Partial Agonist Research Articles

CURRENT STATE OF PSILOCYBIN-ASSISTED THERAPY IN MOOD DISORDERS.

Psychedelics are currently undergoing a scientific renaissance, with modern studies investigating therapeutic efficacy of psychedelic-assisted therapy in a range of psychiatric conditions. In particular, psilocybin-assisted therapy (PAT) has been suggested to have positive effects on patients suffering from depression and psychiatric distress associated with life-threatening disease - contexts with growing needs for alternative treatments - in a therapeutic setting involving fewer doses and less important adverse effect compared to that of classic psychotrope administration. Psychedelics are partial agonists of the serotonin 2A (5-HT2A) G protein-coupled receptors, whose activation likely mediates the acute psychoactive effects. Furthermore, psychedelics seem to induce a hyper-plastic state which allows for adaptation of inflexible pathological thinking patterns. Post-acutely, they are suggested to induce rapid, robust and sustained neuroplasticity. Eight clinical PAT trials have been conducted between January 1st 2001 and March 31st 2023 and are reviewed here. Five of them evaluate the effect on depressive symptomatology in an otherwise general population. The other three evaluate effect on depression and anxiety in patients suffering from somatic life-threatening disease. The studies reviewed here show that PAT is safe and feasible to administer in current clinical models. Preliminary efficacy shows significant improvements in depressive and anxious symptomatology which are immediate and partially sustained. One study comparing PAT to selective serotonergic reuptake inhibitors showed no significant difference of efficacy between the two treatments. Preliminary results regarding efficacy of PAT on mood disorders are promising, but further research is warranted for stronger inferences, with a particular focus on larger, multicentric studies, more diverse populations and a stronger control for expectancy and unblinding.

Structure-Guided Design of Partial Agonists at an Opioid Receptor.

The persistence of chronic pain and continuing overdose deaths from pain-relieving opioids targeting μ opioid receptor (μOR) have fueled the need for reliable long-term analgesics which use different targets and mechanisms. The δ opioid receptor (δOR) is a potential alternative target for non-addictive analgesics to alleviate chronic pain, made more attractive by its lack of respiratory depression associated with μOR agonists. However, early δOR full agonists were found to induce seizures, precluding clinical use. Partial δOR agonists may offer more controlled activation of the receptor compared to full agonists, but the development of such ligands has been hindered by uncertainty over the molecular mechanism mediating partial agonism. Using a structure-based approach, we explored the engagement of the sodium binding pocket in δOR and developed a bitopic ligand, C6-Quino, predicted to be a selective δOR partial agonist. Functional studies of C6-Quino revealed that it displayed δOR partial agonist activity at both G-protein and arrestin pathways. Its interaction with the sodium pocket was confirmed and analyzed using a single particle cryo-EM. Additionally, C6-Quino demonstrated favorable chemical and physiological properties like oral activity, and analgesic activity in multiple chronic pain models. Notably, μOR-related hyperlocomotion and respiratory depression, and δOR-related convulsions, were not observed at analgesic doses of C6-Quino. This fundamentally new approach to designing δOR ligands provides a blueprint for the development of partial agonists as safe analgesics and acts as a generic method to optimize signaling profiles of other Class A GPCRs.

Platelet integrin αIIbβ3 plays a key role in venous thrombogenesis in a mouse model.

Venous thrombosis (VT) is a common vascular disease associated with reduced survival and a high recurrence rate. Previous studies have shown that the accumulation of platelets and neutrophils at sites of endothelial cell activation is a primary event in VT, but a role for platelet αIIbβ3 in the initiation of venous thrombosis has not been established. This task has been complicated by the increased bleeding linked to partial agonism of current αIIbβ3 inhibitory drugs such as tirofiban (Aggrastat ® ). Here, we show that m-tirofiban, an engineered version of tirofiban, is not a partial agonist of αIIbβ3. This is based on its cryo-EM structure in complex with human full-length αIIbβ3 and its inability to increase expression of an activation-sensitive epitope on platelet αIIbβ3. m-tirofiban abolished agonist-induced platelet aggregation ex vivo at concentrations that preserved clot retraction and markedly suppressed the accumulation of platelets, neutrophils, and fibrin on thrombin-activated endothelium in real-time using intravital microscopy in a mouse model of venous thrombogenesis. Unlike tirofiban, however, m-tirofiban did not increase bleeding at the thrombosis-inhibitory dose. These findings establish a key role for αIIbβ3 in the initiation of VT, provide a guiding principle for designing potentially safer inhibitors for other integrins, and suggest that pure antagonists of αIIbβ3 like m-tirofiban merit further consideration as potential thromboprophylaxis agents in patients at high-risk for VT and hemorrhage.

