Non-cannabinoid CB1, non-cannabinoid CB2 antinociceptive effects of several novel compounds in the PPQ stretch test in mice

Cannabinoid Analgesia in Postoperative Pain Management: From Molecular Mechanisms to Clinical Reality

Postoperative pain (POP) is a challenging clinical phenomenon that affects the majority of surgical patients and demands effective management to mitigate adverse outcomes such as persistent pain. The primary goal of POP management is to alleviate suffering and facilitate a seamless return to normal function for the patient. Despite compelling evidence of its drawbacks, opioid analgesia remains the basis of POP treatment. Novel therapeutic approaches rely on multimodal analgesia, integrating different pharmacological strategies to optimize efficacy while minimizing adverse effects. The recognition of the imperative role of the endocannabinoid system in pain regulation has prompted the investigation of cannabinoid compounds as a new therapeutic avenue. Cannabinoids may serve as adjuvants, enhancing the analgesic effects of other drugs and potentially replacing or at least reducing the dependence on other long-term analgesics in pain management. This narrative review succinctly summarizes pertinent information on the molecular mechanisms, clinical therapeutic benefits, and considerations associated with the plausible use of various cannabinoid compounds in treating POP. According to the available evidence, cannabinoid compounds modulate specific molecular mechanisms intimately involved in POP. However, only two of the eleven clinical trials that evaluated the efficacy of different cannabinoid interventions showed positive results.

Effects of Ultramicronized Palmitoylethanolamide (um-PEA) in COVID-19 Early Stages: A Case–Control Study

Ultramicronized palmitoylethanolamide (um-PEA), a compound with antioxidant, anti-inflammatory and neuroprotective properties, appears to be a potential adjuvant treatment for early stages of Coronavirus disease 2019 (COVID-19). In our study, we enrolled 90 patients with confirmed diagnosis of COVID-19 that were randomized into two groups, homogeneous for age, gender and BMI. The first group received oral supplementation based on um-PEA at a dose of 1800 mg/day for a total of 28 days; the second group was the control group (R.S. 73.20). At baseline (T0) and after 28 days of um-PEA treatment (T1), we monitored: routine laboratory parameters, inflammatory and oxidative stress (OS) biomarkers, lymphocytes subpopulation and COVID-19 serological response. At T1, the um-PEA-treated group presented a significant reduction in inflammation compared to the control group (CRP p = 0.007; IL-6 p = 0.0001; neutrophils to lymphocytes ratio p = 0.044). At T1, the controls showed a significant increase in OS compared to the treated group (FORT p = 0.05). At T1, the um-PEA group exhibited a significant decrease in D-dimer levels (p = 0.0001) and higher levels of IgG against SARS-CoV-2 (p = 0.0001) compared to the controls. Our data demonstrated, in a randomized clinical trial, the beneficial effects of um-PEA in both asymptomatic and mild-symptomatic patients related to reductions in inflammatory state, OS and coagulative cascade alterations.

Chronic Pain in Dogs and Cats: Is There Place for Dietary Intervention with Micro-Palmitoylethanolamide?

The management of chronic pain is an integral challenge of small animal veterinary practitioners. Multiple pharmacological agents are usually employed to treat maladaptive pain including opiates, non-steroidal anti-inflammatory drugs, anticonvulsants, antidepressants, and others. In order to limit adverse effects and tolerance development, they are often combined with non-pharmacologic measures such as acupuncture and dietary interventions. Accumulating evidence suggests that non-neuronal cells such as mast cells and microglia play active roles in the pathogenesis of maladaptive pain. Accordingly, these cells are currently viewed as potential new targets for managing chronic pain. Palmitoylethanolamide is an endocannabinoid-like compound found in several food sources and considered a body's own analgesic. The receptor-dependent control of non-neuronal cells mediates the pain-relieving effect of palmitoylethanolamide. Accumulating evidence shows the anti-hyperalgesic effect of supplemented palmitoylethanolamide, especially in the micronized and co-micronized formulations (i.e., micro-palmitoylethanolamide), which allow for higher bioavailability. In the present paper, the role of non-neuronal cells in pain signaling is discussed and a large number of studies on the effect of palmitoylethanolamide in inflammatory and neuropathic chronic pain are reviewed. Overall, available evidence suggests that there is place for micro-palmitoylethanolamide in the dietary management of chronic pain in dogs and cats.

