Nose to brain strategy coupled to nano vesicular system for natural products delivery: Focus on synaptic plasticity in Alzheimer's disease

A wide number of natural molecules demonstrated neuroprotective effects on synaptic plasticity defects induced by amyloid-β (Aβ) in ex vivo and in vivo Alzheimer's disease (AD) models, suggesting a possible use in the treatment of this neurodegenerative disorder. However, several compounds, administered parenterally and orally, are unable to reach the brain due to the presence of the blood-brain barrier (BBB) which prevents the passage of external substances, such as proteins, peptides, or phytocompounds, representing a limit to the development of treatment for neurodegenerative diseases, such as AD. The combination of nano vesicular systems, as colloidal systems, and nose to brain (NtB) delivery depicts a new nanotechnological strategy to overtake this limit and to develop new treatment approaches for brain diseases, including the use of natural molecules in combination therapy for AD. Herein, we will provide an updated overview, examining the literature of the last 20 years and using specific keywords that provide evidence on natural products with the ability to restore synaptic plasticity alterations in AD models, and the possible application using safe and non-invasive strategies focusing on nano vesicular systems for NtB delivery.

Aging as a loss of morphostatic information: A developmental bioelectricity perspective

Maintaining order at the tissue level is crucial throughout the lifespan, as failure can lead to cancer and an accumulation of molecular and cellular disorders. Perhaps, the most consistent and pervasive result of these failures is aging, which is characterized by the progressive loss of function and decline in the ability to maintain anatomical homeostasis and reproduce. This leads to organ malfunction, diseases, and ultimately death. The traditional understanding of aging is that it is caused by the accumulation of molecular and cellular damage. In this article, we propose a complementary view of aging from the perspective of endogenous bioelectricity which has not yet been integrated into aging research. We propose a view of aging as a morphostasis defect, a loss of biophysical prepattern information, encoding anatomical setpoints used for dynamic tissue and organ homeostasis. We hypothesize that this is specifically driven by abrogation of the endogenous bioelectric signaling that normally harnesses individual cell behaviors toward the creation and upkeep of complex multicellular structures in vivo. Herein, we first describe bioelectricity as the physiological software of life, and then identify and discuss the links between bioelectricity and life extension strategies and age-related diseases. We develop a bridge between aging and regeneration via bioelectric signaling that suggests a research program for healthful longevity via morphoceuticals. Finally, we discuss the broader implications of the homologies between development, aging, cancer and regeneration and how morphoceuticals can be developed for aging.

Preventive Treatment with Astaxanthin Microencapsulated with Spirulina Powder, Administered in a Dose Range Equivalent to Human Consumption, Prevents LPS-Induced Cognitive Impairment in Rats

Cognitive alterations are a common feature associated with many neurodegenerative diseases and are considered a major health concern worldwide. Cognitive alterations are triggered by microglia activation and oxidative/inflammatory processes in specific areas of the central nervous system. Consumption of bioactive compounds with antioxidative and anti-inflammatory effects, such as astaxanthin and spirulina, can help in preventing the development of these pathologies. In this study, we have investigated the potential beneficial neuroprotective effects of a low dose of astaxanthin (ASX) microencapsulated within spirulina (ASXSP) in female rats to prevent the cognitive deficits associated with the administration of LPS. Alterations in memory processing were evaluated in the Y-Maze and Morris Water Maze (MWM) paradigms. Changes in microglia activation and in gut microbiota content were also investigated. Our results demonstrate that LPS modified long-term memory in the MWM and increased microglia activation in the hippocampus and prefrontal cortex. Preventive treatment with ASXSP ameliorated LPS-cognitive alterations and microglia activation in both brain regions. Moreover, ASXSP was able to partially revert LPS-induced gut dysbiosis. Our results demonstrate the neuroprotective benefits of ASX when microencapsulated with spirulina acting through different mechanisms, including antioxidant, anti-inflammatory and, probably, prebiotic actions.

Neuropharmacological interventions of quercetin and its derivatives in neurological and psychological disorders

Quercetin is a naturally occurring bioactive flavonoid abundant in many plants and fruits. Quercetin and its derivatives have shown an array of pharmacological activities in preclinical tests against various illnesses and ailments. Owing to its protective role against oxidative stress and neuroinflammation, quercetin is a possible therapeutic choice for the treatment of neurological disorders. Quercetin and its derivatives can modulate a variety of signal transductions, including neuroreceptor, neuroinflammatory receptor, and redox signaling events. The research on quercetin and its derivatives in neurology-related illnesses mainly focused on the targets, such as redox stress, neuroinflammation, and signaling pathways; however, the function of quercetin and its derivatives on specific molecular targets, such as nuclear receptors and proinflammatory mediators are yet to be explored. Findings showed that various molecular targets of quercetin and its derivatives have therapeutic potential against psychological and neurodegenerative disorders.

Plant based food bioactives: A boon or bane for neurological disorders

Neurological disorders are the foremost occurring diseases across the globe resulting in progressive dysfunction, loss of neuronal structure ultimately cell death. Therefore, attention has been drawn toward the natural resources for the search of neuroprotective agents. Plant-based food bioactives have emerged as potential neuroprotective agents for the treatment of neurodegenerative disorders. This comprehensive review primarily focuses on various plant food bioactive, mechanisms, therapeutic targets, in vitro and in vivo studies in the treatment of neurological disorders to explore whether they are boon or bane for neurological disorders. In addition, the clinical perspective of plant food bioactives in neurological disorders are also highlighted. Scientific evidences point toward the enormous therapeutic efficacy of plant food bioactives in the prevention or treatment of neurological disorders. Nevertheless, identification of food bioactive components accountable for the neuroprotective effects, mechanism, clinical trials, and consolidation of information flow are warranted. Plant food bioactives primarily act by mediating through various pathways including oxidative stress, neuroinflammation, apoptosis, excitotoxicity, specific proteins, mitochondrial dysfunction, and reversing neurodegeneration and can be used for the prevention and therapy of neurodegenerative disorders. In conclusion, the plant based food bioactives are boon for neurological disorders.

Medication Rules in Herbal Medicine for Mild Cognitive Impairment: A Network Pharmacology and Data Mining Study

Background

Although traditional Chinese medicine (TCM) has good efficacy in the treatment of mild cognitive impairment (MCI), especially memory improvement and safety, its substance basis and intervention mechanism are particularly complex and unknown. Therefore, based on network pharmacology and data mining, this study aims to explore the rules, active ingredients and mechanism of TCM in the treatment of MCI.

Methods

By searching the GeneCard, OMIM, DisGeNET and DrugBank databases, we obtained the critical targets associated with MCI. We matched the components and herbs corresponding to the important targets in the TCMSP platform. Using Cytoscape 3.7.2 software, we constructed a target-component-herb network and conducted a network topology analysis to obtain the core components and herbs. Molecular docking was used to preliminarily analyze and predict the binding activities and main binding combinations of the core targets and components. Based on the analysis of the properties, flavor and meridian distribution of herbs, the rules of herbal therapy for MCI were summarized.

