Selective blockade of 2-arachidonoylglycerol hydrolysis produces cannabinoid behavioral effects

Development of terphenyl-2-methyloxazol-5(4H)-one derivatives as selective reversible MAGL inhibitors

Monoacylglycerol lipase is a serine hydrolase that plays a major role in the degradation of the endocannabinoid neurotransmitter 2-arachidonoylglycerol. A wide number of MAGL inhibitors are reported in literature; however, many of them are characterised by an irreversible mechanism of action and this behavior determines an unwanted chronic MAGL inactivation, which acquires a functional antagonism of the endocannabinoid system. The possible use of reversible MAGL inhibitors has only recently been explored, due to the lack of known compounds possessing efficient reversible inhibitory activities. In this work, we report a new series of terphenyl-2-methyloxazol-5(4H)-one derivatives characterised by a reversible MAGL-inhibition mechanism. Among them, compound 20b showed to be a potent MAGL reversible inhibitor (IC₅₀ = 348 nM) with a good MAGL/FAAH selectivity. Furthermore, this compound showed antiproliferative activities against two different cancer cell lines that overexpress MAGL.

Human serum albumin: A modulator of cannabinoid drugs

The endocannabinoid system is a unique neuromodulatory system that affects a wide range of biological processes and maintains the homeostasis in all mammal body systems. In recent years, several pharmacological tools to target endocannabinoid neurotransmission have been developed, including direct and indirect cannabinoid agonists and cannabinoid antagonists. Due to their hydrophobic nature, cannabinoid agonists and antagonists need to bind specific transporters to allow their distribution in body fluids. Human serum albumin (HSA), the most abundant plasma protein, is a key determinant of drug pharmacokinetics. As HSA binds both the endocannabinoid anandamide and the active ingredient of Cannabis sativa, Δ-9-tetrahydrocannabinol, we hypothesize that HSA can be the most important carrier of cannabinoid drugs. In silico docking observations strongly indicate that HSA avidly binds the indirect cannabinoid agonists URB597, AM5206, JZL184, JZL195, and AM404, the direct cannabinoid agonists WIN55,212-2 and CP55,940, and the prototypical cannabinoid antagonist/inverse agonist SR141716. Values of the free energy for cannabinoid drugs binding to HSA range between -5.4 kcal mol^-1 and -10.9 kcal mol^-1 . Accounting for the HSA concentration in vivo (∼ 7.5 × 10^-4 M), values of the free energy here determined suggest that the formation of the HSA:cannabinoid drug complexes may occur in vivo. Therefore, HSA appears to be an important determinant for cannabinoid efficacy and may guide the choice of the drug dose regimen to optimize drug efficacy and to avoid drug-related toxicity. © 2017 IUBMB Life, 69(11):834-840, 2017.

Investigation of Diacylglycerol Lipase Alpha Inhibition in the Mouse Lipopolysaccharide Inflammatory Pain Model

Diacylglycerol lipase (DAGL) α and β, the major biosynthetic enzymes of the endogenous cannabinoid (endocannabinoid) 2-arachidonylglycerol (2-AG), are highly expressed in the nervous system and immune system, respectively. Genetic deletion or pharmacological inhibition of DAGL-β protects against lipopolysaccharide (LPS)-induced inflammatory responses in mouse peritoneal macrophages and reverses LPS-induced allodynia in mice. To gain insight into the contribution of DAGL-α in LPS-induced allodynia, we tested global knockout mice as well as DO34, a dual DAGL-α/β inhibitor. Intraperitoneal administration of DO34 (30 mg/kg) significantly decreased whole-brain levels of 2-AG (∼83%), anandamide (∼42%), and arachidonic acid (∼58%). DO34 dose-dependently reversed mechanical and cold allodynia, and these antinociceptive effects did not undergo tolerance after 6 days of repeated administration. In contrast, DO34 lacked acute thermal antinociceptive, motor, and hypothermal pharmacological effects in naive mice. As previously reported, DAGL-β (-/-) mice displayed a protective phenotype from LPS-induced allodynia. However, DAGL-α (-/-) mice showed full allodynic responses, similar to their wild-type littermates. Interestingly, DO34 (30 mg/kg) fully reversed LPS-induced allodynia in DAGL-α (+/+) and (-/-) mice, but did not affect the antinociceptive phenotype of DAGL-β (-/-) mice in this model, indicating a DAGL-α-independent site of action. These findings suggest that DAGL-α and DAGL-β play distinct roles in LPS-induced nociception. Whereas DAGL-α appears to be dispensable for the development and expression of LPS-induced nociception, DAGL-β inhibition represents a promising strategy to treat inflammatory pain.

Functional Redundancy Between Canonical Endocannabinoid Signaling Systems in the Modulation of Anxiety

BACKGROUND

Increasing the available repertoire of effective treatments for mood and anxiety disorders represents a critical unmet need. Pharmacological augmentation of endogenous cannabinoid (eCB) signaling has been suggested to represent a novel approach to the treatment of anxiety disorders; however, the functional interactions between two canonical eCB pathways mediated via anandamide (N-arachidonylethanolamine [AEA]) and 2-arachidonoylglycerol (2-AG) in the regulation of anxiety are not well understood.

METHODS

We utilized pharmacological augmentation and depletion combined with behavioral and electrophysiological approaches to probe the role of 2-AG signaling in the modulation of stress-induced anxiety and the functional redundancy between AEA and 2-AG signaling in the modulation of anxiety-like behaviors in mice.

RESULTS

Selective 2-AG augmentation reduced anxiety in the light/dark box assay and prevented stress-induced increases in anxiety associated with limbic AEA deficiency. In contrast, acute 2-AG depletion increased anxiety-like behaviors, which was normalized by selective pharmacological augmentation of AEA signaling and via direct cannabinoid receptor 1 stimulation with Δ⁹-tetrahydrocannabinol. Electrophysiological studies revealed 2-AG modulation of amygdala glutamatergic transmission as a key synaptic correlate of the anxiolytic effects of 2-AG augmentation.

CONCLUSIONS

Although AEA and 2-AG likely subserve distinct physiological roles, a pharmacological and functional redundancy between these canonical eCB signaling pathways exists in the modulation of anxiety-like behaviors. These data support development of eCB-based treatment approaches for mood and anxiety disorders and suggest a potentially wider therapeutic overlap between AEA and 2-AG augmentation approaches than was previously appreciated.

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".

Effects of centrally administered endocannabinoids and opioids on orofacial pain perception in rats

BACKGROUND AND PURPOSE

Endocannabinoids and opioids play a vital role in mediating pain-induced analgesia. The specific effects of these compounds within the orofacial region are largely unknown. In this study, we tried to determine whether an increase in cannabinoid and opioid concentration in the CSF affects impulse transmission between the motor centres localized in the vicinity of the third and fourth cerebral ventricles.

EXPERIMENTAL APPROACH

The study objectives were realized on rats using a method that allows the recording of the amplitude of evoked tongue jerks (ETJ) in response to noxious tooth pulp stimulation. The amplitude of ETJ was a measure of the effect of neurotransmitters on neural structures.

KEY RESULTS

Perfusion of cerebral ventricles with anandamide (AEA), endomorphin-2 (EM-2), URB597, an inhibitor of fatty acid amide hydrolase (FAAH) and JZL195, a dual inhibitor of FAAH and monoacylglycerol lipase (MAGL) reduced the ETJ amplitude. The antinociceptive effect of AEA, EM-2, URB597 and JZL195 was blocked by CB₁ receptor antagonist, AM251 and by μ receptor-antagonist, β-funaltrexamine. In contrast to AEA, 2-arachidonoylglycerol alone did not decrease ETJ amplitude.

