BU08073 a buprenorphine analogue with partial agonist activity at μ-receptors in vitro but long-lasting opioid antagonist activity in vivo in mice

Searching for Synthetic Opioid Rescue Agents: Identification of a Potent Opioid Agonist with Reduced Respiratory Depression

While in the process of designing more effective synthetic opioid rescue agents, we serendipitously identified a new chemotype of potent synthetic opioid. Here, we report that conformational constraint of a piperazine ring converts a mu opioid receptor (MOR) antagonist into a potent MOR agonist. The prototype of the series, which we have termed atoxifent (2), possesses potent in vitro agonist activity. In mice, atoxifent displayed long-lasting antinociception that was reversible with naltrexone. Repeated dosing of atoxifent produced antinociceptive tolerance and a level of withdrawal like that of fentanyl. In rats, while atoxifent produced complete loss of locomotor activity like fentanyl, it failed to produce deep respiratory depression associated with fentanyl-induced lethality. Assessment of brain biodistribution demonstrated ample distribution of atoxifent into the brain with a Tmax of approximately 0.25 h. These results indicate enhanced safety for atoxifent-like molecules compared to fentanyl.

Molecular mechanisms of morphine tolerance and dependence; novel insights and future perspectives

Drug addiction is a devastating condition that poses a serious burden on the society. The use of some drugs like morphine for their tremendous analgesic properties is also accompanied with developing tolerance, dependence and the withdrawal symptoms. These symptoms are frequently severe enough to reinforce the person in recovery to start over the use of drug again and hinder the clinical use of drugs like morphine for chronic pain. Research into opioid receptors and related molecular pathways has seen resurgence in the wake of the growing opioid epidemic. The current study provides a comprehensive scientific exploration of the molecular mechanisms and underlying signalling in morphine tolerance and dependence. It also critically evaluates current therapeutic approaches, shedding light on their efficacy and limitations, and future prospects.

Buprenorphine for Chronic Pain Management: a Narrative Review

PURPOSE OF REVIEW

The aim of this review is to educate healthcare professionals regarding buprenorphine for the use of opioid use disorder (OUD) as well as for chronic pain management. This review provides physicians and practitioners with updated information regarding the distinct characteristics and intricacies of prescribing buprenorphine.

RECENT FINDINGS

Buprenorphine is approved by the US Food and Drug Administration (FDA) for acute pain, chronic pain, opioid use disorder (OUD), and opioid dependence. When compared to most other opioids, buprenorphine offers superior patient tolerability, an excellent half-life, and minimal respiratory depression. Buprenorphine does have notable side effects as well as pharmacokinetic properties that require special attention, especially if patients require future surgical interventions. Many physicians are not trained to initiate or manage patients on buprenorphine. However, buprenorphine offers a potentially safer alternative for medication management for patients who require chronic opioid therapy for pain or have OUD. This review provides updated information on buprenorphine for both chronic pain and OUD.

An Examination of the Complex Pharmacological Properties of the Non-Selective Opioid Modulator Buprenorphine

The goal of this review is to provide a recent examination of the pharmacodynamics as well as pharmacokinetics, misuse potential, toxicology, and prenatal consequences of buprenorphine. Buprenorphine is currently a Schedule III opioid in the US used for opioid-use disorder (OUD) and as an analgesic. Buprenorphine has high affinity for the mu-opioid receptor (MOR), delta (DOR), and kappa (KOR) and intermediate affinity for the nociceptin (NOR). Buprenorphine's active metabolite, norbuprenorphine, crosses the blood-brain barrier, is a potent metabolite that attenuates the analgesic effects of buprenorphine due to binding to NOR, and is responsible for the respiratory depressant effects. The area under the concentration curves are very similar for buprenorphine and norbuprenorphine, which indicates that it is important to consider this metabolite. Crowding sourcing has identified a buprenorphine street value (USD 3.95/mg), indicating some non-medical use. There have also been eleven-thousand reports involving buprenorphine and minors (age < 19) at US poison control centers. Prenatal exposure to clinically relevant dosages in rats produces reductions in myelin and increases in depression-like behavior. In conclusion, the pharmacology of this OUD pharmacotherapy including the consequences of prenatal buprenorphine exposure in humans and experimental animals should continue to be carefully evaluated.

