The cannabinoid CB(2) receptor: a good friend in the gut

Dietary limonene promotes gastrointestinal barrier function via upregulating tight/adherens junction proteins through cannabinoid receptor type-1 antagonistic mechanism and alters cellular metabolism in intestinal epithelial cells

Limonene, a dietary monocyclic monoterpene commonly found in citrus fruits and various aromatic plants, has garnered increasing interest as a gastrointestinal protectant. This study aimed to assess the effects of limonene on intestinal epithelial barrier function and investigate the involvement of cannabinoid receptor type-1 (CB1R) in vitro. Additionally, the study focused on examining the metabolomic changes induced by limonene in the intestinal epithelial cells (Caco-2). Initial analysis of transepithelial electrical resistance (TEER) revealed that both l-limonene and d-limonene, isomers of limonene, led to a dose- and time-dependent increase in TEER in normal cells and those inflamed by pro-inflammatory cytokines mixture (CytoMix). Furthermore, both types of limonene reduced CytoMix-induced paracellular permeability, as demonstrated by a decrease in Lucifer yellow flux. Moreover, d-limonene and l-limonene treatment increased the expression of tight junction molecules (TJs) such as occludin, claudin-1, and ZO-1, at both the transcriptional and translational levels. d-Limonene upregulates E-cadherin, a molecule involved in adherens junctions (AJs). Mechanistic investigations demonstrated that d-limonene and l-limonene treatment significantly inhibited CB1R at the protein, while the mRNA level remained unchanged. Notably, the inhibitory effect of d-limonene on CB1R was remarkably similar to that of pharmacological CB1R antagonists, such as rimonabant and ORG27569. d-limonene also alters Caco-2 cell metabolites. A substantial reduction in β-glucose and 2-succinamate was detected, suggesting limonene may impact intestinal epithelial cells' glucose uptake and glutamate metabolism. These findings suggest that d-limonene's CB1R antagonistic property could effectively aid in the recovery of intestinal barrier damage, marking it a promising gastrointestinal protectant.

Cannabinoid receptor type 1 in the aging gut regulates the mucosal permeability via miR-191-5p

Background

Aging is associated with a broad loss of function throughout the body, and gastrointestinal (GI) dysfunction can occur with aging. The endocannabinoid (eCB) system plays a pivotal role in various GI diseases, and alterations in the eCB system have been observed during brain and skin aging. Therefore, we investigated the putative role of the eCB system in aging-related changes in the intestine.

Methods

The expression of cannabinoid receptor type 1 (CB1) was investigated in rat intestinal tissues using quantitative real-time PCR. Cellular senescence was induced by hydrogen peroxide (H2O2) and hydroxyurea (HU) in rat and human intestinal epithelial cells. Cellular permeability was evaluated by transepithelial electrical resistance (TEER) measurement.

Results and Discussion

The expression of CB1 was decreased in the small intestine of aged rats compared to that of young rats. Senescent cells showed reduced TEER values and decreased expression of ZO-1, indicating increased intestinal permeability, which is tightly regulated by the CB1 signaling. In silico miRNA analysis suggested that ZO-1 was a direct target gene of miR-191-5p. Increased expression of miR-191-5p by HU was restored by CB1 agonist ACEA co-treatment. Moreover, NF-κB p65 activation was associated with CB1-related miR-191-5p signaling. In conclusion, aging-induced CB1 reduction leads to increased intestinal permeability and decreased ZO-1 expression via upregulation of miR-191-5p and NF-κB p65 activation. Taken together, these results suggest that CB1 signaling may be a useful strategy to reduce intestinal permeability in aging-related and other inflammatory conditions in the gut.

Emerging therapies in the management of Irritable Bowel Syndrome (IBS)

INTRODUCTION

Irritable bowel syndrome (IBS) is a common, symptom-based disorder of chronic abdominal pain and altered bowel habits. The pathogenesis of IBS is multifactorial, leading to the potential for the development of multiple, diverse treatment strategies. This mechanistic heterogeneity also leads to the realization that available therapies are only effective in a subset of IBS suffers. Current US Food and Drug Administration (FDA) approved therapies for IBS with diarrhea (IBS-D) and IBS with constipation (IBS-C) are reviewed. Limited symptom responses and side effect experiences lead to considerable patient dissatisfaction with currently available IBS treatments. Only a small percentage of IBS patients are on prescription therapies underscoring the potential market and need for additional therapeutic options.

AREAS COVERED

: Expanding on currently available therapies, the serotonergic and endogenous opioid receptor systems continue to be a focus of future IBS treatment development. Additional novel emerging therapies include the endogenous cannabinoid system, bile acid secretion and sequestration, and exploit our enhanced understanding of visceral sensory signaling and intestinal secretomotor function.

EXPERT OPINION

While challenges remain for the future development of IBS therapies, the diverse etiologies underlying the disorder present an opportunity for novel therapies. Hence, great potential is anticipated for future IBS treatment options.

Cannabis and Cannabis Derivatives for Abdominal Pain Management in Inflammatory Bowel Disease

For centuries, cannabis and its components have been used to manage a wide variety of symptoms associated with many illnesses. Gastrointestinal (GI) diseases are no exception in this regard. Individuals suffering from inflammatory bowel disease (IBD) are among those who have sought out the ameliorating properties of this plant. As legal limitations of its use have eased, interest has grown from both patients and their providers regarding the potential of cannabis to be used in the clinical setting. Similarly, a growing number of animal and human studies have been undertaken to evaluate the impact of cannabis and cannabinoid signaling elements on the natural history of IBD and its associated complications. There is little clinical evidence supporting the ability of cannabis or related products to treat the GI inflammation underlying these disorders. However, 1 recurring theme from both animal and human studies is that these agents have a significant impact on several IBD-related symptoms, including abdominal pain. In this review, we discuss the role of cannabis and cannabinoid signaling in visceral pain perception, what is currently known regarding the efficacy of cannabis and its derivatives for managing pain, related symptoms and inflammation in IBD, and what work remains to effectively utilize cannabis and its derivatives in the clinical setting.

