Anxiolytics targeting GABAA receptors: Insights on etifoxine

Development of a sample preparation and analysis method for therapeutic monitoring of diazepam and major metabolite in alcohol withdrawal syndrome treatment

Diazepam, a widely prescribed benzodiazepine, is frequently used for the management of alcohol withdrawal syndrome, anxiety, seizures, and muscle spasms. Its monitoring is critical due to its potential for abuse and the therapeutic importance of its metabolite nordiazepam. A sustainable and environmentally friendly high-performance liquid chromatography method was developed and validated for the quantification of diazepam and its active metabolite nordiazepam in human plasma samples. The chromatographic analysis was conducted on an HPLC system equipped with a UV detector. Separation was achieved using a Kinetex F5 column (150 ×4.6 mm, 5 µm). The mobile phase consisted of acetonitrile and phosphate buffer adjusted to pH 4.3 (30:70, v/v), delivered in isocratic mode at a flow rate of 1.0 mL/min, with the pH adjusted to optimize resolution. The method demonstrated excellent sensitivity, reproducibility, and linearity for both compounds, highlighting its applicability for drug monitoring and toxicological studies. Moreover, the environmentally conscious selection of materials and conditions underscores the method's compliance with green analytical chemistry principles. Both analytes were successfully detected and quantified in all fifty-three patients under the treatment of alcohol withdrawal syndrome. The measured concentrations of diazepam (0.23-1.4 µg/mL) and its metabolite nordiazepam (0.22-3.78 µg/mL) displayed considerable variability among individuals.

The translocator protein 18 kDa (TSPO) ligand etifoxine in an animal model of anxiety: Line- and sex-dependent effects on emotionality, stress reactivity, spine density, oxytocin receptors, steroids, and microbiome composition

The treatment of stress-related disorders such as anxiety and depression is still challenging. One potential therapeutical option are neurosteroids. Their synthesis is promoted by ligands of the mitochondrial translocator protein 18 kDa (TSPO). We tested the TSPO ligand etifoxine (ETX) in a rat model of hyper-anxiety and depression-like behavior, i.e., in female and male HAB (high anxiety-related behavior) rats, as well as in respective low anxiety (LAB) and non-selected control (NAB) rats for behavioral, molecular, cellular, and physiological parameters. Daily acute i.p. treatment with ETX or vehicle over 5 or 9 days revealed that ETX was most effective in female HAB rats; it reduced anxiety levels (5 days) and OXT-R binding brain site-specifically (5 and 9 days), and increased spine density (5 days). The behavioral ETX effect exclusively found in female HABs was accompanied by increased 3β5α-THDOC levels, without any effect in female LABs and NABs and on other neurosteroids. In males of all breeding lines, ETX changed a total of 10 out of 23 brain steroids. Passive stress-coping during 10-min forced swimming was not affected by 9-day treatment with ETX, the resulting stress-induced plasma corticosterone levels were higher in ETX-treated NAB rats of both sexes compared with their VEH-treated groups. The fecal bacterial composition was similar but beta diversity differed between HABs and LABs and from NABs independent of sex; ETX treatment had no effect. Therefore, we propose considering the aspect of sex in treatment strategies for anxiety disorders. This is particularly important to establish better treatment regimens for women.

Between Scylla and Charybdis: assessing the multidimensional aspects of pain behaviors in rats using a double avoidance place preference paradigm

ABSTRACT

Although the behavioral response to pain is complex and involves supraspinal processes, assessment of pain symptoms in animal models still mainly relies on reflex-based nociceptive tests, which do not account for the affective-motivational nor cognitive components of pain. We introduce a double avoidance place preference paradigm, an integrated testing procedure in freely moving rats that relies on the conflict between the avoidance of a dark compartment in which a thermal ramp is activated, and the escape towards an aversive brightly lit compartment. We were able to differentiate the first nociceptive threshold from the temperature of definitive escape from the dark compartment, conveying information on the adaptive behavior of animals. Measures were repeated after an hour to evaluate the adaptive learning response upon reexposure. In naive animals, there was a significant decrease in the time spent in the dark compartment at all stages of the testing paradigm upon reexposure, leading to a final escape before the flood had reached nociceptive values. This adaptive behavior was blunted by anxiolytic treatment. In animals exhibiting hyperalgesia following intraplantar complete Freund adjuvant injection, escape thresholds were significantly higher than that of control animals, hinting at a maladaptive affective-motivational response to noxious stimulation. However, in cuff animals, we failed to reveal any hot nociceptive hypersensitivity, but animals exhibited a strong adaptive response to cold simulation upon reexposure. Overall, the proposed paradigm allows for an integrated cortical response leading to a proactive avoidance behavior, while fully complying with ethical standards in animal experimentation.

