Inhibitory Effects of Betulinic Acid on LPS-Induced Neuroinflammation Involve M2 Microglial Polarization via CaMKKβ-Dependent AMPK Activation

Possible Prophylactic Effects of Sulforaphane on LPS-Induced Recognition Memory Impairment Mediated by Regulating Oxidative Stress and Neuroinflammatory Proteins in the Prefrontal Cortex Region of the Brain

BACKGROUND

Alzheimer's disease (AD) presents a significant global health concern, characterized by neurodegeneration and cognitive decline. Neuroinflammation is a crucial factor in AD development and progression, yet effective pharmacotherapy remains elusive. Sulforaphane (SFN), derived from cruciferous vegetables and mainly from broccoli, has shown a promising effect via in vitro and in vivo studies as a potential treatment for AD. This study aims to investigate the possible prophylactic mechanisms of SFN against prefrontal cortex (PFC)-related recognition memory impairment induced by lipopolysaccharide (LPS) administration.

METHODOLOGY

Thirty-six Swiss (SWR/J) mice weighing 18-25 g were divided into three groups (n = 12 per group): a control group (vehicle), an LPS group (0.75 mg/kg of LPS), and an LPS + SFN group (25 mg/kg of SFN). The total duration of the study was 3 weeks, during which mice underwent treatments for the initial 2 weeks, with daily monitoring of body weight and temperature. Behavioral assessments via novel object recognition (NOR) and temporal order recognition (TOR) tasks were conducted in the final week of the study. Inflammatory markers (IL-6 and TNF), antioxidant enzymes (SOD, GSH, and CAT), and pro-oxidant (MDA) level, in addition to acetylcholine esterase (AChE) activity and active (caspase-3) and phosphorylated (AMPK) levels, were evaluated. Further, PFC neuronal degeneration, Aβ content, and microglial activation were also examined using H&E, Congo red staining, and Iba1 immunohistochemistry, respectively.

RESULTS

SFN pretreatment significantly improved recognition memory performance during the NOR and TOR tests. Moreover, SFN was protected from neuroinflammation and oxidative stress as well as neurodegeneration, Aβ accumulation, and microglial hyperactivity.

CONCLUSION

The obtained results suggested that SFN has a potential protective property to mitigate the behavioral and biochemical impairments induced by chronic LPS administration and suggested to be via an AMPK/caspase-3-dependent manner.

Betulinic Acid for Glioblastoma Treatment: Reality, Challenges and Perspectives

Betulinic acid is a naturally occurring compound that can be obtained through methanolic or ethanolic extraction from plant sources, as well as through chemical synthesis or microbial biotransformation. Betulinic acid has been investigated for its potential therapeutic properties, and exhibits anti-inflammatory, antiviral, antimalarial, and antioxidant activities. Notably, its ability to cross the blood-brain barrier addresses a significant challenge in treating neurological pathologies. This review aims to compile information about the impact of betulinic acid as an antitumor agent, particularly in the context of glioblastoma. Importantly, betulinic acid demonstrates selective antitumor activity against glioblastoma cells by inhibiting proliferation and inducing apoptosis, consistent with observations in other cancer types. Compelling evidence published highlights the acid's therapeutic action in suppressing the Akt/NFκB-p65 signaling cascade and enhancing the cytotoxic effects of the chemotherapeutic agent temozolomide. Interesting findings with betulinic acid also suggest a focus on researching the reduction of glioblastoma's invasiveness and aggressiveness profile. This involves modulation of extracellular matrix components, remodeling of the cytoskeleton, and secretion of proteolytic proteins. Drawing from a comprehensive review, we conclude that betulinic acid formulations as nanoparticles and/or ionic liquids are promising drug delivery approaches with the potential for translation into clinical applications for the treatment and management of glioblastoma.

The aging mouse CNS is protected by an autophagy-dependent microglia population promoted by IL-34

Microglia harness an unutilized health-promoting potential in age-related neurodegenerative and neuroinflammatory diseases, conditions like progressive multiple sclerosis (MS). Our research unveils an microglia population emerging in the cortical brain regions of aging mice, marked by ERK1/2, Akt, and AMPK phosphorylation patterns and a transcriptome indicative of activated autophagy - a process critical for cellular adaptability. By deleting the core autophagy gene Ulk1 in microglia, we reduce this population in the central nervous system of aged mice. Notably, this population is found dependent on IL-34, rather than CSF1, although both are ligands for CSF1R. When aging mice are exposed to autoimmune neuroinflammation, the loss of autophagy-dependent microglia leads to neural and glial cell death and increased mortality. Conversely, microglial expansion mediated by IL-34 exhibits a protective effect. These findings shed light on an autophagy-dependent neuroprotective microglia population as a potential target for treating age-related neuroinflammatory conditions, including progressive MS.

Inflammatory signaling pathways in the treatment of Alzheimer's disease with inhibitors, natural products and metabolites (Review)

The intricate nature of Alzheimer's disease (AD) pathogenesis poses a persistent obstacle to drug development. In recent times, neuroinflammation has emerged as a crucial pathogenic mechanism of AD, and the targeting of inflammation has become a viable approach for the prevention and management of AD. The present study conducted a comprehensive review of the literature between October 2012 and October 2022, identifying a total of 96 references, encompassing 91 distinct pharmaceuticals that have been investigated for their potential impact on AD by inhibiting neuroinflammation. Research has shown that pharmaceuticals have the potential to ameliorate AD by reducing neuroinflammation mainly through regulating inflammatory signaling pathways such as NF‑κB, MAPK, NLRP3, PPARs, STAT3, CREB, PI3K/Akt, Nrf2 and their respective signaling pathways. Among them, tanshinone IIA has been extensively studied for its anti‑inflammatory effects, which have shown significant pharmacological properties and can be applied clinically. Thus, it may hold promise as an effective drug for the treatment of AD. The present review elucidated the inflammatory signaling pathways of pharmaceuticals that have been investigated for their therapeutic efficacy in AD and elucidates their underlying mechanisms. This underscores the auspicious potential of pharmaceuticals in ameliorating AD by impeding neuroinflammation.

Onionin A inhibits small-cell lung cancer proliferation through suppressing STAT3 activation induced by macrophages-derived IL-6 and cell-cell interaction with tumor-associated macrophage

Tumor-associated macrophage (TAM)-derived IL-6 is involved in small-cell lung cancer (SCLC) progression and chemoresistance via the activation of signal transducer and activator of transcription 3 (STAT3) in the tumor microenvironment. This study aimed to identify natural compounds that suppress cell-cell interactions between TAMs and SCLC cells by inhibiting STAT3 activation. We used a library of natural compounds to identify candidate agents possessing anti-SCLC effects by inhibiting macrophage-induced tumor proliferation. SBC-3 and SBC-5, human SCLC cell lines, were used for in vitro experiments. Furthermore, we assessed the efficacy of these candidate agents in a murine xenograft model of human SCLC. Among the natural compounds examined, onionin A (ONA) inhibited IL-6-induced STAT3 activation and SCLC cell proliferation. ONA also reduced the secretion of IL-6 from macrophages and interfered with the direct effect of cell-cell interactions between macrophages and SCLC cells. Furthermore, ONA administration suppressed tumor progression in a tumor-bearing mouse model. ONA was identified as the most useful candidate for targeting cell-cell interactions between cancer cells and TAMs for anti-SCLC therapy.