Medical Therapies for Diarrhea-Predominant Irritable Bowel Syndrome

Diarrhea-predominant irritable bowel syndrome is a common functional gastrointestinal disorder that manifests with abdominal pain and diarrheal bowel patterns, without structural explanation. Diarrhea-predominant irritable bowel syndrome is a heterogeneous condition resulting from diverse pathophysiologic processes. Treatment strategies with varied mechanisms of action are beneficial in its management. The clinician must become familiar with a multi-dimensional approach to irritable bowel syndrome. The 3 approved medications are central to disease management. Effective treatment uses off-label medications and emerging therapies and a growing number of over-the-counter and supplemental agents to optimize symptom improvement for the patient with diarrhea-predominant irritable bowel syndrome.

Cannabinoid Type-2 Receptor Agonist, JWH133 May Be a Possible Candidate for Targeting Infection, Inflammation, and Immunity in COVID-19

The COVID-19 pandemic, caused by SARS-CoV-2, is a deadly disease affecting millions due to the non-availability of drugs and vaccines. The majority of COVID-19 drugs have been repurposed based on antiviral, immunomodulatory, and antibiotic potential. The pathogenesis and advanced complications with infection involve the immune-inflammatory cascade. Therefore, a therapeutic strategy could reduce infectivity, inflammation, and immune modulation. In recent years, modulating the endocannabinoid system, particularly activation of the cannabinoid type 2 (CB2) receptor is a promising therapeutic target for modulation of immune-inflammatory responses. JWH133, a selective, full functional agonist of the CB2 receptor, has been extensively studied for its potent anti-inflammatory, antiviral, and immunomodulatory properties. JWH133 modulates numerous signaling pathways and inhibits inflammatory mediators, including cytokines, chemokines, adhesion molecules, prostanoids, and eicosanoids. In this study, we propose that JWH133 could be a promising candidate for targeting infection, immunity, and inflammation in COVID-19, due to its pharmacological and molecular mechanisms in numerous preclinical efficacy and safety studies, along with its immunomodulatory, anti-inflammatory, organoprotective, and antiviral properties. Thus, JWH133 should be investigated in preclinical and clinical studies for its potential as an agent or adjuvant with other agents for its effect on viremia, infectivity, immune modulation, resolution of inflammation, reduction in severity, and progression of complications in COVID-19. JWH133 is devoid of psychotropic effects due to CB2 receptor selectivity, has negligible toxicity, good bioavailability and druggable properties, including pharmacokinetic and physicochemical effects. We believe that JWH133 could be a promising drug and may inspire further studies for an evidence-based approach against COVID-19.

Therapeutic Attributes of Endocannabinoid System against Neuro-Inflammatory Autoimmune Disorders

In humans, various sites like cannabinoid receptors (CBR) having a binding affinity with cannabinoids are distributed on the surface of different cell types, where endocannabinoids (ECs) and derivatives of fatty acid can bind. The binding of these substance(s) triggers the activation of specific receptors required for various physiological functions, including pain sensation, memory, and appetite. The ECs and CBR perform multiple functions via the cannabinoid receptor 1 (CB1); cannabinoid receptor 2 (CB2), having a key effect in restraining neurotransmitters and the arrangement of cytokines. The role of cannabinoids in the immune system is illustrated because of their immunosuppressive characteristics. These characteristics include inhibition of leucocyte proliferation, T cells apoptosis, and induction of macrophages along with reduced pro-inflammatory cytokines secretion. The review seeks to discuss the functional relationship between the endocannabinoid system (ECS) and anti-tumor characteristics of cannabinoids in various cancers. The therapeutic potential of cannabinoids for cancer-both in vivo and in vitro clinical trials-has also been highlighted and reported to be effective in mice models in arthritis for the inflammation reduction, neuropathic pain, positive effect in multiple sclerosis and type-1 diabetes mellitus, and found beneficial for treating in various cancers. In human models, such studies are limited; thereby, further research is indispensable in this field to get a conclusive outcome. Therefore, in autoimmune disorders, therapeutic cannabinoids can serve as promising immunosuppressive and anti-fibrotic agents.

Dexmedetomidine Ameliorates Lung Injury Induced by Intestinal Ischemia/Reperfusion by Upregulating Cannabinoid Receptor 2, Followed by the Activation of the Phosphatidylinositol 3-Kinase/Akt Pathway

Intestinal ischemia/reperfusion (I/R) is a clinical emergency, which often causes lung injury with high morbidity and mortality. Although dexmedetomidine has been identified to have a protective effect on lung injury caused by intestinal I/R, its specific mechanism is still elucidated. In recent years, the cannabinoid (CB₂) receptor pathway has been found to be involved in I/R injury of some organs. In the current study, we investigated whether the CB₂ receptor pathway contributes to the protective effect of dexmedetomidine on the intestinal I/R-induced lung injury in rats. Dexmedetomidine treatment upregulated the expression of CB₂ receptor and suppressed the I/R-induced increases in lung injury scores, inflammatory cell infiltration, lung wet/dry ratio, MPO activity, MDA level, inflammatory cytokines, and caspase-3 expression while augmenting SOD activity and Bcl-2 expression, indicating attenuation of lung injury. Dexmedetomidine treatment also increased the expression of Akt. The protective effects of dexmedetomidine treatment were reversed by the CB₂ receptor antagonist AM630 or the PI3K inhibitor wortmannin. And the CB₂ receptor antagonist AM630 also downregulated the expression of Akt. Thus, our findings suggest that treatment with dexmedetomidine provides a protective role against lung injury caused by intestinal I/R in rats, possibly due to the upregulation of the CB₂ receptor, followed by the activation of the PI3K/Akt pathway.

