathological screening was conducted.

KEY FINDINGS

3-Nitropropionic acid had the ability to perturb the neurotransmission which was reflected in impaired behavioral outcome. All of glycolysis, apoptosis and inflammation markers were elevated after 3-NP acute intoxication but autophagy parameters, except DRAM, were reduced. However, DAPA markedly reversed the abovementioned parameters.

SIGNIFICANCE

Dapagliflozin demonstrated anti-glycolytic, anti-apoptotic, anti-inflammatory and autophagic effects on 3-NP-damaged striatal cells and promoted the behavioral outcome.

International Guidelines for the Treatment of Huntington's Disease

The European Huntington's Disease Network (EHDN) commissioned an international task force to provide global evidence-based recommendations for everyday clinical practice for treatment of Huntington's disease (HD). The objectives of such guidelines are to standardize pharmacological, surgical and non-pharmacological treatment regimen and improve care and quality of life of patients. A formalized consensus method, adapted from the French Health Authority recommendations was used. First, national committees (French and English Experts) reviewed all studies published between 1965 and 2015 included dealing with HD symptoms classified in motor, cognitive, psychiatric, and somatic categories. Quality grades were attributed to these studies based on levels of scientific evidence. Provisional recommendations were formulated based on the strength and the accumulation of scientific evidence available. When evidence was not available, recommendations were framed based on professional agreement. A European Steering committee supervised the writing of the final recommendations through a consensus process involving two rounds of online questionnaire completion with international multidisciplinary HD health professionals. Patients' associations were invited to review the guidelines including the HD symptoms. Two hundred and nineteen statements were retained in the final guidelines. We suggest to use this adapted method associating evidence base-medicine and expert consensus to other rare diseases.

Perceptions of the impact of chorea on health-related quality of life in Huntington disease (HD): A qualitative analysis of individuals across the HD spectrum, family members, and clinicians

Chorea, a hallmark symptom of Huntington's disease (HD), is characterized by jerky involuntary movements affecting the whole body that can interfere with daily functioning and impact health-related quality of life (HRQOL). To characterize chorea's impact on everyday functioning and HRQOL and identify patterns of perception and experiences of chorea among patients, caregivers, and providers. Data from focus groups of individuals with manifest HD (n = 8 early-stage HD; n = 16 late-stage HD), individuals at-risk or prodromal HD (n = 16), family HD caregivers (n = 17), and HD clinicians (n = 25). Focus group recordings were transcribed verbatim and analysed via constant comparison to identify meaningful and salient themes of living with chorea. Global themes of chorea's impact identified included: watching for chorea, experiences of stigma, and constraints on independence and relationships. Themes distinct to specific respondent groups included: Vigilance (at risk, prodromal); adaptation to chorea (early-stage); loss of autonomy and social life (late-stage); monitoring engagement (family caregivers) and safety (clinical providers). Living with chorea significantly constrains daily functioning, interactions, and HRQOL across the HD disease spectrum. Addressing these impacts via appropriate management of chorea can potentially enhance functioning, HRQOL, and overall satisfaction for persons with HD and their families.

Treatment of neurodegenerative disorders through the blood-brain barrier using nanocarriers

Neurodegenerative diseases refer to disorders of the central nervous system (CNS) that are caused by neuronal degradations, dysfunctions, or death. Alzheimer's disease, Parkinson's disease, and Huntington's disease (APHD) are regarded as the three major neurodegenerative diseases. There is a vast body of literature on the causes and treatments of these neurodegenerative diseases. However, the main obstacle in developing an effective treatment strategy is the permeability of the treatment components at the blood-brain barrier (BBB). Several strategies have been developed to improve this obstruction. For example, nanomaterials facilitate drug delivery to the BBB due to their size. They have been used widely in nanomedicine and as nanoprobes for diagnosis purposes among others in neuroscience. Nanomaterials in different forms, such as nanoparticles, nanoemulsions, solid lipid nanoparticles (SLN), and liposomes, have been used to treat neurodegenerative diseases. This review will cover the basic concepts and applications of nanomaterials in the therapy of APHD.

Vocalisation as a Viable Assessment for Phenotyping Minipigs Transgenic for the Huntington Gene?

BACKGROUND

Large animal models, such as the transgenic (tg) Huntington disease (HD) minipig, have been proposed to improve translational reliability and assessment of safety, efficacy and tolerability in preclinical studies. Minipigs are characterised by high genetic homology and comparable brain structures to humans. In addition, behavioural assessments successfully applied in humans could be explored in minipigs to establish similar endpoints in preclinical and clinical studies. Recently, analysis of voice and speech production was established to characterise HD patients.

OBJECTIVE

The aim of this study was to investigate whether vocalisation could also serve as a viable marker for phenotyping minipigs transgenic for Huntington's disease (tgHD) and whether tgHD minipigs reveal changes in this domain compared to wildtype (wt) minipigs.

METHODS

While conducting behavioural testing, incidence of vocalisation was assessed for a cohort of 14 tgHD and 18 wt minipigs. Statistical analyses were performed using Fisher's Exact Test for group comparisons and McNemar's Test for intra-visit differences between tgHD and wt minipigs.

