Cannabinoid 1 and mu-Opioid Receptor Agonists Synergistically Inhibit Abdominal Pain and Lack Side Effects in Mice

Chronic Visceral Pain: New Peripheral Mechanistic Insights and Resulting Treatments

Chronic visceral pain is one of the most common reasons for patients with gastrointestinal disorders, such as inflammatory bowel disease or disorders of brain-gut interaction, to seek medical attention. It represents a substantial burden to patients and is associated with anxiety, depression, reductions in quality of life, and impaired social functioning, as well as increased direct and indirect health care costs to society. Unfortunately, the diagnosis and treatment of chronic visceral pain is difficult, in part because our understanding of the underlying pathophysiologic basis is incomplete. In this review, we highlight recent advances in peripheral pain signaling and specific physiologic and pathophysiologic preclinical mechanisms that result in the sensitization of peripheral pain pathways. We focus on preclinical mechanisms that have been translated into treatment approaches and summarize the current evidence base for directing treatment toward these mechanisms of chronic visceral pain derived from clinical trials. The effective management of chronic visceral pain remains of critical importance for the quality of life of suffers. A deeper understanding of peripheral pain mechanisms is necessary and may provide the basis for novel therapeutic interventions.

Peripherally restricted cannabinoid and mu-opioid receptor agonists synergistically attenuate neuropathic mechanical hypersensitivity in mice

ABSTRACT

Many medications commonly used to treat neuropathic pain are associated with significant, dose-limiting adverse effects, including sedation, dizziness, and fatigue. These adverse effects are due to the activity of these medications within the central nervous system. The objective of this work was to investigate the interactions between peripherally restricted cannabinoid receptor and mu-opioid receptor (MOR) agonists on ongoing and evoked neuropathic pain behaviors in mouse models. RNAscope analysis of cannabinoid receptor type 1 (CB1R) and MOR mRNA demonstrated that the mRNA of both receptors is colocalized in both mouse and human dorsal root ganglion. Single-cell RNAseq of dorsal root ganglion from chronic constriction injury mice showed that the mRNA of both receptors (Cnr1 and Oprm1) is coexpressed across different neuron clusters. Myc-CB1R and FLAG-MOR were cotransfected into immortalized HEK-293T cells and were found to interact at a subcellular level. We also find that CB-13 (a peripherally restricted dual CB1R and cannabinoid receptor type 2 agonist) and DALDA (a peripherally restricted MOR agonist) both attenuate mechanical hypersensitivity in a murine model of neuropathic pain. Using isobolographic analysis, we demonstrate that when coadministered, these agents synergistically attenuate mechanical hypersensitivity. Importantly, combination dosing of these agents does not cause any detectable preferential behaviors or motor impairment. However, repeated dosing of these agents is associated with the development of tolerance to these drugs. Collectively, these findings suggest that leveraging synergistic pain inhibition between cannabinoid receptor and MOR agonists in peripheral sensory neurons may be worth examining in patients with neuropathic pain.

Unveiling the link between chronic pain and misuse of opioids and cannabis

Over 50 million Americans endure chronic pain where many do not receive adequate treatment and self-medicate to manage their pain by taking substances like opioids and cannabis. Research has shown high comorbidity between chronic pain and substance use disorders (SUD) and these disorders share many common neurobiological underpinnings, including hypodopaminergic transmission. Drugs commonly used for self-medication such as opioids and cannabis relieve emotional, bothersome components of pain as well as negative emotional affect that perpetuates misuse and increases the risk of progressing towards drug abuse. However, the causal effect between chronic pain and the development of SUDs has not been clearly established. In this review, we discuss evidence that affirms the proposition that chronic pain is a risk factor for the development of opioid and cannabis use disorders by outlining the clinical evidence and detailing neurobiological mechanisms that link pain and drug misuse. Central to the link between chronic pain and opioid and cannabis misuse is hypodopaminergic transmission and the modulation of dopamine signaling in the mesolimbic pathway by opioids and cannabis. Moreover, we discuss the role of kappa opioid receptor activation and neuroinflammation in the context of dopamine transmission, their contribution to opioid and cannabis withdrawal, along with potential new treatments.

