Endocannabinoids and neuropathic pain: focus on neuron-glia and endocannabinoid-neurotrophin interactions.

“Although originally described as a signalling system encompassing the cannabinoid CB1 and CB2 receptors, their endogenous agonists (the endocannabinoids), and metabolic enzymes regulating the levels of such agonists, the endocannabinoid system is now viewed as being more complex, and including metabolically related endocannabinoid-like mediators and their molecular targets as well.

The function and dysfunction of this complex signalling system in the molecular and cellular mechanisms of pain transduction and control has been widely studied over the last two decades.

In this review article, we describe some of the latest advances in our knowledge on the role of the endocannabinoid system, in its most recent and wider conception, in pain pathways, by focusing on: (1) neuron-glia interactions; and (2) emerging data on endocannabinoid cross-talk with neurotrophins, such as nerve growth factor and brain-derived neurotrophic factor.”

http://www.ncbi.nlm.nih.gov/pubmed/24494680

Neurotrophins, endocannabinoids and thermo-transient receptor potential: a threesome in pain signalling.

“Although pain is multifactorial at cellular and molecular levels, it is widely accepted that neurotrophin (TrkA, p75NTR, Ret and GFRs), cannabinoid (CB1 and CB2), and thermo-transient receptor potential (TRPs; TRPV1, TRPA1 and TRPM8) receptors play a pivotal role.

…the available information confirms that pharmacological modulation of this signalling triad is a highly valuable therapeutic strategy for effectively treating pain syndromes.”

http://www.ncbi.nlm.nih.gov/pubmed/24494676

Peripheral interactions between cannabinoid and opioid systems contribute to the antinociceptive effect of crotalphine.

“Crotalphine is an antinociceptive peptide… we evaluated the involvement of the peripheral cannabinoid system in the crotalphine effect and its interaction with the opioid system…

Crotalphine-induced antinociception involves peripheral CB2 cannabinoid receptors and local release of dynorphin A, which is dependent on CB2 receptor activation.

These results enhance our understanding of the mechanisms involved in the peripheral effect of crotalphine, as well as the interaction between the opioid and cannabinoid systems.”

http://www.ncbi.nlm.nih.gov/pubmed/24460677

Selective inhibition of FAAH produces antidiarrheal and antinociceptive effect mediated by endocannabinoids and cannabinoid-like fatty acid amides.

“The endogenous cannabinoid system (ECS) plays a crucial role in multiple physiological processes in the central nervous system and in the periphery. The discovery that selective cannabinoid (CB) receptor agonists exert a potent inhibitory action on gastrointestinal (GI) motility and pain has placed the ECS in the center of attention as a possible target for the treatment of functional GI diseases…

These data expand our understanding of the ECS function and provide a novel framework for the development of future potential treatments of functional GI disorders.”

http://www.ncbi.nlm.nih.gov/pubmed/24460851

Beyond radio-displacement techniques for Identification of CB1 Ligands: The First Application of a Fluorescence-quenching Assay.

“Cannabinoid type 1 Receptor (CB1) belongs to the GPCR family and it has been targeted, so far, for the discovery of drugs aimed at the treatment of neuropathic pain, nausea, vomit, and food intake disorders. Here, we present the development of the first fluorescent assay enabling the measurement of kinetic binding constants for CB1orthosteric ligands…

…a sustainable valid alternative to the expensive and environmental impacting radiodisplacement techniques and paves the way for an easy, fast and cheap high-throughput drug screening toward CB1 for identification of new orthosteric and allosteric modulators.”

http://www.ncbi.nlm.nih.gov/pubmed/24441508

Endocannabinoid and Cannabinoid-Like Fatty Acid Amide Levels Correlate with Pain-Related Symptoms in Patients with IBS-D and IBS-C: A Pilot Study.

“Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder, associated with alterations of bowel function, abdominal pain and other symptoms related to the GI tract. Recently the endogenous cannabinoid system (ECS) was shown to be involved in the physiological and pathophysiological control of the GI function. The aim of this pilot study was to investigate whether IBS defining symptoms correlate with changes in endocannabinoids or cannabinoid like fatty acid levels in IBS patients.

CONCLUSION:

IBS subtypes and their symptoms show distinct alterations of endocannabinoid and endocannabinoid-like fatty acid levels. These changes may partially result from reduced FAAH expression. The here reported changes support the notion that the ECS is involved in the pathophysiology of IBS and the development of IBS symptoms.”