The Protective Effects of Pre- and Post-Administration of Micronized Palmitoylethanolamide Formulation on Postoperative Pain in Rats

Background: Postoperative pain (PO) is a common form of acute pain. Inadequate PO treatment is an important health problem, as it leads to worse outcomes, such as chronic post-surgical pain. Therefore, it is necessary to acquire new knowledge on PO mechanisms to develop therapeutic options with greater efficacy than those available today and to lower the risk of adverse effects. For this reason, we evaluated the ability of micronized palmitoylethanolamide (PEA-m) to resolve the pain and inflammatory processes activated after incision of the hind paw in an animal model of PO. Methods: The animals were subjected to surgical paw incision and randomized into different groups. PEA-m was administered orally at 10 mg/kg at different time points before or after incision. Results: Our research demonstrated that the pre- and post-treatment with PEA-m reduced the activation of mast cells at the incision site and the expression of its algogenic mediator nerve growth factor (NGF) in the lumbar spinal cord. Furthermore, again at the spinal level, it was able to decrease the activation of phospho-extracellular signal-regulated kinases (p-ERK), ionized calcium binding adaptor molecule 1 (Iba1), glial fibrillary acidic protein (GFAP), and the expression of brain-derived neurotrophic factor (BDNF). PEA-m also reduced the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) spinal pathway, showing a protective effect in a rat model of PO. Conclusion: The results obtained reinforce the idea that PEA-m may be a potential treatment for the control of pain and inflammatory processes associated with PO. In addition, pre- and post-treatment with PEA-m is more effective than treatment alone after the surgery and this limits the time of taking the compound and the abuse of analgesics.

Non-opioid Analgesics and the Endocannabinoid System

Non-steroidal anti-inflammatory drugs produce antinociceptive effects mainly through peripheral cyclooxygenase inhibition. In opposition to the classical non-steroidal anti-inflammatory drugs, paracetamol and dipyrone exert weak anti-inflammatory activity, their antinociceptive effects appearing to be mostly due to mechanisms other than peripheral cyclooxygenase inhibition. In this review, we classify classical non-steroidal anti-inflammatory drugs, paracetamol and dipyrone as “non-opioid analgesics” and discuss the mechanisms mediating participation of the endocannabinoid system in their antinociceptive effects. Non-opioid analgesics and their metabolites may activate cannabinoid receptors, as well as elevate endocannabinoid levels through different mechanisms: reduction of endocannabinoid degradation via fatty acid amide hydrolase and/or cyclooxygenase-2 inhibition, mobilization of arachidonic acid for the biosynthesis of endocannabinoids due to cyclooxygenase inhibition, inhibition of endocannabinoid cellular uptake directly or through the inhibition of nitric oxide synthase production, and induction of endocannabinoid release.

Micronized Palmitoylethanolamide-Polydatin Reduces the Painful Symptomatology in Patients with Interstitial Cystitis/Bladder Pain Syndrome

Aims

To assess the efficacy of a micronized-palmitoylethanolamide-polydatin (m-PEA-Pol) based product on chronic pelvic pain and severity of other symptoms in interstitial cystitis/bladder pain syndrome (IC/BPS) patients refractory to conventional therapies.

Methods

A pilot, open-label bicentric study was carried out involving 32 IC/BPS patients. Chronic, oral m-PEA-Pol treatment lasted 6 months. Bladder pain was evaluated using the visual analog scale, while changes from baseline in other urinary symptoms were evaluated by means of the O'Leary-Sant Interstitial Cystitis Symptom and Problem Index and the Pelvic Pain and Urgency/Frequency (PUF) symptom scale questionnaires. The generalized linear mixed model was used to evaluate significant mean changes across time.

Results

A significant and progressive reduction of pain intensity was observed during m-PEA-Pol treatment (p < 0.0001 for reduction over time). The effect was associated with a reduction in severity of patients' symptoms evaluated with the O'Leary-Sant questionnaire (p=0.0110 and p=0.0014 for cystitis symptoms and problem mean scores, respectively) and the PUF scale (p=0.0163 and p=0.0005 for symptom and bother mean scores, respectively). m-PEA-Pol therapy elicited a significant reduction over time in the urinary frequency evaluated with voiding diary (p=0.0005) and a small but not significant improvement of bladder capacity.

