Effect of superoxide dismutase on infarct size and postischemic recovery of myocardial contractility and metabolism in dogs

HMGB1 Protects the Heart Against Ischemia-Reperfusion Injury via PI3K/AkT Pathway-Mediated Upregulation of VEGF Expression

Delivery of exogenous high mobility group box 1 (HMGB1) may exert a beneficial effect on myocardial ischemia-reperfusion (I/R) injury. Since the expression of vascular endothelial growth factor (VEGF) and phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) in the myocardium mediates the cardioprotective function of basic fibroblast growth factor, we hypothesized that VEGF and the PI3K/Akt signaling pathway also mediate the protective effects of intravenously delivered HMGB1. Thus, the objective of the present study was to analyze the impact of intravenous administration of HMGB1 on the myocardial expression of VEGF, myocardial fibrosis, and cardiac function in rats subjected to acute myocardial I/R. The ischemia was induced by ligation of the left anterior descending coronary artery for 30 min and was followed by 3 h of reperfusion. Myocardial malondialdehyde content, infarct size, and collagen volume fraction decreased, while the activity of superoxide dismutase was increased, the expression of VEGF and p-Akt was upregulated, and cardiac function was improved in the HMGB1-treated group when compared with rats subjected to I/R only (all P < 0.05). However, these effects of HMGB1 were abolished by LY294002. The obtained results demonstrate that the cardioprotective effects of intravenous administration of HMGB1 prior to I/R may be mediated by upregulation of myocardial expression of VEGF, which may activate the PI3K/Akt signaling pathway.

Soy Isoflavone Protects Myocardial Ischemia/Reperfusion Injury through Increasing Endothelial Nitric Oxide Synthase and Decreasing Oxidative Stress in Ovariectomized Rats

There is a special role for estrogens in preventing and curing cardiovascular disease in women. Soy isoflavone (SI), a soy-derived phytoestrogen, has similar chemical structure to endogenous estrogen-estradiol. We investigate to elucidate the protective mechanism of SI on myocardial ischemia/reperfusion (MI/R) injury. Female SD rats underwent bilateral ovariectomy. One week later, rats were randomly divided into several groups, sham ovariectomy (control group), ovariectomy with MI/R, or ovariectomy with sham MI/R. Other ovariectomy rats were given different doses of SI or 17β-estradiol (E2). Four weeks later, they were exposed to 30 minutes of left coronary artery occlusion followed by 6 or 24 hours of reperfusion. SI administration significantly reduced myocardial infarct size and improved left ventricle function and restored endothelium-dependent relaxation function of thoracic aortas after MI/R in ovariectomized rats. SI also decreased serum creatine kinase and lactate dehydrogenase activity, reduced plasma malonaldehyde, and attenuated oxidative stress in the myocardium. Meanwhile, SI increased phosphatidylinositol 3 kinase (PI3K)/Akt/endothelial nitric oxide synthase (eNOS) signal pathway. SI failed to decrease infarct size of hearts with I/R in ovariectomized rats if PI3K was inhibited. Overall, these results indicated that SI protects myocardial ischemia/reperfusion injury in ovariectomized rats through increasing PI3K/Akt/eNOS signal pathway and decreasing oxidative stress.

Examining efficacy of "TAT-less" delivery of a peptide against the L-type calcium channel in cardiac ischemia-reperfusion injury

Increased calcium influx through the L-type Ca(2+) channel or overexpression of the alpha subunit of the channel induces cardiac hypertrophy. Cardiac hypertrophy results from increased oxidative stress and alterations in cell calcium levels following ischemia-reperfusion injury and is an independent risk factor for increased morbidity and mortality. We find that decreasing the movement of the auxiliary beta subunit with a peptide derived against the alpha-interacting domain (AID) of the channel attenuates ischemia-reperfusion injury. We compared the efficacy of delivering the AID peptide using a trans-activator of transcription (TAT) sequence with that of the peptide complexed to multifunctional polymeric nanoparticles. The AID-tethered nanoparticles perfused through the myocardium more diffusely and associated with cardiac myocytes more rapidly than the TAT-labeled peptide but had similar effects on intracellular calcium levels. The AID-complexed nanoparticles resulted in a similar reduction in release of creatine kinase and lactate dehydrogenase after ischemia-reperfusion to the TAT-labeled peptide. Since nanoparticle delivery also holds the potential for dual drug delivery, we conclude that AID-complexed nanoparticles may provide an effective platform for peptide delivery in cardiac ischemia-reperfusion injuries.

