Novel glutamatergic drugs for the treatment of mood disorders

Ketamine effects on resting state functional brain connectivity in major depressive disorder patients: a hypothesis-driven analysis based on a network model of depression

Introduction

Ketamine demonstrates robust and rapidly occurring antidepressant effects in patients with difficult-to-treat major depressive disorder. Ketamine's antidepressant effects and its impact on functional networks in non-resistant forms of major depressive disorder are expected to provide valuable insight into ketamine's mechanism of action related to depression.

Methods

This study employs an existing network model of major depressive disorder to investigate the effects of ketamine on resting state connectivity in a therapy-non-resistant major depressive disorder population. In a randomized, double-blind, placebo-controlled, cross-over study, 0.5 mg/kg racemic ketamine or 0.9%NaCl was administered intravenously in 16 MDD patients. We applied resting-state functional magnetic resonance imaging (rs-fMRI) to explore changes in functional brain connectivity directly at 50, 80 and 165 min (acute) and 24 h (delayed) following ketamine administration. A clinician-rated 10-item scale (MADRS) was administered at 165 min and 24 h after ketamine administration. Connections-of-interest (COIs) were based on the previously published corticolimbic-insular-striatalpallidal-thalamic (CLIPST) circuitry model of major depressive disorder.

Results

Compared with placebo, ketamine significantly (p < 0.0014) reduced the mean (SD) MADRS total score from 21.2 (5.9) pre-dose to 10.3 (4.6) 24 h post-dose. At both acute (p < 0.0172) and delayed (p < 0.0488) time points, significant rs-fMRI connectivity changes occurred only in MDD-related COIs as proposed by the CLIPST model. No changes in functional connectivity were found in non-CLIPST connections.

Discussion

This study demonstrates that ketamine specifically affects depression-related circuitry. Analyzing functional connectivity based on a neurocircuitry model of a specific CNS disease and drug action may be an effective approach that could result in a more targeted analysis in future pharmaco-fMRI studies in CNS drug development.

Excitatory amino acids as therapeutic agents: Reversing neurodegenerative trajectory by tackling excitotoxicity

Neurodegenerative diseases pose significant challenges to healthcare systems globally due to their complex etiology and relentless progression, often rendering conventional treatments ineffective. Recent advances have spotlighted excitatory amino acids, particularly D-amino acids, once considered as products of metabolism of the microbiota or deriving from food intake. This review explores the role of D-amino acids in mitigating excitotoxicity-a process characterized by excessive calcium influx through aberrant N-methyl-D-aspartate receptor (NMDAR) activation, which is implicated in the pathogenesis of diseases like Alzheimer's disease. By providing alternative pathways for neuronal signaling and protecting against excitotoxic damage, D-amino acids offer a novel approach to reversing neurodegenerative trajectories. Future research should focus on elucidating the detailed mechanisms of action of these compounds, evaluating their therapeutic potential through rigorous preclinical and clinical trials, and developing effective delivery systems to optimize their neuroprotective effects. This emerging field holds promise for developing innovative treatment strategies that could significantly improve outcomes for patients with neurodegenerative disorders.

Alzheimer Disease-Link With Major Depressive Disorder and Efficacy of Antidepressants in Modifying its Trajectory

Alzheimer disease (AD) is a devastating neurodegenerative disorder that affects millions of individuals worldwide, with no effective cure. The main symptoms include learning and memory loss, and the inability to carry out the simplest tasks, significantly affecting patients' quality of life. Over the past few years, tremendous progress has been made in research demonstrating a link between AD and major depressive disorder (MDD). Evidence suggests that MDD is commonly associated with AD and that it can serve as a precipitating factor for this disease. Antidepressants such as selective serotonin reuptake inhibitors, which are the first line of treatment for MDD, have shown great promise in the treatment of depression in AD, although their effectiveness remains controversial. The goal of this review is to summarize current knowledge regarding the association between AD, MDD, and antidepressant treatment. It first provides an overview of the interaction between AD and MDD at the level of genes, brain regions, neurotransmitter systems, and neuroinflammatory markers. The review then presents current evidence regarding the effectiveness of various antidepressants for AD-related pathophysiology and then finally discusses current limitations, challenges, and future directions.

Antidepressants for the treatment of depression in people with cancer

BACKGROUND

Major depression and other depressive conditions are common in people with cancer. These conditions are not easily detectable in clinical practice, due to the overlap between medical and psychiatric symptoms, as described by diagnostic manuals such as the Diagnostic and Statistical Manual of Mental Disorders (DSM) and International Classification of Diseases (ICD). Moreover, it is particularly challenging to distinguish between pathological and normal reactions to such a severe illness. Depressive symptoms, even in subthreshold manifestations, have a negative impact in terms of quality of life, compliance with anticancer treatment, suicide risk and possibly the mortality rate for the cancer itself. Randomised controlled trials (RCTs) on the efficacy, tolerability and acceptability of antidepressants in this population are few and often report conflicting results.

OBJECTIVES

To evaluate the efficacy, tolerability and acceptability of antidepressants for treating depressive symptoms in adults (aged 18 years or older) with cancer (any site and stage).

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search date was November 2022.

SELECTION CRITERIA

We included RCTs comparing antidepressants versus placebo, or antidepressants versus other antidepressants, in adults (aged 18 years or above) with any primary diagnosis of cancer and depression (including major depressive disorder, adjustment disorder, dysthymic disorder or depressive symptoms in the absence of a formal diagnosis).

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcome was 1. efficacy as a continuous outcome. Our secondary outcomes were 2. efficacy as a dichotomous outcome, 3. Social adjustment, 4. health-related quality of life and 5. dropouts. We used GRADE to assess certainty of evidence for each outcome.

MAIN RESULTS

We identified 14 studies (1364 participants), 10 of which contributed to the meta-analysis for the primary outcome. Six of these compared antidepressants and placebo, three compared two antidepressants, and one three-armed study compared two antidepressants and placebo. In this update, we included four additional studies, three of which contributed data for the primary outcome. For acute-phase treatment response (six to 12 weeks), antidepressants may reduce depressive symptoms when compared with placebo, even though the evidence is very uncertain. This was true when depressive symptoms were measured as a continuous outcome (standardised mean difference (SMD) -0.52, 95% confidence interval (CI) -0.92 to -0.12; 7 studies, 511 participants; very low-certainty evidence) and when measured as a proportion of people who had depression at the end of the study (risk ratio (RR) 0.74, 95% CI 0.57 to 0.96; 5 studies, 662 participants; very low-certainty evidence). No studies reported data on follow-up response (more than 12 weeks). In head-to-head comparisons, we retrieved data for selective serotonin reuptake inhibitors (SSRIs) versus tricyclic antidepressants (TCAs) and for mirtazapine versus TCAs. There was no difference between the various classes of antidepressants (continuous outcome: SSRI versus TCA: SMD -0.08, 95% CI -0.34 to 0.18; 3 studies, 237 participants; very low-certainty evidence; mirtazapine versus TCA: SMD -4.80, 95% CI -9.70 to 0.10; 1 study, 25 participants). There was a potential beneficial effect of antidepressants versus placebo for the secondary efficacy outcomes (continuous outcome, response at one to four weeks; very low-certainty evidence). There were no differences for these outcomes when comparing two different classes of antidepressants, even though the evidence was very uncertain. In terms of dropouts due to any cause, we found no difference between antidepressants compared with placebo (RR 0.85, 95% CI 0.52 to 1.38; 9 studies, 889 participants; very low-certainty evidence), and between SSRIs and TCAs (RR 0.83, 95% CI 0.53 to 1.22; 3 studies, 237 participants). We downgraded the certainty of the evidence because of the heterogeneous quality of the studies, imprecision arising from small sample sizes and wide CIs, and inconsistency due to statistical or clinical heterogeneity.

