Indirubin-3'-monoxime rescues spatial memory deficits and attenuates β-amyloid-associated neuropathology in a mouse model of Alzheimer's disease

Understanding Glycogen Synthase Kinase-3: A Novel Avenue for Alzheimer's Disease

Alzheimer's Disease (AD) is the most prevalent form of age-related dementia. Even though a century has passed since the discovery of AD, the exact cause of the disease still remains unknown. As a result, this poses a major hindrance in developing effective therapies for treating AD. Glycogen synthase kinase-3 (GSK-3) is one of the kinases that has been investigated recently as a potential therapeutic target for the treatment of AD. It is also known as human tau protein kinase and is a proline-directed serine-threonine kinase. Since dysregulation of this kinase affects all the major characteristic features of the disease, such as tau phosphorylation, amyloid formation, memory, and synaptic function, it is thought to be a major player in the pathogenesis of AD. In this review, we present the most recent information on the role of this kinase in the onset and progression of AD, as well as significant findings that identify GSK-3 as one of the most important targets for AD therapy. We further discuss the potential of treating AD by targeting GSK-3 and give an overview of the ongoing studies aimed at developing GSK-3 inhibitors in preclinical and clinical investigations.

Alkaloids as drug leads in Alzheimer's treatment: Mechanistic and therapeutic insights

Alzheimer's disease (AD) has few effective treatment options and continues to be a major global health concern. AD is a neurodegenerative disease that typically affects elderly people. Alkaloids have potential sources for novel drug discovery due to their diverse chemical structures and pharmacological activities. Alkaloids, natural products with heterocyclic nitrogen-containing structures, are considered potential treatments for AD. This review explores the neuroprotective properties of alkaloids in AD, focusing on their ability to regulate pathways such as amyloid-beta aggregation, oxidative stress, synaptic dysfunction, tau hyperphosphorylation, and neuroinflammation. The FDA has approved alkaloids such as acetylcholinesterase inhibitors like galantamine and rivastigmine. This article explores AD's origins, current market medications, and clinical applications of alkaloids in AD therapy. This review explores the development of alkaloid-based drugs for AD, focusing on pharmacokinetics, blood-brain barrier penetration, and potential adverse effects. Future research should focus on the clinical evaluation of promising alkaloids, developing recently discovered alkaloids, and the ongoing search for novel alkaloids for medical treatment. A pharmaceutical option containing an alkaloid may potentially slow down the progression of AD while enhancing its symptoms. This review highlights the potential of alkaloids as valuable drug leads in treating AD, providing a comprehensive understanding of their mechanisms of action and therapeutic implications.

Gomisin N rescues cognitive impairment of Alzheimer's disease by targeting GSK3β and activating Nrf2 signaling pathway

Oxidative stress is one of the earlier events causing neuronal dysfunction in Alzheimer's disease (AD). Gomisin N (GN), a lignin isolated from Schisandra chinensis, has anti-oxidative stress effects. There are currently no studies on the neuroprotective potential of GN in AD. In this study, two AD models were treated with GN for 8 weeks. The cognitive functions, amyloid deposition, and neuronal death were assessed. Additionally, the expressions of critical proteins in the GSK3β/Nrf2 signaling pathway were determined in vivo and in vitro. We showed that GN significantly upregulated the expressions of Nrf2, p-GSK3βSer9/GSK3β, NQO1 and HO-1 proteins in SHSY-5Y/APPswe cells after H2O2 injury, whereas the PI3K inhibitor LY294002 reversed the increase in the expressions of Nrf2, p-GSK3βSer9/GSK3β, NQO1 and HO-1 proteins induced by GN administration. In a further study, GN could significantly improve the learning and memory dysfunctions of the rat and mouse AD models, reduce the area of Aβ plaques in the hippocampus and cortex, and increase the number and function of neurons. Here, we first demonstrate the neuroprotective effects of GN on AD in vivo and in vitro. A possible mechanism by which GN prevents AD is proposed: GN significantly increased the expressions of Nrf2, p-GSK3Ser9/GSK3β and NQO1 proteins in the brain of AD animal models and promoted Nrf2 nuclear translocation, then activated Nrf2 downstream genes to combat oxidative stress in AD pathogenesis. GN might be a promising therapeutic agent for AD.

Connecting GSK-3β Inhibitory Activity with IKK-β or ROCK-1 Inhibition to Target Tau Aggregation and Neuroinflammation in Alzheimer's Disease-Discovery, In Vitro and In Cellulo Activity of Thiazole-Based Inhibitors

GSK-3β, IKK-β, and ROCK-1 kinases are implicated in the pathomechanism of Alzheimer's disease due to their involvement in the misfolding and accumulation of amyloid β (Aβ) and tau proteins, as well as inflammatory processes. Among these kinases, GSK-3β plays the most crucial role. In this study, we present compound 62, a novel, remarkably potent, competitive GSK-3β inhibitor (IC50 = 8 nM, Ki = 2 nM) that also exhibits additional ROCK-1 inhibitory activity (IC50 = 2.3 µM) and demonstrates anti-inflammatory and neuroprotective properties. Compound 62 effectively suppresses the production of nitric oxide (NO) and pro-inflammatory cytokines in the lipopolysaccharide-induced model of inflammation in the microglial BV-2 cell line. Furthermore, it shows neuroprotective effects in an okadaic-acid-induced tau hyperphosphorylation cell model of neurodegeneration. The compound also demonstrates the potential for further development, characterized by its chemical and metabolic stability in mouse microsomes and fair solubility.

Triaging between post-translational modification of cell cycle regulators and their therapeutics in neurodegenerative diseases

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, present challenges in healthcare because of their complicated etiologies and absence of healing remedies. Lately, the emerging role of post-translational modifications (PTMs), in the context of cell cycle regulators, has garnered big interest as a potential avenue for therapeutic intervention. The review explores the problematic panorama of PTMs on cell cycle regulators and their implications in neurodegenerative diseases. We delve into the dynamic phosphorylation, acetylation, ubiquitination, SUMOylation, Glycation, and Neddylation that modulate the key cell cycle regulators, consisting of cyclins, cyclin-dependent kinases (CDKs), and their inhibitors. The dysregulation of these PTMs is related to aberrant cell cycle in neurons, which is one of the factors involved in neurodegenerative pathologies. Moreover, the effect of exogenous activation of CDKs and CDK inhibitors through PTMs on the signaling cascade was studied in postmitotic conditions of NDDs. Furthermore, the therapeutic implications of CDK inhibitors and associated alteration in PTMs were discussed. Lastly, we explored the putative mechanism of PTMs to restore normal neuronal function that might reverse NDDs.

Drug Delivery to the Brain: Recent Advances and Unmet Challenges

Brain cancers and neurodegenerative diseases are on the rise, treatments for central nervous system (CNS) diseases remain limited. Despite the significant advancement in drug development technology with emerging biopharmaceuticals like gene therapy or recombinant protein, the clinical translational rate of such biopharmaceuticals to treat CNS disease is extremely poor. The blood-brain barrier (BBB), which separates the brain from blood and protects the CNS microenvironment to maintain essential neuronal functions, poses the greatest challenge for CNS drug delivery. Many strategies have been developed over the years which include local disruption of BBB via physical and chemical methods, and drug transport across BBB via transcytosis by targeting some endogenous proteins expressed on brain-capillary. Drug delivery to brain is an ever-evolving topic, although there were multiple review articles in literature, an update is warranted due to continued growth and new innovations of research on this topic. Thus, this review is an attempt to highlight the recent strategies employed to overcome challenges of CNS drug delivery while emphasizing the necessity of investing more efforts in CNS drug delivery technologies parallel to drug development.