ANXIOLYTICS: Origins, drug discovery, and mechanisms

Anxiety is a part of the human condition and has been managed by psychoactive substances for centuries. The current medical need and societal demand for anxiolytic medicines has not abated. The present overview provides a brief historical introduction to the discovery of modern age anxiolytics that include the benzodiazepines together with a discussion of the continuing medical need for new antianxiety medications. The paper also discusses the use and impact of behavioral pharmacology in the preclinical development of anxiolytics. The review then highlights the diversity of mechanisms for creating a new generation of anxiolytics through mechanisms beyond the potentiation of GABAA receptors and the blockade of monoamine uptake. A discussion then follows on the behavioral specificity of action of anxiolytics that includes the concept of creating an anxioselective drug, one that targets anxiety without producing untoward effects that include sedation and dependence. The use of anxiolytics in the treatment of other conditions such as substance use disorder is also briefly reviewed. Finally, a brief summary of the current status of anxiolytic drug development is provided. The review concludes with the idea that despite a host of anxiolytic drugs, the lack of efficacy in some patients and the side-effects and safety issues associated with some of these medications demands alternative medicines. Current preclinical and clinical research is ongoing with the goal of identifying such compounds.

Local and global effects of sedation in resting-state fMRI: a randomized, placebo-controlled comparison between etifoxine and alprazolam

TSPO ligands are promising alternatives to benzodiazepines in the treatment of anxiety, as they display less pronounced side effects such as sedation, cognitive impairment, tolerance development and abuse potential. In a randomized double-blind repeated-measures study we compare a benzodiazepine (alprazolam) to a TSPO ligand (etifoxine) by assessing side effects and acquiring resting-state fMRI data from 34 healthy participants after 5 days of taking alprazolam, etifoxine or a placebo. To study the effects of the pharmacological interventions in fMRI in detail and across different scales, we combine in our study complementary analysis strategies related to whole-brain functional network connectivity, local connectivity analysis expressed in regional homogeneity, fluctuations in low-frequency BOLD amplitudes and coherency of independent resting-state networks. Participants reported considerable adverse effects such as fatigue, sleepiness and concentration impairments, related to the administration of alprazolam compared to placebo. In resting-state fMRI we found a significant decrease in functional connection density, network efficiency and a decrease in the networks rich-club coefficient related to alprazolam. While observing a general decrease in regional homogeneity in high-level brain networks in the alprazolam condition, we simultaneously could detect an increase in regional homogeneity and resting-state network coherence in low-level sensory regions. Further we found a general increase in the low-frequency compartment of the BOLD signal. In the etifoxine condition, participants did not report any significant side effects compared to the placebo, and we did not observe any corresponding modulations in our fMRI metrics. Our results are consistent with the idea that sedation globally disconnects low-level functional networks, but simultaneously increases their within-connectivity. Further, our results point towards the potential of TSPO ligands in the treatment of anxiety and depression.

Phenibut: Review and Pharmacologic Approaches to Treating Withdrawal

β-Phenyl-γ-aminobutyric acid (phenibut) is an analog of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) that was first synthesized in Russia in the early 1960s. It is marketed as a nootropic (smart drug) to improve cognitive performance, and to treat generalized and social anxiety, insomnia, and alcohol withdrawal. The use of phenibut is legal in the USA and it is widely available online without a prescription. Increased public awareness of phenibut has led to a growing number of reports of acute intoxication and withdrawal. In this review, we describe the pharmacology of phenibut, the presentation and management of acute intoxication, and regulatory issues, placing particular emphasis on the treatment of acute withdrawal, for which there are no comparative studies. Among 29 cases of phenibut withdrawal, patients were successfully treated with baclofen, benzodiazepines, and phenobarbital, as individual agents or in various combinations. Ancillary medications included antipsychotics, dexmedetomidine, gabapentin, and pregabalin. After stabilization, a number of patients did well on baclofen tapers, whereas others were weaned off benzodiazepines or phenobarbital. Phenobarbital may be preferred over baclofen, or used as an added agent, in patients at risk for seizures. As long as phenibut remains legal, cases of phenibut intoxication and withdrawal are likely to increase. As urine or plasma drug screening for phenibut is not widely available, it is vital that clinicians obtain a detailed medication history in patients presenting to the emergency department with nonspecific symptoms that may represent phenibut intoxication or withdrawal. Further, clinicians may wish to consult an addiction specialist or toxicologist in these situations.

