Actions of the dual FAAH/MAGL inhibitor JZL195 in a murine neuropathic pain model

Cannabis constituents for chronic neuropathic pain; reconciling the clinical and animal evidence

Chronic neuropathic pain is a debilitating pain syndrome caused by damage to the nervous system that is poorly served by current medications. Given these problems, clinical studies have pursued extracts of the plant Cannabis sativa as alternative treatments for this condition. The vast majority of these studies have examined cannabinoids which contain the psychoactive constituent delta-9-tetrahydrocannabinol (THC). While there have been some positive findings, meta-analyses of this clinical work indicates that this effectiveness is limited and hampered by side-effects. This review focuses on how recent preclinical studies have predicted the clinical limitations of THC-containing cannabis extracts, and importantly, point to how they might be improved. This work highlights the importance of targeting channels and receptors other than cannabinoid CB1 receptors which mediate many of the side-effects of cannabis.

Excessive alcohol intake produces persistent mechanical allodynia and dysregulates the endocannabinoid system in the lumbar dorsal root ganglia of genetically-selected Marchigian Sardinian alcohol-preferring rats

Epidemiological data indicate a strong association between alcohol use disorder (AUD) and neuropathic pain. Genetically-selected Marchigian Sardinian alcohol-preferring (msP) rats exhibit a high preference for alcohol compared with their background strain (Wistar rats), but their sensitivity to mechanical allodynia after chronic alcohol exposure is unknown. The present study compared the development of mechanical allodynia between "low, non-pathological drinker" Wistar rats and "high drinker" msP rats using the two-bottle choice (2BC) free-access procedure. Several studies reported the involvement of endocannabinoids (eCBs) in modulating mechanical allodynia, but there are no data on their role in alcohol-related allodynia. Thus, the present study assessed eCBs and their related lipid species in lumbar dorsal root ganglia (DRG) and correlated them with mechanical allodynia in our model. We found that male and female msP rats developed persistent mechanical allodynia during protracted abstinence from alcohol, presenting no sign of recovery, as opposed to Wistar rats. This effect directly correlated with their total alcohol intake. Notably, we found a correlation between lower lumbar DRG 2-arachidonoylglycerol (2-AG) levels and the development of higher mechanical allodynia during abstinence in msP rats of both sexes but not in Wistar rats. Moreover, alcohol-exposed and abstinent msP and Wistar females but not males exhibited significant alterations of thromboxane B2 and prostaglandin E2/prostaglandin D2 compared with naive rats. These findings demonstrate that DRG 2-AG metabolism is altered in msP rats during prolonged abstinence and represents a potentially interesting pharmacological target for the treatment of mechanical allodynia during alcohol abstinence.

Disrupted stress-induced analgesia in a neuropathic pain state is rescued by the endocannabinoid degradation inhibitor JZL195

Acute stress normally engages descending brain pathways to produce an antinociceptive response, known as stress-induced analgesia. Paradoxically, these descending pain modulatory pathways are also involved in the maintenance of the abnormal pain associated with chronic neuropathic pain. It remains unclear how stress-induced analgesia is affected by neuropathic pain states. We therefore examined the impact of a chronic constriction nerve-injury (CCI) model of neuropathic pain on restraint stress-induced analgesia in C57BL/6 mice. Thirty minutes of restraint stress produced analgesia in the hotplate thermal nociceptive assay that was less in CCI compared to control mice who underwent a sham-surgery. In sham but not CCI mice, stress-induced analgesia was reduced by the opioid receptor antagonist naltrexone. The cannabinoid CB1 receptor antagonist AM281 did not affect stress-induced analgesia in either sham or CCI mice. Low-dose pre-treatment with the dual fatty acid amide hydrolase and monoacylglycerol lipase inhibitor JZL195 increased stress-induced analgesia in CCI but not sham mice. The JZL195 enhancement of stress-induced analgesia in CCI mice was abolished by AM281 but was unaffected by naltrexone. These findings indicate that the acute opioid-mediated analgesic response to a psychological stressor is disrupted in a nerve-injury model of neuropathic pain. Importantly, this impairment of stress-induced analgesia was rescued by blockade of endocannabinoid breakdown via a cannabinoid CB1 receptor dependent mechanism. These findings suggest that subthreshold treatment with endocannabinoid degradation blockers could be used to alleviate the disruption of endogenous pain control systems in a neuropathic pain state.

Modulation of chemotherapy-induced peripheral neuropathy by JZL195 through glia and the endocannabinoid system

Chemotherapy-induced peripheral neuropathy (CIPN) used to treat cancer, is a significant side effect with a complex pathophysiology, and its mechanisms remain unclear. Recent research highlights neuroinflammation, which is modulated by the endocannabinoid system (ECS) and associated with glial activation, and the role of toll-like receptor 4 (TLR4) in CIPN. This study aimed to investigate the effects of JZL195, an inhibitor of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), and explore the connection between cannabinoid receptors and TLR4 in glial cells. A CIPN animal model was developed using cisplatin-injected male C57BL/6 mice. Mechanical and cold allodynia were assessed through von Frey and acetone tests. Western blot analysis was used to examine the expression of catabolic enzymes, cannabinoid receptors, glial cells, and neuroinflammatory factors in the dorsal root ganglia (DRGs) and spinal cord. Immunohistochemistry was used to investigate the colocalization of cannabinoid receptors and TLR4 in glial cells. JZL195 alleviated pain by inhibiting FAAH/MAGL, modulating the ECS and neuroinflammatory factors, and suppressing glial cell activity. Additionally, cannabinoid receptors and TLR4 colocalized with astrocytes and microglia in the spinal cord. This study highlights the therapeutic potential of JZL195 in modulating the ECS and suggests a correlation between cannabinoid receptors and TLR4 in spinal glial cells, providing insight into alleviating pain and neuroinflammation in CIPN.

SGIP1 Deletion in Mice Attenuates Mechanical Hypersensitivity Elicited by Inflammation

Background: Activation of cannabinoid receptor 1 (CB1R) in the nervous system modulates the processing of acute and chronic pain. CB1R activity is regulated by desensitization and internalization. SH3-containing GRB2-like protein 3-interacting protein 1 (SGIP1) inhibits the internalization of CB1R. This causes increased and prolonged association of the desensitized receptor with G protein-coupled receptor kinase 3 (GRK3) and beta-arrestin on the cell membrane and results in decreased activation of extracellular signal-regulated kinase 1/2 (ERK1/2) pathway. Genetic deletion of SGIP1 in mice leads to altered CB1R-related functions, such as decreased anxiety-like behaviors, modified cannabinoid tetrad behaviors, reduced acute nociception, and increased sensitivity to analgesics. In this work, we asked if deletion of SGIP1 affects chronic nociception and analgesic effect of Δ9-tetrahydrocannabinol (THC) and WIN 55,212-2 (WIN) in mice. Methods: We measured tactile responses of hind paws to increasing pressure in wild-type and SGIP1 knock-out mice. Inflammation in the paw was induced by local injection of carrageenan. To determine the mechanical sensitivity, the paw withdrawal threshold (PWT) was measured using an electronic von Frey instrument with the progression of the applied force. Results: The responses to mechanical stimuli varied depending on the sex, genotype, and treatment. SGIP1 knock-out male mice exhibited lower PWT than wild-type males. On the contrary, the female mice exhibited comparable PWT. Following THC or WIN treatment in male mice, SGIP1 knock-out males exhibited PWT lower than wild-type males. THC treatment in SGIP1 knock-out females resulted in PWT higher than after THC treatment of wild-type females. However, SGIP1 knock-out and wild-type female mice exhibited similar PWT after WIN treatment. Conclusions: We provide evidence that SGIP1, possibly by interacting with CB1R, is involved in processing the responses to chronic pain. The absence of SGIP1 results in enhanced sensitivity to mechanical stimuli in males, but not females. The antinociceptive effect of THC is superior to that of WIN in SGIP1 knock-out mice in the carrageenan-induced model of chronic pain.

