Neurocognitive aspects of ketamine and esketamine on subjects with treatment-resistant depression: A comparative, randomized and double-blind study

Long-Term Cognitive Outcomes of Esketamine Nasal Spray in Treatment-Resistant Depression: A Preliminary Report

Background/Objectives: Ketamine/esketamine has a rapid/robust antidepressant effect on treatment-resistant depression (TRD). However, its long-term cognitive effects remain unclear. In this study, we investigated the potential cognitive effects of an esketamine spray on a series of TRD patients. Methods: We evaluated the cognitive performance of eight TRD patients subjected to an esketamine nasal spray as an adjunct treatment for six months. Cognitive assessments were performed before treatment initiation (T0) and at three (T3) and six (T6) months by an experienced neuropsychologist using a comprehensive neuropsychological battery. Depression severity was assessed by the Montgomery-Åsberg Depression Rating Scale. Changes in cognitive performance were analyzed by determining the bias between time points. To investigate the association between the severity of depression and performance on cognitive tests, we used correlation with correction for repeated measures and regression analysis with a general linear mixed model. We used the Tukey method to compare three estimates and the Dunnett method to compare two estimates. Results: Improvements in at least one test from T0 to T6 were found for attention, memory, and the executive functions of working memory, set-shifting, and inhibitory control. Most of the improvements had occurred by T3, but working memory and set-shifting improvements were significant only at T6. The severity of depression decreased significantly from T0 to T6, and most cognitive improvements were correlated with an improvement in depression severity. No test indicated a worsening of cognitive performance from T0 to T6. Conclusions: Our results suggest that the cognitive performance of TRD patients improved with long-term adjunct treatment with an esketamine nasal spray. Confirmatory studies are necessary.

Effects of subanesthetic repeated esketamine infusions on memory function and NGF in patients with depression: An open-label study

BACKGROUND

Subanesthetic ketamine is a rapidly acting antidepressant, yet the effects of ketamine on cognitive function are inconsistent. The primary objective of this study was to explore the effects of esketamine on memory function and plasma levels of nerve growth factor (NGF) in patients with depression.

METHODS

A total of 132 patients with depression completed six intravenous esketamine infusions (0.4 mg/kg) over 11 days. Depressive symptoms and neurocognitive function were assessed using the Montgomery-Asberg Depression Rating Scale (MADRS) and Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Plasma NGF levels were assayed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The mean MADRS score of depressed patients decreased from 32.11 ± 10.06 to 15.10 ± 8.62 after six infusions. Significant improvement in immediate memory, language, attention, and delayed memory were observed. NGF plasma levels increased from 226.13 ± 61.73 to 384.37 ± 56.89. Pearson's correlation analysis showed a positive correlation between memory function and NGF levels at baseline. The baseline memory function was negatively associated with the changes in NGF levels.

LIMITATION

The major limitation of this study is the open-label design.

CONCLUSIONS

Subanesthetic esketamine infusions could improve depressive symptoms and neurocognitive function. Our study showed increased plasma NGF levels in depressed patients after treatment, suggesting that NGF may play a role in the improvement of memory function by esketamine.

Efficacy and safety of esketamine versus propofol in electroconvulsive therapy for treatment-resistant depression: A randomized, double-blind, controlled, non-inferiority trial

BACKGROUND

Electroconvulsive therapy (ECT) is a commonly used alternative for treatment-resistant depression (TRD). Although esketamine has a rapid pharmacological antidepressant action, it has not been studied as an ECT anesthetic. The objective of this study was to compare the efficacy and safety of esketamine with propofol when both are used as ECT anesthetic agents.

METHODS

Forty patients with TRD were assigned to one of two arms in a double-blind, randomized controlled trial: esketamine or propofol anesthesia for a series of eight ECT sessions. Using a non-inferiority design, the primary outcome was the reduction in HAMD-17 depressive symptoms. The other outcomes were: rates of response and remission, anxiety, suicidal ideation, cognitive function, and adverse events. These were compared in an intention-to-treat analysis.

RESULTS

Esketamine-ECT was non-inferior to propofol-ECT for reducing TRD symptoms after 8 sessions (adjusted Δ = 2.0, 95 % CI: -1.2-5.1). Compared to propofol-ECT, esketamine-ECT also had higher depression response (80 % vs. 70 %; p = .06) and remission (65 % vs. 55 %; p = .11) rates but non-inferiority was not established. In four components of cognitive function (speed of processing, working memory, visual learning, and verbal learning) esketamine-ECT was non-inferior to propofol-ECT. The results for anxiety, suicidal ideation, and adverse events (all p's > .05) were inconclusive.

