Cyclin dependent kinase 5: A novel avenue for Alzheimer’s disease

Therapeutic Efficacy of the Inositol D-Pinitol as a Multi-Faceted Disease Modifier in the 5×FAD Humanized Mouse Model of Alzheimer's Amyloidosis

BACKGROUND/OBJECTIVES

Alzheimer's disease (AD), a leading cause of dementia, lacks effective long-term treatments. Current therapies offer temporary relief or fail to halt its progression and are often inaccessible due to cost. AD involves multiple pathological processes, including amyloid beta (Aβ) deposition, insulin resistance, tau protein hyperphosphorylation, and systemic inflammation accelerated by gut microbiota dysbiosis originating from a leaky gut. Given this context, exploring alternative therapeutic interventions capable of addressing the multifaceted components of AD etiology is essential.

METHODS

This study suggests D-Pinitol (DPIN) as a potential treatment modifier for AD. DPIN, derived from carob pods, demonstrates insulin-sensitizing, tau hyperphosphorylation inhibition, and antioxidant properties. To test this hypothesis, we studied whether chronic oral administration of DPIN (200 mg/kg/day) could reverse the AD-like disease progression in the 5×FAD mice.

RESULTS

Results showed that treatment of 5×FAD mice with DPIN improved cognition, reduced hippocampal Aβ and hyperphosphorylated tau levels, increased insulin-degrading enzyme (IDE) expression, enhanced pro-cognitive hormone circulation (such as ghrelin and leptin), and normalized the PI3K/Akt insulin pathway. This enhancement may be mediated through the modulation of cyclin-dependent kinase 5 (CDK5). DPIN also protected the gut barrier and microbiota, reducing the pro-inflammatory impact of the leaky gut observed in 5×FAD mice. DPIN reduced bacterial lipopolysaccharide (LPS) and LPS-associated inflammation, as well as restored intestinal proteins such as Claudin-3. This effect was associated with a modulation of gut microbiota towards a more balanced bacterial composition.

CONCLUSIONS

These findings underscore DPIN's promise in mitigating cognitive decline in the early AD stages, positioning it as a potential disease modifier.

Protein Kinase C-Delta Mediates Cell Cycle Reentry and Apoptosis Induced by Amyloid-Beta Peptide in Post-Mitotic Cortical Neurons

Amyloid-beta peptide (Aβ) is a neurotoxic constituent of senile plaques in the brains of Alzheimer's disease (AD) patients. The detailed mechanisms by which protein kinase C-delta (PKCδ) contributes to Aβ toxicity is not yet entirely understood. Using fully differentiated primary rat cortical neurons, we found that inhibition of Aβ25-35-induced PKCδ increased cell viability with restoration of neuronal morphology. Using cyclin D1, proliferating cell nuclear antigen (PCNA), and histone H3 phosphorylated at Ser-10 (p-Histone H3) as the respective markers for the G1-, S-, and G2/M-phases, PKCδ inhibition mitigated cell cycle reentry (CCR) and subsequent caspase-3 cleavage induced by both Aβ25-35 and Aβ1-42 in the post-mitotic cortical neurons. Upstream of PKCδ, signal transducers and activators of transcription (STAT)-3 mediated PKCδ induction, CCR, and caspase-3 cleavage upon Aβ exposure. Downstream of PKCδ, aberrant neuronal CCR was triggered by overactivating cyclin-dependent kinase-5 (CDK5) via calpain2-dependent p35 cleavage into p25. Finally, PKCδ and CDK5 also contributed to Aβ25-35 induction of p53-upregulated modulator of apoptosis (PUMA) in cortical neurons. Together, we demonstrated that, in the post-mitotic neurons exposed to Aβs, STAT3-dependent PKCδ expression triggers calpain2-mediated p35 cleavage into p25 to overactivate CDK5, thus leading to aberrant CCR, PUMA induction, caspase-3 cleavage, and ultimately apoptosis.

Targeting protein kinases for the treatment of Alzheimer's disease: Recent progress and future perspectives

Alzheimer's disease (AD) is a serious neurodegenerative disease characterized by memory impairment, mental retardation, impaired motor balance, loss of self-care and even death. Among the complex and diverse pathological changes in AD, protein kinases are deeply involved in abnormal phosphorylation of Tau proteins to form intracellular neuronal fiber tangles, neuronal loss, extracellular β-amyloid (Aβ) deposits to form amyloid plaques, and synaptic disturbances. As a disease of the elderly, the growing geriatric population is directly driving the market demand for AD therapeutics, and protein kinases are potential targets for the future fight against AD. This perspective provides an in-depth look at the role of the major protein kinases (GSK-3β, CDK5, p38 MAPK, ERK1/2, and JNK3) in the pathogenesis of AD. At the same time, the development of different protein kinase inhibitors and the current state of clinical advancement are also outlined.

