GABA(A) receptor subtype selectivity underlying anxiolytic effect of 6-hydroxyflavone

In silico investigation of potential phytoconstituents against ligand- and voltage-gated ion channels as antiepileptic agents

The most promising anticonvulsant phytocompounds were explored in this work using docking, molecular dynamic (MD) simulation, and Molecular Mechanics-Poisson-Boltzmann Surface Area (MM-PBSA) approaches. A total of 70 phytochemicals were screened against α-amino-3-hydroxyl-5-methyl-4-isoxazole propionic acid (AMPA), N-methyl-d-aspartate (NMDA), voltage-gated sodium ion channels (VGSC), and carbonic anhydrase enzyme II (CA II) receptors, and the docking results were compared to the reference drug phenytoin. Amentoflavone displayed the highest affinity for AMPA and VGSC receptors, with docking scores of - 10.4 and - 10.1 kcal/mol, respectively. Oliganthin H-NMDA and epigallocatechin-3-gallate-CA II complexes showed docking scores of - 10.9 and - 6.9 kcal/mol, respectively. All four complexes depicted a high dock score compared to the phenytoin complex at the binding site of the corresponding proteins. The MD simulation investigated the stabilities and favorable conformation of apoproteins and ligand/reference-bound complexes. The results revealed that proteins AMPA, VGSC, and CA II were more efficiently stabilized by lead phytochemicals than phenytoin binding. Additionally, principal component analysis and MM-PBSA results suggested that these lead phytocompounds have good compactness and strong binding free energy. Further, physicochemical and pharmacokinetic studies revealed that these final lead phytochemicals would be suitable for oral intake, have sufficient intestinal permeability, and have the ability to cross the blood-brain barrier (BBB). Comprehensively, this study predicted amentoflavone as the best lead phytochemical out of the 70 anticonvulsant phytocompounds that can be used to treat epilepsy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03948-1.

Advances in Flavonoid Research: Sources, Biological Activities, and Developmental Prospectives

At present, the occurrence of a large number of infectious and non-communicable diseases poses a serious threat to human health as well as to drug development for the treatment of these diseases. One of the most significant challenges is finding new drug candidates that are therapeutically effective and have few or no side effects. In this respect, the active compounds in medicinal plants, especially flavonoids, are potentially useful compounds with a wide range of pharmacological activities. They are naturally present in nature and valuable in the treatment of many infectious and non-communicable diseases. Flavonoids are divided into fourteen categories and are mainly derived from plant extraction, chemical synthesis and structural modification, and biosynthesis. The structural modification of flavonoids is an important way to discover new drugs, but biosynthesis is currently considered the most promising research direction with the potential to revolutionize the new production pipeline in the synthesis of flavonoids. However, relevant problems such as metabolic pathway analyses and cell synthesis protocols for flavonoids need to be addressed on an urgent basis. In the present review, new research techniques for assessing the biological activities of flavonoids and the mechanisms of their biological activities are elucidated and their modes of interaction with other drugs are described. Moreover, novel drug delivery systems, such as nanoparticles, bioparticles, colloidals, etc., are gradually becoming new means of addressing the issues of poor hydrophilicity, lipophilicity, poor chemical stability, and low bioavailability of flavonoids. The present review summarizes the latest research progress on flavonoids, existing problems with their therapeutic efficacy, and how these issues can be solved with the research on flavonoids.

Natural Products and Health

A natural product is an organic compound from a living organism that can be isolated from natural sources or synthesized [...].

Possible involvement of GABAergic system on central amygdala Mediated anxiolytic effect of agmatine in rats

OBJECTIVES

To study the pharmacological interactions between agmatine and gamma aminobutyric acid (GABA) modulatory agents in the regulation of anxiety-like behavior in rats.

MATERIALS AND METHODS

Male Wistar rats were treated drugs per se or in combination and 15 min after last injection were subjected to elevated plus-maze (EPM) test. Anxiety-like behavior was evaluated by measuring behavioral conventional readout, open arm activity (duration and/or entries) for 5-minute duration.

RESULTS

Acute intra-central amygdala (CeA) injection of agmatine (0.1-0.6 μmol/site/rat), muscimol (0.25-1 nmol/site/rat), diazepam (5-20 μg/site/rat) and allopregnanolone (2-8 μg/site/rat) increased open arm entries of the rats in EPM suggesting anxiolytic effect in dose dependent manner. Moreover, the anxiolytic effect at subeffective dose of agmatine (0.1 μmol/site/rat) was potentiated by subeffective dose of muscimol (0.25 nmol/site/rat), diazepam (5 μg/site/rat) and allopregnanolone (4 μg/site/rat). Whereas, pretreatment with GABAA receptor antagonist, bicuculline (10 ng/site/rat) blocked the anxiolytic effect of agmatine and its synergistic effect of agmatine plus muscimol. Similarly, benzodiazepine (BZD) receptor antagonist, flumazenil (15 μg/site/rat) and GABA allosteric modulator antagonist, RO 15-45 13 (10 μg/site/rat) reduced the anxiolytic effect of agmatine, given alone and with diazepam and allopregnanolone, respectively.

CONCLUSION

These results indicated that anxiolytic effect of agmatine is medicated via GABAergic mechanisms, probably conciliated by the GABAA receptor subtypes. Modulation of interplay between agmatine and GABAA receptor activity might be a pertinent solution for the regulation of anxiety.

A new gnidiflavanone-flavonol dimer and other constituents from Gnidia apiculata

A new 3,8''-flavanone-flavonol dimer gnidiflavanone-flavonol (1) and 10 known compounds (2-11), including four rare primula-type flavones 2-5, were isolated from the roots of Gnidia apiculata. Compounds 2-5 and 7 were reported for the first time from the plant family Thymelaeceae. Structures of the isolated compounds were established by spectroscopic data, including 1D and 2D NMR (COSY, HMBC, HSQC and ROESY) and mass spectrometry, as well as by the comparison with literature data. The crude roots extract and isolated compounds were evaluated for antimicrobial and antiplasmodial activities. Among isolated compounds, 6-hydroxyflavone (4) and 6-O-acetylflavone (4a) showed antiplasmodial activity against chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum.

