Possible effect of endogenous cannabinoids and rimonabant upon insulin resistance and â-cell function

FLORES LE; ALZUGARAY ME; SUBURO AM; RASCHIA MA; DEL ZOTTO H; GARCÍA M; BORELLI MI; MAIZTEGUI B; MADRID V; MASSA ML; FRANCINI F; GAGLIARDINO JJ

Vienna

Congreso; 45th EASD Annual Meeting; 2009

EASD

Obesity produces a decrease in insulin sensitivity and a compensatory increase in B-cell function. Anandamide (AEA, endocannabinoid) regulates appetite and other metabolic functions; thus, drugs that interact with its specific CB1 and CB2 receptors have been used to treat obese people. Our aim was to study the possible regulatory role of the general and local (pancreatic islets) cannabinoid system upon insulin secretion in rats with insulin resistance (IR) induced by administration of a fructose-rich diet (FRD). Material and Methods: Normal male Wistar rats were divided into 4 groups and fed for 21 days as follows: Control (C): standard commercial powder diet and tap water ad libitum; Fructose (F): C plus 10% w/v fructose in the drinking water; Rimonabant control (RC): C plus 2 mg/rat Rimonabant; and Fructose Rimonabant (FR): RC plus the same amount of fructose as F. Blood samples were drawn at the time of sacrifice to measure glucose, insulin, thiobarbituric acid reactive substances (T-bars) and triglyceride levels. Serum glucose and insulin values were used to calculate insulin sensitivity (HOMA-IR). After sacrifice, pancreases from each C animals were removed to isolate islets (collagenase digestion). Expression of insular CB1 and CB2 receptor genes was checked by RT-PCR and immunocytochemistry (confocal microscopy). We measured insulin secretion from isolated islets incubated with 2.8, 8.3 or 16.7 mM glucose with or without the addition of 0.1-200 µM AEA, 0.1-20 µM ACEA (CB1 agonist), or 0.1-20 µM JWH (CB2 agonist) (RIA). Results: The presence of CB1 and CB2 receptors in normal rat islets was demonstrated by RT-PCR and immunocytochemistry. While CB1 receptors were selectively expressed in glucagon-producing cells, CB2 were expressed in both insulin- and somatostatin-producing cells. AEA at 10 ìM enhanced significantly the release of insulin induced by 8.3 mM glucose (3.5 ± 1.0 vs. 7.4 ± 1.5 ng/islet/h; p<0.05), but these effect was observed with 100 ìM at 16.7 mM glucose at (8.2 ± 0.7 vs. 10.8 ± 0.5 ng/islet/h; p<0.05). ACEA and JWH affected insulin secretion in the presence of 16.7 mM glucose in a dual way: they enhanced and inhibited the secretion at 1 ìM and at 20 ìM, respectively (ACEA: 9.7 ± 0.6, 11.8 ± 0.8 and 6.8 ± 0.8 ng/islet/h at 0, 1 and 20 ìM, respectively.  JWH: 10.4 ± 0.7, 15.1 ± 1.2 and 6.2 ± 0.8 ng/islet/h at 0, 1 and 20 ìM, respectively; p<0.05 in all cases). FRD increased significantly daily caloric intake, body weight, serum glucose, triglyceride, T-bars, insulin concentration and IR state (p<0.05 in all cases). Rimonabant administration corrected significantly (except T-bars), all these abnormalities (p<0.05). Body weight increment Calories Intake Serum Glucose Serum Insulin HOMA-IR Serum T-Bars Serum Triglyceride g cal/rat/day mmol/L ìU/ml pmol/mg prot mg/dl C 47.7 ± 11.9 59.1 ± 1.5 5.0 ± 0.1 10.5 ± 0.8 2.3 ± 0.2 233.1 ± 8.1 56.0 ± 5.3 F 72.0 ± 9.5 86.2 ± 1.8 5.5 ± 0.1 15.9 ± 0.9 3.9 ± 0.2 312.9 ± 8.9 73.7 ± 3.5 CR 34.3 ± 1.8 55.1 ± 2.9 4.9 ± 0.2 8.1 ± 0.9 1.8 ± 0.2 257.2 ± 28.1 58.7 ± 4.2 FR 48.3 ± 10.9 60.1 ± 3.5 5.2 ± 0.3 11.1 ± 0.9 2.6 ± 0.3 325.2 ± 9.8 63.7 ± 1.6 Conclusions: Islets have a specific distribution of CB1 CB2 receptors that modulate insulin secretion. Blockage of the endocannabinoid pathway in vivo corrected most metabolic abnormalities and the IR induced by FRD. This work was supported by an unrestricted grant from Sanofi-Aventis.