Direct Structural Insights into GABAA Receptor Pharmacology

Effect of two novel GABAA receptor positive allosteric modulators on neuropathic and inflammatory pain in mice

Loss of GABAergic inhibition in the spinal dorsal horn (SDH) is implicated in central sensitization and chronic pain. Both agonists and positive allosteric modulators (PAMs) of GABAA receptor are found to be effective in the management of chronic pain. In addition to benzodiazepines, neuroactive steroids (NASs) also act as PAMs through binding to unique sites of GABAA receptors. Thus, it is worth investigating whether these NASs can attenuate chronic pain. This study tested the antinociceptive properties of two novel NAS PAMs, ganaxolone and zuranolone, in segmental spinal nerve ligation (SNL)-induced neuropathic pain and complete Freund's adjuvant (CFA)-induced inflammation pain models. Spinally administered ganaxolone and zuranolone both exhibited dose-dependent analgesic effects but with quite different durations. This antinociceptive effect might be generated from elevated GABAergic inhibition, as the PAMs both enhanced GABA-evoked currents in SDH neurons, and the K+-Cl- cotransporter isoform 2 (KCC2) antagonist reversed the analgesic effect of the PAMs. Different from ganaxolone, zuranolone produced a durable increase in the surface expression of GABAA receptors and of the amplitude of spontaneous inhibitory currents, which may contribute to the long-lasting analgesic effect. Furthermore, the PAMs alleviated SNL-induced mechanical allodynia synergistically with diazepam or GABAA receptor activator muscimol at inactive doses, consistent with the non-competitive activity and distinct binding sites from benzodiazepines. In summary, our findings suggest that NASs may not only acutely modulate GABA receptor activity but also induce sustained metabotropic effects on GABAA receptors and thus exert long-lasting antinociceptive effects.

Lotilaner for Demodex Blepharitis: The Journey from Veterinary Use to Human Medicine

In 2023, Xdemvy® (0.25% lotilaner ophthalmic solution) was approved by the U.S. FDA for treating Demodex blepharitis in humans. This article reviews lotilaner's history, physicochemical properties, pharmacokinetics, pharmacology, clinical outcomes, and other indications for which it is being evaluated clinically. Furthermore, the article discusses Demodex blepharitis, alternative treatments used in the clinic to ameliorate its symptoms, and other drugs in development. Prior to its approval in humans, lotilaner found extensive application in treating parasitic infections in cats and dogs. Lotilaner was previously approved in 2017 as an oral veterinary medicine (Credelio®) for canines to treat demodicosis, other mite infections, and tick infections. Lotilaner belongs to the isoxazoline class of drugs and is a potent arthropod-selective gamma-aminobutyric acid-gated chloride ion channel inhibitor. Like several other drugs in the isoxazoline class, lotilaner has a long plasma half-life and high plasma protein binding of about 99.9%. When used as indicated, lotilaner treats infested Demodex blepharitis in 42 days, with its antiparasitic action starting within 24 h. Furthermore, lotilaner is also being evaluated for its efficacy in other conditions such as Lyme disease and dry eye disease. Other products evaluated for treating Demodex blepharitis include ivermectin eye ointment, ivermectin-metronidazole gel, permethrin cream, terpinen-4-ol wipes, and hypochlorous acid spray. Along with these, azithromycin eye drop, azithromycin/loteprednol eye drop, and other treatments are being evaluated for treating blepharitis. Other drugs from the isoxazoline drug class including afoxolaner, sarolaner, and fluralaner, could also be potentially explored for human use.

Inhibition of NMDA receptors and other ion channel types by membrane-associated drugs

N-methyl-D-aspartate receptors (NMDARs) are ligand-gated ion channels present at most excitatory synapses in the brain that play essential roles in cognitive functions including learning and memory consolidation. However, NMDAR dysregulation is implicated in many nervous system disorders. Diseases that involve pathological hyperactivity of NMDARs can be treated clinically through inhibition by channel blocking drugs. NMDAR channel block can occur via two known mechanisms. First, in traditional block, charged drug molecules can enter the channel directly from the extracellular solution after NMDAR activation and channel opening. Second, uncharged molecules of channel blocking drug can enter the hydrophobic plasma membrane, and upon NMDAR activation the membrane-associated drug can transit into the channel through a fenestration within the NMDAR. This membrane-associated mechanism of action is called membrane to channel inhibition (MCI) and is not well understood despite the clinical importance of NMDAR channel blocking drugs. Intriguingly, a hydrophobic route of access for drugs is not unique to NMDARs. Our review will address inhibition of NMDARs and other ion channels by membrane-associated drugs and consider how the path of access may affect a drug's therapeutic potential.

Beyond surgery: Repurposing anesthetics for treatment of central nervous system disorders

The development of new drugs is a complex, expensive, and time-consuming process, often fraught with a high likelihood of failure. Amid these obstacles, drug repurposing, which identifies new therapeutic applications for already existing medications, offers a more economical and time-saving approach, particularly in the challenging field of neurological and psychiatric disorders. This narrative review explores both preclinical and clinical studies to examine the potential of anesthetics such as ketamine, nitrous oxide, isoflurane, sevoflurane, propofol, dexmedetomidine, and sodium oxybate in treating central nervous system disorders. Various research highlights the potential of anesthetics to provide rapid antidepressant effects, enhance learning and memory, improve synaptic plasticity, and offer neuroprotective benefits, demonstrating promise for treating depression, post-traumatic stress disorder, cognitive decline, traumatic brain injury, and neurodegenerative disorders. Anesthetics appear to alleviate symptoms in neurological conditions, likely by modulating GABAergic and glutamatergic pathways. However, challenges such as dose-dependent neurotoxicity, variability in preclinical and clinical outcomes, as well as environmental concerns remain significant issues. Future research is essential to optimize dosing strategies, ensure long-term safety, and gain a deeper understanding of the precise mechanisms of action. The concept of anesthetics' repurposing presents a unique solution to tackle the challenges in neurological and psychiatric therapy by providing a platform for the development of new and improved therapies.

Structure and Dynamics of Cannabinoid Binding to the GABAA Receptor

Research on medical cannabis is progressing, with several cannabinoids emerging as promising compounds for clinical use. The available evidence suggests that cannabinoids may modulate the glycine receptor (GlyR) and GABAA receptor, which are part of the pentameric ligand-gated ion channels (pLGICs) superfamily and facilitate chemical communication in the nervous system. In a previous study, we employed molecular dynamics (MD) simulations to elucidate the dynamics of the GlyR/Δ9-tetrahydrocannabinol (THC) complex and successfully identified a representative binding mode. Given the structural similarity between GlyR and GABAAR, we employed a similar strategy to investigate GABAAR-cannabinoid interactions. We initially assessed the binding mode of THC to GABAAR-α1β2γ2 at the equivalent binding site of the GlyR-that is, on its two α-subunits-as well as the impact of this binding on the channel's dimensions. Our results indicate, first, that the binding modes of THC to GABAAR and GlyR exhibit comparable characteristics and, second, that THC may function as a potentiator of GABA activity due to a significant opening of the channel pore. Additionally, we aimed to reduce the overall computational cost associated with exploring binding modes. To this end, we developed and validated a simplified model comprising a single-monomer system for cannabinoid binding studies. This model proved to be accurate and cost-effective, accelerating the in silico screening process and allowing for the study of GABAAR-cannabinoid binding through docking and MD simulations. Moreover, the analysis of different cannabinoids in this system suggests that cannabigerol (CBG) and cannabichromene (CBC) could act as ligands for GABAAR, opening unexplored avenues for research.

