Galangin decreases p‑tau, Aβ42 and β‑secretase levels, and suppresses autophagy in okadaic acid‑induced PC12 cells via an Akt/GSK3β/mTOR signaling‑dependent mechanism

Deciphering the multi-functional role of Indian propolis for the management of Alzheimer's disease by integrating LC-MS/MS, network pharmacology, molecular docking, and in-vitro studies

The conventional one-drug-one-disease theory has lost its sheen in multigenic diseases such as Alzheimer's disease (AD). Propolis, a honeybee-derived product has ethnopharmacological evidence of antioxidant, anti-inflammatory, antimicrobial and neuroprotective properties. However, the chemical composition is complex and highly variable geographically. So, to leverage the potential of propolis as an effective treatment modality, it is essential to understand the role of each phytochemical in the AD pathophysiology. Therefore, the present study was aimed at investigating the anti-Alzheimer effect of bioactive in Indian propolis (IP) by combining LC-MS/MS fingerprinting, with network-based analysis and experimental validation. First, phytoconstituents in IP extract were identified using an in-house LC-MS/MS method. The drug likeness and toxicity were assessed, followed by identification of AD targets. The constituent-target-gene network was then constructed along with protein-protein interactions, gene pathway, ontology, and enrichment analysis. LC-MS/MS analysis identified 16 known metabolites with druggable properties except for luteolin-5-methyl ether. The network pharmacology-based analysis revealed that the hit propolis constituents were majorly flavonoids, whereas the main AD-associated targets were MAOB, ESR1, BACE1, AChE, CDK5, GSK3β, and PTGS2. A total of 18 gene pathways were identified to be associated, with the pathways related to AD among the topmost enriched. Molecular docking analysis against top AD targets resulted in suitable binding interactions at the active site of target proteins. Further, the protective role of IP in AD was confirmed with cell-line studies on PC-12, in situ AChE inhibition, and antioxidant assays.

Galangin inhibits lipopolysaccharide-induced inflammation and stimulates osteogenic differentiation of bone marrow mesenchymal stem cells via regulation of AKT/mTOR signaling

BACKGROUND

Bone marrow mesenchymal stem cells (BMSCs), with the abilities of multidirectional differentiation and self-renewal, have been widely used in bone repair and regeneration of inflammation-stimulated oral diseases. Galangin is a flavonoid isolated from Alpinia officinarum, exerts anti-obesity, antitumor, and anti-inflammation pharmacological effects. The roles of galangin in lipopolysaccharide-induced inflammation and osteogenic differentiation of BMSCs were investigated.

METHODS

BMSCs were isolated from rat bone marrow and identified by flow cytometry. The isolated BMSCs were treated with 1 μg/mL lipopolysaccharides or cotreated with lipopolysaccharides and different concentrations of galangin. Cell viability and apoptosis were detected by MTT (tetrazolium component) and flow cytometry. ELISA was used to detect inflammation. Alizarin red staining was used to investigate osteogenic differentiation.

RESULTS

The rat BMSCs showed negative rate of CD34, and positive rate of CD29 and CD44. Lipopolysaccharides treatment reduced cell viability of BMSCs, and promoted the cell apoptosis. Incubation with galangin enhanced cell viability of lipopolysaccharide-stimulated BMSCs, and suppressed the cell apoptosis. Galangin decreased levels of TNF-α, IL-1β, and IL-6 in lipopolysaccharide-stimulated BMSCs through down-regulation of NF-κB phosphorylation (p-NF-κB). Galangin up-regulated expression of osteo-specific proteins, collagen type I alpha 1 (COL1A1), osteopontin (OPN), and runt-related transcription factor 2 (RUNX2), to promote the osteogenic differentiation of lipopolysaccharide-stimulated BMSCs. Protein expression of p-AKT and p-mTOR in lipopolysaccharide-stimulated BMSCs were increased by galangin treatment.

