Activation of Human Complement System by Dextran-Coated Iron Oxide Nanoparticles Is Not Affected by Dextran/Fe Ratio, Hydroxyl Modifications, and Crosslinking

While having tremendous potential as therapeutic and imaging tools, the clinical use of engineered nanoparticles has been associated with serious safety concerns. Activation of the complement cascade and release of proinflammatory factors C3a and C5a may contribute to infusion-related reactions, whereas opsonization with C3 fragments promotes rapid recognition and clearance of nanomaterials by mononuclear phagocytes. We used dextran-coated superparamagnetic iron oxide nanoparticles (SPIO), which are potent activators of the complement system, to study the role of nanoparticle surface chemistry in inciting complement in human serum. Using complement inhibitors and measuring levels of fluid phase markers (sC5b-9, C5a and Bb), we found that the majority of human complement activation by SPIO is through the alternative pathway (AP). SPIO prepared with high dextran/iron ratio showed some complement activation via calcium-sensitive pathways, but the AP was responsible for the bulk of complement activation and amplification. Activation via the AP required properdin, the positive regulator of the alternative C3bBb convertase. Modification of sugar alcohols of dextran with alkylating, acylating, or crosslinking agents did not overcome complement activation and C3 opsonization. These data demonstrate that human complement activation is independent of dextran modification of SPIO and suggest a crucial role of the AP in immune recognition of nano-assemblies in human serum

The Possible "Proton Sponge " Effect of Polyethylenimine (PEI) Does Not Include Change in Lysosomal pH.

Polycations such as polyethylenimine (PEI) are used in many novel nonviral vector designs and there are continuous efforts to increase our mechanistic understanding of their interactions with cells. Even so, the mechanism of polyplex escape from the endosomal/lysosomal pathway after internalization is still elusive. The “proton sponge ” hypothesis remains the most generally accepted mechanism, although it is heavily debated. This hypothesis is associated with the large buffering capacity of PEI and other polycations, which has been interpreted to cause an increase in lysosomal pH even though no conclusive proof has been provided. In the present study, we have used a nanoparticle pH sensor that was developed for pH measurements in the endosomal/lysosomal pathway. We have carried out quantitative measurements of lysosomal pH as a function of PEI content and correlate the results to the “proton sponge ” hypothesis. Our measurements show that PEI does not induce change in lysosomal pH as previously suggested and quantification of PEI concentrations in lysosomes makes it uncertain that the “proton sponge ” effect is the dominant mechanism of polyplex escape

On the issue of transparency and reproducibility in nanomedicine.

Following our call to join in the discussion over the suitability of implementing a reporting checklist for bio-nano papers, the community responds

Cationic carriers of genetic material and cell death: a mitochondrial tale

Central to gene therapy technology has been the use of cationic polymers as vectors for DNA and RNA (polyfectins). These have been presumed to be safer than viral systems which, for example, have been found to switch on oncogenes. Two key polycations that have been intensively researched for use as synthetic vectors are poly(ethylenimine) and poly(l-lysine). A frequent stumbling block with these polyfectins is that long-term gene expression in cell lines has not been achieved. Recently it has transpired that both of these polycations can induce mitochondrially mediated apoptosis. It is the aim of this review to discuss the mechanisms behind the observed polycation toxicity including roles for little studied cellular organelles in the process such as the lysosome and endoplasmic reticulum

Smart polymers in drug delivery: a biological perspective

Key to the widespread application of smart polymers in drug delivery is understanding the mechanistic interplay, as well as consequence, of the presence of these macromolecules within living systems. This review looks at these interactions in terms of host response to macromolecular structure and subsequent clinical implications. In order to highlight this, three distinct routes of drug delivery are discussed, enabling a journey from the outside of the body in to the cell. This is used to contrast the need for different scientific approaches replete to successful drug delivery in these physiologically diverse areas. The discussion initiates with the application of smart polymers to the oral route of drug delivery, followed by macromolecular fate within the systemic circulation and finally intracellular delivery. The advantages, in terms of biological performance, as well as the challenges of using smart polymers within this multifaceted arena are delineated