Identification of image genetic biomarkers of Alzheimer's disease by orthogonal structured sparse canonical correlation analysis based on a diagnostic information fusion

Alzheimer's disease (AD) is an irreversible neurodegenerative disease, and its incidence increases yearly. Because AD patients will have cognitive impairment and personality changes, it has caused a heavy burden on the family and society. Image genetics takes the structure and function of the brain as a phenotype and studies the influence of genetic variation on the structure and function of the brain. Based on the structural magnetic resonance imaging data and transcriptome data of AD and healthy control samples in the Alzheimer's Disease Neuroimaging Disease database, this paper proposed the use of an orthogonal structured sparse canonical correlation analysis for diagnostic information fusion algorithm. The algorithm added structural constraints to the region of interest (ROI) of the brain. Integrating the diagnostic information of samples can improve the correlation performance between samples. The results showed that the algorithm could extract the correlation between the two modal data and discovered the brain regions most affected by multiple risk genes and their biological significance. In addition, we also verified the diagnostic significance of risk ROIs and risk genes for AD. The code of the proposed algorithm is available at https://github.com/Wanguangyu111/OSSCCA-DIF.

Implicative role of epidermal growth factor receptor and its associated signaling partners in the pathogenesis of Alzheimer's disease

Epidermal growth factor receptor (EGFR) plays a pivotal role in early brain development, although its expression pattern declines in accordance with the maturation of the active nervous system. However, recurrence of EGFR expression in brain cells takes place during neural functioning decline and brain atrophy in order to maintain the homeostatic neuronal pool. As a consequence, neurotoxic lesions such as amyloid beta fragment (Aβ_1-42) formed during the alternative splicing of amyloid precursor protein in Alzheimer's disease (AD) elevate the expression of EGFR. This inappropriate peptide deposition on EGFR results in the sustained phosphorylation of the downstream signaling axis, leading to extensive Aβ_1-42 production and tau phosphorylation as subsequent pathogenesis. Recent reports convey that the pathophysiology of AD is correlated with EGFR and its associated membrane receptor complex molecules. One such family of molecules is the annexin superfamily, which has synergistic relationships with EGFR and is known for membrane-bound signaling that contributes to a variety of inflammatory responses. Besides, Galectin-3, tissue-type activated plasminogen activator, and many more, which lineate the secretion of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-18) result in severe neuronal loss. Altogether, we emphasized the perspectives of cellular senescence up-regulated by EGFR and its associated membrane receptor molecules in the pathogenesis of AD as a target for a therapeutical alternative to intervene in AD.

Molecular mechanisms of Alzheimer's disease: From therapeutic targets to promising drugs

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive impairment so widespread that it interferes with a person's ability to complete daily activities. AD is becoming increasingly common, and it is estimated that the number of patients will reach 152 million by 2050. Current treatment options for AD are symptomatic and have modest benefits. Therefore, considering the human, social, and economic burden of the disease, the development of drugs with the potential to alter disease progression has become a global priority. In this review, the molecular mechanisms involved in the pathology of AD were evaluated as therapeutic targets. The main aim of the review is to focus on new knowledge about mitochondrial dysfunction, oxidative stress, and neuronal transmission in AD, as well as a range of cellular signaling mechanisms and associated treatments. Important molecular interactions leading to AD were described in amyloid cascade and in tau protein function, oxidative stress, mitochondrial dysfunction, cholinergic and glutamatergic neurotransmission, cAMP-regulatory element-binding protein (CREB), the silent mating type information regulation 2 homolog 1 (SIRT-1), neuroinflammation (glial cells), and synaptic alterations. This review summarizes recent experimental and clinical research in AD pathology and analyzes the potential of therapeutic applications based on molecular disease mechanisms.

Cdk5-p25 as a key element linking amyloid and tau pathologies in Alzheimer's disease: Mechanisms and possible therapeutic interventions

Despite the fact that the small atypical serine/threonine cyclin-dependent kinase 5 (Cdk5) is expressed in a number of tissues, its activity is restricted to the central nervous system due to the neuron-only localization of its activators p35 and p39. Although its importance for the proper development and function of the brain and its role as a switch between neuronal survival and death are unmistakable and unquestionable, Cdk5 is nevertheless increasingly emerging, as supported by a large number of publications on the subject, as a therapeutic target of choice in the fight against Alzheimer's disease. Thus, its aberrant over activation via the calpain-dependent conversion of p35 into p25 is observed during the pathogenesis of the disease where it leads to the hyperphosphorylation of the β-amyloid precursor protein and tau. The present review highlights the pivotal roles of the hyperactive Cdk5-p25 complex activity in contributing to the development of Alzheimer's disease pathogenesis, with a particular emphasis on the linking function between Aβ and tau that this kinase fulfils and on the fact that Cdk5-p25 is part of a deleterious feed forward loop giving rise to a molecular machinery runaway leading to AD pathogenesis. Additionally, we discuss the advances and challenges related to the possible strategies aimed at specifically inhibiting Cdk5-p25 activity and which could lead to promising anti-AD therapeutics.