Diabetes and Heart Failure: A Literature Review, Reflection and Outlook.

Heart failure (HF) is a complex clinical syndrome caused by structural or functional dysfunction of the ventricular filling or blood supply. Diabetes mellitus (DM) is an independent predictor of mortality for HF. The increase in prevalence, co-morbidity and hospitalization rates of both DM and HF has further fueled the possibility of overlapping disease pathology between the two. For decades, antidiabetic drugs that are known to definitively increase the risk of HF are the thiazolidinediones (TZDs) and saxagliptin in the dipeptidyl peptidase-4 (DPP-4) inhibitor, and insulin, which causes sodium and water retention, and whether metformin is effective or safe for HF is not clear. Notably, sodium-glucose transporter 2 (SGLT2) inhibitors and partial glucagon-like peptide-1 receptor agonists (GLP-1 RA) all achieved positive results for HF endpoints, with SGLT2 inhibitors in particular significantly reducing the composite endpoint of cardiovascular mortality and hospitalization for heart failure (HHF). Further understanding of the mutual pathophysiological mechanisms between HF and DM may facilitate the detection of novel therapeutic targets to improve the clinical outcome. This review focuses on the association between HF and DM, emphasizing the efficacy and safety of antidiabetic drugs and HF treatment. In addition, recent therapeutic advances in HF and the important mechanisms by which SGLT2 inhibitors/mineralocorticoid receptor antagonist (MRA)/vericiguat contribute to the benefits of HF are summarized.

Triclosan affects steroidogenesis in mouse primary astrocytes in vitro with engagement of Sirtuin 1 and 3

Triclosan (TCS) is a widely used antimicrobial, antifungal, and antiviral agent. To date, it has been reported that TCS can enter the human body and disrupt hormonal homeostasis. Therefore, the aim of our paper was to evaluate the impact of TCS on astrocytes, i.e. a crucial population of cells responsible for steroid hormone production. Our data showed that, in mouse primary astrocyte cultures, TCS can act as an endocrine disrupting chemical through destabilization of the production or secretion of progesterone (P4), testosterone (T), and estradiol (E2). TCS affects the mRNA expression of enzymes involved in neurosteroidogenesis, such as Cyp17a1, 17β-Hsd, and Cyp19a1. Our data showed that a partial PPARγ agonist (honokiol) prevented changes in Cyp17a1 mRNA expression caused by TCS. Similarly, honokiol inhibited TCS-stimulated P4 release. However, rosiglitazone (classic PPARγ agonist) or GW9662 (PPARγ antagonist) had a much stronger effect. Therefore, we believe that the changes observed in the P4, T, and E2 levels are a result of dysregulation of the activity of the aforementioned enzymes, whose expression can be affected by TCS through a Pparγ-dependent pathway. TCS was found to decrease the aryl hydrocarbon receptor (AhR) and Sirtuin 3 protein levels, which may be the result of the activation of the these proteins. Since our study showed dysregulation of the production or secretion of neurosteroids in astrocytes, it can be concluded that TCS reaching the brain may contribute to the development of neurodegenerative diseases in which an abnormal amount of neurosteroids is observed.

Treating neuropathic pain and nicotine dependence: Epibatidine derivatives as potential therapeutics

Treating neuropathic pain and nicotine dependence: Epibatidine derivatives as potential therapeutics Lance R. McMahon, Ph.D. and Jenny L. Wilkerson, Ph.D. from Texas Tech University Health Sciences Center, describe the search for the magic bullet to treat both neuropathic pain and nicotine dependence using novel epibatidine derivatives as potential therapeutics. Nicotinic acetylcholine receptors (nAChR), specifically nAChR containing α4β2* subunits (* denotes additional receptor subunits), are known for their role in nicotine dependence and addiction (1). These receptors are found throughout the central and peripheral nervous systems on neuronal, glial, and immune cells (2). Although varenicline, an α4β2 nAChR* partial agonist, is a useful smoking cessation pharmacotherapy, the largest individual cause of preventable death continues to be cigarette smoking. (1)

Cariprazine in the management of emotionally unstable personality disorder in female patients: a case series.

