Browsing by Author "Elhadj, Selim"
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- Chronic Shear Stress Effects on Endothelial Cell ResponseElhadj, Selim (Virginia Tech, 2001-12-10)The overall focus of this dissertation is on how chronic shear stress alters the synthesis and secretion of important regulatory molecules by endothelial cells. Our hypothesis was that inclusion of chronic pulsatile shear stress in our model would lead to changes in endothelial cell release of regulatory molecules. We distinguished between high arterial shear stresses and low venous shear stresses and used static cell cultures as reference. The first part of this research thus entailed the complete characterization of the flow dynamics in our experimental biomechanical model. Cell stretching can have a physiological effect on endothelial cells; hence we implemented a laser based optical technique for real time strain measurement of the growth fibers used in our culture system, and found that no significant strains were occurring during shear treatment. After characterization of the mechanical environment of the cells, we focused the scope of our research on metabolism of proteoglycans and insulin-like growth factor-I (IGF-I) and related IGF binding proteins (IGFBPs) in bovine aortic endothelial cells cultured under chronic pulsatile shear. We found that shear stress increased the release of proteoglycans and significantly altered proteoglycans distribution. We also found that there was an inverse relationship between the shear level treatment used to obtain the purified proteoglycans from endothelial cells and their potency in inhibiting coagulation. IGF-I release and message (IGF-I mRNA) was decreased at high shear stress compared to low shear stress. Further, the levels found under shear were significantly greater than those observed in the static cell culture model. IGFBPs released were also significantly increased by shear. This research thus establishes a link between chronic pulsatile shear stress and the metabolism of both primary (IGF-I) and secondary (IGFBPs, proteoglycans) regulators of vascular cell activity. The improved realism of our experimental biomechanical model has proved to be a valuable tool in improving the relevance of this study to vascular research. Ultimately, this research calls for further investigation in the molecular mechanisms underlying the phenomenological effects documented, which may help in understanding fundamental aspects in cardiovascular disease and its link to hemodynamics but our work is an important first step.
- Economic Feasibility of the Recovery of Therapeutic Proteins From the Milk of Transgenic LivestockElhadj, Selim (Virginia Tech, 1998-05-05)The recovery of pharmaceuticals from blood plasma is often expensive, limited, and is subject to contamination. The objective of this feasibility study is to present recovery designs and the most significant parameters affecting manufacturing costs of human Serum Albumin (hSA), human Protein C (hPC), and Factor VIII (FVIII) from the milk of transgenic livestock. All the processes presented are based on chromatography columns to achieve separation. The sensitivity of the manufacturing cost of the protein to various parameters are illustrated graphically and discussed, along with the cost distribution percentages for each type of process. It was found that manufacturing costs decrease with superficial velocity, expression levels, column yields, column capacities, and scale of production increases with all other parameters remaining constant. However the estimated cost decreases tend to level out at higher values of the parameters. Finally a judicious choice of separation scheme, such as Fall-Through (FT) versus Direct Adsorption (DA) for hSA production, can decrease the protein cost by as much as 38%, due to savings from wash and elution buffers. The costs associated with the production of hSA (DA process), hSA (FT process), hPC, and FVIII are 3.56, 2.20, 129, and 11,780 $/gr respectively. By means of the optimization of manufacturing parameters to reduce costs, key areas of emphasis for process development were identified.