Activation of cannabinoid 2 receptor relieves colonic hypermotility in a rat model of irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a common disease with intestinal dysmotility, whose mechanism remains elusive. The endocannabinoid system is emerging as an important modulator of gastrointestinal (GI) motility in multiple diseases, but its involvement in IBS is unknown. We aimed to determine whether cannabinoid 2 (CB2) receptor modulates intestinal motility associated with stress-induced IBS.

METHODS

A rat IBS model was established by chronic water avoidance stress (WAS). Colonic pathological alterations were detected histologically and intestinal motility was assessed by intestinal transit time (ITT) and fecal water content (FWC). Visceral sensitivity was determined by visceromotor response (VMR) to colorectal distension (CRD). Real-time PCR, western blot, and immunostaining were performed to identify colonic CB2 receptor expression. Colonic muscle strip contractility was studied by isometric transducers and nitric oxide (NO) was detected by the Griess test. The effects of AM1241, a selective agonist of CB2 receptors, on colonic motility were examined.

KEY RESULTS

After 10 days of WAS exposure, ITT was decreased and FWC elevated while VMR magnitude in response to CRD was significantly enhanced. Colon CB2 protein and mRNA levels increased and density of CB2-positive macrophages in the mucosa and enteric neurons in the myenteric plexus was higher than in controls. Pharmacological enhancement of CB2 activity by AM1241 relieved colonic hypermotility in WAS rats in a concentration-dependent manner via inhibition of p38 phosphorylation and elevation of NO production.

CONCLUSION

CB2 receptor may exert an important inhibitory effect in stress-induced colonic hypermotility by modulating NO synthesis through p38 mitogen-activated protein kinase signaling. AM1241 could be used as a potential drug to treat disorders with colonic hypermotility.

Elevated AA/EPA Ratio Represents an Inflammatory Biomarker in Tumor Tissue of Metastatic Colorectal Cancer Patients

Chronic inflammation increases the risk of developing certain types of cancer, such as colorectal cancer (CRC). The oxidative metabolism of polyunsaturated fatty acids (PUFAs) has a strong effect on colonic tumorigenesis and the levels of arachidonic acid (AA) and eicosapentaenoic acid (EPA) can contribute to the development of an inflammatory microenvironment. Aim of this study was to evaluate the possible differences in the AA/EPA ratio tissue levels between CRC patients with and without synchronous metastases. Moreover, the expression of the most important inflammatory enzymes and mediators, linked with the AA/EPA ratio, have been also assessed. Sixty-eight patients with CRC were enrolled in the study, of which 33 patients with synchronous metastasis. Fatty acid profile analysis in tissue samples was done to examine the levels of AA and EPA. High levels of the AA/EPA ratio were detected in tumor tissue of patients with metastatic CRC. Moreover, an increase of expression of the main enzymes and mediators involved in inflammation was also detected in the same samples. The lipidomic approach of inflammation allows to evaluate lipid homeostasis changes that occur in cancer and in its metastatic process, in order to identify new biomarkers to be introduced into clinical practice.

Therapeutic applications of cannabinoids

The psychoactive property of cannabinoids is well known and there has been a continuous controversy regarding the usage of these compounds for therapeutic purposes all over the world. Their use for medical and research purposes are restricted in various countries. However, their utility as medications should not be overshadowed by its negative physiological activities. This review article is focused on the therapeutic potential and applications of phytocannabinoids and endocannabinoids. We further highlights their mode of action, overall effects on physiology, various in vitro and in vivo studies that have been done so far and the extent to which these compounds can be useful in different disease conditions such as cancer, Alzheimer's disease, multiple sclerosis, pain, inflammation, glaucoma and many others. Thus, this work is an attempt to make the readers understand the positive implications of these compounds and indicates the significant developments of utilizing cannabinoids as therapeutic agents.

A Randomized, Double-blind, Placebo-controlled, Parallel-group, Pilot Study of Cannabidiol-rich Botanical Extract in the Symptomatic Treatment of Ulcerative Colitis

BACKGROUND

Cannabidiol (CBD) exhibits anti-inflammatory properties that could improve disease activity in inflammatory bowel disease. This proof-of-concept study assessed efficacy, safety and tolerability of CBD-rich botanical extract in ulcerative colitis (UC) patients.

METHODS

Patients aged 18 years or older, with left-sided or extensive UC, Mayo scores of 4-10 (endoscopy scores ≥1), and on stable 5-aminosalicylic acid dosing, were randomized to 10-weeks' CBD-rich botanical extract or placebo capsules. The primary endpoint was the percentage of patients in remission after treatment. Statistical testing was 2-sided, using a 10% significance level.

RESULTS

Patients were less tolerant of CBD-rich botanical extract compared with placebo, taking on average one-third fewer capsules, and having more compliance-related protocol deviations (principally insufficient exposure), prompting identification of a per protocol (PP) analysis set. The primary endpoint was negative; end of treatment remission rates were similar for CBD-rich botanical extract (28%) and placebo (26%). However, PP analysis of total and partial Mayo scores favoured CBD-rich botanical extract (P = 0.068 and P = 0.038, respectively). Additionally, PP analyses of the more subjective physician's global assessment of illness severity, subject global impression of change, and patient-reported quality-of-life outcomes were improved for patients taking CBD-rich botanical extract (P = 0.069, P = 0.003, and P = 0.065, respectively). Adverse events (AEs) were predominantly mild/moderate with many in the CBD-rich botanical extract group potentially attributable to the ∆9-tetrahydrocannabinol content. A greater proportion of gastrointestinal-related AEs, indicative of UC worsening, was seen on placebo.

