The endogenous cannabinoid system and drug addiction: 20 years after the discovery of the CB1 receptor

Pharmacotherapies for cannabis use disorder: A systematic review and network meta-analysis

OBJECTIVE

This study aimed to determine the efficacy and acceptability of pharmacotherapies for cannabis use disorder (CUD).

METHODS

We conducted a systematic review and frequentist network meta-analysis, searching five electronic databases for randomized placebo-controlled trials of individuals diagnosed with CUD receiving pharmacotherapy with or without concomitant psychotherapy. Primary outcomes were the reduction in cannabis use and retention in treatment. Secondary outcomes were adverse events, discontinuation due to adverse events, total abstinence, withdrawal symptoms, cravings, and CUD severity. We applied a frequentist, random-effects Network Meta-Analysis model to pool effect sizes across trials using standardized mean differences (SMD, g) and rate ratios (RR) with their 95% confidence intervals.

RESULTS

We identified a total of 24 trials (n=1912, 74.9% male, mean age 30.2 years). Nabilone (d=-4.47 [-8.15; -0.79]), topiramate (d=-3.80 [-7.06; -0.54]), and fatty-acid amyl hydroxylase inhibitors (d=-2.30 [-4.75; 0.15]) reduced cannabis use relative to placebo. Dronabinol improved retention in treatment (RR=1.27 [1.02; 1.57]), while topiramate worsened treatment retention (RR=0.62 [0.42; 0.91]). Gabapentin reduced cannabis cravings (d=-2.42 [-3.53; -1.32], while vilazodone worsened craving severity (d=1.69 [0.71; 2.66]. Buspirone (RR=1.14 [1.00; 1.29]), venlafaxine (RR=1.78 [1.40; 2.26]), and topiramate (RR=9.10 [1.27; 65.11]) caused more adverse events, while topiramate caused more dropouts due to adverse events.

CONCLUSIONS

Based on this review, some medications appeared to show promise for treating individual aspects of CUD. However, there is a lack of robust evidence to support any particular pharmacological treatment. There is a need for additional studies to expand the evidence base for CUD pharmacotherapy. While medication strategies may become an integral component for CUD treatment one day, psychosocial interventions should remain the first line given the limitations in the available evidence.

Efficacy and acceptability of cannabinoids for anxiety disorders in adults: A systematic review & meta-analysis

OBJECTIVE

The aim of this study was to assess the efficacy and acceptability of cannabinoids for the treatment of anxiety disorders.

METHODS

For this systematic review and meta-analysis, we searched for randomized trials utilizing cannabinoids for the treatment of adults with anxiety disorders. Primary outcomes were reduction in anxiety disorder symptoms, and study discontinuation due to adverse events. Evidence was synthesized as rate ratios (RRs) and as standardized mean differences (SMDs) using random-effects meta-analyses.

RESULTS

A total of 14 eligible trials representing 1548 individuals (median age: 33 years; range: 28-44; 66% male) were identified. Cannabinoids reduced anxiety symptoms (SMD = -1.85, 95% CI: -2.61 to -1.09) without causing significant adverse events. Greater efficacy was observed among younger patients (p < 0.01) and with longer treatment (p < 0.01). However, publication bias was substantial, and after correction, the overall anxiolytic effect was not statistically significant.

CONCLUSIONS

While cannabinoids may be of potential value in the treatment of anxiety disorders, the routine use of these treatments is not supported by the available evidence after correction for publication bias.

Noradrenergic depletion causes sex specific alterations in the endocannabinoid system in the Murine prefrontal cortex

Brain endocannabinoids (eCB), acting primarily via the cannabinoid type 1 receptor (CB1r), are involved in the regulation of many physiological processes, including behavioral responses to stress. A significant neural target of eCB action is the stress-responsive norepinephrine (NE) system, whose dysregulation is implicated in myriad psychiatric and neurodegenerative disorders. Using Western blot analysis, the protein expression levels of a key enzyme in the biosynthesis of the eCB 2-arachidonoylglycerol (2-AG), diacylglycerol lipase-α (DGL-α), and two eCB degrading enzymes monoacylglycerol lipase (MGL) and fatty acid amide hydrolase (FAAH) were examined in a mouse model that lacks the NE-synthesizing enzyme, dopamine β-hydroxylase (DβH-knockout, KO) and in rats treated with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4). In the prefrontal cortex (PFC), DGL-α protein expression was significantly increased in male and female DβH-KO mice (P < 0.05) compared to wild-type (WT) mice. DβH-KO male mice showed significant decreases in FAAH protein expression compared to WT male mice. Consistent with the DβH-KO results, DGL-α protein expression was significantly increased in male DSP-4-treated rats (P < 0.05) when compared to saline-treated controls. MGL and FAAH protein expression levels were significantly increased in male DSP-4 treated rats compared to male saline controls. Finally, we investigated the anatomical distribution of MGL and FAAH in the NE containing axon terminals of the PFC using immunoelectron microscopy. MGL was predominantly within presynaptic terminals while FAAH was localized to postsynaptic sites. These results suggest that the eCB system may be more responsive in males than females under conditions of NE perturbation, thus having potential implications for sex-specific treatment strategies of stress-related psychiatric disorders.

