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

Attenuation of Streptozotocin-Induced Diabetic Neuropathic Allodynia by Flavone Derivative Through Modulation of GABA-ergic Mechanisms and Endogenous Biomarkers

Diabetic neuropathic pain is one of the most devasting disorders of peripheral nervous system. The loss of GABAergic inhibition is associated with the development of painful diabetic neuropathy. The current study evaluated the potential of 3-Hydroxy-2-methoxy-6-methyl flavone (3-OH-2'MeO6MF), to ameliorate peripheral neuropathic pain using an STZ-induced hyperglycemia rat model. The pain threshold was assessed by tail flick, cold, mechanical allodynia, and formalin test on days 0, 14, 21, and 28 after STZ administration accompanied by evaluation of several biochemical parameters. Administration of 3-OH-2'-MeO6MF (1,10, 30, and 100 mg/kg, i.p) significantly enhanced the tail withdrawal threshold in tail-flick and tail cold allodynia tests. 3-OH-2'-MeO6MF also increased the paw withdrawal threshold in mechanical allodynia and decreased paw licking time in the formalin test. Additionally, 3-OH-2'-MeO6MF also attenuated the increase in concentrations of myeloperoxidase (MPO), thiobarbituric acid reactive substances (TBARS), nitrite, TNF-α, and IL 6 along with increases in glutathione (GSH). Pretreatment of pentylenetetrazole (PTZ) (40 mg/kg, i.p.) abolished the antinociceptive effect of 3-OH-2'-MeO6MF in mechanical allodynia. Besides, the STZ-induced alterations in the GABA concentration and GABA transaminase activity attenuated by 3-OH-2'-MeO6MF treatment suggest GABAergic mechanisms. Molecular docking also authenticates the involvement of α2β2γ2L GABA-A receptors and GABA-T enzyme in the antinociceptive activities of 3-OH-2'-MeO6MF.

Antidepressant Activities of Synthesized Benzodiazepine Analogues in Mice

Depression is a serious psychological disorder which negatively affects human feelings and actions. The use of antidepressants is the therapy of choice while treating depression. However, such drugs are associated with severe side effects. There is a need for efficient and harmless drugs. In this connection, the present study was designed to synthesize several substituted benzodiazepine derivatives and explore their antidepressant potentials in an animal model. The chalcone backbone was initially synthesized, which was then converted into several substituted benzodiazepine derivatives designated as 1-6. The synthesized compounds were identified using spectroscopic techniques. The experimental animals (mice) after acclimatation were subjected to forced swim test (FST) and tail suspension test (TST) after oral administration of the synthesized compounds to evaluate their antidepressant potentials. At the completion of the mentioned test, the animals were sacrificed to determine GABA level in their brain hippocampus. The chloro-substituent compound (2) significantly reduced the immobility time (80.81 ± 1.14 s; p < 0.001 at 1.25 mg/kg body weight and 75.68 ± 3.73 s with p < 0.001 at 2.5 mg/kg body weight dose), whereas nitro-substituent compound (5) reduced the immobility time to 118.95 ± 1.31 and 106.69 ± 3.62 s (p < 0.001), respectively, at the tested doses (FST). For control groups, the recorded immobility time recorded was 177.24 ± 1.82 s. The standard drug diazepam significantly reduced immobility time to 70.13 ± 4.12 s while imipramine reduced it to 65.45 ± 2.81 s (p < 0.001). Similarly, in the TST, the compound 2 reduced immobility time to 74.93 ± 1.14 s (p < 0.001) and 70.38 ± 1.43 s (p < 0.001), while compound 5 reduced it to 88.23 ± 1.89 s (p < 0.001) and 91.31 ± 1.73 s (p < 0.001) at the tested doses, respectively, as compared to the control group immobility time (166.13 ± 2.18 s). The compounds 1, 3, 4, and 6 showed weak antidepressant responses as compared to compounds 2 and 5. The compounds 2 and 5 also significantly enhanced the GABA level in the brain's hippocampus of experimental animals, indicating the possible involvement of GABAergic mechanism in alleviating the depression which is evident from the significant increase in mRNA levels for the α subunit of the GABA_A receptors in the prefrontal cortex of mice as well. From the results, it can be concluded that compound 2 and 5 could be used as alternative drugs of depression. However, further exploration in this connection is needed in other animal models in order to confirm the observed results in this study.