Endocannabinoid Hydrolase Inhibitors: Potential Novel Anxiolytic Drugs

Over the past decade, the idea of targeting the endocannabinoid system to treat anxiety disorders has received increasing attention. Previous studies focused more on developing cannabinoid receptor agonists or supplementing exogenous cannabinoids, which are prone to various adverse effects due to their strong pharmacological activity and poor receptor selectivity, limiting their application in clinical research. Endocannabinoid hydrolase inhibitors are considered to be the most promising development strategies for the treatment of anxiety disorders. More recent efforts have emphasized that inhibition of two major endogenous cannabinoid hydrolases, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), indirectly activates cannabinoid receptors by increasing endogenous cannabinoid levels in the synaptic gap, circumventing receptor desensitization resulting from direct enhancement of endogenous cannabinoid signaling. In this review, we comprehensively summarize the anxiolytic effects of MAGL and FAAH inhibitors and their potential pharmacological mechanisms, highlight reported novel inhibitors or natural products, and provide an outlook on future directions in this field.

The Use of Compounds Derived from Cannabis sativa in the Treatment of Epilepsy, Painful Conditions, and Neuropsychiatric and Neurodegenerative Disorders

Neurological disorders present a wide range of symptoms and challenges in diagnosis and treatment. Cannabis sativa, with its diverse chemical composition, offers potential therapeutic benefits due to its anticonvulsive, analgesic, anti-inflammatory, and neuroprotective properties. Beyond cannabinoids, cannabis contains terpenes and polyphenols, which synergistically enhance its pharmacological effects. Various administration routes, including vaporization, oral ingestion, sublingual, and rectal, provide flexibility in treatment delivery. This review shows the therapeutic efficacy of cannabis in managing neurological disorders such as epilepsy, neurodegenerative diseases, neurodevelopmental disorders, psychiatric disorders, and painful pathologies. Drawing from surveys, patient studies, and clinical trials, it highlights the potential of cannabis in alleviating symptoms, slowing disease progression, and improving overall quality of life for patients. Understanding the diverse therapeutic mechanisms of cannabis can open up possibilities for using this plant for individual patient needs.

Potential Therapeutic Targets to Modulate the Endocannabinoid System in Alzheimer's Disease

Alzheimer's disease (AD), the most common neurodegenerative disease (NDD), is characterized by chronic neuronal cell death through progressive loss of cognitive function. Amyloid beta (Aβ) deposition, neuroinflammation, oxidative stress, and hyperphosphorylated tau proteins are considered the hallmarks of AD pathology. Different therapeutic approaches approved by the Food and Drug Administration can only target a single altered pathway instead of various mechanisms that are involved in AD pathology, resulting in limited symptomatic relief and almost no effect in slowing down the disease progression. Growing evidence on modulating the components of the endocannabinoid system (ECS) proclaimed their neuroprotective effects by reducing neurochemical alterations and preventing cellular dysfunction. Recent studies on AD mouse models have reported that the inhibitors of the fatty acid amide hydrolase (FAAH) and monoacylglycerol (MAGL), hydrolytic enzymes for N-arachidonoyl ethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), respectively, might be promising candidates as therapeutical intervention. The FAAH and MAGL inhibitors alone or in combination seem to produce neuroprotection by reversing cognitive deficits along with Aβ-induced neuroinflammation, oxidative responses, and neuronal death, delaying AD progression. Their exact signaling mechanisms need to be elucidated for understanding the brain intrinsic repair mechanism. The aim of this review was to shed light on physiology and pathophysiology of AD and to summarize the experimental data on neuroprotective roles of FAAH and MAGL inhibitors. In this review, we have also included CB1R and CB2R modulators with their diverse roles to modulate ECS mediated responses such as anti-nociceptive, anxiolytic, and anti-inflammatory actions in AD. Future research would provide the directions in understanding the molecular mechanisms and development of new therapeutic interventions for the treatment of AD.

Inhibitors of Endocannabinoids' Enzymatic Degradation as a Potential Target of the Memory Disturbances in an Acute N-Methyl-D-Aspartate (NMDA) Receptor Hypofunction Model of Schizophrenia in Mice

Treating schizophrenia with the available pharmacotherapy is difficult. One possible strategy is focused on the modulation of the function of the endocannabinoid system (ECS). The ECS is comprised of cannabinoid (CB) receptors, endocannabinoids and enzymes responsible for the metabolism of endocannabinoids (fatty acid hydrolase (FAAH) and monoacylglycerol lipase (MAGL)). Here, the aim of the experiments was to evaluate the impact of inhibitors of endocannabinoids' enzymatic degradation in the brain: KML-29 (MAGL inhibitor), JZL-195 (MAGL/FAAH inhibitor) and PF-3845 (FAAH inhibitor), on the memory disturbances typical for schizophrenia in an acute N-methyl-D-aspartate (NMDA) receptor hypofunction animal model of schizophrenia (i.e., injection of MK-801, an NMDA receptor antagonist). The memory-like responses were assessed in the passive avoidance (PA) test. A single administration of KML-29 or PF-3845 had a positive effect on the memory processes, but an acute administration of JZL-195 impaired cognition in mice in the PA test. Additionally, the combined administration of a PA-ineffective dose of KML-29 (5 mg/kg) or PF-3845 (3 mg/kg) attenuated the MK-801-induced cognitive impairment (0.6 mg/kg). Our results suggest that the indirect regulation of endocannabinoids' concentration in the brain through the use of selected inhibitors may positively affect memory disorders, and thus increase the effectiveness of modern pharmacotherapy of schizophrenia.

Weak Hypotensive Effect of Chronic Administration of the Dual FAAH/MAGL Inhibitor JZL195 in Spontaneously Hypertensive Rats as Revealed by Area under the Curve Analysis

The enhancement of the endocannabinoid tone might have a beneficial influence on hypertension. Polypharmacology proposes multi-target-directed ligands (MTDLs) as potential therapeutic agents for the treatment of complex diseases. In the present paper, we studied JZL195, a dual inhibitor of the two major endocannabinoid-degrading enzymes, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). Hemodynamic parameters were assessed in conscious animals via radiotelemetry and tail-cuff methods and then evaluated by the area under the curve (AUC). Single administration of JZL195 induced dose-dependent weak hypotensive and bradycardic responses in SHR but not in WKY. Similarly, its chronic application revealed only a slight hypotensive potential which, however, effectively prevented the progression of hypertension and did not undergo tolerance. In addition, multiple JZL195 administrations slightly decreased heart rate only in WKY and prevented the gradual weight gain in both groups. JZL195 did not affect organ weights, blood glucose level, rectal temperature and plasma oxidative stress markers. In conclusion, chronic dual FAAH/MAGL inhibition prevents the progression of hypertension in SHR without affecting some basal functions of the body. In addition, our study clearly proves the suitability of AUC for the evaluation of weak blood pressure changes.

Anti-nociceptive potential of an isatin-derived dual fatty acid amide hydrolase-monoacylglycerol lipase inhibitor

BACKGROUND

Recently, we have reported an isatin-derived carbohydrazone, 5-chloro-N'-(6-chloro-2-oxoindolin-3-ylidene)-2-hydroxybenzohydrazide (SIH 3) as dual nanomolar FAAH (fatty acid amide hydrolase)-MAGL (monoacylglycerol lipase) inhibitor with good CNS penetration and neuroprotective activity profile. In this study, we further investigated the pharmacological profile of compound SIH 3 in the neuropathic pain model along with acute toxicity and ex vivo studies.

METHODS

Chronic constrictive injury (CCI) was used to induce neuropathic pain in male Sprague-Dawley rats and the anti-nociceptive activity of the compound SIH 3 was investigated at 25, 50, and 100 mg/kg ip. Subsequently, locomotor activity was measured by rotarod and actophotometer experiments. The acute oral toxicity of the compound was assessed as per the OECD guidelines 423.

RESULTS

Compound SIH 3 showed significant anti-nociceptive activity in the CCI-induced neuropathic pain model without altering the locomotor activity. Furthermore, compound SIH 3 showed an excellent safety profile (up to 2000 mg/kg, po) in the acute oral toxicity study and was also non-hepatotoxic. Further, ex vivo studies revealed that the compound SIH 3 produces a significant antioxidant effect in oxidative stress induced by CCI.

CONCLUSION

Our findings suggest that the investigated compound SIH 3 has the potential to be developed as an anti-nociceptive agent.

