Cannabinoid Analgesia as a Potential New Therapeutic Option in the Treatment of Chronic Pain

Binding Modes and Selectivity of Cannabinoid 1 (CB1) and Cannabinoid 2 (CB2) Receptor Ligands

The cannabinoid (CB) receptors (CB₁R and CB₂R) represent a promising therapeutic target for several indications such as nociception and obesity. The ligands with nonselectivity can be traced to the high similarity in the binding sites of both cannabinoid receptors. Therefore, the need for selectivity, potency, and G-protein coupling bias has further complicated the design of desired compounds. The bias of currently studied cannabinoid agonists is seldom investigated, and agonists that do exhibit bias are typically nonselective. However, certain long-chain endocannabinoids represent a class of selective and potent CB₁R agonists. The binding mode for this class of compounds has remained elusive, limiting the implementation of its binding features to currently studied agonists. Hence, in the present study, the binding poses for these long-chain cannabinoids, along with other interesting ligands, with the receptors have been determined, by using a combination of molecular docking and molecular dynamics (MD) simulations along with molecular mechanics-Poisson-Boltzmann surface area (MM-PBSA) binding free energy calculations. The binding poses for the long-chain cannabinoids implicate that a site surrounded by the transmembrane (TM)2, TM7, and extracellular loop (ECL)2 is vital for providing the long-chain ligands with the selectivity for CB₁R, especially I267 of CB₁R (corresponding to L182 of CB₂R). Based on the obtained binding modes, the calculated relative binding free energies and selectivity are all in good agreement with the corresponding experimental data, suggesting that the determined binding poses are reasonable. The computational strategy used in this study may also prove fruitful in applications with other GPCRs or membrane-bound proteins.

Cannabinoid Receptors and Their Relationship With Chronic Pain: A Narrative Review

The burden of chronic pain has affected many individuals leading to distress and discomfort, alongside numerous side effects with conventional therapeutic approaches. Cannabinoid receptors are naturally found in the human body and have long been an interest in antinociception. These include CB1 and CB2 receptors, which are promising candidates for the treatment of chronic inflammatory pain. The mechanism of action of the receptors and how they approach pain control in inflammatory conditions show that it can be an adjunctive approach towards controlling these symptoms. Numerous studies have shown how the targeted approach towards these receptors has activated them promoting a release in cytokines, all leading to anti-inflammatory effects and immune system regulation. Cannabinoid activation of glycine and gamma-aminobutyric acid (GABA) models also showed efficacy in pain management. Chronic conditions such as osteoarthritis were shown to also benefit from this considerable treatment. However, it is unclear how the cannabinoid system works in relation with the pain pathway. Therefore, in this review we aim to analyse the role of the cannabinoid system in chronic inflammatory pain.

Herbal Preparations of Medical Cannabis: A Vademecum for Prescribing Doctors

Cannabis has been used for centuries for therapeutic purposes. In the last century, the plant was demonized due to its high abuse liability and supposedly insufficient health benefits. However, recent decriminalization policies and new scientific evidence have increased the interest in cannabis therapeutic potential of cannabis and paved the way for the release of marketing authorizations for cannabis-based products. Although several synthetic and standardized products are currently available on the market, patients’ preferences lean towards herbal preparations, because they are easy to handle and self-administer. A literature search was conducted on multidisciplinary research databases and international agencies or institutional websites. Despite the growing popularity of medical cannabis, little data is available on the chemical composition and preparation methods of medical cannabis extracts. The authors hereby report the most common cannabis preparations, presenting their medical indications, routes of administration and recommended dosages. A practical and helpful guide for prescribing doctors is provided, including suggested posology, titration strategies and cannabinoid amounts in herbal preparations obtained from different sources of medical cannabis.

Antinociceptive and Abuse Potential Effects of Cannabinoid/Opioid Combinations in a Chronic Pain Model in Rats

Chronic pain is a persistent and debilitating health problem. Although the use of analgesics such as opioids is useful in mitigating pain, their prolonged use is associated with unwanted effects including abuse liability. This study assesses the antinociceptive effect of combining subtherapeutic doses of two opioids (morphine or tramadol) with the synthetic cannabinoid CP55940 (2-[(1R,2R,5R)-5-hydroxy-2-(3-hydroxypropyl)cyclohexyl]-5-(2-methyloctan -2-yl)phenol). It also evaluates the associated adverse effects of these drugs and combinations. Adult male rats were injected with intraplantar complete Freund’s adjuvant (CFA) to produce mechanical allodyia. Antinociceptive effect of morphine, tramadol, the synthetic cannabinoid CP55940, or their combinations was evaluated three to nine days post-CFA injections. Intracranial self-stimulation (ICSS) was utilized to evaluate the abuse liability of these drugs or their combinations. All drugs alone produced a dose-dependent antinociceptive effect. Morphine produced minimal effect on ICSS, but both tramadol and CP55940 produced dose-dependent depression of ICSS. Morphine at a dose of 0.32 mg/kg enhanced the antinociceptive effects of CP55940, in that, CP55940 produced antinociception at a lower dose (0.1 mg/kg) when compared to the vehicle. The aforementioned combinations did not change CP55940-induced depression of ICSS. On the other hand, tramadol failed to enhance the antinociceptive effect of CP55940. Our data suggest that combining CP55940 with morphine, but not tramadol, shows a better antinociceptive profile with no additional risk of abuse liability, which represents a potential pain management approach.

