Spinal cannabinoid CB2 receptors as a target for neuropathic pain: an investigation using chronic constriction injury

CB2R activation enhances tumor-associated macrophages-mediated phagocytosis of glioma cell

Background

Cannabinoid administration has demonstrated promising anti-tumor effects for glioblastoma (GBM) by inhibiting glioma cell proliferation and inducing glioma cell death. However, the impact of cannabinoids and endocannabinoid receptors on immune cells within the tumor microenvironment (TME) remains largely unexplored. Tumor-associated macrophages (TAMs), the most abundant immune cells in the TME, and their mediated phagocytosis of tumor cells have shown potential in preclinical xenografts of various human malignancies. This study aimed to investigate the effect and mechanism of endocannabinoid receptor 2 (CB2R) on TAMs-mediated phagocytosis in xenografted mice with GL261-GFP cell lines.

Methods

We measured the phagocytic activity using immunofluorescence and flow cytometry, and we used the IVIS Spectrum System for bioluminescent imaging to track the growth of the tumor.

Results

Our findings demonstrated that administering JWH133, a selective CB2R agonist, significantly boosted TAMs-mediated phagocytosis. However, administering AM630, a selective CB2R antagonist, significantly inhibited TAMs-mediated phagocytosis. Mechanistically, CB2R activation upregulated the expression of CD36 on TAMs, a scavenger receptor known to facilitate phagocytosis. Furthermore, sulfo-N-succinimidyl oleate (SSO), an irreversible CD36 inhibitor, could reverse the CB2R activation-induced enhancement of phagocytosis by TAMs. Additionally. JHW133 also effectively augmented the chemotherapeutic efficacy of temozolomide.

Conclusion

Overall, our findings show that CB2R activation promotes TAMs-mediated phagocytosis of tumor cells by enhancing CD36 expression, implying that JWH133 could be a useful therapeutic approach to improving chemotherapeutic efficacy against GBM.

The endocannabinoid system as a therapeutic target in neuropathic pain: a review

INTRODUCTION

This review highlights the critical role of the endocannabinoid system (ECS) in regulating neuropathic pain and explores the therapeutic potential of cannabinoids. Understanding the mechanisms of the ECS, including its receptors, endogenous ligands, and enzymatic routes, can lead to innovative treatments for chronic pain, offering more effective therapies for neuropathic conditions. This review bridges the gap between preclinical studies and clinical applications by emphasizing ECS modulation for better pain management outcomes.

AREAS COVERED

A review mapped the existing literature on neuropathic pain and the effects of modulating the ECS using natural and synthetic cannabinoids. This analysis examined ECS components and their alterations in neuropathic pain, highlighting the peripheral, spinal, and supraspinal mechanisms. This review aimed to provide a thorough understanding of the therapeutic potential of cannabinoids in the management of neuropathic pain.

EXPERT OPINION

Advances in cannabinoid research have shown significant potential for the management of chronic neuropathic pain. The study emphasizes the need for high-quality clinical trials and collaborative efforts among researchers, clinicians, and regulatory bodies to ensure safe and effective integration of cannabinoids into pain management protocols. Understanding the mechanisms and optimizing cannabinoid formulations and delivery methods are crucial for enhancing therapeutic outcomes.

Flipping the GPCR Switch: Structure-Based Development of Selective Cannabinoid Receptor 2 Inverse Agonists

We report a blueprint for the rational design of G protein coupled receptor (GPCR) ligands with a tailored functional response. The present study discloses the structure-based design of cannabinoid receptor type 2 (CB2R) selective inverse agonists (S)-1 and (R)-1, which were derived from privileged agonist HU-308 by introduction of a phenyl group at the gem-dimethylheptyl side chain. Epimer (R)-1 exhibits high affinity for CB2R with Kd = 39.1 nM and serves as a platform for the synthesis of a wide variety of probes. Notably, for the first time these fluorescent probes retain their inverse agonist functionality, high affinity, and selectivity for CB2R independent of linker and fluorophore substitution. Ligands (S)-1, (R)-1, and their derivatives act as inverse agonists in CB2R-mediated cAMP as well as G protein recruitment assays and do not trigger β-arrestin-receptor association. Furthermore, no receptor activation was detected in live cell ERK1/2 phosphorylation and Ca2+-release assays. Confocal fluorescence imaging experiments with (R)-7 (Alexa488) and (R)-9 (Alexa647) probes employing BV-2 microglial cells visualized CB2R expressed at endogenous levels. Finally, molecular dynamics simulations corroborate the initial docking data in which inverse agonists restrict movement of toggle switch Trp2586.48 and thereby stabilize CB2R in its inactive state.

IUPHAR review: Navigating the role of preclinical models in pain research

Chronic pain is a complex and challenging medical condition that affects millions of people worldwide. Understanding the underlying mechanisms of chronic pain is a key goal of preclinical pain research so that more effective treatment strategies can be developed. In this review, we explore nociception, pain, and the multifaceted factors that lead to chronic pain by focusing on preclinical models. We provide a detailed look into inflammatory and neuropathic pain models and discuss the most used animal models for studying the mechanisms behind these conditions. Additionally, we emphasize the vital role of these preclinical models in developing new pain-relief drugs, focusing on biologics and the therapeutic potential of NMDA and cannabinoid receptor antagonists. We also discuss the challenges of TRPV1 modulation for pain treatment, the clinical failures of neurokinin (NK)- 1 receptor antagonists, and the partial success story of Ziconotide to provide valuable lessons for preclinical pain models. Finally, we highlight the overall success and limitations of current treatments for chronic pain while providing critical insights into the development of more effective therapies to alleviate the burden of chronic pain.