Targeting Anti-Inflammatory Pathways to Treat Diabetes-Induced Neuropathy by 6-Hydroxyflavanone

It is evident that inflammation and metabolic syndrome instigated by diabetes mellitus can precipitate diabetes-induced neuropathy (DIN) and pain. In order to find an effective therapeutic method for diabetes-related problems, a multi-target-directed ligand model was used. 6-Hydroxyflavanone (6-HF) carrying anti-inflammatory and anti-neuropathic pain potential due to its quadruplicate mechanisms, targeting cyclooxygenase-2 (COX-2), 5-lipoxygenase (5-LOX), and opioid and GABA-A receptors was investigated. The anti-inflammatory potential of the test drug was confirmed utilizing in silico, in vitro, and in vivo tests. A molecular simulation approach was utilized to observe the interaction of 6-HF with the inflammatory enzyme COX-2 as well as opioid and GABA-A receptors. The same was confirmed via in vitro COX-2 and 5-LOX inhibitory assays. In vivo tests were performed to analyze the thermal anti-nociception in the hot-plate analgesiometer and anti-inflammatory action in the carrageenan-induced paw edema model in rodents. The potential anti-nociceptive effect of 6-HF was evaluated in the DIN model in rats. The Naloxone and Pentylenetetrazole (PTZ) antagonists were used to confirm the underlying mechanism of 6-HF. The molecular modeling studies revealed a favorable interaction of 6-HF with the identified protein molecules. In vitro inhibitory studies revealed that 6-HF inhibited the COX-2 and 5-LOX enzymes significantly. The 6-HF at dosages of 15, 30, and 60 mg/kg substantially reduced heat nociception in a hot plate analgesiometer as well as carrageenan-induced paw edema in rodent models. The authors discovered that 6-HF had anti-nociception properties in a streptozotocin-induced diabetic neuropathy model. According to the findings of this study, 6-HF was demonstrated to diminish inflammation caused by diabetes as well as its anti-nociception effect in DIN.

Amelioration of AlCl3-induced Memory Loss in the Rats by an Aqueous Extract of Guduchi, a Medhya Rasayana

Background

In ayurvedic practice, the Guduchi ( Tinospora cordifolia (Willd.) Miers) stem is used as a Medhya drug for its beneficial effects on memory improvement.

Objectives

The current study was planned to explore the Medhya properties of the Guduchi stem extract by observing its ameliorating effect on AlCl3-induced neurotoxicity in rats that acted as a chronic model of memory loss.

Materials and Methods

The aqueous extract of the Guduchi stem was prepared per the Ayurvedic Pharmacopoeia of India and administered to the AlCl3-treated Wistar rats for 42 days. The biochemical assessment of the brain tissues of the treated animals was done by the acetylcholinesterase (AChE) inhibition assay, protein expression, and oxidative stress assays, namely lipid peroxidation, reduced glutathione, superoxide dismutase, and catalase assay. The neurobehavioral assessment was done using the elevated plus maze (EPM) test.

Results

The EPM test revealed that treatment with Guduchi extract showed marked improvement of memory status in rats along with reduced oxidative stress, and a marked modulation of the AChE inhibition and expression of AChE tubulin proteins.

Conclusion

The results substantiate the Medhya properties of the Guduchi. Detailed investigations are required to be carried out to explore the precise mechanism of the neuroprotective action of the Guduchi stem extract against the AlCl3-induced neurotoxicity in rats.

Calcium Involved in the Enrichment of γ-Aminobutyric Acid (GABA) in Broccoli Sprouts under Fructose Treatment

The effect of fructose on γ-aminobutyric acid (GABA) content and its metabolic pathway in broccoli sprouts was investigated. The results demonstrated that the fructose treatment not only significantly increased the fresh weight, GABA, and glutamate contents in sprouts, but also promoted the activity of glutamic acid decarboxylase (GAD) and the expressions of BoGAD1 and BoGAD2. Meanwhile, fructose treatment inhibited the stem length of broccoli sprouts and enhanced the abscisic acid (ABA) production in comparison with the control. Ca2+, CaM contents, and BoCaM2 expression in broccoli sprouts were also stimulated after fructose treatment. Exogenous fructose increased inositol trisphosphate (IP3) content and activated the activity of phosphatidylinositol-specific phospholipase C (PI-PLC) and the expression of BoPLC2, contributing to Ca2+ influx into the cells. These results suggested that Ca2+ played an essential role in GABA enrichment under fructose treatment, which may be associated with GAD and PI-PLC.

Deciphering the interactions of phytochemicals with ovalbumin, the major food allergen from egg white: spectroscopic and computational studies

Ovalbumin (OVA), the major component of egg white, has been used as a model carrier protein to study the interaction of four bioactive phytochemicals 6-hydroxyflavone, chrysin, naringin, and naringenin. A static quenching mechanism was primarily associated with the complexation of the flavonoids with OVA. Hydrophobic forces play a major part in the stability of the complexes. The structural changes within the protein in response to flavonoid binding revealed a decrease in OVA's α-helical content. The hypothesized binding site for flavonoids in OVA overlaps with one or more immunoglobulin E-binding epitopes that may have some effect in the immunoglobulin E response pathway. The flavonoids remain in the same binding site throughout the simulation time and impart protein stability by forming different noncovalent interactions. This study presents comprehensive information about the interaction of the flavonoids with OVA and the associated structural variations after the binding, which might help researchers better comprehend similar medication pharmacodynamics and provide critical information for future therapeutic development.

Identification of Potential Human Ryanodine Receptor 1 Agonists and Molecular Mechanisms of Natural Small-Molecule Phenols as Anxiolytics

Natural small-molecule phenols (NSMPs) possess certain ubiquitous bioactivities including the anxiolytic effect. Ryanodine receptor 1 (RyR1) may be one of the potentially critical pharmacological targets for studying the anxiolytic activity of NSMPs. However, detailed molecular mechanisms of NSMPs have not been fully clarified. This research was intended to identify potent hRyR1 agonists from NSMPs and investigate whether RyR1 plays a role in their anxiolytic effect. Homology modeling and molecular docking analysis were performed using Accelrys Discovery Studio 2.5. The most appropriate concentrations of NSMPs to activate RyR1 were measured using the MTT assay. Fluorescence analyses of the intracellular calcium levels and western blotting analysis were carried out to validate whether NSMPs could regulate the calcium flux to some extent by activating RyR1. The results demonstrated that xanthotoxol and 5-hydroxy-1,4-naphthalenedione can be screened as hit compounds for potential agonists of hRyR1 to exert the anxiolytic effect. In conclusion, NSMPs might be a kind of pharmacological signal carrier, acting on RyR1 as an agonist and resulting in calcium ion mobilization from intracellular calcium ion store.

