Maintenance of antidepressant and antisuicidal effects by D-cycloserine among patients with treatment-resistant depression who responded to low-dose ketamine infusion: a double-blind randomized placebo-control study

Clinical Trials Studying Suicide Risk Reduction: Who is Excluded From Participation

OBJECTIVE

The use of exclusion criteria in clinical trials can cause research participants to differ markedly from clinical populations, which negatively impacts generalizability of results. This study identifies and quantifies common and recurring exclusion criteria in clinical trials studying suicide risk reduction, and estimates their impact on eligibility among a clinical sample of adults in an emergency department with high suicide risk.

METHOD

Recent trials were identified by searching PubMed (terms suicide, efficacy, effectiveness, limited to clinical trials in prior 5 years). Common exclusion criteria were identified using Qualitative Content Analysis. A retrospective chart review examined a one-month sample of all adults receiving psychiatric evaluation in a large urban academic emergency department.

RESULTS

The search yielded 27 unique clinical trials studying suicide risk reduction as a primary or secondary outcome. After research fundamentals (e.g. informed consent, language fluency), the most common exclusion criteria involved psychosis (77.8%), cognitive problems (66.7%), and substance use (63.0%). In the clinical sample of adults with high suicide risk (N = 232), psychosis exclusions would exclude 53.0% of patients and substance use exclusions would exclude 67.2% of patients. Overall, 5.6% of emergency psychiatry patients would be eligible for clinical trials that use common exclusion criteria.

CONCLUSIONS

Recent clinical trials studying suicide risk reduction have low generalizability to emergency psychiatry patients with high suicide risk. Trials enrolling persons with psychosis and substance use in particular are needed to improve generalizability to this clinical population.

A systematic review of the incidence of medical serious adverse events in sub-anesthetic ketamine treatment of psychiatric disorders

BACKGROUND

Limited published data exists that collates serious adverse outcomes involving ketamine as a psychiatric intervention. This systematic review assesses the reported incidence of medical serious adverse events (MSAEs), including but not limited to cardiovascular events, in patients receiving sub-anesthetic doses of ketamine for psychiatric disorders to guide practitioners during treatment planning, risk-benefit analyses, and the informed consent process.

METHODS

Pubmed database was searched for clinical trials of sub-anesthetic ketamine for psychiatric disorders in non-pregnant adult patients. Of the 2275 articles identified, 93 met inclusion criteria, over half of which were published in 2017 or later. Only studies that reported adverse events were included, and the incidence of MSAEs was calculated.

RESULTS

Of the 3756 participants who received at least one sub-anesthetic dose of ketamine, four participants experienced a MSAE, resulting in an incidence of approximately 0.1 % of individuals. The four MSAEs resolved without reported sequelae. Eighty-three percent of studies reported screening for medical illness and exclusion of high-risk patients. There were no serious cardiac adverse events or deaths observed in any participants; however, most trials' study designs excluded those with high cardiovascular complication risk.

LIMITATIONS

Most studies were small, underpowered for detecting rare MSAEs, at potential high-risk of bias of non-report of MSAEs, and limited mostly to intranasal and intravenous routes.

CONCLUSIONS

Findings suggest that with basic medical screening there is a very low incidence of MSAEs including adverse cardiac or cerebrovascular events in individuals receiving sub-anesthetic ketamine for psychiatric disorders.

D-Cycloserine enhances the bidirectional range of NMDAR-dependent hippocampal synaptic plasticity

The partial N-methyl-D-aspartate receptor (NMDAR) agonist D-Cycloserine (DCS) has been evaluated for the treatment of a wide variety of psychiatric disorders, including dementia, schizophrenia, depression and for the augmentation of exposure-based psychotherapy. Most if not all of the potential psychiatric applications of DCS target an enhancement or restitution of cognitive functions, learning and memory. Their molecular correlate is long-term synaptic plasticity; and many forms of synaptic plasticity depend on the activation of NMDA receptors. Here, we comprehensively examined the modulation of different forms of synaptic plasticity in the hippocampus by DCS and its mechanism. We found that DCS positively modulates NMDAR-dependent forms of long-term synaptic plasticity (long-term synaptic potentiation, LTP, and long-term synaptic depression, LTD) in hippocampal brain slices of juvenile rats without affecting basal synaptic transmission. DCS binds to the D-serine/glycine binding site of the NMDAR. Pharmacological inhibition of this site prevented the induction of LTP, whereas agonism at the D-serine/glycine binding site augmented LTP and could functionally substitute for weak LTP induction paradigms. The most probable origin of endogenous D-serine are astrocytes, and its exocytosis is regulated by astrocytic metabotropic glutamate receptors (mGluR1). Functional eradication of astrocytes, inhibition of mGluR1 receptors and G-protein signaling in astrocytes adjacent to postsynaptic neurons prevented the induction of NMDAR-dependent forms of LTP and LTD. Our results support the enhancement of a bidirectional range of NMDAR-dependent hippocampal synaptic plasticity by DCS and D-serine-mediated gliotransmission. Therefore, the D-serine/glycine-binding site in NMDAR is a major target for psychopharmacological interventions targeting plasticity-related disorders.

The why, when, where, how, and so what of so-called rapidly acting antidepressants

Developing antidepressants that are not only more effective but are rapidly acting is the Holy Grail for psychiatry. We review multiple issues that arise in determining rapid responses in antidepressant trials. The current status of purportedly rapid acting agents is first reviewed. Then, a number of key questions/issues are addressed: Is there a unifying definition for rapid response across studies? Should rapid response criteria be based on required measurable effects on overall improvement? On specific symptoms such as psychomotor retardation, depressed mood, or anhedonia? In associated symptoms such as anxiety or insomnia? When should onset be considered rapid-by Day 3? Day7? Day 14? If there is a rapid response, for how long should the effects be maintained? Is maintenance of effect dependent on continuing the medication? Is rapid response associated with specific mechanisms of action? Do the mechanisms of action suggest possible risk for drug abuse? How important is rapid response really in an often chronic or recurrent depressive disorder? In which types of patients could rapid response be particularly important? What are the study design issues that need to be considered for assessing rapid response, including: selection of specific types of depressed patients, multiple doses of drug studied, designation of primary and secondary outcome measures, specific time points at which to determine efficacy, requirements for demonstrating durability, etc. A framework for approaching this complex area is developed for both researchers and clinicians.

Ketamine in neuropsychiatric disorders: an update

The discovery of ketamine as a rapid-acting antidepressant led to a new era in the development of neuropsychiatric therapeutics, one characterized by an antidepressant response that occurred within hours or days rather than weeks or months. Considerable clinical research supports the use of-or further research with-subanesthetic-dose ketamine and its (S)-enantiomer esketamine in multiple neuropsychiatric disorders including depression, bipolar disorder, anxiety spectrum disorders, substance use disorders, and eating disorders, as well as for the management of chronic pain. In addition, ketamine often effectively targets symptom domains associated with multiple disorders, such as anxiety, anhedonia, and suicidal ideation. This manuscript: 1) reviews the literature on the pharmacology and hypothesized mechanisms of subanesthetic-dose ketamine in clinical research; 2) describes similarities and differences in the mechanism of action and antidepressant efficacy between racemic ketamine, its (S) and (R) enantiomers, and its hydroxynorketamine (HNK) metabolite; 3) discusses the day-to-day use of ketamine in the clinical setting; 4) provides an overview of ketamine use in other psychiatric disorders and depression-related comorbidities (e.g., suicidal ideation); and 5) provides insights into the mechanisms of ketamine and therapeutic response gleaned from the study of other novel therapeutics and neuroimaging modalities.

Short-term ketamine use in bipolar depression: a review of the evidence for short-term treatment management

Bipolar depression constitutes a major problem in psychiatry. It correlates with high suicidality, treatment resistance, chronicity, and poor quality of life. Registered treatment for bipolar depression is limited and insufficient. There is an urgent need for implementing new therapeutic strategies. Intranasal ketamine's enantiomer-esketamine is a novel rapid-acting antidepressant with proven efficacy in treatment-resistant depression. Research on bipolar depression, although not as comprehensive, indicates that it may be a viable and safe substitute with minimal risk for mood polarity changes. Reports suggest that ketamine treatment in bipolar depression may reduce suicidal tendencies, decrease anhedonia, and alleviate anxiety. Ketamine's mood-stabilizing properties are also hypothesized. In this narrative review, we focus on ketamine use as an add-on to standard medication for the acute treatment of bipolar depression.

Ketamine and the neurobiology of depression: Toward next-generation rapid-acting antidepressant treatments

Ketamine has emerged as a transformative and mechanistically novel pharmacotherapy for depression. Its rapid onset of action, efficacy for treatment-resistant symptoms, and protection against relapse distinguish it from prior antidepressants. Its discovery emerged from a reconceptualization of the neurobiology of depression and, in turn, insights from the elaboration of its mechanisms of action inform studies of the pathophysiology of depression and related disorders. It has been 25 y since we first presented our ketamine findings in depression. Thus, it is timely for this review to consider what we have learned from studies of ketamine and to suggest future directions for the optimization of rapid-acting antidepressant treatment.