The pentameric chloride channel BEST1 is activated by extracellular GABA

Bestrophin-1 (BEST1) is a chloride channel expressed in the eye and other tissues of the body. A link between BEST1 and the principal inhibitory neurotransmitter γ-aminobutyric acid (GABA) has been proposed. The most appreciated receptors for extracellular GABA are the GABAB G-protein-coupled receptors and the pentameric GABAA chloride channels, both of which have fundamental roles in the central nervous system. Here, we demonstrate that BEST1 is directly activated by GABA. Through functional studies and atomic-resolution structures of human and chicken BEST1, we identify a GABA binding site on the channel's extracellular side and determine the mechanism by which GABA binding stabilizes opening of the channel's central gate. This same gate, "the neck," is activated by intracellular [Ca2+], indicating that BEST1 is controlled by ligands from both sides of the membrane. The studies demonstrate that BEST1, which shares no structural homology with GABAA receptors, is a GABA-activated chloride channel. The physiological implications of this finding remain to be studied.

GABA and astrocytic cholesterol determine the lipid environment of GABAAR in cultured cortical neurons

The γ-aminobutyric acid (GABA) type A receptor (GABAAR), a GABA activated pentameric chloride channel, mediates fast inhibitory neurotransmission in the brain. The lipid environment is critical for GABAAR function. How lipids regulate the channel in the cell membrane is not fully understood. Here we employed super resolution imaging of lipids to demonstrate that the agonist GABA induces a rapid and reversible membrane translocation of GABAAR to phosphatidylinositol 4,5-bisphosphate (PIP2) clusters in mouse primary cortical neurons. This translocation relies on nanoscopic separation of PIP2 clusters and lipid rafts (cholesterol-dependent ganglioside clusters). In a resting state, the GABAAR associates with lipid rafts and this colocalization is enhanced by uptake of astrocytic secretions. These astrocytic secretions delay desensitization and enhance maximum current. In an Alzheimer's Disease (AD) mouse model with high brain cholesterol, GABAAR shifts into lipid rafts. Our findings suggest cholesterol is a signaling molecule and astrocytes regulates GABAARs in neurons by secreting cholesterol. The findings have implications for treating mood disorders and AD associated with altered brain lipids.

Treatment of Insomnia With Traditional Chinese Medicine Presents a Promising Prospect

Insomnia, a prevalent sleep disorder, significantly impacts global health. While Western medications provide temporary relief, their risks of dependency and cognitive impairment have spurred the search for safer alternatives. Traditional Chinese Medicine (TCM) offers a promising approach to treating insomnia by focusing on harmonizing the balance of Yin and Yang and the functions of internal organs. This review explores recent research advances in TCM for insomnia treatment, integrating classical theories with modern scientific understanding of key pathological mechanisms, including neurotransmitter regulation (GABA, monoamines), immune-inflammatory responses, the HPA axis, and interactions with the gut microbiota. Growing clinical evidence supports the effectiveness of classical TCM prescriptions and treatments like acupuncture in improving sleep quality, particularly when combined with Western medications to enhance efficacy and reduce dependency. However, TCM also has its limitations. Future research directions should focus on modernizing TCM applications, addressing comorbidities associated with insomnia, exploring the role of gut microbiota, and optimizing medicinal and edible homologous products. By integrating traditional knowledge with cutting-edge technologies, TCM holds great potential for advancing personalized and effective insomnia treatments globally.

Discovery and optimization of AAK1 inhibitors based on 1H-indazole scaffold for the potential treatment of SARS-CoV-2 infection

The process of various virus entry into host cells, including SARS-CoV-2, is mediated by clathrin-mediated endocytosis (CME). AP-2 plays a crucial role in this process by recognizing membrane receptors and binding with clathrin, facilitating the formation of clathrin-coated vesicles and promoting CME. AAK1 catalyzes the phosphorylation of AP2M1 subunit at Thr156. Therefore, suppressing AAK1 activity can hinder virus invasion by blocking CME. indicating that AAK1 could be a potential target for developing novel antiviral drugs against SARS-CoV-2. In this study, we present a series of novel AAK1 inhibitors based on previously reported AAK1 inhibitors. Drug design was carried out by fusing the 1H-indazole scaffold of SGC-AAK1-1 with pharmacophore groups of compound 6, and further optimized with the assistance of molecular docking. Among the 42 compounds novelly synthesized, compounds 9i, 9s, 11f and 11l exhibited comparable antiviral activity against SARS-CoV-2 infection compared to reference compound 6 at the concentration of 3 μM. Particularly, 11f showed almost no cytotoxicity at all tested concentrations. Additionally, 11f exhibited favorable predictive pharmacokinetic properties. These findings support the potential of 11f as a lead compound for developing antiviral drugs targeting SARS-CoV-2 infection, as well as potentially other viruses which are dependent on the CME process to enter host cells. In summary, we have expanded the structural types of AAK1 inhibitors and successfully obtained effective AAK1 inhibitors with antiviral capabilities.

Pharmacological mechanism and clinical application of ciprofol

Propofol has become one of the most commonly used anesthetic agents because of its good sedative effects, rapid onset, and fast metabolism. However, its associated respiratory and circulatory depression and injection pain make it difficult for patients to tolerate. Ciprofol, which is structurally similar to propofol but has an additional cyclopropyl group, is less likely to impact respiratory and circulatory function and cause injection pain, highlighting its potential for clinical application. Currently, as research on Ciprofol is still in the exploratory stage, its clinical application is limited because its underlying mechanisms are not yet fully understood. The aim of this article is to review the pharmacological mechanisms of propofol, hypothesize the primary pharmacological effects and potential adverse reactions of Ciprofol, and summarize its current clinical application status, with the goal of providing a reference for future clinical use.

Foods for Sleep Improvement: A Review of the Potential and Mechanisms Involved

Insomnia affects one-third of the world's population; the negative effects of insomnia are significant, and traditional insomnia medications have numerous side effects and cause considerable suffering. This has aroused interest in obtaining sleep-improving substances from foods. This study conducted a comprehensive literature review using Web of Science and PubMed with keywords like "sleep", "insomnia", and "food". A subsequent summary of the literature revealed that certain foods, including milk, Ziziphus jujuba, Lactuca sativa, ginseng, Schisandra chinensis, and Juglans regia, etc., are purported to enhance sleep quality by prolonging sleep duration, reducing sleep latency, and alleviating anxiety. The mechanisms of these foods' effects mainly occur via the central nervous system, particularly the gamma-aminobutyric acid (GABA)ergic and 5-hydroxytryptamine (5-HT)ergic systems. Although this review supports the fact that they have potential, further research is needed. There are also issues such as more limited foods, fewer mechanisms, fewer pharmacokinetic studies, and more traditional research models being involved. These need to be addressed in the future to adequately address the problem of insomnia. It is hoped that this study will contribute to research into foods with sleep-improving properties and, in the future, provide an effective natural alternative for those seeking medication.

Hidden complexity of α7 nicotinic acetylcholine receptor desensitization revealed by MD simulations and Markov state modeling

The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that plays an important role in neuronal signaling throughout the nervous system. Its implication in neurological disorders and inflammation has spurred the development of numerous compounds that enhance channel activation. However, the therapeutic potential of these compounds has been limited by the characteristically fast desensitization of the α7 receptor. Using recent high-resolution structures from cryo-EM, and all-atom molecular dynamic simulations augmented by Markov state modeling, here we explore the mechanism of α7 receptor desensitization and its implication on allosteric modulation. The results provide a precise characterization of the desensitization gate and illuminate the mechanism of ion-pore opening/closing with an agonist bound. In addition, the simulations reveal the existence of a short-lived, open-channel intermediate between the activated and desensitized states that rationalizes the paradoxical pharmacology of the L247T mutant and may be relevant to type-II allosteric modulation. This analysis provides an interpretation of the signal transduction mechanism and its regulation in α7 receptors.

A Dive Into Cerebellar Dysfunction, Motor Deficits and GABAergic Signaling in Down Syndrome

Down syndrome (DS) mouse models and DS human fetus studies clearly indicate severe neurogenesis impairment in the cerebellum. Clinical features of DS include motor dysfunction and cerebellar hypotrophy, with a particularly marked decrease in the number of granule cells (GCs). GCs are crucial for managing sensory communication within the cerebellum via mossy fibers and their interactions with Purkinje cells (PCs) and inhibitory interneurons. The current review discusses cerebellar alterations in DS and its impact on GABAergic transmission, bringing to light the impact on GABAergic signaling and its role in motor coordination dysfunction observed in individuals with DS. The findings highlight the significance of GABAergic transmission in the pathophysiology of DS and its potential as a target for therapeutic innervation. Moreover, understanding the disruptions in GABAergic signaling may provide insights into developing novel treatment strategies.