Perioperative Cannabinoids Significantly Reduce Postoperative Opioid Requirements in Patients Undergoing Coronary Artery Bypass Graft Surgery

Background Opioids, commonly used to control pain associated with surgery, are known to prolong the duration of mechanical ventilation and length of hospital stay. A wide range of adjunctive strategies are currently utilized to reduce postoperative pain, such as local and regional nerve blocks, nerve cryoablation, and adjunctive medications. We hypothesized that dronabinol (a synthetic cannabinoid) in conjunction with standard opioid pain management will reduce opioid requirements to manage postoperative pain. Methods Sixty-eight patients who underwent isolated first-time coronary artery bypass graft surgery were randomized to either the control group, who received only standard opioid-based analgesia, or the dronabinol group, who received dronabinol (a synthetic cannabinoid) in addition to standard opioid-based analgesia. Dronabinol was given in the preoperative unit, before extubation in the ICU, and after extubation on the first postoperative day. Preoperative, intraoperative, and postoperative parameters were compared under an IRB-approved protocol. The primary endpoints were the postoperative opioid requirement, duration of mechanical ventilation, and ICU length of stay, and the secondary endpoints were the duration of inotropic support needed, left ventricular ejection fraction (LVEF), and the change in LVEF. This study was undertaken at Northwest Medical Center, Tucson, AZ, USA. Results Sixty-eight patients were randomized to either the control group (n = 37) or the dronabinol group (n = 31). Groups were similar in terms of demographic features and comorbidities. The total postoperative opioid requirement was significantly lower in the dronabinol group [39.62 vs 23.68 morphine milligram equivalents (MMEs), p = 0.0037], representing a 40% reduction. Duration of mechanical ventilation (7.03 vs 6.03h, p = 0.5004), ICU length of stay (71.43 vs 63.77h, p = 0.4227), and inotropic support requirement (0.6757 vs 0.6129 days, p = 0.7333) were similar in the control and the dronabinol groups. However, there was a trend towards lower durations in each endpoint in the dronabinol group. Interestingly, a significantly better preoperative to postoperative LVEF change was observed in the dronabinol group (3.51% vs 6.45%, p = 0.0451). Conclusions Our study found a 40% reduction in opioid use and a significantly greater improvement in LVEF in patients treated with adjunctive dronabinol. Mechanical ventilation duration, ICU length of stay, and inotropic support requirement tended to be lower in the dronabinol group, though did not reach statistical significance. The results of this study, although limited by sample size, are very encouraging and validate our ongoing investigation.

Impact of Δ9-Tetrahydrocannabinol and oxycodone co-administration on measures of antinociception, dependence, circadian activity, and reward in mice

Oxycodone is commonly prescribed for moderate to severe pain disorders. While efficacious, long-term use can result in tolerance, physical dependence, and the development of opioid use disorder. Cannabis and its derivatives such as Δ9-Tetrahydrocannabinol (Δ9-THC) have been reported to enhance oxycodone analgesia in animal models and in humans. However, it remains unclear if Δ9-THC may facilitate unwanted aspects of oxycodone intake, such as tolerance, dependence, and reward at analgesic doses. This study sought to evaluate the impact of co-administration of Δ9-THC and oxycodone across behavioral measures related to antinociception, dependence, circadian activity, and reward in both male and female mice. Oxycodone and Δ9-THC produced dose-dependent antinociceptive effects in the hotplate assay that were similar between sexes. Repeated treatment (twice daily for 5 days) resulted in antinociceptive tolerance. Combination treatment of oxycodone and Δ9-THC produced a greater antinociceptive effect than either administered alone, and delayed the development of antinociceptive tolerance. Repeated treatment with oxycodone produced physical dependence and alterations in circadian activity, neither of which were exacerbated by co-treatment with Δ9-THC. Combination treatment of oxycodone and Δ9-THC produced CPP when co-administered at doses that did not produce preference when administered alone. These data indicate that Δ9-THC may facilitate oxycodone-induced antinociception without augmenting certain unwanted features of opioid intake (e.g. dependence, circadian rhythm alterations). However, our findings also indicate that Δ9-THC may facilitate rewarding properties of oxycodone at therapeutically relevant doses which warrant consideration when evaluating this combination for its potential therapeutic utility.