Synergistic psychedelic - NMDAR modulator treatment for neuropsychiatric disorders

Modern research data suggest a therapeutic role for serotonergic psychedelics in depression and other neuropsychiatric disorders, although psychotomimetic effects may limit their widespread utilization. Serotonergic psychedelics enhance neuroplasticity via serotonin 2 A receptors (5HT2AR) activation and complex serotonergic-glutamatergic interactions involving the ionotropic glutamate receptors, tropomyosin receptor kinase B (TrkB) and the mammalian target of rapamycin (mTOR). N-methyl-d-aspartate receptors (NMDAR) channel antagonists, i.e. ketamine, and glycine modulatory site full and partial agonists, i.e., D-serine (DSR) and D-cycloserine (DCS), share some of these mechanisms of action and have neuroplastic and antidepressant effects. Moreover, procognitive effects have been reported for DSR and DCS and 5HT2AR-NMDAR interactions modulate neuronal excitability in prefrontal cortex and represent a target for new antipsychotics. We hypothesize that the synchronous administration of a psychedelic and a NMDAR modulator may increase the therapeutic impact of each of the treatment components and allow for dose adjustments and improved safety. We propose to initially focus research on the acute concurrent administration of psilocybin and DSR or DCS in depression.

Courtes A, Jones G, Soares JC, Machado-Vieira R. Pharmacotherapies Targeting GABA-Glutamate Neurotransmission for Treatment-Resistant Depression

Treatment-resistant depression (TRD) is a term used to describe a particular type of major depressive disorder (MDD). There is no consensus about what defines TRD, with various studies describing between 1 and 4 failures of antidepressant therapies, with or without electroconvulsive therapy (ECT). That is why TRD is such a growing concern among clinicians and researchers, and it explains the necessity for investigating novel therapeutic targets beyond conventional monoamine pathways. An imbalance between two primary central nervous system (CNS) neurotransmitters, L-glutamate and γ-aminobutyric acid (GABA), has emerged as having a key role in the pathophysiology of TRD. In this review, we provide an evaluation and comprehensive review of investigational antidepressants targeting these two systems, accessing their levels of available evidence, mechanisms of action, and safety profiles. N-methyl-D-aspartate (NMDA) receptor antagonism has shown the most promise amongst the glutamatergic targets, with ketamine and esketamine (Spravato) robustly generating responses across trials. Two specific NMDA-glycine site modulators, D-cycloserine (DCS) and apimostinel, have also generated promising initial safety and efficacy profiles, warranting further investigation. Combination dextromethorphan-bupropion (AXS-05/Auvelity) displays a unique mechanism of action and demonstrated positive results in particular applicability in subpopulations with cognitive dysfunction. Currently, the most promising GABA modulators appear to be synthetic neurosteroid analogs with positive GABAA receptor modulation (such as brexanolone). Overall, advances in the last decade provide exciting perspectives for those who do not improve with conventional therapies. Of the compounds reviewed here, three are approved by the Food and Drug Administration (FDA): esketamine (Spravato) for TRD, Auvelity (dextromethorphan-bupropion) for major depressive disorder (MDD), and brexanolone (Zulresso) for post-partum depression (PPD). Notably, some concerns have arisen with esketamine and brexanolone, which will be detailed in this study.

Association of Neurofilament Light Chain With the Antidepressant Effects of Low-Dose Ketamine Infusion Among Patients With Treatment-Resistant Depression

BACKGROUND

The role of neurofilament light chain (NFL) in treatment-resistant depression (TRD) is unclear. Whether baseline NFL concentrations are associated with the antidepressant effects of low-dose ketamine infusion has not been determined.

METHODS

The NFL concentrations of 71 patients with TRD and 17 healthy controls were assessed. Patients with TRD were randomly administered a single infusion of 0.5 mg/kg ketamine, 0.2 mg/kg ketamine, or normal saline. Depressive symptoms were assessed before infusion and sequentially at postinfusion timepoints (after 240 minutes and after 2-7 and 14 days) using the Hamilton Depression Rating Scale (HDRS).

RESULTS

After adjustment for age, sex, and body mass index, patients with TRD were more likely to have higher concentrations of NFL than healthy controls (P < .001). A generalized estimating equation model with adjustments for infusion group, age, sex, body mass index, and baseline HDRS scores showed that baseline NFL concentrations were positively associated with subsequent HDRS scores following low-dose ketamine infusion (P = .038).

DISCUSSION

Higher concentrations of NFL were observed among patients with TRD compared with healthy controls. Baseline NFL concentrations may predict the antidepressant effects of low-dose ketamine infusion.

NRX-101 (D-cycloserine plus lurasidone) vs. lurasidone for the maintenance of initial stabilization after ketamine in patients with severe bipolar depression with acute suicidal ideation and behavior: a randomized prospective phase 2 trial

BACKGROUND

We tested the hypothesis that, after initial improvement with intravenous ketamine in patients with bipolar disorder (BD) with severe depression and acute suicidal thinking or behavior, a fixed-dose combination of oral D-cycloserine (DCS) and lurasidone (NRX-101) can maintain improvement more effectively than lurasidone alone.

METHODS

This was a multi-center, double-blind, twostage, parallel randomized trial. Adult BD patients with depression and suicidal ideation or behavior were infused with ketamine or saline (Stage 1); those who improved were randomized to a fixed-dose combination of DCS and lurasidone vs. lurasidone alone (Stage 2) to maintain the improvement achieved in Stage 1. Depression was measured by the Montgomery Åsberg Depression Rating Scale (MADRS), and suicidal thinking and behavior was measured by the Columbia Suicide Severity Rating Scale (C-SSRS); global improvement was measured by the clinical global severity scale (CGI-S).

CLINICALTRIALS

gov NCT02974010; Registered: November 22, 2016.

RESULTS

Thirty-seven patients were screened and 22 were enrolled, randomized, and treated. All 22 patients treated in Stage 1 (17 with ketamine and 5 with saline) were enrolled into Stage 2, and 11 completed the study. The fixed-dose combination of DCS and lurasidone was significantly more effective than lurasidone alone in maintaining improvement in depression (MADRS LMS Δ-7.7; p = 0.03) and reducing suicidal ideation, as measured by C-SSRS (Δ-1.5; p = 0.02) and by CGI-SS (Δ-2.9; p = 0.03), and with a non-statistically significant decrease in depressive relapse (0% vs. 40%; p = 0.07). This sequential treatment regimen did not cause any significant safety events and demonstrated improvements in patient-reported side effects.

CONCLUSIONS

Sequential treatment of a single infusion of ketamine followed by NRX-101 maintenance is a promising therapeutic approach for reducing depression and suicidal ideation in patients with bipolar depression who require hospitalization due to acute suicidal ideation and behavior. On the basis of these findings, Breakthrough Therapy Designation was awarded, and a Special Protocol Agreement was granted by the FDA for a registrational trial.

D-cycloserine is not susceptible to self-administration using an intravenous self-administration model in male ketamine-habituated Sprague-Dawley rats

OBJECTIVE

N-methyl-d-aspartate receptor (NMDAR) antagonist antidepressants have known potential for abuse liability. The aim of this study was to evaluate the abuse liability of D-cycloserine (DCS), using a self-administration paradigm in which DCS was tested for its efficacy in substituting for ketamine in ketamine-dependent rats.

METHODS

A standard intravenous self-administration study was conducted in male adult Sprague-Dawley rats to study compounds' abuse liability. Potential for self-administration was assessed in ketamine-habituated subjects. Subjects were trained to press a lever to obtain food, prior to connection of the lever to the intravenous drug administration apparatus. DCS was provided for self-infusion by test subjects at doses of 1.5, 5.0, and 15 mg/kg per lever press.

RESULTS

S-ketamine was seen to substitute for ketamine and to result in self-administration at the same frequency. DCS was not seen to result in self-administration at any of the test doses. The self-infusion behavior of DCS was similar to control (saline).

CONCLUSION

D-cycloserine, a partial agonist of the NMDAR glycine site, which has been shown to have antidepressant and anti-suicidal properties in clinical studies, has no apparent potential for abuse liability in a standard rodent self-administration model.

Antidepressant and anti-suicidal effects of ketamine in treatment-resistant depression associated with psychiatric and personality comorbidities: A double-blind randomized trial

OBJECTIVE

To evaluate the effects of ketamine treatment on depression and suicidal ideation in treatment resistant depression (TRD) and to determine whether they are influenced by other psychiatric and personality comorbidities.

