Ketamine and rapid acting antidepressants: Are we ready to cure, rather than treat depression?

Opioid use disorder: current trends and potential treatments

Opioid use disorder (OUD) is a major public health threat, contributing to morbidity and mortality from addiction, overdose, and related medical conditions. Despite our increasing knowledge about the pathophysiology and existing medical treatments of OUD, it has remained a relapsing and remitting disorder for decades, with rising deaths from overdoses, rather than declining. The COVID-19 pandemic has accelerated the increase in overall substance use and interrupted access to treatment. If increased naloxone access, more buprenorphine prescribers, greater access to treatment, enhanced reimbursement, less stigma and various harm reduction strategies were effective for OUD, overdose deaths would not be at an all-time high. Different prevention and treatment approaches are needed to reverse the concerning trend in OUD. This article will review the recent trends and limitations on existing medications for OUD and briefly review novel approaches to treatment that have the potential to be more durable and effective than existing medications. The focus will be on promising interventional treatments, psychedelics, neuroimmune, neutraceutical, and electromagnetic therapies. At different phases of investigation and FDA approval, these novel approaches have the potential to not just reduce overdoses and deaths, but attenuate OUD, as well as address existing comorbid disorders.

Insights into the neurobiology of suicidality: explicating the role of glutamatergic systems through the lens of ketamine

Suicidality is a prevalent mental health condition, and managing suicidal patients is one of the most challenging tasks for health care professionals due to the lack of rapid-acting, effective psychopharmacological treatment options. According to the literature, suicide has neurobiological underpinnings that are not fully understood, and current treatments for suicidal tendencies have considerable limitations. To treat suicidality and prevent suicide, new treatments are required; to achieve this, the neurobiological processes underlying suicidal behavior must be thoroughly investigated. Although multiple neurotransmitter systems, particularly serotonergic systems, have been studied in the past, less has been reported in relation to disruptions in glutamatergic neurotransmission, neuronal plasticity, and neurogenesis that result from stress-related abnormalities of the hypothalamic-pituitary-adrenal system. Informed by the literature, which reports robust antisuicidal and antidepressive properties of subanaesthetic doses of ketamine, this review aims to provide an examination of the neurobiology of suicidality (and relevant mood disorders) with implications of pertinent animal, clinical, and postmortem studies. We discuss dysfunctions in the glutamatergic system, which may play a role in the neuropathology of suicidality and the role of ketamine in restoring synaptic connectivity at the molecular levels.

Imaging synaptic density in depression

Major depressive disorder is a prevalent and heterogeneous disorder with treatment resistance in at least 50% of individuals. Most of the initial studies focused on the monoamine system; however, recently other mechanisms have come under investigation. Specific to the current issue, studies show synaptic involvement in depression. Other articles in this issue report on reductions in synaptic density, dendritic spines, boutons and glia associated with stress and depression. Importantly, it appears that some drugs (e.g., ketamine) may lead to rapid synaptic restoration or synaptogenesis. Direct evidence for this comes from preclinical work. However, neuroimaging studies, such as magnetic resonance imaging (MRI) and positron emission tomography (PET), have become useful in assessing these changes in vivo. Here, we describe the use of neuroimaging techniques in the evaluation of synaptic alterations associated with depression in humans, as well as measurement of synaptic restoration after administration of ketamine. Although more research is desired, use of these techniques widen our understanding of depression and move us further along the path to targeted and effective treatment for depression.

Stress, mental disorder and ketamine as a novel, rapid acting treatment

The experience of stress is often utilised in models of emerging mental illness and neurobiological systems are implicated as the intermediary link between the experience of psychological stress and the development of a mental disorder. Chronic stress and prolonged glucocorticoid exposure have potent effects on neuronal architecture particularly in regions that modulate the hypothalamic-pituitary-adrenal (HPA) axis and are commonly associated with psychiatric disorders. This review provides an overview of stress modulating neurobiological and neurochemical systems which underpin stress-related structural and functional brain changes. These changes are thought to contribute not only to the development of disorders, but also to the treatment resistance and chronicity seen in some of our most challenging mental disorders. Reports to date suggest that stress-related psychopathology is the aetiological mechanism of these disorders and thus we review the rapid acting antidepressant ketamine as an effective emerging treatment. Ketamine, an N-methyl D-aspartate (NMDA) receptor antagonist, is shown to induce a robust treatment effect in mental disorders via enhanced synaptic strength and connectivity in key brain regions. Whilst ketamine's glutamatergic effect has been previously examined, we further consider ketamine's capacity to modulate the HPA axis and associated pathways.

