Endocannabinoids acting via CB1 receptors (CB1R) play a critical role in regulating energy homeostasis, which was the rationale for the pharmaceutical development of CB1R antagonists for the ...treatment of obesity. Although the first-in-class CB1R antagonist rimonabant proved to be effective in mitigating obesity and its multiple cardiometabolic complications, it was withdrawn from clinical use due to CNS-mediated neuropsychiatric side effects, which halted the further therapeutic development of the whole class of these compounds. Compared to the brain, CB1Rs are expressed at low yet functional levels in peripheral organs involved in regulating energy homeostasis, including liver, skeletal muscle, adipose tissue and endocrine pancreas. In recent preclinical studies, selective targeting of these receptors by ‘second generation’ peripherally restricted CB1R antagonists replicated the metabolic benefits of rimonabant in rodent models of obesity and diabetes without causing CNS-mediated side effects. Increased CB1R activity also contributes to complex, multifactorial disorders such as various forms of tissue fibrosis, treatment of which may benefit from simultaneous engagement of more than one therapeutic target. Accordingly, novel ‘third generation’ hybrid inhibitors of peripheral CB1R and inducible NO synthase were tested in mouse models of liver and pulmonary fibrosis where their antifibrotic efficacy was found to exceed the efficacy of drugs that inhibit only one of these targets. In this review, we will discuss the challenges and opportunities offered by second and third generation CB1R antagonists and their potential therapeutic uses.
The cannabinoid receptor CB2 is predominately expressed in the immune system, and selective modulation of CB2 without the psychoactivity of CB1 has therapeutic potential in inflammatory, fibrotic, ...and neurodegenerative diseases. Here, we report the crystal structure of human CB2 in complex with a rationally designed antagonist, AM10257, at 2.8 Å resolution. The CB2-AM10257 structure reveals a distinctly different binding pose compared with CB1. However, the extracellular portion of the antagonist-bound CB2 shares a high degree of conformational similarity with the agonist-bound CB1, which led to the discovery of AM10257’s unexpected opposing functional profile of CB2 antagonism versus CB1 agonism. Further structural analysis using mutagenesis studies and molecular docking revealed the molecular basis of their function and selectivity for CB2 and CB1. Additional analyses of our designed antagonist and agonist pairs provide important insight into the activation mechanism of CB2. The present findings should facilitate rational drug design toward precise modulation of the endocannabinoid system.
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•Crystal structure of human CB2 in complex with antagonist AM10257 is determined•A high degree of conformational similarity with the agonist-bound CB1 is uncovered•The yin-yang relationship of CB2 and CB1 will facilitate the design of selective drugs
The structure of the human cannabinoid receptor CB2 reveals how small molecules affect CB2 differently than CB1 and point to principles that could inform rational and selective drug design.
Obesity-related structural and functional changes in the kidney develop early in the course of obesity and occur independently of hypertension, diabetes, and dyslipidemia. Activating the renal ...cannabinoid-1 receptor (CB
R) induces nephropathy, whereas CB
R blockade improves kidney function. Whether these effects are mediated
a specific cell type within the kidney remains unknown. Here, we show that specific deletion of CB
R in the renal proximal tubule cells did not protect the mice from obesity, but markedly attenuated the obesity-induced lipid accumulation in the kidney and renal dysfunction, injury, inflammation, and fibrosis. These effects associated with increased activation of liver kinase B1 and the energy sensor AMP-activated protein kinase, as well as enhanced fatty acid
-oxidation. Collectively, these findings indicate that renal proximal tubule cell CB
R contributes to the pathogenesis of obesity-induced renal lipotoxicity and nephropathy by regulating the liver kinase B1/AMP-activated protein kinase signaling pathway.
Type 2 diabetes mellitus (T2DM) progresses from compensated insulin resistance to beta cell failure resulting in uncompensated hyperglycemia, a process replicated in the Zucker diabetic fatty (ZDF) ...rat. The Nlrp3 inflammasome has been implicated in obesity-induced insulin resistance and beta cell failure. Endocannabinoids contribute to insulin resistance through activation of peripheral CB1 receptors (CB₁Rs) and also promote beta cell failure. Here we show that beta cell failure in adult ZDF rats is not associated with CB₁R signaling in beta cells, but rather in M1 macrophages infiltrating into pancreatic islets, and that this leads to activation of the Nlrp3-ASC inflammasome in the macrophages. These effects are replicated in vitro by incubating wild-type human or rodent macrophages, but not macrophages from CB₁R-deficient (Cnr1(-/-)) or Nlrp3(-/-) mice, with the endocannabinoid anandamide. Peripheral CB₁R blockade, in vivo depletion of macrophages or macrophage-specific knockdown of CB₁R reverses or prevents these changes and restores normoglycemia and glucose-induced insulin secretion. These findings implicate endocannabinoids and inflammasome activation in beta cell failure and identify macrophage-expressed CB₁R as a therapeutic target in T2DM.