CONCLUSIONS AND IMPLICATIONS

We demonstrated that in the orofacial area, analgesic activity is modulated by AEA and that EM-2-induced antinociception was mediated by μ and CB₁ receptors. The action of AEA and EM-2 is tightly regulated by FAAH and FAAH/MAGL, by preventing the breakdown of endogenous cannabinoids in regions where they are produced on demand. Therefore, the current findings support the therapeutic potential of FAAH and FAAH/MAGL inhibitors as novel pharmacotherapeutic agents for orofacial pain.

Inhibition of Endocannabinoid-Metabolizing Enzymes in Peripheral Tissues Following Developmental Chlorpyrifos Exposure in Rats

Repeated developmental exposure to the organophosphate (OP) insecticide chlorpyrifos (CPF) inhibits brain fatty acid amide hydrolase (FAAH) activity at low levels, whereas at higher levels, it inhibits brain monoacylglycerol lipase (MAGL) activity. FAAH and MAGL hydrolyze the endocannabinoids anandamide (AEA) and 2-arachidonylglycerol (2-AG), respectively. Peripherally, AEA and 2-AG have physiological roles in the regulation of lipid metabolism and immune function, and altering the normal levels of these lipid mediators can negatively affect these processes. Exposure to CPF alters brain endocannabinoid hydrolysis activity, but it is unclear whether low-level exposure alters this activity in peripheral tissues important in metabolic and immune function. Therefore, rat pups were exposed orally from day 10 to 16 to 0.5, 0.75, or 1.0 mg/kg CPF or 0.02 mg/kg PF-04457845 (a specific FAAH inhibitor). At 12 hours postexposure, FAAH, MAGL, and cholinesterase (ChE) activities were determined. All treatments inhibited FAAH activity in brain, spleen, and liver. CPF inhibited ChE activity in spleen and liver (all dosages) and in brain (highest dosage only). CPF inhibited total 2-AG hydrolysis and MAGL-specific activity in brain and spleen (high dosage only). In liver, total 2-AG hydrolysis was inhibited by all treatments and could be attributed to inhibition of non-MAGL-mediated 2-AG hydrolysis, indicating involvement of other enzymes. MAGL-specific activity in liver was inhibited only by the high CPF dosage, whereas PF-04457845 slightly increased this activity. Overall, exposure to low levels of CPF and to PF-04457845 can alter endocannabinoid metabolism in peripheral tissues, thus potentially affecting physiological processes.

Inhibition of monoacylglycerol lipase: Another signalling pathway for potential therapeutic targets in migraine?

Background

Drugs that modulate endocannabinoid signalling are effective in reducing nociception in animal models of pain and may be of value in the treatment of migraine.

Methods

We investigated the anti-nociceptive effects of inhibition of monoacylglycerol lipase (MGL), a key enzyme in the hydrolysis of the 2-arachidonoylglycerol, in a rat model of migraine based on nitroglycerin (NTG) administration. We evaluated c-fos expression in specific brain areas and nociceptive behavior in trigeminal and extra-trigeminal body areas.

Results

URB602, a reversible MGL inhibitor, did not show any analgesic effect in the tail flick test, but it inhibited NTG-induced hyperalgesia in both the tail flick test and the formalin test applied to the hind paw or to the orofacial area. Quite unexpectedly, URB602 potentiated formalin-induced hyperalgesia in the trigeminal area when used alone. The latter result was also confirmed using a structurally distinct, irreversible MGL inhibitor, JZL184. URB602 did not induce neuronal activation in the area of interest, but significantly reduced the NTG-induced neuronal activation in the ventrolateral column of the periaqueductal grey and the nucleus trigeminalis caudalis.

Conclusions

These findings support the hypothesis that modulation of the endocannabinoid system may be a valuable approach for the treatment of migraine. The topographically segregated effect of MGL inhibition in trigeminal/extra-trigeminal areas calls for further mechanistic research.

Contrasting effects of selective MAGL and FAAH inhibition on dopamine depletion and GDNF expression in a chronic MPTP mouse model of Parkinson's disease

The modulation of the brain endocannabinoid system has been identified as an option to treat neurodegenerative diseases including Parkinson's disease (PD). Especially the elevation of endocannabinoid levels by inhibition of hydrolytic degradation represents a valuable approach. To evaluate whether monoacylglycerol lipase (MAGL) or fatty acid amide hydrolase (FAAH) inhibition could be beneficial for PD, we examined in parallel the therapeutic potential of the highly selective MAGL inhibitor KML29 elevating 2-arachidonoylglyerol (2-AG) levels and the highly selective FAAH inhibitor PF-3845 elevating anandamide (AEA) levels in a chronic methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid (MPTP/probenecid) mouse model of PD. Chronic administration of KML29 (10 mg/kg) but not PF-3845 (10 mg/kg) attenuated striatal MPTP/probenecid-induced dopamine depletion. Furthermore, KML29 induced an increase in Gdnf but not Bdnf expression, whereas PF-3845 decreased the MPTP/probenecid-induced Cnr2 expression without any effects on neurotrophin expression. Investigation of treatment-naïve striatal mRNA levels revealed a high presence of Gdnf and Mgll in contrast to Bdnf and Faah. Treatment of primary mouse microglia with 2-AG increased Gdnf but not Bdnf expression, suggesting that microglia might mediate the observed KML29-induced increase in Gdnf. In summary, pharmacological MAGL but not FAAH inhibition in the chronic MPTP/probenecid model attenuated the MPTP/probenecid-induced effects on striatal dopamine levels which were accompanied by an increase in 2-AG levels.

Neurotransmission systems in Parkinson’s disease

Parkinson’s disease (PD) is histologically characterized by the accumulation of α-synuclein particles, known as Lewy bodies. The second most common neurodegenerative disorder, PD is widely known because of the typical motor manifestations of active tremor, rigidity, and postural instability, while several prodromal non-motor symptoms including REM sleep behavior disorders, depression, autonomic disturbances, and cognitive decline are being more extensively recognized. Motor symptoms most commonly arise from synucleinopathy of nigrostriatal pathway. Glutamatergic, γ-aminobutyric acid (GABA)ergic, cholinergic, serotoninergic, and endocannabinoid neurotransmission systems are not spared from the global cerebral neurodegenerative assault. Wide intrabasal and extrabasal of the basal ganglia provide enough justification to evaluate network circuits disturbance of these neurotransmission systems in PD. In this comprehensive review, English literature in PubMed, Science direct, EMBASE, and Web of Science databases were perused. Characteristics of dopaminergic and non-dopaminergic systems, disturbance of these neurotransmitter systems in the pathophysiology of PD, and their treatment applications are discussed.

Polyunsaturated fatty acids and endocannabinoids in health and disease

Polyunsaturated fatty acids (PUFAs) are lipid derivatives of omega-3 (docosahexaenoic acid, DHA, and eicosapentaenoic acid, EPA) or of omega-6 (arachidonic acid, ARA) synthesized from membrane phospholipids and used as a precursor for endocannabinoids (ECs). They mediate significant effects in the fine-tune adjustment of body homeostasis. Phyto- and synthetic cannabinoids also rule the daily life of billions worldwide, as they are involved in obesity, depression and drug addiction. Consequently, there is growing interest to reveal novel active compounds in this field. Cloning of cannabinoid receptors in the 90s and the identification of the endogenous mediators arachidonylethanolamide (anandamide, AEA) and 2-arachidonyglycerol (2-AG), led to the characterization of the endocannabinoid system (ECS), together with their metabolizing enzymes and membrane transporters. Today, the ECS is known to be involved in diverse functions such as appetite control, food intake, energy balance, neuroprotection, neurodegenerative diseases, stroke, mood disorders, emesis, modulation of pain, inflammatory responses, as well as in cancer therapy. Western diet as well as restriction of micronutrients and fatty acids, such as DHA, could be related to altered production of pro-inflammatory mediators (e.g. eicosanoids) and ECs, contributing to the progression of cardiovascular diseases, diabetes, obesity, depression or impairing conditions, such as Alzheimer' s disease. Here we review how diets based in PUFAs might be linked to ECS and to the maintenance of central and peripheral metabolism, brain plasticity, memory and learning, blood flow, and genesis of neural cells.