CONCLUSION

Although the primary endpoint was not reached, several signals suggest CBD-rich botanical extract may be beneficial for symptomatic treatment of UC.

Endocannabinoid-related compounds in gastrointestinal diseases

The endocannabinoid system (ECS) is an endogenous signalling pathway involved in the control of several gastrointestinal (GI) functions at both peripheral and central levels. In recent years, it has become apparent that the ECS is pivotal in the regulation of GI motility, secretion and sensitivity, but endocannabinoids (ECs) are also involved in the regulation of intestinal inflammation and mucosal barrier permeability, suggesting their role in the pathophysiology of both functional and organic GI disorders. Genetic studies in patients with irritable bowel syndrome (IBS) or inflammatory bowel disease have indeed shown significant associations with polymorphisms or mutation in genes encoding for cannabinoid receptor or enzyme responsible for their catabolism, respectively. Furthermore, ongoing clinical trials are testing EC agonists/antagonists in the achievement of symptomatic relief from a number of GI symptoms. Despite this evidence, there is a lack of supportive RCTs and relevant data in human beings, and hence, the possible therapeutic application of these compounds is raising ethical, political and economic concerns. More recently, the identification of several EC-like compounds able to modulate ECS function without the typical central side effects of cannabino-mimetics has paved the way for emerging peripherally acting drugs. This review summarizes the possible mechanisms linking the ECS to GI disorders and describes the most recent advances in the manipulation of the ECS in the treatment of GI diseases.

Review: The Role of Cannabinoids on Esophageal Function-What We Know Thus Far

The endocannabinoid system (ECS) primarily consists of cannabinoid receptors (CBRs), endogenous ligands, and enzymes for endocannabinoid biosynthesis and inactivation. Although the presence of CBRs, both CB1 and CB2, as well as a third receptor (G-protein receptor 55 [GPR55]), has been established in the gastrointestinal (GI) tract, few studies have focused on the role of cannabinoids on esophageal function. To date, studies have shown their effect on GI motility, inflammation and immunity, intestinal and gastric acid secretion, nociception and emesis pathways, and appetite control. Given the varying and sometimes limited efficacy of current medical therapies for diseases of the esophagus, further understanding and investigation into the interplay of the ECS on esophageal health and disease may present new therapeutic modalities that may help advance current treatment options. In this brief review, the current understanding of the ECS role in various esophageal functions and disorders is presented.

Cannabimimetic phytochemicals in the diet - an evolutionary link to food selection and metabolic stress adaptation?

The endocannabinoid system (ECS) is a major lipid signalling network that plays important pro-homeostatic (allostatic) roles not only in the nervous system but also in peripheral organs. There is increasing evidence that there is a dietary component in the modulation of the ECS. Cannabinoid receptors in hominids co-evolved with diet, and the ECS constitutes a feedback loop for food selection and energy metabolism. Here, it is postulated that the mismatch of ancient lipid genes of hunter-gatherers and pastoralists with the high-carbohydrate diet introduced by agriculture could be compensated for via dietary modulation of the ECS. In addition to the fatty acid precursors of endocannabinoids, the potential role of dietary cannabimimetic phytochemicals in agriculturist nutrition is discussed. Dietary secondary metabolites from vegetables and spices able to enhance the activity of cannabinoid-type 2 (CB₂ ) receptors may provide adaptive metabolic advantages and counteract inflammation. In contrast, chronic CB₁ receptor activation in hedonic obese individuals may enhance pathophysiological processes related to hyperlipidaemia, diabetes, hepatorenal inflammation and cardiometabolic risk. Food able to modulate the CB₁ /CB₂ receptor activation ratio may thus play a role in the nutrition transition of Western high-calorie diets. In this review, the interplay between diet and the ECS is highlighted from an evolutionary perspective. The emerging potential of cannabimimetic food as a nutraceutical strategy is critically discussed.

LINKED ARTICLES

This article is part of a themed section on Principles of Pharmacological Research of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.11/issuetoc.

Endocannabinoids in the gastrointestinal tract

The endocannabinoid system mainly consists of endogenously produced cannabinoids (endocannabinoids) and two G protein-coupled receptors (GPCRs), cannabinoid receptors 1 and 2 (CB₁ and CB₂). This system also includes enzymes responsible for the synthesis and degradation of endocannabinoids and molecules required for the uptake and transport of endocannabinoids. In addition, endocannabinoid-related lipid mediators and other putative endocannabinoid receptors, such as transient receptor potential channels and other GPCRs, have been identified. Accumulating evidence indicates that the endocannabinoid system is a key modulator of gastrointestinal physiology, influencing satiety, emesis, immune function, mucosal integrity, motility, secretion, and visceral sensation. In light of therapeutic benefits of herbal and synthetic cannabinoids, the vast potential of the endocannabinoid system for the treatment of gastrointestinal diseases has been demonstrated. This review focuses on the role of the endocannabinoid system in gut homeostasis and in the pathogenesis of intestinal disorders associated with intestinal motility, inflammation, and cancer. Finally, links between gut microorganisms and the endocannabinoid system are briefly discussed.

