An update on ketamine and its two enantiomers as rapid-acting antidepressants

(R)-(-)-Ketamine: The Promise of a Novel Treatment for Psychiatric and Neurological Disorders

NMDA receptor antagonists have potential for therapeutics in neurological and psychiatric diseases, including neurodegenerative diseases, epilepsy, traumatic brain injury, substance abuse disorder (SUD), and major depressive disorder (MDD). (S)-ketamine was the first of a novel class of antidepressants, rapid-acting antidepressants, to be approved for medical use. The stereoisomer, (R)-ketamine (arketamine), is currently under development for treatment-resistant depression (TRD). The compound has demonstrated efficacy in multiple animal models. Two clinical studies disclosed efficacy in TRD and bipolar depression. A study by the drug sponsor recently failed to reach a priori clinical endpoints but post hoc analysis revealed efficacy. The clinical value of (R)-ketamine is supported by experimental data in humans and rodents, showing that it is less sedating, does not produce marked psychotomimetic or dissociative effects, has less abuse potential than (S)-ketamine, and produces efficacy in animal models of a range of neurological and psychiatric disorders. The mechanisms of action of the antidepressant effects of (R)-ketamine are hypothesized to be due to NMDA receptor antagonism and/or non-NMDA receptor mechanisms. We suggest that further clinical experimentation with (R)-ketamine will create novel and improved medicines for some of the neurological and psychiatric disorders that are underserved by current medications.

Efficacy of ketamine versus esketamine in the treatment of perioperative depression: A review

Depression is a significant factor contributing to postoperative occurrences, and patients diagnosed with depression have a higher risk for postoperative complications. Studies on cardiovascular surgery extensively addresses this concern. Several studies report that people who undergo coronary artery bypass graft surgery have a 20% chance of developing postoperative depression. A retrospective analysis of medical records spanning 21 years, involving 817 patients, revealed that approximately 40% of individuals undergoing coronary artery bypass grafting (CABG) were at risk of perioperative depression. Patients endure prolonged suffering from illness because each attempt with standard antidepressants requires several weeks to be effective. In addition, multi-drug combination adjuvants or combination medication therapy may alleviate symptoms for some individuals, but they also increase the risk of side effects. Conventional antidepressants primarily modulate the monoamine system, whereas different therapies target the serotonin, norepinephrine, and dopamine systems. Esketamine is a fast-acting antidepressant with high efficacy. Esketamine is the S-enantiomer of ketamine, a derivative of phencyclidine developed in 1956. Esketamine exerts its effect by targeting the glutaminergic system the glutaminergic system. In this paper, we discuss the current depression treatment strategies with a focus on the pharmacology and mechanism of action of esketamine. In addition, studies reporting use of esketamine to treat perioperative depressive symptoms are reviwed, and the potential future applications of the drug are presented.

Mechanistic insights into the potential role of dietary polyphenols and their nanoformulation in the management of Alzheimer's disease

Alzheimer's disease (AD) is a very common neurodegenerative disorder associated with memory loss and a progressive decline in cognitive activity. The two major pathophysiological factors responsible for AD are amyloid plaques (comprising amyloid-beta aggregates) and neurofibrillary tangles (consisting of hyperphosphorylated tau protein). Polyphenols, a class of naturally occurring compounds, are immensely beneficial for the treatment or management of various disorders and illnesses. Naturally occurring sources of polyphenols include plants and plant-based foods, such as fruits, herbs, tea, vegetables, coffee, red wine, and dark chocolate. Polyphenols have unique properties, such as being the major source of anti-oxidants and possessing anti-aging and anti-cancerous properties. Currently, dietary polyphenols have become a potential therapeutic approach for the management of AD, depending on various research findings. Dietary polyphenols can be an effective strategy to tackle multifactorial events that occur with AD. For instance, naturally occurring polyphenols have been reported to exhibit neuroprotection by modulating the Aβ biogenesis pathway in AD. Many nanoformulations have been established to enhance the bioavailability of polyphenols, with nanonization being the most promising. This review comprehensively provides mechanistic insights into the neuroprotective potential of dietary polyphenols in treating AD. It also reviews the usability of dietary polyphenol as nanoformulation for AD treatment.

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic- and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice 24 h post-treatment. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than anxiolytic effects.

Astrocytic GABAergic Regulation in Alcohol Use and Major Depressive Disorders

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system (CNS). Most GABAergic neurons synthesize GABA from glutamate and release it in the synaptic cleft in the CNS. However, astrocytes can also synthesize and release GABA, activating GABA receptors in the neighboring neurons in physiological and pathological conditions. As the primary homeostatic glial cells in the brain, astrocytes play a crucial role in regulating GABA homeostasis and synaptic neurotransmission. Accumulating evidence demonstrates that astrocytic GABA dysregulation is implicated in psychiatric disorders, including alcohol use disorder (AUD) and major depressive disorder (MDD), the most prevalent co-occurring psychiatric disorders. Several current medications and emerging pharmacological agents targeting GABA levels are in clinical trials for treating AUD and MDD. This review offers a concise summary of the role of astrocytic GABA regulation in AUD and MDD. We also provide an overview of the current understanding and areas of debate regarding the mechanisms by which astrocytes regulate GABA in the CNS and their potential significance in the molecular basis of AUD and MDD, paving the way toward future research directions and potential therapeutic target areas within this field.

The Efficacy and Safety of Intranasal Formulations of Ketamine and Esketamine for the Treatment of Major Depressive Disorder: A Systematic Review

Ketamine and its enantiomers represent an innovative glutamatergic agent as a treatment for individuals with treatment-resistant depression (TRD) and major depressive disorder (MDD) with suicidal ideation and behavior. Intranasal (IN) formulations could allow for quick onset of action on depressive symptoms as well as a reduction in side effects by bypassing the blood-brain barrier compared with administration via the intravenous route. The aim of this review was to provide an up-to-date analysis of the data on the efficacy and safety of IN ketamine and IN esketamine for the treatment of MDD. A systematic review following PRISMA guidelines was conducted. Databases (PubMed, Embase, MEDLINE, PsycINFO, and Google Scholar) were searched to capture articles about IN ketamine or IN esketamine for MDD. This systematic review highlighted the interest in IN routes of ketamine and esketamine for MDD patients with TRD or active suicidal ideation. They provide a rapid onset of antidepressant action within the first hours after administration. Nevertheless, the evidence of efficacy is stronger for IN esketamine than for IN ketamine in MDD patients. The safety profile appears to be acceptable for IN esketamine but requires further studies, and a more accurate IN delivery device is required for ketamine.

