Xanthoceraside Inhibits Pro-inflammatory Cytokine Expression in Aβ25–35/IFN-γ–Stimulated Microglia Through the TLR2 Receptor, MyD88, Nuclear Factor-κB, and Mitogen-Activated Protein Kinase Signaling Pathways

Prevention and Treatment of Alzheimer's Disease Via the Regulation of the Gut Microbiota With Traditional Chinese Medicine

Alzheimer's disease (AD) is caused by a variety of factors, and one of the most important factors is gut microbiota dysbiosis. An imbalance in the gut mincrobiota have been shown to change the concentrations of lipopolysaccharide and short-chain fatty acids. These microorganisms synthesize substances that can influence the levels of a variety of metabolites and cause multiple diseases through the immune response, fatty acid metabolism, and amino acid metabolism pathways. Furthermore, these metabolic changes promote the formation of β-amyloid plaques and neurofibrillary tangles. Thus, the microbiota-gut-brain axis plays an important role in AD development. In addition to traditional therapeutic drugs such as donepezil and memantine, traditional Chinese medicines (TCMs) have also showed to significantly decrease the severity of AD symptoms and suppress the underlying related mechanisms. We searched for studies on the effects of different herbal monomers, single herbs, and polyherbal formulas on the gut microbiota of AD patients and identified the relevant pathways through which the gut microbiota affected AD. We conclude that improvements in the gut microbiota not only decrease the occurrence of inflammatory reactions but also reduce the deposition of central pathological products. Herbal monomers have a stronger effect on improving of central pathology. Polyherbal formulas have the most extensive effect on the gut microbiota in patients with AD. Among the effects of formulas, the anti-inflammatory effect is the most essential and is also the main concern regarding the use of TCMs in treating AD from the viewpoint of the gut microbiota. We hope that this review will be helpful for providing new ideas for the clinical application of TCMs in the treatment of AD.

Targeting Microglia in Alzheimer's Disease: Pathogenesis and Potential Therapeutic Strategies

Microglia, as resident macrophages in the central nervous system, play a multifunctional role in the pathogenesis of Alzheimer's disease (AD). Their clustering around amyloid-β (Aβ) deposits is a core pathological feature of AD. Recent advances in single-cell RNA sequencing (scRNA-seq) and single-nucleus RNA sequencing (snRNA-seq) have revealed dynamic changes in microglial phenotypes over time and across different brain regions during aging and AD progression. As AD advances, microglia primarily exhibit impaired phagocytosis of Aβ and tau, along with the release of pro-inflammatory cytokines that damage synapses and neurons. Targeting microglia has emerged as a potential therapeutic approach for AD. Treatment strategies involving microglia can be broadly categorized into two aspects: (1) enhancing microglial function: This involves augmenting their phagocytic ability against Aβ and cellular debris and (2) mitigating neuroinflammation: Strategies include inhibiting TNF-α signaling to reduce the neuroinflammatory response triggered by microglia. Clinical trials exploring microglia-related approaches for AD treatment have garnered attention. Additionally, natural products show promise in enhancing beneficial effects and suppressing inflammatory responses. Clarifying microglial dynamics, understanding their roles, and exploring novel therapeutic approaches will advance our fight against AD.

Drugs to Treat Neuroinflammation in Neurodegenerative Disorders

Neuroinflammation is associated with disorders of the nervous system, and it is induced in response to many factors, including pathogen infection, brain injury, toxic substances, and autoimmune diseases. Astrocytes and microglia have critical roles in neuroinflammation. Microglia are innate immune cells in the central nervous system (CNS), which are activated in reaction to neuroinflammation-inducing factors. Astrocytes can have pro- or anti-inflammatory responses, which depend on the type of stimuli presented by the inflamed milieu. Microglia respond and propagate peripheral inflammatory signals within the CNS that cause low-grade inflammation in the brain. The resulting alteration in neuronal activities leads to physiological and behavioral impairment. Consequently, activation, synthesis, and discharge of various pro-inflammatory cytokines and growth factors occur. These events lead to many neurodegenerative conditions, such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis discussed in this study. After understanding neuroinflammation mechanisms and the involvement of neurotransmitters, this study covers various drugs used to treat and manage these neurodegenerative illnesses. The study can be helpful in discovering new drug molecules for treating neurodegenerative disorders.

Roles of microglia in adult hippocampal neurogenesis in depression and their therapeutics

Adult hippocampal neurogenesis generates functional neurons from neural progenitor cells in the hippocampal dentate gyrus (DG) to complement and repair neurons and neural circuits, thus benefiting the treatment of depression. Increasing evidence has shown that aberrant microglial activity can disrupt the appropriate formation and development of functional properties of neurogenesis, which will play a crucial role in the occurrence and development of depression. However, the mechanisms of the crosstalk between microglia and adult hippocampal neurogenesis in depression are not yet fully understood. Therefore, in this review, we first introduce recent discoveries regarding the roles of microglia and adult hippocampal neurogenesis in the etiology of depression. Then, we systematically discuss the possible mechanisms of how microglia regulate adult hippocampal neurogenesis in depression according to recent studies, which involve toll-like receptors, microglial polarization, fractalkine-C-X3-C motif chemokine receptor 1, hypothalamic-pituitary-adrenal axis, cytokines, brain-derived neurotrophic factor, and the microbiota-gut-brain axis, etc. In addition, we summarize the promising drugs that could improve the adult hippocampal neurogenesis by regulating the microglia. These findings will help us understand the complicated pathological mechanisms of depression and shed light on the development of new treatment strategies for this disease.