Inflammation context in Alzheimer's disease, a relationship intricate to define

Alzheimer's disease (AD), the most common form of dementia, is characterized by the accumulation of amyloid β (Aβ) and hyperphosphorylated tau protein aggregates. Importantly, Aβ and tau species are able to activate astrocytes and microglia, which release several proinflammatory cytokines, such as tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β), together with reactive oxygen (ROS) and nitrogen species (RNS), triggering neuroinflammation. However, this inflammatory response has a dual function: it can play a protective role by increasing Aβ degradation and clearance, but it can also contribute to Aβ and tau overproduction and induce neurodegeneration and synaptic loss. Due to the significant role of inflammation in the pathogenesis of AD, several inflammatory mediators have been proposed as AD markers, such as TNF-α, IL-1β, Iba-1, GFAP, NF-κB, TLR2, and MHCII. Importantly, the use of anti-inflammatory drugs such as NSAIDs has emerged as a potential treatment against AD. Moreover, diseases related to systemic or local inflammation, including infections, cerebrovascular accidents, and obesity, have been proposed as risk factors for the development of AD. In the following review, we focus on key inflammatory processes associated with AD pathogenesis.

5'AMP-activated protein kinase: an emerging target of phytochemicals to treat chronic inflammatory diseases

Inflammation is a defensive response of the organism to traumatic, infectious, toxic, ischemic, and autoimmune injury. Inflammatory mediators are released to effectively eliminate the inflammatory trigger and restore homeostasis. However, failure of these processes can lead to chronic inflammatory conditions and diseases such as inflammatory bowel diseases, rheumatoid arthritis, inflammatory lung diseases, atherosclerosis, and neurodegenerative diseases. The cure of chronic inflammatory diseases remains challenging as current therapies have various limitations, such as pronounced side effects, progressive loss of efficacy, and high cost especially for biologics. In this context, phytochemicals (such as alkaloids, flavonoids, lignans, phenolic acids, saponins, terpenoids, and other classes) are considered as an interesting alternative approach. Among the numerous targets of phytochemicals, AMP-activated protein kinase (AMPK) can be considered as an interesting target in the context of inflammation. AMPK regulates inflammatory response by inhibiting inflammatory pathways (NF-κB, JAK/STAT, and MAPK) and regulating several other processes of the inflammatory response (oxidative stress, autophagy, and apoptosis). In this review, we summarize and discuss the studies focusing on phytochemicals that showed beneficial effects by blocking different inflammatory pathways implicating AMPK activation in chronic inflammatory disease models. We also highlight elements to consider when investigating AMPK in the context of phytochemicals.

Arginine Reduces Glycation in γ2 Subunit of AMPK and Pathologies in Alzheimer's Disease Model Mice

The metabolism disorders are a common convergence of Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM). The characteristics of AD are senile plaques and neurofibrillary tangles (NFTs) composed by deposits of amyloid-β (Aβ) and phosphorylated tau, respectively. Advanced glycation end-products (AGEs) are a stable modification of proteins by non-enzymatic reactions, which could result in the protein dysfunction. AGEs are associated with some disease developments, such as diabetes mellitus and AD, but the effects of the glycated γ2 subunit of AMPK on its activity and the roles in AD onset are unknown.

METHODS

We studied the effect of glycated γ2 subunit of AMPK on its activity in N2a cells. In 3 × Tg mice, we administrated L-arginine once every two days for 45 days and evaluated the glycation level of γ2 subunit and function of AMPK and alternation of pathologies.

RESULTS

The glycation level of γ2 subunit was significantly elevated in 3 × Tg mice as compared with control mice, meanwhile, the level of pT172-AMPK was obviously lower in 3 × Tg mice than that in control mice. Moreover, we found that arginine protects the γ2 subunit of AMPK from glycation, preserves AMPK function, and improves pathologies and cognitive deficits in 3 × Tg mice.

CONCLUSIONS

Arginine treatment decreases glycated γ2 subunit of AMPK and increases p-AMPK levels in 3 × Tg mice, suggesting that reduced glycation of the γ2 subunit could ameliorate AMPK function and become a new target for AD therapy in the future.

Anti-Inflammatory Activity of Panduratin A against LPS-Induced Microglial Activation

Uncontrolled and excessive microglial activation is known to contribute to inflammation-mediated neurodegeneration. Therefore, reducing neurotoxic microglial activation may serve as a new approach to preventing neurodegeneration. Here, we investigated the anti-inflammatory effects of panduratin A against microglial activation induced by lipopolysaccharides (LPS) in the SIMA9 microglial cell line. We initially examined the anti-inflammatory properties of panduratin A by measuring LPS-induced nitric oxide (NO) production and the levels of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6). Panduratin A significantly reduced NO levels and pro-inflammatory cytokines’ production and secretion. In addition, panduratin A enhanced the production of anti-inflammatory cytokines IL-4 and IL-10. The anti-inflammatory effects of panduratin A are related to the suppression of the NF-κB signaling pathway. Together, these results demonstrate the anti-inflammatory properties of panduratin A against LPS-induced microglial activation, suggesting panduratin A has the potential to be further developed as a new agent for the prevention of neuroinflammation-associated neurodegenerative diseases.

Therapeutic roles of plants for 15 hypothesised causal bases of Alzheimer's disease

Alzheimer's disease (AD) is progressive and ultimately fatal, with current drugs failing to reverse and cure it. This study aimed to find plant species which may provide therapeutic bioactivities targeted to causal agents proposed to be driving AD. A novel toolkit methodology was employed, whereby clinical symptoms were translated into categories recognized in ethnomedicine. These categories were applied to find plant species with therapeutic effects, mined from ethnomedical surveys. Survey locations were mapped to assess how this data is at risk. Bioactivities were found of therapeutic relevance to 15 hypothesised causal bases for AD. 107 species with an ethnological report of memory improvement demonstrated therapeutic activity for all these 15 causal bases. The majority of the surveys were found to reside within biodiversity hotspots (centres of high biodiversity under threat), with loss of traditional knowledge the most common threat. Our findings suggest that the documented plants provide a large resource of AD therapeutic potential. In demonstrating bioactivities targeted to these causal bases, such plants may have the capacity to reduce or reverse AD, with promise as drug leads to target multiple AD hallmarks. However, there is a need to preserve ethnomedical knowledge, and the habitats on which this knowledge depends.

Recent Advances Regarding the Molecular Mechanisms of Triterpenic Acids: A Review (Part II)

Triterpenic acids are a widespread class of phytocompounds which have been found to possess valuable therapeutic properties such as anticancer, anti-inflammatory, hepatoprotective, cardioprotective, antidiabetic, neuroprotective, lipolytic, antiviral, and antiparasitic effects. They are a subclass of triterpenes bearing a characteristic lipophilic structure that imprints unfavorable in vivo properties which subsequently limit their applications. The early investigation of the mechanism of action (MOA) of a drug candidate can provide valuable information regarding the possible side effects and drug interactions that may occur after administration. The current paper aimed to summarize the most recent (last 5 years) studies regarding the MOA of betulinic acid, boswellic acid, glycyrrhetinic acid, madecassic acid, moronic acid, and pomolic acid in order to provide scientists with updated and accessible material on the topic that could contribute to the development of future studies; the paper stands as the sequel of our previously published paper regarding the MOA of triterpenic acids with therapeutic value. The recent literature published on the topic has highlighted the role of triterpenic acids in several signaling pathways including PI3/AKT/mTOR, TNF-alpha/NF-kappa B, JNK-p38, HIF-α/AMPK, and Grb2/Sos/Ras/MAPK, which trigger their various biological activities.