A role of splenic heme biosynthesis pathway in the persistent prophylactic actions of arketamine in lipopolysaccharide-treated mice

Relapse is common in remitted patients with major depressive disorder (MDD). Arketamine, an (R)-enantiomer of ketamine, has persistent prophylactic actions in an inflammatory model of depression. However, the precise mechanisms underlying these prophylactic actions remain unknown. Given the role of the brain-spleen axis in depression, we sought to identify splenic molecular targets that play a role in the prophylactic actions of arketamine. Lipopolysaccharide (LPS) (1.0 mg/kg) was administered 6 days after a single injection of arketamine (10 mg/kg) or saline. RNA-sequencing analysis found altered expression in the heme biosynthesis II pathway. Quantitative RT-PCR revealed that pretreatment with arketamine blocked increased expression of genes involved in the heme biosynthesis II pathway in LPS-treated mice, namely, 5-aminolevulinase synthase 2 (Alas2), ferrochelatase (Fech), hydroxymethylbilane synthase (Hmbs). Interestingly, there were positive correlations between the expression of these genes and spleen weight or plasma levels of pro-inflammatory cytokines. We also found higher expression of ALAS2 and FECH in the spleen from MDD patients. Pretreatment with a key intermediate precursor of heme, 5-aminolaevulinic acid (300 mg/kg/day for 3 days), caused splenomegaly, higher plasma levels of pro-inflammatory cytokines, and depression-like behavior in low-dose LPS (0.1 mg/kg)-treated mice. Interestingly, pretreatment with a heme biosynthesis inhibitor, succinyl acetone (120 mg/kg/day for 3 days), had prophylactic effects in LPS (1.0 mg/kg)-treated mice. These data suggest a novel role for the heme biosynthesis II pathway in the spleen for inflammation-related depression. Therefore, the heme biosynthesis pathway could be a new target for the prevention of relapse in MDD patients.

A Broadly Applicable Diels-Alder-Based Synthesis of Ketamine-Related Arylcyclohexylamines

Herein, we report the synthesis of aryl derivatives of ketamine and of ketamine's major metabolites hydroxynorketamine (HNK), norketamine (NK), and dehydronorketamine (DHNK) via a microwave-assisted Diels-Alder reaction to form the substituted cyclohexane core structure. Starting with aryl acrylic esters as dienophiles and siloxybutadienes as diene counterparts, a wide range of substituted arylcyclohexylamines was obtained after several modification steps of the initial Diels-Alder products [El Sheikh, S.; Weber, H.; Kortenbrede, L.; Drouvé, N. A broadly applicable Diels-Alder based Synthesis of Ketamine related Arylcyclohexylamines. ChemRxiv 2022, 10.26434/chemrxiv- 2022-xf1l9].

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT 2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic-and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice 24 h post-treatment. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than an anxiolytic effects.

Binding Affinity and Mechanisms of Potential Antidepressants Targeting Human NMDA Receptors

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

Ketamine as a therapeutic agent in major depressive disorder and posttraumatic stress disorder: Potential medicinal and deleterious effects

Major depressive disorder (MDD) and posttraumatic stress disorder (PTSD) are the most common causes of emotional distress that impair an individual's quality of life. MDD is a chronic mental illness that affects 300 million people across the world. Clinical manifestations of MDD include fatigue, loss of interest in routine tasks, psychomotor agitation, impaired ability to focus, suicidal ideation, hypersomnolence, altered psychosocial functioning, and appetite loss. Individuals with depression also demonstrate a reduced behavioral response while experiencing pleasure, a symptom known as anhedonia. Like MDD, PTSD is a prevalent and debilitating psychiatric disorder resulting from a traumatic incident such as sexual assault, war, severe accident, or natural disaster. Symptoms such as recalling event phases, hypervigilance, irritability, and anhedonia are common in PTSD. Both MDD and PTSD pose enormous socioeconomic burdens across the globe. The search for effective treatment with minimal side effects is still ongoing. Ketamine is known for its anesthetic and analgesic properties. Psychedelic and psychotropic effects of ketamine have been found on the nervous system, which highlights its toxicity. In this article, the effectiveness of ketamine as a potential therapeutic for PTSD and MDD along with its mechanisms of action, clinical trials, and possible side effects have been discussed.

Ketamine and its metabolites: Potential as novel treatments for depression

Depression is a well-known serious mental illness, and the onset of treatment using traditional antidepressants is frequently delayed by several weeks. Moreover, numerous patients with depression fail to respond to therapy. One major breakthrough in antidepressant therapy is that subanesthetic ketamine doses can rapidly alleviate depressive symptoms within hours of administering a single dose, even in treatment-resistant patients. However, specific mechanisms through which ketamine exerts its antidepressant effects remain elusive, leading to concerns regarding its rapid and long-lasting antidepressant effects. N-methyl-d-aspartate receptor (NMDAR) antagonists like ketamine are reportedly associated with serious side effects, such as dissociative symptoms, cognitive impairment, and abuse potential, limiting the large-scale clinical use of ketamine as an antidepressant. Herein, we reviewed the pharmacological properties of ketamine and the mechanisms of action underlying the rapid antidepressant efficacy, including the disinhibition hypothesis and synaptogenesis, along with common downstream effector pathways such as enhanced brain-derived neurotrophic factor and tropomyosin-related kinase B signaling, activation of the mechanistic target of rapamycin complex 1 and transforming growth factor β1. We focused on evidence supporting the relevance of these potential mechanisms of ketamine and its metabolites in mediating the clinical efficacy of the drug. Given its reported antidepressant efficacy in preclinical studies and limited undesirable adverse effects, (R)-ketamine may be a safer, more controllable, rapid antidepressant. Overall, understanding the potential mechanisms of action of ketamine and its metabolites in combination with pharmacology may help develop a new generation of rapid antidepressants that maximize antidepressant effects while avoiding unfavorable adverse effects. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

A role of microRNA-149 in the prefrontal cortex for prophylactic actions of (R)-ketamine in inflammation model

MicroRNAs (or miRNAs) are short, regulatory RNAs that act as post-transcriptional repressors of gene expression. Recently, we reported that the nuclear factor of activated T cells 4 (NFATc4) signaling might contribute to sustained prophylactic effects of new antidepressant (R)-ketamine in lipopolysaccharide (LPS)-treated inflammation model of depression. In this study, we examined the role of miRNAs (miR-149 and miR-7688-5p) which can regulate NFATc4 in the prefrontal cortex (PFC) of male mice after administration of LPS (1.0 mg/kg). There was a positive correlation between the expression of Nfatc4 and the expression of miR-149 in the PFC. There was also a negative correlation between gene expression of Nfatc4 and gene expression of miR-7688-5p in the PFC. Gut microbiota analysis showed that pretreatment with (R)-ketamine (10 mg/kg) could restore altered composition of gut microbiota in LPS-treated mice. A network analysis showed that gut microbiota may regulate gene expression of Nfatc4 and miR-149 (or miR-7688-5p) in the PFC. Finally, inhibition of miR-149 by antagomiR-149 blocked LPS-induced depression-like behavior by attenuating LPS-induced expression of NFATc4 in the PFC. These findings suggest that the regulation of NFATc4 signaling by miR-149 might play a role in persistent prophylactic effects of (R)-ketamine, and that gut microbiota may regulate the gene expression of miRNAs in the PFC through gut-microbiota-brain axis.

