The Cardioprotective Role of the N-3 PUFA Metabolite 19,20-Epoxydocosapentaenoic Acid (19,20-EDP) in the Setting of Ischemia Reperfusion Injury
Creators: Essa, Ahmed M D
Publisher: name: University of Alberta Library
Year: 2022

<p>Ischemic heart disease (IHD) is a leading cause of cardiovascular morbidity and mortality worldwide. Myocardial ischemia occurs when a coronary artery is occluded and consequently blood supply to the heart is restricted depleting it of oxygen and nutrients. Although early myocardial reperfusion, or restoration of blood flow to the ischemic heart, is the standard therapeutic intervention to rescue viable myocardial tissue, reperfusion itself can paradoxically accelerate the death of injured cardiomyocytes, aggravating the damage and increasing the incidence of developing heart failure (HF). This phenomenon is termed as ischemia-reperfusion (IR) injury. Although the use of the currently available therapies, with early reperfusion, has contributed to the reduction in acute mortality rates after ischemic attacks, the risk of development of HF secondary to IR injury is still significantly high. Therefore, development of new therapeutic strategies to mitigate the consequences of IR injury becomes imperative.In the heart, mitochondria are the main source of energy that fuel the contractile apparatus. Accumulating literature demonstrates that impaired mitochondrial function has a significant role in the pathogenesis of myocardial IR injury. Moreover, it has been shown that the reactive oxygen species (ROS) burst from damaged mitochondria triggers the activation of the NLRP3 inflammasome which spread the inflammatory surge to the rest of the myocardium exacerbating cardiac injury secondary to IR injury.Long-chain omega-3 polyunsaturated fatty acids (n-3 PUFA) are essential constituents of the body, which have been attributed to numerous benefits including protection against cardiovascular disease. Docosahexaenoic acid (DHA), a major dietary n-3 PUFA, can be metabolized by cytochromes P450 (CYP) to generate six regioisomeric epoxylipids termed epoxydocosapentaenoic acids (4,5-, 7,8-, 10,11-, 13,14-, 16,17-, 19,20-EDP). There is growing evidence indicating that 19,20-EDP mediate many of the salutary effects of the parent compound DHA. However, EDPs are rapidly converted to the corresponding less biologically active vicinal diol by the enzyme soluble epoxide hydrolase (sEH). Accordingly, we hypothesized in this thesis that enhancing the cardiac levels of 19,20-EDP ameliorates IR injury via mitigating mitochondrial damage and limiting NLRP3 inflammasome activation.First, we investigated the differential cardioprotective effects of n-3 PUFAs and their CYP metabolites in the setting of IR injury. Our results demonstrated that perfusion of isolated wild type (WT) mouse hearts, subjected to IR injury in the Langendorff mode, with 19,20-EDP exerted cardioprotection as evidenced by a significant improvement in postischemic functional recovery associated with preserved mitochondrial function and significant attenuation of NLRP3 inflammasome complex activation. Second, we revealed that enhancing the cardiac levels of these epoxy metabolites via genetic deletion or pharmacological inhibition of sEH can also markedly limit mitochondrial dysfunction and attenuate the activation of the NLRP3 inflammasome complex and thus impart cardioprotection against IR injury. Third, we demonstrated that perfusion of mouse hearts with the more chemically and metabolically stable synthetic EDP surrogate, SA-26, significantly improved postischemic recovery and maintained cardiac ATP levels. Finally, we attempted to elucidate whether mitochondrial sirtuin 3 (SIRT3), the primary mitochondrial deacetylase that plays a pivotal role in regulating mitochondrial homeostasis, is directly involved in mediating the protective effects of 19,20-EDP against myocardial IR injury. Importantly, we revealed perfusion of hearts with 19,20-EDP in the isolated working heart model preserved mitochondrial quality and improved cardiac energy metabolism via directly activating SIRT3. Intriguingly, we demonstrated that 19,20-EDP markedly improved mitochondrial respiration and SIRT3 activity in fresh cardiac fibers isolated from human left ventricular tissues obtained from individuals with ischemic heart disease (IHD) collected through the Human Explanted Heart Program at University of Alberta. Furthermore, using molecular modeling and docking approaches, we proved that 19,20-EDP, via directly binding to the human SIRT3 protein, acts as a positive allosteric modulator (i.e., catalytic enhancer) that triggers SIRT3 activation.In summary, the data presented in this thesis highlight the beneficial role of 19,20-EDP in limiting IR injury via maintaining mitochondrial homeostasis and limiting NLRP3 inflammasome activation. Moreover, to the best of our knowledge, this work is the first to identify SIRT3 as a potential target for the epoxylipid 19,20-EDP and to reveal that direct binding of 19,20-EDP to SIRT3 significantly enhances its enzymatic activity. These studies provide new perspectives for the development of novel pharmacological agents, based on the structure of 19,20-EDP, to improve the clinical outcomes in the setting of IR injury.</p>