Behavioral effects of the novel potent cannabinoid CB1 agonist AM 4054

THC-induced behavioral stereotypy in zebrafish as a model of psychosis-like behavior

High doses of the Cannabis constituent Δ9-tetrahydrocannabinol (THC) increase the risk of psychosis in humans. Highly accessible animal models are needed to address underlying mechanisms. Using zebrafish with a conserved endocannabinoid system, this study investigates the acute effects of THC on adult zebrafish behavior and the mechanisms involved. A concentration-dependent THC-induced behavioral stereotypy akin to THC's effect in rats and the psychotropics phencyclidine and ketamine in zebrafish was established. Distinctive circular swimming during THC-exposure was measured using a novel analytical method that we developed, which detected an elevated Repetition Index (RI) compared to vehicle controls. This was reduced upon co-administration of N-methyl-D-aspartate (NMDA) receptor agonist NMDA, suggesting that THC exerts its effects via biochemical or neurobiological mechanisms associated with NMDA receptor antagonism. Co-treatment of γ-aminobutyric acid receptor antagonist pentylenetetrazol also showed signs of reducing the RI. Since THC-induced repetitive behavior remained in co-administrations with cannabinoid receptor 1 inverse agonist AM251, the phenotype may be cannabinoid receptor 1-independent. Conversely, the inverse cannabinoid receptor 2 agonist AM630 significantly reduced THC-induced behavioral stereotypy, indicating cannabinoid receptor 2 as a possible mediator. A significant reduction of the THC-RI was also observed by the antipsychotic sulpiride. Together, these findings highlight this model's potential for elucidating the mechanistic relationship between Cannabis and psychosis.

Cannabinoid receptor agonists from Conus venoms alleviate pain-related behavior in rats

Cannabinoid (CB) receptor agonists show robust antinociceptive effects in various pain models. However, most of the clinically potent CB1 receptor-active drugs derived from cannabis are considered concerning due to psychotomimetic side effects. Selective CB receptor ligands that do not induce CNS side effects are of clinical interest. The venoms of marine snail Conus are a natural source of various potent analgesic peptides, some of which are already FDA approved. In this study we evaluated the ability of several Conus venom extracts to interact with CB1 receptor. HEK293 cells expressing CB1 receptors were treated with venom extracts and CB1 receptor internalization was analyzed by immunofluorescence. Results showed C. textile (C. Tex) and C. miles (C. Mil) samples as the most potent. These were serially subfractionated by HPLC for subsequent analysis by internalization assays and for analgesic potency evaluated in the formalin test and after peripheral nerve injury. Intrathecal injection of C. Tex and C. Mil subfractions reduced flinching/licking behavior during the second phase of formalin test and attenuated thermal and mechanical allodynia in nerve injury model. Treatment with proteolytic enzymes reduced CB1 internalization of subfractions, indicating the peptidergic nature of CB1 active component. Further HPLC purification revealed two potent antinociceptive subfractions within C. Tex with CB1 and possible CB2 activity, with mild to no side effects in the CB tetrad assessment. CB conopeptides can be isolated from these active Conus venom-derived samples and further developed as novel analgesic agents for the treatment of chronic pain using cell based or gene therapy approaches.

CB1 allosteric modulators and their therapeutic potential in CNS disorders

CB1 is the most abundant GPCR found in the mammalian brain. It has garnered considerable attention as a potential therapeutic drug target. CB1 is involved in a wide range of physiological and psychiatric processes and has the potential to be targeted in a wide range of disease states. However, most of the selective and non-selective synthetic CB1 agonists and antagonists/inverse agonists developed to date are primarily used as research tools. No novel synthetic cannabinoids are currently in the clinic for use in psychiatric illness; synthetic analogues of the phytocannabinoid THC are on the market to treat nausea and vomiting caused by cancer chemotherapy, along with off-label use for pain. Novel strategies are being explored to target CB1, but with emphasis on the elimination or mitigation of the potential psychiatric adverse effects that are observed by central agonism/antagonism of CB1. New pharmacological options are being pursued that may avoid these adverse effects while preserving the potential therapeutic benefits of CB1 modulation. Allosteric modulation of CB1 is one such approach. In this review, we will summarize and critically analyze both the in vitro characterization and in vivo validation of CB1 allosteric modulators developed to date, with a focus on CNS therapeutic effects.