The dual face of microglia (M1/M2) as a potential target in the protective effect of nutraceuticals against neurodegenerative diseases

The pathophysiology of different neurodegenerative illnesses is significantly influenced by the polarization regulation of microglia and macrophages. Traditional classifications of macrophage phenotypes include the pro-inflammatory M1 and the anti-inflammatory M2 phenotypes. Numerous studies demonstrated dynamic non-coding RNA modifications, which are catalyzed by microglia-induced neuroinflammation. Different nutraceuticals focus on the polarization of M1/M2 phenotypes of microglia and macrophages, offering a potent defense against neurodegeneration. Caeminaxin A, curcumin, aromatic-turmerone, myricetin, aurantiamide, 3,6'-disinapoylsucrose, and resveratrol reduced M1 microglial inflammatory markers while increased M2 indicators in Alzheimer's disease. Amyloid beta-induced microglial M1 activation was suppressed by andrographolide, sulforaphane, triptolide, xanthoceraside, piperlongumine, and novel plant extracts which also prevented microglia-mediated necroptosis and apoptosis. Asarone, galangin, baicalein, and a-mangostin reduced oxidative stress and pro-inflammatory cytokines, such as interleukin (IL)-1, IL-6, and tumor necrosis factor-alpha in M1-activated microglia in Parkinson's disease. Additionally, myrcene, icariin, and tenuigenin prevented the nod-like receptor family pyrin domain-containing 3 inflammasome and microglial neurotoxicity, while a-cyperone, citronellol, nobiletin, and taurine prevented NADPH oxidase 2 and nuclear factor kappa B activation. Furthermore, other nutraceuticals like plantamajoside, swertiamarin, urolithin A, kurarinone, Daphne genkwa flower, and Boswellia serrata extracts showed promising neuroprotection in treating Parkinson's disease. In Huntington's disease, elderberry, curcumin, iresine celosia, Schisandra chinensis, gintonin, and pomiferin showed promising results against microglial activation and improved patient symptoms. Meanwhile, linolenic acid, resveratrol, Huperzia serrata, icariin, and baicalein protected against activated macrophages and microglia in experimental autoimmune encephalomyelitis and multiple sclerosis. Additionally, emodin, esters of gallic and rosmarinic acids, Agathisflavone, and sinomenine offered promising multiple sclerosis treatments. This review highlights the therapeutic potential of using nutraceuticals to treat neurodegenerative diseases involving microglial-related pathways.

Protective Effects of Cirsium japonicum var. maackii Flower on Amyloid Beta25-35-Treated C6 Glial Cells

Amyloid beta (Aβ) is a neurotoxic peptide and a key factor causing Alzheimer's disease. Cirsium japonicum var. maackii (CJM) has neuroprotective effects, but the protective effects of the flower from CJM (FCJM) on the neural system remain unclear. This study aimed to identify the fraction of FCJM with the highest neuroprotective potential and investigate its protective mechanisms against Aβ_25-35-induced inflammation in C6 glial cells. The cell viability and generation of reactive oxygen species (ROS) were measured to investigate the positive effect of FCJM on oxidative stress. Treatment with the FCJM extract or fractions increased the cell viability to 60-70% compared with 52% in the Aβ_25-35-treated control group and decreased ROS production to 84% compared with 100% in the control group. The ethyl acetate fraction of FCJM (EFCJM) was the most effective among all the extracts and fractions. We analyzed the protective mechanisms of EFCJM on Aβ_25-35-induced inflammation in C6 glial cells using Western blot. EFCJM downregulated amyloidogenic pathway-related proteins, such as Aβ precursor protein, β-secretase, presenilin 1, and presenilin 2. Moreover, EFCJM attenuated the Bax/Bcl-2 ratio, an index of apoptosis, and upregulated the oxidative stress-related protein, heme oxygenase-1. Therefore, this study demonstrated that FCJM improves cell viability and inhibits ROS in Aβ_25-35-treated C6 glial cells. Furthermore, EFCJM exhibits neuroprotective effects in Aβ_25-35-induced inflammation in C6 glial cells by modulating oxidative stress and amyloidogenic and apoptosis signaling pathways. FCJM, especially EFCJM, can be a promising agent for neurodegenerative disease prevention.

Barrigenol-like triterpenoid saponins from the husks of Xanthoceras sorbifolia bunge and their anti-inflammatory activity by inhibiting COX-2 and iNOS expression

The husks of Xanthoceras sorbifolia Bunge were explored resulting in the isolation of nine undescribed compounds and seven known compounds. Their structures were defined by NMR spectroscopic techniques, HRESIMS analyses and DP4+ possibility analysis. Three of them showed evident inhibition on NO productions in LPS-induced BV-2 cells by controlling the expression of the nuclear factor-kappa-B (NF-κB) signaling pathway. Furthermore, they also markedly decreased the expression of the proteins COX-2 and iNOS. In addition, most compounds showed no cytotoxicity against Hep 3B, A549, HCT 116, AGS, MCF-7 cell lines. These findings showed that the husks of X. sorbifolia might have considerable potential for the prevention of inflammation-related neurodegenerative disorders.