Conclusions

These data highlight the potential benefit of m-PEA-Pol in patients with rare pathology such as IC/BPS and confirm the good safety profile of micronized PEA-based products.

Effects of the glial modulator palmitoylethanolamide on chronic pain intensity and brain function

Background: Chronic neuropathic pain (NP) is a complex disease that results from damage or presumed damage to the somatosensory nervous system. Current treatment regimens are often ineffective. The major impediment in developing effective treatments is our limited understanding of the underlying mechanisms. Preclinical evidence suggests that glial changes are crucial for the development of NP and a recent study reported oscillatory activity differences within the ascending pain pathway at frequencies similar to that of cyclic gliotransmission in NP. Furthermore, there is evidence that glial modifying medications may be effective in treating NP. The aim of this Phase I open-label clinical trial is to determine whether glial modifying medication palmitoylethanolamide (PEA) will reduce NP and whether this is associated with reductions in oscillatory activity within the pain pathway.

Methods: We investigated whether 6 weeks of PEA treatment would reduce pain and infra-slow oscillatory activity within the ascending trigeminal pathway in 22 individuals (17 females) with chronic orofacial NP.

Results: PEA reduced pain in 16 (73%) of the 22 subjects, 11 subjects showed pain reduction of over 20%. Whilst both the responders and non-responders showed reductions in infra-slow oscillatory activity where orofacial nociceptor afferents terminate in the brainstem, only responders displayed reductions in the thalamus. Furthermore, functional connections between the brainstem and thalamus were altered only in responders.

Conclusion: PEA is effective at relieving NP. This reduction is coupled to a reduction in resting oscillations along the ascending pain pathway that are likely driven by rhythmic astrocytic gliotransmission.

Supra-spinal FAAH is required for the analgesic action of paracetamol in an inflammatory context

Paracetamol (acetaminophen) is the most commonly used analgesic in the world. Recently, a new view of its action has emerged: that paracetamol would be a pro-drug that should be metabolized by the FAAH enzyme into AM404, its active metabolite. However, this hypothesis has been demonstrated only in naive animals, a far cry from the clinical pathologic context of paracetamol use. Moreover, FAAH is a ubiquitous enzyme expressed both in the central nervous system and in the periphery. Thus, we explored: (i) the involvement of FAAH in the analgesic action of paracetamol in a mouse model of inflammatory pain; and (ii) the contributions of central versus peripheral FAAH in this action. The analgesic effect of paracetamol was evaluated in thermal hyperalgesia, mechanical allodynia and hyperalgesia induced by an intra-plantar injection of carrageenan (3%) in FAAH knock-out mice or their littermates. Moreover, the contribution of the central and peripheral enzymes was explored by comparing the effect of a global FAAH inhibitor (URB597) to that of a peripherally restricted FAAH inhibitor (URB937) on paracetamol action. Here, we show that in a model of inflammatory pain submitted to different stimuli, the analgesic action of paracetamol was abolished when FAAH was genetically or pharmacologically inhibited. Whereas a global FAAH inhibitor, URB597 (0.3 mg/kg), reduced the anti-hyperalgesic action of paracetamol, a brain-impermeant FAAH inhibitor, URB937 (0.3 mg/kg), had no influence. However, administered intracerebroventricularly, URB937 (5 μg/mouse) reduced the action of paracetamol. These results demonstrate that the supra-spinally-located FAAH enzyme is necessary for the analgesic action of paracetamol.

Inhibition of FAAH, TRPV1, and COX2 by NSAID-serotonin conjugates

Serotonin was linked by amidation to the carboxylic acid groups of a series of structurally diverse NSAIDs. The resulting NSAID-serotonin conjugates were tested in vitro for their ability to inhibit FAAH, TRPV1, and COX2. Ibuprofen-5-HT and Flurbiprofen-5-HT inhibited all three targets with approximately the same potency as N-arachidonoyl serotonin (AA-5-HT), while Fenoprofen-5-HT and Naproxen-5-HT showed activity as dual inhibitors of TRPV1 and COX2.

