Tag Archives: CB(1) and CB(2) receptors

Endocannabinoids and Liver Disease. III. Endocannabinoid effects on immune cells: implications for inflammatory liver diseases

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  “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.”

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2376822/

Endocannabinoids and Liver Disease. II. Endocannabinoids in the pathogenesis and treatment of liver fibrosis

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“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…”

http://ajpgi.physiology.org/content/294/2/G357.long

Endocannabinoids and Liver Disease. I. Endocannabinoids and their receptors in the liver

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  “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.”

http://ajpgi.physiology.org/content/294/1/G9.long

The role of the endocannabinoid system in liver diseases.

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Abstract

“Endogenous cannabinoids (ECs) are ubiquitous lipid signaling molecules provided by a number of central and peripheral effects, which are mediated mainly by the specific receptors CB1 and CB2. In the last decade a considerable number of studies has shown that ECs and their receptors play an important role in the pathophysiology of liver diseases. The EC system is strongly up-regulated during chronic liver diseases. Until now it has been implicated in the pathogenesis of fatty liver disease associated with obesity, alcohol abuse, and hepatitis C, in the progression of fibrosis to cirrhosis, and in the development of portal hypertension, hyperdynamic circulatory syndrome and its complications, and cirrhotic cardiomyopathy. Furthermore, the EC system can participate in the pathogenesis of acute liver injury by modulating the mechanisms responsible for cell injury and inflammatory response. Thus, targeting the CB1 and CB2 receptors represents a potential therapeutic goal for the treatment of liver diseases.”

http://www.ncbi.nlm.nih.gov/pubmed/19285261

Cannabinoid receptors as new targets of antifibrosing strategies during chronic liver diseases.

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Abstract

“Chronic liver injury exposes the patient to liver fibrosis and its end stage, cirrhosis, is a major public health problem worldwide. In western countries, prevailing causes of cirrhosis include chronic alcohol consumption, hepatitis C virus infection and non-alcoholic steatohepatitis. Current treatment of hepatic fibrosis is limited to withdrawal of the noxious agent. Nevertheless, suppression of the cause of hepatic injury is not always feasible and numerous efforts are directed at the development of liver-specific antifibrotic therapies. Along these lines, the authors recently demonstrated that the endocannabinoid system shows promise as a novel target for antifibrotic therapy during chronic liver injury. Indeed, cannabinoid receptors CB1 and CB2 promote dual pro- and antifibrogenic effects, respectively. Therefore, endocannabinoid-based therapies, combining CB2 agonists and CB1 antagonists may open novel therapeutic perspectives for the treatment of chronic liver diseases.”

http://www.ncbi.nlm.nih.gov/pubmed/17298297

[The endocannabinoid system as a novel target for the treatment of liver fibrosis].

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Abstract

 “The cannabinoid system comprises specific G protein-coupled receptors (CB1 and CB2), exogenous (marijuana-derived cannabinoids) and endogenous (endocannabinoids) ligands, and a machinery dedicated to endocannabinoid synthesis and degradation. Studies over two decades have extensively documented the crucial role of the cannabinoid system in the regulation of a variety of pathophysiological conditions. However, its role in liver pathology has only been recently unravelled, probably given the low expression of CB1 and CB2 in the normal liver. We have recently demonstrated that CB1 and CB2 receptors display opposite effects in the regulation of liver fibrogenesis during chronic liver injury. Indeed, both receptors are up-regulated in the liver of cirrhotic patients, and expressed in liver fibrogenic cells. Moreover, CB1 receptors are profibrogenic and accordingly, the CB1 antagonist rimonabant reduces fibrosis progression in three experimental models. In keeping with these results, daily cannabis smoking is a risk factor for fibrosis progression in patients with chronic hepatitis C. In contrast, CB2 display antifibrogenic effects, by a mechanism involving reduction of liver fibrogenic cell accumulation. These results may offer new perspectives for the treatment of liver fibrosis, combining CB2 agonist and CB1 antagonist therapy.”

http://www.ncbi.nlm.nih.gov/pubmed/17412522

Attenuation of Experimental Autoimmune Hepatitis by Exogenous and Endogenous Cannabinoids: Involvement of Regulatory T Cells

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“The endocannabinoid system plays a protective role in various inflammatory diseases, and it is considered an attractive therapeutic target.”