Antiamnesic Effects of Feralolide Isolated from Aloe vera Resin Miller against Learning Impairments Induced in Mice

Feralolide, a dihydroisocoumarin, was isolated from the methanolic extract of resin of Aloe vera. The present study aims to investigate the in vivo ability of feralolide to ameliorate memory impairment induced by scopolamine using a battery of in vitro assays, such as antioxidant and acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition, and in vivo animal models, including elevated plus maze, Morris water maze, passive avoidance, and novel object recognition tests. Feralolide caused a concentration-dependent inhibition of AChE and BuChE enzymes with IC50 values of 55 and 52 μg/mL, respectively, and antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2, 2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) with IC50 values 170 and 220 μg/mL, respectively. Feralolide reversed the scopolamine-induced amnesia as indicated by a dose-dependent decrease in escape latency, path length, and passing frequency in the Morris water maze test compared with the relevant control. The compound also significantly increased the discrimination index in a dose-dependent manner in NORT and decreased transfer latency in EPM, reflective of its memory-enhancing effect. Furthermore, feralolide also caused significant dose-dependent elevation in the step-down latency (SDL) in the passive avoidance test. The results indicated that feralolide might be a helpful memory restorative mediator in treating cognitive disorders such as Alzheimer’s disease.

Phenolics as GABAA Receptor Ligands: An Updated Review

Natural products can act as potential GABA modulators, avoiding the undesirable effects of traditional pharmacology used for the inhibition of the central nervous system such as benzodiazepines (BZD). Phenolics, especially flavonoids and phlorotannins, have been considered as modulators of the BZD-site of GABA_A receptors (GABA_ARs), with sedative, anxiolytic or anticonvulsant effects. However, the wide chemical structural variability of flavonoids shows their potential action at more than one additional binding site on GABA_ARs, which may act either negatively, positively, by neutralizing GABA_ARs, or directly as allosteric agonists. Therefore, the aim of the present review is to compile and discuss an update of the role of phenolics, namely as pharmacological targets involving dysfunctions of the GABA system, analyzing both their different compounds and their mechanism as GABAergic modulators. We focus this review on articles written in English since the year 2010 until the present. Of course, although more research would be necessary to fully establish the type specificity of phenolics and their pharmacological activity, the evidence supports their potential as GABA_AR modulators, thereby favoring their inclusion in the development of new therapeutic targets based on natural products. Specifically, the data compiled in this review allows for the directing of future research towards ortho-dihydroxy diterpene galdosol, the flavonoids isoliquiritigenin (chalcone), rhusflavone and agathisflavone (biflavonoids), as well as the phlorotannins, dieckol and triphlorethol A. Clinically, flavonoids are the most interesting phenolics due to their potential as anticonvulsant and anxiolytic drugs, and phlorotannins are also of interest as sedative agents.

Enhanced neuroprotective and antidepressant activity of curcumin-loaded nanostructured lipid carriers in lipopolysaccharide-induced depression and anxiety rat model

The present study aims to develop curcumin-loaded nanostructured lipid carriers (CUR-NLCs) and investigate their neuroprotective effects in lipopolysaccharide (LPS)-induced depression and anxiety model. Nanotemplate engineering technique was used to prepare CUR-NLCs with Compritol 888 ATO and oleic acid as solid and liquid lipid, respectively. Poloxamer 188, Tween 80 and Span 80 were used as stabilizing agents for solid-liquid lipid core. The physicochemical parameters of CUR-NLCs were determined followed by in vitro drug release and in vivo neuroprotective activity in rats. The optimized CUR-NLCs demonstrated nanometric particle size of 147.8 nm, surface charge of -32.8 mV and incorporation efficiency of 91.0%. CUR-NLCs showed initial rapid followed by a sustained drug release reaching up to 73% after 24 h. CUR-NLCs significantly elevated struggling time and decreased immobility time in forced swim and tail suspension tests. A substantial increase in time spent and number of entries into the light and open compartments was observed in light-dark box and elevated plus maze models. CUR-NLCs improved the tissue architecture and suppressed the expression of p-NF-κB, TNF-α and COX-2 in brain tissues from histological and immunohistochemical analysis. CUR-NLCs improved the neuroprotective effect of curcumin and can be used as a potential therapeutics for depression and anxiety.

