3,5,6,7,8,3′,4′-Heptamethoxyflavone, a citrus flavonoid, on protection against memory impairment and neuronal cell death in a global cerebral ischemia mouse model

Identification and Therapeutic Potential of Polymethoxylated Flavones in Citri Reticulatae Pericarpium for Alzheimer's Disease: Targeting Neuroinflammation

Neuroinflammation is a significant driving force in the pathogenesis and progression of central nervous system (CNS) disorders. Polymethoxylated flavones (PMFs), the key lipid-soluble constituents in Citri Reticulatae Pericarpium (CRP), exhibit excellent blood-brain barrier permeability and anti-inflammatory properties, holding therapeutic potential for CNS disorders. However, the specific bioactive components and therapeutic effects of PMFs in treating CNS disorders are not well understood. This study employed a comprehensive sequential metabolism approach to elucidate the dynamic biotransformation of PMFs in vivo and identified seven brain-targeting components. Subsequently, network pharmacology and experimental validation were utilized to explore the potential mechanisms of PMFs. The results suggested that PMFs have potential therapeutic value for Alzheimer's disease (AD)-like mice, with the inhibition of neuroinflammation likely being a key mechanism of their anti-AD effects. Notably, sinensetin, tangeretin, nobiletin, and 3,5,6,7,8,3',4'-heptamethoxyflavone were identified as potent neuroinflammatory inhibitors. This research elucidated the chemical and therapeutic foundations of PMFs, indicating their potential as treatments or nutritional supplements for AD prevention and treatment. Moreover, the integrated triad approach of sequential metabolism, network pharmacology, and experimental validation may serve as a promising strategy for screening bioactive compounds in herbs or functional foods, as well as for elucidating their therapeutic mechanisms.

Targeting Neuraminidase 4 Attenuates Kidney Fibrosis in Mice

Despite significant progress in therapy, there remains a lack of substantial evidence regarding the molecular factors that lead to renal fibrosis. Neuraminidase 4 (NEU4), an enzyme that removes sialic acids from glycoconjugates, has an unclear role in chronic progressive fibrosis. Here, this study finds that NEU4 expression is markedly upregulated in mouse fibrotic kidneys induced by folic acid or unilateral ureter obstruction, and this elevation is observed in patients with renal fibrosis. NEU4 knockdown specifically in the kidney attenuates the epithelial-to-mesenchymal transition, reduces the production of pro-fibrotic cytokines, and decreases cellular senescence in male mice. Conversely, NEU4 overexpression exacerbates the progression of renal fibrosis. Mechanistically, NEU4254-388aa interacts with Yes-associated protein (YAP) at WW2 domain (231-263aa), promoting its nucleus translocation and activation of target genes, thereby contributing to renal fibrosis. 3,5,6,7,8,3',4'-Heptamethoxyflavone, a natural compound, is identified as a novel NEU4 inhibitor, effectively protecting mice from renal fibrosis in a NEU4-dependent manner. Collectively, the findings suggest that NEU4 may represent a promising therapeutic target for kidney fibrosis.

The impact of flavonoids and BDNF on neurogenic process in various physiological/pathological conditions including ischemic insults: a narrative review

OBJECTIVE

Ischemic stroke is the leading cause of mortality and disability worldwide with more than half of survivors living with serious neurological sequelae thus, it has recently attracted considerable attention in the field of medical research. Neurogenesis is the process of formation of new neurons in the brain, including the human brain, from neural stem/progenitor cells [NS/PCs] which reside in neurogenic niches that contain the necessary substances for NS/PC proliferation, differentiation, migration, and maturation into functioning neurons which can integrate into a pre-existing neural network.Neurogenesis can be modulated by many exogenous and endogenous factors, pathological conditions. Both brain-derived neurotrophic factor, and flavonoids can modulate the neurogenic process in physiological conditions and after various pathological conditions including ischemic insults.

AIM

This review aims to discuss neurogenesis after ischemic insults and to determine the role of flavonoids and BDNF on neurogenesis under physiological and pathological conditions with a concentration on ischemic insults to the brain in particular.

METHOD

Relevant articles assessing the impact of flavonoids and BDNF on neurogenic processes in various physiological/pathological conditions including ischemic insults within the timeline of 1965 until 2023 were searched using the PubMed database.

CONCLUSIONS

The selected studies have shown that ischemic insults to the brain induce NS/PC proliferation, differentiation, migration, and maturation into functioning neurons integrating into a pre-existing neural network. Flavonoids and BDNF can modulate neurogenesis in the brain in various physiological/pathological conditions including ischemic insults. In conclusion, flavonoids and BDNF may be involved in post-ischemic brain repair processes through enhancing endogenous neurogenesis.

Effect of 2-Week Naringin Supplementation on Neurogenesis and BDNF Levels in Ischemia-Reperfusion Model of Rats

BACKGROUND

Ischemic stroke is the leading cause of mortality and disability worldwide with more than half of survivors living with serious neurological sequelae; thus, it has recently attracted a lot of attention in the field of medical study.

PURPOSE

The aim of this study was to determine the effect of naringin supplementation on neurogenesis and brain-derived neurotrophic factor (BDNF) levels in the brain in experimental brain ischemia-reperfusion.

STUDY DESIGN

The research was carried out on 40 male Wistar-type rats (10-12 weeks old) obtained from the Experimental Animals Research and Application Center of Selçuk University. Experimental groups were as follows: (1) Control group, (2) Sham group, (3) Brain ischemia-reperfusion group, (4) Brain ischemia-reperfusion + vehicle group (administered for 14 days), and (5) Brain ischemia-reperfusion + Naringin group (100 mg/kg/day administered for 14 days).

METHODS

In the ischemia-reperfusion groups, global ischemia was performed in the brain by ligation of the right and left carotid arteries for 30 min. Naringin was administered to experimental animals by intragastric route for 14 days following reperfusion. The training phase of the rotarod test was started 4 days before ischemia-reperfusion, and the test phase together with neurological scoring was performed the day before and 1, 7, and 14 days after the operation. At the end of the experiment, animals were sacrificed, and then hippocampus and frontal cortex tissues were taken from the brain. Double cortin marker (DCX), neuronal nuclear antigen marker (NeuN), and BDNF were evaluated in hippocampus and frontal cortex tissues by Real-Time qPCR analysis and immunohistochemistry methods.

