Role Of Cannabinoid 1 Receptor Research Articles

Role of CB1 receptors in the acute regulation of small intestinal permeability: effects of high-fat diet.

The endocannabinoid system of the gastrointestinal tract is involved in the control of intestinal barrier function. Whether the cannabinoid 1 (CB1) receptor is expressed on the intestinal epithelium and acutely regulates barrier function has not been determined. Here, we tested the hypothesis that ligands of the CB1 receptor acutely modulate small intestinal permeability and that this is associated with altered distribution of tight junction proteins. We examined the acute effects of CB1 receptor ligands on small intestinal permeability both in chow-fed and 2-wk high-fat diet (HFD)-fed mice using Ussing chambers. We assessed the distribution of CB1 receptor and tight junction proteins using immunofluorescence and the expression of CB1 receptor using PCR. A low level of CB1 expression was found on the intestinal epithelium. CB1 receptor was highly expressed on enteric nerves in the lamina propria. Neither the CB1/CB2 agonist CP55,940 nor the CB1 neutral antagonist AM6545 altered the flux of 4kDa FITC dextran (FD4) across the jejunum or ileum of chow-fed mice. Remarkably, both CP55,940 and AM6545 reduced FD4 flux across the jejunum and ileum in HFD-fed mice that have elevated baseline intestinal permeability. These effects were absent in CB1 knockout mice. CP55,940 reduced the expression of claudin-2, whereas AM6545 had little effect on claudin-2 expression. Neither ligand altered the expression of ZO-1. Our data suggest that CB1 receptor on the intestinal epithelium regulates tight junction protein expression and restores barrier function when it is increased following exposure to a HFD for 2 wk.NEW & NOTEWORTHY The endocannabinoid system of the gastrointestinal tract regulates homeostasis by acting as brake on motility and secretion. Here we show that when exposed to a high fat diet, intestinal permeability is increased and activation of the CB1 receptor on the intestinal epithelium restores barrier function. This work further highlights the role of the endocannabinoid system in regulating intestinal homeostasis when it is perturbed.

The Cannabinoid Receptor Type 1 Positive Allosteric Modulator ZCZ011 Attenuates Naloxone-Precipitated Diarrhea and Weight Loss in Oxycodone-Dependent Mice.

Opioid use disorder reflects a major public health crisis of morbidity and mortality in which opioid withdrawal often contributes to continued use. However, current medications that treat opioid withdrawal symptoms are limited by their abuse liability or lack of efficacy. Although cannabinoid 1 (CB1) receptor agonists, including Δ9-tetrahydrocannabinol, ameliorate opioid withdrawal in both clinical and preclinical studies of opioid dependence, this strategy elicits cannabimimetic side effects as well as tolerance and dependence after repeated administration. Alternatively, CB1 receptor positive allosteric modulators (PAMs) enhance CB1 receptor signaling and show efficacy in rodent models of pain and cannabinoid dependence but lack cannabimimetic side effects. We hypothesize that the CB1 receptor PAM ZCZ011 attenuates naloxone-precipitated withdrawal signs in opioid-dependent mice. Accordingly, male and female mice given an escalating dosing regimen of oxycodone, a widely prescribed opioid, and challenged with naloxone displayed withdrawal signs that included diarrhea, weight loss, jumping, paw flutters, and head shakes. ZCZ011 fully attenuated naloxone-precipitated withdrawal-induced diarrhea and weight loss and reduced paw flutters by approximately half, but its effects on head shakes were unreliable, and it did not affect jumping behavior. The antidiarrheal and anti-weight loss effects of ZCZ0111 were reversed by a CB1 not a cannabinoid receptor type 2 receptor antagonist and were absent in CB1 (-/-) mice, suggesting a necessary role of CB1 receptors. Collectively, these results indicate that ZCZ011 completely blocked naloxone-precipitated diarrhea and weight loss in oxycodone-dependent mice and suggest that CB1 receptor PAMs may offer a novel strategy to treat opioid dependence. SIGNIFICANCE STATEMENT: Opioid use disorder represents a serious public health crisis in which current medications used to treat withdrawal symptoms are limited by abuse liability and side effects. The CB1 receptor positive allosteric modulator (PAM) ZCZ011, which lacks overt cannabimimetic behavioral effects, ameliorated naloxone-precipitated withdrawal signs through a CB1 receptor mechanism of action in a mouse model of oxycodone dependence. These results suggest that CB1 receptor PAMs may represent a viable strategy to treat opioid withdrawal.

WIN 55,212-2 Reverted Pilocarpine-Induced Status Epilepticus Early Changes of the Interaction among 5-HT2C/NMDA/CB1 Receptors in the Rat Hippocampus.

