Blockade of Glutamate Receptors within the Prelimbic Cortex Attenuate Concentration of Excitatory Amino Acids in the Morphine Self-administration in Rats

Background

The attitude of research on addiction has been done on the key role of glutamate. As a regard, the prelimbic cortex (PrL) has an important role in addiction, learning, and memory. We tried to investigate the level of glutamate and aspartate concentration after glutamate receptors blockade in this region in the morphine-addicted rats.

Materials and Methods

In this study, we examined the effects of local infusion of the N-methyl-D-aspartate receptor and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonists, 2-amino-5-phosphonovaleric acid (AP5), and 6-cyano-7-nitroquinoxaline-2, 3-dione (CNQX), into the PrL cortex on the level of excitatory amino acids (EAAs) and glycine. After 11 days of self-administration, the prelimbic area of the brain was taken out, and the EAAs and glycine concentration was measured by high-performance liquid chromatography.

Results

Morphine resulted in the significant increase in the EAAs concentration within this area (P ≤ 0.001). Microinjection of AP5 into this region before using of morphine significantly decreased the morphine-induced glutamate and aspartate concentration (P ≤ 0.001). CNQX had the same effect and significantly reduced the EAAs concentration compared to the morphine group (P ≤ 0.001). In addition, microinjection of AP5 and CNQX simultaneously increased glycine concentration (P ≤ 0.001).

Conclusions

These results show that morphine stimulates the EAAs release in the prelimbic area. It seems that microinjection of AP5 or CNQX in this region is effective in reducing morphine-induced EAA. It is suggested that EAA transmission in the PrL cortex may be a possible target for treatment of morphine addiction.

In vitro evaluation of effects of metformin on morphine and methadone tolerance through mammalian target of rapamycin signaling pathway

The chronic use of opioids leads to tolerance, psychological, and physical dependence that limits their use as an effective long-term pain control. Several studies have shown that mammalian target of rapamycin (mTOR) plays a crucial role in the development of opioid tolerance. Metformin activates 5' adenosine monophosphate-activated protein kinase (AMPK) which directly suppresses the mTOR complex 1 signaling pathway. On the other hand, metformin can also inhibit mTOR directly and in an AMPK-independent manner. Thus, in the current study, we aimed to investigate the effects of metformin on the development of morphine and/or methadone-induced tolerance in human glioblastoma (T98G) cell line. We examined the effects of chronic treatment of morphine and/or methadone in the presence or absence of metformin with or without AMPK inhibitor (dorsomorphin hydrochloride) on levels of nitric oxide and cyclic adenosine monophosphate (cAMP), phosphorylated and dephosphorylated ribosomal protein S6 kinase β-1 (S6K1) and 4E-binding protein 1 (4E-BP1) in T98G cells. Pretreatment of cells with metformin (40 µM) with or without AMPK inhibitor (dorsomorphin hydrochloride; 1 µM) before adding of morphine (2.5 µM) or methadone (1 µM) revealed a protective effects on the development of opioid tolerance. Prior administration of metformin reversed the elevation of nitric oxide levels induced by morphine (p < 0.001) and methadone (p < 0.001) and also prevented the raise of cAMP levels induced by morphine in T98G cells (p < 0.05). Contribution of mTOR signaling pathway in metformin-induced effect was shown by the inhibition of phosphorylation of S6K1 and 4E-BP1, the downstream targets of mTOR. mTOR activation suppresses opioid-induced antinociception, and its activity has also been increased during opioid tolerance.

Morphine for Refractory Dyspnea in Interstitial Lung Disease: A Phase I Study (JORTC-PAL 05)

Background: Dyspnea is common in interstitial lung disease (ILD) patients and often refractory to conventional treatment. Little is known regarding the safety of systemic morphine in ILD patients. Objective: The objective of this study is to evaluate the safety of a single subcutaneous morphine injection and to determine the recommended dose of morphine for alleviating dyspnea in ILD patients. Design: We conducted a dose-escalation Phase I study for investigating the recommended dose of a single subcutaneous morphine injection to alleviate dyspnea in ILD patients. Setting/Subjects: Eligible subjects were ILD inpatients with dyspnea at rest who were refractory to conventional dyspnea treatment. The morphine doses used were 1 mg and 2 mg in cohort 1 and cohort 2, respectively. The primary endpoint was dose-limiting toxicity, which was defined as (1) respiratory depression, that is, 30% reduction of respiratory rate and 10 Torr increase of PaCO₂ compared with baseline; (2) hypotension, that is, 20% reduction of systemic blood pressure compared with baseline and presentation of hypotension-related symptoms; or (3) grade 3, 4, or 5 treatment-emergent adverse events graded by Common Terminology Criteria for Adverse Events (version 4). Results: A total of six patients were enrolled, with three patients each in cohorts 1 and 2. No dose-limiting toxicities were observed; three patients experienced worsened somnolence, but no patients experienced sedation. Conclusion: We conclude that 2 mg of morphine has a tolerable safety profile in ILD patients with dyspnea, and can be tested in further clinical trials.