Impact of Opioids on Cellular Metabolism: Implications for Metabolic Pathways Involved in Cancer

Opioid utilization for pain management is prevalent among cancer patients. There is significant evidence describing the many effects of opioids on cancer development. Despite the pivotal role of metabolic reprogramming in facilitating cancer growth and metastasis, the specific impact of opioids on crucial oncogenic metabolic pathways remains inadequately investigated. This review provides an understanding of the current research on opioid-mediated changes to cellular metabolic pathways crucial for oncogenesis, including glycolysis, the tricarboxylic acid cycle, glutaminolysis, and oxidative phosphorylation (OXPHOS). The existing literature suggests that opioids affect energy production pathways via increasing intracellular glucose levels, increasing the production of lactic acid, and reducing ATP levels through impediment of OXPHOS. Opioids modulate pathways involved in redox balance which may allow cancer cells to overcome ROS-mediated apoptotic signaling. The majority of studies have been conducted in healthy tissue with a predominant focus on neuronal cells. To comprehensively understand the impact of opioids on metabolic pathways critical to cancer progression, research must extend beyond healthy tissue and encompass patient-derived cancer tissue, allowing for a better understanding in the context of the metabolic reprogramming already undergone by cancer cells. The current literature is limited by a lack of direct experimentation exploring opioid-induced changes to cancer metabolism as they relate to tumor growth and patient outcome.

Hyperactivity in Mice Induced by Opioid Agonists with Partial Intrinsic Efficacy and Biased Agonism Administered Alone and in Combination with Morphine

Opioid analgesics such as morphine and fentanyl induce mu-opioid receptor (MOR)-mediated hyperactivity in mice. Herein, we show that morphine, fentanyl, SR-17018, and oliceridine have submaximal intrinsic efficacy in the mouse striatum using 35S-GTPγS binding assays. While all of the agonists act as partial agonists for stimulating G protein coupling in striatum, morphine, fentanyl, and oliceridine are fully efficacious in stimulating locomotor activity; meanwhile, the noncompetitive biased agonists SR-17018 and SR-15099 produce submaximal hyperactivity. Moreover, the combination of SR-17018 and morphine attenuates hyperactivity while antinociceptive efficacy is increased. The combination of oliceridine with morphine increases hyperactivity, which is maintained over time. These findings provide evidence that noncompetitive agonists at MOR can be used to suppress morphine-induced hyperactivity while enhancing antinociceptive efficacy; moreover, they demonstrate that intrinsic efficacy measured at the receptor level is not directly proportional to drug efficacy in the locomotor activity assay.

Neurobiological mechanisms and related clinical treatment of addiction: a review

Drug addiction or substance use disorder (SUD), has been conceptualized as a three-stage (i.e. binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation/craving) recurring cycle that involves complex changes in neuroplasticity, reward, motivation, desire, stress, memory, and cognitive control, and other related brain regions and brain circuits. Neuroimaging approaches, including magnetic resonance imaging, have been key to mapping neurobiological changes correlated to complex brain regions of SUD. In this review, we highlight the neurobiological mechanisms of these three stages of addiction. The abnormal activity of the ventral tegmental, nucleus accumbens, and caudate nucleus in the binge/intoxication stage involve the reward circuit of the midbrain limbic system. The changes in the orbitofrontal cortex, dorsolateral prefrontal cortex, amygdala, and hypothalamus emotional system in the withdrawal/negative affect stage involve increases in negative emotional states, dysphoric-like effects, and stress-like responses. The dysregulation of the insula and prefrontal lobes is associated with craving in the anticipation stage. Then, we review the present treatments of SUD based on these neuroimaging findings. Finally, we conclude that SUD is a chronically relapsing disorder with complex neurobiological mechanisms and multimodal stages, of which the craving stage with high relapse rate may be the key element in treatment efficacy of SUD. Precise interventions targeting different stages of SUD and characteristics of individuals might serve as a potential therapeutic strategy for SUD.