Results

Twenty-eight critical targets were obtained after the screening. Using the TCMSP platform, 492 components were obtained. After standardization, we obtained 387 herbs. Based on the target-composition-herb network analysis, the core targets were ADRB2, ADRA1B, DPP4, ACHE and ADRA1D. According to the screening, the core ingredients were beta-sitosterol, quercetin, kaempferol, stigmasterol and luteolin. The core herbs were matched to Danshen, Yanhusuo, Gancao, Gouteng and Jiangxiang. It was found that the herbs were mainly warm in nature, pungent in taste and liver and lung in meridian. The molecular docking results showed that most core components exhibited strong binding activity to the target combination regardless of the in or out of network combination.

Conclusion

The results of this study indicate that herbs have great potential in the treatment of MCI. This study provides a reference and basis for clinical application, experimental research and new drug development of herbal therapy for MCI.

The Genus Alternanthera: Phytochemical and Ethnopharmacological Perspectives

Ethnopharmacological relevance: The genus Alternanthera (Amaranthaceae) comprises 139 species including 14 species used traditionally for the treatment of various ailments such as hypertension, pain, inflammation, diabetes, cancer, microbial and mental disorders.

Aim of the review: To search research gaps through critical assessment of pharmacological activities not performed to validate traditional claims of various species of Alternanthera. This review will aid natural product researchers in identifying Alternanthera species with therapeutic potential for future investigation.

Materials and methods: Scattered raw data on ethnopharmacological, morphological, phytochemical, pharmacological, toxicological, and clinical studies of various species of the genus Alternanthera have been compiled utilizing search engines like SciFinder, Google Scholar, PubMed, Science Direct, and Open J-Gate for 100 years up to April 2021.

Results: Few species of Alternanthera genus have been exhaustively investigated phytochemically, and about 129 chemical constituents related to different classes such as flavonoids, steroids, saponins, alkaloids, triterpenoids, glycosides, and phenolic compounds have been isolated from 9 species. Anticancer, antioxidant, antibacterial, CNS depressive, antidiabetic, analgesic, anti-inflammatory, and immunomodulator effects have been explored in the twelve species of the genus. A toxicity study has been conducted on 3 species and a clinical study on 2 species.

Conclusions: The available literature on pharmacological studies of Alternanthera species reveals that few species have been selected based on ethnobotanical surveys for scientific validation of their traditional claims. But most of these studies have been conducted on uncharacterized and non-standardized crude extracts. A roadmap of research needs to be developed for the isolation of new bioactive compounds from Alternanthera species, which can emerge out as clinically potential medicines.

Quercetin Alleviates Demyelination Through Regulating Microglial Phenotype Transformation to Mitigate Neuropsychiatric Symptoms in Mice with Vascular Dementia

Cerebral hypoperfusion plays a pivotal role in the ictus and development of vascular dementia (VaD) with neuropsychiatric symptoms. To date, few pharmacological interventions for neuropsychiatric symptoms are available in the VaD patients with neuropsychiatric impairments. Here, our results demonstrated that the extent of demyelination was dramatically deteriorated and the thickness of myelin sheath was evidently decreased in the presence of cerebral hypoperfusion, whereas Quercetin possessed the potential of abrogating these effects at least in part, then relieving anxiety and depression-like behavior when mice exposed to bilateral carotid artery stenosis (BCAS)/chronic restraint stress (CRS). The underlying mechanism was that Quercetin facilitated secretion of anti-inflammatory cytokines (IL-4 and IL-10) and in turn decreased production of pro-inflammatory factors (TNF-α and IL-1β) due to regulating microglial phenotype transformation, thereafter enhancing the microglial engulfment ability of myelin fragments in vitro and in vivo. Collectively, the results demonstrated that that Quercetin mediated microglial transformation into anti-inflammatory phenotype to reduce demyelination in ventral hippocampus (vHIP), thereafter mitigating neuropsychiatric deficits (including anxiety and depression). The present research broadens the therapeutic scope of Quercetin in central nervous system (CNS) disorders with presence of white matter damage and/or the insufficient activation of anti-inflammatory microglia, particularly for vascular dementia with/without neuropsychiatric symptoms.

Evaluation of the effects of quercetin on the rewarding property of ethanol in mice

BACKGROUND

The flavonoid quercetin has several pharmacological effects on the nervous system. Previous research showed that quercetin has useful influences on some mechanisms that are relevant in drug and substance addiction. Alcohol addiction, also known as alcoholism, is a disorder that influences the population in all walks of life. The purpose of the current study was to investigate whether quercetin affects the acquisition, extinction, and reinstatement of ethanol-induced conditioned place preference (ethanol-CPP) in adolescent mice.

METHODS

CPP was established by administration of intraperitoneal (i.p.) ethanol (2.0 g/kg) in a conditioning trial. The mice were pretreated with quercetin (at doses of 10, 30, and 100 mg/kg, i.p.) 30 minutes before each ethanol injection to test the effects of quercetin on the reward properties of ethanol. Ethanol-CPP was extinguished (13-days) by repeated testing, during which conditioned mice were given different doses of quercetin every day. Lastly, efficacy of quercetin in preventing reinstatement of ethanol-CPP triggers was also assessed by the administration of single dose ethanol (0.4 g/kg, i.p.).

RESULTS

Quercetin pretreatment attenuated the acquisition and reinstatement. In addition, quercetin administration accelerated the extinction of ethanol-CPP.

CONCLUSIONS

In conclusion, these results may cast a novel light on quercetin as an agent that could be potentially useful to attenuate different effects of ethanol and as adjuvant pharmacotherapy for ethanol addiction. However, future studies are needed to demonstrate the detailed underlying mechanisms of quercetin on ethanol addiction.

Quercetin Exhibits α7nAChR/Nrf2/HO-1-Mediated Neuroprotection Against STZ-Induced Mitochondrial Toxicity and Cognitive Impairments in Experimental Rodents

The objective of the present study was to investigate the α7nAChR-mediated Nrf2-dependant protective activity against streptozotocin (STZ)-induced brain mitochondrial toxicity in Alzheimer's disease (AD)-like rats. STZ (3 mg/kg) was injected through an intracerebroventricular route to induce AD-like dementia. Repeated Quercetin (50 mg/kg, i.p.) administration attenuated cognitive impairments in the STZ-challenged animals during Morris water-maze and Y-maze tests. Quercetin significantly mitigated the STZ-induced increase in cholinergic dysfunction, such as the increase in acetylcholinesterase activity, decrease in acetylcholine level, and activity of choline acetyltransferase, and increase in amyloid-beta aggregation and mitochondrial toxicity in respect of mitochondrial bioenergetics, integrity, and oxidative stress in memory-challenged rat hippocampus, prefrontal cortex and, amygdala. Further, Quercetin significantly attenuated STZ-induced reduction in the α7nAChRs and HO-1 expression levels in the selected rat brain regions. On the contrary, trigonelline (10 mg/kg, i.p.) and methyllycaconitine (2 mg/kg; i.p.) abolished the neuroprotective effects of Quercetin against STZ-induced behavioral, molecular, and biochemical alterations in the AD-like animals. Hence, Quercetin exhibits α7nAChR/Nrf2/HO-1-mediated neuroprotection against STZ-challenged AD-like animals. Thus, Quercetin could be considered as a potential therapeutic option in the management of AD.