Natural Products for Neurodegeneration: Regulating Neurotrophic Signals

Neurodegenerative disorders (NDs) are heterogeneous groups of ailments typically characterized by progressive damage of the nervous system. Several drugs are used to treat NDs but they have only symptomatic benefits with various side effects. Numerous researches have been performed to prove the advantages of phytochemicals for the treatment of NDs. Furthermore, phytochemicals such as polyphenols might play a pivotal role in rescue from neurodegeneration due to their various effects as anti-inflammatory, antioxidative, and antiamyloidogenic agents by controlling apoptotic factors, neurotrophic factors (NTFs), free radical scavenging system, and mitochondrial stress. On the other hand, neurotrophins (NTs) including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), NT4/5, and NT3 might have a crucial neuroprotective role, and their diminution triggers the development of the NDs. Polyphenols can interfere directly with intracellular signaling molecules to alter brain activity. Several natural products also improve the biosynthesis of endogenous genes encoding antiapoptotic Bcl-2 as well as NTFs such as glial cell and brain-derived NTFs. Various epidemiological studies have demonstrated that the initiation of these genes could play an essential role in the neuroprotective function of dietary compounds. Hence, targeting NTs might represent a promising approach for the management of NDs. In this review, we focus on the natural product-mediated neurotrophic signal-modulating cascades, which are involved in the neuroprotective effects.

Flavonoids' Effects on Caenorhabditis elegans' Longevity, Fat Accumulation, Stress Resistance and Gene Modulation Involve mTOR, SKN-1 and DAF-16

Flavonoids are potential nutraceutical compounds present in diary food. They are considered health-promoting compounds and promising drugs for different diseases, such as neurological and inflammatory diseases, diabetes and cancer. Therefore, toxicological and mechanistic studies should be done to assert the biological effects and identify the molecular targets of these compounds. In this work we describe the effects of six structurally-related flavonoids—baicalein, chrysin, scutellarein, 6-hydroxyflavone, 6,7-dihydroxyflavone and 7,8-dihydroxyflavone—on Caenorhabditis elegans’ lifespan and stress resistance. The results showed that chrysin, 6-hydroxyflavone and baicalein prolonged C. elegans’ lifespan by up to 8.5%, 11.8% and 18.6%, respectively. The lifespan extensions caused by these flavonoids are dependent on different signaling pathways. The results suggested that chrysin’s effects are dependent on the insulin signaling pathway via DAF-16/FOXO. Baicalein and 6-hydroxyflavone’s effects are dependent on the SKN-1/Nfr2 pathway. In addition, microarray analysis showed that baicalein downregulates important age-related genes, such as mTOR and PARP.

Natural Medicines for the Treatment of Epilepsy: Bioactive Components, Pharmacology and Mechanism

Epilepsy is a chronic disease that can cause temporary brain dysfunction as a result of sudden abnormal discharge of the brain neurons. The seizure mechanism of epilepsy is closely related to the neurotransmitter imbalance, synaptic recombination, and glial cell proliferation. In addition, epileptic seizures can lead to mitochondrial damage, oxidative stress, and the disorder of sugar degradation. Although the mechanism of epilepsy research has reached up to the genetic level, the presently available treatment and recovery records of epilepsy does not seem promising. Recently, natural medicines have attracted more researches owing to their low toxicity and side-effects as well as the excellent efficacy, especially in chronic diseases. In this study, the antiepileptic mechanism of the bioactive components of natural drugs was reviewed so as to provide a reference for the development of potential antiepileptic drugs. Based on the different treatment mechanisms of natural drugs considered in this review, it is possible to select drugs clinically. Improving the accuracy of medication and the cure rate is expected to compensate for the shortage of the conventional epilepsy treatment drugs.

Involvement of selective GABA-A receptor subtypes in amelioration of cisplatin-induced neuropathic pain by 2'-chloro-6-methyl flavone (2'-Cl-6MF)

Cisplatin-induced peripheral neuropathic pain is a common adverse effect of chemotherapy. The present study evaluated the effects of 2'-chloro-6-methylflavone (2'-Cl-6MF) at recombinant α1β2γ2L, α2β1-3γ2L, and α3β1-3γ2L GABA-A receptor subtypes expressed in Xenopus oocytes and subsequently evaluated its effectiveness in cisplatin-induced neuropathic pain. The results showed that 2'-Cl-6MF potentiated GABA-elicited currents at α2β2/3γ2L and α3β2/3γ2L GABA-A receptor subtypes. The potentiation was blocked by the co-application of flumazenil (a benzodiazepine (BDZs) site antagonist). In behavioral studies, mechanical allodynia was induced by intraplantar injection of cisplatin (40 μg/paw) in Sprague Dawley rats, and behavioral assessments were made 24 h after injection. 2'-Cl-6MF (1, 10, 30, and 100 mg/kg, i.p.), was administered 1 h before behavioral evaluation. Administration of 2'-Cl-6MF (30 and 100 mg/kg, i.p) significantly enhanced the paw withdrawal threshold and decreased mechanical allodynia. The standard drugs, gabapentin (GBP) at the dose of 70 mg/kg, and HZ 166 (16 mg/kg), i.p. also significantly enhanced the paw withdrawal threshold in mechanical allodynia. Pretreatment with pentylenetetrazole (PTZ) (15 mg/kg, i.p.) and flumazenil reversed the antinociceptive effect of 2'-Cl-6MF in mechanical allodynia indicating GABAergic mechanisms. Moreover, the binding mechanism of 2'-Cl-6MF was rationalized by in silico modeling tools. The 3D-coordinates of α2β2γ2L and α2β3γ2L were generated after homology modeling of the α2 subtype and 2'-Cl-6MF was at predicted binding sites of the developed models. The α2 model was compared with the α1 and α3 subunits via structural and sequence alignment. Molecular docking depicted that the compound binds efficiently at the neuromodulator binding site of the receptors. The findings of this study revealed that 2'-Cl-6MF ameliorated the manifestations of cisplatin-induced neuropathic pain in rats. Furthermore, we also conclude that GABAergic mechanisms may contribute to the antinociceptive effect of 2'-Cl-6MF. The molecular docking studies also confirm the involvement of the BDZs site of GABA-A receptors. It was observed that Ile230 of α2 stabilize the chlorophenyl ring of 2'-Cl-6MF through hydrophobic interactions, which is replaced by Val203 in α1 subunit. However, the smaller side chain of Val203 does not provide hydrophobic interaction to the compound due to high conformational flexibility of α1 subunit.