AUTHORS' CONCLUSIONS

Despite the impact of depression on people with cancer, the available studies were few and of low quality. This review found a potential beneficial effect of antidepressants against placebo in depressed participants with cancer. However, the certainty of evidence is very low and, on the basis of these results, it is difficult to draw clear implications for practice. The use of antidepressants in people with cancer should be considered on an individual basis and, considering the lack of head-to-head data, the choice of which drug to prescribe may be based on the data on antidepressant efficacy in the general population of people with major depression, also taking into account that data on people with other serious medical conditions suggest a positive safety profile for the SSRIs. Furthermore, this update shows that the usage of the newly US Food and Drug Administration-approved antidepressant esketamine in its intravenous formulation might represent a potential treatment for this specific population of people, since it can be used both as an anaesthetic and an antidepressant. However, data are too inconclusive and further studies are needed. We conclude that to better inform clinical practice, there is an urgent need for large, simple, randomised, pragmatic trials comparing commonly used antidepressants versus placebo in people with cancer who have depressive symptoms, with or without a formal diagnosis of a depressive disorder.

Pathophysiology and Current Drug Treatments for Post-Stroke Depression: A Review

Post-stroke depression (PSD) is a biopsychosocial disorder that affects individuals who have suffered a stroke at any point. PSD has a 20 to 60 percent reported prevalence among stroke survivors. Its effects are usually adverse, can lead to disability, and may increase mortality if not managed or treated early. PSD is linked to several other medical conditions, including anxiety, hyper-locomotor activity, and poor functional recovery. Despite significant awareness of its adverse impacts, understanding the pathogenesis of PSD has proved challenging. The exact pathophysiology of PSD is unknown, yet its complexity has been definitively shown, involving mechanisms such as dysfunction of monoamine, the glutamatergic systems, the gut-brain axis, and neuroinflammation. The current effectiveness of PSD treatment is about 30-40 percent of all cases. In this review, we examined different pathophysiological mechanisms and current pharmacological and non-pharmacological approaches for the treatment of PSD.

Riluzole regulates pancreatic cancer cell metabolism by suppressing the Wnt-β-catenin pathway

Most cancer cells rely on aerobic glycolysis to support uncontrolled proliferation and evade apoptosis. However, pancreatic cancer cells switch to glutamine metabolism to survive under hypoxic conditions. Activation of the Wnt/β-catenin pathway induces aerobic glycolysis by activating enzymes required for glucose metabolism and regulating the expression of glutamate transporter and glutamine synthetase. The results demonstrate that riluzole inhibits pancreatic cancer cell growth and has no effect on human pancreatic normal ductal epithelial cells. RNA-seq experiments identified the involvement of Wnt and metabolic pathways by riluzole. Inhibition of Wnt-β-catenin/TCF-LEF pathway by riluzole suppresses the expression of PDK, MCT1, cMyc, AXIN, and CyclinD1. Riluzole inhibits glucose transporter 2 expression, glucose uptake, lactate dehydrogenase A expression, and NAD + level. Furthermore, riluzole inhibits glutamate release and glutathione levels, and elevates reactive oxygen species. Riluzole disrupts mitochondrial homeostasis by inhibiting Bcl-2 and upregulating Bax expression, resulting in a drop of mitochondrial membrane potential. Finally, riluzole inhibits pancreatic cancer growth in KPC (Pdx1-Cre, LSL-Trp53R172H, and LSL-KrasG12D) mice. In conclusion, riluzole can inhibit pancreatic cancer growth by regulating glucose and glutamine metabolisms and can be used to treat pancreatic cancer.

The Potential Antidepressant Action of Duloxetine Co-Administered with the TAAR1 Receptor Agonist SEP-363856 in Mice

Here, we explored the possible interaction between duloxetine and SEP-363856 (SEP-856) in depression-related reactions. The results showed that oral administration of duloxetine showed powerful antidepressant-like effects in both the forced swimming test (FST) and the suspension tail test (TST). SEP-856 orally administered alone also exerted an antidepressant-like effect in FST and TST, especially at doses of 0.3, 1, and 10 mg/kg. In addition, duloxetine (15 mg/kg) and SEP-856 (15 mg/kg) both showed antidepressant-like effects in the sucrose preference test (SPT). Most importantly, in the above experiments, compared with duloxetine alone, the simultaneous use of duloxetine and SEP-856 caused a more significant antidepressant-like effect. It is worth noting that doses of drug combination in FST and TST did not change the motor activities of mice in the open-field test (OFT). Thus, duloxetine and SEP-856 seem to play a synergistic role in regulating depression-related behaviors and might be beneficial for refractory depression.

Drug-induced stuttering: A comprehensive literature review

Drug-induced stuttering (DIS) is a type of neurogenic stuttering (NS). Although DIS has not been reported as frequently as other cases of NS in the literature, it is not a negligible adverse drug reaction (ADR) which can significantly affect the quality of life if not treated. This literature review aims to evaluate the epidemiological and clinical characteristics of DIS and suggests some pathophysiological mechanisms for this ADR. Relevant English-language reports in Google Scholar, PubMed, Web of Science, and Scopus were identified and assessed without time restriction. Finally, a total of 62 reports were included. Twenty-seven drugs caused 86 episodes of stuttering in 82 cases. The most episodes of DIS were related to antipsychotic drugs (57%), mostly including clozapine, followed by central nervous system agents (11.6%) and anticonvulsant drugs (9.3%). The majority of the cases were male and between the ages of 31 and 40 years. Repetitions were the most frequent core manifestations of DIS. In 55.8% of the episodes of DIS, the offending drug was withdrawn to manage stuttering, which resulted in significant improvement or complete relief of stuttering in all cases. Based on the suggested pathophysiological mechanisms for developmental stuttering and neurotransmitters dysfunctions involved in speech dysfluency, it seems that the abnormalities of several neurotransmitters, especially dopamine and glutamate, in different circuits and areas of the brain, including cortico-basal ganglia-thalamocortical loop and white matter fiber tracts, may be engaged in the pathogenesis of DIS.

Glutamate and depression: Reflecting a deepening knowledge of the gut and brain effects of a ubiquitous molecule

The versatility of glutamate as the brain’s foremost excitatory neurotransmitter and modulator of neurotransmission and function is considered common knowledge. Years of research have continued to uncover glutamate’s effects and roles in several neurological and neuropsychiatric disorders, including depression. It had been considered that a deeper understanding of the roles of glutamate in depression might open a new door to understanding the pathological basis of the disorder, improve the approach to patient management, and lead to the development of newer drugs that may benefit more patients. This review examines our current understanding of the roles of endogenous and exogenous sources of glutamate and the glutamatergic system in the aetiology, progression and management of depression. It also examines the relationships that link the gut-brain axis, glutamate and depression; as it emphasizes how the gut-brain axis could impact depression pathogenesis and management via changes in glutamate homeostasis. Finally, we consider what the likely future of glutamate-based therapies and glutamate-based therapeutic manipulations in depression are, and if with them, we are now on the final chapter of understanding the neurochemical milieu of depressive disorders.

Elevated Brain Glutamate Levels in Bipolar Disorder and Pyruvate Carboxylase-Mediated Anaplerosis

In vivo ¹H magnetic resonance spectroscopy studies have found elevated brain glutamate or glutamate + glutamine levels in bipolar disorder with surprisingly high reproducibility. We propose that the elevated glutamate levels in bipolar disorder can be explained by increased pyruvate carboxylase-mediated anaplerosis in brain. Multiple independent lines of evidence supporting increased pyruvate carboxylase-mediated anaplerosis as a common mechanism underlying glutamatergic hyperactivity in bipolar disorder and the positive association between bipolar disorder and obesity are also described.