Recent advances in CYFIP2-associated neurodevelopmental disorders: From human genetics to molecular mechanisms and mouse models

Cytoplasmic FMR1-interacting protein 2 (CYFIP2) is an evolutionarily conserved protein with a critical role in brain development and function. As a key component of the WAVE regulatory complex, CYFIP2 regulates actin cytoskeleton dynamics, essential for maintaining proper neuronal morphology and circuit formation. Recent studies have also shown that CYFIP2 interacts with various RNA-binding proteins, suggesting its involvement in mRNA processing and translation in neurons. Since 2018, de novo CYFIP2 variants have been identified in patients with neurodevelopmental disorders, particularly developmental and epileptic encephalopathy and West syndrome, characterized by early-onset intractable seizures, intellectual disability, microcephaly, and developmental delay. This review summarizes these CYFIP2 variants and examines their potential impact on the molecular functions of CYFIP2, focusing on its roles in regulating actin dynamics and mRNA processing/translation. Additionally, we review various Cyfip2 mouse models, highlighting the insights they offer into CYFIP2 function, dysfunction, and clinical relevance. Finally, we discuss future research directions aimed at better understanding CYFIP2-associated neurodevelopmental disorders and potential therapeutic strategies.

Resolving native GABAA receptor structures from the human brain

Type A GABA (γ-aminobutyric acid) receptors (GABAA receptors) mediate most fast inhibitory signalling in the brain and are targets for drugs that treat epilepsy, anxiety, depression and insomnia and for anaesthetics1,2. These receptors comprise a complex array of 19 related subunits, which form pentameric ligand-gated ion channels. The composition and structure of native GABAA receptors in the human brain have been inferred from subunit localization in tissue1,3, functional measurements and structural analysis from recombinant expression4-7 and in mice8. However, the arrangements of subunits that co-assemble physiologically in native human GABAA receptors remain unknown. Here we isolated α1 subunit-containing GABAA receptors from human patients with epilepsy. Using cryo-electron microscopy, we defined a set of 12 native subunit assemblies and their 3D structures. We address inconsistencies between previous native and recombinant approaches, and reveal details of previously undefined subunit interfaces. Drug-like densities in a subset of these interfaces led us to uncover unexpected activity on the GABAA receptor of antiepileptic drugs and resulted in localization of one of these drugs to the benzodiazepine-binding site. Proteomics and further structural analysis suggest interactions with the auxiliary subunits neuroligin 2 and GARLH4, which localize and modulate GABAA receptors at inhibitory synapses. This work provides a structural foundation for understanding GABAA receptor signalling and targeted pharmacology in the human brain.

Molecular mechanisms of the GABA type A receptor function

The GABA type A receptor (GABAAR) belongs to the family of pentameric ligand-gated ion channels and plays a key role in inhibition in adult mammalian brains. Dysfunction of this macromolecule may lead to epilepsy, anxiety disorders, autism, depression, and schizophrenia. GABAAR is also a target for multiple physiologically and clinically relevant modulators, such as benzodiazepines (BDZs), general anesthetics, and neurosteroids. The first GABAAR structure appeared in 2014, but the past years have brought a particularly abundant surge in structural data for these receptors with various ligands and modulators. Although the open conformation remains elusive, this novel information has pushed the structure-function studies to an unprecedented level. Electrophysiology, mutagenesis, photolabeling, and in silico simulations, guided by novel structural information, shed new light on the molecular mechanisms of receptor functioning. The main goal of this review is to present the current knowledge of GABAAR functional and structural properties. The review begins with an outline of the functional and structural studies of GABAAR, accompanied by some methodological considerations, especially biophysical methods, enabling the reader to follow how major breakthroughs in characterizing GABAAR features have been achieved. The main section provides a comprehensive analysis of the functional significance of specific structural elements in GABAARs. We additionally summarize the current knowledge on the binding sites for major GABAAR modulators, referring to the molecular underpinnings of their action. The final chapter of the review moves beyond examining GABAAR as an isolated macromolecule and describes the interactions of the receptor with other proteins in a broader context of inhibitory plasticity. In the final section, we propose a general conclusion that agonist binding to the orthosteric binding sites appears to rely on local interactions, whereas conformational transitions of bound macromolecule (gating) and allosteric modulation seem to reflect more global phenomena involving vast portions of the macromolecule.

Ligand Binding and Functional Effect of Novel Bicyclic α5 GABAA Receptor Negative Allosteric Modulators

The significant importance of GABAA receptors in the treatment of central nervous system (CNS) disorders has been known for a long time. However, only in recent years have experimental protein structures been published that can open the door to understanding protein-ligand interactions and may effectively help the rational drug design for the future. In our previous work (Szabó, G. J. Med. Chem. 2022, 65(11), 7876), where a promising selective α5-GABAA negative allosteric modulator (NAM) was developed containing the 3-(4-fluorophenyl)-5-methyl-1,2-oxazole headgroup, we noticed a switch-like effect of a single nitrogen atom for the receptor function in some derivatives having a dihydro-naphthyridinone or dihydro-isoquinolinone moiety. Here, we focused on this chemotype, and a small set of compounds were designed to investigate ligand-receptor interactions experimentally and through computational methods. Elaborated compounds were tested against GABAA α1 and α5 subunit-containing receptors, and binding affinities and functional activities were measured. Starting from the published experimental structure of an engineered, homopentameric, basmisanil-binding GABAA receptor-like construct consisting of modified α5 subunits and an α1-containing GABAA structure, we created a new model of the ligand binding site at the α5/γ2 interface. Using this model, the measured ligand affinities were able to be reproduced well by free energy perturbation (FEP) calculations. In addition, calculations were able to explain the obtained structure-activity relationships, among others, the switch-like effect of the aromatic nitrogen position in the dihydro-naphthyridinone motif for the functional character, and suggest different binding poses for the ligands presenting silent versus negative allosteric effects in this set (SAMs vs. NAMs, respectively). We believe that our results can help design α5 selective GABAA negative allosteric modulators and better understand the GABAA receptor.

Adaptive sampling-based structural prediction reveals opening of a GABAA receptor through the αβ interface

γ-Aminobutyric acid type A (GABAA) receptors are ligand-gated ion channels in the central nervous system with largely inhibitory function. Despite being a target for drugs including general anesthetics and benzodiazepines, experimental structures have yet to capture an open state of classical synaptic α1β2γ2 GABAA receptors. Here, we use a goal-oriented adaptive sampling strategy in molecular dynamics simulations followed by Markov state modeling to capture an energetically stable putative open state of the receptor. The model conducts chloride ions with comparable conductance as in electrophysiology measurements. Relative to experimental structures, our open model is relatively expanded at both the cytoplasmic (-2') and central (9') gates, coordinated with distinctive rearrangements at the transmembrane αβ subunit interface. Consistent with previous experiments, targeted substitutions disrupting interactions at this interface slowed the open-to-desensitized transition rate. This work demonstrates the capacity of advanced simulation techniques to investigate a computationally and experimentally plausible functionally critical of a complex membrane protein yet to be resolved by experimental methods.

GABAA receptor π forms channels that stimulate ERK through a G-protein-dependent pathway

The rare γ-aminobutyric acid type-A receptor (GABAAR) subunit π (GABRP) is highly expressed in certain cancers, where it stimulates growth through extracellular-regulated kinase (ERK) signaling by an uncharacterized pathway. To elucidate GABRP's signaling mechanism, we determined cryoelectron microscopy (cryo-EM) structures of GABRP embedded in native nanodiscs, both in the presence and absence of GABA. Structurally, GABRP homopentamers closely resemble heteropentameric GABAAR anion channels, transitioning from a closed "resting" state to an open "active" state upon GABA binding. However, functional assays reveal that GABRP responds more like a type-B metabotropic receptor. At physiological concentrations of GABA, chloride flux is not detected. Rather, GABRP activates a G-protein-coupled pathway leading to ERK signaling. Ionotropic activity is only triggered at supraphysiological GABA concentrations, effectively decoupling it from GABRP's signaling functions. These findings provide a structural and functional blueprint for GABRP, opening new avenues for targeted inhibition of GABA growth signals in GABRP-positive cancers.