RESULTS

Vocalisation can easily be documented during phenotyping assessments of minipigs. Differences in vocalisation incidences across behavioural conditions were detected between tgHD and wt minipigs. Influence of the genotype on vocalisation was detectable during a period of 1.5 years.

CONCLUSION

Vocalisation may be a viable marker for phenotyping minipigs transgenic for the Huntington gene. Documentation of vocalisation provides a non-invasive opportunity to capture potential disease signs and explore phenotypic development including the age of disease manifestation.

AAV5-miHTT Gene Therapy Demonstrates Broad Distribution and Strong Human Mutant Huntingtin Lowering in a Huntington's Disease Minipig Model

Huntington’s disease (HD) is a fatal neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the huntingtin gene. Previously, we showed strong huntingtin reduction and prevention of neuronal dysfunction in HD rodents using an engineered microRNA targeting human huntingtin, delivered via adeno-associated virus (AAV) serotype 5 vector with a transgene encoding an engineered miRNA against HTT mRNA (AAV5-miHTT). One of the challenges of rodents as a model of neurodegenerative diseases is their relatively small brain, making successful translation to the HD patient difficult. This is particularly relevant for gene therapy approaches, where distribution achieved upon local administration into the parenchyma is likely dependent on brain size and structure. Here, we aimed to demonstrate the translation of huntingtin-lowering gene therapy to a large-animal brain. We investigated the feasibility, efficacy, and tolerability of one-time intracranial administration of AAV5-miHTT in the transgenic HD (tgHD) minipig model. We detected widespread dose-dependent distribution of AAV5-miHTT throughout the tgHD minipig brain that correlated with the engineered microRNA expression. Both human mutant huntingtin mRNA and protein were significantly reduced in all brain regions transduced by AAV5-miHTT. The combination of widespread vector distribution and extensive huntingtin lowering observed with AAV5-miHTT supports the translation of a huntingtin-lowering gene therapy for HD from preclinical studies into the clinic.

Behavioral testing of minipigs transgenic for the Huntington gene-A three-year observational study

BACKGROUND

Large animal models of Huntington's disease (HD) may increase the reliability of translating preclinical findings to humans. Long live expectancy offers opportunities particularly for disease modifying approaches, but also challenges. The transgenic (tg) HD minipig model assessed in this study exhibits a high genetic homology with humans, similar body weight, and comparable brain structures. To test long-term safety, tolerability, and efficacy of novel therapeutic approaches in this model reliable assessments applicable longitudinally for several years are warranted for all phenotypical domains relevant in HD.

OBJECTIVE

To investigate whether the tests proposed assessing motor, cognitive and behavioral domains can be applied repetitively over a 3-year period in minipigs with acceptable variability or learning effects and whether tgHD minipigs reveal changes in these domains compared to wildtype (wt) minipigs suggesting the development of an HD phenotype.

METHODS

A cohort of 14 tgHD and 18 wt minipigs was followed for three years. Tests applied every six months included a tongue coordination and hurdle test for the motor domain, a color discrimination test for cognition, and a dominance test for assessing behavior. Statistical analyses were performed using repeated ANOVA for longitudinal group comparisons and Wilcoxon-tests for intra-visit differences between tgHD and wt minipigs.

RESULTS

All tests applied demonstrated feasibility, acceptable variance and good consistency during the three-year period. No significant differences between tgHD and wt minipigs were detected suggesting lack of a phenotype before the age of four years.

CONCLUSIONS

The assessment battery presented offers measures in all domains relevant for HD and can be applied in long-term phenotyping studies with tgHD minipigs. The observation of this cohort should be continued to explore the timeline of phenotype development and provide information for future interventional studies.

Medical management of motor manifestations of Huntington disease

The motor and movement disorders of Huntington disease (HD) are managed in the context of the other disease features. Chorea and dystonia are the most common HD-associated movement disorders, and they can be assessed on research rating scales. However other motor manifestations have a significant impact. In particular, dysphagia influences choice and tolerance of treatment for the movement disorder, as will comorbidities, patient awareness, and distress related to the motor feature or movement. Treatment for other disease features may aggravate the motor disorder, e.g., increased swallowing difficulty associated with antipsychotic agents. Basic principles in deciding to institute a treatment are outlined as well as treatment of specific motor manifestations and movements. There is a paucity of evidence to support the treatments available for the motor disorder, with only one agent with class 1 evidence, tetrabenazine, for chorea. There are, however, treatments informed by expert opinion which reflect the management of a wider HD phenotype than that represented in clinical trials. Some treatments are based on evidence from use in other conditions. Medical management is usually undertaken later in the disease with concurrent nonmedical interventions after multidisciplinary assessments. Medication review with HD progression is essential.