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.

Nanostructured lipid carriers-mediated brain delivery of carbamazepine for improved in vivo anticonvulsant and anxiolytic activity

The limited brain delivery of carbamezapine (CBZ) presents a major hurdle in the successful epilepsy treatment. The potential of carbamezapine-loaded nanostructured lipid carriers (CBZ-NLCs) for improved brain delivery is investigated in the current study. CBZ-NLCs were prepared by using binary mixture of trilaurin and oleic acid as a lipid core stabilized with Poloxamer 188, Tween 80 and Span 80. CBZ-NLCs were evaluated for physicochemical properties, in vitro release, in vivo brain kinetics, anticonvulsant and anxiolytic activities. The optimized CBZ-NLCs demonstrated nanometric particle size (97.7 nm), surface charge of -22 mV and high drug incorporation (85%). CBZ-NLCs displayed biphasic release pattern with initial fast followed by sustained drug release. CBZ-NLCs significantly enhanced the AUC of CBZ (520.4 µg·h/mL) in brain compared with CBZ dispersion (244.9 µg·h/mL). In vivo anticonvulsant activity of CBZ-NLCs in PTZ-induced seizure model showed a significant increase in the onset time (143.0 sec) and reduction in duration (17.2 sec) of tonic-clonic seizures compared with CBZ dispersion (75.4 and 37.2 sec). The anxiolytic activity in light-dark box and elevated-plus maze models also demonstrated superiority of CBZ-NLCs to CBZ dispersion. From the results, CBZ-NLCs presents a promising strategy to improve brain delivery and therapeutic outcomes of CBZ in epilepsy.

The flavonoid, 2'-methoxy-6-methylflavone, affords neuroprotection following focal cerebral ischaemia

Tonic inhibitory currents, mediated by extrasynaptic GABA_A receptors, are elevated at a delay following stroke. Flavonoids minimise the extent of cellular damage following stroke, but little is known about their mode of action. We demonstrate that the flavonoid, 2'-methoxy-6-methylflavone (0.1-10 µM; 2'MeO6MF), increases GABA_A receptor tonic currents presumably via δ-containing GABA_A receptors. Treatment with 2'MeO6MF 1-6 h post focal ischaemia dose dependently decreases infarct volume and improves functional recovery. The effect of 2'MeO6MF was attenuated in δ^-/- mice, indicating that the effects of the flavonoid were mediated via δ-containing GABA_A receptors. Further, as flavonoids have been shown to have multiple modes of action, we investigated the anti-inflammatory effects of 2'MeO6MF. Using a macrophage cell line, we show that 2'MeO6MF can dampen an LPS-induced elevation in NFkB activity. Assessment of vehicle-treated stroke animals revealed a significant increase in circulating IL1β, TNFα and IFγ levels. Treatment with 2'MeO6MF dampened the stroke-induced increase in circulating cytokines, which was blocked in the presence of the pan-AKT inhibitor, GSK690693. These studies support the hypothesis that compounds that potentiate tonic inhibition via δ-containing GABA_A receptors soon after stroke can afford neuroprotection.

Evidence for the involvement of a GABAergic mechanism in the effectiveness of natural and synthetically modified incensole derivatives in neuropharmacological disorders: A computational and pharmacological approach

In the course of our continuing exploration for novel bioactive lead compounds (s) from the species Boswellia, we have recently reported incensole derivatives isolated from Boswellia papyrifera Hochst. Given the known antidepressant-like effects of incensole and incensole acetate, we herein present that the low dose intraperitoneal administration of incensole derivatives, namely, incensfuran and incensone, showed significant antidepressant-like effects in the forced swim test (FST) and tail suspension test (TST). Furthermore, these compounds were evaluated for their anxiolytic potential in the elevated plus maze (EPM) and light dark box (LDB) tests and anticonvulsant effects in pentylenetetrazole (PTZ)-induced seizure tests. In the EPM test, administration of these compounds led to dose-dependent increases in open arm entries and in the time spent in EPM open arms. Similar results were obtained in the LDB test, wherein compounds these caused significant increases in the number of transitions between lit and dark compartments and the time spent in the lit compartment. The anxiolytic-like effects in the EPM were not reversed by pretreatment with flumazenil, whereas PTZ and bicuculline (BIC) completely abolished the anxiolytic effects, showing the involvement of the non-benzodiazepine binding sites of GABA_A receptors. All four compounds induced significantly elevated brain GABA levels, indicating the involvement of a GABAergic mechanism. Additionally, molecular docking was conducted to elucidate the mode of action for the anxiolytic and anticonvulsant effects of these derivatives. Moreover, these compounds also possess drug-like properties and excellent ADMET profiles.