N-Demethylsinomenine Relieves Neuropathic Pain in Male Mice Mainly via Regulating α2-Subtype GABAA Receptors

AIMS

N-Demethylsinomenine (NDSM) demonstrates good analgesic efficacy in preclinical pain models. However, how NDSM exerts analgesic actions remains unknown.

METHODS

We examined the analgesic effects of NDSM using both pain-evoked and pain-suppressed behavioral assays in two persistent pain models. Then western blot assay and immunofluorescence staining were used to investigate the effects of NDSM on the expression of the GABAA receptor α2 subunit (GABRA2) and inflammatory factors in the spinal cord and brain tissues of male spared nerve injury (SNI) mice. Finally, the individual subtypes of GABAARs (α1, α2, α3, and α5) were respectively silenced by viral-mediated knockdown to explore the involvement of subtypes of GABAARs in the effects of NDSM on the pain-like behaviors in male SNI mice.

RESULTS

NDSM demonstrated significant analgesic effects against chronic pain both in pain-evoked and pain-suppressed behavioral assays. NDSM treatment significantly reversed the SNI induced down-regulation of GABRA2 and up-regulation of TNF-α and IL-1β. The analgesic effects of NDSM were completely blocked by silencing GABRA2 or partially blocked by silencing GABRA3.

CONCLUSION

This study provided the first evidence that the analgesic effects of NDSM are mediated primarily by GABRA2 and partially by GABRA3, and the inhibition of neuroinflammation also contributes to the analgesic effects of NDSM.

Impacts of hexafluoropropylene oxide tetrameric acid (HFPO-TeA) on neurodevelopment and GABAergic signaling in zebrafish larvae

Hexafluoropropylene oxide oligomer acids (HFPOs), an emerging environmental pollutant, are increasingly utilized in the manufacture of fluorinated synthetic materials as a substitute for traditional perfluorooctanoic acid (PFOA), resulting in a corresponding rise in detection rates in aquatic environments, which may present inherent safety hazards to ecosystems and public health. However, few data are available on the issue of their toxicity and mechanism. This study aimed to investigate the potential toxic effects of hexafluoroepoxypropane tetrameric acid (HFPO-TeA), a typical HFPO, on the early developmental stages of zebrafish larvae. It revealed that HFPO-TeA exposure resulted in significant detrimental effects, including adverse impacts on general morphological characteristics, such as eye area, heart rate, and swimming bladder, in zebrafish embryos and larvae. Targeted metabolomics and transcriptomics inquiries clarified that HFPO-TeA exposure reduced the levels of the neurotransmitter gamma-aminobutyric acid (GABA) and downregulated the expression of genes related to the GABA pathway. Simultaneously, transgenic zebrafish exhibited that exposure to HFPO-TeA impedes the growth of GABAergic neurons. Moreover, the molecular docking analysis indicated that GABAA receptors might be the potential targets of HFPO-TeA. Taken together, the current data highlights that the HFPO-TeA might not be safe alternatives to PFOA. This study presented a model for HFPO-TeA-induced neurotoxicity in developing zebrafish that can aid in ecological risk assessments.

Molecular mechanisms and behavioral relevance underlying neural correlates of childhood neglect

BACKGROUND

Childhood neglect is associated with brain changes, yet the molecular mechanisms and behavioral relevance underlying such associations remain elusive.

METHODS

We calculated fractional amplitude of low-frequency fluctuations (fALFF) using resting-state functional MRI and tested their correlation with childhood neglect across a large sample of 510 healthy young adults. Then, we investigated the spatial relationships of the identified neural correlates of childhood neglect with gene expression, neurotransmitter, and behavioral domain atlases.

RESULTS

We found that more severe childhood neglect was correlated with higher fALFF in the bilateral anterior cingulate cortex. Remarkably, the identified neural correlates of childhood neglect were spatially correlated with expression of gene categories primarily involving neuron, synapse, ion channel, cognitive and perceptual processes, and physiological response and regulation. Concurrently, there were significant associations between the neural correlates and specific neurotransmitter systems including serotonin and GABA. Finally, neural correlates of childhood neglect were associated with diverse behavioral domains implicating mental disorders, emotion, cognition, and sensory perception.

LIMITATIONS

The cross-sectional study design cannot unequivocally establish causality.

CONCLUSIONS

Our findings may not only add to the current knowledge regarding the relationship between childhood neglect and mental health, but also have clinical implications for developing preventive strategies for individuals exposed to childhood neglect who are at risk for mental disorders.

The pentameric chloride channel BEST1 is activated by extracellular GABA

Bestrophin 1 (BEST1) is chloride channel expressed in the eye, central nervous system (CNS), and other tissues in the body. A link between BEST1 and the principal inhibitory neurotransmitter γ-aminobutyric acid (GABA) has been proposed. The most appreciated receptors for extracellular GABA are the GABAB G-protein coupled receptors and the pentameric GABAA chloride channels, both of which have fundamental roles in the CNS. Here, we demonstrate that BEST1 is directly activated by GABA. Through functional studies and atomic-resolution structures of human and chicken BEST1, we identify a GABA binding site on the channel's extracellular side and determine the mechanism by which GABA binding induces opening of the channel's central gate. This same gate is activated by intracellular [Ca2+], indicating that BEST1 is controlled by ligands from both sides of the membrane. The studies demonstrate that BEST1, which shares no structural homology with GABAA, is a GABA-activated chloride channel. The physiological implications of this finding remain to be studied.

Fasudil Alleviates Postoperative Neurocognitive Disorders in Mice by Downregulating the Surface Expression of α5GABAAR in Hippocampus

AIM

Postoperative neurocognitive disorder (PND) refers to the cognitive impairment experienced by patients after surgery. As a target of sevoflurane, a kind of inhalation anesthetic, the balance of the GABAergic system can be disrupted during the perioperative period. In this study, we explored the promoting effect of abnormal elevation of the α5 subtype of γ-aminobutyric acid type A (GABAA) receptors caused by sevoflurane and surgical trauma on PND, as well as the therapeutic effect of fasudil on PND.

METHODS

Eight-week-old mice were pretreated with fasudil, and after 10 days, sevoflurane-induced femoral fracture surgery was performed to establish an animal model of PND. The Morris water maze and fear conditioning tests were used to evaluate PND induced by this model. Biochemical and electrophysiological analyses were conducted to assess the protective effect of fasudil on the GABAergic system.

RESULTS

Following artificial fracture, the hippocampus-dependent memory was damaged in these mice. Fasudil pretreatment, however, ameliorated cognitive function impairment in mice induced by sevoflurane and surgery. Mechanistically, fasudil was found to restore the increased hippocampus expression and function of α5GABAARs in mice with PND. In addition, pretreatment with Fasudil inhibited the enhancement in the calcium ion concentration and phosphorylation of Camk2, as well as the activation of the Radixin pathway which led to increased phosphorylation of the ERM family in the hippocampal CA1 region of the PND model.

CONCLUSION

Preadministration of fasudil improved postoperative cognitive function in PND mice by inhibiting the activation of Camk2 and Radixin pathways and finally downregulating the surface expression of α5GABAAR in hippocampus neurons.

Psychiatric disorders associated with fluoroquinolones: a pharmacovigilance analysis of the FDA adverse event reporting system database

Background

Fluoroquinolones are broad-spectrum antibiotics with significant antimicrobial activity. Despite their therapeutic benefits, they are associated with a range of adverse drug reactions (ADRs), particularly those affecting the central nervous system (CNS). This study aimed to analyze the psychiatric ADRs linked to fluoroquinolones using data from the FDA Adverse Event Reporting System (FAERS) database.

