Antioxidant network expression abrogates oxidative posttranslational modifications in mice.

Antioxidant enzymatic pathways form a critical network that detoxifies ROS in response to myocardial stress or injury. Genetic alteration of the expression levels of individual enzymes has yielded mixed results with regard to attenuating in vivo myocardial ischemia-reperfusion injury, an extreme oxidative stress. We hypothesized that overexpression of an antioxidant network (AON) composed of SOD1, SOD3, and glutathione peroxidase (GSHPx)-1 would reduce myocardial ischemia-reperfusion injury by limiting ROS-mediated lipid peroxidation and oxidative posttranslational modification (OPTM) of proteins. Both ex vivo and in vivo myocardial ischemia models were used to evaluate the effect of AON expression. After ischemia-reperfusion injury, infarct size was significantly reduced both ex vivo and in vivo, ROS formation, measured by dihydroethidium staining, was markedly decreased, ROS-mediated lipid peroxidation, measured by malondialdehyde production, was significantly limited, and OPTM of total myocardial proteins, including fatty acid-binding protein and sarco(endo)plasmic reticulum Ca(²+)-ATPase (SERCA)2a, was markedly reduced in AON mice, which overexpress SOD1, SOD3, and GSHPx-1, compared with wild-type mice. These data demonstrate that concomitant SOD1, SOD3, and GSHPX-1 expression confers marked protection against myocardial ischemia-reperfusion injury, reducing ROS, ROS-mediated lipid peroxidation, and OPTM of critical cardiac proteins, including cardiac fatty acid-binding protein and SERCA2a.

Enzyme-independent formation of nitric oxide in biological tissues.

The gaseous free radical nitric oxide (NO.) is an important regulator of a variety of biological functions and also has a role in the pathogenesis of cellular injury. It has been generally accepted that NO. is solely generated in biological tissues by specific nitric oxide synthases, NOSs, which metabolize arginine to citrulline with the formation of NO.. We report that NO. can also be generated in the ischaemic heart by direct reduction of nitrite to NO. under the acidotic and highly reduced conditions that occur. This NO. formation is not blocked by NOS inhibitors, and with long periods of ischaemia progressing to necrosis, this mechanism of NO. formation predominates. We observe that enzyme-independent NO. generation results in myocardial injury with a loss of contractile function. The existence of this enzyme-independent mechanism of NO. formation has important implications in our understanding of the pathogenesis and treatment of tissue injury.

Reactive oxygen species (ROS)-induced ROS release: a new phenomenon accompanying induction of the mitochondrial permeability transition in cardiac myocytes.

We sought to understand the relationship between reactive oxygen species (ROS) and the mitochondrial permeability transition (MPT) in cardiac myocytes based on the observation of increased ROS production at sites of spontaneously deenergized mitochondria. We devised a new model enabling incremental ROS accumulation in individual mitochondria in isolated cardiac myocytes via photoactivation of tetramethylrhodamine derivatives, which also served to report the mitochondrial transmembrane potential, DeltaPsi. This ROS accumulation reproducibly triggered abrupt (and sometimes reversible) mitochondrial depolarization. This phenomenon was ascribed to MPT induction because (a) bongkrekic acid prevented it and (b) mitochondria became permeable for calcein ( approximately 620 daltons) concurrently with depolarization. These photodynamically produced "triggering" ROS caused the MPT induction, as the ROS scavenger Trolox prevented it. The time required for triggering ROS to induce the MPT was dependent on intrinsic cellular ROS-scavenging redox mechanisms, particularly glutathione. MPT induction caused by triggering ROS coincided with a burst of mitochondrial ROS generation, as measured by dichlorofluorescein fluorescence, which we have termed mitochondrial "ROS-induced ROS release" (RIRR). This MPT induction/RIRR phenomenon in cardiac myocytes often occurred synchronously and reversibly among long chains of adjacent mitochondria demonstrating apparent cooperativity. The observed link between MPT and RIRR could be a fundamental phenomenon in mitochondrial and cell biology.

Mitogenic signaling mediated by oxidants in Ras-transformed fibroblasts.