Molecular neuroscience at its "high": bibliometric analysis of the most cited papers on endocannabinoid system, cannabis and cannabinoids

BACKGROUND

Cannabis, cannabinoids and endocannabinoids are heavily investigated topics with many articles published every year. We aimed to identify the 100 most cited manuscripts among the vast literature and analyze their contents.

METHODS

Web of Science (WoS) Core Collection was searched to identify the 100 most cited relevant manuscripts, which were analyzed with reference to (1) authorship, (2) institution, (3) country, (4) document type, (5) journal, (6) publication year, (7) WoS category, and (8) citation count. Semantic content and citation data of the manuscripts were analyzed with VOSviewer.

RESULTS

The most cited manuscripts were published between 1986 and 2016, with the majority being published in the 2000s (n = 51). The number of citations for the top 100 articles ranged from 469 to 3651, with a median citation count of 635.5. The most prolific authors were Vincenzo Di Marzo (n = 11) and Daniele Piomelli (n = 11). The major contributing countries were USA (n = 49), Italy (n = 22), UK (n = 19), and France (n = 11). The most prolific institutions were University of California (n = 14), National Research Council of Italy (n = 12) and National Institutes of Health USA (n = 12). The manuscripts consisted of original articles (n = 75), reviews (n = 24) and a note (n = 1). The most dominant journal was Nature (n = 15). The major WoS categories associated were Multidisciplinary sciences (n = 31), Neurosciences (n = 20), Pharmacology / Pharmacy (n = 16), and General / Internal Medicine (n = 11).

CONCLUSIONS

The top-ranked manuscripts among the 100 were concerning analgesia, weight loss, long-term potentiation, depolarization-induced suppression of inhibition, opiates and other topics. Cannabinoid type 1 (CB1) receptor was studied by more of the top 100 papers in comparison to cannabinoid type 2 (CB2) receptor. The most frequently mentioned chemicals in these publications were 2-arachidonoylglycerol, tetrahydrocannabinol, and anandamide. Together, these manuscripts comprise the most highly cited publications in the topic, literally the molecular neuroscience at its "high".

Repeated administration of a synthetic cannabinoid receptor agonist differentially affects cortical and accumbal neuronal morphology in adolescent and adult rats

Recent studies demonstrate a differential trajectory for cannabinoid receptor expression in cortical and sub-cortical brain areas across postnatal development. In the present study, we sought to investigate whether chronic systemic exposure to a synthetic cannabinoid receptor agonist causes morphological changes in the structure of dendrites and dendritic spines in adolescent and adult pyramidal neurons in the medial prefrontal cortex (mPFC) and medium spiny neurons (MSN) in the nucleus accumbens (Acb). Following systemic administration of WIN 55,212-2 in adolescent (PN 37-40) and adult (P55-60) male rats, the neuronal architecture of pyramidal neurons and MSN was assessed using Golgi-Cox staining. While no structural changes were observed in WIN 55,212-2-treated adolescent subjects compared to control, exposure to WIN 55,212-2 significantly increased dendritic length, spine density and the number of dendritic branches in pyramidal neurons in the mPFC of adult subjects when compared to control and adolescent subjects. In the Acb, WIN 55,212-2 exposure significantly decreased dendritic length and number of branches in adult rat subjects while no changes were observed in the adolescent groups. In contrast, spine density was significantly decreased in both the adult and adolescent groups in the Acb. To determine whether regional developmental morphological changes translated into behavioral differences, WIN 55,212-2-induced aversion was evaluated in both groups using a conditioned place preference paradigm. In adult rats, WIN 55,212-2 administration readily induced conditioned place aversion as previously described. In contrast, adolescent rats did not exhibit aversion following WIN 55,212-2 exposure in the behavioral paradigm. The present results show that synthetic cannabinoid administration differentially impacts cortical and sub-cortical neuronal morphology in adult compared to adolescent subjects. Such differences may underlie the disparate development effects of cannabinoids on behavior.