Compromised Dopaminergic Encoding of Reward Accompanying Suppressed Willingness to Overcome High Effort Costs Is a Prominent Prodromal Characteristic of the Q175 Mouse Model of Huntington's Disease

Huntington's disease (HD) is a heritable neurodegenerative disorder caused by expansion of CAG (glutamine) repeats in the HTT gene. A prodromal stage characterized by psychiatric disturbances normally precedes primary motor symptoms and suppressed motivation represents one of the earliest and most common psychiatric symptoms. Although dopamine in the nucleus accumbens (NAc) critically regulates motivation and altered dopamine signaling is implicated in HD, the nature of dopaminergic deficits and contribution to symptoms in HD is poorly understood. We therefore tested whether altered NAc dopamine release accompanies motivational deficits in the Q175 knock-in HD mouse model. Q175 mice express a CAG expansion of the human mutant huntingtin allele in the native mouse genome and gradually manifest symptoms late in life, closely mimicking the genotypic context and disease progression in human HD. Sub-second extracellular dopamine release dynamics were monitored using fast-scan cyclic voltammetry, whereas motivation was assessed using a progressive ratio reinforcement schedule. As the response ratio (lever presses per reward) escalated, Q175 mice exerted less effort to earn fewer rewards versus wild-type (WT). Moreover, dopamine released at reward delivery dynamically encoded increasing reward cost in WT but not Q175 mice. Deficits were specific to situations of high effortful demand as no difference was observed in locomotion, free feeding, hedonic processing, or reward seeking when the response requirement was low. This compromised dopaminergic encoding of reward delivery coincident with suppressed motivation to work for reward in Q175 mice provides novel, neurobiological insight into an established and clinically relevant endophenotype of prodromal HD.

SIGNIFICANCE STATEMENT

Psychiatric impairments in Huntington's disease (HD) typically manifest early in disease progression, before motor deficits. However, the neurobiological factors contributing to psychiatric symptoms are poorly understood. We used a mouse HD model and assessed whether impaired dopamine release in the nucleus accumbens (NAc), a brain region critical to goal-directed behaviors, accompanies motivational deficits, one of the most common early HD symptoms. HD mice exhibited blunted motivation to work for food reward coincident with diminished dopamine release to reward receipt. Motivational and NAc dopaminergic deficits were not associated with gross motor deficits or impaired food seeking when effortful demands were low. This work identifies a specific prodromal HD phenotype associated with a prominent and previously unidentified neurobiological impairment.

Current Pharmacological Approaches to Reduce Chorea in Huntington's Disease

There are currently no effective pharmacological agents available to stop or prevent the progression of Huntington's disease (HD), a rare hereditary neurodegenerative disorder. In addition to psychiatric symptoms and cognitive impairments, HD causes progressive motor disturbances, in particular choreiform movements, which are characterized by unwanted contractions of the facial muscles, trunk and extremities. Management of choreiform movements is usually advised if chorea interferes with daily functioning, causes social isolation, gait instability, falls, or physical injury. Although drugs to reduce chorea are available, only few randomized controlled studies have assessed the efficacy of these drugs, resulting in a high variety of prescribed drugs in clinical practice. The current pharmacological treatment options to reduce chorea in HD are outlined in this review, including the latest results on deutetrabenazine, a newly developed pharmacological agent similar to tetrabenazine, but with suggested less peak dose side effects. A review of the existing literature was conducted using the PubMed, Cochrane and Medline databases. In conclusion, mainly tetrabenazine, tiapride (in European countries), olanzapine, and risperidone are the preferred first choice drugs to reduce chorea among HD experts. In the existing literature, these drugs also show a beneficial effect on motor symptom severity and improvement of psychiatric symptoms. Generally, it is recommended to start with a low dose and increase the dose with close monitoring of any adverse effects. New interesting agents, such as deutetrabenazine and pridopidine, are currently under development and more randomized controlled trials are warranted to assess the efficacy on chorea severity in HD.

New symptomatic therapies for Huntington disease

Huntington disease (HD), an inherited neurodegenerative disease, results from a CAG repeat expansion creating mutant huntingtin protein and widespread neuronal damage. Motor symptoms such as chorea are often preceded by cognitive and behavioral changes. Tetrabenazine and deutetrabebenazine are the two drugs approved by the Federal Food and Drug Administrationfor HD symptoms, is an effective therapy for chorea. However, there is still a large need for other symptomatic therapies impacting functional issues, including impaired gait, behavioral, and cognitive symptoms. A number of pharmacologic agents are under investigation. Additionally, other mechanisms are being targeted in motor symptom drug development, including phosphodiesterase 10 enzyme inhibition, dopamine modulation, and inhibition of deacetylation. There is perhaps the greatest unmet need in treating nonmotor effects, such as cognition and change in disease course. PBT2, a metal chaperone, and latrepirdine, a mitochondrial stabilizer, are under investigation specifically for the possibility of cognitive benefit. Unfortunately, there is a lack of HD-specific evidence on effective treatments for behavioral and psychiatric symptoms. Further investigation of nonmedication interventions such as physical therapy is necessary. As our understanding of molecular and cellular mechanisms underlying HD broadens, a new set of mechanistic targets will become the focus of HD symptomatic therapies.

Guidelines for clinical pharmacological practices in Huntington's disease

OBJECTIVE

Evidence-based medicine is a difficult goal to achieve in rare diseases where randomized controlled trials are lacking. This report provides guidelines that capitalize on both the literature and expertise of the French National Huntington Disease Reference Centre to optimalize pharmacological therapeutic interventions for Huntington's disease (HD).

MATERIAL AND METHODS

HD experts conducted a systematic analysis of the literature from 1965 to 2013, using a scoring procedure established by the French National Authority for Health. These experts offered their views when evidence was missing to set up provisional guidelines for care in HD. These guidelines were then scored and amended through two subsequent online questionnaires (using SurveyMonkey^® scoring), and one face-to-face meeting with an external multidisciplinary working group as a step towards validation.