Emotionally unstable personality disorder (EUPD) is debilitating psychiatric disorder, particularly common in female and forensic populations. However, appropriate pharmacological treatment to effectively manage symptoms of EUPD remains an unmet clinical need. Dopamine receptor partial agonists (DRPAs), such as aripiprazole, have a favourable tolerability profile and have demonstrated some benefits in targeting symptoms of emotional dysregulation, although, evidence regarding the effects of novel D2/D3 DRPA cariprazine in EUPD patients has been limited. To evaluate the efficacy and tolerability of cariprazine for EUPD in a case series of female forensic inpatients where the diagnosis is more prevalent. Demographic and clinical information of the patients were collected from patient electronic records during their admission in a specialized NHS forensic service. Treatment response was measured using the Positive and Negative Syndrome Scale (PANSS) at baseline, 3 and 6 months and Global Clinical Impression Scale (CGI-scores) at baseline and 6 months. Tolerability and BMI, ECG QTc interval and prolactin levels were recorded prior to initiation and at 6 months. Eight female patients with EUPD (mean age 29.8 years, SD 5.3) were treated with cariprazine (range 3-6mg). Total CGI-scores modestly improved from 5.6 baseline to 5.0 at 6 months. There was a reduction in mean total PANSS scores from baseline to 6 months (92.5, SD 8.1 to 72.4, SD 15.8), general psychopathology (56.1 SD 6.7 to 42.5, SD9.7), positive (21.9 SD 4.6 to 17.1, SD4.8) and negative PANSS scores (14.5 SD 6.3 to 12.8, SD4.6), corresponding to a 21%, 23%, 20% and 3% mean score reduction, respectively. Cariprazine demonstrated a favourable metabolic and hormonal side effect profile with no treatment discontinuation at 6 months follow up. This is the first case series to evaluate the effectiveness of cariprazine in EUPD. Its efficacy in improving PANSS and CGI-S scores was overall modest and highly variable, reflective of an inherently heterogenous and comorbid patient sample but the benefits on treatment perseverance and tolerability were considerable. Cariprazine may be of particular benefit in EUPD where psychotic symptoms are co-morbid, as an augmentation strategy to clozapine, or where previous antipsychotics have caused metabolic or hormonal side effects.

Immunomodulatory of sesquiterpenoids and sesquiterpenoid dimers-based toll-like receptor 4 (TLR4) from Dysoxylum parasiticum stem bark

In recent decades, the interest in natural products with immunomodulatory properties has increased due to their therapeutic potential. These products have a wider range of pharmacological activities and demonstrate lower toxicity levels when compared to their synthetic counterparts. Therefore, this study aimed to investigate the immunomodulatory effects of sesquiterpenoids (SQs) and sesquiterpenoid dimers (SQDs) isolated from Dysoxylum parasiticum (Osbeck) Kosterm. stem bark on human and murine cells, particularly focusing on toll-like receptor 4 (TLR4). Utilizing the secreted alkaline phosphatase (SEAP) assay on engineered human and murine TLR4 of HEK-Blue cells, antagonist TLR4 compounds were identified, including SQs 6, 9, and 10, as well as SQDs 17 and 22. The results showed that 10-hydroxyl-15-oxo-α-cadinol (9) had a potent ability to reduce TLR4 activation induced by LPS stimulation, with minimal toxicity observed in both human and murine cells. The SEAP assay also revealed diverse immune regulatory effects for the same ligand. For instance, SQs 12, 14, and 16 transitioned from antagonism on human to murine TLR4. The SQs (4, 7, 11, and 15) and SQDs (18–20) offered partial antagonist effect exclusively on murine TLR4. Furthermore, these selected SQs and SQDs were assessed for their influence on the production of proinflammatory cytokines TNF-α, IL-1α, IL-1β, and IL-6 of the NF-κB signaling pathway in human and murine macrophage cell lines, showing a dose-dependent manner. Additionally, a brief discussion on the structure-activity relationship was presented.

Diagnosis and Treatment of Presumed Naltrexone-XR-precipitated Opioid Withdrawal in a Patient Chronically Treated With Buprenorphine-XR: A Case Report.

