GM-1020: a novel, orally bioavailable NMDA receptor antagonist with rapid and robust antidepressant-like effects at well-tolerated doses in rodents.

The NMDA receptor (NMDAR) antagonist ketamine has shown great potential as a rapid-acting antidepressant; however, its use is limited by poor oral bioavailability and a side effect profile that necessitates in-clinic dosing. GM-1020 is a novel NMDAR antagonist that was developed to address these limitations of ketamine as a treatment for depression. Here, we present the preclinical characterization of GM-1020 alongside ketamine, for comparison. In vitro, we profiled GM-1020 for binding to NMDAR and functional inhibition using patch-clamp electrophysiology. In vivo, GM-1020 was assessed for antidepressant-like efficacy using the Forced Swim Test (FST) and Chronic Mild Stress (CMS), while motor side effects were assessed in spontaneous locomotor activity and on the rotarod. The pharmacokinetic properties of GM-1020 were profiled across multiple preclinical species. Electroencephalography (EEG) was performed to determine indirect target engagement and provide a potentially translational biomarker. These results demonstrate that GM-1020 is an orally bioavailable NMDAR antagonist with antidepressant-like efficacy at exposures that do not produce unwanted motor effects.

Sustained antidepressant effect of ketamine through NMDAR trapping in the LHb.

Ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist1, has revolutionized the treatment of depression because of its potent, rapid and sustained antidepressant effects2-4. Although the elimination half-life of ketamine is only 13 min in mice5, its antidepressant activities can last for at least 24 h6-9. This large discrepancy poses an interesting basic biological question and has strong clinical implications. Here we demonstrate that after a single systemic injection, ketamine continues to suppress burst firing and block NMDARs in the lateral habenula (LHb) for up to 24 h. This long inhibition of NMDARs is not due to endocytosis but depends on the use-dependent trapping of ketamine in NMDARs. The rate of untrapping is regulated by neural activity. Harnessing the dynamic equilibrium of ketamine-NMDAR interactions by activating the LHb and opening local NMDARs at different plasma ketamine concentrations, we were able to either shorten or prolong the antidepressant effects of ketamine in vivo. These results provide new insights into the causal mechanisms of the sustained antidepressant effects of ketamine. The ability to modulate the duration of ketamine action based on the biophysical properties of ketamine-NMDAR interactions opens up new opportunities for the therapeutic use of ketamine.

Indazole as a Phenol Bioisostere: Structure-Affinity Relationships of GluN2B-Selective NMDA Receptor Antagonists.

Negative allosteric modulation of GluN2B subunit-containing NMDA receptors prevents overstimulation, resulting in neuroprotective effects. Since the phenol of prominent negative allosteric modulators is prone to rapid glucuronidation, its bioisosteric replacement by an indazole was envisaged. The key step in the synthesis was a Sonogashira reaction of non-protected iodoindazoles with propargylpiperidine derivatives. Modification of the alkynyl moiety allowed the introduction of several functional groups. The synthesized indazoles showed very high GluN2B affinity but limited selectivity over σ receptors. Molecular dynamics simulations revealed the same molecular interactions with the ifenprodil binding site as the analogous phenols. In two-electrode voltage-clamp experiments, enantiomeric 3-(4-benzylpiperidin-1-yl)-1-(1H-indazol-5-yl)propan-1-ols (S)-10a and (R)-10a displayed higher inhibitory activity than ifenprodil. In contrast to phenolic GluN2B antagonists, the indazoles were not conjugated with glucuronic acid. It can be concluded that the phenol of potent GluN2B antagonists can be replaced bioisosterically by an indazole, retaining the high GluN2B affinity and activity but inhibiting glucuronidation.

Binding Affinity and Mechanisms of Potential Antidepressants Targeting Human NMDA Receptors.

