Rehashing endocannabinoid antagonists: can we selectively target the periphery to safely treat obesity and type 2 diabetes?

Evaluation of the insulin releasing and antihyperglycaemic activities of GPR55 lipid agonists using clonal beta-cells, isolated pancreatic islets and mice

BACKGROUND AND PURPOSE

G-protein coupled receptor (GPR)55 is a novel lipid sensing receptor activated by both cannabinoid endogenous ligands (endocannabinoids) and other non-cannabinoid lipid transmitters. This study assessed the effects of various GPR55 agonists on glucose homeostasis.

EXPERIMENTAL APPROACH

Insulin secretion and changes in intracellular Ca(2) (+) and cAMP in response to glucose and a range of GPR55 agonists [endogenous ligands (OEA, PEA), chemically synthetic cannabidiol (CBD) analogues (Abn-CBD, 0-1602), an analogue of rimonabant (AM-251) and antagonist (CBD)] were investigated in clonal BRIN-BD11 cells and mouse pancreatic islets. Cytotoxicity was assessed by LDH release, cellular localization by double-staining immunohistochemistry and in vivo effects assessed in mice.

KEY RESULTS

The most potent and selective GPR55 agonist was the synthetic CBD analogue, Abn-CBD (pEC50 10.33), maximum stimulation of 67% at 10(-4)  mol·L(-1) (P < 0.001) in BRIN-BD11 cells. AM-251 (pEC50 7.0), OEA (pEC50 7.0), 0-1602 (pEC50 7.3) and PEA (pEC50 6.0) stimulated insulin secretion. Results were corroborated by islet studies, with no cytotoxic effects. Concentration-dependent insulin secretion by GPR55 agonists was glucose-sensitive and accompanied by elevations of [Ca(2) (+) ]i (P < 0.01-P < 0.001) and cAMP (P < 0.05-P < 0.01). GPR55 agonists exhibited insulinotropic and glucose lowering activity in vivo. GPR55 was expressed on BRIN-BD11 cells and confined to islet beta cells with no distribution on alpha cells.

CONCLUSION AND IMPLICATIONS

These results demonstrate GPR55 is distributed in pancreatic beta cells and is a strong activator of insulin secretion, with glucose-lowering effects in vivo. Development of agents agonizing the GPR55 receptor may have therapeutic potential in the treatment of type 2 diabetes.

Ellagic Acid Reduces Adipogenesis through Inhibition of Differentiation-Prevention of the Induction of Rb Phosphorylation in 3T3-L1 Adipocytes

Ellagic acid (EA) present in many fruits and nuts serves as antiproliferation, anti-inflammatory, and antitumorigenic properties. However, the effect of EA on preadipocytes adipogenesis and its mechanism(s) have not been elucidated. The present study was designed to examine the effect of EA on adipogenesis in 3T3-L1 preadipocytes and underlying mechanism(s) of action involved. Data show that EA administration decreased the accumulation of lipid droplets. The inhibition was diminished when the addition of EA was delayed to days 2–4 of differentiation. Clonal expansion was reduced in the presence of EA. FACS analysis showed that EA blocked the cell cycle at the G1/S transition. EdU incorporation also confirmed that EA refrained cell from entering S phase. Our data also revealed that the differentiation-induced protein expression of Cyclin A and phosphorylation of the retinoblastoma protein (Rb) were impaired by EA. Differentiation-dependent expression and DNA-binding ability of C/EBPα were also inhibited by EA. Alterations in cell cycle-associated proteins may be important with respect to the antiadipogenic action of EA. In conclusion, EA is capable of inhibiting adipogenesis in 3T3-L1 adipocytes possibly through reduction of Cyclin A protein expression and Rb phosphorylation. With the blocking of G1/S phase transition, EA suppresses terminal differentiation and lipid accumulation in 3T3-L1 adipocytes.

Structure-activity relationship studies of novel pyrazole and imidazole carboxamides as cannabinoid-1 (CB1) antagonists

The synthesis and biological evaluation of novel pyrazole and imidazole carboxamides as CB1 antagonists are described. As a part of eastern amide SAR, various chemically diverse motifs were introduced on rimonabant template. The central pyrazole core was also replaced with its conformationally constrained motif and imidazole moieties. In general, a range of modifications were well tolerated. Several molecules with low- and sub-nanomolar potencies were identified as potent CB1 receptor antagonists. The in vivo proof of principle for weight loss is demonstrated with a lead compound in DIO mice model.

Prospective influences of circadian clocks in adipose tissue and metabolism

Circadian rhythms make a critical contribution to endocrine functions that involve adipose tissue. These contributions are made at the systemic, organ and stem cell levels. The transcription factors and enzymes responsible for the maintenance of circadian rhythms in adipose depots and other peripheral tissues that are metabolically active have now been identified. Furthermore, the circadian regulation of glucose and lipid metabolism is well-established. Animal and human models provide strong evidence that disturbances in circadian pathways are associated with an increased risk of type 2 diabetes mellitus, obesity and their comorbidities. Thus, circadian mechanisms represent a novel putative target for therapy in patients with metabolic diseases.

Novel pyrazole-3-carboxamide derivatives as cannabinoid-1 (CB1) antagonists: journey from non-polar to polar amides

The synthesis and biological evaluation of novel pyrazole-3-carboxamide derivatives as CB1 antagonists are described. As a part of eastern amide SAR, various chemically diverse motifs were introduced. In general, a range of modifications were well tolerated. Several molecules with high polar surface area were also identified as potent CB1 receptor antagonists. The in vivo proof of principle for weight loss is exemplified with a lead compound from this series.