Maintenance ketamine treatment for depression: a systematic review of efficacy, safety, and tolerability

Ketamine has rapid yet often transient antidepressant effects in patients with treatment-resistant depression. Different strategies have been proposed to prolong these effects. Maintenance ketamine treatment appears promising, but little is known about its efficacy, safety, and tolerability in depression. We searched Pubmed, Embase, and the Cochrane Library and identified three randomised controlled trials, eight open-label trials, and 30 case series and reports on maintenance ketamine treatment. We found intravenous, intranasal, oral, and possibly intramuscular and subcutaneous maintenance ketamine treatment to be effective in sustaining antidepressant effect in treatment-resistant depression. Tachyphylaxis, cognitive impairment, addiction, and serious renal and urinary problems seem uncommon. Despite the methodological limitations, we conclude that from a clinical view, maintenance ketamine treatment seems to be of therapeutic potential. We recommend both controlled and naturalistic studies with long-term follow-up and sufficient power to determine the position of maintenance ketamine treatment within routine clinical practice.

Where do we go next in antidepressant drug discovery? A new generation of antidepressants: a pivotal role of AMPA receptor potentiation and mGlu2/3 receptor antagonism

INTRODUCTION

Major depressive disorder remains a prevalent world-wide health problem. Currently available antidepressant medications take weeks of dosing, do not produce antidepressant response in all patients, and have undesirable ancillary effects.

AREAS COVERED

The present opinion piece focuses on the major inroads to the creation of new antidepressants. These include N-methyl-D-aspartate (NMDA) receptor antagonists and related compounds like ketamine, psychedelic drugs like psilocybin, and muscarinic receptor antagonists like scopolamine. The preclinical and clinical pharmacological profile of these new-age antidepressant drugs is discussed.

EXPERT OPINION

Preclinical and clinical data have accumulated to predict a next generation of antidepressant medicines. In contrast to the current standard of care antidepressant drugs, these compounds differ in that they demonstrate rapid activity, often after a single dose, and effects that outlive their presence in brain. These compounds also can provide efficacy for treatment-resistant depressed patients. The mechanism of action of these compounds suggests a strong glutamatergic component that involves the facilitation of AMPA receptor function. Antagonism of mGlu2/3 receptors is also relevant to the antidepressant pharmacology of this new class of drugs. Based upon the ongoing efforts to develop these new-age antidepressants, new drug approvals are predicted in the near future.

A key role of miR-132-5p in the prefrontal cortex for persistent prophylactic actions of (R)-ketamine in mice

(R,S)-ketamine is known to elicit persistent prophylactic effects in rodent models of depression. However, the precise molecular mechanisms underlying its action remain elusive. Using RNA-sequencing analysis, we searched for novel molecular target(s) that contribute to the prophylactic effects of (R)-ketamine, a more potent enantiomer of (R,S)-ketamine in chronic restraint stress (CRS) model. Pretreatment with (R)-ketamine (10 mg/kg, 1 day before CRS) significantly ameliorated body weight loss, increased immobility time of forced swimming test, and decreased sucrose preference of sucrose preference test in CRS-exposed mice. RNA-sequencing analysis of prefrontal cortex (PFC) revealed that several miRNAs such as miR-132-5p might contribute to sustained prophylactic effects of (R)-ketamine. Methyl CpG binding protein 2 (MeCP2) is known to regulate brain-derived neurotrophic factor (BDNF) expression. Quantitative RT-PCR confirmed that (R)-ketamine significantly attenuated altered expression of miR-132-5p and its regulated genes (Bdnf, Mecp2, Tgfb1, Tgfbr2) in the PFC of CRS-exposed mice. Furthermore, (R)-ketamine significantly attenuated altered expression of BDNF, MeCP2, TGF-β1 (transforming growth factor β1), and synaptic proteins (PSD-95, and GluA1) in the PFC of CRS-exposed mice. Administration of agomiR-132-5p decreased the expression of Bdnf and Tgfb1 in the PFC, resulting in depression-like behaviors. In contrast, administration of antagomiR-132-5p blocked the increased expression of miR-132-5p and decreased expression of Bdnf in the PFC of CRS-exposed mice, resulting in antidepressant-like effects. In conclusion, our data show a novel role of miR-132-5p in the PFC underlying depression-like phenotypes in CRS model and the sustained prophylactic effects of (R)-ketamine.

Arketamine, a new rapid-acting antidepressant: A historical review and future directions

The N-methyl-d-aspartate receptor (NMDAR) antagonist (R,S)-ketamine causes rapid onset and sustained antidepressant actions in treatment-resistant patients with major depressive disorder (MDD) and other psychiatric disorders, such as bipolar disorder and post-traumatic stress disorder. (R,S)-ketamine is a racemic mixture consisting of (R)-ketamine (or arketamine) and (S)-ketamine (or esketamine), with (S)-enantiomer having greater affinity for the NMDAR. In 2019, an esketamine nasal spray by Johnson & Johnson was approved in the USA and Europe for treatment-resistant depression. In contrast, an increasing number of preclinical studies show that arketamine has greater potency and longer-lasting antidepressant-like effects than esketamine in rodents, despite the lower binding affinity of arketamine for the NMDAR. Importantly, the side effects, i.e., psychotomimetic and dissociative effects and abuse liability, of arketamine are less than those of (R,S)-ketamine and esketamine in animals and humans. An open-label study demonstrated the rapid and sustained antidepressant effects of arketamine in treatment-resistant patients with MDD. A phase 2 clinical trial of arketamine in treatment-resistant patients with MDD is underway. This study was designed to review the brief history of the novel antidepressant arketamine, the molecular mechanisms underlying its antidepressant actions, and future directions.

Effects of (R)-ketamine on reduced bone mineral density in ovariectomized mice: A role of gut microbiota

Depression is a high risk for osteoporosis, suggesting an association between depression and low bone mineral density (BMD). We reported that the novel antidepressant (R)-ketamine could ameliorate the reduced BMD in the ovariectomized (OVX) mice which is an animal model of postmenopausal osteoporosis. Given the role of gut microbiota in depression and bone homeostasis, we examined whether gut microbiota plays a role in the beneficial effects of (R)-ketamine in the reduced BMD of OVX mice. OVX or sham was operated for female mice. Subsequently, saline (10 ml/kg/day, twice weekly) or (R)-ketamine (10 mg/kg/day, twice weekly) was administered intraperitoneally into OVX or sham mice for the six weeks. The reduction of cortical BMD and total BMD in the OVX mice was significantly ameliorated after subsequent repeated intermittent administration of (R)-ketamine. Furthermore, there were significant changes in the α- and β-diversity between OVX + saline group and OVX + (R)-ketamine group. There were correlations between several OTUs and cortical (or total) BMD. There were also positive correlations between the genera Turicibacter and cortical (or total) BMD. Moreover, there were correlations between several metabolites in blood and cortical (or total) BMD. These data suggest that (R)-ketamine may ameliorate the reduced cortical BMD and total BMD in OVX mice through anti-inflammatory actions via gut microbiota. Therefore, it is likely that (R)-ketamine would be a therapeutic drug for depressed patients with low BMD or patients with osteoporosis.

(R)-ketamine as prophylactic and therapeutic drug for neurological disorders: beyond depression

Neurological disorders are the leading cause of disability and the second leading cause of death worldwide. The increasing social and economic burdens of neurological disorders are driven by global population growth and aging. Depression is a common psychiatric symptom in numerous neurological disorders. It is also a risk factor for Alzheimer's disease (AD) and other dementias, Parkinson's disease (PD), and stroke. The rapid-acting and sustained antidepressant actions of (R,S)-ketamine for severe depression was accidentally discovered. Interestingly, (R)-ketamine has greater potency and longer-lasting antidepressant-like effects than (S)-ketamine in rodents. Importantly, its side effects in rodents and humans are lower than those of (R,S)-ketamine and (S)-ketamine. Furthermore, (R)-ketamine could elicit beneficial actions in various rodent models of neurological disorders, including PD, multiple sclerosis (MS), and stroke. In this article, we review the potential of (R)-ketamine as a prophylactic or therapeutic drug for neurological disorders including AD and other dementias, PD, MS, and stroke.