Potent dual MAGL/FAAH inhibitor AKU-005 engages endocannabinoids to diminish meningeal nociception implicated in migraine pain

BACKGROUND

Engaging the endocannabinoid system through inhibition of monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), degrading endocannabinoids (endoCBs) 2-arachidonoylglycerol (2-AG) and anandamide (AEA), was proposed as a promising approach to ameliorate migraine pain. However, the activity of MAGL and FAAH and action of endoCB on spiking activity of meningeal afferents, from which migraine pain originates, has not been explored thus far. Therefore, we here explored the analgesic effects of endoCB enhancement in rat and human meningeal tissues.

METHODS

Both MAGL and FAAH activity and local 2-AG and AEA levels were measured by activity-based protein profiling (ABPP) and LC-MS/MS, respectively, in rat meninges obtained from hemiskulls of P38-P40 Wistar rats and human meninges from elderly patients undergoing non-migraine related neurosurgery. The action on endoCBs upon administration of novel dual MAGL/FAAH inhibitor AKU-005 on meningeal afferents excitability was tested by investigating paired KCl-induced spiking and validation with local (co-)application of either AEA or 2-AG. Finally, the specific TRPV1 agonist capsaicin and blocker capsazepine were tested.

RESULTS

The basal level of 2-AG exceeded that of AEA in rat and human meninges. KCl-induced depolarization doubled the level of AEA. AKU-005 slightly increased spontaneous spiking activity whereas the dual MAGL/FAAH inhibitor significantly decreased excitation of nerve fibres induced by KCl. Similar inhibitory effects on meningeal afferents were observed with local applications of 2-AG or AEA. The action of AKU-005 was reversed by CB1 antagonist AM-251, implying CB1 receptor involvement in the anti-nociceptive effect. The inhibitory action of AEA was also reversed by AM-251, but not with the TRPV1 antagonist capsazepine. Data cluster analysis revealed that both AKU-005 and AEA largely increased long-term depression-like meningeal spiking activity upon paired KCl-induced spiking.

CONCLUSIONS

In the meninges, high anti-nociceptive 2-AG levels can tonically counteract meningeal signalling, whereas AEA can be engaged on demand by local depolarization. AEA-mediated anti-nociceptive effects through CB1 receptors have therapeutic potential. Together with previously detected MAGL activity in trigeminal ganglia, dual MAGL/FAAH inhibitor AKU-005 appears promising as migraine treatment.

Synthesis and evaluation of carbamate derivatives as fatty acid amide hydrolase and monoacylglycerol lipase inhibitors

Fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) are the primary catabolic enzymes for endocannabinoids, anandamide (AEA), and 2-arachidonoyl glycerol. Numerous studies have shown that FAAH and MAGL play an important role in modulating various central nervous system activities; hence, the development of small molecule FAAH/MAGL inhibitors is an active area of research. Several small molecules possessing the carbamate scaffold are documented as potential FAAH/MAGL inhibitors. Here, we designed and synthesized a series of open chain and cyclic carbamates and evaluated their dual FAAH-MAGL inhibition properties. Phenyl [4-(piperidin-1-ylmethyl)phenyl]carbamate (2e) emerged as the most potent MAGL inhibitor (IC₅₀  = 19 nM), benzyl (1H-benzo[d]imidazol-2-yl)carbamate (3h) was the most potent FAAH inhibitor (IC₅₀  = 55 nM), and phenyl (6-fluorobenzo[d]thiazol-2-yl)carbamate (2i) egressed as a nonselective dual FAAH-MAGL inhibitor (FAAH: 82 nM, MAGL: 72 nM). The enzyme kinetics experiments revealed that the compounds inhibit FAAH/MAGL in a covalent-reversible manner, with a mixed binding mode of action. Moreover, the lead compounds were found suitable for blood-brain permeation in the parallel artificial membrane permeation assay. Furthermore, docking simulation experiments suggested that the potency of the lead compounds was governed by hydrogen bonds and hydrophobic interactions with the enzyme active sites. In silico drug-likeness and ADMETox prediction studies provided useful information on the compounds' oral absorption, metabolism, and toxicity profiles. In summary, this study afforded potent multifunctional carbamates with appreciable pharmacokinetic profiles meriting further investigation.

Inhibiting Endocannabinoid Hydrolysis as Emerging Analgesic Strategy Targeting a Spectrum of Ion Channels Implicated in Migraine Pain

Migraine is a disabling neurovascular disorder characterized by severe pain with still limited efficient treatments. Endocannabinoids, the endogenous painkillers, emerged, alternative to plant cannabis, as promising analgesics against migraine pain. In this thematic review, we discuss how inhibition of the main endocannabinoid-degrading enzymes, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), could raise the level of endocannabinoids (endoCBs) such as 2-AG and anandamide in order to alleviate migraine pain. We describe here: (i) migraine pain signaling pathways, which could serve as specific targets for antinociception; (ii) a divergent distribution of MAGL and FAAH activities in the key regions of the PNS and CNS implicated in migraine pain signaling; (iii) a complexity of anti-nociceptive effects of endoCBs mediated by cannabinoid receptors and through a direct modulation of ion channels in nociceptive neurons; and (iv) the spectrum of emerging potent MAGL and FAAH inhibitors which efficiently increase endoCBs levels. The specific distribution and homeostasis of endoCBs in the main regions of the nociceptive system and their generation ‘on demand’, along with recent availability of MAGL and FAAH inhibitors suggest new perspectives for endoCBs-mediated analgesia in migraine pain.

Synthesis and evaluation of dual fatty acid amide hydrolase-monoacylglycerol lipase inhibition and antinociceptive activities of 4-methylsulfonylaniline-derived semicarbazones

Fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) are promising targets for neuropathic pain and other CNS disorders. Based on our previous lead compound SIH 3, we designed and synthesized a series of 4-methylsulfonylphenyl semicarbazones and evaluated for FAAH and MAGL inhibition properties. Most of the compounds showed potency towards both enzymes with leading FAAH selectivity. Compound (Z)-2-(2,6-dichlorobenzylidene)-N-(4-(methylsulfonyl)phenyl)hydrazine-1-carboxamide emerged as the lead inhibitor against both FAAH (IC₅₀ = 11 nM) and MAGL (IC₅₀ = 36 nM). The lead inhibitor inhibited FAAH by non-competitive mode, but showed a mixed-type inhibition against MAGL. Molecular docking study unveiled that the docked ligands bind favorably to the active sites of FAAH and MAGL. The lead inhibitor interacted with FAAH and MAGL via π-π stacking via phenyl ring and hydrogen bonding through sulfonyl oxygen atoms or amide NH. Moreover, the stability of docked complexes was rationalized by molecular simulation studies. PAMPA assay revealed that the lead compound is suitable for blood-brain penetration. The lead compound showed better cell viability in lipopolysaccharide-induced neurotoxicity assay in SH-SY5Y cell lines. Further, in-vivo experiments unveiled that dual inhibitor was safe up to 2000 mg/kg with no hepatotoxicity. The dual FAAH-MAGL inhibitor produced significant anti-nociceptive effect in the CCI model of neuropathic pain without altering locomotion activity. Lastly, the lead compound exhibited promising ex-vivo FAAH/MAGL inhibition activity at the dose of 10 mg/kg and 20 mg/kg. Thus, these findings suggest that the semicarbazone-based lead compound can be a potential template for the development of agents for neuropathic pain.

Effect of the MAGL/FAAH Dual Inhibitor JZL-195 on Streptozotocin-Induced Alzheimer's Disease-like Sporadic Dementia in Mice with an Emphasis on Aβ, HSP-70, Neuroinflammation, and Oxidative Stress

Alzheimer's disease is identified by pathological hallmarks such as intracellular neurofibrillary tangles (NFTs) and extracellular amyloid β plaques. Several hypotheses exist to define the neurodegeneration including microglial activation associated with neuroinflammatory processes. Recently, pharmacological inhibition of endocannabinoid (eCB)-degrading enzymes, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), is being investigated to modulate the pathology of Alzheimer's disease. While MAGL inhibitors upregulate 2-acyl glycerol (2-AG) levels and reduce neuroinflammation, FAAH inhibitors elevate anandamide (AEA) levels and prevent the degradation of HSP-70, thereby preventing the phosphorylation of tau protein and formation of NFTs in neural cells. We investigated the possible neuroprotective potential of the dual MAGL/FAAH inhibitor JZL-195 (20 mg/kg) against ICV-STZ-induced sporadic Alzheimer's disease (SAD) in Swiss albino mice using donepezil (5 mg/kg) as the standard. The protective effects of JZL-195 were observed by the reversal of altered levels of Aβ_1-42, HSP-70, neuroinflammatory cytokines, and oxidative stress markers. However, JZL-195 expressed no cognitive improvement when assessed by spontaneous alternation behavior and Morris water maze tests and no effects on the AChE enzyme level in the hippocampal tissues of mice. Therefore, the findings of the present study indicate that although JZL-195 exhibited no improvement in cognitive deficits associated with sporadic Alzheimer's disease, it displayed significant reversal of the biochemical anomalies, thereby suggesting its therapeutic potential against the sporadic Alzheimer's disease model.

