Role of N-methyl-D-aspartate receptors in antidepressant-like effects of sigma 1 receptor agonist 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride (SA-4503) in olfactory bulbectomized rats

Dextromethorphan-Bupropion for the Treatment of Depression: A Systematic Review of Efficacy and Safety in Clinical Trials

BACKGROUND

A significant proportion of adults with major depressive disorder (MDD) do not respond to treatments which are currently used in clinical practice such as first-generation monoamine-based antidepressants.

OBJECTIVES

The objective of this systematic review was to assess the efficacy, safety, and mechanisms of action of AXS-05, a combination of the NMDA-receptor antagonist dextromethorphan with bupropion, in adults with MDD.

METHODS

We searched PubMed, Embase, Google Scholar, and ClinicalTrials.gov for current studies reporting on efficacy and/or safety of AXS-05 in patients with MDD. The search terms included: "AXS-05" OR "dextromethorphan and bupropion" AND "depression". Studies from database inception to January 2023 were evaluated. Risk of bias was assessed using the Cochrane Risk of Bias tool.

RESULTS

The search yielded 54 studies of which 5 were included. All studies had low risk of bias. Depression severity, measured with the Montgomery-Åsberg Depression Rating Scale (MADRS) significantly decreased as early as 1-week post-treatment from baseline when compared to a placebo-controlled group (LS mean difference 2.2; 95% CI 0.6-3.9; p = 0.007) and at 2 weeks compared to an active control group (LS mean difference 4.7; 95% CI 0.6-8.8; p = 0.024). Treatment efficacy could be maintained for up to 12 months with mean MADRS score reduction of 23 points from baseline. Clinical remission and response rates also improved at week 1 and were maintained for 12 months. The treatment was well-tolerated, with some transient adverse events reported.

CONCLUSION

Current evidence suggests that the combination of dextromethorphan and bupropion is a well-tolerated, rapid-acting treatment option for adults with MDD. Initial success with AXS-05 supports the mechanistic role of glutamatergeric and sigma 1 signaling in the pathophysiology of MDD.

Targeted to neuronal organelles for CNS drug development

Significant evidences indicate that sub-cellular organelle dynamics is critical for both physiological and pathological events and therefore may be attractive drug targets displaying great therapeutic potential. Although the basic biological mechanism underlying the dynamics of intracellular organelles has been extensively studied, relative drug development is still limited. In the present review, we show that due to the development of technical advanced imaging tools, especially live cell imaging methods, intracellular organelle dynamics (including mitochondrial dynamics and membrane contact sites) can be dissected at the molecular level. Based on these identified molecular targets, we review and discuss the potential of drug development to target organelle dynamics, especially mitochondria dynamics and ER-organelle membrane contact dynamics, in the central nervous system for treating human diseases, including neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis.

Sigma-1 Receptors in Depression: Mechanism and Therapeutic Development

Depression is the most common type of neuropsychiatric illness and has increasingly become a major cause of disability. Unfortunately, the recent global pandemic of COVID-19 has dramatically increased the incidence of depression and has significantly increased the burden of mental health care worldwide. Since full remission of the clinical symptoms of depression has not been achieved with current treatments, there is a constant need to discover new compounds that meet the major clinical needs. Recently, the roles of sigma receptors, especially the sigma-1 receptor subtype, have attracted increasing attention as potential new targets and target-specific drugs due to their translocation property that produces a broad spectrum of biological functions. Even clinical first-line antidepressants with or without affinity for sigma-1 receptors have different pharmacological profiles. Thus, the regulatory role of sigma-1 receptors might be useful in treating these central nervous system (CNS) diseases. In addition, long-term mental stress disrupts the homeostasis in the CNS. In this review, we discuss the topical literature concerning sigma-1 receptor antidepressant mechanism of action in the regulation of intracellular proteostasis, calcium homeostasis and especially the dynamic Excitatory/Inhibitory (E/I) balance in the brain. Furthermore, based on these discoveries, we discuss sigma-1 receptor ligands with respect to their promise as targets for fast-onset action drugs in treating depression.