The Rapid and Long-Lasting Antidepressant Effects of Iridoid Fraction in Gardenia Jasminoides J.Ellis Are Dependent on Activating PKA-CREB Signaling Pathway

Lag periods of therapeutic efficacy cause poor compliance of patients, which has made solutions for rapid antidepressants the most urgent need in the depression study field at present. We have identified through our previous studies the rapid antidepressant effects of the traditional herb Gardenia jasminoides J.Ellis [Rubiaceae] (GJ) and its standardized fractions. Through screening different fractions of GJ, we decided to place our focus on the iridoid fraction of GJ (GJ-IF).

Methods: 1. Tail suspension test (TST), forced swimming test (FST), and novelty suppressed-feeding test (NSFT) were performed in sequence on mice after GJ-IF administration. 2. Mice in the model group were under chronic unpredictable mild stress (CUMS) for 3 w. After GJ-IF treatment, mice were placed in an open field test (OFT), Sucrose preference test (SPT), NSFT, TST, and FST. 3. Western Blot was performed to examine the expression of brain-derived neurotrophic factor (BDNF), Synapsin 1, cyclic-AMP dependent protein kinase A (PKA), phosphorylated cyclic-AMP responsive element-binding protein (p-CREB), and cAMP response element-binding protein (CREB). 4. Mice in the test group were administrated with GJ-IF after intraperitoneal injection of PKA blocker H89.

Results: 1. GJ-IF treatment significantly reduced the immobility time of TST at 1 d and FST at 26 h. 2. GJ-IF reversed the deficits induced by 3 w CUMS in SPT, TST, FST, and NSFT at 1 d and 26 h. The antidepressant effects of a single dose of iridoid fraction could also last for at least 14 d. 3. The results of molecule studies suggested that a single dose of GJ-IF activated p-CREB at 2 h and the PKA-CREB pathway at 1 d. The expression of BDNF did not significantly change from 30 min to 1 d after GJ-IF administration. 4. Blockade of PKA-CREB signaling pathway reversed the antidepressant effects of GJ-IF at 1 d, but not 30 min and 2 h.

Conclusion: GJ-IF is the crucial component in the rapid antidepressant of GJ. Rapid and sustained antidepressant effects of GJ-IF were dependent on activating the PKA-CREB signaling pathway.

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.

Antioxidant Biomolecules and Their Potential for the Treatment of Difficult-to-Treat Depression and Conventional Treatment-Resistant Depression

Major depression is a devastating disease affecting an increasing number of people from a young age worldwide, a situation that is expected to be worsened by the COVID-19 pandemic. New approaches for the treatment of this disease are urgently needed since available treatments are not effective for all patients, take a long time to produce an effect, and are not well-tolerated in many cases; moreover, they are not safe for all patients. There is solid evidence showing that the antioxidant capacity is lower and the oxidative damage is higher in the brains of depressed patients as compared with healthy controls. Mitochondrial disfunction is associated with depression and other neuropsychiatric disorders, and this dysfunction can be an important source of oxidative damage. Additionally, neuroinflammation that is commonly present in the brain of depressive patients highly contributes to the generation of reactive oxygen species (ROS). There is evidence showing that pro-inflammatory diets can increase depression risk; on the contrary, an anti-inflammatory diet such as the Mediterranean diet can decrease it. Therefore, it is interesting to evaluate the possible role of plant-derived antioxidants in depression treatment and prevention as well as other biomolecules with high antioxidant and anti-inflammatory potential such as the molecules paracrinely secreted by mesenchymal stem cells. In this review, we evaluated the preclinical and clinical evidence showing the potential effects of different antioxidant and anti-inflammatory biomolecules as antidepressants, with a focus on difficult-to-treat depression and conventional treatment-resistant depression.

Efficacy and safety of repeated esketamine intravenous infusion in the treatment of treatment-resistant depression: A case series

Repeated intravenous administration of esketamine may increase and prolong the treatment efficacy of depressive patients. Firstly, the patient received esketamine (0.4 mg/kg intravenous over 40 min) infusion every other day, and totally 6 times infusion. If the patient's symptoms cannot improve, they got another 6 times esketamine injection (one time per day, 0.4 mg/kg intravenous over 40 min). Our study reported that 12 times intravenous esketamine infusion adjunctive with oral antidepressants sustained the efficacy for 6 months at least. These cases provide evidence of the safety and longtime efficacy of repeated intravenous esketamine for the treatment of treatment resistant depression.

Nuclear factor of activated T cells 4 in the prefrontal cortex is required for prophylactic actions of (R)-ketamine

(R, S)-ketamine has prophylactic antidepressant-like effects in rodents; however, the precise molecular mechanisms underlying its action remain unknown. Using RNA-sequencing analysis, we searched novel molecular target(s) that contribute to the prophylactic effects of (R)-ketamine, a more potent enantiomer of (R, S)-ketamine. Pretreatment with (R)-ketamine (10 mg/kg, 6 days before) significantly ameliorated body weight loss, splenomegaly, and increased immobility time of forced swimming test in lipopolysaccharide (LPS: 1.0 mg/kg)-treated mice. RNA-sequencing analysis of prefrontal cortex (PFC) and subsequent IPA (Ingenuity Pathway Analysis) revealed that the nuclear factor of activated T cells 4 (NFATc4) signaling might contribute to sustained prophylactic effects of (R)-ketamine. Quantitative RT-PCR confirmed that (R)-ketamine significantly attenuated the increased gene expression of NFATc4 signaling (Nfatc4, Cd4, Cd79b, H2-ab1, H2-aa) in the PFC of LPS-treated mice. Furthermore, pretreatment with NFAT inhibitors (i.e., NFAT inhibitor and cyclosporin A) showed prophylactic effects in the LPS-treated mice. Similar to (R)-ketamine, gene knockdown of Nfatc4 gene by bilateral injection of adeno-associated virus (AAV) into the mPFC could elicit prophylactic effects in the LPS-treated mice. In conclusion, our data implicate a novel NFATc4 signaling pathway in the PFC underlying the prophylactic effects of (R)-ketamine for inflammation-related depression.