Polypharmacological Approaches for CNS Diseases: Focus on Endocannabinoid Degradation Inhibition

Polypharmacology breaks up the classical paradigm of “one-drug, one target, one disease” electing multitarget compounds as potential therapeutic tools suitable for the treatment of complex diseases, such as metabolic syndrome, psychiatric or degenerative central nervous system (CNS) disorders, and cancer. These diseases often require a combination therapy which may result in positive but also negative synergistic effects. The endocannabinoid system (ECS) is emerging as a particularly attractive therapeutic target in CNS disorders and neurodegenerative diseases including Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), stroke, traumatic brain injury (TBI), pain, and epilepsy. ECS is an organized neuromodulatory network, composed by endogenous cannabinoids, cannabinoid receptors type 1 and type 2 (CB₁ and CB₂), and the main catabolic enzymes involved in the endocannabinoid inactivation such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). The multiple connections of the ECS with other signaling pathways in the CNS allows the consideration of the ECS as an optimal source of inspiration in the development of innovative polypharmacological compounds. In this review, we focused our attention on the reported polypharmacological examples in which FAAH and MAGL inhibitors are involved.

Dual Inhibition of FAAH and MAGL Counteracts Migraine-like Pain and Behavior in an Animal Model of Migraine

The endocannabinoid system exerts an important role in pain processing and modulation. Modulation of the system with hydrolase inhibitors of anandamide (AEA) or 2-arachidonyl glycerol (2-AG) has proved effective in reducing migraine-like features in animal models of migraine. Here, we investigated the effect of dual inhibition of the AEA and 2-AG catabolic pathways in the nitroglycerin-based animal model of migraine. The dual inhibitor JZL195 was administered to rats 2 h after nitroglycerin or vehicle injection. Rats were then exposed to the open field test and the orofacial formalin test. At the end of the tests, they were sacrificed to evaluate calcitonin gene-related peptide (CGRP) serum levels and gene expression of CGRP and cytokines in the cervical spinal cord and the trigeminal ganglion. The dual inhibitor significantly reduced the nitroglycerin-induced trigeminal hyperalgesia and pain-associated behavior, possibly via cannabinoid 1 receptors-mediated action, but it did not change the hypomotility and the anxiety behaviors induced by nitroglycerin. The decreased hyperalgesia was associated with a reduction in CGRP and cytokine gene expression levels in central and peripheral structures and reduced CGRP serum levels. These data suggest an antinociceptive synergy of the endocannabinoid action in peripheral and central sites, confirming that this system participates in reduction of cephalic pain signals.

Cannabinoids and chronic pelvic pain in women: Focus on endometriosis

Chronic pelvic pain in women is common and frequently difficult to treat. Chronic pelvic pain often develops in the setting of endometriosis, interstitial cystitis/bladder pain syndrome, and vulvodynia. Cannabinoids are a promising treatment modality for non-cancer chronic pain, but have not been studied in women with chronic pelvic pain nor in specific chronic pelvic pain conditions. This review focuses on the interaction of the endocannabinoid system with the menstrual cycles, with endometriotic lesions, and within the bladder. Furthermore, it provides a brief overview of existing literature of the effects of endocannabinoids on chronic pain generally, with a focus on neuropathic pain. Finally, it discusses limited data available regarding the use of cannabinoids in women with chronic pelvic pain conditions. In the opinion of the authors, cannabinoids are a reasonable treatment modality for refractory chronic pelvic pain, especially if a neuropathic component is suspected. Practitioners should expect a modest effect on pain levels with an acceptable safety profile.

Cannabinoids, the endocannabinoid system, and pain: a review of preclinical studies

ABSTRACT

This narrative review represents an output from the International Association for the Study of Pain's global task force on the use of cannabis, cannabinoids, and cannabis-based medicines for pain management, informed by our companion systematic review and meta-analysis of preclinical studies in this area. Our aims in this review are (1) to describe the value of studying cannabinoids and endogenous cannabinoid (endocannabinoid) system modulators in preclinical/animal models of pain; (2) to discuss both pain-related efficacy and additional pain-relevant effects (adverse and beneficial) of cannabinoids and endocannabinoid system modulators as they pertain to animal models of pathological or injury-related persistent pain; and (3) to identify important directions for future research. In service of these goals, this review (1) provides an overview of the endocannabinoid system and the pharmacology of cannabinoids and endocannabinoid system modulators, with specific relevance to animal models of pathological or injury-related persistent pain; (2) describes pharmacokinetics of cannabinoids in rodents and humans; and (3) highlights differences and discrepancies between preclinical and clinical studies in this area. Preclinical (rodent) models have advanced our understanding of the underlying sites and mechanisms of action of cannabinoids and the endocannabinoid system in suppressing nociceptive signaling and behaviors. We conclude that substantial evidence from animal models supports the contention that cannabinoids and endocannabinoid system modulators hold considerable promise for analgesic drug development, although the challenge of translating this knowledge into clinically useful medicines is not to be underestimated.

Inhibition of MAGL activates the Keap1/Nrf2 pathway to attenuate glucocorticoid-induced osteonecrosis of the femoral head

Glucocorticoids (GCs) are used in treating viral infections, acute spinal cord injury, autoimmune diseases, and shock. Several patients develop GC-induced osteonecrosis of the femoral head (ONFH). However, the pathogenic mechanisms underlying GC-induced ONFH remain poorly understood. GC-directed bone marrow mesenchymal stem cells (BMSCs) fate is an important factor that determines GC-induced ONFH. At high concentrations, GCs induce BMSC apoptosis by promoting oxidative stress. In the present study, we aimed to elucidate the molecular mechanisms that relieve GC-induced oxidative stress in BMSCs, which would be vital for treating ONFH. The endocannabinoid system regulates oxidative stress in multiple organs. Here, we found that monoacylglycerol lipase (MAGL), a key molecule in the endocannabinoid system, was significantly upregulated during GC treatment in osteoblasts both in vitro and in vivo. MAGL expression was positively correlated with expression of the NADPH oxidase family and apoptosis-related proteins. Functional analysis showed that MAGL inhibition markedly reduced oxidative stress and partially rescued BMSC apoptosis. Additionally, in vivo studies indicated that MAGL inhibition effectively attenuated GC-induced ONFH. Pathway analysis showed that MAGL inhibition regulated oxidative stress in BMSCs via the Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. The expression of Nrf2, a major regulator of intracellular antioxidants, was upregulated by inhibiting MAGL. Nrf2 activation can mimic the effect of MAGL inhibition and significantly reduce GC-induced oxidative damage in BMSCs. The beneficial effects of MAGL inhibition were attenuated after the blockade of the Keap1/Nrf2 antioxidant signaling pathway. Notably, pharmacological blockade of MAGL conferred femoral head protection in GC-induced ONFH, even after oxidative stress responses were initiated. Therefore, MAGL may represent a novel target for the prevention and treatment of GC-induced ONFH.

