Effects of baicalein on β-amyloid peptide-(25–35)-induced amnesia in mice

Scutellaria baicalensis and its constituents baicalin and baicalein as antidotes or protective agents against chemical toxicities: a comprehensive review

Scutellaria baicalensis (SB), also known as the Chinese skullcap, has a long history of being used in Chinese medicine to treat a variety of conditions ranging from microbial infections to metabolic syndrome and malignancies. Numerous studies have reported that treatment with total SB extract or two main flavonoids found in its root and leaves, baicalin (BA) and baicalein (BE), can prevent or alleviate the detrimental toxic effects of exposure to various chemical compounds. It has been shown that BA and BE are generally behind the protective effects of SB against toxicants. This paper aimed to review the protective and therapeutic effects of SB and its main components BA and BE against chemical compounds that can cause intoxication after acute or chronic exposure and seriously affect different vital organs including the brain, heart, liver, and kidneys. In this review paper, we had a look into a total of 221 in vitro and in vivo studies from 1995 to 2021 from the scientific databases PubMed, Scopus, and Web of Science which reported protective or therapeutic effects of BA, BE, or SB against drugs and chemicals that one might be exposed to on a professional or accidental basis and compounds that are primarily used to simulate disease models. In conclusion, the protective effects of SB and its flavonoids can be mainly attributed to increase in antioxidants enzymes, inhibition of lipid peroxidation, reduction of inflammatory cytokines, and suppression of apoptosis pathway.

Baicalein 5,6-Dimethyl Ether Prevents Memory Deficits in the Scopolamine Zebrafish Model by Regulating Cholinergic and Antioxidant Systems

Baicalein 5,6-dimethyl ether, a bioactive flavonoid isolated for the first time from Alnus rugosa, was explored for its capability to relieve memory deficits and decrease oxidative stress. We examined the neuropharmacological effects of baicalein 5,6-dimethyl ether on scopolamine (Sco)-induced zebrafish (Danio rerio) anxiety, amnesia, and brain oxidative stress and attempted to elucidate the underlying mechanisms. Anxiety-like behavior, exploratory behavior, and memory performance were measured using novel tank-diving test (NTT), Y-maze, and novel object recognition (NOR) tests. For 10 days, baicalein 5,6-dimethyl ether (1, 3, and 5 µg/L) was administered through immersion, whereas Sco (100 μM) was delivered 30 min before behavioral tests. Treatment with baicalein 5,6-dimethyl ether reduced anxiety and memory impairment, and increased exploratory behavior in specific tests, along with significant protection from neuronal oxidative stress in the brain tissue of Sco-treated zebrafish. Antioxidant and anti-acetylcholinesterase (AChE) activities of baicalein 5,6-dimethyl ether in the Sco-induced zebrafish were further confirmed using in vivo assays. In Sco-treated zebrafish, baicalein 5,6-dimethyl ether regulated cholinergic function by inhibiting AChE activity. Baicalein 5,6-dimethyl ether may be a promising candidate compound for treating anxiety and amnesia by restoring cholinergic activity and reducing brain oxidative stress, according to our findings.

Natural Products for the Treatment of Neurodegenerative Diseases

Neurodegenerative diseases are a heterogeneous group of disorders characterized by the progressive degeneration of the structure and function of the central nervous system or peripheral nervous system. Alzheimer's Disease (AD), Parkinson's Disease (PD) and Spinal Cord Injury (SCI) are the common neurodegenerative diseases, which typically occur in people over the age of 60. With the rapid development of an aged society, over 60 million people worldwide are suffering from these uncurable diseases. Therefore, the search for new drugs and therapeutic methods has become an increasingly important research topic. Natural products especially those from the Traditional Chinese Medicines (TCMs), are the most important sources of drugs, and have received extensive interest among pharmacist. In this review, in order to facilitate further chemical modification of those useful natural products by pharmacists, we will bring together recent studies in single natural compound from TCMs with neuroprotective effect.

Baicalein protects PC12 cells from Aβ25-35-induced cytotoxicity via inhibition of apoptosis and metabolic disorders

AIMS

This study aimed to explore the protective effects and possible mechanisms of baicalein on Aβ_25-35-induced toxicity.

MAIN METHODS

Thioflavin-T (Th-T) dye was used to determine the effects of baicalein on Aβ_25-35 aggregation in vitro. PC12 cells were stimulated with Aβ_25-35, then the effects of baicalein on apoptosis, mitochondrial membrane potential (MMP), adenosine triphosphate (ATP), mitochondrial respiratory complex I, reactive oxygen species (ROS) and nitric oxide (NO) levels were determined. Moreover, LC-MS metabolomics approach was used to detect metabolic changes induced by baicalein in Aβ_25-35-injured PC12 cells.

KEY FINDINGS

The results showed that baicalein could inhibit the aggregation of Aβ_25-35 in vitro. Furthermore, pretreatment with baicalein significantly prevented Aβ_25-35-induced cell apoptosis, as manifested by increasing the levels of MMP, ATP and mitochondrial respiratory complex I, decreasing the contents of ROS and NO. LC-MS metabolomics revealed that baicalein can regulate 5 metabolites, mainly involving two metabolic pathways, arginine and proline metabolism, nicotinate and nicotinamide metabolism.

SIGNIFICANCE

Our study revealed that baicalein has a protective effect on Aβ_25-35-induced neurotoxicity in PC12 cells, which may be related to inhibition of apoptosis and metabolic disorders.

Baicalein Inhibits Neuroapoptosis Via Pathways in Sevoflurane Induced Rats

Background

Baicalein, a bioactive flavonoid was explored for its capability to attenuate sevoflurane induced neuronal apoptosis and to improve behavioural and cognitive impairments. Sevoflurane is a frequently used inhalation anesthetic in neonates and children. Neonatal sevoflurane exposure causes widespread neurodegeneration and cognitive impairments. Development of compounds that could effectively prevent/reduce the adverse effects is of tremendous medical value.