Discovery and Optimization of Highly Selective Inhibitors of CDK5

Autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent monogenic human disease, but to date, only one therapy (tolvaptan) is approved to treat kidney cysts in ADPKD patients. Cyclin-dependent kinase 5 (CDK5), an atypical member of the cyclin-dependent kinase family, has been implicated as a target for treating ADPKD. However, no compounds have been disclosed to date that selectively inhibit CDK5 while sparing the broader CDK family members. Herein, we report the discovery of CDK5 inhibitors, including GFB-12811, that are highly selective over the other tested kinases. In cellular assays, our compounds demonstrate CDK5 target engagement while avoiding anti-proliferative effects associated with inhibiting other CDKs. In addition, we show that the compounds in this series exhibit promising in vivo PK profiles, enabling their use as tool compounds for interrogating the role of CDK5 in ADPKD and other diseases.

Therapeutic potential of quinazoline derivatives for Alzheimer's disease: A comprehensive review

Quinazolines are considered as a promising class of bioactive heterocyclic compounds with broad properties. Particularly, the quinazoline scaffold has an impressive role in the design and synthesis of new CNS-active drugs. The drug-like properties and pharmacological characteristics of quinazoline could lead to different drugs with various targets. Among CNS disorders, Alzheimer's disease (AD) is a progressive neurodegenerative disorder with memory loss, cognitive decline and language dysfunction. AD is a complex and multifactorial disease therefore, the need for finding multi-target drugs against this devastative disease is urgent. A literature survey revealed that quinazoline derivatives have diverse therapeutic potential for AD as modulators/inhibitors of β-amyloid, tau protein, cholinesterases, monoamine oxidases, and phosphodiesterases as well as other protective effects. Thus, we describe here the most relevant and recent studies about anti-AD agents with quinazoline structure which can further aid the development and discovery of new anti-AD agents.

Current druggable targets for therapeutic control of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative brain disorder that has an increasingly large burden on health and social care systems. The pathophysiology involves the accumulation of extracellular amyloid-beta plaques (Aβ) and intracellular neurofibrillary tangles contributing to neuronal death and leading to cognition impairment. However, its cause remains poorly understood, and there is no cure for AD despite extensive research and billions of dollars spent over decades. Currently, there are only four US Food and Drug Administration (FDA) approved drugs and one combination therapy available in the market for the symptomatic relief of AD. Since 2003, no new drug has been approved by the FDA for the treatment of AD. Researchers continue to explore new treatments and therapeutic strategies to treat AD. The need for novel discoveries on therapeutic targets and the development of new therapeutic approaches is imminent when considering the current expectations regarding the increased number of AD cases each year and the huge financial cost amounted to healthcare. This review focused on the current status of drugs in the clinical pipeline targeting β-amyloid, tau phosphorylation, or neurotransmitter dysfunction for therapeutic control of Alzheimer's disease.

When Good Kinases Go Rogue: GSK3, p38 MAPK and CDKs as Therapeutic Targets for Alzheimer's and Huntington's Disease

Alzheimer's disease (AD) is a mostly sporadic brain disorder characterized by cognitive decline resulting from selective neurodegeneration in the hippocampus and cerebral cortex whereas Huntington's disease (HD) is a monogenic inherited disorder characterized by motor abnormalities and psychiatric disturbances resulting from selective neurodegeneration in the striatum. Although there have been numerous clinical trials for these diseases, they have been unsuccessful. Research conducted over the past three decades by a large number of laboratories has demonstrated that abnormal actions of common kinases play a key role in the pathogenesis of both AD and HD as well as several other neurodegenerative diseases. Prominent among these kinases are glycogen synthase kinase (GSK3), p38 mitogen-activated protein kinase (MAPK) and some of the cyclin-dependent kinases (CDKs). After a brief summary of the molecular and cell biology of AD and HD this review covers what is known about the role of these three groups of kinases in the brain and in the pathogenesis of the two neurodegenerative disorders. The potential of targeting GSK3, p38 MAPK and CDKS as effective therapeutics is also discussed as is a brief discussion on the utilization of recently developed drugs that simultaneously target two or all three of these groups of kinases. Multi-kinase inhibitors either by themselves or in combination with strategies currently being used such as immunotherapy or secretase inhibitors for AD and knockdown for HD could represent a more effective therapeutic approach for these fatal neurodegenerative diseases.