RESULTS

While ischemia-reperfusion increased the neurological score values, DCX, NeuN, and BDNF levels decreased significantly after ischemia in the hippocampus and frontal cortex tissues. However, naringin supplementation restored the deterioration to a certain extent.

CONCLUSION

The results of the study show that 2 weeks of naringin supplementation may have protective effects on impaired neurogenesis and BDNF levels after brain ischemia and reperfusion in rats.

Regulatory mechanisms of natural compounds from traditional Chinese herbal medicines on the microglial response in ischemic stroke

BACKGROUND

Development of clinically effective neuroprotective agents for stroke therapy is still a challenging task. Microglia play a critical role in brain injury and recovery after ischemic stroke. Traditional Chinese herbal medicines (TCHMs) are based on a unique therapeutic principle, have various formulas, and have long been widely used to treat stroke. Therefore, the active compounds in TCHMs and their underlying mechanisms of action are attracting increasing attention in the field of stroke drug development.

PURPOSE

To summarize the regulatory mechanisms of TCHM-derived natural compounds on the microglial response in animal models of ischemic stroke.

METHODS

We searched studies published until 10 April 2023 in the Web of Science, PubMed, and ScienceDirect using the following keywords: natural compounds, natural products or phytochemicals, traditional Chinese Medicine or Chinese herbal medicine, microglia, and ischemic stroke. This review was prepared according to PRISMA (Preferred Reporting Item for Systematic Reviews and Meta-Analysis) guidelines.

RESULTS

Natural compounds derived from TCHMs can attenuate the M1 phenotype of microglia, which is involved in the detrimental inflammatory response, via inhibition of NF-κB, MAPKs, JAK/STAT, Notch, TLR4, P2X7R, CX3CR1, IL-17RA, the NLRP3 inflammasome, and pro-oxidant enzymes. Additionally, the neuroprotective response of microglia with the M2 phenotype can be enhanced by activating Nrf2/HO-1, PI3K/AKT, AMPK, PPARγ, SIRT1, CB2R, TREM2, nAChR, and IL-33/ST2. Several clinical trials showed that TCHM-derived natural compounds that regulate microglial responses have significant and safe therapeutic effects, but further well-designed clinical studies are needed.

CONCLUSIONS

Further research regarding the direct targets and potential pleiotropic or synergistic effects of natural compounds would provide a more reasonable approach for regulation of the microglial response with the possibility of successful stroke drug development.

Effects of Citrus kawachiensis Peel in Frailty-like Model Mice Induced by Low Protein Nutrition Disorders

"Frailty" caused by a decline in physiological reserve capacity, chronic inflammation, and oxidative stress in the elderly has recently become a major social issue. The present study examined the effects of the peel of Citrus kawachiensis (CK), which exhibits anti-inflammatory, antioxidant, and pro-neurogenesis activities in frailty-like model mice. Male C57BL/6 mice (15 weeks old) were fed an 18% protein diet (CON), a 2.5% protein diet (PM), and PM mixed with 1% dried CK peel powder for approximately 1 month. Mice were euthanized 2 or 8 days after a single intraperitoneal administration of lipopolysaccharide (LPS) and tissues were dissected. Among peripheral tissues, muscle weight, liver weight, and blood glucose levels were significantly higher in the PM-LPS-CK group than in the PM-LPS group. In the behavioral analysis, locomotive activity was significantly lower in the PM-LPS group than in the PM group. The reduction in locomotive activity in the PM-LPS-CK group was significantly smaller than that in the PM-LPS group. The quantification of microglia in the hippocampal stratum lacunosum-moleculare revealed that increases in the PM-LPS group were significantly suppressed by the dried CK peel powder. Furthermore, the quantification of synaptic vesicle membrane proteins in the hippocampal CA3 region showed down-regulated expression in the PM-LPS group, which was significantly ameliorated by the administration of the dried CK peel powder. Collectively, these results suggest that CK inhibits inflammation and oxidative stress induced by PM and LPS in the central nervous system and peripheral tissue. Therefore, C. kawachiensis is highly effective against "frailty".

The molecular mechanism for inhibiting the growth of nasopharyngeal carcinoma cells using polymethoxyflavonoids purified from pericarp of Citrus reticulata 'Chachi' via HSCCC

Polymethoxyflavonoids (PMFs), the main bioactive compounds naturally occurring in the pericarp of Citrus reticulata 'Chachi' (CRCP), possess significant antitumor action. However, the action of PMFs in nasopharyngeal carcinoma (NPC) is currently unknown. The present research study was conducted to investigate the inhibitory mechanisms of PMFs from CRCP on NPC growth in vivo and in vitro. In our research, we used high-speed counter-current chromatography (HSCCC) to separate four PMFs (nobiletin (NOB), 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF), tangeretin (TGN), and 5-hydroxy-6,7,8,3',4'-pentamethoxyflavone (5-HPMF)) from CRCP. CCK-8 assay was used to preliminarily screen cell viability following exposure to the four PMFs. Colony formation, Hoechst-33258 staining, transwell, and wound scratch assays were performed to assess the anti-proliferation, invasion, migration, and apoptosis-inducing effects of HMF on NPC cells. NPC tumors in xenograft tumor transplantation experiments were also established to explore the effect of HMF (100 and 150 mg/kg/day) on NPC. The histopathological changes in the treated rats were observed by H&E staining and Ki-67 detection by immunohistochemical techniques. The expressions of P70S6K, p-P70S6K, S6, p-S6, COX-2, p53, and p-p53 were measured by Western blot. The four PMFs were obtained with high purity (>95.0%). The results of the preliminary screening by CCK-8 assay suggested that HMF had the strongest inhibitory effect on NPC cell growth. The results of the colony formation, Hoechst-33258 staining, transwell, and wound scratch assays indicated that HMF had significant anti-proliferation, invasion, migration, and apoptosis-inducing ability in NPC cells. Moreover, HMF suppressed NPC tumor growth in xenograft tumor transplantation experiments. Further investigation suggested that HMF regulated NPC cells proliferation, apoptosis, migration, and invasion by activating AMPK-dependent signaling pathways. In conclusion, HMF-induced AMPK activation inhibited NPC cell growth, invasion, and metastatic potency by downregulating the activation of the mTOR signaling pathway and COX-2 protein levels, as well as enhancing the p53 phosphorylation level. Our study provides a crucial experimental basis for the clinical treatment of NPC, as well as the development and utilization of PMFs from CRCP.