CONCLUSION

Esketamine was non-inferior to propofol when both are used as anesthetics for TRD patients undergoing ECT. Replication studies with larger samples are needed to examine the inconclusive results.

REGISTRATION NUMBER

ChiCTR2000033715.

Effect of Esketamine on Postoperative Delirium in Patients Undergoing Cardiac Valve Replacement with Cardiopulmonary Bypass: A Randomized Controlled Trial

BACKGROUND

The aim of this study was to investigate the effects of esketamine on the risk of postoperative delirium (POD) in adults undergoing on-pump cardiac valve surgery.

METHODS

In this randomized, triple-blind, controlled trial, 116 adult patients with an American Society of Anesthesiologists (ASA) grade Ⅱ or Ⅲ and a New York Heart Association (NYHA) grade Ⅱ or Ⅲ who underwent cardiac valve surgery with cardiopulmonary bypass were included. Esketamine (0.25 mg/kg) or normal saline was administered intravenously before anesthesia induction. The primary outcome was POD, defined as a positive delirium assessment according to the 3-minute confusion assessment method (CAM) or the confusion assessment method for the intensive care unit (CAM-ICU) on a twice-daily basis for 7 days after surgery. Delirium duration and the delirium subtype were also recorded. The cognitive status of patients was measured according to the Mini-Mental State Examination at baseline, discharge, 30 days postoperatively and 3 months postoperatively.

RESULTS

A total of 112 patients (mean age, 52 years; 53.6% female) were enrolled; 56 were assigned to receive esketamine, and 56 were assigned to receive placebo. POD occurred in 13 (23.2%) patients in the esketamine group and in 25 (44.6%) patients in the placebo group (relative risk [RR], 0.52, 95% confidence interval [CI], 0.28-0.91; P = .018). Thirteen patients (23.2%) in the esketamine group and 24 (42.9%) patients in the placebo group had multiple episodes of delirium (RR, 0.54, 95% CI, 0.28-0.92), and 13 (23.2%) vs 22 (39.3%) patients exhibited the hyperactive subtype.

CONCLUSIONS

A single dose of esketamine (0.25 mg/kg) injected intravenously before anesthesia induction reduced the incidence of delirium in relatively young patients with ASA grade Ⅱ or Ⅲ who underwent on-pump cardiac surgery.

Neurocognitive changes in a patient receiving esketamine for treatment-resistant depression

ABSTRACT

Esketamine, the s(+) enantiomer of ketamine, was approved in 2019 as the first rapid-acting intranasal spray medication for treatment-resistant depression; the drug is given in combination with an antidepressant. The treatment is self-administered in a clinical setting under the supervision of a healthcare provider and usually is well tolerated. Many of its adverse reactions are mild, temporary, and dose-dependent, and they improve with subsequent treatments. Although the prescribing information lists difficulty remembering or thinking as possible adverse reactions, a neurocognitive evaluation is not part of the initial patient evaluation. This case report focuses on a patient whose neurocognitive symptoms worsened with esketamine treatment, necessitating treatment discontinuation.

Diurnal variation of postoperative delirium in elderly patients undergoing esketamine anesthesia for elective noncardiac surgery: a randomized clinical trial

BACKGROUND

Postoperative delirium (POD) is a serious and common complication. The aim of present study is to investigate the diurnal variation of POD and the effects of esketamine in elderly patients.

METHODS

A randomized, double-blind, placebo-controlled clinical trial with factorial design was conducted. Patients (aged 65 to 85 years) with normal Mini-Mental State Examination (MMSE) score were stratified by age (≤70 vs. >70) and American Society of Anesthesiologists physical status classification (Ⅱ vs. Ⅲ), then randomly assigned to either morning (08:00-12:00) or afternoon (14:00-18:00) noncardiac operation under general anesthesia with or without esketamine administration (0.2 mg/kg). The primary outcome was the incidence of POD (3-Minute Diagnostic Interview for Confusion Assessment Method-defined Delirium, 3D-CAM) on postoperative days 1, 3, and 7. The secondary outcomes were the scores of MMSE and Hospital Anxiety and Depression Scale. The intention-to-treat analysis of the outcomes were performed by generalized estimating equation.

RESULTS

Six patients who did not receive an intervention because of canceled operation were excluded after randomization. The datasets containing 426 cases were analyzed following the intention-to-treat principle after handling missing data via multiple imputation method. The incidence of POD declined from about 55% on postoperative day 1 to 31 and 18% on postoperative days 3 and 7, respectively. Afternoon operation [B=-0.583, OR (95% CI) 0.558 (0.319-0.976); P=0.041], but not esketamine, significantly decreased the incidence of POD. Both esketamine and operation time failed to significantly affect MMSE, HAD, and NRS score. There was no interaction among operation time, esketamine, and follow up time.