Behavioral Battery for Testing Candidate Analgesics in Mice. II. Effects of Endocannabinoid Catabolic Enzyme Inhibitors and ∆9-Tetrahydrocannabinol

Enhanced signaling of the endocannabinoid (eCB) system through inhibition of the catabolic enzymes monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH) has received increasing interest for development of candidate analgesics. This study compared effects of MAGL and FAAH inhibitors with effects of ∆9-tetrahydrocannabinol (THC) using a battery of pain-stimulated, pain-depressed, and pain-independent behaviors in male and female mice. Intraperitoneal injection of dilute lactic acid (IP acid) served as an acute visceral noxious stimulus to stimulate two behaviors (stretching, facial grimace) and depress two behaviors (rearing, nesting). Nesting and locomotion were also assessed in the absence of IP acid as pain-independent behaviors. THC and a spectrum of six eCB catabolic enzyme inhibitors ranging from MAGL- to FAAH-selective were assessed for effectiveness to alleviate pain-related behaviors at doses that did not alter pain-independent behaviors. The MAGL-selective inhibitor MJN110 produced the most effective antinociceptive profile, with 1.0 mg/kg alleviating IP acid effects on stretching, grimace, and nesting without altering pain-independent behaviors. MJN110 effects on IP acid-depressed nesting had a slow onset and long duration (40 minutes to 6 hours), were blocked by rimonabant, and tended to be greater in females. As inhibitors increased in FAAH selectivity, antinociceptive effectiveness decreased. PF3845, the most FAAH-selective inhibitor, produced no antinociception up to doses that disrupted locomotion. THC decreased IP acid-stimulated stretching and grimace at doses that did not alter pain-independent behaviors; however, it did not alleviate IP acid-induced depression of rearing or nesting. These results support further consideration of MAGL-selective inhibitors as candidate analgesics for acute inflammatory pain. SIGNIFICANCE STATEMENT: This study characterized a spectrum of endocannabinoid catabolic enzyme inhibitors ranging in selectivity from monoacylglycerol lipase-selective to fatty acid amide hydrolase-selective in a battery of pain-stimulated, pain-depressed, and pain-independent behaviors previously pharmacologically characterized in a companion paper. This battery provides a method for prioritizing candidate analgesics by effectiveness to alleviate pain-related behaviors at doses that do not alter pain-independent behaviors, with inclusion of pain-depressed behaviors increasing translational validity and decreasing susceptibility to motor-depressant false positives.

Distinct Activity of Endocannabinoid-Hydrolyzing Enzymes MAGL and FAAH in Key Regions of Peripheral and Central Nervous System Implicated in Migraine

In migraine pain, cannabis has a promising analgesic action, which, however, is associated with side psychotropic effects. To overcome these adverse effects of exogenous cannabinoids, we propose migraine pain relief via activation of the endogenous cannabinoid system (ECS) by inhibiting enzymes degrading endocannabinoids. To provide a functional platform for such purpose in the peripheral and central parts of the rat nociceptive system relevant to migraine, we measured by activity-based protein profiling (ABPP) the activity of the main endocannabinoid-hydrolases, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH). We found that in trigeminal ganglia, the MAGL activity was nine-fold higher than that of FAAH. MAGL activity exceeded FAAH activity also in DRG, spinal cord and brainstem. However, activities of MAGL and FAAH were comparably high in the cerebellum and cerebral cortex implicated in migraine aura. MAGL and FAAH activities were identified and blocked by the selective and potent inhibitors JJKK-048/KML29 and JZP327A, respectively. The high MAGL activity in trigeminal ganglia implicated in the generation of nociceptive signals suggests this part of ECS as a priority target for blocking peripheral mechanisms of migraine pain. In the CNS, both MAGL and FAAH represent potential targets for attenuation of migraine-related enhanced cortical excitability and pain transmission.

Endocannabinoid signaling regulates the reinforcing and psychostimulant effects of ketamine in mice

The abuse potential of ketamine limits its clinical application, but the precise mechanism remains largely unclear. Here we discovered that ketamine significantly remodels the endocannabinoid-related lipidome and activates 2-arachidonoylglycerol (2-AG) signaling in the dorsal striatum (caudate nucleus and putamen, CPu) of mice. Elevated 2-AG in the CPu is essential for the psychostimulant and reinforcing effects of ketamine, whereas blockade of the cannabinoid CB1 receptor, a predominant 2-AG receptor, attenuates ketamine-induced remodeling of neuronal dendrite structure and neurobehaviors. Ketamine represses the transcription of the monoacylglycerol lipase (MAGL) gene by promoting the expression of PRDM5, a negative transcription factor of the MAGL gene, leading to increased 2-AG production. Genetic overexpression of MAGL or silencing of PRDM5 expression in the CPu robustly reduces 2-AG production and ketamine effects. Collectively, endocannabinoid signaling plays a critical role in mediating the psychostimulant and reinforcing properties of ketamine.

Peripheral deficiency and antiallodynic effects of 2-arachidonoyl glycerol in a mouse model of paclitaxel-induced neuropathic pain

BACKGROUND

Modulation of the endocannabinoid system has been shown to alleviate neuropathic pain. The aim of this study was to evaluate if treatment with paclitaxel, a chemotherapeutic agent that induces neuropathic pain, affects endocannabinoid levels at a time when mice develop paclitaxel-induced mechanical allodynia. We also evaluated the peripheral antiallodynic activity of the endocannabinoid 2-arachidonoyl glycerol (2-AG) and an inhibitor of monoacylglycerol lipase (MAGL), an enzyme responsible for 2-AG hydrolysis.

METHODS

Female BALB/c mice were treated intraperitoneally with paclitaxel to induce mechanical allodynia. Levels of the endocannabinoids, N-arachidonoylethanolamine (anandamide, AEA), 2-AG, and the N-acylethanolamines (NAEs), N-palmitoylethanolamide (PEA) and N-oleoylethanolamide (OEA), which are structurally-related to AEA, in the brain, spinal cord and paw skin were measured using LC-MS/MS. Protein expression of MAGL in the paw skin was measured using Wes™. The effects of subcutaneous (s.c.) injection of 2-AG and JZL184 (a MAGL inhibitor) into the right hind paw of mice with paclitaxel-induced mechanical allodynia were assessed using the dynamic plantar aesthesiometer. The effects of pretreatment, s.c., into the right hind paw, with cannabinoid type 1 (CB₁) receptor antagonist AM251 and CB₂ receptor antagonist AM630 on the antiallodynic effects of 2-AG were also evaluated.

RESULTS

The levels of 2-AG were reduced only in the paw skin of paclitaxel-treated mice, whilst the levels of AEA, PEA and OEA were not significantly altered. There was no change in the expression of MAGL in the paw skin. Administration of 2-AG and JZL184 produced antiallodynic effects against paclitaxel-induced mechanical allodynia in the injected right paw, but did not affect the uninjected left paw. The antiallodynic activity of 2-AG was antagonized by both AM251 and AM630.

CONCLUSION

These results indicate that during paclitaxel-induced mechanical allodynia there is a deficiency of 2-AG in the periphery, but not in the CNS. Increasing 2-AG in the paw by local administration of 2-AG or a MAGL inhibitor, alleviates mechanical allodynia in a CB₁ and CB₂ receptor-dependent manner.

Cannabinoids in the descending pain modulatory circuit: Role in inflammation

The legalization of cannabis in some states has intensified interest in the potential for cannabis and its constituents to lead to novel therapeutics for pain. Our understanding of the cellular mechanisms underlying cannabinoid actions in the brain have lagged behind opioids; however, the current opioid epidemic has also increased attention on the use of cannabinoids as alternatives to opioids for pain, especially chronic pain that requires long-term use. Endogenous cannabinoids are lipid signaling molecules that have complex roles in modulating neuronal function throughout the brain. In this review, we discuss cannabinoid functions in the descending pain modulatory pathway, a brain circuit that integrates cognitive and emotional processing of pain to modulate incoming sensory inputs. In addition, we highlight areas where further studies are necessary to understand cannabinoid regulation of descending pain modulation.

Targeting Peripherally Restricted Cannabinoid Receptor 1, Cannabinoid Receptor 2, and Endocannabinoid-Degrading Enzymes for the Treatment of Neuropathic Pain Including Neuropathic Orofacial Pain

Neuropathic pain conditions including neuropathic orofacial pain (NOP) are difficult to treat. Contemporary therapeutic agents for neuropathic pain are often ineffective in relieving pain and are associated with various adverse effects. Finding new options for treating neuropathic pain is a major priority in pain-related research. Cannabinoid-based therapeutic strategies have emerged as promising new options. Cannabinoids mainly act on cannabinoid 1 (CB1) and 2 (CB2) receptors, and the former is widely distributed in the brain. The therapeutic significance of cannabinoids is masked by their adverse effects including sedation, motor impairment, addiction and cognitive impairment, which are thought to be mediated by CB1 receptors in the brain. Alternative approaches have been developed to overcome this problem by selectively targeting CB2 receptors, peripherally restricted CB1 receptors and endocannabinoids that may be locally synthesized on demand at sites where their actions are pertinent. Many preclinical studies have reported that these strategies are effective for treating neuropathic pain and produce no or minimal side effects. Recently, we observed that inhibition of degradation of a major endocannabinoid, 2-arachydonoylglycerol, can attenuate NOP following trigeminal nerve injury in mice. This review will discuss the above-mentioned alternative approaches that show potential for treating neuropathic pain including NOP.