Anti-nociceptive and Anti-inflammatory Activities of Asparacosin A Involve Selective Cyclooxygenase 2 and Inflammatory Cytokines Inhibition: An in-vitro, in-vivo, and in-silico Approach

Triterpenes possess anti-inflammatory and anti-nociceptive effects. In this study anti-inflammatory activities of Asparacosin A were evaluated' using in-vitro cyclooxygenases 1 and 2 (COX-1/2) inhibition assays. Moreover, anti-nociceptive activities were assessed in-vivo by carrageenan-induced paw edema test, xylene-induced ear edema tests, and acetic acid-induced writhing and formalin tests. Additionally molecular docking was conducted to elucidate the binding mechanism of the compound and to correlate the in-vitro findings with the in-silico data. Oral administration of Asparacosin A at the doses of 10, 20, and 40 mg/kg induced significant anti-inflammatory effects (^*p < 0.05, ^**p < 0.01, and ^***p < 0.001) in a dose-dependent manner in both models. Asparacosin A also inhibited the human recombinant COX-2 enzyme and caused a dose-dependent decrease in the levels of TNF-α, IL-1β, and PGE2 in the carrageenan-induced paws. Moreover, Asparacosin A displayed significant anti-nociceptive effects (^*p < 0.05, ^**p < 0.01, ^***p < 0.001) at the doses of 10, 20, and 40 mg/kg in acetic-acid induced writhing test. However, in formalin test, Asparacosin A (10–40 mg/kg, p.o) produced anti-nociceptive effects only in the late phase, similar to the effect observed with the reference drug celecoxib (50 mg/kg, p.o). Molecular docking was carried out on both COX-1 and COX-2 structures which revealed that Asparacosin A targets allosteric binding site similar to the binding mode of the selective COX inhibitor. In conclusion, Asparacosin A exhibits anti-inflammatory and peripheral anti-nociceptive activities which are likely mediated via inhibition of COX-2 enzyme and inflammatory cytokines. Furthermore, Asparacosin A can serve as a model to obtain new and more selective potent anti-inflammatory and anti-nociceptive drugs.

Phytochemical analysis and antidiabetic potential of Elaeagnus umbellata (Thunb.) in streptozotocin-induced diabetic rats: pharmacological and computational approach

Background

The fruit of Elaeagnus umbellata has high medicinal values and is an excellent source of phytochemicals. This study was aimed to evaluate the antioxidant, enzyme inhibitory and antidiabetic potential of Elaeagnus umbellata.

Methods

The antioxidant potential of the crude extract and subfractions of E. umbellata fruit were determined using DPPH (2, 20-diphenyl-1-picrylhydrazyl) and ABTS (2, 2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid) assays. The enzyme inhibitory potentials of extracts against α-amylase and α-glucosidase enzymes were also determined. The in vivo anti-hyperglycemic effects of the extract in STZ-induced type 2 diabetes were determined using Sprague Dawley adult rats. HPLC system (Agilent 1260) was used for the identification of bioactive compounds present in extracts. Molecular docking was used to identify and compare the interaction between the compounds (active constituents) and standard inhibitor acarbose with the α-amylase and α-glucosidase active sites.

Results

The chloroform, ethyl acetate, and butanol fractions showed significant antioxidant potential with IC₅₀ values of 40, 45 and 60 μg/mL against DPPH and 57, 70 and 120 μg/mL against ABTS free radicals respectively. The chloroform and ethyl acetate were highly active against α-amylase and α-glucosidase (IC₅₀ values 58 and 200 μg/ml against α-amylase 60 and 140 μg/ml against α-glucosidase. The crude extract, chloroform, and ethyl acetate fractions were more potent in controlling the hyperglycemia in STZ-induced type 2 diabetes in rats and considerable reduction of glucose level was observed compared to the non-treated group. Furthermore, the extracts were also found useful in controlling the secondary complications associated with type 2 diabetes mellitus which was evident from the observed substantial reduction in the blood level of serum glutamate oxaloacetate transaminase, serum glutamate pyruvate transaminase, alkaline phosphatase, total cholesterol, low-density lipoproteins, and triglycerides. The molecular docking approach indicated the favorable inhibitory interaction between the docked compounds and the active sites of the α-amylase and α-glucosidase. All docked compounds occupied the same binding site as occupied by acarbose.