Estrogen Regulation of GRK2 Inactivates Kappa Opioid Receptor Signaling Mediating Analgesia, But Not Aversion

Activation of κ opioid receptors (KORs) produces analgesia and aversion via distinct intracellular signaling pathways, but whether G protein-biased KOR agonists can be designed to have clinical utility will depend on a better understanding of the signaling mechanisms involved. We found that KOR activation produced conditioned place aversion and potentiated CPP for cocaine in male and female C57BL/6N mice. Consistent with this, males and females both showed arrestin-mediated increases in phospho-p38 MAPK following KOR activation. Unlike in males, however, KOR activation had inconsistent analgesic effects in females and KOR increased Gβγ-mediated ERK phosphorylation in males, but not females. KOR desensitization was not responsible for the lack of response in females because neither Grk3 nor Pdyn gene knock-out enhanced analgesia. Instead, responsiveness was estrous cycle dependent because KOR analgesia was evident during low estrogen phases of the cycle and in ovariectomized (OVX) females. Estradiol treatment of OVX females suppressed KOR-mediated analgesia, demonstrating that estradiol was sufficient to blunt Gβγ-mediated KOR signals. G protein-coupled receptor kinase 2 (GRK2) is known to regulate ERK activation, and we found that the inhibitory, phosphorylated form of GRK2 was significantly higher in intact females. GRK2/3 inhibition by CMPD101 increased KOR stimulation of phospho-ERK in females, decreased sex differences in KOR-mediated inhibition of dopamine release, and enhanced mu opioid receptor and KOR-mediated analgesia in females. In OVX females, estradiol increased the association between GRK2 and Gβγ. These studies suggest that estradiol, through increased phosphorylation of GRK2 and possible sequestration of Gβγ by GRK2, blunts G protein-mediated signals.SIGNIFICANCE STATEMENT Chronic pain disorders are more prevalent in females than males, but opioid receptor agonists show inconsistent analgesic efficacy in females. κ opioid receptor (KOR) agonists have been tested in clinical trials for treating pain disorders based on their analgesic properties and low addictive potential. However, the molecular mechanisms underlying sex differences in KOR actions were previously unknown. Our studies identify an intracellular mechanism involving estradiol regulation of G protein-coupled receptor kinase 2 that is responsible for sexually dimorphic analgesic responses following opioid receptor activation. Understanding this mechanism will be critical for developing effective nonaddictive opioid analgesics for use in women and characterizing sexually dimorphic effects in other inhibitory G protein-coupled receptor signaling responses.

Opioidergic conditioning of the human heart muscle in nitric oxide-dependent mechanism

BACKGROUND

Opioidergic conditioning is well documented to trigger cardioprotection against ischemia/ reperfusion (I/R) injury. Previous studies on animal models have suggested that nitric oxide (NO) mediates the beneficial effect of opioids, but the role of NO in humans seems to be controversial.

OBJECTIVES

The aim of the study was to assess the influence of NO modulators on opioid-induced cardioprotection in the human myocardium.

MATERIAL AND METHODS

Trabeculae of the human right atria were electrically driven in an organ bath and subjected to simulated I/R injury. The non-selective inhibitor of nitric oxide synthase (NOS) - N-methyl-l-arginine (LNMMA), the donor of NO - S-Nitroso-N-acetylpenicillamine (SNAP) or morphine (in the amount of 10-4 M) were used at the time of re-oxygenation. The additional trabecula was subjected to the hypoxia protocol only (control). The contractility of the myocardium was assessed as the maximal force of a contraction (Amax), the rate of rise of the force of a contraction (Slope L) and the cardiac muscle relaxation - as the rate of decay of the force of a contraction (Slope T).

RESULTS

The application of 100 μM LNMMA resulted in the decrease of Amax, Slope L and Slope T during the re-oxygenation period as compared to control. The application of 10-4 M morphine and/or 100 μM SNAP resulted in a partial reversal of the detrimental influence of LNMMA.

CONCLUSIONS

At the re-oxygenation period, the blockade of NO synthesis has a deleterious effect on the systolic and diastolic function of the human myocardium as well as attenuates the beneficial effect of morphine conditioning.

Comparison of different methods of postoperative analgesia after thoracotomy-a randomized controlled trial

Background

Continuous thoracic epidural analgesia (TEA) is a preferred method of postoperative analgesia in thoracic surgery. Intravenous patient-controlled analgesia (IVPCA) may be an effective alternative. One of the most commonly used opioids in PCA is morphine. It has high antinociceptive efficacy but is associated with many adverse events. Oxycodone can be an alternative. A small number of scientific reports comparing morphine and oxycodone in PCA for the treatment of acute postoperative pain after thoracotomy was the reason to conduct this study.

Methods

Prospective, randomised, observational study. In total of 99 patients scheduled for elective thoracotomy were randomized into three study groups. TEA group received continuous TEA as a method of postoperative pain management, morphine (MF) group received morphine IVPCA, and morphine (OXY) group oxycodone IVPCA. For 48 hours' hemodynamic parameters, level of pain, sedation and the need for rescue analgesia were monitored. After 48 hours' patients were asked about their satisfaction with pain treatment using Likert scale and assessment of opioid related adverse events via overall benefit of analgesia score (OBAS).

Results

The level of pain in visual analogic score (VAS) and Prince Henry Hospital Pain Score (PHHPS) scales was significantly lower in TEA group with no significant difference between groups MF and OXY. Using morphine in PCA was associated with a significantly higher likelihood of need of rescue analgesia. The level of sedation in Ramsay scale was significantly higher in MF compared to OXY and TEA group. There were no significant differences between groups in OBAS scale. TEA group was characterized by the highest degree of patient satisfaction.

