Failure of superoxide dismutase and catalase to alter size of infarction in conscious dogs after 3 hours of occlusion followed by reperfusion

Do reactive oxygen species damage or protect the heart in ischemia and reperfusion? Analysis on experimental and clinical data

The role of reactive oxygen species (ROS) in ischemic and reperfusion (I/R) injury of the heart has been discussed for more than 40 years. It has been demonstrated that reperfusion triggers a multiple increase in free radical generation in the isolated heart. Antioxidants were found to have the ability to mitigate I/R injury of the heart. However, it is unclear whether their cardioprotective effect truly depends on the decrease of ROS levels in myocardial tissues. Since high doses and high concentrations of antioxidants were experimentally used, it is highly likely that the cardioprotective effect of antioxidants depends on their interaction not only with free radicals but also with other molecules. It has been demonstrated that the antioxidant N-2-mercaptopropionyl glycine or NDPH oxidase knockout abolished the cardioprotective effect of ischemic preconditioning. Consequently, there is evidence that ROS protect the heart against the I/R injury.

Role of Mitochondrial Calcium and the Permeability Transition Pore in Regulating Cell Death

Adult cardiomyocytes are postmitotic cells that undergo very limited cell division. Thus, cardiomyocyte death as occurs during myocardial infarction has very detrimental consequences for the heart. Mitochondria have emerged as an important regulator of cardiovascular health and disease. Mitochondria are well established as bioenergetic hubs for generating ATP but have also been shown to regulate cell death pathways. Indeed many of the same signals used to regulate metabolism and ATP production, such as calcium and reactive oxygen species, are also key regulators of mitochondrial cell death pathways. It is widely hypothesized that an increase in calcium and reactive oxygen species activate a large conductance channel in the inner mitochondrial membrane known as the PTP (permeability transition pore) and that opening of this pore leads to necroptosis, a regulated form of necrotic cell death. Strategies to reduce PTP opening either by inhibition of PTP or inhibiting the rise in mitochondrial calcium or reactive oxygen species that activate PTP have been proposed. A major limitation of inhibiting the PTP is the lack of knowledge about the identity of the protein(s) that form the PTP and how they are activated by calcium and reactive oxygen species. This review will critically evaluate the candidates for the pore-forming unit of the PTP and discuss recent data suggesting that assumption that the PTP is formed by a single molecular identity may need to be reconsidered.

Is Cardioprotection Dead?

For >4 decades, the holy grail in the treatment of acute myocardial infarction has been the mitigation of lethal injury. Despite promising initial results and decades of investigation by the cardiology research community, the only treatment with proven efficacy is early reperfusion of the occluded coronary artery. The remarkable record of failure has led us and others to wonder if cardioprotection is dead. The path to translation, like the ascent to Everest, is certainly littered with corpses. We do, however, highlight a therapeutic principle that provides a glimmer of hope: cellular postconditioning. Administration of cardiosphere-derived cells after reperfusion limits infarct size measured acutely, while providing long-term structural and functional benefits. The recognition that cell therapy may be cardioprotective, and not just regenerative, merits further exploration before we abandon the pursuit entirely.

Hemodynamic and Histopathologic Effects of Hydroxyethyl Starch and Superoxide Dismutase Following Splanchnic Arterial Occlusion in a Murine Model

The purpose of this study was to examine biophysical and biochemical approaches that would reduce circulatory collapse produced in a splanchnic artery occlusion (SAO) shock rat model. Sprague-Dawley rats were divided into six groups: (1) control (Ctl) rats—no infusions, n=5; (2) control rats receiving 10 mg/kg superoxide dismutase (SOD), n=7; (3) SAO shock rats—no infusion, n=7; (4) SAO shock rats receiving 1.75 mL of normal saline (Sal), n=7; (5) SAO shock rats receiving 1.75 mL of hydroxyethyl starch (HES), n=7; (6) SAO shock rats receiving SOD, n=7. All animals, except controls, underwent clamping of the celiac and superior mesenteric arteries for fifty minutes. Intravenous heparin (500 units/kg) was administered twenty minutes prior to clamping. Following release of the clamps mean arterial blood pressure (MABP) was monitored for an addi tional one hundred minutes. Animals whose MABP could not be maintained above 50 mmHg at one hundred minutes after reperfusion was initiated were considered nonsur vivors. Blood chemistries and serum osmolarity were measured at the end of each exper iment. HES was conjugated to 10 nm gold particles prior to infusion to allow HES location in electron micrographic (EM) studies. The following results were obtained:

The group 4 (HES) MABP was significantly higher than that in groups 2, 3, and 5 (P<.05), but not when compared with that in group 1 (controls). No significant differ ences were found in serum osmolarity. EM studies showed the HES-gold conjugate localized to the intravascular and interendothelial spaces of capillaries and postcapillary venules as compared with interstitial sites.

The authors conclude that HES can maintain MABP at significantly higher levels in an SAO shock rat model, unlike the results following infusions of normal saline or SOD. HES may act as both a capillary sealant and source of oncotic pressure. The lack of efficacy of SOD in this investigation may be due to the severity of the shock model and an inadequate dosing regimen. Further studies are needed to evaluate the rode of phar macologic agents along with fluid resuscitation and capillary sealants. Their combined use may in fact ultimately prove to be the optimal means to treat SAO shock.

Over-expression of catalase in myeloid cells confers acute protection following myocardial infarction

Cardiovascular disease is the leading cause of death in the United States and new treatment options are greatly needed. Oxidative stress is increased following myocardial infarction and levels of antioxidants decrease, causing imbalance that leads to dysfunction. Therapy involving catalase, the endogenous scavenger of hydrogen peroxide (H₂O₂), has been met with mixed results. When over-expressed in cardiomyocytes from birth, catalase improves function following injury. When expressed in the same cells in an inducible manner, catalase showed a time-dependent response with no acute benefit, but a chronic benefit due to altered remodeling. In myeloid cells, catalase over-expression reduced angiogenesis during hindlimb ischemia and prevented monocyte migration. In the present study, due to the large inflammatory response following infarction, we examined myeloid-specific catalase over-expression on post-infarct healing. We found a significant increase in catalase levels following infarction that led to a decrease in H₂O₂ levels, leading to improved acute function. This increase in function could be attributed to reduced infarct size and improved angiogenesis. Despite these initial improvements, there was no improvement in chronic function, likely due to increased fibrosis. These data combined with what has been previously shown underscore the need for temporal, cell-specific catalase delivery as a potential therapeutic option.

Delineating the relationships among the formation of reactive oxygen species, cell membrane instability and innate autoimmunity in intestinal reperfusion injury

Acute intestinal ischemia is a medical emergency with a high mortality rate, attesting to the need for a better understanding of its pathogenesis and the development of effective therapies. The goal of this study was to delineate the relationships among intracellular and extracellular events in intestinal ischemia/reperfusion (I/R) injury, particularly the formation of reactive oxygen species (ROS), cell membrane instability associated with lipid peroxidation and the innate autoimmune response mediated by natural IgM and complement. A murine model of natural IgM-mediated intestinal I/R was used. Mice overexpressing anti-oxidant enzyme SOD1 were found to have significantly reduced intestinal tissue damage and complete blockage of IgM-mediated complement activation compared with WT controls. To determine if cell membrane instability was an event intermediate between ROS formation and natural IgM-mediated innate autoimmune response, the cell membrane stabilizer (trehalose) was administered to WT mice prior to the induction of intestinal ischemia. Treatment with trehalose significantly protected animals from I/R injury and inhibited IgM-mediated complement activation although it did not prevent membrane lipid peroxidation. These data indicate that in normal mice subjected to I/R injury, intracellular ROS formation is an event upstream of the lipid peroxidation which results in cell membrane instability. The membrane instability leads to an innate autoimmune response by natural IgM and complement. Trehalose, a nontoxic disaccharide tolerated well by animals and humans, has promise as a protective agent for patients with medical conditions related to acute intestinal ischemia.