Depression, a mental disorder that plagues the world, is a burden on many families. There is a great need for new, fast-acting antidepressants to be developed. N-methyl-D-aspartic acid (NMDA) is an ionotropic glutamate receptor that plays an important role in learning and memory processes and its TMD region is considered as a potential target to treat depression. However, due to the unclear binding sites and pathways, the mechanism of drug binding lacks basic explanation, which brings great complexity to the development of new drugs. In this study, we investigated the binding affinity and mechanisms of an FDA-approved antidepressant (S-ketamine) and seven potential antidepressants (R-ketamine, memantine, lanicemine, dextromethorphan, Ro 25-6981, ifenprodil, and traxoprodil) targeting the NMDA receptor by ligand-protein docking and molecular dynamics simulations. The results indicated that Ro 25-6981 has the strongest binding affinity to the TMD region of the NMDA receptor among the eight selected drugs, suggesting its potential effective inhibitory effect. We also calculated the critical binding-site residues at the active site and found that residues Leu124 and Met63 contributed the most to the binding energy by decomposing the free energy contributions on a per-residue basis. We further compared S-ketamine and its chiral molecule, R-ketamine, and found that R-ketamine had a stronger binding capacity to the NMDA receptor. This study provides a computational reference for the treatment of depression targeting NMDA receptors, and the proposed results will provide potential strategies for further antidepressant development and is a useful resource for the future discovery of fast-acting antidepressant candidates.

Ethanol Metabolite, Acetate, Increases Excitability of the Central Nucleus of Amygdala Neurons through Activation of NMDA Receptors.

The central nucleus of the amygdala (CeA) is a key brain region involved in emotional and stressor responses due to its many projections to autonomic regulatory centers. It is also a primary site of action from ethanol consumption. However, the influence of active metabolites of ethanol such as acetate on the CeA neural circuitry has yet to be elucidated. Here, we investigated the effect of acetate on CeA neurons with the axon projecting to the rostral ventrolateral medulla (CeA-RVLM), as well as quantified cytosolic calcium responses in primary neuronal cultures. Whole-cell patch-clamp recordings in brain slices containing autonomic CeA-RVLM neurons revealed a dose-dependent increase in neuronal excitability in response to acetate. N-Methyl-d-aspartate receptor (NMDAR) antagonists suppressed the acetate-induced increase in CeA-RVLM neuronal excitability and memantine suppressed the direct activation of NMDAR-dependent inward currents by acetate in brain slices. We observed that acetate increased cytosolic Ca2+ in a time-dependent manner in primary neuronal cell cultures. The acetate enhancement of calcium signaling was abolished by memantine. Computational modeling of acetic acid at NMDAR/NR1 glutamatergic and glycinergic sites suggests potential active site interactions. These findings suggest that within the CeA, acetate is excitatory at least partially through activation of NMDAR, which may underlie the impact of ethanol consumption on autonomic circuitry.

ß2-microglobulin functions as an endogenous NMDAR antagonist to impair synaptic function.

Down syndrome (DS) is a neurological disorder with multiple immune-related symptoms; however, crosstalk between the CNS and peripheral immune system remains unexplored. Using parabiosis and plasma infusion, we found that blood-borne factors drive synaptic deficits in DS. Proteomic analysis revealed elevation of ß2-microglobulin (B2M), a major histocompatibility complex class I (MHC-I) component, in human DS plasma. Systemic administration of B2M in wild-type mice led to synaptic and memory defects similar to those observed in DS mice. Moreover, genetic ablation of B2m or systemic administration of an anti-B2M antibody counteracts synaptic impairments in DS mice. Mechanistically, we demonstrate that B2M antagonizes NMDA receptor (NMDAR) function through interactions with the GluN1-S2 loop; blocking B2M-NMDAR interactions using competitive peptides restores NMDAR-dependent synaptic function. Our findings identify B2M as an endogenous NMDAR antagonist and reveal a pathophysiological role for circulating B2M in NMDAR dysfunction in DS and related cognitive disorders.

Development of a quaternary ammonium photoswitchable antagonist of NMDA receptors.