Conclusions

TEA provided superior anaesthesia compared to PCA in our study group. Use of PCA oxycodone in postoperative pain management after open thoracotomy provides similar nociception control compared to morphine but is associated with less sedation and patients using oxycodone IVPCA require smaller doses of rescue analgesia compared to systemic morphine IVPCA.

Medication overuse headache following repeated morphine, but not [INCREMENT]9-tetrahydrocannabinol administration in the female rat

The potential of [INCREMENT]-tetrahydrocannabinol (THC) as a treatment for migraine depends on antinociceptive efficacy with repeated administration. Although morphine has good antinociceptive efficacy, repeated administration causes medication overuse headache (MOH) - a condition in which the intensity/frequency of migraine increases. The present study compared the effect of repeated morphine or THC administration on the magnitude and duration of migraine-like pain induced by a microinjection of allyl isothiocyanate (AITC) onto the dura mater of female rats. Acute administration of THC or morphine prevented AITC-induced depression of wheel running. This antinociception was maintained in rats treated repeatedly with THC, but not following repeated administration of morphine. Moreover, repeated morphine, but not THC administration, extended the duration of AITC-induced depression of wheel running. These data indicate that tolerance and MOH develop rapidly to morphine administration. The lack of tolerance and MOH to THC indicates that THC may be an especially effective long-term treatment against migraine.

Relative Oral Bioavailability of an Abuse-deterrent, Extended-release Formulation of Morphine Versus Extended-release Morphine: A 2-period, Single-dose, Randomized Crossover Study in Healthy Subjects

PURPOSE

Morphine ARER is a novel oral, abuse-deterrent, extended-release (ER) formulation of morphine sulfate with physical and chemical properties that deter misuse and abuse by nonoral routes of administration. Here we evaluate the relative bioavailability of morphine ARER and extended-release morphine.

METHODS

This single-dose, 2-treatment, 2-period, 2-sequence, randomized crossover study in healthy adult subjects compared the relative bioavailability of morphine ARER 100 mg to that of ER morphine 100 mg in the fasted condition. At 12 and 1.5 hours before dosing and 12 hours after dosing, all subjects received a 50-mg oral naltrexone tablet to minimize opioid-related side effects. Pharmacokinetic parameters including the AUC_0-t, AUC_0-∞, and C_max of morphine and its metabolite morphine-6-glucuronide (M6G) were determined at various times up to 48 hours postdose. The bioequivalence of morphine ARER and ER morphine was determined using an ANOVA of the least-squares mean values of morphine and M6G bioavailability.

FINDINGS

Forty-nine subjects completed the study. Both morphine ARER and ER morphine exhibited peak plasma morphine and M6G concentrations of ∼30 ng/mL and ∼200 ng/mL, respectively, at 3 hours postdose. The 90% CIs of the ln-transformed values of morphine AUC_0-t, AUC_0-∞, and C_max were within the 80% to 125% range for bioequivalence. M6G values also indicated bioequivalence of morphine ARER and ER morphine. The most common adverse events were nausea and somnolence.

IMPLICATIONS

These data show that, in these subjects, morphine ARER was bioequivalent to ER morphine, a treatment for pain with well-established efficacy and safety profiles.

Anti-nociceptive interactions between opioids and a cannabinoid receptor 2 agonist in inflammatory pain

The cannabinoid 1 receptor and cannabinoid 2 receptor can both be targeted in the treatment of pain; yet, they have some important differences. Cannabinoid 1 receptor is expressed at high levels in the central nervous system, whereas cannabinoid 2 receptor is found predominantly, although not exclusively, outside the central nervous system. The objective of this study was to investigate potential interactions between cannabinoid 2 receptor and the mu-opioid receptor in pathological pain. The low level of adverse side effects and lack of tolerance for cannabinoid 2 receptor agonists are attractive pharmacotherapeutic traits. This study assessed the anti-nociceptive effects of a selective cannabinoid 2 receptor agonist (JWH-133) in pathological pain using mice subjected to inflammatory pain using the formalin test. Furthermore, we examined several ways in which JWH-133 may interact with morphine. JWH-133 produces dose-dependent anti-nociception during both the acute and inflammatory phases of the formalin test. This was observed in both male and female mice. However, a maximally efficacious dose of JWH-133 (1 mg/kg) was not associated with somatic withdrawal symptoms, motor impairment, or hypothermia. After eleven once-daily injections of 1 mg/JWH-133, no tolerance was observed in the formalin test. Cross-tolerance for the anti-nociceptive effects of JWH-133 and morphine were assessed to gain insight into physiologically relevant cannabinoid 2 receptor and mu-opioid receptor interaction. Mice made tolerant to the effects of morphine exhibited a lower JWH-133 response in both phases of the formalin test compared to vehicle-treated morphine-naïve animals. However, repeated daily JWH-133 administration did not cause cross-tolerance for morphine, suggesting opioid and cannabinoid 2 receptor cross-tolerance is unidirectional. However, preliminary data suggest co-administration of JWH-133 with morphine modestly attenuates morphine tolerance. Isobolographic analysis revealed that co-administration of JWH-133 and morphine has an additive effect on anti-nociception in the formalin test. Overall these findings show that cannabinoid 2 receptor may functionally interact with mu-opioid receptor to modulate anti-nociception in the formalin test.