METHODS

A randomized double-blind parallel-arm controlled study on 36 patients with TRD. Patients were divided into two treatment groups: ketamine (K group) and placebo (P group). Patients in the K and P groups received one infusion of medicine per week for two weeks. All participants were assessed using the Structured Interview for the Five-Factor Personality Model (SIFFM), Hamilton Depression Rating Scale (HDRS), Suicide Probability Scale (SPS), and Symptom Checklist 90 (SCL 90).

RESULTS

After treatment, there was a significant decrease in the total HDRS and SPS scores in the K group compared to the P group, but the magnitude of response was not influenced by the presence of other psychiatric symptoms. Regression model, only receive ketamine treatment was significant factor for improve suicide and depression scores.

LIMITATIONS

lack of data on other outcomes that are important to patients (e.g., quality of life, cognition) and need for a larger sample size.

CONCLUSIONS

Ketamine infusions in TRD reduce suicidal ideation and depression despite the presence other psychiatric and personality disorders.

Pharmacotherapies for Treatment-Resistant Depression: How Antipsychotics Fit in the Rapidly Evolving Therapeutic Landscape

One in three adults with major depressive disorder (MDD) do not experience clinically significant improvement after multiple sequential courses of antidepressants and have treatment-resistant depression (TRD). The presence of TRD contributes to the morbidity and excess mortality associated with MDD and has been linked to significantly increased health care expenses. In the absence of a consensus definition of TRD, this report takes a broad approach by considering inadequate response to one or more courses of antidepressants and focuses on atypical antipsychotics that are approved by the U.S. Food and Drug Administration for treatment of depression (aripiprazole, brexpiprazole, cariprazine, extended-release quetiapine, and olanzapine-fluoxetine combination). While multiple acute-phase studies have demonstrated the efficacy of these medications in improving depressive symptoms, clinically meaningful improvement (i.e., remission) remains limited, with significant concerns about side effects (including weight gain, metabolic dysfunction, extrapyramidal symptoms, and tardive dyskinesia), especially with long-term use. With the rapidly evolving landscape of antidepressant treatments over the past few years, which has witnessed approval of rapid-acting antidepressants (e.g., esketamine nasal spray and dextromethorphan-bupropion combination) and several more in the late-stage pipeline (e.g., zuranolone and psilocybin), it remains to be seen whether the use of atypical antipsychotics will go the way of the older and rarely prescribed antidepressants (such as tricyclics and monoamine oxidase inhibitors). Pragmatic clinical trials are needed to compare the effectiveness of atypical antipsychotics with TRD-specific pharmacotherapies and neuromodulation treatments and to identify the optimal sequencing of these varied approaches for patients with MDD. When using atypical antipsychotics, clinicians and patients are encouraged to use a shared decision-making approach by personalizing treatment selection based on anticipated side effects, tolerability, cost, and feasibility.

Glutamatergic neurotransmission: A potential pharmacotherapeutic target for the treatment of cognitive disorders

In the mammalian brain, glutamate is regarded to be the primary excitatory neurotransmitter due to its widespread distribution and wide range of metabolic functions. Glutamate plays key roles in regulating neurogenesis, synaptogenesis, neurite outgrowth, and neuron survival in the brain. Ionotropic and metabotropic glutamate receptors, neurotransmitters, neurotensin, neurosteroids, and others co-ordinately formulate a complex glutamatergic network in the brain that maintains optimal excitatory neurotransmission. Cognitive activities are potentially synchronized by the glutamatergic activities in the brain via restoring synaptic plasticity. Dysfunctional glutamate receptors and other glutamatergic components are responsible for the aberrant glutamatergic activity in the brain that cause cognitive impairments, loss of synaptic plasticity, and neuronal damage. Thus, controlling the brain's glutamatergic transmission and modifying glutamate receptor function could be a potential therapeutic strategy for cognitive disorders. Certain drugs that regulate glutamate receptor activities have shown therapeutic promise in improving cognitive functions in preclinical and clinical studies. However, several issues regarding precise functional information of glutamatergic activity are yet to be comprehensively understood. The present article discusses the scope of developing glutamatergic systems as prospective pharmacotherapeutic targets to treat cognitive disorders. Special attention has been given to recent developments, challenges, and future prospects.

Antidepressants in the post-ketamine Era: Pharmacological approaches targeting the glutamatergic system

The efficacy of currently available medications for depression is unsatisfactory, and that has spurred the development of novel antidepressants based on a hypothesis other than the monoamine hypothesis. Recent studies have revealed the importance of the glutamatergic system as a drug target for depression, and the validity of this hypothesis has been underpinned by the discovery of the antidepressant effects of ketamine, leading to the market launch of Spravato® nasal spray which delivers (S)-ketamine (esketamine). However, both ketamine and esketamine have unwanted adverse effects that hinder their routine use in daily practice. Extensive studies have elucidated the mechanisms underlying the antidepressant effects of ketamine, and that has encouraged numerous drug discovery activities to search for agents that retain a ketamine-like antidepressant profile but with lesser adverse effect liabilities. The discovery activities have included attempts to identify 1) the active substance(s) in the circulation after ketamine administration and 2) agents that act on the proposed mechanisms of action of ketamine. Clinical trials of agents discovered in the course of these activities are underway, and in 2022, AUVELITY™ (AXS-05; dextromethorphan with bupropion) was approved by the United States Food and Drug Administration. Drug development of post-ketamine agents should provide novel antidepressants that are safer, but as potent and rapidly acting as ketamine.

Targeting NMDA receptor signaling for therapeutic intervention in brain disorders

N-Methyl-d-aspartate (NMDA) receptor hyperfunction plays a key role in the pathological processes of depression and neurodegenerative diseases, whereas NMDA receptor hypofunction is implicated in schizophrenia. Considerable efforts have been made to target NMDA receptor function for the therapeutic intervention in those brain disorders. In this mini-review, we first discuss ion flux-dependent NMDA receptor signaling and ion flux-independent NMDA receptor signaling that result from structural rearrangement upon binding of endogenous agonists. Then, we review current strategies for exploring druggable targets of the NMDA receptor signaling and promising future directions, which are poised to result in new therapeutic agents for several brain disorders.

The effect of ketamine and D-cycloserine on the high frequency resting EEG spectrum in humans

RATIONALE

Preclinical studies indicate that high-frequency oscillations, above 100 Hz (HFO:100-170 Hz), are a potential translatable biomarker for pharmacological studies, with the rapid acting antidepressant ketamine increasing both gamma (40-100 Hz) and HFO.

OBJECTIVES

To assess the effect of the uncompetitive NMDA antagonist ketamine, and of D-cycloserine (DCS), which acts at the glycine site on NMDA receptors on HFO in humans.

METHODS

We carried out a partially double-blind, 4-way crossover study in 24 healthy male volunteers. Each participant received an oral tablet and an intravenous infusion on each of four study days. The oral treatment was either DCS (250 mg or 1000 mg) or placebo. The infusion contained 0.5 mg/kg ketamine or saline placebo. The four study conditions were therefore placebo-placebo, 250 mg DCS-placebo, 1000 mg DCS-placebo, or placebo-ketamine.

RESULTS

Compared with placebo, frontal midline HFO magnitude was increased by ketamine (p = 0.00014) and 1000 mg DCS (p = 0.013). Frontal gamma magnitude was also increased by both these treatments. However, at a midline parietal location, only HFO were increased by DCS, and not gamma, whilst ketamine increased both gamma and HFO at this location. Ketamine induced psychomimetic effects, as measured by the PSI scale, whereas DCS did not increase the total PSI score. The perceptual distortion subscale scores correlated with the posterior low gamma to frontal high beta ratio.

CONCLUSIONS

Our results suggest that, at high doses, a partial NMDA agonist (DCS) has similar effects on fast neural oscillations as an NMDA antagonist (ketamine). As HFO were induced without psychomimetic effects, they may prove a useful drug development target.

Antibiotics and mental health: The good, the bad and the ugly

Antibiotics are recognised as, on occasion, producing psychiatric side effects, most notably depression and anxiety. Apart from antimicrobial activity, antibiotics have multiple off-target effects. The brain-gut-microbiota axis has multiple sites for off-target activity, which may produce either positive or negative antibiotic effects. Here we review how antibiotics impact mental health by acting through the brain-gut-microbiota axis. Microbes in the gut influence brain function by acting through the vagus nerve or by altering the production of short-chain fatty acids or the amino acid tryptophan, the building block of serotonin. Not all antimicrobial actions of antibiotics have a negative impact. The first antidepressant discovered was actually an antibiotic: isoniazid is an antibacterial drug developed for treating tuberculosis. Minocycline, which enters the brain and mediates its effects through microglia, shows antidepressant activity. Some antibiotics bring about a significant decrease in gut microbial diversity, and this is viewed as a risk factor for depression. Other risk factors induced by antibiotics include altered gut barrier function, activation of the hypothalamic-pituitary-adrenal axis, reducing levels of brain-derived neurotrophic factor or oxytocin and alteration of vagal tone. Although most patients taking antibiotics do not suffer from an iatrogenic psychiatric disorder, some do. As clinicians, we need to keep this in mind. The development of new antibiotics is primarily focused on antibiotic resistance, but efforts should be made to reduce off-target brain-gut-microbiota effects resulting in mental health problems.