A type II cannabis extract and a 1:1 blend of Δ(9)-tetrahydrocannabinol and cannabidiol display distinct antinociceptive profiles and engage different endocannabinoid targets when administered into the subarachnoid space

Introduction: Cannabis extracts are being increasingly used to mitigate chronic pain. Current guidelines for their prescription rely on Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) content as well as the ratio of these major cannabinoids present in the blend. Here we assessed whether these descriptors were representative of product effectiveness to produce a desired outcome such as analgesia. Methods: In this study, we used a rat model of diabetic neuropathy and assessed the reduction in mechanical allodynia following intrathecal injection of pure THC, pure CBD, a 1:1 mix of these compounds and a "balanced" chemotype II cannabis extract. Engagement of endocannabinoid targets by different treatments was investigated using CB1 (AM251) and CB2 (AM630) receptor antagonists as well as a TRPV1 channel blocker (capsazepine). Results: Antinociceptive responses induced by an equivalent amount of THC administered in its pure form, as a THC:CBD mix or as a "balanced" extract were distinct. Furthermore, the 1:1 THC:CBD mix and the balanced extract had not only different response profiles but their relative engagement of CB1, CB2 receptors and TRPV1 channels was distinct. Discussion: These findings indicate that antinociceptive responses and targets engaged by blended cannabinoids are composition-specific, and cannot be simply inferred from THC and CBD contents. This information may have implications in relation to the way medicinal cannabis products are prescribed.

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.

Microglial Cannabinoid CB2 Receptors in Pain Modulation

Pain, especially chronic pain, can strongly affect patients' quality of life. Cannabinoids ponhave been reported to produce potent analgesic effects in different preclinical pain models, where they primarily function as agonists of G_i/o protein-coupled cannabinoid CB₁ and CB₂ receptors. The CB₁ receptors are abundantly expressed in both the peripheral and central nervous systems. The central activation of CB₁ receptors is strongly associated with psychotropic adverse effects, thus largely limiting its therapeutic potential. However, the CB₂ receptors are promising targets for pain treatment without psychotropic adverse effects, as they are primarily expressed in immune cells. Additionally, as the resident immune cells in the central nervous system, microglia are increasingly recognized as critical players in chronic pain. Accumulating evidence has demonstrated that the expression of CB₂ receptors is significantly increased in activated microglia in the spinal cord, which exerts protective consequences within the surrounding neural circuitry by regulating the activity and function of microglia. In this review, we focused on recent advances in understanding the role of microglial CB₂ receptors in spinal nociceptive circuitry, highlighting the mechanism of CB₂ receptors in modulating microglia function and its implications for CB₂ receptor- selective agonist-mediated analgesia.

Intrathecal Actions of the Cannabis Constituents Δ(9)-Tetrahydrocannabinol and Cannabidiol in a Mouse Neuropathic Pain Model

(1) Background: The psychoactive and non-psychoactive constituents of cannabis, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), synergistically reduce allodynia in various animal models of neuropathic pain. Unfortunately, THC-containing drugs also produce substantial side-effects when administered systemically. We examined the effectiveness of targeted spinal delivery of these cannabis constituents, alone and in combination. (2) Methods: The effect of acute intrathecal drug delivery on allodynia and common cannabinoid-like side-effects was examined in a mouse chronic constriction injury (CCI) model of neuropathic pain. (3) Results: intrathecal THC and CBD produced dose-dependent reductions in mechanical and cold allodynia. In a 1:1 combination, they synergistically reduced mechanical and cold allodynia, with a two-fold increase in potency compared to their predicted additive effect. Neither THC, CBD nor combination THC:CBD produced any cannabis-like side-effects at equivalent doses. The anti-allodynic effects of THC were abolished and partly reduced by cannabinoid CB1 and CB2 receptor antagonists AM281 and AM630, respectively. The anti-allodynic effects of CBD were partly reduced by AM630. (4) Conclusions: these findings indicate that intrathecal THC and CBD, individually and in combination, could provide a safe and effective treatment for nerve injury induced neuropathic pain.

Cannabinoids in Chronic Pain: Therapeutic Potential Through Microglia Modulation

Chronic pain is a complex sensory, cognitive, and emotional experience that imposes a great personal, psychological, and socioeconomic burden on patients. An estimated 1.5 billion people worldwide are afflicted with chronic pain, which is often difficult to treat and may be resistant to the potent pain-relieving effects of opioid analgesics. Attention has therefore focused on advancing new pain therapies directed at the cannabinoid system because of its key role in pain modulation. Endocannabinoids and exogenous cannabinoids exert their actions primarily through Gi/o-protein coupled cannabinoid CB1 and CB2 receptors expressed throughout the nervous system. CB1 receptors are found at key nodes along the pain pathway and their activity gates both the sensory and affective components of pain. CB2 receptors are typically expressed at low levels on microglia, astrocytes, and peripheral immune cells. In chronic pain states, there is a marked increase in CB2 expression which modulates the activity of these central and peripheral immune cells with important consequences for the surrounding pain circuitry. Growing evidence indicate that interventions targeting CB1 or CB2 receptors improve pain outcomes in a variety of preclinical pain models. In this mini-review, we will highlight recent advances in understanding how cannabinoids modulate microglia function and its implications for cannabinoid-mediated analgesia, focusing on microglia-neuron interactions within the spinal nociceptive circuitry.

The CB2 cannabinoid receptor as a therapeutic target in the central nervous system

INTRODUCTION

Targeting CB2 cannabinoid receptor (CB2r) represents a promising approach for the treatment of central nervous system disorders. These receptors were identified in peripheral tissues, but also in neurons in the central nervous system. New findings have highlighted the interest to target these central receptors to obtain therapeutic effects devoid of the classical cannabinoid side-effects.

AREAS COVERED

In this review, we searched PubMed (January 1991-May 2021), ClinicalTrials.gov and Cochrane Library databases for articles, reviews and clinical trials. We first introduce the relevance of CB2r as a key component of the endocannabinoid system. We discuss CB2r interest as a possible novel target in the treatment of pain. This receptor has raised interest as a potential target for neurodegenerative disorders treatment, as we then discussed. Finally, we underline studies revealing a novel potential CB2r interest in mental disorders treatment.

