Possible antidepressive effects of opioids: action of buprenorphine

Synthetic surprise as the foundation of the psychedelic experience

Psychedelic agents, such as LSD and psilocybin, induce marked alterations in consciousness via activation of the 5-HT2A receptor (5-HT2ARs). We hypothesize that psychedelics enforce a state of synthetic surprise through the biased activation of the 5-HTRs system. This idea is informed by recent insights into the role of 5-HT in signaling surprise. The effects on consciousness, explained by the cognitive penetrability of perception, can be described within the predictive coding framework where surprise corresponds to prediction error, the mismatch between predictions and actual sensory input. Crucially, the precision afforded to the prediction error determines its effect on priors, enabling a dynamic interaction between top-down expectations and incoming sensory data. By integrating recent findings on predictive coding circuitry and 5-HT2ARs transcriptomic data, we propose a biological implementation with emphasis on the role of inhibitory interneurons. Implications arise for the clinical use of psychedelics, which may rely primarily on their inherent capacity to induce surprise in order to disrupt maladaptive patterns.

A Review of Therapeutics for Treatment-Resistant Depression in the Older Adult

One-third of older adults with depression meet criteria for treatment resistance, typically defined as a lack of response to two or more adequate trials of an antidepressant. Treatment resistance contributes to an unfavorable prognosis, compromised medical outcomes, heightened disability, accelerated cognitive decline, and an elevated risk of developing dementia. Despite this significant morbidity, evidence is sparse for how to proceed with treatment in this population. Non-pharmacologic therapy (e.g., diet, psychotherapy) can be utilized as adjunctive therapy, despite little published evidence of benefit, given that the risks are low. Pharmacotherapy trials in the treatment-resistant late-life depression population lack strong methods and external validity; however, the use of venlafaxine as monotherapy and add-on therapy, as well as lithium, bupropion, or aripiprazole as add-on therapy to standard antidepressant therapy, have enough evidence that a trial with appropriate monitoring is a prudent strategy. Electroconvulsive therapy remains a well-studied safe therapy, especially when used as maintenance treatment once an initial cycle is completed but is traditionally underutilized in the treatment-resistant late-life depression population. Ensuring non-pharmacologic and pharmacologic strategies are optimized and given a sufficient trial in those with treatment-resistant late-life depression is the best we can do for this vulnerable population.

Effects of Buprenorphine/Naloxone and Methadone on Depressive Symptoms in People with Prescription Opioid Use Disorder: A Pragmatic Randomised Controlled Trial

OBJECTIVE

This study aimed to evaluate the effectiveness of flexible take-home dosing of buprenorphine/naloxone (BUP/NX) and methadone standard model of care in reducing depressive symptoms in people with prescription-type opioid use disorder (POUD). This trial also evaluated whether improvements in depressive symptoms were mediated by opioid use.

METHODS

Analyzed data came from the OPTIMA study (clinicaltrials.gov identifier: NCT03033732), a pragmatic randomised controlled trial comparing flexible take-home dosing of BUP/NX and methadone standard model of care for reducing opioid use in people with POUD. A total of 272 participants were recruited in four Canadian provinces. Participants were randomised 1:1 to BUP/NX or methadone. After treatment induction, past two-week opioid use was measured using the Timeline Followback every two weeks for a total of 24 weeks. Depressive symptoms were measured with the Beck Depression Inventory at baseline, weeks 12 and 24.

RESULTS

Both BUP/NX and methadone significantly reduced depressive symptoms at week 12 (aβ ± SE = -3.167 ± 1.233; P < 0.001) and week 24 (aβ ± SE = -7.280 ± 1.285; P < 0.001), with no interaction between type of treatment and time (P = 0.284). Improvements in depressive symptoms were only partially mediated by a reduction in opioid use (proportion mediated = 36.8%; 95% confidence interval = -1.158 to -0.070; P = 0.015).

CONCLUSIONS

BUP/NX and methadone showed similar effectiveness in decreasing comorbid depressive symptoms in people with POUD. This effect was partially explained by a reduction in opioid use. As both treatments seem equally effective, clinicians are encouraged to tailor the selection of OAT to patients' needs and characteristics.

Contribution of the opioid system to depression and to the therapeutic effects of classical antidepressants and ketamine

Major depressive disorder (MDD) afflicts approximately 5 % of the world population, and about 30-50 % of patients who receive classical antidepressant medications do not achieve complete remission (treatment resistant depressive patients). Emerging evidence suggests that targeting opioid receptors mu (MOP), kappa (KOP), delta (DOP), and the nociceptin/orphanin FQ receptor (NOP) may yield effective therapeutics for stress-related psychiatric disorders. As depression and pain exhibit significant overlap in their clinical manifestations and molecular mechanisms involved, it is not a surprise that opioids, historically used to alleviate pain, emerged as promising and effective therapeutic options in the treatment of depression. The opioid signaling is dysregulated in depression and numerous preclinical studies and clinical trials strongly suggest that opioid modulation can serve as either an adjuvant or even an alternative to classical monoaminergic antidepressants. Importantly, some classical antidepressants require the opioid receptor modulation to exert their antidepressant effects. Finally, ketamine, a well-known anesthetic whose extremely efficient antidepressant effects were recently discovered, was shown to mediate its antidepressant effects via the endogenous opioid system. Thus, although opioid system modulation is a promising therapeutical venue in the treatment of depression further research is warranted to fully understand the benefits and weaknesses of such approach.

The Differential Influence of PZM21, A Nonrewarding μ-opioid Receptor Agonist With G Protein Bias, on Behavioural Despair and Fear Response in Mice

A growing body of evidence points out the involvement of the µ-opioid receptors in the modulation of stress-related behaviour. It has been suggested that µ-opioid receptor agonists may attenuate behavioural despair following animals' exposure to an acute, inescapable stressor. Moreover, morphine was shown to ameliorate fear memories caused by a traumatic experience. As typical µ-opioid receptor agonists entail a risk of serious side effects and addiction, novel, possibly safer and less addictive agonists of this receptor are currently under investigation. One of them, PZM21, preferentially acting via the G protein signalling pathway, was previously shown to be analgesic, but less addictive than morphine. Here, we aimed to further test this ligand in stress-related behavioural paradigms in mice. The study has shown that, unlike morphine, PZM21 does not decrease immobility in the forced swimming and tail suspension tests. On the other hand, we observed that both mice treated with PZM21 and those receiving morphine presented a slight attenuation of freezing across the consecutive fear memory retrievals in the fear conditioning test. Therefore, our study implies that at the range of tested doses, PZM21, a nonrewarding representative of G protein-biased µ-opioid receptor agonists, may interfere with fear memory consolidation while having no beneficial effects on behavioural despair in mice.

The efficacy and safety of buprenorphine for the treatment of depression: A systematic review and meta-analysis

BACKGROUND

Depressive disorders are common. Many patients with major depression do not achieve remission with available treatments. Buprenorphine has been raised as a potential treatment for depression as well as suicidal behavior but may pose certain risks.

METHODS

A meta-analysis comparing the efficacy, tolerability, and safety of buprenorphine (or combinations such as buprenorphine/samidorphan) versus control in improving symptoms in patients with depression. Medline, Cochrane Database, PsycINFO, Excerpta Medica Database and The Cumulative Index to Nursing and Allied Health Literature were searched from inception through January 2, 2022. Depressive symptoms were pooled using Hedge's g with 95% Confidence Intervals (CI). Tolerability, safety, suicide outcomes were summarized qualitatively.