Molecular mechanisms underlying the antidepressant actions of arketamine: beyond the NMDA receptor

The discovery of robust antidepressant actions exerted by the N-methyl-D-aspartate receptor (NMDAR) antagonist (R,S)-ketamine has been a crucial breakthrough in mood disorder research. (R,S)-ketamine is a racemic mixture of equal amounts of (R)-ketamine (arketamine) and (S)-ketamine (esketamine). In 2019, an esketamine nasal spray from Johnson & Johnson was approved in the United States of America and Europe for treatment-resistant depression. However, an increasing number of preclinical studies show that arketamine has greater potency and longer-lasting antidepressant-like effects than esketamine in rodents, despite the lower binding affinity of arketamine for the NMDAR. In clinical trials, non-ketamine NMDAR-related compounds did not exhibit ketamine-like robust antidepressant actions in patients with depression, despite these compounds showing antidepressant-like effects in rodents. Thus, the rodent data do not necessarily translate to humans due to the complexity of human psychiatric disorders. Collectively, the available studies indicate that it is unlikely that NMDAR plays a major role in the antidepressant action of (R,S)-ketamine and its enantiomers, although the precise molecular mechanisms underlying antidepressant actions of (R,S)-ketamine and its enantiomers remain unclear. In this paper, we review recent findings on the molecular mechanisms underlying the antidepressant actions of (R,S)-ketamine and its potent enantiomer arketamine. Furthermore, we discuss the possible role of the brain-gut-microbiota axis and brain-spleen axis in stress-related psychiatric disorders and in the antidepressant-like action of arketamine. Finally, we discuss the potential of arketamine as a treatment for cognitive impairment in psychiatric disorders, Parkinson's disease, osteoporosis, inflammatory bowel diseases, and stroke.

Microglial ERK-NRBP1-CREB-BDNF signaling in sustained antidepressant actions of (R)-ketamine

(R,S)-ketamine elicits rapid-acting and sustained antidepressant actions in treatment-resistant patients with depression. (R)-ketamine produces longer-lasting antidepressant effects than (S)-ketamine in rodents; however, the precise molecular mechanisms underlying antidepressant actions of (R)-ketamine remain unknown. Using isobaric Tag for Relative and Absolute Quantification, we identified nuclear receptor-binding protein 1 (NRBP1) that could contribute to different antidepressant-like effects of the two enantiomers in chronic social defeat stress (CSDS) model. NRBP1 was localized in the microglia and neuron, not astrocyte, of mouse medial prefrontal cortex (mPFC). (R)-ketamine increased the expression of NRBP1, brain-derived neurotrophic factor (BDNF), and phosphorylated cAMP response element binding protein (p-CREB)/CREB ratio in primary microglia cultures thorough the extracellular signal-regulated kinase (ERK) activation. Furthermore, (R)-ketamine could activate BDNF transcription through activation of CREB as well as MeCP2 (methyl-CpG binding protein 2) suppression in microglia. Single intracerebroventricular (i.c.v.) injection of CREB-DNA/RNA heteroduplex oligonucleotides (CREB-HDO) or BDNF exon IV-HDO blocked the antidepressant-like effects of (R)-ketamine in CSDS susceptible mice. Moreover, microglial depletion by colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX3397 blocked the antidepressant-like effects of (R)-ketamine in CSDS susceptible mice. In addition, inhibition of microglia by single i.c.v. injection of mannosylated clodronate liposomes (MCLs) significantly blocked the antidepressant-like effects of (R)-ketamine in CSDS susceptible mice. Finally, single i.c.v. injection of CREB-HDO, BDNF exon IV-HDO or MCLs blocked the beneficial effects of (R)-ketamine on the reduced dendritic spine density in the mPFC of CSDS susceptible mice. These data suggest a novel ERK-NRBP1-CREB-BDNF pathways in microglia underlying antidepressant-like effects of (R)-ketamine.

Mechanisms of the Rapid Effects of Ketamine on Depression and Sleep Disturbances: A Narrative Review

Recently, sleep has been recognized as a crucial factor for health and longevity. The daily sleep/wake cycle provides the basis of biorhythm, which controls whole-body homeostasis and homeodynamics. Sleep disturbances can contribute to several physical and psychological disorders, including cardiovascular disease, obesity, depression, and cognitive dysfunction. The clinical use of the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine began in the 1970s. Over the years, physicians have used it as a short-acting anesthetic, analgesic, and antidepressant; however, in-depth research has revealed new possible applications for ketamine, such as for treating sleep disturbances and circadian rhythm disorders. The aim of this narrative review is to examine the literature on the mechanistic role of the antidepressant ketamine in affecting sleep disturbance. Additionally, we discuss the pharmacologic and pharmacokinetic mechanisms of ketamine as an antidepressant and the predictive biomarkers for ketamine’s effect on sleep and cognitive function.

Repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages prevents schizophrenia-relevant phenotypes in adult offspring after maternal immune activation: a role of TrkB signaling

Maternal immune activation (MIA) plays a role in the etiology of schizophrenia. MIA by prenatal exposure of polyinosinic:polycytidylic acid [poly(I:C)] in rodents caused behavioral and neurobiological changes relevant to schizophrenia in adult offspring. We investigated whether the novel antidepressant (R)-ketamine could prevent the development of psychosis-like phenotypes in adult offspring after MIA. We examined the effects of (R)-ketamine (10 mg/kg/day, twice weekly for 4 weeks) during juvenile and adolescent stages (P28-P56) on the development of cognitive deficits, loss of parvalbumin (PV)-immunoreactivity in the medial prefrontal cortex (mPFC), and decreased dendritic spine density in the mPFC and hippocampus from adult offspring after prenatal poly(I:C) exposure. Furthermore, we examined the role of TrkB in the prophylactic effects of (R)-ketamine. Repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages significantly blocked the development of cognitive deficits, reduced PV-immunoreactivity in the prelimbic (PrL) of mPFC, and decreased dendritic spine density in the PrL of mPFC, CA3 and dentate gyrus of the hippocampus from adult offspring after prenatal poly(I:C) exposure. Furthermore, pretreatment with ANA-12 (TrkB antagonist: twice weekly for 4 weeks) significantly blocked the beneficial effects of (R)-ketamine on cognitive deficits of adult offspring after prenatal poly(I:C) exposure. These data suggest that repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages could prevent the development of psychosis in adult offspring after MIA. Therefore, (R)-ketamine would be a potential prophylactic drug for young subjects with high-risk for psychosis.

Antidepressant-like actions of the mGlu2/3 receptor antagonist TP0178894 in the chronic social defeat stress model: Comparison with escitalopram

The metabotropic glutamate 2/3 (mGlu2/3) receptor antagonists are reported to produce ketamine-like rapid-acting and sustained antidepressant-like effects in rodents. In this study, we compared the effects of single administration of the new mGlu2/3 receptor antagonist TP0178894 and the selective serotonin reuptake inhibitor (SSRI) escitalopram in the chronic social defeat stress (CSDS) model of depression, a model which has been shown to be resistant to treatment with a single dose of SSRI. In the tail suspension test and forced swimming test, high dose (3.0 mg/kg) of TP0178894 significantly attenuated the increased immobility time of these tests in CSDS susceptible mice, compared with vehicle-treated mice. In contrast, low doses (0.3 and 1.0 mg/kg) of TP0178894 and escitalopram (10 mg/kg) did not alter the increased immobility time of these two tests. In the sucrose preference test, TP0178894 (3.0 mg/kg) significantly improved the reduced sucrose preference of CSDS susceptible mice, three and seven days after a single dose. In addition, Western blot analyses showed that TP0178894 (3.0 mg/kg), but not low doses of TP0178894 and escitalopram, significantly attenuated the reduced expression of synaptic proteins [α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (GluA1) and postsynaptic density protein 95 (PSD-95)] in the prefrontal cortex from CSDS susceptible mice. This study suggests that TP0178894 shows rapid-acting and sustained antidepressant-like effects in CSDS model, as ketamine does.