Revisiting the sigma-1 receptor as a biological target to treat affective and cognitive disorders

Depression and cognitive disorders are diseases with complex and not-fully understood etiology. Unfortunately, the COVID-19 pandemic dramatically increased the prevalence of both conditions. Since the current treatments are inadequate in many patients, there is a constant need for discovering new compounds, which will be more effective in ameliorating depressive symptoms and treating cognitive decline. Proteins attracting much attention as potential targets for drugs treating these conditions are sigma-1 receptors. Sigma-1 receptors are multi-functional proteins localized in endoplasmic reticulum membranes, which play a crucial role in cellular signal transduction by interacting with receptors, ion channels, lipids, and kinases. Changes in their functions and expression may lead to various diseases, including depression or memory impairments. Thus, sigma-1 receptor modulation might be useful in treating these central nervous system diseases. Importantly, two sigma-1 receptor ligands entered clinical trials, showing that this compound group possesses therapeutic potential. Therefore, based on preclinical studies, this review discusses whether the sigma-1 receptor could be a promising target for drugs treating affective and cognitive disorders.

Psychedelic Medicines in Major Depression: Progress and Future Challenges

The volume of research on the therapeutic use of psychedelic drugs has been increasing during the last decades. Partly because of the need of innovative treatments in psychiatry, several studies have assessed the safety and efficacy of drugs like psilocybin or ayahuasca for a wide range of mental disorders, including major depression. The first section of this chapter will offer an introduction to psychedelic research, including a brief historical overview and discussions about appropriate terminology. In the second section, the recently published clinical trials in which psychedelic drugs were administered to patients will be analysed in detail. Then, in the third section, the main neurobiological mechanisms of these drugs will be described, noting that while some of these mechanisms could be potentially associated with their therapeutic properties, they are commonly used as adjuvants in psychotherapeutic processes. The last section suggests future challenges for this groundbreaking field of research and therapy.

Small Molecules Selectively Targeting Sigma-1 Receptor for the Treatment of Neurological Diseases

The sigma-1 (σ1) receptor, an enigmatic protein originally classified as an opioid receptor subtype, is now understood to possess unique structural and functional features of its own and play critical roles to widely impact signaling transduction by interacting with receptors, ion channels, lipids, and kinases. The σ1 receptor is implicated in modulating learning, memory, emotion, sensory systems, neuronal development, and cognition and accordingly is now an actively pursued drug target for various neurological and neuropsychiatric disorders. Evaluation of the five selective σ1 receptor drug candidates (pridopidine, ANAVEX2-73, SA4503, S1RA, and T-817MA) that have entered clinical trials has shown that reaching clinical approval remains an evasive and important goal. This review provides up-to-date information on the selective targeting of σ1 receptors, including their history, function, reported crystal structures, and roles in neurological diseases, as well as a useful collation of new chemical entities as σ1 selective orthosteric ligands or allosteric modulators.

Chaperone Sigma1R and Antidepressant Effect

This review analyzes the current scientific literature on the role of the Sigma1R chaperone in the pathogenesis of depressive disorders and pharmacodynamics of antidepressants. As a result of ligand activation, Sigma1R is capable of intracellular translocation from the endoplasmic reticulum (ER) into the region of nuclear and cellular membranes, where it interacts with resident proteins. This unique property of Sigma1R provides regulation of various receptors, ion channels, enzymes, and transcriptional factors. The current review demonstrates the contribution of the Sigma1R chaperone to the regulation of molecular mechanisms involved in the antidepressant effect.

The Roles of Intracellular Chaperone Proteins, Sigma Receptors, in Parkinson's Disease (PD) and Major Depressive Disorder (MDD)

