Zonisamide for the Treatment of Parkinson Disease: A Current Update

Novel and experimental therapeutics for the management of motor and non-motor Parkinsonian symptoms

BACKGROUND  : Both motor and non-motor symptoms of Parkinson's disease (PD) have a substantial detrimental influence on the patient's quality of life. The most effective treatment remains oral levodopa. All currently known treatments just address the symptoms; they do not completely reverse the condition.

METHODOLOGY

In order to find literature on the creation of novel treatment agents and their efficacy for PD patients, we searched PubMed, Google Scholar, and other online libraries.

RESULTS

According to the most recent study on Parkinson's disease (PD), a great deal of work has been done in both the clinical and laboratory domains, and some current scientists have even been successful in developing novel therapies for PD patients.

CONCLUSION

The quality of life for PD patients has increased as a result of recent research, and numerous innovative medications are being developed for PD therapy. In the near future, we will see positive outcomes regarding PD treatment.

MiRAGE: mining relationships for advanced generative evaluation in drug repositioning

MOTIVATION

Drug repositioning, the identification of new therapeutic uses for existing drugs, is crucial for accelerating drug discovery and reducing development costs. Some methods rely on heterogeneous networks, which may not fully capture the complex relationships between drugs and diseases. However, integrating diverse biological data sources offers promise for discovering new drug-disease associations (DDAs). Previous evidence indicates that the combination of information would be conducive to the discovery of new DDAs. However, the challenge lies in effectively integrating different biological data sources to identify the most effective drugs for a certain disease based on drug-disease coupled mechanisms.

RESULTS

In response to this challenge, we present MiRAGE, a novel computational method for drug repositioning. MiRAGE leverages a three-step framework, comprising negative sampling using hard negative mining, classification employing random forest models, and feature selection based on feature importance. We evaluate MiRAGE on multiple benchmark datasets, demonstrating its superiority over state-of-the-art algorithms across various metrics. Notably, MiRAGE consistently outperforms other methods in uncovering novel DDAs. Case studies focusing on Parkinson's disease and schizophrenia showcase MiRAGE's ability to identify top candidate drugs supported by previous studies. Overall, our study underscores MiRAGE's efficacy and versatility as a computational tool for drug repositioning, offering valuable insights for therapeutic discoveries and addressing unmet medical needs.

Drug repurposing for neurodegenerative diseases

Neurodegenerative diseases (NDDs) are neuronal problems that include the brain and spinal cord and result in loss of sensory and motor dysfunction. Common NDDs include Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple Sclerosis (MS), and Amyotrophic Lateral Sclerosis (ALS) etc. The occurrence of these diseases increases with age and is one of the challenging problems among elderly people. Though, several scientific research has demonstrated the key pathologies associated with NDDs still the underlying mechanisms and molecular details are not well understood and need to be explored and this poses a lack of effective treatments for NDDs. Several lines of evidence have shown that NDDs have a high prevalence and affect more than a billion individuals globally but still, researchers need to work forward in identifying the best therapeutic target for NDDs. Thus, several researchers are working in the directions to find potential therapeutic targets to alter the disease pathology and treat the diseases. Several steps have been taken to identify the early detection of the disease and drug repurposing for effective treatment of NDDs. Moreover, it is logical that current medications are being evaluated for their efficacy in treating such disorders; therefore, drug repurposing would be an efficient, safe, and cost-effective way in finding out better medication. In the current manuscript we discussed the utilization of drugs that have been repurposed for the treatment of AD, PD, HD, MS, and ALS.

Role of zonisamide in advanced Parkinson's disease: a randomized placebo-controlled study

BACKGROUND

Zonisamide (ZNS) has shown some efficacy in motor symptoms of PD; however, more evidence is lacking, and its effects on nonmotor symptoms (NMSs) and quality of life (QoL) remain to be investigated. This randomized double-blinded placebo-controlled crossover study investigated the effect of ZNS on motor and NMS symptoms and QoL in advanced PD.

METHODS

PD patients with Hoehn and Yahr stage ≥ 2 ("On" state) and at least 2 h off time daily were randomized to groups: ZNS 25 mg, ZNS 50 mg and placebo. Groups were assessed at baseline and at the 1- and 3-month follow-ups. The primary endpoint was the change in the total MDS-UPDRS III "On", while the secondary endpoint was the change in the total and parts I and IV MDS-UPDRS, Nonmotor Symptoms Scale and Parkinson's disease questionnaire-39 at the final assessment.

