Original Contribution FLAVAN-3-OLS AND PROCYANIDINS PROTECT LIPOSOMES AGAINST LIPID OXIDATION AND DISRUPTION OF THE BILAYER STRUCTURE SANDRA V. VERSTRAETEN,* CARL L. KEEN, † HAROLD H. SCHMITZ, ‡ C´ ESAR G. FRAGA, § and PATRICIA I. OTEIZA* *IQUIFIB-Department of Biological Chemistry (UBA-CONICET), University of Buenos Aires, Buenos Aires, Argentina; † Department of Nutrition, University of California, Davis, CA, USA; ‡ Analytical and Applied Sciences, Mars Inc., Hackettstown, NJ, USA; § Physical Chemistry-PRALIB, School of Pharmacy and Biochemistry, University of Buenos Aires, Buenos Aires, Argentina (Received 6 May 2002; Revised 21 August 2002; Accepted 23 September 2002) Abstract—The antioxidant activity and the membrane effects of the flavanols (-)-epicatechin, (+)-catechin, and their related oligomers, the procyanidins, were evaluated in liposomes composed by phosphatidylcholine:phosphatidylserine (60:40, molar ratio). When liposomes were oxidized with a steady source of free radicals, the flavanols and procyanidins (25 M monomer equivalents) inhibited oxidation in a manner that was related to procyanidin chain length. Flavanols and procyanidins did not influence membrane fluidity or lipid lateral phase separation. However, flavanols and procyanidins induced a decrease in the membrane surface potential and protected membranes from detergent-induced disruption. These effects were dependent on flavonoid concentration, procyanidin chain length, and membrane composition. Flavanol- and procyanidin-induced inhibition of lipid oxidation was correlated with their effect on membrane surface potential and integrity. These results indicate that the interaction of flavanols and procyanidins with phospholipid head groups, particularly with those containing hydroxyl groups, is associated with a reduced rate of membrane lipid oxidation. Thus, flavanols and procyanidins can potentially reduce oxidative modifications of mem- branes by restraining the access of oxidants to the bilayer and the propagation of lipid oxidation in the hydrophobic membrane matrix. © 2002 Elsevier Science Inc. Keywords—Flavonoids, Procyanidins, Catechins, Antioxidants, Lipid oxidation, Membrane physical properties, Cocoa, Free radicals INTRODUCTION The consumption of diets rich in plant foods is associated with a reduced risk for vascular disease and certain cancers. While this association has been observed in numerous epidemiological studies [1–3], there is consid- erable debate over the identity of the factors in plant-rich diets that confer health-promoting effects. While some of the beneficial effects of plant foods can be attributed to the essential nutrients they provide, these foods can also contain many other beneficial nutrients. In this context, a class of nutrients that is receiving increasing attention is the flavonoids. This interest has been sparked by several large epidemiological studies in which the intake of dietary flavonoids is inversely related to the risk for vascular disease [4 – 6]. Buttressing these observations are findings that, in vitro, select flavonoids demonstrate a range of bioactivities consistent with the concept of having a positive influence on cardiovascular health [7–11]. Similarly, in a number of acute and chronic studies, the consumption of flavonoid-rich foods and beverages has been associated with multiple positive cardiovascular effects [12–15]. While the concept that flavonoids can provide positive health effects is gaining acceptance, there is a paucity of information regarding the mechanisms through which these compounds act. Certain cocoas and chocolates are examples of plant- based foods and beverages that can be particularly rich in flavonoids, including the flavan-3-ols (-)-epicatechin and (+)-catechin along with their related flavanol oligomers (dimer-decamers), the procyanidins [16 –18]. It is known Address correspondence to: Dr. Patricia I. Oteiza, Universidad de Buenos Aires, Departamento de Quı ´mica Biolo ´gica, IQUIFIB (UBA- CONICET), Facultad de Farmacia y Bioquı ´mica, Junı ´n 956, C1113AAD Buenos Aires, Argentina; Tel: +54 (11) 4964-8288; Fax: +54 (11) 4962-5457; E-Mail: oteiza@qb.ffyb.uba.ar. Free Radical Biology & Medicine, Vol. 34, No. 1, pp. 84 –92, 2003 Copyright © 2002 Elsevier Science Inc. Printed in the USA. All rights reserved 0891-5849/02/$–see front matter PII S0891-5849(02)01185-1 84