Biodegradable polymeric nanoparticles for neuroprotection against neonatal brain injury

Thesis (Ph.D.)--University of Washington, 2021Hypoxic-ischemic encephalopathy (HIE) is the leading cause of permanent brain injury in term newborns. HIE can lead to significant impairments during development and adulthood including cerebral palsy, learning disability, and epilepsy. Currently, there is no effective cure for HIE, and the standard-of-care only offers a 15% reduction in the risk of death or disability. This thesis project is focused on an engineering approach to the development of novel treatment strategies for this devastating disease. First, we must understand and evaluate the disease physiology in order to determine the desired therapeutic activity: how will a therapeutic enter the brain and interrupt injury pathways? It is well known that HIE is initiated as a result of low flow of oxygen and blood flow to the brain (hypoxic-ischemia, or HI), producing a crisis of energy failure. This crisis precipitates excitotoxicity and neuroinflammation, which propagate the resulting injury over hours, days, and years. However, critical intervention points remain unknown, including the time window for effective treatment and the permeability of delivery barriers in the brain. We demonstrate that injury can be ameliorated by curcumin, a broad-acting anti-inflammatory and antioxidant molecule, when incorporated into a nanoparticle formulation for improved solubility and stability (Chapter 3). This supports the further investigation of drugs which are able to target inflammatory and oxidative stress pathways. We additionally use an ex vivo brain slice model to assess nanoparticle transport in the diseased brain microenvironment, discovering disease-mediated disruptions to the extracellular matrix and changes in microglial uptake of nanoparticles (Chapter 4). This supports the further investigation of nanotechnology for applications in brain-targeted drug delivery. Next, we optimized the nanoformulation to more effectively address delivery challenges. Small molecule drugs and biologics face challenges including limited solubility, low circulation time, and low penetration of the brain. Drug encapsulation in a poly(lactic-co-glycolic acid) (PLGA) nanoparticle is an accessible solution, especially as PLGA nanoparticles have been FDA-approved in other disease applications. As we will demonstrate, the PLGA nanoparticle platform can be tailored for improved brain penetration by modulating surface properties: 1) the conjugation of poly(ethylene glycol) (PEG), which improves nanoparticle diffusive ability through brain tissue, and 2) the inclusion of surfactants in the formulation, specifically polysorbate 80 (P80), which improves brain cell-specific targeting (Chapter 5). The investigation of a brain-penetrating, cell-specific drug delivery platform is relevant for a variety of brain diseases and allows for tailoring the formulation specifically to the HIE model. This project culminates by evaluating the optimized PLGA-PEG/P80 nanoparticle platform for catalase drug delivery after HIE (Chapter 6). Catalase is a therapeutic enzyme that combats oxidative stress disease pathways but exhibits poor nanoparticle encapsulation due to its hydrophilic nature. Using a hydrophobic ion-pairing technique to increase catalase’s hydrophobicity, we formulate catalase-loaded PLGA-PEG/P80 nanoparticles. After in vivo administration in the HIE model, we demonstrate catalase nanoparticle accumulation in the injured tissue and a significant neuroprotective effect. The work in this thesis supports the further investigation of curcumin and catalase nanoformulations for the treatment of HIE. More broadly, it demonstrates that a range of therapeutic cargo can be successfully incorporated into biodegradable, brain-penetrating nanoparticles for application across the spectrum of neurological disorders