Exercise-Induced DNA Damage

: Effects of Hypoxia and Antioxidant Intervention

Abstract

Abstract
Reactive oxygen and nitrogen species (RONS) are continuously produced within the body during oxidative metabolism, and through normal immune function. When contained within a homeostatic balance, these molecules are part of a normal physiological function, and play integral signalling roles in cell growth, proliferation, and differentiation. This equilibrium is tightly regulated by a range of enzymatic and non-enzymatic antioxidants which seek to prevent detrimental reactions to biologically important macromolecules. The purpose of this thesis was twofold. Firstly, the use of various high-intensity exercise protocols was employed to investigate the effect on oxidative stress within circulating peripheral blood mononuclear cells and skeletal muscle tissue with a particular emphasis on DNA damage. Additionally, an environmental stressor was used via normobaric hypoxia to comprehensively elucidate the cell DNA damage-repair response, alongside systemic measures of oxidative stress following constant-load high-intensity exercise. Secondly, this thesis aimed to examine the efficacy of novel antioxidant supplementation on measures of exercise-induced oxidative stress; specifically, a plant-based combination of barley- and wheat-grass juice, and the mitochondrial-targeted antioxidant, Mitoquinone. Across all studies, it was confirmed that exercise of sufficient intensity (regardless of duration) provided a challenging physiological stress capable of inducing oxidative damage to DNA and lipids; likely through the generation of RONS, and concurrent reduction in antioxidant capacity. Furthermore, it was determined that peripheral blood mononuclear cells have an efficient and effective DNA damage-repair response, with maximal repair occurring within 24-hours for both single- and double-strand DNA damage; this response was marginally exacerbated in the hypoxic condition. The aforementioned modifications to DNA as a function of exercise, were concurrently aligned with systemic biomarkers of oxidative stress; including but not limited to, lipid peroxidation, lipid soluble antioxidants, and the ascorbyl free radical. With regards to plant-based antioxidant supplementation, although there was no meaningful prophylactic effect on a statistical level, a combination of barley- and wheat-grass juice did appear to provide a marginal protective effect against exercise-induced oxidative stress. On a more molecular level, mitochondrial-targeted supplementation for 21-days abrogated oxidative damage to the mitochondrial genome following high-intensity intermittent exercise; likely, through the scavenging of exercise-induced RONS, and/or secondary oxidation products of mitochondrial lipid peroxidation. The results of the studies demonstrate an increase in oxidative stress following high-intensity exercise as evidenced by an increase in DNA damage (single-strand breaks, double-strand breaks, base oxidation) across nuclear and mitochondrial genomes, and changes to other systemic measures, such as: lipid hydroperoxides, lipid soluble antioxidants, and the ascorbyl free radical. The DNA damage-repair response was exacerbated by normobaric hypoxia with single- and double-strand DNA damage returning to baseline by 48-hours and 24-hours respectively. Finally, the data also indicates a potential prophylactic effect by supplementing with a plant-based nutraceutical, and mitochondrial-targeted antioxidant; however, further research is warranted to elucidate the underlying biochemical processes.

Date of Award	May 2020
Original language	English
Supervisor	Ciara Hughes (Supervisor) & Gareth Davison (Supervisor)