The effect of FAAH, MAGL, and Dual FAAH/MAGL inhibition on inflammatory and colorectal distension-induced visceral pain models in Rodents

BACKGROUND

Recent studies showed that the pharmacological inhibition of endocannabinoid degrading enzymes such as fatty acid amide hydrolase (FAAH) and monoacyl glycerol lipase (MAGL) elicit promising analgesic effects in a variety of nociceptive models without serious side effects. However, the full spectrum of activities is not observed upon inhibition of either FAAH or MAGL enzymes alone and thus dual FAAH and MAGL inhibitors have been described. Visceral pain is strongly associated with inflammation and distension of the gut. Thus, we explored the comparable effects of FAAH, MAGL, and dual FAAH/MAGL inhibitors on inflammatory and mechanically evoked visceral pain models.

METHODS

Visceral inflammatory and distension-induced pain were assessed with the 0.6% acetic acid writhing test in mice and colorectal distension (CRD) test in rats, respectively. The selective FAAH inhibitor PF 3845, MAGL inhibitor JZL 184, dual inhibitor JZL 195, and the cannabis analog CP 55,940 were given systemically 30 min prior to nociceptive testing.

KEY RESULTS

PF 3845 (5, 10, and 20 mg/kg), JZL 184 (5, 10, and 20 mg/kg), and JZL 195 (5, 10, and 20 mg/kg) elicit dose-dependent antinociceptive in the acetic acid writhing test. In the CRD model, while JZL 195 (5, 10, or 20 mg/kg) and PF3845 (10, 20, and 40 mg/kg) produced dose-dependent antinociceptive effects comparable to those of CP 55,940 (0.1, 0.3, or 1 mg/kg), JZL 184 (10, 20, and 40 mg/kg) alone did not alter the visceromotor response (VMR).

CONCLUSIONS & INFERENCES

The selective FAAH inhibitor and dual FAAH/MAGL inhibitors were effective in both inflammatory and mechanically evoked visceral pain, while the MAGL inhibitor elicited an analgesic effect in inflammatory, but not in distension-induced, visceral pain.

The role of cannabinoids in regulation of nausea and vomiting, and visceral pain

Marijuana derived from the plant Cannabis sativa has been used for the treatment of many gastrointestinal (GI) disorders, including anorexia, emesis, abdominal pain, diarrhea, and others. However, its psychotropic side effects have often limited its use. Several cannabinoid receptors, which include the cannabinoid receptor 1 (CB1), CB2, and possibly GPR55, have been identified throughout the GI tract. These receptors may play a role in the regulation of food intake, nausea and emesis, gastric secretion and gastroprotection, GI motility, ion transport, visceral sensation, intestinal inflammation, and cell proliferation in the gut. However, the regulation of nausea and vomiting by cannabinoids and the endocannabinoid system has shed new knowledge in this field. Thus far, despite evidence of visceral sensitivity inhibition in animal models, data in irritable bowel syndrome (IBS) patients is scarce and not supportive. Furthermore, many compounds that either act directly at the receptor or increase (or reduce) ligand availability have the potential to affect other brain functions and cause side effects. Novel drug targets such as FAAH and monoacylglycerol lipase (MAGL) inhibitors appear to be promising in animal models, but more studies are necessary to prove their efficiency. The promise of emerging drugs that are more selective and peripherally acting suggest that, in the near future, cannabinoids will play a major role in managing an array of GI diseases.

Prokinetics in diabetic gastroparesis

Within the last 50 years, diabetic gastroparesis has become a well recognized complication of type 1 and type 2 diabetes. It is a syndrome characterized by abnormal gastric function, resulting in delayed emptying of the stomach in the absence of any evident mechanical obstruction, predominantly manifested by early satiety, postprandial fullness, nausea, vomiting, and weight loss. The past five years have shown significant advances in its pathophysiology and in new diagnostic tests. Prokinetic medications remain the therapeutic focus for improving clinical symptoms of gastroparesis through enhanced gastric emptying. This article summarizes the present knowledge of prokinetics, with emphasis on medications currently available, as well as drugs under clinical investigation, including some agents in advanced clinical trials that are likely to be used in the treatment of diabetic gastroparesis in the future. These include the ghrelin agonists and newer 5-HT4 agonists devoid of cardiac side effects.

Cannabinoids mediate opposing effects on inflammation-induced intestinal permeability

BACKGROUND AND PURPOSE

Activation of cannabinoid receptors decreases emesis, inflammation, gastric acid secretion and intestinal motility. The ability to modulate intestinal permeability in inflammation may be important in therapy aimed at maintaining epithelial barrier integrity. The aim of the present study was to determine whether cannabinoids modulate the increased permeability associated with inflammation in vitro.

EXPERIMENTAL APPROACH

Confluent Caco-2 cell monolayers were treated for 24 h with IFNγ and TNFα (10 ng·mL(-1) ). Monolayer permeability was measured using transepithelial electrical resistance and flux measurements. Cannabinoids were applied either apically or basolaterally after inflammation was established. Potential mechanisms of action were investigated using antagonists for CB(1) , CB(2) , TRPV1, PPARγ and PPARα. A role for the endocannabinoid system was established using inhibitors of the synthesis and degradation of endocannabinoids.

