Endocannabinoid overload.

The signaling capacity of endogenous cannabinoids ("endocannabinoids") is tightly regulated by degradative enzymes. This Perspective highlights a research article in this issue (p. 996) in which the authors show that genetic disruption of monoacylglycerol lipase (MAGL), the principal degradative enzyme for the endocannabinoid 2-arachidonoylglycerol (2-AG), causes marked elevations in 2-AG levels that lead to desensitization of brain cannabinoid receptors.

The CB2 cannabinoid receptor-selective agonist O-3223 reduces pain and inflammation without apparent cannabinoid behavioral effects.

Although Δ(9)-tetrahydrocannabinol (THC) and other mixed CB(1)/CB(2) receptor agonists are well established to elicit antinociceptive effects, their psychomimetic actions and potential for abuse have dampened enthusiasm for their therapeutic development. Conversely, CB(2) receptor-selective agonists have been shown to reduce pain and inflammation, without eliciting apparent cannabinoid behavioral effects. In the present study, we developed a novel ethyl sulfonamide THC analog, O-3223, and compared its pharmacological effects to those of the potent, mixed CB(1)/CB(2) receptor agonist, CP55,940, in a battery of preclinical pain models.

Chronic monoacylglycerol lipase blockade causes functional antagonism of the endocannabinoid system.

Prolonged exposure to drugs of abuse, such as cannabinoids and opioids, leads to pharmacological tolerance and receptor desensitization in the nervous system. We found that a similar form of functional antagonism was produced by sustained inactivation of monoacylglycerol lipase (MAGL), the principal degradative enzyme for the endocannabinoid 2-arachidonoylglycerol. After repeated administration, the MAGL inhibitor JZL184 lost its analgesic activity and produced cross-tolerance to cannabinoid receptor (CB1) agonists in mice, effects that were phenocopied by genetic disruption of Mgll (encoding MAGL).

Pharmacological evaluation of the natural constituent of Cannabis sativa, cannabichromene and its modulation by Δ(9)-tetrahydrocannabinol.

In contrast to the numerous reports on the pharmacological effects of Δ(9)-tetrahydrocannabinol (THC), the pharmacological activity of another substituent of Cannabis sativa, cannabichromene (CBC) remains comparatively unknown. In the present study, we investigated whether CBC elicits cannabinoid activity in the tetrad assay, which consists of the following four endpoints: hypomotility, antinociception, catalepsy, and hypothermia. Because cannabinoids are well documented to possess anti-inflammatory properties, we examined CBC, THC, and combination of both phytocannabinoids in the lipopolysaccharide (LPS) paw edema assay.

Fatty acid amide hydrolase and monoacylglycerol lipase inhibitors produce anti-allodynic effects in mice through distinct cannabinoid receptor mechanisms.

Unlabelled: The endocannabinoids anandamide and 2-arachidonoylglycerol are predominantly regulated by the respective catabolic enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). Inhibition of these enzymes elevates endocannabinoid levels and attenuates neuropathic pain. In the present study, CB₁ and CB₂ receptor-deficient mice were subjected to chronic constriction injury (CCI) of the sciatic nerve to examine the relative contribution of each receptor for the anti-allodynic effects of the FAAH inhibitor, PF-3845, and the MAGL inhibitor, JZL184.

Are CB(1) Receptor Antagonists Nootropic or Cognitive Impairing Agents?

For more than a decade, a considerable amount of research has examined the effects of rimonabant (SR 141716) and other CB(1) receptor antagonists in both in vivo and in vitro models of learning and memory. In addition to its utility in determining whether the effects of drugs are mediated though a CB(1) receptor mechanism of action, these antagonists are useful in providing insight into the physiological function of the endogenous cannabinoid system. Several groups have reported that CB(1) receptor antagonists enhance memory duration in a variety of spatial and operant paradigms, but not in all paradigms.

Statin-induced Krüppel-like factor 2 expression in human and mouse T cells reduces inflammatory and pathogenic responses.

The transcription factor Krüppel-like factor 2 (KLF2) is required for the quiescent and migratory properties of naive T cells. Statins, a class of HMG-CoA reductase inhibitors, display pleiotropic immunomodulatory effects that are independent of their lipid-lowering capacity and may be beneficial as therapeutic agents for T cell-mediated inflammatory diseases. Statins upregulate KLF2 expression in endothelial cells, and this activity is associated with an antiinflammatory phenotype.

Regulation of inflammatory pain by inhibition of fatty acid amide hydrolase.

Although cannabinoids are efficacious in laboratory animal models of inflammatory pain, their established cannabimimetic actions diminish enthusiasm for their therapeutic development. Conversely, fatty acid amide hydrolase (FAAH), the chief catabolic enzyme regulating the endogenous cannabinoid N-arachidonoylethanolamine (anandamide), has emerged as an attractive target for treating pain and other conditions. Here, we tested WIN 55212-2 [(R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de)-1,4-benzoxazin-6-yl]-1-napthalenylmethanone], a cannabinoid receptor agonist, and genetic deletion or pharmacological inhibition of FAAH in the lipopolysaccharide (LPS) mouse model of inflammatory pain.