The endocannabinoid system mediates aerobic exercise-induced antinociception in rats

Exercise-induced antinociception is widely described in the literature, but the mechanisms involved in this phenomenon are poorly understood. Systemic (s.c.) and central (i.t., i.c.v.) pretreatment with CB₁ and CB₂ cannabinoid receptor antagonists (AM251 and AM630) blocked the antinociception induced by an aerobic exercise (AE) protocol in both mechanical and thermal nociceptive tests. Western blot analysis revealed an increase and activation of CB₁ receptors in the rat brain, and immunofluorescence analysis demonstrated an increase of activation and expression of CB₁ receptors in neurons of the periaqueductal gray matter (PAG) after exercise. Additionally, pretreatment (s.c., i.t. and i.c.v.) with endocannabinoid metabolizing enzyme inhibitors (MAFP and JZL184) and an anandamide reuptake inhibitor (VDM11) prolonged and intensified this antinociceptive effect. These results indicate that exercise could activate the endocannabinoid system, producing antinociception. Supporting this hypothesis, liquid-chromatography/mass-spectrometry measurements demonstrated that plasma levels of endocannabinoids (anandamide and 2-arachidonoylglycerol) and of anandamide-related mediators (palmitoylethanolamide and oleoylethanolamide) were increased after AE. Therefore, these results suggest that the endocannabinoid system mediates aerobic exercise-induced antinociception at peripheral and central levels.

Inhibitory properties of ibuprofen and its amide analogues towards the hydrolysis and cyclooxygenation of the endocannabinoid anandamide

A dual-action cyclooxygenase (COX)-fatty acid amide hydrolase (FAAH) inhibitor may have therapeutic usefulness as an analgesic, but a key issue is finding the right balance of inhibitory effects. This can be done by the design of compounds exhibiting different FAAH/COX-inhibitory potencies. In the present study, eight ibuprofen analogues were investigated. Ibuprofen (1), 2-(4-Isobutylphenyl)-N-(2-(3-methylpyridin-2-ylamino)-2-oxoethyl)propanamide (9) and N-(3-methylpyridin-2-yl)-2-(4'-isobutylphenyl)propionamide (2) inhibited FAAH with IC(50) values of 134, 3.6 and 0.52 µM respectively. The corresponding values for COX-1 were ~29, ~50 and ~60 µM, respectively. Using arachidonic acid as substrate, the compounds were weak inhibitors of COX-2. However, when anandamide was used as COX-2 substrate, potency increased, with approximate IC(50) values of ~6, ~10 and ~19 µM, respectively. Compound 2 was confirmed to be active in vivo in a murine model of visceral nociception, but the effects of the compound were not blocked by CB receptor antagonists.

Implication of allopregnanolone in the antinociceptive effect of N-palmitoylethanolamide in acute or persistent pain

We investigated the involvement of de novo neurosteroid synthesis in the mechanisms underlying the analgesic and antihyperalgesic effects of N-palmitoylethanolamine (PEA) in two models of acute and persistent pain, the formalin test and carrageenan-induced paw edema. The pivotal role of peroxisome proliferator-activated receptor (PPAR)-α in the antinocifensive effect of PEA was confirmed by the lack of this effect in PPAR-α-null mice. PEA antinociceptive activity was partially reduced when the animals were treated with aminoglutethimide or finasteride, implying that de novo neurosteroid synthesis is involved in the effect of PEA. Accordingly, in the spinal cord, the allopregnanolone (ALLO) levels were increased by PEA treatment both in formalin- and carrageenan-exposed mice, as revealed by gas chromatography-mass spectrometry. In agreement with those data, in both pain models, PEA administration in challenged mice specifically restored the expression of two proteins involved in neurosteroidogenensis, the steroidogenic acute regulatory protein (StAR) and cytochrome P450 side-chain cleavage (P450scc) in the ipsilateral horns of spinal cord, without affecting their expression in the contralateral side. These results provide new information about the involvement of de novo neurosteroid synthesis in the modulation of pain behavior by PEA.