Effects of Acupuncture on Oxidative Stress Amelioration via Nrf2/ARE-Related Pathways in Alzheimer and Parkinson Diseases

Oxidative stress is responsible for the pathogeneses of various diseases. Mitochondrial dysfunction, impaired DNA repair, and cellular damage followed by oxidative stress contribute to neurodegenerative diseases, such as Alzheimer disease (AD) and Parkinson disease (PD). Acupuncture is a traditional therapy that has been practiced for >3000 years in Asia. Many studies have demonstrated that acupuncture has notable antioxidative, anti-inflammatory, and antiapoptotic effects. However, the exact mechanism remains unclear. Nuclear factor erythroid 2-related factor (Nrf2) is crucial in regulating the redox equilibrium. Activated Nfr2 translocates into the nucleus, binds to the antioxidant response element (ARE), and initiates antioxidative enzyme transcription. In this review, we demonstrated the effects of acupuncture on oxidative stress amelioration in AD and PD animal models through Nrf2/ARE pathway activation and Nrf2/ARE-related pathway regulation. Thus, acupuncture could be a therapeutic option for AD and PD.

Cyclin-dependent kinase inhibitor roscovitine attenuates liver inflammation and fibrosis by influencing initiating steps of liver injury

Liver diseases present a significant public health burden worldwide. Although the mechanisms of liver diseases are complex, it is generally accepted that inflammation is commonly involved in the pathogenesis. Ongoing inflammatory responses exacerbate liver injury, or even result in fibrosis and cirrhosis. Here we report that roscovitine, a cyclin-dependent kinase (CDK) inhibitor, exerts beneficial effects on acute and chronic liver inflammation as well as fibrosis. Animal models of lipopolysaccharide (LPS)/d-galactosamine- and acute or chronic CCl4-induced liver injury showed that roscovitine administration markedly attenuated liver injury, inflammation and histological damage in LPS/d-galactosamine- and CCl4-induced acute liver injury models, which is consistent with the results in vitro. RNA sequencing (RNA-seq) analysis showed that roscovitine treatment repressed the transcription of a broad set of pro-inflammatory genes involved in many aspects of inflammation, including cytokine production and immune cell proliferation and migration, and inhibited the TGF-β signaling pathway and the biological process of tissue remodeling. For further validation, the beneficial effect of roscovitine against inflammation was evaluated in chronic CCl4-challenged mice. The anti-inflammation effect of roscovitine was observed in this model, accompanied with reduced liver fibrosis. The anti-fibrotic mechanism involved inhibition of profibrotic genes and blocking of hepatic stellate cell (HSC) activation. Our data show that roscovitine administration protects against liver diseases through inhibition of macrophage inflammatory actions and HSC activation at the onset of liver injury.

Sulfur-containing therapeutics in the treatment of Alzheimer's disease

Sulfur is widely existent in natural products and synthetic organic compounds as organosulfur, which are often associated with a multitude of biological activities. OBenzothiazole, in which benzene ring is fused to the 4,5-positions of the thiazolerganosulfur compounds continue to garner increasing amounts of attention in the field of medicinal chemistry, especially in the development of therapeutic agents for Alzheimer's disease (AD). AD is a fatal neurodegenerative disease and the primary cause of age-related dementia posing severe societal and economic burdens. Unfortunately, there is no cure for AD. A lot of research has been conducted on sulfur-containing compounds in the context of AD due to their innate antioxidant potential and some are currently being evaluated in clinical trials. In this review, we have described emerging trends in the field, particularly the concept of multi-targeting and formulation of disease-modifying strategies. SAR, pharmacological targets, in vitro/vivo ADMET, efficacy in AD animal models, and applications in clinical trials of such sulfur compounds have also been discussed. This article provides a comprehensive review of organosulfur-based AD therapeutic agents and provides insights into their future development.

An Isoquinolinium Dual Inhibitor of Cholinesterases and Amyloid β Aggregation Mitigates Neuropathological Changes in a Triple-Transgenic Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurodegenerative disorder affecting millions of people worldwide. The underlying pathologic mechanisms of AD are unclear. Over the decades, the development of single target agent did not lead to any successful treatment for AD. A multitarget agent that could tackle more than one AD phenotype may be helpful as a treatment strategy. Cholinesterases (ChEs) including acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), are currently the drug targets with approved treatments. Moreover, amyloid beta (Aβ) deposition is a hallmark of AD that receives considerable attention. Herein, 9Q, a previously reported dual target inhibitor dealing with cholinergic dysfunction and amyloid deposition for AD treatment, has undergone thorough investigations. In vitro studies revealed that 9Q exhibited over 80% inhibition of ChE activity at 100 μM and more than 30% inhibition of Aβ aggregation at 1 mM concentration. Moreover 9Q was able to penetrate the blood-brain barrier (BBB) and enhance the cerebral acetylcholine level in triple transgenic AD (3xTg-AD) mice. Following one month treatment with 9Q, the amyloid burden and the cognitive deficits in 3xTg-AD mice were significantly ameliorated. It was observed that 9Q treatment mitigated synapse dysfunction, decreased amyloidogenic APP processing, and reduced the tau pathology in 3xTg-AD mice. Taken together, our results suggested that dual inhibition of cholinesterases and Aβ aggregation could be a promising approach in AD treatment.