Super analgesia of intrathecal morphine may be related to ABCB1 (MDR1) gene polymorphism

Intrathecal morphine provides superior analgesia and minimizes side effects with ~1/300th of the oral dose necessary to achieve this effect. The conversion ratios from oral route to intrathecal route vary greatly among individuals, and this may be related with polymorphisms of the ATP-binding cassette B1 (ABCB1)/multiple drug resistance 1 (MDR1) gene encoding the transporter P-glycoprotein in the blood–brain barrier. In the case presented herein, a patient with cancer pain for over 3 months was treated with oxycodone hydrochloride prolonged-release tablets (Oxycontin) and morphine hydrochloride tablets for breakthrough pain. The patient was admitted due to intolerable adverse effects of Oxycontin. During this admission, he was implanted with an intrathecal morphine pump which can deliver morphine into the cerebrospinal fluid. To our surprise, intrathecal morphine at a dose of ~1/540th of oral morphine equivalent dose produced complete analgesia. Our finding revealed homogenous CC at position 3435 (C3435T) in the ABCB1/MDR1 gene in this patient, which encodes P-glycoprotein with good efflux pump functionality. As intrathecal morphine bypasses the blood–brain barrier that oral medications have to pass through, the good pump functionality may have contributed to the super analgesia of intrathecal morphine in this case. Genetic analysis of ABCB1/MDR1 gene polymorphisms can be useful for personalized pain management in patients with intrathecal morphine pump.

Comparative out-of-hospital mortality of long-acting opioids prescribed for non-cancer pain: A retrospective cohort study

PURPOSE

Despite significant growth of opioid prescriptions, only limited data are available regarding the comparative safety of long-acting opioids for chronic non-cancer pain. Recent data suggest that transdermal fentanyl and oxycodone CR may have greater toxicity than morphine SR in patients with non-cancer pain. Thus, we compared the risk of out-of-hospital deaths in patients with non-cancer pain filling prescriptions for transdermal fentanyl or oxycodone CR with that for morphine SR.

METHODS

We conducted a retrospective cohort study in 50 658 patients enrolled in Tennessee Medicaid who filled prescriptions for transdermal fentanyl (n = 8717), oxycodone CR (n = 14 118), or morphine SR (n = 27 823) between 1999 and 2011. We excluded individuals with cancer or other life-threatening diagnoses and used propensity scores to adjust for multiple potential confounders. The primary outcome was out-of-hospital mortality.

RESULTS

During 44 385 person-years of follow-up, 689 patients died. The out-of-hospital mortality rate among all study subjects was 155/10 000 patient-years. Contrary to earlier data suggesting greater risk, mortality was not significantly different in patients filling prescriptions for transdermal fentanyl compared with morphine SR (adjusted HR = 0.96, 95% C.I.: 0.77-1.21); moreover, patients filling prescriptions for oxycodone CR had lower mortality risk compared with those filling prescriptions for morphine SR (adjusted HR = 0.79, 95% C.I. 0.66-0.95).

CONCLUSION

In the study population, long-acting opioids for non-cancer pain were associated with high out-of-hospital mortality rates. We found comparable out-of-hospital mortality risks associated with transdermal fentanyl and morphine SR. The risk of out-of-hospital death for oxycodone CR was lower than that for morphine SR.

Neonatal exposure to oestradiol increases dopaminergic transmission in nucleus accumbens and morphine-induced conditioned place preference in adult female rats

Steroid sex hormones produce physiological effects in reproductive tissues and also in nonreproductive tissues, such as the brain, particularly in cortical, limbic and midbrain areas. Dopamine (DA) neurones involved in processes such as prolactin secretion (tuberoinfundibular system), motor circuit regulation (nigrostriatal system) and driving of motivated behaviour (mesocorticolimbic system) are specially regulated by sex hormones. Indeed, sex hormones promote neurochemical and behavioural effects induced by drugs of abuse by tuning midbrain DA neurones in adult animals. However, the long-term effects induced by neonatal exposure to sex hormones on dopaminergic neurotransmission have not been fully studied. The present study aimed to determine whether a single neonatal exposure with oestradiol valerate (EV) results in a programming of dopaminergic neurotransmission in the nucleus accumbens (NAcc) of adult female rats. To answer this question, electrophysiological, neurochemical, cellular, molecular and behavioural techniques were used. The data show that frequency but not amplitude of the spontaneous excitatory postsynaptic current is significantly increased in NAcc medium spiny neurones of EV-treated rats. In addition, DA content and release are both increased in the NAcc of EV-treated rats, caused by an increased synthesis of this neurotransmitter. These results are functionally associated with a higher percentage of EV-treated rats conditioned to morphine, a drug of abuse, compared to controls. In conclusion, neonatal programming with oestradiol increases NAcc dopaminergic neurotransmission in adulthood, which may be associated with increased reinforcing effects of drugs of abuse.

In silico (computed) modelling of doses and dosing regimens associated with morphine levels above international legal driving limits

BACKGROUND

Morphine can cause central nervous system side effects which impair driving skills. The legal blood morphine concentration limit for driving is 20 µg/L in France/Poland/Netherlands and 80 µg/L in England/Wales. There is no guidance as to the morphine dose leading to this concentration.

AIM

The in silico (computed) relationship of oral morphine dose and plasma concentration was modelled to provide dose estimates for a morphine plasma concentration above 20 and 80 µg/L in different patient groups.

DESIGN

A dose-concentration model for different genders, ages and oral morphine formulations, validated against clinical pharmacokinetic data, was generated using Simcyp^®, a population-based pharmacokinetic simulator.