Grape Seed Proanthocyanidins Exert a Neuroprotective Effect by Regulating Microglial M1/M2 Polarisation in Rats with Spinal Cord Injury

Spinal cord injury (SCI) is a highly disabling disorder for which few effective treatments are available. Grape seed proanthocyanidins (GSPs) are polyphenolic compounds with various biological activities. In our preliminary experiment, GSP promoted functional recovery in rats with SCI, but the mechanism remains unclear. Therefore, we explored the protective effects of GSP on SCI and its possible underlying mechanisms. We found that GSP promoted locomotor recovery, reduced neuronal apoptosis, increased neuronal preservation, and regulated microglial polarisation in vivo. We also performed in vitro studies to verify the effects of GSP on neuronal protection and microglial polarisation and their potential mechanisms. We found that GSP regulated microglial polarisation and inhibited apoptosis in PC12 cells induced by M1-BV2 cells through the Toll-like receptor 4- (TLR4-) mediated nuclear factor kappa B (NF-κB) and phosphatidylinositol 3-kinase/serine threonine kinase (PI3K/AKT) signaling pathways. This suggests that GSP regulates microglial polarisation and prevents neuronal apoptosis, possibly by the TLR4-mediated NF-κB and PI3K/AKT signaling pathways.

Opioid receptor activation suppresses the neuroinflammatory response by promoting microglial M2 polarization

Activation of microglia is considered the most important component of neuroinflammation. Microglia can adopt a pro-inflammatory (M1) or anti-inflammatory (M2) phenotype. Opioid receptors (ORs) have been shown to control neurotransmission of various peptidergic neurons, but their potential role in regulating microglial function is largely unknown. Here, we aimed to investigate the effect of the OR agonists DAMGO, DADLE and U-50488 on the polarization of C8-B4 microglial cells. We observed that opioids suppressed lipopolysaccharide (LPS)-triggered M1 polarization and promoted M2 polarization. This was reflected in lower phagocytic activity, lower production of NO, lower expression of TNF-α, IL-1β, IL-6, IL-86 and IL-12 beta p40 together with higher migration rate, and increased expression of IL-4, IL-10, arginase 1 and CD 206 in microglia, compared to cells affected by LPS. We demonstrated that the effect of opioids on microglial polarization is mediated by the TREM2/NF-κB signaling pathway. These results provide new insights into the anti-inflammatory and neuroprotective effects of opioids and highlight their potential in combating neurodegenerative diseases.

Microglia in the Neuroinflammatory Pathogenesis of Alzheimer's Disease and Related Therapeutic Targets

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease worldwide, characterized by progressive neuron degeneration or loss due to excessive accumulation of β-amyloid (Aβ) peptides, formation of neurofibrillary tangles (NFTs), and hyperphosphorylated tau. The treatment of AD has been only partially successful as the majority of the pharmacotherapies on the market may alleviate some of the symptoms. In the occurrence of AD, increasing attention has been paid to neurodegeneration, while the resident glial cells, like microglia are also observed. Microglia, a kind of crucial glial cells associated with the innate immune response, functions as double-edge sword role in CNS. They exert a beneficial or detrimental influence on the adjacent neurons through secretion of both pro-inflammatory cytokines as well as neurotrophic factors. In addition, their endocytosis of debris and toxic protein like Aβ and tau ensures homeostasis of the neuronal microenvironment. In this review, we will systematically summarize recent research regarding the roles of microglia in AD pathology and latest microglia-associated therapeutic targets mainly including pro-inflammatory genes, anti-inflammatory genes and phagocytosis at length, some of which are contradictory and controversial and warrant to further be investigated.

A Novel Pyrazolo[3,4-d]pyrimidine Induces Heme Oxygenase-1 and Exerts Anti-Inflammatory and Neuroprotective Effects

The anti-oxidant enzyme heme oxygenase-1 (HO-1) is known to exert anti-inflammatory effects. From a library of pyrazolo[3,4-d]pyrimidines, we identified a novel compound KKC080096 that upregulated HO-1 at the mRNA and protein levels in microglial BV-2 cells. KKC080096 exhibited anti-inflammatory effects via suppressing nitric oxide, interleukin-1β (IL-1β), and iNOS production in lipopolysaccharide (LPS)-challenged cells. It inhibited the phosphorylation of IKK and MAP kinases (p38, JNK, ERK), which trigger inflammatory signaling, and whose activities are inhibited by HO-1. Further, KKC080096 upregulated anti-inflammatory marker (Arg1, YM1, CD206, IL-10, transforming growth factor-β [TGF-β]) expression. In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice, KKC080096 lowered microglial activation, protected the nigral dopaminergic neurons, and nigral damage-associated motor deficits. Next, we elucidated the mechanisms by which KKC080096 upregulated HO-1. KKC080096 induced the phosphorylation of AMPK and its known upstream kinases LKB1 and CaMKKbeta, and pharmacological inhibition of AMPK activity reduced the effects of KKC080096 on HO-1 expression and LPS-induced NO generation, suggesting that KKC080096-induced HO-1 upregulation involves LKB1/AMPK and CaMKKbeta/AMPK pathway activation. Further, KKC080096 caused an increase in cellular Nrf2 level, bound to Keap1 (Nrf2 inhibitor protein) with high affinity, and blocked Keap1-Nrf2 interaction. This Nrf2 activation resulted in concurrent induction of HO-1 and other Nrf2-targeted antioxidant enzymes in BV-2 and in dopaminergic CATH.a cells. These results indicate that KKC080096 is a potential therapeutic for oxidative stress- and inflammation-related neurodegenerative disorders such as Parkinson's disease.

Microglia Polarization From M1 to M2 in Neurodegenerative Diseases

Microglia-mediated neuroinflammation is a common feature of neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Microglia can be categorized into two opposite types: classical (M1) or alternative (M2), though there’s a continuum of different intermediate phenotypes between M1 and M2, and microglia can transit from one phenotype to another. M1 microglia release inflammatory mediators and induce inflammation and neurotoxicity, while M2 microglia release anti-inflammatory mediators and induce anti-inflammatory and neuroprotectivity. Microglia-mediated neuroinflammation is considered as a double-edged sword, performing both harmful and helpful effects in neurodegenerative diseases. Previous studies showed that balancing microglia M1/M2 polarization had a promising therapeutic prospect in neurodegenerative diseases. We suggest that shifting microglia from M1 to M2 may be significant and we focus on the modulation of microglia polarization from M1 to M2, especially by important signal pathways, in neurodegenerative diseases.

Oleanolic Acid-Enriched Olive Oil Alleviates the Interleukin-6 Overproduction Induced by Postprandial Triglyceride-Rich Lipoproteins in THP-1 Macrophages

Oleanolic acid (OA), a triterpene that is highly present in olive leaves, has been proposed as a component of functional foods for the prevention of metabolic syndrome, due to its anti-inflammatory activity. We analyzed the effects of OA on inflammatory parameters and signaling proteins in LPS-stimulated THP-1 macrophages. Thus, THP-1 macrophages were incubated with LPS for 48 h after pretreatment with OA at different concentrations. Pretreatment with OA was significantly effective in attenuating IL-6 and TNF-α overproduction induced by LPS in macrophages, and also improved the levels of AMPK-α. We also evaluated the effects of human triglyceride-rich lipoproteins (TRLs) derived from individuals consuming an OA-enriched functional olive oil. For this purpose, TRLs were isolated from healthy adolescents before, 2 and 5 h postprandially after the intake of a meal containing the functional olive oil or common olive oil, and were incubated with THP-1 macrophages. THP-1 macrophages incubated with TRLs isolated at 2 h after the consumption of the OA-enriched olive oil showed significant lower levels of IL-6 compared to the TRLs derived from olive oil. Our results suggest that OA might have potential to be used as a lipid-based formulation in functional olive oils to prevent inflammatory processes underlying metabolic syndrome in adolescents.

