Experimental surgical therapies for Huntington's disease

Break-up and recovery of harmony between direct and indirect pathways in the basal ganglia: Huntington's disease and treatment

The basal ganglia (BG) in the brain exhibit diverse functions for motor, cognition, and emotion. Such BG functions could be made via competitive harmony between the two competing pathways, direct pathway (DP) (facilitating movement) and indirect pathway (IP) (suppressing movement). As a result of break-up of harmony between DP and IP, there appear pathological states with disorder for movement, cognition, and psychiatry. In this paper, we are concerned about the Huntington's disease (HD), which is a genetic neurodegenerative disorder causing involuntary movement and severe cognitive and psychiatric symptoms. For the HD, the number of D2 SPNs ( N D 2 ) is decreased due to degenerative loss, and hence, by decreasing x D 2 (fraction of N D 2 ), we investigate break-up of harmony between DP and IP in terms of their competition degree C d , given by the ratio of strength of DP ( S DP ) to strength of IP ( S IP ) (i.e.,C d = S DP / S IP ). In the case of HD, the IP is under-active, in contrast to the case of Parkinson's disease with over-active IP, which results in increase in C d (from the normal value). Thus, hyperkinetic dyskinesia such as chorea (involuntary jerky movement) occurs. We also investigate treatment of HD, based on optogenetics and GP ablation, by increasing strength of IP, resulting in recovery of harmony between DP and IP. Finally, we study effect of loss of healthy synapses of all the BG cells on HD. Due to loss of healthy synapses, disharmony between DP and IP increases, leading to worsen symptoms of the HD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11571-024-10125-w.

Neurosurgical therapy possibilities in treatment of Huntington disease: An update

INTRODUCTION

Huntington's disease (HD) is a hereditary condition caused by the expansion of the CAG trinucleotide in the huntingtin gene on chromosome 4, resulting in motor, cognitive, and psychiatric disorders that significantly impact patients' quality of life. Despite the lack of effective treatments for the disease, various surgical strategies have been explored to alleviate symptoms and slow its progression.

METHODOLOGY

A comprehensive systematic literature review was conducted, including MeSH terms, yielding only 38 articles that were categorized based on the surgical procedure. The study aimed to describe the types of surgeries performed and their efficacy in HD patients.

RESULTS

Deep brain stimulation (DBS) involved 41 predominantly male patients with bilateral implantation in the globus pallidus, showing a preoperative Unified Huntington's Disease Rating Scale (UHDRS) score of 60.25 ± 16.13 and a marked postoperative value of 48.54 ± 13.93 with a p < 0.018 at one year and p < 0.040 at three years. Patients experienced improvement in hyperkinesia but worsening of bradykinesia. Additionally, cell transplantation in 119 patients resulted in a lower preoperative UHDRS score of 34.61 ± 14.61 and a significant postoperative difference of 32.93 ± 15.87 (p < 0.016), respectively, in the first to third years of following. Some now, less used procedures were crucial for understanding brain function, such as pallidotomies in 3 patients, showing only a 25 % difference from their baseline.

CONCLUSION

Despite advancements in technology, there is still no curative treatment, only palliative options. Promising treatments like trophic factor implantation offer new prospects for the future.