NIH 3T3 fibroblasts stably transformed with a constitutively active isoform of p21(Ras), H-RasV12 (v-H-Ras or EJ-Ras), produced large amounts of the reactive oxygen species superoxide (.O2-). .O2- production was suppressed by the expression of dominant negative isoforms of Ras or Rac1, as well as by treatment with a farnesyltransferase inhibitor or with diphenylene iodonium, a flavoprotein inhibitor. The mitogenic activity of cells expressing H-RasV12 was inhibited by treatment with the chemical antioxidant N-acetyl-L-cysteine. Mitogen-activated protein kinase (MAPK) activity was decreased and c-Jun N-terminal kinase (JNK) was not activated in H-RasV12-transformed cells. Thus, H-RasV12-induced transformation can lead to the production of .O2- through one or more pathways involving a flavoprotein and Rac1. The implication of a reactive oxygen species, probably .O2-, as a mediator of Ras-induced cell cycle progression independent of MAPK and JNK suggests a possible mechanism for the effects of antioxidants against Ras-induced cellular transformation.

A nonpeptidyl mimic of superoxide dismutase with therapeutic activity in rats.

Many human diseases are associated with the overproduction of oxygen free radicals that inflict cell damage. A manganese(II) complex with a bis(cyclohexylpyridine)-substituted macrocyclic ligand (M40403) was designed to be a functional mimic of the superoxide dismutase (SOD) enzymes that normally remove these radicals. M40403 had high catalytic SOD activity and was chemically and biologically stable in vivo. Injection of M40403 into rat models of inflammation and ischemia-reperfusion injury protected the animals against tissue damage. Such mimics may result in better clinical therapies for diseases mediated by superoxide radicals.

Recombinant superoxide dismutase reduces oxygen free radical concentrations in reperfused myocardium.

It has been proposed that oxygen free radicals mediate damage that occurs during postischemic reperfusion. Recombinant human superoxide dismutase (r-h-SOD) has been shown to be effective at reducing reperfusion injury, but it is not known if this infused enzyme actually reduces oxygen free radical concentrations in the myocardial tissue. Electron paramagnetic resonance spectroscopy was used to directly measure the effect of r-h-SOD on free radical concentrations in the postischemic heart. Hearts were freeze clamped at 77 degrees K after 10 min of normothermic global ischemia followed by 10 s of reflow with control perfusate (n = 7) or perfusate containing 60,000 U r-h-SOD (n = 7). The spectra of these hearts exhibited three different signals: signal A isotropic, g = 2.004, identical to the carbon-centered ubiquinone free radical; signal B anisotropic with axial symmetry, g parallel = 2.033, g perpendicular = 2.005, identical to the oxygen-centered alkyl peroxyl free radical; and the signal C an isotropic triplet, g parallel = 2.000, an = 24 G, similar to a nitrogen-centered free radical such as a peroxyl amine. With r-h-SOD administration the concentration of the oxygen free radical, signal B, was reduced 49% from 6.8 +/- 0.3 microM to 3.5 +/- 0.3 microM (P less than 0.01) and the concentration of the nitrogen free radical, signal C, was reduced 38% from 3.4 +/- 0.3 to 2.1 +/- 0.3 microM (P less than 0.01). The concentration of the carbon-centered free radical, signal A, however, was increased 51% from 3.3 +/- 0.2 to 5.0 +/- 0.2 microM (P less than 0.01). Identical reperfusion with peroxide-inactivated r-h-SOD did not alter the concentrations of free radicals indicating that the specific enzymatic activity of r-h-SOD is required to decrease the concentrations of reactive oxygen free radicals. Additional measurements performed varying the duration of reflow demonstrate a burst of oxygen free radical generation peaking at 10 s of reperfusion. r-h-SOD entirely abolished this burst. These studies demonstrate that superoxide-derived free radicals are generated during postischemic reperfusion and suggest that the beneficial effect of r-h-SOD is due to its specific enzymatic scavenging of superoxide free radicals.

Glycolytic inhibition and calcium overload as consequences of exogenously generated free radicals in rabbit hearts.

