The Endocannabinoid System and Its Role in Regulating the Intrinsic Neural Circuitry of the Gastrointestinal Tract

Gut-brain axis interacts with immunomodulation in inflammatory bowel disease

The brain and the gastrointestinal (GI) tract are important sensory organs in the body and the two-way interaction that exists between them regulates key physiological and homeostatic functions. A growing body of research suggests that this bidirectional communication influences the development and progression of functional GI disorders and plays an important role in the treatment of central nervous system (CNS) disorders. Inflammatory bowel disease (IBD) is a classic intestinal disorder with a high prevalence but still unclear pathogenesis that has been widely discussed in recent years. However, in the studies available to date, we find that many authors have chosen to discuss the influence of the brain on intestinal disorders from the top down, starting with physical and psychological disorders. Coming very naturally, based on these substantial research evidence, we focus on exploring the links between bidirectional communication in the gut-brain axis and IBD, and highlight the role of the gut microbiota, vagus nerve (VN), receptors and immune cells involved in regulating IBD through the gut-brain axis in this review.

Cannabis and Cannabinoids in the Perioperative Period

Cannabis use is increasingly common, and with a growing number of jurisdictions implementing legalization frameworks, it is likely that providers will encounter more patients who use cannabis. Therefore, it is important for providers to understand the implications of cannabis use and practical considerations for the perioperative period. Cannabis affects multiple organ systems and may influence intraoperative anesthesia, as well as postoperative pain management. The effects of cannabis and key anesthetic considerations are reviewed here.

Phytocannabinoids Reduce Inflammation of Primed Macrophages and Enteric Glial Cells: An In Vitro Study

Intestinal inflammation is mediated by a subset of cells populating the intestine, such as enteric glial cells (EGC) and macrophages. Different studies indicate that phytocannabinoids could play a possible role in the treatment of inflammatory bowel disease (IBD) by relieving the symptoms involved in the disease. Phytocannabinoids act through the endocannabinoid system, which is distributed throughout the mammalian body in the cells of the immune system and in the intestinal cells. Our in vitro study analyzed the putative anti-inflammatory effect of nine selected pure cannabinoids in J774A1 macrophage cells and EGCs triggered to undergo inflammation with lipopolysaccharide (LPS). The anti-inflammatory effect of several phytocannabinoids was measured by their ability to reduce TNFα transcription and translation in J774A1 macrophages and to diminish S100B and GFAP secretion and transcription in EGCs. Our results demonstrate that THC at the lower concentrations tested exerted the most effective anti-inflammatory effect in both J774A1 macrophages and EGCs compared to the other phytocannabinoids tested herein. We then performed RNA-seq analysis of EGCs exposed to LPS in the presence or absence of THC or THC-COOH. Transcriptomic analysis of these EGCs revealed 23 differentially expressed genes (DEG) compared to the treatment with only LPS. Pretreatment with THC resulted in 26 DEG, and pretreatment with THC-COOH resulted in 25 DEG. To evaluate which biological pathways were affected by the different phytocannabinoid treatments, we used the Ingenuity platform. We show that THC treatment affects the mTOR and RAR signaling pathway, while THC-COOH mainly affects the IL6 signaling pathway.

Role of the Endocannabinoid System in the Regulation of Intestinal Homeostasis

The maintenance of intestinal homeostasis is fundamentally important to health. Intestinal barrier function and immune regulation are key determinants of intestinal homeostasis and are therefore tightly regulated by a variety of signaling mechanisms. The endocannabinoid system is a lipid mediator signaling system widely expressed in the gastrointestinal tract. Accumulating evidence suggests the endocannabinoid system is a critical nexus involved in the physiological processes that underlie the control of intestinal homeostasis. In this review we will illustrate how the endocannabinoid system is involved in regulation of intestinal permeability, fluid secretion, and immune regulation. We will also demonstrate a reciprocal regulation between the endocannabinoid system and the gut microbiome. The role of the endocannabinoid system is complex and multifaceted, responding to both internal and external factors while also serving as an effector system for the maintenance of intestinal homeostasis.

Endocannabinoid Modulation in Neurodegenerative Diseases: In Pursuit of Certainty

Simple Summary

Neurodegenerative diseases represent an important cause of morbidity and mortality worldwide. Existing therapeutic options are limited and focus mostly on improving symptoms and reducing exacerbations. The endocannabinoid system is involved in the pathophysiology of such disorders, an idea which has been highlighted by recent scientific work. The current work focusses its attention on the importance and implications of this system and its synthetic and natural ligands in disorders such as Alzheimer’s, Parkinson’s, Huntington’s and multiple sclerosis.