Effect of Capsaicin on 3-NP-Induced Neurotoxicity: A Pre-Clinical Study

The study objectives are to investigate the ability of capsaicin to revert the toxic effects in glutamate and lipopolysaccharide (LPS)-induced neurotoxicity in Neuro2a (N2a) cells as well as thwarting cognitive impairments, mitochondrial deficits, and oxidative insults induced by 3-nitropropanoic acid (3-NP) in a rodent model of Huntington's disease. In-vitro study with N2a cells was performed through MTT and LDH assay and their biochemical examinations were also performed. 3-NP-administered mice (n = 6) were treated with capsaicin (5, 10, and 20 mg/kg) through the per-oral (p.o.) route for 7 consecutive days. Physiological and behavioral studies were performed in drug-treated mice. After behavioral studies, biochemical parameters were performed for cytokines levels, various oxidative stress parameters, and mitochondrial enzyme complex activities with mitochondrial permeability. N2a cells treated with capsaicin demonstrated neuroprotective effects and reduced neurotoxicity. Based on experimental observation, in an in-vitro study, the effective dose of CAP was 50 µM. Moreover, a 100 µM dose of capsaicin had toxic effects on neuronal cells (N2a cells). On the other hand, the effective dose of 3-NP was 20 mg/kg, (p.o.) in animals (in-vivo). All tested doses of capsaicin upturned the cognitive impairment and motor in-coordination effects induced by 3-NP. 3-NP-injected mice demonstrated substantially increased pro-inflammatory cytokine concentrations, defective mitochondrial complex activity, and augmented oxidative insult. However, capsaicin at different doses reduced oxidative damage and cytokines levels and improved mitochondrial complex activity along with mitochondrial permeability. Furthermore, capsaicin (10 and 20 mg/kg) improved the TNF-α concentration. These findings suggested because of the anti-inflammatory and antioxidant effect, capsaicin can be considered a novel treatment for the management of neurodegenerative disorders by reverting the antioxidant enzyme activity, pro-inflammatory cytokines concentration, and mitochondrial functions.

Focused ultrasound-induced blood brain-barrier opening enhanced vascular permeability for GDNF delivery in Huntington's disease mouse model

BACKGROUND

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the gene encoding the huntingtin (Htt) protein, which results in a protein containing an abnormally expanded polyglutamine (polyQ) sequence. The expanded polyQ in the Htt protein is toxic to brain cells. No therapy exists to delay disease progression.

METHODS

This study describes a gene-liposome system that synergistically applied focused ultrasound (FUS)-blood-brain barrier (BBB) opening for rescuing motor and neuropathological impairments when administered from pre to post-symptomatic transgenic mouse models of HD. DPPC liposomes (LPs) are designed to carry glia cell line-derived neurotrophic factor (GDNF) plasmid DNA (GDNFp) to form a GDNFp-liposome (GDNFp-LPs) complex. Pulsed FUS exposure with microbubbles (MBs) was used to induce BBB opening for non-viral, non-invasive, and targeted gene delivery into the central nervous system (CNS) for therapeutic purposes.

RESULTS

FUS-gene therapy significantly improved motor performance with GDNFp-LPs + FUS treated HD mice equilibrating longer periods in the animal behavior. Reflecting the improvements observed in motor function, GDNF overexpression results in significantly decreased formation of polyglutamine-expanded aggregates, reduced oxidative stress and apoptosis, promoted neurite outgrowth, and improved neuronal survival. Immunoblotting and histological staining further confirmed the neuroprotective effect from delivery of GDNF genes to neuronal cells.

CONCLUSIONS

This study suggests that the GDNFp-LPs plus FUS sonication can provide an effective gene therapy to achieve local extravasation and triggered gene delivery for non-invasive in vivo treatment of CNS diseases.

Potential of Extracellular Vesicles in Neurodegenerative Diseases: Diagnostic and Therapeutic Indications

Extracellular vesicles (EVs) are membrane-bound vesicles, including exosomes and microvesicles. EVs are nanometer sized, found in physiological fluids such as urine, blood, cerebro-spinal fluid (CSF), with a capacity of transferring various biological materials such as microRNAs, proteins, and lipids among cells without direct cell-to-cell contact. Many cells in the nervous system have been shown to release EVs. These vesicles are involved in intercellular communication and a variety of biological processes such as modulation of immune response, signal transduction, and transport of genetic materials with low immunogenicity; therefore, they have also been recently investigated for the delivery of therapeutic molecules such as siRNAs and drugs in the treatment of diseases. In addition, since EV components reflect the physiological status of the cells and tissues producing them, they can be utilized as biomarkers for early detection of various diseases. In this review, we summarize EV application, in diagnosis as biomarker sources and as a carrier tool for drug delivery in EV-based therapies in neurodegenerative diseases.