RESULTS

11 studies (N = 1699) met inclusion criteria. Buprenorphine had a small effect on depressive symptoms (Hedges' g 0.17, 95%CI: 0.05-0.29). Results were driven by six trials of buprenorphine/samidorphan (N = 1,343, Hedges's g 0.17, 95%CI: 0.04-0.29). One study reported significant improvement in suicidal thoughts (Least Squares Mean Change: -7.1, 95%CI: -12.0 - 2.3). Most studies found buprenorphine was well-tolerated with no evidence of abuse behavior or dependency.

CONCLUSIONS

Buprenorphine may have a small benefit for depressive symptoms. Future research should clarify the dose response relationship between buprenorphine and depression.

Inhibition of Microglial GSK3β Activity Is Common to Different Kinds of Antidepressants: A Proposal for an In Vitro Screen to Detect Novel Antidepressant Principles

Depression is a major public health concern. Unfortunately, the present antidepressants often are insufficiently effective, whilst the discovery of more effective antidepressants has been extremely sluggish. The objective of this review was to combine the literature on depression with the pharmacology of antidepressant compounds, in order to formulate a conceivable pathophysiological process, allowing proposals how to accelerate the discovery process. Risk factors for depression initiate an infection-like inflammation in the brain that involves activation microglial Toll-like receptors and glycogen synthase kinase-3β (GSK3β). GSK3β activity alters the balance between two competing transcription factors, the pro-inflammatory/pro-oxidative transcription factor NFκB and the neuroprotective, anti-inflammatory and anti-oxidative transcription factor NRF2. The antidepressant activity of tricyclic antidepressants is assumed to involve activation of GS-coupled microglial receptors, raising intracellular cAMP levels and activation of protein kinase A (PKA). PKA and similar kinases inhibit the enzyme activity of GSK3β. Experimental antidepressant principles, including cannabinoid receptor-2 activation, opioid μ receptor agonists, 5HT2 agonists, valproate, ketamine and electrical stimulation of the Vagus nerve, all activate microglial pathways that result in GSK3β-inhibition. An in vitro screen for NRF2-activation in microglial cells with TLR-activated GSK3β activity, might therefore lead to the detection of totally novel antidepressant principles with, hopefully, an improved therapeutic efficacy.

The Opioid System in Depression

Opioid receptors are widely distributed throughout the brain and play an essential role in modulating aspects of human mood, reward, and well-being. Accumulating evidence indicates the endogenous opioid system is dysregulated in depression and that pharmacological modulators of mu, delta, and kappa opioid receptors hold potential for the treatment of depression. Here we review animal and clinical data, highlighting evidence to support: dysregulation of the opioid system in depression, evidence for opioidergic modulation of behavioural processes and brain regions associated with depression, and evidence for opioidergic modulation in antidepressant responses. We evaluate clinical trials that have examined the safety and efficacy of opioidergic agents in depression and consider how the opioid system may be involved in the effects of other treatments, including ketamine, that are currently understood to exert antidepressant effects through non-opioidergic actions. Finally, we explore key neurochemical and molecular mechanisms underlying the potential therapeutic effects of opioid system engagement, that together provides a rationale for further investigation into this relevant target in the treatment of depression.

Anxiety treatment of methamphetamine-dependent patients with buprenorphine: A randomized, double-blind, clinical trial

Objectives

In this double-blind, randomized clinical trial, the effectiveness of buprenorphine (BUPRE) in the reduction of anxiety symptoms among the methamphetamine (MA) dependents was evaluated.

Materials and Methods

The 60 MA-dependent patients were randomly assigned to three groups (0.1 mg, 1 mg, and 8 mg of BUPRE), The Hamilton Anxiety Rating Scale was administrated to assess the anxiety symptoms daily at baseline and second to the 5^th day after intervention. The inclusion criteria were the MA dependence, age of over 18 years, and absence of any chronic physical illnesses; exclusion criteria were the presence of other drug dependence in combination with MA. The mixed-design analysis of variance was performed for data analysis.

Results

A significant main effect of time (F = 51.456, P < 0.001) and group (F = 4.572, P = 0.014) and group-by-time interaction (F = 8.475, P < 0.001) were detected.

Conclusions

This finding supports the efficacy of BUPRE to decrease anxiety. High doses of the drug (1 and 8 mg) were more effective than 0.1 mg. Here was not a significant difference between anxiety score when patients received 1 mg of BUPRE instead of 8 mg.

Microinduction to Buprenorphine from Methadone for Chronic Pain: Outpatient Protocol with Case Examples

The negative sequelae of full mu agonist chronic opioid analgesic therapy (COAT) are numerous and well documented. One safer alternative to COAT use in chronic, non-cancer pain (CNCP) is a transition to buprenorphine. However, transitioning patients from methadone COAT regimens can be challenging due to the pharmacodynamics of buprenorphine, as well as to the limited commercial formulations of buprenorphine available, and their restrictive instructions for use. Presented here are clinical cases transitioned to buprenorphine from methadone via a novel microinduction protocol during enrollment in an outpatient, group, integrative, multidisciplinary program. The protocol was successful to promote satisfactory and sustained COAT cessation for patients with CNCP and is arguably safer than current conventional practices.

Buprenorphine as a Treatment for Major Depression and Opioid Use Disorder

Rates of major depressive disorder (MDD) are disproportionally high in subjects with opioid use disorder (OUD) relative to the general population. MDD is often more severe in OUD patients, leading to compliance issues with maintenance therapies and poor outcomes. A growing body of literature suggests that endogenous opioid system dysregulation may play a role in the emergence of MDD. Buprenorphine, a mixed opioid receptor agonist/antagonist approved for the treatment of OUD and chronic pain, may have potential as a novel therapeutic for MDD, especially for patients with a dual diagnosis of MDD and OUD. This paper presents a comprehensive review of papers relevant to the assessment of buprenorphine as a treatment for MDD, OUD, and/or suicide compiled using electronic databases per Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The principal goal of this literature review was to compile the clinical studies that have interrogated the antidepressant activity of buprenorphine in opioid naïve MDD patients and OUD patients with comorbid MDD. Evidence supporting buprenorphine's superiority over methadone for treating comorbid OUD and MDD was also considered. Finally, recent evidence for the ability of buprenorphine to alleviate suicidal ideation in both opioid-naïve patients and opioid-experienced patients was evaluated. Synthesizing all of this information, buprenorphine emerges as a potentially effective therapeutic for the dual purposes of treating MDD and OUD.

Novel Targets to Treat Depression: Opioid-Based Therapeutics

After participating in this activity, learners should be better able to:• Identify the effects of dysregulated opioid signalling in depression• Evaluate the use of opioid compounds and ketamine in patients with depression ABSTRACT: Major depressive disorder (MDD) remains one of the leading causes of disability and functional impairment worldwide. Current antidepressant therapeutics require weeks to months of treatment prior to the onset of clinical efficacy on depressed mood but remain ineffective in treating suicidal ideation and cognitive impairment. Moreover, 30%-40% of individuals fail to respond to currently available antidepressant medications. MDD is a heterogeneous disorder with an unknown etiology; novel strategies must be developed to treat MDD more effectively. Emerging evidence suggests that targeting one or more of the four opioid receptors-mu (MOR), kappa (KOR), delta (DOR), and the nociceptin/orphanin FQ receptor (NOP)-may yield effective therapeutics for stress-related psychiatric disorders. Furthermore, the effects of the rapidly acting antidepressant ketamine may involve opioid receptors. This review highlights dysregulated opioid signaling in depression, evaluates clinical trials with opioid compounds, and considers the role of opioid mechanisms in rapidly acting antidepressants.