Anxiolytic-like activity of 5-methoxyflavone in mice with involvement of GABAergic and serotonergic systems - in vivo and in silico evidences

Anxiety disorders are common worldwide and novel compounds are investigated for anxiolytic effect. A few studies have demonstrated the anxiolytic-like activity of natural and synthetic flavonoids. 5-methoxyflavone, a synthetic flavone derivative, has been reported to exhibit central nervous system depressant (sedative-hypnotic) effect in an earlier study. The present study was designed to investigate whether 5-methoxyflavone possesses anxiolytic-like activity in mice by employing two unconditioned models of anxiety such as elevated plus maze and light-dark box test. The possible role played by GABAergic (GABA_A) and serotonergic (5HT_1A) systems in the anxiolytic-like effect of 5-methoxyflavone was also investigated in the elevated plus maze test. Molecular docking studies were performed to ascertain the interaction of 5-methoxyflavone with GABA_A (α₂ subunit-containing) and 5HT_1A receptors. 5-methoxyflavone treatment in mice (10, 20 or 40 mg/kg, i.p) increased the number of entries and time spent in the open arms in an elevated plus maze (p < 0.001). In the light-dark box test a significant increase in the time spent in light compartment (p < 0.001) and prolonged latency to enter the dark compartment (p < 0.01) were also observed. Pretreatment of mice with 5HT_1A antagonist pindolol (10 mg/kg, i.p) or GABA_A antagonist bicuculline (2 mg/kg, i.p) significantly attenuated the effect of 5-methoxyflavone in the elevated plus maze test. In silico studies provided evidences for good binding affinity of 5-methoxyflavone towards GABA_A (α₂ subunit-containing) and serotonergic (5HT_1A) receptors by H-bond interactions. In conclusion, the present study identified a novel anxiolytic-like effect of 5-methoxyflavone involving GABAergic and serotonergic mechanisms.

Exploring the Promise of Flavonoids to Combat Neuropathic Pain: From Molecular Mechanisms to Therapeutic Implications

Neuropathic pain (NP) is the result of irregular processing in the central or peripheral nervous system, which is generally caused by neuronal injury. The management of NP represents a great challenge owing to its heterogeneous profile and the significant undesirable side effects of the frequently prescribed psychoactive agents, including benzodiazepines (BDZ). Currently, several established drugs including antidepressants, anticonvulsants, topical lidocaine, and opioids are used to treat NP, but they exert a wide range of adverse effects. To reduce the burden of adverse effects, we need to investigate alternative therapeutics for the management of NP. Flavonoids are the most common secondary metabolites of plants used in folkloric medicine as tranquilizers, and have been claimed to have a selective affinity to the BDZ binding site. Several studies in animal models have reported that flavonoids can reduce NP. In this paper, we emphasize the potentiality of flavonoids for the management of NP.

Neuroprotective Polyphenols: A Modulatory Action on Neurotransmitter Pathways

BACKGROUND

Balance in neurotransmission is essential for the proper functioning of the nervous system and even a small, but prolonged disturbance, can induce the negative feedback mechanisms leading to various neuropathologies. Neurodegenerative and mood disorders such as Alzheimer's, Parkinson's or affective disorders are increasing medical and social problems. Among the wide spectrum of potentially destructive events, oxidative stress and disrupted metabolism of some neurotransmitters such as acetylcholine, GABA, glutamate, serotonin or dopamine appear to play a decisive role. Biologically active plant polyphenols have been shown to exert a positive impact on the function of the central nervous system by modulation of metabolism and the action of some neurotransmitters.

METHODS

Based on published research, the pharmacological activities of some naturally occurring polyphenols have been reviewed, with a focus on their potential therapeutic importance in the regulation of neurotransmitter systems.

RESULTS

Phytochemicals can be classified into several groups and most of them possess anticancer, antioxidative, anti-inflammatory and neuroprotective properties. They can also modulate the metabolism or action of some neurotransmitters and/or their receptors. Based on these properties, phytochemicals have been used in traditional medicine for ages, although it was focused mainly on treating symptoms. However, growing evidence indicates that polyphenols may also prevent or slow neurological diseases.

CONCLUSION

Phytochemicals seem to be less toxic than synthetic drugs and they can be a safer alternative for currently used preparations, which exert adverse side effects. The neuroprotective actions of some plant polyphenols in the regulation of neurotransmitters metabolism, functioning of neurotransmitters receptors and antioxidative defense have potential therapeutic applications in various neurodegenerative disorders.

In Silico Study of Anti-Insomnia Mechanism for Suanzaoren Prescription

Insomnia is a common and widespread sleeping disorder caused by various risk factors. Though beneficial, conventional treatments of insomnia have significant limitations. As an alternative treatment, Chinese herbal formula Suanzaoren prescription (SZRP), composed of Suanzaoren [seeds of Ziziphus jujuba var. spinosa (Bunge) Hu ex H.F.Chow] and four additional herbs, has been reported with significant anti-insomnia effects. Yet the anti-insomnia mechanism of the herb formulae remains unknown. In this study, we attempted to extrapolate the holistic anti-insomnia mechanism of SZRP through herbal targeting and network pharmacology. The results indicated that the ingredients of Suanzaoren can target multi-neurotransmitter receptors at synapse interface, which was reported to be associated with sedative and hypnotic effects, while the four additional herbs can hit multiple pathways downstream of membrane neurotransmitters. Furthermore, the four additional herbs showed highly cooperative targeting patterns in the paralleled and cross-talked pathways related to inflammatory regulation and endocrine system, which may contribute to the additional relief of insomnia caused by inflammation, anxiety, or endocrine disorder. The interesting complementary mechanism we found among the herbal groups of SZRP may provide an example to study Chinese herbal formula and offers clues to future design of anti-insomnia strategy.

Influence of amide versus ester linkages on the anticancer properties of the new flavone-biotin conjugates

Novel biotinylated C-6 substituted flavones were synthesised by a one-step method that connects biotin to 6-hydroxyflavone and 6-aminoflavone by esterification and amidation of hydroxyl and amino groups, respectively. The obtained compounds, 6-O-biotinylflavone and 6-biotinylamidoflavone, are the bifunctional molecules composed of a flavone moiety as a fluorescent reporter and biotin as a cancer-targeting unit. Antiproliferative activity was evaluated using SRB assays in MCF-7, MCF-10A, HepG2, MDA-MB-231, 4T1, and Balb/3T3 cell lines. In vitro evaluation revealed that compounds with biotin moiety displayed better cell selectivity between the cancer and normal cells than the parental substrates. These results indicate that anticancer effect is not related to the position of biotin moiety, but it is related to the presence of ester or amide bond. 6-O-Biotinylflavone was more active than 6-hydroxyflavone against human breast (MDA-MB-231) and liver (HepG2) cancer cells with IC50 (concentration of tested agent that inhibits proliferation of the cell population by 50%) values equal to 78.5 ± 18.8 μM and 133.2 ± 14.2 μM, respectively. Non biotinylated 6-aminoflavone was more active than 6-biotinylamidoflavone against all tested cell lines, with IC50 values between 34.3 ± 9.1 μM (4T1) and 173.86 ± 24.3 μM (MCF-7).