Methods

Isolated groups of neonatal rats were regulated with baicalein (25, 50 or 100 mg/kg b.wt) from postnatal day 3 (P3) to P21 and were exposed to sevoflurane (3%; 6 h) on P7. Results: Baicalein inhibited sevoflurane induced neuroapoptosis significantly as assessed by TUNEL assay. The raised levels of cleaved caspase-3, Bad and Bax were down-regulated by baicalein with enhanced Bcl-2, Bcl-xL, xIAP, c-IAP-1, c-IAP-2 and survivin expression. Baicalein regulated JNK/ERK signalling and also activated the PI3K/Akt pathway effectively as evident from the increased Akt, phospho-Akt, GSK-3β, phospho-GSK-3β levels. Baicalein, also improved the behaviour of animals in open filed and olfactory tests. The freezing responses and the performance in Morris Water Maze tests were enhanced.

Conclusion

Baicalein reduced neurodegeneration and improved learning and memory retention of rats and as well modulated PI3/Akt/GSK-3β and JNK/ERK signalling pathways.

Baicalein as a potent neuroprotective agent: A review

In recent times, neurodegenerative diseases are the most challenging global health problems. Neuronal cell death or damage is a key factor for many neurodegenerative disorders. Therefore, there has been a growing interest in the development of effective neuroprotective agents, especially from natural sources. In particular, phytochemicals have shown high efficacy with low side effects in various in vitro and in vivo studies. In the various phytoconstituents, flavonoids are important bioactive products and mainly found in various vegetables and fruits. Among them, baicalein is one of the important flavones, which is mainly found in the root of Scutellaria baicalensis Georgi. A number of studies have reported that baicalein has potent neuroprotective properties under in vitro as well as in vivo systems. Hence, the purpose of this paper is to provide a review of the existing literature in connection with the neuroprotective effects of baicalein and its molecular mechanisms of action. The current review highlights could be useful to identify novel therapeutic agents in relation to the treatment of neurotoxicity-mediated diseases.

Therapeutic Potential of Baicalein in Alzheimer's Disease and Parkinson's Disease

Alzheimer's disease and Parkinson's disease are the two most common, progressive central neurodegenerative diseases affecting the population over the age of 60 years. Apart from treatments that temporarily improve symptoms, there is no medicine currently available to inhibit or reverse the progression of Alzheimer's disease and Parkinson's disease. In traditional Chinese medicine, the root of Scutellaria baicalensis Georgi is a classic compatible component in the decoction of herbal medicine used for treating central nervous system diseases. Modern pharmacokinetic studies have confirmed that baicalein (5,6,7-trihydroxyflavone) is a major bioactive flavone constituent root of S. baicalensis Georgi. Studies showed that baicalein possesses a range of key pharmacological properties, such as reducing oxidative stress, anti-inflammatory properties, inhibiting aggregation of disease-specific amyloid proteins, inhibiting excitotoxicity, stimulating neurogenesis and differentiation action, and anti-apoptosis effects. Based on these properties, baicalein shows therapeutic potential for Alzheimer's disease and Parkinson's disease. In this review, we summarize the pharmacological protective actions of baicalein that make it suitable for the treatment of Alzheimer's disease and Parkinson's disease, and discuss the potential mechanisms underlying the effects.

Clinical and Preclinical Cognitive Function Improvement after Oral Treatment of a Botanical Composition Composed of Extracts from Scutellaria baicalensis and Acacia catechu

Dementia and cognitive impairment have become the major concerns worldwide due to a significantly aging population, increasing life span and lack of effective pharmacotherapy. In light of limited pharmaceutical drug choices and the socioeconomic implications of these conditions, the search for safe and effective alternatives from natural sources has gained many attractions within the medical food and dietary supplement industry. Two polyphenol extracts derived from roots of Scutellaria baicalensis and heartwoods of Acacia catechu containing free-B-ring flavonoids and flavans, respectively, were combined into a proprietary blend called UP326. A similar bioflavonoid composition, UP446, has been reported with modulation of pathways related to systemic inflammation. To test the effect of UP326 on memory and learning, a radial arm water maze (RAWM) and contextual fear conditioning (CF) were utilized in aged F344 rats fed with UP326 at doses of 3, 7, and 34 mg/kg for 11 weeks. The 7 and 34 mg/kg dosage groups had significantly fewer errors than aged vehicle control animals and their performance was equivalent to young animal controls. In a separate human clinical trial, test subjects orally given 300 mg of UP326 BID for 30 days showed marked improvement in speed and accuracy of processing complex information in computer tasks and reduced their standard deviation of performance compared to baseline and the placebo group. This data suggest that UP326 may help maintain memory, sustain speed of processing, and reduce the number or memory errors as we age.

Baicalein, a Constituent of Scutellaria baicalensis, Reduces Glutamate Release and Protects Neuronal Cell Against Kainic Acid-Induced Excitotoxicity in Rats

Interest in the health benefits of flavonoids, particularly their effects on neurodegenerative disease, is increasing. This study evaluated the role of baicalein, a flavonoid compound isolated from the traditional Chinese medicine Scutellaria baicalensis, in glutamate release and glutamate neurotoxicity in the rat hippocampus. In the rat hippocampal nerve terminals (synaptosomes), baicalein inhibits depolarization-induced glutamate release, and this phenomenon is prevented by chelating the extracellular Ca[Formula: see text] ions and blocking presynaptic Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel activity. In slice preparations, whole cell patch-clamp experiments revealed that baicalein reduced the frequency of miniature excitatory postsynaptic currents, without affecting their amplitude. In a kainic acid rat model, intraperitoneally administering baicalein to rats before the kainic acid intraperitoneal injection substantially attenuated kainic acid-induced neuronal cell death, c-Fos expression, and the activation of the mammalian target of rapamycin in the hippocampus. This study is the first to demonstrate that the natural compound baicalein inhibits glutamate release from hippocampal nerve terminals, and executes a protective action against kainic acid-induced excitotoxicity in vivo. The findings enhance the understanding of baicalein’s action in the brain, and suggest that this natural compound is valuable for treating brain disorders related to glutamate excitotoxicity.