Small molecule therapeutics for tauopathy in Alzheimer's disease: Walking on the path of most resistance

Alzheimer's disease (AD) is the most common form of dementia characterized by presence of extracellular amyloid plaques and intracellular neurofibrillary tangles composed of tau protein. Currently there are close to 50 million people living with dementia and this figure is expected to increase to 75 million by 2030 putting a huge burden on the economy due to the health care cost. Considering the effects on quality of life of patients and the increasing burden on the economy, there is an enormous need of new disease modifying therapies to tackle this disease. The current therapies are dominated by only symptomatic treatments including cholinesterase inhibitors and N-methyl-D-aspartate receptor blockers but no disease modifying treatments exist so far. After several failed attempts to develop drugs against amyloidopathy, tau targeting approaches have been in the main focus of drug development against AD. After an overview of the tauopathy in AD, this review summarizes recent findings on the development of small molecules as therapeutics targeting tau modification, aggregation, and degradation, and tau-oriented multi-target directed ligands. Overall, this work aims to provide a comprehensive and critical overview of small molecules which are being explored as a lead candidate for discovering drugs against tauopathy in AD.

Isolation and Characterization of Acetylcholinesterase Inhibitors from Piper longum and Binding Mode Predictions

Restoration of cholinergic function is considered a rational approach to enhance cognitive performance. Acetylcholinesterase inhibitors are still the best therapeutic option for Alzheimer's disease. The fruits of Piper longum have been used in traditional medicines for the treatment of memory loss. It was demonstrated that the dichloromethane extract of these fruits is able to inhibit acetylcholinesterase. Thus, the aim of this study was to identify the contained acetylcholinesterase inhibitors. The active zones were presented via TLC-bioautography, and five compounds were isolated in the process of a bioassay-guided phytochemical investigation. Their structures were characterized as piperine, methyl piperate, guineenisine, pipercide, and pellitorine using spectroscopy and spectrometry methods (UV, IR, MS, ¹H-, and ¹³C-NMR). In vitro acetylcholinesterase inhibitory activities of the isolates and their IC₅₀ values were determined via a colorimetric assay. Three of them exhibited enzyme inhibitory activities, with piperine being the most potent compound (IC₅₀ of 0.3 mM). In order to investigate the binding mode of the tested compounds, docking studies were performed using the X-ray crystal structure of acetylcholinesterase from Tetronarce californica with the Protein Data Bank code 1EVE. The content of the active compounds in the extract was determined by a developed HPLC method. Piperine was present in the maximum quantity in the fruits (0.57%), whereas methyl piperate contained the minimum content (0.10%).

Emerging Roles of Inhibitor of Differentiation-1 in Alzheimer's Disease: Cell Cycle Reentry and Beyond

Inhibitor of DNA-binding/differentiation (Id) proteins, a family of helix-loop-helix (HLH) proteins that includes four members of Id1 to Id4 in mammalian cells, are critical for regulating cell growth, differentiation, senescence, cell cycle progression, and increasing angiogenesis and vasculogenesis, as well as accelerating the ability of cell migration. Alzheimer’s disease (AD), the most common neurodegenerative disease in the adult population, manifests the signs of cognitive decline, behavioral changes, and functional impairment. The underlying mechanisms for AD are not well-clarified yet, but the aggregation of amyloid-beta peptides (Aβs), the major components in the senile plaques observed in AD brains, contributes significantly to the disease progression. Emerging evidence reveals that aberrant cell cycle reentry may play a central role in Aβ-induced neuronal demise. Recently, we have shown that several signaling mediators, including Id1, hypoxia-inducible factor-1 (HIF-1), cyclin-dependent kinases-5 (CDK5), and sonic hedgehog (Shh), may contribute to Aβ-induced cell cycle reentry in postmitotic neurons; furthermore, Id1 and CDK5/p25 mutually antagonize the expression/activity of each other. Therefore, Id proteins may potentially have clinical applications in AD. In this review article, we introduce the underlying mechanisms for cell cycle dysregulation in AD and present some examples, including our own studies, to show different aspects of Id1 in terms of cell cycle reentry and other signaling that may be crucial to alter the neuronal fates in this devastating neurodegenerative disease. A thorough understanding of the underlying mechanisms may provide a rationale to make an earlier intervention before the occurrence of cell cycle reentry and subsequent apoptosis in the fully differentiated neurons during the progression of AD or other neurodegenerative diseases.