EXPERT OPINION

In spite of the interest of targeting CB2r for pain, clinical trials evaluating CB2r agonist analgesic efficacy have currently failed. The preferential involvement of CB2r in preventing the development of chronic pain could influence the failure of clinical trials designed for the treatment of already established pain syndromes. Specific trials should be designed to target the prevention of chronic pain development.

Pharmacological potential of JWH133, a cannabinoid type 2 receptor agonist in neurodegenerative, neurodevelopmental and neuropsychiatric diseases

The pharmacological activation of cannabinoid type 2 receptors (CB2R) gained attention due to its ability to mitigate neuroinflammatory events without eliciting psychotropic actions, a limiting factor for the drugs targeting cannabinoid type 1 receptors (CB1R). Therefore, ligands activating CB2R are receiving enormous importance for therapeutic targeting in numerous neurological diseases including neurodegenerative, neuropsychiatric and neurodevelopmental disorders as well as traumatic injuries and neuropathic pain where neuroinflammation is a common accompaniment. Since the characterization of CB2R, many CB2R selective synthetic ligands have been developed with high selectivity and functional activity. Among numerous ligands, JWH133 has been found one of the compounds with high selectivity for CB2R. JWH133 has been reported to exhibit numerous pharmacological activities including antioxidant, anti-inflammatory, anticancer, cardioprotective, hepatoprotective, gastroprotective, nephroprotective, and immunomodulatory. Recent studies have shown that JWH133 possesses potent neuroprotective properties in several neurological disorders, including neuropathic pain, anxiety, epilepsy, depression, alcoholism, psychosis, stroke, and neurodegeneration. Additionally, JWH133 showed to protect neurons from oxidative damage and inflammation, promote neuronal survival and neurogenesis, and serve as an immunomodulatory agent. The present review comprehensively examined neuropharmacological activities of JWH133 in neurological disorders including neurodegenerative, neurodevelopmental and neuropsychiatric using synoptic tables and elucidated pharmacological mechanisms based on reported observations. Considering the cumulative data, JWH133 appears to be a promising CB2R agonist molecule for further evaluation and it can be a prototype agent in drug discovery and development for a unique class of agents in neurotherapeutics. Further, regulatory toxicology and pharmacokinetic studies are required to determine safety and proceed for clinical evaluation.

A focused review on CB2 receptor-selective pharmacological properties and therapeutic potential of β-caryophyllene, a dietary cannabinoid

The endocannabinoid system (ECS), a conserved physiological system emerged as a novel pharmacological target for its significant role and potential therapeutic benefits ranging from neurological diseases to cancer. Among both, CB1 and CB2R types, CB2R have received attention for its pharmacological effects as antioxidant, anti-inflammatory, immunomodulatory and antiapoptotic that can be achieved without causing psychotropic adverse effects through CB1R. The ligands activate CB2R are of endogenous, synthetic and plant origin. In recent years, β-caryophyllene (BCP), a natural bicyclic sesquiterpene in cannabis as well as non-cannabis plants, has received attention due to its selective agonist property on CB2R. BCP has been well studied in a variety of pathological conditions mediating CB2R selective agonist property. The focus of the present manuscript is to represent the CB2R selective agonist mediated pharmacological mechanisms and therapeutic potential of BCP. The present narrative review summarizes insights into the CB2R-selective pharmacological properties and therapeutic potential of BCP such as cardioprotective, hepatoprotective, neuroprotective, nephroprotective, gastroprotective, chemopreventive, antioxidant, anti-inflammatory, and immunomodulator. The available evidences suggest that BCP, can be an important candidate of plant origin endowed with CB2R selective properties that may provide a pharmacological rationale for its pharmacotherapeutic application and pharmaceutical development like a drug. Additionally, given the wide availability in edible plants and dietary use, with safety, and no toxicity, BCP can be promoted as a nutraceutical and functional food for general health and well-being. Further, studies are needed to explore pharmacological and pharmaceutical opportunities for therapeutic and preventive applications of use of BCP in human diseases.

Inhibitory effect of intrathecally administered AM404, an endocannabinoid reuptake inhibitor, on neuropathic pain in a rat chronic constriction injury model

BACKGROUND

The endocannabinoid system modulates a wide variety of pain conditions. Systemically administered AM404, an endocannabinoid reuptake inhibitor, exerts antinociceptive effects via activation of the endocannabinoid system. However, the mechanism and site of AM404 action are not fully understood. Here, we explored the effect of AM404 on neuropathic pain at the site of the spinal cord.

METHODS

Male Sprague-Dawley rats were subjected to chronic constriction injury (CCI) of the sciatic nerve. The effects of intrathecal administration of AM404 on mechanical and cold hyperalgesia were examined using the electronic von Frey test and cold plate test, respectively. Motor coordination was assessed using the rotarod test. To understand the mechanisms underlying the action of AM404, we tested the effects of pretreatment with the cannabinoid type 1 (CB₁) receptor antagonist AM251, CB₂ receptor antagonist AM630, and transient receptor potential vanilloid type 1 (TRPV1) antagonist capsazepine.

RESULTS

AM404 attenuated mechanical and cold hyperalgesia with minimal effects on motor coordination. AM251 significantly inhibited the antihyperalgesic action of AM404, whereas capsazepine showed a potentiating effect.

CONCLUSIONS

These results indicate that AM404 exerts antihyperalgesic effects primarily via CB₁, but not CB₂, receptor activation at the site of the spinal cord. TRPV1 receptors appear to play a pronociceptive role in CCI rats. The endocannabinoid reuptake inhibitor may be a promising candidate treatment for neuropathic pain.

