Date of Award
Fall 2024
Document Type
Open Access Dissertation
Department
Chemical Engineering
First Advisor
Robert Micheal Gower
Abstract
Chronic inflammation is linked to several pathological conditions, including type 2 diabetes and autoimmune disease. Clinical treatments involve the systemic administration of anti-inflammatories (NSAIDs) or glucocorticoids to suppress inflammation. While effective, these treatments lead to side effects especially when in constant use and taken in high doses that are required for therapeutic efficacy. Consequently, it has been of growing interest to develop new strategies that can modulate sources of inflammation. Macrophages are immune cells that are ubiquitous throughout the human body and mediate inflammation. Also, macrophages internalize dying cells via phosphatidylserine (PS) to maintain homeostasis. On the surface of dying cells, PS acts as an “eat me” signal to macrophages. Accordingly, macrophages bind and take up PS-bearing dying cells through receptors. Interestingly, this activity is anti-inflammatory for the macrophage. Inspired by this biological function, we developed poly(lactide-co-glycolide) (PLG) particles that present PS on their surface like that of a dying cell to target macrophages and modulate inflammation. PLG is a biocompatible polymer that is employed in the fabrication of 19 FDA approved drug formulations using the pharma-friendly oil-in-water emulsion technique. We adapted this technique to incorporate PS onto the surface of PLG particles. To target macrophages, PS-presenting PLG (PS:PLG) particles were designed to be 2-3μm because particles in this size range are readily taken up by macrophages and too large for other cell types. We demonstrate that PS presentation increases PLG particles internalization by macrophages by 3-fold compared to control particles with no PS. Also, PS:PLG particles decreased inflammatory cytokine production by LPS activated macrophages. This effect was dependent on PS being presented on the PLG particle and could not be achieved by PS alone. A major contribution of this work is elucidating aspects of cell signaling that underlie the anti-inflammatory response to PS:PLG, which include Mer (a PS receptor), p21-activated kinase 1 (PAK1), and several mitogen-activated protein kinases (MAPKs), including ERK.
PS is found in high concentrations in the brain and thus largely sourced from bovine brains. In our first study, we described the synthesis of a phosphatidylserine (PS)-presenting poly(lactide-co-glycolide) (PLG). The PS used in that study was sourced from porcine brain. The porcine brain-derived PS presenting PLG (B-PS:PLG) particles effectively targeted macrophages and promoted an anti-inflammatory response. However, potential therapeutics sourced from animal brain may not be regarded as clinically safe, especially by the FDA due to the potential transmission of zoonotic diseases such as transmissible spongiform encephalopathy, mad cow disease. Therefore, the aim of this project was to investigate the use of synthetically derived PS, 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) as a safer alternative to porcine brain-derived PS (B-PS). Just like our first study, both the size of DOPS:PLG and B-PS:PLG particles were slightly lower than that observed from PLG particles, but the size of all particle types were within 2-3μm. DOPS:PLG presented with a unique flower-like morphology and B-PS:PLG presented with a spherical morphology after characterization with transmission electron microscopy (TEM). Also, an analysis with nuclear magnetic resonance (NMR) showed that DOPS:PLG particles had similar loading of DOPS, 0.06 mol DOPS/mol PLG compared to a 0.04mol B-PS/mol of PLG on B-PS:PLG particles. More than 80% of both particle formulations were internalized by macrophages while also possessing similar anti-inflammatory profiles. Overall, this study indicated that B-PS can be substituted with DOPS as a presumably safer option in the synthesis of PS-presenting PLG particles to potentially treat chronic inflammatory diseases.
Although PS:PLG particles are really good in targeting and modulating macrophage inflammatory response without any drug payload, PS:PLG was designed to serve as a drug delivery carrier. Hence, the final project explored encapsulating a drug in PS:PLG particles followed by some particle characterization. In addition, using carbodiimide chemistry, different functional groups were crosslinked with PLG polymer. Functionalized PLG polymer were used to synthesize PS:PLG particles with the potential of monitoring particle distribution in vivo and for diagnosis using PET imaging in future studies.
Rights
© 2025, Kidochukwu Justice Atube
Recommended Citation
Atube, K. J.(2024). Phosphatidylserine-Presenting Particles for Cell Targeting. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/8128