FAAH-/- mice display differential tolerance, dependence, and cannabinoid receptor adaptation after delta 9-tetrahydrocannabinol and anandamide administration.

Repeated administration of Delta(9)-tetrahydrocannabinol (THC), the primary psychoactive constituent of Cannabis sativa, induces profound tolerance that correlates with desensitization and downregulation of CB(1) cannabinoid receptors in the CNS. However, the consequences of repeated administration of the endocannabinoid N-arachidonoyl ethanolamine (anandamide, AEA) on cannabinoid receptor regulation are unclear because of its rapid metabolism by fatty acid amide hydrolase (FAAH). FAAH(-/-) mice dosed subchronically with equi-active maximally effective doses of AEA or THC displayed greater rightward shifts in THC dose-effect curves for antinociception, catalepsy, and hypothermia than in AEA dose-effect curves.

Dual blockade of FAAH and MAGL identifies behavioral processes regulated by endocannabinoid crosstalk in vivo.

Delta(9)-tetrahydrocannabinol (THC), the psychoactive component of marijuana, and other direct cannabinoid receptor (CB1) agonists produce a number of neurobehavioral effects in mammals that range from the beneficial (analgesia) to the untoward (abuse potential). Why, however, this full spectrum of activities is not observed upon pharmacological inhibition or genetic deletion of either fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MAGL), enzymes that regulate the two major endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG), respectively, has remained unclear. Here, we describe a selective and efficacious dual FAAH/MAGL inhibitor, JZL195, and show that this agent exhibits broad activity in the tetrad test for CB1 agonism, causing analgesia, hypomotilty, and catalepsy.

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

Considerable preclinical research has demonstrated the efficacy of Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the primary psychoactive constituent of Cannabis sativa, in a wide variety of animal models of pain, but few studies have examined other phytocannabinoids. Indeed, other plant-derived cannabinoids, including cannabidiol (CBD), cannabinol (CBN), and cannabichromene (CBC) elicit antinociceptive effects in some assays. In contrast, tetrahydrocannabivarin (THCV), another component of cannabis, antagonizes the pharmacological effects of Delta(9)-THC.

Fatty acid amide hydrolase (FAAH) knockout mice exhibit enhanced acquisition of an aversive, but not of an appetitive, Barnes maze task.

It is well established that genetic deletion or pharmacological inhibition of the CB(1) receptor disrupts extinction learning in aversive conditioning tasks, but not in appetitive tasks. Consistent with these findings is that genetic deletion or pharmacological inhibition of fatty acid amide hydrolase (FAAH), the primary catabolic enzyme of the endogenous cannabinoid anandamide (AEA), accelerates acquisition as well as extinction in aversive conditioning tasks. However, it is unknown whether FAAH blockade will affect acquisition in an appetitive conditioning task.

Blockade of endocannabinoid-degrading enzymes attenuates neuropathic pain.

Direct-acting cannabinoid receptor agonists are well known to reduce hyperalgesic responses and allodynia after nerve injury, although their psychoactive side effects have damped enthusiasm for their therapeutic development. Alternatively, inhibiting fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), the principal enzymes responsible for the degradation of the respective endogenous cannabinoids, anandamide (AEA) and 2-arachydonylglycerol (2-AG), reduce nociception in a variety of nociceptive assays, with no or minimal behavioral effects. In the present study we tested whether inhibition of these enzymes attenuates mechanical allodynia, and acetone-induced cold allodynia in mice subjected to chronic constriction injury of the sciatic nerve.

Innate and adaptive immunity in atherosclerosis.

Atherosclerosis, a chronic inflammatory disorder, involves both the innate and adaptive arms of the immune response that mediate the initiation, progression, and ultimate thrombotic complications of atherosclerosis. Most fatal thromboses, which may manifest as acute myocardial infarction or ischemic stroke, result from frank rupture or superficial erosion of the fibrous cap overlying the atheroma, processes that occur in inflammatorily active, rupture-prone plaques. Appreciation of the inflammatory character of atherosclerosis has led to the application of C-reactive protein as a biomarker of cardiovascular risk and the characterization of the anti-inflammatory and immunomodulatory actions of the statin class of drugs.

Inhibitors of endocannabinoid-metabolizing enzymes reduce precipitated withdrawal responses in THC-dependent mice.

Abstinence symptoms in cannabis-dependent individuals are believed to contribute to the maintenance of regular marijuana use. However, there are currently no medications approved by the FDA to treat cannabis-related disorders. The only treatment currently shown consistently to alleviate cannabinoid withdrawal in both animals and humans is substitution therapy using the psychoactive constituent of marijuana, Delta(9)-tetrahydrocannabinol (THC).