Mechanism of quercetin therapeutic targets for Alzheimer disease and type 2 diabetes mellitus

Quercetin has demonstrated antioxidant, anti-inflammatory, hypoglycemic, and hypolipidemic activities, suggesting therapeutic potential against type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD). In this study, potential molecular targets of quercetin were first identified using the Swiss Target Prediction platform and pathogenic targets of T2DM and AD were identified using online Mendelian inheritance in man (OMIM), DisGeNET, TTD, DrugBank, and GeneCards databases. The 95 targets shared among quercetin, T2DM, and AD were used to establish a protein-protein interaction (PPI) network, top 25 core genes, and protein functional modules using MCODE. Metascape was then used for gene ontology and kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis. A protein functional module with best score was obtained from the PPI network using CytoHubba, and 6 high-probability quercetin targets (AKT1, JUN, MAPK, TNF, VEGFA, and EGFR) were confirmed by docking simulations. Molecular dynamics simulation was carried out according to the molecular docking results. KEGG pathway enrichment analysis suggested that the major shared mechanisms for T2DM and AD include "AGE-RAGE signaling pathway in diabetic complications," "pathways in cancer," and "MAPK signaling pathway" (the key pathway). We speculate that quercetin may have therapeutic applications in T2DM and AD by targeting MAPK signaling, providing a theoretical foundation for future clinical research.

Neuroprotective Role of Polyphenols in Treatment of Neurological Disorders: A Review

: The most frequent illnesses characterized by the gradual malfunctioning of brain neurons are neurodegenerative disorders (NDs). Genetic mutations and a range of biological processes can produce NDs. Alzheimer's disease (AD), Parkinson's disease (PD), and Multiple Sclerosis (MS) are all related to oxidative stress (OS). Reduced brain activity has become a greater health threat with a growing elderly population. It causes some pathophysiological alterations and is an important risk factor for a range of neurodegenerative illnesses. An increase in reactive oxygen species (ROS) can cause neuronal cell death, and it is thus essential to control ROS levels to maintain normal neuronal activity. Synthetic medicines are often used to treat neurological disorders; however, harmful effects have been reported. Multiple bodies of research have shown the effectiveness of polyphenols in the treatment of various NDs due to their negligible side effects. This review article describes the neuroprotection effects of polyphenols such as resveratrol, epigallocatechin-3-gallate, curcumin, and quercetin, as well as the signaling pathways and immune response controls through polyphenols.

Neuropharmacological Effects of Quercetin: A Literature-Based Review

Quercetin (QUR) is a natural bioactive flavonoid that has been lately very studied for its beneficial properties in many pathologies. Its neuroprotective effects have been demonstrated in many in vitro studies, as well as in vivo animal experiments and human trials. QUR protects the organism against neurotoxic chemicals and also can prevent the evolution and development of neuronal injury and neurodegeneration. The present work aimed to summarize the literature about the neuroprotective effect of QUR using known database sources. Besides, this review focuses on the assessment of the potential utilization of QUR as a complementary or alternative medicine for preventing and treating neurodegenerative diseases. An up-to-date search was conducted in PubMed, Science Direct and Google Scholar for published work dealing with the neuroprotective effects of QUR against neurotoxic chemicals or in neuronal injury, and in the treatment of neurodegenerative diseases. Findings suggest that QUR possess neuropharmacological protective effects in neurodegenerative brain disorders such as Alzheimer’s disease, Amyloid β peptide, Parkinson’s disease, Huntington's disease, multiple sclerosis, and amyotrophic lateral sclerosis. In summary, this review emphasizes the neuroprotective effects of QUR and its advantages in being used in complementary medicine for the prevention and treatment o of different neurodegenerative diseases.

A Pharmacological Perspective on Plant-derived Bioactive Molecules for Epilepsy

Epilepsy is a related chronic neurological condition of a predisposition for recurrent epileptic seizures, with various manifestations and causes. Although there are antiepileptic drugs, complementary natural therapies are widely used. The purpose of this systematic review was to analyze the antiepileptic/anticonvulsant pharmacological properties of plant-food derived bioactive molecules. In this regard, a systematic review of the PubMed database was made based on the inclusion criteria. Natural compounds/herbs with scientifically proven antiepileptic properties were selected. Experimental pharmacological studies in vitro and in vivo have shown that flavonoids, alkaloids and terpenoids may have anticonvulsant mechanisms similar to the new generation antiepileptic drugs. The relationships of structure-anticonvulsant effect, pharmacological models, seizure-inducing factors and response, effective dose were also analyzed and discussed. The results of in vitro and in vivo pharmacological studies analyzed in this systematic review support the clinical importance of plant-food-derived bioactive molecules for the complementary treatment of epilepsy. Thus, are opened new perspectives to develop new natural anticonvulsant drugs.

Repurposing of Anti-Diabetic Agents as a New Opportunity to Alleviate Cognitive Impairment in Neurodegenerative and Neuropsychiatric Disorders

Cognitive impairment is a shared abnormality between type 2 diabetes mellitus (T2DM) and many neurodegenerative and neuropsychiatric disorders, such as Alzheimer’s disease (AD) and schizophrenia. Emerging evidence suggests that brain insulin resistance plays a significant role in cognitive deficits, which provides the possibility of anti-diabetic agents repositioning to alleviate cognitive deficits. Both preclinical and clinical studies have evaluated the potential cognitive enhancement effects of anti-diabetic agents targeting the insulin pathway. Repurposing of anti-diabetic agents is considered to be promising for cognitive deficits prevention or control in these neurodegenerative and neuropsychiatric disorders. This article reviewed the possible relationship between brain insulin resistance and cognitive deficits. In addition, promising therapeutic interventions, especially current advances in anti-diabetic agents targeting the insulin pathway to alleviate cognitive impairment in AD and schizophrenia were also summarized.

Enlightening the neuroprotective effect of quercetin in epilepsy: From mechanism to therapeutic opportunities

Epilepsy is a devastating neurological disorder characterized by the repeated occurrence of epileptic seizures. Epilepsy stands as a global health concern affecting around 70 million people worldwide. The mainstream antiepileptic drugs (AEDs) only exert symptomatic relief and drug-resistant epilepsy occurs in up to 33 percent of patients. Hence, the investigation of novel therapeutic strategies against epileptic seizures that could exert disease modifying effects is of paramount importance. In this context, compounds of natural origin with potential antiepileptic properties have recently gained increasing attention. Quercetin is a plant-derived flavonoid with several pharmacological activities. Emerging evidence has demonstrated the antiepileptic potential of quercetin as well. Herein, based on the available evidence, we discuss the neuroprotective effects of quercetin against epileptic seizures and further analyze the plausible underlying molecular mechanisms. Our review suggests that quercetin might be a potential therapeutic candidate against epilepsy that deserves further investigation, and paves the way for the development of plant-derived antiepileptic treatment approaches.