RESULTS

Sixty-nine patients were assessed for efficacy at the 1-month follow-up, and 58 patients were assessed at the 3-month follow-up. The primary endpoint showed significant improvement in the ZNS 25 mg group compared to the placebo group (p = 0.009). At the final assessment, the ZNS 25 mg group showed significant improvement of total and part VI MDS-UPDRS, bradykinesia, tremor and functional impact of fluctuations compared to placebo. There was no change in dyskinesia, NMSs, QoL or side effects except for sedation.

CONCLUSION

ZNS has a favourable effect on motor symptoms in patients with wearing off as adjunctive therapy with other dopaminergic drugs, with no exacerbation of dyskinesia and a limited impact on NMSs and QoL.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT04182399, in 24/11/2019.

Antiepileptic Drugs as Potential Dementia Prophylactics Following Traumatic Brain Injury

Seizures and other forms of neurovolatility are emerging as druggable prodromal mechanisms that link traumatic brain injury (TBI) to the progression of later dementias. TBI neurotrauma has both acute and long-term impacts on health, and TBI is a leading risk factor for dementias, including chronic traumatic encephalopathy and Alzheimer's disease. Treatment of TBI already considers acute management of posttraumatic seizures and epilepsy, and impressive efforts have optimized regimens of antiepileptic drugs (AEDs) toward that goal. Here we consider that expanding these management strategies could determine which AED regimens best prevent dementia progression in TBI patients. Challenges with this prophylactic strategy include the potential consequences of prolonged AED treatment and that a large subset of patients are refractory to available AEDs. Addressing these challenges is warranted because the management of seizure activity following TBI offers a rare opportunity to prevent the onset or progression of devastating dementias.

Future Directions for Developing Non-dopaminergic Strategies for the Treatment of Parkinson's Disease

The symptomatic treatment of Parkinson's disease (PD) has been dominated by the use of dopaminergic medication, but significant unmet need remains, much of which is related to non-motor symptoms and the involvement of non-dopaminergic transmitter systems. As such, little has changed in the past decades that has led to milestone advances in therapy and significantly improved treatment paradigms and patient outcomes, particularly in relation to symptoms unresponsive to levodopa. This review has looked at how pharmacological approaches to treatment are likely to develop in the near and distant future and will focus on two areas: 1) novel non-dopaminergic pharmacological strategies to control motor symptoms; and 2) novel non-dopaminergic approaches for the treatment of non-motor symptoms. The overall objective of this review is to use a 'crystal ball' approach to the future of drug discovery in PD and move away from the more traditional dopamine-based treatments. Here, we discuss promising non-dopaminergic and 'dirty drugs' that have the potential to become new key players in the field of Parkinson's disease treatment.

Efficacy and Safety of MAO-B Inhibitors Safinamide and Zonisamide in Parkinson's Disease: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND AND OBJECTIVE

In Parkinson's disease, safinamide and zonisamide are novel monoamine oxidase-B inhibitors with a dual mechanism of action involving the inhibition of sodium and calcium channels and the subsequent release of glutamate. The aim of this systematic review and meta-analysis was to examine the efficacy and safety of both drugs compared with placebo on motor symptoms, cognitive function, and quality of life in patients with Parkinson's disease.

METHODS

We searched MEDLINE, EMBASE, Cochrane Central, Scopus, PsycINFO, and trials registries up to March 2023 for randomized controlled trials of adults with Parkinson's disease administered either safinamide or zonisamide and published in English. We excluded single-arm trials or if neither the efficacy nor safety outcomes of interest were reported. Primary outcomes were the change from baseline in Unified Parkinson's Disease Rating Scale section III (UPDRS-III) and serious adverse events. Secondary outcomes included a change from baseline in OFF-time, Parkinson's Disease Questionnaire 39 to evaluate quality of life, and Mini-Mental State Examination for cognitive function assessment. The meta-analysis was conducted using Review Manager 5.4.1. Random-effect models were used to calculate the pooled mean differences (MDs) and risk ratios with 95% confidence intervals (CIs). Subgroup analyses by medication, doses, Parkinson's disease stage, and risk of bias were conducted. We assessed the risk of bias using the Cochrane's risk of bias tool. Sensitivity analysis was conducted, and publication bias were evaluated. This meta-analysis was not externally funded, and the protocol is available on the Open Science Framework Registration ( https://doi.org/10.17605/OSF.IO/AMNP5 ).