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.

Reoxygenation-induced constriction in murine coronary arteries: the role of endothelial NADPH oxidase (gp91phox) and intracellular superoxide

Previous work suggests that superoxide mediates hypoxia/reoxygenation (H/R)-induced constriction of isolated mouse coronary arteries (CA). To determine the source of superoxide overproduction during H/R we studied CA obtained from transgenic (Tg) mice overexpressing human CuZn-superoxide dismutase (SOD) and mice lacking gp91(phox) using an in vitro vascular ring bioassay. We found that under normoxic conditions CA isolated from wild type (wt) mice, CuZn-SOD Tg mice and gp91(phox) knock-out mice had similar contractile responses to U46619 and hypoxia and similar dilation responses to acetylcholine. In wt CA, 30 min of hypoxia (1% O(2)) followed by reoxygenation (16% O(2)) resulted in further coronary vasoconstriction (internal diameter from 105 +/- 11 to 84.5 +/- 17.9 microm), whereas this response was completely blocked in both CuZn-SOD Tg and gp91(phox) knock-out CA (104.3 +/- 10.5 to 120.7 +/- 14 microm and 143.3 +/- 15.3 to 172.7 +/- 12.5 microm, respectively, p < 0.01). Furthermore, we show that H/R enhances the generation of superoxide radicals in wt CA (25.8 +/- 0.7 relative light units per second (RLU/s)), whereas CuZn-SOD Tg CA (12.2 +/- 0.8 RLU/s, p < 0.01) and gp91(phox) CA (12.5 +/- 0.9 RLU/s, p < 0.01) show reduced levels. These results demonstrate that H/R-induced vasoconstriction is mediated by intracellular superoxide overproduction via endothelial NADPH oxidase gp91(phox). Therefore, increasing endogenous levels of CuZn-SOD in CA may provide a novel cardioprotective strategy for maintaining coronary perfusion under conditions of H/R.

The novel guanidine ME10092 protects the heart during ischemia-reperfusion

The novel guanidine N-(3,4-dimethoxy-2-chlorobenzylideneamino)-guanidine [ME10092; a metabolite to the strongly cardioprotective hydroxyguanidine N-(3,4-dimethoxy-2-chlorobenzylideneamino)-N'-hydroxyguanidine (PR5)] was administered intravenously to rats subjected to left coronary artery clamping followed by reperfusion. Administration of 1-10 mg/kg of ME10092 1 or 5 min before 10 min of coronary artery occlusion followed by 20 min reperfusion significantly and dose-dependently inhibited the reperfusion-induced burst of arrhythmia, and markedly improved the survival of the animals. This dose schedule also dose-dependently and significantly inhibited the ST-segment elevation seen on the ECG during the artery occlusion, and attenuated the secondary rise in ST-segment during the reperfusion. Even when ME10092 was administered 5 min after the start of the reperfusion, the ST-segment elevation became significantly attenuated. Administration of ME10092 (3 plus 1.5 mg/kg) to animals subjected to 1 h left coronary occlusion followed by 2 h reperfusion reduced the heart infarction size by about 40%. ME10092 also dose-dependently reduced the heart rate, both during normal conditions and during ischemia and reperfusion. Moreover, the highest dose of ME10092 used (10 mg/kg) strongly attenuated the reduction in blood pressure seen during 10 min left coronary occlusion, as well as it attenuated the rebound rise in blood pressure seen during the 20 min reperfusion phase; that is, resulting in a normalisation of the blood pressure disturbances caused by the ischemia-reperfusion. We also showed that after its p.o. administration, the PR5 hydroxyguanidine became completely metabolised to its guanidine ME10092, with no detectable traces of PR5 being present 30 and 60 min after the administration. Moreover, after the p.o. administration of ME10092, no signs of the formation of PR5 were seen on analysis of the rats' plasma. In view of the practically indistinguishable pharmacological effects of ME10092 and PR5, we suggest the strong cardioprotective effects of these compounds to be mediated by a direct effect by ME10092 per se.