NMDA receptors play critical roles in numerous physiological and pathological processes in CNS that requires development of modulating ligands. In particular, photoswitchable compounds that selectively target NMDA receptors would be particularly useful for analysis of receptor contributions to various processes. Recently, we identified a light-dependent anti-NMDA activity of the azobenzene-containing quaternary ammonium compounds DENAQ (diethylamine-azobenzene-quaternary ammonium) and DMNAQ (dimethylamine-azobenzene-quaternary ammonium). Here, we developed a series of light-sensitive compounds based on the DENAQ structure, and studied their action on glutamate receptors in rat brain neurons using patch-clamp method. We found that the activities of the compounds and the influence of illumination strongly depended on the structural details, as even minor structural modifications greatly altered the activity and sensitivity to illumination. The compound PyrAQ (pyrrolidine-azobenzene-quaternary ammonium) was the most active and produced fast and fully reversible inhibition of NMDA receptors. The IC50 values under ambient and monochromic light conditions were 2 and 14 µM, respectively. The anti-AMPA activity was much weaker. The action of PyrAQ did not depend on NMDA receptor activity, agonist concentration, or membrane voltage, making it a useful tool for photopharmacological studies.

Dual action of ketamine confines addiction liability.

Ketamine is used clinically as an anaesthetic and a fast-acting antidepressant, and recreationally for its dissociative properties, raising concerns of addiction as a possible side effect. Addictive drugs such as cocaine increase the levels of dopamine in the nucleus accumbens. This facilitates synaptic plasticity in the mesolimbic system, which causes behavioural adaptations and eventually drives the transition to compulsion1-4. The addiction liability of ketamine is a matter of much debate, in part because of its complex pharmacology that among several targets includes N-methyl-D-aspartic acid (NMDA) receptor (NMDAR) antagonism5,6. Here we show that ketamine does not induce the synaptic plasticity that is typically observed with addictive drugs in mice, despite eliciting robust dopamine transients in the nucleus accumbens. Ketamine nevertheless supported reinforcement through the disinhibition of dopamine neurons in the ventral tegmental area (VTA). This effect was mediated by NMDAR antagonism in GABA (γ-aminobutyric acid) neurons of the VTA, but was quickly terminated by type-2 dopamine receptors on dopamine neurons. The rapid off-kinetics of the dopamine transients along with the NMDAR antagonism precluded the induction of synaptic plasticity in the VTA and the nucleus accumbens, and did not elicit locomotor sensitization or uncontrolled self-administration. In summary, the dual action of ketamine leads to a unique constellation of dopamine-driven positive reinforcement, but low addiction liability.

Molecular mechanisms underlying the N-methyl-d-aspartate receptor antagonists: Highlighting their potential for transdiagnostic therapeutics.

The so-called "psychedelic renaissance" has stimulated expanded interest in several classes of drugs that appear to possess transdiagnostic effects in the treatment of mental health disorders, specifically. N-methyl-d-aspartate receptor (NMDAR) antagonists are one such class with diverse therapeutic potential. NMDARs mediate excitatory postsynaptic signalling in the central nervous system (CNS) and are integral to normal neurobiological processes including neuronal development, synaptic transmission, and plasticity, and thus involved in learning and memory. However, NMDAR hyper-function is also implicated in acute CNS trauma, neuropsychiatric and neurodegenerative disorders, as well as chronic pain. The complex structure of NMDARs permits several locations for therapeutic inhibition, making these receptors a potential target for multiple drugs which modulate them in different ways. NMDAR antagonists, which may be competitive, non-competitive, or uncompetitive, either block glutamate from binding the receptor or modulate the response to glutamate binding. Despite longstanding concerns about side effects of NMDAR antagonists, recent research suggests that, when appropriately used, these agents have favourable safety profiles. Furthermore, their fast-acting mechanism of action, resulting in rapid effects compared to other therapeutic agents, makes them a promising class of drugs that may yield effective therapeutics for multiple CNS disorders.

Inhibition of NMDA receptors through a membrane-to-channel path.