Methods

A retrospective pharmacovigilance study was conducted using FAERS data from Q1 2004 to Q4 2023. The data processing phase involved the FDA-recommended deduplication method, and ADRs were classified according to Medical Dictionary for Regulatory Activities (MedDRA). Disproportionality analysis was performed using the reporting odds ratio (ROR), and statistical significance was assessed using the Chi-square test or Fisher's exact test.

Results

The study identified 84,777 reports associated with fluoroquinolones, with 359,480 Preferred Terms-annotated entries, 27,816 of these reports were psychiatric ADRs. Mood disorders were the most frequently reported, including anxiety, depression, and delirium, with some reports escalating to suicidal ideation and behaviors. The Standardized MedDRA Query classification system was used to categorize these ADRs into Depression, Suicide/self-injury, Psychosis and psychotic disorders, and Non-infectious encephalopathy/delirium. Ciprofloxacin was most frequently linked to depression and suicidal ideation, while moxifloxacin showed a robust correlation with delirium. The risk of psychiatric ADRs varied by age group, with affective disorders more prevalent in adults under 65 and psychosis and delirium in those over 65.

Conclusion

Fluoroquinolones are associated with a range of psychiatric ADRs, with notable differences between the drugs in the class. The study highlights the need for caution in prescribing fluoroquinolones, particularly for patients with pre-existing mental health conditions or those in higher risk age groups. The findings also underscore the importance of considering age-specific preventive strategies when administering these antibiotics.

3,8-Disubstituted Pyrazolo[1,5-a]quinazoline as GABAA Receptor Modulators: Synthesis, Electrophysiological Assays, and Molecular Modelling Studies

As a continuation of our study in the field of GABAA receptor modulators, we report the design and synthesis of new pyrazolo[1,5-a]quinazoline (PQ) bearing at the 8-position an oxygen or nitrogen function. All the final compounds and some intermediates, showing the three different forms of the pyrazolo[1,5-a]quinazoline scaffold (5-oxo-4,5-dihydro, -4,5-dihydro, and heteroaromatic form), have been screened with an electrophysiological technique on recombinant GABAAR (α1β2γ2-GABAAR), expressed in Xenopus laevis oocytes, by evaluating the variation in produced chlorine current, and permitting us to identify some interesting compounds (6d, 8a, 8b, and 14) on which further functional assays were performed. Molecular modelling studies (docking, minimization of complex ligand-receptor, and MD model) and a statistical analysis by a Hierarchical Cluster Analysis (HCA) have collocated these ligands in the class corresponding to their pharmacological profile. The HCA results are coherent with the model we recently published (Proximity Frequencies), identifying the residues γThr142 and αHis102 as discriminant for the agonist and antagonist profile.

The emergence of antidepressant drugs targeting GABAA receptors: A concise review

Depression is among the most common psychiatric illnesses, which imposes a major socioeconomic burden on patients, caregivers, and the public health system. Treatment with classical antidepressants (e.g. tricyclic antidepressants and selective serotonine reuptake inhibitors), which primarily affect monoaminergic systems has several limitations, such as delayed onset of action and moderate efficacy in a relatively large proportion of depressed patients. Furthermore, depression is highly heterogeneus, and its different subtypes, including post-partum depression, involve distinct neurobiology, warranting a differential approach to pharmacotherapy. Given these shortcomings, the need for novel antidepressants that are superior in efficacy and faster in onset of action is fully justified. The development and market introduction of rapid-acting antidepressants has accelerated in recent years. Some of these new antidepressants act through the GABAergic system. In this review, we discuss the discovery, efficacy, and limitations of treatment with classic antidepressants. We provide a detailed discussion of GABAergic neurotransmission, with a special focus on GABAA receptors, and possible explanations for the mood-enhancing effects of GABAergic medications (in particular neurosteroids acting at GABAA receptors), and, ultimately, we present the most promising molecules belonging to this family which are currently used in clinical practice or are in late phases of clinical development.

Pharmacological chaperones restore proteostasis of epilepsy-associated GABAA receptor variants

Recent advances in genetic diagnosis identified variants in genes encoding GABAA receptors as causative for genetic epilepsy. Here, we selected eight disease-associated variants in the α1 subunit of GABAA receptors causing mild to severe clinical phenotypes and showed that they are loss of function, mainly by reducing the folding and surface trafficking of the α1 protein. Furthermore, we sought client protein-specific pharmacological chaperones to restore the function of pathogenic receptors. Applications of positive allosteric modulators, including Hispidulin and TP003, increase the functional surface expression of the α1 variants. Mechanism of action study demonstrated that they enhance the folding, assembly, and trafficking and reduce the degradation of GABAA variants without activating the unfolded protein response in HEK293T cells and human iPSC-derived neurons. Since these compounds cross the blood-brain barrier, such a pharmacological chaperoning strategy holds great promise to treat genetic epilepsy in a GABAA receptor-specific manner.

Impact of aging on the GABAB receptor-mediated connectome

GABA B receptors (GABABRs) are heterodimeric seven-transmembrane receptors that interact with a range of proteins and form large protein complexes on cholesterol-rich membrane microdomains. As the brain ages, membrane cholesterol levels exhibit alterations, although it remains unclear how these changes impact protein-protein interactions and downstream signaling. Herein, we studied the structural bases for the interaction between GABABR and the KCC2 transporter, including their protein expression and distribution, and we compared data between young and aged rat cerebella. Also, we analyzed lipid profiles for both groups, and we used molecular dynamics simulations on three plasma membrane systems with different cholesterol concentrations, to further explore the GABABR-transporter interaction. Based on our results, we report that a significant decrease in GABAB2 subunit expression occurs in the aged rat cerebella. After performing a comparative co-immunoprecipitation analysis, we confirm that GABABR and KCC2 form a protein complex in adult and aged rat cerebella, although their interaction levels are reduced substantially as the cerebellum ages. On the other hand, our lipid analyses reveal a significant increase in cholesterol and sphingomyelin levels of the aged cerebella. Finally, we used the Martini coarse-grained model to conduct molecular dynamics simulations, from which we observed that membrane cholesterol concentrations can dictate whether the GABABR tail domains physically establish G protein-independent contacts with a transporter, and the timing when those associations eventually occur. Taken together, our findings illustrate how age-related alterations in membrane cholesterol levels affect protein-protein interactions, and how they could play a crucial role in regulating GABABR's interactome-mediated signaling.

Significance Statement

This study elucidates age-related changes in cerebellar GABAB receptors (GABABRs), KCC2, and plasma membrane lipids, shedding light on mechanisms underlying neurological decline. Molecular dynamics simulations reveal how membrane lipids influence protein-protein interactions, offering insights into age-related neurodegeneration. The findings underscore the broader impact of cerebellar aging on motor functions, cognition, and emotional processing in the elderly. By elucidating plasma membrane regulation and GABAergic dynamics, this research lays the groundwork for understanding aging-related neurological disorders and inspires further investigation into therapeutic interventions.

GABA system in the prefrontal cortex involved in psychostimulant addiction

Drug addiction is a chronic and relapse brain disorder. Psychostimulants such as cocaine and amphetamine are highly addictive drugs. Abuse drugs target various brain areas in the nervous system. Recent studies have shown that the prefrontal cortex (PFC) plays a key role in regulating addictive behaviors. The PFC is made up of excitatory glutamatergic cells and gamma-aminobutyric acid (GABAergic) interneurons. Recently, studies showed that GABA level was related with psychostimulant addiction. In this review, we will introduce the role and mechanism of GABA and γ-aminobutyric acid receptors (GABARs) of the PFC in regulating drug addiction, especially in psychostimulant addiction.

Predicting therapeutic and side effects from drug binding affinities to human proteome structures

Evaluation of the binding affinities of drugs to proteins is a crucial process for identifying drug pharmacological actions, but it requires three dimensional structures of proteins. Herein, we propose novel computational methods to predict the therapeutic indications and side effects of drug candidate compounds from the binding affinities to human protein structures on a proteome-wide scale. Large-scale docking simulations were performed for 7,582 drugs with 19,135 protein structures revealed by AlphaFold (including experimentally unresolved proteins), and machine learning models on the proteome-wide binding affinity score (PBAS) profiles were constructed. We demonstrated the usefulness of the method for predicting the therapeutic indications for 559 diseases and side effects for 285 toxicities. The method enabled to predict drug indications for which the related protein structures had not been experimentally determined and to successfully extract proteins eliciting the side effects. The proposed method will be useful in various applications in drug discovery.