Free radicals have been implicated in the pathogenesis of reperfusion injury, but it is unclear how they exert their deleterious effects on cellular metabolism. Several lines of indirect evidence suggest that free radicals elevate intracellular Ca2+ concentration ([Ca2+]i) and inhibit glycolysis as part of their mechanism of injury. We tested these ideas directly in hearts subjected to hydroxyl radicals produced by the Fenton and Haber-Weiss reactions. Nuclear magnetic resonance spectra were obtained from Langendorff-perfused rabbit hearts before, during, and after 4 min of perfusion with H2O2 (0.75 mM) and Fe(3+)-chelate (0.1 mM). Isovolumic left ventricular pressure exhibited progressive functional deterioration and contracture after exposure to H2O2 + Fe3+. Phosphorus nuclear magnetic resonance (NMR) spectra revealed partial ATP depletion and sugar phosphate accumulation indicative of glycolytic inhibition. To measure [Ca2+]i, fluorine NMR spectra were acquired in a separate group of hearts loaded with the Ca2+ indicator 5F-BAPTA [5,5'-difluoro derivative of 1,2-bis-(o-aminophenoxy)ethane- N,N,N',N'-tetraacetic acid]. Mean time-averaged [Ca2+]i increased from 347 +/- 14 nM in control to 1,026 +/- 295 nM 4 min after free radical generation (means +/- SEM, n = 7), and remained elevated thereafter. We conclude that free radicals induce clear-cut, specific derangements of cellular metabolism in the form of glycolytic inhibition and calcium overload. The observed increase in [Ca2+]i suggests that the deleterious effects of free radicals are at least partially mediated by secondary changes in cellular calcium homeostasis.

Hyperoxic sheep pulmonary microvascular endothelial cells generate free radicals via mitochondrial electron transport.

Free radical generation by hyperoxic endothelial cells was studied using electron paramagnetic resonance (EPR) spectroscopy and the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Studies were performed to determine the radical species produced, whether mitochondrial electron transport was involved, and the effect of the radical generation on cell mortality. Sheep pulmonary microvascular endothelial cell suspensions exposed to 100% O2 for 30 min exhibited prominent DMPO-OH and, occasionally, additional smaller DMPO-R signals thought to arise from the trapping of superoxide anion (O2-.), hydroxyl (.OH), and alkyl (.R) radicals. Superoxide dismutase (SOD) quenched both signals suggesting that the observed radicals were derived from O2-.. Studies with deferoxamine suggested that the generation of .R occurred secondary to the formation of .OH from O2-. via an iron-mediated Fenton reaction. Blocking mitochondrial electron transport with rotenone (20 microM) markedly decreased radical generation. Cell mortality increased slightly in oxygen-exposed cells. This increase was not significantly altered by SOD or deferoxamine, nor was it different from the mortality observed in air-exposed cells. These results suggest that endothelial cells exposed to hyperoxia for 30 min produce free radicals via mitochondrial electron transport, but under the conditions of these experiments, this radical generation did not appear cause cell death.

Phenolic Michael reaction acceptors: combined direct and indirect antioxidant defenses against electrophiles and oxidants.

The implications of oxidative stress in the pathogenesis of many chronic human diseases has led to the widely accepted view that low molecular weight antioxidants could be beneficial and postpone or even prevent these diseases. Small molecules of either plant or synthetic origins, which contain Michael acceptor functionalities (olefins or acetylenes conjugated to electron-withdrawing groups) protect against the toxicity of oxidants and electrophiles indirectly, i.e., by inducing phase 2 cytoprotective enzymes. Some of these molecules, e.g., flavonoid and curcuminoid analogues that have phenolic hydroxyl groups in addition to Michael acceptor centers, are also potent direct antioxidants, and may therefore be appropriately designated: bifunctional antioxidants. By use of spectroscopic methods we identified phenolic chalcone and bis(benzylidene)acetone analogues containing one or two Michael acceptor groups, respectively, as very efficient scavengers of two different types of radicals: (a) the nitrogen-centered 2,2'-azinobis-(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS.+) radical cation, and (b) the oxygen-centered galvinoxyl (phenoxyl) radical. The most potent scavengers are those also bearing hydroxyl substituents on the aromatic ring(s) at the ortho-position(s). The initial reaction velocities are very rapid and concentration-dependent. In the human keratinocyte cell line HaCaT, the same compounds coordinately increase the intracellular levels of glutathione, glutathione reductase, and thioredoxin reductase. Thus, such bifunctional antioxidants could exert synergistic protective effects against oxidants and electrophiles which represent the principal biological hazards by: (i) scavenging hazardous oxidants directly and immediately; and (ii) inducing the phase 2 response to prevent and resolve the consequences of hazardous processes that are already in progress, i.e., acting indirectly, but with much more diverse and long-lasting effects.