The effects of social isolation stress and discrimination on mental health

Social isolation and discrimination are growing public health concerns associated with poor physical and mental health. They are risk factors for increased morbidity and mortality and reduced quality of life. Despite their detrimental effects on health, there is a lack of knowledge regarding translation across the domains of experimental research, clinical studies, and real-life applications. Here, we review and synthesize evidence from basic research in animals and humans to clinical translation and interventions. Animal models indicate that social separation stress, particularly in early life, activates the hypothalamic-pituitary-adrenal axis and interacts with monoaminergic, glutamatergic, and GABAergic neurotransmitter systems, inducing long-lasting reductions in serotonin turnover and alterations in dopamine receptor sensitivity. These findings are of particular importance for human social isolation stress, as effects of social isolation stress on the same neurotransmitter systems have been implicated in addictive, psychotic, and affective disorders. Children may be particularly vulnerable due to lasting effects of social isolation and discrimination stress on the developing brain. The effects of social isolation and loneliness are pronounced in the context of social exclusion due to discrimination and racism, during widespread infectious disease related containment strategies such as quarantine, and in older persons due to sociodemographic changes. This highlights the importance of new strategies for social inclusion and outreach, including gender, culture, and socially sensitive telemedicine and digital interventions for mental health care.

Looking beyond the opioid receptor: A desperate need for new treatments for opioid use disorder

The mainstay of treatment for opioid use disorder (OUD) is opioid agonist therapy (OAT), which modulates opioid receptors to reduce substance craving and use. OAT maintains dependence on opioids but helps reduce overdose and negative sequelae of substance abuse. Despite increasing availability of OAT, its effectiveness is limited by difficulty in initiating and maintaining patients on treatment. With the worsening opioid epidemic in the United States and rising overdose deaths, a more durable and effective treatment for OUD is necessary. This paper reviews novel treatments being investigated for OUD, including neuromodulatory interventions, psychedelic drugs, and other novel approaches. Neuromodulatory interventions can stimulate the addiction neural circuitry involving the dorsolateral prefrontal cortex and deeper mesolimbic structures to curb craving and reduce use, and multiple clinical trials for interventional treatment for OUD are currently conducted. Similarly, psychedelic agents are being investigated for efficacy in OUD specifically. There is a resurgence of interest in psychedelic agents' therapeutic potential, with evidence of improving mood symptoms and decreased substance use even after just one dose. Exact mechanism of their anti-addictive effect is not fully elucidated, but psychedelic agents do not maintain opioid dependence and some may even be helpful in abating symptoms of withdrawal. Other potential approaches for OUD include targeting different parts of the dopamine-dependent addiction pathway, identifying susceptible genes and modulating gene products, as well as utilizing vaccines as immunotherapy to blunt the addictive effects of substances. Much more clinical data are needed to support efficacy and safety of these therapies in OUD, but these proposed novel treatments look beyond the opioid receptor to offer hope for a more durably effective OUD treatment.

Ketamine in depression and electroconvulsive therapy

PURPOSE OF REVIEW

The antidepressant effect of subanesthetic doses of ketamine was recognized 20 years ago. This review briefly summarizes the current understanding of the antidepressant mechanisms and the available clinical research on the use of racemic ketamine and enantiomer esketamine for depression.

RECENT FINDINGS

The antidepressant effect of subanesthetic doses of ketamine is currently considered to be predominantly mediated by improved neuroplasticity in cortico-limbic areas in the brain. Single dose of 0.5 mg/kg of ketamine infused intravenously over 40 min, or single intranasal dose of esketamine cause rapid antidepressant and antisuicidal effects within hours of administration, and the antidepressant effect may last up to a week. Repeated administration of nasal spray esketamine is considered to prevent relapse of depression. Longitudinal studies are currently insufficient. When used in various doses for anesthetic induction for electroconvulsive therapy, ketamine improves seizure quality and may possibly diminish posttherapy cognitive impairment.

SUMMARY

A rapid onset antidepressive effect of ketamine and esketamine has been proven conclusively. The results of extensive basic science research of the mechanism of action of low-dose ketamine doses has led to an alternative hypothesis of the pathophysiology of depression and the development of a novel neurotrophic concept of depression. Further longitudinal studies are warranted to determine the safety and efficacy of repeated administration of ketamine and its analogs to prevent relapse and recurrence of depression.

Neurobiology of the Rapid-Acting Antidepressant Effects of Ketamine: Impact and Opportunities

The discovery of the rapid-acting antidepressant effects of ketamine has 1) led to a paradigm shift in our perception of what is possible in treating severe depression; 2) spurred a wave of basic, translation, and clinical research; and 3) provided an unprecedented investigational tool to conduct longitudinal mechanistic studies that may capture behavioral changes as complex as clinical remission and relapse within hours and days of treatment. Unfortunately, these advances did not yet translate into clinical biomarkers or novel treatments, beyond ketamine. In contrast to slow-acting antidepressants, in which targeting monoaminergic receptors identified several efficacious drugs with comparable mechanisms, the focus on the receptor targets of ketamine has failed in several clinical trials over the past decade. Thus, it is becoming increasingly crucial that we concentrate our effort on the downstream molecular mechanisms of ketamine and their effects on the brain circuitry and networks. Honoring the legacy of our mentor, friend, and colleague Ron Duman, we provide a historical note on the discovery of ketamine and its putative mechanisms. We then detail the molecular and circuits effect of ketamine based on preclinical findings, followed by a summary of the impact of this work on our understanding of chronic stress pathology across psychiatric disorders, with particular emphasis on the role of synaptic connectivity and its brain network effects in the pathology and treatment of clinical depression.