CONCLUSION

Galangin exerted an anti-inflammatory effect against lipopolysaccharide- stimulated BMSCs and promoted osteogenic differentiation through the activation of AKT/ mTOR signaling.

New insights into the interplay between autophagy and oxidative and endoplasmic reticulum stress in neuronal cell death and survival

Autophagy is a dynamic process that maintains the normal homeostasis of cells by digesting and degrading aging proteins and damaged organelles. The effect of autophagy on neural tissue is still a matter of debate. Some authors suggest that autophagy has a protective effect on nerve cells, whereas others suggest that autophagy also induces the death of nerve cells and aggravates nerve injury. In mammals, oxidative stress, autophagy and endoplasmic reticulum stress (ERS) constitute important defense mechanisms to help cells adapt to and survive the stress conditions caused by physiological and pathological stimuli. Under many pathophysiological conditions, oxidative stress, autophagy and ERS are integrated and amplified in cells to promote the progress of diseases. Over the past few decades, oxidative stress, autophagy and ERS and their interactions have been a hot topic in biomedical research. In this review, we summarize recent advances in understanding the interactions between oxidative stress, autophagy and ERS in neuronal cell death and survival.

Protective Effects of Flavonoids against Alzheimer's Disease: Pathological Hypothesis, Potential Targets, and Structure-Activity Relationship

Alzheimer’s disease (AD) is a neurodegenerative disease with high morbidity and mortality, for which there is no available cure. Currently, it is generally believed that AD is a disease caused by multiple factors, such as amyloid-beta accumulation, tau protein hyperphosphorylation, oxidative stress, and inflammation. Multitarget prevention and treatment strategies for AD are recommended. Interestingly, naturally occurring dietary flavonoids, a class of polyphenols, have been reported to have multiple biological activities and anti-AD effects in several AD models owing to their antioxidative, anti-inflammatory, and anti-amyloidogenic properties. In this review, we summarize and discuss the existing multiple pathogenic factors of AD. Moreover, we further elaborate on the biological activities of natural flavonoids and their potential mode of action and targets in managing AD by presenting a wide range of experimental evidence. The gathered data indicate that flavonoids can be regarded as prophylactics to slow the advancement of AD or avert its onset. Different flavonoids have different activities and varying levels of activity. Further, this review summarizes the structure–activity relationship of flavonoids based on the existing literature and can provide guidance on the design and selection of flavonoids as anti-AD drugs.

Potential Therapeutic Benefits of Honey in Neurological Disorders: The Role of Polyphenols

Honey is the principal premier product of beekeeping familiar to Homo for centuries. In every geological era and culture, evidence can be traced to the potential usefulness of honey in several ailments. With the advent of recent scientific approaches, honey has been proclaimed as a potent complementary and alternative medicine for the management and treatment of several maladies including various neurological disorders such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and multiple sclerosis, etc. In the literature archive, oxidative stress and the deprivation of antioxidants are believed to be the paramount cause of many of these neuropathies. Since different types of honey are abundant with certain antioxidants, primarily in the form of diverse polyphenols, honey is undoubtedly a strong pharmaceutic candidate against multiple neurological diseases. In this review, we have indexed and comprehended the involved mechanisms of various constituent polyphenols including different phenolic acids, flavonoids, and other phytochemicals that manifest multiple antioxidant effects in various neurological disorders. All these mechanistic interpretations of the nutritious components of honey explain and justify the potential recommendation of sweet nectar in ameliorating the burden of neurological disorders that have significantly increased across the world in the last few decades.

Oxyphylla A ameliorates cognitive deficits and alleviates neuropathology via the Akt-GSK3β and Nrf2-Keap1-HO-1 pathways in vitro and in vivo murine models of Alzheimer's disease

Introduction

Alzheimer’s disease (AD) is a progressive brain disorder, and one of the most common causes of dementia and amnesia. Due to the complex pathogenesis of AD, the underlying mechanisms remain unclear. Although scientists have made increasing efforts to develop drugs for AD, no effective therapeutic agents have been found.