Endocannabinoids: a unique opportunity to develop multitarget analgesics.

“After 4 millennia of more or less documented history of cannabis use, the identification of cannabinoids, and of Δ(9)-tetrahydrocannabinol in particular, occurred only during the early 1960s, and the cloning of cannabinoid CB1 and CB2 receptors, as well as the discovery of endocannabinoids and their metabolic enzymes, in the 1990s.

Despite this initial relatively slow progress of cannabinoid research, the turn of the century marked an incredible acceleration in discoveries on the “endocannabinoid signaling system,” its role in physiological and pathological conditions, and pain in particular, its pharmacological targeting with selective agonists, antagonists, and inhibitors of metabolism, and its previously unsuspected complexity.

The way researchers look at this system has thus rapidly evolved towards the idea of the “endocannabinoidome,” that is, a complex system including also several endocannabinoid-like mediators and their often redundant metabolic enzymes and “promiscuous” molecular targets.

These peculiar complications of endocannabinoid signaling have not discouraged efforts aiming at its pharmacological manipulation, which, nevertheless, now seems to require the development of multitarget drugs, or the re-visitation of naturally occurring compounds with more than one mechanism of action.

In fact, these molecules, as compared to “magic bullets,” seem to offer the advantage of modulating the “endocannabinoidome” in a safer and more therapeutically efficacious way.

This approach has provided so far promising preclinical results potentially useful for the future efficacious and safe treatment of chronic pain and inflammation.”

http://www.ncbi.nlm.nih.gov/pubmed/23623250

Involvement of cannabinoid receptors in peripheral and spinal morphine analgesia.

“The interactions between the cannabinoid and opioid systems for pain modulation are reciprocal. However, the role and the importance of the cannabinoid system in the antinociceptive effects of opioids remain uncertain. We studied these interactions with the goal of highlighting the involvement of the cannabinoid system in morphine-induced analgesia.

In both phases of the formalin test, intra paw and intrathecal morphine produced similar antinociceptive effects in C57BL/6, cannabinoid type 1 and type 2 receptor wildtype (respectively cnr1WT and cnr2WT) mice. In cnr1 and cnr2 knockout (KO) mice, at the dose used the antinociceptive effect of intra paw morphine in the inflammatory phase of the formalin test was decreased by 87% and 76%, respectively. Similarly, the antinociceptive effect of 0.1 μg spinal morphine in the inflammatory phase was abolished in cnr1KO mice and decreased by 90% in cnr2KO mice. Interestingly, the antinociceptive effect of morphine in the acute phase of the formalin test was only reduced in cnr1KO mice. Notably, systemic morphine administration produced similar analgesia in all genotypes, in both the formalin and the hot water immersion tail flick tests.

Because the pattern of expression of the mu opioid receptor (MOP), its binding properties and its G protein coupling remained unchanged across genotypes, it is unlikely that the loss of morphine analgesia in the cnr1KO and cnr2KO mice is the consequence of MOP malfunction or downregulation due to the absence of its heterodimerization with either the CB1 or the CB2 receptors, at least at the level of the spinal cord.”

http://www.ncbi.nlm.nih.gov/pubmed/24365460

The agonist binding mechanism of human CB2 receptor studied by molecular dynamics simulation, free energy calculation and 3D-QSAR studies.

“CB2-selective agonists have drawn attention in drug discovery, since CB2 becomes a promising target for the treatment of neuropathic pain without psychoactive or other CNS-related side effects…

A combinational exploration of both CoMFA steric and potential contour maps for CB2 affinities and the MD studied interaction modes sheds light on the structural requirements for CB2 agonists and serves as a basis for the design of novel CB2 agonists.”

http://www.ncbi.nlm.nih.gov/pubmed/24358778

Cannabinoid CB2 Receptors Regulate Central Sensitization and Pain Responses Associated with Osteoarthritis of the Knee Joint.

“Osteoarthritis (OA) of the joint is a prevalent disease accompanied by chronic, debilitating pain. Recent clinical evidence has demonstrated that central sensitization contributes to OA pain. An improved understanding of how OA joint pathology impacts upon the central processing of pain is crucial for the identification of novel analgesic targets/new therapeutic strategies.

Inhibitory cannabinoid 2 (CB2) receptors attenuate peripheral immune cell function and modulate central neuro-immune responses in models of neurodegeneration…

These findings suggest that targeting CB2 receptors may have therapeutic potential for treating OA pain.”

http://www.ncbi.nlm.nih.gov/pubmed/24282543