Quercetin: Its Main Pharmacological Activity and Potential Application in Clinical Medicine

Quercetin is a flavonoid compound widely present in plants and exhibits a variety of biological activities. Research on quercetin has shown its potential for medical application. In this research, we elucidate its antioxidant mechanism and the broad-spectrum antibacterial and antiparasite properties; summarise its potential application in antioncology and cardiovascular protection and anti-immunosuppression treatment; and demonstrate its ability to alleviate the toxicity of mycotoxins. This research is expected to offer some insights and inspirations for the further study of quercetin, its properties, and the scientific basis for its better application in clinical practice.

Brain Drug Delivery: Overcoming the Blood-brain Barrier to Treat Tauopathies

Tauopathies are neurodegenerative disorders characterized by the deposition of abnormal tau protein in the brain. The application of potentially effective therapeutics for their successful treatment is hampered by the presence of a naturally occurring brain protection layer called the blood-brain barrier (BBB). BBB represents one of the biggest challenges in the development of therapeutics for central nervous system (CNS) disorders, where sufficient BBB penetration is inevitable. BBB is a heavily restricting barrier regulating the movement of molecules, ions, and cells between the blood and the CNS to secure proper neuronal function and protect the CNS from dangerous substances and processes. Yet, these natural functions possessed by BBB represent a great hurdle for brain drug delivery. This review is concentrated on summarizing the available methods and approaches for effective therapeutics' delivery through the BBB to treat neurodegenerative disorders with a focus on tauopathies. It describes the traditional approaches but also new nanotechnology strategies emerging with advanced medical techniques. Their limitations and benefits are discussed.

Evaluation of Neuroprotective Effects of Quercetin against Aflatoxin B1-Intoxicated Mice

Simple Summary

Aflatoxin B1 (AFB1) is a mycotoxin commonly present in feed, characterized by several toxic effects. AFB1 has been described as being responsible for naturally occurring animal kidney disorders. In addition, AFB1 seems to have a neurotoxical effect that leads to memory impairment behavior. AFB1 toxicity involves the induction of the oxidative stress pathway, rising lipid peroxidation, and it decreases antioxidant enzyme levels. Hence, in our research, we wanted to evaluate the potential protective effects of quercetin in AFB1-mediated toxicity in the brain and the ameliorative effect on behavioral alterations. This antioxidant effect of quercetin in the brains of AFB1-intoxicated mice is reflected in better cognitive and spatial memory capacity, as well as a better profile of anxiety and lethargy disorders. In conclusion, our study suggests that quercetin exerts a preventive role against oxidative stress by promoting antioxidative defense systems and limiting lipid peroxidation.

Abstract

Aflatoxin B1 (AFB1) is a mycotoxin commonly present in feed, characterized by several toxic effects. AFB1 seems to have a neurotoxical effect that leads to memory impairment behavior. AFB1 toxicity involves the induction of the oxidative stress pathway, rising lipid peroxidation, and it decreases antioxidant enzyme levels. Hence, in our research, we wanted to evaluate the potential protective effects of quercetin 30 mg/kg in AFB1-mediated toxicity in the brain and the ameliorative effect on behavioral alterations. Oral supplementation with quercetin increased glutathione peroxidase (GSH) levels, superoxidedismutase (SOD) activity and catalase (CAT) in the brain, and it reduced lipid peroxidation in AFB1-treated mice. This antioxidant effect of quercetin in the brains of AFB1-intoxicated mice is reflected in better cognitive and spatial memory capacity, as well as a better profile of anxiety and lethargy disorders. In conclusion, our study suggests that quercetin exerts a preventive role against oxidative stress by promoting antioxidative defense systems and limiting lipid peroxidation.

Dietary Polyphenols and Mitochondrial Function: Role in Health and Disease

Mitochondria are cytoplasmic double-membraned organelles that are involved in a myriad of key cellular regulatory processes. The loss of mitochondrial function is related to the pathogenesis of several human diseases. Over the last decades, an increasing number of studies have shown that dietary polyphenols can regulate mitochondrial redox status, and in some cases, prevent or delay disease progression. This paper aims to review the role of four dietary polyphenols - resveratrol, curcumin, epigallocatechin-3-gallate nd quercetin - in molecular pathways regulated by mitochondria and their potential impact on human health. Cumulative evidence showed that the aforementioned polyphenols improve mitochondrial functions in different in vitro and in vivo experiments. The mechanisms underlying the polyphenols' beneficial effects include, among others, the attenuation of oxidative stress, the regulation of mitochondrial metabolism and biogenesis and the modulation of cell-death signaling cascades, among other mitochondrial-independent effects. The understanding of the chemicalbiological interactions of dietary polyphenols, namely with mitochondria, may have a huge impact on the treatment of mitochondrial dysfunction-related disorders.

Potential Therapeutic Targets of Quercetin and Its Derivatives: Its Role in the Therapy of Cognitive Impairment

Quercetin (QC) is a flavonoid and crucial bioactive compound found in a variety of vegetables and fruits. In preclinical studies, QC has demonstrated broad activity against several diseases and disorders. According to recent investigations, QC is a potential therapeutic candidate for the treatment of nervous system illnesses because of its protective role against oxidative damage and neuroinflammation. QC acts on several molecular signals, including ion channels, neuroreceptors, and inflammatory receptor signaling, and it also regulates neurotrophic and anti-oxidative signaling molecules. While the study of QC in neurological disorders has focused on numerous target molecules, the role of QC on certain molecular targets such as G-protein coupled and nuclear receptors remains to be investigated. Our analysis presents several molecular targets of QC and its derivatives that demonstrate the pharmacological potential against cognitive impairment. Consequently, this article may guide future studies using QC and its analogs on specific signaling molecules. Finding new molecular targets of QC and its analogs may ultimately assist in the treatment of cognitive impairment.

Phytochemicals and cognitive health: Are flavonoids doing the trick?

Flavonoids constitute a large group of polyphenolic compounds with numerous effects on behaviour and cognition. These effects vary from learning and memory enhancement to an improvement of general cognition. Furthermore, flavonoids have been implicated in a) neuronal proliferation and survival, by acting on a variety of cellular signalling cascades, including the ERK/CREB/BDNF and PI3K/Akt pathway, b) oxidative stress reduction and c) relief from Alzheimer's disease-type symptoms. From an electrophysiological aspect, they promote long term potentiation in the hippocampus, supporting the hypothesis of synaptic plasticity mediation. Together, these actions reveal a neuroprotective effect of flavonoid compounds in the brain. Therefore, flavonoid intake could be a potential clinical direction for prevention and/or attenuation of cognitive decline deterioration which accompanies various brain disorders. The purpose of the current review paper was to summarise all these effects on cognition, describe the possible pathways via which they may act on a cellular level and provide a better picture for future research towards this direction.

