Low dosage of rimonabant leads to anxiolytic-like behavior via inhibiting expression levels and G-protein activity of kappa opioid receptors in a cannabinoid receptor independent manner

A systematic review of novel cannabinoids and their targets: Insights into the significance of structure in activity

To provide a comprehensive framework of the current information on the potency and efficacy of interaction between phyto- and synthetic cannabinoids and their respective receptors, an electronic search of the PubMed, Scopus, and EMBASE literature was performed. Experimental studies included reports of mechanistic data providing affinity, efficacy, and half-maximal effective concentration (EC50). Among the 108 included studies, 174 structures, and 16 targets were extracted. The most frequent ligands belonged to the miscellaneous category with 40.2% followed by phytocannabinoid-similar, indole-similar, and pyrrole-similar structures with an abundance of 17.8%, 16.6%, and 12% respectively. 64.8% of structures acted as agonists, 17.1 % appeared as inverse agonists, 10.8% as antagonists, and 7.2% of structures were reported with antagonist/inverse agonist properties. Our outcomes identify the affinity, EC50, and efficacy of the interactions between cannabinoids and their corresponding receptors and the subsequent response, evaluated in the available evidence. Considering structures' significance and very important effects of on the activities, the obtained results also provide clues to drug repurposing.

Kappa opioid receptor blockade in the nucleus accumbens shell prevents sex-dependent alcohol deprivation effect induced by inflammatory pain

ABSTRACT

Pain-induced negative affect reduces life quality of patients by increasing psychiatric comorbidities, including alcohol use disorders (AUDs). Indeed, clinical data suggest pain as a risk factor to suffer AUDs, predicting relapse drinking in abstinent patients. Here, we analyse the impact of pain on alcohol relapse and the role of kappa opioid receptor (KOR) activation in mediating these pain-induced effects because KORs play an important role in pain-driven negative affect and AUD. Female and male Sprague-Dawley rats underwent 2 alcohol intermittent access periods separated by a forced abstinence period. The complete Freund adjuvant model of inflammatory pain was introduced during abstinence, and alcohol intake before and after alcohol reintroduction was assessed. In addition, we used behavioural approaches to measure stress and memory impairment and biochemical assays to measure KOR expression in abstinence and reintroduction periods. Only female CFA-treated rats increased alcohol intake during the reintroduction period. Concomitantly, this group showed enhanced anxiety-like behaviour and increased KOR expression in the nucleus accumbens shell that was developed during abstinence and remained during the reintroduction period. Finally, KOR antagonist norbinaltorphimine was administered in the nucleus accumbens shell during abstinence to prevent a pain-induced alcohol deprivation effect, a phenomenon observed in CFA-female rats. The administration of norbinaltorphimine effectively blocked a pain-induced alcohol deprivation effect in female rats. Our data evidenced that inflammatory pain constitutes a risk factor to increase alcohol consumption during a reintroduction phase only in female rats by the rise and maintenance of stress probably mediated by KOR signalling in the nucleus accumbens.

Behavioral assessment of rimonabant under acute and chronic conditions

Cannabinoid subtype 1 receptor (CB1R) antagonists were originally developed as anti-obesity agents. Unfortunately, SR1417116A (rimonabant), the first marketed inverse agonist of CB1R, produced CNS-related adverse effects including depression and suicidal ideation, and thus it was withdrawn from the market. These effects of rimonabant became evident in patients following chronic dosing. Standard preclinical toxicity studies failed to detect these adverse effects. The goal of these studies was to perform an integrated battery of behavioral assays to better understand the behavioral effects of rimonabant following both acute and chronic administration. In the present study, acute dosing with rimonabant in rats significantly decreased food consumption; decreased measures of locomotor activity; increased scratching, grooming and wet-dog shakes; and increased defecation. Subsequently, animals were tested using a chronic dosing regimen but prior to drug administration for that day. The highest dose of rimonabant tested significantly decreased marble burying behavior, presumably anxiolysis. There were also significant effects in social interaction after chronic dosing. Our results did not reveal significant rimonabant-induced anxiogenic behaviors. Future studies to characterize behavioral screens for anxiogenic effects of CB1 antagonists in rodents should further explore social interaction paradigms and potential comorbid factors of rimonabant dosing such as sex, age, and obesity.