Sigma receptors, including Sigma-1 receptors and Sigma-2 receptors, are highly expressed in the CNS. They are intracellular chaperone proteins. Sigma-1 receptors localize mainly at the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM). Upon stimulation, they translocate from MAM to plasma membrane (PM) and nucleus, where they interact with many proteins and ion channels. Sigma-1 receptor could interact with itself to form oligomers, its oligomerization states affect its ability to interact with client proteins including ion channels and BiP. Sigma-1 receptor shows high affinity for many unrelated and structurally diverse ligands, but the mechanism for this diverse drug receptor interaction remains unknown. Sigma-1 receptors also directly bind many proteins including G protein-coupled receptors (GPCRs) and ion channels. In recent years, significant progress has been made in our understanding of roles of the Sigma-1 receptors in normal and pathological conditions, but more studies are still required for the Sigma-2 receptors. The physiological roles of Sigma-1 receptors in the CNS are discussed. They can modulate the activity of many ion channels including voltage-dependent ion channels including Ca²⁺, Na⁺, K⁺ channels and NMDAR, thus affecting neuronal excitability and synaptic activity. They are also involved in synaptic plasticity and learning and memory. Moreover, the activation of Sigma receptors protects neurons from death via the modulation of ER stress, neuroinflammation, and Ca²⁺ homeostasis. Evidences about the involvement of Sigma-1 receptors in Parkinson’s disease (PD) and Major Depressive Disorder (MDD) are also presented, indicating Sigma-1 receptors might be promising targets for pharmacologically treating PD and MDD.

Pharmacological and proteomic analyses of neonatal polyI:C-treated adult mice

Perinatal virus infection is an environmental risk factor for neurodevelopmental disorders such as schizophrenia. We previously demonstrated that neonatal treatment with a viral mimetic, polyriboinosinic-polyribocytidilic acid (polyI:C), in mice leads to emotional and cognitive deficits in adolescence. Here, we investigated the effects of antipsychotics on polyI:C-induced behavioral abnormalities. We also performed a proteomic analysis in the hippocampus of polyI:C-treated adult mice using two-dimensional electrophoresis to understand the changes in protein expression following neonatal immune activation. Neonatal mice were subcutaneously injected with polyI:C for 5 days (postnatal day 2-6). At 10 weeks, sensorimotor gating, emotional and cognitive function were analyzed in behavioral tests. Clozapine improved PPI deficit and emotional and cognitive dysfunction in polyI:C-treated mice. However, haloperidol improved only PPI deficit. Proteomic analysis revealed that two candidate proteins were obtained in the hippocampus of polyI:C-treated mice, including aldehyde dehydrogenase family 1 member L1 (ALDH1L1) and collapsin response mediator protein 5 (CRMP5). These data suggest that the neonatal polyI:C-treated mouse model may be useful for evaluating antipsychotic activity of compounds. Moreover, changes in the protein expression of ALDH1L1 and CRMP5 support our previous findings that astrocyte-neuron interaction plays a role in the pathophysiology of neurodevelopmental disorders induced by neonatal immune activation.

Corticosteroids Mediate Heart Failure-Induced Depression through Reduced σ1-Receptor Expression

Cardiovascular diseases are risk factors for depression in humans. We recently proposed that σ1 receptor (σ1R) stimulation rescued cardiac hypertrophy and heart failure induced by transverse aortic constriction (TAC) in mice. Importantly, σ1R stimulation reportedly ameliorates depression-like behaviors in rodents. Thus, we hypothesized that impaired σ1R activity in brain triggers depression-like behaviors in animals with cardiovascular disease. Indeed, here we found that cardiac hypertrophy and heart failure induced by TAC were associated with depression-like behaviors concomitant with downregulation of σ1R expression in brain 6 weeks after surgery. σ1R levels significantly decreased in astrocytes in both the hippocampal CA1 region and dentate gyrus. Oral administration of the specific σ1R agonist SA4503 (0.3-1.0mg/kg) significantly improved TAC-induced depression-like behaviors concomitant with rescued astrocytic σ1R expression in CA1 and the dentate gyrus. Plasma corticosterone levels significantly increased 6 weeks after TAC, and chronic treatment of mice with corticosterone for 3 weeks elicited depression-like behaviors concomitant with reduced astrocytic σ1R expression in hippocampus. Furthermore, the glucocorticoid receptor antagonist mifepristone antagonized depressive-like behaviors and ameliorated decreased hippocampal σ1R expression in TAC mice. We conclude that elevated corticosterone levels trigger hippocampal σ1R downregulation and that σ1R stimulation with SA4503 is an attractive therapy to improve not only cardiac dysfunction but depression-like behaviors associated with heart failure.