Naltrexone, buprenorphine, and methadone are Food and Drug Administration-approved medications for the treatment of opioid use disorder in the United States. Naltrexone, an opioid antagonist, can precipitate opioid withdrawal if administered too quickly after the use of full or partial opioid agonists for those with either dependence or use disorder. We describe a case of severe precipitated opioid withdrawal syndrome after reported buprenorphine extended-release (XR) administration, despite the patient having been stable on buprenorphine-XR for several years, with no missed doses or recent opioid use. Naltrexone levels were sent and helped to diagnose suspected inadvertent naltrexone-XR administration in this patient, which was likely the etiology of his precipitated opioid withdrawal syndrome. We suggest the use of high-dose buprenorphine, as well as adjunctive medications including benzodiazepines, as a treatment strategy for naltrexone-XR precipitated withdrawal in the setting of chronic buprenorphine-XR treatment.

Androgen receptor-mediated pharmacogenomic expression quantitative trait loci: implications for breast cancer response to AR-targeting therapy

BackgroundEndocrine therapy is the most important treatment modality of breast cancer patients whose tumors express the estrogen receptor α (ERα). The androgen receptor (AR) is also expressed in the vast majority (80–90%) of ERα-positive tumors. AR-targeting drugs are not used in clinical practice, but have been evaluated in multiple trials and preclinical studies.MethodsWe performed a genome-wide study to identify hormone/drug-induced single nucleotide polymorphism (SNP) genotype - dependent gene-expression, known as PGx-eQTL, mediated by either an AR agonist (dihydrotestosterone) or a partial antagonist (enzalutamide), utilizing a previously well characterized lymphoblastic cell line panel. The association of the identified SNPs-gene pairs with breast cancer phenotypes were then examined using three genome-wide association (GWAS) studies that we have published and other studies from the GWAS catalog.ResultsWe identified 13 DHT-mediated PGx-eQTL loci and 23 Enz-mediated PGx-eQTL loci that were associated with breast cancer outcomes post ER antagonist or aromatase inhibitors (AI) treatment, or with pharmacodynamic (PD) effects of AIs. An additional 30 loci were found to be associated with cancer risk and sex-hormone binding globulin levels. The top loci involved the genes IDH2 and TMEM9, the expression of which were suppressed by DHT in a PGx-eQTL SNP genotype-dependent manner. Both of these genes were overexpressed in breast cancer and were associated with a poorer prognosis. Therefore, suppression of these genes by AR agonists may benefit patients with minor allele genotypes for these SNPs.ConclusionsWe identified AR-related PGx-eQTL SNP-gene pairs that were associated with risks, outcomes and PD effects of endocrine therapy that may provide potential biomarkers for individualized treatment of breast cancer.

Systematic review and meta-analyses of cytisine to support tobacco cessation.

Cytisine (also known as cytisinicline) is a low-cost partial agonist of nicotinic acetylcholine receptors used to assist tobacco cessation. We aimed to review the effectiveness of cytisine for tobacco cessation and the effects of dose and co-use of behavioural or other pharmacological interventions on cessation outcomes. We searched seven databases, Google Scholar, and reference lists of included publications for randomised controlled trials investigating use of cytisine as a tobacco cessation aid. Studies were eligible if participants were ≥15 years old and used tobacco upon study enrolment. We conducted four random effects meta-analyses and sensitivity analyses with fixed effects models. We used the Cochrane risk-of-bias tool for randomised trials version 2 to assess risk of bias in included studies, with adjustments recommended by the Cochrane Tobacco Addiction Group. Participants using cytisine were significantly more likely to quit tobacco than participants who received placebo/no intervention/usual care (risk ratio [RR] = 2.65, 95% confidence interval [CI] = 1.50-4.67, 6 trials, 5194 participants) or nicotine replacement therapy (RR = 1.36, 95% CI = 1.06-1.73, p = 0.0152, 2 trials, 1511 participants). The difference in cessation rates among participants receiving cytisine versus varenicline was not statistically significant (RR = 0.96, 95% CI 0.63-1.45, P = 0.8464, 3 trials, 2508 participants). Two trials examined longer versus shorter treatment duration, finding higher abstinence rates with longer treatment (RR = 1.29, 95% CI = 1.02-1.63, 2 trials, 1009 participants). The differences in the number of adverse events reported by participants who received cytisine versus placebo (RR = 1.19, 95% CI = 0.99-1.41, P = 0.0624; 6 trials; 4578 participants) or cytisine versus varenicline (RR = 1.37, 95% CI = 0.57-3.33, P = 0.4835; 2 trials; 1345 participants) were not statistically significant. Most adverse events were mild (e.g. abnormal dreams, nausea, headaches). Cytisine is an effective aid for tobacco cessation and appears to be more effective for tobacco cessation than placebo, no intervention, usual care and nicotine replacement therapy.

