Peripheral deficiency and antiallodynic effects of 2-arachidonoyl glycerol in a mouse model of paclitaxel-induced neuropathic pain

Effect of cannabinoids on the efficacy and side effects of anticancer therapeutic strategies - Current status of preclinical and clinical research

Cannabinoids have attracted increasing attention in cancer research in recent decades. A major focus of current preclinical and clinical studies is on the interactions and potential risks when combined with chemotherapeutic agents, targeted therapies and other anticancer strategies. Given the extensive preclinical data on additive, synergistic and, in some cases, antagonistic tumor cell killing effects of chemotherapeutic agents and cannabinoids when co-administered, a critical analysis of these data seems essential. The available data mainly relate to combination treatments for glioblastoma, hematological malignancies and breast cancer, but also for other cancer types. Such an analysis also appears necessary because cannabinoids are used as an option to treat nausea and vomiting caused by chemotherapy, as well as tumor-related pain, and cancer patients sometimes take cannabinoids without a medical prescription. In addition, numerous recent preclinical studies also suggest cannabinoid-mediated relief of other chemotherapy-related side effects such as peripheral neuropathy, nephrotoxicity, cardiotoxicity, cystitis, bladder complications and mucositis. To summarize, the data available to date raise the prospect that cannabinoids may increase the efficacy of chemotherapeutic agents while reducing their side effects. However, preclinical studies on anticancer interactions are mostly limited to cytotoxicity analyses. An equally thorough investigation of the effects of such combinations on the immune system and on the tumorigenic levels of angiogenesis, invasion and metastasis is still pending. On this basis, a comprehensive understanding for the evaluation of a targeted additional treatment of various cancers with cannabinoids could be established.

Spatial Transcriptomics Reveals Novel Mechanisms Involved in Perineural Invasion in Pancreatic Ductal Adenocarcinomas

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) has a high incidence of perineural invasion (PNI), a pathological feature of the cancer invasion of nerves. PNI is associated with a poor prognosis, local recurrence and cancer pain. It has been suggested that interactions between nerves and the tumor microenvironment (TME) play a role in PDAC tumorigenesis.

METHODS

Here, we used Nanostring GeoMx Digital Spatial Profiler to analyze the whole transcriptome of both cancer and nerve cells in the microenvironment of PNI and non-PNI foci from 13 PDAC patients.

CONCLUSIONS

We identified previously reported pathways involved in PNI, including Axonal Guidance and ROBO-SLIT Signaling. Spatial transcriptomics highlighted the role of PNI foci in influencing the immune landscape of the TME and similarities between PNI and nerve injury response. This study revealed that endocannabinoid and polyamine metabolism may contribute to PNI, cancer growth and cancer pain. Key members of these pathways can be targeted, offering potential novel research avenues for exploring new cancer treatment and/or pain management options in PDAC.

Modulation of chemotherapy-induced peripheral neuropathy by JZL195 through glia and the endocannabinoid system

Chemotherapy-induced peripheral neuropathy (CIPN) used to treat cancer, is a significant side effect with a complex pathophysiology, and its mechanisms remain unclear. Recent research highlights neuroinflammation, which is modulated by the endocannabinoid system (ECS) and associated with glial activation, and the role of toll-like receptor 4 (TLR4) in CIPN. This study aimed to investigate the effects of JZL195, an inhibitor of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), and explore the connection between cannabinoid receptors and TLR4 in glial cells. A CIPN animal model was developed using cisplatin-injected male C57BL/6 mice. Mechanical and cold allodynia were assessed through von Frey and acetone tests. Western blot analysis was used to examine the expression of catabolic enzymes, cannabinoid receptors, glial cells, and neuroinflammatory factors in the dorsal root ganglia (DRGs) and spinal cord. Immunohistochemistry was used to investigate the colocalization of cannabinoid receptors and TLR4 in glial cells. JZL195 alleviated pain by inhibiting FAAH/MAGL, modulating the ECS and neuroinflammatory factors, and suppressing glial cell activity. Additionally, cannabinoid receptors and TLR4 colocalized with astrocytes and microglia in the spinal cord. This study highlights the therapeutic potential of JZL195 in modulating the ECS and suggests a correlation between cannabinoid receptors and TLR4 in spinal glial cells, providing insight into alleviating pain and neuroinflammation in CIPN.