In vivo electron paramagnetic resonance imaging of tumor heterogeneity and oxygenation in a murine model.

Nitroxides are redox-sensitive probes, which are useful in noninvasively delineating tissue heterogeneity especially with respect to metabolic activity and tissue oxygenation. Recent studies have shown that nitroxides are in vitro and in vivo radioprotectors and selectively protect normal tissue compared to tumor tissue. It has been postulated that the basis for selective radioprotection of normal tissues is greater bioreduction of nitroxides in tumor tissue compared to normal tissue. The aim of the present study was to investigate the distribution and lifetime of nitroxides in tumor and normal tissues. Mice were implanted with tumor cells (RIF-1) in the thigh, and the tumor was allowed to grow to about 10-15 mm in diameter. After i.v. infusion of nitroxides, in vivo electron paramagnetic resonance spectroscopy and imaging of the tumor were performed using a specially built bridged-loop surface resonator. The pharmacokinetic and spatial distribution of the nitroxides in tumor tissue were followed and compared with those in normal tissue. Three-dimensional spatial images showed significant heterogeneity in the nitroxide distribution as well as reduction rates. The nitroxide reduction rates were significantly higher in tumors than in the normal tissue. Measurements using spin label oximetry showed a substantial difference in the level of oxygenation between normal tissue (muscle) and tumor tissue. Average pO2 levels in tumor tissue were found to be 3-fold lower than in a corresponding volume of normal tissue. The lower pO2 levels in tumor compared to normal tissue may explain the more rapid reduction of nitroxides in these tissues. This study demonstrates that electron paramagnetic resonance imaging can perform noninvasive anatomical as well as functional imaging and provide in vivo physiological information regarding cellular metabolism in tumor and normal tissues.

Insulin-like growth factor 1 prevents diastolic and systolic dysfunction associated with cardiomyopathy and preserves adrenergic sensitivity.

AIMS: Insulin-like growth factor 1 (IGF-1)-dependent signalling promotes exercise-induced physiological cardiac hypertrophy. However, the in vivo therapeutic potential of IGF-1 for heart disease is not well established. Here, we test the potential therapeutic benefits of IGF-1 on cardiac function using an in vivo model of chronic catecholamine-induced cardiomyopathy. METHODS: Rats were perfused with isoproterenol via osmotic pump (1 mg kg(-1) per day) and treated with 2 mg kg(-1) IGF-1 (2 mg kg(-1) per day, 6 days a week) for 2 or 4 weeks. Echocardiography, ECG, and blood pressure were assessed. In vivo pressure-volume loop studies were conducted at 4 weeks. Heart sections were analysed for fibrosis and apoptosis, and relevant biochemical signalling cascades were assessed. RESULTS: After 4 weeks, diastolic function (EDPVR, EDP, tau, E/A ratio), systolic function (PRSW, ESPVR, dP/dtmax) and structural remodelling (LV chamber diameter, wall thickness) were all adversely affected in isoproterenol-treated rats. All these detrimental effects were attenuated in rats treated with Iso+IGF-1. Isoproterenol-dependent effects on BP were attenuated by IGF-1 treatment. Adrenergic sensitivity was blunted in isoproterenol-treated rats but was preserved by IGF-1 treatment. Immunoblots indicate that cardioprotective p110α signalling and activated Akt are selectively upregulated in Iso+IGF-1-treated hearts. Expression of iNOS was significantly increased in both the Iso and Iso+IGF-1 groups; however, tetrahydrobiopterin (BH4) levels were decreased in the Iso group and maintained by IGF-1 treatment. CONCLUSION: IGF-1 treatment attenuates diastolic and systolic dysfunction associated with chronic catecholamine-induced cardiomyopathy while preserving adrenergic sensitivity and promoting BH4 production. These data support the potential use of IGF-1 therapy for clinical applications for cardiomyopathies.

Iron-mediated formation of an oxidized adriamycin free radical.