RESULTS

Except for the beneficial effects of tetrabenazine in chorea, none of the published recommendations were grounded on established scientific evidence. Second-generation antipsychotics are nevertheless the first choice for patients with psychiatric manifestations (low level of evidence). All other guidelines are based on low-level evidence and little professional agreement.

CONCLUSION

Patients' care has greatly improved over the last few years despite the lack of high-level evidence standards. Guidelines are based on the expertise of trained specialists from the French National Plan for Rare Diseases. This strategy should now be extended internationally to promote future studies and to harmonize worldwide care of HD.

Huntington's disease: Molecular basis of pathology and status of current therapeutic approaches

Huntington's disease (HD) is a frequent and incurable hereditary neurodegenerative disorder that impairs motor and cognitive functions. Mutations in huntingtin (HTT) protein, which is essential for neuronal development, lead to the development of HD. An increase in the number of CAG repeats within the HTT gene, which lead to an expansion of polyglutamine tract in the resulting mutated HTT protein, which is toxic, is the causative factor of HD. Although the molecular basis of HD is known, there is no known cure for this disease other than symptomatic relief treatment approaches. The toxicity of mutHTT appears to be more detrimental to striatal medium spiny neurons, which degenerate in this disease. Therapeutic strategies addressing a reduction in the mutHTT content at the transcriptional level using zinc finger proteins and at the translational level with RNA interference and antisense oligonucleotides or promoting the proteosomal degradation of mutHTT are being studied extensively in preclinical models and also to a limited extent in clinical trials. The post-translational modification of mutHTT is another possibility that is currently being investigated for drug development. In addition to the pharmacological approaches, several lines of evidence suggested the potential therapeutic use of stem cell therapy, in particular using the patient-derived induced pluripotent stem cells, to replace the lost striatal neurons. The multi-pronged clinical investigations currently underway may identify therapies and potentially improve the quality of life for the HD patients in future.

Astrocytes are key but indirect contributors to the development of the symptomatology and pathophysiology of Huntington's disease

Huntington's disease (HD) is a fatal neurodegenerative disease in which an early and selective vulnerability of striatal Spiny Projection Neurons is observed. However, several studies have highlighted the implication of glial cells, and in particular astrocytes, in the pathophysiological mechanisms of this disease. A better understanding of the respective contributions of neurons and astrocytes in HD is needed and would be important for the development of new therapeutic approaches. Today, no comparable in vivo models expressing the mutant HTT selectively in astrocytes or in neurons are available. In this study, we developed comparable cell-type specific mouse models expressing a fragment of Huntingtin specifically in neurons, astrocytes, or in both cell populations of the adult mouse basal ganglia circuit. This approach allowed us to characterize behavioral alterations occurring as soon as 4 weeks postinjection. Interestingly, less severe but significant behavioral alterations were also observed in the two cell-type specific models. We further showed that astrocytes are less affected by mHTT compared to neurons, in particular concerning mHTT aggregation. Additionally, a more indirect contribution of astrocytes compared to neurons was observed in several pathophysiological mechanisms such as astrogliosis and neuronal dysfunction. Finally, we showed that direct and indirect transcriptional alterations within the glial glutamatergic clearing system are caused by astrocytic and neuronal expression of mHTT, respectively. We anticipate that our study will help to better understand the contributions of astrocytes to HD and guide future therapeutic efforts. GLIA 2016;64:1841-1856.

The P42 peptide and Peptide-based therapies for Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative hereditary disease clinically characterised by the presence of involuntary movements, behavioural problems and cognitive decline. The disease-onset is usually between 30 and 50 years of age. HD is a rare disorder affecting approximately 1.3 in 10,000 people in the European Union. It is caused by an expanded CAG repeat in the first exon of the Huntingtin (HTT) gene, leading to an abnormal form of the Huntingtin protein (Htt) (polyQHtt), containing N-terminus, enlarged polyglutamine strands of variable length that stick together to form aggregates and nuclear inclusions in the damaged brain cells. Treatments currently used for Huntington's disease are symptomatic and aimed at temporally relieving the symptoms of the disease; although some promising therapies are on study, there is no drug capable of stopping disease progression either in the form of delaying onset or slowing disability progression. The utilization of peptides interacting with polyQ stretches or with Htt protein to prevent misfolding and aggregation of the expanded polyQ protein is a fascinating idea, because of low potential toxicity and ability to target very initial steps in the pathophysiological cascade of the disease, such as aggregation or cleavage process. Indeed, several therapeutic peptides have been developed and were found to significantly slow down the progression of symptoms in experimental models of Huntington's disease. This review is essentially focusing on the latest development concerning peptide strategy. In particular, we focused on a 23aa peptide P42, which is a part of the Htt protein. It is expected to work principally by preventing the abnormal Htt protein from sticking together, thereby preventing pathological consequences of aggregation and improving the symptoms of the disease. In the meantime, as P42 is part of the Htt protein, some therapeutic properties might be linked to the physiological actions of the peptide itself, considered as a functional domain of the Htt protein.