N-methyl-D-aspartate receptors (NMDARs) are transmembrane proteins that are activated by the neurotransmitter glutamate and are found at most excitatory vertebrate synapses. NMDAR channel blockers, an antagonist class of broad pharmacological and clinical significance, inhibit by occluding the NMDAR ion channel. A vast literature demonstrates that NMDAR channel blockers, including MK-801, phencyclidine, ketamine, and the Alzheimer's disease drug memantine, can bind and unbind only when the NMDAR channel is open. Here we use electrophysiological recordings from transfected tsA201 cells and cultured neurons, NMDAR structural modeling, and custom-synthesized compounds to show that NMDAR channel blockers can enter the channel through two routes: the well-known hydrophilic path from extracellular solution to channel through the open channel gate, and also a hydrophobic path from plasma membrane to channel through a gated fenestration ("membrane-to-channel inhibition" (MCI)). Our demonstration that ligand-gated channels are subject to MCI, as are voltage-gated channels, highlights the broad expression of this inhibitory mechanism.

Safety and effectiveness of NMDA receptor antagonists for depression: A multidisciplinary review.

Ketamine, an anesthetic available since 1970, and esketamine, its newer S-enantiomer, provide a novel approach for the treatment of depression and other psychiatric disorders. At subanesthetic doses, the two drugs, along with their older congener, phencyclidine (PCP), induce a transient, altered mental state by blocking the N-methyl-D-aspartate (NMDA) receptor for glutamate, the primary excitatory neurotransmitter in the mammalian central nervous system. This multidisciplinary review examines the pharmacology/direct effects on consciousness, effectiveness in depression and acute suicidality, and safety of these fast-acting NMDA antagonists. To capture the essence of 60 years of peer-reviewed literature, we used a semi-structured approach to the subtopics, each of which required a different search strategy. We review the evidence for the three primary reported benefits of the two clinical drugs when used for depression: success in difficult-to-treat patients, rapid onset of action within a day, and immediate effects on suicidality. Key safety issues include the evidence-and lack thereof-for the effects of repeatedly inducing this altered mental state, and whether an adequate safety margin exists to rule out the neurotoxic effects seen in animal studies. This review includes evidence from multiple sources that raise substantial questions about both safety and effectiveness of ketamine and esketamine for psychiatric disorders.

NMDA receptor antagonists engender neuroprotection against gp120-induced cognitive dysfunction in rats through modulation of PKR activation, oxidative stress, ER stress and IRE1α signal pathway.

It is widely accepted that the surface glycoprotein (gp120) of human immunodeficiency virus-1 (HIV-1) plays an important role in HIV-1-induced nerve damage and pathogenesis of HIV-associated neurocognitive disorders (HAND). Our previous work has demonstrated that gp120 enhanced excitatory postsynaptic currents (EPSCs) mediated by N-methyl-d-aspartate receptors (NMDARs) and caused neural injury. However, the relationship between gp120, NMDARs and HAND is still unclear. Several lines of evidence indicate that double-stranded RNA-activated protein kinase (PKR) is involved in NMDA-induced cerebral ischaemia and retinal damage, but because its role in neuropathology is still debated, we examined whether PKR links oxidative stress and endoplasmic reticulum (ER) stress to exert a deleterious role in the rat model with gp120-induced dementia. In this study, we found that NMDAR antagonist memantine or PKR inhibitor C16 improved gp120-induced learning and memory impairment and inhibited gp120-induced PKR activity. Furthermore, memantine or C16 was found to attenuate gp120-induced neuroinflammation, oxidative stress, ER stress and its downstream IRE1α/JNK pathway. Additionally, memantine or C16 evidently inhibited apoptotic pathways by reducing the Bax and caspase-3, -8, -9 expressions and increasing Bcl-2 expression. So the NMDA receptor antagonists could alleviate HIV/gp120-induced dementia in the rat model by altering PKR level. In conclusion, this study demonstrates that NMDARs play a key role in HIV/gp120-induced hippocampal damage and cognitive dysfunction through PKR-mediated oxidative stress, ER stress, and IRE1α/JNK signalling pathway in rats, and implicating PKR inhibitors could provide a novel neuroprotective strategy for HAND via inhibiting ER stress and its downstream IRE1α signalling pathway.

The Role of the Microbiota-Gut-Brain Axis in the Development of Alzheimer's Disease.

