Modulating the endocannabinoid pathway as treatment for peripheral neuropathic pain: a selected review of preclinical studies.

“Chemotherapy-induced neuropathic pain is a distressing and commonly occurring side effect of many commonly used chemotherapeutic agents, which in some cases may prevent cancer patients from being able to complete their treatment.

Cannabinoid based therapies have the potential to manage or even prevent pain associated with this syndrome.

Pre-clinical animal studies that investigate the modulation of the endocannabinoid system (endogenous cannabinoid pathway) are being conducted to better understand the mechanisms behind this phenomenon.

Five recent pre-clinical studies identified from Medline published between 2013 and 2016 were selected for review. All studies evaluated the effect of small-molecule agonists or antagonists on components of the endocannabinoid system in rats or mice, using cisplatin or paclitax-el-induced allodynia as a model of chemotherapy-induced neuropathic pain. Activation of the cannabinoid receptor-2 (CB-2) receptor by AM1710 blocked paclitaxel-induced mechanical and cold allodynia in one study.

Four studies investigating the activation of both cannabinoid receptor-1 (CB-1) and CB-2 receptors by dual-agonists (WIN55,21 and CP55,940), or by the introduction of inhibitors of endocannabinoid metabolisers (URB597, URB937, JZL184, and SA-57) showed reduction of chemotherapy-induced al-lodynia. In addition, their results suggest that anti-allodynic effects may also be mediated by additional receptors, including TRPV1 and 5-hydroxytryptamine (5-HT1A).

Pre-clinical studies demon-strate that the activation of endocannabinoid CB-1 or CB-2 receptors produces physiological effects in animal models, namely the reduction of chemotherapy-induced allodynia. These studies also provide in-sight into the biological mechanism behind the therapeutic utility of cannabis compounds in managing chemotherapy-induced neuropathic pain, and provide a basis for the conduct of future clinical studies in patients of this population.”

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Dronabinol Is a Safe Long-Term Treatment Option for Neuropathic Pain Patients.

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“Treatment of neuropathic pain (NP) symptoms associated with multiple sclerosis (MS) is frequently insufficient. Yet, cannabis is still rarely offered for treatment of pain. This clinical trial aimed at showing the positive benefit-risk ratio of dronabinol. Two hundred forty MS patients with central NP entered a 16-weeks placebo-controlled phase-III study followed by a 32-weeks open-label period. One hundred patients continued therapy for overall up to 119 weeks. Primary endpoint was change of pain intensity on the 11-point Numerical Rating Scale over a 16-weeks treatment period. Safety was assessed on the basis of adverse reactions (ARs), signs of dependency and abuse. Pain intensity during 16-weeks dronabinol and placebo treatment was reduced by 1.92 and 1.81 points without significant difference in between (p = 0.676). Although the proportion of patients with ARs was higher under dronabinol compared to placebo (50.0 vs. 25.9%), it decreased during long-term use of dronabinol (26%). No signs of drug abuse and only one possible case of dependency occurred. The trial results demonstrate that dronabinol is a safe long-term treatment option.” https://www.ncbi.nlm.nih.gov/pubmed/29073592

“Overall, this trial demonstrated the long-lasting therapeutic potential, the good tolerability and favourable safety profile of dronabinol – especially in terms of drug abuse and dependency. Based on the presented results, there is no special focus on the harm caused by dronabinol treatment. Although the statistical proof of efficacy for dronabinol versus placebo treatment is pending, physicians should consider the potential benefits of the multifactorial effects of dronabinol.” https://www.karger.com/Article/FullText/481089

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Medical cannabis for the treatment of chronic pain and other disorders: misconceptions and facts.