Brain targeting stealth lipomers of combined antiepileptic-anti-inflammatory drugs as alternative therapy for conventional anti-Parkinson's

This study presents an alternative therapy to conventional anti-Parkinson's treatment strategies; where motor and non-motor symptomatic complications are considered. Thus; providing sustainability, patient compliance, therapeutic safety and efficiency, based on triggering secretion of endogenous dopamine (DA). Exogenous DA has long been considered the best therapy, however, its poor blood brain barrier (BBB) permeability, fluctuated plasma levels, and non-motor complications negligence, decreased response to therapy with time. Consequently; brain targeting Tween®80-coated pegylated lipomers were tailored for intravenous administration (IV) of L-Dopa, and two drugs of reported neuroprotective effect: lamotrigine (LTG) and tenoxicam (TX). Single-step nanoprecipitation method was used; for its reproducibility and ease of scaling-up. Formulation targeting and anti-PD efficiency was evaluated against marketed standards and L-Dopa. In-vitro and in-vivo pharmacokinetic and dynamic studies were carried out for setting optimization standards upon varying inter-components ratio. Results revealed that lipomers are, generally, significantly efficient in brain targeting compared to oral tablets. LTG-lipomers (LF20) showed the maximum anti-PD compared to its TX and L-Dopa analogues. Combining LTG and TX had synergistic effect; highlighting a new prescription for both drugs. Thus; offering a safe, targeted, and therapeutically efficient sustained dosage form, capable of mitigating PD risk and treating it though weekly administration. Hence; presenting a novel promising anti-neurodegenerative strategy; on employing various mechanisms that were previously achieved through additional therapeutic supplements.

Blood glutamate scavenging as a novel glutamate-based therapeutic approach for post-stroke depression

Post-stroke depression (PSD) is a major complication of stroke that significantly impacts functional recovery and quality of life. While the exact mechanism of PSD is unknown, recent attention has focused on the association of the glutamatergic system in its etiology and treatment. Minimizing secondary brain damage and neuropsychiatric consequences associated with excess glutamate concentrations is a vital part of stroke management. The blood glutamate scavengers, oxaloacetate and pyruvate, degrade glutamate in the blood to its inactive metabolite, 2-ketoglutarate, by the coenzymes glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT), respectively. This reduction in blood glutamate concentrations leads to a subsequent shift of glutamate down its concentration gradient from the blood to the brain, thereby decreasing brain glutamate levels. Although there are not yet any human trials that support blood glutamate scavengers for clinical use, there is increasing evidence from animal research of their efficacy as a promising new therapeutic approach for PSD. In this review, we present recent evidence in the literature of the potential therapeutic benefits of blood glutamate scavengers for reducing PSD and other related neuropsychiatric conditions. The evidence reviewed here should be useful in guiding future clinical trials.

The Effect of Glutamatergic Modulators on Extracellular Glutamate: How Does this Information Contribute to the Discovery of Novel Antidepressants?

•

The complexity of glutamatergic signaling challenges glutamate modulator usage.

•

Functional biomarkers are needed to understand the MOA of glutamate modulators.

•

Evaluating drug effect on EAATs' kinetics may add to antidepressant discovery.

Background

In the search for new antidepressants, clinical researchers have been using drugs that simultaneously modulate multiple targets. During preclinical and clinical trials, the glutamatergic modulators riluzole and ketamine have received particular attention. Glutamatergic agents have a modulatory effect on synaptic transmission, so they can act on both neurons and astrocytes. In addition to influencing the quantity of glutamate released, these modulators can also affect the expression, localization, and functionality of glutamate-binding sites.

Objective

This review discusses the complexity of the glutamatergic system, the ambiguity of data regarding glutamate levels in patients with depression, as well as the mechanisms of action for riluzole and ketamine, which includes their relation to the physiology of glutamatergic transmission. The principal aim is to contribute to the development of novel glutamatergic antidepressant medications whilst emphasizing the need for innovative approaches that evaluate their effects on extracellular glutamate.

Methods

Literature was obtained via PubMed by searching the term depression in combination with each of the following terms: riluzole, ketamine, and glutamate. The search was restricted to full-text articles published in English between 1985 and 2018 relating to both the modulatory mechanisms of glutamatergic-binding proteins and the antidepressant actions of these medicines. Articles about mechanisms associated with synaptic plasticity and antidepressant effects were excluded.

Results

Although experimental data relates glutamatergic signaling to the pathophysiology of major depression and bipolar disorder, the role of glutamate—as well as its extracellular concentration in patients with said disorders—is still unclear. Riluzole's antidepressant action is ascribed to its capacity to reduce glutamate levels in the synaptic cleft, and ketamine's effect has been associated with increased extracellular glutamate levels.

Conclusions

The strategy of using glutamatergic modulators as therapeutic agents requires a better understanding of the role of glutamate in the pathophysiology of depression. Gaining such understanding is a challenge because it entails evaluating different targets as well as the effects of these modulators on the kinetics of glutamate uptake. Essentially, glutamate transport is a dynamic process and, currently, it is still necessary to develop new approaches to assay glutamate in the synaptic cleft. ORCID: 0000-0002-3358-6939.

Clinical Efficacy of Ketamine for Treatment-resistant Depression

Depression is a common psychiatric disorder affecting more than 300 million people worldwide. According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), the diagnosis of depression requires at least two weeks of either low mood or anhedonia as well as four or more other symptoms such as appetite or weight changes, insomnia or hypersomnia, psychomotor agitation or retardation, loss of energy, inability to concentrate, feelings of worthlessness or excessive guilt, and suicidality. Selective serotonin reuptake inhibitors (SSRIs) target the monoaminergic system and are the commonest drugs used for treating depression, but have certain limitations, such as their delayed onset of action. Ketamine, a non-competitive NMDA receptor antagonist, has shown in several randomized controlled trials (RCTs) promising results with rapid antidepressant effects, especially in patients with severe treatment-resistant depression (TRD), which is depression that has not responded to more than two antidepressants. In this review, the clinical efficacy of ketamine in TRD has been discussed, with emphasis placed on the evidence from RCTs.

Effects of glucocorticoids in depression: Role of astrocytes

Astrocytes or astroglia are heterogeneous cells, similar to neurons, that have different properties in different brain regions. The implications of steroid hormones on glial cells and stress-related pathologies have been studied previously. Glucocorticoids (GCs) that are released in response to stress have been shown to be deleterious to neurons in various brain regions. Further, in the light of the effect of GCs on astrocytes, several reports have shown the crucial role of glia. Still, much remains to be done to understand the stress-astrocytes-glucocorticoid interactions associated with the pathological consequences of various CNS disorders. This review is an attempt to summarize the effects of GCs and stress on astrocytes and its implications in depression.

Antidepressants for the treatment of depression in people with cancer

BACKGROUND

Major depression and other depressive conditions are common in people with cancer. These conditions are not easily detectable in clinical practice, due to the overlap between medical and psychiatric symptoms, as described by diagnostic manuals such as the Diagnostic and Statistical Manual of Mental Disorders (DSM) and International Classification of Diseases (ICD). Moreover, it is particularly challenging to distinguish between pathological and normal reactions to such a severe illness. Depressive symptoms, even in subthreshold manifestations, have been shown to have a negative impact in terms of quality of life, compliance with anti-cancer treatment, suicide risk and likely even the mortality rate for the cancer itself. Randomised controlled trials (RCTs) on the efficacy, tolerability and acceptability of antidepressants in this population are few and often report conflicting results.

OBJECTIVES

To assess the efficacy, tolerability and acceptability of antidepressants for treating depressive symptoms in adults (aged 18 years or older) with cancer (any site and stage).

SEARCH METHODS

We searched the following electronic bibliographic databases: the Cochrane Central Register of Controlled Trials (CENTRAL 2017, Issue 6), MEDLINE Ovid (1946 to June week 4 2017), Embase Ovid (1980 to 2017 week 27) and PsycINFO Ovid (1987 to July week 4 2017). We additionally handsearched the trial databases of the most relevant national, international and pharmaceutical company trial registers and drug-approving agencies for published, unpublished and ongoing controlled trials.

SELECTION CRITERIA

We included RCTs comparing antidepressants versus placebo, or antidepressants versus other antidepressants, in adults (aged 18 years or above) with any primary diagnosis of cancer and depression (including major depressive disorder, adjustment disorder, dysthymic disorder or depressive symptoms in the absence of a formal diagnosis).