Natural Products as Novel Neuroprotective Agents; Computational Predictions of the Molecular Targets, ADME Properties, and Safety Profile

Neurodegenerative diseases (NDs) are one of the most challenging public health issues. Despite tremendous advances in our understanding of NDs, little progress has been made in establishing effective treatments. Natural products may have enormous potential in preventing and treating NDs by targeting microglia; yet, there have been several clinical concerns about their usage, primarily due to a lack of scientific evidence for their efficacy, molecular targets, physicochemical properties, and safety. To solve this problem, the secondary bioactive metabolites derived from neuroprotective medicinal plants were identified and selected for computational predictions for anti-inflammatory activity, possible molecular targets, physicochemical properties, and safety evaluation using PASS online, Molinspiration, SwissADME, and ProTox-II, respectively. Most of the phytochemicals were active as anti-inflammatory agents as predicted using the PASS online webserver. Moreover, the molecular target predictions for some phytochemicals were similar to the reported experimental targets. Moreover, the phytochemicals that did not violate important physicochemical properties, including blood-brain barrier penetration, GI absorption, molecular weight, and lipophilicity, were selected for further safety evaluation. After screening 54 neuroprotective phytochemicals, our findings suggest that Aromatic-turmerone, Apocynin, and Matrine are the most promising compounds that could be considered when designing novel neuroprotective agents to treat neurodegenerative diseases via modulating microglial polarization.

The protective effect of Xanthoceras sorbifolia Bunge husks on cognitive disorder based on metabolomics and gut microbiota analysis

AIM OF THE STUDY

The husks of Xanthoceras sorbifolia Bunge mainly used in north China as folk medicine were reported to have potential protective effect on cognitive impairment. However, the mechanism remains unclear. In order to fully understand the mechanism of the protection, a complementary study of the husks was conducted.

MATERIALS AND METHODS

The urinary and fecal metabolomics were used to analyze the potential biomarkers by the liquid chromatography-tandem time of flight mass spectrometry, and the16S rDNA technology was applied to conduct the analysis of microbiota species in the fecal samples of the rats, which is a significant influencing factor for the development of cognitive impairment.

RESULTS

In metabolomics study, ten potential metabolic biomarkers, which are hippuric acid, kynurenic acid, creatinine, phenylalanine, xanthurenic acid, phenylacetylglycine, succinyladenosine, cresol sulfate, tryptophan 2-C-mannoside and N4-Acetylcytidine in urine, along with two, including isoleucine and phenylalanine in feces, were preliminarily identified, involving multiple pathways such as tryptophan, purine, kynurenine, and phenylalanine metabolism. The perturbation of these metabolic pathways could be related with insulin resistance, oxidative stress, energy metabolism deficit and neuroinflammation, which were risk factors to cause cognitive impairment. In gut microbiota analysis, the relative abundance of c_Bacteroidia, c_Alphaproteobacteria, f_Prevotellaceae, f_Sphingomonadaceae, f_Burkholderiaceae, g_Prevotellaceae_NK3B31_group and p_Bacteroidetes was significantly changed in the rats with cognitive impairment. Spearman's analysis showed obvious correlation between the metabolites and the microbiota species. In the rats with pretreatment of the husks extract, metabolites maintained a relative normal level, and the husks extract could regulate the gut microbiota, especially f_Prevotellaceae and g_Prevotellaceae_NK3B31_group, indicating the effect of the husks on the metabolic pathways via GMs. Such amino acids as isoleucine and phenylalanine failed to show any significant correlation with the microbiota species, indicating that the husks exhibited the potential protective effect through gut microbiota and other pathways.

CONCLUSIONS

The husks extract could improve the intestinal microenvironment, and the stability of intestinal microenvironment was associated with normality of tryptophan, purine, kynurenine and phenylalanine metabolic pathways etc, which probably had an effect on cognitive function. This complementary work suggested that gut microbiotas were potential targets of the husks to exert its effect on cognitive impairment.

Xanthoceras sorbifolium Bunge: A Review on Botany, Phytochemistry, Pharmacology, and Applications

Xanthoceras sorbifolium Bunge (Sapindaceae) is a native Chinese plant with promising applications as a biofuel feedstock and a source of novel drugs. Historical records and documents from different periods have mentioned the use of X. sorbifolium and its botanical constituents in treating diseases, highlighting its central role in Chinese and Mongolian traditional medicinal therapies. Phytochemical research has focused on the husks, leaves, trunks, and branches of this herb. A total of 278 chemical compounds have been isolated and divided into 8 categories: triterpenoids, flavonoids, phenylpropanoids, steroids, phenols, fatty acids, alkaloids, and quinones. Modern pharmacological studies on X. sorbifolium have demonstrated positive effects on learning and memory, as well as anti-inflammatory, anti-tumor, and anti-oxidative properties. This review provides a comprehensive analysis of the available research on X. sorbifolium, focusing on the relationship between chemical constituents, traditional uses, and pharmacological effects. We also assess the potential for therapeutic and other applications of this plant in support of further research and development of X. sorbifolium.