Gabrb2-knockout mice displayed schizophrenia-like and comorbid phenotypes with interneuron-astrocyte-microglia dysregulation

Intronic polymorphisms of the GABA_A receptor β₂ subunit gene (GABRB2) under adaptive evolution were associated with schizophrenia and reduced expression, especially of the long isoform which differs in electrophysiological properties from the short isoform. The present study was directed to examining the gene dosage effects of Gabrb2 in knockout mice of both heterozygous (HT) and homozygous (KO) genotypes with respect to possible schizophrenia-like and comorbid phenotypes. The KO mice, and HT mice to a lesser extent, were found to display prepulse inhibition (PPI) deficit, locomotor hyperactivity, stereotypy, sociability impairments, spatial-working and spatial-reference memory deficits, reduced depression and anxiety, and accelerated pentylenetetrazol (PTZ)-induced seizure. In addition, the KO mice were highly susceptible to audiogenic epilepsy. Some of the behavioral phenotypes showed evidence of imprinting, gender effect and amelioration by the antipsychotic risperidone, and the audiogenic epilepsy was inhibited by the antiepileptic diazepam. GABAergic parvalbumin (PV)-positive interneuron dystrophy, astrocyte dystrophy, and extensive microglia activation were observed in the frontotemporal corticolimbic regions, and reduction of newborn neurons was observed in the hippocampus by immunohistochemical staining. The neuroinflammation indicated by microglial activation was accompanied by elevated brain levels of oxidative stress marker malondialdehyde (MDA) and the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). These extensive schizophrenia-like and comorbid phenotypes brought about by Gabrb2 knockout, in conjunction with our previous findings on GABRB2 association with schizophrenia, support a pivotal role of GABRB2 in schizophrenia etiology.

Suanzaoren Formulae for Insomnia: Updated Clinical Evidence and Possible Mechanisms

Insomnia disorder is a widespread and refractory disease. Semen Ziziphi Spinosae, Suanzaoren, a well-known Chinese herbal medicine, has been used for treating insomnia for thousands of years. Here, we aimed to assess the available evidence of Chinese herbal formulae that contains Suanzaoren (FSZR) for insomnia according to high-quality randomized controlled trials (RCTs) and reviewed their possible mechanisms based on animal-based studies. Electronic searches were performed in eight databases from inception to November 2016. The primary outcome measures were polysomnography index and Pittsburgh sleep quality index. The secondary outcome measures were clinical effective rate and adverse events. The methodological quality of RCTs was assessed by Cochrane's collaboration tool, and only RCTs with positive for 4 out of 7 for the Cochrane risk of bias domains were included in analyses. Thirteen eligible studies with 1,454 patients were identified. Meta-analysis of high-quality RCTs showed that FSZR monotherapy was superior to placebo (P < 0.01); FSZR plus Diazepam was superior to Diazepam alone (P < 0.05); there were mixed results comparing FSZR with Diazepam (P > 0.05 or P < 0.05). Furthermore, FSZR caused fewer side effects than that of Diazepam. Suanzaoren contains complex mixtures of phytochemicals including sanjoinine A, Jujuboside A, spinosin and other flavonoids, which has sedative and hypnotic functions primarily mediated by the GABAergic and serotonergic system. In conclusion, the findings of present study supported that FSZR could be an alternative treatment for insomnia in clinic. FSZR exerted sedative and hypnotic actions mainly through the GABAergic and serotonergic system.

Support for Natural Small-Molecule Phenols as Anxiolytics

Natural small-molecule phenols (NSMPs) share some bioactivities. The anxiolytic activity of NSMPs is attracting attention in the scientific community. This paper provides data supporting the hypothesis that NSMPs are generally anxiolytic. The anxiolytic activities of seven simple phenols, including phloroglucinol, eugenol, protocatechuic aldehyde, vanillin, thymol, ferulic acid, and caffeic acid, were assayed with the elevated plus maze (EPM) test in mice. The oral doses were 5, 10 and 20 mg/kg, except for phloroglucinol for which the doses were 2.5, 5 and 10 mg/kg. All tested phenols had anxiolytic activity in mice. The phenolic hydroxyl group in 4-hydroxycinnamic acid (4-OH CA) was essential for the anxiolytic activity in the EPM test in mice and rats compared to 4-chlorocinnamic acid (4-Cl CA). The in vivo spike recording of rats’ hippocampal neurons also showed significant differences between 4-OH CA and 4-Cl CA. Behavioral and neuronal spike recording results converged to indicate the hippocampal CA1 region might be a part of the anxiolytic pathways of 4-OH CA. Therefore, our study provides further experimental data supporting NSMPs sharing anxiolytic activity, which may have general implications for phytotherapy because small phenols occur extensively in herbal medicines.

Ziziphus spinosa seeds for insomnia: A review of chemistry and psychopharmacology

BACKGROUND

In Chinese medicine, Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chou is widely used for the treatment of insomnia.

PURPOSE/SECTIONS

This paper summarises the chemistry, psychopharmacology, and compares the pharmaceutical effects of the seeds of Ziziphus jujuba plant, Ziziphus spinosa (ZS) seeds, with benzodiazepines. Whole extracts and constituent compounds have been evaluated in preclinical and clinical studies.

CONCLUSIONS

ZS secondary metabolites modulate GABAergic activity and the serotonergic system. The actual therapeutic agents require further confirmation/identification so that new insomnia phytomedicines can be discovered.

Anticonvulsant activity of an active fraction extracted from Crinum jagus L. (Amaryllidaceae), and its possible effects on fully kindled seizures, depression-like behaviour and oxidative stress in experimental rodent models

ETHNOPHARMACOLOGICAL RELEVANCE

The leaf extract of Crinum jagus L. (Amaryllidaceae) is widely used in traditional Cameroonian medicine as antiepileptic remedy and for the treatment of convulsion, depression and mood disorders associated with epilepsy.

AIM OF THE STUDY

Hence, this study was conducted to evaluate the effects of an active fraction extracted from the leaves of Crinum jagus against seizures, depression-like behaviour and oxidative stress in pentylenetetrazole (PTZ)-induced kindling in mice.