Translation of in vitro cannabinoid 1 receptor agonist activity to in vivo pharmacodynamic endpoints

INTRODUCTION

Building an understanding of in vivo efficacy based on the evaluation of in vitro affinity or potency is critical in expediting early decision making in drug discovery and can significantly reduce the need for animal studies. The aim of the present study was to understand the translation of in vitro to in vivo endpoints for the cannabinoid receptor 1 (CB1).

METHODS

Using a selection of CB1 agonists we describe an evaluation of in vitro to in vivo translation comparing in vitro receptor affinity or functional potency, using both cAMP and β-arrestin endpoints, to various in vivo CB1 agonist-associated endpoints.

RESULTS

We demonstrate that in vitro CB1 agonism significantly correlates with the CB1-induced cue in the drug discrimination model in vivo, but not with other purported CB1 agonist-mediated in vivo endpoints, including hypothermia and sedation. Thus, these data challenge common perceptions regarding CB1 agonist-induced tetrad effects in rodents.

DISCUSSION

This work exemplifies how in vitro profiling of receptor affinity or potency can predict in vivo pharmacodynamic effects, using the CB1 as an example system. The translatability of in vitro activity to in vivo efficacy allows for the ability to rapidly contextualize off-target CB1 in vitro findings, allowing clear and rapid definition of the risk posed by such activity without the need for extensive animal studies. This has significant implications in terms of early decision making in drug discovery and reducing the use of animals in research, while also outlining a template for expanding the approach for additional targets.

AM-251, A Cannabinoid Antagonist, Modifies the Dynamics of Sleep-Wake Cycles in Rats

Study Objectives: (a) To describe the microarchitecture of wakefulness and sleep following administrations of 5- and 10-mg/kg AM-251 in rats. (b) To develop a new statistical method to follow bout-to-bout dynamics. Method: Wistar rats (n = 6) had been equipped with electroencephalography (EEG) and electromyography (EMG) electrodes. Following their recovery and habituation after the surgery, the animals were injected with vehicle and 5- and 10-mg/kg AM-251 intraperitoneally and EEG, EMG, and motor activity were analyzed for the subsequent 3 h. Results: AM-251 induced a dose- and time-dependent increase in the number of bouts in active wake (AW), and it decreased this number in all other vigilance states except in passive wake (PW). In contrast, the bout duration in PW compensatory decreased. The effect of AM-251 on the sleep transition dynamics was monitored with a new tool we call "transition heatmap." The analysis of bout trajectories with transition heatmaps reveals a highly organized pattern. Conclusion: AM-251 selectively influences the frequency of vigilance state transitions, but it has no direct impact on the state lengths. AM-251 markedly changed the state transition dynamics, which was visualized with the help of state transition heatmaps.

The effect of dronabinol in a male patient with anorexia nervosa suffering from severe acute urge to be physically active

OBJECTIVE

A 27-year-old male suffering from chronic anorexia nervosa was admitted for inpatient psychotherapy suffering from severe urge to be physically active.

METHODS

An off-label treatment with dronabinol was initiated, to reduce his symptoms related to that urge. Several attempts to reduce symptoms including intensive psychotherapy and several psychopharmacological agents had failed in the past.

RESULTS

Following treatment with 7.5 mg dronabinol twice a day, the patient reported a significant reduction in his acute urge to be physically active. Also eating disorder-specific cognitions and compulsive behaviors remitted.

DISCUSSION

Previous studies have applied much lower doses and showed no effect of dronabinol upon the urge to be physically active. Up to date, the patient reported no side effects, especially no psychotropic effects. Implications of this case report are discussed.