CONCLUSION

Elderly patients undergoing elective noncardiac surgery in the afternoon displayed lower POD incidence than those operated in the morning. A single low-dose of esketamine before general anesthesia induction failed to significantly decrease the risk of POD but decrease the risk of intraoperative hypotension and emergence agitation.

Number needed to treat (NNT) for ketamine and esketamine in adults with treatment-resistant depression: A systematic review and meta-analysis

BACKGROUND

Ketamine has been established as efficacious in adults living with Treatment-resistant Depression (TRD). Toward providing a quantifiable estimate of the clinical meaningfulness of the therapeutic benefit of ketamine, herein, we conduct a systematic review that aims to report the Number Needed to Treat (NNT) and the Number Needed to Harm (NNH).

METHODS

This systematic review searched Embase, Medline/Pubmed, PsycINFO and ClinicalTrials.gov from inception up to October 15th 2023, for placebo-controlled, Randomized Controlled Trials (RCTs) assessing racemic ketamine or esketamine therapy for unipolar TRD. We calculated NNT and NNH for ketamine treatments over various time points.

RESULTS

A total of 21 studies with 2042 participants were included. Racemic ketamine treatments had pooled NNTs for response of 7 at 4 h, 3 from one day to one week and 9 for studies at four weeks. Esketamine treatment was found to have a similar efficacy with an NNT of 2 at one day and 11 at four weeks. NNH values indicated low risk for ketamine treatments.

LIMITATIONS

Limitations in the data used include the possibility of functional unblinding and selective reporting bias. Moreover, the meta-analysis may have been limited in its precision by including low threshold definitions of treatment resistance (≥ 1 failed antidepressant) and low-dose ketamine treatments.

CONCLUSION

Herein, we determined that the NNT for ketamine treatment in adults living with TRD across different intervals of observation was <10. We conclude that the NNTs observed herein are highly clinically meaningful in this difficult to treat disorder.

Esketamine enhances memory reconsolidation in the novel object recognition task

Esketamine, the right-handed optical isomer of racemic ketamine, is a rapidly acting antidepressant approved by the FDA for treatment-resistant depression in 2019. However, few studies have investigated esketamine's role in learning and memory, particularly in the context of memory reconsolidation. Herein, we evaluated esketamine's role in memory reconsolidation in 7-week-old male Institute of Cancer Research mice subjected to the novel object recognition (NOR) memory task. The NOR reconsolidation procedure comprised three phases: sampling, reactivation, and testing. Esketamine-enhanced NOR memory performance when injected into mice 0 h after reactivation rather than following a 6 h delay. Conversely, administering esketamine 24 h after sampling without reactivation did not enhance NOR memory performance. Notably, esketamine exhibited no discernible effects on nonspecific responses, such as locomotor activity and exploratory behavior. Furthermore, the α-amino-3‑hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type receptor antagonist NBQX effectively blocked the esketamine-induced enhancement of memory reconsolidation. In conclusion, esketamine treatment markedly improves memory reconsolidation in NOR tasks, and this effect is linked to AMPA receptor activity.

Efficacy of intraoperative subanesthetic dose of ketamine/esketamine in preventing postoperative cognitive dysfunction: a systematic review and meta-analysis

Background

Postoperative cognitive dysfunction (POCD) is a common complication after anesthesia surgery, especially in older people, that can persist weeks or months after surgery as a short-term impairment of cognitive abilities, or even for a prolonged duration over years, potentially progressing into permanent cognitive dysfunction. However, the pathogenesis of POCD is not fully understood, and therefore an optimal solution for preventing POCD has yet to be established. Some studies have shown that intraoperative ketamine/esketamine reduces the incidence of POCD, but this remains controversial.

Objectives

We evaluated the effect of intraoperative subanesthetic doses of ketamine/esketamine versus no intervention in adults undergoing general anesthesia surgery on the incidence of POCD.

Data Sources

We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and searched the PubMed, Embase, Ovid, Cochrane, Scopus, and Web of Science databases for the MeSH terms 'ketamine', 'esketamine', and 'Postoperative Cognitive Complications' from database inception to 25 June 2023.

Results

We found no statistically significant difference in the incidence of POCD within 7 days for intraoperative subanesthetic dose of ketamine/esketamine compared with the control group [relative risk (RR) = 0.57, 95% confidence interval (CI): 0.32, 1.01], and the results from the subgroup analysis based on age (>60 years) also revealed that the difference was not statistically significant (RR = 0.49, 95% CI: 0.23, 1.04).

Conclusion

Compared with controls, intraoperative subanesthetic dose of ketamine/esketamine has no advantage in preventing POCD in patients, or in elderly patients. This study provides reference data for POCD research and clinical drug intervention strategies.

