Regulation, Function, and Dysregulation of Endocannabinoids in Models of Adipose and β-Pancreatic Cells and in Obesity and Hyperglycemia

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Abstract
Context: Cannabinoid CB1 receptor blockade decreases weight and hyperinsulinemia in obese animals and humans in a way greatly independent from food intake. Objective: The objective of this study was to investigate the regulation and function of the endocannabinoid system in adipocytes and pancreatic β-cells. Design, Setting, and Patients: Mouse 3T3-F442A adipocytes and rat insulinoma RIN-m5F β-cells, pancreas and fat from mice with diet-induced obesity, visceral and sc fat from patients with body mass index equal to or greater than 30 kg/m2, and serum from normoglycemic and type 2 diabetes patients were studied. Main Outcome Measure: Endocannabinoid enzyme and adipocyte protein expression, and endocannabinoid and insulin levels were measured. Results: Endocannabinoids are present in adipocytes with levels peaking before differentiation, and in RIN-m5F β-cells, where they are under the negative control of insulin. Chronic treatment of adipocytes with insulin is accompanied by permanently elevated endocannabinoid signaling, whereas culturing of RIN-m5F β-cells in high glucose transforms insulin down-regulation of endocannabinoid levels into up-regulation. Epididymal fat and pancreas from mice with diet-induced obesity contain higher endocannabinoid levels than lean mice. Patients with obesity or hyperglycemia caused by type 2 diabetes exhibit higher concentrations of endocannabinoids in visceral fat or serum, respectively, than the corresponding controls. CB1 receptor stimulation increases lipid droplets and decreases adiponectin expression in adipocytes, and it increases intracellular calcium and insulin release in RIN-m5F β-cells kept in high glucose. Conclusions: Peripheral endocannabinoid overactivity might explain why CB1 blockers cause weight-loss independent reduction of lipogenesis, of hypoadiponectinemia, and of hyperinsulinemia in obese animals and humans.