Signaling through integral membrane G protein-coupled receptors (GPCRs) is influenced by lipid composition of cell membranes. By using novel high affinity ligands of human cannabinoid receptor CB2, ...we demonstrate that cholesterol increases basal activation levels of the receptor and alters the pharmacological categorization of these ligands. Our results revealed that (2-(6-chloro-2-((2,2,3,3-tetramethylcyclopropane-1-carbonyl)imino)benzodthiazol-3(2H)-yl)ethyl acetate ligand (MRI-2646) acts as a partial agonist of CB2 in membranes devoid of cholesterol and as a neutral antagonist or a partial inverse agonist in cholesterol-containing membranes. The differential effects of a specific ligand on activation of CB2 in different types of membranes may have implications for screening of drug candidates in a search of modulators of GPCR activity. MD simulation suggests that cholesterol exerts an allosteric effect on the intracellular regions of the receptor that interact with the G-protein complex thereby altering the recruitment of G protein.
Drug addictions including alcoholism are characterized by degradation of executive control over behavior and increased compulsive drug seeking. These profound behavioral changes are hypothesized to ...involve a shift in the regulation of behavior from prefrontal cortex to dorsal striatum (DLS). Studies in rodents have shown that ethanol disrupts cognitive processes mediated by the prefrontal cortex, but the potential effects of chronic ethanol on DLS-mediated cognition and learning are much less well understood. Here, we first examined the effects of chronic EtOH on DLS neuronal morphology, synaptic plasticity, and endocannabinoid-CB1R signaling. We next tested for ethanol-induced changes in striatal-related learning and DLS in vivo single-unit activity during learning. Mice exposed to chronic intermittent ethanol (CIE) vapor exhibited expansion of dendritic material in DLS neurons. Following CIE, DLS endocannabinoid CB1 receptor signaling was down-regulated, and CB1 receptor-dependent long-term depression at DLS synapses was absent. CIE mice showed facilitation of DLS-dependent pairwise visual discrimination and reversal learning, relative to air-exposed controls. CIE mice were also quicker to extinguish a stimulus–reward instrumental response and faster to reduce Pavlovian approach behavior under an omission schedule. In vivo single-unit recording during learning revealed that CIE mice had augmented DLS neuronal activity during correct responses. Collectively, these findings support a model in which chronic ethanol causes neuroadaptations in the DLS that prime for greater DLS control over learning. The shift to striatal dominance over behavior may be a critical step in the progression of alcoholism.
Hepatocellular carcinoma (HCC) is a deadly form of liver cancer that is increasingly prevalent. We analyzed global gene expression profiling of 361 HCC tumors and 49 adjacent noncancerous liver ...samples by means of combinatorial network-based analysis. We investigated the correlation between transcriptome and proteome of HCC and reconstructed a functional genome-scale metabolic model (GEM) for HCC. We identified fundamental metabolic processes required for cell proliferation using the network centric view provided by the GEM. Our analysis revealed tight regulation of fatty acid biosynthesis (FAB) and highly significant deregulation of fatty acid oxidation in HCC. We predicted mitochondrial acetate as an emerging substrate for FAB through upregulation of mitochondrial acetyl-CoA synthetase (ACSS1) in HCC. We analyzed heterogeneous expression of ACSS1 and ACSS2 between HCC patients stratified by high and low ACSS1 and ACSS2 expression and revealed that ACSS1 is associated with tumor growth and malignancy under hypoxic conditions in human HCC.
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•Reconstruction of a genome-scale metabolic model for HCC tumors•Revealing metabolic alterations in HCC•Analysis of the heterogeneous expression of ACSS1 and ACSS2 between HCC tumors•Induction of ACSS1 in murine and human HCC samples under hypoxic conditions
Stratification of HCC patients is vital for the development of effective treatment strategies. Björnson et al. stratify HCC patients based on acetate utilization and find that mitochondrial acetate is a metabolic fuel under hypoxic conditions. This is mediated by ACSS1, which may be a potential therapeutic target for treatment of HCC.
Significance Diabetic nephropathy is the leading cause of chronic kidney disease in the United States, and one of the most significant long-term complications of both type 1 and type 2 diabetes, ...which currently lack fully effective therapy. Hyperglycemia and activation of the renin-angiotensin system (RAS) are thought to be the two main drivers of this pathology. We have recently shown that selective blockade of peripheral cannabinoid receptor-1 (CB ₁R) delayed and attenuated the development of type 2 diabetes in a rat model. Here we show that the nephropathy-inducing effects of both hyperglycemia and activation of the RAS involve CB ₁R activation in glomerular podocytes, and that antagonism of peripheral CB ₁R could represent a novel, effective, and rational approach to both prevent and reverse diabetic nephropathy.