Hippocampal CB(1) receptors mediate the memory impairing effects of Delta(9)-tetrahydrocannabinol.

It is firmly established that the hippocampus, a brain region implicated in spatial learning, episodic memory, and consolidation, contains a high concentration of CB(1) receptors. Moreover, systemic and intrahippocampal administration of cannabinoid agonists have been shown to impair hippocampal-dependent memory tasks. However, the degree to which CB(1) receptors in the hippocampus play a specific functional role in the memory disruptive effects of marijuana or its primary psychoactive constituent Delta(9)-tetrahydrocannabinol (Delta(9)-THC) is unknown.

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

Although the dominant approach to drug development is the design of compounds selective for a given target, compounds targeting more than one biological process may have superior efficacy, or alternatively a better safety profile than standard selective compounds. Here, this possibility has been explored with respect to the endocannabinoid system and pain. Compounds inhibiting the enzyme fatty acid amide hydrolase (FAAH), by increasing local endocannabinoid tone, produce potentially useful effects in models of inflammatory and possibly neuropathic pain.

Targeting fatty acid amide hydrolase (FAAH) to treat pain and inflammation.

The endogenous cannabinoid N-arachidonoyl ethanolamine (anandamide; AEA) produces most of its pharmacological effects by binding and activating CB(1) and CB(2) cannabinoid receptors within the CNS and periphery. However, the actions of AEA are short lived because of its rapid catabolism by fatty acid amide hydrolase (FAAH). Indeed, FAAH knockout mice as well as animals treated with FAAH inhibitors are severely impaired in their ability to hydrolyze AEA as well as a variety of noncannabinoid lipid signaling molecules and consequently possess greatly elevated levels of these endogenous ligands.

Endocannabinoid modulation of scratching response in an acute allergenic model: a new prospective neural therapeutic target for pruritus.

Pruritus (itch) is a common cause of discomfort by dermatological disorders. Several peripherally and centrally mediated pathologies that induce pruritus do not generally respond to typical allergenic and anti-inflammatory treatments. In accordance, we employed an acute allergenic murine model to determine whether the endogenous cannabinoid system could be targeted to treat pruritus.

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

The present study investigated whether inhibition of fatty acid amide hydrolase (FAAH), the enzyme responsible for anandamide catabolism, produces antinociception in the acetic acid-induced abdominal stretching model of visceral nociception. Genetic deletion or pharmacological inhibition of FAAH reduced acetic acid-induced abdominal stretching. Transgenic mice that express FAAH exclusively in the nervous system displayed the antinociceptive phenotype, indicating the involvement of peripheral fatty acid amides.

Selective blockade of 2-arachidonoylglycerol hydrolysis produces cannabinoid behavioral effects.

2-Arachidonoylglycerol (2-AG) and anandamide are endocannabinoids that activate the cannabinoid receptors CB1 and CB2. Endocannabinoid signaling is terminated by enzymatic hydrolysis, a process that for anandamide is mediated by fatty acid amide hydrolase (FAAH), and for 2-AG is thought to involve monoacylglycerol lipase (MAGL). FAAH inhibitors produce a select subset of the behavioral effects observed with CB1 agonists, which suggests a functional segregation of endocannabinoid signaling pathways in vivo.

T-cell costimulation and coinhibition in atherosclerosis.

Evidence from many human and rodent studies has established that T lymphocytes enhance inflammation in atherosclerotic plaques and contribute to lesion progression and remodeling. Recent work also indicates that regulatory T cells are important in limiting proatherogenic T-cell responses. Given the important role of T cells in atherosclerosis, there is a need to fully understand how proatherogenic T cells are activated and regulated.

Differential endocannabinoid regulation of extinction in appetitive and aversive Barnes maze tasks.

CB 1 receptor-compromised animals show profound deficits in extinguishing learned behavior from aversive conditioning tasks, but display normal extinction learning in appetitive operant tasks. However, it is difficult to discern whether the differential involvement of the endogenous cannabinoid system on extinction results from the hedonics or the required responses associated with the disparate tasks. Here, we report that the CB 1 receptor antagonist rimonabant disrupts extinction learning in an aversive, but not in an appetitive, Barnes maze conditioning task.

CD11c(+) dendritic cells maintain antigen processing, presentation capabilities, and CD4(+) T-cell priming efficacy under hypercholesterolemic conditions associated with atherosclerosis.

Recent reports suggest dyslipidemia impairs dendritic cell (DC) function and adaptive immunity. This study aimed to characterize the effect of hypercholesterolemia on antigen-presenting cell function of DCs and DC-dependent CD4(+) T-cell responses. DCs incubated in vitro with acetylated low-density lipoprotein cholesterol with or without an acyl-coenzyme A:cholesterol acyl-transferase inhibitor maintained their ability to prime CD4(+) T cells.