Small molecule inhibitors of NLRP3 inflammasome and GSK-3β in the management of traumatic brain injury: A review

Traumatic brain injury (TBI) is a debilitating mental condition which causes physical disability and morbidity worldwide. TBI may damage the brain by direct injury that subsequently triggers a series of neuroinflammatory events. The activation of NLRP3 inflammasome and dysregulated host immune system has been documented in various neurological disorders such as TBI, ischemic stroke and multiple sclerosis. The activation of NLRP3 post-TBI increases the production of pro-inflammatory cytokines and caspase-1, which are major drivers of neuroinflammation and apoptosis. Similarly, GSK-3β regulates apoptosis through tyrosine kinase and canonical Wnt signalling pathways. Thus, therapeutic targeting of NLRP3 inflammasome and GSK-3β has emerged as promising strategies for regulating the post-TBI neuroinflammation and neurobehavioral disturbances. In this review, we discuss the identification & development of several structurally diverse and pharmacologically interesting small molecule inhibitors for targeting the NLRP3 inflammasome and GSK-3β in the management of TBI.

Role of GSK-3β Inhibitors: New Promises and Opportunities for Alzheimer's Disease

Glycogen synthase kinase-3 (GSK-3) was discovered to be a multifunctional enzyme involved in a wide variety of biological processes, including early embryo formation, oncogenesis, as well cell death in neurodegenerative diseases. Several critical cellular processes in the brain are regulated by the GSK-3β, serving as a central switch in the signaling pathways. Dysregulation of GSK-3β kinase has been reported in diabetes, cancer, Alzheimer's disease, schizophrenia, bipolar disorder, inflammation, and Huntington's disease. Thus, GSK-3β is widely regarded as a promising target for therapeutic use. The current review article focuses mainly on Alzheimer's disease, an age-related neurodegenerative brain disorder. GSK-3β activation increases amyloid-beta (Aβ) and the development of neurofibrillary tangles that are involved in the disruption of material transport between axons and dendrites. The drug-binding cavities of GSK-3β are explored, and different existing classes of GSK-3β inhibitors are explained in this review. Non-ATP competitive inhibitors, such as allosteric inhibitors, can reduce the side effects compared to ATP-competitive inhibitors. Whereas ATP-competitive inhibitors produce disarrangement of the cytoskeleton, neurofibrillary tangles formation, and lead to the death of neurons, etc. This could be because they are binding to a site separate from ATP. Owing to their interaction in particular and special binding sites, allosteric ligands interact with substrates more selectively, which will be beneficial in resolving drug-induced resistance and also helpful in reducing side effects. Hence, in this review, we focussed on the allosteric GSK-3β inhibitors and discussed their futuristic opportunities as anti-Alzheimer's compounds.

Cognitive dysfunction and increased phosphorylated tau are associated with reduced O-GlcNAc signaling in an aging mouse model of metabolic syndrome

Metabolic syndrome (MetS), characterized by hyperglycemia, obesity, and hyperlipidemia, can increase the risk of developing late-onset dementia. Recent studies in patients and mouse models suggest a putative link between hyperphosphorylated tau, a component of Alzheimer's disease-related dementia (ADRD) pathology, and cerebral glucose hypometabolism. Impaired glucose metabolism reduces glucose flux through the hexosamine metabolic pathway triggering attenuated O-linked N-acetylglucosamine (O-GlcNAc) protein modification. The goal of the current study was to investigate the link between cognitive function, tau pathology, and O-GlcNAc signaling in an aging mouse model of MetS, agouti KKAy+/- . Male and female C57BL/6, non-agouti KKAy-/- , and agouti KKAy+/- mice were aged 12-18 months on standard chow diet. Body weight, blood glucose, total cholesterol, and triglyceride were measured to confirm the MetS phenotype. Cognition, sensorimotor function, and emotional reactivity were assessed for each genotype followed by plasma and brain tissue collection for biochemical and molecular analyses. Body weight, blood glucose, total cholesterol, and triglyceride levels were significantly elevated in agouti KKAy+/- mice versus C57BL/6 controls and non-agouti KKAy-/- . Behaviorally, agouti KKAy+/- revealed impairments in sensorimotor and cognitive function versus age-matched C57BL/6 and non-agouti KKAy-/- mice. Immunoblotting demonstrated increased phosphorylated tau accompanied with reduced O-GlcNAc protein expression in hippocampal-associated dorsal midbrain of female agouti KKAy+/- versus C57BL/6 control mice. Together, these data demonstrate that impaired cognitive function and AD-related pathology are associated with reduced O-GlcNAc signaling in aging MetS KKAy+/- mice. Overall, our study suggests that interaction of tau pathology with O-GlcNAc signaling may contribute to MetS-induced cognitive dysfunction in aging.

Indirubin Inhibits TRAIL-Induced Activation of Death Receptor 5 in Jurkat Cells

Death receptor 5 (DR5) is an apoptosis-inducing membrane receptor that mediates cell death in several life-threatening conditions. There is a crucial need for the discovery of DR5 antagonists for the therapeutic intervention of conditions in which the overactivation of DR5 underlies the pathophysiology. DR5 activation mediates cell death in non-alcoholic fatty liver disease (NAFLD) and neurodegenerative processes including amyloid-beta (Aβ) accumulation, spinal cord injury (SCI), and brain ischemia. In the current work, we used fluorescence resonance energy transfer (FRET) to monitor the conformational dynamics of DR5 that mediate death signaling. We used a time-resolved FRET screening platform to screen the Selleck library of 2863 U.S. Food and Drug Administration (FDA)-approved compounds. The high-throughput screen (HTS) identified 13 compounds that modulated the FRET between DR5 monomers beyond 5 median absolute deviations (MADs) from the DMSO controls. Of these 13 compounds, indirubin was identified to specifically inhibit tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced caspase-8 activity without modulating DR5 surface expression or TRAIL binding. Indirubin inhibited Fas-associated death domain (FADD) oligomerization and increased cellular FLICE-inhibitory protein (c-FLIP) expression; both are molecular mechanisms involved in inhibiting the DR5 signaling cascade. This study has elucidated previously unknown properties of indirubin that make it a promising candidate for therapeutic investigation of diseases in which overactivation of DR5 underlies pathology.

Imipramine and olanzapine block apoE4-catalyzed polymerization of Aβ and show evidence of improving Alzheimer’s disease cognition

Background

The apolipoprotein E (APOE) ε4 allele confers the strongest risk for late-onset Alzheimer’s disease (AD) besides age itself, but the mechanisms underlying this risk are debated. One hypothesis supported by evidence from multiple labs is that apoE4 binds to the amyloid-β (Aβ) peptide and catalyzes its polymerization into neurotoxic oligomers and fibrils. Inhibiting this early step in the amyloid cascade may thereby reduce or prevent neurodegeneration and AD.

