The impact of changes in UK classification of the synthetic cannabinoid receptor agonists in 'Spice'

Background

Spice is the iconic brand name of a smokeable herbal mixture containing synthetic cannabinoid receptor agonists. It has been available on the Internet/in head shops in Europe since at least 2006. The synthetic cannabinoid receptor agonist constituents of Spice were classified in the UK as Class B agents in December 2009. This study assessed the impact of this legislation on the synthetic cannabinoid receptor agonists present in Spice products and whether new synthetic cannabinoid receptor agonists outside of the legislation are now available.

Methods

Spice products were bought, prior to and after the change in the UK legislation, from a range of Internet legal high websites selling to UK consumers. Products were analysed using liquid chromatography high-resolution tandem mass spectrometry (LCMSMS). Identification of the synthetic cannabinoid receptor agonist(s) detected was made by comparison to existing databases or by ‘in silico’ methods.

Results

Sixteen products were purchased prior to the UK control of synthetic cannabinoid receptor agonists; all contained at least one synthetic cannabinoid receptor agonist. 20 products were purchased after the UK control; no active compounds were detected in 3 (15%). The remaining 17 (85%) all contained at least one classified synthetic cannabinoid receptor agonist. Additionally, 2 synthetic cannabinoid receptor agonists not covered under current UK generic legislation (AM-694 and the ‘novel Belarus compound’) were detected.

Conclusion

Despite the UK ‘Spice’ classification, classified synthetic cannabinoid receptor agonists continue to be supplied over the Internet to UK users. Furthermore, new synthetic cannabinoid receptor agonists not covered by the legislation are appearing. Consideration needs to be given to reviewing the UK legislation so that suppliers cannot circumvent it by supplying legal alternatives to the classified synthetic cannabinoid receptor agonists.     

Effects of oxazepam on affective perception,recognition, and event-related potentials

Background  

Little is known about how rapid electrocortical responses (event-related potentials; ERPs) to affective pictures are modulated by benzodiazepine agonists. The present study investigated effects of oxazepam (20 mg p.o.) on behavioral measures and ERPs associated with affective picture processing during perception and recognition memory retrieval.     

Cabergoline, a dopamine receptor agonist, has an antidepressant-like property and enhances brain-derived neurotrophic factor signaling

Rationale  

Dopamine agonists have been implicated in the treatment of depression. Cabergoline is an ergot derivative with a high affinity to dopamine D₂-like receptors; however, there have been few preclinical studies on its antidepressant-like effects.     

Pharmacological effects of cannabinoids on the reference and working memory functions in mice

Rationale

Evidence indicates cannabinoid receptor agonists impair performance in procedures to assess memory that may also be confounded by motivational or motor effects, both of which occur with cannabinoids. Thus, convergence of evidence from a variety of procedures that differ in motivation, attention, arousal and response requirements, but share a common reliance on memory, is required. There are no current reports on cannabinoid effects on mice tested in the radial arm maze.

Objectives

The objective was to determine the effects of the cannabinoid agonist CP 55940 and the dependence of any such effects on the CB1 receptor using the CB1 receptor antagonist SR 141716A on two strains of mice in the eight-arm radial maze procedure.

Methods

Male C57BL/6J (N?=?36) and C3H/HEJ (N?=?12) mice were trained to a criterion and then were treated (IP) with vehicle?+?vehicle, SR 141716A?+?vehicle, vehicle?+?CP 55940 and SR 141716A?+?CP 55940 in a fully balanced mixed design prior to further tests in the maze. Reference (long-term) and working (short-term) memory were assessed.

Results

CP 55940 impaired performance of the reference memory task in the C57BL/6J strain but not the C3H/HEJ strain; SR 141716A reversed the effect of CP 55940 on these measures. CP 55940 also increased working memory errors in the C57BL/6J mice only, which was not affected by SR 141716A.

