Statin use and delayed onset of Huntington's disease

Brain-Periphery Interactions in Huntington's Disease: Mediators and Lifestyle Interventions

Prominent pathological features of Huntington's disease (HD) are aggregations of mutated Huntingtin protein (mHtt) in the brain and neurodegeneration, which causes characteristic motor (such as chorea and dystonia) and non-motor symptoms. However, the numerous systemic and peripheral deficits in HD have gained increasing attention recently, since those factors likely modulate disease progression, including brain pathology. While whole-body metabolic abnormalities and organ-specific pathologies in HD have been relatively well described, the potential mediators of compromised inter-organ communication in HD have been insufficiently characterized. Therefore, we applied an exploratory literature search to identify such mediators. Unsurprisingly, dysregulation of inflammatory factors, circulating mHtt, and many other messenger molecules (hormones, lipids, RNAs) were found that suggest impaired inter-organ communication, including of the gut-brain and muscle-brain axis. Based on these findings, we aimed to assess the risks and potentials of lifestyle interventions that are thought to improve communication across these axes: dietary strategies and exercise. We conclude that appropriate lifestyle interventions have great potential to reduce symptoms and potentially modify disease progression (possibly via improving inter-organ signaling) in HD. However, impaired systemic metabolism and peripheral symptoms warrant particular care in the design of dietary and exercise programs for people with HD.

The Potential Therapeutic Application of Simvastatin for Brain Complications and Mechanisms of Action

Statins are common drugs that are clinically used to reduce elevated plasma cholesterol levels. Based on their solubility, statins are considered to be either hydrophilic or lipophilic. Amongst them, simvastatin has the highest lipophilicity to facilitate its ability to cross the blood-brain barrier. Recent studies have suggested that simvastatin could be a promising therapeutic option for different brain complications and diseases ranging from brain tumors (i.e., medulloblastoma and glioblastoma) to neurological disorders (i.e., Alzheimer's disease, Parkinson's disease, and Huntington's disease). Specific mechanisms of disease amelioration, however, are still unclear. Independent studies suggest that simvastatin may reduce the risk of developing certain neurodegenerative disorders. Meanwhile, other studies point towards inducing cell death in brain tumor cell lines. In this review, we outline the potential therapeutic effects of simvastatin on brain complications and review the clinically relevant molecular mechanisms in different cases.

Association between Genetically Proxied Inhibition of HMG-CoA Reductase and Age at Onset of Huntington’s Disease

Background: Previous studies have found that statins may play a potential role in the age at onset (AAO) of Huntington’s disease (HD). We performed this Mendelian randomization (MR) study to assess the association between genetically proxied inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and low-density lipoprotein (LDL) cholesterol with age at onset of HD. Methods: Single-nucleotide polymorphisms (SNPs) in HMG-CoA reductase associated with LDL cholesterol in a genome-wide association study (GWAS) analysis were used. The summary data of residual AAO of HD were obtained from a GWAS meta-analysis (n = 9064 HD patients). MR estimates representing lifelong inhibition of drug targets were generated using random-effects inverse-variance weighted analysis. Results: Genetically proxied plasma LDL cholesterol (β = 0.039, 95% CI = −0.454 to 0.531) and HMG-CoA reductase inhibition equivalent to a 1 mmol/L (38.7 mg/dL) reduction in LDL cholesterol (β = −2.228, 95% CI = −4.830 to 0.374) were not associated with age at onset of HD. Conclusion: The plasma LDL cholesterol levels and the reduction of plasma LDL cholesterol levels by the inhibition of HMG-CoA reductase (i.e., statins) were not associated with the age of HD onset.