Activation of Extracellular Signal-Regulated Kinase 2 and cAMP Response Element-Binding Protein in Cultured Neurons by the Macrocyclic Ellagitannin Oenothein B

(1) Background: The findings of our recent in vivo study indicated that the oral administration of oenothein B, a unique macrocyclic ellagitannin, activated extracellular signal-regulated kinase (ERK) 2 and cAMP response element-binding protein (CREB) in the mouse brain. A large hydrophilic oenothein B is unable to reach the brain, suggesting that any metabolite(s) of oenothein B might function in the brain. (2) Results: The addition of oenothein B to the culture medium of rat cortical neurons induced the prompt and significant activation of ERK2 and CREB. (3) Conclusions: The activation of ERK2 and CREB is crucial for synaptic transmission and learning/memory formation in the brain. The present results suggest oenothein B exerts neurotrophic/neuroprotective effects in the brain through the modulation of neuronal signaling pathways, if it reaches the brain.

The Effect of Prosopis farcta and Its Bioactive Luteolin on the Hippocampus of Mice after Induced Ischemia Reperfusion

Background

Ischemia plays an important role in increasing damage to the nervous system. This study aimed to evaluate the effect of Prosopis farcta (PFE) and its bioactive luteolin (Lu) and forced swimming exercise on the hippocampus of mice after induced ischemia reperfusion.

Methods

The bioactive component of PFE (Lu) was identified by HPLC. Fifty-six male mice were divided into different groups. Ischemia was induced by ligation of the common carotid artery. After mice training (swimming exercise, 8 weeks) and consuming PFE and Lu, the mice's memory ability was evaluated in the shuttle box. Histological examination was performed by Nissel staining and immunohistochemistry.

Results

Results showed that the ischemic mice exercised and treated with PFE and Lu had higher step-through latency (STL) compared with the nonexercised mice, and this was confirmed with time spent in the dark compartment (TDC). The number of dark cells in the ischemic group exercising and receiving PFE and Lu decreased compared to that of the other groups in the hippocampus. DCX protein expression was increased in nonexercised groups compared to that of the exercised groups and those treated with PFE and Lu, while NeuN decreased.

Conclusions

Forced swimming exercise following ischemia, as well as consumption of PFE and Lu, has reduced cell death and increased neurogenesis in the hippocampus and thus may help improve memory in ischemia.

The mechanism of microglia-mediated immune inflammation in ischemic stroke and the role of natural botanical components in regulating microglia: A review

Ischemic stroke (IS) is one of the most fatal diseases. Neuroimmunity, inflammation, and oxidative stress play important roles in various complex mechanisms of IS. In particular, the early proinflammatory response resulting from the overactivation of resident microglia and the infiltration of circulating monocytes and macrophages in the brain after cerebral ischemia leads to secondary brain injury. Microglia are innate immune cells in the brain that constantly monitor the brain microenvironment under normal conditions. Once ischemia occurs, microglia are activated to produce dual effects of neurotoxicity and neuroprotection, and the balance of the two effects determines the fate of damaged neurons. The activation of microglia is defined as the classical activation (M1 type) or alternative activation (M2 type). M1 type microglia secrete pro-inflammatory cytokines and neurotoxic mediators to exacerbate neuronal damage, while M2 type microglia promote a repairing anti-inflammatory response. Fine regulation of M1/M2 microglial activation to minimize damage and maximize protection has important therapeutic value. This review focuses on the interaction between M1/M2 microglia and other immune cells involved in the regulation of IS phenotypic characteristics, and the mechanism of natural plant components regulating microglia after IS, providing novel candidate drugs for regulating microglial balance and IS drug development.

Poncirin ameliorates oxygen glucose deprivation/reperfusion injury in cortical neurons via inhibiting NOX4-mediated NLRP3 inflammasome activation

Poncirin, a natural flavonoid present abundantly in citrus fruits, possesses anti-oxidant and anti-inflammatory activities that contribute to neuroprotection, but its roles and mechanisms in neuronal injury is still poorly understood. In this study, an oxygen-glucose deprivation/reoxygenation (OGD/R) model was established in primary cortical neurons to induce neuronal injury in vitro. Poncirin effectively attenuated OGD/R-induced neuronal damage by enhancing cell viability, restraining lactate dehydrogenase release, and reducing apoptosis of neurons. Poncirin restrained mitochondrial dysfunction and oxidative stress by increasing mitochondrial membrane potential, declining reactive oxygen species production, lessening malondialdehyde generation, and increasing the activities of antioxidant enzymes in OGD/R-treated neurons. Poncirin also repressed inflammatory responses by reducing the secretion of pro-inflammatory factors, and inhibiting NLRP3 inflammasome activation. Importantly, poncirin administration notably abolished OGD/R-induced upregulation of NADPH oxidase 4 (NOX4), and overexpression of NOX4 neutralized poncirin-mediated neuroprotection. In conclusion, poncirin protects cortical neurons from OGD/R injury via inhibiting NOX4/ROS/NLRP3 axis.

