The goal of this thesis was to produce an animal model that develops atherosclerotic plaque featuring plaque neovascularization leading to intraplaque hemorrhage and is suitable for noninvasive imaging studies. Several strategies were tested for their effectiveness in producing such plaques in the rabbit aorta, including: a high cholesterol diet, vascular endothelial growth factor injections, therapeutic contrast ultrasound, and balloon catheter injury. It was found that a combination of the high cholesterol diet and balloon injury was able to achieve plaque neovascularization in a manner dependent on circulating plasma cholesterol levels. In addition, a contrast-enhanced magnetic resonance imaging technique implemented in the animal model was able to detect plaque neovascularization and monitor its change over time in a single group of animals. In conclusion, an animal model was created where plaque neovascularization occurs in a predictable fashion and can be studied with non-invasive magnetic resonance imaging.

An understanding of the interactions between orthopaedic and dental implant surfaces with the surrounding host tissue is critical in the design of next generation implants to improve osseointegration and clinical success rates. Critical to the process of osseointegration is the rapid establishment of a patent neovasculature in the peri-implant space to allow for the delivery of oxygen, nutrients, and progenitor cells. The central aim of this thesis is to understand how biomaterials regulate cellular and host tissue response to elicit a pro-angiogenic microenvironment at the implant/tissue interface. To address this question, the studies performed in this thesis aim to 1) determine whether biomaterial surface properties can modulate the production and secretion of pro-angiogenic growth factors by cells, 2) determine the role of integrin and VEGF-A signaling in the angiogenic response of cells to implant surface features, and 3) to determine whether neovascularization in response to an implanted biomaterial can be modulated in vivo. The results demonstrate that biomaterial surface microtopography and surface energy can increase the production of pro-angiogenic growth factors by osteoblasts and that these growth factors stimulate the differentiation of endothelial cells in a paracrine manner and the results suggest that signaling through specific integrin receptors affects the production of angiogenic growth factors by osteoblast-like cells. Further, using a novel in vivo model, the results demonstrate that a combination of a rough surface microtopography and high surface energy can improve bone-to-implant contact and neovascularization. The results of these studies also suggest that VEGF-A produced by osteoblast-like cells has both an autocrine and paracrine effect. VEGF-A silenced cells exhibited reduced production of both pro-angiogenic and osteogenic growth factors in response to surface microtopgraphy and surface energy, and conditioned media from VEGF-A silenced osteoblast-like cell cultures failed to stimulate endothelial cell differentiation in an in vitro model. Finally, the results show that by combining angiogenic and osteogenic biomaterials, new bone formation and neovascularization can be enhanced. Taken together, this research helps to provide a better understanding of the role of material properties in cell and host tissue response and will aid in the improvement of the design of new implants.

Computational structural biology Even with rapid advances in structure determination methods, there is a long gap to be bridged between the number of proteins that have been sequenced and the number whose three-dimensional structures have been experimentally elucidated. Experimentally protein structures are determined by X-ray crystallography or by nuclear magnetic resonance spectroscopy (NMR). X-ray crystal structures give a time averaged picture but little information on conformational dynamics. Though NMR gives dynamical information, the technique cannot be applied to systems whose molecular weight is large. Only small proteins fall within the ken of NMR experiments. In most cases the three dimensional structure of the protein alone cannot give a complete picture of its mechanism. It is also essential to know the interactions of proteins with other proteins, with their ligands and substrates in order to have a better understanding of their functioning. Computer modeling and simulations are now indispensable supplements to experimental structural biology. The last word in protein structure prediction method is far from being said but the ever-improving homology and ab-initio modeling methods give rise to optimism that sometime in the near future these methods will become almost as reliable as experimental techniques. Ligand docking onto protein molecules is as challenging a problem as protein structure predicting itself. Computer modeling methods to dock ligands have to search a wide region of conformational space besides taking into consideration issues of charge and shape complementarities.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2009.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 140-156). Also available online.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 140-156). Also available in print.

