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Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cardiac ischemia is characterized by rapid deterioration of cardiac function, which has been linked to the fall in intracellular pH, increased levels of inorganic phosphate and reduction in free energy change of ATP-hydrolysis. Biochemical events responsible for irreversible myocardial injury involve various mechanisms which change the properties of the cardiac cell membrane (disorders in lipid metabolism, free radical formation). Recent evidence suggests that in the heart, xanthine oxidase is a major source of free radical formation. During ischemia, adenine-nucleotide breakdown in the cardiomyocyte proceeds only to the stage of inosine. Due to the localisation of nucleoside phosphorylase and xanthine-oxidase in vascular endothelium, further degradation of inosine to hypoxanthine, xanthine and uric acid occurs predominantly in the vascular space. It is therefore conceivable that the primary site of reperfusion injury in the ischemic heart may be the coronary endothelium damaged by free radicals.
Basic Res Cardiol 1985
PMID:Mechanisms of ischemic injury in the heart. 390 19

The morphological, biochemical and functional characterization of the vascular endothelium has become possible through the broad use of electron microscopic methods, the successful elaboration and application of techniques for the isolation and cultivation of endothelial cells in vitro and through sophisticated studies on vessel and organ preparations, both in vitro and in vivo. In this survey emphasis is placed on certain methodological aspects of endothelial cell culture as well as on biochemical, physiological and pathophysiological features of the vascular endothelium. Endothelial cells can be propagated in culture dishes, the most commonly applied method, on suspended microbeads (dextrane, polyacrylamide), a technique giving large yields, or on thin porous membranes, a procedure suited for the study of transport processes across the endothelial layer. Different structural, biochemical and functional properties of the luminal (apical) and abluminal (basal) cell membrane determine important polarity features of the endothelium. Endothelial cells exhibit a variety of biochemical pathways and are characterized by high metabolic activities. Of particular interest is the large content of ATP in endothelial cells of different vascular origin. The rapid intracellular degradation of adenine nucleotides to nucleosides and bases, which are constantly released, is balanced by synthesis, mainly via salvage pathways. In endothelial cells of microvascular origin uric acid predominates by far as the final purine degradative because of the presence of xanthine dehydrogenase in these cells; in the macrovascular endothelium purine breakdown proceeds only to hypoxanthine, since xanthine dehydrogenase is lacking. In this connection interrelations between nucleotide catabolism in myocardial tissue and in coronary endothelial cells are discussed, also with respect to the participation of endothelial xanthine oxidase in the formation of oxygen radicals during post-ischemic reperfusion of the heart. Vascular endothelial cells of different origin are also capable of a rapid extracellular degradation of ATP, ADP and AMP to adenosine by means of specific ecto-nucleotidases. The subsequent fate of extracellularly formed adenosine appears to be different for endothelial cells of microvascular (preferential adenosine uptake) and macrovascular origin (preferential extracellular adenosine accumulation), thus implying functional consequences for platelet aggregation.(ABSTRACT TRUNCATED AT 400 WORDS)
Basic Res Cardiol
PMID:The vascular endothelium: a survey of some newly evolving biochemical and physiological features. 393 1

Free radicals and lipid peroxides have recently been identified by us [1, 2, 3] as metabolic intermediates during acute myocardial ischemia. The mechanisms by which evolving myocardial ischemia initiates free radical production are not clear. Based on studies in vitro, it is feasible to consider the following possibilities: (a) dissociation of intramitochondrial electron support system and altered phospholipid integrity with inactivation of cytochrome oxidase, which results in release of ubisemiquinone, flavoprotein and superoxide radicals; (b) accumulation and increased release of intra/extracellular metabolites like NADH, lactate flavoproteins and catecholamines which react either with themselves or with O2 and ascorbic acid; (c) interaction of the metabolic product hypoxanthine with O2 in the presence of xanthine oxidase and (d) activation of phospholipase by calcium influx with enhanced arachidonic acid metabolism and superoxide radical production. Detailed in vitro radiobiological studies [4] have demonstrated that free radical reactions occur even at very low O2 tensions (83% of maximum rate of PO2 approximately 6 mmHg and 50% at PO2 approximately 1 mmHg), and Smith [5] has demonstrated that free radical peroxidation takes place quite rapidly in rat brain homogenates incubated in gas mixtures containing only 5% O2. Thus, the low oxygen tensions in ischemic tissue are adequate to support free radical reactions. The free radicals thus produced may initiate and enhance lipid peroxidation by attacking polyunsaturated membrane lipids.
J Mol Cell Cardiol 1983 Oct
PMID:Production of free radicals and lipid peroxides in early experimental myocardial ischemia. 631 60