Dietary phytochemicals that influence gut microbiota: Roles and actions as anti-Alzheimer agents

The last decide has witnessed a growing research interest in the role of dietary phytochemicals in influencing the gut microbiota. On the other hand, recent evidence reveals that dietary phytochemicals exhibit properties of preventing and tackling symptoms of Alzheimer's disease, which is a neurodegenerative disease that has also been linked with the status of the gut microbiota over the last decade. Till now, little serious discussions, however, have been made to link recent understanding of Alzheimer's disease, dietary phytochemicals and the gut microbiota together and to review the roles played by phytochemicals in gut dysbiosis induced pathologies of Alzheimer's disease. Deciphering these connections can provide insights into the development and future use of dietary phytochemicals as anti-Alzheimer drug candidates. This review aims at presenting latest evidence in the modulating role of phytochemicals in the gut microbiota and its relevance to Alzheimer's disease and summarizing the mechanisms behind the modulative activities. Limitations of current research in this field and potential directions will also be discussed for future research on dietary phytochemicals as anti-Alzheimer agents.

Interaction of NF-κB and Wnt/β-catenin Signaling Pathways in Alzheimer's Disease and Potential Active Drug Treatments

The most important neuropathological features of Alzheimer's disease (AD) are extracellular amyloid-β protein (Aβ) deposition, tau protein hyperphosphorylation and activation of neurometabolic reaction in the brain accompanied by neuronal and synaptic damage, and impaired learning and memory function. According to the amyloid cascade hypothesis, increased Aβ deposits in the brain to form the core of the senile plaques that initiate cascade reactions, affecting the synapses and stimulating activation of microglia, resulting in neuroinflammation. A growing number of studies has shown that NF-κB and Wnt/β-catenin pathways play important roles in neurodegenerative diseases, especially AD. In this review, we briefly introduce the connection between neuroinflammation-mediated synaptic dysfunction in AD and elaborated on the mechanism of these two signaling pathways in AD-related pathological changes, as well as their interaction. Based on our interest in natural compounds, we also briefly introduce and conduct preliminary screening of potential therapeutics for AD.

Transcriptional regulation of homeostatic and disease-associated-microglial genes by IRF1, LXRβ, and CEBPα

Microglia transform from homeostatic to disease-associated-microglia (DAM) profiles in neurodegeneration. Within DAM, we recently identified distinct pro-inflammatory and anti-inflammatory sub-profiles although transcriptional regulators of homeostatic and distinct DAM profiles remain unclear. Informed by these studies, we nominated CEBPα, IRF1, and LXRβ as likely regulators of homeostatic, pro-inflammatory and anti-inflammatory DAM states and performed in-vitro siRNA studies in primary microglia to identify roles of each transcriptional factor (TF) in regulating microglial activation, using an integrated transcriptomics, bioinformatics and experimental validation approach. Efficient (>70%) silencing of TFs in microglia revealed reciprocal regulation between each TF specifically following pro-inflammatory activation. Neuroinflammatory transcriptomic profiling of microglia coupled with qPCR validation revealed distinct gene clusters with unique patterns of regulation by each TF, which were independent of LPS stimulation. While all three TFs (especially IRF1 and LXRβ) positively regulated core DAM genes (Apoe, Axl, Clec7a, Tyrobp, and Trem2) as well as homeostatic and pro-inflammatory DAM genes, LPS, and IFNγ increased pro-inflammatory DAM but suppressed homeostatic and anti-inflammatory DAM gene expression via an Erk1/2-dependent signaling pathway. IRF1 and LXRβ silencing suppressed microglial phagocytic activity for polystyrene microspheres as well as fAβ42 while IRF1 silencing strongly suppressed production of pro-inflammatory cytokines in response to LPS. Our studies reveal complex transcriptional regulation of homeostatic and DAM profiles whereby IRF1, LXRβ, and CEBPα positively regulate both pro- and anti-inflammatory DAM genes while activating stimuli independently augment pro-inflammatory DAM responses and suppress homeostatic and anti-inflammatory responses via Erk signaling. This framework can guide development of therapeutic immuno-modulatory strategies for neurodegeneration.

Xanthoceraside Could Ameliorate Alzheimer's Disease Symptoms of Rats by Affecting the Gut Microbiota Composition and Modulating the Endogenous Metabolite Levels

Xanthoceraside (XAN) is a natural-derived compound with anti-Alzheimer activity from the husks of Xanthoceras sorbifolia. Although its therapeutic effect had been confirmed in previous studies, the mechanism was still unclear due to its poor solubility and low permeability. In this study, the pharmacological effect of XAN on Alzheimer's disease (AD) was confirmed by behavior experiments and H&E staining observation. Fecal microbiota transplantation (FMT) experiment also replicated the therapeutic effects, which indicates the potential targets of XAN on gut microbiota. The sequencing of 16S rRNA genes in fecal samples demonstrated that XAN reversed gut microbiota dysbiosis in AD animals. XAN could change the relative abundances of several phyla and genus of bacterial, particularly the ratio of Firmicutes/Bacteroidetes. Among them, Clostridium IV, Desulfovibrio, Corynebacterium, and Enterorhabdus had been reported to be involved in the pathologic developments of AD and other central nervous system disease. In metabolomics study, a series of host endogenous metabolites were detected, including amino acids, lysophosphatidylcholine, dihydrosphingosine, phytosphingosine, inosine, and hypoxanthine, which were all closely associated with the development of AD. Combined with the Spearman's correlation analysis, it was confirmed that the increases of five bacterial strains and decreases of six bacterial strains were closely correlated with the increases of nine host metabolites and the decreases of another five host metabolites. Therefore, XAN can modulate the structure of gut microbiota in AD rats; the changes of gut microbiota were significantly correlated with endogenous metabolites, and symptom of AD was ultimately alleviated. Our findings suggest that XAN may be a potential therapeutic drug for AD, and the gut microbiota may be potential targeting territory of XAN via microbiome-gut-brain pathway.