The molecular basis for temporal lobe epileptogenesis remains poorly defined. Recent evidence shows that serotonin 2C receptors (5-HT2CRs), NR2A and NR2B subunit-containing N-methyl-d-aspartate receptors (NMDARs) and cannabinoid 1 receptors (CB1Rs) may be involved in the progression of the epileptic disorders. Moreover, CB1R activation has been reported to modulate the activity of 5-HT2C and NMDA receptors. Here, we treated Sprague-Dawley rats with the pro-convulsant agent pilocarpine (PILO) to induce status epilepticus (SE) in order to study the effect, with regards to receptor signaling and their interactions, of the preactivation of the CB1Rs on early changes that occur 24 h from the initial insult in the hippocampus. Pretreatment with the synthetic CB1/2R agonist WIN 55,212-2 (2 mg/kg, ip) counteracted PILO-induced 5-HT2CR downregulation. Moreover, WIN 55,212-2 uncoupled PILO-induced 5-HT2CR/NR2A and prevented NR2ATyr1325 phosphorylation indirectly since no 5-HT2CR/CB1R interactions were observed. WIN 55,212-2 treatment also prevented PILO-mediated impairment ofCB1R/NR2B interactions and NR2B subunit internalization, suggesting a possible role of CB1R in NR2B-containing NMDAR turn over. All the effects observed in animals treated with WIN 55,212-2 were blocked by pretreatment with the selective CB1R antagonist AM251 (1 mg/kg, ip) given 45 min before PILO injection. These results, obtained in vivo in post-PILO-induced SE, provide new insights on the early cellular responses during epileptogenesis and identify new CB1R-mediated mechanisms by which cannabinoids may prevent the development of chronic epilepsy.

Characterization of AJ5012 as a Novel Peripheral Cannabinoid 1 Receptor Antagonist in Mouse Models of Obesity

Obesity-induced adipose tissue inflammation, in which the NLRP3 inflammasome is a pivotal mediator, is implicated in the development of insulin resistance. Cannabinoid 1 receptor (CB1R) antagonists have been shown to improve insulin resistance and the associated metabolic abnormalities, but their therapeutic development was discontinued due to neuropsychiatric side effects. Although growing evidence suggests the role of CB1Rs in proinflammatory signaling, their direct effects on adipose tissue inflammation have not yet been evaluated. Here we report that the peripherally restricted CB1R antagonist AJ5012, which exhibits beneficial metabolic effects comparable with its brain-penetrant parent compound rimonabant, suppresses macrophage infiltration into white adipose tissue, activation of the NLRP3 inflammasome, and production of proinflammatory cytokines in diet-induced obese mice. Moreover, we identified the downstream signaling pathways by which CB1R regulates proinflammatory gene expression. These results suggest that peripheral CB1R blockade improves obesity-induced insulin resistance by suppressing adipose tissue inflammation via the NLRP3 inflammasome. Disclosure J. Kim: None. J. Yoon: None. E. Kim: None. S. Yoon: None. W. Kim: None.

Cannabinoid Regulation of Brain Reward Processing with an Emphasis on the Role of CB1 Receptors: A Step Back into the Future.

Over the last decades, the endocannabinoid system has been implicated in a large variety of functions, including a crucial modulation of brain-reward circuits and the regulation of motivational processes. Importantly, behavioral studies have shown that cannabinoid compounds activate brain reward mechanisms and circuits in a similar manner to other drugs of abuse, such as nicotine, alcohol, cocaine, and heroin, although the conditions under which cannabinoids exert their rewarding effects may be more limited. Furthermore, there is evidence on the involvement of the endocannabinoid system in the regulation of cue- and drug-induced relapsing phenomena in animal models. The aim of this review is to briefly present the available data obtained using diverse behavioral experimental approaches in experimental animals, namely, the intracranial self-stimulation paradigm, the self-administration procedure, the conditioned place preference procedure, and the reinstatement of drug-seeking behavior procedure, to provide a comprehensive picture of the current status of what is known about the endocannabinoid system mechanisms that underlie modification of brain-reward processes. Emphasis is placed on the effects of cannabinoid 1 (CB1) receptor agonists, antagonists, and endocannabinoid modulators. Further, the role of CB1 receptors in reward processes is investigated through presentation of respective genetic ablation studies in mice. The vast majority of studies in the existing literature suggest that the endocannabinoid system plays a major role in modulating motivation and reward processes. However, much remains to be done before we fully understand these interactions. Further research in the future will shed more light on these processes and, thus, could lead to the development of potential pharmacotherapies designed to treat reward-dysfunction-related disorders.