Is a Highly Selective and Potent κ Opioid Receptor (KOR) Agonist with an Unexpected Nonreduction in Locomotor Activity

Undue central nervous system (CNS) side effects including dysphoria and sedation remain to be a challenge for the development of κ opioid receptor (KOR) agonists as effective and safe analgesics. On the basis of our previous work on morphinan-based KOR agonists, a series of 7α-methyl-7β-substituted northebaine derivatives were designed, synthesized, and biologically assayed. Among others, compound 4a (SLL-627) has been identified as a highly selective and potent KOR agonist both in vitro and in vivo, and its molecular basis was also examined and discussed. Besides low liability to conditioned place aversion (CPA) test, treatment of SLL-627 was associated with a nonreduction in locomotor activity, compared to most of the other arylacetamide- or morphinan-based KOR agonists which generally exhibited apparently sedative effects. This unexpected finding provides new insights to dissociate analgesia from sedation for future discovery of innovative KOR agonists.

The NOP Receptor System in Neurological and Psychiatric Disorders: Discrepancies, Peculiarities and Clinical Progress in Developing Targeted Therapies

The nociceptin opioid peptide (NOP) receptor and its endogenous ligand nociceptin/orphanin FQ (N/OFQ) are the fourth members of the opioid receptor and opioid peptide families. Although they have considerable sequence homology to the other family members, they are not considered opioid per se because they do not have pharmacological profiles similar to the other family members. The number of NOP receptors in the brain is higher than the other family members, and NOP receptors can be found throughout the brain. Because of the widespread distribution of NOP receptors, N/OFQ and other peptide and small molecule agonists and antagonists have extensive CNS activities. Originally thought to be anti-opioid, NOP receptor agonists block some opioid activities, potentiate others, and modulate other activities not affected by traditional opiates. Because the effect of receptor activation can be dependent upon site of administration, state of the animal, and other variables, the study of NOP receptors has been fraught with contradictions and inconsistencies. In this article, the actions and controversies pertaining to NOP receptor activation and inhibition are discussed with respect to CNS disorders including pain (acute, chronic, and migraine), drug abuse, anxiety and depression. In addition, progress towards clinical use of NOP receptor-directed compounds is discussed.

Buprenorphine: Far Beyond the "Ceiling"

Chronic pain, including neuropathic pain, represents an untreated disease with important repercussions on the quality of life and huge costs on the national health system. It is well known that opioids are the most powerful analgesic drugs, but they represent the second or third line in neuropathic pain, that remain difficult to manage. Moreover, these drugs show several side effects that limit their use. In addition, opioids possess addictive properties that are associated with misuse and drug abuse. Among available opioids compounds, buprenorphine has been suggested advantageous for a series of clinical reasons, including the effectiveness in neuropathic pain. Some properties are partly explained by its unique pharmacological characteristics. However, questions on the dynamic profile remain to be answered. Pharmacokinetics optimization strategies, and additional potentialities, are still to be explored. In this paper, we attempt to conceptualize the potential undiscovered dynamic profile of buprenorphine.

Buprenorphine exposures in adolescents and adults: a 10-year experience of a French Poison Control Center

Buprenorphine has been used in pain and opioid addiction management for nearly 25 years. Compared to methadone, buprenorphine is thought to exhibit less side effects and respiratory depression in case of accidental or suicidal overdose. The aim was to describe the characteristics of exposures reported to a French Poison Control Center (PCC). We conducted a retrospective study including all buprenorphine exposures for which advice of our PCC was required between 2009 and 2018. After data extraction from the electronic medical files and anonymous transfer to an Access base, a statistical descriptive analysis was performed focusing on adolescents over 10 years old and adults. One hundred and ninety-nine cases were analyzed. The major circumstances of exposure were suicide attempts and overdoses in patients with previously identified substance abuse. Buprenorphine exposures have been reduced by 50% between 2009 and 2018. Coingestions, often with benzodiazepines or antidepressants, were almost systematic and 79% of all the series exhibited at least one symptom. Among the symptomatic cases, neurological effects were the most frequent (83%) and respiratory symptoms occurred in 13%. No deaths were registered. Severity did not exceed PSS1 in 80% of all the cases. Treatment was mainly symptomatic even though naloxone was required in at least 5% of the symptomatic cases. Within 24 h after exposure, 120 patients were discharged from the emergency department. Despite loss to follow-up, our results suggest that buprenorphine is relatively safe.