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.

The flavonoid baicalein rescues synaptic plasticity and memory deficits in a mouse model of Alzheimer's disease

Increasing evidence suggests that disruptions of synaptic functions correlate with the severity of cognitive deficit in Alzheimer's disease (AD). Our previous study demonstrated that baicalein enhances long-term potentiation (LTP) in acute rat hippocampal slices and improves hippocampus-dependent contextual fear conditioning in rats. Given that baicalein possess various biological activities, especially its effects on synaptic plasticity and cognitive function, we examined the effect of baicalein on synaptic function both in vitro and in vivo in AD model. The effect of baicalein on Aβ42 oligomer impaired LTP was investigated by electrophysiological methods. Baicalein was administered orally via drinking water to the APP/PS1 mice and sex- and age-matched wild-type mice. Treatment started at 5 months of age and mice were assessed for cognition and AD-like pathology at 7-month-old. Cognition was analyzed by Morris water maze test, fear conditioning test, and novel object recognition test. Changes in hippocampal 12/15 Lipoxygenase (12/15LO) and glycogen synthase kinase 3β (GSK3β) activity, Aβ production, tau phosphorylation, synaptic plasticity, and dendritic spine density were evaluated. Baicalein prevented Aβ-induced impairments in hippocampal LTP through activation of serine threonine Kinase (Akt) phosphorylation. Long-term oral administration of baicalein inhibited 12/15LO and GSK3β activity, reduced β-secretase enzyme (BACE1), decreased the concentration of total Aβ, and prevented phosphorylation of tau in APP/PS1 mice. Meanwhile, baicalein restored spine number, synaptic plasticity, and memory deficits. Our results strengthen the potential of the flavonoid baicalein as a novel and promising oral bioactive therapeutic agent that prevents memory deficits in AD.

Baicalein protects C6 glial cells against hydrogen peroxide-induced oxidative stress and apoptosis through regulation of the Nrf2 signaling pathway

Baicalein, a flavonoid originally obtained from the roots of Scutellaria baicalensis Georgi, has been reported to possess various biological properties. Although several studies have demonstrated the anti-oxidative activity of baicalein, its neuroprotective mechanisms have not been clearly established. The present study aimed to detect the effects of baicalein against hydrogen peroxide (H2O2)-induced neuronal damage in C6 glial cells and to investigate the molecular mechanisms involved in this process. The results demonstrated that baicalein effectively inhibited H2O2-induced growth and reactive oxygen species (ROS) generation. We noted that Baicalein also attenuated the H2O2‑induced formation of comet tail, phosphorylation of p-γH2A.X, loss of mitochondrial membrane potential (MMP or ΔΨm), and changes to apoptosis‑related protein expression, which suggests that it can prevent H2O2‑induced cellular DNA damage and apoptotic cell death. Furthermore, treatment with baicalein effectively induced the expression of nuclear factor-erythroid 2-related factor 2 (Nrf2) as well as heme oxygenase-1 (HO-1) and thioredoxin reductase 1 (TrxR1) in a concentration and time-dependent manner. Moreover, the protective effects of baicalein against H2O2‑induced DNA damage and apoptosis were abolished by zinc protoporphyrin (ZnPP) IX, a HO-1 inhibitor, and auranofin, a TrxR inhibitor. In addition, we noted that the cytoprotective effects of baicalein were attenuated by transient transfection with Nrf2-specific small interfering RNA (siRNA). The findings of our present study suggest that baicalein enhances cellular antioxidant defense capacity through the inhibition of ROS generation and the activation of the Nrf2 signaling pathway, thus protecting C6 cells from H2O2-induced neuronal damage.

Preventive effect of baicalein on methamphetamine-induced amnesia in the passive avoidance test in mice

BACKGROUND/AIMS

Methamphetamine abuse may produce cognitive impairment. Baicalein, a bioactive flavonoid, has antioxidative, anti-inflammatory and neuroprotective effects. This study examined the effects of baicalein pretreatment on memory performance in the passive avoidance test after either one dose or an acute binge of methamphetamine in Institute of Cancer Research (ICR) mice.

METHODS

Methamphetamine was administered by intraperitoneal (i.p.) injection of either one dose (3 mg/kg) or an acute binge (3 mg/kg, 4 i.p. injections at 2-hour intervals). The effects of baicalein pretreatment (1 mg/kg, i.p.) on methamphetamine-induced changes of locomotor activity and memory performance were compared with those of eticlopride, a selective dopamine D2 receptor antagonist. The effects of baicalein on acute binge methamphetamine-induced oxidative stress (malondialdehyde- and nitrotyrosine-modified protein production) in the mouse hippocampus were also examined.

RESULTS

One-dose methamphetamine treatment (i.p., 30 min before or immediately after the training trial) induced hyperlocomotion and amnesia in mice, which were blocked by eticlopride but not by baicalein pretreatment. The memory performance in mice was impaired 5 days after acute binge methamphetamine, which was significantly attenuated by baicalein but not by eticlopride pretreatment. Baicalein pretreatment also attenuated acute binge methamphetamine-induced oxidative stress in the mouse hippocampus.

CONCLUSIONS

Baicalein exhibits antioxidative and neuroprotective effects in attenuating acute binge methamphetamine-induced memory deficits and oxidative hippocampal damage.