Roles of AMPK and Its Downstream Signals in Pain Regulation

Pain is an unpleasant sensory and emotional state that decreases quality of life. A metabolic sensor, adenosine monophosphate-activated protein kinase (AMPK), which is ubiquitously expressed in mammalian cells, has recently attracted interest as a new target of pain research. Abnormal AMPK expression and function in the peripheral and central nervous systems are associated with various types of pain. AMPK and its downstream kinases participate in the regulation of neuron excitability, neuroinflammation and axonal and myelin regeneration. Numerous AMPK activators have reduced pain behavior in animal models. The current understanding of pain has been deepened by AMPK research, but certain issues, such as the interactions of AMPK at each step of pain regulation, await further investigation. This review examines the roles of AMPK and its downstream kinases in neurons and non-neuronal cells, as well as their contribution to pain regulation.

Betulinic Acid Hydroxamate is Neuroprotective and Induces Protein Phosphatase 2A-Dependent HIF-1α Stabilization and Post-transcriptional Dephosphorylation of Prolyl Hydrolase 2

Huntington's disease (HD) is a neurodegenerative disorder characterized by unwanted choreatic movements, behavioral and psychiatric disturbances, and dementia. The activation of the hypoxic response pathway through the pharmacological inhibition of hypoxia-inducing factor (HIF) prolyl-hydroxylases (PHDs) is a promising approach for neurodegenerative diseases, including HD. Herein, we have studied the mechanism of action of the compound Betulinic acid hydroxamate (BAH), a hypoximimetic derivative of betulinic acid, and its efficacy against striatal neurodegeneration using complementary approaches. Firstly, we showed the molecular mechanisms through which BAH modifies the activity of the PHD2 prolyl hydroxylase, thus directly affecting HIF-1α stability. BAH treatment reduces PHD2 phosphorylation on Ser-125 residue, responsible for the control of its hydrolase activity. HIF activation by BAH is inhibited by okadaic acid and LB-100 indicating that a protein phosphatase 2A (PP2A) is implicated in the mechanism of action of BAH. Furthermore, in striatal cells bearing a mutated form of the huntingtin protein, BAH stabilized HIF-1α protein, induced Vegf and Bnip3 gene expression and protected against mitochondrial toxin-induced cytotoxicity. Pharmacokinetic analyses showed that BAH has a good brain penetrability and experiments performed in a mouse model of striatal neurodegeneration induced by 3-nitropropionic acid showed that BAH improved the clinical symptoms. In addition, BAH also prevented neuronal loss, decreased reactive astrogliosis and microglial activation, inhibited the upregulation of proinflammatory markers, and improved antioxidant defenses in the brain. Taken together, our results show BAH's ability to activate the PP2A/PHD2/HIF pathway, which may have important implications in the treatment of HD and perhaps other neurodegenerative diseases.

Natural Terpenoids as Neuroinflammatory Inhibitors in LPS-stimulated BV-2 Microglia

Neuroinflammation is a typical feature of many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Microglia, the resident immune cells of the brain, readily become activated in response to an infection or an injury. Uncontrolled and overactivated microglia can release pro-inflammatory and cytotoxic factors and are the major culprits in neuroinflammation. Hence, research on novel neuroinflammatory inhibitors is of paramount importance for the treatment of neurodegenerative diseases. Bacterial lipopolysaccharide, widely used in the studies of brain inflammation, initiates several major cellular activities that critically contribute to the pathogenesis of neuroinflammation. This review will highlight the progress on terpenoids, an important and structurally diverse group of natural compounds, as neuroinflammatory inhibitors in lipopolysaccharidestimulated BV-2 microglial cells over the last 20 years.

Evaluation of Anti-inflammatory Nutraceuticals in LPS-induced Mouse Neuroinflammation Model: An Update

It is known that peripheral infections, accompanied by inflammation, represent significant risk factors for the development of neurological disorders by modifying brain development or affecting normal brain aging. The acute effects of systemic inflammation on progressive and persistent brain damage and cognitive impairment are well documented. Anti-inflammatory therapies may have beneficial effects on the brain, and the protective properties of a wide range of synthetic and natural compounds have been extensively explored in recent years. In our previous review, we provided an extensive analysis of one of the most important and widely-used animal models of peripherally induced neuroinflammation and neurodegeneration - lipopolysaccharide (LPS)-treated mice. We addressed the data reproducibility in published research and summarized basic features and data on the therapeutic potential of various natural products, nutraceuticals, with known anti-inflammatory effects, for reducing neuroinflammation in this model. Here, recent data on the suitability of the LPS-induced murine neuroinflammation model for preclinical assessment of a large number of nutraceuticals belonging to different groups of natural products such as flavonoids, terpenes, non-flavonoid polyphenols, glycosides, heterocyclic compounds, organic acids, organosulfur compounds and xanthophylls, are summarized. Also, the proposed mechanisms of action of these molecules are discussed.

Metformin prevents stroke damage in non-diabetic female mice with chronic kidney disease

Chronic kidney disease (CKD) worsens ischemic stroke severity in both patients and animals. In mice, these poorer functional outcomes are associated with decreased brain activity of AMP-activated protein kinase (AMPK), a molecule that recently emerged as a potential therapeutic target for ischemic stroke. The antidiabetic drug metformin, a well-known activator of AMPK, has improved stroke outcomes in diabetic patients with normal renal function. We investigated whether chronic metformin pre-conditioning can rescue AMPK activity and prevent stroke damage in non-diabetic mice with CKD. Eight-week-old female C57BL/6J mice were assigned to CKD or SHAM groups. CKD was induced through right kidney cortical electrocautery, followed by left total nephrectomy. Mice were then allocated to receive metformin (200 mg/kg/day) or vehicle for 5 weeks until stroke induction by transient middle cerebral artery occlusion (tMCAO). The infarct volumes were lower in CKD mice exposed to metformin than in vehicle-treated CKD mice 24 h after tMCAO. Metformin pre-conditioning of CKD mice improved their neurological score, grip strength, and prehensile abilities. It also enhanced AMPK activation, reduced apoptosis, increased neuron survival and decreased microglia/macrophage M1 signature gene expression as well as CKD-induced activation of the canonical NF-κB pathway in the ischemic lesions of CKD mice.

Neuron type-specific increase in lamin B1 contributes to nuclear dysfunction in Huntington's disease

Lamins are crucial proteins for nuclear functionality. Here, we provide new evidence showing that increased lamin B1 levels contribute to the pathophysiology of Huntington's disease (HD), a CAG repeat-associated neurodegenerative disorder. Through fluorescence-activated nuclear suspension imaging, we show that nucleus from striatal medium-sized spiny and CA1 hippocampal neurons display increased lamin B1 levels, in correlation with altered nuclear morphology and nucleocytoplasmic transport disruption. Moreover, ChIP-sequencing analysis shows an alteration of lamin-associated chromatin domains in hippocampal nuclei, accompanied by changes in chromatin accessibility and transcriptional dysregulation. Supporting lamin B1 alterations as a causal role in mutant huntingtin-mediated neurodegeneration, pharmacological normalization of lamin B1 levels in the hippocampus of the R6/1 mouse model of HD by betulinic acid administration restored nuclear homeostasis and prevented motor and cognitive dysfunction. Collectively, our work points increased lamin B1 levels as a new pathogenic mechanism in HD and provides a novel target for its intervention.