Mechanisms of QT prolongation by buprenorphine cannot be explained by direct hERG channel block

Buprenorphine is a μ-opioid receptor (MOR) partial agonist used to manage pain and addiction. QT_C prolongation that crosses the 10 msec threshold of regulatory concern was observed at a supratherapeutic dose in two thorough QT studies for the transdermal buprenorphine product BUTRANS^®. Because QT_C prolongation can be associated with Torsades de Pointes (TdP), a rare but potentially fatal ventricular arrhythmia, these results have led to further investigation of the electrophysiological effects of buprenorphine. Drug-induced QT_C prolongation and TdP are most commonly caused by acute inhibition of hERG current (I_hERG) that contribute to the repolarizing phase of the ventricular action potentials (APs). Concomitant inhibition of inward late Na⁺ (I_NaL) and/or L-type Ca²⁺ (I_CaL) current can offer some protection against proarrhythmia. Therefore, we characterized the effects of buprenorphine and its major metabolite norbuprenorphine on cardiac hERG, Ca²⁺, and Na⁺ ion channels, as well as cardiac APs. For comparison, methadone, a MOR agonist associated with QT_C prolongation and high TdP risk, and naltrexone and naloxone, two opioid receptor antagonists, were also studied. Whole cell recordings were performed at 37°C on cells stably expressing hERG, Ca_V1.2, and Na_V1.5 proteins. Microelectrode array (MEA) recordings were made on human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). The results showed that buprenorphine, norbuprenorphine, naltrexone, and naloxone had no effect on I_hERG, I_CaL, I_NaL, and peak Na⁺ current (I_NaP) at clinically relevant concentrations. In contrast, methadone inhibited I_hERG, I_CaL, and I_NaL. Experiments on iPSC-CMs showed a lack of effect for buprenorphine, norbuprenorphine, naltrexone, and naloxone, and delayed repolarization for methadone at clinically relevant concentrations. The mechanism of QT_C prolongation is opioid moiety-specific. This remains undefined for buprenorphine, while for methadone it involves direct hERG channel block. There is no evidence that buprenorphine use is associated with TdP. Whether this lack of TdP risk can be generalized to other drugs with QT_C prolongation not mediated by acute hERG channel block warrants further study.

Molecular Biology of Opioid Analgesia and Its Clinical Considerations

Understanding the molecular biology of opioid analgesia is essential for its proper implementation and mechanistic approach to its modulation in order to maximize analgesia and minimize undesired effects. By appreciating the molecular mechanisms intrinsic to opioid analgesia, one can manipulate a molecular target to augment or diminish a specific effect using adjuvant drugs, select an appropriate opioid for opioid rotation or define a molecular target for new opioid drug development. In this review, we present the cellular and molecular mechanisms of opioid analgesia and that of the associated phenomena of tolerance, dependence, and hyperalgesia. The specific mechanisms highlighted are those that presently can be clinically addressed.

Opioid Overdose Deaths with Buprenorphine Detected in Postmortem Toxicology: a Retrospective Analysis

BACKGROUND

Buprenorphine is a unique μ-opioid receptor partial agonist with avid receptor binding, nominal euphoric reward, and a ceiling effect on sedation and respiratory depression. Despite a pharmacologic profile that enhances safety, cases of fatal opioid overdose with buprenorphine on postmortem toxicology are reported, but details of these cases in the literature are limited.

METHODS

A retrospective review of opioid-involved drug overdose fatalities in Rhode Island (RI) from 2016 to 2018 using the RI Department of Health State Unintentional Drug Overdose Reporting System (SUDORS) database. Deaths with buprenorphine on toxicology testing versus opioid-involved overdose deaths without buprenorphine were compared to assess the type and number of co-exposures.