Effort-related motivational effects of the pro-inflammatory cytokine interleukin-6: pharmacological and neurochemical characterization

RATIONALE

Motivational dysfunctions such as anergia, fatigue, and reduced effort expenditure are common in patients with depression and other disorders. Pro-inflammatory cytokines are implicated in depression, and cytokine administration induces motivational deficits in humans.

OBJECTIVES

These studies focused on the effects of the cytokine interleukin-6 (IL-6) on effort-related decision-making.

METHODS

Rats were assessed using the concurrent fixed ratio 5-lever pressing/chow feeding choice procedure, which measures the tendency of rats to work for a preferred food (high carbohydrate pellets) in the presence of a concurrently available but less preferred substitute (lab chow).

RESULTS

IL-6 (2.0-8.0 μg/kg IP) shifted choice behavior, significantly decreasing lever pressing and increasing chow intake. Further experiments showed that the adenosine A2A antagonist MSX-3 and the stimulant methylphenidate attenuated the effort-related impairments produced by IL-6, increasing lever pressing and decreasing chow intake in IL-6 treated rats. The same doses of IL-6 did not alter food intake or preference in parallel free-feeding choice studies, demonstrating that these low doses were not altering preference for the high carbohydrate pellets or generally suppressing appetite. Also, IL-6 did not affect body temperature. Microdialysis studies showed that 8.0 μg/kg IL-6 significantly decreased extracellular dopamine in nucleus accumbens core.

CONCLUSIONS

In summary, IL-6 reduces the tendency to work for food, even at low doses that do not produce fever or loss of appetite. Dopaminergic mechanisms may be involved in these effort-related effects. This research has implications for the involvement of cytokines in motivational dysfunctions such as anergia and fatigue.

A high efficacy cannabinergic ligand (AM4054) used as a discriminative stimulus: Generalization to other adamantyl analogs and Δ(9)-THC in rats

In addition to endogenous lipids, the two main cloned receptors (CB1R and CB2R) of the endocannabinoid signaling system (ECS) can be activated (and blocked) by various exogenous ligands. A relatively novel template for CB1R activators contains an adamantyl moiety as a key structural subunit, the first being the cannabinergic AM411. Additional chemical optimization efforts using the classical tricyclic scaffold led to AM4054. Here we explored the in vivo consequences of novel adamantyl analogs in rats trained to recognize the effects of the potent adamantyl cannabinergic AM4054. Rats were trained to discriminate between AM4054 (0.1mg/kg) and vehicle. Three AM4054 analogs and Δ(9)-THC were tested for generalization (substitution) and antagonism was assessed with rimonabant. We found that all cannabinergics resulted in response generalization to the target stimulus AM4054. The order of potency was: AM4054≥AM4083≥AM4050>AM4089>Δ(9)-THC. The CB1R antagonist/inverse agonist rimonabant blocked the discriminative stimulus effects of AM4054. Thus the examined structural modifications affected binding affinities but did not markedly change potencies with the exception of AM4089. In vitro (cAMP assay) functional data have suggested that AM4089 behaves as a partial rather than as a full agonist at CB1R which could explain its lower potency compared to AM4054 (Thakur et al., 2013). The 9β-formyl functionality at C-9 position was identified as an important pharmacophore yielding high in vivo potency. Antagonism by rimonabant suggested CB1R mediation.

Effect of dronabinol therapy on physical activity in anorexia nervosa: a randomised, controlled trial

PURPOSE

The level of physical activity is inappropriately high in up to 80% of the patients suffering of anorexia nervosa (AN), as a result of conscious efforts to lose weight, affect regulation and biological adaptive changes to starvation induced by hypothermia and neuroendocrine mechanisms. The purposes of this paper were to (1) assess the effect of dronabinol-a synthetic cannabinoid agonist-on physical activity in patients with chronic and stable AN, and to (2) unravel the role of leptin and cortisol in this process.

METHODS

This prospective, randomised, double-blind, crossover study was conducted at a specialised care centre for eating disorders. Twenty-four adult women with AN of at least 5-year duration received either the dronabinol-placebo or placebo-dronabinol sequence. Physical activity was monitored during the fourth week of each intervention. Body weight, leptin and urinary free cortisol excretion were measured repeatedly during the trial. Changes in behavioural dimensions related to AN were assessed by Eating Disorder Inventory-2.