Methods

Using a design of experiments (DOE) approach, we developed a high-throughput assay to identify inhibitors of apoE4-catalyzed polymerization of Aβ into oligomers and fibrils. We used it to screen the NIH Clinical Collection of small molecule drugs tested previously in human clinical trials. We then evaluated the efficacy and cytotoxicity of the hit compounds in primary neuron models of apoE4-induced Aβ and phosphorylated tau aggregation. Finally, we performed retrospective analyses of the National Alzheimer’s Coordinating Center (NACC) clinical dataset, using Cox regression and Cox proportional hazards models to determine if the use of two FDA-approved hit compounds was associated with better cognitive scores (Mini-Mental State Exam), or improved AD clinical diagnosis, when compared with other medications of the same clinical indication.

Results

Our high-throughput screen identified eight blood-brain barrier (BBB)-permeable hit compounds that reduced apoE4-catalyzed Aβ oligomer and fibril formation in a dose-dependent manner. Five hit compounds were non-toxic toward cultured neurons and also reduced apoE4-promoted Aβ and tau neuropathology in a dose-dependent manner. Three of the five compounds were determined to be specific inhibitors of apoE4, whereas the other two compounds were Aβ or tau aggregation inhibitors. When prescribed to AD patients for their normal clinical indications, two of the apoE4 inhibitors, imipramine and olanzapine, but not other (non-hit) antipsychotic or antidepressant medications, were associated with improvements in cognition and clinical diagnosis, especially among APOE4 carriers.

Conclusions

The critical test of any proposed AD mechanism is whether it leads to effective treatments. Our high-throughput screen identified two promising FDA-approved drugs, imipramine and olanzapine, which have no structural, functional, or clinical similarities other than their shared ability to inhibit apoE4-catalyzed Aβ polymerization, thus identifying this mechanism as an essential contribution of apoE4 to AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01020-9.

Genetics, molecular control and clinical relevance of habituation learning

Habituation is the most fundamental form of learning. As a firewall that protects our brain from sensory overload, it is indispensable for cognitive processes. Studies in humans and animal models provide increasing evidence that habituation is affected in autism and related monogenic neurodevelopmental disorders (NDDs). An integrated application of habituation assessment in NDDs and their animal models has unexploited potential for neuroscience and medical care. With the aim to gain mechanistic insights, we systematically retrieved genes that have been demonstrated in the literature to underlie habituation. We identified 258 evolutionarily conserved genes across species, describe the biological processes they converge on, and highlight regulatory pathways and drugs that may alleviate habituation deficits. We also summarize current habituation paradigms and extract the most decisive arguments that support the crucial role of habituation for cognition in health and disease. We conclude that habituation is a conserved, quantitative, cognition- and disease-relevant process that can connect preclinical and clinical work, and hence is a powerful tool to advance research, diagnostics, and treatment of NDDs.

Glycogen Synthase Kinase 3β Involvement in Neuroinflammation and Neurodegenerative Diseases

BACKGROUND

GSK-3β activity has been strictly related to neuroinflammation and neurodegeneration. Alzheimer's disease is the most studied neurodegenerative disease, but GSK-3β seems to be involved in almost all neurodegenerative diseases including Parkinson's disease, amyotrophic lateral sclerosis, frontotemporal dementia, Huntington's disease and the autoimmune disease multiple sclerosis.

OBJECTIVE

The aim of this review is to help researchers both working on this research topic or not to have a comprehensive overview on GSK-3β in the context of neuroinflammation and neurodegeneration.

METHOD

Literature has been searched using PubMed and SciFinder databases by inserting specific keywords. A total of more than 500 articles have been discussed.

RESULTS

First of all, the structure and regulation of the kinase were briefly discussed and then, specific GSK-3β implications in neuroinflammation and neurodegenerative diseases were illustrated also with the help of figures, to conclude with a comprehensive overview on the most important GSK-3β and multitarget inhibitors. For all discussed compounds, the structure and IC50 values at the target kinase have been reported.

CONCLUSION

GSK-3β is involved in several signaling pathways both in neurons as well as in glial cells and immune cells. The fine regulation and interconnection of all these pathways are at the base of the rationale use of GSK-3β inhibitors in neuroinflammation and neurodegeneration. In fact, some compounds are now under clinical trials. Despite this, pharmacodynamic and ADME/Tox profiles of the compounds were often not fully characterized and this is deleterious in such a complex system.

The GSK-3 Inhibitor CT99021 Enhances the Acquisition of Spatial Learning and the Accuracy of Spatial Memory

Glycogen synthase kinase 3 (GSK-3) is a Ser/Thr protein kinase that regulates many cellular processes, including synaptic plasticity. Previously, we reported that inhibition of GSK-3 prevents the induction of one of the major forms of synaptic plasticity, N-methyl-D-aspartate receptor (NMDAR)-dependent long-term depression (LTD), in hippocampal slices. In the present study, we have investigated the effects of inhibiting GSK-3 on learning and memory in healthy naïve animals. Systemic administration of a highly selective GSK-3 inhibitor, CT99021, reversibly blocked NMDAR-dependent LTD in the CA1 region of the hippocampus in anesthetized adult mice. In behavioral tasks, CT99021 had no effect on locomotor activity, anxiety, hippocampus-dependent contextual fear memory, and hippocampus-dependent reversal learning. However, CT99021 facilitated the rate of learning in the Morris water maze (MWM) and T-maze and enhanced the accuracy of long-term spatial memory in the MWM. These findings suggest that GSK-3 regulates the accuracy of spatial memory acquisition and recall.

Multifunctional Ligands with Glycogen Synthase Kinase 3 Inhibitory Activity as a New Direction in Drug Research for Alzheimer's Disease

Alzheimer's disease (AD) belongs to the most common forms of dementia that causes a progressive loss of brain cells and leads to memory impairment and decline of other thinking skills. There is yet no effective treatment for AD; hence, the search for new drugs that could improve memory and other cognitive functions is one of the hot research topics worldwide. Scientific efforts are also directed toward combating behavioral and psychological symptoms of dementia, which are an integral part of the disease. Several studies have indicated that glycogen synthase kinase 3 beta (GSK3β) plays a crucial role in the pathogenesis of AD. Moreover, GSK3β inhibition provided beneficial effects on memory improvement in multiple animal models of AD. The present review aimed to update the most recent reports on the discovery of novel multifunctional ligands with GSK3β inhibitory activity as potential drugs for the symptomatic and disease-modifying therapy of AD. Compounds with GSK3β inhibitory activity seem to be an effective pharmacological approach for treating the causes and symptoms of AD as they reduced neuroinflammation and pathological hallmarks in animal models of AD and provided relief from cognitive and neuropsychiatric symptoms. These compounds have the potential to be used as drugs for the treatment of AD, but their precise pharmacological, pharmacokinetic, toxicological and clinical profiles need to be defined.