Baicalein ameliorates cognitive deficits in epilepsy-like tremor rat

Baicalein has been shown to possess various pharmacological actions. The current work was designed to assess the neuroprotection of baicalein against cognitive deficits in epilepsy-like tremor rat (TRM). Epileptic characteristics and memory functions were assessed by electroencephalograms recording and Morris water maze test, respectively. The changes of oxidative indicators including malondialdehyde (MDA), catalase (CAT), Cu/Zn-superoxide dismutase (Cu/Zn-SOD), Mn-SOD, glutathione (GSH), glutathione peroxidase (GSH-PX) and 8-isoprostane were measured using corresponding commercial kits. Real-time RT-PCR and immunoassay were employed to detect activities of various inflammatory mediators such as NF-κB p65, TNF-α, IL-1β, IL-6 and IL-10. Western blot analysis was performed to determine heat shock protein (HSP) 70 and mitogen-activated protein kinases (MAPKs) (including ERK, JNK and p38) proteins. Our results illustrated that baicalein significantly ameliorated epileptiform activity and cognitive deficits in TRM. Besides, reduced oxidative stress and inflammatory responses were also found in TRM treated with baicalein. Furthermore, there were evident alterations of HSP70 and MAPK cascades at protein levels after 14-day pretreatment with baicalein. It was concluded that the neuroprotective effect of baicalein against cognitive dysfunction might be associated with suppressing oxidative stress, inhibiting inflammation and mediating HSP70 as well as MAPK cascades in absence-like TRM.

Characterization and uncertainty evaluation of a new certified reference material of baicalein

A new certified reference material (CRM) of baicalein was developed aiming to control the quality of baicalein and relative pharmaceuticals. Sample preparation, homogeneity, stability, value assignment, and uncertainty of a new certified reference material (CRM) of baicalein were presented in this paper. Characterization of the material relied on three different methods, which were differential scanning calorimetry (DSC), coulometric titration method (CT) and mass balance method. DSC and CT were used for purity determination of baicalein firstly. The certified value of baicalein CRM is 99.72% with an expanded uncertainty of 0.25% (k=2). The new CRM of baicalein can be used to validate analytical methods, improve the accuracy of measurement data as well as establish meteorological traceability of analytical results.

Chronic administration of baicalein decreases depression-like behavior induced by repeated restraint stress in rats

Baicalein (BA), a plant-derived active flavonoid present in the root of Scutellaria baicalensis, has been widely used for the treatment of stress-related neuropsychiatric disorders including depression. Previous studies have demonstrated that repeated restraint stress disrupts the activity of the hypothalamic-pituitary-adrenal (HPA) axis, resulting in depression. The behavioral and neurochemical basis of the BA effect on depression remain unclear. The present study used the forced swimming test (FST) and changes in brain neurotransmitter levels to confirm the impact of BA on repeated restraint stress-induced behavioral and neurochemical changes in rats. Male rats received 10, 20, or 40 mg/kg BA (i.p.) 30 min prior to daily exposure to repeated restraint stress (2 h/day) for 14 days. Activation of the HPA axis in response to repeated restraint stress was confirmed by measuring serum corticosterone levels and the expression of corticotrophin-releasing factor in the hypothalamus. Daily BA administration significantly decreased the duration of immobility in the FST, increased sucrose consumption, and restored the stress-related decreases in dopamine concentrations in the hippocampus to near normal levels. BA significantly inhibited the stress-induced decrease in neuronal tyrosine hydroxylase immunoreactivity in the ventral tegmental area and the expression of brain-derived neurotrophic factor (BDNF) mRNA in the hippocampus. Taken together, these findings indicate that administration of BA prior to the repeated restraint stress significantly improves helpless behaviors and depressive symptoms, possibly by preventing the decrease in dopamine and BDNF expression. Thus, BA may be a useful agent for the treatment or alleviation of the complex symptoms associated with depression.

Baicalein reduces β-amyloid and promotes nonamyloidogenic amyloid precursor protein processing in an Alzheimer's disease transgenic mouse model

Baicalein, a flavonoid isolated from the roots of Scutellaria baicalensis, is known to modulate γ-aminobutyric acid (GABA) type A receptors. Given prior reports demonstrating benefits of GABA_A modulation for Alzheimer’s disease (AD) treatment, we wished to determine whether this agent might be beneficial for AD. CHO cells engineered to overexpress wild-type amyloid precursor protein (APP), primary culture neuronal cells from AD mice (Tg2576) and AD mice were treated with baicalein. In the cell cultures, baicalein significantly reduced the production of β-amyloid (Aβ) by increasing APP α-processing. These effects were blocked by the GABA_A antagonist bicuculline. Likewise, AD mice treated daily with i.p. baicalein for 8 weeks showed enhanced APP α-secretase processing, reduced Aβ production, and reduced AD-like pathology together with improved cognitive performance. Our findings suggest that baicalein promotes nonamyloidogenic processing of APP, thereby reducing Aβ production and improving cognitive performance, by activating GABA_A receptors. © 2013 Wiley Periodicals, Inc.

Hippocampal extracellular signal-regulated kinase signaling has a role in passive avoidance memory retrieval induced by GABAA Receptor modulation in mice

Available evidence strongly suggests that the γ-aminobutyric acid type A (GABA(A)) receptor has a crucial role in memory retrieval. However, the signaling mechanisms underlying the role of GABA(A) receptor modulation in memory retrieval are unclear. We conducted one-trial passive avoidance task with pre-retention trial drug administration in the hippocampus to test the effects of GABA(A) receptor modulation on memory retrieval. We further tested the co-involvement of signaling molecules: extracellular signal-regulated kinase (ERK), Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), and cAMP responsive element-binding protein (CREB). First, we observed that the phosphorylation of hippocampal ERK was required for memory retrieval during the task. Accordingly, to investigate whether GABA(A) receptor activation or inhibition induces ERK phosphorylation during memory retrieval, drugs that target the GABA(A) receptor were administered into the hippocampus before the retention trial. Muscimol, a GABA(A) receptor agonist, and diazepam, an agonist to benzodiazepine-binding site of GABA(A) receptor, blocked retention trial-induced ERK phosphorylation and impaired memory retrieval. Furthermore, co-treatment with sub-effective dose of U0126, a mitogen-activated protein kinase inhibitor, blocked the upregulation of ERK phosphorylation and impaired memory retrieval, and bicuculline methiodide (BMI), a GABA(A) receptor antagonist, increased ERK phosphorylation induced by the retention trial and facilitated memory retrieval. Finally, the effects of BMI were blocked by the co-application of a sub-effective dose of U0126. These results suggest that GABA(A) receptor-mediated memory retrieval is closely related to ERK activity.