The discovery and development of inhibitors of fatty acid amide hydrolase (FAAH)

A summary of the discovery and advancement of inhibitors of fatty acid amide hydrolase (FAAH) is presented.

Evaluation of prevalent phytocannabinoids in the acetic acid model of visceral nociception

Considerable preclinical research has demonstrated the efficacy of Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the primary psychoactive constituent of Cannabis sativa, in a wide variety of animal models of pain, but few studies have examined other phytocannabinoids. Indeed, other plant-derived cannabinoids, including cannabidiol (CBD), cannabinol (CBN), and cannabichromene (CBC) elicit antinociceptive effects in some assays. In contrast, tetrahydrocannabivarin (THCV), another component of cannabis, antagonizes the pharmacological effects of Delta(9)-THC. These results suggest that various constituents of this plant may interact in a complex manner to modulate pain. The primary purpose of the present study was to assess the antinociceptive effects of these other prevalent phytocannabinoids in the acetic acid stretching test, a rodent visceral pain model. Of the cannabinoid compounds tested, Delta(9)-THC and CBN bound to the CB(1) receptor and produced antinociceptive effects. The CB(1) receptor antagonist, rimonabant, but not the CB(2) receptor antagonist, SR144528, blocked the antinociceptive effects of both compounds. Although THCV bound to the CB(1) receptor with similar affinity as Delta(9)-THC, it had no effects when administered alone, but antagonized the antinociceptive effects of Delta(9)-THC when both drugs were given in combination. Importantly, the antinociceptive effects of Delta(9)-THC and CBN occurred at lower doses than those necessary to produce locomotor suppression, suggesting motor dysfunction did not account for the decreases in acetic acid-induced abdominal stretching. These data raise the intriguing possibility that other constituents of cannabis can be used to modify the pharmacological effects of Delta(9)-THC by either eliciting antinociceptive effects (i.e., CBN) or antagonizing (i.e., THCV) the actions of Delta(9)-THC.

Pain and beyond: fatty acid amides and fatty acid amide hydrolase inhibitors in cardiovascular and metabolic diseases

Fatty acid amide hydrolase (FAAH) is responsible for the hydrolysis of several important endogenous fatty acid amides (FAAs), including anandamide, oleoylethanolamide and palmitoylethanolamide. Because specific FAAs interact with cannabinoid and vanilloid receptors, they are often referred to as 'endocannabinoids' or 'endovanilloids'. Initial interest in this area, therefore, has focused on developing FAAH inhibitors to augment the actions of FAAs and reduce pain. However, recent literature has shown that these FAAs - through interactions with unique receptors (extracellular and intracellular) - can induce a diverse array of effects that include appetite suppression, modulation of lipid and glucose metabolism, vasodilation, cardiac function and inflammation. This review gives an overview of FAAs and diverse FAAH inhibitors and their potential therapeutic utility in pain and non-pain indications.

Fatty acid amide hydrolase as a potential therapeutic target for the treatment of pain and CNS disorders

BACKGROUND: Fatty acid amide hydrolase (FAAH) is an integral membrane enzyme that hydrolyzes the endocannabinoid anandamide and related amidated signaling lipids. Genetic or pharmacological inactivation of FAAH produces analgesic, anti-inflammatory, anxiolytic, and antidepressant phenotypes without showing the undesirable side effects of direct cannabinoid receptor agonists, indicating that FAAH may be a promising therapeutic target. OBJECTIVES: This review highlights advances in the development of FAAH inhibitors of different mechanistic classes and their in vivo efficacy. Also highlighted are advances in technology for the in vitro and in vivo selectivity assessment of FAAH inhibitors employing activity-based protein profiling (ABPP) and click chemistry-ABPP, respectively. Recent reports on structure-based drug design for human FAAH generated by protein engineering using interspecies active site conversion are also discussed. METHODS: The literature searches of Medline and SciFinder databases were used. CONCLUSIONS: There has been tremendous progress in our understanding in FAAH and development of FAAH inhibitors with in vivo efficacy, selectivity, and drug like pharmacokinetic properties.