Efficacy of Adjunctive D-Cycloserine to Intermittent Theta-Burst Stimulation for Major Depressive Disorder: A Randomized Clinical Trial

Importance

The antidepressant effects of transcranial magnetic stimulation protocols for major depressive disorder (MDD) are thought to depend on synaptic plasticity. The theta-burst stimulation (TBS) protocol synaptic plasticity is known to be N-methyl-D-aspartate (NMDA)-receptor dependent, yet it is unknown whether enhancing NMDA-receptor signaling improves treatment outcomes in MDD.

Objective

To test whether low doses of the NMDA-receptor partial-agonist, D-cycloserine, would enhance intermittent TBS (iTBS) treatment outcomes in MDD.

Design, Setting, and Participants

This was a single-site 4-week, double-blind, placebo-controlled, randomized clinical trial conducted from November 6, 2019, to December 24, 2020, including 50 participants with MDD. Participants were recruited via advertisements and referral. Inclusion criteria were as follows: age 18 to 65 years with a primary diagnosis of MDD, a major depressive episode with score of 18 or more on the 17-item Hamilton Depression Rating Scale, a Young Mania Rating Scale score of 8 or less, and normal blood work (including complete blood cell count, electrolytes, liver function tests, and creatinine level).

Interventions

Participants were randomly assigned 1:1 to either iTBS plus placebo or iTBS plus D-cycloserine (100 mg) for the first 2 weeks followed by iTBS without an adjunct for weeks 3 and 4.

Main Outcomes and Measures

The primary outcome was change in depressive symptoms as measured by the Montgomery-Åsberg Depression Rating Scale (MADRS) at the conclusion of treatment. Secondary outcomes included clinical response, clinical remission, and Clinical Global Impression (CGI) scores.

Results

A total of 50 participants (mean [SD] age, 40.8 [13.4] years; 31 female [62%]) were randomly assigned to treatment groups: iTBS plus placebo (mean [SD] baseline score, 30.3 [4.2]) and iTBS plus D-cycloserine (mean [SD] baseline score, 30.4 [4.5]). The iTBS plus D-cycloserine group had greater improvements in MADRS scores compared with the iTBS plus placebo group (mean difference, -6.15; 95% CI, -2.43 to -9.88; Hedges g = 0.99; 95% CI, 0.34-1.62). Rates of clinical response were higher in the iTBS plus D-cycloserine group than in the iTBS plus placebo group (73.9% vs 29.3%), as were rates of clinical remission (39.1% vs 4.2%). This was reflected in lower CGI-severity ratings and greater CGI-improvement ratings. No serious adverse events occurred.

Conclusions and Relevance

Findings from this clinical trial indicate that adjunctive D-cycloserine may be a promising strategy for enhancing transcranial magnetic stimulation treatment outcomes in MDD using iTBS requiring further investigation.

Trial Registration

ClinicalTrials.gov Identifier: NCT03937596.

An open-label study evaluating the safety, behavioral, and electrophysiological outcomes of low-dose ketamine in children with ADNP syndrome

Activity-dependent neuroprotective protein (ADNP) syndrome is a rare genetic condition associated with intellectual disability and autism spectrum disorder. Preclinical evidence suggests that low-dose ketamine may induce expression of ADNP and that neuroprotective effects of ketamine may be mediated by ADNP. The goal of the proposed research was to evaluate the safety, tolerability, and behavioral outcomes of low-dose ketamine in children with ADNP syndrome. We also sought to explore the feasibility of using electrophysiological markers of auditory steady-state response and computerized eye tracking to assess biomarker sensitivity to treatment. This study utilized a single-dose (0.5 mg/kg), open-label design, with ketamine infused intravenously over 40 min. Ten children with ADNP syndrome ages 6 to 12 years were enrolled. Ketamine was generally well tolerated, and there were no serious adverse events. The most common adverse events were elation/silliness (50%), fatigue (40%), and increased aggression (40%). Using parent-report instruments to assess treatment effects, ketamine was associated with nominally significant improvement in a wide array of domains, including social behavior, attention deficit and hyperactivity, restricted and repetitive behaviors, and sensory sensitivities, a week after administration. Results derived from clinician-rated assessments aligned with findings from the parent reports. Overall, nominal improvement was evident based on the Clinical Global Impressions - Improvement scale, in addition to clinician-based scales reflecting key domains of social communication, attention deficit and hyperactivity, restricted and repetitive behaviors, speech, thinking, and learning, activities of daily living, and sensory sensitivities. Results also highlight the potential utility of electrophysiological measurement of auditory steady-state response and eye-tracking to index change with ketamine treatment. Findings are intended to be hypothesis generating and provide preliminary support for the safety and efficacy of ketamine in ADNP syndrome in addition to identifying useful endpoints for a ketamine clinical development program. However, results must be interpreted with caution given limitations of this study, most importantly the small sample size and absence of a placebo-control group.

Genetic variables of the glutamatergic system associated with treatment-resistant depression: A review of the literature

Depression is a common, recurrent mental disorder and one of the leading causes of disability and global burden of disease worldwide. Up to 15%-40% of cases do not respond to diverse pharmacological treatments and, thus, can be defined as treatment-resistant depression (TRD). The development of biomarkers predictive of drug response could guide us towards personalized and earlier treatment. Growing evidence points to the involvement of the glutamatergic system in the pathogenesis of TRD. Specifically, the N-methyl-D-aspartic acid receptor (NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), which are targeted by ketamine and esketamine, are proposed as promising pathways. A literature search was performed to identify studies on the genetics of the glutamatergic system in depression, focused on variables related to NMDARs and AMPARs. Our review highlights GRIN2B, which encodes the NR2B subunit of NMDAR, as a candidate gene in the pathogenesis of TRD. In addition, several studies have associated genes encoding AMPAR subunits with symptomatic severity and suicidal ideation. These genes encoding glutamatergic receptors could, therefore, be candidate genes for understanding the etiopathogenesis of TRD, as well as for understanding the pharmacodynamic mechanisms and response to ketamine and esketamine treatment.

Baihe Dihuang (Lilium Henryi Baker and Rehmannia Glutinosa) decoction attenuates somatostatin interneurons deficits in prefrontal cortex of depression via miRNA-144-3p mediated GABA synthesis and release

ETHNOPHARMACOLOGICAL RELEVANCE

Baihe Dihuang Decoction is a well-known traditional Chinese medicine prescription (Also known as Lilium Henryi Baker and Rehmannia Glutinosa Decoction, LBRD) composed of Lilium Henryi Baker bulb and raw juice from Rehmannia Glutinosa (Gaertn) DC with the curative efficacy of nourishing yin and clearing heat based on the Chinese herbal medicine theory. It has been used as routine medication in treating depression combined with conventional western medicine in China for years.

AIM OF THE STUDY

LBRD can attenuates GABAergic deficits in the medial prefrontal cortex (mPFC) of depression. This study aimed to investigate the mechanism of antidepressive properties of LBRD in the prefrontal GABAergic interneuron subtypes, including parvalbumin (PV), somatostatin (SST), vasoactive intestinal peptide (VIP)-positive neuron.

MATERIALS AND METHODS

In this project, chronic unpredicted mild stress paradigm was adopted to construct depression model. After treated with LBRD standard decoction and behaviors test, the level of GABA associated miRNA/mRNA and GABAergic subtype-specific markers were detected by qRT-PCR and Western blot. The lncRNAs/miRNAs/GABA regulatory axis was verified by luciferase reporter assay, RNA immunoprecipitation, RNA pull-down assay, and theses changes were measured in LBRD administration with the use of immunofluorescence staining and RNA-fluorescence in situ hybridization.

RESULTS

In the current study, we found that LBRD exhibited high efficacy based on the results of behavioral tests. Meanwhile, LBRD also improved the reduced GABA levels in depression by increasing the expression of lncRNA Neat1 and Malat1, as well as decreasing miRNA-144-3p and miRNA-15b-5p. Moreover, the level of Sst mRNA and protein that were harvested from the mPFC tissues of depression group was significantly lower than those in the control mice. While, these changes can be reverted by LBRD standard decoction administration. Whereas, neither chronic stress nor treatment can change the level of PV and VIP mRNAs and protein expression. In the SST-positive neuron of mPFC tissues, treatment with LBRD standard decoction resulted in the elevation of Gad-67, VGAT, GAT-3 and a reduction of miRNA-144-3p expression.

CONCLUSIONS

These findings suggested that LBRD antidepressant activities may be related to ameliorating the SST-positive neuron deficits via regulating the miRNA-144-3p mediated GABA synthesis and release.