Electron paramagnetic resonance studies are reported which demonstrate that the reduction of Fe3+ to Fe2+ by adriamycin results in the formation of an oxidized adriamycin free radical with an EPR signal at g = 2.004. A transient iron-adriamycin free radical complex is also observed at g = 2.34. The free radical is quantitated and its aerobic stability is determined. Observation of the oxidized adriamycin free radical signal confirms that adriamycin donates an electron to the bound Fe3+. In the presence of glutathione the drug-mediated reduction of Fe3+ to Fe2+ is bypassed, and the oxidized adriamycin radical signal is not observed. The oxidized adriamycin radicals and reduced oxygen radicals which are formed are two different mediators, whose relative concentrations could modulate the therapeutic and toxic effects of adriamycin.

Role of neuronal and endothelial nitric oxide synthase in nitric oxide generation in the brain following cerebral ischemia.

Nitric oxide (NO) plays an important role in the pathogenesis of neuronal injury during cerebral ischemia. The endothelial and neuronal isoforms of nitric oxide synthase (eNOS, nNOS) generate NO, but NO generation from these two isoforms can have opposing roles in the process of ischemic injury. While increased NO production from nNOS in neurons can cause neuronal injury, endothelial NO production from eNOS can decrease ischemic injury by inducing vasodilation. However, the relative magnitude and time course of NO generation from each isoform during cerebral ischemia has not been previously determined. Therefore, electron paramagnetic resonance spectroscopy was applied to directly detect NO in the brain of mice in the basal state and following global cerebral ischemia induced by cardiac arrest. The relative amount of NO derived from eNOS and nNOS was accessed using transgenic eNOS(-/-) or nNOS(-/-) mice and matched wild-type control mice. NO was trapped using Fe(II)-diethyldithiocarbamate. In wild-type mice, only small NO signals were seen prior to ischemia, but after 10 to 20 min of ischemia the signals increased more than 4-fold. This NO generation was inhibited more than 70% by NOS inhibition. In either nNOS(-/-) or eNOS(-/-) mice before ischemia, NO generation was decreased about 50% compared to that in wild-type mice. Following the onset of ischemia a rapid increase in NO occurred in nNOS(-/-) mice peaking after only 10 min. The production of NO in the eNOS(-/-) mice paralleled that in the wild type with a progressive increase over 20 min, suggesting progressive accumulation of NO from nNOS following the onset of ischemia. NOS activity measurements demonstrated that eNOS(-/-) and nNOS(-/-) brains had 90% and < 10%, respectively, of the activity measured in wild type. Thus, while eNOS contributes only a fraction of total brain NOS activity, during the early minutes of cerebral ischemia prominent NO generation from this isoform occurs, confirming its importance in modulating the process of ischemic injury.

Non-enzymatic nitric oxide synthesis in biological systems.

Nitric oxide (NO) is an important regulator of a variety of biological functions, and also has a role in the pathogenesis of cellular injury. It had been generally accepted that NO is solely generated in biological tissues by specific nitric oxide synthases (NOS) which metabolize arginine to citrulline with the formation of NO. However, NO can also be generated in tissues by either direct disproportionation or reduction of nitrite to NO under the acidic and highly reduced conditions which occur in disease states, such as ischemia. This NO formation is not blocked by NOS inhibitors and with long periods of ischemia progressing to necrosis, this mechanism of NO formation predominates. In postischemic tissues, NOS-independent NO generation has been observed to result in cellular injury with a loss of organ function. The kinetics and magnitude of nitrite disproportionation have been recently characterized and the corresponding rate law of NO formation derived. It was observed that the generation and accumulation of NO from typical nitrite concentrations found in biological tissues increases 100-fold when the pH falls from 7.4 to 5.5. It was also observed that ischemic cardiac tissue contains reducing equivalents which reduce nitrite to NO, further increasing the rate of NO formation more than 40-fold. Under these conditions, the magnitude of enzyme-independent NO generation exceeds that which can be generated by tissue concentrations of NOS. The existence of this enzyme-independent mechanism of NO formation has important implications in our understanding of the pathogenesis and treatment of tissue injury.

Redox properties of iron-dithiocarbamates and their nitrosyl derivatives: implications for their use as traps of nitric oxide in biological systems.