Multifunctional Enkephalin Analogs with a New Biological Profile: MOR/DOR Agonism and KOR Antagonism

In our previous studies, we developed a series of mixed MOR/DOR agonists that are enkephalin-like tetrapeptide analogs with an N-phenyl-N-piperidin-4-ylpropionamide (Ppp) moiety at the C-terminus. Further SAR study on the analogs, initiated by the findings from off-target screening, resulted in the discovery of LYS744 (6, Dmt-DNle-Gly-Phe(p-Cl)-Ppp), a multifunctional ligand with MOR/DOR agonist and KOR antagonist activity (GTPγS assay: IC₅₀ = 52 nM, I_max = 122% cf. IC₅₀ = 59 nM, I_max = 100% for naloxone) with nanomolar range of binding affinity (K_i = 1.3 nM cf. K_i = 2.4 nM for salvinorin A). Based on its unique biological profile, 6 is considered to possess high therapeutic potential for the treatment of chronic pain by modulating pathological KOR activation while retaining analgesic efficacy attributed to its MOR/DOR agonist activity.

The phenomics and genetics of addictive and affective comorbidity in opioid use disorder

Opioid use disorder (OUD) creates significant public health and economic burdens worldwide. Therefore, understanding the risk factors that lead to the development of OUD is fundamental to reducing both its prevalence and its impact. Significant sources of OUD risk include co-occurring lifetime and current diagnoses of both psychiatric disorders, primarily mood disorders, and other substance use disorders, and unique and shared genetic factors. Although there appears to be pleiotropy between OUD and both mood and substance use disorders, this aspect of OUD risk is poorly understood. In this review, we describe the prevalence and clinical significance of addictive and affective comorbidities as risk factors for OUD development as a basis for rational opioid prescribing and OUD treatment and to improve efforts to prevent the disorder. We also review the genetic variants that have been associated with OUD and other addictive and affective disorders to highlight targets for future study and risk assessment protocols.

Suicide Risk and Addiction: The Impact of Alcohol and Opioid Use Disorders

Purpose of Review

Suicide is a major public health concern and a leading cause of death in the US. Alcohol and opioid use disorders (AUD/OUD) significantly increase risk for suicidal ideation, attempts, and death, and are the two most frequently implicated substances in suicide risk. We provide a brief overview of shared risk factors and pathways in the pathogenesis of AUD/OUD and suicidal thoughts and behaviors. We also review clinical recommendations on inpatient care, pharmacotherapy, and psychotherapeutic interventions for people with AUD/OUD and co-occurring suicidal ideation and behavior.

Recent Findings

Among people with an underlying vulnerability to risk-taking and impulsive behaviors, chronic alcohol intoxication can increase maladaptive coping behaviors and hinder self-regulation, thereby increasing the risk of suicide. Additionally, chronic opioid use can result in neurobiological changes that lead to increases in negative affective states, jointly contributing to suicide risk and continued opioid use. Despite significantly elevated suicide risk in individuals with AUD/OUD, there is a dearth of research on pharmacological and psychosocial interventions for co-occurring AUD/OUD and suicidal ideation and behavior.

Summary

Further research is needed to understand the effects of alcohol and opioid use on suicide risk, as well as address notable gaps in the literature on psychosocial and pharmacological interventions to lower risk for suicide among individuals with AUD/OUD.

The Role of Dynorphin and the Kappa Opioid Receptor in Schizophrenia and Major Depressive Disorder: A Translational Approach

The kappa opioid receptor (KOR) and its endogenous ligands dynorphins (DYN) have been implicated in the development or symptomatology of a variety of neuropsychiatric disorders. This review covers a brief history of the development of KOR agonists and antagonists, their effects in healthy volunteers, and the potential role of DYN/KOR dysfunction in schizophrenia and major depressive disorder from a translational perspective. The potential role of DYN/KOR dysfunction in schizophrenia is based on several lines of evidence. Selective KOR agonists induce affective states in healthy volunteers with similarities to the symptoms of schizophrenia. Studies have shown increased DYN in patients with schizophrenia, although the data have been mixed. Finally, meta-analytic data have shown that opioid antagonists are associated with reductions in the symptoms of schizophrenia. The potential role of DYN/KOR dysfunction in major depressive disorder is also based on a combination of preclinical and clinical data. Selective KOR agonists have shown pro-depressive effects in human volunteers, while selective KOR antagonists have shown robust efficacy in several preclinical models of antidepressant activity. Small studies have shown that nonselective KOR antagonists may have efficacy in treatment-resistant depression. Additionally, recent clinical data have shown that the KOR may be an effective target for treating anhedonia, a finding relevant to both schizophrenia and depression. Finally, recommendations are provided for translating preclinical models for schizophrenia and major depressive disorder into the clinic.

Lowered endogenous mu-opioid receptor availability in subclinical depression and anxiety

Major depressive disorder is associated with lowered mood, anxiety, anhedonia, sleep problems, and cognitive impairments. Many of these functions are regulated by μ-opioid receptor (MOR) system. Preclinical, in vivo, and post-mortem studies have however yielded inconclusive results regarding the role of the MOR in depression and anxiety. Moreover, it is not known whether alterations in MOR are already present in subclinical depression and anxiety. In a large-scale retrospective cross-sectional study we pooled data from 135 (113 males and 22 females) healthy subjects whose brain's MOR availability was measured with positron emission tomography (PET) using an agonist radioligand [11C]carfentanil that has high affinity for MORs. Depressive and anxious symptomology was addressed with BDI-II and STAI-X questionnaires, respectively. Both anxiety and depression scores in the subclinical range were negatively associated with MOR availability in cortical and subcortical areas, notably in amygdala, hippocampus, ventral striatum, and orbitofrontal and cingulate cortices. We conclude that dysregulated MOR availability is involved in altered mood and pathophysiology of depression and anxiety disorders.

A meta-analysis of the potential antidepressant effects of buprenorphine versus placebo as an adjunctive pharmacotherapy for treatment-resistant depression

BACKGROUND

Numerous reports have suggested that buprenorphine may have antidepressant effects. Many individuals with depressive disorders don't respond to first-line treatment and are classified with treatment-resistant depression (TRD). Novel therapies for depression are required to better treat this population. This meta-analysis of randomized placebo-controlled trials sought to evaluate the potential antidepressant effects of buprenorphine as an adjunctive pharmacological treatment for individuals with TRD.

METHODS

PubMed, Embase, CINAHL, Web of Science, and ClinicalTrials.gov databases were searched until June 2019 for original peer-reviewed reports of buprenorphine used for the treatment of depression. Standardized mean differences (SMD) were generated from random effects models. Risk of publication bias was assessed using a funnel plot. Potential sources of heterogeneity were explored in subgroup analyses.

RESULTS

In six studies that met inclusion criteria, depression symptom severity in individuals with TRD was not significantly decreased after an adjunctive intervention with buprenorphine when compared to placebo (SMD = -0.07, 95% CI: -0.21-0.06, p = 0.30). Five of the six studies utilized a combination of buprenorphine/samidorphan. In these studies, depression symptom severity was also not significantly reduced after intervention compared to placebo (SMD = -0.08, 95% CI: -0.21 - 0.05, p = 0.23).

LIMITATIONS

Five included studies were performed by the same research group with significant conflicts of interest.