Insomnia and related mental health conditions: Essential neurobiological underpinnings towards reduced polypharmacy utilization rates

Insomnia represents a significant public health burden, with a 10% prevalence in the general population. Reduced sleep affects social and working functioning, productivity, and patient's quality of life, leading to a total of $100 billion per year in direct and indirect healthcare costs. Primary insomnia is unrelated to any other mental or medical illness; secondary insomnia co-occurs with other underlying medical, iatrogenic, or mental conditions. Epidemiological studies found a 40-50% comorbidity prevalence between insomnia and psychiatric disorders, suggesting a high relevance of mental health in insomniacs. Sleep disturbances also worsen the outcomes of several psychiatric disorders, leading to more severe psychopathology and incomplete remission, plausibly contributing to treatment-resistant conditions. Insomnia and psychiatric disorder coexistence can lead to polypharmacy, namely, the concurrent use of two or more medications in the same patient, regardless of their purpose or rationale. Polypharmacy increases the risk of using unnecessary drugs, the likelihood of drug interactions and adverse events, and reduces the patient's compliance due to regimen complexity. The workup of insomnia must consider the patient's sleep habits and inquire about any medical and mental concurrent conditions that must be handled to allow insomnia to be remitted adequately. Monotherapy or limited polypharmacy should be preferred, especially in case of multiple comorbidities, promoting multipurpose molecules with sedative properties and with bedtime administration. Also, non-pharmacological interventions for insomnia, such as sleep hygiene, relaxation training and Cognitive Behavioral Therapy may be useful in secondary insomnia to confront behaviors and thoughts contributing to insomnia and help optimizing the pharmacotherapy. However, insomnia therapy should always be patient-tailored, considering drug indications, contraindications, and pharmacokinetics, besides insomnia phenotype, clinical picture, patient preferences, and side effect profile.

Bibliometric Analysis on GABA-A Receptors Research Based on CiteSpace and VOSviewer

Background

GABA-A receptors are the primary mediators of brain inhibitory neurotransmission. In the past years, many studies focused on this channel to decipher the pathogenesis of related diseases but lacked bibliometric analysis research. This study aims to explore the research status and identify the research trends of GABA-A receptor channels.

Methods

Publications related to GABA-A receptor channels were retrieved from the Web of Science Core Collection from 2012 to 2022. After screening, the VOSviewer 1.6.18 and Citespace 5.8 R3 were used for bibliometric analysis from journals, countries, institutions, authors, co-cited references and keywords.

Results

We included 12,124 publications in the field of GABA-A receptor channels for analysis. The data shows that although there was a slight decrease in annual publications from 2012 to 2021, it remained at a relatively high level. Most publications were in the domain of neuroscience. Additionally, the United States was the most prolific country, followed by China. Univ Toronto was the most productive institution, and James M Cook led essential findings in this field. Furthermore, brain activation, GABAAR subunits expression, modulation mechanism in pain and anxiety behaviors and GABA and dopamine were paid attention to by researchers. And top research frontiers were molecular docking, autoimmune encephalitic series, obesity, sex difference, diagnosis and management, EEG and KCC2.

Conclusion

Taken together, academic attention on GABA-A receptor channels was never neglected since 2012. Our analysis identified key information, such as core countries, institutions and authors in this field. Molecular docking, autoimmune encephalitic series, obesity, sex difference, diagnosis and management, EEG and KCC2 will be the future research direction.

GABAergic Effects of Etifoxine and Alprazolam Assessed by Double Pulse TMS

INTRODUCTION

There is a need for novel anxiolytics with improved side effect profiles compared to benzodiazepines. A promising candidate with alternative pharmacodynamics is the translocator protein ligand, etifoxine.

