Opioid antagonists

An overview of pain assessment and management

Pain is a distressing, subjective and complex phenomenon that all nurses will encounter in their clinical practice. Effective pain management requires nurses to undertake a structured assessment to identify the probable causes of pain and guide management. Interventions used to reduce pain can be varied and multimodal. This article provides an overview of pain including its definition, classifications, assessment and management. It emphasises the importance of a person-centred approach to care which reflects Margo McCaffery's seminal quote that pain is 'whatever the experiencing person says it is'.

Cerebral μ-opioid and CB1 receptor systems have distinct roles in human feeding behavior

Eating behavior varies greatly between individuals, but the neurobiological basis of these trait-like differences in feeding remains poorly understood. Central μ-opioid receptors (MOR) and cannabinoid CB₁ receptors (CB₁R) regulate energy balance via multiple neural pathways, promoting food intake and reward. Because obesity and eating disorders have been associated with alterations in the brain's opioid and endocannabinoid signaling, the variation in MOR and CB₁R system function could potentially underlie distinct eating behavior phenotypes. In this retrospective positron emission tomography (PET) study, we analyzed [¹¹C]carfentanil PET scans of MORs from 92 healthy subjects (70 males and 22 females), and [¹⁸F]FMPEP-d₂ scans of CB₁Rs from 35 subjects (all males, all also included in the [¹¹C]carfentanil sample). Eating styles were measured with the Dutch Eating Behavior Questionnaire (DEBQ). We found that lower cerebral MOR availability was associated with increased external eating-individuals with low MORs reported being more likely to eat in response to environment's palatable food cues. CB₁R availability was associated with multiple eating behavior traits. We conclude that although MORs and CB₁Rs overlap anatomically in brain regions regulating food reward, they have distinct roles in mediating individual feeding patterns. Central MOR system might provide a pharmacological target for reducing individual's excessive cue-reactive eating behavior.

Research progress of opioid growth factor in immune-related diseases and cancer diseases

Methionine enkephalin (MENK) has an important role in both neuroendocrine and immune systems. MENK was known as an opioid growth factor (OGF) for its growth regulatory characteristics. OGF interacts with the OGF receptor (OGFr) to inhibit DNA synthesis by upregulating p16 and/or p21, which delays the cell cycle transition from G0/G1 to S phase, and inhibits cell proliferation. In addition, OGF combines with OGFr in immune cells to exert its immunomodulatory activity and regulate immune function. OGF has been studied as an immunomodulator in a variety of autoimmune diseases, including multiple sclerosis, inflammatory bowel disease, diabetes and viral infections, and has been proven to relieve symptoms of certain diseases in animal and in vitro experiments. Also, OGF and OGFr have various anti-tumor molecular mechanisms. OGF can be used as the primary therapy alone or combined with other drugs to treat tumors. This article summarizes the research progress of OGF in immune-related diseases and cancer diseases.

Engineering Quick- and Long-acting Naloxone Delivery Systems for Treating Opioid Overdose

Purpose

Opioids have been the main factor for drug overdose deaths in the United States. Current naloxone delivery systems are effective in mitigating the opioid effects only for hours. Naloxone-loaded poly(lactide-co-glycolide) (PLGA) microparticles were prepared as quick- and long-acting naloxone delivery systems to extend the naloxone effect as an opioid antidote.

Methods

The naloxone-PLGA microparticles were made using an emulsification solvent extraction approach with different formulation and processing parameters. Two PLGA polymers with the lactide:glycolide (L:G) ratios of 50:50 and 75:25 were used, and the drug loading was varied from 21% to 51%. Two different microparticles of different sizes with the average diameters of 23 μm and 50 μm were produced using two homogenization-sieving conditions. All the microparticles were critically characterized, and three of them were evaluated with β-arrestin recruitment assays.

Results

The naloxone encapsulation efficiency (EE) was in the range of 70–85%. The EE was enhanced when the theoretical naloxone loading was increased from 30% to 60%, the L:G ratio was changed from 50:50 to 75:25, and the average size of the particles was reduced from 50 μm to 23 μm. The in vitro naloxone release duration ranged from 4 to 35 days. Reducing the average size of the microparticles from 50 μm to 23 μm helped eliminate the lag phase and obtain the steady-state drug release profile. The cellular pharmacodynamics of three selected formulations were evaluated by applying DAMGO, a synthetic opioid peptide agonist to a μ-opioid receptor, to recruit β-arrestin 2.

