“Cannabis has been used for more than twelve thousand years and for many different purposes (i.e. fiber, medicinal, recreational). However, the endocannabinoid signaling system has only recently been the focus of medical research and considered a potential therapeutic target. Endocannabinoids … Continue reading
Tag Archives: endocannabinoids
Cannabinoid 1 (CB1) receptor–pharmacology, role in pain and recent developments in emerging CB1 agonists.
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Abstract
“Cannabinoids are antinociceptive in animal models of acute pain, tissue injury and nerve injury induced nociception and act via their cognate receptors, cannabinoid receptor 1 and 2. This review examines the underlying biology of the endocannabinoids and behavioural, neurophysiological, neuroanatomical evidence supporting the notion of pain modulation by these ligands with a focus on the current evidence encompassing the pharmacological characterization of CB1 agonists in this therapy. Separating the psychotropic effects of CB1 agonists from their therapeutic benefits is the major challenge facing researchers in the field today and with the discovery of peripherally acting agonists there seems to be a ray of hope emerging for the diverse potential therapeutic applications of this class of ligands.”
Targeting CB2 receptors and the endocannabinoid system for the treatment of pain.
Abstract
“The endocannabinoid system consists of the cannabinoid (CB) receptors, CB(1) and CB(2), the endogenous ligands anandamide (AEA, arachidonoylethanolamide) and 2-arachidonoylglycerol (2-AG), and their synthetic and metabolic machinery. The use of cannabis has been described in classical and recent literature for the treatment of pain, but the potential for psychotropic effects as a result of the activation of central CB(1) receptors places a limitation upon its use. There are, however, a number of modern approaches being undertaken to circumvent this problem, and this review represents a concise summary of these approaches, with a particular emphasis upon CB(2) receptor agonists. Selective CB(2) agonists and peripherally restricted CB(1) or CB(1)/CB(2) dual agonists are being developed for the treatment of inflammatory and neuropathic pain, as they demonstrate efficacy in a range of pain models. CB(2) receptors were originally described as being restricted to cells of immune origin, but there is evidence for their expression in human primary sensory neurons, and increased levels of CB(2) receptors reported in human peripheral nerves have been seen after injury, particularly in painful neuromas. CB(2) receptor agonists produce antinociceptive effects in models of inflammatory and nociceptive pain, and in some cases these effects involve activation of the opioid system. In addition, CB receptor agonists enhance the effect of mu-opioid receptor agonists in a variety of models of analgesia, and combinations of cannabinoids and opioids may produce synergistic effects. Antinociceptive effects of compounds blocking the metabolism of anandamide have been reported, particularly in models of inflammatory pain. There is also evidence that such compounds increase the analgesic effect of non-steroidal anti-inflammatory drugs (NSAIDs), raising the possibility that a combination of suitable agents could, by reducing the NSAID dose needed, provide an efficacious treatment strategy, while minimizing the potential for NSAID-induced gastrointestinal and cardiovascular disturbances. Other potential “partners” for endocannabinoid modulatory agents include alpha(2)-adrenoceptor modulators, peroxisome proliferator-activated receptor alpha agonists and TRPV1 antagonists. An extension of the polypharmacological approach is to combine the desired pharmacological properties of the treatment within a single molecule. Hopefully, these approaches will yield novel analgesics that do not produce the psychotropic effects that limit the medicinal use of cannabis.”
From cannabis to the endocannabinoid system: refocussing attention on potential clinical benefits.
“Cannabis sativa is one of the oldest herbal remedies known to man. Over the past four thousand years, it has been used for the treatment of numerous diseases but due to its psychoactive properties, its current medicinal usage is highly restricted. In this review, we seek to highlight advances made over the last forty years in the understanding of the mechanisms responsible for the effects of cannabis on the human body and how these can potentially be utilized in clinical practice. During this time, the primary active ingredients in cannabis have been isolated, specific cannabinoid receptors have been discovered and at least five endogenous cannabinoid neurotransmitters (endocannabinoids) have been identified. Together, these form the framework of a complex endocannabinoid signalling system that has widespread distribution in the body and plays a role in regulating numerous physiological processes within the body. Cannabinoid ligands are therefore thought to display considerable therapeutic potential and the drive to develop compounds that can be targeted to specific neuronal systems at low enough doses so as to eliminate cognitive side effects remains the ‘holy grail’ of endocannabinoid research.”
Cannabinoid type 1 receptor antagonism delays ascites formation in rats with cirrhosis.
“Endocannabinoids contribute to hemodynamic abnormalities of cirrhosis. Whether this favors renal sodium retention and ascites formation is unknown. We determined whether cannabinoid type 1 receptor antagonism prevents sodium retention and ascites formation in preascitic cirrhotic rats.”
“Cannabinoid type 1 receptor antagonism delays ascites formation in rats with cirrhosis.”
“Rimonabant improves sodium balance and delays decompensation in preascitic cirrhosis. This is achieved though an improvement in systemic and renal hemodynamics, although it cannot be excluded that the antifibrotic effect of the drug may play a role.”
Endocannabinoids as novel mediators of liver diseases.