CONCLUSIONS

This meta-analysis did not reveal a significant reduction in depression symptom severity in individuals with TRD after an adjunctive intervention with buprenorphine when compared to placebo. However, more optimal doses of buprenorphine (2 mg/day) and longer treatment lengths should be explored.

Depression history as a predictor of outcomes during buprenorphine-naloxone treatment of prescription opioid use disorder

BACKGROUND

In the multi-site Prescription Opioid Addiction Treatment Study (POATS), the best predictor of successful opioid use outcome was lifetime diagnosis of major depressive disorder. The primary aim of this secondary analysis of data from POATS was to empirically assess two explanations for this counterintuitive finding.

METHODS

The POATS study was a national, 10-site randomized controlled trial (N = 360 enrolled in the 12-week buprenorphine-naloxone maintenance treatment phase) sponsored by the NIDA Clinical Trials Network. We evaluated how the presence of a history of depression influences opioid use outcome (negative urine drug assays). Using adjusted logistic regression models, we tested the hypotheses that 1) a reduction in depressive symptoms and 2) greater motivation and engagement in treatment account for the association between depression history and good treatment outcome.

RESULTS

Although depressive symptoms decreased significantly throughout treatment (p <.001), this improvement was not associated with opioid outcomes (aOR = 0.98, ns). Reporting a goal of opioid abstinence at treatment entry was also not associated with outcomes (aOR = 1.39, ns); however, mutual-help group participation was associated with good treatment outcomes (aOR = 1.67, p <.05). In each of these models, lifetime major depressive disorder remained associated with good outcomes (aORs = 1.63-1.82, ps = .01-.055).

CONCLUSIONS

Findings are consistent with the premise that greater engagement in treatment is associated with good opioid outcomes. Nevertheless, depression history continues to be associated with good opioid outcomes in adjusted models. More research is needed to understand how these factors could improve treatment outcomes for those with opioid use disorder.

Buprenorphine: prospective novel therapy for depression and PTSD

BACKGROUND

Depression and post-traumatic stress disorder (PTSD) are leading causes of disability and loss of life by suicide. Currently, there are less than satisfactory medical solutions to treat these mental disorders. Here, we explore recent preclinical and clinical studies demonstrating the potential of using buprenorphine to treat major depressive disorder, treatment-resistant depression, and PTSD.

METHOD

Bibliographic databases were searched to include preclinical and clinical studies demonstrating the therapeutic potential of buprenorphine and the involvement of the kappa opioid receptor (KOR) in mediating these effects.

RESULTS

Original clinical studies examining the effectiveness of buprenorphine to treat depression were mixed. The majority of participants in the PTSD studies were males and suffer from chronic pain and/or substance use disorders. Nonetheless, these recent studies and analyses established proof of concept warranting farther investigations. Additionally, KOR likely mediates the antidepressant and some of the anxiolytic effects of buprenorphine. Still, it appears that the full spectrum of buprenorphine's beneficial effects might be due to activity at other opioid receptors as well.

CONCLUSIONS

Pharmaceuticals' abilities to treat medical conditions directly relates to their ability to act upon the endogenous biological systems related to the conditions. Thus, these recent findings are likely a reflection of the central role that the endogenous opioid system has in these mental illnesses. Further studies are necessary to study the involvement of endogenous opioid systems, and specifically KOR, in mediating buprenorphine's beneficial effects and the ability to treat these medical conditions while minimizing risks for misuse and diversion.

Kappa Opioid Receptor Antagonists as Potential Therapeutics for Stress-Related Disorders

Exposure to stressful stimuli activates kappa opioid receptor (KOR) signaling, a process known to produce aversion and dysphoria in humans and other species. This endogenous opioid system is dysregulated in stress-related disorders, specifically in major depressive disorder (MDD). These findings serve as the foundation for a growing interest in the therapeutic potential of KOR antagonists as novel antidepressants. In this review, data supporting the hypothesis of dysregulated KOR function in MDD are considered. The clinical data demonstrating the therapeutic efficacy and safety of selective and mixed opioid antagonists are then presented. Finally, the preclinical evidence illustrating the induction of behaviors relevant to the endophenotypes of MDD and KOR antagonist activity in stress-naïve and stress-exposed animals is evaluated. Overall, this review highlights the emergent literature supporting the pursuit of KOR antagonists as novel therapeutics for MDD and other stress-related disorders.

Delta Opioids: Neuroprotective Roles in Preclinical Studies

Since ancient times, opioids have been used clinically and abused recreationally. In the early stages (about 1,000 AD) of opium history, an Arab physician, Avicenna, administered opioids to control diarrhea and eye diseases. ¹ Opioids have very strong pain relieving properties and they also regulate numerous cellular responses. Opioid receptors are expressed throughout the body, including the nervous system, heart, lungs, liver, gastrointestinal tract, and retina. ^2-6 Delta opioid receptors (DORs) are a very attractive target from the perspective of both receptor function and their therapeutic potential. Due to a rapid progress in mouse mutagenesis and development of small molecules as DOR agonist, novel functions and roles of DORs have emerged in recent years. This review article focuses on the recent advances in the neuroprotective roles of DOR agonists in general and retina neuroprotection in particular. Rather than being exhaustive, this review highlights the selected studies of DOR function in neuroprotection. We also highlight our preclinical studies using rodent models to demonstrate the potentials of DOR agonists for retinal neuroprotection. Based on existing literature and our recently published data on the eye, DOR agonists possess therapeutic abilities that protect the retina and optic nerve injury against glaucoma and perhaps other retinopathies as well. This review also highlights the signaling events associated with DOR for neuroprotection in the eye. There is a need for translational research on DORs to recognize their potential for clinical application such as in glaucoma.

Review: Sex-Based Differences in Treatment Outcomes for Persons With Opioid Use Disorder

BACKGROUND AND OBJECTIVES

In order to address the current opioid crisis, research on treatment outcomes for persons with opioid use disorder (OUD) should account for biological factors that could influence individual treatment response. Women and men might have clinically meaningful differences in their experience in OUD treatment and might also have unique challenges in achieving successful, long-term recovery. This review summarizes and synthesizes the current literature on sex-based differences in OUD treatment outcomes.

METHODS

Relevant literature was identified via automated and manual searches using the terms "opioid treatment outcome sex [or gender] differences" and "opiate treatment outcome sex [or gender] differences." Search methodology was consistent with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), and were conducted within the PubMed electronic database during March and April of 2018.

RESULTS

The initial PubMed search yielded 241 manuscripts and 31 original research articles that met inclusion/exclusion criteria were synthesized in this review. Several important trends emerged, including findings that women are more likely than men to present to treatment with co-occurring mental health conditions such as depression, and that women might respond particularly well to buprenorphine maintenance.

DISCUSSION AND CONCLUSIONS

While much of the literature on this topic is subject to potential cohort effects, interventions that address co-occurring mental health conditions and psychosocial stress might improve treatment outcomes for women with OUD.

SCIENTIFIC SIGNIFICANCE

Funding agencies and researchers should focus attention toward human laboratory studies and clinical trials that are prospectively designed to assess sex-based differences in OUD recovery. (Am J Addict 2019;28:246-261).