While the Fe(2+)-dithiocarbamate complexes have been commonly used as NO traps to estimate NO production in biological systems, these complexes can undergo complex redox chemistry. Characterization of this redox chemistry is of critical importance for the use of this method as a quantitative assay of NO generation. We observe that the commonly used Fe(2+) complexes of N-methyl-D-glucamine dithiocarbamate (MGD) or diethyldithiocarbamate (DETC) are rapidly oxidized under aerobic conditions to form Fe(3+) complexes. Following exposure to NO, diamagnetic NO-Fe(3+) complexes are formed as demonstrated by the optical, electron paramagnetic resonance and gamma-resonance spectroscopy, chemiluminescence and electrochemical methods. Under anaerobic conditions the aqueous NO-Fe(3+)-MGD and lipid soluble NO-Fe(2+)-DETC complexes gradually self transform by reductive nitrosylation into paramagnetic NO-Fe(2+)-MGD complexes with yield of up to 50% and the balance is converted to Fe(3+)-MGD and nitrite. In dimethylsulfoxide this process is greatly accelerated. More efficient transformation of NO-Fe(3+)-MGD into NO-Fe(2+)-MGD (60-90% levels) was observed after addition of reducing equivalents such as ascorbate, hydroquinone or cysteine or with addition of excess Fe(2+)-MGD. With isotope labeling of the NO-Fe(3+)-MGD with (57)Fe, it was shown that these complexes donate NO to Fe(2+)-MGD. NO-Fe(3+)-MGD complexes were also formed by reversible oxidation of NO-Fe(2+)-MGD in air. The stability of NO-Fe(3+)-MGD and NO-Fe(2+)-MGD complexes increased with increasing the ratio of MGD to Fe. Thus, the iron-dithiocarbamate complexes and their NO derivatives exhibit complex redox chemistry that should be considered in their application for detection of NO in biological systems.

Hydrogen peroxide and superoxide modulate leukocyte adhesion molecule expression and leukocyte endothelial adhesion.

While endothelial oxidant generation and subsequent leukocyte chemotaxis and activation are important mechanisms of tissue damage in ischemic organs, it is not known if oxidant generation may be involved in triggering the subsequent leukocyte-mediated injury which occurs. Questions remain whether particular oxidants and oxygen-free radicals are capable of modulating the expression of leukocyte adhesion molecules and effecting leukocyte endothelial adhesion. Studies were performed to determine the effect of different biologically occurring oxidant molecules and oxygen free radicals including: .O2-, .OH, and H2O2 on the expression of integrin and selectin adhesion molecules on the surface of human PMNs and to determine the effect of these alterations on PMN adhesion to the endothelium. Adhesion molecule expression on the surface of human PMNs was measured by immunofluorescence flow cytometry. Electron paramagnetic resonance spectroscopy was applied to characterize the presence of exogenous free radical generation as well as that from activated PMNs. It was observed that these oxidants can cause up-regulation of CD11b and CD18 expression with shedding of L-selectin. The kinetics and dose-response of these effects were analyzed and their functional significance determined by measuring PMN adhesion to cultured human aortic endothelial monolayers. These studies demonstrate that oxygen free radicals and non-radical oxidants can directly trigger PMN activation and adhesion to vascular endothelium.

Superoxide and hydrogen peroxide induce CD18-mediated adhesion in the postischemic heart.

A burst of endothelial derived oxidants including hydrogen peroxide (H2O2) and superoxide (.O2-) occurs on reperfusion of ischemic tissues that directly causes injury; however, it is not known if this also triggers further injury due to subsequent leukocyte adhesion and adhesion molecule expression. Therefore, studies were performed in an isolated heart model developed to enable study of the role of isolated cellular and humoral factors in the mechanism of postischemic injury. Isolated rat hearts were subjected to 20 min of 37 degrees C-global ischemia followed by reperfusion with polymorphonuclear leukocytes (PMNs) and plasma in the presence or absence of superoxide dismutase (SOD), 200 U/ml, or catalase, 500 U/ml. Measurements of contractile function, coronary flow, high-energy phosphates, free radical generation, and PMN accumulation were performed. Adhesion molecule expression was measured on the surface of effluent PMNs by fluorescence flow cytometry and within the tissue using immunohistochemistry. SOD or catalase treatment resulted in 2- to 3-fold higher recoveries of contractile function, coronary flow, and high energy phosphates. EPR spin trapping measurements demonstrated that SOD totally quenched the free radical generation observed upon reperfusion while catalase prevented the formation of hydroxyl and alkyl radicals derived from superoxide. SOD or catalase treatment decreased PMN accumulation in the reperfused heart and prevented the marked upregulation of CD18 expression seen after reperfusion. These experiments demonstrate that in addition to their direct antioxidative actions, SOD and catalase each decrease PMN adhesion and CD18 expression resulting in marked suppression of PMN-mediated injury in the postischemic heart. Thus, endothelial derived H2O2 and .O2- further amplify postischemic injury by triggering CD18 expression on the surface of PMNs leading to increased PMN adhesion within the heart.