Loss of plasma membrane integrity, complement response and formation of reactive oxygen species during early myocardial ischemia/reperfusion

Loss of plasma membrane integrity (LPMI) is a hallmark of necrotic cell death. The involvement of complement and ROS in the development of LPMI during the early stages of murine myocardial ischemia-reperfusion injury was investigated. LPMI developed within 1 h of reperfusion to a level that was sustained through 24 h. C3 deposition became significant at 3-h reperfusion and thus contributed little to LPMI prior to this time. SOD1 transgenic mice had significantly less LPMI compared with WT mice at 1 h of reperfusion but not at later time points. Catalase transgenic mice were not protected from LPMI at 1-h reperfusion compared with WT mice, but had 69% less LPMI at 3-h reperfusion. This protection was transient. At 24-h reperfusion the LPMI of catalase transgenic mice was identical to that of WT mice. The delayed benefits of over-expressed catalase compared with SOD1 are consistent with its antioxidant action downstream of SOD1. The onset of LPMI occurs within 1 h of reperfusion at a level that is maintained through 24 h. ROS contribute significantly to LPMI during the first 3 h of reperfusion, while complement deposition, which becomes significant after 3-h reperfusion, may contribute thereafter.

Adding ROS quenchers to cold K+ cardioplegia reduces superoxide emission during 2-hour global cold cardiac ischemia

We reported that the combination of reactive oxygen species (ROS) quenchers Mn(III) tetrakis (4-benzoic acid) porphyrin (MnTBAP), catalase, and glutathione (MCG) given before 2 hours cold ischemia better protected cardiac mitochondria against cold ischemia and warm reperfusion (IR)-induced damage than MnTBAP alone. Here, we hypothesize that high K(+) cardioplegia (CP) plus MCG would provide added protection of mitochondrial bioenergetics and cardiac function against IR injury. Using fluorescence spectrophotometry, we monitored redox balance, ie reduced nicotinamide adenine dinucleotide and flavin adenine dinucleotide (NADH/FAD), superoxide (O(2) (•-)), and mitochondrial Ca(2+) (m[Ca(2+)]) in the left ventricular free wall. Guinea pig isolated hearts were perfused with either Krebs Ringer's (KR) solution, CP, or CP + MCG, before and during 27°C perfusion followed immediately by 2 hours of global ischemia at 27°C. Drugs were washed out with KR at the onset of 2 hours 37°C reperfusion. After 120 minutes warm reperfusion, myocardial infarction was lowest in the CP + MCG group and highest in the KR group. Developed left ventricular pressure recovery was similar in CP and CP + MCG and was better than in the KR group. O(2) (•-), m[Ca(2+)], and NADH/FAD were significantly different between the treatment and KR groups. O(2) (•-) was lower in CP + MCG than in the CP group. This study suggests that CP and ROS quenchers act in parallel to improve mitochondrial function and to provide protection against IR injury at 27°C.

Targeted intracellular catalase delivery protects neonatal rat myocytes from hypoxia-reoxygenation and ischemia-reperfusion injury

Hypoxia followed by reoxygenation and ischemia reperfusion cause cell death in neonatal rat ventricular myocytes primarily through the generation of oxidative stress. Extracellular catalase has not been effective in reducing or eliminating ischemia reperfusion- or hypoxia-reoxygenation-induced cell death due both to extracellular degradation and to poor cellular uptake.

AIMS

(1) To determine whether a cell-penetrating catalase derivative with enhanced peroxisome targeting efficiency (catalase-SKL) increases intracellular levels of the antioxidant enzyme in neonatal rat ventricular myocytes; and (2) to determine whether catalase-SKL protects against both hypoxia-reoxygenation and ischemia reperfusion injury.

METHODS

Neonatal rat ventricular myocytes were subjected to 3 or 6 h of hypoxia-reoxygenation or to 1 h of ischemia reperfusion. Extracellular catalase concentration, activity, and subcellular distribution were determined using standard techniques. Reactive oxygen species and related oxidative stress were visualized using 2',7'-dichlorofluorescin diacetate. Cell death was measured using trypan blue exclusion or lactate dehydrogenase release assays.

RESULTS

Extracellular catalase activity was higher in (catalase-SKL) transduced myocytes, was concentrated in a membranous cellular fraction, and potently inhibited oxidative stress. In contrast to nontransducible (unmodified) extracellular catalase, catalase-SKL-treated myocytes were protected against both hypoxia-reoxygenation and ischemia reperfusion.

CONCLUSIONS

(1) Catalase-SKL increased myocyte extracellular catalase content and activity and dramatically increased resistance to hydrogen peroxide-induced oxidation; (2) catalase-SKL protects against both hypoxia-reoxygenation and ischemia reperfusion; (3) catalase-SKL may represent a new therapeutic approach to protect hearts against myocardial hypoxia-reoxygenation or ischemia reperfusion.

The inflammatory response and cardiac repair after myocardial infarction

One of the most important therapeutic targets of current cardiology practice is to determine optimal strategies for the minimization of myocardial necrosis and optimization of cardiac repair following an acute myocardial infarction. Myocardial necrosis after acute myocardial infarction induces complement activation and free radical generation, triggering a cytokine cascade initiated by tumor necrosis factor-alpha (TNF-α) release. When reperfusion of the infarcted area is initiated, intense inflammation follows. Chemokines, cytokines and the complement system play an important role in recruiting neutrophils in the ischemic and reperfused myocardium. Cytokines promote adhesive interactions between leukocytes and endothelial cells, resulting in transmigration of inflammatory cells into the site of injury. The recruited neutrophils have potent cytotoxic effects through the release of proteolytic enzymes, and they interact with adhesion molecules on cardiomyocytes. In spite of the potential injury, reperfusion enhances cardiac repair; this may be related to the inflammatory response. Monocyte chemoattractant protein (MCP)-1 is upregulated in reperfused myocardium and can induce monocyte recruitment in the infarcted area. Monocyte subsets play a role in phagocytosis of dead cardiomyocytes and in granulation tissue formation. In addition, the transforming growth factor (TGF)-β plays a crucial role in cardiac repair by suppressing inflammation. Resolution of inflammatory infiltration, containment of inflammation and the reparative response affecting the infarcted area are essential for optimal infarct healing. Here, we review the current literature on the inflammatory response and cardiac repair after myocardial infarction.

Mechanisms underlying acute protection from cardiac ischemia-reperfusion injury

Mitochondria play an important role in cell death and cardioprotection. During ischemia, when ATP is progressively depleted, ion pumps cannot function resulting in a rise in calcium (Ca(2+)), which further accelerates ATP depletion. The rise in Ca(2+) during ischemia and reperfusion leads to mitochondrial Ca(2+) accumulation, particularly during reperfusion when oxygen is reintroduced. Reintroduction of oxygen allows generation of ATP; however, damage to the electron transport chain results in increased mitochondrial generation of reactive oxygen species (ROS). Mitochondrial Ca(2+) overload and increased ROS can result in opening of the mitochondrial permeability transition pore, which further compromises cellular energetics. The resultant low ATP and altered ion homeostasis result in rupture of the plasma membrane and cell death. Mitochondria have long been proposed as central players in cell death, since the mitochondria are central to synthesis of both ATP and ROS and since mitochondrial and cytosolic Ca(2+) overload are key components of cell death. Many cardioprotective mechanisms converge on the mitochondria to reduce cell death. Reducing Ca(2+) overload and reducing ROS have both been reported to reduce ischemic injury. Preconditioning activates a number of signaling pathways that reduce Ca(2+) overload and reduce activation of the mitochondrial permeability transition pore. The mitochondrial targets of cardioprotective signals are discussed in detail.