Registration

Prospective Register of Systematic Reviews (PROSPERO; registration number CRD42023401159).

Hippocampal subfield volumes in treatment resistant depression and serial ketamine treatment

Introduction

Subanesthetic ketamine is a rapidly acting antidepressant that has also been found to improve neurocognitive performance in adult patients with treatment resistant depression (TRD). Provisional evidence suggests that ketamine may induce change in hippocampal volume and that larger pre-treatment volumes might be related to positive clinical outcomes. Here, we examine the effects of serial ketamine treatment on hippocampal subfield volumes and relationships between pre-treatment subfield volumes and changes in depressive symptoms and neurocognitive performance.

Methods

Patients with TRD (N = 66; 31M/35F; age = 39.5 ± 11.1 years) received four ketamine infusions (0.5 mg/kg) over 2 weeks. Structural MRI scans, the National Institutes of Health Toolbox (NIHT) Cognition Battery, and Hamilton Depression Rating Scale (HDRS) were collected at baseline, 24 h after the first and fourth ketamine infusion, and 5 weeks post-treatment. The same data was collected for 32 age and sex matched healthy controls (HC; 17M/15F; age = 35.03 ± 12.2 years) at one timepoint. Subfield (CA1/CA3/CA4/subiculum/molecular layer/GC-ML-DG) volumes corrected for whole hippocampal volume were compared across time, between treatment remitters/non-remitters, and patients and HCs using linear regression models. Relationships between pre-treatment subfield volumes and clinical and cognitive outcomes were also tested. All analyses included Bonferroni correction.

Results

Patients had smaller pre-treatment left CA4 (p = 0.004) and GC.ML.DG (p = 0.004) volumes compared to HC, but subfield volumes remained stable following ketamine treatment (all p > 0.05). Pre-treatment or change in hippocampal subfield volumes over time showed no variation by remission status nor correlated with depressive symptoms (p > 0.05). Pre-treatment left CA4 was negatively correlated with improved processing speed after single (p = 0.0003) and serial ketamine infusion (p = 0.005). Left GC.ML.DG also negatively correlated with improved processing speed after single infusion (p = 0.001). Right pre-treatment CA3 positively correlated with changes in list sorting working memory at follow-up (p = 0.0007).

Discussion

These results provide new evidence to suggest that hippocampal subfield volumes at baseline may present a biomarker for neurocognitive improvement following ketamine treatment in TRD. In contrast, pre-treatment subfield volumes and changes in subfield volumes showed negligible relationships with ketamine-related improvements in depressive symptoms.

Reduction in Cognitive Symptoms Following Intranasal Esketamine Administration in Patients With Chronic Treatment-resistant Depression: A 12-Week Case Series

BACKGROUND

Cognitive symptoms are a core feature of depressive disorders, interfere with full functional recovery and are prominent in patients with treatment-resistant depression (TRD), particularly in severe chronic cases. Intranasal (IN) esketamine was recently approved for the treatment of TRD; however, its effects on cognitive symptoms are unclear. In this article, we describe cognitive changes in 8 patients with chronic TRD who were treated with IN administration of esketamine.

METHODS

Eight outpatients with chronic TRD received IN esketamine over 3 months and were assessed at baseline and after 4, 8, and 12 weeks of treatment using the Montgomery-Åsberg Depression Rating Scale (MADRS), the Digit Symbol Substitution Test (DSST), the Trail Making Test-B (TMT-B), the Patient Deficits Questionnaire for Depression 5-item (PDQ-D5), the Hamilton Anxiety Rating Scale (HARS), and the Clinical Global Impressions Scale (CGI).

FINDINGS

We observed reductions in cognitive symptoms according to DSST, TMT-B, and PDQ-D5 scores within the first 2 months of treatment with IN esketamine. These improvements were observed before patients achieved clinical response (≥50% decrease in baseline MADRS scores), and they also occurred earlier than reductions in HARS scores.

CONCLUSIONS

A clinical response to IN esketamine was detected in severely ill patients with chronic TRD after 3 months of treatment. Interestingly, improvements on measures of cognitive symptoms were observed before patients achieved antidepressant response. These preliminary observations suggest an additional value to the antidepressant properties of IN esketamine. Clinical studies specifically investigating cognition as a primary outcome measure of IN esketamine in TRD are warranted.