Targeting opioid dysregulation in depression for the development of novel therapeutics

Since the serendipitous discovery of the first class of modern antidepressants in the 1950's, all pharmacotherapies approved by the Food and Drug Administration for major depressive disorder (MDD) have shared a common mechanism of action, increased monoaminergic neurotransmission. Despite the widespread availability of antidepressants, as many as 50% of depressed patients are resistant to these conventional therapies. The significant length of time required to produce meaningful symptom relief with these medications, 4-6 weeks, indicates that other mechanisms are likely involved in the pathophysiology of depression which may yield more viable targets for drug development. For decades, no viable candidate target with a different mechanism of action to that of conventional therapies proved successful in clinical studies. Now several exciting avenues for drug development are under intense investigation. One of these emerging targets is modulation of endogenous opioid tone. This review will evaluate preclinical and clinical evidence pertaining to opioid dysregulation in depression, focusing on the role of the endogenous ligands endorphin, enkephalin, dynorphin, and nociceptin/orphanin FQ (N/OFQ) and their respective receptors, mu (MOR), delta (DOR), kappa (KOR), and the N/OFQ receptor (NOP) in mediating behaviors relevant to depression and anxiety. Finally, putative opioid based antidepressants that are under investigation in clinical trials, ALKS5461, JNJ-67953964 (formerly LY2456302 and CERC-501) and BTRX-246040 (formerly LY-2940094) will be discussed. This review will illustrate the potential therapeutic value of targeting opioid dysregulation in developing novel therapies for MDD.

Endogenous opioid system dysregulation in depression: implications for new therapeutic approaches

The United States is in the midst of an opioid addiction and overdose crisis precipitated and exacerbated by use of prescription opioid medicines. The majority of opioid prescriptions are dispensed to patients with comorbid mood disorders including major depressive disorder (MDD). A growing body of research indicates that the endogenous opioid system is directly involved in the regulation of mood and is dysregulated in MDD. This involvement of the endogenous opioid system may underlie the disproportionate use of opioids among patients with mood disorders. Emerging approaches to address endogenous opioid dysregulation in MDD may yield novel therapeutics that have a low or absent risk of abuse and addiction relative to µ-opioid agonists. Moreover, agents targeting the endogenous opioid system would be expected to yield clinical benefits qualitatively different from conventional monaminergic antidepressants. The development of safe and effective agents to treat MDD-associated endogenous opioid dysregulation may represent a distinct and currently underappreciated means of addressing treatment resistant depression with the potential to attenuate the on-going opioid crisis.

Buprenorphine: Therapeutic potential beyond substance abuse

Discussion of buprenorphine and its potential utility for the treatment of inflammatory disorders.

Interactions of Hallucinogens with the Glutamatergic System: Permissive Network Effects Mediated Through Cortical Layer V Pyramidal Neurons

Recordings made from layer V (L5) pyramidal cells of the prefrontal cortex (PFC) and neocortex in rodent slice preparations have shown that serotonin (5-hydroxytryptamine, 5-HT) and serotonergic hallucinogens induce an increase in the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in the apical dendritic field by activating 5-HT_2A receptors. Serotonergic hallucinogens induce late EPSCs and increase recurrent network activity when subcortical or mid-cortical regions are stimulated at low frequencies (e.g., 0.1 Hz). A range of agonists or positive allosteric modulators (PAMs) for mostly G_i/o-coupled receptors, including metabotropic glutamate₂ (mGlu₂), adenosine A₁, or μ-opioid receptors, suppress these effects of 5-HT_2A receptor stimulation. Furthermore, a range of mostly G_q/11-coupled receptors (including orexin₂ [OX₂]; α₁-adrenergic, and mGlu₅ receptors) similarly induce glutamate (Glu) release onto L5 pyramidal cells. Evidence implicates a number of brain regions in mediating these effects of serotonergic hallucinogens and G_q/11-coupled receptors including the midline and intralaminar thalamic nuclei, claustrum, and neurons in deep PFC. These effects on 5-HT_2A receptors and related GPCRs appear to play a major role in the behavioral effects of serotonergic hallucinogens, such as head twitches in rodents and higher order behaviors such as rodent lever pressing on the differential-reinforcement-of-low rate 72-s (DRL 72-s) schedule. This implies that the effects of 5-HT_2A receptor activation on the activity of L5 pyramidal cells may be responsible for mediating a range of behaviors linked to limbic circuitry with connectivity between the PFC, striatum, thalamus, claustrum, striatum, amygdala, and the hippocampal formation.

The Efficacy of Buprenorphine in Major Depression, Treatment-Resistant Depression and Suicidal Behavior: A Systematic Review

Although several pharmacological options to treat depression are currently available, approximately one third of patients who receive antidepressant medications do not respond adequately or achieve a complete remission. Thus, novel strategies are needed to successfully address those who did not respond, or partially respond, to available antidepressant pharmacotherapy. Research findings revealed that the opioid system is significantly involved in the regulation of mood and incentives salience and may be an appropriate target for novel therapeutic agents. The present study aimed to systematically review the current literature about the use of buprenorphine (BUP) for major depression, treatment-resistant depression (TRD), non-suicidal self-injury (NSSI) behavior, and suicidal behavior. We investigated Pubmed and Scopus databases using the following keywords: "buprenorphine AND depression", "buprenorphine AND treatment resistant depression", "buprenorphine AND suicid*", "buprenorphine AND refractory depression". Several evidence demonstrate that, at low doses, BUP is an efficacious, well-tolerated, and safe option in reducing depressive symptoms, serious suicidal ideation, and NSSI, even in patients with TRD. However, more studies are needed to evaluate the long-term effects, and relative efficacy of specific combinations (e.g., BUP + samidorphan (BUP/SAM), BUP + naloxone (BUP/NAL), BUP + naltrexone) over BUP monotherapy or adjunctive BUP treatment with standard antidepressants, as well as to obtain more uniform guidance about the optimal BUP dosing interval.

Use of Buprenorphine in treatment of refractory depression-A review of current literature

OBJECTIVE

Current treatment strategies for depressive disorders have limited efficacy, leaving many patients unimproved or with significant residual symptoms. The development of additional treatments represent a significant unmet need for providers. Several lines of evidence suggest that the opioid system may be involved in regulation of mood and incentives salience. Intervention based on modifying central opioid receptors may represent a novel approach to treatment of depressive disorders among those unresponsive to accepted treatments.

DATA SOURCES

We searched the English language literature using keywords: Buprenorphine AND Major Depression; Buprenorphine AND Bipolar Depression; Buprenorphine AND Affective Disorders.

RESULTS

Use of low dose buprenorphine as augmentation of pharmacotherapy for depression has shown promise in several reported studies. Effect size of available randomized controlled studies is comparable if not greater than most accepted augmentation strategies.

CONCLUSION

Review of available literature on the use of buprenorphine in individuals with treatment resistant depression demonstrated efficacy in the treatment of depressive disorders. Further prospective randomized controlled trials should be undertaken to evaluate the efficacy of buprenorphine as an adjunct for depression refractory to current pharmacotherapies.

Kappa-Opioid Antagonists for Psychiatric Disorders: From Bench to Clinical Trials

Kappa-opioid receptor (KOR) antagonists are currently being considered for the treatment of a variety of neuropsychiatric conditions, including depressive, anxiety, and substance abuse disorders. A general ability to mitigate the effects of stress, which can trigger or exacerbate these conditions, may explain their putative efficacy across such a broad array of conditions. The discovery of their potentially therapeutic effects evolved from preclinical research designed to characterize the molecular mechanisms by which experience causes neuroadaptations in the nucleus accumbens (NAc), a key element of brain reward circuitry. This research established that exposure to drugs of abuse or stress increases the activity of the transcription factor CREB (cAMP response element binding protein) in the NAc, which leads to elevated expression of the opioid peptide dynorphin that in turn causes core signs of depressive- and anxiety-related disorders. Disruption of KORs-the endogenous receptors for dynorphin-produces antidepressant- and anxiolytic-like actions in screening procedures that identify standard drugs of these classes, and reduces stress effects in tests used to study addiction and stress-related disorders. Although interest in this target is high, prototypical KOR antagonists have extraordinarily persistent pharmacodynamic effects that complicate clinical trials. The development of shorter acting KOR antagonists together with more rapid designs for clinical trials may soon provide insight on whether these drugs are efficacious as would be predicted by preclinical work. If successful, KOR antagonists would represent a unique example in psychiatry where the therapeutic mechanism of a drug class is understood before it is shown to be efficacious in humans.