METHODS

To get further insight into its mechanisms of action and side effects compared to the benzodiazepine alprazolam, we performed a double-blind, placebo-controlled, repeated-measures study in 36 healthy male subjects. Participants were examined for trait anxiety and side effects and underwent repeated transcranial magnetic stimulation (TMS) assessments, including motor evoked potentials (MEP), short intracortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP).

RESULTS

We observed attenuation of MEPs by alprazolam but not by etifoxine. SICI was not significantly affected by alprazolam or etifoxine. However, the response pattern indicated a lowered SICI threshold after the administration of etifoxine and alprazolam compared to the placebo. ICF and CSP were influenced by neither medication. Alprazolam led to higher sedation and subjective impairment of concentration compared to etifoxine. Individual anxiety trait scores did not affect TMS parameters.

DISCUSSION

This study indicated a favorable side effect profile of etifoxine in healthy volunteers. Moreover, it revealed differential GABA-related effects on neuromuscular function by means of TMS. The side effects and TMS profile of etifoxine are compatible with the involvement of neurosteroidogenesis and a predominant α3 subunit modulation compared to alprazolam.

Palladium-catalyzed synthesis of 4-sila-4H-benzo[d][1,3]oxazines by intramolecular Hiyama coupling

A palladium-catalyzed synthesis of 4-sila-4H-benzo[d][1,3]oxazines, silicon-switched analogs of biologically relevant 4H-benzo[d][1,3]oxazines, was developed by the intramolecular Hiyama coupling of 3-amido-2-(arylsilyl)aryl triflates.

Long-Term Management of Generalised Anxiety Disorder with Low-Dose Continuous Infusions of Flumazenil: A Case Series

Background: Generalised anxiety disorder (GAD) is a common anxiety disorder associated with social and occupational impairment. Recently, a theory was postulated that dysfunctional gamma aminobutyric acid type A receptors (GABAA) are implicated in anxiety symptomology, which could be corrected by flumazenil, an antagonist at the benzodiazepine binding site on the GABAA receptor. Method: Participants had a primary diagnosis of GAD and were treated initially with an eight-day continuous low-dose flumazenil infusion (total 32 mg at a rate of 4 mg/24 h). Some participants were re-treated with a further four- or eight-day infusion. Treatment response was measured as a 50% reduction in anxiety or stress scores on the Depression Anxiety Stress Scale—21 (DASS-21). Remission was measured as scores ≤3 or ≤7 on the anxiety and stress subscales of the DASS-21, respectively. Results: Eight cases are reported. All cases met the criteria for treatment response on the anxiety and stress subscale of the DASS-21. Remission was achieved in seven participants on the anxiety subscale and in five on the stress subscale. No changes in hepatic, renal, or haematological function were likely attributed to flumazenil. Conclusion: Data suggest that low-dose continuous flumazenil infusion manages GAD symptoms and is safe. Although these results are promising, future randomised control trials are required to confirm these results.

Highly Enantioselective Iridium-Catalyzed Hydrogenation of o-Amidophenyl Ketones Enabled by 1,2-Diphenylethylenediamine-Derived P,N,N-Ligands with Tertiary Amine Terminus

A readily available and highly modular class of chiral P,N,N-ligands based on a structurally flexible nonchiral phosphine-amine framework with an optically active 1,2-diphenylethylenediamine unit bearing a tertiary amine terminus as the chiral source have been developed and successfully applied in the Ir-catalyzed asymmetric hydrogenation of o-amidophenyl ketones. These tridentate P,N,N-ligands exhibited excellent activity, enantioselectivity, and substrate tolerance, thus furnishing various optically active o-amidobenzhydrols in up to 99% yields and with >99% ee. The utility of this protocol has been proven by synthetically diverse product transformation and highly enantioselective production of a rice plant growth regulator, (S)-inabenfide.