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“Recently, many countries have enacted new cannabis policies, including decriminalization of cannabis possession, medical cannabis legalization, and legalization of recreational cannabis.  In this context, patients and their physicians have had an increasing number of conversations about the risks and benefits of cannabis.  While cannabis and cannabinoids continue to be evaluated as pharmacotherapy for medical conditions, currently, the best evidence exists for the following medical conditions: chronic pain, neuropathic pain, and spasticity resulting from multiple sclerosis.  We also reviewed the current state of evidence for cannabis and cannabinoids for a number of other medical conditions while addressing the potential acute and chronic effects of cannabis use, which are issues that physicians must consider before making an official recommendation on the use of medical cannabis to a patient.  As patient requests for medical cannabis increase, physicians must become knowledgeable on the science of medical cannabis and open to a discussion about why the patient feels that medical cannabis may be helpful to them.”

https://www.ncbi.nlm.nih.gov/pubmed/29067992

http://pamw.pl/en/issue/article/29067992

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Efficacy, tolerability and safety of cannabis-based medicines for chronic pain management – An overview of systematic reviews.

European Journal of Pain

“Medicinal cannabis has already entered mainstream medicine in some countries.

Cannabis-based medicines undoubtedly enrich the possibilities of drug treatment of chronic pain conditions.

It remains the responsibility of the health care community to continue to pursue rigorous study of cannabis-based medicines to provide evidence that meets the standard of 21st century clinical care.”

https://www.ncbi.nlm.nih.gov/pubmed/29034533

http://onlinelibrary.wiley.com/doi/10.1002/ejp.1118/abstract

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Efficacy of Cannabis-Based Medicines for Pain Management: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

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“The management of chronic pain is a complex challenge worldwide. Cannabis-based medicines (CBMs) have proven to be efficient in reducing chronic pain, although the topic remains highly controversial in this field.

OBJECTIVES:

This study’s aim is to conduct a conclusive review and meta-analysis, which incorporates all randomized controlled trials (RCTs) in order to update clinicians’ and researchers’ knowledge regarding the efficacy and adverse events (AEs) of CBMs for chronic and postoperative pain treatment.

CONCLUSIONS:

The current systematic review suggests that CBMs might be effective for chronic pain treatment, based on limited evidence, primarily for neuropathic pain (NP) patients. Additionally, GI AEs occurred more frequently when CBMs were administered via oral/oromucosal routes than by inhalation.”

https://www.ncbi.nlm.nih.gov/pubmed/28934780

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Activation of dorsal horn cannabinoid CB2 receptor suppresses the expression of P2Y12 and P2Y13 receptors in neuropathic pain rats.

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“More evidence suggests that dorsal spinal cord microglia is an important site contributing to CB2 receptor-mediated analgesia. The upregulation of P2Y12 and P2Y13 purinoceptors in spinal dorsal horn microglia is involved in the development of pain behavior caused by peripheral nerve injury. However, it is not known whether the expression of P2Y12 and P2Y13 receptors at spinal dorsal horn will be influenced after CB2 receptor activation in neuropathic pain rats. Chronic constriction injury (CCI) and intrathecal ADPbetaS injection were performed in rats to induce neuropathic pain.

In CCI- and ADPbetaS-treated rats, AM1241 pretreatment could efficiently activate CB2 receptor, while inhibiting p38MAPK and NF-kappaB activation in the dorsal spinal cord. CB2 receptor stimulation decreased P2Y13 receptor expression via p38MAPK/NF-kappaB signaling. On the other hand, CB2 receptor activation decreased P2Y12 receptor expression via p38MAPK-independent NF-kappaB signaling pathway.”

https://www.ncbi.nlm.nih.gov/pubmed/28899427

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Attenuation of early phase inflammation by cannabidiol prevents pain and nerve damage in rat osteoarthritis.

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“Osteoarthritis (OA) is a multifactorial joint disease, which includes joint degeneration, intermittent inflammation, and peripheral neuropathy. Cannabidiol (CBD) is a non-euphoria producing constituent of cannabis that has the potential to relieve pain.

The aim of this study was to determine if CBD is anti-nociceptive in OA, and whether inhibition of inflammation by CBD could prevent the development of OA pain and joint neuropathy.

