Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Original Paper Neuroendocrinology 2012;96:24–31 DOI: 10.1159/000333963 Intracerebroventricular Administration of Metformin Inhibits Ghrelin-Induced Hypothalamic AMP-Kinase Signalling and Food Intake Darko Stevanovic a Kristina Janjetovic b, d Maja Misirkic b, d Ljubica Vucicevic b, d Mirjana Sumarac-Dumanovic c Dragan Micic c Vesna Starcevic a Vladimir Trajkovic b Institutes of a Medical Physiology, b Microbiology and Immunology, and c Endocrinology, Diabetes and Diseases of Metabolism, School of Medicine, and d Institute for Biological Research ‘Sinisa Stankovic’, University of Belgrade, Belgrade, Serbia and Raptor, which was associated with the reduced phos- phorylation of mTOR. The mTOR substrate, S6K, was activat- ed by intracerebroventricular ghrelin despite the inhibition of mTOR. Metformin treatment blocked ghrelin-induced activation of hypothalamic AMPK/ACC/Raptor and restored mTOR activity without affecting S6K phosphorylation. Met- formin also reduced food consumption induced by the AMPK activator AICAR while the ghrelin-triggered food in- take was inhibited by the mTOR activator L -leucine. Conclu- sion: Metformin could reduce food intake by preventing ghrelin-induced AMPK signalling and mTOR inhibition in the hypotalamus. Copyright © 2012 S. Karger AG, Basel Introduction Metformin [(1-(diaminomethylidene)-3,3-dimethyl- guanidine] is an antihyperglycaemic drug widely used for the management of type 2 diabetes [1]. The glucoreg- ulatory properties of metformin are mainly attributed to reduced hepatic glucose production and augmented glu- cose uptake by the peripheral tissues [1]. Metformin has also been suggested to reduce weight in diabetic and non- Key Words Metformin  Ghrelin  Food intake  Hypothalamus  AMPK Abstract Background/Aims: The antihyperglycaemic drug metfor- min reduces food consumption through mechanisms that are not fully elucidated. The present study investigated the effects of intracerebroventricular administration of metfor- min on food intake and hypothalamic appetite-regulating signalling pathways induced by the orexigenic peptide ghrelin. Methods: Rats were injected intracerebroventricu- larly with ghrelin (5 g), metformin (50, 100 or 200 g), 5-amino-imidazole-4-carboxamide 1- - D-ribofuranoside (AICAR, 25 g) and L -leucine (1 g) in different combina- tions. Food intake was monitored during the next 4 h. Hypo- thalamic activation of AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase (ACC), regulatory-associated protein of mTOR (Raptor), mammalian target of rapamycin (mTOR) and p70 S6 kinase 1 (S6K) after 1 h of treatment was analysed by immunoblotting. Results: Metformin suppressed the in- crease in food consumption induced by intracerebroventric- ular ghrelin in a dose-dependent manner. Ghrelin increased phosphorylation of hypothalamic AMPK and its targets ACC Received: April 19, 2011 Accepted after revision: September 26, 2011 Published online: February 14, 2012 Vladimir Trajkovic Institute of Microbiology and Immunology, School of Medicine University of Belgrade, D r. Subotica 1 RS–11000 Belgrade (Serbia) Tel. +381 11 3643 233, E-Mail vtrajkovic  @  med.bg.ac.rs © 2012 S. Karger AG, Basel 0028–3835/12/0961–0024$38.00/0 Accessible online at: www.karger.com/nen