Pharmacological and behavioral divergence of ketamine enantiomers: implications for abuse liability

Ketamine, a racemic mixture of (S)-ketamine and (R)-ketamine enantiomers, has been used as an anesthetic, analgesic and more recently, as an antidepressant. However, ketamine has known abuse liability (the tendency of a drug to be used in non-medical situations due to its psychoactive effects), which raises concerns for its therapeutic use. (S)-ketamine was recently approved by the United States' FDA for treatment-resistant depression. Recent studies showed that (R)-ketamine has greater efficacy than (S)-ketamine in preclinical models of depression, but its clinical antidepressant efficacy has not been established. The behavioral effects of racemic ketamine have been studied extensively in preclinical models predictive of abuse liability in humans (self-administration and conditioned place preference [CPP]). In contrast, the behavioral effects of each enantiomer in these models are unknown. We show here that in the intravenous drug self-administration model, the gold standard procedure to assess potential abuse liability of drugs in humans, rats self-administered (S)-ketamine but not (R)-ketamine. Subanesthetic, antidepressant-like doses of (S)-ketamine, but not of (R)-ketamine, induced locomotor activity (in an opioid receptor-dependent manner), induced psychomotor sensitization, induced CPP in mice, and selectively increased metabolic activity and dopamine tone in medial prefrontal cortex (mPFC) of rats. Pharmacological screening across thousands of human proteins and at biological targets known to interact with ketamine yielded divergent binding and functional enantiomer profiles, including selective mu and kappa opioid receptor activation by (S)-ketamine in mPFC. Our results demonstrate divergence in the pharmacological, functional, and behavioral effects of ketamine enantiomers, and suggest that racemic ketamine's abuse liability in humans is primarily due to the pharmacological effects of its (S)-enantiomer.

(R)-ketamine ameliorates the progression of experimental autoimmune encephalomyelitis in mice

Multiple sclerosis (MS) is an immune-mediated neurological disease that attacks the central nervous system, including spinal cord and brain. Experimental autoimmune encephalomyelitis (EAE) is the most commonly used model for MS. Depression is the most prevalent comorbidity in MS patients. We previously demonstrated that (R)-ketamine would be a novel antidepressant without side effects of ketamine. This study was undertaken to investigate whether (R)-ketamine could attenuate disease progression in EAE mouse model. (R)-ketamine (10 mg/kg/day for 15 days) significantly attenuated the reduction of body weight in EAE model mice compared to saline-treated mice. Furthermore, (R)-ketamine ameliorated the clinical EAE scores compared to saline-treated mice. Moreover, (R)-ketamine significantly attenuated the marked increases in the pathological scores, microglial activation, and blood-brain barrier integrity in the spinal cord compared to saline-treated mice. In conclusion, the current study suggests that (R)-ketamine could ameliorate EAE clinical scores and pathological changes in the spinal cord of EAE mice. Therefore, it is likely that (R)-ketamine would be a new potential prophylactic drug for MS.

Intranasal administration of transforming growth factor-β1 elicits rapid-acting antidepressant-like effects in a chronic social defeat stress model: A role of TrkB signaling

(R,S)-ketamine causes rapid-acting and sustained antidepressant effects in treatment-resistant patients with depression although the precise molecular mechanisms underlying its antidepressant action remain unclear. We recently reported that transforming growth factor (TGF)-β1 might contribute to the antidepressant-like effects of (R)-ketamine that is a more potent enantiomer in rodents. Although TrkB signaling plays a role in the antidepressant-like actions of (R,S)-ketamine and its enantiomers, the role of TrkB signaling in the antidepressant effects of TGF-β1 remains unclear. Using behavioral tests such as tail-suspension test (TST), forced swimming test (FST), and 1% sucrose preference test (SPT), we investigated whether a single intranasal administration of the recombinant TGF-β1 (1.5 and 3.0 μg/kg) causes rapid and sustained antidepressant-like effects in a chronic social defeat stress (CSDS) model. Both doses of TGF-β1 significantly attenuated the increased immobility time of TST and FST in the CSDS susceptible mice. High dose of TGF-β1, but not low dose, significantly ameliorated the decreased sucrose preference of SPT in the CSDS susceptible mice. Pretreatment with a TrkB antagonist ANA-12 (0.5 mg/kg) blocked the antidepressant-like effects of TGF-β1 in CSDS susceptible mice. The data suggest that intranasal administration of TGF-β1 could elicit rapid-acting antidepressant-like effects via TrkB stimulation in a CSDS model. Therefore, it is likely that intranasal administration of TGF-β1 would be a novel therapeutic approach for depression.

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

The objective of this study is to evaluate cognition in patients using either ketamine or esketamine to treat TRD. We also evaluate if both ketamine and esketamine as one group influence cognition in patients with TRD. Fifty-four patients with TRD were infused with either ketamine or esketamine and were assessed at three time points: baseline, 24 h, and 7 days after infusion. We applied neuropsychological tests to evaluate executive functions, processing speed, short term memory, and auditory-verbal episodic memory. There is no cognitive difference between ketamine and esketamine, with the exception of one variable. When considered as one group, ketamine and esketamine do not impair cognition; on the contrary, they improve some neuropsychological functions such as visuospatial short-term memory, executive functions, processing speed, and several measures related to episodic verbal memory. Ketamine and esketamine do not present differing cognitive effects when used in antidepressant doses to treat TRD. Furthermore, they rapidly improve many cognitive aspects of patients with TRD at 24 h after the infusion and maintain these effects for at least 7 days.

Novel rapid-acting glutamatergic modulators: Targeting the synaptic plasticity in depression

Major depressive disorder (MDD) is severely prevalent, and conventional monoaminergic antidepressants gradually exhibit low therapeutic efficiency, especially for patients with treatment-resistant depression. A neuroplasticity hypothesis is an emerging advancement in the mechanism of depression, mainly expressed in the glutamate system, e.g., glutamate receptors and signaling. Dysfunctional glutamatergic neurotransmission is currently considered to be closely associated with the pathophysiology of MDD. Biological function, pharmacological action, and signal attributes in the glutamate system both regulate the neural process. Specific functional subunits could be therapeutic targets to explore the novel glutamatergic modulators, which have fast-acting, and relatively sustained antidepressant effects. Here, the present review summarizes the pathophysiology of MDD found in the glutamate system, exploring the role of glutamate receptors and their downstream effects. These convergent mechanisms have prompted the development of other modulators targeting on glutamate system, including N-methyl-d-aspartate receptor antagonists, selective GluN2B-specific antagonists, glycine binding site agents, and regulators of metabotropic glutamate receptors. Relevant researches underly the putative mechanisms of these drugs, which reverse the damage of depression by regulating glutamatergic neurotransmission. It also provides further insight into the mechanism of depression and exploring potential targets for novel agent development.