Along with the increase in life expectancy in the populations of developed and developing countries resulting from better access and improved health care, the number of patients with dementia, including Alzheimer's disease (AD), is growing. The disease was first diagnosed and described at the beginning of the 20th century. However, to this day, there is no effective causal therapy, and symptomatic treatment often improves patients' quality of life only for a short time. The current pharmacological therapies are based mainly on the oldest hypotheses of the disease-cholinergic (drugs affecting the cholinergic system are available), the hypothesis of amyloid-ß aggregation (an anti-amyloid drug was conditionally approved by the FDA in 2020), and one drug is an N-methyl-D-aspartate receptor (NMDAR) antagonist (memantine). Hypotheses about AD pathogenesis focus on the nervous system and the brain. As research progresses, it has become known that AD can be caused by diseases that have been experienced over the course of a lifetime, which could also affect other organs. In this review, we focus on the potential association of AD with the digestive system, primarily the gut microbiota. The role of diet quality in preventing and alleviating Alzheimer's disease is also discussed. The problem of neuroinflammation, which may be the result of microbiota disorders, is also described. An important aspect of the work is the chapter on the treatment strategies for changing the microbiota, potentially protecting against the disease and alleviating its course in the initial stages.

Pharmacological Approaches to the Treatment of Dementia in Down Syndrome: A Systematic Review of Randomized Clinical Studies.

Down Syndrome (DS) is considered the most frequent form of Intellectual Disability, with important expressions of cognitive decline and early dementia. Studies on potential treatments for dementia in this population are still scarce. Thus, the current review aims to synthesize the different pharmacological approaches that already exist in the literature, which focus on improving the set of symptoms related to dementia in people with DS. A total of six studies were included, evaluating the application of supplemental antioxidant therapies, such as alpha-tocopherol; the use of acetylcholinesterase inhibitor drugs, such as donepezil; N-methyl-d-aspartate (NMDA) receptor antagonists, such as memantine; and the use of vitamin E and a fast-acting intranasal insulin. Two studies observed important positive changes related to some general functions in people with DS (referring to donepezil). In the majority of studies, the use of pharmacological therapies did not lead to improvement in the set of symptoms related to dementia, such as memory and general functionality, in the population with DS.

Monitoramento do horizonte tecnológico: Medicamentos para o tratamento do transtorno depressivo maior / Monitoring the technological horizon: Drugs for the treatment of major depressive disorder