Conclusion

It was concluded that E. umbellata can be used in the treatment of type 2 diabetes and oxidative stress. The extracts were also found to be effective in relieving the secondary complications associated with type 2 diabetes.

Graphical abstract

Electronic supplementary material

The online version of this article (10.1186/s12906-018-2381-8) contains supplementary material, which is available to authorized users.

Sedative-hypnotic like effect of 5-methoxyflavone in mice and investigation on possible mechanisms by in vivo and in silico methods

Flavonoids have been shown to possess central nervous system (CNS) depressant effect mediated through the ionotropic GABA_A receptors. In the present study, 5-methoxyflavone was evaluated for sedative-hypnotic like activity in mice and the mechanisms involved by employing a battery of tests including molecular docking studies. In the open field test, 5-methoxyflavone in various doses (50, 100 and 150 mg/kg, i.p) exhibited a significant and dose-dependent reduction in the spontaneous locomotor activity (F (530) = 87.17 P < 0.001). Pretreatment with 5-methoxyflavone decreased the latency to sleep induction after pentobarbitone or ether administration and also significantly increased the duration of sleep (p < 0.001). A significant and dose-dependent myorelaxant effect was observed with 5-methoxyflavone in the inclined plane, horizontal wire test and rota rod test. Pretreatment with picrotoxin, bicuculline, glycine, caffeine or NMDA either decreased or completely abolished the hypnotic effect of 5-methoxyflavone in mice. The above results revealed the involvement of GABA_A, adenosine, glycine and NMDA receptors in the hypnotic effect of 5-methoxyflavone. The results of in silico studies indicated that, 5-methoxyflavone exhibits good binding affinity towards these receptors by H-bond interactions. In conclusion, the present study identified a novel and potential sedative-hypnotic like effect of 5-methoxyflavone involving multiple mechanisms.

Anticonvulsant, Anxiolytic, and Sedative Activities of Verbena officinalis

We describe different neuropharmacological effects of Verbena officinalis crude extract (Vo.Cr). Pentylenetetrazole (PTZ)-induced seizures, elevated plus maze, light-dark box (LDB), open field and thiopental-induced sleeping test models were employed to evaluate Vo.Cr actions in mice. Vo.Cr dose-dependently (100-500 mg/Kg) delayed onset time of myoclonic jerks and tonic-clonic seizures, while decreased duration of tonic-clonic seizures (P < 0.05, P < 0.001 vs. saline group). Vo.Cr at 100 and 300-500 mg/Kg doses reduced animals' mortality in PTZ-induced seizures test to 75 and 0%, respectively. Vo.Cr (50-300 mg/Kg) significantly increased time spent and number of entries into open arms, while decreased time spent and number of entries into closed arms (P < 0.05, P < 0.01, P < 0.001 vs. saline group), measured in elevated plus maze. Vo.Cr (50-300 mg/Kg) increased time spent in light compartment, while decreased time spent in dark compartment (P < 0.01, P < 0.001 vs. saline group) in LDB, like caused by diazepam. In open field test, Vo.Cr decreased number of ambulations and rearings frequencies, while increased the number of central squares crossings. In thiopental-induced sleeping test, Vo.Cr (50-300 mg/Kg) decreased onset time of sleep, while increased the duration of sleep (P < 0.05, P < 0.01, P < 0.001 vs. saline group). These results indicate that Verbena officinalis possess anticonvulsant, anxiolytic and sedative activities, which provides scientific background for its medicinal application in various neurological ailments, such as epilepsy, anxiety, and insomnia.