SETTING/PARTICIPANTS

Healthy Northern European population parameters were used with age, gender and renal function being varied in the different simulation groups. In total, 36,000 simulated human subjects (100 per modelled group of different ages and gender) received repeated simulated morphine dosing with modified-release or immediate-release formulations.

RESULTS

Older age, women, modified-release formulation and worse renal function were associated with higher plasma concentrations. Across all groups, morphine doses below 20 mg/day were unlikely to result in a morphine plasma concentration above 20 µg/L; this was 80 mg/day with the 80 µg/L limit.

CONCLUSION

This novel study provides predictions of the in silico (computed) dose-concentration relationship for international application. Individualised morphine prescribing decisions by clinicians must be informed by clinical judgement considering the individual patient's level of impairment and insight irrespective of the blood morphine concentration as people who have impaired driving will be breaking the law. Taking into account expected morphine concentrations enables improved individualised decision making.

Non-invasive patient-controlled analgesia in the management of acute postoperative pain in the hospital setting

OBJECTIVE

Acute postoperative pain is experienced by the majority of hospitalized patients undergoing surgical procedures, with many reporting inadequate pain relief and/or high levels of dissatisfaction with their pain management. Patient-controlled analgesia (PCA) ensures patient involvement in acute pain control, a key component for implementing a quality management system. This narrative article overviews the clinical evidence for conventional PCA and briefly discusses new, non-invasive PCA systems, namely the sufentanil sublingual tablet system (SSTS) and the fentanyl iontophoretic transdermal system (FITS).

METHODS

A Medline literature search ("patient-controlled analgesia" and "acute postoperative pain") was conducted to 1 April 2017; results from the main clinical trials are discussed. Additional literature was identified from the reference lists of cited publications.

RESULTS

Moderate to low quality evidence supports opioid-based intravenous PCA as an efficacious alternative to non-patient-controlled systemic analgesia for postoperative pain. However, despite the benefits of PCA, conventional intravenous PCA is limited by system-, drug- and human-related issues. The non-invasive SSTS and FITS have demonstrated good efficacy and safety in placebo- and intravenous morphine PCA-controlled trials, and are associated with high patient/healthcare practitioner satisfaction/ease of care ratings and offer early patient mobilization.

CONCLUSIONS

Evidence-based guidelines for acute postoperative pain management support the use of multimodal regimens in many situations. As effective and safe alternatives to conventional PCA, and with the added benefits of being non-invasive, easy to use and allowing early patient mobilization, the newer PCA systems may complement multimodal approaches, or potentially replace certain regimens, in hospitalized patients with acute postoperative pain.

Evaluation of morphine-like effects of the mixed mu/delta agonist morphine-6-O-sulfate in rats: Drug discrimination and physical dependence

Morphine-6-O-sulfate (M6S) is as a mixed-action mu/delta (μ/δ) opioid receptor agonist with high potency and analgesic efficacy. These studies used assays of drug discrimination and schedule-controlled responding to assess abuse-liability, tolerance, and physical dependence as compared to morphine in rats. Attempts to train 0.3 mg/kg (IP) M6S from saline failed, but all rats rapidly acquired the discrimination when the training dose was changed to 3.0 mg/kg morphine, and substitution tests showed that morphine and fentanyl both fully substituted for the training dose, M6S and M3A6S (3-O-acetyl ester of M6S) only partially substituted, and salvinorin A did not elicit morphine-like effects. Tolerance to response rate-decreasing effects was studied in rats administered either 1.0 or 3.0 mg/kg morphine or M6S before food-reinforced operant sessions. At both unit doses, tolerance to M6S-elicited rate suppression developed more slowly than tolerance to morphine-induced reductions in response rates. To assess dependence, rats were maintained on 1.0 mg/kg morphine or 1.0 mg/kg M6S until food-reinforced response rates were stable for at least 5 days. Rats were then administered saline or increasing doses of the opioid antagonist naltrexone (NTX) (0.3, 1.0, 3.0, or 10.0 mg/kg) in order to determine antagonist-precipitated withdrawal. NTX precipitated withdrawal was similar in both morphine-maintained and M6S-maintained rats. In conclusion, the mixed μ/δ agonist activity of M6S failed to completely protect against the development of physical dependence, but delayed tolerance development to behavioral effects and resulted in decreased morphine-like subjective effects, perhaps implying a decreased abuse liability over μ agonists.

Blockade of prelimbic glutamate receptor reduces the reinforcing effect of morphine

The prelimbic cortex (PrL) as a part of the medial prefrontal cortex (mPFC) plays a crucial role in drug addiction. Previous studies have shown that glutamatergic transmission through the NMDA and AMPA receptors plays an important role in morphine rewarding properties. In this study, we evaluated the effect of glutamate receptors blockade within the PrL on morphine self-administration. Male Wistar rats were randomly selected and divided into 7 groups. Trained rats were placed in self-administration apparatus, where they pressed an active lever for receiving morphine (5 mg/mL) in test groups and saline in saline group during 11 consecutive days for 2 h per session. The effects of intra-prelimbic AMPA receptor antagonist (CNQX; 0.5 and 2.5 μg/0.5 μL) and the NMDA antagonist (AP5; 0.1 and 1 μg/0.5 μL) on self-administration were tested. Our results demonstrated that intra-prelimbic injection of different doses of CNQX and AP5, and co-administration of these 2 drugs before self-administration significantly decreased active lever pressing compared with morphine group (p < 0.001). Also, the number of self-infusion significantly decreased in test groups compared with morphine group (p < 0.001). These findings suggest that a reduction in PrL glutamatergic output can modulate morphine reinforcement.