Current and Emerging Pharmacotherapy for Fibromyalgia

Introduction. Fibromyalgia syndrome (FMS) is a pain disorder with an estimated prevalence of 1–5%. It is associated with a variety of somatic and psychological disorders. Its exact pathogenesis is still unclear but is involved with neural oversensitization and decreased conditioned pain modulation (CPM), combined with cognitive dysfunction, memory impairment, and altered information processing. Connectivity between brain areas involved in pain processing, alertness, and cognition is increased in the syndrome, making its pharmacologic therapy complex. Only three drugs, pregabalin, duloxetine, and milnacipran are currently FDA-approved for FM treatment, but many other agents have been tested over the years, with varying efficacy. Areas Covered. The purpose of this review is to summarize current clinical experience with different pharmacologic treatments used for fibromyalgia and introduce future perspectives in developing therapies. Expert Opinion. Future insights into the fields of cannabinoid and opioid research, as well as an integrative approach towards the incorporation of genetics and functional imaging combined with additional fields of research relevant towards the study of complex CNS disorders, are likely to lead to new developments of novel tailor-made treatments for FMS patients.

Druggable targets of the endocannabinoid system: Implications for the treatment of HIV-associated neurocognitive disorder

HIV-associated neurocognitive disorder (HAND) affects nearly half of all HIV-infected individuals. Synaptodendritic damage correlates with neurocognitive decline in HAND, and many studies have demonstrated that HIV-induced neuronal injury results from excitotoxic and inflammatory mechanisms. The endocannabinoid (eCB) system provides on-demand protection against excitotoxicity and neuroinflammation. Here, we discuss evidence of the neuroprotective and anti-inflammatory properties of the eCB system from in vitro and in vivo studies. We examine the pharmacology of the eCB system and evaluate the therapeutic potential of drugs that modulate eCB signaling to treat HAND. Finally, we provide perspective on the need for additional studies to clarify the role of the eCB system in HIV neurotoxicity and speculate that strategies that enhance eCB signaling might slow cognitive decline in HAND.

Cannabinoids: Current and Future Options to Treat Chronic and Chemotherapy-Induced Neuropathic Pain

Increases in cancer diagnosis have tremendous negative impacts on patients and their families, and major societal and economic costs. The beneficial effect of chemotherapeutic agents on tumor suppression comes with major unwanted side effects such as weight and hair loss, nausea and vomiting, and neuropathic pain. Chemotherapy-induced peripheral neuropathy (CIPN), which can include both painful and non-painful symptoms, can persist 6 months or longer after the patient's last chemotherapeutic treatment. These peripheral sensory and motor deficits are poorly treated by our current analgesics with limited effectiveness. Therefore, the development of novel treatment strategies is an important preclinical research focus and an urgent need for patients. Approaches to prevent CIPN have yielded disappointing results since these compounds may interfere with the anti-tumor properties of chemotherapeutic agents. Nevertheless, the first (serotonin noradrenaline reuptake inhibitors [SNRIs], anticonvulsants, tricyclic antidepressants) and second (5% lidocaine patches, 8% capsaicin patches and weak opioids such as tramadol) lines of treatment for CIPN have shown some efficacy. The clinical challenge of CIPN management in cancer patients and the need to target novel therapies with long-term efficacy in alleviating CIPN are an ongoing focus of research. The endogenous cannabinoid system has shown great promise and efficacy in alleviating CIPN in preclinical and clinical studies. In this review, we will discuss the mechanisms through which the platinum, taxane, and vinca alkaloid classes of chemotherapeutics may produce CIPN and the potential therapeutic effect of drugs targeting the endocannabinoid system in preclinical and clinical studies, in addition to cannabinoid compounds diffuse mechanisms of action in alleviation of CIPN.

Endocannabinoid and Prostanoid Crosstalk in Pain

Interfering with endocannabinoid (eCB) metabolism to increase their levels is a proven anti-nociception strategy. However, because the eCB and prostanoid systems are intertwined, interfering with eCB metabolism will affect the prostanoid system and inversely. Key to this connection is the production of the cyclooxygenase (COX) substrate arachidonic acid upon eCB hydrolysis as well as the ability of COX to metabolize the eCBs anandamide (AEA) and 2-arachidonoylglycerol (2-AG) into prostaglandin-ethanolamides (PG-EA) and prostaglandin-glycerol esters (PG-G), respectively. Recent studies shed light on the role of PG-Gs and PG-EAs in nociception and inflammation. Here, we discuss the role of these complex systems in nociception and new opportunities to alleviate pain by interacting with them.

Transition from acute to chronic pain after surgery

Over the past decade there has been an increasing reliance on strong opioids to treat acute and chronic pain, which has been associated with a rising epidemic of prescription opioid misuse, abuse, and overdose-related deaths. Deaths from prescription opioids have more than quadrupled in the USA since 1999, and this pattern is now occurring globally. Inappropriate opioid prescribing after surgery, particularly after discharge, is a major cause of this problem. Chronic postsurgical pain, occurring in approximately 10% of patients who have surgery, typically begins as acute postoperative pain that is difficult to control, but soon transitions into a persistent pain condition with neuropathic features that are unresponsive to opioids. Research into how and why this transition occurs has led to a stronger appreciation of opioid-induced hyperalgesia, use of more effective and safer opioid-sparing analgesic regimens, and non-pharmacological interventions for pain management. This Series provides an overview of the epidemiology and societal effect, basic science, and current recommendations for managing persistent postsurgical pain. We discuss the advances in the prevention of this transitional pain state, with the aim to promote safer analgesic regimens to better manage patients with acute and chronic pain.

Evaluation of different drug classes on transient sciatic nerve injury-depressed marble burying in mice

A great need exists for the identification of new effective analgesics to treat sustained pain. However, most preclinical nociceptive assays measure behavioral responses evoked by noxious stimuli (ie, pain-stimulated behavior), which presents a challenge to distinguish between motor impairing and antinociceptive effects of drugs. Here, we demonstrate that chronic constriction injury (CCI) of the sciatic nerve elicits common pain-stimulated responses (ie, mechanical allodynia and thermal hyperalgesia) as well as reduces marble burying/digging behaviors that occur during the early stages of the neuropathy and resolve within 1 week. Although drugs representing distinct classes of analgesics (ie, morphine, valdecoxib, and gabapentin) reversed both CCI-induced and CCI-depressed nociceptive measures, diazepam lacked antinociceptive effects in all assays and the kappa-opioid receptor agonist U69593 reversed pain-stimulated, but not pain-depressed behaviors. In addition, we tested drugs targeting distinct components of the endocannabinoid system, including agonists at cannabinoid receptors type 1 (CB1) and type 2 (CB2), as well as inhibitors of the endocannabinoid-regulating enzymes fatty acid amide hydrolase and monoacylglycerol lipase. Each of these drugs reversed all CCI-induced nociceptive measures, with the exception of the fatty acid amide hydrolase inhibitor that reversed pain-stimulated behaviors, only. These findings support the use of the mouse marble-burying assay as a model of pain-depressed behavior within the first week of sciatic nerve injury to examine candidate analgesics. These data also support existing preclinical research that cannabinoid receptor agonists and inhibitors of endocannabinoid-regulating enzymes merit consideration for the treatment of pain.