Mesenchymal stem cell-derived extracellular vesicles promote microglial M2 polarization after subarachnoid hemorrhage in rats and involve the AMPK/NF-κB signaling pathway

Subarachnoid hemorrhage (SAH) is an acute and severe disease with high disability and mortality. Inflammatory reactions have been proven to occur throughout SAH. Extracellular vesicles derived from mesenchymal stem cells (MSCs-EVs) have shown broad potential for the treatment of brain dysfunction and neuroprotective effects through neurogenesis and angiogenesis after stroke. However, the mechanisms of EVs in neuroinflammation during the acute phase of SAH are not well known. Our present study was designed to investigate the effects of MSCs-EVs on neuroinflammation and the polarization regulation of microglia to the M2 phenotype and related signaling pathways after SAH in rats. The SAH model was induced by an improved method of intravascular perforation, and MSCs-EVs were injected via the tail vein. Post-SAH assessments included neurobehavioral tests as well as brain water content, immunohistochemistry, PCR and Western blot analyses. Our results showed that MSCs-EVs alleviated the expression of inflammatory cytokines in the parietal cortex and hippocampus 24 h and 48 h after SAH and that MSCs-EVs inhibited NF-κB and activated AMPK to reduce inflammation after SAH. Furthermore, MSC-EVs regulated the polarization of microglia toward the M2 phenotype by downregulating interleukin-1β, cluster of differentiation 16, cluster of differentiation 11b, and inducible nitric oxide synthase and upregulating the expression of cluster of differentiation 206 and arginase-1. Additionally, MSCs-EVs inhibited the neuroinflammatory response and had neuroprotective effects in the brain tissues of rats after SAH. This study may support their use as a potential treatment strategy for early SAH in the future.

Rutin pretreatment promotes microglial M1 to M2 phenotype polarization

Microglial cells are important resident innate immune components in the central nervous system that are often activated during neuroinflammation. Activated microglia can display one of two phenotypes, M1 or M2, which each play distinct roles in neuroinflammation. Rutin, a dietary flavonoid, exhibits protective effects against neuroinflammation. However, whether rutin is able to influence the M1/M2 polarization of microglia remains unclear. In this study, in vitro BV-2 cell models of neuroinflammation were established using 100 ng/mL lipopolysaccharide to investigate the effects of 1-hour rutin pretreatment on microglial polarization. The results revealed that rutin pretreatment reduced the expression of the proinflammatory cytokines tumor necrosis factor-α, interleukin-1β, and interleukin-6 and increased the secretion of interleukin-10. Rutin pretreatment also downregulated the expression of the M1 microglial markers CD86 and inducible nitric oxide synthase and upregulated the expression of the M2 microglial markers arginase 1 and CD206. Rutin pretreatment inhibited the expression of Toll-like receptor 4 and myeloid differentiation factor 88 and blocked the phosphorylation of I kappa B kinase and nuclear factor-kappa B. These results showed that rutin pretreatment may promote the phenotypic switch of microglia M1 to M2 by inhibiting the Toll-like receptor 4/nuclear factor-kappa B signaling pathway to alleviate lipopolysaccharide-induced neuroinflammation.

Roflupram, a novel phosphodiesterase 4 inhibitor, inhibits lipopolysaccharide-induced neuroinflammatory responses through activation of the AMPK/Sirt1 pathway

Roflupram (ROF) is a novel phosphodiesterase 4 inhibitor. We previously found that ROF suppressed the production of pro-inflammatory factors in microglial cells; however, the underlying mechanisms are largely unknown. The present study aimed to elucidate the underlying molecular mechanisms of the anti-neuroinflammatory effects of ROF in lipopolysaccharide (LPS)-activated microglial cells and LPS-challenged mice. Treatment with ROF suppressed LPS-induced expression of interleukin (IL)-6 and tumor necrosis factor (TNF)-α in BV-2 microglia cell line. Immunofluorescence and Western blotting analysis showed that ROF significantly inhibited the activation of microglia, as evidenced by decreased expression of ionized calcium binding adaptor molecule-1 (Iba1). Similar results were obtained in primary cultured microglial cells. ROF induced the phosphorylation of AMP-activated protein kinase (AMPK) and the expression of Sirtuin 1 (Sirt1). Interestingly, the AMPK inhibitor, compound C, blocked the role of ROF in both the phosphorylation of AMPK and the expression of Sirt1 in BV-2 cells stimulated with LPS. More importantly, the Sirt1 inhibitor, EX527, abolished the inhibitory role of ROF on the production of pro-inflammatory factors, and reactivated BV-2 cells. In mice challenged with LPS, ROF improved cognition and decreased the levels of IL-6 and TNF-α in both the cortex and hippocampus. In contrast, EX527 weakened the effects of ROF on cognitive enhancement and reduction of pro-inflammatory factors in the cortex and hippocampus. Furthermore, EX527 blocked the inhibitory role of ROF in the activation of microglial cells in both the hippocampus and cortex. Taken together, our results indicated that ROF attenuated LPS-induced neuroinflammatory responses in microglia, and the AMPK/Sirt1 pathway is essential for the anti-inflammatory effects of ROF.

AMPK in microvascular complications of diabetes and the beneficial effects of AMPK activators from plants

BACKGROUND

Diabetes mellitus is a multifactorial disorder with the risk of micro- and macro-vascular complications. High glucose-induced derangements in metabolic pathways are primarily associated with the initiation and progression of secondary complications namely, diabetic nephropathy, neuropathy, and retinopathy. Adenosine monophosphate-activated protein kinase (AMPK) has emerged as an attractive therapeutic target to treat various metabolic disorders including diabetes mellitus. It is a master metabolic regulator that helps in maintaining cellular energy homeostasis by promoting ATP-generating catabolic pathways and inhibiting ATP-consuming anabolic pathways. Numerous pharmacological and plant-derived bioactive compounds that increase AMP-activated protein kinase activation has shown beneficial effects by mitigating secondary complications namely retinopathy, nephropathy, and neuropathy.

PURPOSE

The purpose of this review is to highlight current knowledge on the role of AMPK and its activators from plant origin in diabetic microvascular complications.

METHODS

Search engines such as Google Scholar, PubMed, Science Direct and Web of Science are used to extract papers using relevant key words. Papers mainly focusing on the role of AMPK and AMPK activators from plant origin in diabetic nephropathy, retinopathy, and neuropathy was chosen to be highlighted.

RESULTS

According to results, decrease in AMPK activation during diabetes play a causative role in the pathogenesis of diabetic microvascular complications. Some of the plant-derived bioactive compounds were beneficial in restoring AMPK activity and ameliorating diabetic microvascular complications.

CONCLUSION

AMPK activators from plant origin are beneficial in mitigating diabetic microvascular complications. These pieces of evidence will be helpful in the development of AMPK-centric therapies to mitigate diabetic microvascular complications.

Effects of compound K, a metabolite of ginsenosides, on memory and cognitive dysfunction in db/db mice involve the inhibition of ER stress and the NLRP3 inflammasome pathway

Accumulating clinical and epidemiological evidence indicates a close relationship between diabetes mellitus and dementia. The ginsenoside compound K (CK) has been reported to ameliorate diabetes mellitus and confer protection to the central nervous system. In this study, we investigated whether CK could improve memory impairment and cognitive dysfunction in diabetic db/db mice. Firstly, we found that CK treatments significantly improved behavioral impairment and cognitive dysfunction based on Morris water maze, Y-maze, and fear conditioning tests. Besides, CK decreased the fasting glucose level, increased lipid metabolism, and ameliorated glucose tolerance, insulin sensitivity, and dyslipidemia in diabetic db/db mice. In addition, CK treatments alleviated oxidative stress and inhibited the inflammatory response in hippocampal tissue. Further investigations showed that CK treatments inhibited the NLRP3 inflammasome pathway, as evidenced by the declined expression of TXNIP, NLRP3 inflammasomes, ASC, cleaved caspase-1, and mature IL-1β in hippocampal tissues. Moreover, CK treatments alleviated ER stress via down-regulating the level of BiP, CHOP, p-PERK, p-IRE1α and ATF6 in the hippocampus of db/db mice. These results suggest that CK improves memory and cognitive dysfunction, possibly by ameliorating glucose tolerance, insulin sensitivity, and dyslipidemia, suppressing oxidative stress and inflammatory response and modulating the NLRP3 inflammasome pathway and ER stress.