RESULTS

Of 3570 screened citations, 16 trials met inclusion criteria (4314 patients with Parkinson's disease). Ten safinamide trials were conducted in several countries. Six zonisamide trials were included, five of which were conducted in Japan and one in India. UPDRS Part III scores were significantly lower with both monoamine oxidase-B inhibitors than with placebo (MD = -  2.18; 95% CI -  2.88 to -  1.49; I 2 =63%; n = 14 studies). A subgroup analysis showed a significant improvement in UPDRS-III in safinamide (MD = -  2.10; 95% CI -  3.09 to -  1.11; I2 = 71%; n = 8 studies) and zonisamide (MD = -  2.31; 95% CI -  3.35 to -  1.27; I2 = 52%; n = 6 studies) compared with placebo. Monoamine oxidase-B inhibitors significantly decreased OFF-time compared with placebo. No significant differences in cognitive function (Mini-Mental State Examination), whereas an improvement in quality of life (Parkinson's Disease Questionnaire 39 scores) was observed. There was no significant difference in incidence rates of serious adverse events among all examined doses of zonisamide and safinamide compared with placebo. Two trials were reported as a high risk of bias and sensitivity analyses confirmed the primary analysis results.

CONCLUSIONS

Evidence suggests that novel monoamine oxidase-B inhibitors not only improve motor symptoms but also enhance patients' quality of life. The meta-analysis showed that both medications have a similar safety profile to placebo with regard to serious adverse events. The overall findings emphasize the effectiveness of safinamide and zonisamide in the treatment of Parkinson's disease as adjunct therapy. Further long-term studies examining the impact of these medications on motor and non-motor symptoms are necessary.

Parkinson's disease therapy: what lies ahead?

The worldwide prevalence of Parkinson's disease (PD) has been constantly increasing in the last decades. With rising life expectancy, a longer disease duration in PD patients is observed, further increasing the need and socioeconomic importance of adequate PD treatment. Today, PD is exclusively treated symptomatically, mainly by dopaminergic stimulation, while efforts to modify disease progression could not yet be translated to the clinics. New formulations of approved drugs and treatment options of motor fluctuations in advanced stages accompanied by telehealth monitoring have improved PD patients care. In addition, continuous improvement in the understanding of PD disease mechanisms resulted in the identification of new pharmacological targets. Applying novel trial designs, targeting of pre-symptomatic disease stages, and the acknowledgment of PD heterogeneity raise hopes to overcome past failures in the development of drugs for disease modification. In this review, we address these recent developments and venture a glimpse into the future of PD therapy in the years to come.

Risk factors for developing dyskinesia among Parkinson's disease patients with wearing-off: J-FIRST

BACKGROUND

Dyskinesia frequently occurs during long-term treatment with levodopa in patients with Parkinson's disease (PD) and impacts quality of life. Few studies have examined risk factors for developing dyskinesia in PD patients exhibiting wearing-off. Therefore, we investigated the risk factors and impact of dyskinesia in PD patients exhibiting wearing-off.

METHODS

We investigated the risk factors and impact of dyskinesia in a 1-year observational study of Japanese PD patients exhibiting wearing-off (J-FIRST). Risk factors were assessed by logistic regression analyses in patients without dyskinesia at study entry. Mixed-effect models were used to evaluate the impact of dyskinesia on changes in Movement Disorder Society-Unified PD Rating Scale (MDS-UPDRS) Part I and PD Questionnaire (PDQ)-8 scores from one timepoint before dyskinesia was observed.

RESULTS

Of 996 patients analyzed, 450 had dyskinesia at baseline, 133 developed dyskinesia within 1 year, and 413 did not develop dyskinesia. Female sex (odds ratio [95% confidence interval]: 2.636 [1.645-4.223]) and administration of a dopamine agonist (1.840 [1.083-3.126]), a catechol-O-methyltransferase inhibitor (2.044 [1.285-3.250]), or zonisamide (1.869 [1.184-2.950]) were independent risk factors for dyskinesia onset. MDS-UPDRS Part I and PDQ-8 scores increased significantly after the onset of dyskinesia (least-squares mean change [standard error] at 52 weeks: 1.11 [0.52], P = 0.0336; 1.53 [0.48], P = 0.0014; respectively).

CONCLUSION

Female sex and administration of a dopamine agonist, a catechol-O-methyltransferase inhibitor, or zonisamide were risk factors for dyskinesia onset within 1 year in PD patients exhibiting wearing-off. Nonmotor symptoms and quality of life deteriorated after dyskinesia onset.