Dextran sulfate sodium-induced inflammation and colitis in mice are ameliorated by (R)-ketamine, but not (S)-ketamine: A role of TrkB signaling

Ulcerative colitis (UC) is a chronic inflammatory bowel disease that causes long-lasting inflammation and colitis in the gastrointestinal tract. Depression is a common symptom in patients with UC. (R)-ketamine is a new safer antidepressant than (R,S)-ketamine and (S)-ketamine. Here, we examined the effects of two ketamine enantiomers on the dextran sulfate sodium (DSS)-induced colitis model of UC. Ingestion of 3% DSS in drinking water for 14 days increased the scores of Disease Activity Index (DAI) in mice. Repeated administration of (R)-ketamine (10 mg/kg/day, 14 days or last 7 days), but not (S)-ketamine (10 mg/kg/day, 14 days or last 7 days), significantly ameliorated the increased DAI score and increased blood levels of interleukin-6 (IL-6) in DSS-treated mice. In addition, (R)-ketamine, but not (S)-ketamine, attenuated the reduced colonic length in DSS-treated mice. Furthermore, DSS-induced increased DAI score and blood IL-6 levels were significantly ameliorated after subsequent repeated administration of (R)-ketamine (10 mg/kg/day for last 7 days), but not 5-aminosalicyclic acid (50 mg/kg/day for last 7 days). Moreover, the pretreatment with a tropomyosin-receptor-kinase B (TrkB) antagonist ANA-12 (0.5 mg/kg) significantly blocked the beneficial effects of (R)-ketamine in DSS-induced UC model. The study shows that (R)-ketamine can produce beneficial effects in DSS-induced colitis model through TrkB stimulation. Therefore, (R)-ketamine may be a novel therapeutic drug for inflammatory bowel diseases such as UC.

Harnessing Drug Repurposing for Exploration of New Diseases: An Insight to Strategies and Case Studies

BACKGROUND

Traditional drug discovery is time consuming, costly, and risky process. Owing to the large investment, excessive attrition, and declined output, drug repurposing has become a blooming approach for the identification and development of new therapeutics. The method has gained momentum in the past few years and has resulted in many excellent discoveries. Industries are resurrecting the failed and shelved drugs to save time and cost. The process accounts for approximately 30% of the new US Food and Drug Administration approved drugs and vaccines in recent years.

METHODS

A systematic literature search using appropriate keywords were made to identify articles discussing the different strategies being adopted for repurposing and various drugs that have been/are being repurposed.

RESULTS

This review aims to describe the comprehensive data about the various strategies (Blinded search, computational approaches, and experimental approaches) used for the repurposing along with success case studies (treatment for orphan diseases, neglected tropical disease, neurodegenerative diseases, and drugs for pediatric population). It also inculcates an elaborated list of more than 100 drugs that have been repositioned, approaches adopted, and their present clinical status. We have also attempted to incorporate the different databases used for computational repurposing.

CONCLUSION

The data presented is proof that drug repurposing is a prolific approach circumventing the issues poised by conventional drug discovery approaches. It is a highly promising approach and when combined with sophisticated computational tools, it also carries high precision. The review would help researches in prioritizing the drugrepositioning method much needed to flourish the drug discovery research.

Intravenous arketamine for treatment-resistant depression: open-label pilot study

We aimed to analyze the efficacy and safety of arketamine, the R(-)-enantiomer of ketamine, for treatment-resistant depression (TRD) in humans. Open-label pilot trial, seven subjects with TRD received a single intravenous infusion of arketamine (0.5 mg/kg); primary outcome was change in Montgomery-Åsberg Depression Rating Scale (MADRS) 24 h after. Mean MADRS dropped from 30.7 before infusion to 10.4 after one day, a mean difference of 20.3 points [CI 95% 13.6-27.0; p < 0.001]; dissociation was nearly absent. Arketamine might produce fast-onset and sustained antidepressant effects in humans with favorable safety profile, like previously reported with animals; further controlled-trials are needed.

Rapid-acting and long-lasting antidepressant-like action of (R)-ketamine in Nrf2 knock-out mice: a role of TrkB signaling

The transcription nuclear factor-erythroid factor 2-related factor 2 (Nrf2) plays a key role in inflammation that is involved in depression. We previously reported that Nrf2 knock-out (KO) mice exhibit depression-like phenotypes through systemic inflammation. (R)-ketamine, an enantiomer of ketamine, has rapid-acting and long-lasting antidepressant-like effects in rodents. We investigated whether (R)-ketamine can produce antidepressant-like effects in Nrf2 KO mice. Effects of (R)-ketamine on the depression-like phenotypes in Nrf2 KO mice were examined. Furthermore, the role of TrkB in the antidepressant-like actions of (R)-ketamine was also examined. In the tail-suspension test (TST) and forced swimming test (FST), (R)-ketamine (10 mg/kg) significantly attenuated the increased immobility times of TST and FST in the Nrf2 KO mice. In the sucrose preference test (SPT), (R)-ketamine significantly ameliorated the reduced preference of SPT in Nrf2 KO mice. Decreased expression of synaptic proteins (i.e., GluA1 and PSD-95) in the medial prefrontal cortex (mPFC) of Nrf2 KO mice was significantly ameliorated after a single injection of (R)-ketamine. Furthermore, the pre-treatment with the TrkB antagonist ANA-12 (0.5 mg/kg) significantly blocked the rapid and long-lasting antidepressant-like effects of (R)-ketamine in Nrf2 KO mice. Furthermore, ANA-12 significantly antagonized the beneficial effects of (R)-ketamine on decreased expression of synaptic proteins in the mPFC of Nrf2 KO mice. These findings suggest that (R)-ketamine can produce rapid and long-lasting antidepressant-like actions in Nrf2 KO mice via TrkB signaling.

Efficacy of anticonvulsant ethosuximide for major depressive disorder: a randomized, placebo-control clinical trial

Results of a preclinical study suggested that the anticonvulsant drug ethosuximide may elicit ketamine-like rapid-acting antidepressant actions. We evaluated the antidepressant efficacy of ethosuximide versus placebo in non-medicated adult patients with major depressive disorder (MDD). This randomized, double-blind, placebo-controlled trial included patients at three mental health centers in China. Eighty eligible adults (aged 18-65 years) met the DSM-5 criteria for MDD. Patients in the acute single study received three doses (500, 1000, or 1500 mg) of ethosuximide or placebo. Patients in the repeated study received ethosuximide (1500 mg/day) or placebo for 2 weeks. The Hamilton Depression Rating Scale (HAM-D), the Montgomery-Åsberg Depression Rating Scale (MADRS), and the Hamilton Anxiety Rating Scale were used to assess antidepressant and antianxiety responses to ethosuximide. No significant reductions in depression and anxiety rating scale scores were observed after a single oral administration of ethosuximide, in comparison with placebo. Furthermore, patients receiving ethosuximide for 2 weeks did not show reductions in depression and anxiety rating scale scores. There were no serious adverse events. Responses to the study's primary and secondary outcome measures, the clinician-rated HAM-D and MADRS, showed no change from baseline to the end of treatment, with either ethosuximide or placebo. These results suggest that ethosuximide does not produce ketamine-like robust antidepressant actions in adult patients with MDD.

