Influence of dendrimer’s structure on its activity against amyloid fibril formation B. Klajnert a, * , M. Cortijo-Arellano b , J. Cladera b , M. Bryszewska a a Department of General Biophysics, University of Lodz, Poland b Department of Biochemistry and Molecular Biology, Universitat Autonoma de Barcelona, Spain Received 3 April 2006 Available online 24 April 2006 Abstract Inhibition of fibril assembly is a potential therapeutic strategy in neurodegenerative disorders such as prion and Alzheimer’s diseases. Highly branched, globular polymers—dendrimers—are novel promising inhibitors of fibril formation. In this study, the effect of polyam- idoamine (PAMAM) dendrimers (generations 3rd, 4th, and 5th) on amyloid aggregation of the prion peptide PrP 185–208 and the Alz- heimer’s peptide Ab 1–28 was examined. Amyloid fibrils were produced in vitro and their formation was monitored using the dye thioflavin T (ThT). Fluorescence studies were complemented with electron microscopy. The results show that the higher the dendrimer generation, the larger the degree of inhibition of the amyloid aggregation process and the more effective are dendrimers in disrupting the already existing fibrils. A hypothesis on dendrimer–peptide interaction mechanism is presented based on the dendrimers’ molecular structure. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Dendrimer; Prion; Alzheimer; Amyloid peptide; Aggregation Amyloid fibrils are aggregates of normally soluble pep- tides or proteins. There is a group of diseases that are char- acterized by the deposition of amyloid fibrils. Among them there are neurological disorders such as Alzheimer’s and prion diseases. Thus, inhibition of fibril assembly is a potential strategy for therapeutic intervention. It has been recently shown that polyamidoamine and polypropylenei- mine dendrimers are promising candidates for the treat- ment of prion diseases [1,2]. These relatively novel macromolecules are globular and are characterized by a densely packed surface. Due to their specific structure they are suitable for a variety of biomedical applications. Den- drimers promote the clearance of pre-existing PrP Sc (the abnormally folded prion protein, which forms amyloid fibrils). Dendrimers also prevent the conversion of the nor- mal cellular PrP C into PrP Sc [1,2]. These branched poly- amines are the first class of compounds that have been shown to be able to cure a prion infection in living cells. This fact received considerable interest and other types of dendrimers were tested as possible anti-prion agents [3,4]. Amyloid fibrils can be produced in vitro by exposing disease-associated peptides to destabilizing conditions. We have chosen this approach with the aim of contributing to the molecular characterization of the interactions between dendrimers and peptides. We have used the third, fourth, and fifth generation of polyamidoamine dendrimers (PAMAM G3, PAMAM G4, and PAMAM G5) in order to study how dendrimers’ structure and size determine their effect on amyloid forma- tion. Dendrimers are built in a cyclic manner from a central core molecule that is surrounded by layers of branched monomers. The more layers are attached, the higher the so-called generation. As generation increases, the amount of surface groups increases too, so the shape of the dendri- mer changes from flat and ellipsoidal to globular [5]. In case of polyamidoamine dendrimers ethylenediamine is the core molecule and branched units are constructed from 0006-291X/$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2006.04.041 * Corresponding author. Fax: +48 42 635 44 74. E-mail address: aklajn@biol.uni.lodz.pl (B. Klajnert). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 345 (2006) 21–28 BBRC