Allosteric Modulation of Sigma-1 Receptors Elicits Rapid Antidepressant Activity

AIMS

Sigma-1 receptors are involved in the pathophysiological process of several neuropsychiatric diseases such as epilepsy, depression. Allosteric modulation represents an important mechanism for receptor functional regulation. In this study, we examined antidepressant activity of the latest identified novel and selective allosteric modulator of sigma-1 receptor 3-methyl-phenyl-2, 3, 4, 5-tetrahydro-1H-benzo[d]azepin-7-ol (SOMCL-668).

METHODS AND RESULTS

A single administration of SOMCL-668 decreased the immobility time in the forced swimming test (FST) and tailing suspended test in mice, which were abolished by pretreatment of sigma-1 receptor antagonist BD1047. In the chronic unpredicted mild stress (CUMS) model, chronic application of SOMCL-668 rapidly ameliorated anhedonia-like behavior (within a week), accompanying with the enhanced expression of brain-derived neurotrophic factor (BDNF) and phosphorylation of glycogen synthase kinase 3β (GSK3β) (Ser-9) in the hippocampus. SOMCL-668 also rapidly promoted the phosphorylation of GSK3β (Ser-9) in an allosteric manner in vitro. In the cultured primary neurons, SOMCL-668 enhanced the sigma-1 receptor agonist-induced neurite outgrowth and the secretion of BDNF.

CONCLUSION

SOMCL-668, a novel allosteric modulator of sigma-1 receptors, elicits a potent and rapid acting antidepressant effect. The present data provide the first evidence that allosteric modulation of sigma-1 receptors may represent a new approach for antidepressant drug discovery.

Sigma-1 receptor mediates acquisition of alcohol drinking and seeking behavior in alcohol-preferring rats

Sigma-1 receptor (Sig-1R) has been proposed as a novel therapeutic target for drug and alcohol addiction. We have shown previously that Sig-1R agonists facilitate the reinforcing effects of ethanol and induce binge-like drinking, while Sig-1R antagonists on the other hand block excessive drinking in genetic and environmental models of alcoholism, without affecting intake in outbred non-dependent rats. Even though significant progress has been made in understanding the function of Sig-1R in alcohol reinforcement, its role in the early and late stage of alcohol addiction remains unclear. Administration of the selective Sig-1R antagonist BD-1063 dramatically reduced the acquisition of alcohol drinking behavior as well as the preference for alcohol in genetically selected TSRI Sardinian alcohol preferring (Scr:sP) rats; the treatment had instead no effect on total fluid intake, food intake or body weight gain, proving selectivity of action. Furthermore, BD-1063 dose-dependently decreased alcohol-seeking behavior in rats trained under a second-order schedule of reinforcement, in which responding is maintained by contingent presentation of a conditioned reinforcer. Finally, an innate elevation in Sig-1R protein levels was found in the nucleus accumbens of alcohol-preferring Scr:sP rats, compared to outbred Wistar rats, alteration which was normalized by chronic, voluntary alcohol drinking. Taken together these findings demonstrate that Sig-1R blockade reduces the propensity to both acquire alcohol drinking and to seek alcohol, and point to the nucleus accumbens as a potential key region for the effects observed. Our data suggest that Sig-1R antagonists may have therapeutic potential in multiple stages of alcohol addiction.

The evaluation of AZ66, an optimized sigma receptor antagonist, against methamphetamine-induced dopaminergic neurotoxicity and memory impairment in mice

Sigma (σ) receptors have recently been identified as potential targets for the development of novel therapeutics aimed at mitigating the effects of methamphetamine. Particularly, σ receptors are believed to mitigate some of the neurotoxic effects of methamphetamine through modulation of dopamine, dopamine transporters and body temperature. Furthermore, recent evidence suggests that targeting σ receptors may prevent cognitive impairments produced by methamphetamine. In the present study, an optimized σ receptor antagonist, AZ66, was evaluated against methamphetamine-induced neurotoxicity and cognitive dysfunction. AZ66 was found to be highly selective for σ receptors compared to 64 other sites tested. Pretreatment of male, Swiss Webster mice with i.p. dosing of AZ66 significantly attenuated methamphetamine-induced striatal dopamine depletions, striatal dopamine transporter reductions and hyperthermia. Additionally, neurotoxic dosing with methamphetamine caused significant memory impairment in the object recognition test, which was attenuated when animals were pretreated with AZ66; similar trends were observed in the step-through passive avoidance test. Taken together, these results suggest that targeting σ receptors may provide neuroprotection against the neurotoxicity and cognitive impairments produced by methamphetamine.