Targeting CYP2J2 to Enhance the Anti-Glioma Efficacy of Cannabinoid Receptor 2 Stimulation by Inhibiting the Pro-Angiogenesis Function of M2 Microglia

Enhancing the therapeutic efficacy of anti-tumor drugs is essential for cancer management. Although cannabinoid receptor 2 (CB2R) stimulation exerts anti-tumor action in glioma cells by regulating cellular proliferation, differentiation, or apoptosis, selective CB2R agonist alone does not achieve a satisfactory therapeutic outcome. Herein, we aimed to evaluate the possible strategy for enhancing the anti-glioma efficacy of JWH133, a selective CB2R agonist. In this study, immunofluorescence and qRT-PCR were used to investigate microglia polarization. Tumor growth was monitored via bioluminescent imaging using the IVIS Spectrum System. The angiogenesis of human brain microvascular endothelial cells (HBMECs) was detected by the tube formation assay. qRT-PCR was used to investigate cytochrome P450 2J2 (CYP2J2) and 11,12-epoxyeicosatrienoic acid (11,12-EET) expression. Our results showed that administration of JWH133 significantly promoted microglial M2 polarization both in vitro and in vivo. The medium supernatant of M2 microglia induced by JWH133 treatment facilitated angiogenesis of HBMECs. CYP2J2 expression and 11,12-EET release in the supernatant of JWH133-induced M2 microglia were significantly upregulated. Treatment with 11,12-EET prompted HBMEC angiogenesis and glioma growth. CYP2J2 knockdown restrained the release of 11,12-EET and significantly enhanced the anti-tumor effect of JWH133 on glioma. This study showed that targeting CYP2J2 might be a beneficial strategy to enhance the anti-glioma efficacy of JWH133 by inhibiting the pro-angiogenesis function of M2 microglia.

Preparation and Characterization of Liposomal β-Caryophyllene (Rephyll) by Nanofiber Weaving Technology and Its Effects on Delayed Onset Muscle Soreness (DOMS) in Humans: A Randomized, Double-Blinded, Crossover-Designed, and Placebo-Controlled Study

Delayed onset muscle soreness (DOMS) is a complex spreading out, which is related to swelling of muscles, tenderness, rigidity, pain, disruption of muscle fiber, alteration in the kinematics of joint, acute tissue damage, and reduction in power and strength. β-Caryophyllene (BCP), a potent phytocannabinoid, could play an important role in managing DOMS because of its wide diversity of biological activities, particularly its anti-inflammatory activity; however, its poor stability in light, temperature, high volatility, and insolubility can restrict the medical practices. In this study, liposomal β-caryophyllene (Rephyll) was designed and established in powder form constructed by the nanofiber weaving technology to improve the bioavailability of BCP with improved stability. Rephyll was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, and differential scanning calorimetry studies. Encapsulation efficiency, loading capacity, and in vitro release studies revealed that Rephyll can be an auspicious drug delivery arrangement for BCP. The effects of Rephyll were evaluated by a randomized, double-blinded, crossover-designed, placebo-controlled study. The oral consumption of Rephyll significantly reduced the pain visual assessment score, revealing that Rephyll effectively reduced DOMS with improved recovery without any side effects due to the bioavailable form of the phytocannabinoid BCP in the liposomal powder formulation.

Cannabinoids in the descending pain modulatory circuit: Role in inflammation

The legalization of cannabis in some states has intensified interest in the potential for cannabis and its constituents to lead to novel therapeutics for pain. Our understanding of the cellular mechanisms underlying cannabinoid actions in the brain have lagged behind opioids; however, the current opioid epidemic has also increased attention on the use of cannabinoids as alternatives to opioids for pain, especially chronic pain that requires long-term use. Endogenous cannabinoids are lipid signaling molecules that have complex roles in modulating neuronal function throughout the brain. In this review, we discuss cannabinoid functions in the descending pain modulatory pathway, a brain circuit that integrates cognitive and emotional processing of pain to modulate incoming sensory inputs. In addition, we highlight areas where further studies are necessary to understand cannabinoid regulation of descending pain modulation.

Opioid-sparing effects of cannabinoids on morphine analgesia: participation of CB1 and CB2 receptors

BACKGROUND AND PURPOSE

Much of the opioid epidemic arose from abuse of prescription opioid drugs. This study sought to determine if the combination of a cannabinoid with an opioid could produce additive or synergistic effects on pain, allowing reduction in the opioid dose needed for maximal analgesia.

EXPERIMENTAL APPROACH

Pain was assayed using the formalin test in mice and the carrageenan assay in rats. Morphine and two synthetic cannabinoids were tested: WIN55,212-2 (WIN), which binds to both CB1 and CB2 receptors, and possibly TRPV1 channels; and GP1a, which has activity at CB2 receptors and is reported to inhibit fatty acid amide hydrolase, thus raising levels of endogenous cannabinoids.

KEY RESULTS

Morphine in combination with WIN in the formalin test gave synergistic analgesia. Studies with selective antagonists showed that WIN was acting through CB1 receptors. Morphine in combination with GP1a in the formalin test was sub-additive. In the carrageenan test, WIN had no added effect when combined with morphine, but GP1a with morphine showed enhanced analgesia. Both WIN and Gp1a used alone had analgesic activity in the formalin pain test, but not in the carrageenan pain test.

CONCLUSIONS AND IMPLICATIONS

The ability of a cannabinoid to produce an additive or synergistic effect on analgesia when combined with morphine varies with the pain assay and may be mediated by CB1 or CB2 receptors. These results hold the promise of using cannabinoids to reduce the dose of opioids for analgesia in certain pain conditions.