published_or_final_version / Anatomy / Master / Master of Philosophy

Medical imaging tools technologically supported by the recent advances in the areas of computer vision can provide systems that aid medical professionals to carry out their expert diagnostics and investigations more effectively and efficiently. Two medical application domains that can benefit by such tools are ophthalmology and Total Hip Replacement (THR). Although a literature review conducted within the research context of this thesis revealed a number of existing solutions these are either very much limited by their application scope, robustness or scope of the extensiveness of the functionality made available. Therefore this thesis focuses on initially investigating a number of requirements defined by leading experts in the respective specialisms and providing practical solutions, well supported by the theoretical advances of computer vision and pattern recognition. This thesis provides three novel algorithms/systems for use within image analysis in the areas of Ophthalmology and THR. The first approach uses Contourlet Transform to analyse and quantify corneal neovascularization. Experimental results are provided to prove that the proposed approach provides improved robustness in the presence of noise, non-uniform illumination and reflections, common problems that exist in captured corneal images. The second approach uses a colour based segmentation approach to segment, measure and analyse corneal ulcers using the HVS colour space. Literature review conducted within the research context of this thesis revealed that there is no such system available for analysis and measurement of corneal ulcers. Finally the thesis provides a robust approach towards detecting and analysing possible dislocations and misalignments in THR X-ray images. The algorithm uses localised histogram equalisation to enhance the quality of X-ray images first prior to using Hough Transforms and filtered back projections to locate and recognise key points of the THR x-ray images. These key points are then used to measure the possible presence of dislocations and misalignments. The thesis further highlights possible extensions and improvements to the proposed algorithms and systems.

This thesis consists of three main parts. An introduction to diode-pumped solid-state lasers, thermal modelling of solid-state lasers and rate-equation modelling of solid-state lasers. The first part explains the basic components and operation principles of a typical diode-end-pumped solid-state laser. The stimulated emission process, solid-state laser gain media, various pump geometries and a basic end-pumped laser resonator configuration are among the topics that are explained. Since thermal effects are one of the main limiting factors in the power-scaling of diode-pumped solid-state lasers, the second part of this thesis describes numerical and analytical thermal models that determine the thermal lens and thermally induced stresses in a laser crystal. As a first step, a time-independent numerical thermal model which calculates the three-dimensional temperature distribution in the laser crystal is implemented. In order to calculate the time dependent thermally induced stresses in a laser crystal, a coupled thermal-stress finite element analysis model was implemented. Even though some steady-state analytical solutions for simple crystal geometries do exist, the finite element analysis approach was taken so that the time dependent thermally induced stresses could be calculated for birefringent crystals of various geometries. In order to validate the numerical results, they are compared to experimental data and analytical solutions where possible. In the last part, the population dynamics inside the laser gain medium are described and modelled with a quasi-three-level rate-equation model. A comprehensive spatially resolved rate-equation model is developed and discussed. In order to simplify the implementation of the rate-equation model as a computer simulation, the spatial dependence of the laser parameters is ignored so that the model reduces to a singleelement plane-wave model. The simplified rate-equation model is implemented and solved numerically. The model is applied to a four-level CW and Q-switched Nd:YLF laser as well as a quasi-three-level QCW Tm:GdV04 laser. The models' predictions are thoroughly verified with experimental results and also with analytical solutions where possible. / Thesis (M.Med.Sc.)-University of KwaZulu-Natal, Durban, 2007.