Repurposing Ketamine in Depression and Related Disorders: Can This Enigmatic Drug Achieve Success?

Repurposing ketamine in the therapy of depression could well represent a breakthrough in understanding the etiology of depression. Ketamine was originally used as an anesthetic drug and later its use was extended to other therapeutic applications such as analgesia and the treatment of addiction. At the same time, the abuse of ketamine as a recreational drug has generated a concern for its psychotropic and potential long-term effects; nevertheless, its use as a fast acting antidepressant in treatment-resistant patients has boosted the interest in the mechanism of action both in psychiatry and in the wider area of neuroscience. This article provides a comprehensive overview of the actions of ketamine and intends to cover: (i) the evaluation of its clinical use in the treatment of depression and suicidal behavior; (ii) the potential use of ketamine in pediatrics; (iii) a description of its mechanism of action; (iv) the involvement of specific brain areas in producing antidepressant effects; (v) the potential interaction of ketamine with the hypothalamic-pituitary-adrenal axis; (vi) the effect of ketamine on neuronal transmission in the bed nucleus of stria terminalis and on its output; (vii) the evaluation of any gender-dependent effects of ketamine; (viii) the interaction of ketamine with the inflammatory processes involved in depression; (ix) the evaluation of the effects observed with single or repeated administration; (x) a description of any adverse or cognitive effects and its abuse potential. Finally, this review attempts to assess whether ketamine's use in depression can improve our knowledge of the etiopathology of depression and whether its therapeutic effect can be considered an actual cure for depression rather than a therapy merely aimed to control the symptoms of depression.

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.

Ketamine: A tale of two enantiomers

The discovery of the rapid antidepressant effects of the dissociative anaesthetic ketamine, an uncompetitive N-Methyl-D-Aspartate receptor antagonist, is arguably the most important breakthrough in depression research in the last 50 years. Ketamine remains an off-label treatment for treatment-resistant depression with factors that limit widespread use including its dissociative effects and abuse potential. Ketamine is a racemic mixture, composed of equal amounts of (S)-ketamine and (R)-ketamine. An (S)-ketamine nasal spray has been developed and approved for use in treatment-resistant depression in the United States and Europe; however, some concerns regarding efficacy and side effects remain. Although (R)-ketamine is a less potent N-Methyl-D-Aspartate receptor antagonist than (S)-ketamine, increasing preclinical evidence suggests (R)-ketamine may have more potent and longer lasting antidepressant effects than (S)-ketamine, alongside fewer side effects. Furthermore, a recent pilot trial of (R)-ketamine has demonstrated rapid-acting and sustained antidepressant effects in individuals with treatment-resistant depression. Research is ongoing to determine the specific cellular and molecular mechanisms underlying the antidepressant actions of ketamine and its component enantiomers in an effort to develop future rapid-acting antidepressants that lack undesirable effects. Here, we briefly review findings regarding the antidepressant effects of ketamine and its enantiomers before considering underlying mechanisms including N-Methyl-D-Aspartate receptor antagonism, γ-aminobutyric acid-ergic interneuron inhibition, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor activation, brain-derived neurotrophic factor and tropomyosin kinase B signalling, mammalian target of rapamycin complex 1 and extracellular signal-regulated kinase signalling, inhibition of glycogen synthase kinase-3 and inhibition of lateral habenula bursting, alongside potential roles of the monoaminergic and opioid receptor systems.

Brain Networks Associated With COVID-19 Risk: Data From 3662 Participants

Background

Our behavioral traits, and subsequent actions, could affect the risk of exposure to the coronavirus disease of 2019 (COVID-19). The current study aimed to determine whether unique brain networks are associated with the COVID-19 infection risk.

Methods

This research was conducted using the UK Biobank Resource. Functional magnetic resonance imaging scans in a cohort of general population (n = 3662) were used to compute the whole-brain functional connectomes. A network-informed machine learning approach was used to identify connectome and nodal fingerprints that are associated with positive COVID-19 status during the pandemic up to February fourth, 2021.

Results

The predictive models successfully identified 6 fingerprints that were associated with COVID-19 positive, compared to negative status (all p values < 0.005). Overall, lower integration across the brain modules and increased segregation, as reflected by internal within module connectivity, were associated with higher infection rates. More specifically, COVID-19 positive status was associated with 1) reduced connectivity between the central executive and ventral salience, as well as between the dorsal salience and default mode networks; 2) increased internal connectivity within the default mode, ventral salience, subcortical and sensorimotor networks; and 3) increased connectivity between the ventral salience, subcortical and sensorimotor networks.

Conclusion

Individuals are at increased risk of COVID-19 infections if their brain connectome is consistent with reduced connectivity in the top-down attention and executive networks, along with increased internal connectivity in the introspective and instinctive networks. These identified risk networks could be investigated as target for treatment of illnesses with impulse control deficits.