KEY RESULTS

Δ(9) -Tetrahydrocannabinol (THC) and cannabidiol accelerated the recovery from cytokine-induced increased permeability; an effect sensitive to CB(1) receptor antagonism. Anandamide and 2-arachidonylglycerol further increased permeability in the presence of cytokines; this effect was also sensitive to CB(1) antagonism. No role for the CB(2) receptor was identified in these studies. Co-application of THC, cannabidiol or a CB(1) antagonist with the cytokines ameliorated their effect on permeability. Inhibiting the breakdown of endocannabinoids worsened, whereas inhibiting the synthesis of endocannabinoids attenuated, the increased permeability associated with inflammation.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that locally produced endocannabinoids, acting via CB(1) receptors play a role in mediating changes in permeability with inflammation, and that phytocannabinoids have therapeutic potential for reversing the disordered intestinal permeability associated with inflammation.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

Gut feelings about the endocannabinoid system

Stemming from the centuries-old and well known effects of Cannabis on intestinal motility and secretion, research on the role of the endocannabinoid system in gut function and dysfunction has received ever increasing attention since the discovery of the cannabinoid receptors and their endogenous ligands, the endocannabinoids. In this article, some of the most recent developments in this field are discussed, with particular emphasis on new data, most of which are published in Neurogastroenterology & Motility, on the potential tonic endocannabinoid control of intestinal motility, the function of cannabinoid type-1 (CB1) receptors in gastric function, visceral pain, inflammation and sepsis, the emerging role of cannabinoid type-2 (CB2) receptors in the gut, and the pharmacology of endocannabinoid-related molecules and plant cannabinoids not necessarily acting via cannabinoid CB1 and CB2 receptors. These novel data highlight the multi-faceted aspects of endocannabinoid function in the GI tract, support the feasibility of the future therapeutic exploitation of this signaling system for the treatment of GI disorders, and leave space for some intriguing new hypotheses on the role of endocannabinoids in the gut.

Mechanisms of Broad-Spectrum Antiemetic Efficacy of Cannabinoids against Chemotherapy-Induced Acute and Delayed Vomiting

Chemotherapy-induced nausea and vomiting (CINV) is a complex pathophysiological condition and consists of two phases. The conventional CINV neurotransmitter hypothesis suggests that the immediate phase is mainly due to release of serotonin (5-HT) from the enterochromaffin cells in the gastrointestinal tract (GIT), while the delayed phase is a consequence of release of substance P (SP) in the brainstem. However, more recent findings argue against this simplistic neurotransmitter and anatomical view of CINV. Revision of the hypothesis advocates a more complex, differential and overlapping involvement of several emetic neurotransmitters/modulators (e.g. dopamine, serotonin, substance P, prostaglandins and related arachidonic acid derived metabolites) in both phases of emesis occurring concomitantly in the brainstem and in the GIT enteric nervous system (ENS) [1]. No single antiemetic is currently available to completely prevent both phases of CINV. The standard antiemetic regimens include a 5-HT₃ antagonist plus dexamethasone for the prevention of acute emetic phase, combined with an NK₁ receptor antagonist (e.g. aprepitant) for the delayed phase. Although NK₁ antagonists behave in animals as broad-spectrum antiemetics against different emetogens including cisplatin-induced acute and delayed vomiting, by themselves they are not very effective against CINV in cancer patients. Cannabinoids such as D⁸-THC also behave as broad-spectrum antiemetics against diverse emetic stimuli as well as being effective against both phases of CINV in animals and patients. Potential side effects may limit the clinical utility of direct-acting cannabinoid agonists which could be avoided by the use of corresponding indirect-acting agonists. Cannabinoids (both phyto-derived and synthetic) behave as agonist antiemetics via the activation of cannabinoid CB₁ receptors in both the brainstem and the ENS emetic loci. An endocannabinoid antiemetic tone may exist since inverse CB₁ agonists (but not the corresponding silent antagonists) cause nausea and vomiting.

Pharmacological effects of cannabinoids on the Caco-2 cell culture model of intestinal permeability

Activation of cannabinoid receptors decreases emesis, inflammation, gastric acid secretion, and intestinal motility. However, the effects of cannabinoids on intestinal permeability have not yet been established. The aim of the present study is to examine the effects of cannabinoids on intestinal permeability in an in vitro model. Caco-2 cells were grown until fully confluent on inserts in 12-well plates. Transepithelial electrical resistance (TEER) measurements were made as a measure of permeability. EDTA (50 μM) was applied to reversibly increase permeability (reduce TEER). The effects of cannabinoids on permeability in combination with EDTA, or alone, were assessed. Potential target sites of action were investigated using antagonists of the cannabinoid (CB)(1) receptor, CB(2) receptor, transient receptor potential vanilloid subtype 1 (TRPV1), peroxisome proliferator-activated receptor (PPAR)γ, PPARα, and a proposed cannabinoid receptor. When applied to the apical or basolateral membrane of Caco-2 cells, Δ(9)-tetrahydrocannabinol (THC) and cannabidiol (CBD) enhanced the speed of recovery of EDTA-induced increased permeability. This effect was sensitive to cannabinoid CB(1) receptor antagonism only. Apical application of endocannabinoids caused increased permeability, sensitive to cannabinoid CB(1) receptor antagonism. By contrast, when endocannabinoids were applied basolaterally, they enhanced the recovery of EDTA-induced increased permeability, and this involved additional activation of TRPV1. All cannabinoids tested increased the mRNA of the tight junction protein zona occludens-1, but only endocannabinoids also decreased the mRNA of claudin-1. These findings suggest that endocannabinoids may play a role in modulating intestinal permeability and that plant-derived cannabinoids, such as THC and CBD, may have therapeutic potential in conditions associated with abnormally permeable intestinal epithelium.

Cannabinoid receptor ligands as potential anticancer agents — high hopes for new therapies?

Objectives

The endocannabinoid system is an endogenous lipid signalling network comprising arachidonic-acid-derived ligands, cannabinoid (CB) receptors, transporters and endocannabinoid degrading enzymes. The CB1 receptor is predominantly expressed in neurons but is also co-expressed with the CB2 receptor in peripheral tissues. In recent years, CB receptor ligands, including Δ9-tetrahydrocannabinol, have been proposed as potential anticancer agents.