Investigational Drugs for the Treatment of Depression (Part 2): Glutamatergic, Cholinergic, Sestrin Modulators, and Other Agents

Many investigational drugs with antidepressant activity are currently explored in different phases of clinical research, with indications such as major depressive disorder, treatment-resistant major depression, bipolar depression, post-partum depression, and late-life depression. Although the vast majority of the antidepressants in clinical use are based on the monoaminergic hypothesis of depression, recent data supported the launching on the market of two new, non-monoamine-modulating drugs. Esketamine for treatment-resistant major depression and brexanolone for post-partum depression are two exceptions from the monoaminergic model, although their use is still limited by high costs, unique way of administration (only intravenously for brexanolone), physicians’ reluctance to prescribe new drugs, and patients’ reticence to use them. Glutamatergic neurotransmission is explored based on the positive results obtained by intranasal esketamine, with subanesthetic intravenous doses of ketamine, and D-cycloserine, traxoprodil, MK-0657, AXS-05, AVP-786, combinations of cycloserine and lurasidone, or dextromethorphan and quinidine, explored as therapeutic options for mono- or bipolar depression. Sestrin modulators, cholinergic receptor modulators, or onabotulinumtoxinA have also been investigated for potential antidepressant activity. In conclusion, there is hope for new treatments in uni- and bipolar depression, as it became clear, after almost 7 decades of monoamine-modulating antidepressants, that new pathogenetic pathways should be targeted to increase the response rate in this population.

Efficacy and safety of racemic ketamine and esketamine for depression: a systematic review and meta-analysis

BACKGROUND

Racemic ketamine and esketamine have demonstrated rapid antidepressant effects. We aimed to review the efficacy and safety of racemic and esketamine for depression.

RESEARCH DESIGN AND METHODS

We conducted a PRISMA-guided review for relevant randomized controlled trials of racemic or esketamine for unipolar or bipolar major depression from database inception through 2021. We conducted random-effects meta-analyses using pooled rate ratios (RRs) and Cohen's standardized mean differences (d) with their 95% confidence intervals (CI).

RESULTS

We found 36 studies (2903 participants, 57% female, 45.1 +/- 7.0 years). Nine trials used esketamine, while the rest used racemic ketamine. The overall study quality was high. Treatment with any form of ketamine was associated with improved response (RR=2.14; 95% CI, 1.72-2.66; I2=65%), remission (RR=1.64; 95% CI, 1.33-2.02; I2=39%), and depression severity (d=-0.63; 95% CI, -0.80 to -0.45; I2=78%) against placebo. Overall, there was no association between treatment with any form of ketamine and retention in treatment (RR=1.00; 95% CI, 0.99-1.01; I2<1%), dropouts due to adverse events (RR=1.56; 95% CI, 1.00-2.45; I2<1%), or the overall number of adverse events reported per participant (OR=2.14; 95% CI, 0.82-5.60; I2=62%) against placebo.

CONCLUSIONS

Ketamine and esketamine are effective, safe, and acceptable treatments for individuals living with depression.

Low-dose ketamine infusion in treatment-resistant double depression: Revisiting the adjunctive ketamine study of Taiwanese patients with treatment-resistant depression

BACKGROUND

Whether a single low-dose ketamine infusion may have rapid antidepressant and antisuicidal effects in patients with treatment-resistant double depression remains unclear.

METHODS

This study enrolled 35 patients with treatment-resistant double depression, 12 of whom received 0.5 mg/kg ketamine, 11 received 0.2 mg/kg ketamine, and 12 received normal saline as a placebo. The patients were assessed using the 17-item Hamilton Rating Scale for Depression (HDRS) prior to the initiation of infusions, at 40 and 240 min post-infusion, and sequentially on Days 2-7 and on Day 14 after ketamine or placebo infusions.

RESULTS

A single 0.5 mg/kg ketamine infusion had rapid antidepressant (p = 0.031, measured by the HDRS) and antisuicidal (p = 0.033, measured by the HDRS item 3 scores) effects in patients with treatment-resistant double depression. However, 0.2 mg/kg ketamine was insufficient to exert rapid antidepressant and antisuicidal effects in this patient population with severe and chronic illness.

DISCUSSION

In this patient population, the commonly used dose of 0.5 mg/kg was sufficient. Additional studies are required to investigate whether repeated infusions of low-dose ketamine may also maintain antidepressant and antisuicidal effects in patients with treatment-resistant double depression.

Clinical effects of low-dose esketamine for anaesthesia induction in the elderly: A randomized controlled trial

WHAT IS KNOWN AND OBJECTIVE

Esketamine is an N-methyl-D-aspartic acid (NMDA) receptor antagonist, which has stronger sedative and analgesic effects and fewer adverse events than ketamine. The effects of low-dose esketamine on haemodynamics and postoperative quality of recovery in elderly patients have not been evaluated. To evaluate whether low-dose esketamine can be safely used for anaesthesia induction in the elderly.

METHODS

Eighty elderly patients were selected for unilateral total knee replacement under general anaesthesia from February 2021 to August 2021. Patients were randomly divided into two groups (n = 40): control group (C group) and esketamine group (K group). During induction of anaesthesia, the control group was intravenously injected with normal saline of equal volume, and the esketamine group was intravenously injected with 0.2-mg/kg esketamine. Both groups were induced by etomidate, sufentanil and rocuronium and maintained by combined intravenous and inhaled anaesthesia during operation.

MAIN OUTCOME MEASURES

HR, SBP, DBP, MAP and BIS values were recorded before induction of anaesthesia (T₀ ), immediately before endotracheal intubation (T₁ ), 1min(T₂ ) and 5min(T₃ ) after endotracheal intubation, surgical skin incision (T₄ ), 1min(T₅ ) and 5min(T₆ ) after surgical skin incision.

RESULTS

Compared with the C group, SBP, DBP, MAP, HR and BIS of the K group were significantly higher at T₁ -T₃ (p < 0.05). There were no significant differences in SBP, DBP, MAP, HR and BIS between the two groups at T₄ -T₆ (p > 0.05). Compared with T₀ , SBP, MAP and BIS values of the two groups at T₁ -T₆ were decreased (p < 0.05). DBP of the K group at T₂ was not significantly different from DBP at T₀ (p < 0.05), but DBP of the C group decreased from T₁ to T₆ (p < 0.05). Compared with T₀ , HR in both groups decreased at T₁ , T₃ , T₄ , T₅ and T₆ (p < 0.05). Compared with the C group, the incidence of cough in the K group was significantly lower (p < 0.05); There was no significant difference in the number of myoclonus during induction between the two groups (p > 0.05). Compared with the C group, the number of hypotension episodes in the K group during induction was much smaller (p < 0.05). There were no significant differences in the incidence of hypertension, bradycardia and tachycardia (p > 0.05). There were no significant differences in postoperative recovery quality and incidence of adverse events between the two groups (p > 0.05).

WHAT IS NEW AND CONCLUSION

Low-dose esketamine for anaesthesia induction in the elderly undergoing knee arthroplasty may better maintain the stability of haemodynamics and has no adverse effect on the quality of early recovery after operation.

Intrinsic Connectivity Networks of Glutamate-Mediated Antidepressant Response: A Neuroimaging Review

Conventional monoamine-based pharmacotherapy, considered the first-line treatment for major depressive disorder (MDD), has several challenges, including high rates of non-response. To address these challenges, preclinical and clinical studies have sought to characterize antidepressant response through monoamine-independent mechanisms. One striking example is glutamate, the brain's foremost excitatory neurotransmitter: since the 1990s, studies have consistently reported altered levels of glutamate in MDD, as well as antidepressant effects following molecular targeting of glutamatergic receptors. Therapeutically, this has led to advances in the discovery, testing, and clinical application of a wide array of glutamatergic agents, particularly ketamine. Notably, ketamine has been demonstrated to rapidly improve mood symptoms, unlike monoamine-based interventions, and the neurobiological basis behind this rapid antidepressant response is under active investigation. Advances in brain imaging techniques, including functional magnetic resonance imaging, magnetic resonance spectroscopy, and positron emission tomography, enable the identification of the brain network-based characteristics distinguishing rapid glutamatergic modulation from the effect of slow-acting conventional monoamine-based pharmacology. Here, we review brain imaging studies that examine brain connectivity features associated with rapid antidepressant response in MDD patients treated with glutamatergic pharmacotherapies in contrast with patients treated with slow-acting monoamine-based treatments. Trends in recent brain imaging literature suggest that the activity of brain regions is organized into coherent functionally distinct networks, termed intrinsic connectivity networks (ICNs). We provide an overview of major ICNs implicated in depression and explore how treatment response following glutamatergic modulation alters functional connectivity of limbic, cognitive, and executive nodes within ICNs, with well-characterized anti-anhedonic effects and the enhancement of "top-down" executive control. Alterations within and between the core ICNs could potentially exert downstream effects on the nodes within other brain networks of relevance to MDD that are structurally and functionally interconnected through glutamatergic synapses. Understanding similarities and differences in brain ICNs features underlying treatment response will positively impact the trajectory and outcomes for adults suffering from MDD and will facilitate the development of biomarkers to enable glutamate-based precision therapeutics.