“The aim of the present study was to determine the immunomodulatory effect of THC in the murine model of ConA-induced hepatitis. We demonstrate that a single injection of THC significantly ameliorates ConA-induced T-cell-mediated liver injury by up-regulating Forkhead helix transcription factor p3 (Foxp3)+ regulatory T cells and down-regulating inflammatory cytokines. Using select cannabinoid receptor agonists and antagonists, we demonstrate that THC mediates immune modulation in this model by signaling through both CB1 and CB2 receptors. We also demonstrate that anandamide, an endocannabinoid can effectively attenuate the disease.”

“There is growing interest in recent years to target cannabinoid receptors for treating liver diseases. In the current study, CB1 or CB2 activation alone had no anti-inflammatory effect on hepatitis. However, cannabinoids that bind to both CB1 and CB2 receptors (THC, CP55,940, WIN55212, and anandamide) effectively attenuated hepatitis. That CB1/CB2 mixed agonists could suppress the disease but not the coadministered CB1 and CB2 agonists indicates that both the cannabinoid receptors need to be activated simultaneously to produce the observed effect and that the different pharmacokinetics of the two coadministered agonists may not allow this to happen. Signaling through both the receptors is important because blocking either CB1 or CB2 could reverse the effect of THC.”

“Taken together, our data suggest that exogenous cannabinoids such as THC upon binding to CB1 and CB2 receptors on immune cells, induce apoptosis in effector T cells, up-regulate Treg function, and suppress inflammatory cytokines there by preventing ConA-induced activated T-cell-mediated liver injury. The observation that the anandamide treatment ameliorates ConA-induced hepatitis, together with FAAH deficiency or inhibition leading to increased resistance to the disease, strongly suggests that the endocannabinoid system serves to attenuate the inflammatory response in ConA-induced acute hepatitis. These findings raise the promising potential of developing novel pharmacological treatments for T-cell-mediated liver diseases.”

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2828293/

Use of cannabinoids as a novel therapeutic modality against autoimmune hepatitis.

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Abstract

“Autoimmune hepatitis is a severe immune mediated chronic liver disease with a prevalence range between 50 and 200 cases per million in Western Europe and North America and mortality rates of up to 80% in untreated patients. The induction of CB1 and CB2 cannabinoid receptors during liver injury and the potential involvement of endocannabinoids in the regulation of this process have sparked significant interest in further evaluating the role of cannabinoid systems during hepatic disease. Cannabinoids have been shown to possess significant immunosuppressive and anti-inflammatory properties. Cannabinoid abuse has been shown to exacerbate liver fibrogenesis in patients with chronic hepatitis C infection involving CB1 receptor. Nonetheless, CB2 receptor activation may play a protective role during chronic liver diseases. Thus, differential targeting of cannabinoid receptors may provide novel therapeutic modality against autoimmune hepatitis. In this review, we summarize current knowledge on the role of endocannabinoids and exocannabinoids in the regulation of autoimmune hepatitis.”

http://www.ncbi.nlm.nih.gov/pubmed/19647124

Alterations in endocannabinoid tone following chemotherapy-induced peripheral neuropathy: Effects of endocannabinoid deactivation inhibitors targeting fatty-acid amide hydrolase and monoacylglycerol lipase in comparison to reference analgesics following cisplatin treatment.