Key findings

This review critically discusses the pharmacology of CB receptor activation as a novel therapeutic anticancer strategy in terms of ligand selectivity, tissue specificity and potency. Intriguingly, antitumour effects mediated by cannabinoids are not confined to inhibition of cancer cell proliferation; cannabinoids also reduce angiogenesis, cell migration and metastasis, inhibit carcinogenesis and attenuate inflammatory processes. In the last decade several new selective CB1 and CB2 receptor agents have been described, but most studies in the area of cancer research have used non-selective CB ligands. Moreover, many of these ligands exert prominent CB receptor-independent pharmacological effects, such as activation of the G-protein-coupled receptor GPR55, peroxisome proliferator-activated receptor gamma and the transient receptor potential vanilloid channels.

Summary

The role of the endocannabinoid system in tumourigenesis is still poorly understood and the molecular mechanisms of cannabinoid anticancer action need to be elucidated. The development of CB2-selective anticancer agents could be advantageous in light of the unwanted central effects exerted by CB1 receptor ligands. Probably the most interesting question is whether cannabinoids could be useful in chemoprevention or in combination with established chemotherapeutic agents.

Role of acylethanolamides in the gastrointestinal tract with special reference to food intake and energy balance

Acylethanolamides (AEs) are a group of lipids occurring in both plants and animals. The best-studied AEs are the endocannabinoid anandamide (AEA), the anti-inflammatory compound palmitoylethanolamide (PEA), and the potent anorexigenic molecule oleoylethanolamide (OEA). AEs are biosynthesized in the gastrointestinal tract, and their levels may change in response to noxious stimuli, food deprivation or diet-induced obesity. The biological actions of AEs within the gut are not limited to the modulation of food intake and energy balance. For example, AEs exert potential beneficial effects in the regulation of intestinal motility, secretion, inflammation and cellular proliferation. Molecular targets of AEs, which have been identified in the gastrointestinal tract, include cannabinoid CB(1) and CB(2) receptors (activated by AEA), transient receptor potential vanilloid type 1 (TRPV1, activated by AEA and OEA), the nuclear receptor peroxisome proliferators-activated receptor-alpha (PPAR-alpha, activated by OEA and, to a less extent, by PEA), and the orphan G-coupled receptors GPR119 (activated by OEA) and GPR55 (activated by PEA and, with lower potency, by AEA and OEA). Modulation of AE levels in the gut may provide new pharmacological strategies not only for the treatment of feeding disorders but also for the prevention or cure of widespread intestinal diseases such as inflammatory bowel disease and colon cancer.

Inhibitory effect of salvinorin A, from Salvia divinorum, on ileitis-induced hypermotility: cross-talk between kappa-opioid and cannabinoid CB(1) receptors

BACKGROUND AND PURPOSE

Salvinorin A, the active component of the hallucinogenic herb Salvia divinorum, inhibits intestinal motility through activation of kappa-opioid receptors (KORs). However, this compound may have target(s) other than the KORs in the inflamed gut. Because intestinal inflammation upregulates cannabinoid receptors and endogenous cannabinoids, in the present study we investigated the possible involvement of the endogenous cannabinoid system in salvinorin A-induced delay in motility in the inflamed gut.

EXPERIMENTAL APPROACH

Motility in vivo was measured by evaluating the distribution of a fluorescent marker along the small intestine; intestinal inflammation was induced by the irritant croton oil; direct or indirect activity at cannabinoid receptors was evaluated by means of binding, enzymic and cellular uptake assays.

KEY RESULTS

Salvinorin A as well as the KOR agonist U-50488 reduced motility in croton oil treated mice. The inhibitory effect of both salvinorin A and U-50488 was counteracted by the KOR antagonist nor-binaltorphimine and by the cannabinoid CB(1) receptor antagonist rimonabant. Rimonabant, however, did not counteract the inhibitory effect of salvinorin A on motility in control mice. Binding experiments showed very weak affinity of salvinorin A for cannabinoid CB(1) and CB(2) and no inhibitory effect on 2-arachidonoylglycerol and anandamide hydrolysis and cellular uptake.

CONCLUSIONS AND IMPLICATIONS

The inhibitory effect of salvinorin A on motility reveals a functional interaction between cannabinoid CB(1) receptors and KORs in the inflamed--but not in the normal--gut in vivo.

Role of cannabinoid receptors in the control of gastrointestinal motility and perception

The identification of endocannabinoids and cannabinoid CB1 receptors in key areas of the intestinal wall, such as cholinergic neurons, supports a role for cannabinoids in the control of gastrointestinal motility. Activation of CB1 receptors inhibits the peristaltic reflex and slows down gastrointestinal and colonic transit. Endocannabinoids play an important inhibitory role in the control of the occurrence of transient lower esophageal sphincter relaxations. Cannabinoid receptor agonists inhibit gastric emptying and intestinal motility in humans. There is strong anatomical support for a role of CB1 receptors in the control of gastrointestinal perception, since these receptors have been identified in key sites of the neuronal circuitry involved in the transmission of visceral pain. Experimental data indicate a visceral antinociceptive action of cannabinoid receptor agonists, which remains to be confirmed in humans.

Cannabidiol, extracted from Cannabis sativa, selectively inhibits inflammatory hypermotility in mice

BACKGROUND AND PURPOSE

Cannabidiol is a Cannabis-derived non-psychotropic compound that exerts a plethora of pharmacological actions, including anti-inflammatory, neuroprotective and antitumour effects, with potential therapeutic interest. However, the actions of cannabidiol in the digestive tract are largely unexplored. In the present study, we investigated the effect of cannabidiol on intestinal motility in normal (control) mice and in mice with intestinal inflammation.

EXPERIMENTAL APPROACH

Motility in vivo was measured by evaluating the distribution of an orally administered fluorescent marker along the small intestine; intestinal inflammation was induced by the irritant croton oil; contractility in vitro was evaluated by stimulating the isolated ileum, in an organ bath, with ACh.