The effect of cannabis laws on opioid use

BACKGROUND

Many Americans rely on opioids at varying dosages to help ameliorate their suffering. However, empirical evidence is mounting that opioids are ineffective at controlling non-cancer related chronic pain, and many argue the strategies meant to relieve patient suffering are contributing to the growing opioid epidemic. Concurrently, several states now allow the use of medical cannabis to treat a variety of medical conditions, including chronic pain. Needing more exploration is the impact of cannabis laws on general opioid reliance and whether chronic pain sufferers are opting to use cannabis medicinally instead of opioids.

METHODS

This study investigates the effect of Medical Marijuana Laws (MML)s on opioid use and misuse controlling for a number of relevant factors using data from several years of the National Survey on Drug Use and Health and multivariate logistic regression and longitudinal analysis strategies.

RESULTS

Results provide evidence that MMLs may be effective at reducing opioid reliance as survey respondents living in states with medical cannabis legislation are much less apt to report using opioid analgesics than people living in states without such laws, net other factors. Results further indicate that the presence of medicinal cannabis legislation appears to have no influence over opioid misuse.

CONCLUSION

MMLs may ultimately serve to attenuate the consequences of opioid overreliance.

A Review of Adjunctive Therapies for Burn Injury Pain During the Opioid Crisis

Opioids are the mainstay of pain management after burn injury. The United States currently faces an epidemic of opioid overuse and abuse, while simultaneously experiencing a nationwide shortage of intravenous narcotics. Adjunctive pain management therapies must be sought and utilized to reduce the use of opioids in burn care to prevent the long-term negative effects of these medications and to minimize the dependence on opioids for analgesia. The purpose of this review was to identify literature on adjunctive pain management therapies that have been demonstrated to reduce pain severity or opioid consumption in adult burn patients. Three databases were searched for prospective studies, randomized controlled trials, and systematic reviews that evaluated adjunctive pain management strategies published between 2008 and 2019 in adult burn patients. Forty-six studies were analyzed, including 24 randomized controlled trials, six crossover trials, and 10 systematic reviews. Various adjunctive pain management therapies showed statistically significant reduction in pain severity. Only one randomized controlled trial on music therapy for acute background pain showed a reduction in opioid use. One cohort study on hypnosis demonstrated reduced opioid use compared with historical controls. We recommend the development of individualized analgesic regimens with the incorporation of adjunctive therapies in order to improve burn pain management in the midst of an abuse crisis and concomitant national opioid shortage.

Drug-Herb Interactions in the Elderly Patient with IBD: a Growing Concern

OPINION STATEMENT

Inflammatory bowel disease (IBD), which includes conditions such as Crohn's disease and ulcerative colitis, is becoming more prevalent with the elderly being the fastest growing group. Parallel to this, there is an increasing interest in the use of complementary and alternative medicine (CAM). Nearly half of patients with IBD have used CAM at one time. The elderly patients, however, are burdened by comorbid conditions, polypharmacy, and altered functional status. With increasing use of complementary and alternative medicine in our elderly patients with IBD, it is vital for the provider to provide counsel on drug-herb potential interactions. CAM includes herbal products, diet, dietary supplements, acupuncture, and prayer. In this paper, we will review common CAM, specifically herbs, that are used in patients with IBD including the herb background, suggested use, evidence in IBD, and most importantly, potential interactions with IBD medications used in elderly patients. Most important evidence-based adverse events and drug-herb interactions are summarized. The herbs discussed include Triticum aestivum (wheat grass), Andrographis paniculata (chiretta), Boswellia serrata, tormentil, bilberry, curcumin (turmeric), Plantago ovata (blond psyllium), Oenothera biennis (evening primrose oil), germinated barley foodstuff, an herbal preparation of myrrh, chamomile and coffee extract, chios mastic gum, wormwood (absinthe, thujone), Cannabis sativa (marijuana, THC), tripterygium wilfordii (thunder god vine), Ulmus rubra (slippery elm bark), trigonella foenugraecum (fenugreek), Dioscorea mexicana (wild yam), Harpagophytum procumbens (devil's claw), ginger, cinnamon, licorice, and peppermint.

Are cannabinoids an effective treatment for chronic non-cancer pain?

The use of cannabinoids has been proposed as an analgesic for different painful conditions, especially for chronic pain refractory to usual treatment. However, its real efficacy and safety remains controversial. We sought to determine whether cannabinoids are an effective treatment for chronic non-cancer pain. To answer this question, we used Epistemonikos, the largest database of systematic reviews in health, which is maintained by screening multiple information sources, including MEDLINE, EMBASE, Cochrane, among others. We identified 37 systematic reviews including 41 studies overall, of which 32 were randomized trials relevant for the question of interest. We extracted data from the systematic reviews, reanalyzed data of primary studies, conducted a meta-analysis and generated a summary of findings table using the GRADE approach. We concluded it is not clear whether cannabinoids decrease pain in patients with chronic non-cancer pain because the certainty of available evidence is very low. On the other hand, they are associated with significant adverse effects.