Abstract

Neurodegenerative diseases are an increasing cause of global morbidity and mortality. They occur in the central nervous system (CNS) and lead to functional and mental impairment due to loss of neurons. Recent evidence highlights the link between neurodegenerative and inflammatory diseases of the CNS. These are typically associated with several neurological disorders. These diseases have fundamental differences regarding their underlying physiology and clinical manifestations, although there are aspects that overlap. The endocannabinoid system (ECS) is comprised of receptors (type-1 (CB1R) and type-2 (CB2R) cannabinoid-receptors, as well as transient receptor potential vanilloid 1 (TRPV1)), endogenous ligands and enzymes that synthesize and degrade endocannabinoids (ECBs). Recent studies revealed the involvement of the ECS in different pathological aspects of these neurodegenerative disorders. The present review will explore the roles of cannabinoid receptors (CBRs) and pharmacological agents that modulate CBRs or ECS activity with reference to Alzheimer’s Disease (AD), Parkinson’s Disease (PD), Huntington’s Disease (HD) and multiple sclerosis (MS).

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.

The endocannabinoid system - current implications for drug development

In this review, the state of the art for compounds affecting the endocannabinoid (eCB) system is described with a focus on the treatment of pain. Amongst directly acting CB receptor ligands, clinical experience with ∆⁹ -tetrahydracannabinol and medical cannabis in chronic non-cancer pain indicates that there are differences between the benefits perceived by patients and the at best modest effect seen in meta-analyses of randomized controlled trials. The reason for this difference is not known but may involve differences in the type of patients that are recruited, the study conditions that are chosen and the degree to which biases such as reporting bias are operative. Other directly acting CB receptor ligands such as biased agonists and allosteric receptor modulators have not yet reached the clinic. Amongst indirectly acting compounds targeting the enzymes responsible for the synthesis and catabolism of the eCBs anandamide and 2-arachidonoylglycerol, fatty acid amide hydrolase (FAAH) inhibitors have been investigated clinically but were per se not useful for the treatment of pain, although they may be useful for the treatment of post-traumatic stress disorder and cannabis use disorder. Dual-acting compounds targeting this enzyme and other targets such as cyclooxygenase-2 or transient potential vanilloid receptor 1 may be a way forward for the treatment of pain.

Endocannabinoid system and its modulation of brain, gut, joint and skin inflammation

The discovery of endogenous cannabinoid receptors CB₁ and CB₂ and their endogenous ligands has generated interest in the endocannabinoid system and has contributed to the understanding of the role of the endocannabinoid system. Its role in the normal physiology of the body and its implication in pathological states such as cardiovascular diseases, neoplasm, depression and pain have been subjects of scientific interest. In this review the authors focus on the endogenous cannabinoids, and the critical role of cannabinoid receptor signaling in neurodegeneration and other inflammatory responses such as gut, joint and skin inflammation. This review also discusses the potential of endocannabinoid pathways as drug targets in the amelioration of some inflammatory conditions. Though the exact role of the endocannabinoid system is not fully understood, the evidence found much clearly points to a great potential in exploiting both its central and peripheral pathways in disease management. Cannabinoid therapy has proven promising in several preclinical and clinical trials.

Targeting the Endocannabinoid System in Borderline Personality Disorder: Corticolimbic and Hypothalamic Perspectives

Borderline Personality Disorder (BPD) is a chronic debilitating psychiatric disorder characterized mainly by emotional instability, chaotic interpersonal relationships, cognitive disturbance (e.g., dissociation and suicidal thoughts) and maladaptive behaviors. BPD has a high rate of comorbidity with other mental disorders and a high burden on society. In this review, we focused on two compromised brain regions in BPD - the hypothalamus and the corticolimbic system, emphasizing the involvement and potential contribution of the endocannabinoid system (ECS) to improvement in symptoms and coping. The hypothalamus-regulated endocrine axes (hypothalamic pituitary - gonadal, thyroid & adrenal) have been found to be dysregulated in BPD. There is also substantial evidence for limbic system structural and functional changes in BPD, especially in the amygdala and hippocampus, including cortical regions within the corticolimbic system. Extensive expression of CB1 and CB2 receptors of the ECS has been found in limbic regions and the hypothalamus. This opens new windows of opportunity for treatment with cannabinoids such as cannabidiol (CBD) as no other pharmacological treatment has shown long-lasting improvement in the BPD population to date. This review aims to show the potential role of the ECS in BPD patients through their most affected brain regions, the hypothalamus and the corticolimbic system. The literature reviewed does not allow for general indications of treatment with CBD in BPD. However, there is enough knowledge to indicate a treatment ratio of a high level of CBD to a low level of THC. A randomized controlled trial investigating the efficacy of cannabinoid based treatments in BPD is warranted.