Abstract
“In the past two decades, cannabinoids have emerged as crucial mediators in a variety of pathophysiological conditions. Awareness of their critical functions in liver pathophysiology is only recent, probably given the low level of expression of cannabinoid receptor type 1 (CB1 receptor) and type 2 (CB2 receptor) in normal liver. However, it has been shown that non-alcoholic fatty liver disease and cirrhosis are associated to a marked upregulation of the hepatic endocannabinoid system, including increases in endocannabinoids and in hepatic CB receptors, both in humans and in rodents. Consequently, a growing number of cannabinoid-related hepatic effects are being unravelled. Hence, hepatic CB1 receptors enhance liver steatogenesis in a mouse model of high fat-induced obesity, and contribute to peripheral arterial vasodilation in cirrhosis, thereby promoting portal hypertension. In addition, CB1 and CB2 receptors elicit dual opposite effects on fibrogenesis associated to chronic liver injury, by promoting pro- and antifibrogenic effects, respectively. Therefore, endocannabinoid-based therapies may open novel therapeutic avenues in the treatment of chronic liver diseases.”
Endocannabinoids in Liver Disease.
“Marijuana has been used for its psychoactive and medicinal properties for millennia. As other plant-derived substances, marijuana has been slow to yield its secrets, with insights into its mechanism of action beginning to emerge only during the last decades. The existence of specific CB receptors in mammalian tissues was first revealed by radioligand binding, followed by the molecular cloning of two G protein-coupled cannabinoid receptors (1). CB1 receptors are the most abundant receptors in the mammalian brain, but are also expressed in peripheral tissues, including various cell types of the liver, at much lower yet functionally relevant concentrations. CB2 receptors are expressed primarily in immune and hematopoietic cells, and have also been detected in the liver in certain pathological states. Additional CB receptors may exist…”
“Endocannabinoids are lipid mediators of the same cannabinoid (CB) receptors that mediate the effects of marijuana. The endocannabinoid system (ECS) consists of CB receptors, endocannabinoids, and the enzymes involved in their biosynthesis and degradation, and is present both in brain and peripheral tissues, including the liver. The hepatic ECS is activated in various liver diseases, which contributes to the underlying pathologies. In cirrhosis of various etiologies, activation of vascular and cardiac CB1 receptors by macrophage- and platelet-derived endocannabinoids contribute to the vasodilated state and cardiomyopathy, which can be reversed by CB1 blockade. In mouse models of liver fibrosis, activation of CB1 receptors on hepatic stellate cells is fibrogenic, and CB1 blockade slows the progression of fibrosis. Fatty liver induced by high-fat diets or chronic alcohol feeding depend on activation of peripheral, including hepatic CB1 receptors, which also contribute to insulin resistance and dyslipidemias. Although the documented therapeutic potential of CB1 blockade is limited by neuropsychiatric side effects, these may be mitigated by using novel, peripherally restricted CB1 antagonists.”
“Concluding Remarks
The ECS is present in the liver and is involved in the control of various hepatic functions with important therapeutic implications. Increased CB1 activity contributes to the hemodynamic abnormalities and promotes fibrosis in liver cirrhosis, whereas CB1 blockade attenuates and delays these changes. Endocannabinoids acting via hepatic CB1 receptors have emerged as mediators of both diet-induced and alcoholic fatty liver which, together, account for the majority of cirrhosis in Western societies. Additionally, hepatic CB1 activation contributes to obesity-related insulin- and leptin-resistance and dyslipidemias. This provides strong rationale for the therapeutic use of CB1 antagonists in these conditions. Although neuropsychiatric side effects limit the therapeutic potential of brain-penetrant CB1 antagonists, the recent emergence of second generation, peripherally-restricted CB1 antagonists may mitigate this problem. Additionally, non-psychoactive CB2 agonists may offer therapeutic benefit in attenuating liver injury and promoting tissue repair in the fibrotic liver.”
Endocannabinoids and Liver Disease. III. Endocannabinoid effects on immune cells: implications for inflammatory liver diseases
“Recent studies have implicated dysregulation of the endocannabinoid system in various liver diseases and their complications (e.g., hepatitis, fibrosis, cirrhosis, cirrhotic cardiomyopathy, and ischemia-reper-fusion), and demonstrated that its modulation by either cannabinoid 2 (CB2) receptor agonists or CB1 antagonists may be of significant therapeutic benefits. This review is aimed to focus on the triggers and sources of endocannabinoids during liver inflammation and on the novel role of CB2 receptors in the interplay between the activated endothelium and various inflammatory cells (leukocytes, lymphocytes, etc.), which play pivotal role in the early development and progression of inflammatory and other liver diseases.”
“Dysregulation of the endocannabinoid system (ECS) has been implicated in virtually all diseases affecting humans, and its pharmacological modulation holds tremendous promise in the treatment of pain, cancer, and metabolic, cardiovascular, and various inflammatory disorders. Numerous recent studies have linked dysregulation of the ECS to a number of liver diseases including hepatitis, nonalcoholic fatty liver disease, hepatic ischemia-reperfusion (I/R) injury, and liver fibrosis and cirrhosis and its hemo-dynamic consequences. In aggregate these studies have suggested that modulation of the ECS by either CB1 antagonists or CB2 receptor agonists may be of significant therapeutic benefit. This synopsis will focus on sources and triggers of endocannabinoids during liver inflammatory disorders (in both leukocytes and parenchymal cells) and on the novel role of CB2 receptors in the interplay between inflammatory cells and the activated endothelium, which plays a crucial role in the early development and progression of inflammatory liver diseases”.