RESULTS

Of 534 opioid-involved deaths, 29 (5.4%) included buprenorphine and/or norbuprenorphine on toxicology. Most frequent co-exposures are as follows: fentanyl (75.9%), norfentanyl (72.4%), cocaine (41.4%), benzoylecgonine (41.4%), cannabinoids (31.0%), ethanol (31.0%), levamisole (31.0%), and free morphine (31.0%). An average number of co-exposures for fatalities with buprenorphine were 9.24 versus 6.68 in those without buprenorphine. In one case buprenorphine was the only drug listed to cause death; all other fatalities with buprenorphine on toxicology reported additional drugs contributing to death.

CONCLUSION

Decedents with buprenorphine detected on toxicology testing commonly had documented polysubstance use. Although data are limited, buprenorphine may provide some risk mitigation against full agonist opioid overdose including fentanyl. Further work should explore the use of postmortem concentrations of buprenorphine, norbuprenorphine, and other opioid metabolites to determine the role of buprenorphine in fatal overdose pharmacology.

A Narrative Pharmacological Review of Buprenorphine: A Unique Opioid for the Treatment of Chronic Pain

Buprenorphine is a Schedule III opioid analgesic with unique pharmacodynamic and pharmacokinetic properties that may be preferable to those of Schedule II full μ-opioid receptor agonists. The structure of buprenorphine allows for multimechanistic interactions with opioid receptors μ, δ, κ, and opioid receptor-like 1. Buprenorphine is considered a partial agonist with very high binding affinity for the μ-opioid receptor, an antagonist with high binding affinity for the δ- and κ-opioid receptors, and an agonist with low binding affinity for the opioid receptor-like 1 receptor. Partial agonism at the μ-opioid receptor does not provide partial analgesia, but rather analgesia equivalent to that of full μ-opioid receptor agonists. In addition, unlike full μ-opioid receptor agonists, buprenorphine may have a unique role in mediating analgesic signaling at spinal opioid receptors while having less of an effect on brain receptors, potentially limiting classic opioid-related adverse events such as euphoria, addiction, or respiratory depression. The pharmacokinetic properties of buprenorphine are also advantageous in a clinical setting, where metabolic and excretory pathways allow for use in patients requiring concomitant medications, the elderly, and those with renal or hepatic impairment. The unique pharmacodynamic and pharmacokinetic properties of buprenorphine translate to an effective analgesic with a potentially favorable safety profile compared with that of full μ-opioid receptor agonists for the treatment of chronic pain.

A Surface-Enhanced Raman Spectral Library of Important Drugs Associated With Point-of-Care and Field Applications

During the past decade, the ability of surface-enhanced Raman spectroscopy (SERS) to measure extremely low concentrations, such as mg/L and below, and the availability of hand-held Raman spectrometers, has led to a significant growth in the number and variety of applications of SERS to real-world problems. Most of these applications involve the measurement of drugs, such as quantifying medication in patients, identifying illicit drugs in impaired drivers, and more recently, identifying drugs used as weapons. Similar to Raman spectroscopy, most of the point-of-care and field applications involve the identification of the drug to determine the course of action. However, unlike Raman spectroscopy, spectral libraries are not readily available to perform the necessary identification. In a large part, this is due to the uniqueness of the commercially available SERS substrates, each of which can produce different spectra for the same drug. In an effort to overcome this limitation, we have measured numerous drugs using the most common, and readily available SERS material and hand-held Raman analyzers, specifically gold colloids and analyzers using 785 nm laser excitation. Here we present the spectra of some 39 drugs of current interest, such as buprenorphine, delta-9 tetrahydrocannabinol, and fentanyl, which we hope will aid in the development of current and future SERS drug analysis applications.