Inhibition of the endocannabinoid-regulating enzyme monoacylglycerol lipase elicits a CB1 receptor-mediated discriminative stimulus in mice

Substantial challenges exist for investigating the cannabinoid receptor type 1 (CB₁)-mediated discriminative stimulus effects of the endocannabinoids, 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (anandamide; AEA), compared with exogenous CB₁ receptor agonists, such as Δ⁹-tetrahydrocannabinol (THC) and the synthetic cannabinoid CP55,940. Specifically, each endocannabinoid is rapidly degraded by the respective hydrolytic enzymes, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH). Whereas MAGL inhibitors partially substitute for THC and fully substitute for CP55,940, FAAH inhibitors do not substitute for either drug. Interestingly, combined FAAH-MAGL inhibition results in full THC substitution, and the dual FAAH-MAGL inhibitor SA-57 serves as its own discriminative training stimulus. Because MAGL inhibitors fully substitute for SA-57, we tested whether the selective MAGL inhibitor MJN110 would serve as a training stimulus. Twelve of 13 C57BL/6J mice learned to discriminate MJN110 from vehicle, and the CB₁ receptor antagonist rimonabant dose-dependently blocked its discriminative stimulus. CP55,940, SA-57, and another MAGL inhibitor JZL184, fully substituted for MJN110. In contrast, the FAAH inhibitor PF-3845 failed to substitute for the MJN110 discriminative stimulus, but produced a 1.6 (1.1-2.2; 95% confidence interval) leftward shift in the MJN110 dose-response curve. Inhibitors of other relevant enzymes (i.e., ABHD6, COX-2) and nicotine did not engender substitution. Diazepam partially substituted for MJN110, but rimonabant failed to block this partial effect. These findings suggest that MAGL normally throttles 2-AG stimulation of CB₁ receptors to a magnitude insufficient to produce cannabimimetic subjective effects. Accordingly, inhibitors of this enzyme may release this endogenous brake producing effects akin to those produced by exogenously administered cannabinoids.

Microdialysis Coupled with LC-MS/MS for In Vivo Neurochemical Monitoring

Microdialysis is a powerful sampling technique used to monitor small molecules in vivo. Despite the many applications of microdialysis sampling, it is limited by the method of analyzing the resulting samples. An emerging technique for analysis of microdialysis samples is liquid chromatography-tandem mass spectrometry (LC-MS/MS). This technique is highly versatile, allowing multiplexed analysis of neurotransmitters, metabolites, and neuropeptides. Using LC-MS/MS for polar neurotransmitters is hampered by weak retention reverse phase LC columns. Several derivatization reagents have been utilized to enhance separation and resolution of neurochemicals in dialysate samples including benzoyl chloride (BzCl), dansyl chloride, formaldehyde, ethylchloroformate, and propionic anhydride. BzCl reacts with amine and phenol groups so that many neurotransmitters can be labeled. Besides improving separation on reverse phase columns, this reagent also increases sensitivity. It is available in a heavy form so that it can be used to make stable-isotope labeled internal standard for improved quantification. Using BzCl with LC-MS/MS has allowed for measuring as many as 70 neurochemicals in a single assay. With slightly different conditions, LC-MS/MS has also been used for monitoring endocannabinoids. LC-MS/MS is also useful for neuropeptide assay because it allows for highly sensitive, sequence specific measurement of most peptides. These advances have allowed for multiplexed neurotransmitter measurements in behavioral, circuit analysis, and drug effect studies.

NHS-Esters As Versatile Reactivity-Based Probes for Mapping Proteome-Wide Ligandable Hotspots

Most of the proteome is considered undruggable, oftentimes hindering translational efforts for drug discovery. Identifying previously unknown druggable hotspots in proteins would enable strategies for pharmacologically interrogating these sites with small molecules. Activity-based protein profiling (ABPP) has arisen as a powerful chemoproteomic strategy that uses reactivity-based chemical probes to map reactive, functional, and ligandable hotspots in complex proteomes, which has enabled inhibitor discovery against various therapeutic protein targets. Here, we report an alkyne-functionalized N-hydroxysuccinimide-ester (NHS-ester) as a versatile reactivity-based probe for mapping the reactivity of a wide range of nucleophilic ligandable hotspots, including lysines, serines, threonines, and tyrosines, encompassing active sites, allosteric sites, post-translational modification sites, protein interaction sites, and previously uncharacterized potential binding sites. Surprisingly, we also show that fragment-based NHS-ester ligands can be made to confer selectivity for specific lysine hotspots on specific targets including Dpyd, Aldh2, and Gstt1. We thus put forth NHS-esters as promising reactivity-based probes and chemical scaffolds for covalent ligand discovery.

Harnessing the Endocannabinoid 2-Arachidonoylglycerol to Lower Intraocular Pressure in a Murine Model

Purpose

Cannabinoids, such as Δ⁹-THC, act through an endogenous signaling system in the vertebrate eye that reduces IOP via CB₁ receptors. Endogenous cannabinoid (eCB) ligand, 2-arachidonoyl glycerol (2-AG), likewise activates CB₁ and is metabolized by monoacylglycerol lipase (MAGL). We investigated ocular 2-AG and its regulation by MAGL and the therapeutic potential of harnessing eCBs to lower IOP.

Methods

We tested the effect of topical application of 2-AG and MAGL blockers in normotensive mice and examined changes in eCB-related lipid species in the eyes and spinal cord of MAGL knockout (MAGL^−/−) mice using high performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). We also examined the protein distribution of MAGL in the mouse anterior chamber.

Results

2-Arachidonoyl glycerol reliably lowered IOP in a CB₁- and concentration-dependent manner. Monoacylglycerol lipase is expressed prominently in nonpigmented ciliary epithelium. The MAGL blocker KML29, but not JZL184, lowered IOP. The ability of CB₁ to lower IOP is not desensitized in MAGL^−/− mice. Ocular monoacylglycerols, including 2-AG, are elevated in MAGL^−/− mice but, in contrast to the spinal cord, arachidonic acid and prostaglandins are not changed.

Conclusions

Our data confirm a central role for MAGL in metabolism of ocular 2-AG and related lipid species, and that endogenous 2-AG can be harnessed to reduce IOP. The MAGL blocker KML29 has promise as a therapeutic agent, while JZL184 may have difficulty crossing the cornea. These data, combined with the relative specificity of MAGL for ocular monoacylglycerols and the lack of desensitization in MAGL^−/− mice, suggest that the development of an optimized MAGL blocker offers therapeutic potential for treatment of elevated IOP.

Chemical probes to potently and selectively inhibit endocannabinoid cellular reuptake

The extracellular effects of the endocannabinoids anandamide and 2-arachidonoyl glycerol are terminated by enzymatic hydrolysis after crossing cellular membranes by facilitated diffusion. The lack of potent and selective inhibitors for endocannabinoid transport has prevented the molecular characterization of this process, thus hindering its biochemical investigation and pharmacological exploitation. Here, we report the design, chemical synthesis, and biological profiling of natural product-derived N-substituted 2,4-dodecadienamides as a selective endocannabinoid uptake inhibitor. The highly potent (IC₅₀ = 10 nM) inhibitor N-(3,4-dimethoxyphenyl)ethyl amide (WOBE437) exerted pronounced cannabinoid receptor-dependent anxiolytic, antiinflammatory, and analgesic effects in mice by increasing endocannabinoid levels. A tailored WOBE437-derived diazirine-containing photoaffinity probe (RX-055) irreversibly blocked membrane transport of both endocannabinoids, providing mechanistic insights into this complex process. Moreover, RX-055 exerted site-specific anxiolytic effects on in situ photoactivation in the brain. This study describes suitable inhibitors to target endocannabinoid membrane trafficking and uncovers an alternative endocannabinoid pharmacology.