A sigma-1 receptor antagonist (NE-100) prevents tunicamycin-induced cell death via GRP78 induction in hippocampal cells

Endoplasmic reticulum (ER) stress is involved in various diseases such as ischemia, Alzheimer's disease, and Parkinson's disease. The widely used selective sigma-1 receptor antagonist, N, N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)-phenyl]-ethylamine monohydrochloride (NE-100), has been shown to suppress ischemia-induced neuronal cell death in the murine hippocampus. In the present study, we investigated whether NE-100 might suppress neuronal cell death that is induced by ER stress in ischemic injury. These studies show that NE-100 protected the ER stress-induced cell death of murine hippocampal HT22 cells, but not the oxidative stress-induced cell death. This suggests that NE-100 may have a protective effect on the ER. However, another sigma-1 receptor antagonist (BD1047) did not suppress ER stress-induced cell death. In addition, NE-100 attenuated the upregulation of C/EBP homologous protein (CHOP) induced by ER stress and upregulated the expression of both the 50-kDa activating transcription factor 6 (p50ATF6) and the 78-kDa glucose-regulated protein (GRP78). However, NE-100 did not impact the expression of phosphorylated eukaryotic initiation factor 2α (p-eIF2α) nor splicing of X-box-binding protein 1 (XBP-1). These findings suggest that NE-100 suppresses ER stress-induced cell death via CHOP expression by the upregulation of GRP78 through ATF6 pathway, independent sigma-1 receptor antagonist effect.

Evidences for the involvement of sigma receptors in antidepressant like effect of quetiapine in mice

Although quetiapine is routinely used in the treatment of schizophrenia and bipolar disorders, the precise mechanism of its antidepressant activity is poorly understood. Since quetiapine binds with sigma receptor, the possibility exists that antidepressant action of quetiapine may be mediated through interaction with sigma receptors. In the present study, quetiapine [40-80 μg/mouse, intracerebroventricular (i.c.v.) and 40 mg/kg, intraperitoneal (i.p.)], sigma1 receptor agonist, (+)-pentazocine (120 μg/mouse, i.c.v.) and sigma2 receptor agonist, PB-28 [1-Cyclohexyl-4-[3-(1,2,3,4-tetrahydro-5-methoxy-1-naphthalenyl)propyl]piperazine] (20 μg/mouse, i.c.v.) significantly decreased immobility time in forced swim test. In combination studies, the antiimmobility effect of quetiapine (20 μg/mouse, i.c.v.) was significantly potentiated by pretreatment with (+)-pentazocine (30 and 60 μg/mouse, i.c.v.) or PB-28 (5 and 10 μg/mouse, i.c.v.). Conversely, prior administration of sigma1 receptor antagonist, BD-1063 [1-[2-(3,4-Dichlorophenyl)ethyl]-4-methylpiperazine] and sigma2 receptor antagonists, SM-21 [(±)-Tropanyl 2-(4-chlorophenoxy)butanoate] antagonized the antiimmobility effect induced by quetiapine and its synergistic combination with sigma receptor agonists. These results demonstrated the involvement of sigma receptors in the antidepressant like effect of quetiapine and suggest that sigma receptors can be explored as a potential therapeutic target for the treatment of depressive disorders.

Cytokines mediated inflammation and decreased neurogenesis in animal models of depression