Cannabinoids for neuropathic pain

Treatment options for neuropathic pain have limited efficacy and use is fraught with dose-limiting adverse effects. The endocannabinoid system has been elucidated over the last several years, demonstrating a significant interface with pain homeostasis. Exogenous cannabinoids have been demonstrated to be effective in a range of experimental neuropathic pain models, and there is mounting evidence for therapeutic use in human neuropathic pain conditions. This article reviews the history, pharmacologic development, clinical trials results, and the future potential of nonsmoked, orally bioavailable, nonpsychoactive cannabinoids in the management of neuropathic pain.

Inhibition of anandamide hydrolysis attenuates nociceptor sensitization in a murine model of chemotherapy-induced peripheral neuropathy

Painful neuropathy frequently develops as a consequence of commonly used chemotherapy agents for cancer treatment and is often a dose-limiting side effect. Currently available analgesic treatments are often ineffective on pain induced by neurotoxicity. Although peripheral administration of cannabinoids, endocannabinoids, and inhibitors of endocannabinoid hydrolysis has been effective in reducing hyperalgesia in models of peripheral neuropathy, including chemotherapy-induced peripheral neuropathy (CIPN), few studies have examined cannabinoid effects on responses of nociceptors in vivo. In this study we determined whether inhibition of fatty acid amide hydrolase (FAAH), which slows the breakdown of the endocannabinoid anandamide (AEA), reduced sensitization of nociceptors produced by chemotherapy. Over the course of a week of daily treatments, mice treated with the platinum-based chemotherapy agent cisplatin developed robust mechanical allodynia that coincided with sensitization of cutaneous C-fiber nociceptors as indicated by the development of spontaneous activity and increased responses to mechanical stimulation. Administration of the FAAH inhibitor URB597 into the receptive field of sensitized C-fiber nociceptors decreased spontaneous activity, increased mechanical response thresholds, and decreased evoked responses to mechanical stimuli. Cotreatment with CB1 (AM281) or CB2 (AM630) receptor antagonists showed that the effect of URB597 was mediated primarily by CB1 receptors. These changes following URB597 were associated with an increase in the endocannabinoid anandamide in the skin. Our results suggest that enhanced signaling in the peripheral endocannabinoid system could be utilized to reduce nociceptor sensitization and pain associated with CIPN.

Use of a synthetic cannabinoid in a correctional population for posttraumatic stress disorder-related insomnia and nightmares, chronic pain, harm reduction, and other indications: a retrospective evaluation

Nabilone is a synthetic cannabinoid that has shown promise for the treatment of posttraumatic stress disorder (PTSD)-related insomnia and nightmares as well as efficacy in the management of chronic pain. It has also been proposed for harm reduction in cannabis dependence. Its effectiveness for management of concurrent disorders in seriously mentally ill correctional populations has not been evaluated. This retrospective study of 104 male inmates with serious mental illness prescribed nabilone analyzes the indications, efficacy, and safety of its use. Medications discontinued with the initiation of nabilone were also reviewed. The results showed nabilone targeting a mean of 3.5 indications per patient, thus likely reducing polypharmacy risk. The mean final dosage was 4.0 mg. Results indicated significant improvement in PTSD-associated insomnia, nightmares, PTSD symptoms, and Global Assessment of Functioning and subjective improvement in chronic pain. Medications associated with greater risk for adverse effects or abuse than nabilone were often able to be discontinued with the initiation of nabilone, most often antipsychotics and sedative/hypnotics. There was no evidence of abuse within this high-risk population or reduction of efficacy when nabilone was given in powder form with water rather than as a capsule. This study supports the promise of nabilone as a safe, effective treatment for concurrent disorders in seriously mentally ill correctional populations. Prospective, randomized controlled trials are required to confirm our preliminary results. Follow-up in the community will be required to confirm effectiveness in harm reduction.

Inhibition of voltage-gated Na⁺ channels by the synthetic cannabinoid ajulemic acid

BACKGROUND

The synthetic cannabinoid ajulemic acid has been demonstrated to alleviate pain in patients suffering from chronic neuropathic pain. Cannabinoids interact with several molecules within the pain circuit, including a potent inhibition of voltage-gated sodium channels. In this study, we closely characterized this property on neuronal and nonneuronal sodium channels.

METHODS

The inhibition of sodium inward currents by ajulemic acid was studied in vitro. Human embryonic kidney 293t cells were used as the expression system for Nav1.2, 1.3, 1.4, 1.5, 1.5N406K, 1.5F1760A, and 1.7; Nav1.8 was transiently expressed in ND7/23 cells. Nav1.2, Nav1.3, and Nav 1.8 were from rats, and Nav1.4, Nav1.5, and Nav1.7 were of human origin. Sodium currents were analyzed by means of the whole cell patch-clamp technique. The investigated concentrations of ajulemic acid were 0.1, 0.3, 1, 3, 10, and 30 μmol/L.

