Antidepressants for neuroprotection in Huntington's disease: A review

The pathobiology of depression in Huntington's disease: an unresolved puzzle

Huntington's disease (HD) is an autosomal-dominant progressive neurodegenerative disease that manifests with a triad of symptoms including motor dysfunctions, cognitive deficits, and prominent neuropsychiatric symptoms, the most common of which is depression, with a prevalence between 30 and 70%. Depressive symptoms occur in all stages of HD, beginning in presymptomatic HD gene carriers, and are strongly associated with suicidal ideation and suicidality, but their relationship with other clinical dimensions in HD is controversial and the underlying pathophysiology is poorly understood. Analysis of the available literature until November 2023 concerned the prevalence, clinical manifestations, neuroimaging, transgenic models, and treatment options of HD depression. While it was believed that depression in HD is due to psychosomatic factors in view of the fatal disease, studies in transgenic models of HD demonstrated molecular changes including neurotrophic and serotonergic dysregulation and disorders of the hypothalamic-pituitary-adrenal axis inducing depression-like changes. While relevant neuropathological data are missing, recent neuroimaging studies revealed correlations between depressive symptoms and dysfunctional connectivities in the default mode network, basal ganglia and prefrontal cortex, and changes in limbic and paralimbic structures related to the basic neurodegenerative process. The impact of response to antidepressants in HD patients is controversial; selective serotonin reuptake inhibitors are superior to serotonin-norepinephrine reuptake inhibitors, while electroconvulsive therapy may be effective for pharmacotherapy resistant cases. Since compared to major depressive disorder and depression in other neurodegenerative diseases, our knowledge of the molecular basis in HD depression is limited, further studies to elucidate the heterogeneous pathogenesis in this fatal disorder are warranted.

Saroglitazar, a PPAR α/γ agonist alleviates 3-Nitropropionic acid induced neurotoxicity in rats: Unveiling the underlying mechanisms

Saroglitazar (SGZ), a peroxisomal proliferated activated receptor α/γ agonist showed neuroprotective effects in various neurodegenerative disorders like Alzheimer's and Parkinson's. However, no studies were performed on Huntington's, so the goal of the current study is to examine the effect of SGZ on Huntington's disease like symptoms induced by 3-Nitropropionic acid. In this protocol, twenty-four rats were divided into four groups, each group consisting of 6 animals. Group 1: The control group received 1 % CMC 10 mg/kg, p.o. for 14 days. Groups 2, 3, and 4 received 3-NP 15 mg/kg, i.p. from Day 1 to Day 7. Groups 3 and 4 received SGZ 5 mg/kg, p.o. and 10 mg/kg, p.o. respectively once daily from day 1 to day 14. Various behavioral tests like OFT, rotarod, hanging wire, narrow beam walk, MWM, and Y-maze were performed. On day-15, the animals were euthanised by cervical dislocation and brain sample were isolated for biochemical and histopathological analysis. Administration of 3-NP showed a significant decrease in motor coordination and cognitive function. Furthermore, 3-NP altered the activity of acetylcholinesterase, anti-oxidant enzymes, Nrf-2, NF-κB, BDNF, CREB levels, and histological features. However, treatment with SGZ showed ameliorative effects in the 3-NP induced neurotoxicity via PPAR α/γ pathway by reducing motor dysfunction, memory impairment, cholinesterase levels, oxidative stress, neuroinflammation. It also enhanced the levels of Nrf-2, BDNF, and CREB expression and improved histological features. In conclusion, treatment with Saroglitazar attenuated Huntington's disease-like symptoms in rats which are induced by 3-NP via activation of PPAR α/γ pathway.

Neuroprotective effects of levothyroxine on cognition deficits and memory in an experimental model of Huntington's disease in rats: An electrophysiological study