Analgesic Properties of Next-Generation Modulators of Endocannabinoid Signaling: Leveraging Modern Tools for the Development of Novel Therapeutics

Targeting the endocannabinoid (eCB) signaling system for pain relief is an important treatment option that is only now beginning to be mechanistically explored. In this review, we focus on two recently appreciated cannabinoid-based targeting strategies, treatments with cannabidiol (CBD) and α/β-hydrolase domain containing 6 (ABHD6) inhibitors, which have the exciting potential to produce pain relief through distinct mechanisms of action and without intoxication. We review evidence on plant-derived cannabinoids for pain, with an emphasis on CBD and its multiple molecular targets expressed in pain pathways. We also discuss the function of eCB signaling in regulating pain responses and the therapeutic promises of inhibitors targeting ABHD6, a 2-arachidonoylglycerol (2-AG)-hydrolyzing enzyme. Finally, we discuss how the novel cannabinoid biosensor GRABeCB2.0 may be leveraged to enable the discovery of targets modulated by cannabinoids at a circuit-specific level. SIGNIFICANCE STATEMENT: Cannabis has been used by humans as an effective medicine for millennia, including for pain management. Recent evidence emphasizes the therapeutic potential of compounds that modulate endocannabinoid signaling. Specifically, cannabidiol and inhibitors of the enzyme ABHD6 represent promising strategies to achieve pain relief by modulating endocannabinoid signaling in pain pathways via distinct, nonintoxicating mechanisms of action.

Chemotherapy-Induced Peripheral Neuropathy: A Recent Update on Pathophysiology and Treatment

Chemotherapy-induced peripheral neuropathy (CIPN) is a major long-lasting side effect of some chemotherapy drugs, which threatens cancer survival rate. CIPN mostly affects sensory neurons and occasionally motor neurons, causing numbness, tingling, discomfort, and burning pain in the upper and lower extremities. The pathophysiology of CIPN is not completely understood; however, it is believed that chemotherapies induce peripheral neuropathy via directly damaging mitochondria, impairing the function of ion channels, triggering immunological mechanisms, and disrupting microtubules. The treatment of CIPN is a medical challenge, and there are no approved pharmacological options. Currently, duloxetine and other antidepressants, antioxidant, anti-inflammatory, and ion-channel targeted therapies are commonly used in clinics to relieve the symptoms of CIPN. Several other types of drugs, such as cannabinoids, sigma-1 receptor antagonists, and nicotinamides ribose, are being evaluated in preclinical and clinical studies. This paper summarizes the information related to the physiology of CIPN and medicines that could be used for treating this condition.

Additive antinociceptive action of intrathecal anandamide reuptake inhibitor and morphine in the management of post-incisional pain in rats

Spinal opioids have mixed efficacy and their adverse effects force treatment cessation of postoperative pain. Consequently, there is an ongoing search for new therapeutic strategies. Here, we evaluated the analgesic efficacy of intrathecal UCM707, an anandamide reuptake inhibitor, and morphine combination. Firstly, we assessed the effects of morphine (1, 5 and 10 μg), UCM707 (75 μg) and its combination in the hot plate. Then, morphine + UCM707 at sub-effective doses was evaluated in a rat post-incisional pain model. In addition, μ-, CB1r-, CB2r- and TRPV1-antagonists were pre-administered before the combination. Activation of μ-opioid and CB1r, and Cnr1, Cnr2, Oprm1 and TRPV1 expressions were evaluated in the lumbar sacra and periaqueductal grey by [35 S]-GTPγS binding autoradiography and qPCR studies. In the hot plate, morphine (1 μg) and UCM707 (75 μg) induced a more robust analgesic effect than each drug alone. Morphine plus UCM707 did not modify μ-opioid nor CB1 receptor function in the PAG or LS. Cnr1 and TRPV1 expression increased in the lumbar sacra (LS). Morphine plus UCM707 significantly reduced post-incisional pain at 1 and 4 days after surgery. Cnr1, Cnr2 and TRPV1 expressions increased in the LS. Blockade of μ-opioid receptor reduced combination effects on days 1 and 4. CB1r- and CB2r-antagonism reduced morphine + UCM707 effects on days 1 and 4, respectively. CB1r and TRPV1-antagonism improved their antinociceptive effects on day 4. These results revealed a synergistic/additive analgesic effect of UCM707 and morphine combination controlling postincisional pain. CB1r, CB2r and TRPV1 contribute differently as central sensitization occurs.

Licofelone, a Dual COX/LOX Inhibitor, Ameliorates Paclitaxel-Induced Mechanical Allodynia in Rats in a Cannabinoid Receptor-Dependent Manner