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Abstract

“Cisplatin, a platinum-derived chemotherapeutic agent, produces mechanical and cold allodynia reminiscent of chemotherapy-induced neuropathy in humans. The endocannabinoid system represents a novel target for analgesic drug development. The endocannabinoid consists of endocannabinoids (e.g. anandamide (AEA) and 2-arachidonoylglycerol (2-AG)), cannabinoid receptors (e.g. CB(1) and CB(2)) and the enzymes controlling endocannabinoid synthesis and degradation. AEA is hydrolyzed by fatty-acid amide hydrolase (FAAH) whereas 2-AG is hydrolyzed primarily by monoacylglycerol lipase (MGL). We compared effects of brain permeant (URB597) and impermeant (URB937) inhibitors of FAAH with an irreversible inhibitor of MGL (JZL184) on cisplatin-evoked behavioral hypersensitivities. Endocannabinoid modulators were compared with agents used clinically to treat neuropathy (i.e. the opioid analgesic morphine, the anticonvulsant gabapentin and the tricyclic antidepressant amitriptyline). Cisplatin produced robust mechanical and cold allodynia but did not alter responsiveness to heat. After neuropathy was fully established, groups received acute intraperitoneal (i.p.) injections of vehicle, amitriptyline (30mg/kg), gabapentin (100mg/kg), morphine (6mg/kg), URB597 (0.1 or 1mg/kg), URB937 (0.1 or 1mg/kg) or JZL184 (1, 3 or 8mg/kg). Pharmacological specificity was assessed by coadministering each endocannabinoid modulator with either a CB(1) (AM251 3mg/kg), CB(2) (AM630 3mg/kg), TRPV1 (AMG9810 3mg/kg) or TRPA1 (HC030031 8mg/kg) antagonist. Effects of cisplatin on endocannabinoid levels and transcription of receptors (CB(1), CB(2), TRPV1, TRPA1) and enzymes (FAAH, MGL) linked to the endocannabinoid system were also assessed. URB597, URB937, JZL184 and morphine reversed cisplatin-evoked mechanical and cold allodynia to pre-cisplatin levels. By contrast, gabapentin only partially reversed the neuropathy while amitriptyline, administered acutely, was ineffective. CB(1) or CB(2) antagonist completely blocked the anti-allodynic effects of both FAAH (URB597, URB937) and MGL (JZL184) inhibitors to mechanical and cold stimulation, while TRPV1 antagonist AMG9810 blocked only the anti-allodynic efficacy of both FAAH inhibitors, but not the MGL inhibitor. By contrast, the TRPA1 antagonist HC30031 did not attenuate anti-allodynic efficacy of any endocannabinoid modulator. When the levels of endocannabinoids were examined, cisplatin increased both anandamide (AEA) and 2-arachidonoylglycerol (2-AG) levels in the lumbar spinal cord and decreased 2-AG levels (but not AEA) in dorsal hind paw skin. RT-PCR showed that mRNA for FAAH, but not other markers, was upregulated by cisplatin treatment in dorsal root ganglia. The present studies demonstrate that cisplatin alters endocannabinoid tone and that inhibition of endocannabinoid hydrolysis alleviates chemotherapy-induced mechanical and cold allodynia. The anti-allodynic effects of FAAH and MGL inhibitors are mediated by CB(1) and CB(2) cannabinoid receptors, whereas TRPV1, but not TRPA1, -dependent mechanisms contribute to the anti-allodynic efficacy of FAAH (but not MGL) inhibitors. Strikingly, endocannabinoid modulators potently suppressed cisplatin-evoked allodynia with a rapid onset and showed efficacy that equaled or exceeded that of major classes of anti-neuropathic pain medications used clinically. Thus, inhibition of endocannabinoid hydrolysis, via FAAH or MGL inhibitors, represents an efficacious pharmacological approach for suppressing chemotherapy-induced neuropathic pain.”

http://www.ncbi.nlm.nih.gov/pubmed/23127915

 

Inhibitors of monoacylglycerol lipase, fatty-acid amide hydrolase and endocannabinoid transport differentially suppress capsaicin-induced behavioral sensitization through peripheral endocannabinoid mechanisms

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 “Monoacylglycerol lipase (MGL) and fatty acid amide hydrolase (FAAH) degrade the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide (AEA), respectively… peripheral inhibition of enzymes hydrolyzing 2-AG and AEA suppresses capsaicin-evoked behavioral sensitization with distinct patterns of pharmacological specificity… Modulation of endocannabinoids in the periphery suppressed capsaicin-evoked nocifensive behavior and thermal hyperalgesia through either CB1 or CB2 receptor mechanisms but suppressed capsaicin-evoked mechanical allodynia through CB1 mechanisms only. Inhibition of endocannabinoid transport was more effective in suppressing capsaicin-induced sensitization compared to inhibition of either FAAH or MGL alone. These studies are the first to unveil the effects of pharmacologically increasing peripheral endocannabinoid levels on capsaicin-induced behavioral hypersensitivities. Our data suggest that 2-AG, the putative product of MGL inhibition, and AEA, the putative product of FAAH inhibition, differentially suppress capsaicin-induced nociception through peripheral cannabinoid mechanisms.”

“Cannabis has been used for centuries for its pain-relieving properties. The main active ingredient of cannabis, Δ9-tetrahydrocannabinol, produces antinociception by binding to G protein-coupled CB1 and CB2 receptors. Cannabinoids produce antinociception in animal models of both acute and chronic pain.”

Read more: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2900457/