ANALYSIS OF LIPID-METABOLISM IN ADIPOCYTES USING A FLUORESCENT FATTY-ACID DERIVATIVE .1. INSULIN STIMULATION OF LIPOGENESIS

Stimulation of lipid synthesis (lipogenesis) is one of the most pronou nced metabolic actions of insulin. Here we demonstrate insulin-stimula ted lipogenesis in isolated rat adipocytes using a fatty acid derivati ve which carries a fluorophore. Three major fluorescent lipid products (lipids 1, 2, 3) are generated as revealed by TLC analysis and subseq uent fluorescent scanning or imaging. Lipolytic digestion and labeling studies suggest monoacylglycerol-3-phosphate and diacylglycerol (-3-p hosphate) structures harboring a single fluorescent fatty acyl residue each for lipids 1 and 3 (2), respectively. Fluorescent triglycerides are not generated. Assaying acylation with isolated microsomes using t he purified lipids 1 and 3 indicates that incorporation of one fluores cent fatty acyl residue into glycerol(-3-phosphate) interferes with su bsequent esterification. Pretreatment of the adipocytes with insulin s ignificantly stimulates synthesis of lipids 1 and 2, only, The insulin concentration-response relationship (EC50 = 0.5 nM) and the maximal i nsulin response for synthesis of lipid 1 (stimulation factor = 14- to 20-fold at low glucose and 3- to 7-fold at high glucose) are comparabl e with those for incorporation of [3-H-3]glucose into total adipocyte lipids. Thus this fluorescence-based assay may be useful for studying insulin action and lipogenesis. (C) 1997 Elsevier Science B.V.