Working memory- and anxiety-related behavioral effects of repeated nicotine as a stressor: the role of cannabinoid receptors

Background

Like emotional symptoms such as anxiety, modulations in working memory are among the frequently-reported but controversial psychiatric symptoms associated with nicotine (NC) administration. In the present study, repeated NC-induced modulations in working memory, along with concurrently-observed anxiety-related behavioral alterations, were investigated in mice, and compared with the effects of a typical cognition-impairing stressor, immobilization stress (IM). Furthermore, considering the structural and functional contributions of brain cannabinoid (CB) receptors in NC-induced psychiatric symptoms including emotional symptoms, the interactive effects of brain CB receptor ligands (CB ligands) and NC and/or IM on the working memory- and anxiety-related behaviors were examined.

Results

Statistically significant working memory impairment-like behavioral alterations in the Y-maze test and anxiety-like behavioral alterations in the elevated plus-maze (EPM) test were observed in the groups of mice treated with 0.8 mg/kg NC (subcutaneous (s.c.) 0.8 mg/kg treatment, 4 days) and/or IM (10 min treatment, 4 days). In the group of mice treated with NC plus IM (NC-IM group), an enhancement of the behavioral alterations was observed. Among the CB type 1 (CB1) antagonist AM 251 (AM), the non-selective CB agonist CP 55,940 (CP), and the CB1 partial agonist/antagonist virodhamine (VD), significant recovering effects were provided by AM (0.2-2.5 mg/kg) and VD (5 mg/kg) against the working memory impairment-like behaviors, whereas significant anxiolytic-like effects (recoveries from both attenuated percentage of entries into open arms and attenuated percentage of time spent on open arms) were provided by VD (1–10 mg/kg) and CP (2 mg/kg) against the anxiety-like behaviors.

Conclusions

Although working memory impairment- and anxiety-like behavioral alterations were commonly induced in the NC, IM, and NC-IM groups and the therapeutic involvement of CB receptors was shown, there were discrepancies in the types of effective CB ligands between the working memory- and anxiety-related behaviors. The differential involvements of CB receptor subtypes and indirectly activated neurotransmitter systems may contribute to these discrepancies.

Cannabis use and age at onset of psychosis: further evidence of interaction with COMT Val158Met polymorphism

OBJECTIVE

To examine, in a sample of young psychiatric patients, (n = 157, mean age 17.01 years (SD = 3.6)) whether i) age at first cannabis use and age at emergence of psychiatric disorders are related and ii) such a relationship is modulated by the Val158Met polymorphism in the COMT gene.

METHOD

Cannabis use profiles and COMT Val158Met genotypes were obtained from 80 inpatients with schizophrenia-spectrum disorders and 77 inpatients with other non-psychotic disorders.

RESULTS

First, age at first cannabis use correlates with age at onset in both schizophrenia-spectrum and other psychiatric disorder groups: those who started using cannabis earlier had an earlier age at onset of psychiatric disorders. Second, the distribution of the Val158Met genotypes was not different either between diagnosis groups or between cannabis users and non-users. Third, an interaction between Val158Met genotypes and cannabis use was observed specifically on age at emergence of psychotic disorders, with Val/Val genotype carriers showing an earlier age at onset than Met carriers.

CONCLUSION

Our results suggest the importance of brain maturation timing in which exposure to cannabis occurs. The COMT Val158Met genotype seems to modulate the association between cannabis and age at onset of psychotic disorders. These results are consistent with previous studies.

The brain endocannabinoid system in the regulation of energy balance

The role played by the endocannabinoid system in the regulation of energy balance is currently generating a great amount of interest among several groups of investigators. This interest in large part comes from the urgent need to develop anti-obesity and anti-cachexia drugs around target systems (such as the endocannabinoid system), which appears to be genuinely involved in energy balance regulation. When activated, the endocannabinoid system favors energy deposition through increasing energy intake and reducing energy expenditure. This system is activated in obesity and following food deprivation, which further supports its authentic function in energy balance regulation. The cannabinoid receptor type 1 (CB1), one of the two identified cannabinoid receptors, is expressed in energy-balance brain structures that are also able to readily produce or inactivate N-arachidonoyl ethanolamine (anandamide) and 2-arachidonoylglycerol (2AG), the most abundantly formed and released endocannabinoids. The brain action of endocannabinoid system on energy balance seems crucial and needs to be delineated in the context of the homeostatic and hedonic controls of food intake and energy expenditure. These controls require the coordinated interaction of the hypothalamus, brainstem and limbic system and it appears imperative to unravel those interplays. It is also critical to investigate the metabolic endocannabinoid system while considering the panoply of functions that the endocannabinoid system fulfills in the brain and other tissues. This article aims at reviewing the potential mechanisms whereby the brain endocannabinoid system influences the regulation energy balance.