Glycogen synthase kinase-3 signaling in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of neurodegenerative disorder with dementia, accounting for approximately 70% of the all cases. Currently, 5.8 million people in the U.S. are living with AD and by 2050 this number is expected to double resulting in a significant socio-economic burden. Despite intensive research, the exact mechanisms that trigger AD are still not known and at the present there is no cure for it. In recent years, many signaling pathways associated with AD neuropathology have been explored as possible candidate targets for the treatment of this condition including glycogen synthase kinase-3β (GSK3-β). GSK3-β is considered a key player in AD pathophysiology since dysregulation of this kinase influences all the major hallmarks of the disease including: tau phosphorylation, amyloid-β production, memory, neurogenesis and synaptic function. The present review summarizes the current understanding of the GSK3-β neurobiology with particular emphasis on its effects on specific signaling pathways associated with AD pathophysiology. Moreover, it discusses the feasibility of targeting GSK3-β for AD treatment and provides a summary of the current research effort to develop GSK3-β inhibitors in preclinical and clinical studies.

Viral Induced Oxidative and Inflammatory Response in Alzheimer's Disease Pathogenesis with Identification of Potential Drug Candidates: A Systematic Review using Systems Biology Approach

Alzheimer's disease (AD) is genetically complex with multifactorial etiology. Here, we aim to identify the potential viral pathogens leading to aberrant inflammatory and oxidative stress response in AD along with potential drug candidates using systems biology approach. We retrieved protein interactions of amyloid precursor protein (APP) and tau protein (MAPT) from NCBI and genes for oxidative stress from NetAge, for inflammation from NetAge and InnateDB databases. Genes implicated in aging were retrieved from GenAge database and two GEO expression datasets. These genes were individually used to create protein-protein interaction network using STRING database (score≥0.7). The interactions of candidate genes with known viruses were mapped using virhostnet v2.0 database. Drug molecules targeting candidate genes were retrieved using the Drug- Gene Interaction Database (DGIdb). Data mining resulted in 2095 APP, 116 MAPT, 214 oxidative stress, 1269 inflammatory genes. After STRING PPIN analysis, 404 APP, 109 MAPT, 204 oxidative stress and 1014 inflammation related high confidence proteins were identified. The overlap among all datasets yielded eight common markers (AKT1, GSK3B, APP, APOE, EGFR, PIN1, CASP8 and SNCA). These genes showed association with hepatitis C virus (HCV), Epstein- Barr virus (EBV), human herpes virus 8 and Human papillomavirus (HPV). Further, screening of drugs targeting candidate genes, and possessing anti-inflammatory property, antiviral activity along with a suggested role in AD pathophysiology yielded 12 potential drug candidates. Our study demonstrated the role of viral etiology in AD pathogenesis by elucidating interaction of oxidative stress and inflammation causing candidate genes with common viruses along with the identification of potential AD drug candidates.

Traditional Ayurvedic and herbal remedies for Alzheimer's disease: from bench to bedside

INTRODUCTION

Alzheimer's disease (AD) is a progressive, neurodegenerative disorder prevalent worldwide among elderly populations. Owing to limited efficacy, side effects, and poor patient compliance for current rationally designed therapies, options are being searched from alternate therapies such as Indian (Ayurvedic), Chinese, or other traditional systems. Areas covered: Following a comprehensive literature search, the authors provide a review encompassing: (1) pathophysiological changes involved in AD, (2) Ayurvedic holistic approach and herbal medicines to manage dementia and AD, and (3) traditional plants and their phytoconstituents effective in AD with description of possible mechanism of action. Expert opinion: Traditional remedies could be adjunct therapeutic options to allay wide-ranging pathological cascades of AD. Ayurveda offers a holistic approach of treatment along with a list of nootropic herbs and formulations that are the rich sources of antioxidants, anti-amyloidogenic, neuroprotective, adaptogenic, anti-inflammatory, and immunomodulatory compounds that are found to modulate neuroendocrine-immune activities, enhance memory, intellect, rejuvenate brain functions, and improve quality of life. A strong knowledge base of traditional systems coupled with contemporary science may provide new functional leads for age-associated neurodegenerative disorders at preventive, promotive, and curative levels, and evolution of new drug therapies and development processes, though further research is needed.

Indirubin-3'-monoxime prevents aberrant activation of GSK-3β/NF-κB and alleviates high fat-high fructose induced Aβ-aggregation, gliosis and apoptosis in mice brain

Deciphering the molecular mechanisms of amyloid pathology and glial cell-mediated neuroinflammation, offers a novel avenue for therapeutic intervention against neurodegeneration. Recent findings demonstrate a crucial link between activation of glycogen synthase kinase-3β (GSK-3β), amyloid deposition and a neuroinflammatory state. However, studies demonstrating the pharmacological effects of GSK-3β inhibition and the interlinked molecular mechanisms still remain elusive. The present study explores whether high fat-high fructose diet (HFFD)-induced neuropathological changes could be alleviated by indirubin-3'-monoxime (IMX), a GSK-3β inhibitor. Male Swiss albino mice (8 weeks old) were fed with normal pellet or HFFD for 60 days. HFFD mice were treated with IMX once daily for last 7 days of the experimental period. HFFD fed-mice had significant amyloid deposits in cerebral cortex and hippocampus, and protein expression analyses showed activation of GSK-3β, nuclear translocation of NF-κB p65 and upregulation of inflammatory (TNF-α, IL-6, COX-2), astrocytic (GFAP), glial surface (CD-68) and pro-apoptotic markers (Bax and caspase-3). IMX treatment promotes the inhibitory phosphorylation of GSK-3β at Ser⁹ and moreover, a marked reduction in the phosphorylation of IKK-β, which prevents translocation and activation of NF-κB. Protein expression studies in IMX-treated brain tissues positively correlate with the anti-neuroinflammatory effects of GSK-3β inhibition. Taken together, our results provide substantial evidence that IMX could potentially attenuate neuroinflammation in coordination with the master transcription factor-NF-κB.

Preparation and investigation of indirubin-loaded SLN nanoparticles and their anti-cancer effects on human glioblastoma U87MG cells

Indirubin, an ingredient in traditional Chinese medicine, is considered as an anti-cancer agent. However, due to its hydrophobic nature, clinical efficiency has been limited. Drug delivery via nanotechnology techniques open new windows toward treatment of cancerous patients. Glioblastoma multiforme (GBM) is the most severe and common type of brain primary tumors. Of common problems in targeting therapies of glioblastoma is the availability of drug in tumoric tissues. In this study, Indirubin loaded solid lipid nanoparticles were prepared and their therapeutic potentials and antitumoric effects were assessed on GBM cell line (U87MG). The SLNs were prepared with Cetyl palmitate and Polysorbat 80 via high-pressure homogenization (HPH) methods in hot mode. Then, properties of SLNs including size, zeta potential, drug encapsulation efficacy (EE %) and drug loading were characterized. SLNs morphology and size were observed using SEM and TEM. The crystalinity of formulation was determined by different scattering calorimetry (DSC). The amount of drug release and antitumor efficiency were evaluated at both normal brain pH of 7.2 and tumoric pH of 6.8. The prapared SLNs had mean size of 130 nm, zeta potential of -16 mV and EE of 99.73%. The results of DSC showed proper encapsulation of drug into SLNs. Drug release assessment in both pH displayed sustain release property. The result of MTT test exhibited a remarkable increment in antitumor activity of Indirubin loaded SLN in comparison with free form of drug and blank SLN on multiform GB. This study indicated that Indirubin loaded SLNs could act as a useful anticancer drugs.