Huntington's disease (HD) is a neurodegenerative disorder characterized by cognitive deficits and motor function. Levothyroxine (L-T4) is a synthetic form of Thyroxine (T4), which can improve cognitive ability. The aim of the present study was to determine the neuroprotective effect of L-T4 administration in rats with 3-nitropropionic acid (3-NP)-induced Huntington's disease. Forty-eight Wistar male rats were divided into six groups (n = 8): Group 1 control group that received physiological saline, Group 2 and 3: which received L-T4 (30 and 100 μg/kg), Group 4: HD group that received 3-NP and Groups 5 and 6: The treatment of the HD rats with L-T4 (30 and 100 μg/kg). Spatial memory, locomotor activity, and frequency of neuronal firing were assessed. After decapitation, the Brain-Derived Neurotrophic Factor (BDNF) and Total antioxidant capacity (TAC) levels in the striatum was measured. The results showed that the indices of spatial memory (mean path length and latency time) and motor dysfunction (immobility time) significantly increased, while time spent in the goal quadrant, swimming speed, spike rate, and striatum levels of BDNF significantly decreased in the HD group compared to the control group. L-T4 treatment significantly enhanced time spent in the goal quadrant, swimming speed, motor activity (number of line crossing and rearing), spike rate and striatal BDNF level. This research showed that L-T4 prevented the disruption of motor activity and cognitive deficiencies induced by 3-NP. The beneficial effects of L-T4 may be due to an increase in the concentration of BDNF and enhancement of the spike rate in the striatum.

Bilirubin and Redox Stress in Age-Related Brain Diseases

Cellular redox status has a crucial role in brain physiology, as well as in pathologic conditions. Physiologic senescence, by dysregulating cellular redox homeostasis and decreasing antioxidant defenses, enhances the central nervous system's susceptibility to diseases. The reduction of free radical accumulation through lifestyle changes, and the supplementation of antioxidants as a prophylactic and therapeutic approach to increase brain health, are strongly suggested. Bilirubin is a powerful endogenous antioxidant, with more and more recognized roles as a biomarker of disease resistance, a predictor of all-cause mortality, and a molecule that may promote health in adults. The alteration of the expression and activity of the enzymes involved in bilirubin production, as well as an altered blood bilirubin level, are often reported in neurologic conditions and neurodegenerative diseases (together denoted NCDs) in aging. These changes may predict or contribute both positively and negatively to the diseases. Understanding the role of bilirubin in the onset and progression of NCDs will be functional to consider the benefits vs. the drawbacks and to hypothesize the best strategies for its manipulation for therapeutic purposes.

Theoretical design for covering Engeletin with functionalized nanostructure-lipid carriers as neuroprotective agents against Huntington's disease via the nasal-brain route

Objective: To propose a theoretical formulation of engeletin-nanostructured lipid nanocarriers for improved delivery and increased bioavailability in treating Huntington's disease (HD). Methods: We conducted a literature review of the pathophysiology of HD and the limitations of currently available medications. We also reviewed the potential therapeutic benefits of engeletin, a flavanol glycoside, in treating HD through the Keap1/nrf2 pathway. We then proposed a theoretical formulation of engeletin-nanostructured lipid nanocarriers for improved delivery across the blood-brain barrier (BBB) and increased bioavailability. Results: HD is an autosomal dominant neurological illness caused by a repetition of the cytosine-adenine-guanine trinucleotide, producing a mutant protein called Huntingtin, which degenerates the brain's motor and cognitive functions. Excitotoxicity, mitochondrial dysfunction, oxidative stress, elevated concentration of ROS and RNS, neuroinflammation, and protein aggregation significantly impact HD development. Current therapeutic medications can postpone HD symptoms but have long-term adverse effects when used regularly. Herbal medications such as engeletin have drawn attention due to their minimal side effects. Engeletin has been shown to reduce mitochondrial dysfunction and suppress inflammation through the Keap1/NRF2 pathway. However, its limited solubility and permeability hinder it from reaching the target site. A theoretical formulation of engeletin-nanostructured lipid nanocarriers may allow for free transit over the BBB due to offering a similar composition to the natural lipids present in the body a lipid solubility and increase bioavailability, potentially leading to a cure or prevention of HD. Conclusion: The theoretical formulation of engeletin-nanostructured lipid nanocarriers has the potential to improve delivery and increase the bioavailability of engeletin in the treatment of HD, which may lead to a cure or prevention of this fatal illness.

Extracellular Vesicles, Stem Cells and the Role of miRNAs in Neurodegeneration

There are different modalities of intercellular communication governed by cellular homeostasis. In this review, we will explore one of these forms of communication called extracellular vesicles (EVs). These vesicles are released by all cells in the body and are heterogeneous in nature. The primary function of EVs is to share information through their cargo consisting of proteins, lipids and nucleic acids (mRNA, miRNA, dsDNA etc.) with other cells, which have a direct consequence on their microenvironment. We will focus on the role of EVs of mesenchymal stem cells (MSCs) in the nervous system and how these participate in intercellular communication to maintain physiological function and provide neuroprotection. However, deregulation of this same communication system could play a role in several neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, multiple sclerosis, prion disease and Huntington's disease. The release of EVs from a cell provides crucial information to what is happening inside the cell and thus could be used in diagnostics and therapy. We will discuss and explore new avenues for the clinical applications of using engineered MSC-EVs and their potential therapeutic benefit in treating neurodegenerative diseases.