Behavioral phenotyping of minipigs transgenic for the Huntington gene

BACKGROUND

While several novel therapeutic approaches for HD are in development, resources to conduct clinical trials are limited. Large animal models have been proposed to improve assessment of safety, tolerability and especially to increase translational reliability of efficacy signals obtained in preclinical studies. They may thus help to select candidates for translation to human studies. We here introduce a battery of novel tests designed to assess the motor, cognitive and behavioral phenotype of a transgenic (tg) HD minipig model.

NEW METHODS

A group of tgHD and wildtype (wt) Libechov minipigs (n=36) was available for assessment with (1) a gait test using the GAITRite(®) automated acquisition system, (2) a hurdle-test, (3) a tongue coordination test, (4) a color discrimination test, (5) a startbox back and forth test and (6) a dominance test. Performance of all tests and definition of measures obtained is presented.

RESULTS

Minipigs were able to learn performance of all tests. All tests were safe, well tolerated and feasible. Exploratory between group comparisons showed no differences between groups of tgHD and wt minipigs assessed, but low variability within and between groups.

COMPARISON WITH EXISTING METHOD(S)

So far there are no established or validated assessments to test minipigs in the domains described.

CONCLUSIONS

The data shows that the tests presented are safe, well tolerated and all measures defined can be assessed. Prospective longitudinal application of these tests is warranted to determine their test-retest reliability, sensitivity and validity in assessing motor, cognitive and behavioral features of tg and wt minipigs.

Characterising Upper Limb Movements in Huntington's Disease and the Impact of Restricted Visual Cues

BACKGROUND

Voluntary motor deficits are a common feature in Huntington's disease (HD), characterised by movement slowing and performance inaccuracies. This deficit may be exacerbated when visual cues are restricted.

OBJECTIVE

To characterize the upper limb motor profile in HD with various levels of difficulty, with and without visual targets.

METHODS

Nine premanifest HD (pre-HD), nine early symptomatic HD (symp-HD) and nine matched controls completed a motor task incorporating Fitts' law, a model of human movement enabling the quantification of movement timing, via the manipulation of task difficulty (i.e., target size, and distance between targets). The task required participants to make reciprocal movements under cued and blind conditions. Dwell times (time stationary between movements), speed, accuracy and variability of movements were compared between groups.

RESULTS

Symp-HD showed significantly prolonged and less consistent movement times, compared with controls and pre-HD. Furthermore, movement planning and online control were significantly impaired in symp-HD, compared with controls and pre-HD, evidenced by prolonged dwell times and deceleration times. Speed and accuracy were comparable across groups, suggesting that group differences observed in movement time, variability, dwell time and deceleration time were evident over and above simple performance measures. The presence of cues resulted in greater movement time variability in symp-HD, compared with pre-HD and controls, suggesting that the deficit in movement consistency manifested only in response to targeted movements.

CONCLUSIONS

Collectively, these findings provide evidence of a deficiency in both motor planning, particularly in relation to movement timing and online control, which became exacerbated as a function of task difficulty during symp-HD stages. These variables may provide a more sensitive measure of motor dysfunction than speed and/or accuracy alone in symp-HD.

Emotional dysfunctions in neurodegenerative diseases

Neurodegenerative diseases are characterized primarily by motor signs but are also accompanied by emotional disturbances. Because of the limited knowledge about these dysfunctions, this Review provides an overview of emotional competencies in Huntington's disease (HD), Parkinson's disease (PD), and multiple sclerosis (MS), with a focus on emotion recognition, emotion regulation, and depression. Most studies indicate facial emotion recognition deficits in HD and PD, whereas data for MS are inconsistent. On a neural level, dysfunctions of amygdala and striatum, among others, have been linked to these impairments. These dysfunctions also tap brain regions that are part of the emotion regulation network, suggesting problems in this competency, too. Research points to dysfunctional emotion regulation in MS, whereas findings for PD and HD are missing. The high prevalence of depression in all three disorders emphasizes the need for effective therapies. Research on emotional disturbances might improve treatment, thereby increasing patients' and caregivers' well-being.

Clinical trials in Huntington's disease: Interventions in early clinical development and newer methodological approaches

Since the identification of the Huntington's disease (HD) gene, knowledge has accumulated about mechanisms directly or indirectly affected by the mutated Huntingtin protein. Transgenic and knock-in animal models of HD facilitate the preclinical evaluation of these targets. Several treatment approaches with varying, but growing, preclinical evidence have been translated into clinical trials. We review major landmarks in clinical development and report on the main clinical trials that are ongoing or have been recently completed. We also review clinical trial settings and designs that influence drug-development decisions, particularly given that HD is an orphan disease. In addition, we provide a critical analysis of the evolution of the methodology of HD clinical trials to identify trends toward new processes and endpoints. Biomarker studies, such as TRACK-HD and PREDICT-HD, have generated evidence for the potential usefulness of novel outcome measures for HD clinical trials, such as volumetric imaging, quantitative motor (Q-Motor) measures, and novel cognitive endpoints. All of these endpoints are currently applied in ongoing clinical trials, which will provide insight into their reliability, sensitivity, and validity, and their use may expedite proof-of-concept studies. We also outline the specific opportunities that could provide a framework for a successful avenue toward identifying and efficiently testing and translating novel mechanisms of action in the HD field.