Previous research has shown that heart mitochondria are able to produce reactive species of oxygen such as superoxide radicals, hydrogen peroxide and hydroxyl radicals [10, 11]. When these compounds are formed beyond a certain level they are not completely removed by the enzymatic and metabolic processes which neutralize their toxicity, and as a result they are able to produce structural and functional damages that impair mitochondrial function [5, 10]. In order to study the molecular mechanism/s by which the oxygen radicals may function as mediators of cellular injury a flow of these radicals by chemical, enzymatic or photochemical methods has been generated in vitro in the presence of cellular preparations. For example, the exposure of isolated subcellular particles to the enzymatic flow of oxygen radicals produced by the reaction of xanthine oxidase upon xanthine reduced both calcium uptake velocity and Ca2+-ATPase activity in sarcoplasmic reticulum [7], while it reduced Ca2+-stimulated ATPase activity in myofibrillar preparations [4]. In addition, incubation with the xanthine oxidase reaction produced an impairment of the respiratory functions associated with an increased lipid peroxidation in the isolated mitochondria [5, 10]. These negative effects were augmented in alpha-tocopherol-deficient mitochondria [3], but were opposed by the exogenous addition of superoxide dismutase [10]. This report shows that the superoxide radicals generated by the xanthine oxidase reaction reduced rat heart mitochondrial respiration induced by pyruvate. This negative effect was partially prevented by superoxide dismutase and catalase and by thiol protecting agents. Moreover, the generation of free radicals caused a significant reduction in the rate of (1-14C) -pyruvate decarboxylation, while it did not change the transport of pyruvate into mitochondria.
J Mol Cell Cardiol 1983 Dec
PMID:Effect of superoxide generation on rat heart mitochondrial pyruvate utilization. 631 22

We strongly support the original intriguing hypothesis of Hearse et al. that the oxygen paradox and the calcium paradox are facets of the same problem. We would propose that the major similarity is a final common pathway leading to intracellular calcium overload and the sequelae of the resultant increase in intracellular calcium. In addition, we would propose that the oxygen paradox and ischemic/reperfusion injury are also facets of the same problem with the major similarity being the reintroduction of molecular oxygen to a previously hypoxic myocardium. Finally, we would suggest that the common pathway leading to intracellular calcium overload in the oxygen paradox and ischemic/reperfusion injury and to a lesser extent the calcium paradox involves the generation of oxygen free radicals. The source of oxygen free radical generation in the calcium paradox is perhaps less obvious than in the oxygen paradox. It is proposed that during calcium-free perfusion, calcium is leached from the plasmalemma of the myocyte. There is a resulting increase in membrane fluidity. Within the plasmalemma are a number of calcium sensitive phospholipases. Upon reperfusion with a calcium replete medium, calcium could pool around these membrane bound phospholipases initiating a chain reaction of lipid peroxidation which actually is perpetuated by free radical generation (Equations 5A-5C). Lipid peroxidation opens channels within the plasmalemma rendering a 'leaky' sarcolemma. It is through these channels that calcium could flow down its concentration gradient into the cell. The increased calcium accumulation at the mitochondria would lead to an uncoupling of oxidative phosphorylation. With depleted energy stores, the mitochondria and sarcoplasmic reticulum no longer serve as calcium sinks. This would contribute to the calcium overload seen upon reperfusion. The role of oxygen free radical production would appear to occur during the hypoxic phase of the oxygen paradox and the ischemic phase of ischemic/reperfusion injury and during the reoxygenation/reperfusion phases. With the onset of hypoxia and/or myocardial ischemia there is an increase in reducing equivalents, disturbance and dissociation of intramitochondrial electron transport and release of ubisemiquinone, flavoproteins and superoxide radicals. The increase in reducing equivalents includes NADPH and, in ischemia, catecholamines, hypoxanthine and an increase on xanthine oxidase activity. All of these substrates are capable of participating in free radical production. This increase in free radical production in ischemic tissue is enhanced by acidosis which in the ischemic and hypoxic myocardium approaches pH 6.0-6.4.(ABSTRACT TRUNCATED AT 400 WORDS)
J Mol Cell Cardiol 1984 Nov
PMID:Molecular oxygen: friend and foe. The role of the oxygen free radical system in the calcium paradox, the oxygen paradox and ischemia/reperfusion injury. 639 65

