General framework

This introductory chapter briefly presents some of the main notions that appear in the subsequent chapters of this book. We recap a few definitions and results from combinatorics on groups and words, formal language theory, morphic words, k-automatic and k-regular sequences, and dynamical systems. Our aim is not to be exhaustive. The reader can consult this chapter when studying other parts of this book. © Springer International Publishing AG, part of Springer Nature 2018

Influence of surface functionality of poly(propylene imine) dendrimers on protease resistance and propagation of the scrapie prion protein

Accumulation of PrP(Sc), 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 antiprion 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 antiprion activity, suggesting that the presence of cationic surface groups is not essential for dendrimer action. PPI and mPPI dendrimers 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 pre-existing 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

Distribution and Kinetics of Lipoprotein-Bound Endotoxin

Lipopolysaccharide (LPS), the major glycolipid component of gram-negative bacterial outer membranes, is a potent endotoxin responsible for pathophysiological symptoms characteristic of infection. The observation that the majority of LPS is found in association with plasma lipoproteins has prompted the suggestion that sequestering of LPS by lipid particles may form an integral part of a humoral detoxification mechanism. Previous studies on the biological properties of isolated lipoproteins used differential ultracentrifugation to separate the major subclasses. To preserve the integrity of the lipoproteins, we have analyzed the LPS distribution, specificity, binding capacity, and kinetics of binding to lipoproteins in human whole blood or plasma by using high-performance gel permeation chromatography and fluorescent LPS of three different chemotypes. The average distribution of O111:B4, J5, or Re595 LPS in whole blood from 10 human volunteers was 60% (±8%) high-density lipoprotein (HDL), 25% (±7%) low-density lipoprotein, and 12% (±5%) very low density lipoprotein. The saturation capacity of lipoproteins for all three LPS chemotypes was in excess of 200 μg/ml. Kinetic analysis however, revealed a strict chemotype dependence. The binding of Re595 or J5 LPS was essentially complete within 10 min, and subsequent redistribution among the lipoprotein subclasses occurred to attain similar distributions as O111:B4 LPS at 40 min. We conclude that under simulated physiological conditions, the binding of LPS to lipoproteins is highly specific, HDL has the highest binding capacity for LPS, the saturation capacity of lipoproteins for endotoxin far exceeds the LPS concentrations measured in clinical situations, and the kinetics of LPS association with lipoproteins display chemotype-dependent differences