Natural products as a potential modulator of microglial polarization in neurodegenerative diseases

Neurodegenerative diseases (NDs) are characterized by the progressive loss of structure and function of neurons most common in elderly population, mainly including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). Neuroinflammation caused by microglia as the resident macrophages of the central nervous system (CNS) plays a contributory role in the onset and progression of NDs. Activated microglia, as in macrophages, to be heterogeneous, can polarize into M1 (pro-inflammatory) and M2 (anti-inflammatory) functional phenotypes. The former elaborate pro-inflammatory mediators promoting neuroinflammation and neuronal damage. In contrast, the latter generate anti-inflammatory mediators and neurotrophins that inhibit neuroinflammation and promote neuronal healing. Consistently, the regulation of microglial polarization from M1 to M2 phenotype appears as an outstanding therapeutic and preventive approach for NDs treatment. Although non-steroidal anti-inflammatory drugs (NSAIDs) currently used to alleviate M1 microglia-associated neuroinflammation responsible for the development of NDs, these drugs have different degrees of adverse effects and limited efficacy. As the advantages of novel structure, multi-target, high efficiency and low toxicity, natural products as the modulators of microglial polarization have attracted considerable concerns in the therapeutic areas of NDs. In this review, we mainly summarized the therapeutic potential of natural products and their various molecular mechanisms for NDs treatment through modulating microglial polarization. The aim of the current review is expected to be useful to develop innovative modulators of microglial polarization from natural products for the amelioration and treatment of NDs.

Xanthoceraside prevented synaptic loss and reversed learning-memory deficits in APP/PS1 transgenic mice

Xanthoceraside, a novel triterpenoid saponin, has been found to attenuate learning and memory impairments in AD animal models. However, whether xanthoceraside has a positive effect on synaptic morphology remains unclear. Herein, we evaluated the effects of xanthoceraside on learning and memory impairments and the abnormalities of synaptic structure in APP/PS1 transgenic mice. The behavioral experiments demonstrated that xanthoceraside attenuated the imaginal memory and spatial learning impairments, and improved social interaction. Transmission electron microscopy and Golgi staining showed that xanthoceraside ameliorated synapse morphology abnormalities and dendritic spine density deficits, respectively. Western-blot analysis identified that xanthoceraside increased the expression of SYP and PSD95, activated BDNF/TrkB/MAPK/ERK and PI3K/Akt signaling pathways, meanwhile decreased the expression of RhoA, ROCK and Snk, increased the levels of SPAR, and activated the BDNF/TrkB/cofilin signaling pathway. Taken together, our study indicated that xanthoceraside improved cognitive function and protected both synaptic morphology and dendritic spine in APP/PS1 transgenic mice, which might be related in part to its activation in the BDNF/TrkB pathway.

Natural barrigenol-like triterpenoids: A comprehensive review of their contributions to medicinal chemistry

Barrigenol-like triterpenoids (BATs), which contain an unusual oleanane substituted by many hydroxyl groups as the skeleton, are subdivided into five subtypes: barrigenol A₁, barrigenol A₂, barrigenol R₁, barringtogenol C, and 16-deoxybarringtogenol C. The variations in acyl derivatives, hydroxyl groups, and carbohydrate chains in their structures have enhanced the diversity of BATs. Moreover, the stable polyhydroxy-replaced pentacyclic skeleton provides an ideal platform for structural modifications. To date, more than 500 BAT derivatives have been isolated from plants. Synchronously, BATs possess anti-tumour, anti-Alzheimer's disease, anti-inflammatory, anti-microbial, anti-obesity and anti-allergic activities by regulating numerous cellular molecules. Some BAT derivatives, such as escin obtained from Aesculus hippocastanum L. and xanthoceraside isolated from Xanthoceras sorbifolia Bunge, have been used to treat encephaloedema or inflammatory diseases. This review aims to provide comprehensive information about the chemistry, sources, bioavailability, and anti-tumour effects of BATs, with a particular emphasis on the molecular mechanisms of action. The pharmacokinetics and clinical progress are also concerned. More than 300 structures identified over past 25 years are summarized here (249 compounds) and in the supplementary information (114 compounds). Accordingly, the pharmaceutical activity of barrigenol triterpenoids suggests that some compounds should be developed as promising anti-tumour or anti- Alzheimer's disease agents in future.