DATA COLLECTION AND ANALYSIS

Two review authors independently checked eligibility and extracted data using a form specifically designed for the aims of this review. The two authors compared the data extracted and then entered data into Review Manager 5 using a double-entry procedure. Information extracted included study and participant characteristics, intervention details, outcome measures for each time point of interest, cost analysis and sponsorship by a drug company. We used the standard methodological procedures expected by Cochrane.

MAIN RESULTS

We retrieved a total of 10 studies (885 participants), seven of which contributed to the meta-analysis for the primary outcome. Four of these compared antidepressants and placebo, two compared two antidepressants, and one three-armed study compared two antidepressants and placebo. In this update we included one additional unpublished study. These new data contributed to the secondary analysis, while the results of the primary analysis remained unchanged.For acute-phase treatment response (6 to 12 weeks), we found no difference between antidepressants as a class and placebo on symptoms of depression measured both as a continuous outcome (standardised mean difference (SMD) -0.45, 95% confidence interval (CI) -1.01 to 0.11, five RCTs, 266 participants; very low certainty evidence) and as a proportion of people who had depression at the end of the study (risk ratio (RR) 0.82, 95% CI 0.62 to 1.08, five RCTs, 417 participants; very low certainty evidence). No trials reported data on follow-up response (more than 12 weeks). In head-to-head comparisons we only retrieved data for selective serotonin reuptake inhibitors (SSRIs) versus tricyclic antidepressants, showing no difference between these two classes (SMD -0.08, 95% CI -0.34 to 0.18, three RCTs, 237 participants; very low certainty evidence). No clear evidence of a beneficial effect of antidepressants versus either placebo or other antidepressants emerged from our analyses of the secondary efficacy outcomes (dichotomous outcome, response at 6 to 12 weeks, very low certainty evidence). In terms of dropouts due to any cause, we found no difference between antidepressants as a class compared with placebo (RR 0.85, 95% CI 0.52 to 1.38, seven RCTs, 479 participants; very low certainty evidence), and between SSRIs and tricyclic antidepressants (RR 0.83, 95% CI 0.53 to 1.30, three RCTs, 237 participants). We downgraded the certainty (quality) of the evidence because the included studies were at an unclear or high risk of bias due to poor reporting, imprecision arising from small sample sizes and wide confidence intervals, and inconsistency due to statistical or clinical heterogeneity.

AUTHORS' CONCLUSIONS

Despite the impact of depression on people with cancer, the available studies were very few and of low quality. This review found very low certainty evidence for the effects of these drugs compared with placebo. On the basis of these results, clear implications for practice cannot be deduced. The use of antidepressants in people with cancer should be considered on an individual basis and, considering the lack of head-to-head data, the choice of which agent to prescribe may be based on the data on antidepressant efficacy in the general population of individuals with major depression, also taking into account that data on medically ill patients suggest a positive safety profile for the SSRIs. To better inform clinical practice, there is an urgent need for large, simple, randomised, pragmatic trials comparing commonly used antidepressants versus placebo in people with cancer who have depressive symptoms, with or without a formal diagnosis of a depressive disorder.

Therapeutic Modulation of Glutamate Receptors in Major Depressive Disorder

Current pharmacotherapies for major depressive disorder (MDD) have a distinct lag of onset that can prolong distress and impairment for patients, and realworld effectiveness trials further suggest that antidepressant efficacy is limited in many patients. All currently approved antidepressant medications for MDD act primarily through monoaminergic mechanisms, e.g., receptor/reuptake agonists or antagonists with varying affinities for serotonin, norepinephrine, or dopamine. Glutamate is the major excitatory neurotransmitter in the central nervous system, and glutamate and its cognate receptors are implicated in the pathophysiology of MDD, as well as in the development of novel therapeutics for this disorder. Since the rapid and robust antidepressant effects of the N-methyl-D-aspartate (NMDA) antagonist ketamine were first observed in 2000, other NMDA receptor antagonists have been studied in MDD. These have been associated with relatively modest antidepressant effects compared to ketamine, but some have shown more favorable characteristics with increased potential in clinical practice (for instance, oral administration, decreased dissociative and/or psychotomimetic effects, and reduced abuse/diversion liability). This article reviews the clinical evidence supporting the use of glutamate receptor modulators with direct affinity for cognate receptors: 1) non-competitive NMDA receptor antagonists (ketamine, memantine, dextromethorphan, AZD6765); 2) subunit (NR2B)-specific NMDA receptor antagonists (CP- 101,606/traxoprodil, MK-0657); 3) NMDA receptor glycine-site partial agonists (D-cycloserine, GLYX- 13); and 4) metabotropic glutamate receptor (mGluR) modulators (AZD2066, RO4917523/basimglurant). Several other theoretical glutamate receptor targets with preclinical antidepressant-like efficacy, but that have yet to be studied clinically, are also briefly discussed; these include α-amino-3-hydroxyl-5-methyl-4- isoxazoleproprionic acid (AMPA) agonists, mGluR2/3 negative allosteric modulators, and mGluR7 agonists.

Regulation of persistent sodium currents by glycogen synthase kinase 3 encodes daily rhythms of neuronal excitability

How neurons encode intracellular biochemical signalling cascades into electrical signals is not fully understood. Neurons in the central circadian clock in mammals provide a model system to investigate electrical encoding of biochemical timing signals. Here, using experimental and modelling approaches, we show how the activation of glycogen synthase kinase 3 (GSK3) contributes to neuronal excitability through regulation of the persistent sodium current (I_NaP). I_NaP exhibits a day/night difference in peak magnitude and is regulated by GSK3. Using mathematical modelling, we predict and confirm that GSK3 activation of I_NaP affects the action potential afterhyperpolarization, which increases the spontaneous firing rate without affecting the resting membrane potential. Together, these results demonstrate a crucial link between the molecular circadian clock and electrical activity, providing examples of kinase regulation of electrical activity and the propagation of intracellular signals in neuronal networks.

It is not clear how circadian biochemical cascades are encoded into neural electrical signals. Here, using a combination of electrophysiology and modelling approaches in mice, the authors show activation of glycogen synthase kinase 3 modulates neural activity in the suprachiasmatic nuclei via regulation of the persistent sodium current, INaP.

Side effect profile similarities shared between antidepressants and immune-modulators reveal potential novel targets for treating major depressive disorders

Background

Side effects, or the adverse effects of drugs, contain important clinical phenotypic information that may be useful in predicting novel or unknown targets of a drug. It has been suggested that drugs with similar side-effect profiles may share common targets. The diagnostic class, Major Depressive Disorder, is increasingly viewed as being comprised of multiple depression subtypes with different biological root causes. One ‘type’ of depression generating substantial interest today focuses on patients with high levels of inflammatory burden, indicated by elevated levels of C-reactive proteins (CRP) and pro-inflammatory cytokines such as interleukin 6 (IL-6). It has been suggested that drugs targeting the immune system may have beneficial effect on this subtype of depressed patients, and several studies are underway to test this hypothesis directly. However, patients have been treated with both anti-inflammatory and antidepressant compounds for decades. It may be possible to exploit similarities in clinical readouts to better understand the antidepressant effects of immune-related drugs.

Methods

Here we explore the space of approved drugs by comparing the drug side effect profiles of known antidepressants and drugs targeting the immune system, and further examine the findings by comparing the human cell line expression profiles induced by them with those induced by antidepressants.

Results

We found 7 immune-modulators and 14 anti-inflammatory drugs sharing significant side effect profile similarities with antidepressants. Five of the 7 immune modulators share most similar side effect profiles with antidepressants that modulate dopamine release and/or uptake. In addition, the immunosuppressant rapamycin and the glucocorticoid alclometasone induces transcriptional changes similar to multiple antidepressants.

Conclusions

These findings suggest that some antidepressants and some immune-related drugs may affect common molecular pathways. Our findings support the idea that certain medications aimed at the immune system may be helpful in relieving depressive symptoms, and suggest that it may be of value to test immune-modulators for antidepressant-like activity in future proof-of-concept studies.

