Retrochalcone derivatives are positive allosteric modulators at synaptic and extrasynaptic GABA(A) receptors in vitro

Antinociceptive activity of doliroside B

CONTEXT

Dolichos trilobus Linn (Leguminosae) is often used in Yi ethnic medicine to treat pain, fracture, and rheumatism.

OBJECTIVE

To explore the therapeutic potential of doliroside B (DB) from D. trilobus and its disodium salt (DBDS) and the underlying mechanism in pain.

MATERIALS AND METHODS

In the writhing test, Kunming mice were orally treated with DB and DBDS at doses of 0.31, 0.62, 1.25, 2.5, and 5 mg/kg. Vehicle, morphine, indomethacin, and acetylsalicylic acid were used as negative and positive control on the nociception-induced models, respectively. In the hot plate test, mice were orally treated with DB and DBDS at doses of 2.5, 5, 10, and 20 mg/kg. In the formalin test, mice were orally treated with DB and DBDS at doses of 2.5, 5, 10, and 20 mg/kg. In the meanwhile, lipopolysaccharide-induced inflammatory model in RAW264.7 macrophages was adopted to study the mechanism of pain alleviation for DBDS.

RESULTS

DBDS (5 mg/kg) inhibited the writhing number by 80.2%, which exhibited the highest antinociceptive activity in pain models. DBDS could selectively inhibite the activity of COX-1. Meanwhile, it also reduced the production of NO, iNOS, and IL-6 by 55.8%, 69.0%, and 49.9% inhibition, respectively. It was found that DBDS also positively modulated the function of GABA_A1 receptor.

DISCUSSION AND CONCLUSIONS

DBDS displayed antinociceptive activity by acting on both the peripheral and central nervous systems, which may act on multitargets. Further work is warranted for developing DBDS into a potential drug for the treatment of pain.

Targeting GABA receptors with chalcone derivative compounds, what is the evidence?

INTRODUCTION

In medicinal chemistry, privileged structures have been frequently exploited as a successful template for drug discovery. Common simple scaffolds like chalcone are present in a wide range of naturally occurring chemicals. Chalcone exhibits extensive biological activity and has drawn attention in this context due to its function in the GABA receptor. Epilepsy and GABA receptors are related. It is a chronic neurological condition that affects globally.

AREAS COVERED

Numerous neurological disorders, including anxiety and epilepsy, have been related to GABA, the brain's most prevalent inhibitory neurotransmitter. We go through the role of GABA receptors in anxiety and epilepsy in this review. The structure-activity relationship of chalcone and its derivatives on the GABA receptor is covered in our final section.

EXPERT OPINION

GABA is a potential therapeutic target for issues associated with the nervous system. We talk about the potential effects of chalcone as a treatment for epilepsy and anxiety on the GABA receptor. Therefore, thorough research is necessary in this regard; the value of in silico tools in developing and enhancing GABA agonists is significant.

Isolation and structural characterization of dihydrobenzofuran congeners of licochalcone A

In an effort to explore the residual complexity of naturally occurring chalcones from the roots of Glycyrrhiza inflata (Fabaceae), two new licochalcone A (LicA) derivatives were isolated as trace metabolites from enriched fractions. Both constituents contain a dihydrofuran moiety linked to carbons C-4 and C-5 of the retrochalcone core. Compound 1 (LicAF1) represents a new chemical entity, whereas compound 2 (LicAF2) has previously been reported as a Lewis acid catalyzed rearrangement of LicA. Evaluation of chirality revealed that both dihydrofuran derivatives existed as a mixture of R and S enantiomers. Interestingly, when solutions were exposed to sunlight, both dihydrofuran retrochalcones, initially isolated as trans isomers, were found to rapidly isomerize yielding trans and cis isomers. Analysis of the 1D ¹H NMR spectra of the photolysis products revealed the presence of two sets of proton resonances ascribed to each of the geometric isomers. An up-field shift of all proton resonances arising from the cis isomer was observed, suggesting that anisotropic shielding effects were introduced through an overall perturbation of the 3-dimensional structure upon photoisomerization. Similar up-field shifts were observed in the ¹³C spectrum of the cis isomer, except for the CO, C-α, and C-6 carbons, which experienced downfield shifts. Analogous NMR results were observed for LicA. Hence, the results presented herein encompass the isolation and full characterization of LicAF analogs 1 and 2, and observations of their trans-to-cis photoisomerization through the systematic analysis of their NMR spectra.

Synthesis and multistate characterization of bis-flavylium dications – symmetric resorcinol- and phloroglucinol-type derivatives as stochastic systems

Two as one! Full kinetic and thermodynamic characterization of two easy-to-prepare bis-flavylium multistate systems showed stochastic behavior, thus revealing lack of interactions between flavylium moieties.

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.

3-Hydroxy-2'-methoxy-6-methylflavone: a potent anxiolytic with a unique selectivity profile at GABA(A) receptor subtypes

Genetic and pharmacological studies have demonstrated that α2- and α4-containing GABA(A) receptors mediate the anxiolytic effects of a number of agents. Flavonoids are a class of ligands that act at GABA(A) receptors and possess anxiolytic effects in vivo. Here we demonstrate that the synthetic flavonoid, 3-hydroxy-2'-methoxy-6-methylflavone (3-OH-2'MeO6MF) potentiates GABA-induced currents at recombinant α1/2β2, α1/2/4/6β1-3γ2L but not α3/5β1-3γ2L receptors expressed in Xenopus oocytes. The enhancement was evident at micromolar concentrations (EC(50) values between 38 and 106 μM) and occurred in a flumazenil-insensitive manner. 3-OH-2'MeO6MF displayed preference for β2/3- over β1-containing receptors with the highest efficacy observed at α2β2/3γ2L, displaying a 4-11-fold increase in efficacy over α2β1γ2L and α1/4/6-containing subtypes. In contrast, 3-OH-2'MeO6MF acted as a potent bicuculline-sensitive activator, devoid of potentiation effects at extrasynaptic α4β2/3δ receptors expressed in oocytes. The affinity of 3-OH-2'MeO6MF for α4β2/3δ receptors (EC(50) values between 1.4 and 2.5 μM) was 10-fold higher than at α4β1δ GABA(A) receptors. 3-OH-2'MeO6MF acted as a full agonist at α4β2/3δ (105% of the maximal GABA response) but as a partial agonist at α4β1δ (61% of the maximum GABA response) receptors. In mice, 3-OH-2'MeO6MF (1-100 mg/kg i.p.) induced anxiolytic-like effects in two unconditioned models of anxiety: the elevated plus maze and light/dark paradigms. No sedative or myorelaxant effects were detected using holeboard, actimeter and horizontal wire tests and only weak barbiturate potentiating effects on the loss of righting reflex test. Taken together, these data suggest that 3-OH-2'MeO6MF is an anxiolytic without sedative and myorelaxant effects acting through positive allosteric modulation of the α2β2/3γ2L and direct activation of α4β2/3δ GABA(A) receptor subtypes.