Interaction of the cannabinoid and opioid systems in the modulation of nociception

Cannabinoids and opioids produce antinociceptive synergy. Cannabinoids such as Delta-9-tetrahydrocannabinol (THC) release endogenous opioids and endocannabinoids such as anandamide (AEA) also alter endogenous opioid tone. Opioids and cannabinoids bind distinct receptors that co-localize in areas of the brain involved with the processing of pain signals. Therefore, it is logical to look at interactions of these two systems in the modulation of both acute and chronic pain. These drugs are often co-abused. In addition, the lack of continued effectiveness of opioids due to tolerance development limits the use of such drugs. The cost to society and patients in terms of dollars, loss of productivity, as well as quality of life, is staggering. This review summarizes the data indicating that with cannabinoid/opioid therapy one may be able to produce long-term antinociceptive effects at doses devoid of substantial side effects, while preventing the neuronal biochemical changes that accompany tolerance. The clinical utility of modulators of the endocannabinoid system as a potential mimic for THC-like drugs in analgesia and tolerance-sparing effects of opioids is a critical future direction also addressed in the review.

The case for the development of novel analgesic agents targeting both fatty acid amide hydrolase and either cyclooxygenase or TRPV1

Although the dominant approach to drug development is the design of compounds selective for a given target, compounds targeting more than one biological process may have superior efficacy, or alternatively a better safety profile than standard selective compounds. Here, this possibility has been explored with respect to the endocannabinoid system and pain. Compounds inhibiting the enzyme fatty acid amide hydrolase (FAAH), by increasing local endocannabinoid tone, produce potentially useful effects in models of inflammatory and possibly neuropathic pain. Local increases in levels of the endocannabinoid anandamide potentiate the actions of cyclooxygenase inhibitors, raising the possibility that compounds inhibiting both FAAH and cyclooxygenase can be as effective as non-steroidal anti-inflammatory drugs but with a reduced cyclooxygenase inhibitory 'load'. An ibuprofen analogue active in models of visceral pain and with FAAH and cyclooxygenase inhibitory properties has been identified. Another approach, built in to the experimental analgesic compound N-arachidonoylserotonin, is the combination of FAAH inhibitory and transient receptor potential vanilloid type 1 antagonist properties. Although finding the right balance of actions upon the two targets is a key to success, it is hoped that dual-action compounds of the types illustrated in this review will prove to be useful analgesic drugs.

Synergy between enzyme inhibitors of fatty acid amide hydrolase and cyclooxygenase in visceral nociception

The present study investigated whether inhibition of fatty acid amide hydrolase (FAAH), the enzyme responsible for anandamide catabolism, produces antinociception in the acetic acid-induced abdominal stretching model of visceral nociception. Genetic deletion or pharmacological inhibition of FAAH reduced acetic acid-induced abdominal stretching. Transgenic mice that express FAAH exclusively in the nervous system displayed the antinociceptive phenotype, indicating the involvement of peripheral fatty acid amides. The cannabinoid receptor 1 (CB(1)) receptor antagonist, rimonabant, but not the cannabinoid receptor 2 (CB(2)) receptor antagonist, SR144528, blocked the antinociceptive phenotype of FAAH(-/-) mice and the analgesic effects of URB597 (3'-carbamoyl-biphenyl-3-yl-cyclohexylcarbamate) or OL-135 (1-oxo-1[5-(2-pyridyl)-2-yl]-7-phenyl heptane), respective irreversible and reversible FAAH inhibitors, administered to C57BL/6 mice. The opioid receptor antagonist, naltrexone, did not block the analgesic effects of either FAAH inhibitor. URB597, ED(50) [95% confidence interval (CI) = 2.1 (1.5-2.9) mg/kg], and the nonselective cyclooxygenase inhibitor, diclofenac sodium [ED(50) (95% CI) = 9.8 (8.2-11.7) mg/kg], dose-dependently inhibited acetic acid-induced abdominal stretching. Combinations of URB597 and diclofenac yielded synergistic analgesic interactions according to isobolographic analysis. It is important that FAAH(-/-) mice and URB597-treated mice displayed significant reductions in the severity of gastric irritation caused by diclofenac. URB597 lost its gastroprotective effects in CB(1)(-/-) mice, whereas it maintained its efficacy in CB(2)(-/-) mice, indicating a CB(1) mechanism of action. Taken together, the results of the present study suggest that FAAH represents a promising target for the treatment of visceral pain, and a combination of FAAH inhibitors and NSAIDs may have great utility to treat visceral pain, with reduced gastric toxicity.