RESULTS

Ajulemic acid reversibly and concentration-dependently inhibited all voltage-gated sodium channel (Nav) isoforms investigated in this study, including Nav1.2, 1.3, 1.4, 1.5, 1.7, and 1.8. Tonic block of resting channels yielded half-maximal inhibitory concentration values between 2 and 9 μmol/L and was strongly enhanced on inactivated channels, suggesting state-dependent inhibition by ajulemic acid. Tonic block did not differ significantly when comparing Nav1.2 and Nav1.3, Nav1.4 and Nav1.5, and Nav1.7 and Nav1.8. Statistical analysis of other combinations of subunits (e.g., Nav1.2 and Nav1.4) by analysis of variance yielded a significant difference in block. Although we did not observe any relevant use-dependent block, ajulemic acid induced a strong hyperpolarizing shift of the voltage dependency of fast inactivation and modest shift of slow inactivation. The local anesthetic-insensitive Nav1.5 constructs N406K and F1760A displayed a preserved sensitivity to block by ajulemic acid. Finally, we found that low concentrations of ajulemic acid efficiently inhibited Navβ4 peptide-mediated resurgent currents in Nav1.5.

CONCLUSIONS

Our data suggest that block of sodium channels can be a relevant mechanism by which ajulemic acid alleviates neuropathic pain. The potent inhibition of resurgent currents and the preserved block on local anesthetic-insensitive channels indicates that ajulemic acid interacts with a conserved but yet unknown site of sodium channels.

The endocannabinoid system, cannabinoids, and pain

The endocannabinoid system is involved in a host of homeostatic and physiologic functions, including modulation of pain and inflammation. The specific roles of currently identified endocannabinoids that act as ligands at endogenous cannabinoid receptors within the central nervous system (primarily but not exclusively CB 1 receptors) and in the periphery (primarily but not exclusively CB 2 receptors) are only partially elucidated, but they do exert an influence on nociception. Exogenous plant-based cannabinoids (phytocannabinoids) and chemically related compounds, like the terpenes, commonly found in many foods, have been found to exert significant analgesic effects in various chronic pain conditions. Currently, the use of Δ9-tetrahydrocannabinol is limited by its psychoactive effects and predominant delivery route (smoking), as well as regulatory or legal constraints. However, other phytocannabinoids in combination, especially cannabidiol and β-caryophyllene, delivered by the oral route appear to be promising candidates for the treatment of chronic pain due to their high safety and low adverse effects profiles. This review will provide the reader with the foundational basic and clinical science linking the endocannabinoid system and the phytocannabinoids with their potentially therapeutic role in the management of chronic pain.

Comparison of the analgesic effects of dronabinol and smoked marijuana in daily marijuana smokers

Recent studies have demonstrated the therapeutic potential of cannabinoids to treat pain, yet none have compared the analgesic effectiveness of smoked marijuana to orally administered Δ(9)-tetrahydrocannabinol (THC; dronabinol). This randomized, placebo-controlled, double-dummy, double-blind study compared the magnitude and duration of analgesic effects of smoked marijuana and dronabinol under well-controlled conditions using a validated experimental model of pain. Healthy male (N=15) and female (N=15) daily marijuana smokers participated in this outpatient study comparing the analgesic, subjective, and physiological effects of marijuana (0.00, 1.98, or 3.56% THC) to dronabinol (0, 10, or 20 mg). Pain response was assessed using the cold-pressor test (CPT): participants immersed their left hand in cold water (4 °C), and the time to report pain (pain sensitivity) and withdraw the hand from the water (pain tolerance) were recorded. Subjective pain and drug effect ratings were also measured as well as cardiovascular effects. Compared with placebo, marijuana and dronabinol decreased pain sensitivity (3.56%; 20 mg), increased pain tolerance (1.98%; 20 mg), and decreased subjective ratings of pain intensity (1.98, 3.56%; 20 mg). The magnitude of peak change in pain sensitivity and tolerance did not differ between marijuana and dronabinol, although dronabinol produced analgesia that was of a longer duration. Marijuana (1.98, 3.56%) and dronabinol (20 mg) also increased abuse-related subjective ratings relative to placebo; these ratings were greater with marijuana. These data indicate that under controlled conditions, marijuana and dronabinol decreased pain, with dronabinol producing longer-lasting decreases in pain sensitivity and lower ratings of abuse-related subjective effects than marijuana.

Selective cannabinoid receptor type 2 (CB2) agonists: optimization of a series of purines leading to the identification of a clinical candidate for the treatment of osteoarthritic pain

A focused screening strategy identified thienopyrimidine 12 as a cannabinoid receptor type 2 agonist (hCB2) with moderate selectivity over the hCB1 receptor. This initial hit suffered from poor in vitro metabolic stability and high in vivo clearance. Structure-activity relationships describe the optimization and modification to a new more polar series of purine CB2 agonists. Examples from this novel scaffold were found to be highly potent and fully efficacious agonists of the human CB2 receptor with excellent selectivity against CB1, often having no CB1 agonist activity at the highest concentration measured (>100 μM). Compound 26 is a centrally penetrant molecule which possesses good biopharmaceutical properties, is highly water-soluble, and demonstrates robust oral activity in rodent models of joint pain. In addition, the peripherally restricted molecule 22 also demonstrated significant efficacy in the same analgesic model of rodent inflammatory pain.