The use of paclitaxel as a chemotherapeutic drug is limited by the development of dose-dependent paclitaxel-induced neuropathic pain (PINP). Recently, we observed that the combination of indomethacin plus minocycline (IPM) attenuates PINP in a mouse model in a cannabinoid (CB) receptor-dependent manner. Indomethacin inhibits cyclooxygenase (COX) activity, and minocycline inhibits 5-lipoxygenase (5-LOX) activity. Male Sprague Dawley rats with paclitaxel-induced mechanical allodynia were treated with indomethacin, minocycline, IPM combination, licofelone (a dual COX/LOX inhibitor), or their vehicles. AM251, a CB1 receptor antagonist, and AM630, a CB2 receptor antagonist, were administered before the IPM combination or licofelone. Mechanical allodynia was measured using a dynamic plantar aesthesiometer. Molecular docking was performed using CB-Dock2. Licofelone and IPM combination had antiallodynic effects, which were significantly higher than either indomethacin or minocycline alone. AM251 and AM630 blocked the antiallodynic effects of IPM combination and licofelone. Molecular docking showed that licofelone binds to both CB1 and CB2 receptors with a high affinity similar to the phytocannabinoid 1-trans-delta-9-tetrahydrocannabinol and the synthetic cannabinoid WIN 55,212-2. Licofelone inhibits COX and LOX and/or directly interacts with CB receptors to produce antiallodynic effects in a rat model of PINP. The findings further suggest that licofelone could be a therapeutic agent for managing PINP.

Cannabidiol ameliorates PTSD-like symptoms by inhibiting neuroinflammation through its action on CB2 receptors in the brain of male mice

Post-traumatic stress disorder (PTSD) is a debilitating mental health disease related to traumatic experience, and its treatment outcomes are unsatisfactory. Accumulating research has indicated that cannabidiol (CBD) exhibits anti-PTSD effects, however, the underlying mechanism of CBD remains inadequately investigated. Although many studies pertaining to PTSD have primarily focused on aberrations in neuronal functioning, the present study aimed to elucidate the involvement and functionality of microglia/macrophages in PTSD while also investigated the modulatory effects of CBD on neuroinflammation associated with this condition. We constructed a modified single-prolonged stress (SPS) mice PTSD model and verified the PTSD-related behaviors by various behavioral tests (contextual freezing test, elevated plus maze test, tail suspension test and novel object recognition test). We observed a significant upregulation of Iba-1 and alteration of microglial/macrophage morphology within the prefrontal cortex and hippocampus, but not the amygdala, two weeks after the PTSD-related stress, suggesting a persistent neuroinflammatory phenotype in the PTSD-modeled group. CBD (10 mg/kg, i.p.) inhibited all PTSD-related behaviors and reversed the alterations in both microglial/macrophage quantity and morphology when administered prior to behavioral assessments. We further found increased pro-inflammatory factors, decreased PSD95 expression, and impaired synaptic density in the hippocampus of the modeled group, all of which were also restored by CBD treatment. CBD dramatically increased the level of anandamide, one of the endocannabinoids, and cannabinoid type 2 receptors (CB2Rs) transcripts in the hippocampus compared with PTSD-modeled group. Importantly, we discovered the expression of CB2Rs mRNA in Arg-1-positive cells in vivo and found that the behavioral effects of CBD were diminished by CB2Rs antagonist AM630 (1 mg/kg, i.p.) and both the behavioral and molecular effects of CBD were abolished in CB2Rs knockout mice. These findings suggest that CBD would alleviate PTSD-like behaviors in mice by suppressing PTSD-related neuroinflammation and upregulation and activation of CB2Rs may serve as one of the underlying mechanisms for this therapeutic effect. The present study offers innovative experimental evidence supporting the utilization of CBD in PTSD treatment from the perspective of its regulation of neuroinflammation, and paves the way for leveraging the endocannabinoid system to regulate neuroinflammation as a potential therapeutic approach for psychiatric disorders.

Neurophysiology of corneal neuropathic pain and emerging pharmacotherapeutics

The altered activity generated by corneal neuronal injury can result in morphological and physiological changes in the architecture of synaptic connections in the nervous system. These changes can alter the sensitivity of neurons (both second-order and higher-order projection) projecting pain signals. A complex process involving different cell types, molecules, nerves, dendritic cells, neurokines, neuropeptides, and axon guidance molecules causes a high level of sensory rearrangement, which is germane to all the phases in the pathomechanism of corneal neuropathic pain. Immune cells migrating to the region of nerve injury assist in pain generation by secreting neurokines that ensure nerve depolarization. Furthermore, excitability in the central pain pathway is perpetuated by local activation of microglia in the trigeminal ganglion and alterations of the descending inhibitory modulation for corneal pain arriving from central nervous system. Corneal neuropathic pain may be facilitated by dysfunctional structures in the central somatosensory nervous system due to a lesion, altered synaptogenesis, or genetic abnormality. Understanding these important pathways will provide novel therapeutic insight.

