Modulation of Tau Protein Fibrillization by Oleocanthal Maria Chiara Monti, Luigi Margarucci, Raffaele Riccio, and Agostino Casapullo* Dipartimento di Scienze Farmaceutiche e Biomediche, Universita ̀ degli Studi di Salerno, Via Ponte don Melillo, 84084 Fisciano, Italy * S Supporting Information ABSTRACT: Among the phenolic compounds extracted from extra virgin olive oil, oleocanthal (1) has attracted considerable attention in the modulation of many human diseases, such as inflammation and Alzheimer’s disease (AD). Indeed, 1 is capable of altering the fibrillization of tau protein, which is one of the key factors at the basis of neuro- degenerative diseases, and of covalently reacting with lysine ε- amino groups of the tau fragment K18 in an unspecific fashion. In the present study, an investigation of the recognition process and the reaction profile between 1 and the wild-type tau protein has been conducted by a circular dichroism, surface plasmon resonance, fluorescence, and mass spectrometry combined approach. As a result, 1 has been found to interact with tau-441, inducing stable conformational modifications of the protein secondary structure and also interfering with tau aggregation. These findings provide experimental support for the potential reduced risk of AD and related neurodegenerative diseases associated with olive oil consumption and may offer a new chemical scaffold for the development of AD-modulating agents. E xtra virgin olive oil, one of the principal constituents of the Mediterranean diet, has been associated for a long time with health benefits. 1,2 Indeed, the occurrence of breast and colon cancers and cardiovascular diseases 3-5 is remarkably low in the Mediterranean area compared to other geographical regions of the world. In this context, the biological properties of phenolic compounds present in extra virgin olive oil from Olea europea L. (Oleaceae) and their involvement in some pathogenic processes have attracted wide attention since their discovery. 6-10 Among the phenolic olive oil constituents, (-)-oleocanthal (1), the dialdehydic form of (-)-deacetoxyligstroside aglycone, found mainly in freshly pressed extra virgin olive oil, has shown an anti-inflammatory profile similar to the nonsteroidal anti- inflammatory drug ibuprofen. 11 Indeed, after the completion of the total synthesis, 1 was subjected to extensive biological investigations. 12 In some of these studies, 1 has been suggested to reduce the polymerization of tau protein through a possible covalent mechanism. 13,14 Since the aggregation of tau correlates with clinical progression of Alzheimer’s disease (AD), it seems likely that inhibition or reversal of tau aggregation could protect the affected neurons. 15,16 Tau protein, found in six isoforms from 352 to 441 amino acids in length, is involved in the stabilization of the microtubules (MTs) by direct interaction through a micro- tubule-binding domain (MBD), 17,18 thereby modulating the plasticity of the cytoskeleton. It has been reported recently that two VQIXXK motifs in the MT binding region, named PHF6 (from V 306 to K 311 ) and PHF6* (from V 275 to K 280 ), are responsible for β-sheet structural development and the initiation of tau fibrils formation. 19 Indeed, tau is a highly soluble protein with a random conformation in aqueous solution and hardly shows any tendency to assemble under physiological conditions. 20 In the brains of AD patients, however, it dissociates from axonal microtubules and abnormally aggregates to form insoluble paired helical filaments (PHFs), which are implicated in neurodegeneration. 19 Since the amount of tau aggregates has been correlated with neuron loss and the severity of dementia, the analysis of its self- assembly mechanism and the discovery of lead compounds able to reduce the PHF formation 21-24 could provide essential information to develop an effective way to slow the neurodegenerative process. With this background, compound 1 has been studied herein to potentially better understand its interaction profile with wild- type tau protein (tau-441). Recently, its chemical reactivity profile with K18, a tau-441 fragment containing all four MT- binding domains responsible for the fibrillization process, has been analyzed thoroughly, demonstrating that this peptide is prone to covalent modification by 1 in an unspecific fashion, due to its unstructured conformation. 14 Starting with this information, the ability of oleocanthal to interfere with the tau fibrillization process has been analyzed along with an Received: May 31, 2012 Article pubs.acs.org/jnp © XXXX American Chemical Society and American Society of Pharmacognosy A dx.doi.org/10.1021/np300384h | J. Nat. Prod. XXXX, XXX, XXX-XXX