An update on Huntington's disease: from the gene to the clinic

PURPOSE OF REVIEW

This review highlights the recent advances in Huntington's disease, with a particular focus on development of disease biomarkers for use in therapeutic trials in the premotor phase of the disease, as well as the growing literature regarding pathophysiological mechanisms and their relevance to potential therapeutic targets.

RECENT FINDINGS

There have been continued advances in the development of disease biomarkers, and promising neuroprotection trials are beginning to emerge in the premotor stage of Huntington's disease. Deeper understanding of the pathophysiological mechanisms is being translated into potential therapeutic strategies.

SUMMARY

The premotor stage of Huntington's disease provides an ideal time to trial disease-modifying therapy, but reliable biomarkers are required for monitoring disease progression, and this remains an area of intense research. Our understanding of the underlying pathophysiological mechanisms continues to expand, and a number of promising therapeutic strategies are emerging, including strategies to silence mutant huntingtin expression.

Developing stem cell therapies for juvenile and adult-onset Huntington's disease

Stem cell therapies have been explored as a new avenue for the treatment of neurologic disease and damage within the CNS in part due to their native ability to mimic repair mechanisms in the brain. Mesenchymal stem cells have been of particular clinical interest due to their ability to release beneficial neurotrophic factors and their ability to foster a neuroprotective microenviroment. While early stem cell transplantation therapies have been fraught with technical and political concerns as well as limited clinical benefits, mesenchymal stem cell therapies have been shown to be clinically beneficial and derivable from nonembryonic, adult sources. The focus of this review will be on emerging and extant stem cell therapies for juvenile and adult-onset Huntington's disease.

Update on Huntington's disease: advances in care and emerging therapeutic options

INTRODUCTION

Huntington's disease (HD) is the most common hereditary neurodegenerative disorder. Despite the fact that both the gene and the mutation causing this monogenetic disorder were identified more than 20 years ago, disease-modifying therapies for HD have not yet been established.

REVIEW

While intense preclinical research and large cohort studies in HD have laid foundations for tangible improvements in understanding HD and caring for HD patients, identifying targets for therapeutic interventions and developing novel therapeutic modalities (new chemical entities and advanced therapies using DNA and RNA molecules as therapeutic agents) continues to be an ongoing process. The authors review recent achievements in HD research and focus on approaches towards disease-modifying therapies, ranging from huntingtin-lowering strategies to improving huntingtin clearance that may be promoted by posttranslational HTT modifications.

CONCLUSION

The nature and number of upcoming clinical studies/trials in HD is a reason for hope for HD patients and their families.

Current therapeutic options for Huntington's disease: good clinical practice versus evidence-based approaches?

Therapeutic decision-making in Huntington's disease (HD) is often guided by clinical experience, because of the limited empirical evidence available. The only medication for HD that has met the regulatory hurdle for approval is tetrabenazine, indicated for the treatment of chorea. However, its use has limitations, and in the setting of specific contraindications or comorbidities the treatment of choice for chorea is still the multipurpose antipsychotics. For the management of psychiatric disturbances, selective serotonin reuptake inhibitors (SSRIs) and mood stabilizers are often used, although empirical evidence is lacking. Finally, no known effective treatment is available for cognitive dysfunction in HD. We discuss the limited evidence available and current expert opinion on medical treatment of the dominant motor, psychiatric, and cognitive features of HD. This follows a brief introduction on the general principles of HD management and on evidence-based medicine in relation to clinical practice.

Acute-phase proteins in relation to neuropsychiatric symptoms and use of psychotropic medication in Huntington's disease

Activation of the innate immune system has been postulated in the pathogenesis of Huntington's disease (HD). We studied serum concentrations of C-reactive protein (CRP) and low albumin as positive and negative acute-phase proteins in HD. Multivariate linear and logistic regression was used to study the association between acute-phase protein levels in relation to clinical, neuropsychiatric, cognitive, and psychotropic use characteristics in a cohort consisting of 122 HD mutation carriers and 42 controls at first biomarker measurement, and 85 HD mutation carriers and 32 controls at second biomarker measurement. Significant associations were found between acute-phase protein levels and Total Functioning Capacity (TFC) score, severity of apathy, cognitive impairment, and the use of antipsychotics. Interestingly, all significant results with neuropsychiatric symptoms disappeared after additional adjusting for antipsychotic use. High sensitivity CRP levels were highest and albumin levels were lowest in mutation carriers who continuously used antipsychotics during follow-up versus those that had never used antipsychotics (mean difference for CRP 1.4 SE mg/L; P=0.04; mean difference for albumin 3 SE g/L; P<0.001). The associations found between acute-phase proteins and TFC score, apathy, and cognitive impairment could mainly be attributed to the use of antipsychotics. This study provides evidence that HD mutation carriers who use antipsychotics are prone to develop an acute-phase response.

Deep brain stimulation for Huntington's disease: long-term results of a prospective open-label study

OBJECT.: To date, experience of globus pallidus internus (GPi) deep brain stimulation (DBS) in the treatment of Huntington's disease (HD) has been limited to a small number of case reports. The aim of this study was to analyze long-term motor outcome of a cohort of HD patients treated with GPi DBS.