Effective Management of "OFF" Episodes in Parkinson's Disease: Emerging Treatment Strategies and Unmet Clinical Needs

Motor complications related to the chronic administration of levodopa and failure to prevent the neurodegenerative disease process counterbalance the pivotal discovery of levodopa as the cornerstone of PD treatment. Excellent motor control is offered early during the course of treatment, but this diminishes as pathological changes in the striatum lead to synaptic dopamine levels becoming completely dependent on exogenous dopamine. This non-physiologic stimulation of dopamine receptors eventually manifests as OFF episodes. As no disease modifying therapy exists for PD that can disrupt these pathological changes, most research and treatment focuses on optimization of dopaminergic stimulation of striatal receptors so that they mimic tonic, physiologic stimulation as closely as possible. Strategies focusing on these challenges have included non-pharmacologic approaches, optimizing levodopa pharmacokinetics, using adjunctive treatments including those with non-dopaminergic mechanisms, and implementing rescue therapies. Device aided therapies, including surgery, are also available. In this review, we will focus on effective management of motor symptoms related to OFF periods, including emerging strategies. Unmet clinical needs will be discussed, including non-motor symptoms, targeted molecular therapies and disease modifying therapy.

Changed firing activity of nigra dopaminergic neurons in Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease which is characterized by selective degeneration of dopaminergic neurons in the substantia nigra pars compacta. The intrinsic neuronal firing activity is critical for the functional organization of brain and the specific deficits of neuronal firing activity may be associated with different brain disorders. It is known that the surviving nigra dopaminergic neurons exhibit altered firing activity, such as decreased spontaneous firing frequency, reduced number of firing neurons and increased burst firing in Parkinson's disease. Several ionic mechanisms are involved in changed firing activity of dopaminergic neurons under parkinsonian state. In this review, we summarize the changes of spontaneous firing activity as well as the possible mechanisms of nigra dopaminergic neurons in Parkinson's disease. This review may let us clearly understand the involvement of neuronal firing activity of nigra dopaminergic neurons in Parkinson's disease.

Zonisamide add-on in tremor-dominant Parkinson's disease- A randomized controlled clinical trial

INTRODUCTION

and objective: Tremor is a disabling symptom of PD that usually responds poorly to available standard pharmacological agents. This study aimed to assess the effect of Zonisamide 25 mg on tremor in tremor-dominant PD patients as compared to placebo.

METHODS

This was a randomized, placebo-controlled, double-blind study. Parkinson's disease patients were allocated either to the intervention group (standard treatment along with Zonisamide 25 mg add-on) or the placebo group (standard treatment along with placebo). Baseline Unified Parkinson's Disease Rating Scale (UPDRS) and Tremor Research Group Essential Tremor Rating Scale (TETRAS) scores, as well as accelerometric tremor analysis were done and follow-up assessments of the same were done after 12 weeks of intervention. Percentage change from baseline in the UPDRS tremor score was the primary outcome whereas percentage change from baseline of total UPDRS score, UPDRS rigidity and bradykinesia scores, TETRAS score, and accelerometric tremor analysis values were the secondary outcomes.

RESULTS

There was no significant difference in the percentage change from baseline UPDRS tremor scores between the two groups (placebo: 8.33 [-19.89-23.86] vs drug: 26.14 [-35.58 to -16.07], p-value: 0.164, CI: 0.157-0.171). Best-case analysis for missing values showed a significant improvement in the drug group, compared to the placebo group (p-value: < 0.001, CI: <0.001 - <0.001).

CONCLUSION

Zonisamide at a dose of 25 mg per day did not improve tremor in tremor-dominant PD patients, however, a positive trend was seen as compared to Placebo in the UPDRS tremor score. Larger studies are required to confirm this finding.

Identifying Protective Drugs for Parkinson's Disease in Health-Care Databases Using Machine Learning

BACKGROUND

Available treatments for Parkinson's disease (PD) are only partially or transiently effective. Identifying existing molecules that may present a therapeutic or preventive benefit for PD (drug repositioning) is thus of utmost interest.

OBJECTIVE

We aimed at detecting potentially protective associations between marketed drugs and PD through a large-scale automated screening strategy.

METHODS

We implemented a machine learning (ML) algorithm combining subsampling and lasso logistic regression in a case-control study nested in the French national health data system. Our study population comprised 40,760 incident PD patients identified by a validated algorithm during 2016 to 2018 and 176,395 controls of similar age, sex, and region of residence, all followed since 2006. Drug exposure was defined at the chemical subgroup level, then at the substance level of the Anatomical Therapeutic Chemical (ATC) classification considering the frequency of prescriptions over a 2-year period starting 10 years before the index date to limit reverse causation bias. Sensitivity analyses were conducted using a more specific definition of PD status.