Levonantradol: asymmetric synthesis and structural analysis

The first asymmetric synthesis of a synthetic cannabinoid levonantradol was accomplished, and the 3-D solution structure of its core architecture was confirmed by NMR and computational methods.

N-Methyl-3-(tetrahydro-2H-pyran-4-yl)-2,3,4,9-tetrahydro-1H-carbazole-6-carboxamides as a novel class of cannabinoid receptors agonists with low CNS penetration

Cannabinoid CB(1) receptor agonists exhibit potent analgesic effects in rodents and humans, but their clinical utility as analgesic drugs is often limited by centrally mediated side effects. We report herein the preparation of N-methyl-3-(tetrahydro-2H-pyran-4-yl)-2,3,4,9-tetrahydro-1H-carbazole-6-carboxamides as a novel class of hCB(1)/hCB(2) dual agonists with attractive physicochemical properties. More specifically, (R)-N,9-dimethyl-N-(4-(methylamino)-4-oxobutyl)-3-(tetrahydro-2H-pyran-4-yl)-2,3,4,9-tetrahydro-1H-carbazole-6-carboxamide, displayed an extremely low level of CNS penetration (Rat Cbr/Cplasma=0.005 or 0.5%) and was devoid of CNS side effects during pharmaco-dynamic testing.

Cannabinoids suppress inflammatory and neuropathic pain by targeting α3 glycine receptors

Systemic and intrathecal administration of derivatives of a nonpsychoactive component of marijuana significantly suppresses chronic inflammatory and neuropathic pain, without causing analgesic tolerance, in several rodent models.

Certain types of nonpsychoactive cannabinoids can potentiate glycine receptors (GlyRs), an important target for nociceptive regulation at the spinal level. However, little is known about the potential and mechanism of glycinergic cannabinoids for chronic pain treatment. We report that systemic and intrathecal administration of cannabidiol (CBD), a major nonpsychoactive component of marijuana, and its modified derivatives significantly suppress chronic inflammatory and neuropathic pain without causing apparent analgesic tolerance in rodents. The cannabinoids significantly potentiate glycine currents in dorsal horn neurons in rat spinal cord slices. The analgesic potency of 11 structurally similar cannabinoids is positively correlated with cannabinoid potentiation of the α3 GlyRs. In contrast, the cannabinoid analgesia is neither correlated with their binding affinity for CB1 and CB2 receptors nor with their psychoactive side effects. NMR analysis reveals a direct interaction between CBD and S296 in the third transmembrane domain of purified α3 GlyR. The cannabinoid-induced analgesic effect is absent in mice lacking the α3 GlyRs. Our findings suggest that the α3 GlyRs mediate glycinergic cannabinoid-induced suppression of chronic pain. These cannabinoids may represent a novel class of therapeutic agents for the treatment of chronic pain and other diseases involving GlyR dysfunction.

γ-Carbolines: a novel class of cannabinoid agonists with high aqueous solubility and restricted CNS penetration

An oral, peripherally restricted CB1/CB2 agonist could provide an interesting approach to treat chronic pain by harnessing the analgesic properties of cannabinoids but without the well-known central side effects. γ-Carbolines are a novel class of potent mixed CB1/CB2 agonists characterized by attractive physicochemical properties including high aqueous solubility. Optimization of the series has led to the discovery of 29, which has oral activity in a rat inflammatory pain model and limited brain exposure at analgesic doses, consistent with a lower risk of CNS-mediated tolerability issues.

Functional role of cannabinoid receptors in urinary bladder

Cannabinoids, the active components of Cannabis sativa (maijuana), and their derivatives produce a wide spectrum of central and peripheral effects, some of which may have clinical applications. The discovery of specific cannabinoid receptors and a family of endogenous ligands of those receptors has attracted much attention to the general cannabinoid pharmacology. In recent years, studies on the functional role of cannabinoid receptors in bladder have been motivated by the therapeutic effects of cannabinoids on voiding dysfunction in multiple sclerosis patients. In this review, we shall summarize the literature on the expression of cannabinoid receptors in urinary bladder and the peripheral influence of locally and systemically administered cannabinoids in the bladder. The ongoing search for cannabinoid-based therapeutic strategies devoid of psychotropic effects can be complemented with local delivery into bladder by the intravesical route. A greater understanding of the role of the peripheral CB₁ and CB₂ receptor system in lower urinary tract is necessary to allow the development of new treatment for pelvic disorders.