Introduction Angiogenesis, the growth of new blood vessels from the pre-existing vasculature, is a pre-requisite for tumour growth and metastasis. Tumour-angiogenesis is regulated by various pro- and anti-angiogenic factors released by both endothelial and tumour cells, as well as by the micro-environment. Numerous studies have implicated various systems in the acquisition of the angiogenic phenotype. The present study sought to investigate the role of the kallikrein-kinin system (KKS) in tumour-angiogenesis. The kallikreins consist of two serine proteases, plasma and tissue kallikrein (TK), involved in the release of kinin peptides by enzymatic cleavage of kininogens. Stimulation of the cognate bradykinin receptors (BKR), B1R and B2R, mediates the mitogenic and vasoactive properties of kinins. In addition, TK activates matrix metallo-proteinases (MMPs) involved in extracellular matrix (ECM) degradation. The expression profiles of TK and kinins have been found to be dys-regulated in numerous human cancers, and several studies have demonstrated the involvement of the KKS in growth and metastasis of prostate tumours. Further, previous in vitro models in our laboratory have established an association between the KKS and prostate tumour-angiogenesis. In those studies it was postulated that the up-regulated TK (produced by endothelial and tumour cells) stimulated endothelial cell proliferation. Thus, the aim of the present study was to define the effects of the KKS and seek a direct correlation with angiogenesis using in vitro models with tumour conditioned medium (CM), kinin receptor agonists and antagonists. Methods Ethical approval for this project was granted by the Biomedical Research Ethics Committee, University of KwaZulu-Natal (reference number BE152/08). Micro-vascular endothelial cells represent a suitable in vitro angiogenic model and dermal micro-vascular endothelial cells (dMVECs) were obtained commercially for this purpose. The tumour model used in this study was an immortalised prostate cancer (DU145) cell line. The CM model involves the treatment of one cell line with the metabolites of another. In the angiogenic model, dMVECs were exposed to increasing concentrations of DU145 CM. Stimulation was further augmented with BKR agonists. Specific BKR antagonists were used to test the specificity of stimulation. In addition, vascular endothelial growth factor (VEGF) was tested as a positive proliferation control. The potential of these agents to induce proliferation and migration was determined using the 3-[4,5 dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and a modified Boyden chamber assay, respectively. Previous studies investigating the pro-angiogenic effects of CM differed, in many respects, in terms of their models and methodologies. In an attempt to fully explore the pro-mitogenic effects of CM on endothelial cells, various modifications, as well as alternate endothelial and tumour cell types, were employed in the present study. The mitogenic and migratory effect of BKR agonists and antagonists on DU145 cells was also assessed. Further, the tumour model was expanded to investigate the autocrine potential of the KKS, by investigating the effect of DU145 CM on DU145 migration. Results In the angiogenic model, although the addition of DU145 CM elicited a statistically significant increase in micro-vascular endothelial cell proliferation, this increase was very small (<10%) and not dose-dependent. Pre-incubation of dMVECs with a B1R or B2R antagonist did not influence this small effect of CM on proliferation. In addition, neither B1R nor B2R agonists, at any concentration, produced any significant proliferative effect on endothelial cells. In contrast to these findings VEGF, a well-known mitogen, was able to stimulate proliferation of dMVECs. Migration assays revealed that DU145 CM failed to stimulate endothelial cell motility. Further, neither BKR agonist displayed any chemo-attractant potential in those assays. The most important finding was in the tumour model, where stimulation with a B1R agonist significantly enhanced proliferation and especially migration of DU145 cells. In addition, pre-treatment with a B1R antagonist abolished both these effects. B2R agonists could not produce the same positive effect as the B1R agonist on growth and migration of prostate tumour cells. DU145 CM did not prove to be a migratory stimulus for DU145 cells at any concentration. Discussion Previous studies in our laboratory have shown prostate-tumour CM to promote proliferation of endothelial cells and have postulated that TK up-regulation may be the reason for this. However, the present study could not reproduce this effect of CM. Further, BKR antagonists had no notable or consistent effect on the minimal promotion of proliferation that had been produced by DU145 CM. In addition, selective BKR agonists failed to induce proliferation or migration of endothelial cells, key events in the angiogenic cascade. Although in contrast to some studies, the present study was unable to implicate the KKS in angiogenesis, tumour neo-vascularisation is a consequence of several angiogenic factors functioning together as opposed to a single, isolated factor. For example, we were able to demonstrate a positive mitogenic effect of VEGF on endothelial cells and it may be this as well as other factors in the CM that are responsible for the small proliferation we observed. Up-regulation of kallikreins and kinins in tumours may enhance fundamental events in tumourigenesis in an autocrine manner, and bradykinin (BK) has previously been shown to promote tumour growth in mouse models. Our study supported the involvement of the KKS in tumourigenesis. Although CM from DU145 cells did not self-stimulate the migration of these cells, a B1R agonist enhanced both proliferation and migration, an effect that was also abrogated by the relevant antagonist, indicating a role for kinins. In contrast to the findings of another study, stimulation of the B2R failed to significantly promote tumour growth or motility. However, this is not an unexpected finding because it is thought that the ubiquitous B2R mediates physiological effects in the prostate while the inducible B1R plays a role in prostate cancer pathology. In summary, this study lends support to the ongoing exploration of BKR antagonists as possible candidates in the development of alternate approaches to cancer therapy. This may be particularly beneficial to hormone-independent tumours, such as those of the prostate, for which there exists few effective treatment options. / Thesis (M.Med.)-University of KwaZulu-Natal, Durban, 2012.