Short- and long-term insulin-like effects of monoamine oxidases and semicarbazide-sensitive amine oxidase substrates in cultured adipocytes Christian Carpe ´ne ´ 4 , Danie `le Daviaud, Jeremie Boucher, Sandy Bour, Virgile Visentin, Sandra Gre `s, Carine Duffaut, Emi Fontana, Xavier Testar, Jean-Se ´bastien Saulnier-Blache, Philippe Valet Institut National de la Sante ´ et de la Recherche Me ´dicale, U586 INSERM, IFR 31, CHU Rangueil, 31432 Toulouse cedex 4, France Departamento de Bioquimica y Biologia Molecular, Facultad de Biologia, Universidad de Barcelona, 08028 Barcelona, Spain Received 7 July 2005; accepted 16 June 2006 Abstract Semicarbazide-sensitive amine oxidase (SSAO) is known to increase during in vitro adipogenesis and to be one of the most highly expressed membrane proteins of white adipocytes. Although less well documented, mitochondrial monoamine oxidases (MAOs) are also present in adipocytes and share with SSAO the capacity to generate hydrogen peroxide. This work therefore aimed to compare several biologic effects of MAO and SSAO substrates in 3T3-F442A adipocytes. In differentiated cells, tyramine oxidation was predominantly MAO dependent, whereas benzylamine oxidation was SSAO dependent. Both amines partially mimicked insulin actions, including stimulation of Akt phosphorylation and glucose uptake. In addition, tyramine and benzylamine impaired tumor necrosis factor a –dependent nitric oxide formation in a pargyline- and semicarbazide-sensitive manner, respectively. Various biogenic amines were tested in competition for tyramine or benzylamine oxidation and classified as MAO-preferring (methoxytyramine, tryptamine) or SSAO-preferring substrates (methylamine, octopamine). Short-term incubation with 1 mmol/L of all amines except histamine stimulated glucose uptake up to 20% to 50% of maximal insulin activation. One-week treatment with either MAO or SSAO substrates alone allowed postconfluent cells to differentiate into adipocytes, reproducing 60% of insulin-promoted lipid accumulation. All amines also exerted a slight improvement in the adipogenic action of insulin. Therefore, like SSAO, substrate activation of MAO can interact with adipocyte metabolism by mimicking diverse effects of insulin in addition to preventing tumor necrosis factor a –dependent responses. D 2006 Elsevier Inc. All rights reserved. 1. Introduction Adipocytes accumulate energy in the form of triacylgly- cerols, which, in turn, can be hydrolyzed and released as glycerol plus free fatty acids. When energy intake is dominant, excess lipid storage in white adipose tissue can be obtained via an increase in the size of mature adipocytes and/or via the recruitment of preadipocytes. This may lead not only to obesity but also to related pathologies such as type 2 diabetes mellitus because adipose tissue is not simply an insulin-responsive tissue that converts glucose into fat stores, but is also an endocrine organ participating in the regulation of energy balance [1,2]. Adipogenesis has been extensively studied in vitro through murine preadipocyte lineages. Adipose conversion from such fibroblastic pre- cursors is divided into at least 3 steps: cell commitment, clonal amplification, and phenotype expression [3]. Initial events involve the induction of expression of several adipose-specific genes, whereas later events result in the appearance of functional characteristics of mature adipo- cytes such as increased glucose transport capacity, through expression of insulin-responsive glucose transporters, which represent a key step in lipogenesis, leading to progressive lipid accumulation. In addition to the well-defined molecular events triggered by insulin [4], a strong increase in the expression of semi- carbazide-sensitive amine oxidase (SSAO) has repeatedly 0026-0495/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.metabol.2006.06.011 4 Corresponding author. U586 INSERM, IFR 31, CHU Rangueil, 31432 Toulouse cedex 4, France. Tel.: +33 5 62 17 29 55; fax: +33 5 61 33 17 21. E-mail address: carpene@toulouse.inserm.fr (C. Carpe ´ne ´). Metabolism Clinical and Experimental 55 (2006) 1397 – 1405 www.elsevier.com/locate/metabol