The endocannabinoid system as a target for addiction treatment: Trials and tribulations

Addiction remains a major public health concern, and while pharmacotherapies can be effective, clinicians are limited by the paucity of existing interventions. Endocannabinoid signaling is involved in reward and addiction, which raises the possibility that drugs targeting this system could be used to treat substance use disorders. This review discusses findings from randomized controlled trials evaluating cannabinergic medications for addiction. Current evidence suggests that pharmacotherapies containing delta-9-tetrahydrocannabinol, such as dronabinol and nabiximols, are effective for cannabis withdrawal. Dronabinol may also reduce symptoms of opioid withdrawal. The cannabinoid receptor 1 (CB1) inverse agonist rimonabant showed promising effects for smoking cessation but also caused psychiatric side effects and currently lacks regulatory approval. Few trials have investigated cannabinergic medications for alcohol use disorder. Overall, the endocannabinoid system remains a promising target for addiction treatment. Development of novel medications such as fatty acid amide hydrolase inhibitors and neutral CB1 antagonists promises to extend the range of available interventions. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Endocannabinoid Turnover

In this review, we consider the biosynthetic, hydrolytic, and oxidative metabolism of the endocannabinoids anandamide and 2-arachidonoylglycerol. We describe the enzymes associated with these events and their characterization. We identify the inhibitor profile for these enzymes and the status of therapeutic exploitation, which to date has been limited to clinical trials for fatty acid amide hydrolase inhibitors. To bring the review to a close, we consider whether point block of a single enzyme is likely to be the most successful approach for therapeutic exploitation of the endocannabinoid system.

Design of Benzoxathiazin-3-one 1,1-Dioxides as a New Class of Irreversible Serine Hydrolase Inhibitors: Discovery of a Uniquely Selective PNPLA4 Inhibitor

The design and examination of 4,1,2-benzoxathiazin-3-one 1,1-dioxides as candidate serine hydrolase inhibitors are disclosed, and represent the synthesis and study of a previously unexplored heterocycle. This new class of activated cyclic carbamates provided selective irreversible inhibition of a small subset of serine hydrolases without release of a leaving group, does not covalently modify active site catalytic cysteine and lysine residues of other enzyme classes, and was found to be amenable to predictable structural modifications that modulate intrinsic reactivity or active site recognition. Even more remarkable and within the small pilot series of candidate inhibitors examined in an initial study, an exquisitely selective inhibitor for a poorly characterized serine hydrolase (PNPLA4, patatin-like phospholipase domain-containing protein 4) involved in adipocyte triglyceride homeostasis was discovered.

MAGL inhibition modulates gastric secretion and motility following NSAID exposure in mice

Non-steroidal anti-inflammatory drugs (NSAIDs) are common analgesic drugs that also cause well-known, negative gastrointestinal (GI) side effects. The physiological mechanism(s) of NSAID-induced GI damage are unclear and are likely due to multiple causes. The most studied contributing mechanisms are increased gastric acid secretion and increased gastric motility. The present study was designed to determine which ulcerogenic effects of the NSAID diclofenac sodium are reversed by blocking the endocannabinoid catabolic enzyme monoacylglycerol lipase (MAGL). Both male and female mice were used to identify possible sex differences. We hypothesized that the MAGL inhibitor JZL184 would attenuate diclofenac-induced increases in both gastric acid secretion and gastric motility. Diclofenac dose-dependently induced gastric hemorrhages to a similar extent in both male and female mice. Gastric hemorrhage severity significantly correlated with gastric levels of myeloperoxidase, an objective measure of neutrophil infiltration. Similarly, JZL184 reduced gastric acidity, in controls as well as mice treated with pentagastrin, which stimulates gastric acid release. As hypothesized, JZL184 decreased gastric motility. Surprisingly, diclofenac also slowed gastric emptying, indicating that diclofenac-induced ulcers most likely occur through increased gastric acid secretion, and not increased gastric motility, as measured in the present study. Thus, MAGL inhibition may proffer gastroprotection through modulating the secretory pathway of gastric hemorrhage. These data underscore the importance of sampling multiple time points and using both sexes in research, in addition to multiple mechanistic targets, and contribute to the basic understanding of NSAID-induced gastric inflammation.

Therapeutic effects of cannabinoids in animal models of seizures, epilepsy, epileptogenesis, and epilepsy-related neuroprotection

The isolation and identification of the discrete plant cannabinoids in marijuana revived interest in analyzing historical therapeutic claims made for cannabis in clinical case studies and anecdotes. In particular, sources as old as the 11th and 15th centuries claimed efficacy for crude marijuana extracts in the treatment of convulsive disorders, prompting a particularly active area of preclinical research into the therapeutic potential of plant cannabinoids in epilepsy. Since that time, a large body of literature has accumulated describing the effects of several of the >100 individual plant cannabinoids in preclinical models of seizures, epilepsy, epileptogenesis, and epilepsy-related neuroprotection. We surveyed the literature for relevant reports of such plant cannabinoid effects and critically reviewed their findings. We found that acute CB₁R agonism in simple models of acute seizures in rodents typically produces anti-convulsant effects whereas CB₁R antagonists exert converse effects in the same models. However, when the effects of such ligands are examined in more complex models of epilepsy, epileptogenesis and neuroprotection, a less simplistic narrative emerges. Here, the complex interactions between (i) brain regions involved in a given model, (ii) relative contributions of endocannabinoid signaling to modulation of synaptic transmission in such areas, (iii) multi-target effects, (iv) cannabinoid type 1 and type 2 receptor signaling interactions and, (v) timing, (vi) duration and (vii) localization of ligand administration suggest that there is both anti-epileptic therapeutic potential and a pro-epileptic risk in up- and down-regulation of endocannabinoid signaling in the central nervous system. Factors such receptor desensitization and specific pharmacology of ligands used (e.g. full vs partial agonists and neutral antagonists vs inverse agonists) also appear to play an important role in the effects reported. Furthermore, the effects of several plant cannabinoids, most notably cannabidiol (CBD) and cannabidavarin (CBDV), in models of seizures, epilepsy, epileptogenesis, and neuroprotection are less ambiguous, and consistent with reports of therapeutically beneficial effects of these compounds in clinical studies. However, continued paucity of firm information regarding the therapeutic molecular mechanism of CBD/CBDV highlights the continued need for research in this area in order to identify as yet under-exploited targets for drug development and raise our understanding of treatment-resistant epilepsies. The recent reporting of positive results for cannabidiol treatment in two Phase III clinical trials in treatment-resistant epilepsies provides pivotal evidence of clinical efficacy for one plant cannabinoid in epilepsy. Moreover, risks and/or benefits associated with the use of unlicensed Δ⁹-THC containing marijuana extracts in pediatric epilepsies remain poorly understood. Therefore, in light of these paradigm-changing clinical events, the present review's findings aim to drive future drug development for newly-identified targets and indications, identify important limitations of animal models in the investigation of plant cannabinoid effects in the epilepsies, and focuses future research in this area on specific, unanswered questions regarding the complexities of endocannabinoid signaling in epilepsy. This article is part of a Special Issue titled Cannabinoids and Epilepsy.

Emerging roles of lipid metabolism in cancer metastasis

Cancer cells frequently display fundamentally altered cellular metabolism, which provides the biochemical foundation and directly contributes to tumorigenicity and malignancy. Rewiring of metabolic programmes, such as aerobic glycolysis and increased glutamine metabolism, are crucial for cancer cells to shed from a primary tumor, overcome the nutrient and energy deficit, and eventually survive and form metastases. However, the role of lipid metabolism that confers the aggressive properties of malignant cancers remains obscure. The present review is focused on key enzymes in lipid metabolism associated with metastatic disease pathogenesis. We also address the function of an important membrane structure-lipid raft in mediating tumor aggressive progression. We enumerate and integrate these recent findings into our current understanding of lipid metabolic reprogramming in cancer metastasis accompanied by new and exciting therapeutic implications.