Syringic acid (SA) ‒ A Review of Its Occurrence, Biosynthesis, Pharmacological and Industrial Importance

The use of phytochemicals in control of human diseases have been considerable public and scientific interest in current days. Syringic acid (SA), a phenolic compound often found in fruits and vegetables and which is synthesized via shikimic acid pathway in plants. It shows a wide range of therapeutic applications in prevention of diabetes, CVDs, cancer, cerebral ischemia; as well as it possess anti-oxidant, antimicrobial, anti-inflammatory, antiendotoxic, neuro and hepatoprotective activities. It has an effective free radical scavenger and alleviates the oxidative stress markers. The therapeutic property of SA is attributed by the presence of methoxy groups onto the aromatic ring at positions 3 and 5. The strong antioxidant activity of SA may confer its beneficial effects for human health. SA has the potential to modulate enzyme activity, protein dynamics and diverse transcription factors involved in diabetes, inflammation, cancer and angiogenesis. In vivo experimental data and histopathological studies on SA activity has delineated its possible therapeutic mechanisms. Besides usage in biomedical field, SA has greater industrial applications in bioremediation, photocatalytic ozonation, and laccase based catalysis. The present review deals about SA natural sources, biosynthesis, bioavailability, biomedical applications (in vivo and in vito. The review addresses basic information about molecular mechanisms, therapeutic and industrial potential of SA.

Arginine vasopressin ameliorates spatial learning impairments in chronic cerebral hypoperfusion via V1a receptor and autophagy signaling partially

Chronic cerebral hypoperfusion (CCH) is a major factor contributing to neurological disorders and cognitive decline. Autophagy activation is believed to provide both beneficial and detrimental roles during hypoxic/ischemic cellular injury. Although arginine vasopressin (AVP) has been strongly involved in many behaviors, especially in learning and memory, the effects of AVP on CCH and their molecular mechanisms remain unclear. Here, to investigate whether there was neuroprotective effects of AVP on CCH through V1a receptor (an AVP receptor) signaling, permanent bilateral carotid arteries occlusion (two vessel occlusion, 2VO) was used to establish a rat model of CCH, and hypertonic saline (5.3%) was injected intraperitoneally to induce the secretion of AVP. Results showed that hypertonic saline effectively alleviated spatial learning and memory deficit, enhanced synaptic plasticity of CA3-CA1 hippocampal synapses, upregulated N-methyl-d-aspartate receptor subunit 2B (NR2B) and postsynaptic density protein 95 (PSD-95) surface expressions, reduced oxidative stress and increased Nissl bodies in 2VO model rats. These phenomena were significantly decreased by V1a receptor antagonist SR49059. Interestingly, hypertonic saline also upregulated autophagy in the hippocampus of 2VO rats partly through V1a receptor. These findings imply that AVP has a beneficial role for the treatment of cognitive impairments partly through V1a receptor signaling in CCH, which is possibly related to improving synaptic plasticity by promoting NR2B and PSD-95 externalization and by enhancing autophagy.

Neuroprotection against apoptosis of SK-N-MC cells using RMP-7- and lactoferrin-grafted liposomes carrying quercetin

A drug delivery system of quercetin (QU)-encapsulated liposomes (LS) grafted with RMP-7, a bradykinin analog, and lactoferrin (Lf) was developed to permeate the blood-brain barrier (BBB) and rescue degenerated neurons, acting as an Alzheimer's disease (AD) pharmacotherapy. This colloidal formulation of QU-encapsulated LS grafted with RMP-7 and Lf (RMP-7-Lf-QU-LS) was used to traverse human brain microvascular endothelial cells (HBMECs) regulated by human astrocytes (HAs) and to treat SK-N-MC cells after an insult with cytotoxic β-amyloid (Aβ) fibrils. We found that surface RMP-7 and Lf enhanced the ability of QU to cross the BBB without inducing strong toxicity and damaging the tight junction. In addition, RMP-7-Lf-QU-LS significantly reduced Aβ-induced neurotoxicity and improved the viability of SK-N-MC cells. Compared with free QU, RMP-7-Lf-QU-LS could also significantly inhibit the expression of phosphorylated c-Jun N terminal kinase, phosphorylated p38, and phosphorylated tau protein at serine 202 by SK-N-MC cells, indicating an important role of RMP-7, Lf, and LS in protecting neurons against apoptosis. RMP-7-Lf-QU-LS is a promising carrier targeting the BBB to prevent Aβ-insulted neurodegeneration and may have potential in managing AD in future clinical applications.

Bioactive effects of quercetin in the central nervous system: Focusing on the mechanisms of actions

Quercetin, a ubiquitous flavonoid that is widely distributed in plants is classified as a cognitive enhancer in traditional and oriental medicine. The protective effects of quercetin for the treatment of neurodegenerative disorders and cerebrovascular diseases have been demonstrated in both in vitro and in vivo studies. The free radical scavenging activity of quercetin has been well-documented, wherein quercetin has been observed to exhibit protective effects against oxidative stress mediated neuronal damage by modulating the expression of NRF-2 dependent antioxidant responsive elements, and attenuation of neuroinflammation by suppressing NF-κB signal transducer and activator of transcription-1 (STAT-1). Several in vitro and in vivo studies have also shown that quercetin destabilizes and enhances the clearance of abnormal protein such as beta- amyloid peptide and hyperphosphorlyated tau, the key pathological hallmarks of Alzheimer's disease. Quercetin enhances neurogenesis and neuronal longevity by modulating a broad number of kinase signaling cascades such as phophoinositide 3- kinase (P13-kinase), AKT/PKB tyrosine kinase and Protein kinase C (PKC). Quercetin has also been well reported for its ability to reverse cognitive impairment and memory enhancement during aging. The current review focuses on summarizing the recent findings on the neuroprotective effect of quercetin, its mechanism of action and its possible roles in the prevention of neurological disorders.

Differential Effects of Quercetin and Quercetin Glycosides on Human α7 Nicotinic Acetylcholine Receptor-Mediated Ion Currents

Quercetin is a flavonoid usually found in fruits and vegetables. Aside from its antioxidative effects, quercetin, like other flavonoids, has a various neuropharmacological actions. Quercetin-3-O-rhamnoside (Rham1), quercetin-3-O-rutinoside (Rutin), and quercetin-3-(2(G)-rhamnosylrutinoside (Rham2) are mono-, di-, and tri-glycosylated forms of quercetin, respectively. In a previous study, we showed that quercetin can enhance α7 nicotinic acetylcholine receptor (α7 nAChR)-mediated ion currents. However, the role of the carbohydrates attached to quercetin in the regulation of α7 nAChR channel activity has not been determined. In the present study, we investigated the effects of quercetin glycosides on the acetylcholine induced peak inward current (I_ACh) in Xenopus oocytes expressing the α7 nAChR. I_ACh was measured with a two-electrode voltage clamp technique. In oocytes injected with α7 nAChR copy RNA, quercetin enhanced I_ACh, whereas quercetin glycosides inhibited I_ACh. Quercetin glycosides mediated an inhibition of I_ACh, which increased when they were pre-applied and the inhibitory effects were concentration dependent. The order of I_ACh inhibition by quercetin glycosides was Rutin≥Rham1>Rham2. Quercetin glycosides-mediated I_ACh enhancement was not affected by ACh concentration and appeared voltage-independent. Furthermore, quercetin-mediated I_ACh inhibition can be attenuated when quercetin is co-applied with Rham1 and Rutin, indicating that quercetin glycosides could interfere with quercetin-mediated α7 nAChR regulation and that the number of carbohydrates in the quercetin glycoside plays a key role in the interruption of quercetin action. These results show that quercetin and quercetin glycosides regulate the α7 nAChR in a differential manner.