Timosaponin derivative YY-23 acts as a non-competitive NMDA receptor antagonist and exerts a rapid antidepressant-like effect in mice

AIM

N-methyl-D-aspartic acid (NMDA) receptor modulators have shown promising results as potential antidepressant agents, whereas timosaponins extracted from the Chinese herb Rhizoma Anemarrhenae exhibit antidepressant activities. In the present study we examined whether YY-23, a modified metabolite of timosaponin B-III, could affect NMDA receptors in rat hippocampal neurons in vitro, and evaluated its antidepressant-like effects in stressed mice.

METHODS

NMDA-induced currents were recorded in acutely dissociated rat hippocampal CA1 neurons using a whole-cell recording technique. C57BL/6 mice were exposed to a 6-week chronic mild stress (CMS) or a 10-d chronic social defeat stress (CSDS). The stressed mice were treated with YY-23 (20 mg·kg(-1)·d(-1)) or a positive-control drug, fluoxetine (10 mg·kg(-1)·d(-1)) for 3 weeks. Behavioral assessments were carried out every week.

RESULTS

In acutely dissociated rat hippocampal CA1 neurons, YY-23 selectively and reversibly inhibited NMDA-induced currents with an EC50 value of 2.8 μmol/L. This inhibition of NMDA-induced currents by YY-23 was non-competitive, and had no features of voltage-dependency or use-dependency. Treatment of the stressed mice with YY-23 not only reversed CMS-induced deficiency of sucrose preference and immobility time, and CSDS-induced reduction of social interaction, but also had faster onset as compared to fluoxetine.

CONCLUSION

YY-23 is a novel non-competitive antagonist of NMDA receptors with promising rapid antidepressant-like effects in mouse models of CMS and CSDS depression.

Guanosine Anxiolytic-Like Effect Involves Adenosinergic and Glutamatergic Neurotransmitter Systems

Accumulating evidences indicate that endogenous modulators of excitatory synapses in the mammalian brain are potential targets for treating neuropsychiatric disorders. Indeed, glutamatergic and adenosinergic neurotransmissions were recently highlighted as potential targets for developing innovative anxiolytic drugs. Accordingly, it has been shown that guanine-based purines are able to modulate both adenosinergic and glutamatergic systems in mammalian central nervous system. Here, we aimed to investigate the potential anxiolytic-like effects of guanosine and its effects on the adenosinergic and glutamatergic systems. Acute/systemic guanosine administration (7.5 mg/kg) induced robust anxiolytic-like effects in three classical anxiety-related paradigms (elevated plus maze, light/dark box, and round open field tasks). These guanosine effects were correlated with an enhancement of adenosine and a decrement of glutamate levels in the cerebrospinal fluid. Additionally, pre-administration of caffeine (10 mg/kg), an unspecific adenosine receptors' antagonist, completely abolished the behavioral and partially prevented the neuromodulatory effects exerted by guanosine. Although the hippocampal glutamate uptake was not modulated by guanosine (both ex vivo and in vitro protocols), the synaptosomal K⁺-stimulated glutamate release in vitro was decreased by guanosine (100 μM) and by the specific adenosine A₁ receptor agonist, 2-chloro-N ⁶-cyclopentyladenosine (CCPA, 100 nM). Moreover, the specific adenosine A₁ receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 100 nM) fully reversed the inhibitory guanosine effect in the glutamate release. The pharmacological modulation of A_2a receptors has shown no effect in any of the evaluated parameters. In summary, the guanosine anxiolytic-like effects seem closely related to the modulation of adenosinergic (A₁ receptors) and glutamatergic systems.

Repurposing antipsychotics as glioblastoma therapeutics: Potentials and challenges

Glioblastoma multiforme (GBM) is the most common and most lethal primary brain tumor, with tragically little therapeutic progress over the last 30 years. Surgery provides a modest benefit, and GBM cells are resistant to radiation and chemotherapy. Despite significant development of the molecularly targeting strategies, the clinical outcome of GBM patients remains dismal. The challenges inherent in developing effective GBM treatments have become increasingly clear, and include resistance to standard treatments, the blood-brain barrier, resistance of GBM stem-like cells, and the genetic complexity and molecular adaptability of GBM. Recent studies have collectively suggested that certain antipsychotics harbor antitumor effects and have potential utilities as anti-GBM therapeutics. In the present review, the anti-tumorigenic effects and putative mechanisms of antipsychotics, and the challenges for the potential use of antipsychotic drugs as anti-GBM therapeutics are reviewed.

Alteration by p11 of mGluR5 localization regulates depression-like behaviors

Mood disorders and antidepressant therapy involve alterations of monoaminergic and glutamatergic transmission. The protein S100A10 (p11) was identified as a regulator of serotonin receptors, and it has been implicated in the etiology of depression and in mediating the antidepressant actions of selective serotonin reuptake inhibitors. Here we report that p11 can also regulate depression-like behaviors via regulation of a glutamatergic receptor in mice. p11 directly binds to the cytoplasmic tail of metabotropic glutamate receptor 5 (mGluR5). p11 and mGluR5 mutually facilitate their accumulation at the plasma membrane, and p11 increases cell surface availability of the receptor. Whereas p11 overexpression potentiates mGluR5 agonist-induced calcium responses, overexpression of mGluR5 mutant, which does not interact with p11, diminishes the calcium responses in cultured cells. Knockout of mGluR5 or p11 specifically in glutamatergic neurons in mice causes depression-like behaviors. Conversely, knockout of mGluR5 or p11 in GABAergic neurons causes antidepressant-like behaviors. Inhibition of mGluR5 with an antagonist, 2-methyl-6-(phenylethynyl)pyridine (MPEP), induces antidepressant-like behaviors in a p11-dependent manner. Notably, the antidepressant-like action of MPEP is mediated by parvalbumin-positive GABAergic interneurons, resulting in a decrease of inhibitory neuronal firing with a resultant increase of excitatory neuronal firing. These results identify a molecular and cellular basis by which mGluR5 antagonism achieves its antidepressant-like activity.

Involvement of adrenoceptors, dopamine receptors and AMPA receptors in antidepressant-like action of 7-O-ethylfangchinoline in mice

AIM

7-O-ethylfangchinoline (YH-200) is a bisbenzylisoquinoline derivative. The aim of this study was to investigate the antidepressant-like action and underlying mechanisms of YH-200 in mice.

METHODS

Mice were treated with YH-200 (15, 30, and 60 mg/kg, ig) or tetrandrine (30 and 60 mg/kg, ig) before conducting forced swimming test (FST), tail suspension test (TST), or open field test (OFT).

RESULTS

YH-200 (60 mg/kg) significantly decreased the immobility time in both FST and TST, and prolonged the latency to immobility in FST. YH-200 (60 mg/kg) was more potent than the natural bisbenzylisoquinoline alkaloid tetrandrine (60 mg/kg) in FST. Pretreatment with α1-adrenoceptor antagonist prazosin (1 mg/kg), β-adrenoceptor antagonist propranolol (2 mg/kg), dopamine D1/D5 receptor antagonist SCH23390 (0.05 mg/kg), dopamine D2/D3 receptor antagonist haloperidol (0.2 mg/kg) or AMPA receptor antagonist NBQX (10 mg/kg) prevented the antidepressant-like action of YH-200 (60 mg/kg) in FST. In contrast, pretreatment with α2 adrenoceptor antagonist yohimbine (1 mg/kg) augmented the antidepressant-like action of YH-200 (30 mg/kg) in FST. Chronic administration of YH-200 (30 and 60 mg/kg for 14 d) did not produce drug tolerance; instead its antidepressant-like action was strengthened. Chronic administration of YH-200 did not affect the body weight of mice compared to control mice.

CONCLUSION

YH-200 exerts its antidepressant-like action in mice via acting at multi-targets, including α1, α2 and β-adrenoceptors, D1/D5 and D2 /D3 receptors, as well as AMPA receptors.