Baicalein antagonizes rotenone-induced apoptosis in dopaminergic SH-SY5Y cells related to Parkinsonism

Background

Two active compounds, baicalein and its glycoside baicalin were found in the dried root of Scutellaria baicalensis Georgi, and reported to be neuroprotective in vitro and in vivo. This study aims to evaluate the protective effects of baicalein on the rotenone-induced apoptosis in dopaminergic SH-SY5Y cells related to parkinsonism.

Methods

Cell viability and cytotoxicity were determined by MTT assay. The degree of nuclear apoptosis was evaluated with a fluorescent DNA-binding probe Hoechst 33258. The production of reactive oxidative species (ROS) and loss of mitochondrial membrane potential (ΔΨm) were determined by fluorescent staining with DCFH-DA and Rhodanmine 123, respectively. The expression of Bax, Bcl-2, cleaved caspase-3 and phosphorylated ERK1/2 was determined by the Western blots.

Results

Baicalein significantly increased viability and decreased rotenone-induced death of SH-SY5Y cells in a dose-dependent manner. Pre- and subsequent co-treatment with baicalein preserved the cell morphology and attenuated the nuclear apoptotic characteristics triggered by rotenone. Baicalein antagonized rotenone-induced overproduction of ROS, loss of ΔΨm, the increased expression of Bax, cleaved caspase-3 and phosphorylated ERK1/2 and the decreased expression of Bcl-2.

Conclusion

The antioxidative effect, mitochondrial protection and modulation of anti-and pro-apoptotic proteins are related to the neuroprotective effects of baicalein against rotenone induced cell death in SH-SY5Y cells.

The flavonoid baicalein promotes NMDA receptor-dependent long-term potentiation and enhances memory

BACKGROUND AND PURPOSE

There is growing interest in the physiological functions of flavonoids, especially in their effects on cognitive function and on neurodegenerative diseases. The aim of the current investigation was to evaluate the role of the flavonoid baicalein in long-term potentiation (LTP) in the hippocampal CA1 region and cognitive behavioural performance.

EXPERIMENTAL APPROACH

Effects of baicalein on LTP in rat hippocampal slices were investigated by electrophysiological methods. Phosphorylation of Akt (at Ser(473)), the extracellular signal-regulated kinase (ERK1/2) and the transcription factor cAMP response element-binding protein (CREB) (at Ser(133)) were analysed by Western blot. Fear conditioning was used to determine whether baicalein could improve learning and memory in rats.

KEY RESULTS

Baicalein enhanced the N-methyl-d-aspartate glutamate receptor-dependent LTP in a bell-shaped concentration-dependent manner. Addition of the lipoxygenase metabolites 12(S)-HETE and 12(S)-HPETE did not reverse these effects of baicalein. Baicalein treatment enhanced phosphorylation of Akt during induction of LTP with the same bell-shaped dose-response curve. LTP potentiation induced by baicalein was blocked by inhibitors of phosphoinositide 3-kinase. CREB phosphorylation was also increased in the CA1 region of baicalein-treated slices. Baicalein-treated rats performed significantly better than controls in a hippocampus-dependent contextual fear conditioning task. Furthermore, baicalein treatment selectively increased the phosphorylation of Akt and CREB in the CA1 region of hippocampus, but not in the prefrontal cortex, after fear conditioning training.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that the flavonoid baicalein can facilitate memory, and therefore it might be useful in the treatment of patients with memory disorders.

Effects of Scutellaria baicalensis on chronic cerebral hypoperfusion-induced memory impairments and chronic lipopolysaccharide infusion-induced memory impairments

ETHNOPHARMACOLOGICAL RELEVANCE

Extracts of the roots of Scutellaria baicalensis Georgi (Labiatae) have been widely used to relieve fever related to bacterial infection and inflammatory diseases in traditional Korean medicine and have been reported to be effective in brain diseases. These experiments were conducted to examine the effects of oral administration of Scutellaria baicalensis extracts on the rescue of memory impairments induced by chronic cerebral hypoperfusion or chronic lipopolysaccharide (LPS) infusion. In addition, the underlying mechanisms of these effects were investigated.

MATERIALS AND METHODS

In the first experiment, chronic cerebral hypoperfusion was induced in male Wister rats by bilateral common carotid artery occlusion (BCCAo). Daily administration of Scutellaria baicalensis extracts was started on 20 day after BCCAo and given for 40 days. A Morris water maze was then used to evaluate the status of the hippocampal-dependent spatial learning and hippocampal mitogen-activated protein kinase (MAPK) signaling was examined in control rats, rats with chronic cerebral hypoperfusion, and rats with chronic cerebral hypoperfusion that was administered Scutellaria baicalensis. In the second experiment, hippocampal microglial activation was induced by chronic infusions of LPS into the fourth ventricle of Fisher-344 rat brains. Daily administration of Scutellaria baicalensis extracts was started on 7 day after the surgery of LPS infusion and given for 32 days. Spatial memory and hippocampal microglial activation was then examined in control rats with an artificial cerebrospinal fluid infusion, rats with chronic LPS infusion, and rats with chronic LPS infusion that were administered Scutellaria baicalensis.

