Memantine as a neuroprotective agent in ischemic stroke: Preclinical and clinical analysis

Advances in Alzheimer's Therapy: Exploring Neuropathological Mechanisms to Revolutionize the Future Therapeutic Landscape

Alzheimer's disease (AD) is still an excessively complicated neurological disorder that impacts millions of individuals globally. The ideal defensive feature of the central nervous system (CNS) is the intimate junction of endothelial cells, which functions as a biological barrier to safely control molecular transport throughout the brain. The blood-brain barrier (BBB) comprises tightly locked astrocyte cell junctions on CNS blood capillaries. This biological barrier shields the brain from hazardous toxins by preventing the entry of polar medications, cells, and ions. However, it is very challenging to provide any treatment to the brain for neurodegenerative illnesses like Alzheimer's. Different causative mechanisms, such as amyloid-β (Aβ) plaques, tubulin-associated unit (Tau) tangles, and neuroinflammation, cause neuronal dysfunction, leading to dementia and memory loss in the subject. Several treatments are approved for AD therapy, whereas most only help treat related symptoms. Disappointingly, current remedies have not been able to control the progression of AD due to associated side effects. Specific pathogenic mechanisms are involved in the initiation and development of this disease. Therefore, the expected survival of a patient with AD is limited and is approximately ten years. Hence, the pathogenic mechanism behind AD progression must be understood to better comprehend and improve the overall survival rate. This review highlighted the recent insights into AD pathogenesis, molecular mechanisms, advancements in theragnostic techniques, the existing updates of clinical trials, and emerging innovations for AD medicinal development. That has helped researchers develop other strategies to address the shortcomings of traditional medications.

Significance of NMDA receptor-targeting compounds in neuropsychological disorders: An in-depth review

N-methyl-D-aspartate receptors (NMDARs), a subclass of glutamate-gated ion channels, play an integral role in the maintenance of synaptic plasticity and excitation-inhibition balance within the central nervous system (CNS). Any irregularities in NMDAR functions, whether hypo-activation or over-activation, can destabilize neural networks and impair CNS function. Several decades of experimental and clinical investigations have demonstrated that NMDAR dysfunction is implicated in the pathophysiology of various neurological disorders. Despite designing a long list of compounds that differentially modulate NMDARs, success in developing drugs that can selectively and effectively regulate various NMDAR subtypes while showing encouraging efficacy in clinical settings remains limited. A better understanding of the basic mechanism of NMDAR function, particularly its selective regulation in pathological conditions, could aid in designing effective drugs for the treatment of neurological conditions. Here, we reviewed the experimental and clinical investigations that studied the effects of available NMDAR modulators in various neurological disorders and weighed up the pros and cons of the use of these substances on the improvement of functional outcomes of these disorders. Despite numerous efforts to develop NMDAR modulatory drugs that did not produce the desired outcomes, NMDARs remain a significant target for advancing novel drugs to treat neurological disorders. This article reviews the complexity of NMDAR signaling dysfunction in different neurological diseases, the efforts taken to examine designed compounds targeting specific subtypes of NMDARs, including challenges associated with using these substances, and the potential enhancements in drug discovery for NMDAR modulatory compounds by innovative technologies.

Neurostimulant Use for Rehabilitation and Recovery After Stroke: A Narrative Literature Review

BACKGROUND

Stroke often results in significant impairments across various domains, including movement, language, cognition, and mood. Neurostimulants have been proposed as potential therapeutic interventions to enhance recovery in these areas.

METHODS

This narrative literature review examines clinical trials investigating the efficacy of neurostimulants in poststroke recovery. It evaluates outcomes related to aphasia, motor deficits, cognition, fatigue, and depression.

RESULTS

The qualitative analysis included 34 trials testing the following neurostimulants: methylphenidate (n=6), amphetamines (n=8), memantine (n=2), modafinil (n=2), levodopa (n=14), amantadine (n=1), bromocriptine (n=3), and ropinirole (n=1). Of the 34 studies, 31 were randomized, placebo-controlled (double-blind, n=27; single-blind, n=2; unblinded n=2), 2 were randomized and not placebo-controlled, and 1 was not randomized. Study design was either multiarm (n=23), crossover (n=10), or used subjects as their own control (n=1). Mean sample size was 49.4 (5-593).