Conclusion

The present study provides evidence for a strain-specific effect of a dose of CP 55940 on reference memory. While the cannabinoid agonist also impaired working memory in one strain, this effect was apparently not mediated by CB1 receptors.     

Intracerebroventricular administration of cannabinoid CB1 receptor antagonists AM251 and AM4113 fails to alter food-reinforced behavior in rats

Rationale  

Drugs that interfere with cannabinoid CB1 transmission suppress food-motivated behaviors and may be useful as appetite suppressants, but there is uncertainty about the locus of action for the feeding-suppression effects of these drugs.     

Effects of the delta-opioid agonist SNC80 on the abuse liability of methadone in rhesus monkeys: a behavioral economic analysis

Rationale  

Delta-opioid agonists enhance the antinociceptive efficacy of methadone and other mu-opioid agonists. However, relatively little is known about the degree to which delta agonists might enhance the abuse-related effects of mu agonists.     

Urethane,but not pentobarbitone,attenuates presynaptic receptor function in rats: a contribution to the choice of anaesthetic

Background and purpose:

We examined whether cannabinoid CB₁ and histamine H₃ receptors resemble α₂-adrenoceptors in that their presynaptically mediated cardiovascular effects are less marked in urethane- than in pentobarbitone-anaesthetized pithed rats.

Experimental approach:

Effects of the cannabinoid agonist CP-55,940 and the H₃ receptor agonist imetit on electrically induced tachycardic and vasopressor responses, respectively, was compared in pithed rats anaesthetized with urethane or pentobarbitone. The affinity of urethane for the three receptors was measured by radioligand binding studies in rat brain cortex membranes and its potency assessed in superfused mouse tissues preincubated with ³H-noradrenaline.

Key results:

The neurogenic tachycardic response was less markedly inhibited by CP-55,940 in urethane- than in pentobarbitone-anaesthetized pithed rats. Imetit inhibited the neurogenic vasopressor response after pentobarbitone but not after urethane. The catecholamine-induced tachycardic and vasopressor response did not differ between rats anaesthetized with either compound. Urethane 10 mM (plasma concentration reached under anaesthesia) did not affect binding to CB₁ or H₃ receptors and α₂ adrenoceptors, nor did it alter the inhibitory effect of agonists at the three receptors on electrically evoked ³H-noradrenaline release.

Conclusions and implications:

Urethane, but not pentobarbitone, abolished the H₃ receptor-mediated vascular response in pithed rats and attenuated the CB₁ receptor-mediated cardiac response much more than pentobarbitone. The weaker effects of CB₁, H₃ and α₂ receptor agonists cannot be explained by antagonism by urethane at the three receptors in vitro. Pentobarbitone, but not urethane, is suitable as an anaesthetic for investigations of inhibitory presynaptic receptor function in pithed and anaesthetized rats.     

Central mediation and differential blockade by cannabinergics of the discriminative stimulus effects of the cannabinoid CB<Subscript>1</Subscript> receptor antagonist rimonabant in rats

Rationale  

Discovery of an endocannabinoid signaling system launched the development of the blocker rimonabant, a cannabinoid CB1 receptor (CB₁R) antagonist/inverse agonist. Due to untoward effects, this medication was withdrawn and efforts have been directed towards discovering chemicals with more benign profiles.     

Evaluation of cannabinoid agonists using punished responding and midazolam discrimination procedures in squirrel monkeys