Emerging Role of Flavonoids as the Treatment of Depression

Depression is one of the most frequently observed psychological disorders, affecting thoughts, feelings, behavior and a sense of well-being in person. As per the WHO, it is projected to be the primitive cause of various other diseases by 2030. Clinically, depression is treated by various types of synthetic medicines that have several limitations such as side-effects, slow-onset action, poor remission and response rates due to complicated pathophysiology involved with depression. Further, clinically, patients cannot be given the treatment unless it affects adversely the job or family. In addition, synthetic drugs are usually single targeted drugs. Unlike synthetic medicaments, there are many plants that have flavonoids and producing action on multiple molecular targets and exhibit anti-depressant action by affecting multiple neuronal transmissions or pathways such as noradrenergic, serotonergic, GABAnergic and dopaminergic; inhibition of monoamine oxidase and tropomyosin receptor kinase B; simultaneous increase in nerve growth and brain-derived neurotrophic factors. Such herbal drugs with flavonoids are likely to be useful in patients with sub-clinical depression. This review is an attempt to analyze pre-clinical studies, structural activity relationship and characteristics of reported isolated flavonoids, which may be considered for clinical trials for the development of therapeutically useful antidepressant.

An overview on therapeutic and medicinal potential of poly-hydroxy flavone viz. Heptamethoxyflavone, Kaempferitrin, Vitexin and Amentoflavone for management of Alzheimer's and Parkinson's diseases: a critical analysis on mechanistic insight

Neurodegenerative disorders occur when nerve cells in the brain or peripheral nervous system partial or complete fail in their functions and sometimes even die due to some injuries or aging. Neurodegenerative disorders such as Alzheimer's Disease (AD) and Parkinson's Disease (PD), have been majorly resulted due to degeneration of neurons and neuroinflammation progressively. There are many similarities that correlates both AD and PD on a cellular and sub-cellular level. Therefore, a hope for therapeutic advancement for simultaneous upgradation in both the diseases are directly depending on the discovery of common mechanism at molecular and cellular level. Recent and past evidences from scientific literature supporting the efficacy of plants flavonoids in treatment and protection of both AD and PD. Further, dietary flavones, specially Heptamethoxyflavone, Kaempferitrin, Vitexin and Amentoflavone gains recently much more attention for producing many health beneficiary effects including neuroprotection. Despite of these evidence a detailed updated overview of neuroprotective effects against both AD and PD by Heptamethoxyflavone, Kaempferitrin, Vitexin and Amentoflavone are still missing. In this context several published studies were assessed by using various online electronic search engines/databases to meet the objective from 1981 to 2021 (Approx. 224). Therefore, present review was designed to deliver the detailed description on these flavones including therapeutic benefits in AD, PD and other CNS complications with critical analysis on underlying mechanisms.

UHPLC/MS and NMR-Based Metabolomic Analysis of Dried Water Extract of Citrus-Type Crude Drugs

Citrus-type crude drugs (CCDs) are commonly used to formulate decoctions in Kampo formula (traditional Japanese medicine). Our previous study reported metabolomic analyses for differentiation of the methanol extracts of Citrus-type crude drugs (CCDs) using ultra-HPLC (UHPLC)/MS, and ¹³C- and ¹H-NMR. The present study expanded the scope of its application by analyzing four CCD water extracts (Kijitsu, Tohi, Chimpi, and Kippi); these CCDs are usually used as decoction ingredients in the Kampo formula. A principal component analysis score plot of processed UPLC/MS and NMR analysis data indicated that the CCD water extracts could be classified into three groups. The loading plots showed that naringin and neohesperidin were the distinguishing components. Three primary metabolites, α-glucose, β-glucose, and sucrose were identified as distinguishing compounds by NMR spectroscopy. During the preparation of CCD dry extracts, some compounds volatilized or decomposed. Consequently, fewer compounds were detected than in our previous studies using methanol extract. However, these results suggested that the combined NMR- and LC/MS-based metabolomics can discriminate crude drugs in dried water extracts of CCDs.

Polymethoxyflavones in orange peel extract prevent skeletal muscle damage induced by eccentric exercise in rats

Polymethoxyflavones (PMFs) contained in the peel of citrus fruits have anti-inflammatory, anticancer, and antidepressant effects. However, their effects on skeletal muscle are unknown. We investigated whether PMFs could prevent skeletal muscle damage induced by eccentric exercise in rats. Downhill running for 90 min increased the levels of the inflammatory cytokines, monocyte chemotactic protein-1 (MCP-1), and interleukin-1β (IL-1β) in skeletal muscles, especially in vastus lateralis, and the plasma creatine kinase levels. These increases were attenuated by a single oral administration of orange peel extract (OPE) 30 min before downhill running. A mixture of nobiletin, sinensetin, 3,5,6,7,8,3',4'-heptamethoxyflavone, and tangeretin, which are the major PMFs of OPE, also showed similar effects on muscle damage. These results suggest that OPE has a protective effect against eccentric exercise-induced skeletal muscle damage, and that the effects may be attributed to the 4 major PMFs.

[Search for Neuroprotective Compounds -From 4-Methycatechol to Citrus Compounds]

In the 1980s, the authors developed the enzyme immunoassay (EIA) system for mouse nerve growth factor (NGF) to clarify its important physiological roles. Our EIA system was a new and powerful tool for measurement of extremely low levels of NGF in vitro and in vivo, and it contributed to investigation into the regulatory mechanism of NGF synthesis. After that, we demonstrated that the compounds with a low molecular weight, such as 4-methylcatechol, which elicit stimulatory activity toward NGF synthesis, were useful and practical for therapeutic purposes; as NGF has potent activity on neuronal degeneration in both the central nervous system (CNS) and the peripheral nervous system. Since 2008, we have been searching for and isolating neuroprotective component(s) from citrus peels. As a result, our study revealed that 1) 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF) has neuroprotective ability in the CNS by inducing brain-derived neurotrophic factor (BDNF) and by suppressing inflammation; 2) auraptene (AUR) also has neuroprotective ability in the CNS by suppressing inflammation and by probably inducing neurotrophic factor(s). As the content of AUR in the peels of Kawachi Bankan is exceptionally high, 1) we found this peel powder to exert neuroprotective effects in the brain of various pathological model mice; 2) some of the AUR transited from the peel to the juice during the squeezing process to obtain the juice. Therefore, K. Bankan juice, which is enriched in AUR by adding peel paste to the raw juice, was shown to be practical for suppression of cognitive dysfunction of aged healthy volunteers.