CONCLUSIONS

Current evidence suggests that memantine may be effective for aphasia, although few phase III trials exist, whereas bromocriptine and amphetamines lack sufficient evidence for long-term recovery of aphasia. Levodopa may improve motor aphasias but has not shown long-term benefits for motor recovery. Similarly, ropinirole has not been shown to improve poststroke motor outcomes. Methylphenidate has limited efficacy for cognitive improvement but may enhance poststroke functionality and mood. Modafinil may help with poststroke fatigue. In conclusion, there are promising results of positive effects of neurostimulants with few side effects, though studies are limited by heterogeneous designs and small sample sizes. Neurostimulant efficacy must be assessed in conjunction with specific rehabilitation modalities as part of larger, well-designed studies to best understand their effects on impairment.

Calycosin Inhibit PANoptosis and Alleviate Brain Damage: A Bioinformatics and Experimental Verification Approach

PANoptosis is a newly identified form of cell death that encompasses pyroptosis, apoptosis, and necroptosis. Numerous studies have highlighted the significance of PANoptosis in brain ischemia-reperfusion (I/R) injury. Calycosin, a natural product with diverse biological activities, has demonstrated a significant reduction in neuronal death caused by ischemic brain injury by modulating multiple cell death pathways. In order to investigate the potential mechanisms underlying the neuroprotective role of calycosin in alleviating PANoptosis-induced damage in ischemic stroke therapy, we used mouse hippocampal neuronal cell line HT22 to stimulate ischemia in vitro through Oxygen and Glucose Deprivation/Reperfusion (OGD/R) and established molecular docking to assess the binding affinity of Calycosin with key targets and molecular dynamics simulations (MDS) to study the stability of the ligand-protein complex. The results demonstrate that Calycosin could improve the cell growth of HT22, leading to enhanced cell viability, reduced lactate dehydrogenase leakage, and decreased cell apoptosis after OGD/R. It also regulated the expression of PANoptosis-related genes such as NLRP3, GSDMD, MLKL, and RIPK1 and increased the Bcl-2/Bax ratio, effectively reducing cellular damage and providing protection. Molecular docking and MDS simulations demonstrated strong binding activity and stability between Calycosin and PANoptosis-related targets. Furthermore, Calycosin successfully passed the drug similarity (DS) evaluation and exhibited favorable absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties and biological activity. In conclusion, Calycosin could alleviate ischemic stroke by inhibiting PANoptosis, reducing neuronal inflammation and apoptosis, and improving damage caused by the OGD/R. Thus, it could serve as a potential therapy for ischemic stroke.

Imino and Thioureidic Derivatives as New Tools for Alzheimer's Disease: Preliminary Studies

Alzheimer's disease is a neurodegenerative chronic disease with a severe social and economic impact in the societies, which still lacks an efficient therapy. Several pathophysiological events (β-amyloid [Aβ] deposits, τ-protein aggregation, loss of cholinergic activity, and oxidative stress) occurs in the progression of the disease. Therefore, the search for efficient multi-targeted agents for the treatment of Alzheimer's disease becomes indispensable. In this paper we evaluated the AChE inhibition by Ellman's method and antioxidant activity by DPPH assay of nine synthetic compounds: two hydroxy-benzene derivatives (1 and 2), three bis-thioureidic derivatives (3-5), two imidazole derivatives (6 and 7), and two phenylacetamide derivatives (8 and 9). The compound 2, (3s,5s,7s)-adamantan-1-yl 4-(((E)-2,5-dihydroxybenzylidene)amino)benzoate, exhibited the best antioxidant activity (30.00 ± 1.05 μM eq Trolox) and compound 4 showed the highest AChE inhibition value (IC50 [μM] 8.40 ± 0.32). In the search for a compound showing combined activities (antioxidant and AChE inhibition), the compound 4, octane-1,8-diyl-bis-S-amidinothiourea dihydrobromide, (19.02 ± 1.52 μM eq Trolox; IC50 [μM] 8.40 ± 0.32) was chosen to carry out a molecular docking study. The results showed that compound 4 has the ability to bind the active site of acetylcholinesterase with considerable affinity (estimated binding energies of -8.5 kcal/mol). All data indicate that compound 4 has the potential to be further investigated as a possible candidate in the Alzheimer's disease treatment.