RESULTS

Six drug subgroups were detected by our algorithm among the 374 screened. Sulfonamide diuretics (ATC-C03CA), in particular furosemide (C03CA01), showed the most robust signal. Other signals included adrenergics in combination with anticholinergics (R03AL) and insulins and analogues (A10AD).

CONCLUSIONS

We identified several signals that deserve to be confirmed in large studies with appropriate consideration of the potential for reverse causation. Our results illustrate the value of ML-based signal detection algorithms for identifying drugs inversely associated with PD risk in health-care databases. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Investigation of the Utility of Multivariate Meta-Analysis Methods in Estimating the Summary Dose Response Curve

BACKGROUND

Traditional meta-analyses often assess the effectiveness of different doses of the same intervention separately or examine the overall differences between intervention and placebo groups. The present study aimed to model the effect sizes obtained from different doses in multiple studies using a two-stage dose-response meta-analytic approach while taking dose variations into account.

METHODS

Different dose-response meta-analysis models using linear, quadratic, and restricted cubic spline (RCS) functions were fitted. A two-stage approach utilizing multivariate meta-analysis was performed and the obtained results were compared with those of the univariate meta-analysis. A random effect dose-response meta-analysis was performed using data from an existing systematic review on combination therapy with zonisamide and anti-Parkinson drugs for Parkinson's disease. The effective or optimum dose for producing maximum response was also investigated. Moreover, a sensitivity analysis was performed by changing the knots of the RCS model.

RESULTS

Dose-response meta-analysis was performed using data from four double-blinded randomized controlled trials with 724 and 309 patients with Parkinson's disease in dose and placebo arms, respectively. The quadratic model yielded the smallest Akaike information criterion (AIC), compared to the linear and RCS models, indicating it to be the best fit for the data.

CONCLUSION

Compared to the traditional approach, the two-stage approach could model the dose-dependent effect of zonisamide on the Unified Parkinson's Disease Rating Scale (UPRDS) part III score and predict the outcome for different doses through a single analysis.

Why do 'OFF' periods still occur during continuous drug delivery in Parkinson's disease?

Continuous drug delivery (CDD) is used in moderately advanced and late-stage Parkinson’s disease (PD) to control motor and non-motor fluctuations (‘OFF’ periods). Transdermal rotigotine is indicated for early fluctuations, while subcutaneous apomorphine infusion and levodopa-carbidopa intestinal gel are utilised in advanced PD. All three strategies are considered examples of continuous dopaminergic stimulation achieved through CDD. A central premise of the CDD is to achieve stable control of the parkinsonian motor and non-motor states and avoid emergence of ‘OFF’ periods. However, data suggest that despite their efficacy in reducing the number and duration of ‘OFF’ periods, these strategies still do not prevent ‘OFF’ periods in the middle to late stages of PD, thus contradicting the widely held concepts of continuous drug delivery and continuous dopaminergic stimulation. Why these emergent ‘OFF’ periods still occur is unknown. In this review, we analyse the potential reasons for their persistence. The contribution of drug- and device-related involvement, and the problems related to site-specific drug delivery are analysed. We propose that changes in dopaminergic and non-dopaminergic mechanisms in the basal ganglia might render these persistent ‘OFF’ periods unresponsive to dopaminergic therapy delivered via CDD.

Zonisamide's Efficacy and Safety on Parkinson's Disease and Dementia with Lewy Bodies: A Meta-Analysis and Systematic Review

Objective

Clinical data has recently shown an association between Parkinson's disease (PD), Dementia with Lewy bodies (DLB), and zonisamide. The purpose of this study was to thoroughly evaluate the efficacy and safety of zonisamide in PD and DLB.

Methods

Pubmed, the Cochrane Library, Web of Science, and Embase databases were searched for all randomized clinical trials (RCTS) on the role of zonisamide in PD and DLB that were completed by April 18, 2022. UPDRS II (off) total score, UPDRS III total score, Daily "off" time, and UPDRS Part IV, Nos. 32, 33, and 34 were used as clinical efficacy endpoints. Adverse events reported in the RCTs will be considered in the final safety analysis. To better understand the effect of zonisamide on the efficacy and safety of PD and DLB, the UPDRS III total score and the six overlapping adverse events were examined in subgroups. Either a fixed effects model analysis (OR) or a random effects model analysis (MD) is used to figure out the mean difference (MD) and the relative risk.