Antidepressants for the treatment of depression in people with cancer

BACKGROUND

Major depression and other depressive conditions are common in people with cancer. These conditions are not easily detectable in clinical practice, due to the overlap between medical and psychiatric symptoms, as described by diagnostic manuals such as the Diagnostic and Statistical Manual of Mental Disorders (DSM) and International Classification of Diseases (ICD). Moreover, it is particularly challenging to distinguish between pathological and normal reactions to such a severe illness. Depressive symptoms, even in subthreshold manifestations, have been shown to have a negative impact in terms of quality of life, compliance with anti-cancer treatment, suicide risk and likely even the mortality rate for the cancer itself. Randomised controlled trials (RCTs) on the efficacy and tolerability of antidepressants in this population group are few and often report conflicting results.

OBJECTIVES

To assess the effects and acceptability of antidepressants for treating depressive symptoms in adults (18 years or older) with cancer (any site and stage).

SEARCH METHODS

We searched the following electronic bibliographic databases: the Cochrane Central Register of Controlled Trials (CENTRAL 2014, Issue 3), MEDLINE Ovid (1946 to April week 3, 2014), EMBASE Ovid (1980 to 2014 week 17) and PsycINFO Ovid (1987 to April week 4, 2014). We additionally handsearched the trial databases of the most relevant national, international and pharmaceutical company trial registers and drug-approving agencies for published, unpublished and ongoing controlled trials.

SELECTION CRITERIA

We included RCTs allocating adults (18 years or above) with any primary diagnosis of cancer and depression (including major depressive disorder, adjustment disorder, dysthymic disorder or depressive symptoms in the absence of a formal diagnosis) comparing antidepressants versus placebo, or antidepressants versus other antidepressants.

DATA COLLECTION AND ANALYSIS

Two review authors independently checked eligibility and extracted data using a form specifically designed for the aims of this review. The two authors compared the data extracted and then entered data into RevMan 5 with a double-entry procedure. Information extracted included study and participant characteristics, intervention details, outcome measures for each time point of interest, cost analysis and sponsorship by a drug company. We used the standard methodological procedures expected by The Cochrane Collaboration.

MAIN RESULTS

We retrieved a total of nine studies (861 participants), with seven studies contributing to the meta-analysis for the primary outcome. Four of these compared antidepressants and placebo, two compared two antidepressants and one-three armed study compared two antidepressants and a placebo arm. For the acute phase treatment response (6 to 12 weeks), we found very low quality evidence for the effect of antidepressants as a class on symptoms of depression compared with placebo when measured as a continuous outcome (standardised mean difference (SMD) -0.45, 95% confidence interval (CI) -1.01 to 0.11, five RCTs, 266 participants) or as a proportion of people who had depression (risk ratio (RR) 0.82, 95% CI 0.62 to 1.08, five RCTs, 417 participants). No trials reported data on the follow-up response (more than 12 weeks). In head-to-head comparisons we only retrieved data for selective serotonin reuptake inhibitors (SSRIs) versus tricyclic antidepressants, providing very low quality evidence for the difference between these two classes (SMD -0.08, 95% CI -0.34 to 0.18, three RCTs, 237 participants). No clear evidence of an effect of antidepressants versus either placebo or other antidepressants emerged from the analyses of the secondary efficacy outcomes (dichotomous outcome, response at 6 to 12 weeks, very low quality evidence). We found very low quality evidence for the effect of antidepressants as a class in terms of dropouts due to any cause compared with placebo (RR 0.87, 95% CI 0.49 to 1.53, six RCTs, 455 participants), as well as between SSRIs and tricyclic antidepressants (RR 0.83, 95% CI 0.53 to 1.30, three RCTs, 237 participants). We downgraded the quality of the evidence because the included studies were at an unclear or high risk of bias due to poor reporting, imprecision arising from small sample sizes and wide confidence intervals, and inconsistency due to statistical or clinical heterogeneity.

AUTHORS' CONCLUSIONS

Despite the impact of depression on people with cancer, available studies were very few and of low quality. This review found very low quality evidence for the effects of these drugs compared with placebo. On the basis of these results clear implications for practice cannot be made. The use of antidepressants in people with cancer should be considered on an individual basis and, considering the lack of head-to-head data, the choice of which agent should be prescribed may be based on the data on antidepressant efficacy in the general population of individuals with major depression, also taking into account that data on medically ill patients suggest a positive safety profile for the SSRIs. Large, simple, randomised, pragmatic trials comparing commonly used antidepressants versus placebo in people with cancer with depressive symptoms, with or without a formal diagnosis of a depressive disorder, are urgently needed to better inform clinical practice.

Emerging drugs for the treatment of anxiety

INTRODUCTION

Anxiety disorders are among the most prevalent and disabling psychiatric disorders in the United States and worldwide. Basic research has provided critical insights into the mechanism regulating fear behavior in animals and a host of animal models have been developed in order to screen compounds for anxiolytic properties. Despite this progress, no mechanistically novel agents for the treatment of anxiety have come to market in more than two decades.

AREAS COVERED

The current review will provide a critical summary of current pharmacological approaches to the treatment of anxiety and will examine the pharmacotherapeutic pipeline for treatments in development. Anxiety and related disorders considered herein include panic disorder, social anxiety disorder, generalized anxiety disorder and post-traumatic stress disorder. The glutamate, neuropeptide and endocannabinoid systems show particular promise as future targets for novel drug development.

EXPERT OPINION

In the face of an ever-growing understanding of fear-related behavior, the field awaits the translation of this research into mechanistically novel treatments. Obstacles will be overcome through close collaboration between basic and clinical researchers with the goal of aligning valid endophenotypes of human anxiety disorders with improved animal models. Novel approaches are needed to move basic discoveries into new, more effective treatments for our patients.

Antidepressants for the treatment of depression in people with cancer

BACKGROUND

Major depression and other depressive conditions are common in people with cancer. These conditions are not easily detectable in clinical practice, due to the overlap between medical and psychiatric symptoms, as described by diagnostic manuals such as the Diagnostic and Statistical Manual of Mental Disorders (DSM) and International Classification of Diseases (ICD). Moreover, it is particularly challenging to distinguish between pathological and normal reactions to such a severe illness. Depressive symptoms, even in subthreshold manifestations, have been shown to have a negative impact in terms of quality of life, compliance with anti-cancer treatment, suicide risk and likely even the mortality rate for the cancer itself. Randomised controlled trials (RCTs) on the efficacy and tolerability of antidepressants in this population group are few and often report conflicting results.

OBJECTIVES

To assess the effects and acceptability of antidepressants for treating depressive symptoms in adults (18 years or older) with cancer (any site and stage).

SEARCH METHODS

We searched the following electronic bibliographic databases: the Cochrane Central Register of Controlled Trials (CENTRAL 2014, Issue 3), MEDLINE Ovid (1946 to April week 3, 2014), EMBASE Ovid (1980 to 2014 week 17) and PsycINFO Ovid (1987 to April week 4, 2014). We additionally handsearched the trial databases of the most relevant national, international and pharmaceutical company trial registers and drug-approving agencies for published, unpublished and ongoing controlled trials.

SELECTION CRITERIA

We included RCTs allocating adults (18 years or above) with any primary diagnosis of cancer and depression (including major depressive disorder, adjustment disorder, dysthymic disorder or depressive symptoms in the absence of a formal diagnosis) comparing antidepressants versus placebo, or antidepressants versus other antidepressants.

DATA COLLECTION AND ANALYSIS

Two review authors independently checked eligibility and extracted data using a form specifically designed for the aims of this review. The two authors compared the data extracted and then entered data into RevMan 5 with a double-entry procedure. Information extracted included study and participant characteristics, intervention details, outcome measures for each time point of interest, cost analysis and sponsorship by a drug company. We used the standard methodological procedures expected by The Cochrane Collaboration.