Is one or two infusions better in the first week of low-dose ketamine treatment for medication-resistant depression? A post hoc pooled analysis of randomized placebo-controlled and open-label trials

BACKGROUND

Whether a second ketamine infusion in the first week improves the antidepressant, antisuicidal, and anti-inflammatory effects of the first low-dose ketamine infusion remains unclear.

METHODS

A total of 78 patients with medication-resistant depression were allocated to receive two ketamine infusions (n = 30; days 1 and 4), a single ketamine infusion (n = 24; only day 1), or normal saline placebo infusion (n = 24; only day 1). The Montgomery-Asberg Depression Scale (MADRS) and 17-item Hamilton Rating Scale for Depression (HDRS) were administered before and at 40 min, 240 min, day 2, day 4, day 5, and day 7 after infusion. Serum concentrations of interleukin (IL)-2 and tumor necrosis factor (TNF)-α were assessed.

RESULTS

Two ketamine infusions improved the overall depressive symptoms (p < 0.001) and melancholic symptoms (p < 0.001) than a single ketamine or placebo infusion. The antisuicidal effect did not differ between the ketamine treatment groups. Two ketamine infusions increased TNF-α levels compared with a single ketamine or placebo infusion (p = 0.015). A single ketamine infusion improved the TNF-α-to-IL-2 ratio, an index of average anti-inflammatory effect, than two ketamine infusions or a single placebo infusion (p = 0.027).

DISCUSSION

Repeated low-dose ketamine infusions improved the antidepressant effect, but not the antisuicidal effect, compared with a single infusion. However, repeated ketamine infusions may exert a lesser anti-inflammatory effect than a single infusion.

The rapid anti-suicidal ideation effect of ketamine: A systematic review

In many countries suicide rates have been trending upwards for close to twenty years-presenting a public health crisis. Most suicide attempts and deaths are associated with psychiatric illness, usually a depressive disorder. Subanesthetic ketamine is the only FDA-approved antidepressant that works in hours not weeks-thus potentially transforming treatment of suicidal patients. We reviewed all randomized controlled trials of the effect of ketamine on suicidal ideation to determine if ketamine rapidly reduces suicidal ideation [SI] in depressed patients and how long the benefit persists after one dose and if the route of administration or dose affects the outcome. A systematic review was conducted as per PRISMA [preferred reporting items for systematic reviews and meta-analyses] criteria. PubMed search inclusive of "ketamine" and "suicide" yielded 358 results. Papers (N = 354) were then read by at least two authors, identifying 12 meeting eligibility requirements and eleven RCTs examining whether ketamine treatment ameliorated SI. Four of five RCTs examined racemic ketamine (0.5 mg/kg) given intravenously and found an advantage for ketamine over control for rapid reduction in SI in acutely depressed patients. Two studies examined intranasal esketamine in depressed suicidal patients and found no advantage over saline. One study examined outcome six weeks after a single intravenous dose of ketamine and found benefit for SI sustained relative to 24 h post-dose. Further research is warranted into: optimal dosing strategy, including number and frequency; and long-term efficacy and safety. Ultimately, it remains to be shown that ketamine's benefit for SI translates into prevention of suicidal behavior.

Age affects temporal response, but not durability, to serial ketamine infusions for treatment refractory depression

RATIONALE

Ketamine is a novel, rapid-acting antidepressant for treatment refractory depression (TRD); however, clinical durability is poor and treatment response trajectories vary. Little is known about which patient characteristics predict faster or more durable ketamine responses. Ketamine's antidepressant mechanism may involve modulation of glutamatergic signaling and long-term potentiation (LTP); these neuroplasticity pathways are also attenuated with older age.

OBJECTIVE

A retrospective analysis examining the impact of patient age on the speed and durability of ketamine's antidepressant effects in 49 veterans receiving serial intravenous ketamine infusions for TRD.

METHOD

The relationship between age and percent change in Beck Depression Inventory (BDI-II) scores was compared across six serial ketamine infusions (twice-weekly for 3 weeks) using a linear-mixed model.

RESULTS

A significant Age-X-Infusion number interaction (F = 3.01, p = .0274) indicated that the relationship between age and treatment response depended on infusion number. Follow-up tests showed that younger age significantly predicted greater clinical improvement at infusion #4 (t = 3.02, p = .004); this relationship was attenuated at infusion #5 (t = 1.95, p = .057) and was absent at infusion #6. Age was not a significant predictor of treatment durability, defined as percent change in BDI-II 3 weeks following infusion #6.

CONCLUSIONS

These data preliminarily suggest that younger age is associated with a faster response over six serial ketamine infusions; by infusion #6 and subsequent weeks of clinical follow-up, age no longer predicts ketamine's antidepressant activity. Age may mediate the speed but not the durability or total efficacy of ketamine treatment, suggesting that dissociable mechanisms may underlie differing aspects of ketamine's antidepressant activity.

Ventromedial prefrontal cortex/anterior cingulate cortex Glx, glutamate, and GABA levels in medication-free major depressive disorder

Glutamate (Glu) and gamma-aminobutyric acid (GABA) are implicated in the pathophysiology of major depressive disorder (MDD). GABA levels or GABAergic interneuron numbers are generally low in MDD, potentially disinhibiting Glu release. It is unclear whether Glu release or turnover is increased in depression. Conversely, a meta-analysis of prefrontal proton magnetic resonance spectroscopy (¹H MRS) studies in MDD finds low Glx (combination of glutamate and glutamine) in medicated MDD. We hypothesize that elevated Glx or Glu may be a marker of more severe, untreated MDD. We examined ventromedial prefrontal cortex/anterior cingulate cortex (vmPFC/ACC) Glx and glutamate levels using ¹H MRS in 34 medication-free, symptomatic, chronically ill MDD patients and 32 healthy volunteers, and GABA levels in a subsample. Elevated Glx and Glu were observed in MDD compared with healthy volunteers, with the highest levels seen in males with MDD. vmPFC/ACC GABA was low in MDD. Higher Glx levels correlated with more severe depression and lower GABA. MDD severity and diagnosis were both linked to higher Glx in vmPFC/ACC. Low GABA in a subset of these patients is consistent with our hypothesized model of low GABA leading to glutamate disinhibition in MDD. This finding and model are consistent with our previously reported findings that the NMDAR-antagonist antidepressant effect is proportional to the reduction of vmPFC/ACC Glx or Glu levels.

Efficacy of ketamine for major depressive episodes at 2, 4, and 6-weeks post-treatment: A meta-analysis

RATIONALE

Major depressive episodes are severe mood episodes which occur both in major depressive disorder and bipolar I and II disorder. Major depressive episodes are characterized by debilitating symptoms that often persist and interfere with typical daily functioning. Various treatments exist for major depressive episodes; however, most primary pharmacologic treatments may take weeks to months to provide relief from depressive symptoms. Ketamine is a demonstrated treatment for major depressive episodes, as relief from depressive symptoms can occur rapidly following treatment.

OBJECTIVES

Prior meta-analyses have been conducted to analyze the effectiveness of ketamine for the treatment of major depressive episodes, but at the time of this writing, no meta-analysis had been conducted to observe ketamine treatment efficacy beyond 2 weeks.

METHODS

The present meta-analysis evaluated the efficacy of ketamine for the treatment of major depressive episodes; observations of depressive episode severity were analyzed at 2, 4, and 6-weeks post-treatment.

RESULTS

The present meta-analysis observed large effects at 2 weeks (g = -1.28), 4 weeks, (g = -1.28), and 6 weeks (g = -1.36) post-treatment.

CONCLUSIONS

The results from the present meta-analysis indicate that ketamine can be an effective pharmacologic intervention for major depressive episodes, with treatment effects lasting up to 6 weeks post-ketamine administration, which has many positive implications for treatment.