In patients with major depression or in animal models of depression, significantly increases in the concentrations of pro-inflammatory cytokines have been consistently reported. Proinflammatory cytokines can stimulate the hypothalamic-pituitary-adrenal (HPA) axis to release stress hormone, glucocorticoids. As a consequence of excessive inflammatory response triggered by pro-inflammatory cytokines in the periphery, free radicals, oxidants and glucocorticoids are over-produced, which can affect glial cell functions and damage neurons in the brain. Indeed, decreased neurogenesis and the dysfunction of neurotrophic system (up- or down-regulations of neurotrophins and their receptors) have been recently found. Effective treatments for depressive symptoms, such as antidepressants and omega-3 fatty acids can increase or modulate neurotrophic system and enhance neurogenesis. However, the relationship between glial cells; microglia (mostly involved in neuroinflammation) and astrocytes (producing neurotrophins), and the contribution of inflammation to decreased neurogenesis and dysfunction of neurotrophic system are almost unknown. This review first introduces changes in behavior, neurotransmitter, cytokine and neurogenesis aspects in depressed patients and several animal models of depression, secondly explores the possible relationship between pro- and anti-inflammatory cytokines and neurogenesis in these models, then discusses the effects of current treatments on inflammation, neurotrophic system and neurogenesis, and finally pointes out the limitations and future research directions.

Pharmacology and therapeutic potential of sigma(1) receptor ligands

Sigma (σ) receptors, initially described as a subtype of opioid receptors, are now considered unique receptors. Pharmacological studies have distinguished two types of σ receptors, termed σ₁ and σ₂. Of these two subtypes, the σ₁ receptor has been cloned in humans and rodents, and its amino acid sequence shows no homology with other mammalian proteins. Several psychoactive drugs show high to moderate affinity for σ₁ receptors, including the antipsychotic haloperidol, the antidepressant drugs fluvoxamine and sertraline, and the psychostimulants cocaine and methamphetamine; in addition, the anticonvulsant drug phenytoin allosterically modulates σ₁ receptors. Certain neurosteroids are known to interact with σ₁ receptors, and have been proposed to be their endogenous ligands. These receptors are located in the plasma membrane and in subcellular membranes, particularly in the endoplasmic reticulum, where they play a modulatory role in intracellular Ca²⁺ signaling. Sigma₁ receptors also play a modulatory role in the activity of some ion channels and in several neurotransmitter systems, mainly in glutamatergic neurotransmission. In accordance with their widespread modulatory role, σ₁ receptor ligands have been proposed to be useful in several therapeutic fields such as amnesic and cognitive deficits, depression and anxiety, schizophrenia, analgesia, and against some effects of drugs of abuse (such as cocaine and methamphetamine). In this review we provide an overview of the present knowledge of σ₁ receptors, focussing on σ₁ ligand neuropharmacology and the role of σ₁ receptors in behavioral animal studies, which have contributed greatly to the potential therapeutic applications of σ₁ ligands.

Sigma receptors: potential targets for a new class of antidepressant drug

Despite the widespread and devastating impact of depression on society, our current understanding of its pathogenesis is limited. Likewise, existing treatments are inadequate, providing relief to only a subset of people suffering from depression. The search for more effective antidepressant drugs includes the investigation of new molecular targets. Among them, current data suggests that sigma receptors are involved in multiple processes effecting antidepressant-like actions in vivo and in vitro. This review summarizes accumulated evidence supporting a role for sigma receptors in antidepressant effects and provides a conceptual framework for delineating their potential roles over the course of antidepressant treatment.

Neonatal polyI:C treatment in mice results in schizophrenia-like behavioral and neurochemical abnormalities in adulthood

It has been reported that viral infection in the first and second trimesters of pregnancy in humans increases the risk of subsequently developing schizophrenia. To develop a mouse model of immune activation during the early postnatal period, neonatal ICR mice were repeatedly injected with polyriboinosinic-polyribocytidilic acid (polyI:C; an inducer of strong innate immune responses) for 5 days (postnatal day 2-6) which may correspond, in terms of brain development, to the early second trimester in human. Cognitive and emotional behavior as well as the extracellular level of glutamate in the hippocampus were analyzed at the age of 10-12 weeks old. PolyI:C-treated mice showed anxiety-like behavior, impairment of object recognition memory and social behavior, and sensorimotor gating deficits, as compared to the saline-treated control group. Depolarization-evoked glutamate release in the hippocampus was impaired in polyI:C-treated mice compared to saline-treated control mice. Furthermore, to investigate the effect of neonatal immune activation on the expression levels of schizophrenia-related genes, we analyzed mRNA levels in the hippocampus 2 and 24h after polyI:C treatment. No significant differences or only transient and marginal changes were observed between polyI:C-treated and saline-treated control mice in the expression levels of schizophrenia-related genes in the hippocampus.