The synthetic cannabinoid WIN 55212-2 differentially modulates thigmotaxis but not spatial learning in adolescent and adult animals

Unlike Δ(9)-THC, the synthetic compound WIN 55212-2 (WIN) is a full agonist of endogenous cannabinoid receptors. Previous work has shown Δ(9)-THC to affect adolescent and adult animals differently on numerous behavioral measures of spatial memory, anxiety, and locomotor activity. However, far less is known about the developmental and neurobehavioral effects of WIN. To address this, we assessed the effect of WIN (1mg/kg) on spatial learning in adolescent and adult rats using the Morris water maze. While all animals demonstrated decreased swim distance across days, WIN affected adolescents and adults differently. It improved performance in adolescents and resulted in a nearly significant performance decrement in adults. However, these effects were significantly related to thigmotaxis, which declined across days in the water maze testing protocol. WIN reduced thigmotaxis on days 1 and 2 (but not days 3-5) only in adolescents. The effect of age, treatment, and the age×treatment interaction was eliminated after controlling for thigmotaxis. These results indicate that WIN affects thigmotaxis rather than spatial reference memory. More importantly, these findings indicate a dissociation between the developmental effects of THC and the synthetic CB1 receptor agonist, WIN 55212-2. We suggest that the role of thigmotaxis be carefully evaluated in future neurodevelopmental studies of spatial learning, especially those investigating the endocannabinoid system.

Deciphering the mechanism(s) of action of natural products: analgesic peroxide oil as example

BACKGROUND

There are multiple reports of natural products having therapeutic effect. In an era of evidence-based medicine, clinical trials inform clinical decisions regarding use of the product, but prevailing preference is to identify and use a single 'active ingredient'. Yet, the clinical benefit of a natural product might derive from the fortuitous combination of its multiple components. Therefore, the elucidation of the mechanism(s) of action of natural products is important, but presents significant challenges. This article examines this issue using peroxide oil (essential oxygen oil) as an illustrative example.

OBJECTIVE

To review the published literature of a natural product in an effort to elucidate postulated mechanism(s) of action of a complex mixture.

METHODS

The clinical and preclinical literature was reviewed from the perspective of its contribution to elucidating a mechanism of analgesic action of a natural product.

RESULTS

Peroxide oil contains ingredients that are associated with analgesic mechanisms, such inhibition of lipid peroxidation and arachidonic acid metabolism and non-opioid, glibenclamide-sensitive receptor-mediated and K(ATP) -NO-cGMP channel pathways.

CONCLUSION

Although its exact mechanism remains unknown, peroxide oil provides an example of how a natural product can be evaluated for plausible mechanistic explanation of its purported therapeutic efficacy. Such an approach seems valuable, since, as in this case, the constituents appear to contribute in an additive or synergistic manner, something not possible with a single substance.

A systematic review of pharmacologic treatments of pain after spinal cord injury

OBJECTIVE

To conduct a systematic review of published research on the pharmacologic treatment of pain after spinal cord injury (SCI).

DATA SOURCES

MEDLINE, CINAHL, EMBASE, and PsycINFO databases were searched for articles published 1980 to June 2009 addressing the treatment of pain post SCI. Randomized controlled trials (RCTs) were assessed for methodologic quality using the Physiotherapy Evidence Database (PEDro) assessment scale, whereas non-RCTs were assessed by using the Downs and Black (D&B) evaluation tool. A level of evidence was assigned to each intervention by using a modified Sackett scale.

STUDY SELECTION

The review included RCTs and non-RCTs, which included prospective controlled trials, cohort, case series, case-control, pre-post studies, and post studies. Case studies were included only when there were no other studies found.

DATA EXTRACTION

Data extracted included the PEDro or D&B score, the type of study, a brief summary of intervention outcomes, the type of pain, the type of pain scale, and the study findings.

DATA SYNTHESIS

Articles selected for this particular review evaluated different interventions in the pharmacologic management of pain after SCI. Twenty-eight studies met inclusion criteria; there were 21 randomized controlled trials; of these, 19 had level 1 evidence. Treatments were divided into 5 categories: anticonvulsants, antidepressants, analgesics, cannabinoids, and antispasticity medications.

CONCLUSIONS

Most studies did not specify participants' types of pain, making it difficult to identify the type of pain being targeted by the treatment. Anticonvulsant and analgesic drugs had the highest levels of evidence and were the drugs most often studied. Gabapentin and pregabalin had strong evidence (5 level 1 RCTs) for effectiveness in treating post-SCI neuropathic pain as did intravenous analgesics (lidocaine, ketamine, and morphine), but the latter only had short-term benefits. Tricyclic antidepressants only showed benefit for neuropathic pain in depressed persons. Intrathecal baclofen reduced musculoskeletal pain associated with spasticity; however, there was conflicting evidence for the reduction in neuropathic pain. Studies assessing the effectiveness of opioids were limited and revealed only small benefits. Cannabinoids showed conflicting evidence in improving spasticity-related pain. Clonidine and morphine when given together had a significant synergistic neuropathic pain-relieving effect.