Rationale  Clinical studies have suggested that marijuana and nabilone have anxiolytic effects in humans, yet studies of anxiolytic-like effects of cannabinoid agonists in mice and rats have yielded mixed results. Objective  The purpose of the present study was to compare the effects of cannabinoid agonists and clinically used anxiolytic drugs in monkeys using punished responding and midazolam discrimination procedures. Methods  Monkeys were trained to discriminate an i.m. injection of 0.3 mg/kg midazolam from saline or, in a separate group, to respond under a multiple schedule of food reinforcement composed of punished and nonpunished components. Effects of the cannabinoid agonists Δ⁹-tetrahydrocannabinol (Δ⁹-THC; 0.01–3 mg/kg), WIN 55,212-2 (0.03–1 mg/kg) and CP 55,940 (0.003–0.03 mg/kg), and the benzodiazepine midazolam (0.01–1 mg/kg) and the barbiturate pentobarbital (1–18 mg/kg) were evaluated. Results  Δ⁹-THC and CP 55,940 did not have antipunishment effects and Δ⁹-THC and WIN 55,212-2 did not produce midazolam-like discriminative stimulus effects up to doses that substantially decreased response rate. In contrast, pentobarbital, like midazolam, increased punished responding at doses comparable to those that substituted for the midazolam discriminative stimulus. Conclusion  Cannabinoid agonists do not have anxiolytic-like effects in behavioral procedures commonly used to characterize benzodiazepines and other drugs in squirrel monkeys.     

Tolerance to cannabinoid-induced behaviors in mice treated chronically with ethanol

Rationale  

Chronic ethanol (EtOH) treatment decreases the motor-impairing effects of cannabinoids and downregulates the cannabinoid type 1 (CB1) receptor. However, these studies have been limited to measures of ataxia and analysis of CB1 expression from whole-brain or hippocampal preparations.     

Effects of morphine on pain-elicited and pain-suppressed behavior in CB1 knockout and wildtype mice

Rationale  

Pharmacological manipulations of the type 1 cannabinoid receptor (CB1) suggest a role for CB1 in morphine-induced antinociception, but studies utilizing CB1 knockout (KO) mice do not support this conclusion. Since studies using CB1 KO mice to study morphine’s antinociceptive effects have only examined thermal nociception, this study examines these interactions in models that employ a chemical stimulus.     

Tolerance and cross-tolerance to cannabinoids in mice: schedule-controlled responding and hypothermia

Rationale  

Cannabinoid CB₁ receptor agonists vary in efficacy in vitro; however, relationships between efficacy and behavioral effects are unclear.     

PPI deficit induced by amphetamine is attenuated by the histamine H1 antagonist pyrilamine, but is exacerbated by the serotonin 5-HT2 antagonist ketanserin

Rationale  

Prepulse inhibition (PPI) of the startle response is a classic model of sensorimotor gating. Robust PPI impairments can be induced by dopamine agonists such as the indirect agonist amphetamine. The antipsychotic clozapine can attenuate PPI impairment induced by dopamine agonists. Clozapine is a complex drug with antagonistic effects on a variety of receptors, including serotonin and histamine. The relative contribution of its component actions to its efficacy is still unclear.     

Immunodensity and mRNA expression of A<Subscript>2A</Subscript> adenosine,D<Subscript>2</Subscript> dopamine,and CB<Subscript>1</Subscript> cannabinoid receptors in postmortem frontal cortex of subjects with schizophrenia: effect of antipsychotic treatment

Rationale  

Dopamine D₂ receptors are the main target of antipsychotic drugs. In the brain, D₂ receptors coexpress with adenosine A_2A and CB₁ cannabinoid receptors, leading to functional interactions.     

Repeated administration of the GABA<Subscript>B</Subscript> receptor positive modulator BHF177 decreased nicotine self-administration,and acute administration decreased cue-induced reinstatement of nicotine seeking in rats

Rationale  

γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain and is implicated in the modulation of central reward processes. Acute or chronic administration of GABA_B receptor agonists or positive modulators decreased self-administration of various drugs of abuse. Furthermore, GABA_B receptor agonists inhibited cue-induced reinstatement of nicotine- and cocaine-seeking behavior. Because of their fewer adverse side effects compared with GABA_B receptor agonists, GABA_B receptor positive modulators are potentially improved therapeutic compounds for the treatment of drug dependence compared with agonists.     