Metabolic Dysfunction in Motor Neuron Disease: Shedding Light through the Lens of Autophagy

Amyotrophic lateral sclerosis (ALS) patients show a myriad of energetic abnormalities, such as weight loss, hypermetabolism, and dyslipidaemia. Evidence suggests that these indices correlate with and ultimately affect the duration of survival. This review aims to discuss ALS metabolic abnormalities in the context of autophagy, the primordial system acting at the cellular level for energy production during nutrient deficiency. As the primary pathway of protein degradation in eukaryotic cells, the fundamental role of cellular autophagy is the adaptation to metabolic demands. Therefore, autophagy is tightly coupled to cellular metabolism. We review evidence that the delicate balance between autophagy and metabolism is aberrant in ALS, giving rise to intracellular and systemic pathophysiology observations. Understanding the metabolism autophagy crosstalk can lead to the identification of novel therapeutic targets for ALS.

Altered Cholesterol Homeostasis in Huntington’s Disease

Huntington’s disease (HD) is an autosomal dominant genetic disorder caused by an expansion of the CAG repeat in the first exon of Huntingtin’s gene. The associated neurodegeneration mainly affects the striatum and the cortex at early stages and progressively spreads to other brain structures. Targeting HD at its earlier stages is under intense investigation. Numerous drugs were tested, with a rate of success of only 3.5% approved molecules used as symptomatic treatment. The restoration of cholesterol metabolism, which is central to the brain homeostasis and strongly altered in HD, could be an interesting disease-modifying strategy. Cholesterol is an essential membrane component in the central nervous system (CNS); alterations of its homeostasis have deleterious consequences on neuronal functions. The levels of several sterols, upstream of cholesterol, are markedly decreased within the striatum of HD mouse model. Transcription of cholesterol biosynthetic genes is reduced in HD cell and mouse models as well as post-mortem striatal and cortical tissues from HD patients. Since the dynamic of brain cholesterol metabolism is complex, it is essential to establish the best method to target it in HD. Cholesterol, which does not cross the blood-brain-barrier, is locally synthesized and renewed within the brain. All cell types in the CNS synthesize cholesterol during development but as they progress through adulthood, neurons down-regulate their cholesterol synthesis and turn to astrocytes for their full supply. Cellular levels of cholesterol reflect the dynamic balance between synthesis, uptake and export, all integrated into the context of the cross talk between neurons and glial cells. In this review, we describe the latest advances regarding the role of cholesterol deregulation in neuronal functions and how this could be a determinant factor in neuronal degeneration and HD progression. The pathways and major mechanisms by which cholesterol and sterols are regulated in the CNS will be described. From this overview, we discuss the main clinical strategies for manipulating cholesterol metabolism in the CNS, and how to reinstate a proper balance in HD.

Perspective insights of repurposing the pleiotropic efficacy of statins in neurodegenerative disorders: An expository appraisal

Neurodegenerative disorders which affects a larger population pose a great clinical challenge. These disorders impact the quality of life of an individual by damaging the neurons, which are the unit cells of the brain. Clinicians are faced with the grave challenge of inhibiting the progression of these diseases as available treatment options fail to meet the clinical demand. Thus, treating the disease/disorder symptomatically is the Hobson's choice. The goal of the researchers is to introduce newer therapies in this segment and introducing a new molecule will take long years of development. Hence, drug repurposing/repositioning can be a better substitute in comparison to time consuming and expensive drug discovery and development cycle. Presently, a paradigm shift towards the re-purposing of drugs can be witnessed. Statins which have been previously approved as anti-hyperlipidemic agents are in the limelight of research for re-purposed drugs. Owing to their anti-inflammatory and antioxidant nature, statins act as neuroprotective in several brain disorders. Further they attenuate the amyloid plaques and protein aggregation which are the triggering factors in the Alzheimer's and Parkinson's respectively. In case of Huntington disease and Multiple sclerosis they help in improving the psychomotor symptoms and stimulate remyelination thus acting as neuroprotective. This article reviews the potential of statins in treating neurodegenerative disorders along with a brief discussion on the safety concerns associated with use of statins and human clinical trial data linked with re-tasking statins for neurodegenerative disorders along with the regulatory perspectives involved with the drug repositioning.

