ABSTRACT
Protein therapeutics have the potential to treat a wide range of ailments due to the high specificity in their function and their ability to replace missing or mutated genes that encode for key cellular processes. Despite these advantages, protein drugs alone can cause adverse effects, such as the development of cross-reactive neutralizing antibodies. Through the encapsulation of proteins into nanoparticles, adverse effects and protein degradation can be minimized, thus improving protein delivery to sites of interest in the body. Nanoparticles comprised of poly(lactic acid-co-glycolic acid)-polyethylene glycol (PLGA-PEG) diblock copolymer are promising protein delivery systems as they are well characterized, non-toxic, and biocompatible. Desirable nanoparticle characteristics, such as neutral surface charge and uniformity in size and dispersity, can be achieved but often require the iterative manipulation of formulation parameters. Chain conformations in the formulation process are very important, and determining whether or not an extended or semi-collapsed polymer chain in the presence of a protein results in more favorable binding has yet to be investigated experimentally. Therefore, this work used atomistic molecular dynamics to examine the role of polymer extension on protein binding and its impact on the encapsulation process within PLGA-PEG nanoparticles. Three polymers (PLGA-PEG, PLGA, and PEG) were evaluated and iduronate-2-sulphatase (ID2S) was used as a model protein. We found highly expanded PLGA-PEG conformations led to more favorable binding with ID2S. Furthermore, PEG oligomers were observed to undergo transient binding with ID2S that was generally less favorable when compared to the other polymer types. The results also suggest that the relaxation times of the PLGA homopolymer and the PLGA-PEG copolymer at different molecular weights in relevant solvent mediums should be considered.
ABSTRACT
Neonatal hypoxic-ischemic encephalopathy is the leading cause of permanent brain injury in term newborns and currently has no cure. Catalase, an antioxidant enzyme, is a promising therapeutic due to its ability to scavenge toxic reactive oxygen species and improve tissue oxygen status. However, upon in vivo administration, catalase is subject to a short half-life, rapid proteolytic degradation, immunogenicity, and an inability to penetrate the brain. Polymeric nanoparticles can improve pharmacokinetic properties of therapeutic cargo, although encapsulation of large proteins has been challenging. In this paper, we investigated hydrophobic ion pairing as a technique for increasing the hydrophobicity of catalase and driving its subsequent loading into a poly(lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG) nanoparticle. We found improved formation of catalase-hydrophobic ion complexes with dextran sulfate (DS) compared to sodium dodecyl sulfate (SDS) or taurocholic acid (TA). Molecular dynamics simulations in a model system demonstrated retention of native protein structure after complexation with DS, but not SDS or TA. Using DS-catalase complexes, we developed catalase-loaded PLGA-PEG nanoparticles and evaluated their efficacy in the Vannucci model of unilateral hypoxic-ischemic brain injury in postnatal day 10 rats. Catalase-loaded nanoparticles retained enzymatic activity for at least 24 h in serum-like conditions, distributed through injured brain tissue, and delivered a significant neuroprotective effect compared to saline and blank nanoparticle controls. These results encourage further investigation of catalase and PLGA-PEG nanoparticle-mediated drug delivery for the treatment of neonatal brain injury.