Conclusions

Naloxone released from the three selected formulations could inhibit DAMGO-induced β-arrestin 2 recruitment. This indicates that the proposed naloxone delivery system is adequate for opioid reversal during the naloxone release duration.

Evaluation of Injectable Naloxone-Releasing Hydrogels

The opioid epidemic in the United States is a serious public health crisis affecting over 1.7 million Americans. In the last two decades, almost 450 000 people have died from an opioid overdose, with nearly 20% of these deaths occurring in 2017 and 2018 alone. During an overdose, overstimulation of the μ-opioid receptor leads to severe and potentially fatal respiratory depression. Naloxone is a competitive μ-opioid-receptor antagonist that is widely used to displace opioids and rescue from an overdose. Here, we describe the development of a slow-release, subcutaneous naloxone formulation for potential management of opioid overdose, chronic pain, and opioid-induced constipation. Naloxone is loaded into self-assembling peptide hydrogels for controlled drug release. The mechanical, chemical, and structural properties of the nanofibrous hydrogel enable subcutaneous administration and slow, diffusion-based release kinetics of naloxone over 30 days in vitro. The naloxone hydrogel scaffold showed cytocompatibility and did not alter the β-sheet secondary structure or thixotropic properties characteristic of self-assembling peptide hydrogels. Our results show that this biocompatible and injectable self-assembling peptide hydrogel may be useful as a vehicle for tunable, sustained release of therapeutic naloxone. This therapy may be particularly suited for preventing renarcotization in patients who refuse additional medical assistance following an overdose.

Prevention of Opioid Abuse and Treatment of Opioid Addiction: Current Status and Future Possibilities

Prescription opioid medications have seen a dramatic rise in misuse and abuse, leading regulators and scientists to develop policies and abuse-deterrent technologies to combat the current opioid epidemic. These abuse-deterrent formulations (ADFs) are intended to deter physical and chemical tampering of opioid-based products, while still providing safe and effective delivery for therapeutic purposes. Even though formulations with varying abuse-deterrent technologies have been approved, questions remain about their effectiveness. While these formulations provide a single means to combat the epidemic, a greater emphasis should be placed on formulations for treatment of addiction and overdose to help those struggling with opioid dependence. This article analyzes various ADFs currently in clinical use and explores potential novel systems for treatment of addiction and prevention of overdose.

Progress in understanding mechanisms of opioid-induced gastrointestinal adverse effects and respiratory depression

Opioids evoke analgesia through activation of opioid receptors (predominantly the μ opioid receptor) in the central nervous system. Opioid receptors are abundant in multiple regions of the central nervous system and the peripheral nervous system including enteric neurons. Opioid-related adverse effects such as constipation, nausea, and vomiting pose challenges for compliance and continuation of the therapy for chronic pain management. In the post-operative setting opioid-induced depression of respiration can be fatal. These critical limitations warrant a better understanding of their underpinning cellular and molecular mechanisms to inform the design of novel opioid analgesic molecules that are devoid of these unwanted side-effects. Research efforts on opioid receptor signalling in the past decade suggest that differential signalling pathways and downstream molecules preferentially mediate distinct pharmacological effects. Additionally, interaction among opioid receptors and, between opioid receptor and non-opioid receptors to form signalling complexes shows that opioid-induced receptor signalling is potentially more complicated than previously thought. This complexity provides an opportunity to identify and probe relationships between selective signalling pathway specificity and in vivo production of opioid-related adverse effects. In this review, we focus on current knowledge of the mechanisms thought to transduce opioid-induced gastrointestinal adverse effects (constipation, nausea, vomiting) and respiratory depression.

Anesthetic implications of recreational drug use

PURPOSE

As the use of recreational drugs increases, the likelihood of an anesthesiologist perioperatively encountering patients using or addicted to these drugs will also increase.