Cannabinoids and the Microbiota-Gut-Brain Axis: Emerging Effects of Cannabidiol and Potential Applications to Alcohol Use Disorders

The endocannabinoid system (ECS) has emerged in recent years as a potential treatment target for alcohol use disorders (AUD). In particular, the nonpsychoactive cannabinoid cannabidiol (CBD) has shown preclinical promise in ameliorating numerous clinical symptoms of AUD. There are several proposed mechanism(s) through which cannabinoids (and CBD in particular) may confer beneficial effects in the context of AUD. First, CBD may directly impact specific brain mechanisms underlying AUD to influence alcohol consumption and the clinical features of AUD. Second, CBD may influence AUD symptoms through its actions across the digestive, immune, and central nervous systems, collectively known as the microbiota-gut-brain axis (MGBA). Notably, emerging work suggests that alcohol and cannabinoids exert opposing effects on the MGBA. Alcohol is linked to immune dysfunction (e.g., chronic systemic inflammation in the brain and periphery) as well as disturbances in gut microbial species (microbiota) and increased intestinal permeability. These MGBA disruptions have been associated with AUD symptoms such as craving and impaired cognitive control. Conversely, existing preclinical data suggest that cannabinoids may confer beneficial effects on the gastrointestinal and immune system, such as reducing intestinal permeability, regulating gut bacteria, and reducing inflammation. Thus, cannabinoids may exert AUD harm-reduction effects, at least in part, through their beneficial actions across the MGBA. This review will provide a brief introduction to the ECS and the MGBA, discuss the effects of cannabinoids (particularly CBD) and alcohol in the brain, gut, and immune system (i.e., across the MGBA), and put forth a theoretical framework to inform future research questions.

Role of Dietary Lipids in Modulating Inflammation through the Gut Microbiota

Inflammation and its resolution is a tenuous balance that is under constant contest. Though several regulatory mechanisms are employed to maintain homeostasis, disruptions in the regulation of inflammation can lead to detrimental effects for the host. Of note, the gut and microbial dysbiosis are implicated in the pathology of systemic chronic low-grade inflammation which has been linked to several metabolic diseases. What remains to be described is the extent to which dietary fat and concomitant changes in the gut microbiota contribute to, or arise from, the onset of metabolic disorders. The present review will highlight the role of microorganisms in host energy regulation and several mechanisms that contribute to inflammatory pathways. This review will also discuss the immunomodulatory effects of the endocannabinoid system and its link with the gut microbiota. Finally, a brief discussion arguing for improved taxonomic resolution (at the species and strain level) is needed to deepen our current knowledge of the microbiota and host inflammatory state.

Emotion recognition and its relation to prefrontal function and network in heroin plus nicotine dependence: a pilot study

Many patients with substance use disorders (SUDs) live in a stressful environment, and comorbidity is not uncommon. Understanding the neural mechanisms underlying heroin and nicotine dependences and their relationships to social cognition could facilitate behavioral therapy efficacy. We aimed to provide a translational approach that leads to identifying potential biomarkers for opioid use disorder (OUD) susceptibility during recovery. We examined the clinical characters and the relationships between theory of mind (ToM) and executive functions in three groups: heroin plus nicotine-dependent (HND) patients who had remained heroin abstinent ( ≥ 3 months), nicotine-dependent (ND) subjects, and healthy controls (C). The domains included emotion recognition, inhibition, shifting, updating, access, and processing speed. Resting-state functional connectivity (rsFC), ToM task-induced functional connectivity, and brain networks were then explored among 21 matched subjects using functional near-infrared spectroscopy. HND enhanced the severities of anxiety, depression, and hyperactivity. Inhibition domain was impaired in both HND and ND. No impairment in domains of emotion recognition, access, and update was observed. HND demonstrated enhanced rsFC in the medial prefrontal cortex and orbitofrontal cortex (OFC) and decreased ToM-induced connectivity across the PFC. The right superior frontal gyrus in the OFC (oSFG; x = 22 , y = 77 , and z = 6 ) was associated with working memory and emotion recognition in HND. Using a neuroimaging tool, these results supported the prominent reward-deficit-and-stress-surfeit hypothesis in SUDs, especially OUD, after protracted withdrawal. This may provide an insight in identifying potential biomarkers related to a dynamic environment.