A pharmacological basis of herbal medicines for epilepsy

Epilepsy is the most common chronic neurological disease, affecting about 1% of the world's population during their lifetime. Most people with epilepsy can attain a seizure-free life upon treatment with antiepileptic drugs (AEDs). Unfortunately, seizures in up to 30% do not respond to treatment. It is estimated that 90% of people with epilepsy live in developing countries, and most of them receive no drug treatment for the disease. This treatment gap has motivated investigations into the effects of plants that have been used by traditional healers all over the world to treat seizures. Extracts of hundreds of plants have been shown to exhibit anticonvulsant activity in phenotypic screens performed in experimental animals. Some of those extracts appear to exhibit anticonvulsant efficacy similar to that of synthetic AEDs. Dozens of plant-derived chemical compounds have similarly been shown to act as anticonvulsants in various in vivo and in vitro assays. To a significant degree, anticonvulsant effects of plant extracts can be attributed to widely distributed flavonoids, (furano)coumarins, phenylpropanoids, and terpenoids. Flavonoids and coumarins have been shown to interact with the benzodiazepine site of the GABAA receptor and various voltage-gated ion channels, which are targets of synthetic AEDs. Modulation of the activity of ligand-gated and voltage-gated ion channels provides an explanatory basis of the anticonvulsant effects of plant secondary metabolites. Many complex extracts and single plant-derived compounds exhibit antiinflammatory, neuroprotective, and cognition-enhancing activities that may be beneficial in the treatment of epilepsy. Thus, botanicals provide a base for target-oriented antiepileptic drug discovery and development. In the future, preclinical work should focus on the characterization of the effects of plant extracts and plant-derived compounds on well-defined targets rather than on phenotypic screening using in vivo animal models of acute seizures. At the same time, available data provide ample justification for clinical studies with selected standardized botanical extracts and plant-derived compounds. This article is part of a Special Issue entitled "Botanicals for Epilepsy".

Nano-antioxidants: An emerging strategy for intervention against neurodegenerative conditions

Oxidative stress has for long been linked to the neuronal cell death in many neurodegenerative conditions. Conventional antioxidant therapies have been less effective in preventing neuronal damage caused by oxidative stress due to their inability to cross the blood brain barrier. Nanoparticle antioxidants constitute a new wave of antioxidant therapies for prevention and treatment of diseases involving oxidative stress. It is believed that nanoparticle antioxidants have strong and persistent interactions with biomolecules and would be more effective against free radical induced damage. Nanoantioxidants include inorganic nanoparticles possessing intrinsic antioxidant properties, nanoparticles functionalized with antioxidants or antioxidant enzymes to function as an antioxidant delivery system. Nanoparticles containing antioxidants have shown promise as high-performance therapeutic nanomedicine in attenuating oxidative stress with potential applications in treating and preventing neurodegenerative conditions. However, to realize the full potential of nanoantioxidants, negative aspects associated with the use of nanoparticles need to be overcome to validate their long term applications.

The mechanisms of action of flavonoids in the brain: Direct versus indirect effects

The projected increase in the incidence of dementia in the population highlights the urgent need for a more comprehensive understanding of how different aspects of lifestyle, in particular exercise and diet, may affect neural function and consequent cognitive performance throughout the life course. In this regard, flavonoids, found in a variety of fruits, vegetables and derived beverages, have been identified as a group of promising bioactive compounds capable of influencing different aspects of brain function, including cerebrovascular blood flow and synaptic plasticity, both resulting in improvements in learning and memory in mammalian species. However, the precise mechanisms by which flavonoids exert these actions are yet to be fully established, although accumulating data indicate an ability to interact with neuronal receptors and kinase signaling pathways which are key to neuronal activation and communication and synaptic strengthening. Alternatively or concurrently, there is also compelling evidence derived from human clinical studies suggesting that flavonoids can positively affect peripheral and cerebrovascular blood flow, which may be an indirect effective mechanism by which dietary flavonoids can impact on brain health and cognition. The current review examines the beneficial effects of flavonoids on both human and animal brain function and attempts to address and link direct and indirect actions of flavonoids and their derivatives within the central nervous system (CNS).

The flavonoid quercetin ameliorates Alzheimer's disease pathology and protects cognitive and emotional function in aged triple transgenic Alzheimer's disease model mice

Alzheimer's disease (AD) is the most common senile dementia in the world. Although important progress has been made in understanding the pathogenesis of AD, current therapeutic approaches provide only modest symptomatic relief. In this study, we evaluated the neuroprotective effect of quercetin (25 mg/kg) administration via i.p. injection every 48 h for 3 months on aged (21-24 months old) triple transgenic AD model (3xTg-AD) mice. Our data show that quercetin decreases extracellular β-amyloidosis, tauopathy, astrogliosis and microgliosis in the hippocampus and the amygdala. These results were supported by a significant reduction in the paired helical filament (PHF), β-amyloid (βA) 1-40 and βA 1-42 levels and a decrease in BACE1-mediated cleavage of APP (into CTFβ). Additionally, quercetin induced improved performance on learning and spatial memory tasks and greater risk assessment behavior based on the elevated plus maze test. Together, these findings suggest that quercetin reverses histological hallmarks of AD and protects cognitive and emotional function in aged 3xTg-AD mice.