Psychotropic Drugs in Terminally Ill Patients: A Review of the Clinical and Research Literature

The principal psychopharmacological drugs used with terminally ill persons were briefly reviewed, and special consideration for various terminal illnesses were discussed. Sections on the analgesic effects of psychotropic drugs, the psychotropic properties of opioids, the beneficial effects of marijuana, and the use of LSD in terminal cancer patients are included.

Effect of dehydroepiandrosterone add-on therapy on mood, decision making and subsequent relapse of polydrug users

A major problem in the treatment of addiction is predicting and preventing relapse following a rehabilitation program. Recently, in preclinical rodent studies dehydroepiandrosterone (DHEA) was found to markedly improve the resistance to drug reuse. In a double-blind, placebo-controlled study, we examined the effect of DHEA on relapse rates in adult polydrug users taking part in a detoxification program enriched with intensive psychosocial interventions and aftercare. During treatment, participants (79 percent males, mean age 28) consumed DHEA (100 mg/day) or placebo daily for at least 30 days. Of the 121 initial volunteers, 64 participated for at least 1 month. While in treatment, DHEA reduced negative affect on the Positive and Negative Affect Scale (F = 4.25, P = 0.04). Furthermore, in a 16-month follow-up, we found that reuse rates in the DHEA condition were about a third compared with placebo (12 versus 38 percent; χ(2)  = 5.03, P = 0.02). DHEA treatment also resulted in an increase in DHEA sulfate (DHEA-S) 1 month following treatment, and the level of DHEA-S predicted relapse in the follow-up assessment.

Synthetic and Receptor Signaling Explorations of the Mitragyna Alkaloids: Mitragynine as an Atypical Molecular Framework for Opioid Receptor Modulators

Mu-opioid receptor agonists represent mainstays of pain management. However, the therapeutic use of these agents is associated with serious side effects, including potentially lethal respiratory depression. Accordingly, there is a longstanding interest in the development of new opioid analgesics with improved therapeutic profiles. The alkaloids of the Southeast Asian plant Mitragyna speciosa, represented by the prototypical member mitragynine, are an unusual class of opioid receptor modulators with distinct pharmacological properties. Here we describe the first receptor-level functional characterization of mitragynine and related natural alkaloids at the human mu-, kappa-, and delta-opioid receptors. These results show that mitragynine and the oxidized analogue 7-hydroxymitragynine, are partial agonists of the human mu-opioid receptor and competitive antagonists at the kappa- and delta-opioid receptors. We also show that mitragynine and 7-hydroxymitragynine are G-protein-biased agonists of the mu-opioid receptor, which do not recruit β-arrestin following receptor activation. Therefore, the Mitragyna alkaloid scaffold represents a novel framework for the development of functionally biased opioid modulators, which may exhibit improved therapeutic profiles. Also presented is an enantioselective total synthesis of both (-)-mitragynine and its unnatural enantiomer, (+)-mitragynine, employing a proline-catalyzed Mannich-Michael reaction sequence as the key transformation. Pharmacological evaluation of (+)-mitragynine revealed its much weaker opioid activity. Likewise, the intermediates and chemical transformations developed in the total synthesis allowed the elucidation of previously unexplored structure-activity relationships (SAR) within the Mitragyna scaffold. Molecular docking studies, in combination with the observed chemical SAR, suggest that Mitragyna alkaloids adopt a binding pose at the mu-opioid receptor that is distinct from that of classical opioids.

Effects of buprenorphine on responses to social stimuli in healthy adults

In addition to its classical role in mediating responses to pain, the opioid system is strongly implicated in the regulation of social behavior. In young laboratory animals, low doses of opioid analgesic drugs reduce responses to isolation distress and increase play behavior. However, little is known about how opioid drugs affect responses to social stimuli in humans. Here we examined the effects of buprenorphine, a mu-opioid partial agonist and kappa-antagonist, on three dimensions of social processing: (i) responses to simulated social rejection, (ii) attention to emotional facial expressions, and (iii) emotional responses to images with and without social content. Healthy adults (N=36) attended two sessions during which they received either placebo or 0.2mg sublingual buprenorphine in randomized order, under double-blind conditions. Ninety minutes after drug administration, they completed three behavioral tasks: (i) a virtual ball-toss game in which they were first included and then excluded by the other players; (ii) an attention task in which they were shown pairs of faces (one emotional and one neutral), while the direction of their gazes was recorded using electrooculography, and (iii) a picture-viewing task, in which they rated standardized images with and without social content. During the ball-toss game, buprenorphine decreased perceived social rejection. During the attention task, the drug reduced initial attention to fearful facial expressions, without influencing attention to angry, happy, or sad faces. Finally, during the picture-viewing task, buprenorphine increased ratings of positivity of images with social content without affecting ratings of nonsocial images. These results suggest that even at low doses, opioid analgesic drugs reduce responses to some types of negative social stimuli while enhancing positive responses to social stimuli. This provides further support for the role of the opioid system in mediating responses to social rejection and social reward.

Sex Differences in Kappa Opioid Receptor Function and Their Potential Impact on Addiction

Behavioral, biological, and social sequelae that lead to drug addiction differ between men and women. Our efforts to understand addiction on a mechanistic level must include studies in both males and females. Stress, anxiety, and depression are tightly linked to addiction, and whether they precede or result from compulsive drug use depends on many factors, including biological sex. The neuropeptide dynorphin (DYN), an endogenous ligand at kappa opioid receptors (KORs), is necessary for stress-induced aversive states and is upregulated in the brain after chronic exposure to drugs of abuse. KOR agonists produce signs of anxiety, fear, and depression in laboratory animals and humans, findings that have led to the hypothesis that drug withdrawal-induced DYN release is instrumental in negative reinforcement processes that drive addiction. However, these studies were almost exclusively conducted in males. Only recently is evidence available that there are sex differences in the effects of KOR activation on affective state. This review focuses on sex differences in DYN and KOR systems and how these might contribute to sex differences in addictive behavior. Much of what is known about how biological sex influences KOR systems is from research on pain systems. The basic molecular and genetic mechanisms that have been discovered to underlie sex differences in KOR function in pain systems may apply to sex differences in KOR function in reward systems. Our goals are to discuss the current state of knowledge on how biological sex contributes to KOR function in the context of pain, mood, and addiction and to explore potential mechanisms for sex differences in KOR function. We will highlight evidence that the function of DYN-KOR systems is influenced in a sex-dependent manner by: polymorphisms in the prodynorphin (pDYN) gene, genetic linkage with the melanocortin-1 receptor (MC1R), heterodimerization of KORs and mu opioid receptors (MORs), and gonadal hormones. Finally, we identify several gaps in our understanding of “if” and “how” DYN and KORs modulate addictive behavior in a sex-dependent manner. Future work may address these gaps by building on the mechanistic studies outlined in this review. Ultimately this will enable the development of novel and effective addiction treatments tailored to either males or females.