Translocator Protein Ligand Etifoxine Attenuates MPTP-Induced Neurotoxicity

Parkinson’s disease (PD) is a neurodegenerative disease, but the currently available treatments for this disease are symptomatic treatments. There is evidence that translocator protein (18 kDa) (TSPO) expression is upregulated in some neurodegenerative diseases, and TSPO ligands have obvious neuroprotective effects. However, the neuroprotective effects and other potential effects of the TSPO ligand etifoxine in PD remain unclear. Therefore, the present study was designed to explore the impacts of etifoxine on a mouse model of PD induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We found that etifoxine significantly reduced motor function deficits, decreased the loss of tyrosine hydroxylase-positive neurons in the substantia nigra, and attenuated the decrease in striatal dopamine levels in mice that received MPTP. Etifoxine diminished the production of inflammatory mediators and infiltration of leukocytes in the brain after MPTP exposure. In vitro studies suggested that microglia contribute to etifoxine’s neuroprotective effect. The results showed that etifoxine can alleviate MPTP-induced neurotoxicity and neuroinflammation, providing a new idea for the treatment of PD.

Searching for new anxiolytic agents among derivatives of 11-dialkylaminoethyl-2,3,4,5-tetrahydrodiazepino[1,2-a]benzimidazole

A study on the anxiolytic activity of the new derivatives of 11-dialkylaminoethyl-2,3,4,5-tetrahydrodiazepino[1,2-a]benzimidazole, containing privileged scaffolds of benzodiazepine and benzimidazole in their structure, was conducted. The cytotoxic properties of low levels of six compounds were preliminary determined in vitro using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide test. The screening of these substances for anxiolytic activity was conducted using elevated plus maze (EPM) test in vivo, and DAB-21 was found to be the most active compound. The acute toxicity of DAB-21 was determined as less toxic than that of diazepam. The dose-dependent effect of the most active compound revealed a minimum dose of 1.26 mg/kg, which resulted in the maximum counterphobic effect. The effect of DAB-21 was superior in a number of tests compared with that of diazepam, which indicated a high level of tranquilizing activity for DAB-21. The results of in silico docking analysis suggest that DAB-21 should have a slightly lower anxiolytic activity than diazepam, but should exhibit greater specific affinity for the benzodiazepine site of the GABA_A receptor, in comparison with its GABA-binding site. The interaction between DAB-21 and flumazenil in terms of EPM verifies the GABAergic mechanism of action of DAB-21. Our results highlight the potential of 11-dialkylaminomethyl-2,3,4,5-tetrahydrodiazepino[1,2-a]benzimidazoles as promising compounds in the search for new highly effective anxiolytics.

Long-lasting analgesic and neuroprotective action of the non-benzodiazepine anxiolytic etifoxine in a mouse model of neuropathic pain

Neuropathic pain is frequently associated with anxiety and major depressive disorders, which considerably impact the overall patient experience. Favoring GABAergic inhibition through the pain matrix has emerged as a promising strategy to restore proper processing of nociceptive and affective information in neuropathic pain states. In this context, the non-benzodiazepine anxiolytic etifoxine (EFX), known to amplify GABAergic inhibition through positive modulation of GABA_A receptors and neurosteroidogenesis, presents several advantages. Therefore, we sought to investigate the preclinical therapeutic potential of EFX on the somatosensory and affective components of neuropathic pain. Here, we used a murine model in which neuropathic pain was induced by the implantation of a compressive cuff around the sciatic nerve (mononeuropathy). We showed that the intraperitoneal EFX treatment for five consecutive days (50 mg/kg) relieved mechanical allodynia in a sustained manner. Besides its effect on evoked mechanical hypersensitivity, EFX also alleviated aversiveness of ongoing pain as well as anxiodepressive-like consequences of neuropathic pain following cuff-induced mononeuropathy. This effect was also seen 12 weeks after induction of the neuropathy when allodynia was no longer present. Analgesic and neuroprotective actions of EFX were also seen by the absence of neuropathic pain symptoms if a second sciatic nerve constriction injury was applied to the contralateral hindpaw. Mass spectrometry analysis revealed a normalization of brainstem serotonin levels in EFX-treated animals and an increase in norepinephrine. This study suggests that EFX presents promising therapeutic potential for the relief of both somatosensory and affective consequences of neuropathic pain, a beneficial effect that is likely to involve monoamine descending controls.