Isolation and Characterization of Neuroprotective Components from Citrus Peel and Their Application as Functional Food

The elderly experience numerous physiological alterations. In the brain, aging causes degeneration or loss of distinct populations of neurons, resulting in declining cognitive function, locomotor capability, etc. The pathogenic factors of such neurodegeneration are oxidative stress, mitochondrial dysfunction, inflammation, reduced energy homeostatis, decreased levels of neurotrophic factor, etc. On the other hand, numerous studies have investigated various biologically active substances in fruit and vegetables. We focused on the peel of citrus fruit to search for neuroprotective components and found that: 1) 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF) and auraptene (AUR) in the peel of Kawachi Bankan (Citrus kawachiensis) exert neuroprotective effects; 2) both HMF and AUR can pass through the blood-brain barrier, suggesting that they act directly in the brain; 3) the content of AUR in the peel of K. Bankan was exceptionally high, and consequently the oral administration of the dried peel powder of K. Bankan exerts neuroprotective effects; and 4) intake of K. Bankan juice, which was enriched in AUR by adding peel paste to the raw juice, contributed to the prevention of cognitive dysfunction in aged healthy volunteers. This review summarizes our studies in terms of the isolation/characterization of HMF and AUR in K. Bankan peel, analysis of their actions in the brain, mechanisms of their actions, and trials to develop food that retains their functions.

Beneficial Effects of Citrus-Derived Polymethoxylated Flavones for Central Nervous System Disorders

The number of patients with central nervous system disorders is increasing. Despite diligent laboratory and clinical research over the past 30 years, most pharmacologic options for the prevention and long-term treatment of central nervous system disorders and neurodegenerative disorders have been unsuccessful. Therefore, the development of drugs and/or functional foods to prevent the onset of neurodegenerative disorders is highly expected. Several reports have shown that polymethoxylated flavones (PMFs) derived from citrus fruit, such as nobiletin, tangeretin, and 3,3',4',5,6,7,8-heptamethoxyflavone, are promising molecules for the prevention of neurodegenerative and neurological disorders. In various animal models, PMFs have been shown to have a neuroprotective effect and improve cognitive dysfunction with regard to neurological disorders by exerting favorable effects against their pathological features, including oxidative stress, neuroinflammation, neurodegeneration, and synaptic dysfunction as well as its related mechanisms. In this review, we describe the profitable and ameliorating effects of citrus-derived PMFs on cognitive impairment and neural dysfunction in various rat and murine models or in several models of central nervous system disorders and identify their mechanisms of action.

[The Search for Citrus Components with Neuroprotective and Anti-dementia Effects in the Mouse Brain]

Citrus kawachiensis (Kawachi Bankan), is a citrus species grown in Ehime, Japan, and its peel is abundant in 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF). We have recently revealed that HMF, one of the citrus flavonoids, has anti-inflammatory activity and neuroprotective abilities in the brain against global cerebral ischemia. HMF rescued neuronal cell death in the hippocampus and suppressed the activation of microglia, whose activation have been shown to significantly aggravate neurological deficit scores for ischemic mice. In the Y-maze test, HMF showed protection against ischemia-induced short-term memory dysfunction; in addition, HMF enhanced the expression of brain-derived neurotrophic factor and accelerated neurogenesis in the hippocampus. Similarly, the powder of the peel of C. kawachiensis showed anti-inflammatory activity and neuroprotective abilities in the ischemic brain. To further examine the effect of the peel of C. kawachiensis, we administered it to senescence-accelerated-mouse prone 8 (SAMP8) mice, which show memory impairment and brain inflammation, tau hyperphosphorylation, and neuronal dysfunction. The C. kawachiensis treatment inhibited microglial activation and the hyperphosphorylation of tau protein in hippocampal neurons, and also relieved the suppression of neurogenesis in the dentate gyrus of the hippocampus in SAMP8. These results suggest that HMF and the peel of C. kawachiensis have potential effects as neuroprotective and anti-dementia agents.

Intracerebroventricular microinjection of kaempferol on memory retention of passive avoidance learning in rats: involvement of cholinergic mechanism(s)

Purpose of the study: Kaempferol (KM) is a flavonoid found in plant-derived foods and medicinal plants. Recently, it is well established that KM plays a protective role to develop Alzheimer's disease. The current study aimed at evaluating the effect of intracerebroventricular micro-injection of KM on memory retention of passive avoidance learning (MRPAM) and identifying the potentially related cholinergic mechanisms (ChMs) in rats. Materials and methods: In the current study, male Wistar rats randomly divided into control, vehicle and KM (10, 20 and 40 μg/rat) groups. Moreover, MRPAM was evaluated by shuttle box test. The role of ChM was studied using non-selective and selective acetylcholine antagonists (scopolamine [SCN], 4-DAMP and methoctramine [MN], respectively) as well as pirenzepine (PZ) in combination with KM. Results: The employment of KM (40 μg/rat) improved the SCN-induced memory impairment in MRPAM. Co-treatment with KM (40 μg/rat) plus 4-DAMP significantly increased the step-through latency (STL, P < 0.05; 167 ± 28 s) and decreased the total dark chamber (TDC, P < 0.05; 121 ± 31 s) compared with those of the 4-DAMP group (STL: 75 ± 13 s; TDC: 178 ± 46 s). Co-treatment with KM (40 μg/rat) plus PZ attenuated STL, and also increased TDC (P < 0.01; 220 ± 28 s) compared with those of the PZ group. Co-treatment with KM (10 and 20 μg/rat) and MN increased STL (P < 0.05), and deceased TDC compared with those of the MN group (P < 0.01). Conclusions: Totally, the results of the present study showed that cholinergic system may be involved in improving effect of KM on SCN-induced memory impairment.

Citrus flavonoid 3,5,6,7,8,3',4'-heptamethoxyflavone induces BDNF via cAMP/ERK/CREB signaling and reduces phosphodiesterase activity in C6 cells

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is associated with onset of several central nervous system disorders, e.g., Parkinson's disease, Alzheimer's disease, depression, epilepsy, and chronic pain. In our previous in vivo studies using ischemic and depression mouse models, we revealed that citrus flavonoid 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF) exerts neuroprotective effects by enhancing the expression of BDNF in astrocytes within the hippocampus. Therefore, in the present study, we examined the mechanism of BDNF induction by HMF in vitro using rat C6 glioma cells.