An aqueous Commiphora myrrha extract ameliorates paclitaxel-induced peripheral neuropathic pain in mice

Background: Chemotherapy-induced neuropathic pain (CINP) is a debilitating side effect in individuals undergoing cancer treatment. Treatment of CINP with the current available classes of drugs is limited and often yields unsatisfactory results. Finding therapeutic alternatives of plant origin could provide a new way for the management of CINP. Commiphora myrrha (CM) resin extract has been reported to have anti-inflammatory and analgesic activities, but the effect of CM on neuropathic pain is yet to be investigated in CINP. Objectives: The aim of this study was to investigate the antinociceptive effect of CM extract in a mouse model of paclitaxel-induced neuropathic pain (PINP). Methods: The effects of CM on thermal hyperalgesia and mechanical allodynia were assessed in female BALB/c mice with PINP using a hot plate and a plantar aesthesiometer, respectively. Motor coordination was evaluated using a rotarod apparatus. The involvement of transient receptor potential vanilloid channel 1 (TRPV1) in CM actions was investigated using a capsaicin (a TRPV1 agonist)-induced nociception test. The genetic expression of Trpv1, Nrf2, Sod2, and Hmox1 was assessed using real-time PCR, while protein expression of TRPV1, Iba-1, and CD11b was assessed using Wes™. Results: Administration of CM to mice with established PINP produced a dose-dependent reduction in thermal hyperalgesia. Prophylactic treatment of mice with CM prevented the development of paclitaxel-induced thermal hyperalgesia and mechanical allodynia. CM did not change the motor coordination of mice, as the reaction latency and the rotational velocity of animals pretreated with CM extract were similar to those of animals pretreated with vehicle. CM significantly decreased the number and duration of the flick responses following capsaicin injection into the dorsal surface of the hind paw of mice. The protein expression of TRPV1 was upregulated in the spinal cord of paclitaxel-treated animals compared to vehicle-only-treated control animals, while CM-treated animals had values similar to vehicle-only-treated control animals. The mRNA expression of Nrf2, a major antioxidant transcription factor, was upregulated in the paw skin of mice treated with CM compared to those treated with paclitaxel alone. Conclusion: These results indicate that CM may both treat established and prevent the development of paclitaxel-induced thermal hyperalgesia and mechanical allodynia without any impairment in the motor activity of mice. CM may mediate its action through the peripheral inhibition of TRPV1 channel activity, restoration of normal TRPV1 protein expression in the spinal cord, and elevation of cellular antioxidant defenses. CM has the potential to be used as a therapeutic alternative to treat CINP.

Microneedle-mediated delivery of Ziconotide-loaded liposomes fused with exosomes for analgesia

Ziconotide (ZIC) is an N-type calcium channel antagonist for treating severe chronic pain that is intolerable, or responds poorly to the administration of other drugs, such as intrathecal morphine and systemic analgesics. As it can only work in the brain and cerebrospinal fluid, intrathecal injection is the only administration route for ZIC. In this study, borneol (BOR)-modified liposomes (LIPs) were fused with exosomes from mesenchymal stem cells (MSCs) and loaded with ZIC to prepare microneedles (MNs) to improve the efficiency of ZIC across the blood-brain barrier. To evaluate local analgesic effects of MNs, the sensitivity of behavioral pain to thermal and mechanical stimuli was tested in animal models of peripheral nerve injury, diabetes-induced neuropathy pain, chemotherapy-induced pain, and ultraviolet-B (UV-B) radiation-induced neurogenic inflammatory pain. BOR-modified LIPs loaded with ZIC were spherical or nearly spherical, with a particle size of about 95 nm and a Zeta potential of -7.8 mV. After fusion with MSC exosomes, the particle sizes of LIPs increased to 175 nm, and their Zeta potential increased to -3.8 mV. The nano-MNs constructed based on BOR-modified LIPs had good mechanical properties and could effectively penetrate the skin to release drugs. The results of analgesic experiments showed that ZIC had a significant analgesic effect in different pain models. In conclusion, the BOR-modified LIP membrane-fused exosome MNs constructed in this study for delivering ZIC provide a safe and effective administration for chronic pain treatment, as well as great potential for clinical application of ZIC.

The role of the endocannabinoid 2-arachidonoylglycerol in the in vivo spinal oxytocin-induced antinociception in male rats

Oxytocin receptor (OTR) activation at the spinal level produces antinociception. Some data suggest that central OTR activation enhances social interaction via an increase of endocannabinoids (eCB), but we do not know if this could occur at the spinal level, modulating pain transmission. Considering that oxytocin via OTR stimulates diacylglycerol formation, a key intermediate in synthesizing 2-arachidonylglycerol (2-AG), an eCB molecule, we sought to test the role of the eCB system on the spinal oxytocin-induced antinociception. Behavioral and electrophysiological experiments were conducted in naïve and formalin-treated (to induce long-term mechanical hypersensitivity) male Wistar rats. Intrathecal RHC 80267 injections, an inhibitor of the enzyme diacylglycerol lipase (thus, decreasing 2-AG formation), produces transient mechanical hypersensitivity, an effect unaltered by oxytocin but reversed by gabapentin. Similarly, in in vivo extracellular recordings of naïve spinal wide dynamic range cells, juxtacellular picoinjection of RHC 80267 increases the firing of nociceptive Aδ-, C-fibers, and post-discharge, an effect unaltered by oxytocin. Interestingly, in sensitized rats, oxytocin picoinjection reverses the RHC 80627-induced hyperactivity of Aδ-fibers (but not C- or post-discharge activity). In contrast, a sub-effective dose of JZL184 (a monoacylglycerol lipase inhibitor, thus favoring 2-AG levels), which does not have per se an antinociceptive effect in the formalin-induced hypernociception, the oxytocin-induced antinociception is boosted. Similarly, electrophysiological experiments suggest that juxtacellular JZL184 diminishes the neuronal firing of nociceptive fibers, and co-injection with oxytocin prolongs and enhances the antinociceptive effect. These data may imply that 2-AG formation may play a role in the spinal antinociception induced by oxytocin.