Cyclin-dependent Kinase 5 Regulates Cortical Neurotransmission and Neural Circuits Associated with Motor Control in the Secondary Motor Cortex in the Mouse

Cyclin-dependent kinase 5 (Cdk5) is a regulator of axon growth and radial neuronal migration in the developing mouse brain, and it plays critical roles in cortical structure formation and brain function. However, the function of Cdk5 in cortico-cortical and cortico-sensorimotor networks in the adult remains largely unknown. In this study, we investigated the function of Cdk5 in the rostral secondary motor cortex (M2) in the male mouse using CRISPR/Cas9 gene editing and somatic brain transgenesis, to produce M2-specific knockdown of Cdk5 in neurons in the male mouse. Mouse deficient in Cdk5 in the M2 exhibited a reduction in both the number of functional synapses and the total basal dendritic length, as well as motor dysfunction. Furthermore, whole-cell patch-clamp recordings in layer V green fluorescent protein (GFP)-tag pyramidal neurons revealed a decrease in the frequency and amplitude of miniature EPSCs and miniature IPSCs, as well as a reduction in the population synaptic responses (fEPSPs) in these mice. Specifically, retrograde labeling showed that Cdk5 knockdown in the M2 caused a reduction in long-range projections to the M2 from the thalamus/prefrontal cortex and claustrum. Collectively, our findings show a new regulatory role of Cdk5 in neural circuit maintenance, and that the changes in neural transmission and circuits in the mice with Cdk5 knockdown in the M2 likely contribute to the motor dysfunction in these animals.

Tau Protein Aggregation in Alzheimer's Disease: Recent Advances in the Development of Novel Therapeutic Agents

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Major research in Alzheimer’s disease (AD) related to disease-modifying agents is concentrated on pharmacological approaches related to diagnostic markers, neurofibrillary tangles and amyloid plaques. Although most studies focus on anti-amyloid strategies, investigations on tau protein have produced significant advances in the modulation of the pathophysiology of several neurodegenerative diseases. Since the discovery of phenothiazines as tau protein aggregation inhibitors (TAGIs), many additional small molecule inhibitors have been discovered and characterized in biological model systems, which exert their interaction effects by covalent and noncovalent means. In this paper, we summarize the latest advances in the discovery and development of tau aggregation inhibitors using a specialized approach in their chemical classes. The design of new TAGIs and their encouraging use in in vivo and clinical trials support their potential therapeutic use in AD.

Physiological and Pathological Roles of Cdk5: Potential Directions for Therapeutic Targeting in Neurodegenerative Disease

Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine (ser)/threonine (Thr) kinase that has been demonstrated to be one of the most functionally diverse kinases within neurons. Cdk5 is regulated via binding with its neuron-specific regulatory subunits, p35 or p39. Cdk5-p35 activity is critical for a variety of developmental and cellular processes in the brain, including neuron migration, memory formation, microtubule regulation, and cell cycle suppression. Aberrant activation of Cdk5 via the truncated p35 byproduct, p25, is implicated in the pathogenesis of several neurodegenerative diseases. The present review highlights the importance of Cdk5 activity and function in the brain and demonstrates how deregulation of Cdk5 can contribute to the development of neurodegenerative conditions such as Alzheimer's and Parkinson's disease. Additionally, we cover past drug discovery attempts at inhibiting Cdk5-p25 activity and discuss which types of targeting strategies may prove to be the most successful moving forward.

Inhibition of acetylcholinesterase activity and β-amyloid oligomer formation by 6-bromotryptamine A, a multi-target anti-Alzheimer's molecule

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by learning and memory impairments. Recent studies have suggested that AD can be induced by multiple factors, such as cholinergic system dysfunction and β-amyloid (Aβ) neurotoxicity. It was reported that 6-bromo-N-propionyltryptamine could treat neurological diseases, including AD. In the present study, 6-bromotryptamine A, a derivative of 6-bromo-N-propionyltryptamine, was synthesized by the condensation of 2-(6-bromo-1H-indol-3-yl)ethan-1-amine and 2-(4-bromophenyl)acetic acid, and was used as a potential anti-AD molecule. Furthermore, scopolamine can induce impairments of learning and memory, and was widely used to establish AD animal models. The results demonstrated that 6-bromotryptamine A significantly prevented scopolamine-induced short-term cognitive impairments, as revealed by various behavioral tests in mice. Furthermore, an acetylcholinesterase (AChE) activity assay revealed that 6-bromotryptamine A directly inhibited AChE activity. Notably, it was observed that 6-bromotryptamine A blocked the formation of Aβ oligomer, as evaluated by the dot blot assay. All these results suggested that 6-bromotryptamine A may be used to prevent impairments in short-term learning and memory ability possibly via the inhibition of AChE and the blockade of Aβ oligomer formation.