Objectives

Natural products and their constituents have shown promise for treating neurodegenerative diseases, including AD. Thus, in-depth study of medical plants, and the main active ingredients thereof against AD, is necessary to devise therapeutic agents.

Methods

In this study, N2a/APP cells and SAMP8 mice were employed as in vitro and in vivo models of AD. Multiple molecular biological methods were used to investigate the potential therapeutic actions of oxyphylla A, and the underlying mechanisms.

Results

Results showed that oxyphylla A, a novel compound extracted from Alpinia oxyphylla, could reduce the expression levels of amyloid precursor protein (APP) and amyloid beta (Aβ) proteins, and attenuate cognitive decline in SAMP8 mice. Further investigation of the underlying mechanisms showed that oxyphylla A exerted an antioxidative effect through the Akt-GSK3β and Nrf2-Keap1-HO-1 pathways.

Conclusions.

Taken together, our results suggest a new horizon for the discovery of therapeutic agents for AD.

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

Mitochondria-associated membranes (MAMs): a potential therapeutic target for treating Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is a leading global health concern for individuals and society. However, the potential mechanisms underlying the pathogenesis of AD have not yet been elucidated. Currently, the most widely acknowledged hypothesis is amyloid cascade owing to the brain characteristics of AD patients, including great quantities of extracellular β-amyloid (Aβ) plaques and intracellular neurofibrillary tangles (NFTs). Nevertheless, the amyloid cascade hypothesis cannot address certain pathologies that precede Aβ deposition and NFTs formation in AD, such as aberrant calcium homeostasis, abnormal lipid metabolism, mitochondrial dysfunction and autophagy. Notably, these earlier pathologies are closely associated with mitochondria-associated membranes (MAMs), the physical structures connecting the endoplasmic reticulum (ER) and mitochondria, which mediate the communication between these two organelles. It is plausible that MAMs might be involved in a critical step in the cascade of earlier events, ultimately inducing neurodegeneration in AD. In this review, we focus on the role of MAMs in the regulation of AD pathologies and the potential molecular mechanisms related to MAM-mediated pathological changes in AD. An enhanced recognition of the preclinical pathogenesis in AD could provide new therapeutic strategies, shifting the modality from treatment to prevention.

Galangin Inhibits LPS-Induced MMP-9 Expression via Suppressing Protein Kinase-Dependent AP-1 and FoxO1 Activation in Rat Brain Astrocytes

Purpose

Neuroinflammation, characterized by the increased expression of inflammatory proteins such as matrix metalloproteinases (MMPs), plays a critical role in neurodegenerative disorders. Lipopolysaccharide (LPS) has been shown to upregulate MMP-9 expression through the activation of various transcription factors, including activator protein 1 (AP-1) and forkhead box protein O1 (FoxO1). The flavonoid 3,5,7-trihydroxy-2-phenyl-4H-1-benzopyran-4-one (galangin) has been demonstrated to possess antioxidant and anti-inflammatory properties in various types of cells. Here, we investigated the mechanisms underlying the inhibitory effect of galangin on LPS-induced MMP-9 expression in rat brain astrocytes (RBA-1 cells).

Methods

Pharmacological inhibitors and siRNAs were employed to explore the effects of galangin on LPS-challenged RBA-1 cells. Gelatin zymography, Western blotting, real-time PCR, and a luciferase reporter assay were used to detect MMP-9 activity, protein expression, mRNA levels, and promoter activity, respectively. The protein kinases involved in the LPS-induced MMP-9 expression were determined by Western blot. A chromatin immunoprecipitation (ChIP) assay was employed to evaluate the activity of c-Jun at the MMP-9 promoter.