Hepatoprotective activity of viscosine is mediated by attenuation of hepatic macrophages and iNOS expression in CCl4-intoxicated rats

This study investigated the molecular mechanism(s) of the protective effects of a C-alkylated flavonoid, viscosine on an animal model of CCl₄-induced hepatotoxicity. Viscosine at 20, 50 and 100 mg kg^-1 was orally administered in a dose dependent manner per day for 3 days before the CCl₄ (1 : 1 v/v in olive oil, 1 ml kg^-1) treatment and 2 days after the treatment. Hepatoprotection was assessed in terms of reduction in serum enzyme activities (ALT, AST, and ALP) that occur after CCl₄ injury, and by histopathology and immunohistochemistry. The rise in serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) in CCl₄-intoxicated rats was markedly suppressed by viscosine in a concentration dependent manner. The decrease in the activity of hepatic antioxidant enzyme, SOD, was significantly prevented by viscosine, likewise gradually the levels of MDA and GSH were also normalized compared to silymarin. Viscosine also reduced the CCl₄-induced damaged area from 2% to 0% as assessed by histopathology and prevented the mixed inflammatory infiltrate. Viscosine attenuated the inflammation in the liver around the injured central vein region by downregulating the CCl₄ induced activation of hepatic CD68+ macrophages, thereby reducing their number as well. The expression of inducible nitric oxide synthase (iNOS) was more potentially suppressed by viscosine compared to the FDA approved positive control silymarin. The results of this study indicate that viscosine could be effective in protecting the liver from acute CCl₄-induced injury. The hepatoprotective mechanisms of viscosine may be related to the free radical scavenging and attenuation of oxidative stress, as well as to the inhibition of inflammatory response in the liver. Here, we are proposing a novel mechanism of action of viscosine and suggesting that it may be a safe and better in vivo antioxidant.

Zolpidem is a potent stoichiometry-selective modulator of α1β3 GABAA receptors: evidence of a novel benzodiazepine site in the α1-α1 interface

Zolpidem is not a typical GABA_A receptor hypnotic. Unlike benzodiazepines, zolpidem modulates tonic GABA currents in the rat dorsal motor nucleus of the vagus, exhibits residual effects in mice lacking the benzodiazepine binding site, and improves speech, cognitive and motor function in human patients with severe brain injury. The receptor by which zolpidem mediates these effects is not known. In this study we evaluated binary α1β3 GABA_A receptors in either the 3α1:2β3 or 2α1:3β3 subunit stoichiometry, which differ by the existence of either an α1-α1 interface, or a β3-β3 interface, respectively. Both receptor stoichiometries are readily expressed in Xenopus oocytes, distinguished from each other by using GABA, zolpidem, diazepam and Zn²⁺. At the 3α1:2β3 receptor, clinically relevant concentrations of zolpidem enhanced GABA in a flumazenil-sensitive manner. The efficacy of diazepam was significantly lower compared to zolpidem. No modulation by either zolpidem or diazepam was detected at the 2α1:3β3 receptor, indicating that the binding site for zolpidem is at the α1-α1 interface, a site mimicking the classical α1-γ2 benzodiazepine site. Activating α1β3 (3α1:2β3) receptors may, in part, mediate the physiological effects of zolpidem observed under distinct physiological and clinical conditions, constituting a potentially attractive drug target.

GABA-A Receptor Modulation and Anticonvulsant, Anxiolytic, and Antidepressant Activities of Constituents from Artemisia indica Linn

Artemisia indica, also known as “Mugwort,” has been widely used in traditional medicines. However, few studies have investigated the effects of nonvolatile components of Artemisia indica on central nervous system's function. Fractionation of Artemisia indica led to the isolation of carnosol, ursolic acid, and oleanolic acid which were evaluated for their effects on GABA-A receptors in electrophysiological studies in Xenopus oocytes and were subsequently investigated in mouse models of acute toxicity, convulsions (pentylenetetrazole induced seizures), depression (tail suspension and forced swim tests), and anxiety (elevated plus maze and light/dark box paradigms). Carnosol, ursolic acid, and oleanolic acid were found to be positive modulators of α1β2γ2L GABA-A receptors and the modulation was antagonized by flumazenil. Carnosol, ursolic acid, and oleanolic acid were found to be devoid of any signs of acute toxicity (50–200 mg/kg) but elicited anticonvulsant, antidepressant, and anxiolytic activities. Thus carnosol, ursolic acid, and oleanolic acid demonstrated CNS activity in mouse models of anticonvulsant, antidepressant, and anxiolysis. The anxiolytic activity of all three compounds was ameliorated by flumazenil suggesting a mode of action via the benzodiazepine binding site of GABA-A receptors.