MAIN RESULTS

We retrieved a total of nine studies (861 participants), with seven studies contributing to the meta-analysis for the primary outcome. Four of these compared antidepressants and placebo, two compared two antidepressants and one-three armed study compared two antidepressants and a placebo arm. For the acute phase treatment response (6 to 12 weeks), we found very low quality evidence for the effect of antidepressants as a class on symptoms of depression compared with placebo when measured as a continuous outcome (standardised mean difference (SMD) -0.45, 95% confidence interval (CI) -1.01 to 0.11, five RCTs, 266 participants) or as a proportion of people who had depression (risk ratio (RR) 0.82, 95% CI 0.62 to 1.08, five RCTs, 417 participants). No trials reported data on the follow-up response (more than 12 weeks). In head-to-head comparisons we only retrieved data for selective serotonin reuptake inhibitors (SSRIs) versus tricyclic antidepressants, providing very low quality evidence for the difference between these two classes (SMD -0.08, 95% CI -0.34 to 0.18, three RCTs, 237 participants). No clear evidence of an effect of antidepressants versus either placebo or other antidepressants emerged from the analyses of the secondary efficacy outcomes (dichotomous outcome, response at 6 to 12 weeks, very low quality evidence). We found very low quality evidence for the effect of antidepressants as a class in terms of dropouts due to any cause compared with placebo (RR 0.87, 95% CI 0.49 to 1.53, six RCTs, 455 participants), as well as between SSRIs and tricyclic antidepressants (RR 0.83, 95% CI 0.53 to 1.30, three RCTs, 237 participants). We downgraded the quality of the evidence because the included studies were at an unclear or high risk of bias due to poor reporting, imprecision arising from small sample sizes and wide confidence intervals, and inconsistency due to statistical or clinical heterogeneity.

AUTHORS' CONCLUSIONS

Despite the impact of depression on people with cancer, available studies were very few and of low quality. This review found very low quality evidence for the effects of these drugs compared with placebo. On the basis of these results clear implications for practice cannot be made. The use of antidepressants in people with cancer should be considered on an individual basis and, considering the lack of head-to-head data, the choice of which agent should be prescribed may be based on the data on antidepressant efficacy in the general population of individuals with major depression, also taking into account that data on medically ill patients suggest a positive safety profile for the SSRIs. Large, simple, randomised, pragmatic trials comparing commonly used antidepressants versus placebo in people with cancer with depressive symptoms, with or without a formal diagnosis of a depressive disorder, are urgently needed to better inform clinical practice.

The promise of ketamine for treatment-resistant depression: current evidence and future directions

Major depressive disorder (MDD) is one of the most disabling diseases worldwide and is becoming a significant public health threat. Current treatments for MDD primarily consist of monoamine-targeting agents and have limited efficacy. However, the glutamate neurotransmitter system has recently come into focus as a promising alternative for novel antidepressant treatments. We review the current data on the glutamate NMDA receptor antagonist ketamine, which has been shown in clinical trials to act as a rapid antidepressant in MDD. We also examine ketamine efficacy on dimensions of psychopathology, including anhedonia, cognition, and suicidality, consistent with the NIMH Research Domain Criteria initiative. Other aspects of ketamine reviewed in this paper include safety and efficacy, different administration methods, and the risks of misuse of ketamine outside of medical settings. Finally, we conclude with a discussion of glutamatergic agents other than ketamine currently being tested as novel antidepressants.

A randomized controlled trial of intranasal ketamine in major depressive disorder

BACKGROUND

The N-methyl-D-aspartate glutamate receptor antagonist ketamine, delivered via an intravenous route, has shown rapid antidepressant effects in patients with treatment-resistant depression. The current study was designed to test the safety, tolerability, and efficacy of intranasal ketamine in patients with depression who had failed at least one prior antidepressant trial.

METHODS

In a randomized, double-blind, crossover study, 20 patients with major depression were randomly assigned, and 18 completed 2 treatment days with intranasal ketamine hydrochloride (50 mg) or saline solution. The primary efficacy outcome measure was change in depression severity 24 hours after ketamine or placebo, measured using the Montgomery-Åsberg Depression Rating Scale. Secondary outcomes included persistence of benefit, changes in self-reports of depression, changes in anxiety, and proportion of responders. Potential psychotomimetic, dissociative, hemodynamic, and general adverse effects associated with ketamine were also measured.

RESULTS

Patients showed significant improvement in depressive symptoms at 24 hours after ketamine compared to placebo (t = 4.39, p < .001; estimated mean Montgomery-Åsberg Depression Rating Scale score difference of 7.6 ± 3.7; 95% confidence interval, 3.9-11.3). Response criteria were met by 8 of 18 patients (44%) 24 hours after ketamine administration compared with 1 of 18 (6%) after placebo (p = .033). Intranasal ketamine was well tolerated with minimal psychotomimetic or dissociative effects and was not associated with clinically significant changes in hemodynamic parameters.

CONCLUSIONS

This study provides the first controlled evidence for the rapid antidepressant effects of intranasal ketamine. Treatment was associated with minimal adverse effects. If replicated, these findings may lead to novel approaches to the pharmacologic treatment of patients with major depression.

Effects of prefrontal cortex and hippocampal NMDA NR1-subunit deletion on complex cognitive and social behaviors

Glutamate N-methyl-D-aspartate receptors (NMDARs) in the medial prefrontal cortex (mPFC) and hippocampus may play an integral role in complex cognitive and social deficits associated with a number of psychiatric illnesses including autism, mood disorders, and schizophrenia. We used localized infusions of adeno-associated virus Cre-recombinase in adult, targeted knock-in mice with loxP sites flanking exons 11-22 of the NR1 gene to investigate the effects of chronic NMDAR dysfunction in the mPFC and CA3 hippocampus on cognitive and social behavior. A 5-choice serial reaction time task (5-CSRTT) was used to monitor aspects of cognitive function that included attention and response inhibition. Social behavior was assessed using Crowley׳s sociability and preference for social novelty protocol. Chronic NMDAR dysfunction localized to the anterior cingulate/prelimbic mPFC or dorsal CA3 hippocampus differentially affected the response inhibition and social interaction. mPFC NR1-deletion increased perseverative responding in the 5-CSRTT and enhanced preference for social novelty, whereas CA3 NR1-deletion increased premature responding in the 5-CSRTT and decreased social approach behavior. These findings suggest that mPFC and CA3 NMDARs play selective roles in regulating compulsive and impulsive behavior, respectively. Furthermore, these findings are consistent with emerging evidence that these behaviors are mediated by distinct, albeit overlapping, neural circuits. Our data also suggest that NMDARs in these regions uniquely contribute to the expression of normal social behavior. In this case, mPFC and CA3 NMDARs appear to inhibit and facilitate aspects of social interaction, respectively. The latter dissociation raises the possibility that distinct circuits contribute to the expression of social intrusiveness and impoverished social interaction.

Fluoxetine and all other SSRIs are 5-HT2B Agonists - Importance for their Therapeutic Effects

Fluoxetine and other serotonin-specific re-uptake inhibitors (SSRIs) are generally thought to owe their therapeutic potency to inhibition of the serotonin transporter (SERT). However, research in our laboratory showed that it affects, with relatively high affinity the 5-HT2B receptor in cultured astrocytes; this finding was confirmed by independent observations showing that fluoxetine loses its ability to elicit SSRI-like responses in behavioral assays in mice in which the 5-HT2B receptor was knocked-out genetically or inhibited pharmacologically. All clinically used SSRIs are approximately equipotent towards 5-HT2B receptors and exert their effect on cultured astrocytes at concentrations similar to those used clinically, a substantial difference from their effect on SERT. We have demonstrated up-regulation and editing of astrocytic genes for ADAR2, the kainate receptor GluK2, cPLA2 and the 5-HT2B receptor itself after chronic treatment of cultures, which do not express SERT and after treatment of mice (expressing SERT) for 2 weeks with fluoxetine, followed by isolation of astrocytic and neuronal cell fractionation. Affected genes were identical in both experimental paradigms. Fluoxetine treatment also altered Ca(2+) homeostatic cascades, in a specific way that differs from that seen after treatment with the anti-bipolar drugs carbamazepine, lithium, or valproic acid. All changes occurred after a lag period similar to what is seen for fluoxetine's clinical effects, and some of the genes were altered in the opposite direction by mild chronic inescapable stress, known to cause anhedonia, a component of major depression. In the anhedonic mice these changes were reversed by treatment with SSRIs.