Longitudinal Evaluation of the Effect of Tricyclic Antidepressants and Neuroleptics on the Course of Huntington's Disease-Data from a Real World Cohort

Background: Reducing the progress of neurodegeneration is a key goal in Huntington´s disease (HD). A previously performed systematic screening for medications with neuroprotective features identified tricyclic antidepressants and neuroleptics as neuroprotective and mitochondrioprotective agents. Here, we analyzed the characteristics of disease manifestation, progression and potential beneficial effects in HD patients treated with afore-mentioned medications compared to un- and otherwise treated motor-manifest patients in a large real-world cohort over two years. Methods: We analyzed cross-sectional data of the largest cohort worldwide of motor-manifest HD patients using the ENROLL-HD database, including demographic, moleculargenetic, clinical-motoric, cognitive and functional data. Longitudinal data of up to two years were obtained to analyze potential effects on disease progression between groups with different medications used. Data were analyzed using repeated ANOVA-analyses while controlling for the co-variates age and CAG-repeat length. Results: We identified n = 7397 motor-manifest HD patients using no or different medication (HD-ctrl) and subgroups treated with clomipramine (n = 56), clozapine (n = 66), chlorpromazine (n = 17), doxepine (n = 34) and desi-, imi- or trimipramine (n = 19). Demographic parameters, disease onset and CAP-score did not differ. Total motor scores (TMS) at baseline were higher in patients treated with clozapine (p < 0.001), chlorpromazine and clomipramine (p < 0.05) compared to HD-ctrl with higher sub scores for bradykinesia (all p < 0.01) and dystonia in clozapine treated patients (p < 0.001). Functional and cognitive capacities were worse in medication groups in comparison to HD-ctrl at baseline (p < 0.001). Repeated measures analysis of variance documented no differences regarding motoric, functional and cognitive disease progressions between groups. Conclusions: We identified group differences, potentially caused by side effects or potential selection bias in terms of bradykinetic motoric symptoms, more dystonia and lower functional and cognitive performance in some treatment groups at baseline, which were not entirely explained because of underlying fundamental characteristics. Disease progression regarding clinical, functional and cognitive outcomes over two years was not affected by any of the treatment groups compared to HD-ctrl. Our data do not support our hypothesis of a potential neuroprotective effect of these drugs on disease progression.

PPARγ/PGC1α signaling as a potential therapeutic target for mitochondrial biogenesis in neurodegenerative disorders

Neurodegenerative diseases represent some of the most devastating neurological disorders, characterized by progressive loss of the structure and function of neurons. Current therapy for neurodegenerative disorders is limited to symptomatic treatment rather than disease modifying interventions, emphasizing the desperate need for improved approaches. Abundant evidence indicates that impaired mitochondrial function plays a crucial role in pathogenesis of many neurodegenerative diseases and so biochemical factors in mitochondria are considered promising targets for pharmacological-based therapies. Peroxisome proliferator-activated receptors-γ (PPARγ) are ligand-inducible transcription factors involved in regulating various genes including peroxisome proliferator-activated receptor gamma co-activator-1 alpha (PGC1α). This review summarizes the evidence supporting the ability of PPARγ-PGC1α to coordinately up-regulate the expression of genes required for mitochondrial biogenesis in neurons and provide directions for future work to explore the potential benefit of targeting mitochondrial biogenesis in neurodegenerative disorders. We have highlighted key roles of NRF2, uncoupling protein-2 (UCP2), and paraoxonase-2 (PON2) signaling in mediating PGC1α-induced mitochondrial biogenesis. In addition, the status of PPARγ modulators being used in clinical trials for Parkinson's disease (PD), Alzheimer's disease (AD) and Huntington's disease (HD) has been compiled. The overall purpose of this review is to update and critique our understanding of the role of PPARγ-PGC1α-NRF2 in the induction of mitochondrial biogenesis together with suggestions for strategies to target PPARγ-PGC1α-NRF2 signaling in order to combat mitochondrial dysfunction in neurodegenerative disorders.

Estimating the causal effects of modifiable, non-genetic factors on Huntington disease progression using propensity score weighting

INTRODUCTION

Despite being genetically inherited, it is unclear how non-genetic factors (e.g., substance use, employment) might contribute to the progression and severity of Huntington's disease (HD).