Xanthoceraside modulates neurogenesis to ameliorate cognitive impairment in APP/PS1 transgenic mice

Neuronal loss is reported to be an important pathological process in Alzheimer's disease (AD). Neurogenesis is a process of generation of new neurons to fill the neuronal loss. Xanthoceraside has been shown to attenuate the cognitive deficits in several AD animal models. However, little is known about the effect of xanthoceraside on neurogenesis in APP/PS1 transgenic mice. Thus, in this study, we investigated whether xanthoceraside can ameliorate learning and memory impairment by promoting NSCs proliferation and neuronal differentiation. The results suggested that xanthoceraside significantly ameliorated the cognitive impairment and induced NSCs proliferation and neuronal differentiation in APP/PS1 transgenic mice. Meanwhile, in vitro study revealed that xanthoceraside increased the size of NSCs and induced NSCs differentiation into neurons compared with amyloid beta-peptide (25-35) (Aβ25-35) treatment. Furthermore, we found that xanthoceraside significantly increased the expression of Wnt3a and p-GSK3β, decreased the expression of p-β-catenin, and induced nuclear translocation of β-catenin in APP/PS1 transgenic mice. Furthermore, in vitro study found that the effect of xanthoceraside on inducing NSCs proliferation and neuronal differentiation were inhibited by Wnt pathway inhibitor Dickkopf-1 (Dkk-1). Our data demonstrated that xanthoceraside may promote the proliferation and differentiation of NSCs into neurons by up-regulating the Wnt/β-catenin pathway to fill the neuronal loss, thereby improving learning and memory impairment in APP/PS1 transgenic mice.

Inhibition of cyclin-dependent kinase 5 affects early neuroinflammatory signalling in murine model of amyloid beta toxicity

BACKGROUND

Cyclin-dependent kinase 5 (Cdk5) belongs to the family of proline-directed serine/threonine kinases and plays a critical role in neuronal differentiation, migration, synaptogenesis, plasticity, neurotransmission and apoptosis. The deregulation of Cdk5 activity was observed in post mortem analysis of brain tissue of Alzheimer's disease (AD) patients, suggesting the involvement of Cdk5 in the pathomechanism of this neurodegenerative disease. However, our recent study demonstrated the important function of Cdk5 in regulating inflammatory reaction.

METHODS

Since the role of Cdk5 in regulation of inflammatory signalling in AD is unknown, we investigated the involvement of Cdk5 in neuroinflammation induced by single intracerebroventricular (icv) injection of amyloid beta protein (Aβ) oligomers in mouse. The brain tissue was analysed up to 35 days post injection. Roscovitine (intraperitoneal administration) was used as a potent Cdk5 inhibitor. The experiments were also performed on human neuroblastoma SH-SY5Y as well as mouse BV2 cell lines treated with exogenous oligomeric Aβ.

RESULTS

Our results demonstrated that single injection of Aβ oligomers induces long-lasting activation of microglia and astrocytes in the hippocampus. We observed also profound, early inflammatory response in the mice hippocampus, leading to the significant elevation of pro-inflammatory cytokines expression (e.g. TNF-α, IL-1β, IL-6). Moreover, Aβ oligomers elevated the formation of truncated protein p25 in mouse hippocampus and induced overactivation of Cdk5 in neuronal cells. Importantly, administration of roscovitine reduced the inflammatory processes evoked by Aβ in the hippocampus, leading to the significant decrease of cytokines level.

CONCLUSIONS

These studies clearly show the involvement of Cdk5 in modulation of brain inflammatory response induced by Aβ and may indicate this kinase as a novel target for pharmacological intervention in AD.

A time-of-flight mass spectrometry based strategy to fast screen triterpenoids in Xanthoceras sorbifolia Bunge husks for bioactive substances against Alzheimer's disease

Xanthoceras sorbifolia Bunge is a folk medicine in China. Recently, the triterpenoids in its husks have attracted more and more attention for potential prevention against Alzheimer's disease. However, current studies on its bioactive substances were still insufficient. To reveal more bioactive substances, an efficient and practical strategy based on high resolution mass spectra coupled with multiple data mining techniques was developed to characterize the barrigenol type triterpenoids in the husks and dosed rat plasma. A total of 50 barrigenol type triterpenoids were identified in the husks, and 6 of these were detected in the rat plasma, which were regarded as bioactive candidates. To find the real bioactive substances, the neuroprotective effect of the candidates was further tested by calculating the PC12 cell viability against amyloid-β-induced cytotoxicity. As a result, three out of the six candidates exhibited obvious neuroprotction against amyloid-β-induced cytotoxicity on PC12 cells, indicating their potential to be bioactive substances against Alzheimer's disease. This study will be a valuable reference of the bioactive substances in Xanthoceras sorbifolia Bunge husks against Alzheimer's disease and the provided strategy can also be applied to the exploration of the effective constituents in other medicines.

An efficient strategy was developed to reveal the neuroprotective substances in X. sorbifolia husks.

Xanthoceraside attenuates amyloid β peptide1-42-induced memory impairments by reducing neuroinflammatory responses in mice