Complementary and Alternative Medicine Strategies for Therapeutic Gut Microbiota Modulation in Inflammatory Bowel Disease and their Next-Generation Approaches

The human gut microbiome exerts a major impact on human health and disease, and therapeutic gut microbiota modulation is now a well-advocated strategy in the management of many diseases, including inflammatory bowel disease (IBD). Scientific and clinical evidence in support of complementary and alternative medicine, in targeting intestinal dysbiosis among patients with IBD, or other disorders, has increased dramatically over the past years. Delivery of "artificial" stool replacements for fecal microbiota transplantation (FMT) could provide an effective, safer alternative to that of human donor stool. Nevertheless, optimum timing of FMT administration in IBD remains unexplored, and future investigations are essential.

The Role of the Endocannabinoid System in the Brain-Gut Axis

The actions of cannabis are mediated by receptors that are part of an endogenous cannabinoid system. The endocannabinoid system (ECS) consists of the naturally occurring ligands N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), their biosynthetic and degradative enzymes, and the cannabinoid (CB) receptors CB1 and CB2. The ECS is a widely distributed transmitter system that controls gut functions peripherally and centrally. It is an important physiologic regulator of gastrointestinal motility. Polymorphisms in the gene encoding CB1 (CNR1) have been associated with some forms of irritable bowel syndrome. The ECS is involved in the control of nausea and vomiting and visceral sensation. The homeostatic role of the ECS also extends to the control of intestinal inflammation. We review the mechanisms by which the ECS links stress and visceral pain. CB1 in sensory ganglia controls visceral sensation, and transcription of CNR1 is modified through epigenetic processes under conditions of chronic stress. These processes might link stress with abdominal pain. The ECS is also involved centrally in the manifestation of stress, and endocannabinoid signaling reduces the activity of hypothalamic-pituitary-adrenal pathways via actions in specific brain regions, notably the prefrontal cortex, amygdala, and hypothalamus. Agents that modulate the ECS are in early stages of development for treatment of gastrointestinal diseases. Increasing our understanding of the ECS will greatly advance our knowledge of interactions between the brain and gut and could lead to new treatments for gastrointestinal disorders.

Endocannabinoids in the Gut

Cannabis has been used medicinally for centuries to treat a variety of disorders, including those associated with the gastrointestinal tract. The discovery of our bodies' own "cannabis-like molecules" and associated receptors and metabolic machinery - collectively called the endocannabinoid system - enabled investigations into the physiological relevance for the system, and provided the field with evidence of a critical function for this endogenous signaling pathway in health and disease. Recent investigations yield insight into a significant participation for the endocannabinoid system in the normal physiology of gastrointestinal function, and its possible dysfunction in gastrointestinal pathology. Many gaps, however, remain in our understanding of the precise neural and molecular mechanisms across tissue departments that are under the regulatory control of the endocannabinoid system. This review highlights research that reveals an important - and at times surprising - role for the endocannabinoid system in the control of a variety of gastrointestinal functions, including motility, gut-brain mediated fat intake and hunger signaling, inflammation and gut permeability, and dynamic interactions with gut microbiota.

Cannabinoid Receptors in Regulating the GI Tract: Experimental Evidence and Therapeutic Relevance

Cannabinoid receptors are fundamentally involved in all aspects of intestinal physiology, such as motility, secretion, and epithelial barrier function. They are part of a broader entity, the so-called endocannabinoid system which also includes their endocannabinoid ligands and the ligands' synthesizing/degrading enzymes. The system has a strong impact on the pathophysiology of the gastrointestinal tract and is believed to maintain homeostasis in the gut by controlling hypercontractility and by promoting regeneration after injury. For instance, genetic knockout of cannabinoid receptor 1 leads to inflammation and cancer of the intestines. Derivatives of Δ⁹-tetrahydrocannabinol, such as nabilone and dronabinol, activate cannabinoid receptors and have been introduced into the clinic to treat chemotherapy-induced emesis and loss of appetite; however, they may cause many psychotropic side effects. New drugs that interfere with endocannabinoid degradation to raise endocannabinoid levels circumvent this obstacle and could be used in the future to treat emesis, intestinal inflammation, and functional disorders associated with visceral hyperalgesia.