RESULTS

Rats that received chronic cerebral hypoperfusion or chronic LPS infusion showed spatial memory impairments relative to their control rats; however, these symptoms were reduced by daily administration of Scutellaria baicalensis. Administration of Scutellaria baicalensis mitigated alterations of hippocampal MAPK signaling by chronic cerebral infusion and microglial activation by chronic LPS infusion.

CONCLUSIONS

These results indicate that Scutellaria baicalensis may possess therapeutic potential for the prevention of Alzheimer's disease and vascular dementia.

Baicalein inhibits formation of α-synuclein oligomers within living cells and prevents Aβ peptide fibrillation and oligomerisation

Abnormal protein aggregation in the brain is linked to the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Recent studies revealed that the oligomeric form of aggregates is most likely the toxic species, and thus could be a good therapeutic target. To screen for potent inhibitors that can inhibit both oligomerisation and fibrillation of α-synuclein (α-syn), we systematically compared the antioligomeric and antifibrillar activities of eight compounds that were extracted from Chinese herbal medicines through three platforms that can monitor the formation of α-syn fibrils and oligomers in cell-free or cellular systems. Our results revealed that baicalein, a flavonoid extracted from the Chinese herbal medicine Scutellaria baicalensis Georgi ("huang qin" in Chinese), is a potent inhibitor of α-syn oligomerisation both in cell-free and cellular systems, and is also an effective inhibitor of α-syn fibrillation in cell-free systems. We further tested the protective effect of baicalein against α-syn-oligomer-induced toxicity in neuronal cells. Our data showed that baicalein inhibited the formation of α-syn oligomers in SH-SY5Y and Hela cells, and protected SH-SY5Y cells from α-syn-oligomer-induced toxicity. We also explored the effect of baicalein on amyloid-β peptide (Aβ) aggregation and toxicity. We found that baicalein can also inhibit Aβ fibrillation and oligomerisation, disaggregate pre-formed Aβ amyloid fibrils and prevent Aβ fibril-induced toxicity in PC12 cells. Our study indicates that baicalein is a good inhibitor of amyloid protein aggregation and toxicity. Given the role of these processes in neurodegenerative diseases such as AD and PD, our results suggest that baicalein has potential as a therapeutic agent for the treatment of these devastating disorders.

Mismatch between changes in baicalein-induced memory-related biochemical parameters and behavioral consequences in mouse

Baicalein is one of the major flavonoids originally isolated from the roots of Scutellaria baicalensis Georgi (Labiatae). Reports on baicalein-induced changes in memory-related biochemical parameters including extracellular signal-regulated kinases (ERK), Akt, cAMP response element-binding protein (CREB), and brain-derived neurotrophic factor (BDNF) have been scarce, and the action of baicalein is controversial. Baicalein promotes phosphorylation of ERK under normal conditions; on the other hand, it inhibits phosphorylation of ERK extracellularly under oxidative conditions. In the present study, we observed that baicalein (20mg/kg, p.o.) as compared to vehicle significantly increased the expression of phosphorylated ERK (pERK), phosphorylated CREB (pCREB), and BDNF but did not increase phosphorylated Akt expression in the hippocampus of naive mice. Baicalein also significantly increased the expression of pERK and BDNF in the cortex of naive mice. However, baicalein had no effect on memory acquisition in the step-through passive avoidance task. On the contrary, baicalein (20mg/kg, p.o.) co-injected with flumazenil (10mg/kg, i.p.) significantly increased the retention latency in the passive avoidance task in comparison to the flumazenil-treated group, baicalein-treated group, and vehicle-treated control group. In addition, the number of platform crossings in the Morris water maze test during the probe trial session was significantly increased by co-administration of baicalein with flumazenil. Furthermore, the expressions level of BDNF was significantly increased in the baicalein with flumazenil-treated group compared to the baicalein- or flumazenil-treated groups in the hippocampus after an acquisition trial. These results suggest that the reasons why baicalein does not exert cognitive enhancement although it enhances the expression levels of pERK, pCREB, and BDNF are, in part, derived from its GABA(A) receptor agonistic property which is antagonized by flumazenil.

Baicalein reduces E46K alpha-synuclein aggregation in vitro and protects cells against E46K alpha-synuclein toxicity in cell models of familiar Parkinsonism

The E46K is a point mutation in alpha-synuclein (alpha-syn) that causes familial Parkinsonism with Lewy body dementia. We have now generated a cell model of Parkinsonism/Parkinson's disease (PD) and demonstrated cell toxicity after expression of E46K in the differentiated PC12 cells. E46K alpha-syn inhibited proteasome activity and induced mitochondrial depolarization in the cell model. Baicalein has been reported to inhibit fibrillation of wild type alpha-syn in vitro, and to protect neurons against several chemical-induced models of PD. We now report that baicalein significantly attenuated E46K-induced mitochondrial depolarization and proteasome inhibition, and protected cells against E46K-induced toxicity in a cell model of PD. Baicalein also reduced E46K fibrilization in vitro, with a concentration-dependent decrease in beta sheet conformation, though it increased some oligomeric species, and decreased formation of E46K alpha-syn-induced aggregates and rescued toxicity in N2A cells. Taken together, these data indicate that mitochondrial dysfunction, proteasome inhibition and specific aspects of abnormal E46K aggregation accompany E46K alpha-syn-induced cell toxicity, and baicalein can protect as well as altering aggregation properties. Baicalein has potential as a tool to understand the relation between different aggregation species and toxicity, and might be a candidate compound for further validation by using in vivo alpha-syn genetic PD models.