Satisfactory Analgesia with Minimal Emesis in Day Surgeries (SAME DayS): a protocol for a randomised controlled trial of morphine versus hydromorphone

INTRODUCTION

There has been an exponential increase in the number of ambulatory surgeries (AS). Pain and postoperative nausea vomiting (PONV) affects the recovery, discharge and overall satisfaction of patients having AS. Opioids remain the primary modality for moderate to severe pain. Since there is no perfect opioid, physicians should ideally use the opioid that optimally balances benefits and risks. Present decisions on the choice between morphine (M) and hydromorphone (HM) are based on individual experience and observation. Our primary objective is to compare the proportion of patients having AS achieving satisfactory analgesia without significant PONV when using M compared with HM. Secondarily we will compare the proportion of patients with adverse events, analgesic used, patient satisfaction, time to discharge and postdischarge symptoms.

METHODS AND ANALYSIS

This is a two-arm, multicentre, parallel group, randomised controlled trial of 400 patients having AS. Eligible patients undergoing AS of the abdominal and pelvic regions with a potential to cause moderate to severe pain will be recruited in the preoperative clinic. Using a computer-generated randomization, with a 1:1 allocation ratio, patients will be randomised to M or HM. Patients, healthcare providers and research personnel will be blinded. Study interventions will be administered in the recovery using equianalgesic doses of M or HM in concealed syringes. Patients will be followed in hospital and up to 3 months. Intention-to-treat approach will be used for analysis.

ETHICS AND DISSEMINATION

This study has been approved by the Hamilton integrated research ethics board. We plan to publish our trial findings and present our findings at scientific meetings.

TRAIL REGISTRATION NUMBER

NCT02223377; Pre-results.

Opioid Medications in Expensive Formulations Are Sold at a Lower Price than Immediate-Release Morphine in Countries throughout the World: Third Phase of Opioid Price Watch Cross-Sectional Study

BACKGROUND

International Association for Hospice and Palliative Care implemented Opioid Price Watch (OPW) to monitor availability, dispensing prices and affordability of opioids. We found that opioids with complex delivery mechanisms [fentanyl transdermal (TD) patches, sustained-release (SR) morphine, and SR oxycodone] had lower dispensing prices than immediate-release (IR) morphine formulations.

OBJECTIVE

Identify the extent that SR and TD formulations are dispensed at lower prices than generic IR morphine and the possible reasons to explain this observation.

DESIGN

Using OPW data for 30-day treatment Defined Daily Dosages, we identified where SR and TD formulations are dispensed at lower prices than IR morphine. Then we analyzed national lists of essential medicines (EML) in middle- and low-income countries to answer two questions: (1) Do they have opioids included? If yes, (2) Which ones? We then sought information on selection, budget allocation, and procurement for EML. OPW participants confirmed/verified the EML information.

RESULTS

Eighteen countries reported higher dispensing prices for IR morphine (oral and/or injectable) than TD or SR formulation. Injectable morphine was highest in seven and lowest in two (range: $74-$742). SR morphine was the least expensive, while TD fentanyl was second. Median dispensing price for IR oral morphine was higher than SR morphine. The EML for 10 countries include opioids in TD and/or SR formulations.

CONCLUSIONS

Opioids in expensive formulations are being favored over IR morphine both at the dispensing level and in their inclusion in national EML. Governments must take decisions based on efficacy, safety, and cost-effectiveness of medications.

A lateral flow strip based on gold nanoparticles to detect 6-monoacetylmorphine in oral fluid

We used lateral flow strips based on gold nanoparticles to detect 6-monoacetylmorphine (6-MAM; heroin's unique metabolite) in oral fluid samples. In this competitive lateral chromatographic immunoassay, the 6-MAM was chemically synthesized and conjugated to bovine serum albumin. The results were qualitatively detected via the colour change of the test line. By using a proper sample pad, a suitable nitrocellulose membrane and a customized sponge device adsorbed the oral fluid directly from the mouth; the total test time was 3 min. The sensitivity of the assay was 4.0 ng ml-1 without any cross-reactivity with 10 normal drugs, which are widely subject to abuse, including morphine and codeine. This test could be easily used on site to detect heroin in oral fluid, and it could be a promising product in the future including for driving under the influence.

Evaluating the early impacts of delisting high-strength opioids on patterns of prescribing in Ontario

INTRODUCTION

Ontario delisted high-strength fentanyl, hydromorphone and morphine from the public drug formulary for non-palliative care prescribers on 31 January, 2017. Our aim is to assess the early impact of this policy on prescribing patterns and to examine whether this impact varied by prescriber type, opioid type and opioid strength.

METHODS

We conducted a population-based, cross-sectional study on palliative and non-palliative care patients dispensed fentanyl, hydromorphone or morphine through the Ontario public drug program between 1 January, 2014, and 31 July, 2017. For each month during the study period, we reported the total number of high-strength opioid recipients stratified by prescriber type, and the total volume of each drug dispensed, stratified by strength. We used interventional autoregressive integrated moving average (ARIMA) models to assess the policy's impact on prescribing patterns.