Relationship of Brain Glutamate Response to D-Cycloserine and Lurasidone to Antidepressant Response in Bipolar Depression: A Pilot Study

N-methyl-D-aspartate glutamate-receptor (NMDAR) antagonists such as ketamine have demonstrated efficacy in both major depressive disorder (MDD) and bipolar disorder depression (BP-D). We have previously reported that reduction in Glx (glutamate + glutamine) in the ventromedial prefrontal cortex/anterior cingulate cortex (vmPFC/ACC), measured by proton magnetic resonance spectroscopy (1H MRS) at 3T during a ketamine infusion, mediates the relationship of ketamine dose and blood level to improvement in depression. In the present study, we assessed the impact of D-cycloserine (DCS), an oral NMDAR antagonist combined with lurasidone in BP-D on both glutamate and Glx. Subjects with DSM-V BP-D-I/II and a Montgomery-Asberg Depression Rating Scale (MADRS) score>17, underwent up to three 1H MRS scans. During Scan 1, subjects were randomized to receive double-blind lurasidone 66 mg or placebo. During Scan 2, all subjects received single-blind DCS 950 mg + lurasidone 66 mg, followed by 4 weeks of open label phase of DCS+lurasidone and an optional Scan 3. Five subjects received lurasidone alone and three subjects received placebo for Scan 1. Six subjects received DCS+lurasidone during Scan 2. There was no significant baseline or between treatment-group differences in acute depression improvement or glutamate response. In Scan 2, after a dose of DCS+lurasidone, peak change in glutamate correlated negatively with improvement from baseline MADRS (r = -0.83, p = 0.04). There were no unexpected adverse events. These preliminary pilot results require replication but provide further support for a link between antidepressant effect and a decrease in glutamate by the NMDAR antagonist class of antidepressants.

Strategies to Prolong Ketamine's Efficacy in Adults with Treatment-Resistant Depression

INTRODUCTION

Ketamine treatment is capable of significant and rapid symptom improvement in adults with treatment-resistant depression (TRD). A limitation of ketamine treatment in TRD is the relatively short duration of time to relapse (e.g., median 2-4 weeks). The objective of the systematic review herein is to identify strategies capable of prolonging the acute efficacy of ketamine in adults with TRD.

METHODS

PubMed/MEDLINE databases were searched from inception to December 2020 for clinical studies written in English using the following key terms: ketamine, prolong, and depression. A total of 454 articles were identified from the literature search which included all clinical studies regarding prolonging the antidepressant effects of ketamine. Twenty-two articles were included: ten randomized controlled trials (RCTs), eight prospective open-label trials, one retrospective chart review, and three case reports. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used for data extraction. The primary outcome was prolonged effect, defined as statistically significant antidepressant effects following acute ketamine treatment.

RESULTS

A total of 454 articles were identified, and 22 articles were included. Different treatment modalites including pharmacological interventions, manualized-based psychotherapies, electroconvulsive therapy, transcranial magnetic stimulation, and intravenous monotherapy were examined to determine their impact on the prolongation of antidepressant effects following acute ketamine treatment. No treatment modality, other than repeat-dose IV ketamine, has demonstrated ability to significantly prolong the acute efficacy of IV ketamine in TRD.

CONCLUSION

Hitherto, available open-label data and controlled trial data support repeat administration of IV ketamine as an effective strategy to prolong the efficacy of ketamine's antidepressant effects (although not the focus of the study herein, maintenance repeat-dose esketamine treatment is proven effective in esketamine responders). There is a need to identify multimodality strategies that are safe and capable of prolonging the efficacy of ketamine in adults with TRD.

Treatment-resistant bipolar depression: concepts and challenges for novel interventions

Treatment-resistant bipolar depression (TRBD) has been reported in about one-quarter of patients with bipolar disorders, and few interventions have shown clear and established effectiveness. We conducted a narrative review of the published medical literature to identify papers discussing treatment-resistant depression concepts and novel interventions for bipolar depression that focus on TRBD. We searched for potentially relevant English-language articles published in the last decade. Selected articles (based on the title and abstract) were retrieved for a more detailed evaluation. A number of promising new interventions, both pharmacological and non-pharmacological, are being investigated for TRBD treatment, including ketamine, lurasidone, D-cycloserine, pioglitazone, N-acetylcysteine, angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, cyclooxygenase 2 inhibitors, magnetic seizure therapy, intermittent theta-burst stimulation, deep transcranial magnetic stimulation, vagus nerve stimulation therapy, and deep brain stimulation. Although there is no consensus about the concept of TRBD, better clarification of the neurobiology associated with treatment non-response could help identify novel strategies. More research is warranted, mainly focusing on personalizing current treatments to optimize response and remission rates.

Ketamine for Bipolar Depression: A Systematic Review

BACKGROUND

Ketamine appears to have a therapeutic role in certain mental disorders, most notably unipolar major depressive disorder. However, its efficacy in bipolar depression is less clear. This study aimed to assess the efficacy and tolerability of ketamine for bipolar depression.

METHODS

We conducted a systematic review of experimental studies using ketamine for the treatment of bipolar depression. We searched PubMed, MEDLINE, Embase, PsycINFO, and the Cochrane Central Register for relevant studies published since each database's inception. We synthesized evidence regarding efficacy (improvement in depression rating scores) and tolerability (adverse events, dissociation, dropouts) across studies.

RESULTS

We identified 6 studies, with 135 participants (53% female; 44.7 years; standard deviation, 11.7 years). All studies used 0.5 mg/kg of add-on intravenous racemic ketamine, with the number of doses ranging from 1 to 6; all participants continued a mood-stabilizing agent. The overall proportion achieving a response (defined as those having a reduction in their baseline depression severity of at least 50%) was 61% for those receiving ketamine and 5% for those receiving a placebo. The overall response rates varied from 52% to 80% across studies. Ketamine was reasonably well tolerated; however, 2 participants (1 receiving ketamine and 1 receiving placebo) developed manic symptoms. Some participants developed significant dissociative symptoms at the 40-minute mark following ketamine infusion in 2 trials.

CONCLUSIONS

There is some preliminary evidence supporting use of intravenous racemic ketamine to treat adults with bipolar depression. There is a need for additional studies exploring longer-term outcomes and alterative formulations of ketamine.

Targeting the dysfunction of glutamate receptors for the development of novel antidepressants

Increasing evidence indicates that dysfunction of glutamate receptors is involved in the pathophysiology of major depressive disorder (MDD). Although accumulating efforts have been made to elucidate the applications and mechanisms underlying antidepressant-like effects of ketamine, a non-selective antagonist of N-methyl-d-aspartate receptor (NMDAR), the role of specific glutamate receptor subunit in regulating depression is not completely clear. The current review aims to discuss the relationships between glutamate receptor subunits and depressive-like behaviors. Research literatures were searched from inception to July 2020. We summarized the alterations of glutamate receptor subunits in patients with MDD and animal models of depression. Animal behaviors in response to dysfunction of glutamate receptor subunits were also surveyed. To fully understand mechanisms underlying antidepressant-like effects of modulators targeting glutamate receptors, we discussed effects of each glutamate receptor subunit on serotonin system, synaptic plasticity, neurogenesis and neuroinflammation. Finally, we collected most recent clinical applications of glutamate receptor modulators and pointed out the limitations of these candidates in the treatment of MDD.

Suicidality Associated With Deep Brain Stimulation in Extrapyramidal Diseases: A Critical Review and Hypotheses on Neuroanatomical and Neuroimmune Mechanisms

Deep brain stimulation (DBS) is a very well-established and effective treatment for patients with extrapyramidal diseases. Despite its generally favorable clinical efficacy, some undesirable outcomes associated with DBS have been reported. Among such complications are incidences of suicidal ideation (SI) and behavior (SB) in patients undergoing this neurosurgical procedure. However, causal associations between DBS and increased suicide risk are not demonstrated and they constitute a debated issue. In light of these observations, the main objective of this work is to provide a comprehensive and unbiased overview of the literature on suicide risk in patients who received subthalamic nucleus (STN) and internal part of globus pallidum (GPi) DBS treatment. Additionally, putative mechanisms that might be involved in the development of SI and SB in these patients as well as caveats associated with these hypotheses are introduced. Finally, we briefly propose some clinical implications, including therapeutic strategies addressing these potential disease mechanisms. While a mechanistic connection between DBS and suicidality remains a controversial topic that requires further investigation, it is of critical importance to consider suicide risk as an integral component of candidate selection and post-operative care in DBS.

Intracellular Signaling Cascades in Bipolar Disorder

Bipolar spectrum disorders carry a significant public health burden. Disproportionately high rates of suicide, incarceration, and comorbid medical conditions necessitate an extraordinary focus on understanding the intricacies of this disease. Elucidating granular, intracellular details seems to be a necessary preamble to advancing promising therapeutic opportunities. In this chapter, we review a wide range of intracellular mechanisms including mitochondrial energetics, calcium signaling, neuroinflammation, the microbiome, neurotransmitter metabolism, glycogen synthase kinase 3-beta (GSK3β), protein kinase C (PKC) and diacylglycerol (DAG), and neurotrophins (especially BDNF), as well as the glutamatergic, dopaminergic, purinergic, and neurohormonal systems. Owing to the relative lack of understanding and effective therapeutic options compared to the rest of the spectrum, special attention is paid in the chapter to the latest developments in bipolar depression. Likewise, from a therapeutic standpoint, special attention should be paid to the pervasive mechanistic actions of lithium as a means of amalgamating numerous, disparate cascades into a digestible cognitive topology.

Advances in the psychopharmacotherapy of bipolar disorder type I

INTRODUCTION

Research into the pharmacologic management of bipolar type I illness continues to progress.