Structural insights into GABAA receptor potentiation by Quaalude

Methaqualone, a quinazolinone marketed commercially as Quaalude, is a central nervous system depressant that was used clinically as a sedative-hypnotic, then became a notorious recreational drug in the 1960s-80s. Due to its high abuse potential, medical use of methaqualone was eventually prohibited, yet it persists as a globally abused substance. Methaqualone principally targets GABAA receptors, which are the major inhibitory neurotransmitter-gated ion channels in the brain. The restricted status and limited accessibility of methaqualone have contributed to its pharmacology being understudied. Here, we use cryo-EM to localize the GABAA receptor binding sites of methaqualone and its more potent derivative, PPTQ, to the same intersubunit transmembrane sites targeted by the general anesthetics propofol and etomidate. Both methaqualone and PPTQ insert more deeply into subunit interfaces than the previously-characterized modulators. Binding of quinazolinones to this site results in widening of the extracellular half of the ion-conducting pore, following a trend among positive allosteric modulators in destabilizing the hydrophobic activation gate in the pore as a mechanism for receptor potentiation. These insights shed light on the underexplored pharmacology of quinazolinones and further elucidate the molecular mechanisms of allosteric GABAA receptor modulation through transmembrane binding sites.

Forty Years Searching for Neurosteroid Binding Sites on GABAA Receptors

Brain inhibition is a vital process for controlling and sculpting the excitability of the central nervous system in healthy individuals. This level of control is provided over several timescales and involves the neurotransmitter GABA acting at inhibitory synapses to: rapidly inhibit neurons by activating the GABAA receptor; over a slower timescale, to tonically activate extrasynaptic GABAA receptors to provide a low level of background inhibition; and finally, to activate G-protein coupled GABAB receptors to control transmitter release by inhibiting presynaptic Ca2+ channels whilst providing postsynaptic inhibition via K+ channel activation. From this plethora of roles for GABA and its receptors, the GABAA receptor isoform is of major interest due to its dynamic functional plasticity, which in part, is due to being targeted by modulatory brain neurosteroids derived from sex and stress hormones. This family of neurosteroids can, depending on their structure, potentiate, activate and also inhibit the activity of GABAA receptors to affect brain inhibition. This review tracks the methods that have been deployed in probing GABAA receptors, and charts the sterling efforts made by several groups to locate the key neurosteroid binding sites that affect these important receptors. Increasing our knowledge of these binding sites will greatly facilitate our understanding of the physiological roles of neurosteroids and will help to advance their use as novel therapeutics to combat debilitating brain diseases.

GABA and astrocytic cholesterol determine the lipid environment of GABAAR in cultured cortical neurons

The γ-aminobutyric acid (GABA) type A receptor (GABAAR), a GABA activated pentameric chloride channel, mediates fast inhibitory neurotransmission in the brain. The lipid environment is critical for GABAAR function. How lipids regulate the channel in the cell membrane is not fully understood. Here we employed super resolution imaging of lipids to demonstrate that the agonist GABA induces a rapid and reversible membrane translocation of GABAAR to phosphatidylinositol 4,5-bisphosphate (PIP2) clusters in mouse primary cortical neurons. This translocation relies on nanoscopic separation of PIP2 clusters and lipid rafts (cholesterol-dependent ganglioside clusters). In a resting state, the GABAAR associates with lipid rafts and this colocalization is enhanced by uptake of astrocytic secretions. These astrocytic secretions enhance endocytosis and delay desensitization. Our findings suggest intercellular signaling from astrocytes regulates GABAAR location based on lipid uptake in neurons. The findings have implications for treating mood disorders associated with altered neural excitability.

Structural basis of ligand specificity and channel activation in an insect gustatory receptor

Gustatory receptors (GRs) are critical for insect chemosensation and are potential targets for controlling pests and disease vectors, making their structural investigation a vital step toward such applications. We present structures of Bombyx mori Gr9 (BmGr9), a fructose-gated cation channel, in agonist-free and fructose-bound states. BmGr9 forms a tetramer similar to distantly related insect odorant receptors (ORs). Upon fructose binding, BmGr9's channel gate opens through helix S7b movements. In contrast to ORs, BmGr9's ligand-binding pocket, shaped by a kinked helix S4 and a shorter extracellular S3-S4 loop, is larger and solvent accessible in both agonist-free and fructose-bound states. Also, unlike ORs, fructose binding by BmGr9 involves helix S5 and a pocket lined with aromatic and polar residues. Structure-based sequence alignments reveal distinct patterns of ligand-binding pocket residue conservation in GR subfamilies associated with different ligand classes. These data provide insight into the molecular basis of GR ligand specificity and function.

Structural Basis for Molecular Recognition of Cannabinoids by Inhibitory Cys-Loop Channels

Cannabis sativa has a long history of medicinal use, dating back to ancient times. This plant produces cannabinoids, which are now known to interact with several human proteins, including Cys-loop receptors for glycine (GlyR) and gamma-aminobutyric acid (GABAAR). As these channels are the primary mediators of inhibitory signals, they contribute to the diverse effects of cannabinoids on the nervous system. Evidence suggests that cannabinoid binding sites are located within the transmembrane domain, although their precise location has remained undetermined for over a decade. The process of identification of the binding site and the computational approaches employed are the main subjects of this Perspective, which includes an analysis of the most recently resolved cryo-EM structures of zebrafish GlyR bound to Δ9-tetrahydrocannabinol and the THC-GlyR complex obtained through molecular dynamics simulations. With this work, we aim to contribute to guiding future studies investigating the molecular basis of cannabinoid action on inhibitory channels.

Structural mechanisms of α7 nicotinic receptor allosteric modulation and activation

The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that plays an important role in cholinergic signaling throughout the nervous system. Its unique physiological characteristics and implications in neurological disorders and inflammation make it a promising but challenging therapeutic target. Positive allosteric modulators overcome limitations of traditional α7 agonists, but their potentiation mechanisms remain unclear. Here, we present high-resolution structures of α7-modulator complexes, revealing partially overlapping binding sites but varying conformational states. Structure-guided functional and computational tests suggest that differences in modulator activity arise from the stable rotation of a channel gating residue out of the pore. We extend the study using a time-resolved cryoelectron microscopy (cryo-EM) approach to reveal asymmetric state transitions for this homomeric channel and also find that a modulator with allosteric agonist activity exploits a distinct channel-gating mechanism. These results define mechanisms of α7 allosteric modulation and activation with implications across the pentameric receptor superfamily.

Neuropharmacological assessment and identification of possible lead compound (apomorphine) from Hygrophila spinosa through in-vivo and in-silico approaches

The aim of this research is to examine possible neurological activity of methanol, ethyl acetate, and aqueous extracts of Hygrophila spinosa and identify possible lead compounds through in silico analysis. In vivo, neuropharmacological activity was evaluated by using four distinct neuropharmacological assessment assays. Previously reported GC-MS data and earlier literature were utilized to identify the phytochemicals present in Hygrophila spinosa. Computational studies notably molecular docking and molecular dynamic simulations were conducted with responsible receptors to assess the stability of the best interacting compound. Pharmacokinetics properties like absorption, distribution, metabolism, excretion, and toxicity were considered to evaluate the drug likeliness properties of the identified compounds. All the in vivo results support the notion that different extracts (methanol, ethyl acetate, and aqueous) of Hygrophila spinosa have significant (*p = 0.05) sedative-hypnotic, anxiolytic, and anti-depressant activity. Among all the extracts, specifically methanol extracts of Hygrophila spinosa (MHS 400 mg/kg.b.w.) showed better sedative, anxiolytic and antidepressant activity than aqueous and ethyl acetate extracts. In silico molecular docking analysis revealed that among 53 compounds 7 compounds showed good binding affinities and one compound, namely apomorphine (CID: 6005), surprisingly showed promising binding affinity to all the receptors . An analysis of molecular dynamics simulations confirmed that apomorphine (CID: 6005) had a high level of stability at the protein binding site. Evidence suggests that Hygrophila spinosa has significant sedative, anxiolytic, and antidepressant activity. In silico analysis revealed that a particular compound (apomorphine) is responsible for this action. Further research is required in order to establish apomorphine as a drug for anxiety, depression, and sleep disorders.