Hemoglobin-derived peptides and mood regulation

Evidence accumulated over the past decades has revealed that red blood cells and hemoglobin (Hb) in the blood play important roles in modulating moods and emotions. The number of red blood cells affects the mood. Hb is the principal content in the red blood cells besides water. Denatured Hb is hydrolyzed to produce bioactive peptides. RVD-hemopressin α (RVD-Hpα), which is a fragment of α-chain (95-103) in Hb, functions as a negative allosteric modulator of cannabinoid receptor 1 and a positive allosteric modulator of cannabinoid receptor 2. Hemorphins, which are fragments of β-chain in Hb, exert their effects on opioid receptors. Two hemorphins, namely, LVV-hemorphin-6 and LVV-hemorphin-7, could induce anxiolytic-like effects. The use of Hb-derived bioactive peptides for the treatment of mood disorders is desirable due to cannabinoid-opioid cross modulation and the critical roles of the two systems in physiological processes, such as memory, mood and emotion.

Rimonabant, a potent CB1 cannabinoid receptor antagonist, is a Gαi/o protein inhibitor

Rimonabant is a potent and selective cannabinoid CB1 receptor antagonist widely used in animal and clinical studies. Besides its antagonistic properties, numerous studies have shown that, at micromolar concentrations rimonabant behaves as an inverse agonist at CB1 receptors. The mechanism underpinning this activity is unclear. Here we show that micromolar concentrations of rimonabant inhibited Gα_i/o-type G proteins, resulting in a receptor-independent block of G protein signaling. Accordingly, rimonabant decreased basal and agonist stimulated [³⁵S]GTPγS binding to cortical membranes of CB1- and GABA_B-receptor KO mice and Chinese Hamster Ovary (CHO) cell membranes stably transfected with GABA_B or D2 dopamine receptors. The structural analog of rimonabant, AM251, decreased basal and baclofen-stimulated GTPγS binding to rat cortical and CHO cell membranes expressing GABA_B receptors. Rimonabant prevented G protein-mediated GABA_B and D2 dopamine receptor signaling to adenylyl cyclase in Human Embryonic Kidney 293 cells and to G protein-coupled inwardly rectifying K⁺ channels (GIRK) in midbrain dopamine neurons of CB1 KO mice. Rimonabant suppressed GIRK gating induced by GTPγS in CHO cells transfected with GIRK, consistent with a receptor-independent action. Bioluminescent resonance energy transfer (BRET) measurements in living CHO cells showed that, in presence or absence of co-expressed GABA_B receptors, rimonabant stabilized the heterotrimeric Gαi/o-protein complex and prevented conformational rearrangements induced by GABA_B receptor activation. Rimonabant failed to inhibit Gαs-mediated signaling, supporting its specificity for Gα_i/o-type G proteins. The inhibition of Gα_i/o protein provides a new site of rimonabant action that may help to understand its pharmacological and toxicological effects occurring at high concentrations.

Cannabinoid receptor-1 signaling contributions to sign-tracking and conditioned reinforcement in rats

RATIONALE

Endocannabinoids (eCBs) are critical gatekeepers of dopaminergic signaling, and disrupting cannabinoid receptor-1 (CB1) signaling alters DA dynamics to attenuate cue-motivated behaviors. Prior studies suggest that dopamine (DA) release plays a critical role in driving sign-tracking.

OBJECTIVES

Here, we determine whether systemic injections of rimonabant, a CB1 receptor inverse agonist, during Pavlovian lever autoshaping impair the expression of sign-tracking. We next examine whether rimonabant blocks the reinforcing properties of the Pavlovian lever cue in a conditioned reinforcement test.

METHODS

In Exp. 1, we trained rats in Pavlovian lever autoshaping prior to systemic rimonabant injections (0, 1, 3 mg/kg) during early and late Pavlovian lever autoshaping sessions. In Exp. 2, we trained rats in Pavlovian lever autoshaping prior to systemic rimonabant injections (0, 1 mg/kg) during a conditioned reinforcement test.