Oxidative stress in myocardial ischaemia reperfusion injury: a renewed focus on a long-standing area of heart research

Advances in the treatment of coronary artery disease have seen a significant drop in mortality and morbidity particularly amongst patients with acute myocardial infarction (MI). In particular, percutaneous trans-luminal balloon angioplasty (PTCA) with stenting to re-open atherosclerotic coronary arteries has yielded marked improvement in clinical outcome for patients with acute MI. Furthermore, with the advent of drug-eluting stents occurrence rates for coronary artery restenosis, one common clinical problem associated with angioplasty and stent deployment, have declined markedly. However, coronary restenosis in diabetic patients remains an on-going problem. The success of drug-eluting stents has seen a renewed focus on myocardial ischaemia reperfusion (IR) injury as this represents one area of research where many questions remain unanswered. In particular, the relationship between myocardial IR injury and decreased myocardial micro-vasculature re-flow post PTCA (that ultimately leads to poor clinical outcome and myocardial damage/dysfunction) is one area of research with the potential to decrease current complication rates further in patients suffering myocardial IR injury sustained during MI. This review discusses the role for oxidative stress, oxidant source(s) and both gene regulation and stem-cell therapy as potential strategic targets in the ischaemic myocardium, with the ultimate aim of providing significant cardioprotection in the setting of acute MI.

Hyperbaric oxygen: a new drug in myocardial revascularization and protection?

Ischemia-reperfusion injury (IRI) occurs following coronary artery revascularization. Reactive oxygen species (ROS) were initially thought to play a role in the pathogenesis of this injury. However, the evidence for this is inconclusive. Recent studies involving ischemic preconditioning have identified ROS as potential mediators for the cardioprotective effects observed following this technique. Furthermore, cardiac studies involving IRI and the use of hyperbaric oxygen (HBO) have demonstrated the ability of HBO to induce cardioprotection and to attenuate IRI. This review suggests the possible role for HBO as a new drug in the arena of myocardial revascularization and cellular protection. While there is mounting clinical evidence for this, a methodological understanding of HBO's cellular mechanisms of actions appears to be lacking. As such, this article attempts to draw the similarity between HBO and other protective oxidative stress mechanisms and then to speculate in an evidence-based manner its possible cellular mechanistic role as a drug via the generation of ROS.

Bosentan, the mixed ETA–ETB endothelin receptor antagonist, attenuated oxidative stress after experimental myocardial ischemia and reperfusion

Endothelin-1 has been shown to be associated with greater myocardial ischemia and reperfusion injury in which oxidative stress plays a key role. The efficacy of bosentan, a mixed ETA-ETB endothelin receptor antagonist, in protecting the myocardium from ischemia-reperfusion injury and oxidative stress was studied in open-chest Wistar rats. Anesthetized adult male rats (175-250 g b wt) underwent sham operation (SHAM group) or were subjected to 40 min of myocardial ischemia (MI) induced by temporary occlusion of the left anterior descending coronary artery (LAD) followed by 2 h reperfusion (R). Rats submitted to the MI-R protocol were administered bosentan at a dose of 3 mg/kg i.v. 20 min (BOS group) or saline (CON group) 20 min post-occlusion of LAD. After the 2 h reperfusion period the animals were euthanized and the heart rapidly excised. Cardiac tissue samples were snap frozen in liquid nitrogen for biochemical assay and were fixed in 10% formalin solution for histologic evaluation. Myocardial I-R resulted in a significant increase (p < 0.05) in the myocardial malondialdehyde levels and a decrease (p < 0.01) in the myocardial reduced glutathione content. These changes were associated with significant decreases in the myocardial activity of antioxidant enzymes superoxide dismutase (p < 0.05) and catalase (p < 0.01) and severe tissue damage in the jeopardized myocardium in the CON group as compared with the non-myocardial ischemia-reperfusion (NMI-R) SHAM group. Bosentan exerted marked tissue protective effect as assessed by histologic evaluation of the myocardium. The drug significantly (p < 0.05) attenuated myocardial oxidative stress and restored the cellular antioxidant defense mechanisms as compared with the saline-treated controls subjected to the MI-R protocol. Furthermore, bosentan also exerted a marked effect on peripheral hemodynamics and heart rate during the reperfusion phase (data reported elsewhere). These results are consistent with the concept that endothelin-1 may be involved in the pathogenesis of myocardial ischemia and infarction. This study demonstrates the antioxidant effect of non-selective endothelin receptor antagonism elucidating that, part of the aetiology of ischemia and reperfusion induced myocardial injury involves impaired antioxidant defenses.

Preischemic and postischemic administration of AEOL10113 reduces infarct size in a rat model of myocardial ischemia and reperfusion

Reactive oxygen species (ROS) have been implicated as important mediators of cellular damage during ischemia/reperfusion. AEOL10113 is a low-molecular-weight superoxide dismutase mimetic that has dismutase activity against ROS. The objective of this study was to test the cardioprotective efficacy of postischemic administration of AEOL10113 in a rat model of left ventricular ischemia and reperfusion. Left ventricular infarction was produced by 25 min of left coronary artery occlusion followed by 3 h of reperfusion. Infarct size (IS) is reported as IS/area at risk (AAR). The control group had an IS/AAR of 67.5 +/- 2.6%. Postischemic administration of AEOL10113 beginning 5 min prior to reperfusion at doses of 0.03, 0.1, and 0.3 mg/kg resulted in an IS/AAR of 69.3 +/- 3.4%, 57.8 +/- 3.3% (P < 0.05), and 55.0 +/- 2.9% (P < 0.05), respectively. Preischemic administration of AEOL10113 beginning 5 min prior to occlusion at a dose of 0.3 mg/kg resulted in an IS/AAR of 44.2 +/- 5.9% (P < 0.0125). AAR as a percentage of the left ventricle and rate-pressure product were unaffected by any dose tested. The data from this study demonstrate that pre- and postischemic administration of AEOL10113 reduces IS in a rat model of myocardial ischemia and reperfusion.

Role of intracellular antioxidant enzymes after in vivo myocardial ischemia and reperfusion

Reactive oxygen species induce myocardial damage after ischemia and reperfusion in experimental animal models. Numerous studies have investigated the deleterious effects of ischemia-reperfusion (I/R)-induced oxidant production using various pharmacological interventions. More recently, in vitro studies have incorporated gene-targeted mice to decipher the role of antioxidant enzymes in myocardial reperfusion injury. We examined the role of cellular antioxidant enzymes in the pathogenesis of myocardial I/R (MI/R) injury in vivo in gene-targeted mice. Neither deficiency nor overexpression of Cu-Zn superoxide dismutase (SOD) altered the extent of myocardial necrosis. Overexpression of glutathione peroxidase did not affect the degree of myocardial injury. Conversely, overexpression of manganese (Mn)SOD significantly attenuated myocardial necrosis after MI/R. Transthoracic echocardiography was performed on MnSOD-overexpressing and wild-type mice that were subjected to a more prolonged period of reperfusion. Cardiac output was significantly depressed in the nontransgenic but not the transgenic MnSOD-treated mice. Anterior wall motion was significantly impaired in the nontransgenic mice. These findings demonstrate an important role for MnSOD but not Cu/ZnSOD or glutathione peroxidase in mice after in vivo MI/R.