Changes in the expression of endocannabinoid system components in an experimental model of chemotherapy-induced peripheral neuropathic pain: Evaluation of sex-related differences

Chemotherapy-induced neuropathic pain is a serious clinical problem and one of the major side effects in cancer treatment. The endocannabinoid system (ECS) plays a crucial role in regulating pain neurotransmission, and changes in the expression of different components of the ECS have been reported in experimental models of persistent pain. In addition, sex differences have been observed in ECS regulation and function. The aim of our study was to evaluate whether administration of oxaliplatin, a neurotoxic antineoplastic agent, induced changes in the expression of ECS components in peripheral and central stations of the pain pathway, and if those changes exhibited sexual dimorphism. Adult male and female rats were injected with oxaliplatin or saline, and mechanical and cold hypersensitivity and allodynia were evaluated using Von Frey and Choi Tests. The mRNA levels corresponding to cannabinoid receptors (CB1, CB2), cannabinoid-related receptors (GPR55, 5HT1A, TRPV1) and to the main enzymes involved in the synthesis (DAGL, DAGL, NAPE-PLD) and degradation (MGL, FAAH) of endocannabinoids were assessed in lumbar dorsal root ganglia (DRGs) and spinal cord by using real time RT-PCR. In addition, the levels of the main endocannabinoids, 2-arachidonoylglycerol (2-AG) and anandamide (AEA), were evaluated using commercial ELISA kits. Oxaliplatin administration induced the development of mechanical and cold hypersensitivity and allodynia in male and female animals. Oxaliplatin also induced early and robust changes in the expression of several components of the ECS in DRGs. A marked upregulation of CB1, CB2, 5HT1A and TRPV1 was detected in both sexes. Interestingly, while DAGL mRNA levels remained unchanged, DAGL was downregulated in male and upregulated in female rats. Finally, MGL and NAPE-PLD showed increased levels only in male animals, while FAAH resulted upregulated in both sexes. In parallel, reduced 2-AG and AEA levels were detected in DRGs from male or female rats, respectively. In the lumbar spinal cord, only TRPV1 mRNA levels were found to be upregulated in both sexes. Our results reveal previously unreported changes in the expression of cannabinoid receptors, ligands and enzymes occurring mainly in the peripheral nervous system and displaying certain sexual dimorphism. These changes may contribute to the physiopathology of oxaliplatin-induced neuropathic pain in male and female rats. A better understanding of these dynamic changes will facilitate the development of mechanism- and sex-specific approaches to optimize the use of cannabinoid-based medicines for the treatment of chemotherapy-induced pain.

2-Arachidonoylglycerol-mediated endocannabinoid signaling modulates mechanical hypersensitivity associated with alcohol withdrawal in mice

BACKGROUND

Alcohol use disorder (AUD) commonly occurs in patients with chronic pain, and a major barrier to achieving abstinence and preventing relapse is the emergence of hyperalgesia during alcohol withdrawal. Elucidating novel therapeutic approaches to target hyperalgesia associated with alcohol withdrawal could have important implications for treating AUD. Here, we examined the role of 2-arachidonoylglycerol (2-AG)-mediated endocannabinoid (eCB) signaling in the regulation of hyperalgesia associated with alcohol withdrawal in mice. We tested the hypothesis that pharmacological augmentation of 2-AG signaling could reduce hyperalgesia during withdrawal.

METHODS

Male and female C57BL/6J mice were tested during withdrawal from a continuous access two-bottle choice (2BC) paradigm to investigate how eCB signaling modulates mechanical and thermal sensitivity during withdrawal. Mice were pretreated with the monoacylglycerol lipase (MAGL) inhibitor JZL184 to elevate levels of 2-AG. Rimonabant or AM630 were given to block CB1 and CB2 receptor activity, respectively. DO34 was given to reduce 2-AG by inhibiting the 2-AG synthetic enzyme diacylglycerol lipase (DAGL).