METHODS

Seven patients with pharmacologically resistant chorea and functional impairment were included in a prospective open-label study from 2008 to 2011. The main outcome measure was the motor section of the Unified Huntington's Disease Rating Scale. The primary end point was reduction of chorea.

RESULTS

Patients underwent MRI-guided bilateral GPi implantation. The median duration of follow-up was 3 years. A significant reduction of chorea was observed in all patients, with sustained therapeutic effect; the mean improvement on the chorea subscore was 58.34% at the 12-month follow-up visit (p = 0.018) and 59.8% at the 3-year visit (p = 0.040). Bradykinesia and dystonia showed a nonsignificant trend toward progressive worsening related to disease evolution and partly to DBS. The frequency of stimulation was 130 Hz for all patients. DBS-induced bradykinesia was managed by pulse-width reduction or bipolar settings. Levodopa mildly improved bradykinesia in 4 patients. Regular off-stimulation tests confirmed a persistent therapeutic effect of DBS on chorea.

CONCLUSIONS

GPi DBS may provide sustained chorea improvement in selected HD patients with pharmacologically resistant chorea, with transient benefit in physical aspects of quality of life before progression of behavioral and cognitive disorders. DBS therapy did not improve dystonia or bradykinesia. Further studies including quality of life measures are needed to evaluate the impact of DBS in the long-term outcome of HD.

Effectiveness of anti-psychotics and related drugs in the Huntington French-speaking group cohort

PURPOSE

Huntington's disease is a rare condition. Patients are commonly treated with antipsychotics and tetrabenazine. The evidence of their effect on disease progression is limited and no comparative study between these drugs has been conducted. We therefore compared the effectiveness of antipsychotics on disease progression.

METHODS

956 patients from the Huntington French Speaking Group were followed for up to 8 years between 2002 and 2010. The effectiveness of treatments was assessed using Unified Huntington's Disease Rating Scale (UHDRS) scores and then compared using a mixed model adjusted on a multiple propensity score.

RESULTS

63% of patients were treated with antipsychotics during the survey period. The most commonly prescribed medications were dibenzodiazepines (38%), risperidone (13%), tetrabenazine (12%) and benzamides (12%). There was no difference between treatments on the motor and behavioural declines observed, after taking the patient profiles at the start of the drug prescription into account. In contrast, the functional decline was lower in the dibenzodiazepine group than the other antipsychotic groups (Total Functional Capacity: 0.41 ± 0.17 units per year vs. risperidone and 0.54 ± 0.19 vs. tetrabenazine, both p<0.05). Benzamides were less effective than other antipsychotics on cognitive evolution (Stroop interference, Stroop color and Literal fluency: p<0.05).

CONCLUSIONS

Antipsychotics are widely used to treat patients with Huntington's disease. Although differences in motor or behavioural profiles between patients according to the antipsychotics used were small, there were differences in drug effectiveness on the evolution of functional and cognitive scores.

The role of dopamine in Huntington's disease

Alterations in dopamine (DA) neurotransmission in Parkinson's disease are well known and widely studied. Much less is known about DA changes that accompany and underlie some of the symptoms of Huntington's disease (HD), a dominant inherited neurodegenerative disorder characterized by chorea, cognitive deficits, and psychiatric disturbances. The cause is an expansion in CAG (glutamine) repeats in the HTT gene. The principal histopathology of HD is the loss of medium-sized spiny neurons (MSNs) and, to a lesser degree, neuronal loss in cerebral cortex, thalamus, hippocampus, and hypothalamus. Neurochemical, electrophysiological, and behavioral studies in HD patients and genetic mouse models suggest biphasic changes in DA neurotransmission. In the early stages, DA neurotransmission is increased leading to hyperkinetic movements that can be alleviated by depleting DA stores. In contrast, in the late stages, DA deficits produce hypokinesia that can be treated by increasing DA function. Alterations in DA neurotransmission affect glutamate receptor modulation and could contribute to excitotoxicity. The mechanisms of DA dysfunction, in particular the increased DA tone in the early stages of the disease, are presently unknown but may include initial upregulation of DA neuron activity caused by the genetic mutation, reduced inhibition resulting from striatal MSN loss, increased excitation from cortical inputs, and DA autoreceptor dysfunction. Targeting both DA and glutamate receptor dysfunction could be the best strategy to treat HD symptoms.

Development of an ELISA assay for the quantification of soluble huntingtin in human blood cells

Background

Huntington’s disease (HD) is a monogenic disorder caused by an aberrant expansion of CAG repeats in the huntingtin gene (HTT). Pathogenesis is associated with expression of the mutant (mHTT) protein in the CNS, with its levels most likely related to disease progression and symptom severity. Since non-invasive methods to quantify HTT in the CNS do not exist, measuring amount of soluble HTT in peripheral cells represents an important step in development of disease-modifying interventions in HD.

Results

An ELISA assay using commercially available antibodies was developed to quantify HTT levels in complex matrices like mammalian cell cultures lysates and human samples. The immunoassay was optimized using a recombinant full-length HTT protein, and validated both on wild-type and mutant HTT species. The ability of the assay to detect significant variations of soluble HTT levels was evaluated using an HSP90 inhibitor that is known to enhance HTT degradation. Once optimized, the bioassay was applied to peripheral blood mononuclear cells (PBMCs) from HD patients, demonstrating good potential in tracking the disease course.