Therapeutic Effect of the Substrate-Selective COX-2 Inhibitor IMMA in the Animal Model of Chronic Constriction Injury

Enhancement of endocannabinoid signaling has emerged as an attractive strategy for the treatment of pain. In addition to the well-characterized hydrolytic pathways, cyclooxygenase-2 (COX-2) mediated oxygenation is thought to be an alternative route for endocannabinoid metabolism and therefore provides a new avenue for drug intervention. In this study, we examined the therapeutic effect of indomethacin morpholinamide (IMMA), a novel substrate-selective COX-2 inhibitor, in the chronic constriction injury (CCI) mouse model. Treatment with IMMA significantly alleviated hyperalgesia and mechanical allodynia demonstrated by increased thermal withdrawal latency in Hargreaves test and tactile thresholds in Von Frey test. Accumulation of astrocytes and microglia in spinal cord dorsal horn and infiltration of macrophages into the dorsal root ganglion and sciatic nerve were reduced by drug treatment. Co-administration of the CB2 receptor antagonist, but not the CB1 receptor antagonist partially reversed the inhibitory effect of IMMA on pain sensitivity and inflammatory infiltrates. IMMA downregulated the mRNA expression of TNF-α and IL-1β and the production of IL-6 and MCP-1 proteins in the ipsilateral sciatic nerve. The enhanced NF-κB DNA binding activity in the CCI mouse dorsal spinal cord was also significantly reduced, suggesting that inactivation of NF-κB contributes to the anti-inflammatory property of IMMA. However, different from the previous reports showing that IMMA can increase endocannabinoids without interfering with arachidonic acid metabolism, treatment with IMMA failed to elevate the endogenous levels of AEA and 2-AG, but significantly reduced the production of prostaglandin E₂ (PGE₂). Furthermore, the mRNA expression of enzymes involved in PGE₂ production, COX-2 and prostaglandin E synthase 2 in the ipsilateral sciatic nerve was also suppressed by IMMA treatment. Taken together, these results suggested that IMMA might exert anti-nociceptive effects through multiple mechanisms which include, but are not limited to, CB2 receptor activation and reduced PGE₂ production.

Sex-Dependent Effects of Cannabis and Cannabinoids: A Translational Perspective

Recent policy changes have led to significant increases in the use of cannabis for both medical and recreational purposes. Although men are more likely to endorse past month cannabis use and are more frequently diagnosed with Cannabis Use Disorder relative to women, a growing proportion of medical cannabis users are reported to be women. The increased popularity of cannabis for medical purposes and the narrowing gap in prevalence of use between men and women raises questions regarding sex-dependent effects related to therapeutic efficacy and negative health effects of cannabis and cannabinoids. The objective of this review is to provide a translational perspective on the sex-dependent effects of cannabis and cannabinoids by synthesizing findings from preclinical and clinical studies focused on sex comparisons of their therapeutic potential and abuse liability, two specific areas that are of significant public health relevance. Hormonal and pharmacological mechanisms that may underlie sex differences in the effects of cannabis and cannabinoids are highlighted.

The Endogenous Cannabinoid System: A Budding Source of Targets for Treating Inflammatory and Neuropathic Pain

A great need exists for the development of new medications to treat pain resulting from various disease states and types of injury. Given that the endogenous cannabinoid (that is, endocannabinoid) system modulates neuronal and immune cell function, both of which play key roles in pain, therapeutics targeting this system hold promise as novel analgesics. Potential therapeutic targets include the cannabinoid receptors, type 1 and 2, as well as biosynthetic and catabolic enzymes of the endocannabinoids N-arachidonoylethanolamine and 2-arachidonoylglycerol. Notably, cannabinoid receptor agonists as well as inhibitors of endocannabinoid-regulating enzymes fatty acid amide hydrolase and monoacylglycerol lipase produce reliable antinociceptive effects, and offer opioid-sparing antinociceptive effects in myriad preclinical inflammatory and neuropathic pain models. Emerging clinical studies show that 'medicinal' cannabis or cannabinoid-based medications relieve pain in human diseases such as cancer, multiple sclerosis, and fibromyalgia. However, clinical data have yet to demonstrate the analgesic efficacy of inhibitors of endocannabinoid-regulating enzymes. Likewise, the question of whether pharmacotherapies aimed at the endocannabinoid system promote opioid-sparing effects in the treatment of pain reflects an important area of research. Here we examine the preclinical and clinical evidence of various endocannabinoid system targets as potential therapeutic strategies for inflammatory and neuropathic pain conditions.

Cannabinoid CB2 Agonist GW405833 Suppresses Inflammatory and Neuropathic Pain through a CB1 Mechanism that is Independent of CB2 Receptors in Mice

GW405833, widely accepted as a cannabinoid receptor 2 (CB2) agonist, suppresses pathologic pain in preclinical models without the unwanted central side effects of cannabinoid receptor 1 (CB1) agonists; however, recent in vitro studies have suggested that GW405833 may also behave as a noncompetitive CB1 antagonist, suggesting that its pharmacology is more complex than initially appreciated. Here, we further investigated the pharmacologic specificity of in vivo antinociceptive actions of GW405833 in models of neuropathic (i.e., partial sciatic nerve ligation model) and inflammatory (i.e., complete Freund's adjuvant model) pain using CB2 and CB1 knockout (KO) mice, their respective wild-type (WT) mice, and both CB2 and CB1 antagonists. GW405833 (3, 10, and 30 mg/kg i.p.) dose dependently reversed established mechanical allodynia in both pain models in WT mice; however, the antiallodynic effects of GW405833 were fully preserved in CB2KO mice and absent in CB1KO mice. Furthermore, the antiallodynic efficacy of GW405833 (30 mg/kg i.p.) was completely blocked by the CB1 antagonist rimonabant (10 mg/kg i.p.) but not by the CB2 antagonist SR144528 (10 mg/kg i.p.). Thus, the antinociceptive properties of GW405833 are dependent on CB1 receptors. GW405833 (30 mg/kg i.p.) was also inactive in a tetrad of tests measuring cardinal signs of CB1 activation. Additionally, unlike rimonabant (10 mg/kg i.p.), GW405833 (10 mg/kg, i.p.) did not act as a CB1 antagonist in vivo to precipitate withdrawal in mice treated chronically with Δ9-tetrahydrocannabinol. The present results suggest that the antiallodynic efficacy of GW405833 is CB1-dependent but does not seem to involve engagement of the CB1 receptor's orthosteric site.