Knock-in mutagenesis in Drosophila Rdl underscores the critical role of the conserved M3 glycine in mediating the actions of broflanilide and isocycloseram on GABA receptors

γ-Aminobutyric acid receptors (GABARs) are crucial targets for pest control chemicals, including meta-diamide and isoxazoline insecticides, which act as negative allosteric modulators of insect GABARs. Previous cell-based assays have indicated that amino acid residues in the transmembrane cavity between adjacent subunits of Drosophila RDL GABAR (i.e., Ile276, Leu280, and Gly335) are involved in mediating the action of meta-diamides. In this study, to confirm this result at the organismal level, we employed CRISPR/Cas9-mediated genome editing, generated six transgenic Drosophila strains carrying substitutions in these amino acid residues, and investigated their sensitivity to broflanilide and isocycloseram. Flies homozygous for the I276F mutation did not exhibit any change in sensitivity to the tested insecticides compared to the control flies. Conversely, I276C homozygosity was lethal, and heterozygous flies exhibited ∼2-fold lower sensitivity to broflanilide than the control flies. Flies homozygous for the L280C mutation survived into adulthood but exhibited infertility. Both heterozygous and homozygous L280C flies exhibited ∼3- and ∼20-fold lower sensitivities to broflanilide and isocycloseram, respectively, than the control flies. The reduction in sensitivity to isocycloseram in L280C flies diminished to ∼3-fold when treated with piperonyl butoxide. Flies homozygous for the G335A mutation reached the adult stage. However, they were sterile, had small bodies, and exhibited reduced locomotion, indicating the critical role of Gly335 in RDL function. These flies exhibited markedly increased tolerance to topically applied broflanilide and isocycloseram, demonstrating that the conserved Gly335 is the target of the insecticidal actions of broflanilide and isocycloseram. Considering the significant fitness costs, the Gly335 mutation may not pose a serious risk for the development of resistance in field populations of insect pests. However, more careful studies using insect pests are needed to investigate whether our perspective applies to resistance development under field conditions.

Integrated workflow for the identification of new GABAA R positive allosteric modulators based on the in silico screening with further in vitro validation. Case study using Enamine's stock chemical space

Numerous studies reported an association between GABAA R subunit genes and epilepsy, eating disorders, autism spectrum disorders, neurodevelopmental disorders, and bipolar disorders. This study was aimed to find some potential positive allosteric modulators and was performed by combining the in silico approach with further in vitro evaluation of its real activity. We started from the GABAA R-diazepam complexes and assembled a lipid embedded protein ensemble to refine it via molecular dynamics (MD) simulation. Then we focused on the interaction of α1β2γ2 with some Z-drugs (non-benzodiazepine compounds) using an Induced Fit Docking (IFD) into the relaxed binding site to generate a pharmacophore model. The pharmacophore model was validated with a reference set and applied to decrease the pre-filtered Enamine database before the main docking procedure. Finally, we succeeded in identifying a set of compounds, which met all features of the docking model. The aqueous solubility and stability of these compounds in mouse plasma were assessed. Then they were tested for the biological activity using the rat Purkinje neurons and CHO cells with heterologously expressed human α1β2γ2 GABAA receptors. Whole-cell patch clamp recordings were used to reveal the GABA induced currents. Our study represents a convenient and tunable model for the discovery of novel positive allosteric modulators of GABAA receptors. A High-throughput virtual screening of the largest available database of chemical compounds resulted in the selection of 23 compounds. Further electrophysiological tests allowed us to determine a set of 3 the most outstanding active compounds. Considering the structural features of leader compounds, the study can develop into the MedChem project soon.

Application of ensemble learning for predicting GABAA receptor agonists

BACKGROUND

Over the past few decades, agonists binding to the benzodiazepine site of the GABAA receptor have been successfully developed as clinical drugs. Different modulators (agonist, antagonist, and reverse agonist) bound to benzodiazepine sites exhibit different or even opposite pharmacological effects, however, their structures are so similar that it is difficult to distinguish them based solely on molecular skeleton. This study aims to develop classification models for predicting the agonists.

METHODS

306 agonists or non-agonists were collected from literature. Six machine learning algorithms including RF, XGBoost, AdaBoost, GBoost, SVM, and ANN algorithms were employed for model development. Using six descriptors including 1D/2D Descriptors, ECFP4, 2D-Pharmacophore, MACCS, PubChem, and Estate fingerprint to characterize chemical structures. The model interpretability was explored by SHAP method.

RESULTS

The best model demonstrated an AUC value of 0.905 and an MCC value of 0.808 for the test set. The PubMac-based model (PubMac-GB) achieved best AUC values of 0.935 for test set. The SHAP analysis results emphasized that MaccsFP62, ECFP_624, ECFP_724, and PubchemFP213 were the crucial molecular features. Applicability domain analysis was also performed to determine reliable prediction boundaries for the model. The PubMac-GB model was applied to virtual screening for potential GABAA agonists and the top 100 compounds were given.

CONCLUSION

Overall, our ensemble learning-based model (PubMac-GB) achieved comparable performance and would be helpful in effectively identifying agonists of GABAA receptors.

Discovery of lipid binding sites in a ligand-gated ion channel by integrating simulations and cryo-EM

Ligand-gated ion channels transduce electrochemical signals in neurons and other excitable cells. Aside from canonical ligands, phospholipids are thought to bind specifically to the transmembrane domain of several ion channels. However, structural details of such lipid contacts remain elusive, partly due to limited resolution of these regions in experimental structures. Here, we discovered multiple lipid interactions in the channel GLIC by integrating cryo-electron microscopy and large-scale molecular simulations. We identified 25 bound lipids in the GLIC closed state, a conformation where none, to our knowledge, were previously known. Three lipids were associated with each subunit in the inner leaflet, including a buried interaction disrupted in mutant simulations. In the outer leaflet, two intrasubunit sites were evident in both closed and open states, while a putative intersubunit site was preferred in open-state simulations. This work offers molecular details of GLIC-lipid contacts particularly in the ill-characterized closed state, testable hypotheses for state-dependent binding, and a multidisciplinary strategy for modeling protein-lipid interactions.

Structure of an insect gustatory receptor

Gustatory Receptors (GRs) are critical for insect chemosensation and are potential targets for controlling pests and disease vectors. However, GR structures have not been experimentally determined. We present structures of Bombyx mori Gr9 (BmGr9), a fructose-gated cation channel, in agonist-free and fructose-bound states. BmGr9 forms a tetramer similar to distantly related insect Olfactory Receptors (ORs). Upon fructose binding, BmGr9's ion channel gate opens through helix S7b movements. In contrast to ORs, BmGR9's ligand-binding pocket, shaped by a kinked helix S4 and a shorter extracellular S3-S4 loop, is larger and solvent accessible in both agonist-free and fructose-bound states. Also unlike ORs, fructose binding by BmGr9 involves helix S5 and a binding pocket lined with aromatic and polar residues. Structure-based sequence alignments reveal distinct patterns of ligand-binding pocket residue conservation in GR subfamilies associated with distinct ligand classes. These data provide insight into the molecular basis of GR ligand specificity and function.