Results

Seven articles involving 1749 patients (916 PD and 833 DLB) were included in this study. Compared to the control group, zonisamide could significantly reduce the UPDRS III total score in patients with PD and DLB (WMD-2.27 [95% CI: -3.06, -1.48], p < 0.0001). For patients with PD, compared to the control group, zonisamide could significantly reduce the UPDRS II (off) total score (WMD-0.81 [95% CI: -1.36, -0.26], p = 0.004), daily "off" time (WMD-0.67 [95% CI: -1.10, 0.24], p = 0.002), and UPDRS part IV, No. 32 worsen (OR-3.48 [95% CI: 1.20, 10.10], p = 0.02). In terms of safety, compared with the control group, for patients with DLB, zonisamide could significantly increase the incidence of contusion (OR-0.60 [95% CI: 0.38, 0.96], p = 0.03) and may increase the probability of reduced appetite (OR-3.13 [95% CI: 1.61, 6.08], p = 0.0008). And for patients with PD, zonisamide may increase the probability of somnolence (OR-2.17 [95% CI: 1.25, 3.76], p = 0.006).

Conclusions

For the analysis of the current study results, our results show that zonisamide could improve the motor function in patients with PD and DLB and improve the activities of daily living (off) and wearing off and decrease the duration of dyskinesia in patients with PD. In terms of safety, the use of zonisamide significantly increases the probability of contusion in patients with DLB and may increase the probability of reduced appetite in patients with DLB and somnolence in patients with PD. Zonisamide appears to be a new treatment option for patients with PD and DLB. However, the effectiveness and safety of zonisamide in the treatment of PD and DLB need to be further investigated.

Pretreatment with Zonisamide Mitigates Oxaliplatin-Induced Toxicity in Rat DRG Neurons and DRG Neuron–Schwann Cell Co-Cultures

Oxaliplatin (OHP) is a platinum-based agent that can cause peripheral neuropathy, an adverse effect in which the dorsal root ganglion (DRG) neurons are targeted. Zonisamide has exhibited neuroprotective activities toward adult rat DRG neurons in vitro and therefore, we aimed to assess its potential efficacy against OHP-induced neurotoxicity. Pretreatment with zonisamide (100 μM) alleviated the DRG neuronal death caused by OHP (75 μM) and the protective effects were attenuated by a co-incubation with 25 μM of the mitogen-activated protein kinase (MAPK; MEK/ERK) inhibitor, U0126, or the phosphatidyl inositol-3′-phosphate-kinase (PI3K) inhibitor, LY294002. Pretreatment with zonisamide also suppressed the OHP-induced p38 MAPK phosphorylation in lined DRG neurons, ND7/23, while the OHP-induced DRG neuronal death was alleviated by pretreatment with the p38 MAPK inhibitor, SB239063 (25 μM). Although zonisamide failed to protect the immortalized rat Schwann cells IFRS1 from OHP-induced cell death, it prevented neurite degeneration and demyelination-like changes, as well as the reduction of the serine/threonine-specific protein kinase (AKT) phosphorylation in DRG neuron–IFRS1 co-cultures exposed to OHP. Zonisamide’s neuroprotection against the OHP-induced peripheral sensory neuropathy is possibly mediated by a stimulation of the MEK/ERK and PI3K/AKT signaling pathways and suppression of the p38 MAPK pathway in DRG neurons. Future studies will allow us to solidify zonisamide as a promising remedy against the neurotoxic adverse effects of OHP.

Newly Approved and Investigational Drugs for Motor Symptom Control in Parkinson's Disease

Motor symptoms are a core feature of Parkinson’s disease (PD) and cause a significant burden on patients’ quality of life. Oral levodopa is still the most effective treatment, however, the motor benefits are countered by inherent pharmacologic limitations of the drug. Additionally, with disease progression, chronic levodopa leads to the appearance of motor complications including motor fluctuations and dyskinesia. Furthermore, several motor abnormalities of posture, balance, and gait may become less responsive to levodopa. With these unmet needs and our evolving understanding of the neuroanatomic and pathophysiologic underpinnings of PD, several advances have been made in defining new therapies for motor symptoms. These include newer levodopa formulations and drug delivery systems, refinements in adjunctive medications, and non-dopaminergic treatment strategies. Although some are in early stages of development, these novel treatments potentially widen the available options for the management of motor symptoms allowing clinicians to provide an individually tailored care for PD patients. Here, we review the existing and emerging interventions for PD with focus on newly approved and investigational drugs for motor symptoms, motor fluctuations, dyskinesia, and balance and gait dysfunction.