Comprehensive molecular pharmacology screening reveals potential new receptor interactions for clinically relevant opioids

Most clinically used opioids are thought to induce analgesia through activation of the mu opioid receptor (MOR). However, disparities have been observed between the efficacy of opioids in activating the MOR in vitro and in inducing analgesia in vivo. In addition, some clinically used opioids do not produce cross-tolerance with each other, and desensitization produced in vitro does not match tolerance produced in vivo. These disparities suggest that some opioids could be acting through other targets in vivo, but this has not been comprehensively tested. We thus screened 9 clinically relevant opioids (buprenorphine, hydrocodone, hydromorphone, morphine, O-desmethyl-tramadol, oxycodone, oxymorphone, tapentadol, tramadol) against 9 pain-related receptor targets (MOR, delta opioid receptor [DOR], kappa opioid receptor [KOR], nociceptin receptor [NOP], cannabinoid receptor type 1 [CB1], sigma-1 receptor [σ1R], and the monoamine transporters [NET/SERT/DAT]) expressed in cells using radioligand binding and functional activity assays. We found several novel interactions, including monoamine transporter activation by buprenorphine and σ1R binding by hydrocodone and tapentadol. Tail flick anti-nociception experiments with CD-1 mice demonstrated that the monoamine transporter inhibitor duloxetine selectively promoted buprenorphine anti-nociception while producing no effects by itself or in combination with the most MOR-selective drug oxymorphone, providing evidence that these novel interactions could be relevant in vivo. Our findings provide a comprehensive picture of the receptor interaction profiles of clinically relevant opioids, which has not previously been performed. Our findings also suggest novel receptor interactions for future investigation that could explain some of the disparities observed between opioid performance in vitro and in vivo.

Readiness and recovery: Transferring between methadone and buprenorphine/naloxone for the treatment of opioid use disorder

Long-acting opioids are prescribed as part of treatment for opioid use disorders; methadone and buprenorphine are well researched and commonly prescribed for the treatment of opioid use disorder. Meta-analysis suggests that buprenorphine has a slightly poorer retention rate in treatment as compared to methadone. Benefits of buprenorphine/naloxone include greater ease in ceasing treatment and less use of illicit opioids while in treatment as compared to methadone. There are a number of qualitative and mixed-method studies that ask patients about their experiences of methadone maintenance and buprenorphine maintenance treatment. This research aimed to understand perspectives of receiving buprenorphine/naloxone for the treatment of opioid use disorder. A qualitative descriptive approach was used. Seven participants with a current diagnosis of opioid use disorder treated with buprenorphine/naloxone were interviewed. Thematic analysis extracted four themes: drivers for opioid substitution treatment change; readiness for buprenorphine/naloxone substitution treatment; absence of effect from buprenorphine/naloxone; and an increased sense of citizenship on buprenorphine/naloxone. This study identified a number of factors influencing participants' decision-making in transferring between methadone and buprenorphine/naloxone for the treatment of their opioid use disorder. Methadone was preferred by those seeking sedation and wishing to continue using other opioids, and buprenorphine/naloxone was most effective for participants no longer wishing to experience sedation and seeing opioid abstinence as an end point in their recovery. Changing treatment expectations are important to consider when determining medication selection and highlight the importance of quality information when determining the most suitable medication for the treatment of opioid use disorder.

DARK Classics in Chemical Neuroscience: Opium, a Friend or Foe

Opium has found great use medicinally for its analgesic properties and has been witnessed as one of the most popular medications used in psychiatry. Opium derivatives have been shown as efficacious for relieving pain and the treatment of epileptic seizures, but progressive research toward their use in the treatment of neurodegenerative diseases remain elusive. To gain more insight into the other properties of opium such as anti-inflammatory properties, herein we discuss basic information regarding opium, opium content and mechanism of action, pharmacology of opium derivatives, the role of opium in the prevention of neurodegeneration, and adverse effects of opium derivatives on neuronal health.

Synthesis, Biological Evaluation, and SAR Studies of 14β-phenylacetyl Substituted 17-cyclopropylmethyl-7, 8-dihydronoroxymorphinones Derivatives: Ligands With Mixed NOP and Opioid Receptor Profile

A series of 14β-acyl substituted 17-cyclopropylmethyl-7,8-dihydronoroxymorphinone compounds has been synthesized and evaluated for affinity and efficacy for mu (MOP), kappa (KOP), and delta (DOP) opioid receptors and nociceptin/orphanin FQ peptide (NOP) receptors. The majority of the new ligands displayed high binding affinities for the three opioid receptors, and moderate affinity for NOP receptors. The affinities for NOP receptors are of particular interest as most classical opioid ligands do not bind to NOP receptors. The predominant activity in the [35S]GTPγS assay was partial agonism at each receptor. The results are consistent with our prediction that an appropriate 14β side chain would access a binding site within the NOP receptor and result in substantially higher affinity than displayed by the parent compound naltrexone. Molecular modeling studies, utilizing the recently reported structure of the NOP receptor, are also consistent with this interpretation.

