Attenuation of β-amyloid induced toxicity by sialic acid-conjugated dendrimeric polymers Dhara Patel, James Henry 1 , Theresa Good ⁎ Department of Chemical and Biochemical Engineering, University of Maryland Baltimore County (UMBC), 1000 Hilltop Circle, Baltimore, MD 21250, USA Received 18 April 2006; received in revised form 10 August 2006; accepted 11 August 2006 Available online 17 August 2006 Abstract β-amyloid (Aβ) is the primary protein component of senile plaques in Alzheimer's disease and is believed to be associated with neurotoxicity in the disease. We and others have shown that Aβ binds with relatively high affinity to clustered sialic acid residues on cell surfaces and that removal of cell surface sialic acids attenuate Aβ toxicity. In the current work, we have prepared sialic acid conjugated dendrimeric polymers and assessed the ability of these sialic acid conjugated dendrimers to prevent Aβ toxicity. Flow cytometry was used to analyze viability of SH-SY5Y neuroblastoma cells and the effects of soluble and clustered sialic acid mimics on Aβ cell toxicity. Soluble sialic acid attenuation of Aβ induced toxicity was effective only at high sialic acid concentrations and low Aβ concentration. The sialic acid conjugated dendrimeric polymers were able to attenuate Aβ toxicity at micromolar concentrations, or approximately three orders of magnitude lower concentrations than the soluble sialic acid. The toxicity prevention properties of the sialic acid modified dendrimers were a function of dendrimer size. This work may lead to the development of new classes of therapeutics for the prevention of Aβ toxicity. © 2006 Elsevier B.V. All rights reserved. Keywords: Alzheimer's disease; Amyloid; Dendrimer; Sialic acid; Toxicity 1. Introduction Alzheimer's disease (AD) is the leading cause of neurode- generation in the United States, affecting approximately 4.5 million Americans in 2003 [1], with an annual cost of care for these individuals estimated at over $100 billion [2]. One of the pathological hallmarks of AD is the formation of amyloid plaques in the cerebral cortex, the primary protein component of which is the 39–43 amino acid peptide β-amyloid (Aβ) [3]. Aβ, in a number of aggregated states including fibrils, protofibrils, and spherical oligomers, has been shown to be toxic to neurons and neuron like cells in culture [4–6]. It is believed that Aβ may play a major role in neurodegeneration associated with AD. To that end, agents which either sequester Aβ or interfere with Aβ interaction/binding to cells have been sought after as a means to reduce the pathological effects of Aβ [7–11]. A variety of evidence suggests that Aβ binds to cells via an interaction with surface glycolipids or glycoproteins [12–22], and that the affinity of this interaction increases when the gangliosides or sialic acid molecules on the cell surface are clustered [15,23]. Based on these data, we hypothesized that membrane mimics could be synthesized which would reproduce the clustered sialic acid structure of the cell surface, and therefore compete with the cell surface for Aβ binding. To that end, we prepared sialic acid conjugated dendrimeric polymers and tested their ability to attenuate Aβ toxicity in a cell culture model. The sialic acid conjugated dendrimeric polymers were more effective than unconjugated dendrimers alone at reducing Aβ toxicity. Moreover, the same level of attenuation of Aβ toxicity was achieved at lower concentrations for sialic acid conjugated dendrimers with greater sialic acid functionality when compared to dendrimers with lower sialic acid function- ality. These results could have implications for the design of Biochimica et Biophysica Acta 1760 (2006) 1802 – 1809 www.elsevier.com/locate/bbagen ⁎ Corresponding author. Tel.: +1 410 455 3403; fax: +1 410 455 1049. E-mail address: tgood@umbc.edu (T. Good). 1 Current address: Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803, USA. 0304-4165/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.bbagen.2006.08.008