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

sigma 2 Receptor Ligand-Mediated Inhibition of Inward ly Rectifying K+ Channels in the Heart

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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

Respective contributions of α-adrenergic and non-adrenergic mechanisms in the hypotensive effect of imidazoline-like drugs

1. The hypotensive effect of imidazoline-like drugs, such as clonidine, was first attributed to the exclusive stimulation of central α 2-adrenoceptors (α 2ARs). 2. However, a body of evidence suggests that non-adrenergic mechanisms may also account for this hypotension. 3. This work aims (i) to check whether imidazoline-like drugs with no α 2adrenergic agonist activity may alter blood pressure (BP) and (ii) to seek a possible interaction between such a drug and an α 2ARs agonist α-methylnoradrenaline (α-MNA). 4. We selected S23515 and S23757, two imidazoline-like drugs with negligible affinities and activities at α 2ARs but with high affinities for non-adrenergic imidazoline binding sites (IBS). 5. S23515 decreased BP dose-dependently (-27±5% maximal effect) when administered intracisternally (i.c.) to anaesthetized rabbits. The hypotension induced by S23515 (100 μg kg -1 i.c.) was prevented by S23757 (1 mg kg -1 i.c.) and efaroxan (10 μgkg -1 i.c.), while these compounds, devoid of haemodynamic action by themselves, did not alter the hypotensive effect of α-MNA (3 and 30 μg kg -1 i.c.). Moreover, the α 2ARs antagonist rauwolscine (3 μg kg -1 i.c.) did not prevent the effect of S23515. 6. Finally, whilst 3 μg kg -1 of S23515 or 0.5 μg kg -1 of α-MNA had weak hypotensive effects, the sequential i.c. administration of these two drugs induced a marked hypotension (-23±2%). 7. These results indicate that an imidazoline-like drug with no α 2-adrenergic properties lowers BP and interacts synergistically with an α 22ARs agonist.link_to_subscribed_fulltex

Increased expression of blood muscarinic receptors in patients with reflex syncope

International audienceAIMS:Pathophysiology of reflex syncope is not fully understood but a vagal overactivity might be involved in this syncope. Previously, overexpression of muscarinic M2 receptors and acetylcholinesterase was found in particular in the heart and in lymphocytes of rabbits with vagal overactivity as well as in hearts of Sudden Infant Death Syndromes. The aim of this present study was to look at M2 receptor expression in blood of patients with reflex syncope. The second objective was to measure acetylcholinesterase expression in these patients.METHODS AND RESULTS:136 subjects were enrolled. This monocenter study pooled 45 adults exhibiting recurrent reflex syncope compared with 32 healthy adult volunteers (18-50 years) and 38 children exhibiting reflex syncope requiring hospitalization compared with 21 controls (1-17 years). One blood sample was taken from each subject and blood mRNA expression of M2 receptors was assessed by qRT-PCR. Taking into account the non-symmetric distributions of values in both groups, statistical interferences were assessed using bayesian techniques. A M2 receptor overexpression was observed in adult and pediatric patients compared to controls. The medians [q1;q3] were 0.9 [0.3;1.9] in patients versus 0.2 [0.1;1.0] in controls; the probability that M2 receptor expression was higher in patients than in controls (Pr[patients>controls]) was estimated at 0.99. Acetylcholinesterase expression was also increased 0.7 [0.4;1.6] in patients versus 0.4 [0.2;1.1] in controls; the probability that acetylcholinesterase expression was higher in patients than in controls (Pr[patients>controls]) was estimated at 0.97. Both in adults and children, the expression ratio of M2 receptors over acetylcholinesterase was greater in the patient group compared with the control group.CONCLUSION:M2 receptor overexpression has been detected in the blood of both, adults and children, exhibiting reflex syncope. As in our experimental model, i.e. rabbits with vagal overactivity, acetylcholinesterase overexpression was associated with M2 receptor overexpression. For the first time, biological abnormalities are identified in vagal syncope in which only clinical signs are, so far, taken into account for differential diagnosis and therapeutic management. Further work will be needed to validate potential biomarkers of risk or severity associated with the cholinergic system