Xanthoceraside, a novel triterpenoid saponin extracted from the husks of Xanthoceras sorbifolia Bunge, has neuroprotective effects in vivo and anti-inflammatory properties in vitro. However, the exact mechanism of xanthoceraside on anti-amyloid beta (Aβ)-induced neuroinflammatory responses has not been elucidated. Therefore, we used intracerebroventricular injection of amyloid _1-42 (Aβ_1-42) to establish a mouse model to test the effects of xanthoceraside on Aβ-induced cognitive impairments and the TLR2/NF-κB and MAPK pathways. The mice received xanthoceraside (0.02, 0.08 or 0.32mg/kg) or vehicle from the day of Aβ_1-42 injection. The Morris water maze test was performed 4 days after Aβ_1-42 injection. The levels of inflammatory cytokines (interleukin (IL)-6 and IL-4) were measured by enzyme-linked immunosorbent assay (ELISA). The expression levels of glial fibrillary acidic protein (GFAP) and cluster of differentiation 11b (CD11b) in the hippocampus were determined with an immunohistochemistry assay. Inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) were analysed by Western blotting; iNOS, COX-2 and Toll-like receptor 2 (TLR2) mRNA expression levels were measured by reverse transcription-polymerase chain reaction (RT-PCR). Here, we observed that xanthoceraside at doses of 0.08 and 0.32mg/kg significantly improved learning and memory impairments and significantly inhibited GFAP and CD11b overexpression induced by Aβ_1-42 in mice. ELISA results revealed that xanthoceraside suppressed IL-6 release and increased IL-4 levels. Western blotting results showed that xanthoceraside reduced iNOS and COX-2 protein levels in hippocampus; xanthoceraside also inhibited translocation of NF-κB p50 and p65 into the nucleus and phosphorylation of extracellular signal-regulated kinase (ERK), Jun N-terminal kinase (JNK) and p38. RT-PCR confirmed that xanthoceraside decreased iNOS, COX-2 and TLR2 mRNA levels. These results suggest that xanthoceraside inhibition of the TLR2 pathway and down-regulation of MAPK and NF-κB activities may be related to the improvement in learning and memory impairments.

Chronoinflammaging in Alzheimer; A systematic review on the roles of toll like receptor 2

Aging is associated with a range of chronic low-grade inflammation (Chronoinflammaging) which may play a significant role in some chronic inflammatory based diseases, such as Alzheimer disease (AD). However, the events which lead to the induction of chronoinflammaging in AD are yet to be clarified. It has been proposed that the recognition of endogenous ligands by pathogen recognition receptors (PRRs) may be involved in the induction of chronoinflammaging. Toll like receptors (TLRs) are a family of PRRs which recognize endogenous damage associated molecular patterns (DAMPs) and subsequently induce inflammation. Therefore, TLRs are worthy of investigation to elucidate their roles in chronoinflammaging associated AD. This review article explores the main roles played by TLR2 in the pathogenesis of chronoinflammaging in patients suffering from AD.

Reprint of: Microglial toll-like receptors and Alzheimer's disease

Microglial activation represents an important pathological hallmark of Alzheimer's disease (AD), and emerging data highlight the involvement of microglial toll-like receptors (TLRs) in the course of AD. TLRs have been observed to exert both beneficial and detrimental effects on AD-related pathologies, and transgenic animal models have provided direct and credible evidence for an association between TLRs and AD. Moreover, analyses of genetic polymorphisms have suggested interactions between genetic polymorphisms in TLRs and AD risk, further supporting the hypothesis that TLRs are involved in AD. In this review, we summarize the key evidence in this field. Future studies should focus on exploring the mechanisms underlying the potential roles of TLRs in AD.

Microglial toll-like receptors and Alzheimer's disease

Microglial activation represents an important pathological hallmark of Alzheimer's disease (AD), and emerging data highlight the involvement of microglial toll-like receptors (TLRs) in the course of AD. TLRs have been observed to exert both beneficial and detrimental effects on AD-related pathologies, and transgenic animal models have provided direct and credible evidence for an association between TLRs and AD. Moreover, analyses of genetic polymorphisms have suggested interactions between genetic polymorphisms in TLRs and AD risk, further supporting the hypothesis that TLRs are involved in AD. In this review, we summarize the key evidence in this field. Future studies should focus on exploring the mechanisms underlying the potential roles of TLRs in AD.

Association of Neuroprotective Effect of Di-O-Demethylcurcumin on Aβ25-35-Induced Neurotoxicity with Suppression of NF-κB and Activation of Nrf2

Amyloid-β peptides (Aβ), a major component of senile plaques, play an important role in the development and progression of Alzheimer's disease. Several lines of evidence have demonstrated that Aβ-induced neuronal death is mediated by oxidative stress. The present study aimed to evaluate the potential involvement of di-O-demethylcurcumin, an analog of curcuminoid, on Aβ-induced neurotoxicity in culture neuroblastoma cells (SK-N-SH cells) through the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway and the suppression of nuclear factor-κB (NF-κB) signaling pathway and their downstream targets. The results showed that pretreatment with di-O-demethylcurcumin elevated cell viability and decreased the level of reactive oxygen species. Moreover, treatment with di-O-demethylcurcumin promoted the translocation of Nrf2 protein from the cytoplasm to the nucleus, increased the expression of Nrf2-ARE pathway-related downstream proteins including heme oxygenase (HO-1), NAD(P)H:quinone oxidoreductase 1 and glutamate-cysteine ligase catalytic subunit, and increased the activity of superoxide dismutase enzymes. On the other hand, di-O-demethylcurcumin suppressed the degradation of IκBα, translocation of the p65 subunit of NF-κB from cytoplasm to nucleus and thereby, attenuated the expression of inducible nitric oxide synthase protein and nitric oxide production. Taken together, these results suggest that neuroinflammatory effect of di-O-demethylcurcumin might potentially be due to inhibit NF-κB and activate Nrf2 signaling pathways induced by Aβ25-35.

