Influence of oxygenated perfluorocarbon (oxyPFC) on survival and free radical production of ischemic cardiomyocytes [Elektronische Ressource] / vorgelegt von Jin Wang
Aus der Medizinischen Universitätsklinikder Albert-Ludwigs-Universität Freiburg i.Br.Abteilung Innere Medizin IIISchwerpunkt Kardiologie und AngiologieInfluence of Oxygenated Perfluorocarbon (oxyPFC) on Survival andFree Radical Production of Ischemic CardiomyocytesINAUGURAL-DISSERTATIONZur Erlangung des Medizinischen Doktorgrades der Medizinischen Fakultätder Albert-Ludwigs-Universität Freiburg i.Br.vorgelegt 2004vonJinWanggeboren in Beijin, ChinaiDekan: Prof. Dr. med. J. Zentner1. Gutachter: Prof. Dr. med. C. Hehrlein2. Gutachter: PD Dr. med. J. MartinJahr der Promotion: 2004ii本论文献给一贯支持我事业的家人和朋友To my husband, Ming Du, my son, William Du,my sister, Jing Wang, and my parentsiiiContents1.Introduction……………….……………………………………………………..111.1 Reperfusion injury……………………………………………………………..1 1.1.1 Definition of reperfusion injury…………………………………………...3 1.1.2. The mediators of reperfusion injury……………………………………...51.2. Therapeutic strategies for reperfusion injury…………………………………5 1.2.1. Free radical scavengers and antioxidants6 1.2.2. Inhibitors of neutrophils………………………………………………….6 1.2.3. Calcium channel blockers………………………………………………... 1.2.4. Administrtion of endogenous cardioprotectants – adenosine and nitric 6 oxide (NO)………………………………………………………………..7 1.2.5. Anti-apoptotic agents……………………………………………………..81.3 Perfluorocarbons..……………………………………………………………..8 1.3.1 History perspective………………………………………………………..8 1.3.
Aus der Medizinischen Universitätsklinik der AlbertLudwigsUniversität Freiburg i.Br. Abteilung Innere Medizin III Schwerpunkt Kardiologie und Angiologie
Influence of Oxygenated Perfluorocarbon (oxyPFC) on Survival and
Free Radical Production of Ischemic Cardiomyocytes
INAUGURALDISSERTATION
Zur Erlangung des Medizinischen Doktorgrades der Medizinischen Fakultät der AlbertLudwigsUniversität Freiburg i.Br.
1.1 Reperfusion injury Reestablishment of coronary flow (reperfusion) is necessary to resuscitate the ischemic or hypoxic myocardium. Timely reperfusion facilitates cardiomyocyte salvage and decreases cardiac morbidity and mortality. Modalities for reperfusion include thrombolysis, percutaneous coronary intervention (PCI), and coronary artery bypass grafting (CABG). Reperfusion of an ischemic area may lead to additional tissue injury beyond that generated by ischemia alone, this phenomenon is termed ‘reperfusion injury’ (Vermaet al., 2002).
1.1.1 Definition of reperfusion injury Reperfusion injury results in cardiomyocyte damage via myocardial stunning, microvascular and endothelial injury, and leads to irreversible cell damage or necrosis termed lethal reperfusion injury (Yellon and Baxter, 2000; Ambrosio and Tritto, 1999) (see Fig. 1).
Myocardial stunning Myocardial stunning is the bestestablished manifestation of reperfusion injury (Kloneret al., 2001; Ambrosio and Tritto, 2001). It is defined as ‘prolonged postischemic dysfunction of viable tissue salvaged by reperfusion’ (Kloner and Jennings, 2001a; 2001b; Braunwald and Kloner, 1982). In this scenario, reperfusion of either a globally or regionally ischemic myocardial tissue results in a period of prolonged, yet reversible, contractile dysfunction. The myocardium is essentially ‘stunned’ and requires a prolonged period of time before complete functional recovery (Kloner and Jennings, 2001a; 2001b; Kloneret al., 2001).
Microvascular dysfunction Microvascular dysfunction is another manifestation of reperfusion injury (Granger, 1999; Park and Lucchesi, 1999; Agati, 1999). Reperfusion causes marked endothelial cell
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dysfunction, which results in vasoconstriction, platelet and leukocyte activation, increased oxidant production, and increased fluid and protein extravasation. Although rare, severe microvascular dysfunction may limit adequate perfusion after reperfusion, a phenomenon termed noreflow . ‘’
Lethal reperfusion injury Lethal reperfusion injury is that reperfusion of a severely ischemic myocardium results in myocyte death and necrosis. This form of reperfusion injury is the most severe and is clearly irreversible (Vermaet al., 2002).
