0260 Imidazoline I1 receptor ligands activate hepatic adiponectin pathways and thus improve insulin sensitivity

Metabolic syndrome is defined as a cluster of cardiovascular and metabolic disorders. Previous studies in rat models of metabolic syndrome have demonstrated that ligands selective for I1 imidazoline receptor (LNPs) increase insulin sensitivity through central sympathoinhibition and an additional peripheral effect attributable to adiponectin, a major insulin-sensitizer adipokine. The objective of this study was to explore possible direct actions on hepatocytes, one of the target cells of insulin and adiponectin.Experiments were carried out in HepG2 cells, a cell line of hepatocytes. In order to evaluate the effect of LNPs on insulin sensitivity, the activation (i.e. phosphorylation) of a key actor of insulin pathways, AKT, was evaluated by measuring the ratio pAKT/AKT by Western Blot. Similarly, the effect of LNPs on adiponectin signaling was evaluated by measuring the rate of phosphorylation of the central kinase involved in adiponectin pathways, AMPK, by Western Blot. Insulin (10μM) induced the phosphorylation of AKT (pAKT/ AKT=0.49±0.16) compared to control without insulin (pAKT/AKT=0.11±0.03; p≤0.05) whereas LNPs (1μM) alone did not. Interestingly, pretreatment by LNPs (1μM) during 60 min could potentiate the insulin-induced activation of AKT: LNP509: pAKT/AKT=1.13±0.18 (p≤0.05 vs insulin alone); LNP599: pAKT/AKT=1.23±0.16 (p=0.0545 vs insulin alone).Concerning adiponectin signaling pathways, LNPs alone (from 10−9M to 10−4M) increased AMPK phosphorylation in a concentration- and time-dependent manner. The maximal effect was obtained after 10 min exposure of LNPs 10μM (untreated cells: pAMPK/AMPK=0.18±0.04; LNP 509 pAMPK/ AMPK=0.38±0.05 p≤0.05; LNP599 pAMPK/AMPK=0.46±0.17). These data suggest that LNPs on hepatic cells activate adiponectin pathways and potentiate insulin action. These two direct effects on insulin sensitive cells could account for the ameliorated insulin sensitivity observed in vivo

Effects of imidazoline-like drugs on liver and adipose tissues, and their role in preventing obesity and associated cardio-metabolic disorders

International audienceBackground/objectives: We previously observed that selective agonists of the sympatho-inhibitory I1 imidazoline receptors (LNP ligands) have favorable effects on several cardiovascular and metabolic disorders defining the metabolic syndrome, including body weight. The objectives of this study were to explore the effects of LNPs on adiposity and the mechanisms involved, and to evaluate their impact on metabolic homeostasis.Methods: Young Zucker fa/fa rats were treated with LNP599 (10 mg/kg/day) for 12 weeks. Effects on body weight, adiposity (regional re-distribution, morphology, and function of adipose tissues), cardiovascular and metabolic homeostasis, and liver function were evaluated. Direct effects on insulin and AMP-activated protein kinase (AMPK) signaling were studied in human hepatoma HepG2 cells.Results: LNP599 treatment limited the age-dependent remodeling and inflammation of subcutaneous, epididymal, and visceral adipose tissues, and prevented total fat deposits and the development of obesity. Body-weight stabilization was not related to reduced food intake but rather to enhanced energy expenditure and thermogenesis. Cardiovascular and metabolic parameters were also improved and were significantly correlated with body weight but not with plasma norepinephrine. Insulin and AMPK signaling were enhanced in hepatic tissues of treated animals, whereas blood markers of hepatic disease and pro-inflammatory cytokine levels were reduced. In cultured HepG2 cells, LNP ligands phosphorylated AMPK and the downstream acetyl-CoA carboxylase and prevented oleic acid-induced intracellular lipid accumulation. They also significantly potentiated insulin-mediated AKT activation and this was independent from AMPK.Conclusions: Selective I1 imidazoline receptor agonists protect against the development of adiposity and obesity, and the associated cardio-metabolic disorders. Activation of I1 receptors in the liver, leading to stimulation of the cellular energy sensor AMPK and insulin sensitization, and in adipose tissues, leading to improvement of morphology and function, are identified as peripheral mechanisms involved in the beneficial actions of these ligands