MATERIALS AND METHODS

Bioactive-guided fractionation of the leaf extract of Crinum jagus by using 70mg/kg PTZ-induced convulsions in mice, afforded a potent anticonvulsant fraction (flavonol kaempferol; C4.4). The effects of C4.4 on 30mg/kg PTZ-induced kindling, kindling-induced depression like-behaviour and oxidative stress was evaluated. Mice were injected PTZ (30mg/kg, i.p.) once every alternate day (48±1h) until the development of kindling. Depression was assessed using tail suspension test and forced swim test while the oxidative stress parameters were estimated in the whole brain at the end of experiments. Mice were submitted to the rota-rod task and open-field test in order to assess any non-specific muscle-relaxant or sedative effects of C4.4. Acute toxicity of C4.4 was also assessed in mice.

RESULTS

Convulsions-induced by 70mg/kg PTZ were strongly antagonized by C4.4. Oral administration of C4.4 significantly increased the latency to myoclonic jerks, clonic seizures as well as generalized tonic-clonic seizures, improved the seizure mean stage and decreased the number of myoclonic jerks in PTZ-kindled mice. The data indicated also that C4.4 significantly reduced the immobility times in the tail suspension test and the forced swim test. This active fraction has also antioxidant properties by decreasing the lipid peroxidation, and augmenting endogenous antioxidant enzymes in brain. C4.4 administered (12.5-50mg/kg) did not alter the locomotion of animals in the open-field or rotarod tests, which suggest a lack of a central depressant effect. The animals did not exhibit any acute toxicity to C4.4 at the therapeutic doses.

CONCLUSION

These results suggest that pretreatment with C4.4 ameliorates convulsions-induced by PTZ, protects mice against kindling development, depression-like behaviour and oxidative stress in PTZ-kindled mice. These finding provides scientific rationale for the use of Crinum jagus extracts for the amelioration of epilepsy observed in traditional medicine in Cameroon.

Neuroprotective effects of quercetin on memory and anxiogenic-like behavior in diabetic rats: Role of ectonucleotidases and acetylcholinesterase activities

The present study investigated the protective effect of quercetin (Querc) on memory, anxiety-like behavior and impairment of ectonucleotidases and acetylcholinesterase (AChE) activities in brain of streptozotocin-induced diabetic rats (STZ-diabetes). The type 1 diabetes mellitus was induced by an intraperitoneal injection of 70mg/kg of streptozotocin (STZ), diluted in 0.1M sodium-citrate buffer (pH 4.5). Querc was dissolved in 25% ethanol and administered by gavage at the doses of 5, 25 and 50mg/kg once a day during 40days. The animals were distributed in eight groups of ten animals as follows: vehicle, Querc 5mg/kg, Querc 25mg/kg, Querc 50mg/kg, diabetes, diabetes plus Querc 5mg/kg, diabetes plus Querc 25mg/kg and diabetes plus Querc 50mg/kg. Querc was able to prevent the impairment of memory and the anxiogenic-like behavior induced by STZ-diabetes. In addition, Querc prevents the decrease in the NTPDase and increase in the adenosine deaminase (ADA) activities in SN from cerebral cortex of STZ-diabetes. STZ-diabetes increased the AChE activity in SN from cerebral cortex and hippocampus. Querc 50mg/kg was more effective to prevent the increase in AChE activity in the brain of STZ-diabetes. Querc also prevented an increase in the malondialdehyde levels in all the brain structures. In conclusion, the present findings showed that Querc could prevent the impairment of the enzymes that regulate the purinergic and cholinergic extracellular signaling and improve the memory and anxiety-like behavior induced by STZ-diabetes.

A Strategy to Employ Clitoria ternatea as a Prospective Brain Drug Confronting Monoamine Oxidase (MAO) Against Neurodegenerative Diseases and Depression

Ayurveda is a renowned traditional medicine practiced in India from ancient times and Clitoria ternatea is one such prospective medicinal herb incorporated as an essential constituent in a brain tonic called as medhya rasayan for treating neurological disorders. This work emphasises the significance of the plant as a brain drug there by upholding Indian medicine. The phytochemicals from the root extract were extricated using gas chromatography-mass spectrometry assay and molecular docking against the protein Monoamine oxidase was performed with four potential compounds along with four reference compounds of the plant. This persuades the prospect of C. ternatea as a remedy for neurodegenerative diseases and depression. The in silico assay enumerates that a major compound (Z)-9,17-octadecadienal obtained from the chromatogram with a elevated retention time of 32.99 furnished a minimum binding affinity energy value of -6.5 kcal/mol against monoamine oxidase (MAO-A). The interactions with the amino acid residues ALA 68, TYR 60 and TYR 69 were analogous to the reference compound kaempferol-3-monoglucoside with a least score of -13.90/-12.95 kcal/mol against the isoforms (MAO) A and B. This study fortifies the phytocompounds of C. ternatea as MAO-inhibitors and to acquire a pharmaceutical approach in rejuvenating Ayurvedic medicine.

GABA(A) receptor modulation and neuropharmacological activities of viscosine isolated from Dodonaea viscosa (Linn)

The objective of the present study was to evaluate the modulation of GABA-evoked currents by the flavonoid viscosine at recombinant GABA(A) receptors, and subsequently to study its anxiolytic, sedative and anticonvulsant activities. Viscosine (1-300μM) positively modulated GABA-evoked currents at human α1β2γ2L and α2β2γ2L GABA(A) receptors expressed in Xenopus oocytes in a flumazenil insensitive manner. In behavioral studies, viscosine at doses of 10-100mg/kg (i.p.) exerted significant anxiolytic effects in the elevated plus maze, light-dark and open field tests (*P<0.05, **P<0.01, ***P<0.001 n=6, One-way ANOVA post-Dunnett's test), and sedative effects at high doses (100mg/kg i.p.) in hole board and thiopental induced sleep time tests. The anxiolytic effect in the elevated plus maze test was not blocked by flumazenil whereas pentylenetetrazole (PTZ) completely attenuated the effect, indicating that the activity was mediated via the non-benzodiazepine sites of GABA(A) receptors. Furthermore, viscosine at doses of 10-100mg/kg (i.p.) exerted anticonvulsant effects in a dose-dependent manner in PTZ, picrotoxin and bicuculline induced seizure paradigms (*P<0.05, **P<0.01,***P<0.001 n=6, One-way ANOVA post-Dunnett's test). In conclusion, the results of the present study suggest that the anxiolytic and anticonvulsant actions of viscosine are likely mediated via its positive allosteric modulatory action of GABA at different GABA(A) receptor subtypes.