The combination of indirubin and isatin attenuates dextran sodium sulfate induced ulcerative colitis in mice

Indirubin and isatin have been used in the treatment of inflammatory diseases due to their anti-inflammatory properties. This study aimed to evaluate the combined effect of indirubin and isatin on dextran sulfate sodium (DSS)-induced ulcerative colitis (UC). UC was induced by the administration of 3% (w/v) DSS solution, and then the model mice were administered indirubin (10 mg/kg body mass) and (or) isatin (10 mg/kg body mass) by gavage once daily for 7 days. The results showed that indirubin and isatin, individually or combined, significantly inhibited weight loss, lowered disease activity index (DAI), ameliorated pathological changes, decreased the levels of pro-inflammatory mediators and myeloperoxidase (MPO) activity, increased the expression of anti-inflammatory cytokines and Foxp3, suppressed CD4⁺ T cell infiltration, and inhibited oxidative stress and epithelial cell apoptosis. Additionally, indirubin and isatin, both individually and combined, can also inhibit activation of the NF-κB and MAPK pathways induced by DSS. The protective effect of combination therapy against UC was superior to that of single-agent treatment. These results suggest that indirubin combined with isatin attenuates DSS-induced UC, and changes to the NF-κB and MAPK signaling pathways may mediate the protective effects of indirubin and isatin in UC.

Indirubin Derivative 7-Bromoindirubin-3-Oxime (7Bio) Attenuates Aβ Oligomer-Induced Cognitive Impairments in Mice

Indirubins are natural occurring alkaloids extracted from indigo dye-containing plants. Indirubins could inhibit various kinases, and might be used to treat chronic myelocytic leukemia, cancer and neurodegenerative disorders. 7-bromoindirubin-3-oxime (7Bio), an indirubin derivative derived from indirubin-3-oxime, possesses inhibitory effects against cyclin-dependent kinase-5 (CDK5) and glycogen synthase kinase-3β (GSK3β), two pharmacological targets of Alzheimer's disease (AD). In this study, we have discovered that 2.3–23.3 μg/kg 7Bio effectively prevented β-amyloid (Aβ) oligomer-induced impairments of spatial cognition and recognition without affecting bodyweight and motor functions in mice. Moreover, 7Bio potently inhibited Aβ oligomer-induced expression of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). Furthermore, 7Bio significantly prevented the decreased expression of synapsin-1 and PSD-95, biomarkers of pre-synaptic and post-synaptic proteins in Aβ oligomer-treated mice. The mean optical density (OD) with hyper-phosphorylated tau (pTau), glial fibrillary acidic protein (GFAP) and CD45 positive staining in the hippocampus of 7Bio-treated mice were significantly decreased compared to those of Aβ oligomer-treated mice. In addition, Western blotting analysis showed that 7Bio attenuated Aβ oligomer-decreased expression of pSer9-GSK3β. Those results suggested that 7Bio could potently inhibit Aβ oligomer-induced neuroinflammation, synaptic impairments, tau hyper-phosphorylation, and activation of astrocytes and microglia, which may contribute to the neuroprotective effects of 7Bio. Based on these findings, we expected that 7Bio might be developed as a novel anti-AD lead compound.

Targeting of CDK9 with indirubin 3'-monoxime safely and durably reduces HIV viremia in chronically infected humanized mice

Successful propagation of HIV in the human host requires entry into a permissive cell, reverse transcription of viral RNA, integration into the human genome, transcription of the integrated provirus, and assembly/release of new virus particles. Currently, there are antiretrovirals against each of these viral steps, except for provirus transcription. An inhibitor of HIV transcription could both increase potency of treatment and suppress drug-resistant strains. Cellular cyclin-dependent kinase 9 (CDK9) serves as a cofactor for the HIV Tat protein and is required for effective transcription of the provirus. Previous studies have shown that the CDK9 inhibitor Indirubin 3’-monoxime (IM) inhibits HIV transcription in vitro and in short-term in vivo studies of HIV acute infection in humanized mice (PBMC-NSG model), suggesting a therapeutic potential. The objective of this study is to evaluate the toxicity, pharmacokinetics and long-term antiviral activity of IM during chronic HIV infection in humanized mice (HSC-NSG model). We show that IM concentrations above EC₅₀ values are rapidly achieved and sustained for > 3 h in plasma, and that non-toxic concentrations durably reduce HIV RNA levels. In addition, IM enhanced the antiviral activity of antiretrovirals from the reverse transcriptase, protease and integrase inhibitor classes in in vitro infectivity assays. In summary, IM may enhance current antiretroviral treatments and could help achieve a “functional cure” in HIV patients by preventing expression of proviruses.

Targeting CCR3 to Reduce Amyloid-β Production, Tau Hyperphosphorylation, and Synaptic Loss in a Mouse Model of Alzheimer's Disease

The majority of Alzheimer's disease (AD) patients have a late onset, and chronic neuroinflammation, characterized by glial activation and secretion of pro-inflammatory cytokines and chemokines, plays a role in the pathogenesis of AD. The chemokine CCL11 has been shown to be a causative factor of cognitive decline in the process of aging, but little is known whether it is involved in the pathogenesis of AD. In the present study, we showed that CCR3, the receptor for CCL11, was expressed by hippocampal neurons and treatment of primary hippocampal neuronal cultures (14 days in vitro) with CCL11 resulted in activation of cyclin-dependent kinase 5 and glycogen synthase kinase-3β, associated with elevated tau phosphorylation at multiple sites. CCL11 treatment also induced the production of Aβ and dendritic spine loss in the hippocampal neuronal cultures. All these effects were blocked by the CCR3 specific antagonist, GW766994. An age-dependent increase in CCL11, predominantly expressed by the activated microglia, was observed in the cerebrospinal fluid of both APP/PS1 double transgenic mice and wild-type (WT) littermates, with a markedly higher level in APP/PS1 double transgenic mice than that in WT littermates. Deletion of CCR3 in APP/PS1 double transgenic mice significantly reduced the phosphorylation of CDK5 and GSK3β, tau hyperphosphorylation, Aβ deposition, microgliosis, astrogliosis, synaptic loss, and spatial learning and memory deficits. Thus, the age-related increase in CCL11 may be a risk factor of AD, and antagonizing CCR3 may bring therapeutic benefits to AD.

Indirubin-3'-monoxime suppresses amyloid-beta-induced apoptosis by inhibiting tau hyperphosphorylation

Indirubin-3′-monoxime is an effective inhibitor of cyclin-dependent protein kinases, and may play an obligate role in neuronal apoptosis in Alzheimer's disease. Here, we found that indirubin-3′-monoxime improved the morphology and increased the survival rate of SH-SY5Y cells exposed to amyloid-beta 25–35 (Aβ_25–35), and also suppressed apoptosis by reducing tau phosphorylation at Ser199 and Thr205. Furthermore, indirubin-3′-monoxime inhibited phosphorylation of glycogen synthase kinase-3β (GSK-3β). Our results suggest that indirubin-3′-monoxime reduced Aβ_25–35-induced apoptosis by suppressing tau hyperphosphorylation via a GSK-3β-mediated mechanism. Indirubin-3′-monoxime is a promising drug candidate for Alzheimer's disease.

