Influence of Surface Functionality of Poly(propylene imine) Dendrimers on Protease Resistance and Propagation of the Scrapie Prion Protein

Abstract

Accumulation of PrPSc , an insoluble and protease-resistant pathogenic isoform of the cellular prion protein (PrP C ) is a hallmark in prion diseases. Branched polyamines, including PPI (poly(propylene imine)) dendrimers are able to remove protease resistant PrP Sc and abolish infectivity, offering possible applications for therapy. These dendrimer types are thought to act through their positively charged amino surface groups. In the present study the molecular basis of the anti-prion activity of dendrimers was further investigated employing modified PPI dendrimers, in which the positively charged amino surface groups were substituted with neutral carbohydrate units of maltose (mPPI) or maltotriose (m3PPI). Modification of surface groups greatly reduced the toxicity associated with unmodified PPI, but did not abolish its anti-prion activity, suggesting that the presence of cationic surface groups is not essential for dendrimer action. PPI and mPPI dendrimer of generation 5 were equally effective in reducing levels of protease-resistant PrP Sc (PrP res ) in a dose-and time-dependent manner in ScN2a cells, and in preexisting aggregates in homogenates from infected brain. Solubility assays revealed that total levels of PrP Sc in scrapie infected mouse neuroblastoma (ScN2a) cells were reduced by mPPI. Coupled with the known ability of polyamino dendrimers to render protease-resistant PrP Sc in pre-existing aggregates of PrP Sc susceptible to proteolysis, these findings strongly suggest that within infected cells dendrimers reduce total amounts of PrP Sc by mediating its denaturation and subsequent elimination.

Differentiating Prion Strains Using Dendrimers

“…[20,37] PPIg4 and PAMAMg5 have a cationic surface charge, whilst the surface charge of 0.5mPPIg5 is also cationic, but lower in comparison to PPIg5. [19,20] In contrast to this, a neutral surface charge is present for the dense shell glycodendrimer mPPIg5. [19,20] The structure and molecular weights of the dendrimers used in this study are presented in Figure 1.…”

“…[19,20] In contrast to this, a neutral surface charge is present for the dense shell glycodendrimer mPPIg5. [19,20] The structure and molecular weights of the dendrimers used in this study are presented in Figure 1.…”

“…A minimum of three repeats was performed. [19,20] (A). Molecular structure of cationic 4 th generation poly(propylene imine) (PPIg4) with the smallest size used in biological experiments (B).…”

“…Dendrimers with cationic surface groups (PPIg4, PAMAMg5 and 0.5mPPIg5) were generally more potent and effective against a wider range of prion strains than mPPIg5, a dendrimer with neutral maltose surface groups (recently demonstrated to possess anti-prion properties due to H-bond driven interactions with PrP res ). [19,20] In fact mPPIg5 only exhibited activity against a single prion strain (RML) and required high concentrations to exhibit this effect (54 and 72µM). The potency of the different cationic dendrimers examined varied, indicating structure and size of dendrimer are important features in determining the efficacy of a dendrimer.…”

Nanomedicine for prion disease treatment

“…1 Since then numerous other dendrimer species have demonstrated anti-prion activity including phosphorous dendrimers, maltose-based glycodendrimers (mPPI), Poly(propyleneimine) (PPI) and the dendrimer like hyperbranched polymer poly(ethyleneimine) (PEI). [1][2][3][4][5] The ability of these dendrimers to eliminate PrP Sc from infected cells is dose and time dependent and increases with the generation number of the dendrimer. In addition, mPPI, PPI, PAMAM and high MW PEI are all capable of eliminating protease resistant PrP Sc from RML-infected brain homogenate, making these synthetic polymers the only known therapeutics to be effective against prions in both an intracellular and in vitro setting.…”