Cross-validated stable-isotope dilution GC-MS and LC-MS/MS assays for monoacylglycerol lipase (MAGL) activity by measuring arachidonic acid released from the endocannabinoid 2-arachidonoyl glycerol

2-Arachidonoyl glycerol (2AG) is an endocannabinoid that activates cannabinoid (CB) receptors CB1 and CB2. Monoacylglycerol lipase (MAGL) inactivates 2AG through hydrolysis to arachidonic acid (AA) and glycerol, thus modulating the activity at CB receptors. In the brain, AA released from 2AG by the action of MAGL serves as a substrate for cyclooxygenases which produce pro-inflammatory prostaglandins. Here we report stable-isotope GC-MS and LC-MS/MS assays for the reliable measurement of MAGL activity. The assays utilize deuterium-labeled 2AG (d₈-2AG; 10μM) as the MAGL substrate and measure deuterium-labeled AA (d₈-AA; range 0-1μM) as the MAGL product. Unlabelled AA (d₀-AA, 1μM) serves as the internal standard. d₈-AA and d₀-AA are extracted from the aqueous buffered incubation mixtures by ethyl acetate. Upon solvent evaporation the residue is reconstituted in the mobile phase prior to LC-MS/MS analysis or in anhydrous acetonitrile for GC-MS analysis. LC-MS/MS analysis is performed in the negative electrospray ionization mode by selected-reaction monitoring the mass transitions [M-H]^-→[M-H - CO₂]^-, i.e., m/z 311→m/z 267 for d₈-AA and m/z 303→m/z 259 for d₀-AA. Prior to GC-MS analysis d₈-AA and d₀-AA were converted to their pentafluorobenzyl (PFB) esters by means of PFB-Br. GC-MS analysis is performed in the electron-capture negative-ion chemical ionization mode by selected-ion monitoring the ions [M-PFB]^-, i.e., m/z 311 for d₈-AA and m/z 303 for d₀-AA. The GC-MS and LC-MS/MS assays were cross-validated. Linear regression analysis between the concentration (range, 0-1μM) of d₈-AA measured by LC-MS/MS (y) and that by GC-MS (x) revealed a straight line (r²=0.9848) with the regression equation y=0.003+0.898x, indicating a good agreement. In dog liver, we detected MAGL activity that was inhibitable by the MAGL inhibitor JZL-184. Exogenous eicosatetraynoic acid is suitable as internal standard for the quantitative determination of d₈-AA produced from d₈-2AG by hepatic MAGL activity. The formation of d₈-prostaglandin E₂ by the consecutive catalytic action of recombinant MAGL on d₈-2AG and recombinant cyclooxygenase-2 (COX) on d₈-AA was demonstrated by GC-MS/MS.

The Endocannabinoid Metabolite Prostaglandin E2 (PGE2)-Glycerol Inhibits Human Neutrophil Functions: Involvement of Its Hydrolysis into PGE2 and EP Receptors

The endocannabinoids 2-arachidonoyl-glycerol and N-arachidonoyl-ethanolamine mediate an array of pro- and anti-inflammatory effects. These effects are related, in part, to their metabolism by eicosanoid biosynthetic enzymes. For example, N-arachidonoyl-ethanolamine and 2-arachidonoyl-glycerol can be metabolized by cyclooxygenase-2 into PG-ethanolamide (PG-EA) and PG-glycerol (PG-G), respectively. Although PGE₂ is a recognized suppressor of neutrophil functions, the impact of cyclooxygenase-derived endocannabinoids such as PGE₂-EA or PGE₂-G on neutrophils is unknown. This study's aim was to define the effects of these mediators on neutrophil functions and the underlying cellular mechanisms involved. We show that PGE₂-G, but not PGE₂-EA, inhibits leukotriene B₄ biosynthesis, superoxide production, migration, and antimicrobial peptide release. The effects of PGE₂-G were prevented by EP₁/EP₂ receptor antagonist AH-6809 but not the EP₄ antagonist ONO-AE2-227. The effects of PGE₂-G required its hydrolysis into PGE₂, were not observed with the non-hydrolyzable PGE₂-serinol amide, and were completely prevented by methyl-arachidonoyl-fluorophosphate and palmostatin B, and partially prevented by JZL184 and WWL113. Although we could detect six of the documented PG-G hydrolases in neutrophils by quantitative PCR, only ABHD12 and ABHD16A were detected by immunoblot. Our pharmacological data, combined with our protein expression data, did not allow us to pinpoint one PGE₂-G lipase, and rather support the involvement of an uncharacterized lipase and/or of multiple hydrolases. In conclusion, we show that PGE₂-G inhibits human neutrophil functions through its hydrolysis into PGE₂, and by activating the EP₂ receptor. This also indicates that neutrophils could regulate inflammation by altering the balance between PG-G and PG levels in vivo.

Cell-Autonomous Excitation of Midbrain Dopamine Neurons by Endocannabinoid-Dependent Lipid Signaling

The major endocannabinoid in the mammalian brain is the bioactive lipid 2-arachidonoylglycerol (2-AG). The best-known effects of 2-AG are mediated by G-protein-coupled cannabinoid receptors. In principle, 2-AG could modify neuronal excitability by acting directly on ion channels, but such mechanisms are poorly understood. Using a preparation of dissociated mouse midbrain dopamine neurons to isolate effects on intrinsic excitability, we found that 100 nM 2-AG accelerated pacemaking and steepened the frequency-current relationship for burst-like firing. In voltage-clamp experiments, 2-AG reduced A-type potassium current (I_A) through a cannabinoid receptor-independent mechanism mimicked by arachidonic acid, which has no activity on cannabinoid receptors. Activation of orexin, neurotensin, and metabotropic glutamate G_q/11-linked receptors mimicked the effects of exogenous 2-AG and their actions were prevented by inhibiting the 2-AG-synthesizing enzyme diacylglycerol lipase α. The results show that 2-AG and related lipid signaling molecules can directly tune neuronal excitability in a cell-autonomous manner by modulating I_A.

Monoglyceride lipase as a drug target: At the crossroads of arachidonic acid metabolism and endocannabinoid signaling

Monoglyerides (MGs) are short-lived, intermediary lipids deriving from the degradation of phospho- and neutral lipids, and monoglyceride lipase (MGL), also designated as monoacylglycerol lipase (MAGL), is the major enzyme catalyzing the hydrolysis of MGs into glycerol and fatty acids. This distinct function enables MGL to regulate a number of physiological and pathophysiological processes since both MGs and fatty acids can act as signaling lipids or precursors thereof. The most prominent MG species acting as signaling lipid is 2-arachidonoyl glycerol (2-AG) which is the most abundant endogenous agonist of cannabinoid receptors in the body. Importantly, recent observations demonstrate that 2-AG represents a quantitatively important source for arachidonic acid, the precursor of prostaglandins and other inflammatory mediators. Accordingly, MGL-mediated 2-AG degradation affects lipid signaling by cannabinoid receptor-dependent and independent mechanisms. Recent genetic and pharmacological studies gave important insights into MGL's role in (patho-)physiological processes, and the enzyme is now considered as a promising drug target for a number of disorders including cancer, neurodegenerative and inflammatory diseases. This review summarizes the basics of MG (2-AG) metabolism and provides an overview on the therapeutic potential of MGL.