Cardiac protection by pharmacological modulation of inflammation

Inflammation is a reaction to primary injury of various kinds, such as infection and trauma, which has both beneficial and detrimental effects. Inflammation has been associated with major diseases of the heart and vessels. Research has focused not only on ischaemia but also on post-ischaemic reperfusion, which is known to activate and amplify the inflammatory response. Although reperfusion should always be attempted in the clinical environment, it has been shown experimentally that it can cause some cardiac damage, in addition to that caused by ischaemia. Therefore, it is reasonable to attempt to increase the benefit obtainable with reperfusion by modulating inflammatory processes triggered by reperfusion itself. In this field, different potential therapeutic targets have been identified and interventions have been tested over the last 30 years. With the exception of adenosine, which probably does not act merely through inhibition of the inflammatory response, no other compounds have yet proven successful in clinical trials. Active research is ongoing. Broadening the approach from the heart to the cardiovascular system, promising data is emerging on cardiovascular protection conferred by statins in patients with coronary heart disease (CHD) and high levels of C-reactive protein (CRP), a systemic marker of inflammation. Similarly, results of trials aimed at preventing cardiovascular events by eradicating chronic infections will be among the first to directly test whether such therapies will decrease risks of cardiovascular disease.

Cardioprotective effects of N-hydroxyguanidine PR5 in myocardial ischaemia and reperfusion in rats

1. The potential for the N-hydroxyguanidine compound PR5 (N-(3, 4-dimethoxy-2-chlorobenzylideneamino)-N'-hydroxyguanidine) as a cardioprotective agent in heart ischaemia and reperfusion injury was investigated using rat models. 2. Administration of 1-10 mg kg-1 of PR5 5 min before 10 min of left coronary artery occlusion, followed by 20 min reperfusion, strongly inhibited reperfusion burst of arrhythmias and markedly improved the survival of the animals (e.g. ventricular fibrillation incidence 93 vs 43% (P<0.05); mortality 47 vs 0% (P<0.05), for controls and for 3 mg kg-1 of PR5, respectively). 3. Administration of 3 mg kg-1 of PR5 1 min before reperfusion to rats subjected to 10 min occlusion, 20 min reperfusion was most effective in reducing arrhythmias and decreasing mortality (43 vs 0%, P<0.05), but effects were also seen when PR5 was administered 0, 1 and 5 min after start of reperfusion. 4. Coronary occlusion/reperfusion (10 - 20 min) increased malondialdehyde (MDA) of rat hearts (0.88+/-0.13 for sham vs 1.45+/-0.12 nmol mg-1 protein for ischaemic; P<0.05). In rats where 3 mg kg-1 PR5 were administered 1 min before reperfusion the increase was attenuated (MDA being 1.04+/-0.12; P<0.05 vs ischaemic). 5. PR5 caused a substantial reduction of the infarction size in rats subjected to 180 min left coronary artery occlusion, followed by 120 min of reperfusion; the necrotic zone being 326+/-32 mg for controls vs 137+/-21 mg for animals treated with 3x3 mg kg-1 of PR5 (P<0.01). 6. PR5 reduced the elevation of the ST-segment of the ECGs, as well as caused pronounced attenuation of the rapid blood pressure drop seen at the start of reperfusion following coronary artery occlusion. 7 We conclude that the N-hydroxyguanidine PR5 provides remarkable protection against ischaemia and reperfusion induced myocardial necrosis and life-threatening arrhythmias. These effects of PR5 are discussed in relation to a recently discovered ability of N-hydroxyguanidines to function as electron acceptors at the xanthine oxidase enzyme.

