Oleoylethanolamide, a natural ligand for PPAR-alpha, inhibits insulin receptor signalling in HTC rat hepatoma cells María Martínez de Ubago a , Inmaculada García-Oya a , Antonio Pérez-Pérez a , Alberto Canfrán-Duque a , Rocio Quintana-Portillo a , Fernando Rodríguez de Fonseca b , Carmen González-Yanes a , Víctor Sánchez-Margalet a, ⁎ a Department of Medical Biochemistry and Molecular Biology, School of Medicine, Investigation Unit, Virgen Macarena University Hospital, Av. Dr. Fedriani 3, Seville 41071, Spain b Investigation Unit, Fundación IMABIS, Hospital Carlos Haya, Malaga, Spain abstract article info Article history: Received 16 October 2008 Received in revised form 20 March 2009 Accepted 23 March 2009 Available online 5 April 2009 Keywords: Oleylethanolamide PPAR-alpha Insulin receptor Insulin resistance Signal transduction Oleoylethanolamide (OEA) is a lipid mediator belonging to the fatty acid ethanolamides family. It is produced by intestine and adipose tissue. It inhibits food intake and body weight gain, and has hypolipemiant action in vivo, as well as a lipolytic effect in vitro. OEA is a PPAR-alpha agonist, and recently it has been found that OEA is an endogenous ligand of an orphan receptor. Previously, we have shown that OEA inhibits insulin- stimulated glucose uptake in isolated adipocytes, and produces glucose intolerance in rats. In the present work, we have studied another insulin target cell, the hepatocyte using a rat hepatoma cell line (HTC), and we have studied the cross-talk of OEA signalling with metabolic and mitotic signal transduction of insulin receptor. OEA dose-dependently activates JNK and p38 MAPK, and inhibits insulin receptor phosphorylation. OEA inhibits insulin receptor activation, blunting insulin signalling in the downstream PI3K pathway, decreasing phosphorylation of PKB and its target GSK-3. OEA also inhibits insulin-dependent MAPK pathway, as assessed by immunoblot of phosphorylated MEK and MAPK. These effects were reversed by blocking JNK or p38 MAPK using pharmacological inhibitors (SP 600125, and SB 203580). Since OEA is an endogenous PPAR-alpha agonist, we investigated whether a pharmacologic agonist (WY 14643) may mimic the OEA effect on insulin receptor signalling. Activation of PPAR-alpha by the pharmacological agonist WY14643 in HTC hepatoma cells is sufficient to inhibit insulin signalling and this effect is also dependent on p38 MAPK but not JNK kinase. In summary, OEA inhibits insulin metabolic and mitogenic signalling by activation of JNK and p38 MAPK via PPAR-alpha. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Impaired glucose tolerance precedes type 2 diabetes and is characterized by hyperinsulinemia, which develops to balance peripheral resistance [1]. Type 2 diabetes is caused by a progressive decrease in insulin action and gradual development of chronic hyperglycemia. Initial peripheral insulin resistance, is compensated by increased insulin secretion from pancreatic β-cells, leading to hyperinsulinemia [2]. At the molecular level, insulin resistance correlates with impaired insulin signalling [3]. Identification of molecular mechanisms of the transducer proteins involved in metabolic and anabolic pathways is crucial for under- standing the energy homeostasis in the human body and to develop new therapeutic agents for the treatment of chronic metabolic disorders such as atherosclerosis and diabetes [4]. Moreover, the rapidly increasing prevalence of obesity in westernized societies and in some developing countries has focused the efforts on the search for new, efficacious, and safe treatments to counter this problem [5]. Agents that alter various physiological signalling system are being found, that attenuate hunger signals or elicit premature satiety following meal ingestion, and that may act as novel anti-obesity therapies [6]. Several fatty acid ethanolamides have been shown to act as ligands at G protein-coupled receptors (GPRCs) [6], (Briscoe et al. 2003), [7,8], and fatty acids derivatives including anandamide (arachidonoylethanolamide; AEA) and 2-arachidonyl-glycerol may be endogenous ligands for the cannabinoid receptors (CB1 and CB2) [9–12]. The endogenous fatty acid ethanolamide oleoylethanolamide (OEA) has recently been described as a peripherally acting agent that suppresses food intake and, upon subchronic intraperitoneal admin- istration, reduces body weight gain in rodents feeding models [13–17]. Besides it has been shown that OEA has a hypolipemiant action. OEA is synthesized in the intestine in response to feeding, increasing its levels in portal blood after the meal. Moreover, OEA is produced by adipose tissue and a lipolytic effect in vitro has been found [18]. The mechanism of OEA action is, however, not completely understood. It's known that OEA is an endogenous ligand of PPAR-alpha [19], and recently, an orphan seven spanning-membrane domains receptor has Biochimica et Biophysica Acta 1791 (2009) 740–745 ⁎ Corresponding author. E-mail address: margalet@us.es (V. Sánchez-Margalet). 1388-1981/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.bbalip.2009.03.014 Contents lists available at ScienceDirect Biochimica et Biophysica Acta journal homepage: www.elsevier.com/locate/bbalip