Oxidative Stress

Matt Simonson, PhD

Introduction

Coronary Heart Disease (CHD) is the major mortality cause in the Western Hemisphere. Reinstituting blood flow in the acutely occluded coronary vessel became the standard intervention to prevent Myocardial Infarct (MI) progression. Ever since their conception, thrombolysis, Percutaneous Coronary Intervention (PCI) and Coronary Artery Bypass Grafting (CABG) have been at the forefront of CHD treatment, thus limiting MI size (5). However, it quickly became apparent that after a period of ischemia, reperfusion itself sets off a cascade of events leading to cell injury (5). It seems that cellular changes in the ischemic period, prime the cell for a loss of homeostasis once blood flow returns (5). Generation of reactive oxygen species (ROS) has been found to be the main culprit in both ischemia-reperfusion injury (3).

These reactive oxygen species (ROS) are continuously formed in biological systems. ROS comes in common forms such as Superoxide (O2•−). These free radicals wreak havoc on the cell and lead to protein dysfunction, DNA damage, and lipid peroxidation, resulting in apoptosis as a result (3). Any increase in radical production or decrease in the defense against ROS induces oxidative stress. This imbalance between ROS formation and ROS detoxification is involved in a variety of pathogenic processes, such as ischemia-reperfusion (I/R) injury. Although mammalian cells including cardiomyocytes express endogenous free radical scavenging enzymes, such as superoxide dismutase (SOD), catalase, and glutathione peroxidase, these antioxidative defenses are overwhelmed after ischemia and reperfusion and homeostasis is not maintained (4). During the reperfusion phase following ischemia, production of ROS increases remarkably in complex I and III of the mitochondrial electron transport chain, thus leading to the breakdown of antioxidant systems and generation of rapid and severe damage (3).

Nonetheless, the cellular and molecular mechanisms behind this are far from being completely elucidated. Novel insight about this interplay and details about the extent by which each of these players contributes to ischemia-reperfusion injury may allow scientists to devise and design proper interventions that ultimately reduce I/R injury in clinical practice. This research explores the mechanisms behind reactive oxygen species production and possible relevant inhibitors in order to mitigate the effects of reperfusion following ischemia.

The Hydroxyl Radical

Hydrogen Peroxide specifically, is thought to be converted to the hydroxyl radical, which is considered to be one of the most highly oxidizing and reactive free radicals (2). This is proposed by many to be produced by the Fenton Reaction (1).

                                          Fe2+ + H2O2 ----> Fe3+ + •OH + -OH (2)

Analytic Methods

Spin Trapping Technique

Being so highly reactive and therefore dangerous, the hydroxyl radical has a very short in vivo half life of 10e-9 seconds, thus making it hard to isolate and study (4). In order to observe this radical and study it via electron paramagnetic resonance (EPR), e a spin trapping technique was utilized with the goal of perceiving a longer lasting and observable EPR signal. 100 microLiters of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used as this spin trap in a 10 mL 100 mM solution of Hydrogen Peroxide to form the DMPO-OH spin adduct. This was then reacted with a 10 mL 100 mM solution of Iron (II) Sulfate as the source of Iron for the proposed Fenton Reaction. At a rate of 0.250 mL per minute and an age of approximately 7.5 seconds, the following DMPO-OH radical signal was observed via electron paramagnetic resonance.

It is important to realize that DMPO-OH adduct can also form by a slow process that involves the nucleophilic addition of water to DMPO. Because water is the most abundant nucleophile in biological systems, it is not surprising that ti might lead to the formation of DMPO-OH. In order to observe this possible complication, a control trial can be carried out just as defined above except without any hydrogen peroxide present so as to observe the validity of utilizing DMPO as a spin trap.

References

1. Buettner, Gary, The Pecking Order of Free Radicals and Antioxidants: Lipid Peroxidation, α-Tocopherol, and Ascorbate, Archives of Biochemistry and Biophysics, 300, 2, pp 535-543. 1993.

2. LLoyd, Roger; Hanna, Phillip; Mason, Ronald, The origin of the hydroxyl radical oxygen in the fenton reaction, Free Radical Biology and Medicine, 22, 5, pp 885-888. 1997.

3. Finkel, T; Holbrook, NJ, Oxidants, oxidative stress and the biology of ageing, Nature, 408, pp 239-247. 2000

4. Valko, M; Leibfritz, D; Moncol, J; Cronin, M; Mazur, M.; Tesler, J, Free Radicals and Antioxidants in normal physiological Functions and Human Disease, The International Journal of Biochemistry & Cell Biology, 39, pp 44-84. 2007.

5. Bompotis, Georgios C; Deftereos, Spyridon; Angelidis, Christos; Choidis, Efthymios; Panagopoulou, Vasiliki; Kaoukis, Andreas; Vassilikos, Vassilios P; Cleman, Michael; Giannopoulos, Georgios, Altered Calcium Handling in Reperfusion Injury, Medicinal Chemistry, 12, 2, pp 114-130. 2016.