METHODS

We used propensity score (PS) weighting in a large (n = 2914) longitudinal dataset (Enroll-HD) to examine the impact of education, employment status, and use of tobacco, alcohol, and recreational and therapeutic drugs on HD progression. Each factor was investigated in isolation while controlling for 19 other factors to ensure that groups were balanced at baseline on potential confounders using PS weights. Outcomes were compared several years later using doubly robust models.

RESULTS

Our results highlighted cases where modifiable (non-genetic) factors - namely light and moderate alcohol use and employment - would have been associated with HD progression in models that did not use PS weights to control for baseline imbalances. These associations did not hold once we applied PS weights to balance baseline groups. We also found potential evidence of a protective effect of substance use (primarily marijuana use), and that those who needed antidepressant treatment were likely to progress faster than non-users.

CONCLUSIONS

Our study is the first to examine the effect of non-genetic factors on HD using a novel application of PS weighting. We show that previously-reported associated factors - including light and moderate alcohol use - are reduced and no longer significantly linked to HD progression after PS weighting. This indicates the potential value of PS weighting in examining non-genetic factors contributing to HD as well as in addressing the known biases that occur with observational data.

Biocompatible Inhibitor Based on Chitosan and Amphiphilic Peptide against Mutant Huntingtin Toxicity

Huntington's disease (HD) is classified as a protein-misfolding disease correlated with the mutant Huntingtin (mHtt) protein with abnormally expanded polyglutamine (polyQ) domains. Because no effective drugs have yet been reported, attempts to develop better therapy to delay the age of onset are in urgent demand. In this study, an amphiphilic peptide consisting of negatively charged hexaglutamic acid and a stretch of decaglutamine (E₆ Q₁₀ ) was chemically synthesized as an inhibitor against polyQ and mHtt toxicity. It is found that E₆ Q₁₀ selfassembles into spherical vesicles, as shown by means of TEM, cryoelectron microscopy, and dynamic light scattering. Assembled E₆ Q₁₀ prevented the polyQ-rich peptide (KKWQ₂₀ AKK) from forming amyloid fibrils. To enable the cell-penetration ability of E₆ Q₁₀ , the E₆ Q₁₀ ⋅chitosan complex was generated. It is demonstrated that the complex penetrates cells, interferes with the mHtt oligomerization and aggregation process, and prevents mHtt cytotoxicity. By combining positively charged chitosan and amphiphilic peptides with a negatively charge moiety, a new strategy is provided to develop biocompatible and biodegradable inhibitors against mHtt toxicity.

The Emerging Role of microRNAs in Polyglutamine Diseases

MicroRNAs (miRNAs) are small non-coding molecules that regulate a large amount of post-transcriptional repressor genes by recognizing semi-complementary target sequences that are normally located in the 3' UTR of the mRNA. Altered expression of miRNA has been related to several pathological processes, including polyglutamine (Poly Q) diseases. Specific expression patterns in the circulating fluids and brain parenchyma have been speculated as potential biomarkers for Poly Q disease diagnosis and prognosis. Several miRNAs have been consistently identified in diseases including Huntington's disease (HD) and spinocerebellar ataxia (SCA). In our review, we describe the emerging role of miRNAs in Poly Q diseases and provide an overview on general miRNA biology, implications in pathophysiology, and their potential roles as future biomarkers and applications for therapy.

Is Autophagy Involved in the Diverse Effects of Antidepressants?

Autophagy has received increased attention as a conserved process governing cellular energy and protein homeostasis that is thus relevant in a range of physiological and pathophysiological conditions. Recently, autophagy has also been linked to depression, mainly through its involvement in the action of antidepressants. Some antidepressant drugs and psychotropic medication have been reported to exert beneficial effects in other diseases, for example, in cancer and neurodegenerative diseases. This review collates the evidence for the hypothesis that autophagy contributes to the effects of antidepressants beyond depression treatment.