Previous studies in other systems have shown that beta-receptor blockers may effectively inhibit oxygen radical-induced lipid peroxidation. On the other hand, it has been recently proposed that oxygen free radicals can induce peroxidation of human low density lipoproteins (LDL), and that peroxidized LDL may be an atherogenic stimulus. Chemically modified LDL are internalized by macrophages via a specific cell surface receptor that was termed the scavenger receptor. This phenomenon may induce foam cells transformation in vivo. In the present study we investigated whether beta-blockers may reduce oxygen radical-mediated LDL peroxidation. Purified human LDL were oxidized by exposure to oxygen free radicals generated by xanthine (0.2 mM) and xanthine oxidase (100 mU) at 37 degrees C after a pre-incubation (30 min) in presence of different concentrations (from 1 to 30 microM) of acebutolol, metoprolol or propranolol, three agents with a different degree of lipophilicity. Peroxidation was measured from malonyldihaldehyde (MDA) production. Data have shown a significant percent inhibition of MDA formation in presence of beta-blockers (from 33 to 85%). Thus, beta-blockers reduced peroxidation of human LDL in vitro at clinically relevant concentrations. The order of potency appears to follow the degree of lipophilicity. These data suggest that, although beta-blockers are known to adversely effect lipid metabolism, these agents might on the other hand prevent atherogenesis via a mechanism of inhibition of LDL peroxidation in vivo and reduced foam cells formation.
G Ital Cardiol 1994 Apr
PMID:[Protection by blockers against human low density lipoprotein peroxidation induced by oxygen free radicals]. 791 99

Xanthine dehydrogenase (XDH) is an important precursor to the oxygen radical producing enzyme xanthine oxidase (XO). We found that the apparent activity of rabbit myocardial XDH increased from 2 +/- 1 to 50 +/- 3 microU/g (P < 0.05) following extraction of tissue homogenate with butanol. Further studies suggested that the basis for this observation was a high molecular weight compound which consumes the XDH cofactor, NAD+. Addition of myocardial homogenate to exogenous NAD+ resulted in depletion of NAD+ and concomitant formation of an additional compound (peak A). Both NAD+ consumption and peak A formation were abrogated by prior extraction of homogenate with butanol. Separation of myocardial homogenate by Sephadex chromatography revealed a high molecular weight compound which suppressed activity of purified milk XDH but not xanthine oxidase (XO). This activity co-eluted with the ability of myocardial homogenate to consume added NAD+ and form peak A. The NAD(+)-consuming activity was heat and acid-labile. In addition, nicotinamide was both a product and an inhibitor of the NADase activity, consistent with the existence of a previously described myocardial glycohydrolase. Extraction of tissue with butanol may be necessary to detect low levels of XDH activity in vitro.
J Mol Cell Cardiol 1994 Feb
PMID:Suppression of rabbit myocardial xanthine dehydrogenase activity by an endogenous compound. 800 74

The role of free radicals and the protective action of calcium antagonists have been established in myocardial stunning in canine hearts, which contain a considerable level of xanthine oxidase, a free radical producing enzyme. However, myocardial stunning in hearts which lack xanthine oxidase and its modification by calcium antagonists in vivo remain uncharacterized. The present study examined this issue using open-chest anesthetized rabbits. Myocardial stunning was induced by a 10-min coronary occlusion and reperfusion. Regional systolic thickening fraction (TF) was determined using an epicardial Doppler sensor, together with other hemodynamic parameters. In untreated control rabbits, recovery of TF from the 10 min transient ischemia was 43 +/- 3% of the baseline at 30 min after reperfusion. Administration of verapamil (200 micrograms/kg bolus plus 40 micrograms/kg/min), which was started before the onset of ischemia and continued until 20 min after reperfusion, significantly improved the recovery of TF to 74 +/- 6% (p < 0.05). A similar improvement in post-ischemic contractile function (TF = 77 +/- 10%) was observed when verapamil was injected at the same rate, but the infusion was discontinued 1 min after the coronary occlusion. Myocardial ATP depletion after the 10 min ischemia was significantly less in the verapamil-pretreated rabbits compared with untreated controls (10.1 +/- 1.0 vs. 6.2 +/- 0.7 mumol/g dry wt., p < 0.05). The difference in TF between the rabbit with and without verapamil treatment could not be explained by afterload reduction. When verapamil (100 micrograms/kg bolus plus 20 micrograms/kg/min) was given during the reperfusion period alone, TF recovery was poorer (TF = 22 +/- 8%) than the control value. Thus, it was concluded that verapamil attenuates myocardial stunning in the hearts with trace levels of xanthine oxidase, and that the beneficial effect is achieved only by pretreatment, not by post-ischemic treatment with verapamil.
Basic Res Cardiol
PMID:Effects of verapamil on myocardial stunning in xanthine-oxidase deficient hearts: pre-treatment vs. post-ischemic treatment. 801 Sep 31