Altered neural cell junctions and ion-channels leading to disrupted neuron communication in Parkinson's disease

Parkinson’s disease (PD) is a neurological disorder that affects the movement of the human body. It is primarily characterized by reduced dopamine levels in the brain. The causative agent of PD is still unclear but it is generally accepted that α-synuclein has a central role to play. It is also known that gap-junctions and associated connexins are complicated structures that play critical roles in nervous system signaling and associated misfunctioning. Thus, our current article emphasizes how, alongside α-synuclein, ion-channels, gap-junctions, and related connexins, all play vital roles in influencing multiple metabolic activities of the brain during PD. It also highlights that ion-channel and gap-junction disruptions, which are primarily mediated by their structural-functional changes and alterations, have a role in PD. Furthermore, we discussed available drugs and advanced therapeutic interventions that target Parkinson’s pathogenesis. In conclusion, it warrants creating better treatments for PD patients. Although, dopaminergic replenishment therapy is useful in treating neurological problems, such therapies are, however, unable to control the degeneration that underpins the disease, thereby declining their overall efficacy. This creates an additional challenge and an untapped scope for neurologists to adopt treatments for PD by targeting the ion-channels and gap-junctions, which is well-reviewed in the present article.

Molecular Mechanisms and Therapeutic Strategies for Levodopa-Induced Dyskinesia in Parkinson's Disease: A Perspective Through Preclinical and Clinical Evidence

Parkinson's disease (PD) is the second leading neurodegenerative disease that is characterized by severe locomotor abnormalities. Levodopa (L-DOPA) treatment has been considered a mainstay for the management of PD; however, its prolonged treatment is often associated with abnormal involuntary movements and results in L-DOPA-induced dyskinesia (LID). Although LID is encountered after chronic administration of L-DOPA, the appearance of dyskinesia after weeks or months of the L-DOPA treatment has complicated our understanding of its pathogenesis. Pathophysiology of LID is mainly associated with alteration of direct and indirect pathways of the cortico-basal ganglia-thalamic loop, which regulates normal fine motor movements. Hypersensitivity of dopamine receptors has been involved in the development of LID; moreover, these symptoms are worsened by concurrent non-dopaminergic innervations including glutamatergic, serotonergic, and peptidergic neurotransmission. The present study is focused on discussing the recent updates in molecular mechanisms and therapeutic approaches for the effective management of LID in PD patients.

Zonisamide Ameliorates Microglial Mitochondriopathy in Parkinson’s Disease Models

Mitochondrial dysfunction and exacerbated neuroinflammation are critical factors in the pathogenesis of both familial and non-familial forms of Parkinson’s disease (PD). This study aims to understand the possible ameliorative effects of zonisamide on microglial mitochondrial dysfunction in PD. We prepared 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and lipopolysaccharide (LPS) co-treated mouse models of PD to investigate the effects of zonisamide on mitochondrial reactive oxygen species generation in microglial cells. Consequently, we utilised a mouse BV2 cell line that is commonly used for microglial studies to determine whether zonisamide could ameliorate LPS-treated mitochondrial dysfunction in microglia. Flow cytometry assay indicated that zonisamide abolished microglial reactive oxygen species (ROS) generation in PD models. Extracellular flux assays showed that LPS exposure to BV2 cells at 1 μg/mL drastically reduced the mitochondrial oxygen consumption rate (OCR) and extracellular acidification rate (ECAR). Zonisamide overcame the inhibitory effects of LPS on mitochondrial OCR. Our present data provide novel evidence on the ameliorative effect of zonisamide against microglial mitochondrial dysfunction and support its clinical use as an antiparkinsonian drug.

Kynurenic acid in neurodegenerative disorders-unique neuroprotection or double-edged sword?

AIMS

The family of kynurenine pathway (KP) metabolites includes compounds produced along two arms of the path and acting in clearly opposite ways. The equilibrium between neurotoxic kynurenines, such as 3-hydroxykynurenine (3-HK) or quinolinic acid (QUIN), and neuroprotective kynurenic acid (KYNA) profoundly impacts the function and survival of neurons. This comprehensive review summarizes accumulated evidence on the role of KYNA in Alzheimer's, Parkinson's and Huntington's diseases, and discusses future directions of potential pharmacological manipulations aimed to modulate brain KYNA.

DISCUSSION

The synthesis of specific KP metabolites is tightly regulated and may considerably vary under physiological and pathological conditions. Experimental data consistently imply that shift of the KP to neurotoxic branch producing 3-HK and QUIN formation, with a relative or absolute deficiency of KYNA, is an important factor contributing to neurodegeneration. Targeting specific brain regions to maintain adequate KYNA levels seems vital; however, it requires the development of precise pharmacological tools, allowing to avoid the potential cognitive adverse effects.