Indirubin-3-Oxime Prevents H2O2-Induced Neuronal Apoptosis via Concurrently Inhibiting GSK3β and the ERK Pathway

Oxidative stress-induced neuronal apoptosis plays an important role in many neurodegenerative disorders. In this study, we have shown that indirubin-3-oxime, a derivative of indirubin originally designed for leukemia therapy, could prevent hydrogen peroxide (H₂O₂)-induced apoptosis in both SH-SY5Y cells and primary cerebellar granule neurons. H₂O₂ exposure led to the increased activities of glycogen synthase kinase 3β (GSK3β) and extracellular signal-regulated kinase (ERK) in SH-SY5Y cells. Indirubin-3-oxime treatment significantly reversed the altered activity of both the PI3-K/Akt/GSK3β cascade and the ERK pathway induced by H₂O₂. In addition, both GSK3β and mitogen-activated protein kinase inhibitors significantly prevented H₂O₂-induced neuronal apoptosis. Moreover, specific inhibitors of the phosphoinositide 3-kinase (PI3-K) abolished the neuroprotective effects of indirubin-3-oxime against H₂O₂-induced neuronal apoptosis. These results strongly suggest that indirubin-3-oxime prevents H₂O₂-induced apoptosis via concurrent inhibiting GSK3β and the ERK pathway in SH-SY5Y cells, providing support for the use of indirubin-3-oxime to treat neurodegenerative disorders caused or exacerbated by oxidative stress.

Indirubin Increases CD4+CD25+Foxp3+ Regulatory T Cells to Prevent Immune Thrombocytopenia in Mice

Indirubin, a traditional Chinese medicine, is used to treat autoimmune diseases in clinics. However, the effects of indirubin on the immunosuppressive CD4+CD25+Foxp3+ regulatory T cells (Treg) have not been addressed. Thus, we aimed to investigate the effects of indirubin on CD4+CD25+Treg cells in immune thrombocytopenia (ITP) CBA mice, which were established by immunization with Wistar rat platelets. 50 mg/kg indirubin treatment daily for 4 weeks significantly decreased anti-platelet antibody production and prevented the decrease of platelets caused by immunization in ITP mice. Consistently, indirubin significantly enhanced the percentage and cell number of CD4+CD25+Foxp3+Treg cells in the peripheral blood, spleen and lymph nodes. We also observed a significant increase of the frequency and cell number of CD4+CD25+Foxp3+Treg cells in the thymus upon indirubin treatment. Furthermore, CD4+CD25+Treg cells from indirubin-treated mice showed similar immunosuppression on T effector cells as compared to those from control mice. Altogether, indirubin ameliorates ITP by enhancing CD4+CD25+Foxp3+Treg cell level with preserving immunosuppressive function.

Indirubin-3-Oxime Effectively Prevents 6OHDA-Induced Neurotoxicity in PC12 Cells via Activating MEF2D Through the Inhibition of GSK3β

Indirubin-3-oxime (I3O), a synthetic derivative of indirubin, was originally designed as potent inhibitors of cyclin-dependent kinases (CDKs) and glycogen synthase kinase 3β (GSK3β) for leukemia therapy. In the current study, we have shown, for the first time, that I3O prevented 6-hydroxydopamine (6OHDA)-induced neuronal apoptosis and intracellular reactive oxygen species accumulation in PC12 cells in a concentration-dependent manner. GSK3β inhibitors but not CDK5 inhibitors reduced the neurotoxicity induced by 6OHDA. Moreover, the activation of GSK3β was observed after 6OHDA treatment. Furthermore, 6OHDA substantially decreased the transcriptional activity of myocyte enhancer factor 2D (MEF2D), a transcription factor that plays an important role in dopaminergic neuron survival, and reduced nuclear localized MEF2D expression. Interestingly, indirubin-3-oxime and GSK3β inhibitors prevented 6OHDA-induced dysregulation of MEF2D. In addition, short hairpin RNA-mediated decrease of MEF2D expression significantly abolished the neuroprotective effects of indirubin-3-oxime. Collectively, our results strongly suggested that indirubin-3-oxime prevented 6OHDA-induced neurotoxicity via activating MEF2D, possibly through the inhibition of GSK3β. In view of the capability of indirubin-3-oxime to cross the blood-brain barrier, our findings further indicated that indirubin-3-oxime might be a novel drug candidate for neurodegenerative disorders, including Parkinson's disease in particular.

Plant alkaloids as drug leads for Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative illness associated with dementia and is most prevalent among the elderly population. Current medications can only treat symptoms. Alkaloids are structurally diverse and have been an important source of therapeutics for various brain disorders. Two US Food and Drug Administration (FDA)-approved acetylcholinesterase inhibitors for AD, galantamine and rivastigmine, are in fact alkaloids. In addition, clinical trials of four other extensively studied alkaloids-huperzine A, caffeine, nicotine, and indomethacin-have been conducted but do not convincingly demonstrate their clinical efficacy for AD. Interestingly, rhynchophylline, a known neuroprotective alkaloid, was recently discovered by in silico screening as an inhibitor of EphA4, a novel target for AD. Here, we review the pathophysiological mechanisms underlying AD, current treatment strategies, and therapeutic potential of several selected plant alkaloids in AD, highlighting their various drug targets and the key supportive preclinical and clinical studies. Future research should include more rigorous clinical studies of the most promising alkaloids, the further development of recently discovered candidate alkaloids, and the continual search for new alkaloids for relevant drug targets. It remains promising that an alkaloid drug candidate could significantly affect the progression of AD in addition to providing symptomatic relief.

Glycogen synthase kinase-3 as a therapeutic target for cognitive dysfunction in neuropsychiatric disorders

The serine/threonine kinase glycogen synthase kinase-3 (GSK-3) is involved in a broad range of cellular processes including cell proliferation, apoptosis and inflammation. It is now also increasingly acknowledged as having a role to play in cognitive-related processes such as neurogenesis, synaptic plasticity and neural cell survival. Cognitive impairment represents a major debilitating feature of many neurodegenerative and psychiatric disorders, including Alzheimer's disease, mood disorders, schizophrenia and fragile X syndrome, as well as being a result of traumatic brain injury or cranial irradiation. Accordingly, GSK-3 has been identified as an important therapeutic target for cognitive impairment, and recent preclinical studies have yielded important evidence demonstrating that GSK-3 inhibitors may be useful therapeutic interventions for restoring cognitive function in some of these brain disorders. The current review summarises the role of GSK-3 as a regulator of cognitive-dependent functions, examines current preclinical and clinical evidence of the potential of GSK-3 inhibitors as therapeutic agents for cognitive impairments in neuropsychiatric disorders, and offers some insight into the current obstacles that are impeding the clinical use of selective GSK-3 inhibitors in the treatment of cognitive impairment.

GSK-3β, a pivotal kinase in Alzheimer disease

Alzheimer disease (AD) is the most common form of age-related dementia. The etiology of AD is considered to be multifactorial as only a negligible percentage of cases have a familial or genetic origin. Glycogen synthase kinase-3 (GSK-3) is regarded as a critical molecular link between the two histopathological hallmarks of the disease, namely senile plaques and neurofibrillary tangles. In this review, we summarize current data regarding the involvement of this kinase in several aspects of AD development and progression, as well as key observations highlighting GSK-3 as one of the most relevant targets for AD treatment.