Cannabinoids and Pain: New Insights From Old Molecules

Cannabis has been used for medicinal purposes for thousands of years. The prohibition of cannabis in the middle of the 20th century has arrested cannabis research. In recent years there is a growing debate about the use of cannabis for medical purposes. The term ‘medical cannabis’ refers to physician-recommended use of the cannabis plant and its components, called cannabinoids, to treat disease or improve symptoms. Chronic pain is the most commonly cited reason for using medical cannabis. Cannabinoids act via cannabinoid receptors, but they also affect the activities of many other receptors, ion channels and enzymes. Preclinical studies in animals using both pharmacological and genetic approaches have increased our understanding of the mechanisms of cannabinoid-induced analgesia and provided therapeutical strategies for treating pain in humans. The mechanisms of the analgesic effect of cannabinoids include inhibition of the release of neurotransmitters and neuropeptides from presynaptic nerve endings, modulation of postsynaptic neuron excitability, activation of descending inhibitory pain pathways, and reduction of neural inflammation. Recent meta-analyses of clinical trials that have examined the use of medical cannabis in chronic pain present a moderate amount of evidence that cannabis/cannabinoids exhibit analgesic activity, especially in neuropathic pain. The main limitations of these studies are short treatment duration, small numbers of patients, heterogeneous patient populations, examination of different cannabinoids, different doses, the use of different efficacy endpoints, as well as modest observable effects. Adverse effects in the short-term medical use of cannabis are generally mild to moderate, well tolerated and transient. However, there are scant data regarding the long-term safety of medical cannabis use. Larger well-designed studies of longer duration are mandatory to determine the long-term efficacy and long-term safety of cannabis/cannabinoids and to provide definitive answers to physicians and patients regarding the risk and benefits of its use in the treatment of pain. In conclusion, the evidence from current research supports the use of medical cannabis in the treatment of chronic pain in adults. Careful follow-up and monitoring of patients using cannabis/cannabinoids are mandatory.

Cannabinoids and agmatine as potential therapeutic alternatives for cisplatin-induced peripheral neuropathy

Cisplatin is a widely used antineoplastic agent in the treatment of various cancers. Peripheral neuropathy is a well-known side effect of cisplatin and has the potential to result in limiting and/or reducing the dose, decreasing the quality of life. Unfortunately, the mechanism for cisplatin-induced neuropathy has not been completely elucidated. Currently, available treatments for neuropathic pain (NP) are mostly symptomatic, insufficient and are often linked with several detrimental side effects; thus, effective treatments are needed. Cannabinoids and agmatine are endogenous modulators that are implicated in painful states. This review explains the cisplatin-induced neuropathy and antinociceptive effects of cannabinoids and agmatine in animal models of NP and their putative therapeutic potential in cisplatin-induced neuropathy.

Inhibition of Fatty Acid Amide Hydrolase (FAAH) by Macamides

The pentane extract of the Peruvian plant, Lepidium meyenii (Maca), has been demonstrated to possess neuroprotective activity in previous in vitro and in vivo studies (Pino-Figueroa et al. in Ann N Y Acad Sci 1199:77-85, 2010; Pino-Figueroa et al. in Am J Neuroprot Neuroregener 3:87-92, 2011). This extract contains a number of macamides that may act on the endocannabinoid system (Pino-Figueroa et al. in Ann N Y Acad Sci 1199:77-85, 2010; Pino-Figueroa et al., 2011; Dini et al. in Food Chem 49:347-349, 1994). The aim of this study was to characterize the inhibitory activity of four of these maccamides (N-benzylstearamide, N-benzyloleamide, N-benzyloctadeca-9Z,12Z-dienamide, and N-benzyloctadeca-9Z,12Z,15Z-trienamide) on fatty acid amide hydrolase (FAAH), an enzyme that is responsible for endocannabinoid degradation in the nervous system (Kumar et al. in Anaesthesia 56:1059-1068, 2001). The four compounds were tested at concentrations between 1 and 100 μM, utilizing an FAAH inhibitor screening assay. The results demonstrated concentration-dependent FAAH inhibitory activities for the four macamides tested. N-Benzyloctadeca-9Z,12Z-dienamide demonstrated the highest FAAH inhibitory activity whereas N-benzylstearamide had the lowest inhibitory activity. In addition, N-benzylstearamide, N-benzyloleamide, and N-benzyloctadeca-9Z,12Z-dienamide demonstrated time-dependent inhibition when tested after a pre-incubation period, indicating that the mechanism of inhibition for these compounds most likely is irreversible. Of interest, unsaturation in the fatty acid moiety resulted in greater FAAH inhibitory activity. LC/MS/MS analysis demonstrated that FAAH was able to hydrolyze N-benzyloctadeca-9Z,12Z-dienamide, suggesting that N-benzyloctadeca-9Z,12Z-dienamide is also a slow substrate for FAAH. These results provide useful information about the mechanism of action of Lepidium meyenii and may help with the development of new compounds with FAAH inhibitory or modulatory activity.

Enhanced endocannabinoid tone as a potential target of pharmacotherapy

The endocannabinoid system is up-regulated in numerous pathophysiological states such as inflammatory, neurodegenerative, gastrointestinal, metabolic and cardiovascular diseases, pain, and cancer. It has been suggested that this phenomenon primarily serves an autoprotective role in inhibiting disease progression and/or diminishing signs and symptoms. Accordingly, enhancement of endogenous endocannabinoid tone by inhibition of endocannabinoid degradation represents a promising therapeutic approach for the treatment of many diseases. Importantly, this allows for the avoidance of unwanted psychotropic side effects that accompany exogenously administered cannabinoids. The effects of endocannabinoid metabolic pathway modulation are complex, as endocannabinoids can exert their actions directly or via numerous metabolites. The two main strategies for blocking endocannabinoid degradation are inhibition of endocannabinoid-degrading enzymes and inhibition of endocannabinoid cellular uptake. To date, the most investigated compounds are inhibitors of fatty acid amide hydrolase (FAAH), an enzyme that degrades the endocannabinoid anandamide. However, application of FAAH inhibitors (and consequently other endocannabinoid degradation inhibitors) in medicine became questionable due to a lack of therapeutic efficacy in clinical trials and serious adverse effects evoked by one specific compound. In this paper, we discuss multiple pathways of endocannabinoid metabolism, changes in endocannabinoid levels across numerous human diseases and corresponding experimental models, pharmacological strategies for enhancing endocannabinoid tone and potential therapeutic applications including multi-target drugs with additional targets outside of the endocannabinoid system (cyclooxygenase-2, cholinesterase, TRPV1, and PGF_2α-EA receptors), and currently used medicines or medicinal herbs that additionally enhance endocannabinoid levels. Ultimately, further clinical and preclinical studies are warranted to develop medicines for enhancing endocannabinoid tone.

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

A great need exists for the development of new medications to treat pain resulting from various disease states and types of injury. Given that the endogenous cannabinoid (that is, endocannabinoid) system modulates neuronal and immune cell function, both of which play key roles in pain, therapeutics targeting this system hold promise as novel analgesics. Potential therapeutic targets include the cannabinoid receptors, type 1 and 2, as well as biosynthetic and catabolic enzymes of the endocannabinoids N-arachidonoylethanolamine and 2-arachidonoylglycerol. Notably, cannabinoid receptor agonists as well as inhibitors of endocannabinoid-regulating enzymes fatty acid amide hydrolase and monoacylglycerol lipase produce reliable antinociceptive effects, and offer opioid-sparing antinociceptive effects in myriad preclinical inflammatory and neuropathic pain models. Emerging clinical studies show that 'medicinal' cannabis or cannabinoid-based medications relieve pain in human diseases such as cancer, multiple sclerosis, and fibromyalgia. However, clinical data have yet to demonstrate the analgesic efficacy of inhibitors of endocannabinoid-regulating enzymes. Likewise, the question of whether pharmacotherapies aimed at the endocannabinoid system promote opioid-sparing effects in the treatment of pain reflects an important area of research. Here we examine the preclinical and clinical evidence of various endocannabinoid system targets as potential therapeutic strategies for inflammatory and neuropathic pain conditions.

Monoacylglycerol lipase inhibition alters social behavior in male and female rats after post-weaning social isolation

Post-weaning social isolation (PSI) has been shown to increase aggressive behavior and alter medial prefrontal cortex (mPFC) function in rats. The present study sought to determine whether this phenotype would be normalized by increasing levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) using pharmacological inhibition of monoacylglycerol lipase (MAGL). Male and female Sprague-Dawley rats were exposed to either 4 weeks of PSI or social rearing (SR) starting on postnatal day 21, then underwent a 15 min trial of social interaction with a novel, same-sex juvenile rat. Rats were administered an acute injection of the MAGL inhibitor MJN110 or vehicle prior to the social interaction. Rats received either 0 mg/kg (vehicle), 1 mg/kg, or 5 mg/kg of MJN110. Both doses of MJN110 decreased aggressive grooming, a measure of agonistic behavior, in both males and females, largely driven by decreased aggressive grooming in PSI rats. There were no effects of MJN110 on overall social behavior or play behavior, while modest effects were observed on locomotor activity in SR rats only. While social interaction increased c-Fos expression in the mPFC of both males and females, MJN110 reduced c-Fos preferentially in females. These results suggest that 2-AG can modulate specific social behaviors during adolescence, and may affect mPFC function differentially in males and females.

