The dietary flavanol (-)-epicatechin protects against nitration and oxidation reactions of the inflammatory mediator peroxynitrite in hydrophilic and hydrophobic environments. Bioavailability and cellular uptake of (-)-epicatechin are not yet fully characterized. Here, the octanol/buffer partition coefficient of (-)-epicatechin is observed to be 1.5, indicating that the flavanol is soluble in aqueous as well as lipophilic cellular phases, thus capable of permeating the cell membrane. In line with this, the ability of murine aortic endothelial cells (MAECs) to remove (-)-epicatechin from cell culture media is demonstrated. Epicatechin accumulates in cells. likely due to epicatechin binding to cellular proteins. Even after repeated washing, (-)-epicatechin accumulated by MAEC affords protection of the cells against peroxynitrite-induced nitration of protein tyrosyl residues and against oxidation of intracellular dichlorodihydrofluorescein. (C) 2003 Elsevier Science (USA). All rights reserved.