RESULTS

After 72 h of withdrawal, male and female mice exhibited increased mechanical, but not thermal, hypersensitivity, which normalized by 7 days. This effect was reversed by pretreatment with JZL184. The effects of JZL184 were prevented by coadministration of either the CB1 or the CB2 antagonist. DO34, Rimonabant, and AM630 exacerbated mechanical hypersensitivity during alcohol withdrawal, causing an earlier onset and persistent hypersensitivity even 1 week into withdrawal.

CONCLUSIONS

Our findings demonstrate the critical role of 2-AG signaling in the bidirectional regulation of mechanical sensitivity during alcohol withdrawal, with enhancement of 2-AG levels reducing sensitivity, and inhibition of 2-AG signaling exacerbating sensitivity. These data suggest that 2-AG augmentation represents a novel approach to the treatment of alcohol withdrawal-associated hyperalgesia and AUD in patients with comorbid pain disorders.

Pristimerin, a triterpene that inhibits monoacylglycerol lipase activity, prevents the development of paclitaxel-induced allodynia in mice

Background: Triterpenes such as euphol and pristimerin, which are plant secondary metabolites, were the first to be characterized as monoacylglycerol lipase (MAGL) inhibitors. MAGL inhibitors alleviate chemotherapy-induced neuropathic pain (CINP) in rodent models. Pristimerin has been shown to have additive anticancer activity with paclitaxel, a chemotherapeutic drug. However, the activity of pristimerin on CINP has not been evaluated.

Objectives: The aims of this study were to evaluate whether various triterpenes had activity against recombinant human MAGL and MAGL activity in mouse tissues, and whether pristimerin could prevent development of paclitaxel-induced mechanical allodynia.

Methods: The effects of four triterpenes betulinic acid, cucurbitacin B, euphol, and pristimerin on the activity human recombinant MAGL and MAGL activity of mice brain and paw skin tissues were evaluated using MAGL inhibitor screening and MAGL activity assay kits. The effects of treatment of female BALB/c mice with pristimerin intraperitoneally on the development of paclitaxel-induced mechanical allodynia were assessed using the dynamic plantar aesthesiometer and on nuclear factor-2 erythroid related factor-2 (Nrf2) gene expression in the paw skin were evaluated by real time polymerase chain reaction.

Results: Pristimerin inhibited the human recombinant MAGL activity in a concentration-dependent manner like JZL-195, a MAGL inhibitor. Betulinic acid, cucurbitacin B and euphol inhibited human recombinant MAGL activity but their effects were not concentration dependent and were less to that of pristimerin. Pristimerin inhibited both mouse brain and paw skin MAGL activity in a concentration-dependent manner. Paclitaxel induced mechanical allodynia and increase in MAGL activity in the paw skin. Treatment with pristimerin prevented the development of paclitaxel-induced mechanical allodynia and the paclitaxel-induced increase in MAGL activity. Pristimerin significantly upregulated mRNA expression of Nrf2, a regulator of endogenous antioxidant defense.

Conclusion: These results indicate that triterpenes inhibit human recombinant MAGL activity with varying degrees. Pristimerin inhibits both mouse brain and paw skin MAGL activity in a concentration-dependent manner, prevents both the development of paclitaxel-induced mechanical allodynia and the associated increase in MAGL activity in the paw skin, and might protect against paclitaxel-induced oxidative stress. Co-treatment with pristimerin and paclitaxel could be useful in the treatment of cancer and prevention of CINP.

Current and Emerging Pharmacotherapeutic Interventions for the Treatment of Peripheral Nerve Disorders

Peripheral nerve disorders are caused by a range of different aetiologies. The range of causes include metabolic conditions such as diabetes, obesity and chronic kidney disease. Diabetic neuropathy may be associated with severe weakness and the loss of sensation, leading to gangrene and amputation in advanced cases. Recent studies have indicated a high prevalence of neuropathy in patients with chronic kidney disease, also known as uraemic neuropathy. Immune-mediated neuropathies including Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy may cause significant physical disability. As survival rates continue to improve in cancer, the prevalence of treatment complications, such as chemotherapy-induced peripheral neuropathy, has also increased in treated patients and survivors. Notably, peripheral neuropathy associated with these conditions may be chronic and long-lasting, drastically affecting the quality of life of affected individuals, and leading to a large socioeconomic burden. This review article explores some of the major emerging clinical and experimental therapeutic agents that have been investigated for the treatment of peripheral neuropathy due to metabolic, toxic and immune aetiologies.