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.

In Vitro Pharmacological Characterization of Buprenorphine, Samidorphan, and Combinations Being Developed as an Adjunctive Treatment of Major Depressive Disorder

A combination of buprenorphine (BUP) and samidorphan (SAM) at a 1:1 (mg/mg) fixed-ratio dose is being investigated as an adjunctive treatment of major depressive disorder (BUP/SAM, ALKS 5461). Both [³H]BUP and [³H]SAM bound to the μ-, κ-, and δ-opioid receptors (MOR, KOR, and DOR, respectively) with K_d values of 3 nM or less. [³H]BUP dissociated from the MOR more slowly than [³H]SAM did. In the [³⁵S]GTPγS assay, BUP was a partial agonist at the MOR, KOR, and DOR. SAM was an antagonist at the MOR and a partial agonist at the KOR and DOR. The pharmacology of the combination of SAM and BUP was characterized at ratios like the molar ratios of both compounds at steady state in humans. In all assessments, SAM reduced the efficacy of BUP at the MOR without altering its potency. At the KOR, SAM had no significant effect on the activity of BUP. In bioluminescent resonance energy transfer assays, SAM, naltrexone, and naloxone were partial agonists when the MOR was coupled to the Gα _oB and Gα _z, and were antagonists when coupled to Gα _i At the KOR, SAM was a partial agonist activating Gα _oA and Gα _oB and a full agonist in stimulating Gα _z SAM inhibited BUP's recruitment of β-arrestin to the MOR, suggesting an attenuation of BUP's efficacy in activating G proteins correlated with an inhibition of β-arrestin recruitment. The collective data suggest that SAM attenuates the efficacy of BUP under all conditions tested at the MOR and DOR but had little effect on BUP activity at the KOR.

Treating Chronic Pain: An Overview of Clinical Studies Centered on the Buprenorphine Option

The buprenorphine receptor binding profile is unique in that it binds to all three major opioid receptors (mu, kappa, delta), and also binds to the orphan-like receptor, the receptor for orphanin FQ/nociceptin, with lower affinity. Within the mu receptor group, buprenorphine analgesia in rodents is dependent on the recently discovered arylepoxamide receptor target in brain, which involves a truncated 6-transmembrane mu receptor gene protein, distinguishing itself from morphine and most other mu opioids. Although originally designed as an analgesic, buprenorphine has mainly been used for opioid maintenance therapy and only now is increasingly recognized as an effective analgesic with an improved therapeutic index relative to certain potent opioids. Albeit a second-, third-, or fourth-line analgesic, buprenorphine is a reasonable choice in certain clinical situations. Transdermal patches and buccal film formulations are now commercially available as analgesics. This review discusses buprenorphine pharmacodynamics and pharmacokinetics, use in certain populations, and provides a synopsis of systematic reviews and randomized analgesic trials. We briefly discuss postoperative management in patients receiving buprenorphine maintenance therapy, opioid equivalence to buprenorphine, rotations to buprenorphine from other opioids, and clinical relevance of buprenorphine-related QTc interval changes.

Pharmacodynamic and pharmacokinetic evaluation of buprenorphine + samidorphan for the treatment of major depressive disorder

INTRODUCTION

Treatment resistant depression (TRD) represents approximately 20% of all individuals receiving care for major depressive disorder. The opioidergic system is identified as a novel target which hitherto has not been sufficiently investigated in adults with TRD. The combination product buprenorphine + samidorphan is an opioid modulatory agent which has demonstrated replicated evidence of efficacy in TRD without abuse liability. Areas covered: Databases Pubmed, Google Scholar and clinicaltrials.gov were searched from inception through December 2017 for clinical trial information, pharmacokinetics, and pharmacodynamics of buprenorphine + samidorphan. Herein we provide a summary of the available information. Eight clinical trials were identified for inclusion, of the eight trials, five trials had available results and are included in detail in our review. Expert opinion: Buprenorphine + samidorphan has demonstrated efficacy in TRD. Extant evidence surrounding the safety and tolerability profile of buprenorphine + samidorphan does not identify any significant safety concerns. Additional studies are needed in order to assess the long-term safety and efficacy of this product.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Mediation of buprenorphine analgesia by a combination of traditional and truncated mu opioid receptor splice variants

