Mechanism of thioflavin T accumulation inside cells overexpressing P-glycoprotein or multidrug resistance-associated protein: Role of lipophilicity and positive charge q Nacira Darghal, Arlette Garnier-Suillerot, Milena Salerno * Laboratoire de Biophysique Mole ´culaire, Cellulaire et Tissulaire (BioMoCeTi), UMR CNRS 7033, Universite ´ Paris 13 et Paris 6, 74 rue Marcel Cachin, 93017 Bobigny, France Received 6 March 2006 Available online 15 March 2006 Abstract Alzheimer’s disease is characterized by the presence of amyloid deposition. Thioflavin T (ThT) has been one of the molecules of choice to attempt the detection of these amyloid deposits. However, it has been reported that ThT was unable to cross blood–brain barrier (BBB). Our aim was to understand the mechanism according to which it has been said that ThT is not able to cross the BBB. For this purpose we have used cellular models overexpressing P-glycoprotein (P-gp) or multidrug resistance-associated protein (MRP1), two pro- teins overexpressed in BBB. Our results show that: (i) ThT is able to cross membranes and to penetrate inside the cells; (ii) ThT is a P-gp substrate; (iii) ThT is poor MRP1 substrate. In conclusion, our results suggest that two factors could be involved in the low accumulation of ThT in the brain: ThT is a P-gp substrate and its lipophilicity is low. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Alzheimer; Blood–brain barrier; Thioflavin T; b-Amyloid; P-glycoprotein; MRP1 In developed countries, the number of elderly people is growing rapidly and, therefore, an increase in neurodegen- erative and cerebrovascular disorders causing dementia is expected. Alzheimer’s disease (AD) is the most common cause of dementia. Early recognition and intervention facil- itates optimal care of Alzheimer’s patients and delays the morbidity with this progressive illness [1]. Alzheimer’s disease is a progressive neurodegenerative disorder characterized by the presence of amyloid deposi- tion and neurofibrillary tangles [2]. Quantitative detection of the b-amyloid deposits would provide an excellent bio- marker. Unfortunately, the lack of early detection in vivo of this amyloid deposits makes preclinical diagnosis of AD impossible, and it precludes assessment of therapies aimed at preventing or to reversing the course of the dis- ease. The major difficulty is attributed to the poor passage through the blood–brain barrier (BBB) of molecules able to detect the amyloid plaques within the brain [3,4]. The BBB is located between the blood and the brain extracellular space, in the endothelial cells of brain capillar- ies joined by tight junctions. The BBB is a major impedi- ment to the entry of many therapeutic drugs into the brain. A very significant number of molecules, among them many useful therapeutic drugs, have lower brain perme- ability because these molecules are substrates for the ABC-transporters which are present in the BBB. The activ- ity of these transporters very efficiently removes the drug from the central nervous system, thus limiting brain uptake [5]. P-glycoprotein (P-gp) was the first of these ABC-trans- porters to be described, followed by the multidrug resis- tance-associated proteins (MRP1) and more recently breast cancer resistance protein (BCRP). All are expressed 0006-291X/$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2006.03.024 q Abbreviations: AD, Alzheimer’s disease; BBB, blood–brain barrier; P-gp, P-glycoprotein; MRP1, multidrug resistance-associated protein; ThT, Thioflavin T. * Corresponding author. Fax: +33 1 48 38 88 88. E-mail address: m.salerno@smbh.univ-paris13.fr (M. Salerno). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 343 (2006) 623–629 BBRC