Role of Cannabinoids in Gastrointestinal Mucosal Defense and Inflammation

Modulating the activity of the endocannabinoid system influences various gastrointestinal physiological and pathophysiological processes, and cannabinoid receptors as well as regulatory enzymes responsible for the synthesis or degradation of endocannabinoids representing potential targets to reduce the development of gastrointestinal mucosal lesions, hemorrhage and inflammation. Direct activation of CB₁ receptors by plant-derived, endogenous or synthetic cannabinoids effectively reduces both gastric acid secretion and gastric motor activity, and decreases the formation of gastric mucosal lesions induced by stress, pylorus ligation, nonsteroidal anti-inflammatory drugs (NSAIDs) or alcohol, partly by peripheral, partly by central mechanisms. Similarly, indirect activation of cannabinoid receptors through elevation of endocannabinoid levels by globally acting or peripherally restricted inhibitors of their metabolizing enzymes (FAAH, MAGL) or by inhibitors of their cellular uptake reduces the gastric mucosal lesions induced by NSAIDs in a CB₁ receptor-dependent fashion. Dual inhibition of FAAH and cyclooxygenase enzymes induces protection against both NSAID-induced gastrointestinal damage and intestinal inflammation. Moreover, in intestinal inflammation direct or indirect activation of CB₁ and CB₂ receptors exerts also multiple beneficial effects. Namely, activation of both CB receptors was shown to ameliorate intestinal inflammation in various murine colitis models, to decrease visceral hypersensitivity and abdominal pain, as well as to reduce colitis-associated hypermotility and diarrhea. In addition, CB₁ receptors suppress secretory processes and also modulate intestinal epithelial barrier functions. Thus, experimental data suggest that the endocannabinoid system represents a promising target in the treatment of inflammatory bowel diseases, and this assumption is also confirmed by preliminary clinical studies.

Towards broad spectrum activity-based glycosidase probes: synthesis and evaluation of deoxygenated cyclophellitol aziridines

Deoxygenated cyclophellitol aziridines enable activity-based inter-class labeling of glycosidases including LC-MS/MS identification.

Structural Optimization of 4-Chlorobenzoylpiperidine Derivatives for the Development of Potent, Reversible, and Selective Monoacylglycerol Lipase (MAGL) Inhibitors

Monoacylglycerol lipase (MAGL) inhibitors are considered potential therapeutic agents for a variety of pathological conditions, including several types of cancer. Many MAGL inhibitors are reported in literature; however, most of them showed an irreversible mechanism of action, which caused important side effects. The use of reversible MAGL inhibitors has been only partially investigated so far, mainly because of the lack of compounds with good MAGL reversible inhibition properties. In this study, starting from the (4-(4-chlorobenzoyl)piperidin-1-yl)(4-methoxyphenyl)methanone (CL6a) lead compound that showed a reversible mechanism of MAGL inhibition (K_i = 8.6 μM), we started its structural optimization and we developed a new potent and selective MAGL inhibitor (17b, K_i = 0.65 μM). Furthermore, modeling studies suggested that the binding interactions of this compound replace a structural water molecule reproducing its H-bonds in the MAGL binding site, thus identifying a new key anchoring point for the development of new MAGL inhibitors.

Chemical Methods for Probing Virus-Host Proteomic Interactions

Interactions between host and pathogen proteins constitute an important aspect of both infectivity and the host immune response. Different viruses have evolved complex mechanisms to hijack host-cell machinery and metabolic pathways to redirect resources and energy flow toward viral propagation. These interactions are often critical to the virus, and thus understanding these interactions at a molecular level gives rise to opportunities to develop novel antiviral strategies for therapeutic intervention. This review summarizes current advances in chemoproteomic methods for studying these molecular altercations between different viruses and their hosts.

Oxyradical stress increases the biosynthesis of 2-arachidonoylglycerol: involvement of NADPH oxidase

NADPH oxidase (Nox)-derived oxyradicals contribute to atherosclerosis by oxidizing low-density lipoproteins (LDL), leading to their phagocytosis by vascular macrophages. Endocannabinoids, such as 2-arachidonoylglycerol (2-AG), might be an important link between oxidative stress and atherosclerosis. We hypothesized that 2-AG biosynthesis in macrophages is enhanced following ligation of oxidized LDL by scavenger receptors via a signal transduction pathway involving Nox-derived ROS that activates diacylglycerol lipase-β (DAGL-β), the 2-AG biosynthetic enzyme. To test this idea, we challenged macrophage cell lines and murine primary macrophages with a xanthine oxidase system or with nonphysiological and physiological Nox stimulants [phorbol 12-myristate 13-acetate (PMA) and arachidonic acid (AA)]. Each stressor increased cellular superoxide levels and enhanced 2-AG biosynthetic activity in a Nox-dependent manner. Levels of cytosolic phospholipase A₂-dependent AA metabolites (eicosanoids) in primary macrophages were also dependent on Nox-mediated ROS. In addition, 2-AG levels in DAGL-β-overexpressing COS7 cells were attenuated by inhibitors of Nox and DAGL-β. Furthermore, ROS induced by menadione (a redox cycling agent) or PMA could be partially attenuated by the cannabinoid 1/2 receptor agonist (WIN 55,212-2). Finally, cells that overexpress Nox2 components (Phox-COS7) synthesized larger amounts of 2-AG compared with the parental COS7 cells. Together, the results suggest a positive correlation between heightened oxygen radical flux and 2-AG biosynthesis in macrophage cell lines and primary macrophages. Because of the antioxidant and anti-inflammatory effects associated with 2-AG, the increased levels of this bioactive lipid might be an adaptive response to oxidative stress. Thus oxyradical stress may be counteracted by the enhanced endocannabinoid tone.

Coordinated regulation of endocannabinoid-mediated retrograde synaptic suppression in the cerebellum by neuronal and astrocytic monoacylglycerol lipase

The endocannabinoid 2-arachidonoylglycerol (2-AG) mediates retrograde synaptic depression including depolarization-induced suppression of excitation (DSE) and inhibition (DSI). 2-AG is degraded primarily by monoacylglycerol lipase (MAGL), which is expressed in neurons and astrocytes. Using knockout mice in which MAGL is deleted globally or selectively in neurons or astrocytes, we investigated the relative contribution of neuronal and astrocytic MAGL to the termination of DSE and DSI in Purkinje cells (PCs) in cerebellar slices. We report that neuronal MAGL plays a predominant role in terminating DSE at climbing fiber (CF) to PC synapses, while both neuronal and astrocytic MAGL significantly contributes to the termination of DSE at parallel fiber (PF) to PC synapses and DSI at putative Stellate cell to PC synapses. Thus, DSE and DSI at different synapses is not uniformly affected by global and cell type-specific knockout of MAGL. Additionally, MAGL global knockout, but not cell type-specific knockout, caused tonic activation and partial desensitization of the CB₁ receptor at PF-PC synapses. This tonic CB₁ activation is mediated by 2-AG since it was blocked by the diacylglycerol lipase inhibitor DO34. Together, these results suggest that both neuronal and astrocytic MAGL contribute to 2-AG clearance and prevent CB₁ receptor over-stimulation in the cerebellum.

Adverse Social Experiences in Adolescent Rats Result in Enduring Effects on Social Competence, Pain Sensitivity and Endocannabinoid Signaling

Social affiliation is essential for many species and gains significant importance during adolescence. Disturbances in social affiliation, in particular social rejection experiences during adolescence, affect an individual’s well-being and are involved in the emergence of psychiatric disorders. The underlying mechanisms are still unknown, partly because of a lack of valid animal models. By using a novel animal model for social peer-rejection, which compromises adolescent rats in their ability to appropriately engage in playful activities, here we report on persistent impairments in social behavior and dysregulations in the endocannabinoid (eCB) system. From postnatal day (pd) 21 to pd 50 adolescent female Wistar rats were either reared with same-strain partners (control) or within a group of Fischer 344 rats (inadequate social rearing, ISR), previously shown to serve as inadequate play partners for the Wistar strain. Adult ISR animals showed pronounced deficits in social interaction, social memory, processing of socially transmitted information, and decreased pain sensitivity. Molecular analysis revealed increased CB1 receptor (CB1R) protein levels and CP55, 940 stimulated [³⁵S]GTPγS binding activity specifically in the amygdala and thalamus in previously peer-rejected rats. Along with these changes, increased levels of the eCB anandamide (AEA) and a corresponding decrease of its degrading enzyme fatty acid amide hydrolase (FAAH) were seen in the amygdala. Our data indicate lasting consequences in social behavior and pain sensitivity following peer-rejection in adolescent female rats. These behavioral impairments are accompanied by persistent alterations in CB1R signaling. Finally, we provide a novel translational approach to characterize neurobiological processes underlying social peer-rejection in adolescence.

