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Design of novel biologically active polymers to enhance drug delivery across epithelial barriers.

Phelps, Karen. 2006. Design of novel biologically active polymers to enhance drug delivery across epithelial barriers. PhD Thesis, Cardiff University.

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Numerous linear, water-soluble polymers (particularly polyanions) are biologically active and can induce cytokines such as tumour necrosis factor-alpha (TNF-a), interferon-gamma (IFN-y) and interleukin-2 (IL-2) from cells depending on their molecular weight (MW), and composition. The proinflammatory cytokines TNF-a and IFN-y are able to permeabilise epithelial barriers by affecting the protein composition of the tight junctions (TJ) (Walsh et al, 2000). The aim of this work was to identify polymers that would promote enhanced drug delivery due to their inherent ability to stimulate TNF-a, IFN-y and IL-2 release, and therefore transiently permeabilise epithelial barriers. Several linear polyanions already used as excipients, including alginate, hyaluronic acid (HA), and polyacrylic acids (PAcA; MW 30,000, 100,000, or 450,000 Da), were chosen as the first polymer library to investigate. Branched polymers including polyamidoamine (PAMAM) generation 3.5 dendrimers and the polycation polyethylenimine, PEI (MW 750,000 Da), were also studied. Polyanions showed little cytotoxicity towards B16F10 cells and ECV304 cells at 72 h except PAcA of MW 100,000 Da in both cell lines, and 450,000 Da in B16F10. PEI was cytotoxic at low concentrations. Decreasing the incubation time to 1 h reduced polymer cytotoxicity (IC50 > 1 mg/mL) with the exception of PEI. Highest amounts of TNF-a, IL-2 and IFN-γ release from B16F10 and RAW 246.7 cells were seen with PEI (1 mg/mL). HA and HA sodium salt induced TNF-y release from DU937 cells in concentration-dependant manner. In transport studies, FITC-dextran transfer was greatest in the Ap-Bas direction, and in the absence of Peyer's patches. Cytokines had no significant effect on FITC-dextran transport, at either physiological or ng/mL concentrations. Polymers appeared to inhibit FITC-dextran transport in all directions and tissue types, though apically applied PAcA (MW 30,000 Da) and HA (1 mg/mL), showed some increase. This data was not significant. Lastly, PAcA (MW 30,000 Da) and PAMAM generation 3.5 dendrimers were labelled with OG cadaverine (OGcad) to monitor their transport across rat intestinal tissue (with or without Peyer's patches) also using the vertical diffusion system. The uptake of the polymers into Caco-2BBe cells (chosen as an enterocyte model) was investigated using flow cytometry. Fluorescently-labelled PAcA- (MW = 30,000 Da) and PAMAM-OG conjugates showed a greater rate of transport in the Bas-Ap direction. The conjugates did not appear to be taken up by Caco-2BBc cells. Although the scientific literature had suggested that certain polymers promote cytokine release, and that specific cytokines increase gastrointestinal permeability, it proved difficult here to validate the hypothesis that polymers might be designed to enhance transport in a reproducible and safe manner.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Pharmacy
Subjects: R Medicine > RM Therapeutics. Pharmacology
ISBN: 9781303175077
Funders: BBSRC
Date of First Compliant Deposit: 30 March 2016
Last Modified: 12 Feb 2016 23:12

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