Endogenous cannabinoid system regulates intestinal barrier function in vivo through cannabinoid type 1 receptor activation

The deleterious effects of stress on the gastrointestinal tract seem to be mainly mediated by the induction of intestinal barrier dysfunction and subsequent subtle mucosal inflammation. Cannabinoid 1 receptor (CB1R) is expressed in the mammalian gut under physiological circumstances. The aim of this investigation is to study the possible role of CB1R in the maintenance of mucosal homeostasis after stress exposure. CB1R knockout mice (CB1R(-/-)) and their wild-type (WT) counterparts were exposed to immobilization and acoustic (IA) stress for 2 h per day during 4 consecutive days. Colonic protein expression of the inducible forms of the nitric oxide synthase and cyclooxygenase (NOS2 and COX2), IgA production, permeability to (51)Cr-EDTA, and bacterial translocation to mesenteric lymph nodes were evaluated. Stress exposure induced greater expression of proinflammatory enzymes NOS2 and COX2 in colonic mucosa of CB1R(-/-) mice when compared with WT animals. These changes were related with a greater degree of colonic barrier dysfunction in CB1R(-/-) animals determined by 1) a significantly lower IgA secretion, 2) higher paracellular permeability to (51)Cr-EDTA, and 3) higher bacterial translocation, both under basal conditions and after IA stress exposure. Pharmacological antagonism with rimonabant reproduced stress-induced increase of proinflammatory enzymes in the colon described in CB1R(-/-) mice. In conclusion, CB1R exerts a protective role in the colon in vivo through the regulation of intestinal secretion of IgA and paracellular permeability. Pharmacological modulation of cannabinoid system within the gastrointestinal tract might be therapeutically useful in conditions on which intestinal inflammation and barrier dysfunction takes place after exposure to stress.

Inhibition of the cannabinoid-1 receptor enhances the cerebrocortical hyperemic response to hypoxia/hypercapnia

Activation of cannabinoid-1 (CB1) receptors may evoke diverse vascular effects under physiological conditions: it has been shown to induce vasodilation but also to increase the vascular tone by inhibition of the endothelium-derived hyperpolarizing factor (EDHF). However, the role of CB1 receptors in certain pathophysiological states is obscure. We hypothesized that activation of the CB1 receptors may influence the cerebral hyperemic response to hypoxia/hypercapnia (H/H). Therefore, we investigated the effect of the CB1-antagonist AM-251 on H/H-induced vasodilation in the cerebral cortex. Adult male Wistar rats were anesthetized with intraperitoneal injection of 1.3 g/kg Urethane. Femoral arteries were cannulated for monitoring arterial blood pressure and for measuring arterial blood gas and acid-base parameters. CBF was measured in the parietal cortex simultaneously on both sides by laser-Doppler (LD) flowmetry. H/H was induced by inhalation of different gas mixtures. In the first step, during mild H/H, animals inhaled a gas mixture of 10%O2-10%CO2-80%N2, which produced arterial pO2 of 75-85 mmHg and pCO2 of 50-60 mmHg. In the second step, during moderate H/H, animals inhaled a gas mixture of 5%O2-20%CO2-75%N2, which produced arterial pO2 of 55-65 mmHg and pCO2 of 80-90 mmHg. In the third step, during severe H/H, animals inhaled a gas mixture of 0%O2-20%CO2-80%N2, which produced arterial pO2 of 45-50 mmHg and pCO2 of 90-100 mmHg. In the first experimental group, animals were subjected to these three steps of H/H, then brought back to physiological conditions. After steady state obtained, 10 mg/kg AM-251 was injectedintravenously, followed by repetition of the stepwise H/H. In the second, control group the same protocol was performed, but between the two series of H/H only the vehicle (ethanol and emulphor, dissolved in saline) was administered intravenously. Inhalation of the different gas mixtures induced similar changes of the blood gas tensions and acid-base parameters before and after administration of AM-251 or its vehicle. Application of AM-251 did not alter baseline LD flow or arterial blood pressure. AM-251 has significantly increased, however the H/H-induced hyperemia in each step: by 30% during mild H/H, by 22% during moderate H/H, and by 14% during severe H/H. In contrast, vehicle of AM-251 had no significant effect. H/H did not change significantly the mean arterial pressure of the untreated or vehicle-treated animals, but it has induced slight hypertension (116 mmHg) following AM-251 treatment. The observed enhancement of the cerebrocortical hyperemic response to H/H after blockade of the CB1 receptors indicates that during hypoxia/hypercapnia the activation of CB1 receptors attenuates the vasodilation in the cerebral cortex. A possible explanation of these results is that endothelial CB1 receptors suppress the production of EDHF or other vasodilator mediators during H/H. If this is the case, increased cannabinoid levels during H/H limit the magnitude of reactive hyperemia in the brain tissue. Alternatively, activation of neuronal CB1 receptors may also affect the cerebrocortical blood flow during H/H by influencing the cerebral metabolic rate or the neural regulatory mechanisms of the cerebrovascular tone.