Delta9-tetrahydrocannabinol is a full agonist at CB1 receptors on GABA neuron axon terminals in the hippocampus

Marijuana impairs learning and memory through actions of its psychoactive constituent, delta-9-tetrahydrocannabinol (Delta(9)-THC), in the hippocampus, through activation of cannabinoid CB1 receptors (CB1R). CB1Rs are found on glutamate and GABA neuron axon terminals in the hippocampus where they control neurotransmitter release. Previous studies suggest that Delta(9)-THC is a partial agonist of CB1Rs on glutamate axon terminals in the hippocampus, whereas its effects on GABA terminals have not been described. Using whole-cell electrophysiology in brain slices from C57BL6/J mice, we examined Delta(9)-THC effects on synaptic GABA IPSCs and postsynaptic GABA currents elicited by laser-induced photo-uncaging (photolysis) of alpha-carboxy-2-nitrobenzyl (CNB) caged GABA. Despite robust inhibition of synaptic IPSCs in wildtype mice by the full synthetic agonist WIN55,212-2, using a Tween-80 and DMSO vehicle, Delta(9)-THC had no effects on IPSCs in this, or in a low concentration of another vehicle, randomly-methylated beta-cyclodextrin (RAMEB, 0.023%). However, IPSCs were inhibited by Delta(9)-THC in 0.1% RAMEB, but not in neurons from CB1R knockout mice. Whereas Delta(9)-THC did not affect photolysis-evoked GABA currents, these responses were prolonged by a GABA uptake inhibitor. Concentration-response curves revealed that the maximal effects of Delta(9)-THC and WIN55,212-2 were similar, indicating that Delta(9)-THC is a full agonist at CB1Rs on GABA axon terminals. These results suggest that Delta(9)-THC inhibits GABA release, but does not directly alter GABA(A) receptors or GABA uptake in the hippocampus. Furthermore, full agonist effects of Delta(9)-THC on IPSCs likely result from a much higher expression of CB1Rs on GABA versus glutamate axon terminals in the hippocampus.

The endocannabinoid system and pain

The therapeutic potential of cannabinoids has been the topic of extensive investigation following the discovery of cannabinoid receptors and their endogenous ligands. Cannabinoid receptors and their endogenous ligands are present at supraspinal, spinal and peripheral levels. Cannabinoids suppress behavioral responses to noxious stimulation and suppress nociceptive processing through activation of cannabinoid CB(1) and CB(2) receptor subtypes. Endocannabinoids, the brain's own cannabis-like substances, share the same molecular target as Delta(9)-tetrahydrocannabinol, the main psychoactive component in cannabis. Endocannabinoids serve as synaptic circuit breakers and regulate multiple physiological and pathological conditions, e.g. regulation of food intake, immunomodulation, inflammation, analgesia, cancer, addictive behavior, epilepsy and others. This review will focus on uncovering the roles of anandamide and 2-arachidonoylglycerol, the two best characterized endocannabinoids identified to date, in controlling nociceptive responding. The roles of anandamide and 2-arachidonoylglycerol, released under physiological conditions, in modulating nociceptive responding at different levels of the neuraxis will be emphasized in this review. Effects of modulation of endocannabinoid levels through inhibition of endocannabinoid hydrolysis and uptake is also compared with effects of exogenous administration of synthetic endocannabinoids in acute, inflammatory and neuropathic pain models. Finally, the therapeutic potential of the endocannabinoid signaling system is discussed in the context of identifying novel pharmacotherapies for the treatment of pain.

Translational pain research: achievements and challenges

The achievements in both preclinical and clinical pain research over the past 4 decades have led to significant progress in clinical pain management. However, pain research still faces enormous challenges and there remain many obstacles in the treatment of clinical pain, particularly chronic pain. Translational pain research needs to involve a number of important areas including: 1) bridging the gap between pain research and clinical pain management; 2) developing objective pain-assessment tools; 3) analyzing current theories of pain mechanisms and their relevance to clinical pain; 4) exploring new tools for both preclinical and clinical pain research; and 5) coordinating research efforts among basic scientists, clinical investigators, and pain-medicine practitioners. These issues are discussed in this article in light of the achievements and challenges of translational pain research.

PERSPECTIVE

The subjective nature of clinical pain calls for innovative research approaches. As translational pain research emerges as an important field in pain medicine, it will play a unique role in improving clinical pain management through coordinated bidirectional research approaches between bedside and bench.

The role of the CB1 receptor in the regulation of sleep

During the 1990s, transmembranal proteins in the central nervous system (CNS) that recognize the principal compound of marijuana, the delta-9-tetrahydrocannabinol (Delta9-THC) were described. The receptors were classified as central or peripheral, CB1 and CB2, respectively. To this date, it has been documented the presence in the CNS of specific lipids that bind naturally to the CB1/CB2 receptors. The family of endogenous cannabinoids or endocannabinoids comprises oleamide, arachidonoylethanolamine, 2-arachidonylglycerol, virodhamine, noladin ether and N-arachidonyldopamine. Pharmacological experiments have shown that those compounds induce cannabimimetic effects. Endocannabinoids are fatty acid derivates that have a variety of biological actions, most notably via activation of the cannabinoid receptors. The endocannabinoids have an active role modulating diverse neurobiological functions, such as learning and memory, feeding, pain perception and sleep generation. Experimental evidence shows that the administration of Delta9-THC promotes sleep. The activation of the CB1 receptor leads to an induction of sleep, this effect is blocked via the selective antagonist. Since the system of the endogenous cannabinoids is present in several species, including humans, this leads to the speculation of the neurobiological role of the endocannabinoid system on diverse functions such as sleep modulation. This review discusses the evidence of the system of the endocannabinoids as well as their physiological role in diverse behaviours, including the modulation of sleep.