Fig. 1 Mechanisms and mediators of reperfusion injury.Reperfusion includes routine treatment for acute myocardial infarction like thrombolysis and percutaneous coronary intervention, coronary artery bypass grafting, and cardiac transplantation. Reperfusion injury results from several complex and interdependent mechanisms that involve the generation of oxygen free radicals, endothelial dysfunction and microvascular injury, alteration in calcium handling, altered myocardial metabolism, and insufficiency of endogenous protective mechanisms. Reperfusion injury results in myocardial stunning, microvascular and endothelial injury, and irreversible cell damage or necrosis termed lethal reperfusion injury.
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1.1.2 The mediators of reperfusion injury Several mechanisms and mediators of reperfusion injury have been described. The most frequently cited include oxygen free radicals, endothelial and microvascular dysfunction, intracellular calcium overload, altered myocardial metabolism, and endogenous protective mechanisms (Granger, 1999; Park and Lucchesi, 1999; Agati, 1999; Carden and Granger, 2000).
Generation of oxygen free radicals The generation of oxygen free radicals is a key process in the development of reperfusion injury (Beard al., et 1994). Bolliet al. first showed that potent oxidant radicals are produced within the first few minutes of reflow and play a crucial role in the development of reperfusion injury (Bolliet al.,1989). Molecules involved in free radical reactions include superoxide anion, hydroxyl radical, hydrogen peroxide, peroxynitrite, and hypochlorous acid. Free radicals contain an unpaired electron and are accordingly highly reactive (Beard al., et Oxygen free radicals can be generated by 1994). mitochondria during oxidative phosphorylation and by activation of cellular enzymes including NAD(P)H oxidase, cyclooxygenase, nitric oxide synthase and xanthine oxidase (Mohazzabet al.,1994; Bolliet al.,1989; Xia and Zweier, 1997). Oxygenderived free radicals produce damage by reacting with polyunsaturated fatty acids, resulting in the formation of lipid peroxides and hydroperoxides that damage the sarcolemma and impair the function of membranebound enzyme systems. Free radicals stimulate the endothelial release of platelet activating factor, which attracts more neutrophils and amplifies the production of oxidant radicals and the degree of reperfusion injury. Hydrogen peroxide also quench nitric oxide, exaggerating endothelial injury and microvascular dysfunction. In addition to an increased production, there is also a relative deficiency in endogenous oxidant scavenging enzymes, which further exaggerates free radicalmediated cardiac dysfunction (Jordanet al., 1999).
Endothelial dysfunction and microvascular injury Reperfusion causes marked endothelial cell dysfunction. It impairs endothelium dependent vasodilatation, whereas the responses to endotheliumdependent
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vasoconstrictors are exaggerated. Increased production of potent vasoconstrictors, such as endothelin1 and oxygen free radicals, increases coronary vasoconstriction and reduces blood flow. Furthermore, endothelial dysfunction facilitates the expression of a prothrombotic phenotype characterized by platelet and neutrophil activation, important mediators of reperfusion injury (Granger, 1999; Jordanet al., 1999; Carden and Granger, 2000).
Alterations in calcium turnover Ischemia and reperfusion are associated with increased levels of intracellular calcium. Intracellular calcium overload alters myofilament sensitivity to calcium (Gaoet al., 1996; 1997). The rise in intracellular calcium also causes an increase in mitochondrial calcium. This leads to a decrease of mitochondrial ability to generate ATP limiting metabolic recovery of the myocyte (Silverman and Stern, 1994).
Altered myocardial metabolism Production of lactate contributes to a delayed functional recovery of the myocardium (Raoet al., 2001). The activity of mitochondrial pyruvate dehydrogenase is inhibited by 40% after ischemia and remains depressed for up to 30 minutes after reperfusion (Meranteet al., 1998; Raoet al., 1998).
Insufficiency of endogenous protective mechanisms The most important endogenous protective mechanisms are adenosine production, opening of mitochondrial ATPsensitive potassium (mitoK+ATP) channels, and release of nitric oxide (NO) (Przyklenk, 2001). Adenosine is an endogenous cardioprotective agent and is present in low concentrations in the normal myocardium. It increases during ischemia and reperfusion and is released during ischemia exerting its beneficial effects via opening of mitoK+ATP channels (VintenJohansenet al., 1999; Olafssonet al., 1987). Endotheliumderived NO produces a variety of biological actions that indicate a protective role during myocardial ischemia and reperfusion. NO is a powerful vasodilator and may improve blood flow during reperfusion. In addition, NO inhibits adherence of