Repurposing of CNS drugs to treat COVID-19 infection: targeting the sigma-1 receptor

The novel coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The escalating number of SARS-CoV-2-infected individuals has conferred the viral spread with the status of global pandemic. However, there are no prophylactic or therapeutic drugs available on the market to treat COVID-19, although several drugs have been approved. Recently, two articles using the comparative viral-human protein-protein interaction map revealed that the sigma-1 receptor in the endoplasmic reticulum plays an important role in SARS-CoV-2 replication in cells. Knockout and knockdown of SIGMAR1 (sigma-1 receptor, encoded by SIGMAR1) caused robust reductions in SARS-CoV-2 replication, which indicates that the sigma-1 receptor is a key therapeutic target for SARS-CoV-2 replication. Interestingly, a recent clinical trial demonstrated that treatment with the antidepressant fluvoxamine, which has a high affinity at the sigma-1 receptor, could prevent clinical deterioration in adult outpatients infected with SARS-CoV-2. In this review, we discuss the brief history of the sigma-1 receptor and its role in SARS-CoV-2 replication in cells. Here, we propose repurposing of traditional central nervous system (CNS) drugs that have a high affinity at the sigma-1 receptor (i.e., fluvoxamine, donepezil, ifenprodil) for the treatment of SARS-CoV-2-infected patients. Finally, we discussed the potential of other CNS candidates such as cutamesine and arketamine.

Advances in novel molecular targets for antidepressants

Depression is the most common psychiatric illness affecting numerous people world-wide. The currently available antidepressant treatment presents low response and remission rates. Thus, new effective antidepressants need to be developed or discovered. Aiming to give an overview of novel possible antidepressant drug targets, we summarized the molecular targets of antidepressants and the underlying neurobiology of depression. We have also addressed the multidimensional perspectives on the progress in the psychopharmacological treatment of depression and on the new potential approaches with effective drug discovery.

Splenic NKG2D confers resilience versus susceptibility in mice after chronic social defeat stress: beneficial effects of (R)-ketamine

The spleen is a large immune organ that plays a key role in the immune system. The precise molecular mechanisms underlying the relationship between the spleen and stress-related psychiatric disorders are unknown. Here we investigated the role of spleen in stress-related psychiatric disorders. FACS analysis was applied to determine the contribution of the spleen to susceptibility and resilience in mice that were subjected to chronic social defeat stress (CSDS). We found a notable increase in splenic volume and weight in CSDS-susceptible mice compared to control (no CSDS) mice and CSDS-resilient mice. The number of granulocytes, but not of T cells and B cells, in the spleen of susceptible mice was higher than in the spleen of both control and resilient mice. Interestingly, NKG2D (natural killer group 2, member D) expression in the spleen of CSDS-susceptible mice was higher than that in control mice and CSDS-resilient mice. In addition, NKG2D expression in the spleen of patients with depression was higher than that in controls. Both increased splenic weight and increased splenic NKG2D expression in CSDS-susceptible mice were ameliorated after a subsequent administration of (R)-ketamine. The present findings indicate a novel role of splenic NKG2D in stress susceptibility versus resilience in mice subjected to CSDS. Furthermore, abnormalities in splenic functions in CSDS-susceptible mice were ameliorated after subsequent injection of (R)-ketamine. Thus, the brain-spleen axis might, at least in part, contribute to the pathogenesis of stress-related psychiatric disorders such as depression.

Comparative efficacy of racemic ketamine and esketamine for depression: A systematic review and meta-analysis

BACKGROUND

Ketamine appears to have a therapeutic role in certain mental disorders, most notably depression. However, the comparative performance of different formulations of ketamine is less clear.

OBJECTIVES

This study aimed to assess the comparative efficacy and tolerability of racemic and esketamine for the treatment of unipolar and bipolar major depression.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

We searched PubMed, MEDLINE, Embase, PsycINFO, the Cochrane Central Register of Controlled Clinical Trials, and the Cochrane Database of Systematic Reviews for relevant studies published since database inception and December 17, 2019.

STUDY ELIGIBILITY CRITERIA

We considered randomized controlled trials examining racemic or esketamine for the treatment of unipolar or bipolar major depression.

OUTCOMES

Primary outcomes were response and remission from depression, change in depression severity, suicidality, retention in treatment, drop-outs, and drop-outs due to adverse events.

ANALYSIS

Evidence from randomized controlled trials was synthesized as rate ratios (RRs) for treatment response, disorder remission, adverse events, and withdrawals and as standardized mean differences (SMDs) for change in symptoms, via random-effects meta-analyses.

FINDINGS

24 trials representing 1877 participants were pooled. Racemic ketamine relative to esketamine demonstrated greater overall response (RR = 3.01 vs. RR = 1.38) and remission rates (RR = 3.70 vs. RR = 1.47), as well as lower dropouts (RR = 0.76 vs. RR = 1.37).

CONCLUSIONS

Intravenous ketamine appears to be more efficacious than intranasal esketamine for the treatment of depression.

Repurposing of Drugs-The Ketamine Story

An intranasal formulation of esketamine, the S enantiomer of ketamine, in conjunction with an oral antidepressant, has been approved by the FDA for treating treatment-resistant major depressive disorder (TRD) in 2019, almost 50 years after it was approved as an intravenous anesthetic. In contrast to traditional antidepressants, ketamine shows a rapid (within 2 h) and sustained (∼7 days) antidepressant effect and has significant positive effects on antisuicidal ideation. Ketamine's antidepressant mechanism is predominantly mediated by the N-methyl-d-aspartate receptor (NMDA) receptor, although NMDA-independent mechanisms are not ruled out. At the neurocircuitry level, ketamine affects the brain's reward and mood circuitry located in the corticomesolimbic structures involving the hippocampus, nucleus accumbens, and prefrontal cortex. Repurposing of ketamine for treating TRD provided a new understanding of the pathophysiology of depression, a paradigm shift from monoamine to glutamatergic neurotransmission, thus making it a unique tool to investigate the brain and its complex neurocircuitries.

Decreased bone mineral density in ovariectomized mice is ameliorated after subsequent repeated intermittent administration of (R)-ketamine, but not (S)-ketamine

Aim

Depression is a common symptom in people with osteoporosis. (R)‐ketamine produced greater potency and longer‐lasting antidepressant‐like actions than (S)‐ketamine in rodents. Here, we examined the effects of two ketamine enantiomers on the reduced bone mineral density (BMD) in the ovariectomized (OVX) mice which is an animal model of postmenopausal osteoporosis.

Methods

Female ddY mice were OVX or sham‐operated. Subsequently, saline (10 mL/kg/d, twice weekly), (R)‐ketamine (10 mg/kg/d, twice weekly), or (S)‐ketamine (10 mg/kg/d, twice weekly) was administered intraperitoneally into OVX or sham mice for the 6 weeks. The femur from all mice was collected 3 days after the final injection, and BMD in the femur was measured.

Results

The reduction of cortical BMD and total BMD in the OVX mice was significantly ameliorated after subsequent repeated intermittent administration of (R)‐ketamine, but not (S)‐ketamine.

Conclusion

The study shows that (R)‐ketamine can ameliorate the reduced cortical BMD and total BMD in OVX mice. Therefore, (R)‐ketamine would be a novel therapeutic drug for women with osteoporosis.

(R)‐ketamine, but not (S)‐ketamine, ameliorated decreased bone mineral density in ovariectomized mice. Therefore, (R)‐ketamine would be a novel therapeutic drug for women with osteoporosis.