Quercetin reverses hypobaric hypoxia-induced hippocampal neurodegeneration and improves memory function in the rat

Inadequate oxygen availability at high altitude causes elevated oxidative stress, resulting in hippocampal neurodegeneration and memory impairment. Though oxidative stress is known to be a major cause of neurodegeneration in hypobaric hypoxia, neuroprotective and ameliorative potential of quercetin, a flavonoid with strong antioxidant properties in reversing hypobaric hypoxia-induced memory impairment has not been studied. Four groups of male adult Sprague Dawley rats were exposed to hypobaric hypoxia for 7 days in an animal decompression chamber at an altitude of 7600 meters. Rats were supplemented with quercetin orally by gavage during 7 days of hypoxic exposure. Spatial working memory was assessed by a Morris Water Maze before and after exposure to hypobaric hypoxia. Changes in oxidative stress markers and apoptotic marker caspase 3 expression in hippocampus were assessed. Histological assessment of neurodegeneration was performed by cresyl violet and fluoro Jade B staining. Our results showed that quercetin supplementation during exposure to hypobaric hypoxia decreased reactive oxygen species levels and consequent lipid peroxidation in the hippocampus by elevating antioxidant status and free radical scavenging enzyme system. There was reduction in caspase 3 expression, and decrease in the number of pyknotic and fluoro Jade B-positive neurons in hippocampus after quercetin supplementation during hypoxic exposure. Behavioral studies showed that quercetin reversed the hypobaric hypoxia-induced memory impairment. These findings suggest that quercetin provides neuroprotection to hippocampal neurons during exposure to hypobaric hypoxia through antioxidative and anti-apoptotic mechanisms, and possesses promising therapeutic potential to ameliorate hypoxia-induced memory dysfunction.

Chronic administration of quercetin prevent spatial learning and memory deficits provoked by chronic stress in rats

There are several reports that cognitive impairment is observed in stress related disorders and chronic stress impairs learning and memory. However, very few studies have looked into the possible ways of preventing this stress-induced deficit. This research study was conducted to evaluate the effects of quercetin, a natural flavonoid, with strong antioxidant and free radical scavenger properties, on chronic stress induced learning and memory deficits and oxidative stress in hippocampus. For chronic stress, rats were restrained daily for 6h/day (from 9:00 to 15:00) for 21 days in well-ventilated plexiglass tubes without access to food and water. The animals were injected with quercetin or vehicle 60 min before restraint stress over a period of 21 days. Then, rats trained with six trials per day for 6 consecutive days in the water maze. On day 28, a probe test was done to measure memory retention. In addition, oxidative stress markers in the hippocampus were evaluated. Results of this study demonstrated that chronic stress exposure rats exhibited higher escape latency during training trials and reduced time spent in target quadrant, higher escape location latency and average proximity in probe trial test. Quercetin (50mg/kg) treatment during restraint stress (21 days) markedly decreased escape latency and increased time spent in target quadrant during Morris water maze task. In comparison to vehicle treated group, chronic-stress group had significantly higher malondialdehyde (MDA) levels, significantly higher superoxide dismutase (SOD) activity and significantly lower glutathione peroxidase (GPx) activity in the hippocampus. Quercetin treatment caused a significant decrease in the hippocampus MDA levels and improves SOD and GPx activities in stressed animals. Finally, quercetin significantly decreased plasma corticosterone levels in stressed animals. Based on results of this study, chronic stress has detrimental effects on learning and memory and quercetin treatment can prevent from oxidative stress and impairment of learning and memory induced by chronic stress.

In vitro antiophidian mechanisms of Hypericum brasiliense choisy standardized extract: quercetin-dependent neuroprotection

The neuroprotection induced by Hypericum brasiliense Choisy extract (HBE) and its main active polyphenol compound quercetin, against Crotalus durissus terrificus (Cdt) venom and crotoxin and crotamine, was enquired at both central and peripheral mammal nervous system. Cdt venom (10 μg/mL) or crotoxin (1 μg/mL) incubated at mouse phrenic nerve-diaphragm preparation (PND) induced an irreversible and complete neuromuscular blockade, respectively. Crotamine (1 μg/mL) only induced an increase of muscle strength at PND preparations. At mouse brain slices, Cdt venom (1, 5, and 10 μg/mL) decreased cell viability. HBE (100 μg/mL) inhibited significantly the facilitatory action of crotamine (1 μg/mL) and was partially active against the neuromuscular blockade of crotoxin (1 μg/mL) (data not shown). Quercetin (10 μg/mL) mimicked the neuromuscular protection of HBE (100 μg/mL), by inhibiting almost completely the neurotoxic effect induced by crotoxin (1 μg/mL) and crotamine (1 μg/mL). HBE (100 μg/mL) and quercetin (10 μg/mL) also increased cell viability in mice brain slices. Quercetin (10 μg/mL) was more effective than HBE (100 μg/mL) in counteracting the cell lysis induced by Cdt venom (1 and 10 μg/mL, resp.). These results and a further phytochemical and toxicological investigations could open new perspectives towards therapeutic use of Hypericum brasiliense standardized extract and quercetin, especially to counteract the neurotoxic effect induced by snake neurotoxic venoms.

VEGF ameliorates cognitive impairment in in vivo and in vitro ischemia via improving neuronal viability and function

Vascular endothelial growth factor (VEGF) has recently been proved to be a potential therapeutic drug in ischemic disorders depending on the dose, route and time of administration, especially in focal cerebral ischemia. Whether VEGF could exert protection in a long-term total cerebral ischemic model is still uncertain, and the cellular mechanism has not been clarified so far. In order to answer the above issue, an experiment was performed in non-invasively giving exogenous VEGF to a total cerebral ischemic model rats and examining their spatial cognitive function by performing Morris water maze and long-term potential test. Moreover, we performed in vitro experiment to explore the cellular mechanism of VEGF protection effect. In an in vitro ischemia model oxygen-glucose deprivation (OGD), whole-cell patch-clamp recording was employed to examine neuronal function. Additionally, hematoxylin-eosin and propidium iodide staining were applied in vivo and in vitro in the neuropathological and viability study, separately. Our results showed that intranasal administration of VEGF could improve the cognitive function, synaptic plasticity and damaged hippocampal neurons in a global cerebral ischemia model. In addition, VEGF could retain the membrane potential, neuronal excitability and spontaneous excitatory postsynaptic currents in the early stage of ischemia, which further demonstrated that there was an acute effect of VEGF in OGD-induced pyramidal neurons. Simultaneously, it was also found that the death of CA1 pyramidal neuronal was significantly reduced by VEGF, but there was no similar effect in VEGF coexists with SU5416 group. These results indicated that VEGF could ameliorate cognitive impairment and synaptic plasticity via improving neuronal viability and function through acting on VEGFR-2.

Polyphenols: multipotent therapeutic agents in neurodegenerative diseases

Aging leads to numerous transitions in brain physiology including synaptic dysfunction and disturbances in cognition and memory. With a few clinically relevant drugs, a substantial portion of aging population at risk for age-related neurodegenerative disorders require nutritional intervention. Dietary intake of polyphenols is known to attenuate oxidative stress and reduce the risk for related neurodegenerative diseases such as Alzheimer's disease (AD), stroke, multiple sclerosis (MS), Parkinson's disease (PD), and Huntington's disease (HD). Polyphenols exhibit strong potential to address the etiology of neurological disorders as they attenuate their complex physiology by modulating several therapeutic targets at once. Firstly, we review the advances in the therapeutic role of polyphenols in cell and animal models of AD, PD, MS, and HD and activation of drug targets for controlling pathological manifestations. Secondly, we present principle pathways in which polyphenol intake translates into therapeutic outcomes. In particular, signaling pathways like PPAR, Nrf2, STAT, HIF, and MAPK along with modulation of immune response by polyphenols are discussed. Although current polyphenol researches have limited impact on clinical practice, they have strong evidence and testable hypothesis to contribute clinical advances and drug discovery towards age-related neurological disorders.