AREAS COVERED

Randomized clinical trials performed with type I bipolar disorder in the years 2015 to August 2020 are reviewed. There are new indications for the use of cariprazine, for bipolar mania and depression, and a long-acting injectable formulation of aripiprazole has also been approved for relapse prevention in bipolar illness. Most of the randomized clinical trials are effectiveness studies.

EXPERT OPINION

Over the 20 years from 1997 through 2016, the use of lithium and other mood stabilizers has declined by 50%, while the use of both second-generation antipsychotics (SGAs) and antidepressants has increased considerably. Over the same time period (1990-2017), disability-adjusted life years (DALYs) increased by 54.4%, from 6.02 million in 1990 to 9.29 million in 2017 which is greater than the 47.74% increase in incidence of the disease, suggesting that the changes in prescribing patterns have not been helpful for our patients. Furthermore, recent effectiveness studies continue to confirm the superiority of lithium and other mood stabilizers in the management of bipolar illness for both psychiatric and medical outcomes, reaffirming their role as foundational treatments in the management of type I bipolar disorder. Clinicians need to reassess their prescribing habits.

New agents and perspectives in the pharmacological treatment of major depressive disorder

Despite the important advances in the understanding of the pathophysiology of MDD, a large proportion of depressed patients do not respond well to currently available pharmacological agents. The present review focuses on new targets and future directions in the pharmacological treatment of MDD. Novel agents and their efficacy in the treatment of depression are discussed, with a focus on the respectively target pathophysiological pathways and the level of available evidence. Although it is expected that classic antidepressants will remain the cornerstone of MDD treatment, at least for the near future, a large number of novel compounds is currently under investigation as for their efficacy in the treatment of MDD, many of which with promising results.

Using classification and regression tree modelling to investigate treatment response to a single low-dose ketamine infusion: Post hoc pooled analyses of randomized placebo-controlled and open-label trials

BACKGROUND

Evidence suggests that clinical markers, such as comorbid anxiety, body weight, and others can assist in predicting response to low-dose ketamine infusion in treatment resistant depression patients. However, whether a composite of clinical markers may improve the predicted probability of response is uncertain.

METHODS

The current study investigated the results of our previous randomized placebo-controlled and open-label trials in which 73 patients with treatment-resistant depression (TRD) received a single ketamine infusion of 0.5 mg/kg. Clinical characteristics at baseline, including depression severity, duration of the current episode, obesity, comorbidity of anxiety disorder, and current suicide risk, were assessed as potential predictors in a classification and regression tree model for treatment response to ketamine infusion.

RESULTS

The predicted probability of a composite of age at disease onset, depression severity, duration of current episode, and obesity/overweight was significantly greater (area under curve = .736, p = .001) than that of any one marker (all p > .05). The most powerful predictors of treatment response to ketamine infusion were younger age at disease onset and obesity/overweight. The strongest predictors of treatment nonresponse were longer duration of the current episode and greater depression severity at baseline.

DISCUSSION

Depression severity, duration of the current episode, obesity, and age at disease onset may predict treatment response versus nonresponse to low-dose ketamine infusion. However, whether our predicted probability for a single infusion may be applied to repeated infusions would require further investigation.

CLINICAL TRIAL REGISTRATION

UMIN Clinical Trials Registry (UMIN000023581 and UMIN000016985).

Increased use of ketamine for the treatment of depression: Benefits and concerns

Ketamine was initially used as an anesthetic which could induce cognitive impairment and psychomimetic effects. In initial randomized controlled trials (RCTs) that mostly included a small sample size and were investigator-initiated, ketamine reportedly exerted antidepressant effects 1 to 2 h after a single intravenous infusion in patients with major depressive episodes, particularly treatment-resistant depression (TRD). Interest in ketamine was reported in systematic reviews and meta-analyses, however, many were primarily focused on the rapid onset of ketamine effects without equal attention to its safety and tolerability. Furthermore, several meta-analyses were based on many duplicated RCTs. The initial trends emphasized the clinical utility of ketamine as an antidepressant. The development of esketamine nasal spray by a pharmaceutical company led to an RCT with a large sample size and segmented therapeutic strategy, which provided results applicable to patients with TRD in the real-world clinical environment. However, possible effects of ketamine on cognitive function have not yet been investigated in RCTs. In numerous studies, chronic, recreational use of ketamine reportedly substantially impaired cognitive function in most domains. Although results of several human and animal studies indicated the therapeutic use of ketamine for treatment of depression did not induce cognitive impairment, this issue should be further investigated. Based on the current knowledge about ketamine, future antidepressants are expected to be glutamatergic drugs without ketamine-like adverse events (e.g., psychomimetic symptoms and cognitive impairment), but having only ketamine-like therapeutic properties (e.g., rapid antidepressants effects without time lag).

Glutamatergic dysregulation in mood disorders: opportunities for the discovery of novel drug targets

INTRODUCTION

Recently, a considerable attention has been paid to glutamatergic conception of mood disorders. The development of new treatment strategies targeted at glutamate provides new opportunities for the treatment of mood disorders. It is expected that these novel therapeutic options will provide a fast and sustained antidepressant effect and will be better tolerated by patients than the currently available antidepressants.

AREAS COVERED

This paper discusses glutamatergic abnormalities in mood disorders and reviews novel glutamate-based drugs developed for the treatment of these disorders. We have searched the PubMed and EMBASE databases, presented the results of relevant clinical studies and also describe novel glutamate-based agents that are under investigation.

EXPERT OPINION

The glutamatergic system plays many important roles in energy metabolism of the brain and neurotransmission; therefore, any attempt to identify novel therapeutic targets within this system seems justified. The effective development of new glutamate-based drugs requires, among others, a more in-depth exploration and understanding of the anatomy, function, and localization of different glutamatergic receptors in the brain. In our opinion, novel glutamate-based antidepressants will find application in the treatment of mood disorders and present an option will be widely used in clinical practice in the future.

Next-Step Treatment Considerations for Patients With Treatment-Resistant Depression That Responds to Low-Dose Intravenous Ketamine

Numerous short-term randomized trials support the acute-phase efficacy of low-dose intravenous (IV) ketamine for patients with treatment-resistant unipolar or bipolar depression. Ketamine's antidepressive effects generally have limited duration, highlighting the need for maintenance treatment after an acute-phase response. It is increasingly likely that psychiatrists will be called upon to manage the care of patients with treatment-resistant unipolar or bipolar depression who have responded acutely to ketamine and to recommend or initiate next-step treatments. However, there is a paucity of controlled evidence to guide best practices for managing treatment of patients with treatment-resistant unipolar or bipolar depression who have had a positive initial response to ketamine. This article reviews the available evidence supporting specific strategies for extending and maintaining acute antidepressive responses to low-dose IV ketamine in patients with treatment-resistant unipolar or bipolar depression and provides some preliminary considerations for clinical practice.

A Randomized Trial of the N-Methyl-d-Aspartate Receptor Glycine Site Antagonist Prodrug 4-Chlorokynurenine in Treatment-Resistant Depression

BACKGROUND

Ketamine has rapid-acting antidepressant effects but is associated with psychotomimetic and other adverse effects. A 7-chlorokynurenic acid is a potent and specific glycine site N-methyl-d-aspartate receptor antagonist but crosses the blood-brain barrier inefficiently. Its prodrug, L-4-chlorokynurenine (4-Cl-KYN), exerts acute and sustained antidepressant-like effects in rodents and has no reported psychotomimetic effects in either rodents or healthy volunteers. This study examined whether 4-Cl-KYN has rapid antidepressant effects in individuals with treatment-resistant depression.

METHODS

After a 2-week drug-free period, 19 participants with treatment-resistant depression were randomized to receive daily oral doses of 4-Cl-KYN monotherapy (1080 mg/d for 7 days, then 1440 mg/d for 7 days) or placebo for 14 days in a randomized, placebo-controlled, double-blind, crossover manner. The primary outcome measure was the Hamilton Depression Rating Scale score, assessed at several time points over a 2-week period; secondary outcome measures included additional rating scale scores. Pharmacokinetic measures of 7-chlorokynurenic acid and 4-Cl-KYN and pharmacodynamic assessments were obtained longitudinally and included 1H-magnetic resonance spectroscopy brain glutamate levels, resting-state functional magnetic resonance imaging, and plasma and cerebrospinal fluid measures of kynurenine metabolites and neurotrophic factors.

RESULTS

Linear mixed models detected no treatment effects, as assessed by primary and secondary outcome measures. No difference was observed for any of the peripheral or central biological indices or for adverse effects at any time between groups. A 4-Cl-KYN was safe and well-tolerated, with generally minimal associated adverse events.

CONCLUSIONS

In this small crossover trial, 4-Cl-KYN monotherapy exerted no antidepressant effects at the doses and treatment duration studied.ClinicalTrials.gov identifier: NCT02484456.