METHODS

C6 glioma cells were treated with HMF (10 μM) or HMF + U0126 (10 μM), HMF + H89 (1 μM), or HMF + K252a (200 nM) for 48 h. The protein level of mature BDNF (m-BDNF), phosphorylated-ERK (p-ERK) and phosphorylated-cAMP-response element binding protein (p-CREB) were measured using western blot analysis. To clarify the mechanism of HMF for increasing m-BDNF, the inhibitory effect of phosphodiesterase 4B (PDE4B) and PDE4D, and intracellular cAMP levels were examined by ELISA.

RESULTS

Our findings revealed that the m-BDNF-inducing activity of HMF was abolished by U0126 but not by H89 or K252a. HMF was found to phosphorylate (activate) ERK and cAMP-response element binding protein (CREB), a BDNF transcription factor. HMF inhibited PDE4B and PDE4D activity. Moreover, 10 μM HMF elevated intracellular cAMP levels in C6 cells.

CONCLUSIONS

These findings suggest that HMF might exert its neuroprotective effects by inducing m-BDNF expression in C6 cells, model cell line of astrocytes, via the activation of cAMP/ERK/CREB signaling and inhibiting PDE4B or PDE4D.

Identification of sinensetin and nobiletin as major antitrypanosomal factors in a citrus cultivar

Cases of human African trypanosomiasis caused by infection with a protozoan parasite, Trypanosoma brucei, are decreasing due to enhanced surveillance and control. However, effective and safe treatments for this disease are still needed. In this study, we investigated the antitrypanosomal activity of citrus fruit peel. When 19 citrus cultivars were examined for activity against T. brucei in vitro, significant activities were observed in four closely related cultivars and a distantly related one. Among these five cultivars, "Setoka" was selected for identification of its active components due to exhibiting the highest activity. Solvent extraction and gel filtration followed by preparative thin-layer chromatography succeeded in isolating two compounds exhibiting IC₅₀s of 4.8 and 2.4 μg/mL, respectively. The spectral data of these two compounds were well consistent with those of sinensetin and nobiletin belonging to the class of polymethoxyflavones. Authentic compounds also showed similar IC₅₀s. These results indicate that the two polymethoxyflavones are the major active components involved in the inhibition of T. brucei proliferation and are abundant in Setoka cultivar peel compared with the levels in the other cultivars. Setoka peel and the naturally occurring polymethoxyflavones might serve as dietary components imparting resistance to T. brucei.

Inhibitory Effects of Auraptene and Naringin on Astroglial Activation, Tau Hyperphosphorylation, and Suppression of Neurogenesis in the Hippocampus of Streptozotocin-Induced Hyperglycemic Mice

Auraptene, a citrus-related compound, exerts anti-inflammatory effects in peripheral tissues, and we demonstrated these effects in the brains of a lipopolysaccharide-injected systemic inflammation animal model and a brain ischemic mouse model. Naringin, another citrus-related compound, has been shown to exert antioxidant effects in several animal models. Hyperglycemia induces oxidative stress and inflammation and causes extensive damage in the brain; therefore, we herein evaluated the anti-inflammatory and other effects of auraptene and naringin in streptozotocin-induced hyperglycemic mice. Both compounds inhibited astroglial activation and the hyperphosphorylation of tau at 231 of threonine in neurons, and also recovered the suppression of neurogenesis in the dentate gyrus of the hippocampus in hyperglycemic mice. These results suggested that auraptene and naringin have potential effects as neuroprotective agents in the brain.

Suppressive effects of the peel of Citrus kawachiensis (Kawachi Bankan) on astroglial activation, tau phosphorylation, and inhibition of neurogenesis in the hippocampus of type 2 diabetic db/db mice

We previously reported that the dried peel powder of Citrus kawachiensis exerted anti-inflammatory effects in the brain in several animal models. Hyperglycemia induces inflammation and oxidative stress and causes massive damage in the brain; therefore, we herein examined the anti-inflammatory and other effects of the dried peel powder of C. kawachiensis in the streptozotocin-induced hyperglycemia mice model and in the type 2 diabetic db/db mice model. The C. kawachiensis administration inhibited microglial activation in the hippocampus in the streptozotocin-injected mice. Moreover, The C. kawachiensis treatment inhibited astroglial activation in the hippocampus and the hyperphosphorylation of tau at 231 of threonine and 396 of serine in hippocampal neurons, and also relieved the suppression of neurogenesis in the dentate gyrus of the hippocampus in the db/db mice. It was suggested that the dried peel powder of C. kawachiensis exerts anti-inflammatory and neuroprotective effects in the brain.

Neuroprotective effect of Citrus kawachiensis (Kawachi Bankan) peels, a rich source of naringin, against global cerebral ischemia/reperfusion injury in mice

Cerebral ischemia/reperfusion is known to induce the generation of reactive oxygen species and inflammatory responses. Numerous studies have demonstrated that naringin (NGIN) has anti-oxidant and anti-inflammatory properties. We previously reported that Citrus kawachiensis contains a large quantity of NGIN in its peel. In the present study, we orally (p.o.) administered dried peel powder of C. kawachiensis to mice of a transient global ischemia model and found in the hippocampus region that it 1) suppressed neuronal cell death, 2) reversed the reduction in the level of phosphorylated calcium-calmodulin-dependent protein kinase II, 3) had the tendency to reverse the reduction in the level of glutathione, and 4) blocked excessive activation of microglia and astrocytes. These results suggested that the dried peel powder of C. kawachiensis had a neuroprotective effect against ischemic brain via anti-oxidative and anti-inflammatory effects. We also showed that these effects of the dried peel powder were more powerful than those obtained with a comparable amount of NGIN alone.