Controlled reperfusion after myocardial ischemia in a canine model monitored by two-dimensional phosphorus 31 chemical shift spectroscopic imaging

Phosphorus 31 magnetic resonance spectroscopy at 2 T was used to monitor high-energy phosphate metabolism over a 3-week period in a canine model of myocardial infarction and reperfusion. Twenty animals were divided into two groups: group 1 (n = 11) received intravenous nitroglycerin beginning at the onset of coronary occlusion; group 2 (n = 9) received a 105-minute infusion of superoxide dismutase (SOD) beginning at the onset of reperfusion. A metabolic protective effect was observed (vs controls) with both agents, manifested by a reduction in the degree of pH decline from baseline values and preservation of the adenosine triphosphate/total phosphate ratio during occlusion and reperfusion. Further, both treatments, compared with controls, produced a lower infarct/zone at risk ratio: controls, 1.5 +/- 1.2; nitroglycerin, 0.52 +/- 0.50; and SOD, 0.64 +/- 0.40. The technique of 31P magnetic resonance spectroscopy demonstrated its use for the noninvasive assessment of myocardial metabolism in response to therapeutic intervention.

Graft dysfunction following liver transplantation: role of free radicals

BACKGROUND/AIMS

Following orthotopic liver transplantation primary graft non-function occurs in about 10% of patients, and survival depends on early retransplantation. The aetiology has yet to be defined, but reperfusion injury as a result of free radical production has been considered as a possible mechanism. In this study we looked for evidence of free radical generation intraoperatively and assessed the relationship between free radical production and graft function.

METHODS/RESULTS

Twenty-one patients (M:F 10:11, mean age; 53 +/- 3.8 years) who underwent liver transplantation for end-stage liver disease were studied. Free radical activity increased significantly following reperfusion, as shown by: (i) the diene conjugated method, where the percentage molar ratio increased from a baseline of 10.87 +/- 0.78% to 24.42 +/- 7.8% (p < 0.01), and (ii) by electron paramagnetic resonance, where a more than a twofold rise in radical concentration was detected (p < 0.05). The increase in free radical activity detected by the diene conjugated method was significantly higher in patients with poor outcome as compared with those who had uneventful recovery (p < 0.01).

CONCLUSION

Free radical activity is increased following reperfusion of liver graft during transplantation, and the magnitude of the rise is related to the severity of graft dysfunction.

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.

Myoglobin protects against endothelial cell membrane damage associated with hydrogen peroxide or xanthine/xanthine oxidase

Oxymyoglobin at 'physiological' concentrations of 20-100 micromolar protected cultured endothelial cells from damage by xanthine/xanthine oxidase or by hydrogen peroxide. Metmyoglobin also provided a degree of protection, but apomyoglobin was ineffective. Protection was enhanced in the presence of ascorbate (0.01-1 mM). Myoglobin may have a physiological role in the protection of muscular tissue from ischaemia/reperfusion-induced damage.

Oxygen free radicals and cardiac reperfusion abnormalities

Oxygen free radicals are highly reactive compounds causing peroxidation of lipids and proteins and are thought to play an important role in the pathogenesis of reperfusion abnormalities including myocardial stunning, irreversible injury, and reperfusion arrhythmias. Free radical accumulation has been measured in ischemic and reperfused myocardium directly using techniques such as electron paramagnetic resonance spectroscopy and tissue chemiluminescence and indirectly using biochemical assays of lipid peroxidation products. Potential sources of free radicals during ischemia and reperfusion have been identified in myocytes, vascular endothelium, and leukocytes. In several different experimental models exogenous free radical-generating systems have been shown to produce alterations in cardiac function that resemble the various reperfusion abnormalities described above. Injury to processes involved in regulation of the intracellular Ca2+ concentration may be a common mechanism underlying both free radical-induced and reperfusion abnormalities. Direct effects of free radicals on each of the known Ca(2+)-regulating mechanisms of the cell as well as the contractile proteins and various ionic membrane currents have been described. Free radicals also inhibit critical enzymes in anaerobic and aerobic metabolic pathways, which may limit the metabolic reserve of reperfused myocardium and contribute to intracellular Ca2+ overload. Inhibiting free radical accumulation during myocardial ischemia/reperfusion with free radical scavengers and inhibitors has been demonstrated to reduce the severity of myocardial stunning, irreversible injury, and reperfusion arrhythmias in many, but not all, studies. This evidence strongly implicates free radical accumulation during myocardial ischemia/reperfusion as an important pathophysiological mechanism of reperfusion abnormalities, although many issues remain unresolved.