Synthesis and evaluation of (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate analogs as competitive partial agonists of butyrophilin 3A1

Phosphoantigens (pAgs) induce conformational changes after binding to the intracellular region of BTN3A1 which result in its clustering with BTN2A1, forming an activating ligand for the Vγ9Vδ2 T cell receptor. Here, we designed a small panel of bulky analogs of the prototypical pAg (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) that contain an aromatic ring attached to the C-3 position in place of methyl group. These compounds bind with high affinity to BTN3A1 but fail to fully support its interaction with BTN2A1 and only partially trigger T cell activation relative to HMBPP. Furthermore, they can compete with HMBPP for cellular binding to BTN3A1 and reduce the cellular response to HMBPP, a classic partial agonist phenotype. Trifluoromethyl analog 6e was the weakest agonist but the strongest inhibitor of HMBPP ELISA response. Our study provides a rationale for the mode of action of pAg-induced γδ T cell activation and provides insights into other naturally occurring BTN proteins and their respective ligands.

The Agonistic Activity of the Human Epidermal Growth Factor is Reduced by the D46G Substitution.

Resistance to anti-tumor agents targeting the epidermal growth factor receptor (EGFR) reduces treatment response and requires the development of novel EGFR antagonists. Mutant epidermal growth factor (EGF) forms with reduced agonistic activity could be promising agents in cancer treatment. EGF D46G affinity to EGFR domain III was assessed with affinity chromatography. EGF D46G acute toxicity in Af albino mice at 320 and 3200 μg/kg subcutaneous doses was evaluated. EGF D46G activity in human epidermoid carcinoma cells at 10 ng/mL concentration in serum-free medium and in subcutaneous Ehrlich ascites carcinoma mice model at 320 μg/kg dose was studied. The D46G substitution decreases the thermal stability of EGF complexes with EGFR domain III by decreasing the ability of the C-terminus to be released from the intermolecular β- sheet. However, with remaining binding sites for EGFR domain I, EGF D46G effectively competes with other EGF-like growth factors for binding to EGFR and does not demonstrate toxic effects in mice. EGF D46G inhibits the proliferation of human epidermoid carcinoma cells compared to native EGF. A single subcutaneous administration of EGF D46G along with Ehrlich carcinoma cells injection inhibits the proliferation of these cells and delays tumor formation for up to seven days. EGF D46G can be defined as a partial EGFR agonist as this mutant form demonstrates reduced agonistic activity compared to native EGF. The study emphasizes the role of the EGF C-terminus in establishing interactions with EGFR domain III, which are necessary for EGFR activation and subsequent proliferation of cells.

The versatile binding landscape of the TAAR1 pocket for LSD and other antipsychotic drug molecules

Increasing global concerns about psychoactive substance addiction and psychotic disorders highlight the need for comprehensive research into the structure-function relationship governing ligand recognition between these substances and their receptors in the brain. Recent studies indicate the significant involvement of trace amine-associated receptor 1 (TAAR1) in the signaling regulation of the hallucinogen lysergic acid diethylamide (LSD) and other antipsychotic drugs. This study presents structures of the TAAR1-Gs protein complex recognizing LSD, which exhibits a polypharmacological profile, and the partial agonist RO5263397, which is a drug candidate for schizophrenia and addiction. Moreover, we elucidate the cross-species recognition and partial activation mechanism for TAAR1, which holds promising implications from a drug discovery perspective. Through mutagenesis, functional studies, and molecular dynamics (MD) simulations, we provide a comprehensive understanding of a versatile TAAR1 pocket in recognizing various ligands as well as in the ligand-free state, underpinning the structural basis of its high adaptability. These findings offer valuable insights for the design of antipsychotic drugs.