Anti-inflammatory Property of AMP-activated Protein Kinase

BACKGROUND

One of the many debated topics in inflammation research is whether this scenario is really an accelerated form of human wound healing and immunityboosting or a push towards autoimmune diseases. The answer requires a better understanding of the normal inflammatory process, including the molecular pathology underlying the possible outcomes. Exciting recent investigations regarding severe human inflammatory disorders and autoimmune conditions have implicated molecular changes that are also linked to normal immunity, such as triggering factors, switching on and off, the influence of other diseases and faulty stem cell homeostasis, in disease progression and development.

METHODS

We gathered around and collected recent online researches on immunity, inflammation, inflammatory disorders and AMPK. We basically searched PubMed, Scopus and Google Scholar to assemble the studies which were published since 2010.

RESULTS

Our findings suggested that inflammation and related disorders are on the verge and interfere in the treatment of other diseases. AMPK serves as a key component that prevents various kinds of inflammatory signaling. In addition, our table and hypothetical figures may open a new door in inflammation research, which could be a greater therapeutic target for controlling diabetes, obesity, insulin resistance and preventing autoimmune diseases.

CONCLUSION

The relationship between immunity and inflammation becomes easily apparent. Yet, the essence of inflammation turns out to be so startling that the theory may not be instantly established and many possible arguments are raised for its clearance. However, this study might be able to reveal some possible approaches where AMPK can reduce or prevent inflammatory disorders.

A Network Pharmacology Approach to Reveal the Underlying Mechanisms of Paeonia lactiflora Pall. On the Treatment of Alzheimer's Disease

OBJECTIVE

To investigate the potential active compounds and underlying mechanisms of Paeonia lactiflora Pall. (PLP) on the treatment of Alzheimer's disease (AD) based on network pharmacology.

METHODS

The active components of PLP were collected from Traditional Chinese Medicine System Pharmacology (TCMSP) database, and their possible target proteins were predicted using TCMSP, SwissTargetPrediction, and STITCH databases. The putative AD-related target proteins were identified from Therapeutic Target Database (TTD), GeneCards, and MalaCards database. The compound-target-disease network interactions were established to obtain the key targets about PLP acting on AD by network topology analysis. Then, the function annotation and signaling pathways of key targets were performed by GO and KEGG enrichment analysis using DAVID tools. Finally, the binding capacity between active ingredients and key targets was validated by molecular docking using SystemsDock tools.

RESULTS

There were 7 active compounds involving in 151 predicted targets identified in PLP. Besides, a total of 160 AD-related targets were identified. Among these targets, 30 shared targets of PLP and AD were acquired. After topological analysis of the PLP potential target-AD target network, 33 key targets that were highly responsible for the therapeutic effects of PLP on AD were obtained. Further GO and KEGG enrichment analysis showed that these key targets were significantly involved in multiple biological processes and pathways which participated in cell apoptosis and inflammatory response and maintained the function of neurons to accomplish the anti-AD activity. The molecular docking analysis verified that the 7 active compounds had definite affinity with the key targets.

CONCLUSIONS

The ameliorative effects of PLP on AD were predicted to be associated with regulating neural cell apoptosis, inflammatory response, and neurotrophy via various pathways such as PI3K-Akt signaling pathway, MAPK signaling pathway, and neurotrophin signaling pathway.

Isovitexin-Mediated Regulation of Microglial Polarization in Lipopolysaccharide-Induced Neuroinflammation via Activation of the CaMKKβ/AMPK-PGC-1α Signaling Axis

Microglia are the brain's immune cells and play an important role in regulating the microenvironment in the central nervous system. Activated microglia are capable of acquiring the pro-inflammatory (M1) phenotype and anti-inflammatory (M2) phenotype. Overactivation of microglia is neurotoxic and may lead to neuroinflammatory brain disorders. Neuroinflammation in the brain plays a crucial role part in the pathophysiology of many psychiatric and neurological diseases. The inhibition of M1 microglia and promotion of M2 microglia was demonstrated to treat and prevent these diseases through reduced neuroinflammation. Isovitexin (IVX) has anti-inflammatory properties and passes through the blood-brain barrier; however, the molecular mechanism that modulates IVX-mediated microglial polarization remains unclear. In BV-2 cells and mouse primary microglia, IVX suppressed the expression of M1 microglial markers, enhanced the expression of M2 microglial markers, and enhanced the release of interleukin 10 (IL-10). IVX promoted the expression of peroxisome proliferator-activated receptor-γ (PPARγ) and PPARγ coactivator-1α (PGC-1α) in LPS-induced microglial activation. The inhibition of PPARγ and PGC-1α attenuated the regulatory effect of IVX in LPS-induced microglial polarization. IVX increased the expression of p-CaMKKβ, p-AMPK, and PGC-1α in BV-2 cells. Inhibition of CaMKKβ with STO-609 or knockdown of CaMKKβ with CaMKKβ siRNA attenuated IVX-mediated M2 microglial polarization in LPS-treated cells. In LPS-treated mice, the inhibition of CaMKKβ and PGC-1α attenuated the IVX-mediated prevention of sickness behavior and enhanction of IVX-mediated M2 microglial polarization. IVX promoted M2 microglial polarization which exerted anti-inflammatory effects on LPS-induced neuroinflammation via the activation of the CaMKKβ/AMPK-PGC-1α signaling axis.

Involvement of AMP-activated protein kinase in neuroinflammation and neurodegeneration in the adult and developing brain

Microglial activation followed by neuroinflammation is a defense mechanism of the brain to eliminate harmful endogenous and exogenous materials including pathogens and damaged tissues, while excessive or chronic neuroinflammation may cause or exacerbate neurodegeneration observed in brain injuries and neurodegenerative diseases. Depending on conditions/environments during activation, microglia acquire distinct phenotypes, such as pro-inflammatory, anti-inflammatory, and disease-associated phenotypes, and show their ability to phagocytose various objects and produce pro-and anti-inflammatory mediators. Prevention of excessive inflammation by regulating the microglia's pro/anti-inflammatory balance is important for alleviating progression of brain injuries and diseases. Among many factors involved in the regulation of microglial phenotypes, cellular energy status plays an important role. Adenosine monophosphate-activated protein kinase (AMPK), which serves as a master sensor and regulator of energy balance, is considered a candidate molecule. Accumulating evidence from adult rodent studies indicates that AMPK activation promotes anti-inflammatory responses in microglia exposed to danger signals or various stressors mainly through inhibition of the nuclear factor κB (NF-κB) signaling and activation of the nuclear factor erythroid-2-related factor-2 (Nrf2) pathway. However, AMPK activation in neurons exposed to stressors/insults may exacerbate neuronal damage if AMPK activation is excessive or prolonged. While AMPK affects microglial activation states and neuronal cell survival rates in both the adult and the developing brain, studies in the developing brain are still scarce, even though activated AMPK is highly expressed especially in the neonatal brain. More in depth studies in the developing brain are important, because neuroinflammation/neurodegeneration occurred during development can result in long-lasting brain damage.