Regulation of GABAA and 5-HT Receptors Involved in Anxiolytic Mechanisms of Jujube Seed: A System Biology Study Assisted by UPLC-Q-TOF/MS and RT-qPCR Method

The increase of the prevalence of anxiety greatly impacts the quality of life in China and globally. As the most popular traditional Chinese medicinal ingredient for nourishing health and tranquilizing mind, Jujube seed (Ziziphus jujuba Mill., Rhamnaceae) (SZJ) has been proved to exert anxiolytic effects in previous reports. In this study, a system biology method assisted by UPLC-Q-TOF/MS and RT-qPCR was developed to systematically demonstrate the anxiolytic mechanisms of SZJ. A total of 35 phytochemicals were identified from SZJ extract (Ziziphus jujuba Mill. var. spinosa [Bunge] Hu ex H.F. Chow), which interact with 71 anxiolytic targets. Protein-protein interaction, genes cluster, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis were subsequently conducted, and results demonstrated that regulation of serotonergic and GABAergic synapse pathways were dominantly involved in the anxiolytic mechanisms of SZJ extract. The effects of SZJ extract on mRNA expressions of multiple GABA_A (gamma-aminobutyric acid type A) and 5-HT (serotonin) receptors subtypes were further validated in human neuroblastoma SH-SY5Y cells using RT-qPCR. Results showed that SZJ extract (250 μg/mL) significantly up-regulated the mRNA level of GABRA1 and GABRA3 as well as HTR1A, HTR2A, and HTR2B in non-H₂O₂ treated SH-SY5Y cells. However, it exerted an inhibitive effect on the overexpressed mRNA of GABRA1, GABRA2, HTR1A, and HTR2A in H₂O₂ treated SH-SY5Y cells. Taken together, our findings suggest that anxiolytic mechanisms of SZJ mostly involve the regulation of GABAergic and serotonergic synapse pathways, especially a two-way modulation of GABRA1, HTR1A, and HTR2A. Our current results provide potential direction for future investigation of SZJ as an anxiolytic agent.

Imepitoin for treatment of idiopathic head tremor syndrome in dogs: A randomized, blinded, placebo-controlled study

Background

Idiopathic head tremor syndrome is a paroxysmal movement disorder of unknown etiology. Spontaneous remission may occur, but owners may request treatment in severely affected dogs with continued episodes. Controlled studies of the disease are not available.

Hypothesis/Objectives

A drug with gamma amino butyric acid‐ergic and anxiolytic effects will decrease head tremor episodes.

Animals

Twenty‐four dogs with severe nonremitting head tremor and presumptive clinical diagnosis of idiopathic head tremor syndrome.

Methods

Prospective, blinded, placebo‐controlled clinical trial to compare imepitoin with placebo in dogs with frequent episodes of idiopathic head tremor. Evaluation of efficacy used the quotient T2/T1 that represented prolongation of the head tremor‐free period compared to a 3‐month baseline. A dog was considered a responder if tremors subsided or if the head tremor‐free period was 3× longer than the longest period during baseline (T2/T1 ≥ 3). Sample size calculations considered a large effect of imepitoin on T2/T1 (Cohen's d = 0.8).

Results

There were no responders in the placebo group (0/12). In the imepitoin group, the responder rate was 17% (2/12; P = .18) with T2/T1 3.8 and 4.0. Mean T2/T1 was 1.0 ± 1.4 in the imepitoin and 0.4 ± 0.4 in the placebo group (P = .37).

Conclusion and Clinical Importance

Imepitoin did not result in a significant overall benefit. Future studies should focus on treatment of subgroups with a common pathophysiology and similar comorbidities.

TSPO ligand etifoxine attenuates LPS-induced cognitive dysfunction in mice

The translocator protein (TSPO), once known as peripheral-type benzodiazepine receptor, was reported to be related with several physiological functions. Etifoxine is a clinically available anxiolytic drug, and has recently shown neuroprotective effects as a TSPO ligand. The aim of the present study was to investigate the influence of etifoxine on LPS-induced neuroinflammation and cognitive dysfunction. C57/BL6 male mice were injected with etifoxine (50 mg/kg, i.p.) three days before lipopolysaccharide (LPS, 500 μg/kg, i.p.) administration. Etifoxine pretreatment alleviated hippocampal inflammation, increased brain levels of progesterone, allopregnanolone and attenuated cognitive dysfunction in LPS-injected mice. While LPS increased expression of caspase-3 and decreased p-Akt/Akt, etifoxine returned caspase-3 and p-Akt/Akt to control levels. Finasteride, a 5α-reductase inhibitor that blocked allopregnanolone production, partially reversed the effects of etifoxine. We concluded that etifoxine exerted neuroprotective effects in LPS-induced neuroinflammation and the neuroprotection may be related with increase of neurosteroids synthesis and decrease of apoptosis.