RESULTS

Rimonabant dose-dependently decreased lever contact and probability, and increased sign-tracker's latency to approach the lever cue early in Pavlovian training. With extended training, many previously goal-tracking and intermediate rats shifted to lever approach, which remained dose-dependently sensitive to rimonabant. Rimonabant attenuated cue-evoked food cup approach early, but not late, in conditioning, and did not affect pellet retrieval or consumption. The inserted lever cue served as a robust conditioned reinforcer after Pavlovian lever autoshaping, and 1 mg/kg rimonabant blocked conditioned reinforcement.

CONCLUSIONS

Together, our results suggest that CB1 signaling mediates two critical properties of incentive stimuli; their ability to attract (Exp. 1) and their ability to reinforce (Exp. 2) behavior.

Cannabinoids Modulate Neuronal Activity and Cancer by CB1 and CB2 Receptor-Independent Mechanisms

Cannabinoids include the active constituents of Cannabis or are molecules that mimic the structure and/or function of these Cannabis-derived molecules. Cannabinoids produce many of their cellular and organ system effects by interacting with the well-characterized CB1 and CB2 receptors. However, it has become clear that not all effects of cannabinoid drugs are attributable to their interaction with CB1 and CB2 receptors. Evidence now demonstrates that cannabinoid agents produce effects by modulating activity of the entire array of cellular macromolecules targeted by other drug classes, including: other receptor types; ion channels; transporters; enzymes, and protein- and non-protein cellular structures. This review summarizes evidence for these interactions in the CNS and in cancer, and is organized according to the cellular targets involved. The CNS represents a well-studied area and cancer is emerging in terms of understanding mechanisms by which cannabinoids modulate their activity. Considering the CNS and cancer together allow identification of non-cannabinoid receptor targets that are shared and divergent in both systems. This comparative approach allows the identified targets to be compared and contrasted, suggesting potential new areas of investigation. It also provides insight into the diverse sources of efficacy employed by this interesting class of drugs. Obtaining a comprehensive understanding of the diverse mechanisms of cannabinoid action may lead to the design and development of therapeutic agents with greater efficacy and specificity for their cellular targets.

Exploring the first Rimonabant analog-opioid peptide hybrid compound, as bivalent ligand for CB1 and opioid receptors

Cannabinoid (CB) and opioid systems are both involved in analgesia, food intake, mood and behavior. Due to the co-localization of µ-opioid (MOR) and CB1 receptors in various regions of the central nervous system (CNS) and their ability to form heterodimers, bivalent ligands targeting to both these systems may be good candidates to investigate the existence of possible cross-talking or synergistic effects, also at sub-effective doses. In this work, we selected from a small series of new Rimonabant analogs one CB1R reverse agonist to be conjugated to the opioid fragment Tyr-D-Ala-Gly-Phe-NH₂. The bivalent compound (9) has been used for in vitro binding assays, for in vivo antinociception models and in vitro hypothalamic perfusion test, to evaluate the neurotransmitters release.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

The endocannabinoid system in the baboon (Papio spp.) as a complex framework for developmental pharmacology

INTRODUCTION

The consumption of marijuana (exogenous cannabinoid) almost doubled in adults during last decade. Consumption of exogenous cannabinoids interferes with the endogenous cannabinoid (or "endocannabinoid" (eCB)) system (ECS), which comprises N-arachidonylethanolamide (anandamide, AEA), 2-arachidonoyl glycerol (2-AG), endocannabinoid receptors (cannabinoid receptors 1 and 2 (CB1R and CB2R), encoded by CNR1 and CNR2, respectively), and synthesizing/degrading enzymes (FAAH, fatty-acid amide hydrolase; MAGL, monoacylglycerol lipase; DAGL-α, diacylglycerol lipase-alpha). Reports regarding the toxic and therapeutic effects of pharmacological compounds targeting the ECS are sometimes contradictory. This may be caused by the fact that structure of the eCBs varies in the species studied.

OBJECTIVES

First: to clone and characterize the cDNAs of selected members of ECS in a non-human primate (baboon, Papio spp.), and second: to compare those cDNA sequences to known human structural variants (single nucleotide polymorphisms and haplotypes).

MATERIALS AND METHODS

Polymerase chain reaction-amplified gene products from baboon tissues were transformed into Escherichia coli. Amplicon-positive clones were sequenced, and the obtained sequences were conceptually translated into amino-acid sequences using the genetic code.