Lecithinized Cu, Zn-superoxide dismutase limits the infarct size following ischemia-reperfusion injury in rat hearts in vivo

Covalent binding of 4 molecules of phosphatidylcholine palmitoyl to human recombinant superoxide dismutase (SOD) results in a compound (lecithinized SOD) that has a longer half-life and greater affinity to the cell membrane than unmodified SOD. We investigated whether lecithinized SOD played a protective role against myocardial ischemia-reperfusion injuries in rats. Rats underwent 45 min of myocardial ischemia by occluding the left coronary artery followed by 120 min of reperfusion. They were randomly assigned to receive either lecithinized SOD, polyethylene glycol conjugated SOD (PEG-SOD), unmodified SOD, free lecithin derivative, or PBS intravenously at 5 min prior to reperfusion. Myocardial infarct area assessed by TTC staining was smaller in lecithinized SOD group than PEG-SOD, unmodified SOD, free lecithin derivative or control group. Blood pressure and heart rate was similar in each group. ELISA demonstrated SOD level in the heart was significantly high in lecithinized SOD group, especially in the heart of ischemia at risk. Although serum SOD level of PEG-SOD was as high as lecithinized SOD, SOD level of the heart was low. These data suggested lecithinized SOD had a protective effect in myocardial ischemia-reperfusion injuries through its increased bioavailability.

Gene therapeutic approaches to oxidative stress-induced cardiac disease: principles, progress, and prospects

Heart and vascular diseases continue to rank among the most frequent and devastating disorders to affect adults in many parts of the world. Increasing evidence from a variety of experimental models indicates that reactive oxygen species can play a key role in the development of myocardial damage from ischemia/reperfusion, the development of cardiac hypertrophy, and the transition of hypertrophy to cardiac failure. The recent dramatic increase in availability of genomic data has included information on the genetic modulation of reactive oxygen species and the antioxidant systems that normally prevent damage from these radicals. Nearly simultaneously, progressively more sophisticated and powerful methods for altering the genetic complement of selected tissues and cells have permitted application of gene therapeutic methods to understand better the pathophysiology of reactive oxygen species-mediated myocardial damage and to attenuate or treat that damage. Although exciting and promising, gene therapy approaches to these common disorders are still in the experimental and developmental stages. Improved understanding of pathophysiology, better gene delivery systems, and specific gene therapeutic strategies will be needed before gene therapy of oxyradical-mediated myocardial damage becomes a clinical reality.

Antioxidant vitamins and enzymatic and synthetic oxygen-derived free radical scavengers in the prevention and treatment of cardiovascular disease

Oxygen-derived free radical formation can lead to cellular injury and death. Under normal situations, the human body has a free radical scavenger system (catalase, superoxide dismutase) that can detoxify free radicals. Antioxidant vitamins and enzymatic and synthetic oxygen-derived free radical scavengers have been used clinically to prevent the formation of oxidized LDL and to prevent reperfusion injury, which is often caused by free radicals. In this article, the pathogenesis of free radical production and cell injury are discussed, and therapeutic approaches for disease prevention are presented.

Radical scavenging properties of novel benzopyran derivatives, TA248 and TA276, and effects of the compounds on ischemic/reperfused myocardium in dogs

Characteristics of novel benzopyran derivatives, TA248 and TA276, and their effects on myocardial contraction in ischemic/reperfused hearts in dogs were examined. TA248 and TA276 inhibited NADPH-dependent lipid peroxidation induced by Fe(3+) in the rat brain homogenate. Both compounds reduced *O(2-) produced by xanthine-xanthine oxidase system in a dose-dependent manner. TA276 scavenged.OH generated by Fenton reaction in a dose-dependent manner. TA248 also inhibited the.OH production, but the effect was neither complete nor dose dependent. Myocardial contraction was assessed as segment shortening of the left ventricular wall in pentobarbital-anesthetized open-chest dogs. The segment shortening was decreased by the left anterior descending coronary artery ligation (ischemia) and returned by release of the ligated artery (reperfusion). The segment shortening did not recover fully during reperfusion. Either TA248 or TA276 injected 10 min before ischemia improved the recovery of myocardial contraction during reperfusion. Both compounds preserved the level of ATP in the 60-min reperfused myocardium. However, the level of lipid peroxides was not changed by TA248 and TA276. TA248 and TA276 may protect myocardium against ischemic/reperfusion insult, partly because of their free radical scavenging activity, but no significant change in myocardial lipid peroxide level was observed.

Oxidative stress and cardiac disease

Reactive oxygen species (ROS) are formed at an accelerated rate in postischemic myocardium. Cardiac myocytes, endothelial cells, and infiltrating neutrophils contribute to this ROS production. Exposure of these cellular components of the myocardium to exogenous ROS can lead to cellular dysfunction and necrosis. While it remains uncertain whether ROS contribute to the pathogenesis of myocardial infarction, there is strong support for ROS as mediators of the reversible ventricular dysfunction (stunning) that often accompanies reperfusion of the ischemic myocardium. The therapeutic potential of free radical-directed drugs in cardiac disease has not been fully realized.

Phagocytes and oxidative stress

Neutrophils and other phagocytes manufacture O(2)(-) (superoxide) by the one-electron reduction of oxygen at the expense of NADPH. Most of the O(2)(-) reacts with itself to form H(2)O(2) (hydrogen peroxide). From these agents a large number of highly reactive microbicidal oxidants are formed, including HOCl (hypochlorous acid), which is produced by the myeloperoxidase-catalyzed oxidation of Cl(-) by H(2)O(2); OH(*) (hydroxyl radical), produced by the reduction of H(2)O(2) by Fe(++) or Cu(+); ONOO(-) (peroxynitrite), formed by the reaction between O(2)(-) and NO(*); and many others. These reactive oxidants are manufactured for the purpose of killing invading microorganisms, but they also inflict damage on nearby tissues, and are thought to be of pathogenic significance in a large number of diseases. Included among these are emphysema, acute respiratory distress syndrome, atherosclerosis, reperfusion injury, malignancy and rheumatoid arthritis.

Mechanisms of myocardial reperfusion injury

Reperfusion of the ischemic myocardium results in irreversible tissue injury and cell necrosis, leading to decreased cardiac performance. While early reperfusion of the heart is essential in preventing further tissue damage due to ischemia, reintroduction of blood flow can expedite the death of vulnerable, but still viable, myocardial tissue, by initiating a series of events involving both intracellular and extracellular mechanisms. In the last decade, extensive efforts have focused on the role of cytotoxic reactive oxygen species, complement activation, neutrophil adhesion, and the interactions between complement and neutrophils during myocardial reperfusion injury. Without reperfusion, myocardial cell death evolves slowly over the course of hours. In contrast, reperfusion after an ischemic insult of sufficient duration initiates an inflammatory response, beginning with complement activation, followed by the recruitment and accumulation of neutrophils into the reperfused myocardium. Modulation of the inflammatory response, therefore, constitutes a potential pharmacological target to protect the heart from reperfusion injury. Recognition of the initiating factor(s) involved in myocardial reperfusion injury should aid in development of pharmacological interventions to selectively or collectively attenuate the sequence of events that mediate extension of tissue injury beyond that caused by the ischemic insult.

Myocardial protection with endogenous overexpression of manganese superoxide dismutase

BACKGROUND

Superoxide dismutase (SOD) is a potent candidate for myocardial protection against ischemia-reperfusion injury; however, its clinical significance by means of exogenous administration remains controversial.

METHODS

To determine a role of endogenously overexpressed manganese SOD (Mn-SOD) in myocardial tolerance, rat hearts were transfected with Mn-SOD gene (group M) or no gene (group C) through intracoronary infusion of hemagglutinating virus of Japan (HVJ) liposome. Each group was divided into two subgroups to be subjected to ischemia-reperfusion using Langendorff apparatus with (subgroups M+ and C+) or without (M- and C-) administration of recombinant SOD.

RESULTS

Mn-SOD overexpression was confirmed in M with ELISA, activity measurement, and immunohistochemistry. The highest recoveries of maximum and minimum dp/dt and the least creatine phosphokinase (CPK) leakage were observed in M+. These recoveries were higher in M- than in C- and C+.

CONCLUSIONS

Thus, endogenous overexpression of Mn-SOD improved myocardial tolerance and its protective effect was enhanced by exogenous administration of SOD. These results suggest a possible strategy for myocardial protection with SOD: a combination of endogenous introduction through gene transfer with exogenous administration.

