The Negative Effect of Soy Extract on Erythrocyte Membrane Fluidity: An Electron Paramagnetic Resonance Study Vladimir Ajdz ˇanovic ´ • Ivan Spasojevic ´ • Branka S ˇ os ˇic´-Jurjevic ´ • Branko Filipovic ´ • Svetlana Trifunovic ´ • Milka Sekulic ´ • Verica Milos ˇevic ´ Received: 19 July 2010 / Accepted: 15 November 2010 / Published online: 4 December 2010 Ó Springer Science+Business Media, LLC 2010 Abstract A decrease of erythrocyte membrane fluidity can contribute to the pathophysiology of hypertension. Soy products, which are used asalternative therapeutics in some cardiovascular conditions, contain various isoflav- ones (genistein, daidzein, and their glucosides, genistin and daidzin),which can incorporate cellular membrane and change its fluidity. The aim of this study was to examine the effects of soy extract (which generally corresponds to the soy products of isoflavone composition) on erythrocyte membrane fluidity at graded depths. We used electron paramagnetic resonance spectroscopy and fatty acid spin probes(5-DS and 12-DS),the spectraof which are dependent on membrane fluidity. After being treated with soy extract, erythrocytes showed a significant (P = 0.016) decrease of membrane fluidity near the hydrophilic surface, while there were no significant changes of fluidity in dee- per hydrophobic membrane regions. These results suggest thatsoy products containing high levels of genistein and isoflavoneglucosidesmay notbe suitablefor use in hypertension because they decrease erythrocyte membrane fluidity. Keywords Soy extract Isoflavone glucoside Genistein Erythrocytes Electron paramagnetic resonance Membrane fluidity Spin probes Introduction Microcirculation is a complex and integrated system in which erythrocytes represent the main definers of blood viscosity.The mechanical properties of the erythrocyte membrane, such as fluidity, seem to be of crucial impor- tance forthe ability oferythrocytes to pass through the smallest blood vessels. Some previous data have pointed out higher microviscosity of the erythrocyte membrane in spontaneously hypertensive rats in comparison to controls (Orlov et al. 1982).Hence,a link has been proposed between the alterations of mechanical properties of the erythrocyte membrane and the pathophysiology of hyper- tension (Postnov and Orlov 1984). Further investigations have confirmed this, showing that erythrocyte membrane fluidity is significantlylower in both spontaneously hypertensive rats and patients with essential hypertension than in normotensive controls (Tsuda et al. 1987),which led to the conclusion that decreased fluidity of the eryth- rocyte membrane contributes to the pathophysiology of hypertension and other cardiovascular diseases (Zicha et 1999). Soy products contain non-nutrient constituents known a isoflavones, which gained significant attention from the scientific community as a result of their potentially bene- ficial effects on human health. It has been documented th isoflavones can lower the concentration of cholesterol in the serum (Setchell 1985) and slow down the developmen of atherosclerotic plaques(Rainesand Ross1995),so soy productsare increasingly consumed as alternative Vladimir Ajdz ˇanovic ´ and Ivan Spasojevic ´ contributed equally to this study. V. Ajdz ˇanovic ´ (&) B. S ˇ os ˇic´-Jurjevic ´ B. Filipovic ´ S. Trifunovic ´ M. Sekulic ´ V. Milos ˇevic ´ Department of Cytology, Institute for Biological Research ‘‘Sinis ˇa Stankovic ´’’, University of Belgrade, Despot Stefan Blvd. 142,11060 Belgrade, Serbia e-mail: avlada@ibiss.bg.ac.rs I. Spasojevic ´ Life Systems Department, Institute for Multidisciplinary Research, University of Belgrade, Kneza Vis ˇeslava 1, 11000 Belgrade, Serbia 123 J Membrane Biol (2011) 239:131–135 DOI 10.1007/s00232-010-9332-8