The effects of d-amphetamine, methylphenidate, sydnocarb, and caffeine on prepulse inhibition of the startle reflex in DBA/2 mice

Rationale  

Dopamine (DA) agonists decrease prepulse inhibition (PPI) and are widely used in translational models for the sensorimotor gating deficits in schizophrenia. Reductions in PPI induced by DA agonists are routinely reversed by antipsychotics in these translational models. Nevertheless, under conditions of low-baseline PPI, DA agonists may increase PPI in humans and experimental animals. DBA/2 mice have naturally low-baseline PPI, which as in the drug-induced translational models, is increased by antipsychotics.     

Contribution of limbic norepinephrine to cannabinoid-induced aversion

Rationale  

The cannabinoid system has risen to the forefront in the development of novel treatments for a number of pathophysiological processes. However, significant side effects have been observed in clinical trials raising concerns regarding the potential clinical utility of cannabinoid-based agents. Understanding the neural circuits and neurochemical substrates impacted by cannabinoids will provide a better means of gaging their actions within the central nervous system that may contribute to the expression of unwanted side effects.     

Effect of tandospirone, a serotonin-1A receptor partial agonist, on information processing and locomotion in dizocilpine-treated rats

Rationale  

Augmentation therapy with serotonin-1A receptor (5-HT1A) partial agonists has been suggested to ameliorate psychotic symptoms in patients with schizophrenia.     

Randomized, controlled, double-blind trial of taranabant for smoking cessation

Rationale  

It has been proposed that cannabinoid-1 receptor inverse agonists might be effective for smoking cessation. We evaluated this hypothesis with the cannabinoid-1 receptor inverse agonist taranabant.     

Evaluation of the insulin releasing and antihyperglycaemic activities of GPR55 lipid agonists using clonal beta-cells,isolated pancreatic islets and mice

Background and Purpose

G-protein coupled receptor (GPR)55 is a novel lipid sensing receptor activated by both cannabinoid endogenous ligands (endocannabinoids) and other non-cannabinoid lipid transmitters. This study assessed the effects of various GPR55 agonists on glucose homeostasis.

Experimental Approach

Insulin secretion and changes in intracellular Ca²⁺ and cAMP in response to glucose and a range of GPR55 agonists [endogenous ligands (OEA, PEA), chemically synthetic cannabidiol (CBD) analogues (Abn-CBD, 0–1602), an analogue of rimonabant (AM-251) and antagonist (CBD)] were investigated in clonal BRIN-BD11 cells and mouse pancreatic islets. Cytotoxicity was assessed by LDH release, cellular localization by double-staining immunohistochemistry and in vivo effects assessed in mice.

Key Results

The most potent and selective GPR55 agonist was the synthetic CBD analogue, Abn-CBD (pEC₅₀ 10.33), maximum stimulation of 67% at 10⁻⁴ mol·L⁻¹ (P < 0.001) in BRIN-BD11 cells. AM-251 (pEC₅₀ 7.0), OEA (pEC₅₀ 7.0), 0–1602 (pEC₅₀ 7.3) and PEA (pEC₅₀ 6.0) stimulated insulin secretion. Results were corroborated by islet studies, with no cytotoxic effects. Concentration-dependent insulin secretion by GPR55 agonists was glucose-sensitive and accompanied by elevations of [Ca²⁺]_i (P < 0.01–P < 0.001) and cAMP (P < 0.05–P < 0.01). GPR55 agonists exhibited insulinotropic and glucose lowering activity in vivo. GPR55 was expressed on BRIN-BD11 cells and confined to islet beta cells with no distribution on alpha cells.

Conclusion and Implications

These results demonstrate GPR55 is distributed in pancreatic beta cells and is a strong activator of insulin secretion, with glucose-lowering effects in vivo. Development of agents agonizing the GPR55 receptor may have therapeutic potential in the treatment of type 2 diabetes.