An Online Model for Neurosurgical Research in Developing Countries: A One-Year Experience in Mexico and Latin America

BACKGROUND

Mexico is under-represented in global neurosurgical research. High-income countries represent roughly 10% of the world's population but utilize about 90% of the research funding for medical research, highlighting the need for promoting research initiatives in low- and middle-income countries. We present an online-based research initiative in Mexico that aims to reduce the research gap in neurosurgery.

METHODS

Implemented in early 2023, our online-based research initiative included weekly modules covering study types, statistical analysis, meta-analysis, and scientific writing. The first cohort of 22 students completed the 12-week program and then served as tutors for subsequent cohorts. The research model was promoted via word of mouth and social media platforms to medical students, graduates, and specialists across Latin America. Post-program, tutors and the author conducted weekly planning sessions to assist with project planning, analysis, and article writing.

RESULTS

From 833 registrations, over 800 students completed at least 1 training module. The program published 7 articles and presented 12 abstracts at major international neurosurgical meetings. We performed a bibliographic analysis in PubMed and found that from 2021 to 2022, 33,637 neurosurgical articles were published, with 197 involving collaboration from Mexico (0.5%). From 2023 to 2024, 24,121 articles were published, with 205 involving collaboration from Mexico (0.8%), a significant increase (P < 0.001). Our collaboration contributed to 3.4% of these, representing a significant addition in 2023-2024 (P = 0.026).

CONCLUSIONS

This online-based neurosurgical model contributed to 3.4% of the neurosurgical research productivity in Mexico. Our findings suggest that this model can effectively bridge the research gap and enhance scientific contributions in developing countries.

Memantine and the Kynurenine Pathway in the Brain: Selective Targeting of Kynurenic Acid in the Rat Cerebral Cortex

Cytoprotective and neurotoxic kynurenines formed along the kynurenine pathway (KP) were identified as possible therapeutic targets in various neuropsychiatric conditions. Memantine, an adamantane derivative modulating dopamine-, noradrenaline-, serotonin-, and glutamate-mediated neurotransmission is currently considered for therapy in dementia, psychiatric disorders, migraines, or ischemia. Previous studies have revealed that memantine potently stimulates the synthesis of neuroprotective kynurenic acid (KYNA) in vitro via a protein kinase A-dependent mechanism. Here, the effects of acute and prolonged administration of memantine on brain kynurenines and the functional changes in the cerebral KP were assessed in rats using chromatographic and enzymatic methods. Five-day but not single treatment with memantine selectively activated the cortical KP towards neuroprotective KYNA. KYNA increases were accompanied by a moderate decrease in cortical tryptophan (TRP) and L-kynurenine (L-KYN) concentrations without changes in 3-hydroxykynurenine (3-HK) levels. Enzymatic studies revealed that the activity of cortical KYNA biosynthetic enzymes ex vivo was stimulated after prolonged administration of memantine. As memantine does not directly stimulate the activity of KATs' proteins, the higher activity of KATs most probably results from the increased expression of the respective genes. Noteworthy, the concentrations of KYNA, 3-HK, TRP, and L-KYN in the striatum, hippocampus, and cerebellum were not affected. Selective cortical increase in KYNA seems to represent one of the mechanisms underlying the clinical efficacy of memantine. It is tempting to hypothesize that a combination of memantine and drugs could strongly boost cortical KYNA and provide a more effective option for treating cortical pathologies at early stages. Further studies should evaluate this issue in experimental animal models and under clinical scenarios.

Signaling pathways in brain ischemia: Mechanisms and therapeutic implications

Ischemic stroke occurs when the arteries supplying blood to the brain are narrowed or blocked, inducing damage to brain tissue due to a lack of blood supply. One effective way to reduce brain damage and alleviate symptoms is to reopen blocked blood vessels in a timely manner and reduce neuronal damage. To achieve this, researchers have focused on identifying key cellular signaling pathways that can be targeted with drugs. These pathways include oxidative/nitrosative stress, excitatory amino acids and their receptors, inflammatory signaling molecules, metabolic pathways, ion channels, and other molecular events involved in stroke pathology. However, evidence suggests that solely focusing on protecting neurons may not yield satisfactory clinical results. Instead, researchers should consider the multifactorial and complex mechanisms underlying stroke pathology, including the interactions between different components of the neurovascular unit. Such an approach is more representative of the actual pathological process observed in clinical settings. This review summarizes recent research on the multiple molecular mechanisms and drug targets in ischemic stroke, as well as recent advances in novel therapeutic strategies. Finally, we discuss the challenges and future prospects of new strategies based on the biological characteristics of stroke.