The integrated treatment of eating disorders, posttraumatic stress disorder, and psychiatric comorbidity: a commentary on the evolution of principles and guidelines

Psychiatric comorbidity is the norm in the assessment and treatment of eating disorders (EDs), and traumatic events and lifetime PTSD are often major drivers of these challenging complexities. Given that trauma, PTSD, and psychiatric comorbidity significantly influence ED outcomes, it is imperative that these problems be appropriately addressed in ED practice guidelines. The presence of associated psychiatric comorbidity is noted in some but not all sets of existing guidelines, but they mostly do little to address the problem other than referring to independent guidelines for other disorders. This disconnect perpetuates a "silo effect," in which each set of guidelines do not address the complexity of the other comorbidities. Although there are several published practice guidelines for the treatment of EDs, and likewise, there are several published practice guidelines for the treatment of PTSD, none of them specifically address ED + PTSD. The result is a lack of integration between ED and PTSD treatment providers, which often leads to fragmented, incomplete, uncoordinated and ineffective care of severely ill patients with ED + PTSD. This situation can inadvertently promote chronicity and multimorbidity and may be particularly relevant for patients treated in higher levels of care, where prevalence rates of concurrent PTSD reach as high as 50% with many more having subthreshold PTSD. Although there has been some progress in the recognition and treatment of ED + PTSD, recommendations for treating this common comorbidity remain undeveloped, particularly when there are other co-occurring psychiatric disorders, such as mood, anxiety, dissociative, substance use, impulse control, obsessive-compulsive, attention-deficit hyperactivity, and personality disorders, all of which may also be trauma-related. In this commentary, guidelines for assessing and treating patients with ED + PTSD and related comorbidity are critically reviewed. An integrated set of principles used in treatment planning of PTSD and trauma-related disorders is recommended in the context of intensive ED therapy. These principles and strategies are borrowed from several relevant evidence-based approaches. Evidence suggests that continuing with traditional single-disorder focused, sequential treatment models that do not prioritize integrated, trauma-focused treatment approaches are short-sighted and often inadvertently perpetuate this dangerous multimorbidity. Future ED practice guidelines would do well to address concurrent illness in more depth.

Neurocognitive effects of subanesthetic serial ketamine infusions in treatment resistant depression

INTRODUCTION

Ketamine treatment prompts a rapid antidepressant response in treatment-resistant depression (TRD). We performed an exploratory investigation of how ketamine treatment in TRD affects different cognitive domains and relates to antidepressant response.

METHODS

Patients with TRD (N = 66; 30 M/35F; age = 39.5 ± 11.1 years) received four ketamine infusions (0.5 mg/kg). Neurocognitive function and depressive symptoms were assessed at baseline, 24 h after the first and fourth ketamine infusion, and 5 weeks following end of treatment. Mixed effect models tested for changes in seven neurocognitive domains and antidepressant response, with post-hoc pairwise comparisons between timepoints, including follow-up. Relationships between change in neurocognitive function and antidepressant response over the course of treatment were tested with Pearson's correlation and mediation analyses. Associations between baseline neurocognitive performance and antidepressant response were tested with Pearson's correlation.

RESULTS

Significant improvements in inhibition, working memory, processing speed, and overall fluid cognition were observed after the first and fourth ketamine infusion. Improvements in processing speed and overall fluid cognition persisted through follow-up. Significant improvements in depressive symptoms reverted towards baseline at follow-up. Baseline working memory and change in inhibition were moderately correlated with antidepressant response, however, improvements in neurocognitive performance were statistically independent from antidepressant response.

CONCLUSION

Antidepressant ketamine leads to improved neurocognitive function, which persist for at least 5 weeks. Neurocognitive improvements observed appear independent of antidepressant response, suggesting ketamine may target overlapping but distinct functional brain systems. Limitations Research investigating repeated serial ketamine treatments is important to determine cognitive safety. This study is a naturalistic design and does not include placebo.

Eating disorder patients with and without PTSD treated in residential care: discharge and 6-month follow-up results

INTRODUCTION

We studied whether provisional posttraumatic stress disorder (PTSD) moderated discharge (DC) and 6-month follow-up (FU) outcomes of multi-modal, integrated eating disorder (ED) residential treatment (RT) based upon principles of cognitive processing therapy (CPT).

METHODS

ED patients [N = 609; 96% female; mean age (± SD) = 26.0 ± 8.8 years; 22% LGBTQ +] with and without PTSD completed validated assessments at admission (ADM), DC and 6-month FU to measure severity of ED, PTSD, major depressive disorder (MDD), state-trait anxiety (STA) symptoms, and eating disorder quality of life (EDQOL). We tested whether PTSD moderated the course of symptom change using mixed models analyses and if ED diagnosis, ADM BMI, age of ED onset and LGBTQ + orientation were significant covariates of change. Number of days between ADM and FU was used as a weighting measure.

