Xanthine oxidase is not a source of free radicals in the ischemic rabbit heart

doi:10.1016/S0022-2828(87)80350-4

Journal of Molecular and Cellular Cardiology

Volume 19, Issue 11, November 1987, Pages 1053-1060

https://doi.org/10.1016/S0022-2828(87)80350-4 Get rights and content

The xanthine oxidase pathway has been proposed as a source ofoxygen-derived free radicals in ischemic and reperfused myocardium. A spectrophotometric assay was employed to measure the xanthine oxidase activity of rat and rabbit hearts exposed to varying durations of global ischemia. In the rat 24.6±4.8 mIU/g wet wt of xanthine dehydrogenase + xanthine oxidase activity were detected in both ischemic and normally perfused myocardium. In the non-ischemic state only 6% of this activity was associated with the free radical-producing oxidase form. After 5 min of ischemia however about 25% of the enzyme was in the oxidase form, a value which remained unchanged over the following 25 min. Neither xanthine dehydrogenase nor xanthine oxidase could be detected in the rabbit heart. Failure of allopurinol, an inhibitor of xanthine oxidase, to limit infarct size in a rabbit model of ischemia/reperfusion provides further evidence that this species has insignificant amounts of xanthine oxidase in its heart. Anesthetized rabbits were subjected to coronary artery ligation for 45 min and 3 h of reperfusion. The volume of the zone of underperfusion was assessed with fluorescent microspheres and infarct size was assessed by tetrazolium staining. In control animals 67.5±3.8% of the zone of underperfusion became necrotic. In rabbits given superoxide dismutase (15000 IU/kg)+catalase (50000 IU/kg) for 90 min starting 15 min before occlusion, infarct size was only 35.4±3.3% of the zone of underperfusion. However, in rabbits pretreated with allopurinol (75 mg p.o. 24 h before study +30 mg/kg 5 min before occlusion) infarct size was 65.8±8.7%. In conclusion, while ischemic rat heart has abundant xanthine oxidase, the rabbit heart contains insignificant amounts of the enzyme. Other mechanisms for free radical production apparently exist in the rabbit heart since a free radical scavenger did reduce the injury following ischemia and reperfusion.

