Cannabidiol and mitragynine exhibit differential interactive effects in the attenuation of paclitaxel-induced mechanical allodynia, acute antinociception, and schedule-controlled responding in mice.

BACKGROUND: For many chemotherapy patients peripheral neuropathy is a debilitating side effect. Mitragyna speciosa (kratom) contains the alkaloid mitragynine (MG), which produces analgesia in multiple preclinical pain models. In humans, anecdotal reports suggest cannabidiol (CBD) may enhance kratom-related analgesia. We examined the interactive activity of MG and CBD in a mouse chemotherapy-induced peripheral neuropathy (CIPN) model. We also examined MG + CBD in acute antinociception and schedule-controlled responding assays, as well as examined underlying receptor mechanisms. METHODS: Male and female C57BL/6J mice received a cycle of intraperitoneal (ip) paclitaxel injections (cumulative dose 32 mg/kg). The von Frey assay was utilized to assess CIPN allodynia. In paclitaxel-naïve mice, schedule-controlled responding for food was conducted under a fixed ratio (FR)-10, and hot plate antinociception was examined. RESULTS: MG dose-relatedly attenuated CIPN allodynia (ED50 102.96 mg/kg, ip), reduced schedule-controlled responding (ED50 46.04 mg/kg, ip), and produced antinociception (ED50 68.83 mg/kg, ip). CBD attenuated allodynia (ED50 85.14 mg/kg, ip) but did not decrease schedule-controlled responding or produce antinociception. Isobolographic analysis revealed 1:1, 3:1 MG + CBD mixture ratios additively attenuated CIPN allodynia. All combinations decreased schedule-controlled responding and produced antinociception. WAY-100635 (serotonin 5-HT1A receptor antagonist) pretreatment (0.01 mg/kg, ip) antagonized CBD anti-allodynia. Naltrexone (pan opioid receptor antagonist) pretreatment (0.032 mg/kg, ip) antagonized MG anti-allodynia and acute antinociception but produced no change in MG-induced decreased schedule-controlled behavior. Yohimbine (α2 receptor antagonist) pretreatment (3.2 mg/kg, ip) antagonized MG anti-allodynia and produced no change in MG-induced acute antinociception or decreased schedule-controlled behavior. CONCLUSIONS: Although more optimization is needed, these data suggest CBD combined with MG may be useful as a novel CIPN therapeutic.

Evaluation of the terpenes ß-caryophyllene, α-terpineol, and γ-terpinene in the mouse chronic constriction injury model of neuropathic pain: possible cannabinoid receptor involvement.

Pain is one of the most common reasons to seek medical attention, and chronic pain is a worldwide epidemic. Anecdotal reports suggest cannabis may be an effective analgesic. As cannabis contains the terpenes α-terpineol, ß-caryophyllene, and γ-terpinene, we hypothesized these terpenes would produce analgesia in a mouse model of neuropathic pain. We used the chronic constriction injury of the sciatic nerve mouse model, which produces mechanical allodynia, assessed via the von Frey assay, as well as thermal hyperalgesia assessed via the hotplate assay. Compounds were further assessed in tests of locomotor activity, hypothermia, and acute antinociception. Each terpene produced dose-related reversal of mechanical allodynia and thermal hyperalgesia. Thermal hyperalgesia displayed higher sensitivity to the effects of each terpene than mechanical allodynia, and the rank order potency of the terpenes was α-terpineol > ß-caryophyllene > γ-terpinene. To examine the involvement of cannabinoid receptors, further tests were conducted in mice lacking either functional cannabinoid type 1 receptors (CB1R (-/-)) or cannabinoid type 2 receptors (CB2R (-/-)). Compared to wild type mice, CB1R (-/-) mice treated with α-terpineol displayed a 2.91-fold decrease in potency to reverse mechanical allodynia; in CB2R (-/-) mice, the potency of α-terpineol was decreased 11.73-fold. The potency of ß-caryophyllene to reverse mechanical allodynia decreased 1.80-fold in CB2R (-/-) mice. Each terpene produced a subset of effects in tests of locomotor activity, hypothermia, and acute antinociception. These findings suggest α-terpineol, ß-caryophyllene, and γ-terpinene may have differential cannabinoid receptor activity and a pharmacological profile that may yield new efficacious analgesics.