Fatty acid amide hydrolase inhibition for the symptomatic relief of Parkinson's disease

Elements of the endocannabinoid system are strongly expressed in the basal ganglia where they suffer profound rearrangements after dopamine depletion. Modulation of the levels of the endocannabinoid 2-arachidonoyl-glycerol by inhibiting monoacylglycerol lipase alters glial phenotypes and provides neuroprotection in a mouse model of Parkinson's disease. In this study, we assessed whether inhibiting fatty acid amide hydrolase could also provide beneficial effects on the time course of this disease. The fatty acid amide hydrolase inhibitor, URB597, was administered chronically to mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and probenecid (MPTPp) over 5weeks. URB597 (1mg/kg) prevented MPTPp induced motor impairment but it did not preserve the dopamine levels in the nigrostriatal pathway or regulate glial cell activation. The symptomatic relief of URB597 was confirmed in haloperidol-induced catalepsy assays, where its anti-cataleptic effects were both blocked by antagonists of the two cannabinoid receptors (CB1 and CB2), and abolished in animals deficient in these receptors. Other fatty acid amide hydrolase inhibitors, JNJ1661010 and TCF2, also had anti-cataleptic properties. Together, these results demonstrate an effect of fatty acid amide hydrolase inhibition on the motor symptoms of Parkinson's disease in two distinct experimental models that is mediated by cannabinoid receptors.

Robust anti-nociceptive effects of monoacylglycerol lipase inhibition in a model of osteoarthritis pain

Background and Purpose

Chronic pain is often a symptom of knee osteoarthritis (OA) for which current analgesics are either inadequate or are associated with serious side effects. The endocannabinoid system may offer alternative targets for pain relief. We evaluated the effects of a potent and selective monoacylglycerol (MAG) lipase inhibitor (MJN110) on OA pain behaviour, spinal mechanisms of action and joint histopathology in the rat.

Experimental Approach

Intra‐articular injection of monosodium iodoacetate (MIA) models OA pain and mimics clinical joint pathology. Effects of MJN110 on MIA‐induced weight‐bearing asymmetry and lowered paw withdrawal thresholds (PWTs), changes in spinal gene expression and brain levels of relevant lipids were determined.

Key Results

Acute MJN110 (5 mg·kg⁻¹) significantly reversed MIA‐induced weight‐bearing asymmetry (MIA/vehicle: 68 ± 6 g; MIA/MJN110: 35 ± 4 g) and lowered ipsilateral PWTs (MIA/vehicle: 7 ± 0.8 g; MIA/MJN110: 11 ± 0.6 g), via both CB₁ and CB₂ receptors. Repeated treatment with MJN110 (5 mg·kg⁻¹) resulted in anti‐nociceptive tolerance. A lower dose of MJN110 (1 mg·kg⁻¹) acutely inhibited pain behaviour, which was maintained for 1 week of repeated administration but had no effect on joint histology. MJN110 significantly inhibited expression of membrane‐associated PGE synthase‐1 in the ipsilateral dorsal horn of the spinal cord of MIA rats, compared with vehicle‐treated MIA rats. Both doses of MJN110 significantly elevated brain levels of the endocannabinoid 2‐arachidonoylglycerol.

Conclusions and Implications

Our data support further assessment of the therapeutic potential of MAG lipase inhibitors for the treatment of OA pain.

Female Mice are Resistant to Fabp1 Gene Ablation-Induced Alterations in Brain Endocannabinoid Levels

Although liver fatty acid binding protein (FABP1, L-FABP) is not detectable in the brain, Fabp1 gene ablation (LKO) markedly increases endocannabinoids (EC) in brains of male mice. Since the brain EC system of females differs significantly from that of males, it was important to determine if LKO differently impacted the brain EC system. LKO did not alter brain levels of arachidonic acid (ARA)-containing EC, i.e. arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG), but decreased non-ARA-containing N-acylethanolamides (OEA, PEA) and 2-oleoylglycerol (2-OG) that potentiate the actions of AEA and 2-AG. These changes in brain potentiating EC levels were not associated with: (1) a net decrease in levels of brain membrane proteins associated with fatty acid uptake and EC synthesis; (2) a net increase in brain protein levels of cytosolic EC chaperones and enzymes in EC degradation; or (3) increased brain protein levels of EC receptors (CB1, TRVP1). Instead, the reduced or opposite responsiveness of female brain EC levels to loss of FABP1 (LKO) correlated with intrinsically lower FABP1 level in livers of WT females than males. These data show that female mouse brain endocannabinoid levels were unchanged (AEA, 2-AG) or decreased (OEA, PEA, 2-OG) by complete loss of FABP1 (LKO).

Depth-resolved mid-infrared photothermal imaging of living cells and organisms with submicrometer spatial resolution

Chemical contrast has long been sought for label-free visualization of biomolecules and materials in complex living systems. Although infrared spectroscopic imaging has come a long way in this direction, it is thus far only applicable to dried tissues because of the strong infrared absorption by water. It also suffers from low spatial resolution due to long wavelengths and lacks optical sectioning capabilities. We overcome these limitations through sensing vibrational absorption-induced photothermal effect by a visible laser beam. Our mid-infrared photothermal (MIP) approach reached 10 μM detection sensitivity and submicrometer lateral spatial resolution. This performance has exceeded the diffraction limit of infrared microscopy and allowed label-free three-dimensional chemical imaging of live cells and organisms. Distributions of endogenous lipid and exogenous drug inside single cells were visualized. We further demonstrated in vivo MIP imaging of lipids and proteins in Caenorhabditis elegans. The reported MIP imaging technology promises broad applications from monitoring metabolic activities to high-resolution mapping of drug molecules in living systems, which are beyond the reach of current infrared microscopy.

Activity-based protein profiling for mapping and pharmacologically interrogating proteome-wide ligandable hotspots

Despite the completion of human genome sequencing efforts nearly 15 years ago that brought with it the promise of genome-based discoveries that would cure human diseases, most protein targets that control human diseases have remained largely untranslated, in-part because they represent difficult protein targets to drug. In addition, many of these protein targets lack screening assays or accessible binding pockets, making the development of small-molecule modulators very challenging. Here, we discuss modern methods for activity-based protein profiling-based chemoproteomic strategies to map 'ligandable' hotspots in proteomes using activity and reactivity-based chemical probes to allow for pharmacological interrogation of these previously difficult targets. We will showcase several recent examples of how these technologies have been used to develop highly selective small-molecule inhibitors against disease-related protein targets.