Ketamine exposure in early development impairs specification of the primary germ cell layers

Preclinical and clinical evidence implicates N-methyl-d-aspartate receptor (NMDAr) signaling in early embryological development. However, the role of NMDAr signaling in early development has not been well studied. Here, we use a mouse embryonic stem cell model to perform a step-wise exploration of the effects of NMDAr signaling on early cell fate specification. We found that antagonism of the NMDAr impaired specification into the neuroectodermal and mesoendodermal cell lineages, with little or no effect on specification of the extraembryonic endoderm cell lineage. Consistent with these findings, exogenous NMDA promoted neuroectodermal differentiation. Finally, NMDAr antagonism modified expression of several key targets of TGF-β superfamily signaling, suggesting a mechanism for these findings. In summary, this study shows that NMDAr antagonism interferes with the normal developmental pathways of embryogenesis, and suggests that interference is most pronounced prior to neuroectodermal and mesoendodermal cell fate specification.

Pregnanolone Glutamate, a Novel Use-Dependent NMDA Receptor Inhibitor, Exerts Antidepressant-Like Properties in Animal Models

A number of studies demonstrated a rapid onset of an antidepressant effect of non-competitive N-methyl-d-aspartic acid receptor (NMDAR) antagonists. Nonetheless, its therapeutic potential is rather limited, due to a high coincidence of negative side-effects. Therefore, the challenge seems to be in the development of NMDAR antagonists displaying antidepressant properties, and at the same time maintaining regular physiological function of the NMDAR. Previous results demonstrated that naturally occurring neurosteroid 3α5β-pregnanolone sulfate shows pronounced inhibitory action by a use-dependent mechanism on the tonically active NMDAR. The aim of the present experiments is to find out whether the treatment with pregnanolone 3αC derivatives affects behavioral response to chronic and acute stress in an animal model of depression. Adult male mice were used throughout the study. Repeated social defeat and forced swimming tests were used as animal models of depression. The effect of the drugs on the locomotor/exploratory activity in the open-field test was also tested together with an effect on anxiety in the elevated plus maze. Results showed that pregnanolone glutamate (PG) did not induce hyperlocomotion, whereas both dizocilpine and ketamine significantly increased spontaneous locomotor activity in the open field. In the elevated plus maze, PG displayed anxiolytic-like properties. In forced swimming, PG prolonged time to the first floating. Acute treatment of PG disinhibited suppressed locomotor activity in the repeatedly defeated group-housed mice. Aggressive behavior of isolated mice was reduced after the chronic 30-day administration of PG. PG showed antidepressant-like and anxiolytic-like properties in the used tests, with minimal side-effects. Since PG combines GABA_A receptor potentiation and use-dependent NMDAR inhibition, synthetic derivatives of neuroactive steroids present a promising strategy for the treatment of mood disorders.

Highlights: -

3α5β-pregnanolone glutamate (PG) is a use-dependent antagonist of NMDA receptors.

-

We demonstrated that PG did not induce significant hyperlocomotion.

-

We showed that PG displayed anxiolytic-like and antidepressant-like properties.

Innovative drugs to treat depression: did animal models fail to be predictive or did clinical trials fail to detect effects?

Over recent decades, encouraging preclinical evidence using rodent models pointed to innovative pharmacological targets to treat major depressive disorder. However, subsequent clinical trials have failed to show convincing results. Two explanations for these rather disappointing results can be put forward, either animal models of psychiatric disorders have failed to predict the clinical effectiveness of treatments or clinical trials have failed to detect the effects of these new drugs. A careful analysis of the literature reveals that both statements are true. Indeed, in some cases, clinical efficacy has been predicted on the basis of inappropriate animal models, although the contrary is also true, as some clinical trials have not targeted the appropriate dose or clinical population. On the one hand, refinement of animal models requires using species that have better homological validity, designing models that rely on experimental manipulations inducing pathological features, and trying to model subtypes of depression. On the other hand, clinical research should consider carefully the results from preclinical studies, in order to study these compounds at the correct dose, in the appropriate psychiatric nosological entity or symptomatology, in relevant subpopulations of patients characterized by specific biomarkers. To achieve these goals, translational research has to strengthen the dialogue between basic and clinical science.

Disturbance of the glutamatergic system in mood disorders

The role of glutamatergic system in the neurobiology of mood disorders draws increasing attention, as disturbance of this system is consistently implicated in mood disorders including major depressive disorder and bipolar disorder. Thus, the glutamate hypothesis of mood disorders is expected to complement and improve the prevailing monoamine hypothesis, and may indicate novel therapeutic targets. Since the contribution of astrocytes is found to be crucial not only in the modulation of the glutamatergic system but also in the maintenance of brain energy metabolism, alterations in the astrocytic function and neuroenergetic environment are suggested as the potential neurobiological underpinnings of mood disorders. In the present review, the evidence of glutamatergic abnormalities in mood disorders based on postmortem and magnetic resonance spectroscopy (MRS) studies is presented, and disrupted energy metabolism involving astrocytic dysfunction is proposed as the underlying mechanism linking altered energy metabolism, perturbations in the glutamatergic system, and pathogenesis of mood disorders.

Signal Transduction in Astrocytes during Chronic or Acute Treatment with Drugs (SSRIs, Antibipolar Drugs, GABA-ergic Drugs, and Benzodiazepines) Ameliorating Mood Disorders

Chronic treatment with fluoxetine or other so-called serotonin-specific reuptake inhibitor antidepressants (SSRIs) or with a lithium salt “lithium”, carbamazepine, or valproic acid, the three classical antibipolar drugs, exerts a multitude of effects on astrocytes, which in turn modulate astrocyte-neuronal interactions and brain function. In the case of the SSRIs, they are to a large extent due to 5-HT_2B-mediated upregulation and editing of genes. These alterations induce alteration in effects of cPLA₂, GluK2, and the 5-HT_2B receptor, probably including increases in both glucose metabolism and glycogen turnover, which in combination have therapeutic effect on major depression. The ability of increased levels of extracellular K⁺ to increase [Ca²⁺]_i is increased as a sign of increased K⁺-induced excitability in astrocytes. Acute anxiolytic drug treatment with benzodiazepines or GABA_A receptor stimulation has similar glycogenolysis-enhancing effects. The antibipolar drugs induce intracellular alkalinization in astrocytes with lithium acting on one acid extruder and carbamazepine and valproic acid on a different acid extruder. They inhibit K⁺-induced and transmitter-induced increase of astrocytic [Ca²⁺]_i and thereby probably excitability. In several cases, they exert different changes in gene expression than SSRIs, determined both in cultured astrocytes and in freshly isolated astrocytes from drug-treated animals.

Neuroplasticity and the next wave of antidepressant strategies

Depression is a common chronic psychiatric disorder that is also often co-morbid with numerous neurological and immune diseases. Accumulating evidence indicates that disturbances of neuroplasticity occur with depression, including reductions of hippocampal neurogenesis and cortical synaptogenesis. Improper trophic support stemming from stressor-induced reductions of growth factors, most notably brain derived neurotrophic factor (BDNF), likely drives such aberrant neuroplasticity. We posit that psychological and immune stressors can interact upon a vulnerable genetic background to promote depression by disturbing BDNF and neuroplastic processes. Furthermore, the chronic and commonly relapsing nature of depression is suggested to stem from "faulty wiring" of emotional circuits driven by neuroplastic aberrations. The present review considers depression in such terms and attempts to integrate the available evidence indicating that the efficacy of current and "next wave" antidepressant treatments, whether used alone or in combination, is at least partially tied to their ability to modulate neuroplasticity. We particularly focus on the N-methyl-D-aspartate (NMDA) antagonist, ketamine, which already has well documented rapid antidepressant effects, and the trophic cytokine, erythropoietin (EPO), which we propose as a potential adjunctive antidepressant agent.