Suvorexant and mirtazapine improve chronic pain-related changes in parameters of sleep and voluntary physical performance in mice with sciatic nerve ligation

Both chronic pain and sleep disorders are associated with a reduction in the quality of life. They can be both a cause and a consequence of each other, and should therefore be simultaneously treated. However, optimal treatments for chronic pain-related sleep disorders are not well established. Here, we aimed to investigate the effects of suvorexant, a novel sleep drug, and mirtazapine, a noradrenergic and specific serotonergic antidepressant, on pain-related changes in sleep parameters in a preclinical chronic pain mice model, by partial sciatic nerve ligation. We evaluated the quantity, duration, and depth of sleep by analyzing the electroencephalogram and voluntary activity by counting the number of wheel rotations to determine various symptoms of sleep disorders, including reduced total sleep time, fragmentation, low quality, and impaired activity in the daytime. Suvorexant and mirtazapine normalized the reduction in sleep time and fragmented sleep, further regaining the sleep depth at sleep onset in the chronic pain state in nerve-ligated mice. Mirtazapine also increased the percentage of rapid eye movement sleep in mice. Suvorexant decreased voluntary activity, which was prolonged after administration; however, mirtazapine did not decrease it. Although the effects of suvorexant and mirtazapine on sleep and activity are different, both suvorexant and mirtazapine could be potential therapeutic agents for chronic pain-related sleep disorders.

Neuro-immune interactions in paclitaxel-induced peripheral neuropathy

BACKGROUND

Paclitaxel is a taxane-based chemotherapeutic agent used as a treatment in breast cancer. There is no effective prevention or treatment strategy for the most common side effect of peripheral neuropathy. In this manuscript, we reviewed the molecular mechanisms that contribute to paclitaxel-induced peripheral neuropathy (PIPN) with an emphasis on immune-related processes.

METHODS

A systematic search of the literature was conducted in PubMed, EMBASE and Cochrane Library. The SYRCLE's risk of bias tool was used to assess internal validity.

RESULTS

156 studies conducted with rodent models were included. The risk of bias was high due to unclear methodology. Paclitaxel induces changes in myelinated axons, mitochondrial dysfunction, and mechanical hypersensitivity by affecting ion channels expression and function and facilitating spinal transmission. Paclitaxel-induced inflammatory responses are important contributors to PIPN.

CONCLUSION

Immune-related processes are an important mechanism contributing to PIPN. Studies in humans that validate these mechanistic data are highly needed to facilitate the development of therapeutic strategies.

Targeting Monoacylglycerol Lipase in Pursuit of Therapies for Neurological and Neurodegenerative Diseases

Neurological and neurodegenerative diseases are debilitating conditions, and frequently lack an effective treatment. Monoacylglycerol lipase (MAGL) is a key enzyme involved in the metabolism of 2-AG (2-arachidonoylglycerol), a neuroprotective endocannabinoid intimately linked to the generation of pro- and anti-inflammatory molecules. Consequently, synthesizing selective MAGL inhibitors has become a focus point in drug design and development. The purpose of this review was to summarize the diverse synthetic scaffolds of MAGL inhibitors concerning their potency, mechanisms of action and potential therapeutic applications, focusing on the results of studies published in the past five years. The main irreversible inhibitors identified were derivatives of hexafluoroisopropyl alcohol carbamates, glycol carbamates, azetidone triazole ureas and benzisothiazolinone, whereas the most promising reversible inhibitors were derivatives of salicylketoxime, piperidine, pyrrolidone and azetidinyl amides. We reviewed the results of in-depth chemical, mechanistic and computational studies on MAGL inhibitors, in addition to the results of in vitro findings concerning selectivity and potency of inhibitors, using the half maximal inhibitory concentration (IC50) as an indicator of their effect on MAGL. Further, for highlighting the potential usefulness of highly selective and effective inhibitors, we examined the preclinical in vivo reports regarding the promising therapeutic applications of MAGL pharmacological inhibition.

Targeting the endocannabinoid system for management of HIV-associated neuropathic pain: A systematic review

Human immunodeficiency virus (HIV) infection and antiretroviral therapy can independently induce HIV-associated neuropathic pain (HIV-NP). There is a dearth of drugs or therapeutic modalities that can alleviate HIV-NP. Smoked cannabis has been reported to improve pain measures in patients with neuropathic pain. Cannabis, phytocannabinoids, and the endocannabinoids such N-arachidonoylethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG), produce some of their effects via cannabinoid receptors (CBRs). Endocannabinoids are degraded by various enzymes such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase. We searched PubMed, Google Scholar, clinicaltrials.gov and clinicaltrialsregister.eu using various key words and their combinations for published papers that studied HIV-NP and cannabis, cannabinoids, or endocannabinoids up to 27th December 2020. All original research articles that evaluated the efficacy of molecules that modulate the endocannabinoid system (ECS) for the prevention and/or treatment of pain in HIV-NP animal models and patients with HIV-NP were included. The PubMed search produced a total of 117 articles, whereas the Google Scholar search produced a total of 9467 articles. Amongst the 13 articles that fulfilled the inclusion criteria 11 articles were found in both searches whereas 2 articles were found in Google Scholar only. The clinicaltrials.gov and clinicaltrialsregister.eu searches produced five registered trials of which three were completed and with results. Ten preclinical studies found that the endocannabinoids (2-AG and AEA), synthetic mixed CB1R/CB2R agonist WIN 55,212-2, a CB2R-selective phytocannabinoid β-caryophyllene, synthetic CB2R-selective agonists (AM1710, JWH015, JWH133 and Gp1a, but not HU308); FAAH inhibitors (palmitoylallylamide, URB597 and PF-3845) and a drug combination of indomethacin plus minocycline, which produces its effects in a CBR-dependent manner, either prevented the development of and/or attenuated established HIV-NP. Two clinical trials demonstrated greater efficacy of smoked cannabis over placebo in alleviating HIV-NP, whereas another clinical trial demonstrated that cannabidivarin, a cannabinoid that does not activate CBRs, did not reduce HIV-NP. The available preclinical results suggest that targeting the ECS for prevention and treatment of HIV-NP is a plausible therapeutic option. Clinical evidence shows that smoked cannabis alleviates HIV-NP. Further research is needed to find out if non-psychoactive drugs that target the ECS and are delivered by other routes than smoking could be useful as treatment options for HIV-NP.