Orchestrated activation of mGluR5 and CB1 promotes neuroprotection

The metabotropic glutamate receptor 5 (mGluR5) and the cannabinoid receptor 1 (CB₁) exhibit a functional interaction, as CB₁ regulates pre-synaptic glutamate release and mGluR5 activation increases endocannabinoid synthesis at the post-synaptic site. Since both mGluR5 and CB₁ promote neuroprotection, we delineated experiments to investigate a possible link between CB₁ and mGluR5 activation in the induction of neuroprotection using primary cultured corticostriatal neurons. We find that either the pharmacological blockade or the genetic ablation of either mGluR5 or CB₁ can abrogate both CB₁- and mGluR5-mediated neuroprotection against glutamate insult. Interestingly, decreased glutamate release and diminished intracellular Ca²⁺ do not appear to play a role in CB₁ and mGluR5-mediated neuroprotection. Rather, these two receptors work cooperatively to trigger the activation of cell signaling pathways to promote neuronal survival, which involves MEK/ERK1/2 and PI3K/AKT activation. Interestingly, although mGluR5 activation protects postsynaptic terminals and CB₁ the presynaptic site, intact signaling of both receptors is required to effectively promote neuronal survival. In conclusion, mGluR5 and CB₁ act in concert to activate neuroprotective cell signaling pathways and promote neuronal survival.

FABP-1 gene ablation impacts brain endocannabinoid system in male mice

Liver fatty acid-binding protein (FABP1, L-FABP) has high affinity for and enhances uptake of arachidonic acid (ARA, C20:4, n-6) which, when esterified to phospholipids, is the requisite precursor for synthesis of endocannabinoids (EC) such as arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG). The brain derives most of its ARA from plasma, taking up ARA and transporting it intracellularly via cytosolic fatty acid-binding proteins (FABPs 3,5, and 7) localized within the brain. In contrast, the much more prevalent cytosolic FABP1 is not detectable in the brain but is instead highly expressed in the liver. Therefore, the possibility that FABP1 outside the central nervous system may regulate brain AEA and 2-AG was examined in wild-type (WT) and FABP1 null (LKO) male mice. LKO increased brain levels of AA-containing EC (AEA, 2-AG), correlating with increased free and total ARA in brain and serum. LKO also increased brain levels of non-ARA that contain potentiating endocannabinoids (EC*) such as oleoyl ethanolamide (OEA), PEA, 2-OG, and 2-PG. Concomitantly, LKO decreased serum total ARA-containing EC, but not non-ARA endocannabinoids. LKO did not elicit these changes in the brain EC and EC* as a result of compensatory up-regulation of brain protein levels of enzymes in EC synthesis (NAPEPLD, DAGLα) or cytosolic EC chaperone proteins (FABPs 3, 5, 7, SCP-2, HSP70), or cannabinoid receptors (CB1, TRVP1). These data show for the first time that the non-CNS fatty acid-binding protein FABP1 markedly affected brain levels of both ARA-containing endocannabinoids (AEA, 2-AG) as well as their non-ARA potentiating endocannabinoids. Fatty acid-binding protein-1 (FABP-1) is not detectable in brain but instead is highly expressed in liver. The possibility that FABP1 outside the central nervous system may regulate brain endocannabinoids arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG) was examined in wild-type (WT) and FABP-1 null (LKO) male mice. LKO increased brain levels of arachidonic acid-containing endocannabinoids (AEA, 2-AG), correlating with increased free and total arachidonic acid in brain and serum. Read the Editorial Highlight for this article on page 371.

In Vivo Characterization of the Ultrapotent Monoacylglycerol Lipase Inhibitor {4-[bis-(benzo[d][1,3]dioxol-5-yl)methyl]-piperidin-1-yl}(1H-1,2,4-triazol-1-yl)methanone (JJKK-048)

Monoacylglycerol lipase (MAGL) is a serine hydrolase that acts as a principal degradative enzyme for the endocannabinoid 2-arachidonoylglycerol (2-AG). In addition to terminating the signaling function of 2-AG, MAGL liberates arachidonic acid to be used as a primary source for neuroinflammatory prostaglandin synthesis in the brain. MAGL activity also contributes to cancer pathogenicity by producing precursors for tumor-promoting bioactive lipids. Pharmacological inhibitors of MAGL provide valuable tools for characterization of MAGL and 2-AG signaling pathways. They also hold great therapeutic potential to treat several pathophysiological conditions, such as pain, neurodegenerative disorders, and cancer. We have previously reported piperidine triazole urea, {4-[bis-(benzo[d][1,3]dioxol-5-yl)methyl]-piperidin-1-yl}(1H-1,2,4-triazol-1-yl)methanone (JJKK-048), to be an ultrapotent and highly selective inhibitor of MAGL in vitro. Here, we characterize in vivo effects of JJKK-048. Acute in vivo administration of JJKK-048 induced a massive increase in mouse brain 2-AG levels without affecting brain anandamide levels. JJKK-048 appeared to be extremely potent in vivo. Activity-based protein profiling revealed that JJKK-048 maintains good selectivity toward MAGL over other serine hydrolases. Our results are also the first to show that JJKK-048 promoted significant analgesia in a writhing test with a low dose that did not cause cannabimimetic side effects. At a high dose, JJKK-048 induced analgesia both in the writhing test and in the tail-immersion test, as well as hypomotility and hyperthermia, but not catalepsy.

Effect of Pharmacological Modulation of the Endocannabinoid System on Opiate Withdrawal: A Review of the Preclinical Animal Literature

Over the years, animal studies have revealed a role for the endocannabinoid system in the regulation of multiple aspects of opiate addiction. The current review provides an overview of this literature in regards to opiate withdrawal. The opiate withdrawal syndrome, hypothesized to act as a negative reinforcer in mediating continued drug use, can be characterized by the emergence of spontaneous or precipitated aversive somatic and affective states following the termination of drug use. The behaviors measured to quantify somatic opiate withdrawal and the paradigms employed to assess affective opiate withdrawal (e.g., conditioned place aversion) in both acutely and chronically dependent animals are discussed in relation to the ability of the endocannabinoid system to modulate these behaviors. Additionally, the brain regions mediating somatic and affective opiate withdrawal are elucidated with respect to their modulation by the endocannabinoid system. Ultimately, a review of these findings reveals dissociations between the brain regions mediating somatic and affective opiate withdrawal, and the ability of cannabinoid type 1 (CB1) receptor agonism/antagonism to interfere with opiate withdrawal within different brain sub regions.

Inhibition of Endocannabinoid Degradation Improves Outcomes from Mild Traumatic Brain Injury: A Mechanistic Role for Synaptic Hyperexcitability

Traumatic brain injury (TBI) is an increasingly prevalent condition affecting soldiers, athletes, and motor vehicle accident victims. Unfortunately, it currently lacks effective therapeutic interventions. TBI is defined as a primary mechanical insult followed by a secondary cascade involving inflammation, apoptosis, release of reactive oxygen species, and excitotoxicity, all of which can cause synaptic changes, altered neuronal signaling, and, ultimately, behavioral changes. Previously we showed that preventing degradation of the endocannabinoid (EC) 2-acylglycerol (2-AG) with JZL184 after mild TBI attenuated neuroinflammation and improved recovery of neurobehavioral function during the early 24 h post-TBI period. The aim of this study was to extend the timeline of observations to 2 weeks post-injury and to investigate JZL184's impact on synaptic transmission, which we view as a potential mechanism for TBI-induced cellular and behavioral pathology. Adult male rats underwent mild TBI (mTBI) followed by a single intraperitoneal injection of JZL184 or vehicle 30 min post-injury. JZL184 administered-TBI animals showed improved neurobehavioral recovery compared with vehicle-injected TBI animals beginning 24 h post-injury and persisting for 2 weeks. JZL184-treated animals had significantly diminished gray and white matter astrocyte activation when compared with vehicle-treated animals at day 7 post-TBI. JZL184 administration significantly attenuated the increased pGluR1^S845/GluR1 and pERK 1/2/ERK and the increases in miniature excitatory postsynaptic potential (mEPSC) frequency and amplitude observed in layer 5 pyramidal neurons at 10 days post-TBI. These results suggest a neuroprotective role for ECs in ameliorating the TBI-induced neurobehavioral, neuroinflammatory, and glutamate dyshomeostasis from mTBI. Further studies elucidating the cellular mechanisms involved are warranted.