POSSIBLE EFFECT OF ENDOGENOUS CANNABINOIDS AND RIMONABANT UPON INSULIN RESISTANCE AND B-CELL FUNCTION

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

Viena, Austria

Congreso; 45th EASD Annual Meeting; 2009

European Association for the Study of Diabetes

 B. Maiztegui1, V. Madrid1, M.L. Massa1, F. Francini1 and J.J. Gagliardino1 Background and aims: Obesity decreases insulin sensitivity and causes a compensatory increase in â-cell function. The endocannabinoid anandamide (AEA) regulates appetite and other metabolic functions; therefore, drugs interacting with its specific CB1 and CB2 receptors have been used to treat obese people. We studied 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 in 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 C animals were removed to isolate islets (collagenase digestion). The expression of islet CB1 and CB2 receptor genes was checked by RT-PCR and immunocytochemistry (confocal microcopy). 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); at 16.7 mM glucose, this effect was observed with 100 ìM AEA (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 and 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 and T-bars levels, insulin concentration and IR state (p<0.05 in all cases). Rimonabant administration corrected significantly all these abnormalities, except for T-bars (p<0.05). Body weight increment Calorie 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 Conclusion: 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 FRD -induced IR. Grant Acknowledgement: This study was supported by an unrestricted grant from sanofi-aventis.