Cannabinoids and Pain: Sites and Mechanisms of Action

The endocannabinoid system, consisting of the cannabinoid₁ receptor (CB₁R) and cannabinoid₂ receptor (CB₂R), endogenous cannabinoid ligands (endocannabinoids), and metabolizing enzymes, is present throughout the pain pathways. Endocannabinoids, phytocannabinoids, and synthetic cannabinoid receptor agonists have antinociceptive effects in animal models of acute, inflammatory, and neuropathic pain. CB₁R and CB₂R located at peripheral, spinal, or supraspinal sites are important targets mediating these antinociceptive effects. The mechanisms underlying the analgesic effects of cannabinoids likely include inhibition of presynaptic neurotransmitter and neuropeptide release, modulation of postsynaptic neuronal excitability, activation of the descending inhibitory pain pathway, and reductions in neuroinflammatory signaling. Strategies to dissociate the psychoactive effects of cannabinoids from their analgesic effects have focused on peripherally restricted CB₁R agonists, CB₂R agonists, inhibitors of endocannabinoid catabolism or uptake, and modulation of other non-CB₁R/non-CB₂R targets of cannabinoids including TRPV1, GPR55, and PPARs. The large body of preclinical evidence in support of cannabinoids as potential analgesic agents is supported by clinical studies demonstrating their efficacy across a variety of pain disorders.

Endocannabinoid activation of CB1 receptors contributes to long-lasting reversal of neuropathic pain by repetitive spinal cord stimulation

BACKGROUND

Spinal cord stimulation (SCS) has been shown to be effective in the management of certain neuropathic pain conditions, however, the underlying mechanisms are incompletely understood. In this study, we investigated repetitive SCS in a rodent neuropathic pain model, revealing long-lasting and incremental attenuation of hyperalgesia and a mechanism of action involving endocannabinoids.

METHOD

Animals were implanted with monopolar electrodes at the time of partial sciatic nerve injury. Dorsal columns at spinal segments T12/13 were stimulated 3 days later (early SCS), and again at day 7 (late SCS) using low-frequency parameters. Hypersensitivity to cutaneous mechanical stimuli was assessed using von Frey filaments. Pharmacological agents, selected to identify endocannabinoid and opioid involvement, were administered intraperitoneally, 10 min before SCS.

RESULTS

Early SCS caused partial reversal of mechanical hypersensitivity with corresponding changes in the biomarker of central sensitization, [phospho-Tyr¹⁴⁷² ]-GluN2B. The partial reversal of hyperalgesia by early SCS was amplified by co-administration of LY 2183240, an inhibitor of endocannabinoid reuptake/breakdown. This amplification was inhibited by a CB₁ R antagonist, AM251, but not by a CB₂ R antagonist, AM630. Early SCS-induced reversal of hyperalgesia was attenuated by naloxone, indicating a role for opioids. Late SCS resulted in an incremental level of reversal of hyperalgesia, which was inhibited by AM251, but not by CB₂ or opioid receptor antagonists.

CONCLUSION

The endocannabinoid system, and in particular the CB₁ R, plays a pivotal role in the long-lasting and incremental reversal of hyperalgesia induced by repetitive SCS in a neuropathic pain model.

SIGNIFICANCE

Alternative parameters for repetitive spinal cord stimulation (SCS) at 25/10 Hz elicit particularly long-lasting and incremental reversal of hyperalgesia in a neuropathic pain model through a mechanism involving endocannabinoids.

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.

The central cannabinoid receptor type-2 (CB2) and chronic pain

Cannabinoid receptor type-2 (CB2, CB2 receptor or CB2-R) mediates analgesia via two mechanisms. CB2 receptors contained in peripheral immune tissue mediate analgesia by altering cytokine profiles, and thus have little adverse effects on central nervous systems (CNSs). CB2 is also expressed in the neurons and glial cells of the CNS. This neuronal expression may also contribute to pain attenuation. The CB2 receptor has been proposed as a potential target in treating chronic pain of several etiologies.

Cannabinoids to treat spinal cord injury

Spinal cord injury (SCI) is a devastating condition for which there is no standard treatment beyond rehabilitation strategies. In this review, we discuss the current knowledge on the use of cannabinoids to treat this condition. The endocannabinoid system is expressed in the intact spinal cord, and it is dramatically upregulated after lesion. Endogenous activation of this system counteracts secondary damage following SCI, and treatments with endocannabinoids or synthetic cannabinoid receptor agonists promote a better functional outcome in experimental models. The use of cannabinoids in SCI is a new research field and many questions remain open. Here, we discuss caveats and suggest some future directions that may help to understand the role of cannabinoids in SCI and how to take advantage of this system to regain functions after spinal cord damage.

Neuronal expression of CB2 cannabinoid receptor mRNAs in the mouse hippocampus

In the brain, CB1 cannabinoid receptors primarily mediate the effects of cannabinoids, but CB2 cannabinoid receptors (CB2Rs) have recently been discovered in the nervous system and also implicated in neuromodulatory roles. To understand the mechanisms of CB2R functions in the brain, it is essential to localize CB2Rs, but the types of cells expressing CB2Rs have been controversial. Unequivocal localization of CB2Rs in the brain has been impeded in part by the low expression levels of CB2Rs and poor specificity of detection methods. Here, we used an ultrasensitive and specific in situ hybridization method called the RNAscope to determine the spatial pattern of CB2R mRNA expression in the mouse hippocampus. CB2R mRNAs were mostly expressed in a subset of excitatory and inhibitory neurons in the CA1, CA3 and dentate gyrus areas, but rarely in microglia. CB2R knock-out mice were used as a negative control. Using the quantitative real-time polymerase chain reaction, we also found that the temporal pattern of CB2R mRNA expression was stable during postnatal development. Consistent with previous reports, the immunological detection of CB2Rs was not reliable, implying extremely low levels of the protein expression and/or insufficient specificity of the current anti-CB2R antibodies. Our findings of the expression patterns of CB2R mRNAs may help determine the cell types involved in, and hence the mechanisms of, the CB2R-mediated neuromodulation.