Evolving acidic microenvironments during colitis provide selective analgesic targets for a pH-sensitive opioid

ABSTRACT

Targeting the acidified inflammatory microenvironment with pH-sensitive opioids is a novel approach for managing visceral pain while mitigating side effects. The analgesic efficacy of pH-dependent opioids has not been studied during the evolution of inflammation, where fluctuating tissue pH and repeated therapeutic dosing could influence analgesia and side effects. Whether pH-dependent opioids can inhibit human nociceptors during extracellular acidification is unexplored. We studied the analgesic efficacy and side-effect profile of a pH-sensitive fentanyl analog, (±)- N -(3-fluoro-1-phenethylpiperidine-4-yl)- N -phenyl propionamide (NFEPP), during the evolution of colitis induced in mice with dextran sulphate sodium. Colitis was characterized by granulocyte infiltration, histological damage, and acidification of the mucosa and submucosa at sites of immune cell infiltration. Changes in nociception were determined by measuring visceromotor responses to noxious colorectal distension in conscious mice. Repeated doses of NFEPP inhibited nociception throughout the course of disease, with maximal efficacy at the peak of inflammation. Fentanyl was antinociceptive regardless of the stage of inflammation. Fentanyl inhibited gastrointestinal transit, blocked defaecation, and induced hypoxemia, whereas NFEPP had no such side effects. In proof-of-principle experiments, NFEPP inhibited mechanically provoked activation of human colonic nociceptors under acidic conditions mimicking the inflamed state. Thus, NFEPP provides analgesia throughout the evolution of colitis with maximal activity at peak inflammation. The actions of NFEPP are restricted to acidified layers of the colon, without common side effects in normal tissues. N -(3-fluoro-1-phenethylpiperidine-4-yl)- N -phenyl propionamide could provide safe and effective analgesia during acute colitis, such as flares of ulcerative colitis.

Endogenous opiates and behavior: 2022

This paper is the forty-fifth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2022 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

The Selective CB2 Agonist COR167 Reduced Symptoms in a Mice Model of Trauma-Induced Peripheral Neuropathy through HDAC-1 Inhibition

Neuropathic pain is a chronic disabling condition with a 7-10% of prevalence in the general population that is largely undertreated. Available analgesic therapies are poorly effective and are often accompanied by numerous side effects. Growing evidence indicates cannabinoids are a valuable treatment opportunity for neuropathic pain. The endocannabinoid system is an important regulator of pain perception through the CB1 receptors, but CB1 agonists, while largely effective, are not always satisfactory pain-relieving agents in clinics because of their serious adverse effects. Recently, several CB2 agonists have shown analgesic, anti-hyperalgesic, and anti-allodynic activity in the absence of CB1-induced psychostimulant effects, offering promise in neuropathic pain management. The aim of this study was to evaluate the anti-neuropathic activity of a novel selective CB2 agonist, COR167, in a preclinical model of peripheral neuropathy, the spared nerve injury (SNI). Oral COR167, in a dose-dependent manner, attenuated mechanical allodynia and thermal hyperalgesia after acute and repeated administration, showing the absence of tolerance induction. At anti-neuropathic doses, COR167 did not show any alteration in the locomotor behavior. SNI mice showed increased microglial levels of HDAC1 protein in the ipsilateral side of the spinal cord, along with NF-kB activation. COR167 treatment prevented the HDAC1 overexpression and the NF-kB activation and increased the levels of the anti-inflammatory cytokine IL-10 through a CB2-mediated mechanism. Oral administration of COR167 shows promising therapeutic potential in the management of neuropathic pain conditions.