Delta opioid agonists: a concise update on potential therapeutic applications

WHAT IS KNOWN AND OBJECTIVE

The endogenous opioid system co-evolved with chemical defences, or at times symbiotic relationships, between plants and other autotrophs and heterotrophic predators - thus, it is not surprising that endogenous opioid ligands and exogenous mimetic ligands produce diverse physiological effects. Among the endogenous opioid peptides (endomorphins, enkephalins, dynorphins and nociception/orphanin FQ) derived from the precursors encoded by four genes (PNOC, PENK, PDYN and POMC) are the pentapeptides Met-enkephalin (Tyr-Gly-Gly-Phe-Met) and Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu). The physiological effects of the enkephalins are mediated via 7-transmembrane G protein-coupled receptors, including delta opioid receptor (DOR). We present a concise update on the status of progress and opportunities of this approach.

METHODS

A literature search of the PUBMED database and a combination of keywords including delta opioid receptor, analgesia, mood and individual compounds identified therein, from industry and other source, and from www.clinicaltrials.com.

RESULTS AND DISCUSSION

DOR agonist and antagonist ligands have been developed with ever increasing affinity and selectivity for DOR over other opioid receptor subtypes and studied for therapeutic utility, primarily for pain relief, but also for other clinical endpoints.

WHAT IS NEW AND CONCLUSION

Selective DOR agonists have been designed with a large increase in therapeutic window for a variety of potential CNS applications including pain, depression, and learning and memory among others.

Association Between Placebo-Activated Neural Systems and Antidepressant Responses: Neurochemistry of Placebo Effects in Major Depression

IMPORTANCE

High placebo responses have been observed across a wide range of pathologies, severely impacting drug development.

OBJECTIVE

To examine neurochemical mechanisms underlying the formation of placebo effects in patients with major depressive disorder (MDD).

DESIGN, SETTING, AND PARTICIPANTS

In this study involving 2 placebo lead-in phases followed by an open antidepressant administration, we performed a single-blinded 2-week crossover randomized clinical trial of 2 identical oral placebos (described as having either active or inactive fast-acting antidepressant-like effects) followed by a 10-week open-label treatment with a selective serotonin reuptake inhibitor or, in some cases, another agent as clinically indicated. The volunteers (35 medication-free patients with MDD at a university health system) were studied with positron emission tomography and the µ-opioid receptor-selective radiotracer [11C]carfentanil after each 1-week inactive and active oral placebo treatment. In addition, 1 mL of isotonic saline was administered intravenously within sight of the volunteer during positron emission tomographic scanning every 4 minutes over 20 minutes only after the 1-week active placebo treatment, with instructions that the compound may be associated with the activation of brain systems involved in mood improvement. This challenge stimulus was used to test the individual capacity to acutely activate endogenous opioid neurotransmision under expectations of antidepressant effect.

MAIN OUTCOMES AND MEASURES

Changes in depressive symptoms in response to active placebo and antidepressant. Baseline and activation measures of µ-opioid receptor binding.

RESULTS

Higher baseline µ-opioid receptor binding in the nucleus accumbens was associated with better response to antidepressant treatment (r = 0.48; P = .02). Reductions in depressive symptoms after 1 week of active placebo treatment, compared with the inactive, were associated with increased placebo-induced µ-opioid neurotransmission in a network of regions implicated in emotion, stress regulation, and the pathophysiology of MDD, namely, the subgenual anterior cingulate cortex, nucleus accumbens, midline thalamus, and amygdala (nucleus accumbens: r = 0.6; P < .001). Placebo-induced endogenous opioid release in these regions was associated with better antidepressant treatment response, predicting 43% of the variance in symptom improvement at the end of the antidepressant trial.

CONCLUSIONS AND RELEVANCE

These data demonstrate that placebo-induced activation of the µ-opioid system is implicated in the formation of placebo antidepressant effects in patients with MDD and also participate in antidepressant responses, conferring illness resiliency, during open administration.

TRIAL REGISTRATION

clinicaltrials.gov Identifier:NCT02178696.

Combined administration of buprenorphine and naltrexone produces antidepressant-like effects in mice

Opiates have been used historically for the treatment of depression. Renewed interest in the use of opiates as antidepressants has focused on the development of kappa opioid receptor (κ-receptor) antagonists. Buprenorphine acts as a partial µ-opioid receptor agonist and a κ-receptor antagonist. By combining buprenorphine with the opioid antagonist naltrexone, the activation of µ-opioid receptors will be reduced and the κ-antagonist properties enhanced. We have established that a combination dose of buprenorphine (1 mg/kg) with naltrexone (1 mg/kg) functions as a short-acting κ-antagonist in the mouse tail withdrawal test. Furthermore, this dose combination is neither rewarding nor aversive in the conditioned place preference paradigm, and is without significant locomotor effects. We have shown for the first time that systemic co-administration of buprenorphine (1 mg/kg) with naltrexone (1 mg/kg) in CD-1 mice produced an antidepressant-like response in behaviours in both the forced swim test and novelty induced hypophagia task. Behaviours in the elevated plus maze and light dark box were not significantly altered by treatment with buprenorphine alone, or in combination with naltrexone. We propose that the combination of buprenorphine with naltrexone represents a novel, and potentially a readily translatable approach, to the treatment of depression.

Evaluation of opioid modulation in major depressive disorder

Although opioids have known antidepressant activity, their use in major depressive disorder (MDD) has been greatly limited by risk of abuse and addiction. Our aim was to determine whether opioid modulation achieved through a combination of a μ-opioid partial agonist, buprenorphine (BUP), and a potent μ-opioid antagonist, samidorphan (SAM), would demonstrate antidepressant activity without addictive potential. A placebo-controlled crossover study assessed the opioid pharmacodynamic profile following escalating doses of SAM co-administered with BUP in opioid-experienced adults. A subsequent 1-week, placebo-controlled, parallel-group study was conducted in subjects with MDD and an inadequate response to standard antidepressant therapy. This second study evaluated safety and efficacy of ratios of BUP/SAM that were associated with partial and with maximal blockade of opioid responses in the initial study. Pupillometry, visual analog scale assessments, and self-reported questionnaires demonstrated that increasing amounts of SAM added to a fixed dose of BUP resulted in dose-dependent reductions in objective and subjective opioid effects, including euphoria and drug liking, in opioid-experienced adults. Following 7 days of treatment in subjects with MDD, a 1 : 1 ratio of BUP and SAM, the ratio associated with maximal antagonism of opioid effects, exhibited statistically significant improvement vs placebo in HAM-D17 total score (p=0.032) and nearly significant improvement in Montgomery-Åsberg Depression Rating Scale (MADRS) total score (p=0.054). Overall, BUP/SAM therapy was well tolerated. A combination of BUP and SAM showed antidepressant activity in subjects with MDD. Balanced agonist-antagonist opioid modulation represents a novel and potentially clinically important approach to the treatment of MDD and other psychiatric disorders.

Improved memory for reward cues following acute buprenorphine administration in humans

In rodents, there is abundant evidence for the involvement of the opioid system in the processing of reward cues, but this system has remained understudied in humans. In humans, the happy facial expression is a pivotal reward cue. Happy facial expressions activate the brain's reward system and are disregarded by subjects scoring high on depressive mood who are low in reward drive. We investigated whether a single 0.2mg administration of the mixed mu-opioid agonist/kappa-antagonist, buprenorphine, would influence short-term memory for happy, angry or fearful expressions relative to neutral faces. Healthy human subjects (n38) participated in a randomized placebo-controlled within-subject design, and performed an emotional face relocation task after administration of buprenorphine and placebo. We show that, compared to placebo, buprenorphine administration results in a significant improvement of memory for happy faces. Our data demonstrate that acute manipulation of the opioid system by buprenorphine increases short-term memory for social reward cues.