Activation of cannabinoid CB2 receptors reduces hyperalgesia in an experimental autoimmune encephalomyelitis mouse model of multiple sclerosis

Clinical trials investigating the analgesic efficacy of cannabinoids in multiple sclerosis have yielded mixed results, possibly due to psychotropic side effects mediated by cannabinoid CB1 receptors. We hypothesized that, a CB2-specific agonist (JWH-133) would decrease hyperalgesia in an experimental autoimmune encephalomyelitis mouse model of multiple sclerosis. Four weeks after induction of experimental autoimmune encephalomyelitis, we found that intrathecal administration of JWH-133 (10-100μg) dose-dependently reduced both mechanical and cold hypersensitivity without producing signs of sedation or ataxia. The anti-hyperalgesic effects of JWH-133 could be dose-dependently prevented by intrathecal co-administration of the CB2 antagonist, AM-630 (1-3μg). Our results suggest that JWH-133 acts at CB2 receptors, most likely within the dorsal horn of the spinal cord, to suppress the hypersensitivity associated with experimental autoimmune encephalomyelitis. These are the first pre-clinical studies to directly promote CB2 as a promising target for the treatment of central pain in an animal model of multiple sclerosis.

Effect of styrene maleic acid WIN55,212-2 micelles on neuropathic pain in a rat model

Cannabinoid receptor agonists are moderately effective at reducing neuropathic pain but are limited by psychoactivity. We developed a styrene maleic acid (SMA) based on the cannabinoid WIN 55,212-2 (WIN) and tested in a rat model of neuropathic pain and in the rotarod test. We hypothesized that miceller preparation can ensure prolonged plasma half-life being above the renal threshold of excretion. Furthermore, SMA-WIN could potentially reduce the central nervous system effects of encapsulated WIN by limiting its transport across the blood-brain barrier. Using the chronic constriction injury model of sciatic neuropathy, the SMA-WIN micelles were efficacious in the treatment of neuropathic pain for a prolonged period compared to control (base WIN). Attenuation of chronic constriction injury-induced mechanical allodynia occurred for up to 8 h at a dose of 11.5 mg/kg of SMA-WIN micelles. To evaluate central effects on motor function, the rotarod assessment was utilized. Results showed initial impairment caused by SMA-WIN micelles to be identical to WIN control for up to 1.5 h. Despite this, the SMA-WIN micelle formulation was able to produce prolonged analgesia over a time when there was decreased impairment in the rotarod test compared with base WIN.

Cannabinoids and the endocannabinoid system in lower urinary tract function and dysfunction

AIMS

To review knowledge on cannabinoids and the endocannabinoid system in lower urinary tract function and dysfunction.

METHODS

Review of MEDLINE using defined search terms, and manual analysis. Articles published in English were included.

RESULTS AND DISCUSSION

Components of the endocannabinoid system—cannabinoid (CB)receptor types 1 and 2, anandamide, and fatty acid amide hydrolase (FAAH), which degrades anandamide and related fatty-acid amides—have been located to lower urinary tract tissues of mice, rats, monkeys, and humans. Studies have located CB receptors in urothelium and sensory nerves and FAAH in the urothelium. CB receptor- and FAAH-related activities have also been reported in the lumbosacral spinal cord. Data on supraspinal CB functions in relation to micturition are lacking. Cannabinoids are reported to reduce sensory activity of isolated tissues, cause antihyperalgesia in animal studies of bladder inflammation, affect urodynamics parameters reflecting sensory functions in animals models, and appear to have effects on storage symptoms in humans. FAAH inhibitors have affected sensory bladder functions and reduced bladder overactivity in rat models. Cannabinoids may modify nerve-mediated functions of isolated lower urinary tract tissues.

CONCLUSIONS

Evidence suggests components of the endocannabinoid system are involved in regulation of bladder function, possibly at several levels of the micturition pathway. It is unclear if either CB receptor has a dominant role in modification of sensory signals or if differences exist at peripheral and central nervous sites. Amplification of endocannabinoid activity by FAAH inhibitors may be an attractive drug target in specific pathways involved in LUTS.

Validating Antibodies to the Cannabinoid CB2 Receptor: Antibody Sensitivity Is Not Evidence of Antibody Specificity

Antibody-based methods for the detection and quantification of membrane integral proteins, in particular, the G protein-coupled receptors (GPCRs), have been plagued with issues of primary antibody specificity. In this report, we investigate one of the most commonly utilized commercial antibodies for the cannabinoid CB2 receptor, a GPCR, using immunoblotting in combination with mass spectrometry. In this way, we were able to develop powerful negative and novel positive controls. By doing this, we are able to demonstrate that it is possible for an antibody to be sensitive for a protein of interest—in this case CB2—but still cross-react with other proteins and therefore lack specificity. Specifically, we were able to use western blotting combined with mass spectrometry to unequivocally identify CB2 protein in over-expressing cell lines. This shows that a common practice of validating antibodies with positive controls only is insufficient to ensure antibody reliability. In addition, our work is the first to develop a label-free method of protein detection using mass spectrometry that, with further refinement, could provide unequivocal identification of CB2 receptor protein in native tissues.