Therapeutic targeting of immunometabolism reveals a critical reliance on hexokinase 2 dosage for microglial activation and Alzheimer’s progression

Neuroinflammation is a prominent feature of Alzheimer's disease (AD). Activated microglia undergo a reprogramming of cellular metabolism necessary to power their cellular activities during disease. Thus, selective targeting of microglial immunometabolism might be of therapeutic benefit for treating AD. In the AD brain, the levels of microglial hexokinase 2 (HK2), an enzyme that supports inflammatory responses by promoting glycolysis, are significantly increased. In addition, HK2 displays non-metabolic activities that extend its inflammatory role beyond glycolysis. The antagonism of HK2 affects microglial phenotypes and disease progression in a gene-dose-dependent manner. HK2 complete loss fails to improve pathology by exacerbating inflammation, while its haploinsufficiency reduces pathology in 5xFAD mice. We propose that the partial antagonism of HK2 is effective in slowing disease progression by modulating NF-κB signaling through its cytosolic target, IKBα. The complete loss of HK2 affects additional inflammatory mechanisms related to mitochondrial dysfunction.

Co-stimulation of muscarinic M1 and M4 acetylcholine receptors prevents later cocaine reinforcement in male and female mice, but not place-conditioning

Acute stimulation of M1 or M4 muscarinic cholinergic receptors reduces cocaine abuse-related effects in mice and rats. The combined activation of these receptor subtypes produces synergistic effects on some behavioural endpoints in mice. M1 and M1 + M4 receptor stimulation in a cocaine vs. food choice assay in rats and microdialysis in rats showed delayed and lasting “anticocaine effects”. Here, we tested whether these putative lasting neuroplastic changes are sufficient to occlude the reinforcing effects of cocaine at the behavioural level in mice. Mice were pre-treated with the M1 receptor partial agonist VU0364572, M4 receptor positive allosteric modulator VU0152100, or VU0364572 + VU0152100 two weeks prior to acquisition of cocaine intravenous self-administration (IVSA). Male C57BL/6JRj mice received vehicle, VU0364572, VU0152100, or VU0364572 + VU0152100. Female mice were tested with two VU0364572 + VU0152100 dose combinations or vehicle. To attribute potential effects to either reduced rewarding effects or increased aversion to cocaine, we tested VU0364572 alone and VU0364572 + VU0152100 in acquisition of cocaine-conditioned place preference (CPP) in male mice using an unbiased design. The acquisition of cocaine IVSA was drastically reduced and/or slowed in male and female mice receiving VU0364572 + VU0152100, but not either drug alone. Food-maintained operant behaviour was unaffected, indicating that the treatment effects were cocaine-specific. No treatment altered the acquisition of cocaine-CPP, neither in the post-test, nor in a challenge 14 days later. The cocaine IVSA findings confirm unusual long-lasting “anticocaine” effects of muscarinic M1 + M4 receptor stimulation. Thus, in mice, simultaneous stimulation of both receptor subtypes seems to produce potential neuroplastic changes that yield lasting effects.

NMDA and GABA Receptor-Mediated Plasticity Induced by 10-Hz Repetitive Transcranial Magnetic Stimulation.

Although 10-Hz repetitive transcranial magnetic stimulation (rTMS) is an FDA-approved treatment for depression, we have yet to fully understand the mechanism through which rTMS induces therapeutic and durable changes in the brain. Two competing theories have emerged suggesting that 10-Hz rTMS induces N-methyl-D-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP), or alternatively, removal of inhibitory gamma-aminobutyric acid receptors (GABARs). We examined these two proposed mechanisms of action in the human motor cortex in a double-blind, randomized, four-arm crossover study in healthy subjects. We tested motor-evoked potentials (MEPs) before and after 10-Hz rTMS in the presence of four drugs separated by 1-week each: placebo, NMDAR partial agonist d-cycloserine (DCS 100mg), DCS 100mg + NMDAR partial antagonist dextromethorphan (DMO 150mg; designed to "knock down" DCS-mediated facilitation), and GABAR agonist lorazepam (LZP 2.5mg). NMDAR agonism by DCS enhanced rTMS-induced cortical excitability more than placebo. This enhancement was blocked by combining DCS with NMDAR antagonist, DMO. If GABARs are removed by rTMS, GABAR agonism via LZP should lack its inhibitory effect yielding higher post/pre MEPs. However, MEPs were reduced after rTMS indicating stability of GABAR numbers. These data suggest that 10-Hz rTMS facilitation in the healthy motor cortex may enact change in the brain through NMDAR-mediated LTP-like mechanisms rather than through GABAergic reduction.