Activation of CB1R alleviates central sensitization by regulating HCN2-pNR2B signaling in a chronic migraine rat model

BACKGROUND

Central sensitization has been widely accepted as an underlying pathophysiological mechanism of chronic migraine (CM), activation of cannabinoid type-1 receptor (CB1R) exerts antinociceptive effects by relieving central sensitization in many pain models. However, the role of CB1R in the central sensitization of CM is still unclear.

METHODS

A CM model was established by infusing inflammatory soup (IS) into the dura of male Wistar rats for 7 days, and hyperalgesia was assessed by the mechanical and thermal thresholds. In the periaqueductal gray (PAG), the mRNA and protein levels of CB1R and hyperpolarization-activated cyclic nucleotide-gated cation channel 2 (HCN2) were measured by qRT-PCR and western blotting. After intraventricular injection of Noladin ether (NE) (a CB1R agonist), ZD 7288 (an HCN2 blocker), and AM 251 (a CB1R antagonist), the expression of tyrosine phosphorylation of N-methyl-D-aspartate receptor subtype 2B (pNR2B), calcium-calmodulin-dependent kinase II (CaMKII), and phosphorylated cAMP-responsive element binding protein (pCREB) was detected, and central sensitization was evaluated by the expression of calcitonin gene-related peptide (CGRP), c-Fos, and substance P (SP). Synaptic-associated protein (postsynaptic density protein 95 (PSD95) and synaptophysin (Syp)) and synaptic ultrastructure were detected to explore synaptic plasticity in central sensitization.

RESULTS

We observed that the mRNA and protein levels of CB1R and HCN2 were both significantly increased in the PAG of CM rats. The application of NE or ZD 7288 ameliorated IS-induced hyperalgesia; repressed the pNR2B/CaMKII/pCREB pathway; reduced CGRP, c-Fos, SP, PSD95, and Syp expression; and inhibited synaptic transmission. Strikingly, the application of ZD 7288 relieved AM 251-evoked elevation of pNR2B, CGRP, and c-Fos expression.

CONCLUSIONS

These data reveal that activation of CB1R alleviates central sensitization by regulating HCN2-pNR2B signaling in CM rats. The activation of CB1R might have a positive influence on the prevention of CM by mitigating central sensitization.

Cannabidiol regulates behavioral and brain alterations induced by spontaneous alcohol withdrawal

The main goal of this study was to evaluate if the administration of cannabidiol (CBD) regulates behavioral and gene expression alterations induced by spontaneous alcohol withdrawal (SAW) in mice. Increasing doses of ethanol were administered to C57BL/6J male mice for 15 days (2.5, 3 and 3.5 g/kg/12 h, p. o.), and SAW was studied at 6, 12, 24, and 72 h after the last ethanol administration. The efficacy of acute CBD (10, 20, and 40 mg/kg, i. p.) to regulate behavioral changes induced by SAW was explored at 6 h. Gene expression analyses of cannabinoid receptors 1 (Cnr1) and 2 (Cnr2), mu-opioid receptor (Opmr1), and proopiomelanocortin (Pomc) in the nucleus accumbens (NAcc), and Pomc and tyrosine hydroxylase (Th) in the ventral tegmental area (VTA), were carried out by real time-PCR. Pearson correlation was used to identify potential associations between the gene expression data and the anxiety-like behaviors. Biostatistical studies suggest associations between gene expression data and the anxiogenic behaviors in mice exposed to the SAW model and treated with VEH and 40 mg/kg of CBD. Mice exposed to the SAW model showed significant somatic withdrawal signs, anxiety-like behaviors, and remarkable changes in the gene expression of all brain targets at 6 h. CBD dose-dependently normalized the behavioral, somatic withdrawal signs and anxiety-like behaviors and modulated gene expression changes in the NAcc, but not in the VTA. The results of this study suggest that CBD may regulate specific alcohol withdrawal-associated alterations. However, further studies are required to explore the possible mechanisms involved.