Glycogen synthase kinase-3 inhibitors: Rescuers of cognitive impairments

Impairment of cognitive processes is a devastating outcome of many diseases, injuries, and drugs affecting the central nervous system (CNS). Most often, very little can be done by available therapeutic interventions to improve cognitive functions. Here we review evidence that inhibition of glycogen synthase kinase-3 (GSK3) ameliorates cognitive deficits in a wide variety of animal models of CNS diseases, including Alzheimer's disease, Fragile X syndrome, Down syndrome, Parkinson's disease, spinocerebellar ataxia type 1, traumatic brain injury, and others. GSK3 inhibitors also improve cognition following impairments caused by therapeutic interventions, such as cranial irradiation for brain tumors. These findings demonstrate that GSK3 inhibitors are able to ameliorate cognitive impairments caused by a diverse array of diseases, injury, and treatments. The improvements in impaired cognition instilled by administration of GSK3 inhibitors appear to involve a variety of different mechanisms, such as supporting long-term potentiation and diminishing long-term depression, promotion of neurogenesis, reduction of inflammation, and increasing a number of neuroprotective mechanisms. The potential for GSK3 inhibitors to repair cognitive deficits associated with many conditions warrants further investigation of their potential for therapeutic interventions, particularly considering the current dearth of treatments available to reduce loss of cognitive functions.

Synthesis and identification of new flavonoids targeting liver X receptor β involved pathway as potential facilitators of Aβ clearance with reduced lipid accumulation

Alzheimer's disease (AD) is associated with impaired Aβ degradation in the brain. Enhancing the process of Aβ clearance is an attractive potential AD therapy. Treatment with LXR agonists may reduce Aβ levels in vivo. However, the clinical potential of many LXR agonists is limited because of their nonselective actions on LXRα/β, which lead to undesired hepatic lipogenesis via LXRα-dependent pathways. In this study, ABCA1 up-regulators were identified from a series of flavonoids and were found to preferentially activate LXRβ and up-regulate expression of ABCA1 and apoE in different cell lines. Further investigations confirmed that these compounds facilitate intracellular Aβ clearance in Aβ-loaded BV2 cells. Administration of compound 19 reduced total brain Aβ and plaque burden in APP/PS1 double transgenic mice, associated with elevated ABCA1 and apoE expression. Compared with the nonselective LXR agonists, the active compounds reported here induced less accumulation of undesired lipids and triglycerides in HepG2 cells.

Drug pipeline in neurodegeneration based on transgenic mice models of Alzheimer's disease

Alzheimer's disease (AD) is one of the most important neurodegenerative disorders, bringing about huge medical and social burden in the elderly worldwide. Many aspects of its pathogenesis have remained unclear and no effective treatment exists for it. Within the past 20 years, various mice models harboring AD-related human mutations have been produced. These models imitate diverse AD-related pathologies and have been used for basic and therapeutic investigations in AD. In this regard, there are a wide variety of preclinical trials of potential therapeutic modalities using AD mice models which are of paramount importance for future clinical trials and applications. This review summarizes more than 140 substances and treatment modalities being used in transgenic AD mice models from 2001 to 2011. We also discuss advantages and disadvantages of each model to be used in therapeutic development for AD.

Berberine ameliorates β-amyloid pathology, gliosis, and cognitive impairment in an Alzheimer's disease transgenic mouse model

The accumulation of β-amyloid (Aβ) peptide derived from abnormal processing of amyloid precursor protein (APP) is a common pathological hallmark of Alzheimer's disease (AD) brains. In this study, we evaluated the therapeutic effect of berberine (BBR) extracted from Coptis chinensis Franch, a Chinese medicinal herb, on the neuropathology and cognitive impairment in TgCRND8 mice, a well established transgenic mouse model of AD. Two-month-old TgCRND8 mice received a low (25 mg/kg per day) or a high dose of BBR (100 mg/kg per day) by oral gavage until 6 months old. BBR treatment significantly ameliorated learning deficits, long-term spatial memory retention, as well as plaque load compared with vehicle control treatment. In addition, enzyme-linked immunosorbent assay (ELISA) measurement showed that there was a profound reduction in levels of detergent-soluble and -insoluble β-amyloid in brain homogenates of BBR-treated mice. Glycogen synthase kinase (GSK)3, a major kinase involved in APP and tau phosphorylation, was significantly inhibited by BBR treatment. We also found that BBR significantly decreased the levels of C-terminal fragments of APP and the hyperphosphorylation of APP and tau via the Akt/glycogen synthase kinase 3 signaling pathway in N2a mouse neuroblastoma cells stably expressing human Swedish mutant APP695 (N2a-SwedAPP). Our results suggest that BBR provides neuroprotective effects in TgCRND8 mice through regulating APP processing and that further investigation of the BBR for therapeutic use in treating AD is warranted.

GSK-3 Inhibitors: Preclinical and Clinical Focus on CNS

Inhibiting glycogen synthase kinase-3 (GSK-3) activity via pharmacological intervention has become an important strategy for treating neurodegenerative and psychiatric disorders. The known GSK-3 inhibitors are of diverse chemotypes and mechanisms of action and include compounds isolated from natural sources, cations, synthetic small-molecule ATP-competitive inhibitors, non-ATP-competitive inhibitors, and substrate-competitive inhibitors. Here we describe the variety of GSK-3 inhibitors with a specific emphasis on their biological activities in neurons and neurological disorders. We further highlight our current progress in the development of non-ATP-competitive inhibitors of GSK-3. The available data raise the hope that one or more of these drug design approaches will prove successful at stabilizing or even reversing the aberrant neuropathology and cognitive deficits of certain central nervous system disorders.

Chemical modulation of memory formation in larval zebrafish

Whole organism-based small-molecule screens have proven powerful in identifying novel therapeutic chemicals, yet this approach has not been exploited to identify new cognitive enhancers. Here we present an automated high-throughput system for measuring nonassociative learning behaviors in larval zebrafish. Using this system, we report that spaced training blocks of repetitive visual stimuli elicit protein synthesis-dependent long-term habituation in larval zebrafish, lasting up to 24 h. Moreover, repetitive acoustic stimulation induces robust short-term habituation that can be modulated by stimulation frequency and instantaneously dishabituated through cross-modal stimulation. To characterize the neurochemical pathways underlying short-term habituation, we screened 1,760 bioactive compounds with known targets. Although we found extensive functional conservation of short-term learning between larval zebrafish and mammalian models, we also discovered several compounds with previously unknown roles in learning. These compounds included a myristic acid analog known to interact with Src family kinases and an inhibitor of cyclin dependent kinase 2, demonstrating that high-throughput chemical screens combined with high-resolution behavioral assays provide a powerful approach for the discovery of novel cognitive modulators.