KEY RESULTS

In vivo, cannabidiol did not affect motility in control mice, but normalized croton oil-induced hypermotility. The inhibitory effect of cannabidiol was counteracted by the cannabinoid CB1 receptor antagonist rimonabant, but not by the cannabinoid CB2 receptor antagonist SR144528 (N-[-1S-endo-1,3,3-trimethyl bicyclo [2.2.1] heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide), by the opioid receptor antagonist naloxone or by the alpha2-adrenergic antagonist yohimbine. Cannabidiol did not reduce motility in animals treated with the fatty acid amide hydrolase (FAAH) inhibitor N-arachidonoyl-5-hydroxytryptamine, whereas loperamide was still effective. In vitro, cannabidiol inhibited ACh-induced contractions in the isolated ileum from both control and croton oil-treated mice.

CONCLUSIONS AND IMPLICATIONS

Cannabidiol selectively reduces croton oil-induced hypermotility in mice in vivo and this effect involves cannabinoid CB1 receptors and FAAH. In view of its low toxicity in humans, cannabidiol may represent a good candidate to normalize motility in patients with inflammatory bowel disease.

Gastrointestinal regulation of food intake: general aspects and focus on anandamide and oleoylethanolamide

The gastrointestinal tract plays a pivotal role in the regulation of food intake and energy balance. Signals from the gastrointestinal tract generally function to limit ingestion in the interest of efficient digestion. These signals may be released into the bloodstream or may activate afferent neurones that carry information to the brain and its cognitive centres, which regulates food intake. The rate at which nutrients become systemically available is also influenced by gastrointestinal motility: a delay in gastric emptying may evoke a satiety effect. Recent evidence suggests that the endocannabinoid anandamide and the related acylethanolamide oleoylethanolamide are produced in the intestine and might regulate feeding behaviour by engaging sensory afferent neurones that converge information to specific areas of the brain. The intestinal levels of these acylethanolamides are inversely correlated to feeding, as food deprivation increases intestinal levels of anandamide (which acts in the gut as a 'hunger signal'), while it decreases the levels of oleoylethanolamide (which acts in the gut as a 'satiety signal'). Additionally, these acylethanolamides, whose gastric levels change in response to diet-induced obesity, alter gastrointestinal motility, which might contribute to their effect on food intake and nutrient absorption.

Inhibitory effect of the anorexic compound oleoylethanolamide on gastric emptying in control and overweight mice

Gastric emptying regulates food intake. Oleoylethanolamide (OEA), an endogenous acylethanolamide chemically related to the endocannabinoid anandamide, inhibits food intake, but its effect on gastric emptying is unknown. Here, we investigated the effect and the role of OEA on gastric emptying in mice fed either a standard (STD) or a high-fat diet (HFD) for 14 weeks. Gastric emptying was reduced by OEA, but not by its saturated analog, palmitoylethanolamide. The effect of OEA was unaffected by rimonabant (cannabinoid CB1 receptor antagonist), SR144528 (cannabinoid CB2 receptor antagonist), 5'-iodoresiniferatoxin (transient receptor potential vanilloid type 1 antagonist), or MK886 (peroxisome proliferator-activated receptor-alpha) antagonist. Compared to STD mice, HFD mice showed delayed gastric emptying and higher levels of gastric OEA. HFD-induced increase in OEA levels was accompanied by increased expression of the OEA-synthesizing enzyme N-acyl-phosphatidylethanolamine-selective phospholipase D and decreased expression of the OEA-degrading enzyme fatty acid amide hydrolase. These results might suggest that elevation of gastric OEA could possibly contribute to the delayed gastric emptying observed in HFD-fed animals. HFD regulates OEA levels in the stomach through an increase of its biosynthesis and a decrease of its enzymatic degradation. The inhibitory effect of OEA on gastric emptying here observed might underlie part of the anorexic effects of this compound previously reported.

The role of endocannabinoids in the regulation of gastric emptying: alterations in mice fed a high-fat diet

BACKGROUND AND PURPOSE

Endocannabinoids (via cannabinoid CB(1) receptor activation) are physiological regulators of intestinal motility and food intake. However, their role in the regulation of gastric emptying is largely unexplored. The purpose of the present study was to investigate the involvement of the endocannabinoid system in the regulation of gastric emptying in mice fed either a standard diet (STD) or a high-fat diet (HFD) for 14 weeks.

EXPERIMENTAL APPROACH

Gastric emptying was evaluated by measuring the amount of phenol red recovered in the stomach after oral challenge; CB(1) expression was analysed by quantitative reverse transcription-PCR; endocannabinoid (anandamide and 2-arachidonoyl glycerol) levels were measured by liquid chromatography-mass spectrometry.

KEY RESULTS

Gastric emptying was reduced by anandamide, an effect counteracted by the CB(1) receptor antagonist rimonabant, but not by the CB(2) receptor antagonist SR144528 or by the transient receptor potential vanilloid type 1 (TRPV1) antagonist 5'-iodoresiniferatoxin. The fatty acid amide hydrolase (FAAH) inhibitor N-arachidonoyl-5-hydroxytryptamine (but not the anandamide uptake inhibitor OMDM-2) reduced gastric emptying in a way partly reduced by rimonabant. Compared to STD mice, HFD mice exhibited significantly higher body weight and fasting glucose levels, delayed gastric emptying and lower anandamide and CB(1) mRNA levels. N-arachidonoylserotonin (but not rimonabant) affected gastric emptying more efficaciously in HFD than STD mice.

CONCLUSIONS AND IMPLICATIONS

Gastric emptying is physiologically regulated by the endocannabinoid system, which is downregulated following a HFD leading to overweight.