Extrasynaptic NMDA receptors in acute and chronic excitotoxicity: implications for preventive treatments of ischemic stroke and late-onset Alzheimer's disease

Stroke and late-onset Alzheimer's disease (AD) are risk factors for each other; the comorbidity of these brain disorders in aging individuals represents a significant challenge in basic research and clinical practice. The similarities and differences between stroke and AD in terms of pathogenesis and pathophysiology, however, have rarely been comparably reviewed. Here, we discuss the research background and recent progresses that are important and informative for the comorbidity of stroke and late-onset AD and related dementia (ADRD). Glutamatergic NMDA receptor (NMDAR) activity and NMDAR-mediated Ca²⁺ influx are essential for neuronal function and cell survival. An ischemic insult, however, can cause rapid increases in glutamate concentration and excessive activation of NMDARs, leading to swift Ca²⁺ overload in neuronal cells and acute excitotoxicity within hours and days. On the other hand, mild upregulation of NMDAR activity, commonly seen in AD animal models and patients, is not immediately cytotoxic. Sustained NMDAR hyperactivity and Ca²⁺ dysregulation lasting from months to years, nevertheless, can be pathogenic for slowly evolving events, i.e. degenerative excitotoxicity, in the development of AD/ADRD. Specifically, Ca²⁺ influx mediated by extrasynaptic NMDARs (eNMDARs) and a downstream pathway mediated by transient receptor potential cation channel subfamily M member (TRPM) are primarily responsible for excitotoxicity. On the other hand, the NMDAR subunit GluN3A plays a "gatekeeper" role in NMDAR activity and a neuroprotective role against both acute and chronic excitotoxicity. Thus, ischemic stroke and AD share an NMDAR- and Ca²⁺-mediated pathogenic mechanism that provides a common receptor target for preventive and possibly disease-modifying therapies. Memantine (MEM) preferentially blocks eNMDARs and was approved by the Federal Drug Administration (FDA) for symptomatic treatment of moderate-to-severe AD with variable efficacy. According to the pathogenic role of eNMDARs, it is conceivable that MEM and other eNMDAR antagonists should be administered much earlier, preferably during the presymptomatic phases of AD/ADRD. This anti-AD treatment could simultaneously serve as a preconditioning strategy against stroke that attacks ≥ 50% of AD patients. Future research on the regulation of NMDARs, enduring control of eNMDARs, Ca²⁺ homeostasis, and downstream events will provide a promising opportunity to understand and treat the comorbidity of AD/ADRD and stroke.

β-Secretase-1: In Silico Drug Reposition for Alzheimer's Disease

The β-secretase-1 enzyme (BACE-1) performs a key role in the production of beta-Amyloid protein (Aβ), which is associated with the development of Alzheimer's disease (AD). The inhibition of BACE-1 has been an important pharmacological strategy in the treatment of this neurodegenerative disease. This study aims to identify new potential candidates for the treatment of Alzheimer's with the help of in silico studies, such as molecular docking and ADME prediction, from a broad list of candidates provided by the DrugBank database. From this analysis, 1145 drugs capable of interacting with the enzyme with a higher coupling energy than Verubecestat were obtained, subsequently only 83 presented higher coupling energy than EJ7. Applying the oral route of administration as inclusion criteria, only 41 candidates met this requirement; however, 6 of them are associated with diagnostic tests and not treatment, so 33 candidates were obtained. Finally, five candidates were identified as possible BACE-1 inhibitors drugs: Fluphenazine, Naratriptan, Bazedoxifene, Frovatriptan, and Raloxifene. These candidates exhibit pharmacophore-specific features, including the indole or thioindole group, and interactions with key amino acids in BACE-1. Overall, this study provides insights into the potential use of in silico methods for drug repurposing and identification of new candidates for the treatment of Alzheimer's disease, especially those targeting BACE-1.