Access Type

Open Access Dissertation

Date of Award

January 2020

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Biomedical Engineering

First Advisor

Mahendra . Kavdia

Abstract

Oxidative stress and endothelial dysfunction are reported in the cardiovascular and neurovascular diseases. Oxidative stress is caused due to an increase in the generation of reactive oxygen (ROS) and nitrogen species (RNS) and incapacity of antioxidant systems to eliminate ROS and RNS. Endothelial dysfunction is characterized by a reduction in nitric oxide (NO) bioavailability. NO is constitutively produced by enzyme endothelial nitric oxide synthase (eNOS). A reduction in tetrahydrobiopterin (BH4), which is an essential cofactor of eNOS, can lead to eNOS uncoupling. There is complex interplay between the ROS/RNS and antioxidant system underlying pathophysiologies of vascular diseases, however our quantitative understanding of the oxidative stress and these biochemical species in endothelial cell is not complete. The overall objective of this dissertation is to investigate mechanistically the complex interactions of eNOS uncoupling, cellular oxidative stress, BH4 bioavailability and antioxidant levels in endothelial cells. We developed a series of mathematical models for eNOS biochemical pathway and downstream reactions involving interactions of ROS/RNS with antioxidant systems. Using these models, we investigated the effects of BH4 synthesis, ascorbate (ASC) and glutathione (GSH) on cellular ROS and RNS. Our model results showed that variations in the generation rates of superoxide (O2•-) and NO produces a wide range of outcomes for ROS/RNS levels that determines the cellular levels of oxidative stress. Variation in endothelial cell oxidative stress levels increases the extent of eNOS uncoupling and introduces instabilities in the eNOS based NO/ O2•- production rate. ASC supplementation removed these instabilities and resulted in improved NO and BH4 bioavailability. Enhancement of BH4 synthesis also showed improvement in eNOS uncoupling and NO production rate. ASC supplementation also resulted in increasing RNS level such as peroxynitrite (ONOO-). The GSH and glutathione peroxidase (GPX) kept in check the levels of ROS/RNS including ONOO- and hydrogen peroxide (H2O2) and resulted in decreasing cellular oxidative stress. Collectively, these models provide qualitative information about ROS/RNS levels in endothelial dysfunction. In addition, the therapeutic potential of cofactors, substrates and antioxidants can be analyzed using these models for effective treatments as well as earlier intervention in treating cardiovascular and neurovascular diseases.

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