Results

Galangin treatment attenuated the LPS-mediated induction of MMP-9 protein and mRNA expression, as well as the activity at the MMP-9 promoter. In addition, galangin exerted its inhibitory effects on MMP-9 expression through suppressing the LPS-stimulated activation of proline-rich tyrosine kinase (Pyk2), platelet-derived growth factor receptor beta (PDGFRβ), phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), mammalian target of rapamycin (mTOR), and mitogen-activated protein kinases (MAPKs). Pretreatment with galangin attenuated the LPS-induced phosphorylation of c-Jun and FoxO1. LPS-induced cell migration was also suppressed by galangin pretreatment.

Conclusion

Galangin attenuates the LPS-induced inflammatory responses, including the induction of MMP-9 expression and cell migration, via inhibiting Pyk2/PDGFRβ/PI3K/Akt/mTOR/JNK1/JNK2 and p44/p42 MAPK cascade-dependent AP-1 and FoxO1 activities. These results provide new insights into the mechanisms through which galangin mitigates LPS-induced inflammatory responses, and suggest novel strategies for the management of LPS-related brain diseases.

Melatonin and Autophagy in Aging-Related Neurodegenerative Diseases

With aging, the nervous system gradually undergoes degeneration. Increased oxidative stress, endoplasmic reticulum stress, mitochondrial dysfunction, and cell death are considered to be common pathophysiological mechanisms of various neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), organophosphate-induced delayed neuropathy (OPIDN), and amyotrophic lateral sclerosis (ALS). Autophagy is a cellular basic metabolic process that degrades the aggregated or misfolded proteins and abnormal organelles in cells. The abnormal regulation of neuronal autophagy is accompanied by the accumulation and deposition of irregular proteins, leading to changes in neuron homeostasis and neurodegeneration. Autophagy exhibits both a protective mechanism and a damage pathway related to programmed cell death. Because of its "double-edged sword", autophagy plays an important role in neurological damage and NDDs including AD, PD, HD, OPIDN, and ALS. Melatonin is a neuroendocrine hormone mainly synthesized in the pineal gland and exhibits a wide range of biological functions, such as sleep control, regulating circadian rhythm, immune enhancement, metabolism regulation, antioxidant, anti-aging, and anti-tumor effects. It can prevent cell death, reduce inflammation, block calcium channels, etc. In this review, we briefly discuss the neuroprotective role of melatonin against various NDDs via regulating autophagy, which could be a new field for future translational research and clinical studies to discover preventive or therapeutic agents for many NDDs.

Prokineticin 2 (PK2) Rescues Cardiomyocytes from High Glucose/High Palmitic Acid-Induced Damage by Regulating the AKT/GSK3β Pathway In Vitro

Prokineticin 2 (PK2) is a small 8 kDa protein that participates in many physiological processes, such as angiogenesis, inflammation, and neurogenesis. This experiment investigated the effect of PK2 on high glucose/high palmitic acid-induced oxidative stress, apoptosis, and autophagy in cardiomyocytes and the AKT/GSK3β signalling pathway. H9c2 cells were exposed to normal and high concentrations (33 mM) of glucose and palmitic acid (150 μM) with or without PK2 (10 nM) for 48 h. Reactive oxygen species were detected using the fluorescent probes DCFH-DA and DHE. Changes in apoptosis were assessed using flow cytometry, and autophagosomes were detected using Ad-GFP-LC3. Apoptotic proteins, such as Cleaved Caspase3, Bax, and Bcl-2; autophagy proteins, including Beclin-1 and LC3B; and PK2/PKR/AKT/GSK3β signals were evaluated using western blotting. Cardiomyocytes exposed to high glucose/high palmitic acid exhibited increases in intracellular ROS, apoptosis, and autophagosomes, and these increases were robustly prevented by PK2. In addition, high glucose/high palmitic acid remarkably suppressed PK2, PKR1, and PKR2 expression and p-AKT/AKT and p-GSK3β/GSK3β ratios, and these effects were significantly prevented by PK2. Moreover, an AKT1/2 kinase inhibitor (AKT inhibitor, 10 μM) blocked the effects of PK2 on the changes in cardiomyocyte exposure to high glucose/high palmitic acid. These results suggest that PK2 attenuates high glucose/high palmitic acid-induced cardiomyocyte apoptosis by inhibiting oxidative stress and autophagosome accumulation and that this protective effect is most likely mediated by the AKT-related signalling pathway.