RESULTS

Despite sustained improvements with RT in the total group, the PTSD group had significantly higher scores on all measures at all time points (p ≤ .001). Patients with (n = 261) and without PTSD (n = 348) showed similar symptom improvements from ADM to DC and outcomes remained statistically improved at 6-month FU compared to ADM. The only significant worsening observed between DC and FU was with MDD symptoms, yet all measures remained significantly lower than ADM at FU (p ≤ .001). There were no significant PTSD by time interactions for any of the measures. Age of ED onset was a significant covariate in the EDI-2, PHQ-9, STAI-T, and EDQOL models such that an earlier age of ED onset was associated with a worse outcome. ADM BMI was also a significant covariate in the EDE-Q, EDI-2, and EDQOL models, such that higher ADM BMI was associated with a worse ED and quality of life outcome.

CONCLUSIONS

Integrated treatment approaches that address PTSD comorbidity can be successfully delivered in RT and are associated with sustained improvements at FU. Improving strategies to prevent post-DC recurrence of MDD symptoms is an important and challenging area of future work.

An update on potential pharmacotherapies for cognitive impairment in bipolar disorder

INTRODUCTION

Cognitive impairment is a core feature of bipolar disorder (BD) that impedes recovery by preventing the return to optimal socio-occupational functioning and reducing quality of life. Presently, there are no efficacious treatments for cognitive impairment in BD, but many pharmacological interventions are being considered as they have the potential to target the underlying pathophysiology of the disorder.

AREAS COVERED

This review summarizes the available evidence for pharmacological interventions for cognitive impairment in bipolar disorder. We searched PubMed, MedLine, and PsycInfo from inception to December 1^st, 2022. Traditional treatments, such as lithium, anticonvulsants (lamotrigine), antipsychotics (aripiprazole, asenapine, cariprazine, lurasidone, and olanzapine), antidepressants (vortioxetine, fluoxetine, and tianeptine) and psychostimulants (modafinil), and emerging interventions, such as acetylcholinesterase inhibitors (galantamine and donepezil), dopamine agonists (pramipexole), erythropoietin, glucocorticoid receptor antagonists (mifepristone), immune modulators (infliximab, minocycline and doxycycline), ketamine, metabolic agents (insulin, metformin, and liraglutide), probiotic supplements, and Withania somnifera are discussed.

EXPERT OPINION

The investigation of interventions for cognitive impairment in BD is a relatively under-researched area. In the past, methodological pitfalls in BD cognition trials have also been a critical limiting factor. Expanding on the existing literature and identifying novel pharmacological and non-pharmacological treatments for cognitive impairment in BD should be a priority.

The Effects of Acute and Repeated Administration of Ketamine on Memory, Behavior, and Plasma Corticosterone Levels in Female Mice

Ketamine is an anesthetic drug that has recently been approved for the treatment of treatment-resistant depression. Females are diagnosed with Major Depressive Disorder at higher rates than males, yet most of the pre-clinical research on ketamine has been conducted in male subjects. Additionally, the literature on the acute and long-term behavioral and cognitive effects of ketamine shows conflicting results. It is important to examine the acute and long-term cognitive and behavioral effects of ketamine exposure at lower sub-anesthetic doses, as the recreational use of the drug at higher doses is associated with cognitive and memory impairments. The current study examined the effects of acute and repeated ketamine exposure on anxiety-like behavior, novel object recognition memory, depression-like behavior, and plasma corticosterone levels in 20 adult female C57BL/6J mice. Mice were exposed acutely or repeatedly for 10 consecutive days to saline or 15 mg/kg ketamine and behavior was measured in the open field test, novel object recognition test, and the Porsolt forced swim test. Plasma corticosterone levels were measured following behavioral testing. Acute ketamine exposure decreased locomotor activity and increased anxiety-like behavior in the open field test compared to controls, while repeated ketamine exposure impaired memory in the novel object recognition test. There were no effects of acute or repeated ketamine exposure on depression-like behavior in the Porsolt forced swim test or on plasma corticosterone levels. These findings suggest that a subanesthetic dose of ketamine alters behavior and cognition in female mice and the effects are dependent on the duration of exposure.

Esketamine for treatment‑resistant depression: A review of clinical evidence (Review)

Treatment-resistant depression (TRD) is a challenge for psychiatrists, even after more than seven decades since the first antidepressants were used in clinical practice. Non-monoaminergic-based drugs with antidepressant properties have been developed, but to date, only esketamine and brexanolone have been approved for TRD and postpartum depression, respectively. A narrative review on the efficacy and safety of esketamine in the main categories of depressive disorders has been conducted through four electronic databases (Pubmed, Cochrane, EMBASE and Clarivate/Web of Science) The primary objective of the present review was to find evidence that may support the usefulness of esketamine for patients diagnosed with TRD as well as data about its potential adverse effects in the short and long term. A total of 14 papers were reviewed, and their results support the recommendation of esketamine for treatment of TRD as an add-on to antidepressants, but more data is needed in order to assess its long-term efficacy and safety. It must also be mentioned that there have been a few trials which did not report a significant effect on the severity of depressive symptoms with esketamine in TRD, therefore, caution is indicated for patients initiated on this adjuvant agent. There has been insufficient data to formulate specific guidelines about esketamine administration because evidence about favorable or negative prognostic factors of this treatment has been lacking, and the duration of its administration has not been unanimously accepted. Novel directions for research have been identified, especially in the case of patients with TRD and substance use disorders, geriatric or bipolar depression or in major depression with psychotic features.