OCP002, a Mixed Agonist of Opioid and Cannabinoid Receptors, Produces Potent Antinociception With Minimized Side Effects

BACKGROUND

Increasing attention has been attracted to the development of bifunctional compounds to minimize the side effects of opioid analgesics. Pharmacological studies have verified the functional interaction between opioid and cannabinoid systems in pain management, suggesting that coactivation of the opioid and cannabinoid receptors may provide synergistic analgesia with fewer adverse reactions. Herein, we developed and characterized a novel bifunctional compound containing the pharmacophores of the mu-opioid receptor agonist DALDA and the cannabinoid peptide VD-Hpα-NH2, named OCP002.

METHODS

The opioid and cannabinoid agonistic activities of OCP002 were investigated in calcium mobilization and western blotting assays, respectively. Moreover, the central and peripheral antinociceptive effects of OCP002 were evaluated in mouse preclinical models of tail-flick test, carrageenan-induced inflammatory pain, and acetic acid-induced visceral pain, respectively. Furthermore, the potential opioid and cannabinoid side effects of OCP002 were systematically investigated in mice after intracerebroventricular (ICV) and subcutaneous (SC) administrations.

RESULTS

OCP002 functioned as a mixed agonist toward mu-opioid, kappa-opioid, and cannabinoid CB1 receptors in vitro. ICV and SC injections of OCP002 produced dose-dependent antinociception in mouse models of nociceptive (the median effective dose [ED50] values with 95% confidence interval [CI] are 0.14 [0.12-0.15] nmol and 0.32 [0.29-0.35] μmol/kg for ICV and SC injections, respectively), inflammatory (mechanical stimulation: ED50 values [95% CI] are 0.76 [0.64-0.90] nmol and 1.23 [1.10-1.38] μmol/kg for ICV and SC injections, respectively; thermal stimulation: ED50 values [95% CI] are 0.13 [0.10-0.17] nmol and 0.23 [0.08-0.40] μmol/kg for ICV and SC injections, respectively), and visceral pain (ED50 values [95% CI] are 0.0069 [0.0050-0.0092] nmol and 1.47 [1.13-1.86] μmol/kg for ICV and SC injections, respectively) via opioid and cannabinoid receptors. Encouragingly, OCP002 cannot cross the blood-brain barrier and exerted nontolerance-forming analgesia over 6-day treatment at both supraspinal and peripheral levels. Consistent with these behavioral results, repeated OCP002 administration did not elicit microglial hypertrophy and proliferation, the typical features of opioid-induced tolerance, in the spinal cord. Furthermore, at the effective analgesic doses, SC OCP002 exhibited minimized opioid and cannabinoid side effects on motor performance, body temperature, gastric motility, physical and psychological dependence, as well as sedation in mice.

CONCLUSIONS

This study demonstrates that OCP002 produces potent and nontolerance-forming antinociception in mice with reduced opioid- and cannabinoid-related side effects, which strengthen the candidacy of bifunctional drugs targeting opioid/cannabinoid receptors for translational-medical development to replace or assist the traditional opioid analgesics.

Association of cannabis and/or opioid with quality of life and healthcare utilization in patients with chronic pain

Background

Opioids have been commonly used to treat chronic pain, but they are associated with significant morbidity and mortality. Cannabis has been advocated as an alternative; however, a growing number of patients are now using a combination of opioid and cannabis and the impact of this combination is not well-studied.

Aim

We characterized use of opioid and/or cannabis in patients with chronic pain; and compared utilization of healthcare resources.

Methods

We conducted a cross-sectional study to determine if measures of physical, psychological and social functioning differed among patients according to whether they used opioids and/or cannabis. We used our learning healthcare system - CHOIR - to capture NIH Patient Reported Outcomes Measure Information System surveys, and legacy pain and treatment specific questions.

Results

Patients who report use of opioid and/or cannabis experience higher levels of physical, psychological and social distress. After adjusting for inversed weight of propensity scores, they have higher odds of visiting an emergency room, staying overnight at the hospital, and visiting a physician.

Conclusion

Our results show that use of opioid and/or cannabis is associated with worse baseline characteristics and outcomes. Our study however cannot determine if worse outcomes are due to the opioids and/or cannabis or simply that these patients are worse off before using opioids and/or cannabis. Thus, it is important to characterize the trajectory of these patients in a prospective longitudinal study.