Conclusions

The method described here represents a validated, simple and rapid bio-molecular assay to evaluate soluble HTT levels in blood cells as useful tool in disease and pharmacodynamic marker identification for observational and clinical trials.

Fused 3-Hydroxy-3-trifluoromethylpyrazoles Inhibit Mutant Huntingtin Toxicity

Here, we describe the selection and optimization of a chemical series active in both a full-length and a fragment-based Huntington's disease (HD) assay. Twenty-four thousand small molecules were screened in a phenotypic HD assay, identifying a series of compounds bearing a 3-hydroxy-3-trifluoromethylpyrazole moiety as able to revert the toxicity induced by full-length mutant Htt by up to 50%. A chemical exploration around the series led to the identification of compound 4f, which demonstrated to be active in a Htt171-82Q rat primary striatal neuron assay and a PC12-Exon-1 based assay. This compound was selected for testing in R6/2 mice, in which it was well-tolerated and showed a positive effect on body weight and a positive trend in preventing ventricular volume enlargment. These studies provide strong rationale for further testing the potential benefits of 3-hydroxy-3-trifluoromethylpyrazoles in treating HD.

Binding of the repressor complex REST-mSIN3b by small molecules restores neuronal gene transcription in Huntington's disease models

Transcriptional dysregulation is a hallmark of Huntington's disease (HD) and one cause of this dysregulation is enhanced activity of the REST-mSIN3a-mSIN3b-CoREST-HDAC repressor complex, which silences transcription through REST binding to the RE1/NRSE silencer. Normally, huntingtin (HTT) prevents this binding, allowing expressing of REST target genes. Here, we aimed to identify HTT mimetics that disrupt REST complex formation in HD. From a structure-based virtual screening of 7 million molecules, we selected 94 compounds predicted to interfere with REST complex formation by targeting the PAH1 domain of mSIN3b. Primary screening using DiaNRSELuc8 cells revealed two classes of compounds causing a greater than two-fold increase in luciferase. In particular, quinolone-like compound 91 (C91) at a non-toxic nanomolar concentration reduced mSIN3b nuclear entry and occupancy at the RE1/NRSE within the Bdnf locus, and restored brain-derived neurotrophic factor (BDNF) protein levels in HD cells. The mRNA levels of other RE1/NRSE-regulated genes were similarly increased while non-REST-regulated genes were unaffected. C91 stimulated REST-regulated gene expression in HTT-knockdown Zebrafish and increased BDNF mRNA in the presence of mutant HTT. Thus, a combination of virtual screening and biological approaches can lead to compounds reducing REST complex formation, which may be useful in HD and in other pathological conditions.

Dopamine imbalance in Huntington's disease: a mechanism for the lack of behavioral flexibility

Dopamine (DA) plays an essential role in the control of coordinated movements. Alterations in DA balance in the striatum lead to pathological conditions such as Parkinson's and Huntington's diseases (HD). HD is a progressive, invariably fatal neurodegenerative disease caused by a genetic mutation producing an expansion of glutamine repeats and is characterized by abnormal dance-like movements (chorea). The principal pathology is the loss of striatal and cortical projection neurons. Changes in brain DA content and receptor number contribute to abnormal movements and cognitive deficits in HD. In particular, during the early hyperkinetic stage of HD, DA levels are increased whereas expression of DA receptors is reduced. In contrast, in the late akinetic stage, DA levels are significantly decreased and resemble those of a Parkinsonian state. Time-dependent changes in DA transmission parallel biphasic changes in glutamate synaptic transmission and may enhance alterations in glutamate receptor-mediated synaptic activity. In this review, we focus on neuronal electrophysiological mechanisms that may lead to some of the motor and cognitive symptoms of HD and how they relate to dysfunction in DA neurotransmission. Based on clinical and experimental findings, we propose that some of the behavioral alterations in HD, including reduced behavioral flexibility, may be caused by altered DA modulatory function. Thus, restoring DA balance alone or in conjunction with glutamate receptor antagonists could be a viable therapeutic approach.

Two decades of Huntington disease testing: patient's demographics and reproductive choices

Predictive testing for Huntington disease (HD) has been available in the United States (US) since 1987, and the Indiana University Predictive Testing Program has been providing this testing since 1990. To date there has been no published description of those who present for such testing in the US. Here we describe demographics of 141 individuals and reproductive decision making of a subset of 16 of those individuals who underwent predictive HD testing between 1990 and 2010 at one site in the US. This study is a retrospective chart review of the "Personal History Questionnaire" participants completed prior to testing. As seen in other studies, most participants were female (64.5 %), in their mid-30s (mean = 34), and had at least one child prior to testing (54 %). Multiple demographic datum points are described, and the reproductive decision making of these at-risk individuals was analyzed using Fisher's Exact Tests. Of those women who had children before learning of their risk to inherit HD, those who attended church more frequently, had three or more children total, or whose mother was affected with HD were more likely to be comfortable with their choice to have children. We conclude that these demographic factors influence the reproductive decision-making of individuals at risk for HD. Psychologists, clinical geneticists, and genetic counselors may be able to use this information to help counsel at-risk patients regarding current or past reproductive decision making.