RESULTS

We observed a 98% decrease in the total number of publicly funded recipients of high-strength opioids between December 2016 and July 2017 (5930 to 133 recipients) for all prescribers. The policy led to a significant decline in the total volume of all three opioids dispensed: hydromorphone from 20 374 621 to 16 952 097 mg (p < .01); morphine from 40 644 190 to 33 555 480 mg (p < .03); and fentanyl from 9 604 913 to 5 842 405 mcg/h (p < .01). For both fentanyl and hydromorphone, this reduction generally corresponded to an increase in the number of low-strength opioids dispensed.

CONCLUSION

Delisting high-strength opioids substantially reduced the number of highstrength opioid recipients and reduced the overall volume of long-acting opioids dispensed in Ontario through the public drug program. Future studies should examine its impact on patient outcomes.

Regulator of G-Protein Signaling 4 (RGS4) Controls Morphine Reward by Glutamate Receptor Activation in the Nucleus Accumbens of Mouse Brain

Crosstalk between G-protein signaling and glutamatergic transmission within the brain reward circuits is critical for long-term emotional effects (depression and anxiety), cravings, and negative withdrawal symptoms associated with opioid addiction. A previous study showed that Regulator of G-protein signaling 4 (RGS4) may be implicated in opiate action in the nucleus accumbens (NAc). However, the mechanism of the NAc-specific RGS4 actions that induce the behavioral responses to opiates remains largely unknown. The present study used a short hairpin RNA (shRNA)-mediated knock-down of RGS4 in the NAc of the mouse brain to investigate the relationship between the activation of ionotropic glutamate receptors and RGS4 in the NAc during morphine reward. Additionally, the shRNA-mediated RGS4 knock-down was implemented in NAc/striatal primary-cultured neurons to investigate the role that striatal neurons have in the morphine-induced activation of ionotropic glutamate receptors. The results of this study show that the NAc-specific knockdown of RGS4 significantly increased the behaviors associated with morphine and did so by phosphorylation of the GluR1 (Ser831) and NR2A (Tyr1325) glutamate receptors in the NAc. Furthermore, the knock-down of RGS4 enhanced the phosphorylation of the GluR1 and NR2A glutamate receptors in the primary NAc/striatal neurons during spontaneous morphine withdrawal. These findings show a novel molecular mechanism of RGS4 in glutamatergic transmission that underlies the negative symptoms associated with morphine administration.

Continuous local bupivacaine wound infusion with neuraxial morphine reduces opioid consumption after cesarean delivery

Background: As a part of a quality improvement program, maternal postoperative opioid use and pain scores were compared between those receiving continuous infusion of bupivacaine for local incisional pain control with multimodal pain management and neuraxial morphine versus multimodal pain management with neuraxial morphine alone. Objective: We compared postoperative opioid use and pain scores between the multimodal pain management group with neuraxial morphine and the group receiving multimodal pain management, neuraxial morphine, and continuous infusion of bupivacaine for local incisional pain control. Study design: A retrospective cohort analysis of cesarean deliveries from January of 2015 through March of 2016 was undertaken. Deliveries were grouped by utilization of continuous infusion of bupivacaine for local incisional pain control. For each postoperative day, the average daily opioid use, antiemetic use and pain scores were determined. Patients received 1-2 tablets oxycodone-acetaminophen (5-325 mg) every 4 h as needed with oxycodone 5-10 mg immediate release tablets every 4 h as needed for breakthrough pain in addition to acetaminophen and ibuprofen. Total dose of narcotic, antiemetic use, and pain scores was compared between groups utilizing t-test for continuous variables and chi square for categorical data. A linear mixed model with unstructured covariance was utilized to analyze the daily dose of narcotic and pain scores from postoperative day 1 through day 4. Results: Patients in the standard multimodal group with neuraxial morphine used more opioids versus those receiving continuous wound infusion of bupivacaine in total postoperative dosing (122.79 ± 61.92 mg versus 89.88 ± 51.38 mg, p = .0063). There was a statistically significant difference between the standard group and local infusion of bupivacaine group on postoperative days 1 and 2 (32.79 ± 15.56 mg versus 22.13 ± 15.73 mg, p = .0011 and 40.25 ± 19.84 mg versus 29.13 ± 14.58 mg, p = .0018, respectively). There was no difference in narcotic use for postoperative days 3 and 4. There was a higher mean number of antiemetic doses in the standard group (0.31 ± 0.70 versus 0.10 ± 0.30, p = .0396). Pain scores did not differ between groups, although there was a correlation between opioid dosing and pain scores. The standard group received more IV ketorolac (87.72 ± 42.01 mg versus 64.50 ± 53.3 mg, p = .0165) and more IV acetaminophen (634.89 ± 706.42 mg versus 375.0 ± 490.29 mg, p = .0315) within the first 24 h postoperatively. In addition, the standard group received more oral acetaminophen (6969.67 ± 3230.14 mg versus 5248.75 ± 2711.71 mg, p = .0064). No difference was seen in regard to ibuprofen between groups. These results remained constant when adjusted for differences in gestational age, variation in intraoperative opioid dosing, as well as differences in uterine incision type. Conclusion: We found a significant reduction in postoperative opioid use when continuous infusion of bupivacaine for local incisional pain control was added to our standard pain management with neuraxial morphine after cesarean delivery. As a result of this quality improvement initiative, we have implemented this intervention universally as a part of our multimodal postoperative pain management strategy.