Gene Therapies for Polyglutamine Diseases

Polyglutamine diseases are hereditary degenerative disorders of the nervous system that have remained, to this date, untreatable. Promisingly, investigation into their molecular etiology and the development of increasingly perfected tools have contributed to the design of novel strategies with therapeutic potential. Encouraging studies have explored gene therapy as a means to counteract cell demise and loss in this context. The current chapter addresses the two main focuses of research in the area: the characteristics of the systems used to deliver nucleic acids to cells and the molecular and cellular actions of the therapeutic agents. Vectors used in gene therapy have to satisfyingly reach the tissues and cell types of interest, while eliciting the lowest toxicity possible. Both viral and non-viral systems have been developed for the delivery of nucleic acids to the central nervous system, each with its respective advantages and shortcomings. Since each polyglutamine disease is caused by mutation of a single gene, many gene therapy strategies have tried to halt degeneration by silencing the corresponding protein products, usually recurring to RNA interference. The potential of small interfering RNAs, short hairpin RNAs and microRNAs has been investigated. Overexpression of protective genes has also been evaluated as a means of decreasing mutant protein toxicity and operate beneficial alterations. Recent gene editing tools promise yet other ways of interfering with the disease-causing genes, at the most upstream points possible. Results obtained in both cell and animal models encourage further delving into this type of therapeutic strategies and support the future use of gene therapy in the treatment of polyglutamine diseases.

Behavioral and neurophysiological evidence for the enhancement of cognitive control under dorsal pallidal deep brain stimulation in Huntington's disease

Deep brain stimulation of the dorsal pallidum (globus pallidus, GP) is increasingly considered as a surgical therapeutic option in Huntington's disease (HD), but there is need to identify outcome measures useful for clinical trials. Computational models consider the GP to be part of a basal ganglia network involved in cognitive processes related to the control of actions. We examined behavioural and event-related potential (ERP) correlates of action control (i.e., error monitoring) and evaluated the effects of deep brain stimulation (DBS). We did this using a standard flanker paradigm and evaluated error-related ERPs. Patients were recruited from a prospective pilot trial for pallidal DBS in HD (trial number NCT00902889). From the initial four patients with Huntington's chorea, two patients with chronic external dorsal pallidum stimulation were available for follow-up and able to perform the task. The results suggest that the external GP constitutes an important basal ganglia element not only for error processing and behavioural adaptation but for general response monitoring processes as well. Response monitoring functions were fully controllable by switching pallidal DBS stimulation on and off. When stimulation was switched off, no neurophysiological and behavioural signs of error and general performance monitoring, as reflected by the error-related negativity and post-error slowing in reaction times were evident. The modulation of response monitoring processes by GP-DBS reflects a side effect of efforts to alleviate motor symptoms in HD. From a clinical neurological perspective, the results suggest that DBS in the external GP segment can be regarded as a potentially beneficial treatment with respect to cognitive functions.

Transplantation of GABAergic cells derived from bioreactor-expanded human neural precursor cells restores motor and cognitive behavioral deficits in a rodent model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder that is characterized by progressive dementia, choreiform involuntary movements, and emotional deterioration. Neuropathological features include the progressive degeneration of striatal γ-aminobutyric acid (GABA) neurons. New therapeutic approaches, such as the transplantation of human neural precursor cells (hNPCs) to replace damaged or degenerated cells, are currently being investigated. The aim of this study was to investigate the potential for utilizing telencephalic hNPCs expanded in suspension bioreactors for cell restorative therapy in a rodent model of HD. hNPCs were expanded in a hydrodynamically controlled and homogeneous environment under serum-free conditions. In vitro analysis revealed that the bioreactor-expanded telencephalic (BET)-hNPCs could be differentiated into a highly enriched population of GABAergic neurons. Behavioral assessments of unilateral striatal quinolinic acid-lesioned rodents revealed a significant improvement in motor and memory deficits following transplantation with GABAergic cells differentiated from BET-hNPCs. Immunohistochemical analysis revealed that transplanted BET-hNPCs retained a GABAergic neuronal phenotype without aberrant transdifferentiation or tumor formation, indicating that BET-hNPCs are a safe source of cells for transplantation. This preclinical study has important implications as the transplantation of GABAergic cells derived from predifferentiated BET-hNPCs may be a safe and feasible cell replacement strategy to promote behavioral recovery in HD.