RESULTS

The total duration of physical activity did not change, while its average intensity increased by 20% (P = 0.01) during dronabinol therapy, resulting in an increased energy expenditure with 68.2 kcal/day (P = 0.01) above placebo.

CONCLUSIONS

This randomised, double-blind study revealed that cannabinoid agonist treatment was associated with a modest increase in physical activity in adult women with severe and longstanding AN. Additionally, we detected a strong relationship between the circulating levels of leptin and physical activity in these chronically undernourished patients.

Effort-related motivational effects of the pro-inflammatory cytokine interleukin 1-beta: studies with the concurrent fixed ratio 5/ chow feeding choice task

RATIONALE

Effort-related motivational symptoms such as anergia and fatigue are common in patients with depression and other disorders. Research implicates pro-inflammatory cytokines in depression, and administration of cytokines can induce effort-related motivational symptoms in humans.

OBJECTIVES

The present experiments focused on the effects of the pro-inflammatory cytokine interleukin 1-beta (IL-1β) on effort-related choice behavior.

METHODS

Rats were tested on a concurrent fixed ratio 5 lever pressing/chow feeding choice procedure, which assesses the tendency of rats to work for a preferred food (high carbohydrate pellets) in the presence of a concurrently available but less preferred substitute (laboratory chow).

RESULTS

IL-1β (1.0-4.0 μg/kg IP) shifted choice behavior, significantly decreasing lever pressing and increasing intake of the freely available chow. The second experiment assessed the ability of the adenosine A2A antagonist (E)-phosphoric acid mono-[3-[8-[2-(3-methoxyphenyl)vinyl]-7-methyl-2,6-dioxo-1-prop-2-ynyl-1,2,6,7-tetrahydropurin-3-yl] propyl] ester disodium salt (MSX-3) to reverse the behavioral effects of IL-1β. MSX-3 attenuated the effort-related impairments produced by IL-1β, increasing lever pressing and also decreasing chow intake. In the same dose range that shifted effort-related choice behavior, IL-1β did not alter food intake or preference in parallel free-feeding choice studies, indicating that these low doses were not generally suppressing appetite or altering preference for the high carbohydrate pellets. In addition, IL-1β did not affect core body temperature.

CONCLUSIONS

These results indicate that IL-1β can reduce the tendency to work for food, even at low doses that do not produce a general sickness, malaise, or loss of appetite. This research has implications for the involvement of cytokines in motivational symptoms such as anergia and fatigue.

Effects of a novel CB1 agonist on visual attention in male rats: role of strategy and expectancy in task accuracy

The effects of cannabinoid CB1 agonists (including Δ9-tetrahydrocannabinol, the main psychoactive component of marijuana) on attention are uncertain, with reports of impairments, no effects, and occasionally performance enhancements. To better understand these effects, we sought to uncover a role of changing online (within-session) strategy as a possible mediator of the effects of the novel, potent CB1 agonist AM 4054, on a model of sustained attention in male Sprague-Dawley rats. In this operant, two-choice reaction time (RT) task, AM 4054 decreased accuracy in an asymmetric manner; that is, performance was spared on one lever but impaired on the other. Furthermore, this pattern was enhanced by the outcome of the previous trial such that AM 4054 strengthened a win-stay strategy on the "preferred" lever and a lose-shift strategy on the "nonpreferred" lever. This pattern is often found in tests of expectancy; therefore, in a second experiment AM 4054 enhanced expectancy that we engendered by altering the probability of the two stimulus cues. Accuracy was impaired in reporting the less frequent cue, but only after two or more presentations of the more frequent cue. Taking the results of the experiments together, AM 4054 engendered expectancy by increasing the role of previous trial location and outcome on performance of future trials, diminishing stimulus control (and therefore, accuracy). This novel effect of CB1 receptor agonism may contribute to the deleterious effects of cannabinoids on attention.