CONCLUSIONS

Boosting KYNA levels, through interference with the KP enzymes or through application of prodrugs/analogs with high bioavailability and potency, is a promising clinical approach. The use of KYNA, alone or in combination with other compounds precisely influencing specific populations of neurons, is awaiting to become a significant therapy for neurodegenerative disorders.

Are ion channels potential therapeutic targets for Parkinson's disease?

Parkinson's disease (PD) is primarily associated with the progressive neurodegeneration of the dopaminergic neurons in the substantia nigra region of the brain. The resulting motor symptoms are managed with the help of dopamine replacement therapies. However, these therapeutics do not prevent the neurodegeneration underlying the disease and therefore lose their effectiveness in managing disease symptoms over time. Thus, there is an urgent need to develop newer therapeutics for the benefit of patients. The release of dopamine and the firing activity of substantia nigra neurons is regulated by several ion channels that act in concert. Dysregulations of these channels cause the aberrant movement of various ions in the intracellular milieu. This eventually leads to disruption of intracellular signalling cascades, alterations in cellular homeostasis, and bioenergetic deficits. Therefore, ion channels play a central role in driving the high vulnerability of dopaminergic neurons to degenerate during PD. Targeting ion channels offers an attractive mechanistic strategy to combat the process of neurodegeneration. In this review, we highlight the evidence pointing to the role of various ion channels in driving the PD processes. In addition, we also discuss the various drugs or compounds that target the ion channels and have shown neuroprotective potential in the in-vitro and in-vivo models of PD. We also discuss the current clinical status of various drugs targeting the ion channels in the context of PD.

Epilepsy in Neurodegenerative Diseases: Related Drugs and Molecular Pathways

Epilepsy is a chronic disease of the central nervous system characterized by an electrical imbalance in neurons. It is the second most prevalent neurological disease, with 50 million people affected around the world, and 30% of all epilepsies do not respond to available treatments. Currently, the main hypothesis about the molecular processes that trigger epileptic seizures and promote the neurotoxic effects that lead to cell death focuses on the exacerbation of the glutamate pathway and the massive influx of Ca2+ into neurons by different factors. However, other mechanisms have been proposed, and most of them have also been described in other neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, or multiple sclerosis. Interestingly, and mainly because of these common molecular links and the lack of effective treatments for these diseases, some antiseizure drugs have been investigated to evaluate their therapeutic potential in these pathologies. Therefore, in this review, we thoroughly investigate the common molecular pathways between epilepsy and the major neurodegenerative diseases, examine the incidence of epilepsy in these populations, and explore the use of current and innovative antiseizure drugs in the treatment of refractory epilepsy and other neurodegenerative diseases.

The Pharmacology and Clinical Efficacy of Antiseizure Medications: From Bromide Salts to Cenobamate and Beyond

Epilepsy is one of the most common and disabling chronic neurological disorders. Antiseizure medications (ASMs), previously referred to as anticonvulsant or antiepileptic drugs, are the mainstay of symptomatic epilepsy treatment. Epilepsy is a multifaceted complex disease and so is its treatment. Currently, about 30 ASMs are available for epilepsy therapy. Furthermore, several ASMs are approved therapies in nonepileptic conditions, including neuropathic pain, migraine, bipolar disorder, and generalized anxiety disorder. Because of this wide spectrum of therapeutic activity, ASMs are among the most often prescribed centrally active agents. Most ASMs act by modulation of voltage-gated ion channels; by enhancement of gamma aminobutyric acid-mediated inhibition; through interactions with elements of the synaptic release machinery; by blockade of ionotropic glutamate receptors; or by combinations of these mechanisms. Because of differences in their mechanisms of action, most ASMs do not suppress all types of seizures, so appropriate treatment choices are important. The goal of epilepsy therapy is the complete elimination of seizures; however, this is not achievable in about one-third of patients. Both in vivo and in vitro models of seizures and epilepsy are used to discover ASMs that are more effective in patients with continued drug-resistant seizures. Furthermore, therapies that are specific to epilepsy etiology are being developed. Currently, ~ 30 new compounds with diverse antiseizure mechanisms are in the preclinical or clinical drug development pipeline. Moreover, therapies with potential antiepileptogenic or disease-modifying effects are in preclinical and clinical development. Overall, the world of epilepsy therapy development is changing and evolving in many exciting and important ways. However, while new epilepsy therapies are developed, knowledge of the pharmacokinetics, antiseizure efficacy and spectrum, and adverse effect profiles of currently used ASMs is an essential component of treating epilepsy successfully and maintaining a high quality of life for every patient, particularly those receiving polypharmacy for drug-resistant seizures.