A DOENÇA: O transtorno depressivo maior (TDM) é considerado um grave problema de saúde pública que afeta mais de 264 milhões de pessoas em todo o mundo (1). No Brasil, a prevalência nacional da depressão estimada pelo Global Burden of Disease 2017 foi de 3,3% e esta condição está entre as quatro principais causas de invalidez, afetando a produtividade e qualidade de vida dos pacientes. Nas populações vulneráveis como os idosos, esse número é significativamente maior, uma revisão sistemática publicada em 2019 estimou uma prevalência de 21,9% em idosos brasileiros residentes na comunidade. Segundo projeções da Organização Mundial da Saúde (OMS) para 2030, a depressão ocuparia o primeiro lugar entre as principais doenças incapacitantes. TRATAMENTO RECOMENDADO: Atualmente não existem Protocolos Clínicos e Diretrizes Terapêuticas (PCDT) do Ministério da Saúde, bem como avaliações da Conitec sobre esse tema. O tratamento da TDM depende da gravidade da doença, nos indivíduos com depressão grave, em que há risco de suicídio, o encaminhamento para o especialista deve ser imediato e a hospitalização pode ser um recurso necessário. Nos casos moderados, em geral, se sugere a combinação de psicoterapia e medicamentos antidepressivos, sendo que diversas classes são consideradas opções terapêuticas, como Inibidores seletivos da recaptação da serotonina; Inibidores seletivos da recaptação da noradrenalina; Antidepressivos atípicos; Moduladores da serotonina; Antidepressivos tricíclicos; Inibidores da monoaminoxidase. ESTRATÉGIA DE BUSCA: Uma busca no repositório de protocolos de estudos clínicos ClinicalTrials.gov foi realizada com o objetivo de localizar os medicamentos em fase de pesquisa clínica e/ou recentemente aprovados para TDM. Foram excluídos medicamentos com registro na Anvisa superior a dois anos para a indicação de depressão maior, assim como procedimentos, produtos da medicina tradicional chinesa, vitaminas e testes diagnósticos. MEDICAMENTOS APROVADOS RECENTEMENTE: ESCETAMINA SPRAY NASAL: A escetamina, o enantiômero "S" da cetamina racêmica, é um antagonista não seletivo, não competitivo do receptor N-metil-D-aspartato (NMDA), que atua como um modulador do receptor de glutamato, o que parece aumentar a sinalização entre as células, restaurando a função normal nas regiões cerebrais. Embora a ligação da escetamina ao receptor NMDA aumente o glutamato do sistema nervoso central (SNC), o mecanismo de ação exato como antidepressivo permanece incerto. Esse medicamento possui registro nas agências norte-americana e europeia (FDA e EMA) e, em dezembro de 2020, foi aprovado pela Anvisa para tratamento do TDM em pacientes com ideação suicida e de depressão resistente ao tratamento. Depressão resistente ao tratamento: MEDICAMENTOS EM FASE DE PESQUISA CLÍNICA: RAPASTINEL: O rapastinel (GLYX-13) é um anticorpo monoclonal com apresentação para administração endovenosa, que atua como agonista parcial funcional do receptor de N-metil-D-aspartato (NMDA) com ação no sistema glutamatérgico. INFORMAÇÕES ADICIONAIS: Atualmente existem diferentes tecnologias sendo estudadas para o tratamento de TDM, sendo que neste informe, foram descritas as tecnologias que estão em um horizonte mais próximo para aprovação por agências regulatórias ou foram aprovadas pela Anvisa recentemente. A escetamina spray nasal e brexpiprazol foram aprovados pela Anvisa em 2020, com o objetivo de avaliar a incorporação dessas tecnologias no mundo, uma busca foi realizada em novembro de 2021 nos websites das agências de ATS do Reino Unido, Canadá e Austrália. CONSIDERAÇÕES FINAIS O TDM: é um grave problema de saúde pública por afetar milhões de pessoas em todo o mundo. Apesar de haver muitos estudos em andamento para o tratamento dessa condição clínica, em geral os resultados dos estudos demonstraram que não há diferença significativa na eficácia dos medicamentos quando comparados ao placebo. O rapastinel, que recebeu designação Breakthough Therapy pela FDA em 2016, caracterizando-o como medicamento inovador para uma necessidade médica não atendida e que teria prioridade para avaliação na FDA, apresentou resultados promissores para estudo de fase 2, entretanto eles não foram confirmados nos ECR fase 3, duplo-cego, controlados por placebo, tanto em monoterapia como tratamento adjuvante para TDM. O medicamento REL-1017 (ou d-metadona), também é um inibidor do receptor NMDA e recebeu designação FastTrack pela FDA em 2017 para o tratamento adjuvante de TDM. Apesar dos dados do estudo de fase 2 mostrarem resultados promissores, o estudo de fase 3 ainda está em andamento. Também, esperam-se os dados das diversas pesquisas fase 3, realizadas em diferentes cenários (adjuvante ou monoterapia, por exemplo), e que avaliaram o medicamento SAGE-217, um modulador do receptor GABA que mostrou resultados positivos no estudo fase 2. O brexpiprazol foi aprovado pela Anvisa em 2020, indicado para o tratamento de depressão maior em adultos em associação a um antidepressivo, em caso de inefetividade da monoterapia com antidepressivo anterior. Os ensaios clínicos randomizados fase 3 avaliaram que o uso do medicamento reduziu o escore basal de MADRS na semana 6. O brexipiprazol para tratamento de depressão não foi avaliado por nenhuma agência de ATS até o momento. A escetamina spray nasal teve registro sanitário aprovado pela Anvisa em novembro de 2020 para pacientes com ideação suicida e de depressão resistente ao tratamento - a partir da avaliação da redução do escore basal de MADRS em 24h e após 28 dias. Mas esse medicamento não foi recomendado para incorporação pelas agências de ATS do Reino Unido e Canadá. Os medicamentos em desenvolvimento para depressão incluem populações específicas e frequentemente são usados em associação a outros antidepressivos. O tratamento da depressão grave e não responsiva a tratamentos prévios ainda é uma necessidade médica não atendida, assim como tratamentos específicos para populações vulneráveis como idosos. Também é importante destacar que todos os resultados descritos neste documento são dados precoces e devem ser avaliados com cautela. Dessa maneira, considerando os estudos de fase 3 citados neste documento, conclui-se que ainda são poucas as opções promissoras em estudo para um horizonte de curto a médio prazo.