Study of the regulation of the endocannabinoid system in a virus model of multiple sclerosis reveals a therapeutic effect of palmitoylethanolamide

Cannabinoids have recently been approved as a treatment for pain in multiple sclerosis (MS). Increasing evidence from animal studies suggests that this class of compounds could also prove efficient to fight neurodegeneration, demyelination, inflammation and autoimmune processes occurring in this pathology. However, the use of cannabinoids is limited by their psychoactive effects. In this context, potentiation of the endogenous cannabinoid signalling could represent a substitute to the use of exogenously administrated cannabinoid ligands. Here, we studied the expression of different elements of the endocannabinoid system in a chronic model of MS in mice. We first studied the expression of the two cannabinoid receptors, CB(1) and CB(2), as well as the putative intracellular cannabinoid receptor peroxisome proliferator-activated receptor-alpha. We observed an upregulation of CB(2), correlated to the production of proinflammatory cytokines, at 60 days after the onset of the MS model. At this time, the levels of the endocannabinoid, 2-arachidonoylglycerol, and of the anti-inflammatory anandamide congener, palmithoylethanolamide, were enhanced, without changes in the levels of anandamide. These changes were not due to differences in the expression of the degradation enzymes, fatty acid amide hydrolase and monoacylglycerol lipase, or of biosynthetic enzymes, diacylglycerol lipase-alpha and N-acylphosphatidylethanolamine phospholipase-D at this time (60 days). Finally, the exogenous administration of palmitoylethanolamide resulted in a reduction of motor disability in the animals subjected to this model of MS, accompanied by an anti-inflammatory effect. This study overall highlights the potential therapeutic effects of endocannabinoids in MS.

Endocannabinoid and serotonergic systems are needed for acetaminophen-induced analgesia

Acetaminophen is the most used analgesic/antipyretic drug. Its unclear mechanism of action could rely on cyclooxygenase inhibition, NO synthesis blockade or reinforcement of the serotonergic system. Here we show that in thermal, mechanical and chemical pain tests, AM-251, a specific CB(1) receptor antagonist, abolished the analgesic action of acetaminophen, which was also lost in CB(1) receptor knockout mice. Moreover, acetaminophen was shown unable to bind to CB(1) receptors demonstrating an indirect involvement of these receptors in the analgesic effect of this compound. Accordingly with these results, we also demonstrated that the inhibition of FAAH, an enzyme involved in the cerebral metabolism of acetaminophen into AM404, known to reinforce the activity of the endocannabinoid system, suppressed the antinociceptive effect of acetaminophen. In addition, similarly to the interaction of acetaminophen with bulbospinal serotonergic pathways and spinal serotonin receptors, we observed that the antinociceptive activity of ACEA, a CB(1) receptor agonist, was inhibited by lesion of bulbospinal serotonergic pathways and antagonists of spinal 5-HT receptors. We therefore propose that acetaminophen-induced analgesia could involve the following sequence: (1) FAAH-dependent metabolism of acetaminophen into AM404; (2) indirect involvement of CB(1) receptors by this metabolite; (3) endocannabinoid-dependent reinforcement of the serotonergic bulbospinal pathways, and (4) involvement of spinal pain-suppressing serotonergic receptors.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

The diverse CB1 and CB2 receptor pharmacology of three plant cannabinoids: delta9-tetrahydrocannabinol, cannabidiol and delta9-tetrahydrocannabivarin