Methods of correction of hyperprolactinemia induced by antipsychotics: current state of the problem and development prospects

Hyperprolactinemia is one of the common undesirable phenomena of antipsychotic therapy, as it is associated with a number of mental and somatic complications. To date, there are several strategies for the correction of antipsychotics induced hyperprolactinemia, the most evidential basis of which has an addition to the current treatment of partial dopamine agonist — aripiprazole.Other drugs in this group, cariprazine and brexpiprazole, due to a similar mechanism of action with aripiprazole, belong to prolactin-saving drugs. However, their differences in pharmacodynamics may determine features in prolactin effects and attract attention for further study of their prolactin-saving activity.

G protein-coupled receptor endocytosis generates spatiotemporal bias in β-arrestin signaling.

The stabilization of different active conformations of G protein-coupled receptors is thought to underlie the varying efficacies of biased and balanced agonists. Here, profiling the activation of signal transducers by angiotensin II type 1 receptor (AT1R) agonists revealed that the extent and kinetics of β-arrestin binding exhibited substantial ligand-dependent differences, which were lost when receptor internalization was inhibited. When AT1R endocytosis was prevented, even weak partial agonists of the β-arrestin pathway acted as full or near-full agonists, suggesting that receptor conformation did not exclusively determine β-arrestin recruitment. The ligand-dependent variance in β-arrestin translocation was much larger at endosomes than at the plasma membrane, showing that ligand efficacy in the β-arrestin pathway was spatiotemporally determined. Experimental investigations and mathematical modeling demonstrated how multiple factors concurrently shaped the effects of agonists on endosomal receptor-β-arrestin binding and thus determined the extent of functional selectivity. Ligand dissociation rate and G protein activity had particularly strong, internalization-dependent effects on the receptor-β-arrestin interaction. We also showed that endocytosis regulated the agonist efficacies of two other receptors with sustained β-arrestin binding: the V2 vasopressin receptor and a mutant β2-adrenergic receptor. In the absence of endocytosis, the agonist-dependent variance in β-arrestin2 binding was markedly diminished. Our results suggest that endocytosis determines the spatiotemporal bias in GPCR signaling and can aid in the development of more efficacious, functionally selective compounds.

Mapping the molecular motions of 5-HT3 serotonin-gated channel by voltage-clamp fluorometry.

The serotonin-gated ion channel (5-HT3R) mediates excitatory neuronal communication in the gut and the brain. It is the target for setrons, a class of competitive antagonists widely used as antiemetics, and is involved in several neurological diseases. Cryo-electron microscopy (cryo-EM) of the 5-HT3R in complex with serotonin or setrons revealed that the protein has access to a wide conformational landscape. However, assigning known high-resolution structures to actual states contributing to the physiological response remains a challenge. In the present study, we used voltage-clamp fluorometry (VCF) to measure simultaneously, for 5-HT3R expressed at a cell membrane, conformational changes by fluorescence and channel opening by electrophysiology. Four positions identified by mutational screening report motions around and outside the serotonin-binding site through incorporation of cysteine-tethered rhodamine dyes with or without a nearby quenching tryptophan. VCF recordings show that the 5-HT3R has access to four families of conformations endowed with distinct fluorescence signatures: 'resting-like' without ligand, 'inhibited-like' with setrons, 'pre-active-like' with partial agonists, and 'active-like' (open channel) with partial and strong agonists. Data are remarkably consistent with cryo-EM structures, the fluorescence partners matching respectively apo, setron-bound, 5-HT bound-closed, and 5-HT-bound-open conformations. Data show that strong agonists promote a concerted motion of all fluorescently labeled sensors during activation, while partial agonists, especially when loss-of-function mutations are engineered, stabilize both active and pre-active conformations. In conclusion, VCF, though the monitoring of electrophysiologically silent conformational changes, illuminates allosteric mechanisms contributing to signal transduction and their differential regulation by important classes of physiological and clinical effectors.