Translational control by ketamine and its implications for comorbid cognitive deficits in depressive disorders

Ketamine has shown antidepressant effects in patients with major depressive disorder (MDD) resistant to first-line treatments and approved for use in this patient population. Ketamine induces several forms of synaptic plasticity, which are proposed to underlie its antidepressant effects. However, the molecular mechanism of action directly responsible for ketamine's antidepressant effects remains under active investigation. It was recently demonstrated that the effectors of the mammalian target of rapamycin complex 1 (mTORC1) signalling pathway, namely, eukaryotic initiation factor 4E (eIF4E) binding proteins 1 and 2 (4E-BP1 and 4E-BP2), are central in mediating ketamine-induced synaptic plasticity and behavioural antidepressant-like effect. 4E-BPs are a family of messenger ribonucleic acid (mRNA) translation repressors inactivated by mTORC1. We observed that their expression in inhibitory interneurons mediates ketamine's effects in the forced swim and novelty suppressed feeding tests and the long-lasting inhibition of GABAergic neurotransmission in the hippocampus. In addition, another effector pathway that regulates translation elongation downstream of mTORC1, the eukaryotic elongation factor 2 kinase (eEF2K), has been implicated in ketamine's behavioural effects. We will discuss how ketamine's rapid antidepressant effect depends on the activation of neuronal mRNA translation through 4E-BP1/2 and eEF2K. Furthermore, given that these pathways also regulate cognitive functions, we will discuss the evidence of ketamine's effect on cognitive function in MDD. Overall, the data accrued from pre-clinical research have implicated the mRNA translation pathways in treating mood symptoms of MDD. However, it is yet unclear whether the pro-cognitive potential of subanesthetic ketamine in rodents also engages these pathways and whether such an effect is consistently observed in the treatment-resistant MDD population.

A Systematic Review of Neurocognitive Effects of Subanesthetic Doses of Intravenous Ketamine in Major Depressive Disorder, Post-Traumatic Stress Disorder, and Healthy Population

BACKGROUND AND OBJECTIVE: Ketamine, a noncompetitive, high-affinity antagonist of the N-methyl-D-aspartate type glutamate receptor, has been investigated for its high efficacy and rapid antidepressant effect and, more recently, for its potential utility in post-traumatic stress disorder (PTSD). The proposal that ketamine's antidepressant and anti-suicidal mechanism may be in part due to its procognitive effect contrasts with the well-established decreased performance on spatial working memory and pattern recognition memory among long-term frequent users. We aimed to review the neurocognitive effects of subanesthetic doses of intravenous ketamine in pharmacological studies among healthy subjects and patients with PTSD or depression.

METHODS

We included studies in English, among healthy adults, or with PTSD or unipolar or bipolar depression where the primary or secondary cognitive outcomes were measured by means of validated neuropsychological test. We excluded studies that reported the use of ketamine only in combination with other drugs or psychotherapy, or studies investigating emotion-laden cognitive functions.

RESULTS

Ketamine administration among patients with depression and possibly with PTSD does not show significant impairment of cognitive functions in the short-term, in contrast with the immediate altered cognitive dysfunction found in healthy subjects. The potential procognitive effects of ketamine seem more pronounced in cognitive domains of executive function, which is in line with the putative molecular, cellular, and synaptic mechanisms of ketamine's therapeutic action.

CONCLUSIONS

The potential procognitive effect of ketamine deserves further exploration. Whether ketamine has transient or sustained neurocognitive benefits beyond its antidepressant effects is unknown. Improved cognition by ketamine might be used to facilitate psychotherapy interventions for PTSD and depression.

Research advances in the clinical application of esketamine

Esketamine is dextrorotatory ketamine, which is an enantiomer of ketamine. Compared with ketamine, it has the advantages of a fast metabolism, fewer side effects, and strong pharmacological effects, so it is more suitable for clinical use. Esketamine has a powerful analgesic effect and has little effect on breathing. It has a wide range of applications in the fields of pediatric anesthesia, conscious sedation anesthesia, and emergency analgesia. In addition, it is also used for pain that is difficult to relieve with conventional drugs and to prevent postoperative pain. Various routes of administration are also suitable for patients who need short-term analgesia and sedation. As a drug, esketamine inevitably brings some side effects when it is used clinically. In this article, by introducing the mechanism of action and pharmacological characteristics of esketamine, its clinical application is reviewed, and it provides a reference for the more reasonable and safe clinical application of esketamine.