The down-regulation of tyrosine phosphatase SHP2 activity is involved in the removal of surface AMPA receptors in long term depression.

Hebbian-type synaptic plasticity which includes long term potentiation (LTP) and long term depression (LTD), is the main cellular mechanism underlying learning and memory. Effective activity and synaptic content of tyrosine phosphatase SHP2 are required for AMPA receptor trafficking during LTP. However, the role of SHP2 in LTD has not been fully elucidated. This study shows that the phosphorylation level of SHP2 at Y542 decreased after LTD induction either in hippocampal cultures or acute CA1 mini slices. This change occurred at least 10 min after LTD induction and was alleviated by administration of NMDA receptor antagonist, APV. Furthermore, the SHP2 mutant (D61G), found in Noonan syndrome patients, prevented the removal of surface AMPA receptors during chemical-induced LTD on cultured hippocampal neurons. The results revealed a molecular basis of regulatory role of SHP2 in long term depression, thus expands our understanding of the SHP2 function in learning and memory.

Mechanisms of NMDA receptor inhibition by nafamostat, gabexate and furamidine.

N-methyl-D-aspartate (NMDA) receptors are affected by many pharmaceuticals. In this work, we studied the action of the serine protease inhibitors nafamostat, gabexate and camostat, and an antiprotozoal compound, furamidine, on native NMDA receptors in rat hippocampal pyramidal neurons. Nafamostat, furamidine and gabexate inhibited these receptors with IC50 values of 0.20 ± 0.04, 0.64 ± 0.13 and 16 ± 3 µM, respectively, whereas camostat was ineffective. Nafamostat and furamidine showed voltage-dependent inhibition, while gabexate showed practically voltage-independent inhibition. Nafamostat and furamidine demonstrated tail currents, implying a 'foot-in-the-door' mechanism of action; gabexate did not demonstrate any signs of 'foot-in-the-door' or trapping channel block. Gabexate action was also not competitive, suggesting allosteric inhibition of NMDA receptors. Furamidine and nafamostat are structurally similar to the previously studied diminazene and all three demonstrated a 'foot-in-the-door' mechanism. They have a rather rigid, elongated structures and cannot fold into more compact forms. By contrast, the gabexate molecule can fold, but its folded structure differs drastically from that of typical NMDA receptor blockers, in agreement with its voltage-independent inhibition. These findings provide a better understanding of the structural determinants of NMDA receptor antagonism, while also supporting the potential clinical repurposing of these drugs as neuroprotectors for glaucoma and other neurodegenerative diseases.

Development and characterization of functional antibodies targeting NMDA receptors.

N-methyl-D-aspartate receptors (NMDARs) are critically involved in basic brain functions and neurodegeneration as well as tumor invasiveness. Targeting specific subtypes of NMDARs with distinct activities has been considered an effective therapeutic strategy for neurological disorders and diseases. However, complete elimination of off-target effects of small chemical compounds has been challenging and thus, there is a need to explore alternative strategies for targeting NMDAR subtypes. Here we report identification of a functional antibody that specifically targets the GluN1-GluN2B NMDAR subtype and allosterically down-regulates ion channel activity as assessed by electrophysiology. Through biochemical analysis, x-ray crystallography, single-particle electron cryomicroscopy, and molecular dynamics simulations, we show that this inhibitory antibody recognizes the amino terminal domain of the GluN2B subunit and increases the population of the non-active conformational state. The current study demonstrates that antibodies may serve as specific reagents to regulate NMDAR functions for basic research and therapeutic objectives.