Diabetic nephropathy is a major cause of end-stage kidney disease, and overactivity of the endocannabinoid/cannabinoid 1 receptor (CB ₁R) system contributes to diabetes and its complications. Zucker diabetic fatty (ZDF) rats develop type 2 diabetic nephropathy with albuminuria, reduced glomerular filtration, activation of the renin-angiotensin system (RAS), oxidative/nitrative stress, podocyte loss, and increased CB ₁R expression in glomeruli. Peripheral CB ₁R blockade initiated in the prediabetic stage prevented these changes or reversed them when animals with fully developed diabetic nephropathy were treated. Treatment of diabetic ZDF rats with losartan, an angiotensin II receptor-1 (Agtr1) antagonist, attenuated the development of nephropathy and down-regulated renal cortical CB ₁R expression, without affecting the marked hyperglycemia. In cultured human podocytes, CB ₁R and desmin gene expression were increased and podocin and nephrin content were decreased by either the CB ₁R agonist arachydonoyl-2′-chloroethylamide, angiotensin II, or high glucose, and the effects of all three were antagonized by CB ₁R blockade or siRNA-mediated knockdown of CNR1 (the cannabinoid type 1 receptor gene). We conclude that increased CB ₁R signaling in podocytes contributes to the development of diabetic nephropathy and represents a common pathway through which both hyperglycemia and increased RAS activity exert their deleterious effects, highlighting the therapeutic potential of peripheral CB ₁R blockade.
Hepatocellular carcinoma (HCC) has high mortality and no adequate treatment. Endocannabinoids interact with hepatic cannabinoid 1 receptors (CB1Rs) to promote hepatocyte proliferation in liver ...regeneration by inducing cell cycle proteins involved in mitotic progression, including Forkhead Box M1. Because this protein is highly expressed in HCC and contributes to its genesis and progression, we analyzed the involvement of the endocannabinoid/CB1R system in murine and human HCC. Postnatal diethylnitrosamine treatment induced HCC within 8 months in wild‐type mice but fewer and smaller tumors in CB1R–/– mice or in wild‐type mice treated with the peripheral CB1R antagonist JD5037, as monitored in vivo by serial magnetic resonance imaging. Genome‐wide transcriptome analysis revealed CB1R‐dependent, tumor‐induced up‐regulation of the hepatic expression of CB1R, its endogenous ligand anandamide, and a number of tumor‐promoting genes, including the GRB2 interactome as well as Forkhead Box M1 and its downstream target, the tryptophan‐catalyzing enzyme indoleamine 2,3‐dioxygenase. Increased indoleamine 2,3‐dioxygenase activity and consequent induction of immunosuppressive T‐regulatory cells in tumor tissue promote immune tolerance. Conclusion: The endocannabinoid/CB1R system is up‐regulated in chemically induced HCC, resulting in the induction of various tumor‐promoting genes, including indoleamine 2,3‐dioxygenase; and attenuation of these changes by blockade or genetic ablation of CB1R suppresses the growth of HCC and highlights the therapeutic potential of peripheral CB1R blockade. (Hepatology 2015;61:1615–1626)
Obesity-related leptin resistance manifests in loss of leptin’s ability to reduce appetite and increase energy expenditure. Obesity is also associated with increased activity of the endocannabinoid ...system, and CB1 receptor (CB1R) inverse agonists reduce body weight and the associated metabolic complications, although adverse neuropsychiatric effects halted their therapeutic development. Here we show that in mice with diet-induced obesity (DIO), the peripherally restricted CB1R inverse agonist JD5037 is equieffective with its brain-penetrant parent compound in reducing appetite, body weight, hepatic steatosis, and insulin resistance, even though it does not occupy central CB1R or induce related behaviors. Appetite and weight reduction by JD5037 are mediated by resensitizing DIO mice to endogenous leptin through reversing the hyperleptinemia by decreasing leptin expression and secretion by adipocytes and increasing leptin clearance via the kidney. Thus, inverse agonism at peripheral CB1R not only improves cardiometabolic risk in obesity but has antiobesity effects by reversing leptin resistance.
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► Peripheral CB1 receptor inverse agonist reduces obesity and its metabolic sequelae ► Peripheral CB1 blockade reduces food intake and body weight via endogenous leptin ► CB1 blockade restores leptin sensitivity by reversing hyperleptinemia of obesity ► Hyperleptinemia is reversed via reduced secretion and increased clearance of leptin
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