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.

Coronary angioplasty results in leukocyte and platelet activation with adhesion molecule expression. Evidence of inflammatory responses in coronary angioplasty.

OBJECTIVES: This study sought to characterize leukocyte and platelet activation and adhesion molecule expression after coronary angioplasty. BACKGROUND: Coronary angioplasty can be regarded as a clinical model of postischemic inflammation because this intervention leads to the release of inflammatory mediators as a result of plaque rupture and endothelial injury. METHODS: In 13 patients with stable angina (mean [ +/- SEM] age 56.0 +/- 2.4 years, range 44 to 79), blood samples were drawn from the aorta and coronary sinus immediately before and immediately and 15 min after coronary angioplasty. Subsequently, leukocyte and platelet functions were determined. Eleven control patients (57.5 +/- 2.3 years, range 52 to 78) underwent coronary arteriography. RESULTS: Coronary arteriography and angioplasty showed no difference in number of leukocytes between the coronary sinus and the aorta. However, 15 min after coronary angioplasty, there was an increase in neutrophil CD18 and CD11b, monocyte CD14 and platelet glycoprotein IIb/IIIa expression and a decrease in neutrophil L-selectin expression (189 +/- 25%, 163 +/- 27%, 158 +/- 35%, 141 +/- 22% and 31 +/- 10%, respectively, p < 0.01). In the control subjects, no change in adhesion molecule expression occurred. Superoxide production and aggregation in ex vivo-stimulated neutrophils collected from the coronary sinus 15 min after coronary angioplasty was significantly decreased compared with that after coronary arteriography (54 +/- 12% vs. 106 +/- 30% and 58 +/- 11% vs. 102 +/- 29%, respectively, p < 0.01). The reduced responses to phorbol ester stimulation may be explained by previous in vivo activation of neutrophils during coronary angioplasty. CONCLUSIONS: Coronary angioplasty increases neutrophil, monocyte and platelet adhesion molecule expression and induces a significant decrease in ex vivo-stimulated neutrophil superoxide generation and aggregation. These findings suggest that coronary angioplasty triggers cellular activation with an inflammatory response that could contribute to restenosis.

Effects of afterload on regional left ventricular torsion.

OBJECTIVE: To determine if left ventricular torsion, as measured by magnetic resonance tissue tagging, is afterload dependent in a canine isolated heart model in which neurohumoral responses are absent, and preload is constant. METHODS: In ten isolated, blood perfused, ejecting, canine hearts, three afterloads were studied, while keeping preload constant: low afterload, high afterload (stroke volume reduced by approx. 50% of low afterload), and isovolumic loading (infinite afterload). RESULTS: There were significant effects of afterload on both torsion (P < 0.05) and circumferential shortening (P < 0.0005). Between low and high afterloads, at the anterior region of the endocardium only, where torsion was maximal, there was a significant reduction in torsion (15.1 +/- 2.2 degrees to 7.8 +/- 1.8 degrees, P < 0.05). Between high afterload and isovolumic loading there was no significant change in torsion (7.8 +/- 1.8 degrees to 6.2 +/- 1.5 degrees, P = NS). Circumferential shortening at the anterior endocardium was significantly reduced both between low and high afterload (-0.19 +/- 0.02 to -0.11 +/- 0.02, P < 0.0005), and also between high afterload and isovolumic loading (-0.11 +/- 0.02 to 0.00 +/- 0.02, P < 0.05). Plots of strains with respect to end-systolic volume demonstrated a reduction in both torsion and shortening with afterload-induced increases in end-systolic volume. Torsion, but not circumferential shortening, persisted at isovolumic loading. CONCLUSIONS: Maximal regional torsion of the left ventricle is afterload dependent. The afterload response of torsion appears related to the effects of afterload on end-systolic volume.