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Citation Excerpt :
XDH preferentially use NAD+ as an electron acceptor whereas XO uses oxygen as the terminal electron acceptor, thereby generating ROS. The evidence for a role of XOR in IR injury is provocative [74–76]. NOS catalyzes the formation of nitric oxide (NO) from L-arginine, using tetrahydrobiopterin (BH4) as an essential cofactor.
Ischemia-reperfusion (IR) injury is central to the pathology of major cardiovascular diseases, such as stroke and myocardial infarction. IR injury is mediated by several factors including the elevated production of reactive oxygen species (ROS), which occurs particularly at reperfusion. The mitochondrial respiratory chain and NADPH oxidases of the NOX family are major sources of ROS in cardiomyocytes. The first part of this review discusses recent findings and controversies on the mechanisms of superoxide production by the mitochondrial electron transport chain during IR injury, as well as the contribution of the NOX isoforms expressed in cardiomyocytes, NOX1, NOX2 and NOX4, to this damage. It then focuses on the effects of ROS on the opening of the mitochondrial permeability transition pore (mPTP), an inner membrane non-selective pore that causes irreversible damage to the heart. The second part analyzes the redox mechanisms of cardiomyocyte mitochondrial protection; specifically, the activation of the hypoxia-inducible factor (HIF) pathway and the antioxidant transcription factor Nrf2, which are both regulated by the cellular redox state. Redox mechanisms involved in ischemic preconditioning, one of the most effective ways of protecting the heart against IR injury, are also reviewed. Interestingly, several of these protective pathways converge on the inhibition of mPTP opening during reperfusion. Finally, the clinical and translational implications of these cardioprotective mechanisms are discussed.
Reperfusion injury and reactive oxygen species: The evolution of a concept
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Some of the inconsistent findings have been attributed to differences in XOR abundance/activity between animal species. For example, rabbit heart, which is not protected against reperfusion injury by allopurinol treatment, is virtually devoid of XO activity [117], much like the human heart [119]. However, intestine and liver, which exhibit significant and ubiquitous expression of XOR across species (including humans) [120,121], have yielded more consistent findings regarding a role for the enzyme in reperfusion injury [122,123].
Reperfusion injury, the paradoxical tissue response that is manifested by blood flow-deprived and oxygen-starved organs following the restoration of blood flow and tissue oxygenation, has been a focus of basic and clinical research for over 4-decades. While a variety of molecular mechanisms have been proposed to explain this phenomenon, excess production of reactive oxygen species (ROS) continues to receive much attention as a critical factor in the genesis of reperfusion injury. As a consequence, considerable effort has been devoted to identifying the dominant cellular and enzymatic sources of excess ROS production following ischemia-reperfusion (I/R). Of the potential ROS sources described to date, xanthine oxidase, NADPH oxidase (Nox), mitochondria, and uncoupled nitric oxide synthase have gained a status as the most likely contributors to reperfusion-induced oxidative stress and represent priority targets for therapeutic intervention against reperfusion-induced organ dysfunction and tissue damage. Although all four enzymatic sources are present in most tissues and are likely to play some role in reperfusion injury, priority and emphasis has been given to specific ROS sources that are enriched in certain tissues, such as xanthine oxidase in the gastrointestinal tract and mitochondria in the metabolically active heart and brain. The possibility that multiple ROS sources contribute to reperfusion injury in most tissues is supported by evidence demonstrating that redox-signaling enables ROS produced by one enzymatic source (e.g., Nox) to activate and enhance ROS production by a second source (e.g., mitochondria). This review provides a synopsis of the evidence implicating ROS in reperfusion injury, the clinical implications of this phenomenon, and summarizes current understanding of the four most frequently invoked enzymatic sources of ROS production in post-ischemic tissue.
The cellular and molecular origin of reactive oxygen species generation during myocardial ischemia and reperfusion
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Citation Excerpt :
Shortly thereafter, Grum et al. (1986) failed to detect any appreciable xanthine oxidase or dehydrogenase activity in the rabbit heart. Similarly undetectable xanthine oxidase activity was reported in the human heart (Eddy et al., 1987; Podzuweit et al., 1991), and its contribution to post-ischemic O2•– production in the rabbit heart was discounted (Downey et al., 1987). These results contradict allopurinol-mediated free-radical reduction.
Myocardial ischemia-reperfusion injury is an important cause of impaired heart function in the early postoperative period subsequent to cardiac surgery. Reactive oxygen species (ROS) generation increases during both ischemia and reperfusion and it plays a central role in the pathophysiology of intraoperative myocardial injury. Unfortunately, the cellular source of these ROS during ischemia and reperfusion is often poorly defined. Similarly, individual ROS members tend to be grouped together as free radicals with a uniform reactivity towards biomolecules and with deleterious effects collectively ascribed under the vague umbrella of oxidative stress. This review aims to clarify the identity, origin, and progression of ROS during myocardial ischemia and reperfusion. Additionally, this review aims to describe the biochemical reactions and cellular processes that are initiated by specific ROS that work in concert to ultimately yield the clinical manifestations of myocardial ischemia-reperfusion. Lastly, this review provides an overview of several key cardioprotective strategies that target myocardial ischemia-reperfusion injury from the perspective of ROS generation. This overview is illustrated with example clinical studies that have attempted to translate these strategies to reduce the severity of ischemia-reperfusion injury during coronary artery bypass grafting surgery.