Medical marijuana and the developing role of the pharmacist

PURPOSE

The pharmacology, therapeutic uses, safety, drug-drug interactions, and drug-disease interactions of medical marijuana are reviewed, and the legal issues related to its use and the implications of medical marijuana for the pharmacist are presented.

SUMMARY

Marijuana contains more than 460 active chemicals and over 60 unique cannabinoids. The legal landscape surrounding marijuana is surprisingly complex and unsettled. In the United States, 11 states and several municipalities have legalized medical marijuana. Another state provides legislation that allows patients to claim a defense of medical necessity. Nevertheless, patients using medical marijuana may never interact with a pharmacist. Marijuana is a Schedule I controlled substance and its use is illegal under federal law. Marijuana has a number of purported therapeutic uses with a broad range of supporting evidence. There are five general indications for medical marijuana: (1) severe nausea and vomiting associated with cancer chemotherapy or other causes, (2) weight loss associated with debilitating illnesses, including HIV infection and cancer, (3) spasticity secondary to neurologic diseases, such as multiple sclerosis, (4) pain syndromes, and (5) other uses, such as for glaucoma. Marijuana is associated with adverse psychiatric, cardiovascular, respiratory, and immunologic events. Moreover, marijuana may interact with a number of prescription drugs and concomitant disease states.

CONCLUSION

Several states have legalized the use of marijuana for chronic and debilitating medication conditions. Pharmacists need to understand the complex legal framework surrounding this issue so that they can protect themselves and better serve their patients.

Targeting cannabinoid agonists for inflammatory and neuropathic pain

The cannabinoid receptors CB(1) and CB(2) are class A G-protein-coupled receptors. It is well known that cannabinoid receptor agonists produce relief of pain in a variety of animal models by interacting with cannabinoid receptors. CB(1) receptors are located centrally and peripherally, whereas CB(2) receptors are expressed primarily on immune cells and tissues. A large body of preclinical data supports the hypothesis that either CB(2)-selective agonists or CB(1) agonists acting at peripheral sites, or with limited CNS exposure, will inhibit pain and neuroinflammation without side effects within the CNS. There has been a growing interest in developing cannabinoid agonists. Many new cannabinoid ligands have been synthesized and studied covering a wide variety of novel structural scaffolds. This review focuses on the present development of cannabinoid agonists with an emphasis on selective CB(2) agonists and peripherally restricted CB(1) or CB(1)/CB(2) dual agonists for treatment of inflammatory and neuropathic pain.

Meta-analysis of cannabis based treatments for neuropathic and multiple sclerosis-related pain

OBJECTIVE

Debilitating pain, occurring in 50-70% of multiple sclerosis (MS) patients, is poorly understood and infrequently studied. We summarized efficacy and safety data of cannabinoid-based drugs for neuropathic pain.

DATA SOURCES

Studies were identified from Medline, Embase, and Cochrane databases; Bayer Healthcare provided additional trials.

STUDY SELECTION

Accepted were randomized, double-blinded placebo-controlled trials of cannabinoid-based treatments for MS-related/neuropathic pain in adults > or = 18 years of age.

DATA EXTRACTION

Two reviewers identified studies and extracted data; a third adjudicated disagreements. Data included baseline and endpoint pain scores on visual analog or 11-point ordinal scales.

DATA SYNTHESIS

Of 18 articles and three randomized controlled trial (RCT) reports identified, 12 articles and two reports were rejected (9 = inappropriate disease or outcome, 1 = duplicate, 1 = review, and 1 = abstract); six accepted articles and one RCT-report involved 298 patients (222 treated, 76 placebo); four examined Sativex (a cannabidiol/delta-9-tetrahydrocannabinol (THC) buccal spray) (observations = 196), five cannabidiol (n = 41), and three dronabinol (n = 91). Homogeneity chi(2) values were non-significant, allowing data combination. Analyses focused on baseline-endpoint score differences. The cannabidiol/THC buccal spray decreased pain 1.7 +/- 0.7 points (p = 0.018), cannabidiol 1.5 +/- 0.7 (p = 0.044), dronabinol 1.5 +/- 0.6 (p = 0.013), and all cannabinoids pooled together 1.6 +/- 0.4 (p < 0.001). Placebo baseline-endpoint scores did not differ (0.8 +/- 0.4 points, p = 0.023). At endpoint, cannabinoids were superior to placebo by 0.8 +/- 0.3 points (p = 0.029). Dizziness was the most commonly observed adverse event in the cannabidiol/THC buccal spray arms (39 +/- 16%), across all cannabinoid treatments (32.5 +/- 16%) as well as in the placebo arms (10 +/- 4%).

CONCLUSION

Cannabinoids including the cannabidiol/THC buccal spray are effective in treating neuropathic pain in MS.

LIMITATIONS

This review was based on a small number of trials and patients. Pain related to MS was assumed to be similar to neuropathic pain.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.