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-ß), fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), α/ß 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.

Characterization of a mouse neuropathic pain model caused by the highly active antiviral therapy (HAART) Stavudine.

BACKGROUND: Although highly active antiviral therapies (HAART) exert control over viral replication in persons with Acquired Immunodeficiency Syndrome (AIDS), neuropathic pain is a side effect. Symptoms include hyperalgesia and allodynia. Stavudine, also known as D4T, is a HAART used to treat Human Immunodeficiency Virus (HIV). This study examined the extent to which D4T produces neuropathic pain and examined pharmacological management with a standard opioid analgesic. METHODS: Male and female C57BL/6 J mice were injected intraperitoneally with one dose of vehicle or D4T (10-56 mg/kg). Mice were tested through day 92 post injection for mechanical allodynia, assessed with von Frey filaments, and thermal hyperalgesia, assessed via the hotplate test. Separate cohorts received vehicle or 56 mg/kg D4T, the presence of allodynia and thermal hyperalgesia confirmed, and mice received intraperitoneal vehicle, morphine, or 0.032 mg/kg naltrexone + morphine. RESULTS: D4T produced dose- and time-dependent mechanical allodynia and thermal hyperalgesia. The smallest effective D4T dose was 17.8 mg/kg. This dose produced mechanical allodynia but not thermal hyperalgesia. Larger D4T doses (32 and 56 mg/kg) produced mechanical allodynia and thermal hyperalgesia lasting 92 days. Morphine dose-dependently alleviated both mechanical allodynia and thermal hyperalgesia in D4T-treated mice with ED50 values of 4.4 and 1.2 mg/kg, respectively. Naltrexone produced a rightward shift of the morphine dose-response function, i.e., increased the ED50 value of morphine by at least 3.8-fold. CONCLUSION: Stavudine produced neuropathic pain as a function of dose and time in mice. Opioid analgesics appear to be effective in alleviating neuropathic pain in a D4T-induced mouse model.

Alterations in mouse spinal cord and sciatic nerve microRNAs after the chronic constriction injury (CCI) model of neuropathic pain.

Pain is one of the most common reasons to seek medical attention and chronic pain is a worldwide epidemic. There are currently no relevant biomarkers for the diagnosis of chronic pain, and new therapeutic strategies for chronic pain treatment are desperately needed. The chronic constriction injury (CCI) of the sciatic nerve is a widely used preclinical model of pathological neuropathic pain. Over the past decade, investigators have come to appreciate the many contributions of noncoding RNA including microRNA (miRNA), and other long and short noncoding (nc) RNAs. The development and/or maintenance of chronic pain could be controlled epigenetically through ncRNAs. Here we seek to characterize CNS tissues in a mouse model of neuropathic pain as this may serve to elucidate potential biomarkers relevant to pathological pain in humans. Male C57BL6/J mice (6 CCI and 6 sham procedure) underwent surgery for sciatic nerve ligation with chromic gut sutures. Following 7 days, mechanical allodynia was quantified using the von Frey assay. Mice were then euthanized for collection of spinal cord and sciatic nerve. cDNA was synthesized to 627 unique mature miRNAs from the total RNA. In the CCI mice that displayed mechanical allodynia, 11 and 125 miRNAs were differentially expressed (i.e., greater than 1.5-fold increase or decrease; P < 0.05) in the spinal cord and sciatic nerve, respectively, as compared to sham controls. Among those differentially expressed miRNAs in the sciatic nerve of CCI mice, the following passed the more stringent Bonfferoni correction: miR-138-3p, miR-138-5p and miR-676-3p, reduced and miR-142-5p, increased. Our data support miRNAs as promising therapeutic targets for the treatment of pathological pain.

Axially Chiral Cannabinols: A New Platform for Cannabinoid-Inspired Drug Discovery.