The role of flavonoids on oxidative stress in epilepsy

Backgrounds. Oxidative stress can result from excessive free-radical production and it is likely implicated as a possible mechanism involved in the initiation and progression of epileptogenesis. Flavonoids can protect the brain from oxidative stress. In the central nervous system (CNS) several flavonoids bind to the benzodiazepine site on the GABA_A-receptor resulting in anticonvulsive effects. Objective. This review provides an overview about the role of flavonoids in oxidative stress in epilepsy. The mechanism of action of flavonoids and its relation to the chemical structure is also discussed. Results/Conclusions. There is evidence that suggests that flavonoids have potential for neuroprotection in epilepsy.

Interactions of flavonoids with ionotropic GABA receptors

In this overview, we highlight some recent advances in the interaction of natural and synthetic flavonoids with ionotropic GABA receptors. Examples of positive, negative, and neutralizing allosteric modulators as well as allosteric agonists are given. Flavonoids appear to act via multiple binding sites on GABA receptors. Unraveling these active sites remains a major task.

CAPON-nNOS coupling can serve as a target for developing new anxiolytics

Anxiety disorders are highly prevalent psychiatric diseases. There is need for a deeper understanding of anxiety control mechanisms in the mammalian brain and for development of new anxiolytic agents. Here we report that the coupling between neuronal nitric oxide synthase (nNOS) and its carboxy-terminal PDZ ligand (CAPON) can serve as a target for developing new anxiolytic agents. Augmenting nNOS-CAPON interaction in the hippocampus of mice by overexpressing full-length CAPON gave rise to anxiogenic-like behaviors, whereas dissociating CAPON from nNOS by overexpressing CAPON-125C or CAPON-20C (the C-terminal 125 or 20 amino acids of CAPON) or delivering Tat-CAPON-12C (a peptide comprising Tat and the 12 C-terminal amino acids of CAPON) in the hippocampus of mice produced anxiolytic-like effects. Mice subjected to chronic mild stress (CMS) displayed a substantial increase in nNOS-CAPON coupling in the hippocampus and a consequent anxiogenic-like phenotype. Disrupting nNOS-CAPON coupling reversed the CMS-induced anxiogenic-like behaviors. Moreover, small-molecule blockers of nNOS-CAPON binding rapidly produced anxiolytic-like effects. Dexamethasone-induced ras protein 1 (Dexras1)-extracellular signal-regulated kinase (ERK) signaling was involved in the behavioral effects of nNOS-CAPON association. Thus, nNOS-CAPON association contributes to the modulation of anxiety-related behaviors via regulating Dexras1-ERK signaling and can serve as a target for developing potential anxiolytics.

Ecology and neurophysiology of sleep in two wild sloth species

STUDY OBJECTIVES

Interspecific variation in sleep measured in captivity correlates with various physiological and environmental factors, including estimates of predation risk in the wild. However, it remains unclear whether prior comparative studies have been confounded by the captive recording environment. Herein we examine the effect of predation pressure on sleep in sloths living in the wild.

DESIGN

Comparison of two closely related sloth species, one exposed to predation and one free from predation.

SETTING

Panamanian mainland rainforest (predators present) and island mangrove (predators absent).

PARTICIPANTS

Mainland (Bradypus variegatus, five males and four females) and island (Bradypus pygmaeus, six males) sloths.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Electroencephalographic (EEG) and electromyographic (EMG) activity was recorded using a miniature data logger. Although both species spent between 9 and 10 h per day sleeping, the mainland sloths showed a preference for sleeping at night, whereas island sloths showed no preference for sleeping during the day or night. Standardized EEG activity during nonrapid eye movement (NREM) sleep showed lower low-frequency power, and increased spindle and higher frequency power in island sloths when compared to mainland sloths.

CONCLUSIONS

In sloths sleeping in the wild, predation pressure influenced the timing of sleep, but not the amount of time spent asleep. The preference for sleeping at night in mainland sloths may be a strategy to avoid detection by nocturnal cats. The pronounced differences in the NREM sleep EEG spectrum remain unexplained, but might be related to genetic or environmental factors.

Effects of 6-Hydroxyflavone on Osteoblast Differentiation in MC3T3-E1 Cells

Osteoblast differentiation plays an essential role in bone integrity. Isoflavones and some flavonoids are reported to have osteogenic activity and potentially possess the ability to treat osteoporosis. However, limited information concerning the osteogenic characteristics of hydroxyflavones is available. This study investigates the effects of various hydroxyflavones on osteoblast differentiation in MC3T3-E1 cells. The results showed that 6-hydroxyflavone (6-OH-F) and 7-hydroxyflavone (7-OH-F) stimulated ALP activity. However, baicalein and luteolin inhibited ALP activity and flavone showed no effect. Up to 50 μM of each compound was used for cytotoxic effects study; flavone, 6-OH-F, and 7-OH-F had no cytotoxicity on MC3T3-E1 cells. Moreover, 6-OH-F activated AKT and serine/threonine kinases (also known as protein kinase B or PKB), extracellular signal-regulated kinases (ERK 1/2), and the c-Jun N-terminal kinase (JNK) signaling pathways. On the other hand, 7-OH-F promoted osteoblast differentiation mainly by activating ERK 1/ 2 signaling pathways. Finally, after 5 weeks of 6-OH-F induction, MC3T3-E1 cells showed a significant increase in the calcein staining intensity relative to merely visible mineralization observed in cells cultured in the osteogenic medium only. These results suggested that 6-OH-F could activate AKT, ERK 1/2, and JNK signaling pathways to effectively promote osteoblastic differentiation.