Modulation of leukocyte-endothelial interactions by reactive metabolites of oxygen and nitrogen: relevance to ischemic heart disease

Ischemia and reperfusion (I/R) are thought to play an important role in the pathophysiology of ischemic diseases of the heart. It is now well appreciated that leukocyte-endothelial cell interactions are important determinants for I/R-induced microvascular injury and dysfunction. There is a growing body of experimental data to suggest that reactive metabolites of oxygen and nitrogen are important physiological modulators of leukocyte-endothelial cell interactions. A number of investigators have demonstrated that I/R enhances oxidant production within the microcirculation resulting in increases in leukocyte adhesion and transendothelial cell migration. Several other studies have shown that exogenous nitric oxide (NO) donors may attenuate leukocyte and platelet adhesion and/or aggregation in a number of different inflammatory conditions including I/R. The objective of this review is to discuss the physiological chemistry of reactive metabolites of oxygen and nitrogen with special attention given to those interactions that may modulate leukocyte-endothelial cell interactions, provide an overview of the evidence implicating reactive metabolites of oxygen and nitrogen as modulators of leukocyte-endothelial cell interactions in vivo, and discuss how these mechanisms may be involved in the pathophysiology of ischemic heart disease.

Effect of Poloxamer 188 on Collateral Blood Flow, Myocardial Infarct Size, and Left Ventricular Function in a Canine Model of Prolonged (3-Hour) Coronary Occlusion and Reperfusion

Poloxamer 188 is a surfactant with hemorheological, antithrombotic, and neutrophil-inhibitory properties. This agent has been demonstrated to reduce infarct size and to improve left ventricular function in animal models of myocardial infarction and reperfusion, and recently in a randomized trial of patients receiving thrombolytic therapy for acute myocardial infarction. In addition to reducing reperfusion injury, poloxamer 188 might be beneficial by increasing collateral blood flow. The purpose of this study was to determine the effect of poloxamer 188 on collateral blood flow, myocardial infarct size, and left ventricular function in a canine model of prolonged (3 hours) coronary occlusion and reperfusion. Closed-chest dogs (n = 21) underwent a 3-hour coronary occlusion and 3 hours of reperfusion. At 1 hour of occlusion, dogs received poloxamer 188, 75 mg/kg IV bolus, followed by 150 mg/kg/h IV for the final 2 hours of coronary occlusion and throughout reperfusion, or a saline placebo. Regional myocardial blood flow was measured using colored microspheres. Myocardial infarct size and area at risk were determined by postmortem histochemical staining. Compared with controls, poloxamer 188-treated dogs showed no significant increase in collateral blood flow during the final 2 hours of a 3-hour coronary artery occlusion. In addition, poloxamer 188 treatment had no beneficial effect on infarct size or left ventricular function in this model. Increased collateral blood flow is unlikely to be a beneficial mechanism of poloxamer 188 in myocardial infarction. These data also question the benefit of this agent to reduce reperfusion injury in the setting of more prolonged (3-hour) coronary occlusion.

Overexpression of human copper, zinc-superoxide dismutase (SOD1) prevents postischemic injury

Superoxide and superoxide-derived oxidants have been hypothesized to be important mediators of postischemic injury. Whereas copper, zinc-superoxide dismutase, SOD1, efficiently dismutates superoxide, there has been controversy regarding whether increasing intracellular SOD1 expression would protect against or potentiate cellular injury. To determine whether increased SOD1 protects the heart from ischemia and reperfusion, studies were performed in a newly developed transgenic mouse model in which direct measurement of superoxide, contractile function, bioenergetics, and cell death could be performed. Transgenic mice with overexpression of human SOD1 were studied along with matched nontransgenic controls. Immunoblotting and immunohistology demonstrated that total SOD1 expression was increased 10-fold in hearts from transgenic mice compared with nontransgenic controls, with increased expression in both myocytes and endothelial cells. In nontransgenic hearts following 30 min of global ischemia a reperfusion-associated burst of superoxide generation was demonstrated by electron paramagnetic resonance spin trapping. However, in the transgenic hearts with overexpression of SOD1 the burst of superoxide generation was almost totally quenched, and this was accompanied by a 2-fold increase in the recovery of contractile function, a 2.2-fold decrease in infarct size, and a greatly improved recovery of high energy phosphates compared with that in nontransgenic controls. These results demonstrate that superoxide is an important mediator of postischemic injury and that increasing intracellular SOD1 dramatically protects the heart from this injury. Thus, increasing intracellular SOD1 expression may be a highly effective approach to decrease the cellular injury that occurs following reperfusion of ischemic tissues.

Evaluation of purine nucleotide loss, lipid peroxidation and ultrastructural alterations in post-hypoxic hepatocytes

1. Hypoxic alterations in isolated rat hepatocytes were demonstrated by a 90% ATP loss during 60 min of ischaemia and temporary increases of nucleotide degradation products. 2. The oxidative stress during reoxygenation was demonstrated in these cells by a decrease in reduced glutathione (GSH) concentration (30%) and a threefold increase in lipid peroxidation products such as 4-hydroxynonenal and thiobarbituric acid-reactive substances (TBA-RSs). The tremendous GSH loss could not be balanced by the slight oxidized glutathione (GSSG) increase during reoxygenation. 3. For the first time the involvement of free radicals was directly demonstrated using electron spin resonance (ESR) spectroscopy in reoxygenated liver cells. Using the spin trap 5,5-dimethylpyrroline-1-oxide (DMPO), a carbon-centred radical and the adduct of the hydroxyl radical could be detected during early reoxygenation. 4. Morphological alteration of cells was observed, beginning during hypoxia and increasing during post-hypoxic reoxygenation. Electron microscopic findings of hypoxic and post-hypoxic cell damage included pyknosis of nuclei, spherical transformation of mitochondria and increased number of vesicles.

Reperfusion Injury: Basic Concepts and Protection Strategies

Prolonged ischemia such as that following myocardial infarction or occurring during long-term coronary bypass procedures causes serious damage to the myocardium. Early reperfusion is an absolute prerequisite for the survival of ischemic tissue. However, reperfusion has been referred to as the "double edged sword" because reperfusing ischemic myocardium carries with it a component of injury known as reperfusion injury. Reperfusion injury includes a number of events, such as reperfusion arrhythmias, myocardial infarction, stunning, vascular damage, and endothelial dysfunction. The underlying mechanism of reperfusion injury is not entirely known, but the existing evidence suggests that oxygen free radicals generated during the first few minutes of reflow lead to damage of cellular membranes, intracellular calcium overload, and uncoupling of excitation-contraction coupling. Although controversial, free radical scavengers, in general, are highly effective in the attenuation of reperfusion injury in animal models. Newer endogenous protection strategies, which include ischemic and heat shock preconditioning, are known to reduce reperfusion injury following ischemia.

Prolonged coronary artery occlusion-reperfusion sequences reduce myocardial free radical production: an electron paramagnetic resonance study

Our purpose was to determine whether prolonged myocardial ischemia attenuates free radical production after early reperfusion. Twenty-two mongrel dogs underwent left anterior descending coronary artery occlusion for 20, 40, or 60 minutes followed by 30 minutes of reperfusion. Electron paramagnetic resonance spectroscopy was used to measure ascorbate free radical in the coronary vein effluent. Ascorbate free radical production during reperfusion was significantly (p < 0.05) reduced in the dogs undergoing 60 minutes of coronary artery occlusion compared with the dogs undergoing 40 and 20 minutes of occlusion. We conclude that prolonged myocardial ischemia results in less free radical production on reperfusion than do shorter periods of ischemia followed by reperfusion.