3,5,6,7,8,3',4'-Heptamethoxyflavone, a Citrus Flavonoid, Inhibits Collagenase Activity and Induces Type I Procollagen Synthesis in HDFn Cells

Citrus fruits contain various types of flavonoids with powerful anti-aging and photoprotective effects on the skin, and have thus been attracting attention as potential, efficacious skincare agents. Here, we aimed to investigate the chemical composition of Citrus unshiu and its protective effects on photoaging. We isolated and identified a bioactive compound, 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF), from C. unshiu peels using ethanol extraction and hexane fractionation. HMF inhibited collagenase activity and increased type I procollagen content in UV-induced human dermal fibroblast neonatal (HDFn) cells. HMF also suppressed the expression of matrix metalloproteinases 1 (MMP-1) and induced the expression of type I procollagen protein in UV-induced HDFn cells. Additionally, HMF inhibited ultraviolet B (UVB)-induced phosphorylation of the mitogen-activated protein kinases (MAPK) cascade signaling components-ERK, JNK, and c-Jun-which are involved in the induction of MMP-1 expression. Furthermore, HMF affected the TGF-β/Smad signaling pathway, which is involved in the regulation of type I procollagen expression. In particular, HMF induced Smad3 protein expression and suppressed Smad7 protein expression in UV-induced HDFn cells in a dose-dependent manner. These findings suggest a role for Citrusunshiu in the preparation of skincare products in future.

The peel of Citrus kawachiensis (kawachi bankan) ameliorates microglial activation, tau hyper-phosphorylation, and suppression of neurogenesis in the hippocampus of senescence-accelerated mice

We previously reported that the dried peel powder of Citrus kawachiensis, one of the citrus products of Ehime, Japan, exerted anti-inflammatory effects in the brain of a lipopolysaccharide-injected systemic inflammation animal model. Inflammation is one of the main mechanisms underlying aging in the brain; therefore, we herein evaluated the anti-inflammatory and other effects of the dried peel powder of C. kawachiensis in the senescence-accelerated mouse-prone 8 (SAMP8) model. The C. kawachiensis treatment inhibited microglial activation in the hippocampus, the hyper-phosphorylation of tau at 231 of threonine in hippocampal neurons, and ameliorated the suppression of neurogenesis in the dentate gyrus of the hippocampus. These results suggest that the dried peel powder of C. kawachiensis exert anti-inflammatory and neuroprotective effects.

Antidepressant Flavonoids and Their Relationship with Oxidative Stress

Depression is a serious disorder that affects hundreds of millions of people around the world and causes poor quality of life, problem behaviors, and limitations in activities of daily living. Therefore, the search for new therapeutic options is of high interest and growth. Research on the relationship between depression and oxidative stress has shown important biochemical aspects in the development of this disease. Flavonoids are a class of natural products that exhibit several pharmacological properties, including antidepressant-like activity, and affects various physiological and biochemical functions in the body. Studies show the clinical potential of antioxidant flavonoids in treating depressive disorders and strongly suggest that these natural products are interesting prototype compounds in the study of new antidepressant drugs. So, this review will summarize the chemical and pharmacological perspectives related to the discovery of flavonoids with antidepressant activity. The mechanisms of action of these compounds are also discussed, including their actions on oxidative stress relating to depression.

Neurotrophic function of phytochemicals for neuroprotection in aging and neurodegenerative disorders: modulation of intracellular signaling and gene expression

Bioactive compounds in food and beverages have been reported to promote health and prevent age-associated decline in cognitive, motor and sensory activities, and emotional function. Phytochemicals, a ubiquitous class of plant secondary metabolites, protect neuronal cells by interaction with cellular activities, in addition to the antioxidant and anti-inflammatory function. In aging and age-associated neurodegenerative disorders, phytochemicals protect neuronal cells by neurotrophic factor-mimic activity, in addition to suppression of apoptosis signaling in mitochondria. This review presents the cellular mechanisms underlying anti-apoptotic function and neurotrophic function of phytochemicals in the brain. Phytochemicals bind to receptors of neurotrophic factors, and also receptors for γ-aminobutyric acid, acetylcholine, serotonin, and glutamate and estrogen, and activate downstream signal pathways. Phytochemicals also directly intervene intracellular signaling molecules to modify the brain function. Finally, phytochemicals enhance the endogenous biosynthesis of genes coding anti-apoptotic Bcl-2 and neurotrophic factors, such as brain-derived and glial cell line-derived neurotrophic factor. The gene induction may play a major role in the neuroprotective function of dietary compounds shown by epidemiological studies. Quantitative measurement of neurotrophic factors induced by phytochemicals in the serum, cerebrospinal fluid, and other clinical samples is proposed as a surrogate assay method to evaluate the neuroprotective potency. Development of novel neuroprotective compounds is expected among compounds chemically synthesized from the brain-permeable basic structure of phytochemicals.

Permeation of Polymethoxyflavones into the Mouse Brain and Their Effect on MK-801-Induced Locomotive Hyperactivity

Accumulating data have indicated that citrus polymethoxyflavones (PMFs) have the ability to affect brain function. In the present study, we showed that 3,5,6,7,8,3',4'-heptamethoxy- flavone (HMF) given intraperitoneally to mice was immediately detected in the brain and that the permeability of the brain tissues to it was significantly higher than that of other citrus PMFs (nobiletin, tangeretin, and natsudaidain). The permeation of these PMFs into the brain well correlated with their abilities to suppress MK-801-induced locomotive hyperactivity, suggesting that HMF had the ability to act directly in the brain. We also obtained data suggesting that the suppressive effect of HMF on MK-801-induced locomotive hyperactivity was mediated by phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2) in the hippocampus.

Involvement of the GABAergic system in the neuroprotective and sedative effects of acacetin 7-O-glucoside in rodents

Purpose: Characterization of sedative, possible anticonvulsant, and protective effects of Acacetin-7-O-glucoside (7-ACAG).

Methods: 7-ACAG was separated and its purity was analyzed. Its sedative and anti-seizure effects (1, 10, 20, and 40 mg/kg) were evaluated in male mice. Synaptic responses were acquired from area CA1 of hippocampal slices obtained from male Wistar rats. Rats were subjected to stereotaxic surgeries to allow Electroencephalographic (EEG) recordings. Functional recovery was evaluated by measuring the time rats spent in completing the motor task. Then the rats were subjected to right hemiplegia and administered 7-ACAG (40 mg/kg) 1 h or 24 h after surgery. Brains of each group of rats were prepared for histological analysis.