PRINCIPAL FINDINGS

Addicted patients may present for anesthetic care in a variety of circumstances in everyday elective surgeries or in acute or life-saving situations, such as emergency Cesarean delivery or trauma surgery. Therefore, it is important for anesthesiologists to know about the most common illicit drugs being used, their clinical presentation and side effects, and the anesthetic options that are beneficial or detrimental to these patients. The most frequently used illicit substances, apart from alcohol and tobacco, are cannabis, cocaine, heroin, prescription opioids, methamphetamine, and hallucinogens. When planning anesthetic care, it is important for anesthesiologists to understand the effects of these agents, including various drug interactions, to predict tolerance to some anesthetic agents, to recognize drug withdrawal signs and symptoms, and to be prepared to manage all these factors in the perioperative period.

CONCLUSIONS

For optimal patient care through the perioperative period, it is critical to obtain information about patient drug use and other associated treatment in order to construct an appropriate anesthetic plan, including specific considerations during surgery, emergence, and in the postanesthesia care unit.

New opioid receptor antagonist: Naltrexone-14-O-sulfate synthesis and pharmacology

Opioid antagonists, naloxone and naltrexone have long been used in clinical practice and research. In addition to their low selectivity, they easily pass through the blood-brain barrier. Quaternization of the amine group in these molecules, (e.g. methylnaltrexone) results in negligible CNS penetration. In addition, zwitterionic compounds have been reported to have limited CNS access. The current study, for the first time gives report on the synthesis and the in vitro [competition binding, G-protein activation, isolated mouse vas deferens (MVD) and mouse colon assay] pharmacology of the zwitterionic compound, naltrexone-14-O-sulfate. Naltrexone, naloxone, and its 14-O-sulfate analogue were used as reference compounds. In competition binding assays, naltrexone-14-O-sulfate showed lower affinity for µ, δ or κ opioid receptor than the parent molecule, naltrexone. However, the μ/κ opioid receptor selectivity ratio significantly improved, indicating better selectivity. Similar tendency was observed for naloxone-14-O-sulfate when compared to naloxone. Naltrexone-14-O-sulfate failed to activate [³⁵S]GTPγS-binding but inhibit the activation evoked by opioid agonists (DAMGO, Ile^5,6deltorphin II and U69593), similarly to the reference compounds. Schild plot constructed in MVD revealed that naltrexone-14-O-sulfate acts as a competitive antagonist. In mouse colon, naltrexone-14-O-sulfate antagonized the inhibitory effect of morphine with lower affinity compared to naltrexone and higher affinity when compared to naloxone or naloxone-14-O-sulfate. In vivo (mouse tail-flick test), subcutaneously injected naltrexone-14-O-sulfate antagonized morphine's antinociception in a dose-dependent manner, indicating it's CNS penetration, which was unexpected from such zwitter ionic structure. Future studies are needed to evaluate it's pharmacokinetic profile.

Opioids and cancer recurrence

PURPOSE OF REVIEW

With the majority of deaths from cancer because of their metastases, strategies to reduce this from occurring are at the forefront of treatment. It has been hypothesized that morphine may result in an increase in cancer metastases, following many in-vitro and animal studies, but the evidence from human retrospective data is inconclusive. This article will explore the possible mechanisms by which opioids can impact on the natural history of the cancer cell and whether they are likely to be harmful in individuals with cancer.

RECENT FINDINGS

Although there have been trials demonstrating benefits with regional anaesthesia techniques (opioid sparing) in the surgical population, it is not clear whether the source of the benefit arises directly from the avoidance of opioids or an added benefit afforded by regional anaesthesia. Research has shown that in particular cancer cell types, morphine may actually be beneficial and that the μ-opioid receptor (MOR) plays a role in cancer disease. With the crystal structure of the MOR having recently been elucidated, this may offer new opportunities for treatments aimed at reducing cancer metastasis.

SUMMARY

The role opioids play in the development of cancer metastasis and recurrence is far from clear and appears to differ depending on the cancer cell type in question. Prospective randomized controlled trials are currently underway in humans to help clarify the situation further and there results are awaited with anticipation. The negative impact of pain on the immune system is well documented and it appears that appropriate analgesia is paramount in minimizing this. Opioids still constitute a central role in the management of moderate-to-severe cancer pain.