The therapeutic and prophylactic effects of peripheral CBD (100-300μg) were assessed. In end stage OA, CBD dose-dependently decreased joint afferent firing rate, and increased withdrawal threshold and weight bearing (p<0.0001; n=8). Acute, transient joint inflammation was reduced by local CBD treatment (p<0.0001; n=6). Prophylactic administration of CBD prevented the development of MIA-induced joint pain at later time points (p<0.0001; n=8), and was also found to be neuroprotective (p<0.05; n=6-8).

The data presented here indicate that local administration of CBD blocked OA pain. Prophylactic CBD treatment prevented the later development of pain and nerve damage in these OA joints.

These findings suggest that CBD may be a safe, useful therapeutic for treating OA joint neuropathic pain.”

https://www.ncbi.nlm.nih.gov/pubmed/28885454             https://insights.ovid.com/crossref?an=00006396-900000000-99152

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Cannabis constituent synergy in a mouse neuropathic pain model.

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“Cannabis and its psychoactive constituent Δ9-tetrahydrocannabinol (THC) have efficacy against neuropathic pain however, this is hampered by their side-effects. It has been suggested that co-administration with another major constituent cannabidiol (CBD) might enhance the analgesic actions of THC and minimise its deleterious side-effects.

We examined the basis for this phytocannabinoid interaction in a mouse chronic constriction injury (CCI) model of neuropathic pain. Acute systemic administration of THC dose-dependently reduced CCI-induced mechanical and cold allodynia, but also produced motor incoordination, catalepsy and sedation. CBD produced a lesser dose-dependent reduction in allodynia, but did not produce the cannabinoid side-effects. When co-administered in a fixed ratio, THC and CBD produced a biphasic dose-dependent reduction in allodynia. At low doses, the THC:CBD combination displayed a 200-fold increase in anti-allodynic potency, but had lower efficacy compared to that predicted for an additive drug interaction. By contrast, high THC:CBD doses had lower potency, but greater anti-allodynic efficacy compared to that predicted for an additive interaction. Only the high dose THC:CBD anti-allodynia was associated with cannabinoid side-effects and these were similar to those of THC alone. Unlike THC, the low dose THC:CBD anti-allodynia was not cannabinoid receptor mediated.

These findings demonstrate that CBD synergistically enhances the pain relieving actions of THC in an animal neuropathic pain model, but has little impact on the THC-induced side-effects. This suggests that low dose THC:CBD combination treatment has potential in the treatment of neuropathic pain.”

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Managing neuropathic pain in multiple sclerosis: Pharmacological interventions.

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“Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). Of the plethora of motor and sensory disturbances experienced by sufferers, neuropathic pain is a highly prevalent and debilitating symptom, and at present remains extremely difficult to treat. Common forms of neuropathic pain seen in MS patients include central neuropathic pain, Lhermitte’s phenomenon and trigeminal neuralgia, which are all speculated to arise from specific patterns of lesion formation.

OBJECTIVE:

Efficacious pharmacological interventions for the treatment of neuropathic pain associated with MS are lacking, and have been largely informed by drug trials in peripheral neuropathies and spinal cord injury.

METHOD/RESULTS:

Neuropathic pain in MS is inadequately relieved by conventional analgesics, and first-line therapies are generally comprised of anti-depressive and anti-convulsive drugs. A range of alternatives have been proposed and tested with variable success, including cannabinoids and certain opioid analgesics. Animals with experimental autoimmune encephalomyelitis (EAE), an autoimmune model of MS, also exhibit neuropathic pain symptoms.

CONCLUSION:

Studies aimed at understanding the mechanisms underlying EAE-induced neuropathic pain and investigating the efficacy of novel pharmacological interventions at the animal level offer an exciting area of future research, and may inform future therapeutic options for MS-associated neuropathic pain.”

https://www.ncbi.nlm.nih.gov/pubmed/28875858

 

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

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“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 (ie, 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.

Here, we examine the preclinical and clinical evidence of various endocannabinoid system targets as potential therapeutic strategies for inflammatory and neuropathic pain conditions.”

https://www.ncbi.nlm.nih.gov/pubmed/28857069

https://www.nature.com/npp/journal/vaop/naam/abs/npp2017204a.html

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