The Direct Actions of GABA, 2'-Methoxy-6-Methylflavone and General Anaesthetics at β3γ2L GABAA Receptors: Evidence for Receptors with Different Subunit Stoichiometries

2'-Methoxy-6-methylflavone (2'MeO6MF) is an anxiolytic flavonoid which has been shown to display GABAA receptor (GABAAR) β2/3-subunit selectivity, a pharmacological profile similar to that of the general anaesthetic etomidate. Electrophysiological studies suggest that the full agonist action of 2'MeO6MF at α2β3γ2L GABAARs may mediate the flavonoid's in vivo effects. However, we found variations in the relative efficacy of 2'MeO6MF (2'MeO6MF-elicited current responses normalised to the maximal GABA response) at α2β3γ2L GABAARs due to the presence of mixed receptor populations. To understand which receptor subpopulation(s) underlie the variations observed, we conducted a systematic investigation of 2'MeO6MF activity at all receptor combinations that could theoretically form (α2, β3, γ2L, α2β3, α2γ2L, β3γ2L and α2β3γ2L) in Xenopus oocytes using the two-electrode voltage clamp technique. We found that 2'MeO6MF activated non-α-containing β3γ2L receptors. In an attempt to establish the optimal conditions to express a uniform population of these receptors, we found that varying the relative amounts of β3:γ2L subunit mRNAs resulted in differences in the level of constitutive activity, the GABA concentration-response relationships, and the relative efficacy of 2'MeO6MF activation. Like 2'MeO6MF, general anaesthetics such as etomidate and propofol also showed distinct levels of relative efficacy across different injection ratios. Based on these results, we infer that β3γ2L receptors may form with different subunit stoichiometries, resulting in the complex pharmacology observed across different injection ratios. Moreover, the discovery that GABA and etomidate have direct actions at the α-lacking β3γ2L receptors raises questions about the structural requirements for their respective binding sites at GABAARs.

Comparative pharmacological evaluation of the cathinone derivatives, mephedrone and methedrone, in mice

Mephedrone and methedrone are cathinone-related compounds, which act as non-selective substrates for monoamine transporters, facilitating a neurotransmitter release. We compared the acute pharmacological effects of mephedrone and methedrone, attempting to further evaluate the action mechanisms of methedrone by responsibly and ethically using mice under approved procedures. The effects of both compounds were examined from 10 to 60 min, in a series of behavioral paradigms, namely open-field, plus-maze, hot-plate and tail suspension tests, whereas neurotransmitter brain tissue levels were determined ex vivo by HPLC. Separate groups were pre-treated with the dopamine (DA) antagonist haloperidol, or the serotonin (5-HT) synthesis inhibitor ρCPA, to further assess the mechanisms underlying methedrone effects. The compounds caused marked hyperlocomotion, displaying dissimilar stereotyped behavior, in an open-field arena. Mephedrone caused anxiolytic-like effects, while methedrone induced anxiogenic-like actions in the elevated plus-maze. Both compounds displayed thermal antinociception, with a reduced immobility time in the tail suspension model. Mephedrone triggered a 2- and 3-fold increment of dopamine and serotonin tissue levels, respectively, in the nucleus accumbens, with a 1.5-fold elevation of tissue dopamine in the frontal cortex. Methedrone caused a 2-fold increment of tissue dopamine in the nucleus accumbens and in the striatum, and a 1.5-fold increment of serotonin tissue levels in the hippocampus and striatum. In vivo methedrone effects were partially inhibited by a pre-treatment with haloperidol or ρCPA. Despite similar actions on locomotion, analgesia, and depression-like behavior, the acute administration of mephedrone and methedrone elicited divergent effects on anxiety-like behavior and stereotyped movements in mice, which might be related to the distinct modulation of brain tissue neurotransmitter levels.

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.

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.

