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Polymer therapeutics to modify cellular responses in impaired human wound healing.

Hardwicke, Joseph Thomas. 2009. Polymer therapeutics to modify cellular responses in impaired human wound healing. PhD Thesis, Cardiff University.

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Abstract

Chronic ulceration of the lower limb represents a significant clinical challenge in today's aging society. Depletion of growth factors at the chronic wound site by proteinases and reactive oxygen species, can lead to a protracted non-healing wound. Growth factors are known to act in concert to promote wound repair, but their topical application rarely leads to a significant clinical improvement in chronic wounds, due to premature inactivation in the wound environment. The aim of this Study was to synthesise and characterise a polymer-growth factor conjugate and to investigate whether the novel concept, called Polymer-masking-UnMasking-Protein Therapy (PUMPT), may be used to generate bioresponsive, polymer therapeutics, promoting tissue repair. Dextrin and recombinant human epidermal growth factor (rhEGF) were chosen as a first model combination. Dextrin was first modified by succinoylation and conjugated to rhEGF. The synthesised dextrin-rhEGF conjugate exhibited increased stability towards proteolytic degradation by the clinically relevant enzyme, neutrophil elastase. The dextrin component was degraded on exposure to physiological levels of a-amylase, leading to sustained release of free rhEGF. Biological activity was assessed in proliferation assays in vitro, using cells involved in the normal healing response. Polymer conjugation reduced rhEGF bioactivity, however, after exposure to physiological concentrations of a-amylase, dextrin degradation led to restoration of bioactivity of rhEGF, to the level observed with unmodified rhEGF. Dextrin-rhEGF was demonstrated to induce phosphorylation of the epidermal growth factor receptor (EGFR), and confirmed a mechanism of action by stimulation of classical signal transduction pathways. Analysis of ex vivo acute and chronic wound fluids, confirmed the presence of a-amylase, at levels similar to those used in vitro. Chronic wound fluid also contained active neutrophil elastase. In an ex vivo organotypic model of acute corneal wound healing, a-amylase-exposed dextrin-rhEGF was demonstrated to enhance wound healing, above that of free rhEGF. In an in vivo model of impaired wound healing in the genetically diabetic (db/db) mouse, dextrin-rhEGF was observed to significantly enhance dermal wound healing, on topical application, at delayed intervals. This is the first application of the PUMPT hypothesis in vivo, and supports the further development of polymer-protein conjugates as bioresponsive nanomedicines for tissue repair.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Dentistry
Subjects: R Medicine > R Medicine (General)
R Medicine > RK Dentistry
ISBN: 9781303197048
Funders: The Healing Foundation, Welsh Office for Research and Development
Date of First Compliant Deposit: 30 March 2016
Last Modified: 12 Feb 2016 23:12
URI: http://orca.cf.ac.uk/id/eprint/54515

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