Sex- and estrous-cycle dependent dorsal hippocampal phosphoproteomic changes induced by low-dose ketamine

Numerous emotional and cognitive processes mediated by the hippocampus present differences between sexes and can be markedly influenced by hormonal status in males and females of several species. In rodents, the dorsal hippocampus (dHPC) is known to contribute to the rapid antidepressant actions of the NMDA receptor antagonist ketamine. We and others have demonstrated a greater sensitivity to the fast-acting antidepressant ketamine in female versus male rats that is estrogen- and progesterone-dependent. However, the underlying mechanisms remain unclear. Using an acute low dose (2.5 mg/kg) of ketamine that is behaviorally effective in female but not male rats, a label-free phosphoproteomics approach was employed to identify ketamine-induced changes in signaling pathway activation and phosphoprotein abundance within the dHPC of intact adult male rats and female rats in either diestrus or proestrus. At baseline, males and females showed striking dissimilarities in the dHPC proteome and phosphoproteome related to synaptic signaling and mitochondrial function-differences also strongly influenced by cycle stage in female rats. Notably, phosphoproteins enriched in PKA signaling emerged as being both significantly sex-dependent at baseline and also the primary target of ketamine-induced protein phosphorylation selectively in female rats, regardless of cycle stage. Reduced phosphoprotein abundance within this pathway was observed in males, suggesting bi-directional effects of low-dose ketamine between sexes. These findings present biological sex and hormonal milieu as critical modulators of ketamine's rapid actions within this brain region and provide greater insight into potential translational and post-translational processes underlying sex- and hormone-dependent modulation of ketamine's therapeutic effects.

(R,S)-ketamine and (2R,6R)-hydroxynorketamine differentially affect memory as a function of dosing frequency

A single subanesthetic infusion of ketamine can rapidly alleviate symptoms of treatment-resistant major depression. Since repeated administration is required to sustain symptom remission, it is important to characterize the potential untoward effects of prolonged ketamine exposure. While studies suggest that ketamine can alter cognitive function, it is unclear to what extent these effects are modulated by the frequency or chronicity of treatment. To test this, male and female adolescent (postnatal day [PD] 35) and adult (PD 60) BALB/c mice were treated for four consecutive weeks, either daily or thrice-weekly, with (R,S)-ketamine (30 mg/kg, intraperitoneal) or its biologically active metabolite, (2R,6R)-hydroxynorketamine (HNK; 30 mg/kg, intraperitoneal). Following drug cessation, memory performance was assessed in three operationally distinct tasks: (1) novel object recognition to assess explicit memory, (2) Y-maze to assess working memory, and (3) passive avoidance to assess implicit memory. While drug exposure did not influence working memory performance, thrice-weekly ketamine and daily (2R,6R)-HNK led to explicit memory impairment in novel object recognition independent of sex or age of exposure. Daily (2R,6R)-HNK impaired implicit memory in the passive-avoidance task whereas thrice-weekly (2R,6R)-HNK tended to improve it. These differential effects on explicit and implicit memory possibly reflect the unique mechanisms by which ketamine and (2R,6R)-HNK alter the functional integrity of neural circuits that subserve these distinct cognitive domains, a topic of clinical and mechanistic relevance to their antidepressant actions. Our findings also provide additional support for the importance of dosing frequency in establishing the cognitive effects of repeated ketamine exposure.

Neuroplasticity as a convergent mechanism of ketamine and classical psychedelics

The emerging therapeutic efficacy of ketamine and classical psychedelics for depression has inspired tremendous interest in the underlying neurobiological mechanisms. We review preclinical and clinical evidence supporting neuroplasticity as a convergent downstream mechanism of action for these novel fast-acting antidepressants. Through their primary glutamate or serotonin receptor targets, ketamine and psychedelics [psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltryptamine (DMT)] induce synaptic, structural, and functional changes, particularly in pyramidal neurons in the prefrontal cortex. These include increased glutamate release, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) activation, brain-derived neurotrophic factor (BDNF) and mammalian target of rapamycin (mTOR)-mediated signaling, expression of synaptic proteins, and synaptogenesis. Such influences may facilitate adaptive rewiring of pathological neurocircuitry, thus providing a neuroplasticity-focused framework to explain the robust and sustained therapeutic effects of these compounds.