Results: Effective sedative doses of 7-ACAG comprised those between 20 and 40 mg/kg. Latency and duration of the epileptiform crisis were delayed by this flavonoid. 7-ACAG decreased the synaptic response in vitro, similar to Gamma-aminobutyric acid (GABA) effects. The flavonoid facilitated functional recovery. This data was associated with preserved cytoarchitecture in brain cortex and hippocampus.

Conclusions: 7-ACAG possesses anticonvulsive and sedative effects. Results suggest that GABAergic activity and neuroprotection are involved in the mechanism of action of 7-ACAG and support this compound’s being a potential drug for treatment of anxiety or post-operative conditions caused by neurosurgeries.

3,5,6,7,8,3',4'-Heptamethoxyflavone reduces interleukin-4 production in the spleen cells of mice

In our previous studies, we reported anti-inflammatory functions of 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF), which is a polymethoxyflavone rich in various citrus fruits. Here, we investigated the immunomodulatory function of HMF in mice. HMF administration (50 mg/kg, i.p., 2 times/week) tended to reduce the production of antigen-specific IgE induced by ovalbumin in combination with aluminum hydroxide gel. Fluorescence-activated cell sorting analysis revealed the reduction of interleukin-4(+)CD4(+) spleen cells and sustained presence of interferon-γ(+)CD4(+) spleen cells in mice administered HMF, whereas the ratio of CD4(+)CD8(-) versus CD4(-)CD8(+) spleen cells was not affected. Interleukin-4 release from CD3/CD28-stimulated spleen cells of mice administered HMF was reduced, whereas interferon-γ release was not affected. These results suggest that HMF has an immunomodulatory function via reduced interleukin-4 expression.

3,5,6,7,8,3',4'-Heptamethoxyflavone, a Citrus Flavonoid, Ameliorates Corticosterone-Induced Depression-like Behavior and Restores Brain-Derived Neurotrophic Factor Expression, Neurogenesis, and Neuroplasticity in the Hippocampus

We previously reported that the citrus flavonoid 3,5,6,7,8,3′,4′-heptamethoxyflavone (HMF) increased the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus of a transient global ischemia mouse model. Since the BDNF hypothesis of depression postulates that a reduction in BDNF is directly involved in the pathophysiology of depression, we evaluated the anti-depressive effects of HMF in mice with subcutaneously administered corticosterone at a dose of 20 mg/kg/day for 25 days. We demonstrated that the HMF treatment ameliorated (1) corticosterone-induced body weight loss, (2) corticosterone-induced depression-like behavior, and (3) corticosterone-induced reductions in BDNF production in the hippocampus. We also showed that the HMF treatment restored (4) corticosterone-induced reductions in neurogenesis in the dentate gyrus subgranular zone and (5) corticosterone-induced reductions in the expression levels of phosphorylated calcium-calmodulin-dependent protein kinase II and extracellular signal-regulated kinase1/2. These results suggest that HMF exerts its effects as an anti-depressant drug by inducing the expression of BDNF.

Disease chemopreventive effects and molecular mechanisms of hydroxylated polymethoxyflavones

Recent increasing attention in research of polymethoxyflavones (PMFs) from Citrus genus because of their wide range of biological properties has been reported in various studies. Hydroxylated PMFs are unique flavones and recognized as the methoxy group of PMFs that is substituted for hydroxyl one. Hydroxylated PMFs are naturally existed in citrus peel and other plants as well as occurred as metabolites of their PMFs counterparts. Several in vitro and in vivo studies have documented the chemopreventive effects of hydroxylated PMFs including anti-cancer, anti-inflammation, anti-atherosclerosis, and neuroprotection. They function to regulate cell death, proliferation, differentiation, repair, and metabolism through acting on modulation of signaling cascade, gene transcription, and protein function and enzyme activity. The mechanisms of action of hydroxylated PMFs in disease chemoprevention depend on their structure, the number, and position of hydroxyl group. Although the efficacy of hydroxylated PMFs in chemoprevention and the oral bioavailability requires further investigation, they still provide great promise for improving human health. This review highlights the recent published data of hydroxylated PMFs with chemopreventive potential and the underlying mechanism involved.

3,5,6,7,8,3',4'-heptamethoxyflavone, a citrus polymethoxylated flavone, attenuates inflammation in the mouse hippocampus

Citrus polymethoxylated flavones (PMFs) have recently been shown to suppress inflammation in peripheral tissues. In the present study, we investigated the effects of 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF), one of the PMFs, on inflammation in the brain in vivo using mice injected intrahippocampally with lipopolysaccharide (LPS). We demonstrated that subcutaneously injected HMF suppressed: (1) LPS-induced losses in body weight; (2) LPS-induced microglial activation in the hippocampus; and (3) LPS-induced interleukin-1β mRNA expression in the hippocampus. These results suggest that HMF has the ability to reduce neuroinflammation in the brain.

Edaravone enhances brain-derived neurotrophic factor production in the ischemic mouse brain

Edaravone, a clinical drug used to treat strokes, protects against neuronal cell death and memory loss in the ischemic brains of animal models through its antioxidant activity. In the present study, we subcutaneously administrated edaravone to mice (3 mg/kg/day) for three days immediately after bilateral common carotid artery occlusion, and revealed through an immunohistochemical analysis that edaravone (1) accelerated increases in the production of brain-derived neurotrophic factor (BDNF) in the hippocampus; (2) increased the number of doublecortin-positive neuronal precursor cells in the dentate gyrus subgranular zone; and (3) suppressed the ischemia-induced inactivation of calcium-calmodulin-dependent protein kinase II in the hippocampus. We also revealed through a Western blotting analysis that edaravone (4) induced the phosphorylation of cAMP response element-binding (CREB), a transcription factor that regulates BDNF gene expression; and (5) induced the phosphorylation of extracellular signal-regulated kinases 1/2, an upstream signal factor of CREB. These results suggest that the neuroprotective effects of edaravone following brain ischemia were mediated not only by the elimination of oxidative stress, but also by the induction of BDNF production.