The oral administration of trans-caryophyllene attenuates acute and chronic pain in mice

Trans-caryophyllene is a sesquiterpene present in many medicinal plants' essential oils, such as Ocimum gratissimum and Cannabis sativa. In this study, we evaluated the antinociceptive activity of trans-caryophyllene in murine models of acute and chronic pain and the involvement of trans-caryophyllene in the opioid and endocannabinoid systems. Acute pain was determined using the hot plate test (thermal nociception) and the formalin test (inflammatory pain). The chronic constriction injury (CCI) of the sciatic nerve induced hypernociception was measured by the hot plate and von Frey tests. To elucidate the mechanism of action, mice were pre-treated with naloxone or AM630 30 min before the trans-caryophyllene treatment. Afterwards, thermal nociception was evaluated. The levels of IL-1β were measured in CCI-mice by ELISA. Trans-caryophyllene administration significantly minimized the pain in both the acute and chronic pain models. The antinociceptive effect observed during the hot plate test was reversed by naloxone and AM630, indicating the participation of both the opioid and endocannabinoid system. Trans-caryophyllene treatment also decreased the IL-1β levels. These results demonstrate that trans-caryophyllene reduced both acute and chronic pain in mice, which may be mediated through the opioid and endocannabinoid systems.

Endocannabinoid system and pain: an introduction

The endocannabinoid (EC) system consists of two main receptors: cannabinoid type 1 receptor cannabinoid receptors are found in both the central nervous system (CNS) and periphery, whereas the cannabinoid type 2 receptor cannabinoid receptor is found principally in the immune system and to a lesser extent in the CNS. The EC family consists of two classes of well characterised ligands; the N-acyl ethanolamines, such as N-arachidonoyl ethanolamide or anandamide (AEA), and the monoacylglycerols, such as 2-arachidonoyl glycerol. The various synthetic and catabolic pathways for these enzymes have been (with the exception of AEA synthesis) elucidated. To date, much work has examined the role of EC in nociceptive processing and the potential of targeting the EC system to produce analgesia. Cannabinoid receptors and ligands are found at almost every level of the pain pathway from peripheral sites, such as peripheral nerves and immune cells, to central integration sites such as the spinal cord, and higher brain regions such as the periaqueductal grey and the rostral ventrolateral medulla associated with descending control of pain. EC have been shown to induce analgesia in preclinical models of acute nociception and chronic pain states. The purpose of this review is to critically evaluate the evidence for the role of EC in the pain pathway and the therapeutic potential of EC to produce analgesia. We also review the present clinical work conducted with EC, and examine whether targeting the EC system might offer a novel target for analgesics, and also potentially disease-modifying interventions for pathophysiological pain states.

Dynamic changes to the endocannabinoid system in models of chronic pain

The analgesic effects of cannabinoid ligands, mediated by CB1 receptors are well established. However, the side-effect profile of CB1 receptor ligands has necessitated the search for alternative cannabinoid-based approaches to analgesia. Herein, we review the current literature describing the impact of chronic pain states on the key components of the endocannabinoid receptor system, in terms of regionally restricted changes in receptor expression and levels of key metabolic enzymes that influence the local levels of the endocannabinoids. The evidence that spinal CB2 receptors have a novel role in the modulation of nociceptive processing in models of neuropathic pain, as well as in models of cancer pain and arthritis is discussed. Recent advances in our understanding of the spinal location of the key enzymes that regulate the levels of the endocannabinoid 2-AG are discussed alongside the outcomes of recent studies of the effects of inhibiting the catabolism of 2-AG in models of pain. The complexities of the enzymes capable of metabolizing both anandamide (AEA) and 2-AG have become increasingly apparent. More recently, it has come to light that some of the metabolites of AEA and 2-AG generated by cyclooxygenase-2, lipoxygenases and cytochrome P450 are biologically active and can either exacerbate or inhibit nociceptive signalling.

Full inhibition of spinal FAAH leads to TRPV1-mediated analgesic effects in neuropathic rats and possible lipoxygenase-mediated remodeling of anandamide metabolism

Neuropathic pain elevates spinal anandamide (AEA) levels in a way further increased when URB597, an inhibitor of AEA hydrolysis by fatty acid amide hydrolase (FAAH), is injected intrathecally. Spinal AEA reduces neuropathic pain by acting at both cannabinoid CB1 receptors and transient receptor potential vanilloid-1 (TRPV1) channels. Yet, intrathecal URB597 is only partially effective at counteracting neuropathic pain. We investigated the effect of high doses of intrathecal URB597 on allodynia and hyperalgesia in rats with chronic constriction injury (CCI) of the sciatic nerve. Among those tested, the 200 µg/rat dose of URB597 was the only one that elevated the levels of the FAAH non-endocannabinoid and anti-inflammatory substrates, oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), and of the endocannabinoid FAAH substrate, 2-arachidonoylglycerol, and fully inhibited thermal and tactile nociception, although in a manner blocked almost uniquely by TRPV1 antagonism. Surprisingly, this dose of URB597 decreased spinal AEA levels. RT-qPCR and western blot analyses demonstrated altered spinal expression of lipoxygenases (LOX), and baicalein, an inhibitor of 12/15-LOX, significantly reduced URB597 analgesic effects, suggesting the occurrence of alternative pathways of AEA metabolism. Using immunofluorescence techniques, FAAH, 15-LOX and TRPV1 were found to co-localize in dorsal spinal horn neurons of CCI rats. Finally, 15-hydroxy-AEA, a 15-LOX derivative of AEA, potently and efficaciously activated the rat recombinant TRPV1 channel. We suggest that intrathecally injected URB597 at full analgesic efficacy unmasks a secondary route of AEA metabolism via 15-LOX with possible formation of 15-hydroxy-AEA, which, together with OEA and PEA, may contribute at producing TRPV1-mediated analgesia in CCI rats.