“Collectively, the studies discussed above emphasize the potential immunoregulatory role of the endocannabinoid system in a variety of inflammatory liver disorders, opening new avenues for their pharmacotherapy. There is considerable interest in the development of selective CB2 receptor agonists, which are devoid of psychoactive properties of CB1 agonists, for various inflammatory disorders. Selective CB2 cannabinoid agonists may protect against hepatic inflammatory disorders by attenuating the endothelial cell activation/inflammatory response (e.g., the expression of adhesion molecules, release of chemotactic factors, inflammatory mediators, etc.) and by decreasing the migration and the adhesion of inflammatory cells to the endothelium, transendothelial migration, adhesion to parenchymal cells and activation, and interrelated oxidativenitrosative stress-inflammatory response. It appears that CB1 antagonists might be beneficial in slowing the progression of liver fibrosis and the neurological decline associated with hepatic encephalopathy, in addition to the attenuation of the adverse hemodynamic consequences of cirrhosis, thus extending life until a suitable liver becomes available for transplantation. CB1 antagonists may also be useful in the treatment of obesity-associated liver diseases and related features of metabolic syndrome by improving dyslipidemia and attenuating systemic and liver inflammation.”
Endocannabinoids and Liver Disease. II. Endocannabinoids in the pathogenesis and treatment of liver fibrosis
“Plant-derived cannabinoids such as delta-9-tetrahydrocannabinol (THC) have been used for medicinal purposes for thousands of years. Two G protein-coupled receptors termed CB1 and CB2 were identified in the early 1990s as receptors for cannabinoids…”
“Hepatic fibrosis is the response of the liver to chronic injury and is associated with portal hypertension, progression to hepatic cirrhosis, liver failure, and high incidence of hepatocellular carcinoma. On a molecular level, a large number of signaling pathways have been shown to contribute to the activation of fibrogenic cell types and the subsequent accumulation of extracellular matrix in the liver. Recent evidence suggests that the endocannabinoid system is an important part of this complex signaling network. In the injured liver, the endocannabinoid system is upregulated both at the level of endocannabinoids and at the endocannabinoid receptors CB1 and CB2. The hepatic endocannabinoid system mediates both pro- and antifibrogenic effects by activating distinct signaling pathways that differentially affect proliferation and death of fibrogenic cell types. Here we will summarize current findings on the role of the hepatic endocannabinoid system in liver fibrosis and discuss emerging options for its therapeutic exploitation.”
“There is overwhelming evidence that the endocannabinoid system plays a major role in the pathophysiology of chronic liver injury and wound healing responses and that modulation of the endocannabinoid system may be exploited for the treatment of liver fibrosis. Among all candidates, CB1 represents the most promising target for antifibrotic therapies. In addition to the antifibrogenic effects of CB1 blockade, one can expect positive effects on other complications such as portal hypertension, ascites formation, hepatic encephalopathy, and cardiomyopathy. Moreover, CB1 antagonism appears to have beneficial effects on hepatic steatosis…”
Endocannabinoids and Liver Disease. I. Endocannabinoids and their receptors in the liver
“The medicinal properties of cannabis (Cannabis sativa, marijuana) have been known for millennia, as shown by reports from China and India underscoring its analgesic, antiemetic, and appetite-stimulating properties. During the 19th century, the prescription of cannabis gained popularity for a variety of conditions ranging from epilepsy to rheumatism and abdominal symptoms. Concerns about abuse led to discontinuation of therapeutic use in the 1940s. The characterization of marijuana-derived bioactive molecules began during the early 20th century with the identification of several hydrophobic compounds and culminated in 1964 with the isolation of Δ9-tetrahydrocannabinol (THC), the main psychoactive constituent of the plant. Subsequent studies identified over 60 other phytocannabinoids and allowed the synthesis of active analogs with varying potencies. This step was critical in the identification of the endocannabinoid system, comprising specific cannabinoid binding sites (CB1 and CB2), their endogenous ligands (endocannabinoids), and synthetic and degradative pathways.”
“Cannabinoid receptors (CB1 and CB2) and their endogenous ligands (endocannabinoids) have recently emerged as novel mediators of liver diseases. Endogenous activation of CB1 receptors promotes nonalcoholic fatty liver disease (NAFLD) and progression of liver fibrosis associated with chronic liver injury; in addition, CB1 receptors contribute to the pathogenesis of portal hypertension and cirrhotic cardiomyopathy. CB2 receptor-dependent effects are also increasingly characterized, including antifibrogenic effects and regulation of liver inflammation during ischemia-reperfusion and NAFLD. It is likely that the next few years will allow us to delineate whether molecules targeting CB1 and CB2 receptors are useful therapeutic agents for the treatment of chronic liver diseases.”