Exploring the bi-directional relationship between autophagy and Alzheimer's disease

Alzheimer's disease (AD) is characterized by β-amyloid (Aβ) deposition and Tau phosphorylation, in which its pathogenesis has not been cleared so far. The metabolism of Aβ and Tau is critically affected by the autophagy. Abnormal autophagy is thought to be involved in the pathogenesis of AD, regulating autophagy may become a new strategy for AD treatment. In the early stage of AD, the presence of Aβ and Tau can induce autophagy to promote their clearance by means of mTOR-dependent and independent manners. As AD progress, the autophagy goes aberrant. As a result, Aβ and Tau generate continually, which aggravates both autophagy dysfunction and AD. Besides, several related genes and proteins of AD can also adapt autophagy to make an effect on the AD development. There seems to be a bi-directional relationship between AD pathology and autophagy. At present, this article reviews this relationship from these aspects: (a) the signaling pathways of regulating autophagy; (b) the relationships between the autophagy and the processing of Aβ; (c) Aβ and Tau cause autophagy dysfunction; (d) normal autophagy promotes the clearance of Aβ and Tau; (e) the relationships between the autophagy and both genes and proteins related to AD: TFEB, miRNAs, Beclin-1, Presenilin, and Nrf2; and (f) the small molecules regulating autophagy on AD therapy. All of the above may help to further elucidate the pathogenesis of AD and provide a theoretical basis for clinical treatment of AD.

Perinatal nicotine exposure alters Akt/GSK-3β/mTOR/autophagy signaling, leading to development of hypoxic-ischemic-sensitive phenotype in rat neonatal brain

Maternal cigarette smoking is a major perinatal insult that contributes to an increased risk of cardiovascular and neurodevelopmental diseases in offspring. Our previous studies revealed that perinatal nicotine exposure reprograms a sensitive phenotype in neonatal hypoxic-ischemic encephalopathy (HIE), yet the underlying molecular mechanisms remain largely elusive. The present study tested the hypothesis that perinatal nicotine exposure impacts autophagy signaling in the developing brain, resulting in enhanced susceptibility to neonatal HIE. Nicotine was administered to pregnant rats via subcutaneous osmotic minipumps. Neonatal HIE was conducted in 9-day-old male rat pups. Protein kinase B/glycogen synthase kinase-3β/mammalian target of rapamycin (Akt/GSK-3β/mTOR) signaling and key autophagy markers were determined by Western blotting analysis. Rapamycin and MK2206 were administered via intracerebroventricular injection. Nicotine exposure significantly inhibited autophagy activities in neonatal brain tissues, characterized by an increased ratio of phosphoylated (p-) to total mTOR protein expression but reduced levels of autophagy-related 5, Beclin 1, and LC3βI/II. Treatment with mTOR inhibitor rapamycin effectively blocked nicotine-mediated autophagy deficiency and, more importantly, reversed the nicotine-induced increase in HI brain infarction. In addition, nicotine exposure significantly upregulated p-Akt and p-GSK-3β. Treatment with the Akt selective inhibitor MK2206 reversed the enhanced p-Akt and p-GSK-3β, restored basal autophagic flux, and abolished nicotine-mediated HI brain injury. These findings suggest that perinatal nicotine-mediated alteration of Akt/GSK-3β/mTOR signaling plays a key role in downregulation of autophagic flux, which contributes to the development of hypoxia/ischemia-sensitive phenotype in the neonatal brain.