The safety and efficacy of ketamine NMDA receptor blocker as a therapeutic intervention for PTSD review of a randomized clinical trial.

OBJECTIVE: Posttraumatic stress disorder (PTSD) has long-lasting debilitating symptoms. PTSD causes a significant burden on healthcare workers and victims' families. The US Food Drug Administration (FDA) has approved only two Serotonin Selective Reuptake Inhibitors (SSRI), sertraline, and paroxetine as pharmacological interventions for PTSD. SSRI has a 50-60% response rate and up to 30% remission rate with a high relapse rate. Ketamine is an NMDA receptor blocker, has a rapid effective onset, a potent antidepressant with anti-suicidal, neuroprotective, and cognitive-enhancement properties. METHOD: We retrieved randomized clinical trials (RCT) on PubMed, PubMed Central, and Medline Database of clinical trial studies until Jan/2022. We used the following keywords: "posttraumatic stress disorder. "AND "Ketamine." AND "Esketamine" AND "NMDA receptor antagonist" AND "treatment, pharmacological intervention, management. ". We used Medical Subject Heading [Mesh] Term for "ketamine" and "Esketamine" And "Receptors, N-Methyl-D-Aspartate" and "Stress Disorders, Post-Traumatic" and "Disease management.". RESULT: All qualified five randomized clinical studies showed rapid and clear benefits of Ketamine infusion for PTSD symptoms resistant to conventional medications. The clinical improvements were evident in three of the four PTSD symptom categories, intrusions, avoidance, and negative alterations in cognitions and mood. In addition, Ketamine administration was safe well-tolerated, with transient dissociation as the main side effect reported. Ketamine infusion also positively affects comorbidities like chronic pain, alcohol use disorder, and major depression. CONCLUSION: Ketamine showed fast, safe, highly effective pharmaceutical intervention for chronic PTSD symptoms. No correlation between ketamine potency and patient age, sex and/or body mass index. Further studies are needed to understand the appropriate therapeutic dose, onset, route of administration, duration of the treatment and comorbidity benefit.

Effect of NMDA receptor agonist and antagonist on spermatogonial stem cells proliferation in 2- and 3- dimensional culture systems.

BACKGROUND: The main purpose of this study was to investigate the effect of D-serine (DS) and Dizocilpine (MK-801) on the proliferation of spermatogonial stem cells (SSCs) in two-dimensional (2D) and three-dimensional (3D) culture systems. METHODS AND RESULTS: The SSCs of male NMRI mice were isolated by enzymatic digestion and cultured for two weeks. Then, the identity of SSCs was validated by anti-Plzf and anti-GFR-α1 antibodies via immunocytochemistry (ICC). The proliferation capacity of SSCs was evaluated by their culture on a layer of the decellularized testicular matrix (DTM) prepared from mouse testis, as well as two-dimensional (2D) with different mediums. After two weeks of the initiation of proliferation culture on 3D and 2D medium, the pre-meiotic at the mRNA and protein levels were evaluated via qRT-PCR and flow cytometry methods, respectively. The results showed that the proliferation rate of SSCs in 3D culture with 50 mM glutamic acid and 20 mM D-serine was significantly different from other groups after 14 days treatment. mRNA expression levels of promyelocytic leukemia zinc finger (Plzf) in 3D cultures supplemented by 20 mM D-serine and 50 mM glutamic acid were considerably higher than the 3D control group (p < 0.001). The flow cytometry analysis revealed that the amount of Plzf in the 2D-culture groups of SSCs with 20 mM MK-801 was considerably lower compared to the 2D-culture control group (p < 0.001). CONCLUSIONS: This study indicated that decellularized testicular matrix supplemented with D-serine and glutamic acid could be considered a promising vehicle to support cells and provide an appropriate niche for the proliferation of SSCs.