Cannabis sativa is the source of a unique set of compounds known collectively as plant cannabinoids or phytocannabinoids. This review focuses on the manner with which three of these compounds, (-)-trans-delta9-tetrahydrocannabinol (delta9-THC), (-)-cannabidiol (CBD) and (-)-trans-delta9-tetrahydrocannabivarin (delta9-THCV), interact with cannabinoid CB1 and CB2 receptors. Delta9-THC, the main psychotropic constituent of cannabis, is a CB1 and CB2 receptor partial agonist and in line with classical pharmacology, the responses it elicits appear to be strongly influenced both by the expression level and signalling efficiency of cannabinoid receptors and by ongoing endogenous cannabinoid release. CBD displays unexpectedly high potency as an antagonist of CB1/CB2 receptor agonists in CB1- and CB2-expressing cells or tissues, the manner with which it interacts with CB2 receptors providing a possible explanation for its ability to inhibit evoked immune cell migration. Delta9-THCV behaves as a potent CB2 receptor partial agonist in vitro. In contrast, it antagonizes cannabinoid receptor agonists in CB1-expressing tissues. This it does with relatively high potency and in a manner that is both tissue and ligand dependent. Delta9-THCV also interacts with CB1 receptors when administered in vivo, behaving either as a CB1 antagonist or, at higher doses, as a CB1 receptor agonist. Brief mention is also made in this review, first of the production by delta9-THC of pharmacodynamic tolerance, second of current knowledge about the extent to which delta9-THC, CBD and delta9-THCV interact with pharmacological targets other than CB1 or CB2 receptors, and third of actual and potential therapeutic applications for each of these cannabinoids.

The pharmacology of the cannabinoid system--a question of efficacy and selectivity

Our knowledge of the function of the cannabinoid system in the body has been aided by the availability of pharmacological agents that affect its function. This has been achieved by the design of agents that either directly interact with the receptor (agonists and antagonist/inverse agonists) and agents that indirectly modulate the receptor output by changing the levels of the endogenous cannabinoids (endocannabinoids). In this review, examples of the most commonly used receptor agonists, antagonists/inverse agonists, and indirectly acting agents (anandamide uptake inhibitors, fatty acid amide hydrolase inhibitors, monoacylglycerol lipase inhibitors) are given, with particular focus upon their selectivity and, in the case of the directly acting compounds, efficacy. Finally, the links between the endocannabinoid and cyclooxygenase pathways are explored, in particular, with respect to agents whose primary function is to inhibit cyclooxygenase activity, but which also interact with the endocannabinoid system.

The antinociceptive effect of Delta9-tetrahydrocannabinol in the arthritic rat involves the CB(2) cannabinoid receptor

Cannabinoid CB(2) receptors have been implicated in antinociception in animal models of both acute and chronic pain. We evaluated the role both cannabinoid CB(1) and CB(2) receptors in mechanonociception in non-arthritic and arthritic rats. The antinociceptive effect of Delta(9)-tetrahydrocannabinol (Delta(9)THC) was determined in rats following administration of the cannabinoid CB(1) receptor-selective antagonist, SR141716A, the cannabinoid CB(2) receptor-selective antagonist, SR144528, or vehicle. Male Sprague-Dawley rats were rendered arthritic using Freund's complete adjuvant and tested for mechanical hyperalgesia in the paw-pressure test. Arthritic rats had a baseline paw-pressure of 83 +/- 3.6 g versus a paw-pressure of 177 +/- 6.42 g in non-arthritic rats. SR144528 or SR141716A (various doses mg/kg; i.p.) or 1:1:18 (ethanol:emulphor:saline) vehicle were injected 1 h prior to Delta(9)THC (4 mg/kg; i.p) or 1:1:18 vehicle and antinociception determined 30min post Delta(9)THC. AD(50)'s for both antagonists were calculated with 95% confidence limits. In addition, midbrain and spinal cord were removed for determination of cannabinoid CB(1) and CB(2) receptor protein density in the rats. SR144528 significantly attenuated the antinociceptive effect of Delta(9)THC in the arthritic rats [AD(50) = 3.3 (2.7-4) mg/kg], but not in the non-arthritic rats at a dose of 10/mg/kg. SR141716A significantly attenuated Delta(9)THC-induced antinociception in both the non-arthritic [AD(50) = 1.4 (0.8-2) mg/kg] and arthritic rat [AD(50) = 2.6 (1.8-3.1) mg/kg]. SR141716A or SR144528 alone did not result in a hyperalgesic effect as compared to vehicle. Our results indicate that the cannabinoid CB(2) receptor plays a critical role in cannabinoid-mediated antinociception, particularly in models of chronic inflammatory pain.