Mesenchymal stem cells enhance microglia M2 polarization and attenuate neuroinflammation through TSG-6

Microglia are the primary cells that exert immune function in the central nervous system (CNS), and they play an important role in the pathogenesis and progression of neuroinflammation-related diseases. Mesenchymal stem cells (MSCs) have been demonstrated to promote functional recovery in many neurological diseases. The mechanisms underlying this may be that MSCs can reduce inflammatory responses through various soluble factors. Among these factors, tumor necrosis factor-α-induced gene/protein 6 (TSG-6) is a key factor influencing MSCs immunomodulatory properties; however, the precise mechanisms underlying the anti-inflammatory effects are not fully understood. Here, we aim to investigate the potential effects of MSCs on neuroinflammation and to reveal the underlying mechanisms. First, we confirmed that administration of MSCs could inhibit the lipopolysaccharide (LPS)-induced neuroinflammatory responses in a mouse model. Then, we found that MSCs promoted M2 polarization and inhibited M1 polarization both in vivo and in vitro. Moreover, we demonstrated that the effect of MSCs on microglial polarization was dependent on TSG-6. This study demonstrated that MSCs promoted M2 polarization of microglia via TSG-6, thus conferring anti-neuroinflammatory effects.

Microglial polarization: novel therapeutic mechanism against Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease that results in progressive dementia, and exhibits high disability and fatality rates. Recent evidence has demonstrated that neuroinflammation is critical in the pathophysiological processes of AD, which is characterized by the activation of microglia and astrocytes. Under different stimuli, microglia are usually activated into two polarized states, termed the classical 'M1' phenotype and the alternative 'M2' phenotype. M1 microglia are considered to promote inflammatory injury in AD; in contrast, M2 microglia exert neuroprotective effects. Imbalanced microglial polarization, in the form of excessive activation of M1 microglia and dysfunction of M2 microglia, markedly promotes the development of AD. Furthermore, an increasing number of studies have shown that the transition of microglia from the M1 to M2 phenotype could potently alleviate pathological damage in AD. Hence, this article reviews the current knowledge regarding the role of microglial M1/M2 polarization in the pathophysiology of AD. In addition, we summarize several approaches that protect against AD by altering the polarization states of microglia. This review aims to contribute to a better understanding of the pathogenesis of AD and, moreover, to explore the potential of novel drugs for the treatment of AD in the future.

Betulin and its derivatives as novel compounds with different pharmacological effects

Betulin (B) and Betulinic acid (BA) are natural pentacyclic lupane-structure triterpenoids which possess a wide range of pharmacological activities. Recent evidence indicates that B and BA have several properties useful for the treatment of metabolic disorders, infectious diseases, cardiovascular disorders, and neurological disorders. In the current review, we discuss B and BA structures and derivatives and then comprehensively explain their pharmacological effects in relation to various diseases. We also explain antiviral, antibacterial and anti-cancer effects of B and BA. Finally, we discuss the delivery methods, in which these compounds most effectively target different systems.

Inhibitory Effects of the Two Novel TSPO Ligands 2-Cl-MGV-1 and MGV-1 on LPS-induced Microglial Activation

The 18 kDa translocator protein (TSPO) ligands 2-Cl-MGV-1 and MGV-1 can attenuate cell death of astrocyte-like cells (U118MG) and induce differentiation of neuronal progenitor cells (PC-12). Lipopolysaccharide (LPS) is a bacterial membrane endotoxin that activates cellular inflammatory pathways by releasing pro-inflammatory molecules, including cytokines and chemokines. The aim of the present study was to assess the immuno-modulatory effect of TSPO ligands in activated microglial cells. We demonstrated that the TSPO ligands 2-Cl-MGV-1 and MGV-1 can prevent LPS-induced activation of microglia (BV-2 cell line). Co-treatment of LPS (100 ng/mL) with these TSPO ligands (final concentration- 25 µM) reduces significantly the LPS-induced release of interleukin-6 (IL-6) from 16.9-fold to 2.5-fold, IL-β from 8.3-fold to 1.6-fold, interferon-γ from 16.0-fold to 2.2-fold, and tumor necrosis factor-α from 16.4-fold to 1.8-fold. This anti-inflammatory activity seems to be achieved by inhibition of NF-κB p65 activation. Assessment of initiation of ROS generation and cell metabolism shows significant protective effects of these two novel TSPO ligands. The IL-10 and IL-13 levels were not affected by any of the TSPO ligands. Thus, it appears that the ligands suppress the LPS-induced activation of some inflammatory responses of microglia. Such immunomodulatory effects may be relevant to the pharmacotherapy of neuro-inflammatory diseases.

Hydrogen-rich saline promotes microglia M2 polarization and complement-mediated synapse loss to restore behavioral deficits following hypoxia-ischemic in neonatal mice via AMPK activation

Background

Hypoxia-ischemia (HI) during the perinatal period is one of the most common causes of acute mortality and chronic neurologic morbidity. Hydrogen-rich saline (HS) treatment in neonatal mice has been reported to alleviate brain injury following HI, but the mechanisms involved are not known.

Methods

A modified version of the Rice-Vannucci method for the induction of neonatal HI brain injury was performed on postnatal day 7 mouse pups. Animals or BV2-cells received HS and an AMPK inhibitor at indicative time post-injury.

Results

In the current study, we show that HS treatment attenuated the accumulation of CD11b⁺/CD45^high cells, suppressed HI-induced neuro-inflammation, induced microglial anti-inflammatory M2 polarization, was associated with promoting AMPK activation, and inhibited nuclear factor-κB activation as demonstrated both in vivo and in vitro. In addition, HS treatment reversed HI-induced neurological disabilities, was associated with improving damaged synapses, and restored the expression levels of synaptophysin and postsynaptic density protein 95 following HI insult. Furthermore, HI insult which increased levels of complement component C1q, C3, and C3aR1 was observed. Importantly, C1q deposited in the infarct core and lesion boundary zone following HI injury, was found to co-localize within regions of synapse loss, whereas HS treatment reversed these effects of HI on synapse loss and complement component levels. Notably, the AMPK inhibitor reversed the beneficial effects of HS as described above.

Conclusions

These results demonstrate that HS restored behavioral deficits after HI in neonatal mice. These beneficial effects, in part, involve promoting microglia M2 polarization and complement-mediated synapse loss via AMPK activation.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1488-2) contains supplementary material, which is available to authorized users.

Neuroprotective Effects of BHDPC, a Novel Neuroprotectant, on Experimental Stroke by Modulating Microglia Polarization

This study mainly investigated the therapeutic effects of BHDPC on ischemic stroke and its underlying mechanisms. In vivo, the transient middle cerebral artery occlusion (MCAO) was used to induce ischemic model. In vitro, oxygen and glucose deprivation/reperfusion (OGD/R)-induced ischemic stroke in BV-2 microglia and primary neurons, and bEnd.3 mouse cerebral microvascular endothelial cells (ECs) were also used. First, we found that BHDPC exerts considerable neuroprotection against MCAO-induced ischemic injury to mice via alleviating neurological deficits and brain infarcts, inhibiting neuronal cell loss and apoptosis, and attenuating blood-brain barrier disruption and tight junction protein changes. Next, we observed that BHDPC significantly reduced microglial M1 activation but enhanced M2 polarization in MCAO-induced ischemic brain. Further experiments in vitro indicated that BHDPC suppressed microglial activation but promoted M2 microglial polarization in OGD/R-induced BV-2 microglia. In addition, conditioned medium (CM) experiments showed that CM from BHDPC-treated BV-2 microglia provided protections against OGD/R-induced ischemic damage in primary neurons and bEnd.3 ECs. Moreover, we found that BHDPC actions on microglial inflammation were associated with the inactivation of NF-κB signaling. Interestingly, we also found that BHDPC enhanced phosphorylation of protein kinase A (PKA) and cAMP-response element-binding protein (CREB). The pharmacological inhibition or gene knockdown of PKA/CREB signaling diminished BHDPC-promoted microglial M2 polarization. In summary, BHDPC conferred neuroprotection against ischemic injury in experimental stroke models. Modulating microglial activation and polarization contributes to BHDPC-mediated neuroprotective actions, which in part were mediated by nuclear factor kappa B and PKA/CREB signaling pathway.