Acute myocardial infarction, reperfusion injury, and intravenous magnesium therapy: basic concepts and clinical implications

The concept of reperfusion-induced injury has aroused special interest during the past decade as thrombolysis and direct angioplasty were introduced for early restoration of coronary blood flow in patients with acute myocardial infarction. There is experimental and clinical evidence that oxygen-derived free radicals (oxyradical hypothesis), activation of the complement system (complement hypothesis), and disturbance in calcium homeostasis (calcium hypothesis), may account for the development of reperfusion injury. Data from numerous animal experiments and clinical trials suggest that magnesium, a physiologic calcium blocker, may be efficacious for reduction of reperfusion injury. Despite encouraging results from previous clinical trials that revealed beneficial effects of intravenous magnesium therapy with respect to mortality, left ventricular function, and infarct size, a recently published large-scale trial (ISIS-4) provided conflicting data and caused major controversy. Further clinical trials, well-designed and carefully conducted, should elucidate the beneficial effects of magnesium in acute myocardial infarction, especially in conjunction with new and aggressive reperfusion techniques.

Methods for studying experimental myocardial ischemic and reperfusion injury

This review describes methodologies used to study experimental myocardial ischemic and reperfusion injury. Myocardial reperfusion injury may be manifest as myocardial stunning, ventricular arrhythmias, coronary vascular dysfunction, or the extension of the area of myocyte necrosis beyond that due to the ischemic insult alone. This review discusses methodology pertaining to the latter form of reperfusion injury. The pathophysiology of the reperfusion injury process is complex, including primarily cellular and humoral components of inflammation, as well as myocellular ionic and metabolic disturbances. Since the extent of injury may be influenced by methodological considerations this review aims to discuss the principle means of characterizing reperfusion injury in the experimental setting. The methods discussed are principally those related to in vivo research. Where appropriate, advantages, disadvantages, or alternate methods will be presented. Lastly, as understanding of the pathophysiology of reperfusion injury increases, newer techniques utilizing murine models, the study of apoptotic cell death, and the role of gender may be used more frequently and are thus briefly reviewed.

Transvalvular left ventricular assistance in acute myocardial infarction with cardiogenic shock and high risk angioplasty: experimental and clinical results with the Hemopump

The Hemopump has been shown to be an effective left ventricular assist device. It is capable of supporting the circulation in patients with profound left ventricular dysfunction in the setting of cardiogenic shock. In experimental animals it seems possible that supporting the circulation immediately prior to reperfusion will produce a significant decrease in infarct size, which has important clinical ramifications, particularly in the setting of patients with large anterior myocardial infarction. The mechanism for this infarct salvage is unclear at the present time and requires further investigation, at a more basic level. The current tools available to the cardiologist include the intraaortic balloon pump and the cardiopulmonary support system (CPS), (PCs, BARD, Inc.). The Hemopump is available in Europe, but not in the United States at the present time. Clearly, the CPS system is the most powerful of the devices available, producing up to 61/m of flow. Unfortunately, there are a number of drawbacks with the CPS system, including its need for an oxygenator, which limits its useful period of support to approximately 8 hours. Additionally, support with the PCS system may be associated with adverse physiological events. The intraaortic balloon pump requires synchronization with the cardiac cycle, and hence, is not suitable for patients with significant tachyarrhythmias. Patients with overt cardiac arrest, similarly, cannot be supported with the intraaortic balloon pump. Nonetheless, the balloon pump has been associated with improved infarct salvage in an experimental animal model. On the other hand, the Hemopump, in its first version, required a surgical incision and placement of a graft onto the femoral artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of adenosine deaminase inhibition with pentostatin on myocardial stunning in dogs

Pentostatin (2-deoxycoformycin) is a potent inhibitor of adenosine deaminase and has been demonstrated to augment endogenous adenosine levels during regional and global myocardial ischemia. Based on the rationale that increasing endogenous adenosine during ischemia may be cardioprotective, the objective of this study was to determine if adenosine deaminase inhibition with pentostatin could improve postischemic contractile dysfunction (stunning) in open-chest anesthetized dogs. All animals underwent 15 min of coronary occlusion followed by 3 h of reperfusion preceded by an intravenous bolus of either 0.2 mg/kg of pentostatin (n = 8) or saline (n = 7). Sonomicrometers were placed in the ischemic area and were used to measure systolic wall thickening before, during, and after occlusion of the left anterior descending artery. Myocardial blood flow was measured with tracer labeled microspheres at baseline, 10 min of occlusion and at 1 h of reperfusion. Both groups were equally dyskinetic during occlusion (-21 +/- 5% of baseline thickening in the controls and -28 +/- 8% in the pentostatin group). The pentostatin group, however, demonstrated better contractile function at all time points during reperfusion, which was significantly different from the control group at 3 h of reperfusion. The improvement in regional function in the pentostatin group was not due to significant disparities in hemodynamic variables, size of the region at risk, or in collateral blood flow. These results indicate that pentostatin can ameliorate the severity of myocardial stunning, an effect we propose is due to increasing endogenous levels of adenosine during the ischemic interval. Although significant improvement was detected with pentostatin, the improvement was modest compared to controls, suggesting that the utility of inhibiting adenosine deaminase to modify regional mechanical stunning is limited.

gamma-Glutamylcysteine ethyl ester for myocardial protection in dogs during ischemia and reperfusion

OBJECTIVES

The aim of this study was to examine the infarct-limiting effects of gamma-glutamylcysteine ethyl ester, a newly discovered synthetic precursor of glutathione biosynthesis, in a canine model of myocardial infarction.

BACKGROUND

Reduced glutathione plays an important role in protecting cells against damage induced by reactive oxygen species during myocardial ischemia and reperfusion. Gamma-glutamylcysteine ethyl ester is capable of penetrating into cells in its intact form and increasing intracellular glutathione levels.

METHODS

Dogs were subjected to a 90-min coronary occlusion followed by 5 h of reperfusion. An intravenous bolus injection of gamma-glutamylcysteine ethyl ester (3 or 10 mg/kg body weight) was administered immediately before reperfusion. Regional myocardial blood flow was measured with the use of colored microspheres.

RESULTS

Gamma-glutamylcysteine ethyl ester effectively reduced infarct size in a dose-dependent manner (mean +/- SEM 26.4 +/- 3.5% in the low dose group [3 mg/kg, n = 10] and 19.0 +/- 3.4% in the high dose group [10 mg/kg, n = 10]; each p < 0.05 vs. the value in the control group [40.6 +/- 4.8%, n = 10]). There were no differences between the control and treated groups in hemodynamic variables or regional myocardial blood flow either during the ischemic period or after reperfusion. The reduced glutathione content of ischemic myocardium in the control group (0.62 +/- 0.11 mumol/g, p < 0.01) was significantly lower than that in nonischemic myocardium (1.46 +/- 0.07 mumol/g), and it was preserved by treatment in a dose-dependent manner (3 mg/kg, 0.83 +/- 0.06 mumol/g; 10 mg/kg, 0.92 +/- 0.14 mumol/g; each p < 0.05 vs. control level). There were no differences in oxidized glutathione content between nonischemic and ischemic myocardium or among the three groups.

CONCLUSIONS

Gamma-glutamylcysteine ethyl ester, a precursor of glutathione, significantly attenuates myocardial ischemia and reperfusion injury when administered immediately before reperfusion.

Recombinant human superoxide dismutase (h-SOD) fails to improve recovery of ventricular function in patients undergoing coronary angioplasty for acute myocardial infarction

BACKGROUND

Animal studies have demonstrated a burst of oxygen free radical generation after reperfusion of ischemic myocardium that could be blocked by administration of the free radical scavenger recombinant human superoxide dismutase (h-SOD). A multicenter, randomized, placebo-controlled clinical trial was designed to test the hypothesis that free radical-mediated reperfusion injury could be reduced by intravenous administration of h-SOD begun before percutaneous transluminal coronary angioplasty (PTCA) in patients with acute transmural myocardial infarction.