The cannabinoid system and pain

Chronic pain states are highly prevalent and yet poorly controlled by currently available analgesics, representing an enormous clinical, societal, and economic burden. Existing pain medications have significant limitations and adverse effects including tolerance, dependence, gastrointestinal dysfunction, cognitive impairment, and a narrow therapeutic window, making the search for novel analgesics ever more important. In this article, we review the role of an important endogenous pain control system, the endocannabinoid (EC) system, in the sensory, emotional, and cognitive aspects of pain. Herein, we briefly cover the discovery of the EC system and its role in pain processing pathways, before concentrating on three areas of current major interest in EC pain research; 1. Pharmacological enhancement of endocannabinoid activity (via blockade of EC metabolism or allosteric modulation of CB1receptors); 2. The EC System and stress-induced modulation of pain; and 3. The EC system & medial prefrontal cortex (mPFC) dysfunction in pain states. Whilst we focus predominantly on the preclinical data, we also include extensive discussion of recent clinical failures of endocannabinoid-related therapies, the future potential of these approaches, and important directions for future research on the EC system and pain. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

A novel inhibitor of endocannabinoid catabolic enzymes sheds light on behind the scene interplay between chronic pain, analgesic tolerance, and heroin dependence

From the Aristotelian ancient Greece, pain has been associated with appetites or emotions and is opposite to pleasure. Reward and addiction is also linked to pleasure and compulsive drug seeking reinstates pleasure. Alleviation of chronic pain can induce a euphoric phase similar to what is found in addiction. Both chronic pain and addiction are recognized as a disease of the central nervous system. They share many characteristics and brain regions/mechanisms. Evidence points to the usefulness of cannabinoids as a new class of agents to add to the pharmaceutical toolbox in the management of chronic pain. Wilkerson and colleagues, in this issue, examine SA-57, an inhibitor of two different endocannabinoid catabolic enzymes FAAH and MAGL, demonstrating its analgesic effectiveness and morphine-sparing properties in a chronic pain model, as well as its ability to reduce heroin seeking behavior in a self-administration paradigm in mice. This timely study emphasizes the need for development of more efficacious chronic pain therapeutics with minimized abuse potential and/or reinforcing properties. It also highlights the need for better understanding of the overlapping circuitry of chronic pain, reward, and addiction.

The endocannabinoid hydrolysis inhibitor SA-57: Intrinsic antinociceptive effects, augmented morphine-induced antinociception, and attenuated heroin seeking behavior in mice

Although opioids are highly efficacious analgesics, their abuse potential and other untoward side effects diminish their therapeutic utility. The addition of non-opioid analgesics offers a promising strategy to reduce required antinociceptive opioid doses that concomitantly reduce opioid-related side effects. Inhibitors of the primary endocannabinoid catabolic enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) show opioid-sparing effects in preclinical models of pain. As simultaneous inhibition of these enzymes elicits enhanced antinociceptive effects compared with single enzyme inhibition, the present study tested whether the dual FAAH-MAGL inhibitor SA-57 [4-[2-(4-chlorophenyl)ethyl]-1-piperidinecarboxylic acid 2-(methylamino)-2-oxoethyl ester] produces morphine-sparing antinociceptive effects, without major side effects associated with either drug class. SA-57 dose-dependently reversed mechanical allodynia in the constriction injury (CCI) of the sciatic nerve model of neuropathic pain and carrageenan inflammatory pain model. As previously reported, SA-57 was considerably more potent in elevating anandamide (AEA) than 2-arachidonyl glycerol (2-AG) in brain. Its anti-allodynic effects required cannabinoid (CB)₁ and CB₂ receptors; however, only CB₂ receptors were necessary for the anti-edematous effects in the carrageenan assay. Although high doses of SA-57 alone were required to produce antinociception, low doses of this compound, which elevated AEA and did not affect 2-AG brain levels, augmented the antinociceptive effects of morphine, but lacked cannabimimetic side effects. Because of the high abuse liability of opioids and implication of the endocannabinoid system in the reinforcing effects of opioids, the final experiment tested whether SA-57 would alter heroin seeking behavior. Strikingly, SA-57 reduced heroin-reinforced nose poke behavior and the progressive ratio break point for heroin. In conclusion, the results of the present study suggest that inhibition of endocannabinoid degradative enzymes represents a promising therapeutic approach to decrease effective doses of opioids needed for clinical pain control, and may also possess therapeutic potential to reduce opioid abuse.

The Role of the Endocannabinoid System in the Brain-Gut Axis

The actions of cannabis are mediated by receptors that are part of an endogenous cannabinoid system. The endocannabinoid system (ECS) consists of the naturally occurring ligands N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), their biosynthetic and degradative enzymes, and the cannabinoid (CB) receptors CB1 and CB2. The ECS is a widely distributed transmitter system that controls gut functions peripherally and centrally. It is an important physiologic regulator of gastrointestinal motility. Polymorphisms in the gene encoding CB1 (CNR1) have been associated with some forms of irritable bowel syndrome. The ECS is involved in the control of nausea and vomiting and visceral sensation. The homeostatic role of the ECS also extends to the control of intestinal inflammation. We review the mechanisms by which the ECS links stress and visceral pain. CB1 in sensory ganglia controls visceral sensation, and transcription of CNR1 is modified through epigenetic processes under conditions of chronic stress. These processes might link stress with abdominal pain. The ECS is also involved centrally in the manifestation of stress, and endocannabinoid signaling reduces the activity of hypothalamic-pituitary-adrenal pathways via actions in specific brain regions, notably the prefrontal cortex, amygdala, and hypothalamus. Agents that modulate the ECS are in early stages of development for treatment of gastrointestinal diseases. Increasing our understanding of the ECS will greatly advance our knowledge of interactions between the brain and gut and could lead to new treatments for gastrointestinal disorders.

Opioid and cannabinoid synergy in a mouse neuropathic pain model

BACKGROUND AND PURPOSE

Clinical studies have reported that pan-cannabinoid receptor agonists may have efficacy in neuropathic pain states and that this might be enhanced by co-administration with opioids. While cannabinoid-opioid analgesic synergy has been demonstrated in animal models of acute pain, it has not been examined in neuropathic pain models. We examined the effect of combination treatment with cannabinoid and opioid receptor agonists on allodynia and side effects in a nerve injury-induced neuropathic pain model.

EXPERIMENTAL APPROACH

C57BL/6 mice were subjected to chronic constriction injury (CCI) of the sciatic nerve. The effects of systemic administration of morphine and the pan-cannabinoid receptor agonist, WIN55212, on allodynia and side effects were examined at 7-10 days post-CCI surgery. Isobolographic analysis was used to determine whether the effects of the combination were synergistic.

KEY RESULTS

The opioid agonist morphine reduced CCI-induced mechanical and cold allodynia and produced motor incoordination, in a dose-dependent manner. WIN55212 reduced CCI-induced allodynia and produced motor incoordination, catalepsy and sedation, in a dose-dependent manner, as we have observed previously. When administered together, WIN55212 and morphine reduced allodynia in a synergistic manner but had only an additive effect on motor incoordination.

CONCLUSIONS AND IMPLICATIONS

These findings indicate that administration of a combination of a non-selective opioid and cannabinoid receptor agonist synergistically reduces nerve injury-induced allodynia, while producing side effects in an additive manner. This suggests that this combination treatment has an improved anti-allodynic potency and therapeutic index in a neuropathic pain model.

Harnessing the pyrroloquinoxaline scaffold for FAAH and MAGL interaction: definition of the structural determinants for enzyme inhibition

The pharmacogenic pyrroloquinoxaline scaffold has been exploited for developing piperazine and 4-aminopiperidine carboxamides/carbamates as inhibitors of the endocannabinoids’ catabolic enzymes fatty acid amide hydrolase and monoacylglycerol lipase.