The present study focuses on the sequential development of myocardial ultrastructural changes produced by oxygen radicals. Isolated rat hearts were perfused with oxygen radicals, generated by hypoxanthine and xanthine oxidase, for 5 and 10 min followed by a 35-min recovery period. The frequency of, and the association between, ultrastructural changes were examined by semiquantitative morphometry using the micrograph as unit. In each micrograph sarcolemmal, myocytic mitochondrial and myofilamental alterations were observed and graded as slight, moderate or severe. The myocytic nucleus and the endothelial cells were scored as normal or altered. Five min group: Among the cellular organelles examined, the myocytic mitochondria showed the highest frequency of alteration (in 15.3% of the micrographs). Among the grades of myocytic mitochondrial ultrastructural changes, slight alterations predominated (12.5%). Slight myocytic mitochondrial alterations were not significantly associated with the occurrence of ultrastructural changes of other cellular organelles. Endothelial ultrastructural alterations were sparse (1.5%). Ten min group: The frequency of altered organelles was greater when compared to the 5 min group. The myocytic mitochondria were still the most frequently altered component (61.7%), and myocytic mitochondrial ultrastructural alterations of all grades were strongly associated with the occurrence of other myocytic ultrastructural changes. In conclusion, the present study showed that myocytic mitochondrial changes predominated after both 5 and 10 min of oxygen radical exposure followed by recovery. In the 5 min group slight myocytic mitochondrial changes appeared independent of other myocardial changes, but in the 10 min group, however, myocytic mitochondrial changes were strongly associated with other myocardial ultrastructural changes. These results indicate that myocytic mitochondria are especially vulnerable to oxygen radicals, and further that myocytic mitochondrial ultrastructural changes may be a crucial step in the development of oxygen radical-induced myocardial damage.
Basic Res Cardiol
PMID:Ultrastructural changes in the myocardial myocytic mitochondria: crucial step in the development of oxygen radical-induced damage in isolated rat hearts? 807 37

The effects of perfusate calcium reduction, allopurinol and dimethylthiourea on reperfusion-induced arrhythmias and purine wash-out in isolated rabbit and rat hearts were compared. The overall incidence of reperfusion-induced ventricular tachycardia (VT) was 88% and 94% and that of ventricular fibrillation (VF) was 44% and 88% in the control rabbit and rat hearts, respectively. VF was reduced to 10% and 0% in rat and rabbit hearts subjected to perfusate calcium reduction (0.4 mM for 1 min before ischemia and for 1 min before and throughout reperfusion), respectively. In allopurinol, 1 mM, perfused rat hearts the overall incidence of VF was not changed and only the incidence of a sustained VF (that lasting for at least 10 min) was reduced. VT and VF were prevented in allopurinol-perfused rabbit hearts. Dimethylthiourea, 10 mM, reduced the incidence of VF in rat hearts to 16% and did not significantly affect VT and VF in rabbit hearts. In untreated rat hearts, the major purine compounds washed out upon reperfusion were inosine, hypoxanthine, xanthine and urate. Allopurinol augmented the wash-out of adenosine and abolished that of xanthine and urate. In untreated rabbit hearts, the major purine washed out were inosine, adenosine and hypoxanthine. Allopurinol did not cause further increase in adenosine wash-out in rabbit hearts. We speculate that: (1) calcium mediated arrhythmogenic mechanism is operating both in reperfused rat and rabbit heart; (2) free radical mediated mechanism is of an importance only in rat heart; (3) neither a decreased free radical production secondary to xanthine oxidase inhibition nor the augmentation of adenosine wash-out is a likely explanation for the antiarrhythmic effect of allopurinol in reperfused hearts; and (4) high level of myocardial adenosine accumulation during ischemia, probably secondary to low xanthine oxidase activity, may play a role of a natural defence mechanism in ischemic/reperfused rabbit heart.
J Mol Cell Cardiol 1993 Jul
PMID:Reperfusion arrhythmias and purine wash-out in isolated rat and rabbit heart. Effect of allopurinol, dimethylthiourea and calcium reduction. 823 Feb 46


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