Orphan G Protein Coupled Receptors in Affective Disorders

G protein coupled receptors (GPCRs) are the main mediators of signal transduction in the central nervous system. Therefore, it is not surprising that many GPCRs have long been investigated for their role in the development of anxiety and mood disorders, as well as in the mechanism of action of antidepressant therapies. Importantly, the endogenous ligands for a large group of GPCRs have not yet been identified and are therefore known as orphan GPCRs (oGPCRs). Nonetheless, growing evidence from animal studies, together with genome wide association studies (GWAS) and post-mortem transcriptomic analysis in patients, pointed at many oGPCRs as potential pharmacological targets. Among these discoveries, we summarize in this review how emotional behaviors are modulated by the following oGPCRs: ADGRB2 (BAI2), ADGRG1 (GPR56), GPR3, GPR26, GPR37, GPR50, GPR52, GPR61, GPR62, GPR88, GPR135, GPR158, and GPRC5B.

Animal models of post-traumatic stress disorder and novel treatment targets

Understanding the neurobiological basis of post-traumatic stress disorder (PTSD) is fundamental to accurately diagnose this neuropathology and offer appropriate treatment options to patients. The lack of pharmacological effects, too often observed with the most currently used drugs, the selective serotonin reuptake inhibitors (SSRIs), makes even more urgent the discovery of new pharmacological approaches. Reliable animal models of PTSD are difficult to establish because of the present limited understanding of the PTSD heterogeneity and of the influence of various environmental factors that trigger the disorder in humans. We summarize knowledge on the most frequently investigated animal models of PTSD, focusing on both their behavioral and neurobiological features. Most of them can reproduce not only behavioral endophenotypes, including anxiety-like behaviors or fear-related avoidance, but also neurobiological alterations, such as glucocorticoid receptor hypersensitivity or amygdala hyperactivity. Among the various models analyzed, we focus on the social isolation mouse model, which reproduces some deficits observed in humans with PTSD, such as abnormal neurosteroid biosynthesis, changes in GABAA receptor subunit expression and lack of pharmacological response to benzodiazepines. Neurosteroid biosynthesis and its interaction with the endocannabinoid system are altered in PTSD and are promising neuronal targets to discover novel PTSD agents. In this regard, we discuss pharmacological interventions and we highlight exciting new developments in the fields of research for novel reliable PTSD biomarkers that may enable precise diagnosis of the disorder and more successful pharmacological treatments for PTSD patients.

Stress and drug abuse-related disorders: The promising therapeutic value of neurosteroids focus on pregnenolone-progesterone-allopregnanolone pathway

The pregnenolone-progesterone-allopregnanolone pathway is receiving increasing attention in research on the role of neurosteroids in pathophysiology, particularly in stress-related and drug use disorders. These disorders involve an allostatic change that may result from deficiencies in allostasis or adaptive responses, and may be downregulated by adjustments in neurotransmission by neurosteroids. The following is an overview of findings that assess how pregnenolone and/or allopregnanolone concentrations are altered in animal models of stress and after consumption of alcohol or cannabis-type drugs, as well as in patients with depression, anxiety, post-traumatic stress disorder or psychosis and/or in those diagnosed with alcohol or cannabis use disorders. Preclinical and clinical evidence shows that pregnenolone and allopregnanolone, operating according to a different or common pharmacological profile involving GABAergic and/or endocannabinoid system, may be relevant biomarkers of psychiatric disorders for therapeutic purposes. Hence, ongoing clinical trials implicate synthetic analogs of pregnenolone or allopregnanolone, and also modulators of neurosteroidogenesis.