Targeting NADPH oxidase and phospholipases A2 in Alzheimer's disease

Alzheimer's disease (AD) is marked by an increase in the production of extracellular beta amyloid plaques and intracellular neurofibrillary tangles associated with a decline in brain function. Increases in oxidative stress are regarded as an early sign of AD pathophysiology, although the source of reactive oxygen species (ROS) and the mechanism(s) whereby beta amyloid peptides (Abeta) impact oxidative stress have not been adequately investigated. Recent studies provide strong evidence for the involvement of NADPH oxidase and its downstream oxidative signaling pathways in the toxic effects elicited by Abeta. ROS produced by NADPH oxidase activate multiple signaling pathways leading to neuronal excitotoxicity and glial cell-mediated inflammation. This review describes recent studies demonstrating the neurotoxic effects of Abeta in conjunction with ROS produced by NADPH oxidase and the downstream pathways leading to activation of cytosolic phospholipase A(2) (PLA(2)) and secretory PLA(2). In addition, this review also describes recent studies using botanical antioxidants to protect against oxidative damage associated with AD. Investigating the metabolic and signaling pathways involving Abeta NADPH oxidase and PLA(2) can help understand the mechanisms underlying the neurodegenerative effects of oxidative stress in AD. This information should provide new therapeutic approaches for prevention of this debilitating disease.

Erratum: Neural protection by naturopathic compounds-an example of tetramethylpyrazine from retina to brain

Given the advantages of being stable in the ambient environment, being permeable to the blood-brain and/or blood-eye barriers and being convenient for administration, naturopathic compounds have growingly become promising therapeutic candidates for neural protection. Extracted from one of the most common Chinese herbal medicines, tetramethylpyrazine (TMP), also designated as ligustrazine, has been suggested to be neuroprotective in the central nervous system as well as the peripheral nerve network. Although the detailed molecular mechanisms of its efficacy for neural protection are understood limitedly, accumulating evidence suggests that antioxidative stress, antagonism for calcium, and suppression of pro-inflammatory factors contribute significantly to its neuroprotection. In animal studies, systemic administration of TMP (subcutaneous injection, 50 mg/kg) significantly blocked neuronal degeneration in hippocampus as well as the other vulnerable regions in brains of Sprague-Dawley rats following kainate-induced prolonged seizures. Results from us and others also demonstrated potent neuroprotective efficacy of TMP for retinal cells and robust benefits for brain in Alzheimer's disease or other brain injury. These results suggest a promising prospect for TMP to be used as a treatment of specific neurodegenerative diseases. Given the assessment of the distribution, metabolism, excretion, and toxicity information that is already available on most neuroprotective naturopathic compounds such as TMP, preclinical data to justify bringing such therapeutic compounds to clinical trials in humans is feasible.[This corrects the article on p. in vol. .].

Neural protection by naturopathic compounds-an example of tetramethylpyrazine from retina to brain

Given the advantages of being stable in the ambient environment, being permeable to the blood–brain and/or blood–eye barriers and being convenient for administration, naturopathic compounds have growingly become promising therapeutic candidates for neural protection. Extracted from one of the most common Chinese herbal medicines, tetramethylpyrazine (TMP), also designated as ligustrazine, has been suggested to be neuroprotective in the central nervous system as well as the peripheral nerve network. Although the detailed molecular mechanisms of its efficacy for neural protection are understood limitedly, accumulating evidence suggests that antioxidative stress, antagonism for calcium, and suppression of pro-inflammatory factors contribute significantly to its neuroprotection. In animal studies, systemic administration of TMP (subcutaneous injection, 50 mg/kg) significantly blocked neuronal degeneration in hippocampus as well as the other vulnerable regions in brains of Sprague–Dawley rats following kainate-induced prolonged seizures. Results from us and others also demonstrated potent neuroprotective efficacy of TMP for retinal cells and robust benefits for brain in Alzheimer’s disease or other brain injury. These results suggest a promising prospect for TMP to be used as a treatment of specific neurodegenerative diseases. Given the assessment of the distribution, metabolism, excretion, and toxicity information that is already available on most neuroprotective naturopathic compounds such as TMP, it would not take much preclinical data to justify bringing such therapeutic compounds to clinical trials in humans.

Baicalein protects rat brain mitochondria against chronic cerebral hypoperfusion-induced oxidative damage

This study investigated the effects of baicalein, a natural compound isolated from the root of scutellaria, on cognitive and motor ability impaired by chronic cerebral hypoperfusion in rats, as well as its effects on brain mitochondria. Rats subjected to permanent bilateral common carotid artery occlusion experienced cognitive deficits, oxidative stress and mitochondria dysfunction, which was associated with the elevation of reactive oxygen species level, the decrease of oxidative phosphorylation parameters, the loss of mitochondrial membrane potential, the reduce in Bcl-2/Bax ratio, and the release of cytochrome c. Baicalein alleviated cognitive and motor impairments and decreased mitochondria reactive oxygen species production, in accordance with its improvements on membrane potential level, oxidative phosphorylation process, mitochondrial swelling degree, Bcl-2/Bax ratio and cytochrome c release. These data indicated that baicalein might have therapeutic potential for the treatment of dementia caused by chronic cerebral hypoperfusion, contributed to its protections on brain mitochondrial homeostasis and function.

Baicalein improves cognitive deficits induced by chronic cerebral hypoperfusion in rats

The aim of this study is to investigate the effects of baicalein on cognitive impairment and neuronal degeneration in a rat model of chronic cerebral hypoperfusion induced by permanent occlusion of bilateral common carotid arteries (2VO). It was found that baicalein (2 or 4 mg/kg/day, i.p.) significantly improved 2VO-induced cognitive deficits and neuropathological changes. Biochemical and histological examinations revealed that baicalein reduced the increased activities of superoxide dismutase (SOD) and malondialdehyde (MDA), and attenuated the decreased activities of glutathione peroxidase (GPx) and catalase in 2VO rats. The results of the present observation suggest that baicalein has therapeutic potential for the treatment of vascular dementia, which is most likely related, at least in part, to its antioxidant action.