Monoamine oxidases (MAO) in the pathogenesis of heart failure and ischemia/reperfusion injury
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Citation Excerpt :
These include Nox, xanthine oxidase (XO) and nitric oxide synthase that, when uncoupled, can become a powerful ROS generator [42,43,68,69]. Concerning XO, it must be said upfront that in some species, including humans, the heart appears not to contain any [70,71]. Therefore, an explanation for the protective effects exerted by the XO inhibitor allopurinol in these species should be sought elsewhere.
Recent evidence highlights monoamine oxidases (MAO) as another prominent source of oxidative stress. MAO are a class of enzymes located in the outer mitochondrial membrane, deputed to the oxidative breakdown of key neurotransmitters such as norepinephrine, epinephrine and dopamine, and in the process generate H₂O₂. All these monoamines are endowed with potent modulatory effects on myocardial function. Thus, when the heart is subjected to chronic neuro-hormonal and/or peripheral hemodynamic stress, the abundance of circulating/tissue monoamines can make MAO-derived H₂O₂ production particularly prominent. This is the case of acute cardiac damage due to ischemia/reperfusion injury or, on a more chronic stand, of the transition from compensated hypertrophy to overt ventricular dilation/pump failure. Here, we will first briefly discuss mitochondrial status and contribution to acute and chronic cardiac disorders. We will illustrate possible mechanisms by which MAO activity affects cardiac biology and function, along with a discussion as to their role as a prominent source of reactive oxygen species. Finally, we will speculate on why MAO inhibition might have a therapeutic value for treating cardiac affections of ischemic and non-ischemic origin. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.
Animal models for the study of myocardial protection against ischemia
2005, Drug Discovery Today: Disease Models
Research efforts have focused on ways to attenuate deleterious consequences of coronary occlusion in humans. However, clinical research is hampered by the inability to measure morphological, biochemical and molecular changes produced by interventions. Accordingly, a variety of experimental models have been used. However, selection of the particular model is influenced by many considerations: species, physiologic parameter to be measured, perfusate (blood or cell-free), whole organ or isolated cardiomyocyte, among others. This review highlights these considerations.
Nitric oxide and related factors linked to oxidation and inflammation as possible biomarkers of heart failure
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Como enfermedad cardiovascular prevalente, la insuficiencia cardíaca es una de las principales causas de morbimortalidad prematura. Por ello, existe un especial interés sobre el estudio de marcadores eficientes asociados al riesgo y/o predicción de eventos cardiovasculares. En consecuencia se proponen a múltiples candidatos, pero sobresalen especialmente aquellos implicados en procesos oxidativos e inflamatorios propios de la enfermedad cardiovascular como el anión superóxido, óxido nítrico y peroxinitrito. En este sentido, existe una falta de conocimiento sobre las potenciales utilidades de estos sistemas como biomarcadores. La presente revisión procura contribuir a la mayor comprensión de estos sistemas para una mejor caracterización de pacientes. Por otra parte, un profundo conocimiento de estos complejos sistemas también permitiría proponer nuevas líneas de investigación para el desarrollo de inéditas herramientas terapéuticas como una auspiciosa frontera para el abordaje de esta patología.
As a prevalent cardiovascular disease, heart failure is one of the leading causes of morbidity and premature mortality. Therefore, there is a special interest in the study of efficient markers associated with risk and / or prediction of cardiovascular events. Multiple candidates are proposed, especially those involved in oxidative and inflammatory processes typical of cardiovascular disease, such as superoxide anion, nitric oxide, and peroxynitrite. There is a lack of knowledge on the potential usefulness of these systems as biomarkers. This review aims to contribute to a better understanding of these systems, as well as an improved patient profile. Furthermore, a deep knowledge of these complex systems would also allow proposing new lines of research for the development of new therapeutic tools as a promising start for new approaches to this disease.

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Xanthine oxidase is not a source of free radicals in the ischemic rabbit heart

J Mol Cell Cardiol

Comp Biochem Physiol

Gastroenterology

Infarct size limitation by the xanthine oxidase inhibitor, allopurinol, in closed-chest dogs with small infarcts

Cardiovasc Res

Milk xanthine oxidase: type D and type O

Biochem J

Effect of allopurinol on myocardial ischemic damage

Fed Proc

Sulfhydryl oxidase-catalysed conversion of xanthine dehydrogenase to xanthine oxidase

Acta Biochem Biophys

Lack of spontaneous or verapamil-induced salvage of potentially necrotic myocardium during 24 hours of coronary artery occlusion in the rabbit

J Appl Cardiol

The free radical producing enzyme, xanthine oxidase, is undetectable in human hearts

Am J Physiol

Quantitative aspects of the production of superoxide anion radical by milk xanthine oxidase