The new indirubin derivative inhibitors of glycogen synthase kinase-3, 6-BIDECO and 6-BIMYEO, prevent tau phosphorylation and apoptosis induced by the inhibition of protein phosphatase-2A by okadaic acid in cultured neurons

Alterations in glycogen synthase kinase-3β (GSK3β) and protein phosphatase-2A (PP2A) have been proposed to be involved in the abnormal tau phosphorylation and aggregation linked to Alzheimer's disease (AD). Interconnections between GSK3β and PP2A signaling pathways are well established. Targeting tau kinases was proposed to represent a therapeutic strategy for AD. However, which tau kinases should be blocked and to what extent, keeping in mind that kinases have physiological roles? Because most kinase inhibitors are relatively specific and many of them interfere with the cell cycle, it is necessary to develop more specific tau kinase inhibitors devoid of cell toxicity. Here, we used the PP2A inhibition by okadaic acid (OKA) in primary cultured cortical neurons as an in vitro model of increased tau phosphorylation and apoptosis. We tested the effects of two newly characterized indirubin derivative inhibitors of GSK3, 6-BIDECO (6-bromoindirubin-3'-[O-(N,N-diethylcarbamyl)-oxime] and 6-BIMYEO (6-bromoindirubin-3'-[O-(2-morpholin-1-ylethyl)-oxime] hydrochloride) on OKA-induced tau phosphorylation and neuronal apoptosis. Both compounds exhibit higher selectivity toward GSK3 compared with other tau kinases (for 6-BIDECO, IC50 is 0.03 μM for GSK3, >10 μM for CDK1, and 10 μM for CDK5; for 6-BIMYEO, IC50 is 0.11 μM for GSK3, 1.8 μM for CDK1, and 0.9 μM for CDK5). We show that 6-BIDECO and 6-BIMYEO used at micromolar concentrations are not neurotoxic and potently reversed tau phosphorylation and apoptosis induced by OKA. The neuroprotection by these compounds should be further validated in animal models of AD.

Tau phosphorylation and neuronal apoptosis induced by the blockade of PP2A preferentially involve GSK3β

Overactivation of GSK3β (glycogen synthase kinase-3β) and downregulation of PP2A (protein phosphatase-2A) have been proposed to be involved in the abnormal tau phosphorylation and aggregation in Alzheimer's disease (AD). GSK3β and PP2A signaling pathways were reported to be interconnected. Targeting tau kinases was suggested to represent a therapeutic strategy for AD. Here, tau phosphorylation and neuronal apoptosis were induced in cortical cultured neurons by the inhibition of PP2A by okadaic acid (OKA). In this in vitro model of 'tau pathology' and neurodegeneration, we tested whether GSK3β and other tau kinases including DYRK1A and CDK5 were implicated. Our results show that the inhibitors of GSK3β, lithium and 6-BIO (6-bromoindirubin-3'-oxime), prevented OKA-induced tau phosphorylation and neuronal apoptosis. The implication of GSK3β in these OKA-induced effects was confirmed by its silencing by hairpin siRNA. By contrast, inhibition of DYRK1A (dual-specificity tyrosine-phosphorylation regulated kinase-1A) and CDK5 (cyclin-dependent kinase-5) reversed OKA-induced tau phosphorylation at certain sites but failed to prevent neuronal apoptosis. These results indicate that OKA-induced effects, especially neuronal apoptosis, are preferentially mediated by GSK3β. Furthermore, since chronic exposure to lithium and 6-BIO might be deleterious for neurons, we tested the effect of a new 6-BIO derivative, 6-BIBEO (6-bromoindirubin-3'-(2-bromoethyl)-oxime), which is much less cytotoxic and more selectively inhibits GSK3β compared to lithium and 6-BIO. We show that 6-BIBEO efficiently reversed OKA-induced tau phosphorylation and neuronal apoptosis. It will be interesting to test neuroprotection by 6-BIBEO in an in vivo model of tau pathology and neurodegeneration.

Glycogen synthase kinase-3β: a mediator of inflammation in Alzheimer's disease?

Proliferation and activation of microglial cells is a neuropathological characteristic of brain injury and neurodegeneration, including Alzheimer's disease. Microglia act as the first and main form of immune defense in the nervous system. While the primary function of microglia is to survey and maintain the cellular environment optimal for neurons in the brain parenchyma by actively scavenging the brain for damaged brain cells and foreign proteins or particles, sustained activation of microglia may result in high production of proinflammatory mediators that disturb normal brain functions and even cause neuronal injury. Glycogen synthase kinase-3β has been recently identified as a major regulator of immune system and mediates inflammatory responses in microglia. Glycogen synthase kinase-3β has been extensively investigated in connection to tau and amyloid β toxicity, whereas reports on the role of this enzyme in neuroinflammation in Alzheimer's disease are negligible. Here we review and discuss the role of glycogen synthase-3β in immune cells in the context of Alzheimer's disease pathology.

4-O-Methylhonokiol attenuates memory impairment in presenilin 2 mutant mice through reduction of oxidative damage and inactivation of astrocytes and the ERK pathway

Presenilin 2 (PS2) mutation increases Aβ generation and neuronal cell death in the brains of Alzheimer disease (AD) patients. In a previous study, we showed that increased oxidative damage and activation of extracellular signal-regulated kinase (ERK) were associated with Aβ generation and neuronal cell death in neuronal cells expressing mutant PS2. In this study, we show that oral treatment with 4-O-methylhonokiol, a novel compound isolated from Magnolia officinalis, for 3 months (1.0mg/kg) prevented PS2 mutation-induced memory impairment and neuronal cell death accompanied by a reduction in Aβ(1-42) accumulation. We also found that 4-O-methylhonokiol inhibited PS2 mutation-induced activation of ERK and β-secretase, and oxidative protein and lipid damage, but recovered glutathione levels in the cortex and hippocampus of PS2 mutant mice. Additionally, 4-O-methylhonokiol prevented PS2 mutation-induced activation of astrocytes as well as production of TNF-α, IL-1β, reactive oxygen species (ROS), and nitric oxide (NO) in neurons. Generation of TNF-α, IL-1β, ROS, and NO and ERK activation in cultured astrocytes treated with lipopolysaccharide (1μg/ml) were also prevented by 4-O-methylhonokiol in a dose-dependent manner. These results suggest that the improving effects of 4-O-methylhonokiol on memory function may be associated with a suppression of the activation of ERK and astrocytes as well as a reduction in oxidative damage. Thus, 4-O-methylhonokiol may be useful in the prevention and treatment of AD.

Indirubin-3'-oxime inhibits inflammatory activation of rat brain microglia

Microglial cells play critical roles in the immune and inflammatory responses of the brain. Under pathological conditions, the activation of microglia helps to restore brain homeostasis. However, chronic microglial activation endangers neuronal survival through the release of various proinflammatory and neurotoxic factors. As such, regulators of microglial activation have been considered as potential therapeutic candidates to reduce the risk of neurodegeneration associated with neurodegenerative diseases, including Alzheimer's and, Parkinson's diseases. Indirubin-3'-oxime, a potent inhibitor of cyclin-dependent kinases and glycogen synthase kinase-3β, has been shown to have neuroprotective potential. The specific aim of this study was to examine the efficacy of indirubin-3'-oxime in the repression of microglial activation. Indirubin-3'-oxime was shown to effectively inhibit lipopolysaccharide (LPS)-induced nitric oxide release from cultured rat brain microglia. This compound reduced the LPS-stimulated productions of tumor necrosis factor-α, interleukin-1β, prostaglandin E(2), and intracellular reactive oxygen species and also effectively reduced LPS-elicited NF-κB activation. In organotypic hippocampal slice cultures, indirubin-3'-oxime blocked LPS-related hippocampal cell death. These results suggest that indirubin-3'-oxime provides neuroprotection by reducing the productions of various neurotoxic molecules in activated microglia.