RESULTS

Among the ECS members, CNR1 was the best conserved gene between humans and baboons. The phenotypes associated with mutations in the untranslated regions of this gene in humans have not been described in baboons. One difference in the structure of CNR2 between humans and baboons was detected in the region with the only known clinically relevant polymorphism in a human receptor. All of the differences in the amino-acid structure of DAGL-α between humans and baboons were located in the hydroxylase domain, close to phosphorylation sites. None of the differences in the amino-acid structure of MAGL observed between baboons and humans were located in the area critical for enzyme function.

CONCLUSION

The evaluation of the data, obtained in non-human primate model of cannabis-related developmental exposure should take into consideration possible evolutionary-determined species-specific differences in the CB1R expression, CB2R transduction pathway, and FAAH and DAGLα substrate-enzyme interactions.

Possible Therapeutic Doses of Cannabinoid Type 1 Receptor Antagonist Reverses Key Alterations in Fragile X Syndrome Mouse Model

Fragile X syndrome (FXS) is the most common monogenetic cause of intellectual disability. The cognitive deficits in the mouse model for this disorder, the Fragile X Mental Retardation 1 (Fmr1) knockout (KO) mouse, have been restored by different pharmacological approaches, among those the blockade of cannabinoid type 1 (CB1) receptor. In this regard, our previous study showed that the CB1 receptor antagonist/inverse agonist rimonabant normalized a number of core features in the Fmr1 knockout mouse. Rimonabant was commercialized at high doses for its anti-obesity properties, and withdrawn from the market on the bases of mood-related adverse effects. In this study we show, by using electrophysiological approaches, that low dosages of rimonabant (0.1 mg/kg) manage to normalize metabotropic glutamate receptor dependent long-term depression (mGluR-LTD). In addition, low doses of rimonabant (from 0.01 mg/kg) equally normalized the cognitive deficit in the mouse model of FXS. These doses of rimonabant were from 30 to 300 times lower than those required to reduce body weight in rodents and to presumably produce adverse effects in humans. Furthermore, NESS0327, a CB1 receptor neutral antagonist, was also effective in preventing the novel object-recognition memory deficit in Fmr1 KO mice. These data further support targeting CB1 receptors as a relevant therapy for FXS.

Receptome: Interactions between three pain-related receptors or the "Triumvirate" of cannabinoid, opioid and TRPV1 receptors

A growing amount of data demonstrates the interactions between cannabinoid, opioid and the transient receptor potential (TRP) vanilloid type 1 (TRPV1) receptors. These interactions can be bidirectional, inhibitory or excitatory, acute or chronic in their nature, and arise both at the molecular level (structurally and functionally) and in physiological processes, such as pain modulation or perception. The interactions of these three pain-related receptors may also reserve important and new therapeutic applications for the treatment of chronic pain or inflammation. In this review, we summarize the main findings on the interactions between the cannabinoid, opioid and the TRPV1 receptor regarding to pain modulation.

Elucidating cannabinoid biology in zebrafish (Danio rerio)

The number of annual cannabinoid users exceeds 100,000,000 globally and an estimated 9% of these individuals will suffer from dependency. Although exogenous cannabinoids, like those contained in marijuana, are known to exert their effects by disrupting the endocannabinoid system, a dearth of knowledge exists about the potential toxicological consequences on public health. Conversely, the endocannabinoid system represents a promising therapeutic target for a plethora of disorders because it functions to endogenously regulate a vast repertoire of physiological functions. Accordingly, the rapidly expanding field of cannabinoid biology has sought to leverage model organisms in order to provide both toxicological and therapeutic insights about altered endocannabinoid signaling. The primary goal of this manuscript is to review the existing field of cannabinoid research in the genetically tractable zebrafish model-focusing on the cannabinoid receptor genes, cnr1 and cnr2, and the genes that produce enzymes for synthesis and degradation of the cognate ligands anandamide and 2-arachidonylglycerol. Consideration is also given to research that has studied the effects of exposure to exogenous phytocannabinoids and synthetic cannabinoids that are known to interact with cannabinoid receptors. These results are considered in the context of either endocannabinoid gene expression or endocannabinoid gene function, and are integrated with findings from rodent studies. This provides the framework for a discussion of how zebrafish may be leveraged in the future to provide novel toxicological and therapeutic insights in the field of cannabinoid biology, which has become increasingly significant given recent trends in cannabis legislation.