Insight Into the Emerging Role of Striatal Neurotransmitters in the Pathophysiology of Parkinson's Disease and Huntington's Disease: A Review

Alteration in neurotransmitters signaling in basal ganglia has been consistently shown to significantly contribute to the pathophysiological basis of Parkinson's disease and Huntington's disease. Dopamine is an important neurotransmitter which plays a critical role in coordinated body movements. Alteration in the level of brain dopamine and receptor radically contributes to irregular movements, glutamate mediated excitotoxic neuronal death and further leads to imbalance in the levels of other neurotransmitters viz. GABA, adenosine, acetylcholine and endocannabinoids. This review is based upon the data from clinical and preclinical studies to characterize the role of various striatal neurotransmitters in the pathogenesis of Parkinson's disease and Huntington's disease. Further, we have collected data of altered level of various neurotransmitters and their metabolites and receptor density in basal ganglia region. Although the exact mechanisms underlying neuropathology of movement disorders are not fully understood, but several mechanisms related to neurotransmitters alteration, excitotoxic neuronal death, oxidative stress, mitochondrial dysfunction, neuroinflammation are being put forward. Restoring neurotransmitters level and downstream signaling has been considered to be beneficial in the treatment of Parkinson's disease and Huntington's disease. Therefore, there is an urgent need to identify more specific drugs and drug targets that can restore the altered neurotransmitters level in brain and prevent/delay neurodegeneration.

ASPsiRNA: A Resource of ASP-siRNAs Having Therapeutic Potential for Human Genetic Disorders and Algorithm for Prediction of Their Inhibitory Efficacy

Allele-specific siRNAs (ASP-siRNAs) have emerged as promising therapeutic molecules owing to their selectivity to inhibit the mutant allele or associated single-nucleotide polymorphisms (SNPs) sparing the expression of the wild-type counterpart. Thus, a dedicated bioinformatics platform encompassing updated ASP-siRNAs and an algorithm for the prediction of their inhibitory efficacy will be helpful in tackling currently intractable genetic disorders. In the present study, we have developed the ASPsiRNA resource (http://crdd.osdd.net/servers/aspsirna/) covering three components viz (i) ASPsiDb, (ii) ASPsiPred, and (iii) analysis tools like ASP-siOffTar. ASPsiDb is a manually curated database harboring 4543 (including 422 chemically modified) ASP-siRNAs targeting 78 unique genes involved in 51 different diseases. It furnishes comprehensive information from experimental studies on ASP-siRNAs along with multidimensional genetic and clinical information for numerous mutations. ASPsiPred is a two-layered algorithm to predict efficacy of ASP-siRNAs for fully complementary mutant (Eff^mut) and wild-type allele (Eff^wild) with one mismatch by ASPsiPred^SVM and ASPsiPred^matrix, respectively. In ASPsiPred^SVM, 922 unique ASP-siRNAs with experimentally validated quantitative Eff^mut were used. During 10-fold cross-validation (10nCV) employing various sequence features on the training/testing dataset (T737), the best predictive model achieved a maximum Pearson’s correlation coefficient (PCC) of 0.71. Further, the accuracy of the classifier to predict Eff^mut against novel genes was assessed by leave one target out cross-validation approach (LOTOCV). ASPsiPred^matrix was constructed from rule-based studies describing the effect of single siRNA:mRNA mismatches on the efficacy at 19 different locations of siRNA. Thus, ASPsiRNA encompasses the first database, prediction algorithm, and off-target analysis tool that is expected to accelerate research in the field of RNAi-based therapeutics for human genetic diseases.

The Complexity of Clinical Huntington's Disease: Developments in Molecular Genetics, Neuropathology and Neuroimaging Biomarkers

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterised by extensive neuronal loss in the striatum and cerebral cortex, and a triad of clinical symptoms affecting motor, cognitive/behavioural and mood functioning. The mutation causing HD is an expansion of a CAG tract in exon 1 of the HTT gene. This chapter provides a multifaceted overview of the clinical complexity of HD. We explore recent directions in molecular genetics including the identification of loci that are genetic modifiers of HD that could potentially reveal therapeutic targets beyond the HTT gene transcript and protein. The variability of clinical symptomatology in HD is considered alongside recent findings of variability in cellular and neurochemical changes in the striatum and cerebral cortex in human brain. We review evidence from structural neuroimaging methods of progressive changes of striatum, cerebral cortex and white matter in pre-symptomatic and symptomatic HD, with a particular focus on the potential identification of neuroimaging biomarkers that could be used to test promising disease-specific and modifying treatments. Finally we provide an overview of completed clinical trials in HD and future therapeutic developments.

Revisiting the neuropsychiatry of Huntington's disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease classified under the choreas. Besides motor symptoms, HD is marked by cognitive and behavioral symptoms, impacting patients' functional capacity. The progression of cognitive impairment and neuropsychiatric symptoms occur in parallel with neurodegeneration. The nature of these symptoms is very dynamic, and the major clinical challenges include executive dysfunction, apathy, depression and irritability. Herein, we provide a focused updated review on the cognitive and psychiatric features of HD.