[Effect of Corydalis Rhizoma and L-tetrahydropalmatine on dopamine system of hippocampus and striatum in morphine-induced conditioned place preference rats]

To investigate the effects of Corydalis Rhizoma and L-tetrahydropalma-tine (L-THP) on the levels of dopamine neurotransmitter (DA), dopamine transporter (DAT) and the second dopamine receptor (D2R) in learning and memory-related brain areas, hippocampus and striatum, the DA, DAT and D2R were detected in conditioned place preference (CPP) rats suffered from morphine. And comparation the degree of similarity and consistency of the pharmacological effects was also studied. The rats were trained in black compartments and white ones (drug-paired compartment) with the increasing doses of morphine for 10 days (hypodermically injected from 10 mg•kg⁻¹ to 100 mg•kg⁻¹). Models of CPP were validated in those psychological dependence rats after 48 h training. The dopamine contents were detected as soon as the materials of hippocampus and striatum are harvested from rats of NS control group and model group. The DAT and D2R levels are measured by Western blot. The high, medium and low dose group of Corydalis Rhizoma are given Corydalis Rhizoma 2, 1, 0.5 g•kg⁻¹ water extraction liquid respectively (which contains L-THP were 0.274, 0.137 and 0.137 mg respectively), and the high, medium and low dose group of L-THP were given L-THP 3.76, 1.88, 0.94 mg•kg⁻¹ lavage treatment respectively, NS treatment group were lavaged normal saline for 6 days and they were killed after test of CPP, again tested DA levels and expression of DAT and D2R similar to the front of materials. The reduction effects of CPP were observed in the groups of both Corydalis Rhizoma (2, 1 g•kg⁻¹) and L-THP (3.76, 1.88 mg•kg⁻¹) subjected to medicine for 6 days (P<0.01). Compared with the NS treatment group and the model group, the higher values including in the contents of neurotransmitter dopamine were detected of hippocampus and striatum (P<0.01, P<0.05), the DAT and D2R protein expression of Corydalis Rhizoma (2, 1 g•kg⁻¹) and L-THP (3.76, 1.88 mg•kg⁻¹) increased in hippocampus and striatum (P<0.01). Learning and memory-related brain regions hippocampus and striatum was another neuroanatomical sites of action in the treatment of mental dependence of fumarate and L-THP, its mechanism was related to lowering its elevated DA neurotransmitter levels, and increasing the expression of DAT and D2R. Corydalis Rhizoma could be play 14-times roles in effect of L-THP. The similar effects were observed on the neurotransmitter dopamine, DAT and D2R in learning and memory-related brain areas, hippocampus and striatum of the morphine- dependent rats.

In vivo profiling of four centrally administered opioids for antinociception, constipation and respiratory depression: Between-colony differences in Sprague Dawley rats

Outbred rodent stocks including Sprague Dawley rats, are known for their genetic diversity and so they are often used to develop animal models of human disease. Although between-colony differences in pharmaco-behavioural studies have been published previously, a direct head-to-head comparison study, whereby all research was performed in the same laboratory by the same experimenter utilising the supraspinal route of drug administration in the same strain of rat, is lacking. Herein, we report our head-to-head comparison study, involving assessment of antinociception, constipation and respiratory depression evoked by single bolus intracerebroventricular (ICV) doses of morphine, buprenorphine, DPDPE and U69,593 using male Sprague Dawley rats sourced from a different breeding colony (BC2) from that (BC1) used by us previously. Our data show that there are marked differences in the potency rank order for morphine and buprenorphine between rats sourced from BC2 and BC1. Although ICV morphine evoked a bell-shaped dose-response curve in the constipation test for rats from both colonies, this occurred at higher doses for rats from BC2. In conclusion, our head-to-head comparison shows considerable between-colony differences for the same rat strain, in the potency rank order of two clinically important strong opioid analgesics given by the ICV route.

Codeinone reductase isoforms with differential stability, efficiency and product selectivity in opium poppy

Codeinone reductase (COR) catalyzes the reversible NADPH-dependent reduction of codeinone to codeine as the penultimate step of morphine biosynthesis in opium poppy (Papaver somniferum). It also irreversibly reduces neopinone, which forms by spontaneous isomerization in aqueous solution from codeinone, to neopine. In a parallel pathway involving 3-O-demethylated analogs, COR converts morphinone to morphine, and neomorphinone to neomorphine. Similar to neopine, the formation of neomorphine by COR is irreversible. Neopine is a minor substrate for codeine O-demethylase (CODM), yielding morphine. In the plant, neopine levels are low and neomorphine has not been detected. Silencing of CODM leads to accumulation of upstream metabolites, such as codeine and thebaine, but does not result in a shift towards higher relative concentrations of neopine, suggesting a mechanism in the plant for limiting neopine production. In yeast (Saccharomyces cerevisiae) engineered to produce opiate alkaloids, the catalytic properties of COR lead to accumulation of neopine and neomorphine as major products. An isoform (COR-B) was isolated from opium poppy chemotype Bea's Choice that showed higher catalytic activity than previously characterized CORs, and it yielded mostly neopine in vitro and in engineered yeast. Five catalytically distinct COR isoforms (COR1.1-1.4 and COR-B) were used to determine sequence-function relationships that influence product selectivity. Biochemical characterization and site-directed mutagenesis of native COR isoforms identified four residues (V25, K41, F129 and W279) that affected protein stability, reaction velocity, and product selectivity and output. Improvement of COR performance coupled with an ability to guide pathway flux is necessary to facilitate commercial production of opiate alkaloids in engineered microorganisms.