Implications on the Therapeutic Potential of Statins via Modulation of Autophagy

Statins, which are functionally known as 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) inhibitors, are lipid-lowering compounds widely prescribed in patients with cardiovascular diseases (CVD). Several biological and therapeutic functions have been attributed to statins, including neuroprotection, antioxidation, anti-inflammation, and anticancer effects. Pharmacological characteristics of statins have been attributed to their involvement in the modulation of several cellular signaling pathways. Over the past few years, the therapeutic role of statins has partially been attributed to the induction of autophagy, which is critical in maintaining cellular homeostasis and accounts for the removal of unfavorable cells or specific organelles within cells. Dysregulated mechanisms of the autophagy pathway have been attributed to the etiopathogenesis of various disorders, including neurodegenerative disorders, malignancies, infections, and even aging. Autophagy functions as a double-edged sword during tumor metastasis. On the one hand, it plays a role in inhibiting metastasis through restricting necrosis of tumor cells, suppressing the infiltration of the inflammatory cell to the tumor niche, and generating the release of mediators that induce potent immune responses against tumor cells. On the other hand, autophagy has also been associated with promoting tumor metastasis. Several anticancer medications which are aimed at inducing autophagy in the tumor cells are related to statins. This review article discusses the implications of statins in the induction of autophagy and, hence, the treatment of various disorders.

The Association between CAG Repeat Length and Age of Onset of Juvenile-Onset Huntington's Disease

There is a known negative association between cytosine-adenine-guanine (CAG) repeat length and the age of motor onset (AMO) in adult-onset Huntington's Disease (AOHD). This relationship is less clear in patients with juvenile-onset Huntington's disease (JOHD), however, given the rarity of this patient population. The aim of this study was to investigate this relationship amongst a relatively large group of patients with JOHD using data from the Kids-JOHD study. Additionally, we analyzed data from the Enroll-HD platform and the Predict-HD study to compare the relationship between CAG repeat length and AMO amongst patients with AOHD to that amongst patients with JOHD using linear regression models. In line with previous reports, the variance in AMO that was predicted by CAG repeat length was 59% (p < 0.0001) in the Predict-HD study and 57% from the Enroll-HD platform (p < 0.0001). However, CAG repeat length predicted 84% of the variance in AMO amongst participants from the Kids-JOHD study (p < 0.0001). These results indicate that there may be a stronger relationship between CAG repeat length and AMO in patients with JOHD as compared to patients with AOHD. These results provide additional information that may help to model disease progression of JOHD, which is beneficial for the planning and implementation of future clinical trials.

Dysregulated Brain Cholesterol Metabolism Is Linked to Neuroinflammation in Huntington's Disease

Huntington's disease is an autosomal-dominant, neurodegenerative disorder caused by a CAG repeat expansion in exon-1 of the huntingtin gene. Alterations in cholesterol metabolism and distribution have been reported in Huntington's disease, including abnormal interactions between mutant huntingtin and sterol regulatory element-binding proteins, decreased levels of apolipoprotein E/cholesterol/low-density lipoprotein receptor complexes, and alterations in the synthesis of ATP-binding cassette transporter A1. Plasma levels of 24S-hydroxycholestrol, a key intermediary in cholesterol metabolism and a possible marker in neurodegenerative diseases, decreased proportionally to the degree of caudate nucleus atrophy. The interaction of mutant huntingtin with sterol regulatory element-binding proteins is of particular interest given that sterol regulatory element-binding proteins play a dual role: They take part in lipid and cholesterol metabolism, but also in the inflammatory response that induces immune cell migration as well as toxic effects, particularly in astrocytes. This work summarizes current evidence on the metabolic and immune implications of sterol regulatory element-binding protein dysregulation in Huntington's disease, highlighting the potential use of drugs that modulate these alterations. © 2020 International Parkinson and Movement Disorder Society.