Differential modulation of GABA(A) receptor function by aryl pyrazoles

Several aryl pyrazoles characterized by a different molecular structure (flexible vs constrained), but chemically related to rimonabant and AM251, were tested for their ability to modulate the function of recombinant α1β2γ2L GABAA receptors expressed in Xenopus laevis oocytes. The effects of 6Bio-R, 14Bio-R, NESS 0327, GP1a and GP2a (0.3-30 μM) were evaluated using a two-electrode voltage-clamp technique. 6Bio-R and 14Bio-R potentiated GABA-evoked Cl(-) currents. NESS 0327, GP1a and GP2a did not affect the GABAA receptor function, but they acted as antagonists of 6Bio-R. Moreover, NESS 0327 inhibited the potentiation of the GABAA receptor function induced by rimonabant. The benzodiazepine site seems to participate in the action of these compounds. In fact, flumazenil antagonized the potentiation of the GABAA receptor induced by 6Bio-R, and NESS 0327 reduced the action of lorazepam and zolpidem. On the contrary, NESS 0327 did not antagonize the action of "classic" GABAergic modulators (propanol, anesthetics, barbiturates or steroids). In α1β2 receptors 6Bio-R potentiated the GABAergic function, but flumazenil was still able to antagonize the potentiation induced by 6Bio-R. Aryl pyrazole derivatives activity at the GABAA receptor depends on their molecular structure. These compounds bind to both an αβγ binding site, and to an α/β site which do not require the γ subunit and that may provide structural leads for drugs with potential anticonvulsant effects.

Evaluation of antidiabetic and antihyperlipidemic activity of Artemisia indica linn (aeriel parts) in Streptozotocin induced diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetes mellitus is a major metabolic disorder affecting a huge population all over the world. Artemisia species have been extensively used for the management of diabetes in folkloric medicine. The present study is designed to investigate the antidiabetic and antihyperlipidemic effects of aeriel parts of Artemisia indica.

MATERIALS AND METHODS

Hydromethanolic crude extracts, chloroform, ethyl acetate and n-butanol fractions of aerial parts of Artemisia indica were tested for their antidiabetic potential in Streptozotocin (STZ) (50mg/kg, i.p.) induced diabetic Sprague-Dawley rats. Blood glucose level, body weight, serum lipid profile and activities of liver enzymes were determined. The extracts were further subjected to preliminary phytochemical analysis.

RESULTS

A daily oral dose of hydromethanolic crude extracts (200 and 400mg/kg b.w.) and chloroform fraction (200mg/kg b.w.) of Artemisia indica for 15 days showed a significant reduction in blood glucose level which was comparable to that of the standard antidiabetic drug, glibenclamide (500 μg/kg, p.o.). Artemisia indica extracts also showed reduction in total cholesterol, triglycerides and low density lipoproteins as well as serum creatinine level, serum glutamate pyruvate transaminase (SGPT), serum glutamate oxaloacetate transaminase (SGOT) and alkaline phosphatase (ALP) in diabetic rats.

CONCLUSION

According to the results Artemisia indica possesses hypoglycemic, antihyperlipidemic and valuable effects on liver and renal functions in diabetic rats, which seems to validate its traditional usage.

Modulation of ionotropic GABA receptors by 6-methoxyflavanone and 6-methoxyflavone

We evaluated the effects of 6-methoxyflavanone and 6-methoxyflavone on wild-type α1/α2β2γ2L GABAA and ρ1 GABAC receptors and on mutant ρ1I307S, ρ1W328 M, ρ1I307S/W328 M GABAC receptors expressed in Xenopus oocytes using two-electrode voltage clamp and radioligand binding. 6-Methoxyflavanone and 6-methoxyflavone act as a flumazenil-insensitive positive allosteric modulator of GABA responses at human recombinant α1β2γ2L and α2β2γ2L GABAA receptors. However, unlike 6-methoxyflavone, 6-methoxyflavanone was relatively inactive at α1β2 GABAA receptors. 6-Methoxyflavanone inhibited [(3)H]-flunitrazepam binding to rat brain membranes. Both flavonoids were found to be inactive as modulators at ρ1, ρ1I307S and ρ1W328 M GABA receptors but acted as positive allosteric modulators of GABA at the benzodiazepine sensitive ρ1I307S/W328 M GABA receptors. This double mutant retains ρ1 properties of being insensitive to bicuculline and antagonised by TPMPA and THIP. Additionally, 6-methoxyflavanone was also a partial agonist at ρ1W328 M GABA receptors. The relative inactivity of 6-methoxyflavanone at α1β2 GABAA receptors and it's partial agonist action at ρ1W328 M GABA receptors suggest that it exhibits a unique profile not matched by other flavonoids.

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.

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.