Berberine Facilitates Angiogenesis Against Ischemic Stroke Through Modulating Microglial Polarization via AMPK Signaling

Evidence suggests that microglia/macrophages can change their phenotype to M1 or M2 and participate in tissue damage or repair. Berberine (BBR) has shown promise in experimental stroke models, but its effects on microglial polarization and long-term recovery after stroke are elusive. Here, we investigated the effects of BBR on angiogenesis and microglial polarization through AMPK signaling after stroke. In the present study, C57BL/6 mice were subjected to transient middle cerebral artery occlusion (tMCAO), intragastrically administrated with BBR at 50 mg/kg/day. Neo-angiogenesis was observed by ⁶⁸Ga-NODAGA-RGD micro-PET/CT and immunohistochemistry. Immunofluorescent staining further exhibited an increase of M2 microglia and a reduction of M1 microglia at 14 days after stroke. In vitro studies, the lipopolysaccharide (LPS)-induced BV2 microglial cells were used to confirm the AMPK activation effect of BBR. RT-PCR, Flow cytometry, and ELISA all demonstrated that BBR could inhibit M1 polarization and promote M2 polarization. Furthermore, treatment of human umbilical vein endothelial cells (HUVEC) with conditioned media collected from BBR-treated BV2 cells promoted angiogenesis. All effects stated above were reversed by AMPK inhibitor (Compound C) and AMPK siRNA. In conclusion, BBR treatment improves functional recovery and promotes angiogenesis following tMCAO via AMPK-dependent microglial M2 polarization.

L-Cysteine-Derived H2S Promotes Microglia M2 Polarization via Activation of the AMPK Pathway in Hypoxia-Ischemic Neonatal Mice

We have reported previously that L-cysteine-derived hydrogen sulfide (H₂S) demonstrates a remarkable neuroprotective effect against hypoxia-ischemic (HI) insult in neonatal animals. Here, we assessed some of the mechanisms of this protection as exerted by L-cysteine. Specifically, we examined the capacity for L-cysteine to stimulate microglial polarization of the M2 phenotype and its modulation of complement expression in response to HI in neonatal mice. L-cysteine treatment suppressed the production of inflammatory cytokines, while dramatically up-regulating levels of anti-inflammatory cytokines in the damaged cortex. This L-cysteine administration promoted the conversion of microglia from an inflammatory M1 to an anti-inflammatory M2 phenotype, an effect which was associated with inhibiting the p38 and/or JNK pro-inflammatory pathways, nuclear factor-κB activation and a decrease in HI-derived levels of the C1q, C3a and C3a complement receptor proteins. Notably, blockade of H₂S-production clearly prevented L-cysteine-mediated M2 polarization and complement expression. L-cysteine also inhibited neuronal apoptosis as induced by conditioned media from activated M1 microglia in vitro. We also show that L-cysteine promoted AMP-activated protein kinase (AMPK) activation and the AMPK inhibitor abolished these anti-apoptotic and anti-inflammatory effects of L-cysteine. Taken together, our findings demonstrate that L-cysteine-derived H₂S attenuated neuronal apoptosis after HI and suggest that these effects, in part, result from enhancing microglia M2 polarization and modulating complement expression via AMPK activation.

Effects of Betaine on LPS-Stimulated Activation of Microglial M1/M2 Phenotypes by Suppressing TLR4/NF-κB Pathways in N9 Cells

Microglia mediate multiple facets of neuroinflammation. They can be phenotypically divided into a classical phenotype (pro-inflammatory, M1) or an alternative phenotype (anti-inflammatory, M2) with different physiological characteristics and biological functions in the inflammatory process. Betaine has been shown to exert anti-inflammatory effects. In this study, we aimed to verify the anti-inflammatory effects of betaine and elucidate its possible molecular mechanisms of action in vitro. Lipopolysaccharide (LPS)-activated microglial cells were used as an inflammatory model to study the anti-inflammatory efficacy of betaine and explore its mechanism of regulating microglial polarisation by investigating the morphological changes and associated inflammatory changes. Cytokine and inflammatory mediator expression was also measured by ELISA, flow cytometry, immunofluorescence, and western blot analysis. Toll-like receptor (TLR)-myeloid differentiation factor 88 (Myd88)-nuclear factor-kappa B (NF-κB) p65, p-NF-κB p65, IκB, p-IκB, IκB kinase (IKK), and p-IKK expression was determined by western blot analysis. Betaine significantly mitigated the production of pro-inflammatory cytokines and increased the release of anti-inflammatory cytokines. It promoted the conversion of the microglia from M1 to M2 phenotype by decreasing the expression of inducible nitric oxide synthase and CD16/32 and by increasing that of CD206 and arginase-1. Betaine treatment inhibited the TLR4/NF-κB pathways by attenuating the expression of TLR4-Myd88 and blocking the phosphorylation of IκB and IKK. In conclusion, betaine could significantly alleviate LPS-induced inflammation by regulating the polarisation of microglial phenotype; thus, it might be an effective therapeutic agent for neurological disorders.

Targeting MAPK Pathways by Naringenin Modulates Microglia M1/M2 Polarization in Lipopolysaccharide-Stimulated Cultures

Neuroinflammation is considered to be an important and inevitable pathological process associated with all types of damages to, and disorders of, the central nervous system. The hallmark of neuroinflammation is the microglia activation. In response to different micro-environmental disturbances, microglia could polarize into either an M1 pro-inflammatory phenotype, exacerbating neurotoxicity, or an M2 anti-inflammatory phenotype, exerting neuroprotection. Therefore, shifting the polarization of microglia toward the M2 phenotype could possess a more viable strategy for the neuroinflammatory disorders treatment. Naringenin (NAR) is naturally a grapefruit flavonoid and possesses various kinds of pharmacological activities, such as anti-inflammatory and neuroprotective activities. In the present study, we aimed to investigate the potential effects of NAR on microglial M1/M2 polarization and further reveal the underlying mechanisms of actions. First, NAR inhibited lipopolysaccharide (LPS)-induced microglial activation. Then, NAR shifted the M1 pro-inflammatory microglia phenotype to the M2 anti-inflammatory M2 microglia state as demonstrated by the decreased expression of M1 markers (i.e., inducible TNF-α and IL-1β) and the elevated expression of M2 markers (i.e., arginase 1, IL-4, and IL-10). In addition, the effects of NAR on microglial polarization were dependent on MAPK signaling, particularly JNK inactivation, as evidenced by the fact that the selective activator of JNK abolished NAR-promoted M2 polarization and further NAR-inhibited microglial activation. Together, this study demonstrated that NAR promoted microglia M1/M2 polarization, thus conferring anti-neuroinflammatory effects via the inhibition of MAPK signaling activation. These findings might provide new alternative avenues for neuroinflammation-related disorders treatment.

Hypothalamic Microglial Activation in Obesity: A Mini-Review

Emerging data demonstrate that microglia activation plays a pivotal role in the development of hypothalamic inflammation in obesity. Early after the introduction of a high-fat diet, hypothalamic microglia undergo morphological, and functional changes in response to excessive dietary saturated fats. Initially the resident microglia are affected; however, as diet-induced obesity persists, bone marrow-derived myeloid cells gradually replace resident microglia. Genetic and pharmacological approaches aimed at dampening the inflammatory activity in the hypothalamus of experimental models of obesity have proven beneficial to correct the obese phenotype and improve metabolic abnormalities commonly associated with obesity. These approaches provide an experimental proof-of-concept that hypothalamic inflammation is central to the pathophysiology of obesity; understanding the details of the roles played by microglia in this process may help the development of preventive and therapeutic advances in the field. In this review, we discuss the potential mechanisms underlying hypothalamic microglial activation in high-fat induced obesity.