METHODS AND RESULTS

One hundred twenty patients were randomized to receive placebo (n = 59) or h-SOD (n = 61) given as a 10-mg/kg intravenous bolus followed by a 60-minute infusion of 0.2 mg.kg-1.min-1. Left ventricular function was analyzed via paired contrast left ventriculograms performed before PTCA and after 6 to 10 days and paired radionuclide ventriculograms performed within 24 hours of PTCA and after 4 to 6 weeks. Both h-SOD- and placebo-treated patients showed improvement in global and regional left ventricular function after successful reperfusion. Compared with the placebo group, no additional improvement was observed in the patients treated with h-SOD.

CONCLUSIONS

The results of this clinical trial failed to demonstrate a beneficial effect of h-SOD on global or regional left ventricular function in patients who underwent successful PTCA for treatment of acute myocardial infarction.

Free radicals and the heart

Because of the molecular configuration, most free radicals are highly reactive and can cause cell injury. Protective mechanisms have evolved to provide defense against free-radical injury. Any time these defense systems are overwhelmed, such as during disease states, cell dysfunction may occur. In this review we discuss cellular sources as well as the significance of free radicals, oxidative stress, and antioxidants. A probable role of oxidative stress in various cardiac pathologies has been also analyzed. Although some methods for the detection of free radicals as well as oxidative stress have been cited, better methods to study the quantity as well as subcellular distribution of free radicals are needed in order to understand fully the role of free radicals in both health and disease.

High- and low-dose superoxide dismutase plus catalase does not reduce myocardial infarct size in a subhuman primate model

Oxygen free radical scavengers have been found to decrease infarct size in dogs subjected to myocardial ischemia-reperfusion injury. A baboon open-chest model was used to determine if superoxide dismutase (SOD), an oxygen free radical scavenger, together with catalase would be equally effective in subhuman primates (baboons). The left anterior descending coronary artery (LAD) was ligated for 2 hours. Before reperfusion, the animals received the following: Group 1 (low-dose SOD/catalase; n = 5) received 15,000 IU/kg of SOD and 55,000 IU/kg of catalase IV over 1 hour, 15 minutes before reperfusion. Group 2 (high-dose human SOD [h-SOD]/catalase; n = 5) received an intraatrial bolus of 400,000 IU of recombinant h-SOD and 27,500 IU/kg of catalase over 30 seconds, followed by 300,000 IU of h-SOD and 55,000 IU/kg of catalase over 1 hour, beginning 15 seconds before reperfusion. Group 3 (n = 8) were control animals. Baboons were put to death 22 hours after reperfusion. Their hearts were excised and sectioned after the perfusion bed distal to the site of ligation was delineated with microvascular dye. The infarct zone was determined histologically. Areas of the perfusion bed and infarct zone were measured by planimetry. Infarct size did not differ significantly between the three groups: control, 66 +/- 7%; low-dose SOD/catalase, 68 +/- 5%; and high-dose h-SOD/catalase, 74 +/- 4%. In this model, high- and low-dose SOD with catalase did not result in any significant reduction in infarct size.

Effect of zinc deficiency on lipid peroxidation status and infarct size in rat hearts

The objective of this study was to investigate the effect of dietary zinc on endogenous production of lipid peroxides, and on myocardial infarct size in rats. Male rats were fed a zinc-deficient diet containing 4 ppm zinc, or a standard diet containing 60 ppm zinc. After 3 weeks of diet, half of the animals underwent occlusion of the left coronary artery. The remaining animals underwent sham operation without occlusion. Forty-eight hours later, the hearts were sampled and lipid peroxide levels and infarct size were evaluated. Coronary occlusion was associated with an increase in cardiac lipid peroxide levels which were more pronounced in the zinc deficient group. However, infarct size appeared to be independent from zinc deficiency, despite the free radical-mediated lipid peroxide augmentation reported here. The pharmacological limitation of infarct size in rats with permanent coronary occlusion is discussed.

Superoxide dismutase restores contractile and metabolic dysfunction through augmentation of adenosine release in coronary microembolization

BACKGROUND

This study was undertaken to test the hypothesis that administration of superoxide dismutase (SOD) restores the contractile and metabolic dysfunction in coronary microembolization and that these beneficial effects of SOD are attributable to the restoration of 5'-nucleotidase activity and subsequent augmentation of adenosine release.

METHODS AND RESULTS

In 78 dogs before and after an injection of microspheres (15 microns in diameter) into the left anterior descending coronary artery, regional coronary blood flow (CBF), fractional shortening (FS), and lactate extraction ratio (LER) were measured with and without administration of recombinant human SOD (50 micrograms/kg/min i.c.). In the untreated dogs (n = 6), both FS and LER decreased after coronary microembolization (2.0 x 10(5) microspheres per ml CBF [mL/min]). FS and LER decreased from 24.2 +/- 1.3% to 5.1 +/- 1.2% and from 23.0 +/- 1.1% to -10.5 +/- 2.9%, respectively. These ischemic changes were associated with coronary hyperemic flow (141 +/- 8 versus 92 +/- 1 mL/100 g/min) and adenosine release (5.8 +/- 0.5 versus 0.4 +/- 0.1 nmol/100 g/min). Pretreatment with SOD augmented the hyperemic flow to 164 +/- 4 mL/100 g/min and enhanced the release of adenosine (9.6 +/- 0.6 nmol/100 g/min) associated with improvement of functional and metabolic dysfunction (FS, 14.8 +/- 2.3%; LER, 15.1 +/- 3.1%). Administration of SOD at 10 minutes (n = 5) and 30 minutes (n = 5) after coronary embolization restored the contractile function and lactate metabolism (at 10 minutes: FS, 16.7 +/- 2.2% and LER, 16.7 +/- 3.9%; at 30 minutes: FS, 11.1 +/- 1.3% and LER, 7.2 +/- 3.1%). However, administration of SOD 60 minutes after coronary embolization (n = 6) did not restore the contractile and metabolic dysfunction. The restoration of the contractile and metabolic dysfunction by SOD treatment was blunted by adenosine receptor blockade with 8-phenyltheophylline (n = 5). Myocardial 5'-nucleotidase activity at 2 hours after embolization was restored with SOD treatment at 10 minutes (n = 5) and 30 minutes (n = 5) after embolization. However, SOD treatment at 60 minutes after embolization (n = 6) did not restore 5'-nucleotidase activity compared with the SOD pretreatment group. Furthermore, coronary submaximal vasodilation induced by papaverine (n = 5) and adenosine (n = 5) abolished the beneficial effects of SOD.

CONCLUSIONS

We conclude that 1) in sustained myocardial ischemia, SOD treatment attenuates ischemic injury caused by coronary microembolization by restoration of 5'-nucleotidase activity and augmentation of adenosine release; 2) this beneficial effect of SOD is observed even after coronary microembolization; and 3) the beneficial effects of SOD are attributable to coronary vasodilation produced by augmented adenosine release.