Untapped endocannabinoid pharmacological targets: Pipe dream or pipeline?

It has been established that the endogenous cannabinoid (endocannabinoid) system plays key modulatory roles in a wide variety of pathological conditions. The endocannabinoid system comprises both cannabinoid receptors, their endogenous ligands including 2-arachidonoylglycerol (2-AG), N-arachidonylethanolamine (anandamide, AEA), and enzymes that regulate the synthesis and degradation of endogenous ligands which include diacylglycerol lipase alpha (DAGL-α), diacylglycerol lipase beta (DAGL-β), fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), α/β hydrolase domain 6 (ABHD6). As the endocannabinoid system exerts considerable involvement in the regulation of homeostasis and disease, much effort has been made towards understanding endocannabinoid-related mechanisms of action at cellular, physiological, and pathological levels as well as harnessing the various components of the endocannabinoid system to produce novel therapeutics. However, drug discovery efforts within the cannabinoid field have been slower than anticipated to reach satisfactory clinical endpoints and raises an important question into the validity of developing novel ligands that therapeutically target the endocannabinoid system. To answer this, we will first examine evidence that supports the existence of an endocannabinoid system role within inflammatory diseases, neurodegeneration, pain, substance use disorders, mood disorders, as well as metabolic diseases. Next, this review will discuss recent clinical studies, within the last 5 years, of cannabinoid compounds in context to these diseases. We will also address some of the challenges and considerations within the cannabinoid field that may be important in the advancement of therapeutics into the clinic.

Role of the endocannabinoid system in a mouse model of Fragile X undergoing neuropathic pain

BACKGROUND

Neuropathic pain is a complex condition characterized by sensory, cognitive and affective symptoms that magnify the perception of pain. The underlying pathogenic mechanisms are largely unknown and there is an urgent need for the development of novel medications. The endocannabinoid system modulates pain perception and drugs targeting the cannabinoid receptor type 2 (CB2) devoid of psychoactive side effects could emerge as novel analgesics. An interesting model to evaluate the mechanisms underlying resistance to pain is the fragile X mental retardation protein knockout mouse (Fmr1KO), a model of fragile X syndrome that exhibits nociceptive deficits and fails to develop neuropathic pain.

METHODS

A partial sciatic nerve ligation was performed to wild-type (WT) and Fmr1KO mice having (HzCB2 and Fmr1KO-HzCB2, respectively) or not (WT and Fmr1KO mice) a partial deletion of CB2 to investigate the participation of the endocannabinoid system on the pain-resistant phenotype of Fmr1KO mice.

RESULTS

Nerve injury induced canonical hypersensitivity in WT and HzCB2 mice, whereas this increased pain sensitivity was absent in Fmr1KO mice. Interestingly, Fmr1KO mice partially lacking CB2 lost this protection against neuropathic pain. Similarly, pain-induced depressive-like behaviour was observed in WT, HzCB2 and Fmr1KO-HzCB2 mice, but not in Fmr1KO littermates. Nerve injury evoked different alterations in WT and Fmr1KO mice at spinal and supra-spinal levels that correlated with these nociceptive and emotional alterations.

CONCLUSIONS

This work shows that CB2 is necessary for the protection against neuropathic pain observed in Fmr1KO mice, raising the interest in targeting this receptor for the treatment of neuropathic pain.

SIGNIFICANCE

Neuropathic pain is a complex chronic pain condition and current treatments are limited by the lack of efficacy and the incidence of important side effects. Our findings show that the pain-resistant phenotype of Fmr1KO mice against nociceptive and emotional manifestations triggered by persistent nerve damage requires the participation of the cannabinoid receptor CB2, raising the interest in targeting this receptor for neuropathic pain treatment. Additional multidisciplinary studies more closely related to human pain experience should be conducted to explore the potential use of cannabinoids as adequate analgesic tools.