Identification of brain-targeted bioactive dietary quercetin-3-O-glucuronide as a novel intervention for Alzheimer's disease

Epidemiological and preclinical studies indicate that polyphenol intake from moderate consumption of red wines may lower the relative risk for developing Alzheimer's disease (AD) dementia. There is limited information regarding the specific biological activities and cellular and molecular mechanisms by which wine polyphenolic components might modulate AD. We assessed accumulations of polyphenols in the rat brain following oral dosage with a Cabernet Sauvignon red wine and tested brain-targeted polyphenols for potential beneficial AD disease-modifying activities. We identified accumulations of select polyphenolic metabolites in the brain. We demonstrated that, in comparison to vehicle-control treatment, one of the brain-targeted polyphenol metabolites, quercetin-3-O-glucuronide, significantly reduced the generation of β-amyloid (Aβ) peptides by primary neuron cultures generated from the Tg2576 AD mouse model. Another brain-targeted metabolite, malvidin-3-O-glucoside, had no detectable effect on Aβ generation. Moreover, in an in vitro analysis using the photo-induced cross-linking of unmodified proteins (PICUP) technique, we found that quercetin-3-O-glucuronide is also capable of interfering with the initial protein-protein interaction of Aβ(1-40) and Aβ(1-42) that is necessary for the formation of neurotoxic oligomeric Aβ species. Lastly, we found that quercetin-3-O-glucuronide treatment, compared to vehicle-control treatment, significantly improved AD-type deficits in hippocampal formation basal synaptic transmission and long-term potentiation, possibly through mechanisms involving the activation of the c-Jun N-terminal kinases and the mitogen-activated protein kinase signaling pathways. Brain-targeted quercetin-3-O-glucuronide may simultaneously modulate multiple independent AD disease-modifying mechanisms and, as such, may contribute to the benefits of dietary supplementation with red wines as an effective intervention for AD.

Quercetin protects against the Aβ(25-35)-induced amnesic injury: involvement of inactivation of rage-mediated pathway and conservation of the NVU

Quercetin has demonstrated protective effects against Aβ-induced toxicity on both neurons and endothelial cells. However, whether or not quercetin has an effect on the neurovascular coupling is unclear. In the present study, we aim to investigate the anti-amnesic effects of quercetin and to explore the underlying mechanisms. Aβ(25-35) (10 nmol) was administrated to mice i.c.v. Quercetin was administrated orally for 8 days after injection. Learning and memory behaviors were evaluated by measuring spontaneous alternation in Morris Water Maze test and the step-through positive avoidance test. The regional cerebral blood flow was monitored before the Aβ(25-35) injection and on seven consecutive days after injection. Mice were sacrificed and cerebral cortices were isolated on the last day. The effects of quercetin on the neurovascular unit (NVU) integrity, microvascular function and cholinergic neuronal changes, and the modification of signaling pathways were tested. Our results demonstrate that quercetin treatment for Aβ(25-35)-induced amnesic mice improved the learning and memory capabilities and conferred robust neurovascular coupling protection, involving maintenance of the NVU integrity, reduction of neurovascular oxidation, modulation of microvascular function, improvement of cholinergic system, and regulation of neurovascular RAGE signaling pathway and ERK/CREB/BDNF pathway. In conclusion, in Aβ(25-35)-induced amnesic mice, optimal doses of quercetin administration were beneficial. Quercetin protected the NVU likely through reduction of oxidative damage, inactivation of RAGE-mediated pathway and preservation of cholinergic neurons, offering an alternative medication for Alzheimer's disease.

Quercetin attenuates cell apoptosis in focal cerebral ischemia rat brain via activation of BDNF-TrkB-PI3K/Akt signaling pathway

Many studies have demonstrated that apoptosis play an important role in cerebral ischemic pathogenesis and may represent a target for treatment. Neuroprotective effect of quercetin has been shown in a variety of brain injury models including ischemia/reperfusion. It is not clear whether BDNF-TrkB-PI3K/Akt signaling pathway mediates the neuroprotection of quercetin, though there has been some reports on the quercetin increased brain-derived neurotrophic factor (BDNF) level in brain injury models. We therefore first examined the neurological function, infarct volume and cell apoptosis in quercetin treated middle cerebral artery occlusion (MCAO) rats. Then the protein expression of BDNF, cleaved caspase-3 and p-Akt were evaluated in either the absence or presence of PI3K inhibitor (LY294002) or tropomyosin receptor kinase B (TrkB) receptor antagonist (K252a) by immunohistochemistry staining and western blotting. Quercetin significantly improved neurological function, while it decreased the infarct volume and the number of TdT mediated dUTP nick end labeling positive cells in MCAO rats. The protein expression of BDNF, TrkB and p-Akt also increased in the quercetin treated rats. However, treatment with LY294002 or K252a reversed the quercetin-induced increase of BDNF and p-Akt proteins and decrease of cleaved caspase-3 protein in focal cerebral ischemia rats. These results demonstrate that quercetin can decrease cell apoptosis in the focal cerebral ischemia rat brain and the mechanism may be related to the activation of BDNF-TrkB-PI3K/Akt signaling pathway.

Quercetin protects against chronic aluminum-induced oxidative stress and ensuing biochemical, cholinergic, and neurobehavioral impairments in rats

In this study, we investigated the protective effect of chronic quercetin (a natural flavanoid) administration against Al-induced cognitive impairments, oxidative damage, and cholinergic dysfunction in male Wistar rats. Al lactate (10 mg/kg b.wt./day) was administered intragastrically to rats which were pre-treated with quercetin (10 mg/kg b.wt./day, intragastrically) for 12 weeks. At the end of 6 or 12 weeks of the study, several behavioral parameters were carried out to evaluate cognitive functions. Further after 12 weeks of exposure, various biochemical tests and H&E staining were performed to assess the extent of oxidative damage and neurodegeneration, respectively. Al levels were also estimated in HC and CS regions of rat brain. Chronic administration of quercetin caused significant improvement in the muscle coordination, cognition, anxiety, locomotion, and initial exploratory patterns in Al-treated rats. Quercetin supplementation to Al-treated animals also reduced oxidative stress, decreased ROS production, increased MnSOD activity and glutathione levels with decreased lipid peroxidation and protein oxidation. It increased AChE activity and ATP levels in HC and CS regions of rat brain compared to Al-treated rats. Quercetin administration ameliorates Al-induced neurodegenerative changes in Al-treated rats as seen by H&E staining. Further with the help of atomic absorption spectrophotometer, we found that quercetin supplementation to Al-treated rats also decreases the accumulation of Al in the HC and CS regions of rat brain. Taken together the results of this study show that quercetin offers neuroprotection against Al-induced cognitive impairments, cholinergic dysfunction, and associated oxidative damage in rats.