Quercetin antagonism of GABAAρ₁ receptors is prevented by ascorbic acid through a redox-independent mechanism

Quercetin is a natural flavonoid widely distributed in plants that acts as a neuroprotective agent and modulates the activity of different synaptic receptors and ion channels, including the ionotropic GABA receptors. GABA(Aρ₁) receptors were shown to be antagonized by quercetin, but the mechanisms underlying these antagonistic actions are still unknown. We have analyzed here if the antagonistic action produced by quercetin on GABA(Aρ₁) receptors was related to its redox activity or due to alternative mechanism/s. Homomeric GABA(Aρ₁) receptors were expressed in frog oocytes and GABA-evoked responses electrophysiologically recorded. Quercetin effects on GABA(Aρ₁) receptors were examined in the absence or presence of ascorbic acid. Chemical protection of cysteines by selective sulfhydryl reagents and site directed mutagenesis experiments were also used to determine ρ₁ subunit residues involved in quercetin actions. Quercetin antagonized GABA(Aρ₁) receptor responses in a dose-dependent, fast and reversible manner. Quercetin inhibition was prevented in the presence of ascorbic acid, but not by thiol reagents that modify the extracellular Cys-loop of these receptors. H141, an aminoacidic residue located near to the ρ₁ subunit GABA binding site, was involved in the allosteric modulation of GABA(Aρ₁) receptors by several agents including ascorbic acid. Quercetin similarly antagonized GABA-evoked responses mediated by mutant (H141D)GABA(Aρ₁) and wild-type receptors, but prevention exerted by ascorbic acid on quercetin effects was impaired in mutant receptors. Taken together the present results suggest that quercetin antagonistic actions on GABA(Aρ₁) receptors are mediated through a redox-independent allosteric mechanism.

Anxiolytic effects of Julibroside C1 isolated from Albizzia julibrissin in mice

Julibroside C1 is a saponin-containing compound isolated from Albizzia julibrissin Durazz. In this study, we investigated the putative anxiolytic effects of Julibroside C1 using the elevated plus maze (EPM) in mice. Julibroside C1 at doses of 0.5 and 1 mg/kg significantly increased the time spent in the open arms and the number of entries into the open arms of the EPM compared to the control group. Moreover, the anxiolytic-like effects of Julibroside C1 (0.5 mg/kg) were blocked by WAY-100635 (5-HT1A receptor antagonist), bicuculline (GABA(A) receptor antagonist), and flumazenil (antagonist of the GABA(A) receptor benzodiazepine site). However, Julibroside C1 did not change locomotor activity or induce myorelaxant effects. We used quantitative receptor autoradiography to investigate the effects of Julibroside C1 on alterations in mouse brain receptors. After acute treatment with Julibroside C1 (0.5 mg/kg), [(3)H]-8-OH-DPAT binding was significantly decreased in the CA1 region of the hippocampus and [(3)H]-flunitrazepam binding was decreased remarkably in the cingulate cortex region. However, [(3)H]-muscimol binding did not show a significant change in any brain region. Taken together, our findings suggest that Julibroside C1 shows anxiolytic-like effects, which might be mediated by the 5-HT1A and GABA(A)-benzodiazepine receptor systems.

2'-Methoxy-6-methylflavone: a novel anxiolytic and sedative with subtype selective activating and modulating actions at GABA(A) receptors

BACKGROUND AND PURPOSE

Flavonoids are known to have anxiolytic and sedative effects mediated via actions on ionotropic GABA receptors. We sought to investigate this further.

EXPERIMENTAL APPROACH

We evaluated the effects of 2'-methoxy-6-methylflavone (2'MeO6MF) on native GABA(A) receptors in new-born rat hippocampal neurons and determined specificity from 18 human recombinant GABA(A) receptor subtypes expressed in Xenopus oocytes. We used ligand binding, two-electrode voltage clamp and patch clamp studies together with behavioural studies.

KEY RESULTS

2'MeO6MF potentiated GABA at α2β1γ2L and all α1-containing GABA(A) receptor subtypes. At α2β2/3γ2L GABA(A) receptors, however, 2'MeO6MF directly activated the receptors without potentiating GABA. This activation was attenuated by bicuculline and gabazine but not flumazenil indicating a novel site. Mutation studies showed position 265 in the β1/2 subunit was key to whether 2'MeO6MF was an activator or a potentiator. In hippocampal neurons, 2'MeO6MF directly activated single-channel currents that showed the hallmarks of GABA(A) Cl(-) currents. In the continued presence of 2'MeO6MF the single-channel conductance increased and these high conductance channels were disrupted by the γ2(381-403) MA peptide, indicating that such currents are mediated by α2/γ2-containing GABA(A) receptors. In mice, 2'MeO6MF (1-100 mg·kg(-1) ; i.p.) displayed anxiolytic-like effects in two unconditioned models of anxiety: the elevated plus maze and light/dark tests. 2'MeO6MF induced sedative effects at higher doses in the holeboard, actimeter and barbiturate-induced sleep time tests. No myorelaxant effects were observed in the horizontal wire test.

CONCLUSIONS AND IMPLICATIONS

2'MeO6MF will serve as a tool to study the complex nature of the activation and modulation of GABA(A) receptor subtypes.

Flavonoids as GABAA receptor ligands: the whole story?

Benzodiazepines are the most widely prescribed class of psychoactive drugs in current therapeutic use, despite the important unwanted side effects that they produce, such as sedation, myorelaxation, ataxia, amnesia, and ethanol and barbiturate potentiation and tolerance. They exert their therapeutic effects via binding to the benzodiazepine binding site of gamma-aminobutyric acid (GABA) type A receptors, and allosterically modulating the chloride flux through the ion channel complex. First isolated from plants used as tranquilizers in folkloric medicine, some natural flavonoids have been shown to possess selective affinity for the benzodiazepine binding site with a broad spectrum of central nervous system effects. Since the initial search for alternative benzodiazepine ligands amongst the flavonoids, a list of successful synthetic derivatives has been generated with enhanced activities. This review provides an update on research developments that have established the activity of natural and synthetic flavonoids on GABA type A receptors. Flavonoids are prominent drugs in the treatment of mental disorders, and can also be used as tools to study modulatory sites at GABA type A receptors and to develop GABA type A selective agents further.

Flavonoid modulation of GABA(A) receptors

There has been a resurgence of interest in synthetic and plant-derived flavonoids as modulators of γ-amino butyric acid-A (GABA(A) ) receptor function influencing inhibition mediated by the major inhibitory neurotransmitter GABA in the brain. Areas of interest include (i) flavonoids that show subtype selectivity in recombinant receptor studies in vitro consistent with their behavioural effects in vivo, (ii) flumazenil-insensitive modulation of GABA(A) receptor function by flavonoids, (iii) the ability of some flavonoids to act as second-order modulators of first-order modulation by benzodiazepines and (iv) the identification of the different sites of action of flavonoids on GABA(A) receptor complexes. An emerging area of interest is the activation of GABA(A) receptors by flavonoids in the absence of GABA. The relatively rigid shape of flavonoids means that they are useful scaffolds for the design of new therapeutic agents. Like steroids, flavonoids have wide-ranging effects on numerous biological targets. The challenge is to understand the structural determinants of flavonoid effects on particular targets and to develop agents specific for these targets.