Brain targeting of 9c,11t-Conjugated Linoleic Acid, a natural calpain inhibitor, preserves memory and reduces Aβ and P25 accumulation in 5XFAD mice

Deregulation of Cyclin-dependent kinase 5 (CDK5) by binding to the activated calpain product p25, is associated with the onset of neurodegenerative diseases, such as Alzheimer's disease (AD). Conjugated Linoleic Acid (CLA), a calpain inhibitor, is a metabolite of Punicic Acid (PA), the main component of Pomegranate seed oil (PSO). We have shown recently that long-term administration of Nano-PSO, a nanodroplet formulation of PSO, delays mitochondrial damage and disease advance in a mouse model of genetic Creutzfeldt Jacob disease (CJD). In this project, we first demonstrated that treatment of mice with Nano-PSO, but not with natural PSO, results in the accumulation of CLA in their brains. Next, we tested the cognitive, biochemical and pathological effects of long-term administration of Nano-PSO to 5XFAD mice, modeling for Alzheimer's disease. We show that Nano-PSO treatment prevented age-related cognitive deterioration and mitochondrial oxidative damage in 5XFAD mice. Also, brains of the Nano-PSO treated mice presented reduced accumulation of Aβ and of p25, a calpain product, and increased expression of COX IV-1, a key mitochondrial enzyme. We conclude that administration of Nano-PSO results in the brain targeting of CLA, and suggest that this treatment may prevent/delay the onset of neurodegenerative diseases, such as AD and CJD.

Ginsenoside compound K ameliorates Alzheimer's disease in HT22 cells by adjusting energy metabolism

Energy metabolism disorders have been shown to exert detrimental effects on the pathology of Alzheimer's disease (AD). The ginsenoside compound K (CK), a major intestinal metabolite underlying the pharmacological actions of orally administered ginseng, has an ameliorating effect against AD, but the relevant molecular mechanism remains unclear. We hypothesized that the improvement of AD by CK is mediated by the energy metabolism signaling pathway induced by amyloid β peptide (Aβ) and tested this hypothesis in HT22 cells. HT22 cells were incubated with CK and exposed to Aβ. Cell viability was analyzed using the MTT assay. Cell growth curves were derived from real-time cell analysis. Apoptosis was determined by flow cytometry, Aβ localization and expression by immunofluorescence, and ATP content by a specific assay kit. The expression of proteins related to the energy metabolism signaling pathway was analyzed using Western blotting. CK treatment improved cell viability, cell growth, and apoptosis induced by Aβ, and the cellular localization and expression of Aβ. Moreover, CK increased ATP content by promoting the activity of glucose transporters (GLUTs). Therefore, the neuroprotective effect of CK against Aβ injury was mainly realized through the activation of the energy metabolism signaling pathway. CK treatment inhibits neuronal damage caused by Aβ through the activation of the energy metabolism signaling pathway, revealing that CK might be one of the key bioactive ingredients of ginseng in the treatment of Alzheimer's disease and may serve as a preventive or therapeutic agent for Alzheimer's disease.

Acylphloroglucinols as kinase inhibitors from Sargassum nigrifoloides

Three new acylphloroglucinols (1-3) and four known biosynthetically related analogs (4-7) were isolated from the ethanol extract of a brown alga Sargassum nigrifoloides. Structures for 1-7 were characterized via detailed spectroscopic analyses especially 2D NMR data. Screening of these compounds in Alzheimer's diseases-related bioassays revealed moderate inhibitory activities against two therapeutically important kinases, CDK5 and GSK3β. A preliminary structure-activity relationship was also discussed.

Developments with multi-target drugs for Alzheimer's disease: an overview of the current discovery approaches

Introduction: Alzheimer's disease (AD), the most common type of dementia among older adults, is a chronic neurodegenerative pathology that causes a progressive loss of cognitive functioning with a decline of rational skills. It is well known that AD is multifactorial, so there are many different pharmacological targets that can be pursued. Areas covered: The authors highlight the strategic value of privileged scaffolds in a multi-target lead compound generation against AD, exploring the concept of multi-target design, with a special emphasis on hybrid compounds. Hence, the most promising building blocks for designing and synthesizing hybrid anti-AD drugs are shown, while also presenting the more advanced hybrid compounds. Expert opinion: The available therapeutic arsenal for AD, designed under the traditional paradigm of 'one-drug/one target/one-disease', is based on the inhibition of brain acetylcholinesterase (AChE) to increase acetylcholine (ACh) levels. However, this classical approach has not been sufficiently effective when used to treat any multifactor-depending pathology (cancer, diabetes or AD). The multi-target drug concept has been quickly adopted by medicinal chemists. The basic research developments reported in recent years are a solid foundation that will pave the way for the construction of future AD therapeutics.

