Date of Award

12-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Bioengineering

Committee Member

Dr. Martine LaBerge, Committee Co-Chair

Committee Member

Dr. Agneta Simionescu, Committee Co-Chair

Committee Member

Dr. Dan Simionescu

Committee Member

Dr. Eugene M. Langan III

Abstract

Drug-eluting stents have revolutionized the field of interventional cardiology and with the advent of their second-generation, percutaneous coronary intervention with drug-eluting stents is the clinically preferred method. These stents have shown remarkable performance in reducing neointimal hyperplasia and thus, clinical manifestation of restenosis. Despite significant technological advances in DES, high-risk patient populations are still affected by in-stent restenosis. Diabetes and hypertension are the two most common patient-specific complications that result in the development of restenosis even in DES era. Currently, percutaneous interventional approaches are not designed specifically to address the pathophysiological progression of restenosis in diabetic and hypertensive patients and as a result these high-risk patient cohorts continue to experience poorer prognosis. Absence of diabetes and/or hypertension specific stents or percutaneous interventional approaches is in part due to less emphasized basic research on understanding cellular response in diabetes and hypertension associated conditions owing to the lack of in vitro testing platforms capable of capturing the clinically relevant cellular response. Diabetes is characterized by hyperglycemia, insulin resistance and requires external insulin administration. Chronic high-glucose acclimation resulted in significantly greater phenotypic modulation of vascular smooth muscle cells under clinically relevant loading. In the current dissertation, an in vitro model has been developed simulating conditions observed in diabetic and hypertensive patients to better evaluate the response of VSMC, predict in-stent restenosis and evaluate the efficacy of sirolimus. This model combined insulin administration and elevated circumferential strain associated with diabetes and hypertension respectively, with low wall-shear stress induced by the presence of stent struts. Cellular response under these conditions closely simulates clinical conditions, in comparison to the current gold standard of conventional static cultures. Additionally, this model allows for a better understanding of VSMC response subjected to diabetes and hypertension simulated conditions during dynamic mechanical loading. Using this novel approach of combining mechanical loading and patient-specific biochemical environment, this dissertation successfully demonstrates significantly greater phenotypic modulation of chronic high-glucose acclimated rat aortic smooth muscle cells due to insulin administration under clinically relevant mechanical forces. Evaluation of phenotypic modulation was performed by comparing cell-cycle progression, induction of apoptosis, expression of contractile-state associated proteins all of which demonstrated significantly greater modulation with insulin administration under dynamic loading (p <0.0001 for all). Hypertension-associated elevated mechanical strain resulted in a proliferative phenotype (p < 0.001), induced apoptosis (p < 0.001) and reduced the expression of contractile state proteins (p < 0.001). Subjecting cells to insulin administration under hypertension-associated cyclic mechanical strain with low-flow shear stress further enhances dedifferentiation of RASMCs. The combined effects of hypertensive mechanical forces and insulin administration associated with diabetes management significantly affected cell response where cells under hypertensive loading during insulin administration demonstrated significantly greater percentage of cells in the S (p< 0.0001) and G2/M phase (p< 0.0001). These conditions also resulted in significantly reduced expression of contractile markers (p-value < 0.0001 for αSM-actin and SM22α). As a model application, sirolimus a commonly used drug in stents was evaluated under diabetic-hypertensive conditions. Lower efficacy of sirolimus was observed under these conditions which necessitates development and identification of novel drugs and therapeutic targets, to address the greater phenotypic modulation associated with these patient-specific conditions and may also explain the poorer outcomes of sirolimus -eluting stents in diabetic patients requiring insulin administration and presenting with hypertension. The proposed cell-response evaluation model provides a tool to investigate cellular and molecular mechanisms, testing novel drug and identifying important molecular targets for the specific patient cohort.

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