0321 : Imidazoline-like Drug Improves Insulin Sensitivity Through a Direct Stimulation of Adiponectin Secretion in Primary Adipocytes

Altered adiponectin signaling has been proposed as a key factor in the development of metabolic syndrome. We previously showed that one imidazoline I1 receptor (I1R) ligand, LNP509, can improve insulin sensitivity and glucose tolerance partly through increased adiponectin plasma level. The objective of this study was to explore direct actions of I1R ligands on adipocytes. Experiments were carried out in primary adipocytes isolated from the epididymal white adipose tissue of aged male Wistar rats. Expression of I1R on adipocytes was verified with binding assays. I1R ligand effect was evaluated by treating adipocytes with increasing concentrations of LNP509 ±I1R antagonist efaroxan (10-4 M). To identify the intracellular signaling pathways involved in the action of LNPs, wortmannin (PI3K-inhibitor), IBMX (phosphodiesterase blocker) and AS1842856 (FOXO1 inhibitor) were added 45 min prior LNP509 exposure. After 3h, adiponectin content was measured in the culture medium by ELISA assay. Competition binding assays confirmed the expression of I1R in adipocyte membrane. Treatment by LNP509 dose-dependently induced adiponectin secretion: from 18±5 ng/ml at 10-9 M to 66±15 ng/ml at 10-4 M; p≤0.05 vs medium alone (25 ng/ml). The adiponectin secretion induced by the highest LNP509 concentration was similar to the one elicited by 10 μM insulin (61 ng/ml); the secretion was totally prevented by a pretreatment with efaroxan (10-4 M). The LNP509-induced adipokine secretion was unchanged by wortmannin, but was reduced after phosphodiesterase and FOXO1 blockade (-80% and -44% respectively, compared to LNP509 alone). LNP509, through I1R, promotes adiponectin secretion by inhibiting cAMP and SIRT1/FOXO1 pathways. These effects could lead to PPARγ activation in order to promote adiponectin synthesis. Future studies should confirm the proposed signaling pathways.