Structure and dynamics of differential ligand binding in the human ρ-type GABAA receptor

The neurotransmitter γ-aminobutyric acid (GABA) drives critical inhibitory processes in and beyond the nervous system, partly via ionotropic type-A receptors (GABAARs). Pharmacological properties of ρ-type GABAARs are particularly distinctive, yet the structural basis for their specialization remains unclear. Here, we present cryo-EM structures of a lipid-embedded human ρ1 GABAAR, including a partial intracellular domain, under apo, inhibited, and desensitized conditions. An apparent resting state, determined first in the absence of modulators, was recapitulated with the specific inhibitor (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid and blocker picrotoxin and provided a rationale for bicuculline insensitivity. Comparative structures, mutant recordings, and molecular simulations with and without GABA further explained the sensitized but slower activation of ρ1 relative to canonical subtypes. Combining GABA with picrotoxin also captured an apparent uncoupled intermediate state. This work reveals structural mechanisms of gating and modulation with applications to ρ-specific pharmaceutical design and to our biophysical understanding of ligand-gated ion channels.

External amino acid residues of insect GABA receptor channels dictate the action of the isoxazoline ectoparasiticide fluralaner

BACKGROUND

Fluralaner is the first isoxazoline ectoparasiticide developed to protect companion animals from fleas and ticks. Fluralaner primarily inhibits arthropod γ-aminobutyric acid receptors (GABARs), which are ligand-gated ion channels comprising five subunits arranged around the channel pore. We previously reported that the action site of fluralaner resides at the M1-M3 transmembrane interface between adjacent GABAR subunits. To investigate whether fluralaner interacts with the second transmembrane segment (M2) located deep in the interface, we generated four housefly RDL GABAR mutants with non-conservative amino acid substitutions in the M2 region.

RESULTS

Electrophysiological analysis of GABARs expressed in Xenopus oocytes indicated that S313A and S314A mutants exhibited fluralaner sensitivities similar to that of the wild type. M312S mutant exhibited approximately seven-fold lower sensitivity than that of the wild type. Notably, the N316L mutant was almost insensitive to fluralaner.

CONCLUSION

The findings of this study indicate that the conserved external amino acid residues of insect GABAR channels play a critical role in the antagonistic effect of fluralaner. © 2023 Society of Chemical Industry.

Investigation of cannabidiol's potential targets in limbic seizures. In-silico approach

Even though the vast armamentarium of FDA-approved antiepileptic drugs is currently available, over one-third of patients do not respond to medication, which arises a need for alternative medicine. In clinical and preclinical studies, various investigations have shown the advantage of specific plant-based cannabidiol (CBD) products in treating certain groups of people with limbic epilepsy who have failed to respond to conventional therapies. This work aims to investigate possible mechanisms by which CBD possesses its anticonvulsant properties. Molecular targets for CBD's treatment of limbic epilepsy, including hyperpolarization-activated cyclic nucleotide-gated channel 1 (HCN1), gamma-aminobutyric acid aminotransferase (GABA-AT), and gamma-aminobutyric acid type A receptor (GABAA), were used to evaluate its binding affinity. Interactions with the CB1 receptor were initially modeled as a benchmark, which further proved the efficiency of proposed here approach. Considering the successful benchmark, we further used the same concept for in silico investigation, targeting proteins of interest. As a result of molecular docking, molecular mechanics, and molecular dynamics simulations models of CBD-receptor complexes were proposed and evaluated. While CBD possessed decently high affinity and stability within the binding pockets of GABA-AT and some binding sites of GABAA, the most effective binding was observed in the CBD complex with HCN1 receptor. 100 ns molecular dynamics simulation revealed that CBD binds the open pore of HCN1 receptor, forming a similar pattern of interactions as potent Lamotrigine. Therefore, we can propose that HCN1 can serve as a most potent target for cannabinoid antiepileptic treatment. Communicated by Ramaswamy H. Sarma.

Structural insights into opposing actions of neurosteroids on GABAA receptors

γ-Aminobutyric acid type A (GABAA) receptors mediate fast inhibitory signaling in the brain and are targets of numerous drugs and endogenous neurosteroids. A subset of neurosteroids are GABAA receptor positive allosteric modulators; one of these, allopregnanolone, is the only drug approved specifically for treating postpartum depression. There is a consensus emerging from structural, physiological and photolabeling studies as to where positive modulators bind, but how they potentiate GABA activation remains unclear. Other neurosteroids are negative modulators of GABAA receptors, but their binding sites remain debated. Here we present structures of a synaptic GABAA receptor bound to allopregnanolone and two inhibitory sulfated neurosteroids. Allopregnanolone binds at the receptor-bilayer interface, in the consensus potentiator site. In contrast, inhibitory neurosteroids bind in the pore. MD simulations and electrophysiology support a mechanism by which allopregnanolone potentiates channel activity and suggest the dominant mechanism for sulfated neurosteroid inhibition is through pore block.

Pharmacological Analysis of GABAA Receptor and Sigma1R Chaperone Interaction: Research Report I-Investigation of the Anxiolytic, Anticonvulsant and Hypnotic Effects of Allosteric GABAA Receptors' Ligands

Two groups of facts have been established in previous drug development studies of the non-benzodiazepine anxiolytic fabomotizole. First, fabomotizole prevents stress-induced decrease in binding ability of the GABAA receptor's benzodiazepine site. Second, fabomotizole is a Sigma1R chaperone agonist, and exposure to Sigma1R antagonists blocks its anxiolytic effect. To prove our main hypothesis of Sigma1R involvement in GABAA receptor-dependent pharmacological effects, we performed a series of experiments on BALB/c and ICR mice using Sigma1R ligands to study anxiolytic effects of benzodiazepine tranquilizers diazepam (1 mg/kg i.p.) and phenazepam (0.1 mg/kg i.p.) in the elevated plus maze test, the anticonvulsant effects of diazepam (1 mg/kg i.p.) in the pentylenetetrazole-induced seizure model, and the hypnotic effects of pentobarbital (50 mg/kg i.p.). Sigma1R antagonists BD-1047 (1, 10, and 20 mg/kg i.p.), NE-100 (1 and 3 mg/kg i.p.), and Sigma1R agonist PRE-084 (1, 5, and 20 mg/kg i.p.) were used in the experiments. Sigma1R antagonists have been found to attenuate while Sigma1R agonists can enhance GABAARs-dependent pharmacological effects.

Mutational Analysis of Anesthetic Binding Sites and Their Effects on GABAA Receptor Activation and Modulation by Positive Allosteric Modulators of the α7 Nicotinic Receptor

The positive allosteric modulators (PAMs) of the α7 nicotinic receptor N-(5-Cl-2-hydroxyphenyl)-N'-[2-Cl-5-(trifluoromethyl)phenyl]-urea (NS-1738) and (E)-3-(furan-2-yl)-N-(p-tolyl)-acrylamide (PAM-2) potentiate the α1β2γ2L GABAA receptor through interactions with the classic anesthetic binding sites located at intersubunit interfaces in the transmembrane domain of the receptor. In the present study, we employed mutational analysis to investigate in detail the involvement and contributions made by the individual intersubunit interfaces to receptor modulation by NS-1738 and PAM-2. We show that mutations to each of the anesthetic-binding intersubunit interfaces (β+/α-, α+/β-, and γ+/β-), as well as the orphan α+/γ- interface, modify receptor potentiation by NS-1738 and PAM-2. Furthermore, mutations to any single interface can fully abolish potentiation by the α7-PAMs. The findings are discussed in the context of energetic additivity and interactions between the individual binding sites.

Pharmacological chaperones restore proteostasis of epilepsy-associated GABAA receptor variants

Recent advances in genetic diagnosis identified variants in genes encoding GABAA receptors as causative for genetic epilepsy. Here, we selected eight disease-associated variants in the α 1 subunit of GABAA receptors causing mild to severe clinical phenotypes and showed that they are loss of function, mainly by reducing the folding and surface trafficking of the α 1 protein. Furthermore, we sought client protein-specific pharmacological chaperones to restore the function of pathogenic receptors. Applications of positive allosteric modulators, including Hispidulin and TP003, increase the functional surface expression of the α 1 variants. Mechanism of action study demonstrated that they enhance the folding and assembly and reduce the degradation of GABAA variants without activating the unfolded protein response in HEK293T cells and human iPSC-derived neurons. Since these compounds cross the blood-brain barrier, such a pharmacological chaperoning strategy holds great promise to treat genetic epilepsy in a GABAA receptor-specific manner.