Efflux of baicalin, a flavone glucuronide of Scutellariae Radix, on Caco-2 cells through multidrug resistance-associated protein 2

Baicalin and its aglycone, baicalein, being are strong antioxidants and have various pharmacological actions. Baicalein has shown a unique metabolic fate in rat intestine, being excreted into the intestinal lumen from mucosal (epithelial) cells following glucuronidation of baicalein absorbed after oral administration. The purpose of this study was to examine the absorption and excretion of baicalin and baicalein in a Caco-2 cell monolayer model to evaluate the disposition of baicalin and baicalein in the human intestine. When baicalein at 5 microM was loaded on the apical side of the Caco-2 cell monolayer, baicalein was not transferred to the basolateral side, but more baicalin was excreted onto the apical side than was being absorbed onto the basolateral side. The amount of baicalin recovered on both sides accounted for more than 90% of the baicalein absorbed from the apical surface. This was supported by the fact that Caco-2 cell microsomes showed UDP-glucuronate glucuronosyltransferase activity towards baicalein to form baicalin. On the other hand, when baicalein was loaded at higher concentrations, baicalin excretion became saturated, and then baicalein was transferred to the basolateral side. Furthermore, baicalin efflux was not inhibited by MDR1/P-glycoprotein substrates such as ciclosporin and vinblastine, but significantly inhibited by multidrug resistance-associated protein 2 (MRP2, ABCC2) substrates such as probenecid and genistein. MRP2 was also detected in Caco-2 cells by Western blotting using specific antibodies. In addition, baicalin, but not baicalein, enhanced dose-dependently the vanadate-sensitive ATPase activity of human MRP2. These results indicated that, in Caco-2 cells, any baicalein absorbed after loading at low concentrations of baicalein was not transferred to the basolateral side, but was first transformed into baicalin in the cells and excreted through the action of MRP2, mainly to the apical side.

The ameliorating effect of oroxylin A on scopolamine-induced memory impairment in mice

Oroxylin A is a flavonoid and was originally isolated from the root of Scutellaria baicalensis Georgi., one of the most important medicinal herbs in traditional Chinese medicine. The aim of this study was to investigate the ameliorating effects of oroxylin A on memory impairment using the passive avoidance test, the Y-maze test, and the Morris water maze test in mice. Drug-induced amnesia was induced by administering scopolamine (1 mg/kg, i.p.) or diazepam (1 mg/kg, i.p.). Oroxylin A (5 mg/kg) significantly reversed cognitive impairments in mice by passive avoidance and the Y-maze testing (P<.05). Oroxylin A also improved escape latencies in training trials and increased swimming times and distances within the target zone of the Morris water maze (P<.05). Moreover, the ameliorating effects of oroxylin A were antagonized by both muscimol and diazepam (0.25 mg/kg, i.p., respectively), which are GABA(A) receptor agonists. Furthermore, oroxylin A (100 microM) was found to inhibit GABA-induced inward Cl(-) current in a single cortical neuron. These results suggest that oroxylin A may be useful for the treatment of cognitive impairments induced by cholinergic dysfunction via the GABAergic nervous system.

Effects of ginseng saponins on beta-amyloid-induced amnesia in rats

We have previously demonstrated that ginseng saponins (GS) can reverse the inhibitory effect of beta-amyloid on acetylcholine (ACh) release in the hippocampal slices. The present study was carried out to examine whether GS has any beneficial effects against amnesia induced by beta-amyloid peptides in vivo. Intracerebroventricular injection of 50 microg, but not 10 microg, beta-amyloid fragment(25-35) markedly impaired the performance of rats in avoiding a shock prod, confirming the amnesiac effect of beta-amyloid. Chronically treating the rats with GS (orally, 5 days before icv beta-amyloid injection and 7 days afterward) resulted in a dose-related improvement against beta-amyloid-induced amnesia; a significant reversion was observed at the highest GS dose (80 mg/kg/day). Post-treatment analysis on K(+)-evoked [(3)H]-ACh release from the hippocampal slices showed that beta-amyloid-treatment significantly reduced ACh release from that of the control group. However, pre-treatment with GS completely protected the animal against beta-amyloid-induced reduction of hippocampal ACh release. In contrast, treating the animals with the same optimal dose of GS and duration but only after icv beta-amyloid injection was found to be ineffective in obliterating beta-amyloid's amnesiac effect. Taken together, these observations indicated that GS pre-treatment can functionally prevent the beta-amyloid-induced memory loss possibly by minimizing the inhibitory effect of beta-amyloid on hippocampal cholinergic transmission.

Effect of a Nutritive-Tonic Drink on Scopolamine-Induced Memory Impairment in Mice

The effects of a liquid nutritive and tonic drug (NTD) selected from a modification of the "Kai-xin-shou-yu-shen-qi-wan" prescription, on scopolamine-induced amnesia in mice were investigated using the passive avoidance and water-maze tasks. A popular NTD in Japan that contains 17 crude (natural) drug extracts together with synthetic drugs such as taurine, caffeine, various vitamins and ethanol, and the natural drug extracts is based on a prescription of "Kampo" origin in Chinese medicine. Scopolamine (0.4 mg/kg, i.p.) reduces the step-through latency of the passive avoidance test and fear reaction behavior at 24 and 48 h after treatment. A single oral administration of the NTD (10 ml/kg) increased the step-through latency and the fear reaction behavior score in scopolamine-treated mice. Administration of the natural drug extracts found in the NTD tended to extend the step-through latency in the retention test at 48 h, but not 24 h after the initial scopolamine trial. However, administration of the synthetic drugs found in the NTD did not improve either the step-through latency or the behavioral score. The NTD and the natural drug extracts also improved the scopolamine-induced spatial memory impairment as assessed using the Morris water-maze test. In contrast, the synthetic drugs did not affect the escape latencies. Both NTD and the synthetic drugs increased the locomotor activity in scopolamine-treated mice, whereas the natural drug extracts did not. These results suggest that NTD improves scopolamine-induced amnesia, and that this action is attributable to the natural drug extracts in the NTD.