Phytocannabinoids (and synthetic analogs thereof) are gaining significant attention as promising leads in modern medicine. Considering this, new directions for the design of phytocannabinoid-inspired molecules is of immediate interest. In this regard, we have hypothesized that axially-chiral-cannabinols (ax-CBNs), unnatural and unknown isomers of cannabinol (CBN) may be valuable scaffolds for cannabinoid-inspired drug discovery. There are two main factors directing our interest to these scaffolds: (a) ax-CBNs would have ground-state three-dimensionality; ligand-receptor interactions can be more significant with complimentary 3D-topology, and (b) ax-CBNs at their core structure are biaryl molecules, generally attractive platforms for pharmaceutical development due to their ease of functionalization and stability. Herein we report a synthesis of ax-CBNs, examine physical properties experimentally and computationally, and perform a comparative analysis of ax-CBN and THC in mice behavioral studies.

The Effects of Morphine, Baclofen, and Buspirone Alone and in Combination on Schedule-Controlled Responding and Hot Plate Antinociception in Rats.

Better therapeutic options are needed for pain. Baclofen, buspirone, and morphine are characterized as having analgesic properties. However, little is known about potential interactions between analgesic effects of these drugs when combined. Furthermore, it is not known if the magnitude of these potential interactions will be similar for all drug effects. Thus, we tested the effects of these drugs alone and in combination for their capacity to produce thermal antinociception and to decrease food-maintained responding. Four male and four female Sprague-Dawley rats responded for food under a fixed-ratio 10 schedule; afterward they were immediately placed on a 52°C hot plate. Morphine, baclofen, and buspirone were examined alone and in 1:1 combinations, based upon ED50 values. Morphine and baclofen effects were evaluated with the opioid antagonist naltrexone and the GABAB antagonist (3-Aminopropyl)(diethoxymethyl)phosphinic acid (CGP35348), respectively. Morphine, baclofen, and buspirone dose dependently decreased operant responding, with the calculated ED50 values being 7.09, 3.42, and 0.57 mg/kg, respectively. The respective antinociception ED50 values were 16.15, 8.75, and 2.20 mg/kg. Analysis of 1:1 combinations showed the effects of morphine plus baclofen to decrease schedule-controlled responding and to produce thermal antinociception were synergistic. Effects of morphine plus buspirone and baclofen plus buspirone to decrease schedule-controlled responding were additive. Effects of the two combinations to produce thermal antinociception were synergistic. Naltrexone and CGP35348 antagonized the effects of morphine and baclofen, respectively. Synergistic antinociceptive effects, in conjunction with additive effects on food-maintained responding, highlight the therapeutic utility of opioid and non-opioid drug combinations.

The effects of mitragynine and morphine on schedule-controlled responding and antinociception in rats.

RATIONALE: Mitragyna speciosa (kratom) may hold promise as both an analgesic and treatment for opioid use disorder. Mitragynine, its primary alkaloid constituent, is an opioid receptor ligand. However, the extent to which the in vivo effects of mitragynine are mediated by opioid receptors, or whether mitragynine interacts with other opioid agonists, is not fully established. OBJECTIVES: The effects of mitragynine and the prototypical opioid agonist morphine were compared for their capacity to decrease operant responding for food delivery, and to increase response latency to a thermal stimulus. METHODS: Male and female Sprague-Dawley rats responded under a multiple cycle fixed ratio 10 schedule of food delivery and were tested on a hot plate (52 °C) immediately after each cycle. Morphine and mitragynine were administered alone, in combination with each other, and in combination with the opioid antagonist naltrexone. RESULTS: Morphine and mitragynine dose-dependently decreased schedule-controlled responding; the ED50 values were 7.3 and 31.5 mg/kg, respectively. Both drugs increased thermal antinociception; the ED50 value for morphine was 18.3. Further, doses of naltrexone that antagonized morphine did not antagonize mitragynine. Mitragynine (17.8 mg/kg) did not alter the rate-decreasing or antinociceptive effects of morphine. CONCLUSIONS: The antinociceptive effects of mitragynine and morphine occur at doses larger than those that disrupt learned behavior. Opioid receptors do not appear to mediate the disruptive effects of mitragynine on learned behavior. Mitragynine had lesser antinociceptive effects than morphine, and these did not appear to be mediated by opioid receptors. The pharmacology of mitragynine includes a substantial non-opioid mechanism.