Comparisons of ESR and HPLC methods for the detection of OH. radicals in ischemic/reperfused hearts. A relationship between the genesis of free radicals and reperfusion arrhythmias

In this study we compared two methods, electron spin resonance (ESR) spectroscopy and high performance liquid chromatography (HPLC), which are currently used to detect directly hydroxyl radical (OH.) formation in the ischemic and reperfused heart. Isolated buffer-perfused rat hearts were subjected to 30 min of normothermic global ischemia followed by 30 min of reperfusion. 5,5-Dimethyl-pyrroline-N-oxide (DMPO) was used as a spin-trap agent to detect OH. radicals by ESR and HPLC. In additional HPLC studies, salicylic acid was infused into the heart for the detection of OH. radicals. In all studies, the effects of superoxide dismutase (SOD) and catalase (CAT) on the OH. generation were examined. The results of our studies indicate that, irrespective of the method, OH. was always detected when an ischemic heart was reperfused and showed ventricular fibrillation. The OH. concentration increased dramatically between 60 and 90 sec of reperfusion, peaked between 180 and 210 sec, and then progressively decreased. In all cases, both SOD and CAT were able to reduce the formation of OH. radicals, with SOD being relatively more effective. Our results indicate that OH. was produced only in the fibrillating hearts that peaked between 180 and 210 sec (1.64 +/- 0.09 nmol/mL measured by ESR), but not in the non-fibrillating hearts. Although SOD or CAT reduced the OH. formation, they had no effects on the incidence of reperfusion-induced ventricular fibrillation (VF) and ventricular tachycardia (VT). However, when SOD (5 x 10(4) IU/L) was coadministered with CAT (5 x 10(4) IU +/- L), the incidence of reperfusion-induced VF (total) and VT was reduced from their control value of 92 and 100 to 33 (P < 0.05) and 50% (P < 0.05), respectively. The results of this study indicate that the HPLC method, as well as ESR, can be used to detect OH. formation in ischemic/reperfused hearts. Because of the convenience, reproducibility and greater sensitivity, the HPLC technique may be more suitable for OH. detection. Our results further suggest the potential therapeutic value of the combination therapy of SOD and CAT for the reduction of reperfusion-induced VF and VT.

Direct measurement of myocardial free radical generation in an in vivo model: effects of postischemic reperfusion and treatment with human recombinant superoxide dismutase

OBJECTIVES

The purpose of this study was to determine whether postischemic reperfusion of the heart in living rabbits induces a burst of oxygen free radical generation that can be attenuated by recombinant human superoxide dismutase administered at the moment of reflow.

BACKGROUND

This phenomenon was previously demonstrated in crystalloid perfused, globally ischemic rabbit hearts.

METHODS

Thirty-two open chest rabbits were assigned to one of four groups of eight animals each: Group I (control animals), no coronary artery occlusion; Group II, 30 min of circumflex marginal coronary artery occlusion without reperfusion; Group III, 30 min of coronary occlusion followed by 60 s of reperfusion, and Group IV, 30 min of coronary occlusion followed by treatment with recombinant human superoxide dismutase (a 20-mg/kg body weight bolus 90 s before reperfusion and a 0.17-mg/kg infusion during 60 s of reperfusion). Full thickness biopsy specimens taken from the ischemic region were then rapidly freeze clamped and electron paramagnetic resonance spectroscopy was performed at 77 degrees K.

RESULTS

Three radical signals similar to those previously identified in the isolated, crystalloid perfused rabbit heart were observed: an isotropic signal with g = 2.004 suggestive of a semiquinone, an anisotropic signal with g parallel = 2.033 and g perpendicular = 2.005 suggestive of an oxygen-centered alkyl peroxy radical, and a triplet with g = 2.000 and aN = 24 G suggestive of a nitrogen-centered radical. In addition, a fourth signal consistent with an iron-sulfur center was seen. The oxygen-centered free radical concentration during normal perfusion (Group I) was 1.8 +/- 0.8 mumol compared with 4.4 +/- 0.9 mumol after 30 min of regional ischemia without reperfusion (Group II) and 13.0 +/- 2.5 mumol after 60 s of reperfusion (Group III) (p < 0.05 among all three groups). In contrast, superoxide dismutase treated-rabbits (Group IV) demonstrated a peak oxygen radical concentration of only 5.9 +/- 1.2 mumol (p < 0.05 vs. Group III).

CONCLUSIONS

This study demonstrates that reperfusion after regional myocardial ischemia in the intact rabbit is associated with a burst of oxygen-centered free radicals. The magnitude of this burst is greater than that seen after a comparable duration of global ischemia in the isolated, buffer-perfused rabbit heart preparation and is significantly reduced by superoxide dismutase administration begun just before reflow.

Does the antiarrhythmic effect of DMPO originate from its oxygen radical trapping property or the structure of the molecule itself?

Using the isolated perfused rat heart with transient (30 min) normothermic global ischemia, it was shown that DMPO (5,5-dimethyl-pyrroline-N-oxide), an organic spin trap agent designed specifically to trap free radicals, dramatically reduced the vulnerability of the myocardium to reperfusion-induced ventricular fibrillation (VF) and ventricular tachycardia (VT). DMPO (concentration range 30-500 mumol/l) infused in the heart at the moment and during the first 10 min of reperfusion exerted a dose-dependent antiarrhythmic effect. Thus, the doses of 30, 100, and 500 mumol/l of DMPO reduced the incidence of reperfusion-induced VF and VT from their control values of 100% and 100% to 83% and 91%, 50% (p < 0.05) and 67%, 25% (p < 0.01) and 50% (p < 0.05), respectively. Furthermore, the recovery of myocardial function was improved during postischemic reperfusion. A modification in the molecular structure of DMPO leading to HMIO (1,2,2,4,5,5-hexamethyl-3-imidazoline-oxide), so-called inactive DMPO which does not trap free radicals in the presence of a radical generating system or in the effluent of reperfused hearts, failed to reduce the incidence of reperfusion-induced arrhythmias or improve the recovery of postischemic reperfused myocardium. These findings suggest that the free radical trapping properties of DMPO or the effects of the formed DMPO-OH, a stable nitroxyl radical adduct, are responsible for the reduction of reperfusion-induced arrhythmias, and not the molecular structure of DMPO itself. Finally, it is of interest to note that the detection of free radicals was observed in fibrillating hearts, but not in nonfibrillating hearts. This consideration should be taken into account when making therapeutic interventions and risk assessments of a radical scavenger in this setting.

PEG-SOD and myocardial protection. Studies in the blood- and crystalloid-perfused rabbit and rat hearts

BACKGROUND

Polyethylene glycol, covalently linked to superoxide dismutase (PEG-SOD), has a long plasma half-life (greater than 30 hours) and has been proposed as an effective agent for reducing free radical-mediated injury ischemia and reperfusion.

METHODS AND RESULTS

Using an isolated rabbit heart perfused with arterial blood from a support rabbit, we have demonstrated that pretreatment with PEG-SOD (30,000 units/kg, intravenous bolus, 12-24 hours before 60 minutes of normothermic global ischemia), combined with addition of PEG-SOD to the blood perfusion circuit (30,000 units/kg to the support rabbit) and inclusion of PEG-SOD (150 micrograms/ml) in a cardioplegic solution, enhanced the postischemic recovery of left ventricular developed pressure (LVDP) from 51 +/- 6 to 74 +/- 9 mm Hg (p less than 0.05; n = 9 per group). In further studies we showed that, whereas maximum protection was obtained when PEG-SOD was given as a combined pretreatment and additive to both the cardioplegic and the reperfusate solutions (postischemic LVDP recovery increased from 44 +/- 4% in the control group to 70 +/- 3% in the PEG-SOD group), the administration of PEG-SOD during pretreatment plus cardioplegia or during reperfusion alone also resulted in a significant improvement in postischemic function (62 +/- 7% and 60 +/- 3%, respectively). However, the use of PEG-SOD as a cardioplegic additive alone failed to afford protection (47 +/- 4% recovery of LVDP). In dose-response studies (with 0, 3,000, 6,000, 12,000, 30,000, or 60,000 units/kg; n = 8 per group), maximum recovery of LVDP was obtained with the administration of 12,000 units/kg of PEG-SOD. Studies of the plasma activity of PEG-SOD confirmed its long half-life and showed that the treatment with PEG-SOD either 1 hour or 12-24 hours before the study resulted in similar levels of plasma activity. In an attempt to assess any involvement of blood-borne elements in the protection afforded by PEG-SOD, studies were also carried out in the crystalloid-perfused rabbit heart, and no protection was observed. Similarly, no protection was observed at any one of a variety of doses in the crystalloid-perfused rat heart.

CONCLUSIONS

PEG-SOD can afford protection in the blood-perfused rabbit heart; this protection is dose dependent and probably involves some action of PEG-SOD on blood-borne elements, possibly leukocytes.