Role of pro-inflammatory cytokines released from microglia in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the brain, which is characterized by the formation of extracellular amyloid plaques (or senile plaques) and intracellular neurofibrillary tangles. However, increasing evidences demonstrated that neuroinflammatory changes, including chronic microgliosis are key pathological components of AD. Microglia, the resident immune cells of the brain, is constantly survey the microenvironment under physiological conditions. In AD, deposition of β-amyliod (Aβ) peptide initiates a spectrum of cerebral neuroinflammation mediated by activating microglia. Activated microglia may play a potentially detrimental role by eliciting the expression of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) influencing the surrounding brain tissue. Emerging studies have demonstrated that up-regulation of pro-inflammatory cytokines play multiple roles in both neurodegeneration and neuroprotection. Understanding the pro-inflammatory cytokines signaling pathways involved in the regulation of AD is crucial to the development of strategies for therapy. This review will discuss the mechanisms and important role of pro-inflammatory cytokines in the pathogenesis of AD, and the ongoing drug targeting pro-inflammatory cytokine for therapeutic modulation.

Significance of NF-κB as a pivotal therapeutic target in the neurodegenerative pathologies of Alzheimer's disease and multiple sclerosis

INTRODUCTION

Advances in molecular pathogenesis suggest that the chronic inflammation is a shared mechanism in the initiation and progression of multiple neurodegenerative diseases with diverse clinical manifestations such as Alzheimer's disease (AD) and Multiple sclerosis (MS). Restricted cell renewal and regenerative capacity make the neural tissues extremely vulnerable to the uncontrolled inflammatory process leading to irreversible tissue damage.

AREAS COVERED

A predominant consequence of increased inflammatory signaling is the upregulation of the transcription factor, NF-κB with subsequent neuroprotective or deleterious effects depending on the strength of the signal and the type of NF-κB dimers activated. We discuss the interplay between neuroinflammation and neurodegeneration keeping in focus NF-κB signaling as the point of convergence of multiple pathways associated with the development of the neurodegenerative pathologies, AD and MS.

EXPERT OPINION

Considerable interest exists in developing efficient NF-κB inhibitors for neurodegenerative diseases. The review includes an overview of natural compounds and rationally designed agents that inhibit NF-κB and mediate neuroprotection in AD and MS. The key chemical moieties of the natural and the synthetic compounds provide efficient leads for the development of effective small molecule inhibitors that selectively target NF-κB activation; this would result in the desired benefit to risk therapeutic effects.

Targeting microglia for the treatment of Alzheimer's disease

INTRODUCTION

Activated microglia are associated with the progression of Alzheimer's disease (AD), as well as many other neurodegenerative diseases of aging. Microglia are therefore key targets for therapeutic intervention.

AREAS COVERED

β-amyloid (Aβ) deposits activate the complement system, which, in turn, stimulates microglia to release neurotoxic materials. Research has focused primarily on anti-inflammatory agents to temper this toxic effect. More recently there has been a focus on converting microglia from this M1 state to an M2 state in which the toxic effects are reduced and their phagocytic activity toward Aβ enhanced. Studies in transgenic mice have suggested a number of possible anti-inflammatory approaches but they may not always be a good model. An example is vaccination with antibodies to Aβ, which is effective in mouse models, but has repeatedly failed in clinical trials. Biomarker studies indicate that AD commences many years prior to clinical onset.

EXPERT OPINION

A hopeful approach to a disease-modifying treatment of AD is to administer agents that inhibit the inflammatory stimulation of microglia or successfully convert them to an M2 state. However, any such treatment must be started early in the disease.

Xanthoceraside induces apoptosis in melanoma cells through the activation of caspases and the suppression of the IGF-1R/Raf/MEK/ERK signaling pathway

Xanthoceraside, a saponin extracted from the husks of Xanthoceras sorbifolia Bunge, suppresses inflammation and oxidative stress. However, the antitumor properties of xanthoceraside as well as its mechanism of action remain unclear. Therefore, we proposed to investigate its potential anticancer property. In this study, the viability of cells was measured by the MTT assay. Cell cycle and mitochondrial membrane potential were measured by flow cytometry, and the expressions of procaspase-9, procaspase-3, Cyto.c, Apaf-1, Bcl-2, Bcl-xL, Bad, p53, and IGF-1R/Raf/MEK/ERK were tested by Western blotting. Xanthoceraside significantly inhibited the proliferation of human melanoma A375.S2 cells in a concentration- and time-dependent manner but did not impair the viability of normal cells (peripheral blood mononuclear cells). Further analysis revealed that xanthoceraside induced apoptosis by activating caspase-3 and caspase-9 in a time-dependent manner through the mitochondrial pathway but did not activate caspase-8 in the cells. In addition, xanthoceraside inhibited the expression of the insulin-like growth factor-1 receptor (IGF-1R), which is an important prosurvival, antiapoptotic signaling growth factor receptor that is frequently overexpressed in cancer cells and used as a therapeutic target for multiple cancers. Interestingly, xanthoceraside also decreased the expression of Raf, p-MEK, and p-ERK, the downstream effectors of IGF-1R. Taken together, these findings indicate that xanthoceraside induces apoptosis through a mitochondria-mediated apoptotic pathway, which is induced by the downregulation of IGF-1R/Raf/MEK/ERK cascades in A375.S2 cells.