Novel pharmacological targets in drug development for the treatment of anxiety and anxiety-related disorders

Current medication for anxiety disorders is suboptimal in terms of efficiency and tolerability, highlighting the need for improved drug treatments. In this review an overview of drugs being studied in different phases of clinical trials for their potential in the treatment of fear-, anxiety- and trauma-related disorders is presented. One strategy followed in drug development is refining and improving compounds interacting with existing anxiolytic drug targets, such as serotonergic and prototypical GABAergic benzodiazepines. A more innovative approach involves the search for compounds with novel mechanisms of anxiolytic action using the growing knowledge base concerning the relevant neurocircuitries and neurobiological mechanisms underlying pathological fear and anxiety. The target systems evaluated in clinical trials include glutamate, endocannabinoid and neuropeptide systems, as well as ion channels and targets derived from phytochemicals. Examples of promising novel candidates currently in clinical development for generalised anxiety disorder, social anxiety disorder, panic disorder, obsessive compulsive disorder or post-traumatic stress disorder include ketamine, riluzole, xenon with one common pharmacological action of modulation of glutamatergic neurotransmission, as well as the neurosteroid aloradine. Finally, compounds such as D-cycloserine, MDMA, L-DOPA and cannabinoids have shown efficacy in enhancing fear-extinction learning in humans. They are thus investigated in clinical trials as an augmentative strategy for speeding up and enhancing the long-term effectiveness of exposure-based psychotherapy, which could render chronic anxiolytic drug treatment dispensable for many patients. These efforts are indicative of a rekindled interest and renewed optimism in the anxiety drug discovery field, after decades of relative stagnation.

An update on the anxiolytic and neuroprotective properties of etifoxine: from brain GABA modulation to a whole-body mode of action

Treating the signs and symptoms of anxiety is an everyday challenge in clinical practice. When choosing between treatment options, anxiety needs to be understood in the situational, psychiatric, and biological context in which it arises. Etifoxine, a non-benzodiazepine anxiolytic drug belonging to the benzoxazine class, is an effective treatment for anxiety in response to a stressful situation. In the present review, we focused on several aspects of the cerebral and somatic biological mechanisms involved in anxiety and investigated the extent to which etifoxine's mode of action can explain its anxiolytic activity. Its two mechanisms of action are the modulation of GABAergic neurotransmission and neurosteroid synthesis. Recent data suggest that the molecule possesses neuroprotective, neuroplastic, and anti-inflammatory properties. Etifoxine was first shown to be an effective anxiolytic in patients in clinical studies comparing it with clobazam, sulpiride, and placebo. Randomized controlled studies have demonstrated its anxiolytic efficacy in patients with adjustment disorders (ADs) with anxiety, showing it to be superior to buspirone and comparable to lorazepam and phenazepam, with a greater number of markedly improved responders and a better therapeutic index. Etifoxine's noninferiority to alprazolam has also been demonstrated in a comparative trial. Significantly less rebound anxiety was observed after abrupt cessation of etifoxine compared with lorazepam or alprazolam. Consistent with this finding, etifoxine appears to have a very low dependence potential. Unlike lorazepam, it has no effect on psychomotor performance, vigilance, or free recall. Severe adverse events are in general rare. Skin and subcutaneous disorders are the most frequently reported, but these generally resolve after drug cessation. Taken together, its dual mechanisms of action in anxiety and the positive data yielded by clinical trials support the use of etifoxine for treating the anxiety signs and symptoms of individuals with ADs.

TSPO Ligands Promote Cholesterol Efflux and Suppress Oxidative Stress and Inflammation in Choroidal Endothelial Cells

Choroidal endothelial cells supply oxygen and nutrients to retinal pigment epithelial (RPE) cells and photoreceptors, recycle metabolites, and dispose of metabolic waste through the choroidal blood circulation. Death of the endothelial cells of the choroid may cause abnormal deposits including unesterified and esterified cholesterol beneath RPE cells and within Bruch’s membrane that contribute to the progression of age-related macular degeneration (AMD), the most prevalent cause of blindness in older people. Translocator protein (TSPO) is a cholesterol-binding protein that is involved in mitochondrial cholesterol transport and other cellular functions. We have investigated the role of TSPO in choroidal endothelial cells. Immunocytochemistry showed that TSPO was localized to the mitochondria of choroidal endothelial cells. Choroidal endothelial cells exposed to TSPO ligands (Etifoxine or XBD-173) had significantly increased cholesterol efflux, higher expression of cholesterol homeostasis genes (LXRα, CYP27A1, CYP46A1, ABCA1 and ABCG1), and reduced biosynthesis of cholesterol and phospholipids from [¹⁴C]acetate, when compared to untreated controls. Treatment with TSPO ligands also resulted in reduced production of reactive oxygen species (ROS), increased antioxidant capacity, and reduced release of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α and VEGF) induced by oxidized LDL. These data suggest TSPO ligands may offer promise for the treatment of AMD.