Antidepressant-like effects of buprenorphine in rats are strain dependent

The prevalence of major depressive disorder and the limited efficacy of conventional drug treatments provide significant impetus to develop novel and more rapidly acting antidepressants for individuals with treatment resistant forms of depression. The primary goal of these studies was to ascertain whether buprenorphine (BPN), a medically available drug with mixed effects at opioid receptors, was effective in behavioral tests using the Wistar Kyoto (WKY) rat strain, a rodent model of exaggerated depressive and anxiety behaviors that demonstrates resistance to certain antidepressants. As WKY rats are maintained by different sources, we assessed the behavioral effects of BPN using the modified rat forced swim test (FST) and the emergence test in WKY rat colonies obtained from different vendors. BPN dose-dependently reduced immobility and increased swimming behavior in the FST and reduced emergence latencies in two WKY lines (Charles River (WKY/NCrl) and Harlan laboratories (WKY/NHsd)) that also showed high baseline immobility in the FST. WKY rats from Taconic (WKY/NTac) did not show high baseline immobility in the FST or anxiety as had been previously reported, suggesting a drift in the phenotype of rats from this supplier. Furthermore, BPN did not reduce immobility in the FST or reduce latencies in the emergence test in WKY rats from Taconic. BPN also failed to produce antidepressant-like effects in Wistar and Sprague-Dawley rats. These results indicate a striking strain-selectivity for the effects of BPN, producing antidepressant and anxiolytic-like responses in WKY/NCrl and WKY/NHsd lines but not in the normosensitive control Wistar and Sprague-Dawley strains.

Antidepressant-like and anxiolytic-like effects following activation of the μ-δ opioid receptor heteromer in the nucleus accumbens

Treatment-resistant major depressive disorder remains inadequately treated with currently available antidepressants. Opioid receptors (ORs) are involved in the pathophysiology of depression yet remain an untapped therapeutic intervention. The μ-δ OR heteromer represents a unique signaling complex with distinct properties compared with μ- and δ-OR homomers; however, its role in depression has not been characterized. As there are no ligands exclusively targeting the μ-δ heteromer, we devised a strategy to selectively antagonize the function of the μ-δOR complex using a specific interfering peptide derived from the δOR distal carboxyl tail, a sequence implicated in μ-δOR heteromerization. In vitro studies using a minigene expressing this peptide demonstrated a loss of the unique pharmacological and trafficking properties of δ-agonists at the μ-δ heteromer, with no effect on μ- or δ-OR homomers, and a dissociation of the μ-δOR complex. Intra-accumbens administration of the TAT-conjugated interfering peptide abolished the antidepressant-like and anxiolytic-like actions of the δ-agonist UFP-512 (H-Dmt-Tic-NH-CH(CH2-COOH)-Bid) measured in the forced swim test, novelty-induced hypophagia and elevated plus maze paradigms in rats. UFP-512's antidepressant-like and anxiolytic-like actions were abolished by pretreatment with either μOR or δOR antagonists. Overall, these findings demonstrate that the μ-δ heteromer may be a potential suitable therapeutic target for treatment-resistant depression and anxiety disorders.

The multi-site prescription opioid addiction treatment study: 18-month outcomes

Despite the high prevalence of prescription opioid dependence in the U.S., little is known about the course of this disorder and long-term response to treatment. We therefore examined 18-month post-randomization outcomes of participants in the Prescription Opioid Addiction Treatment Study, a multi-site, randomized controlled trial examining varying durations of buprenorphine-naloxone treatment and different intensities of counseling for prescription opioid dependence. Thus the current follow-up study provides a unique contribution to the field by reporting longer-term outcomes of a well-characterized population of treatment-seeking prescription opioid dependent patients. Participants from the treatment trial (N=252/653) completed an 18-month follow-up telephone assessment. Multivariable analyses examined associations between participant characteristics and key indicators of month-18 status: opioid abstinence, DSM-IV opioid dependence, and opioid agonist treatment. Overall, participants showed improvement from baseline to month 18: 49.6% were abstinent in the previous 30 days, with only 16.3% opioid-dependent. Some participants, however, had initiated past-year heroin use (n=9) or opioid injection (n=17). Most participants (65.9%) engaged in substance use disorder treatment during the past year, most commonly opioid agonist therapy (48.8%). Of particular interest in this population, multivariable analysis showed that greater pain severity at baseline was associated with opioid dependence at 18 months. In conclusion, although opioid use outcomes during the treatment trial were poor immediately following a buprenorphine-naloxone taper compared to those during 12 weeks of buprenorphine-naloxone stabilization, opioid use outcomes at 18-month follow-up showed substantial improvement over baseline and were comparable to the rate of successful outcomes during buprenorphine-naloxone stabilization in the treatment trial.

Faster, better, stronger: towards new antidepressant therapeutic strategies

Major depression is a highly prevalent disorder and is predicted to be the second leading cause of disease burden by 2020. Although many antidepressant drugs are currently available, they are far from optimal. Approximately 50% of patients do not respond to initial first line antidepressant treatment, while approximately one third fail to achieve remission following several pharmacological interventions. Furthermore, several weeks or months of treatment are often required before clinical improvement, if any, is reported. Moreover, most of the commonly used antidepressants have been primarily designed to increase synaptic availability of serotonin and/or noradrenaline and although they are of therapeutic benefit to many patients, it is clear that other therapeutic targets are required if we are going to improve the response and remission rates. It is clear that more effective, rapid-acting antidepressants with novel mechanisms of action are required. The purpose of this review is to outline the current strategies that are being taken in both preclinical and clinical settings for identifying superior antidepressant drugs. The realisation that ketamine has rapid antidepressant-like effects in treatment resistant patients has reenergised the field. Further, developing an understanding of the mechanisms underlying the rapid antidepressant effects in treatment-resistant patients by drugs such as ketamine may uncover novel therapeutic targets that can be exploited to meet the Olympian challenge of developing faster, better and stronger antidepressant drugs.

Preclinical modeling of primal emotional affects (Seeking, Panic and Play): gateways to the development of new treatments for depression

Mammalian brains contain at least 7 primal emotional systems--Seeking, Rage, Fear, Lust, Care, Panic and Play (capitalization reflects a proposed primary-process terminology, to minimize semantic confusions and mereological fallacies). These systems help organisms feel affectively balanced (e.g. euthymic) and unbalanced (e.g. depressive, irritable, manic), providing novel insights for understanding human psychopathologies. Three systems are especially important for understanding depression: The separation distress (Panic) system mediates the psychic pain of separation distress (i.e. excessive sadness and grief), which can be counteracted by minimizing Panic arousals (as with low-dose opioids). Depressive dysphoria also arises from reduced brain reward-seeking and related play urges (namely diminished enthusiasm (Seeking) and joyful exuberance (Play) which promote sustained amotivational states). We describe how an understanding of these fundamental emotional circuits can promote the development of novel antidepressive therapeutics--(i) low-dose buprenorphine to counteract depression and suicidal ideation emanating from too much psychic pain (Panic overarousal), (ii) direct stimulation of the Seeking system to counteract amotivational dysphoria, and (iii) the discovery and initial clinical testing of social-joy-promoting molecules derived from the analysis of the Play system.