Buprenorphine has long been classified as a mu analgesic, although its high affinity for other opioid receptor classes and the orphanin FQ/nociceptin ORL1 receptor may contribute to its other actions. The current studies confirmed a mu mechanism for buprenorphine analgesia, implicating several subsets of mu receptor splice variants. Buprenorphine analgesia depended on the expression of both exon 1-associated traditional full length 7 transmembrane (7TM) and exon 11-associated truncated 6 transmembrane (6TM) MOR-1 variants. In genetic models, disruption of delta, kappa1 or ORL1 receptors had no impact on buprenorphine analgesia, while loss of the traditional 7TM MOR-1 variants in an exon 1 knockout (KO) mouse markedly lowered buprenorphine analgesia. Loss of the truncated 6TM variants in an exon 11 KO mouse totally eliminated buprenorphine analgesia. In distinction to analgesia, the inhibition of gastrointestinal transit and stimulation of locomotor activity were independent of truncated 6TM variants. Restoring expression of a 6TM variant with a lentivirus rescued buprenorphine analgesia in an exon 11 KO mouse that still expressed the 7TM variants. Despite a potent and robust stimulation of (35) S-GTPγS binding in MOR-1 expressing CHO cells, buprenorphine failed to recruit β-arrestin-2 binding at doses as high as 10 µM. Buprenorphine was an antagonist in DOR-1 expressing cells and an inverse agonist in KOR-1 cells. Buprenorphine analgesia is complex and requires multiple mu receptor splice variant classes but other actions may involve alternative receptors.

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.

Random Forest Segregation of Drug Responses May Define Regions of Biological Significance

The ability to assess brain responses in unsupervised manner based on fMRI measure has remained a challenge. Here we have applied the Random Forest (RF) method to detect differences in the pharmacological MRI (phMRI) response in rats to treatment with an analgesic drug (buprenorphine) as compared to control (saline). Three groups of animals were studied: two groups treated with different doses of the opioid buprenorphine, low (LD), and high dose (HD), and one receiving saline. PhMRI responses were evaluated in 45 brain regions and RF analysis was applied to allocate rats to the individual treatment groups. RF analysis was able to identify drug effects based on differential phMRI responses in the hippocampus, amygdala, nucleus accumbens, superior colliculus, and the lateral and posterior thalamus for drug vs. saline. These structures have high levels of mu opioid receptors. In addition these regions are involved in aversive signaling, which is inhibited by mu opioids. The results demonstrate that buprenorphine mediated phMRI responses comprise characteristic features that allow a supervised differentiation from placebo treated rats as well as the proper allocation to the respective drug dose group using the RF method, a method that has been successfully applied in clinical studies.

Buprenorphine - an attractive opioid with underutilized potential in treatment of chronic pain

Despite proven clinical utility, buprenorphine has not been used widely for the treatment of chronic pain. Questions about “ceiling effect” or bell-shaped curve observed for analgesia in preclinical studies and potential withdrawal issues on combining with marketed μ-agonists continue to hinder progress in expanding full potential of buprenorphine in the treatment of cancer and noncancer pain. Mounting evidence from clinical studies and conclusions drawn by a panel of experts strongly support superior safety and efficacy profile of buprenorphine vs marketed opioids. No ceiling on analgesic effect has been reported in clinical studies. The receptor pharmacology and pharmacokinetics profile of buprenorphine is complex but unique and contributes to its distinct safety and efficacy. The buprenorphine pharmacology also allows it to be combined with other μ-receptor opioids for additivity in efficacy. Transdermal delivery products of buprenorphine have been preferred choices for the management of pain but new delivery options are under investigation for the treatment of both opioid dependence and chronic pain.