Licoflavonol Reduces Aβ Secretion by Increasing BACE1 Phosphorylation to Facilitate BACE1 Degradation

SCOPE

In the previous study, Glycyrrhiza uralensis Fisch extract (GUE) inhibited Aβ secretion by inhibiting β-site APP-cleaving enzyme 1 (BACE1) transcription, and the active compounds semilicoisoflavone B (SB) and licoflavonol (LF) inhibited Aβ secretion. SB corresponds to the same mechanism as GUE, but LF has a different mechanism. In this study, the mechanism underlying inhibition of Aβ by LF is investigated.

METHODS AND RESULTS

The effects of LF on Aβ, sAPPα, and sAPPβ secretion are evaluated by ELISA, and the effect of LF on BACE1 expression is detected by western blotting. It is found that the effect of LF on Aβ secretion is due to promotion of BACE1 protein degradation, and that the effect of LF on Aβ and BACE1 expression is attenuated after cotreatment with the lysosome inhibitor chloroquine. In a subsequent mechanistic study, it is found that LF increases BACE1 phosphorylation to increase its interactions with ADP ribosylation factor-binding proteins 1 and 3 (GGA1 and GGA3, respectively) and eventually facilitate BACE1 delivery to lysosomes for degradation.

CONCLUSION

This study is the first to demonstrate that the BACE1 phosphorylation inducer LF can modulate BACE1 trafficking and lead to facilitating degradation of BACE1, eventually decreasing Aβ secretion.

Recent therapeutic strategies targeting beta amyloid and tauopathies in Alzheimer's disease

Alzheimer's disease (AD) has been a global concern for years due to its severe implications that affects the quality of life of the patients. The available line of therapy for treating Alzheimer's includes acetylcholinesterase inhibitors, NMDA(N-methyl-D-aspartate) antagonists and their combination which gives only symptomatic relief rather than treating the root cause of AD. Senile plaques and neurofibrillary tangles are the characteristic features underlying Alzheimer's pathology. Several attempts have been made towards exploring the niceties of these hallmarks and targeting various aspects of amyloid and tau pathology at different stages to eliminate the ultimate cause. Approaches targeting cleavage and formation of toxic amyloid fragments by secretases, aggregation of amyloid monofilaments, and immunotherapy against amyloid deposits has been extensively studied to treat amyloid pathology. Similarly, for tau pathology, tau hyperphosphorylation, microtubule stabilization, anti-tau immunotherapy has been explored. This article focuses on AD pathology and current pharmacotherapy, precisely for amyloid and tau. Furthermore, preclinical and clinical studies along with potential leads discovered under these approaches have also been included in this article. However, despite extensive research in drug development, overcoming clinical barrier still remain a major challenge for Alzheimer's pharmacotherapy.

Cocaine reward is reduced by decreased expression of receptor-type protein tyrosine phosphatase D (PTPRD) and by a novel PTPRD antagonist

Receptor-type protein tyrosine phosphatase D (PTPRD) is a neuronal cell-adhesion molecule/synaptic specifier that has been implicated in addiction vulnerability and stimulant reward by human genomewide association and mouse cocaine-conditioned place-preference data. However, there have been no reports of effects of reduced expression on cocaine self-administration. There have been no reports of PTPRD targeting by any small molecule. There are no data about behavioral effects of any PTPRD ligand. We now report (i) robust effects of heterozygous PTPRD KO on cocaine self-administration (These data substantially extend prior conditioned place-preference data and add to the rationale for PTPRD as a target for addiction therapeutics.); (ii) identification of 7-butoxy illudalic acid analog (7-BIA) as a small molecule that targets PTPRD and inhibits its phosphatase with some specificity; (iii) lack of toxicity when 7-BIA is administered to mice acutely or with repeated dosing; (iv) reduced cocaine-conditioned place preference when 7-BIA is administered before conditioning sessions; and (v) reductions in well-established cocaine self-administration when 7-BIA is administered before a session (in WT, not PTPRD heterozygous KOs). These results add to support for PTPRD as a target for medications to combat cocaine use disorders. 7-BIA provides a lead compound for addiction therapeutics.

Myelin injury in the central nervous system and Alzheimer's disease

Myelin is a membrane wrapped around the axon of the nerve cell, which is composed of the mature oligodendrocytes. The role of myelin is to insulate and prevent the nerve electrical impulses from the axon of the neurons to the axons of the other neurons, which is essential for the proper functioning of the nervous system. Minor changes in myelin thickness could lead to substantial changes in conduction speed and may thus alter neural circuit function. Demyelination is the myelin damage, which characterized by the loss of nerve sheath and the relative fatigue of the neuronal sheath and axon. Studies have shown that myelin injury may be closely related to neurodegenerative diseases and may be an early diagnostic criteria and therapeutic target. Thus this review summarizes the recent result of pathologic effect and signal pathways of myelin injury in neurodegenerative diseases, especially the Alzheimer's disease to provide new and effective therapeutic targets.