Superoxide dismutase therapy for myocardial ischemia

Possible anti-oxidative effects of long-term administration of Juzen-taiho-to in dogs

It is known that oxidative stress is related to disease in humans and dogs. Many traditional Chinese medicines have been reported to have anti-oxidative effects, but there are no reports that they have anti-oxidative effects in dogs. In this study, we examined the anti-oxidative effects of Juzen-taiho-to, a traditional Chinese medicine, in dogs. Five healthy female beagle dogs (38–41 months of age weighing 8.6–10.7 kg) were orally administered Juzen-taiho-to at 450 mg/kg with food for 28 days. Blood samples were taken from all five dogs on days 0, 7, 14, 21, and 28. Using the blood samples, improvement of the antioxidant level as assessed by the biological antioxidant potential (BAP), reduced oxidative stress level as assessed by derivatives of reactive oxygen metabolites (d-ROMs), and improvement of blood fluidity were examined. Regarding the antioxidant level and blood fluidity, no significant difference was observed, but the oxidative stress level on days 14, 21, and 28 was significantly lower than that on day 0. Thus, Juzen-taiho-to may have anti-oxidative effects in dogs by reducing oxidative stress and be useful for oxidative stress-related diseases in dogs.

Cardioprotective effect of Malva sylvestris L. in myocardial ischemic/reprefused rats

PURPOSE

The present investigation evaluated the cardioprotective effect of Malva sylvestris L. (MS) on myocardial ischemic/reperfusion (MI/R) in rats.

METHODS

All animals were divided into four groups: the sham operated group, ischemia/reperfusion group (MI/R), and the MS (250 and 500mg/kg) treated groups, who received MS 250 and 500mg/kg intragastrically for 15 consecutive days, respectively. At the end of the protocol, concentrations of aspartate transaminase (AST), creatine kinase-MB fraction (CK-MB) and lactate dehydrogenase (LDH) were estimated in serum and the concentrations of other parameters, such as C-reactive protein, macrophage inflammatory protein 1 alpha (MIP-1α), and nitric oxide (NO) were also estimated in the blood. Tissue homogenate concentrations of inflammatory cytokines, such as tumour necrosis factor-α (TNF-α), interlukin-1β (IL-1β), IL-10 and IL-6 as well as oxidative stress parameters, such as lipid peroxidation, catalase, and superoxide dismutase were estimated in MI/R rats.

RESULT

Significant decreases (p<0.01) in AST, LDH, and CK-MB levels were observed in the MS-treated group compared with those in the MI/R group. C-reactive protein and MIP-1α levels decreased in the MS-treated group compared with those in the MI/R group. Plasma NO level was significantly enhanced in the MS-treated group than in the MI/R group. Moreover, treatment with MS significantly reduced TNF-α, IL-1β, and IL-6 levels and increased IL-10 levels in the MS group compared with the MI/R group. Treatment with MS also attenuated the altered oxidative stress parameters in MI/R rats.

CONCLUSION

The present results indicate the cardioprotective effects of MS of reducing oxidative stress and the inflammatory response in MI/R rats.

Singlet Oxygen Enhances Intrinsic Thrombolysis: The Intrinsic Oxidative Clot Lysis Assay (INOXCLA)

Granulocytes are important cells of inflammation and cellular thrombolysis. They produce urokinase (u-PA) and chloramines. In this study, u-PA/chloramine—mediated fibrinolysis is imitated in a microtiter-plate. Seventy-five microliters plasma are incubated with 50 μL 50% Pathromtin SL, 6% BSA, and 38 mM CaCl2 for 30 minutes (37°C). Then, 50 μL 10 mM chloramine-T in PBS are added. After 30 minutes (37°C), 50 μL 0, 100, or 10 IU/mL u-PA in 6% BSA-PBS are added and the turbidity is determined at 405 nm after 0, 3, or 16 hours. Clot lysis was increased more than tenfold by 0.5 to 1 μmoles chloramine (ED50 after 3h = about 0.25 μmoles = 2mM final concentration). The normal range for the present intrinsic oxidative clot lysis assay (INOXCLA) is 100% ± 25% (MV ± SD; 100 relative % of norm; the normal lysis being 60 absolute %; CVs < 10%). Fifty percent lysis of adherent microclots occurred after 0.75 hours, 2 hours, 14 hours, 13 days, or 17 days when using 1000, 100, 10, 1, or 0 IU/mL u-PA reagent. If the u-PA activity is quenched by PAI-2, no clot lysis appears. Chloramines are important physiologic generators of nonradical excited singlet oxygen and enhance u-PA—mediated lysis of plasma clots. Based on the u-PA/chloramines coaction, a new global fibrinolysis assay has been derived.

Evaluation of lecithinized human recombinant super oxide dismutase as cardioprotectant in anthracycline-treated breast cancer patients

AIM

Anthracycline-induced cardiotoxicity is (partly) mediated by free radical overload. A randomized study was performed in breast cancer patients to investigate whether free radical scavenger super oxide dismutase (SOD) protects against anthracycline-induced cardiotoxicity as measured by changes in echo, electrocardiography and an array of biomarkers.

METHOD AND RESULTS

Eighty female, chemotherapy-naïve breast cancer patients (median age 49, range 24-67 years) scheduled for four or five courses of adjuvant 3 weekly doxorubicin plus cyclophosphamide (AC) chemotherapy, were randomly assigned to receive 80 mg PC-SOD (human recombinant SOD bound to lecithin) or placebo, administered intravenously (i.v.) immediately prior to each AC course. The primary end point was protection against cardiac damage evaluated using echocardiography, QT assessments and a set of biochemical markers for myocardial function, oxidative stress and inflammation. Assessments were performed before and during each course of chemotherapy, and at 1, 4 and 9 months after completion of the chemotherapy regimen. In all patients cardiac effects such as increases in NT-proBNP concentration and prolongation of the QTc interval were noticed. There were no differences between the PC-SOD and placebo-treated patients in systolic or diastolic cardiac function or for any other of the biomarkers used to assess the cardiac effects of anthracyclines.

CONCLUSION

PC-SOD at a dose of 80 mg i.v. is not cardioprotective in patients with breast carcinoma treated with anthracyclines.

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.

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.

Low levels of soluble receptor for advanced glycation end products in non-ST elevation myocardial infarction patients

BACKGROUND

Interaction of the receptors for advanced glycation end products (RAGEs) with advanced glycation end products (AGEs) results in expression of inflammatory mediators (tumor necrosis factor-alpha [TNF-α] and soluble vascular cell adhesion molecule-1 [sVCAM-1]), activation of nuclear factor-kappa B and induction of oxidative stress - all of which have been implicated in atherosclerosis. Soluble RAGE (sRAGE) acts as a decoy for the RAGE ligand and is protective against atherosclerosis.

OBJECTIVES

To determine whether levels of serum sRAGE are lower, and whether levels of serum AGEs, TNF-α and sVCAM-1 are higher in non-ST elevation myocardial infarction (NSTEMI) patients than in healthy control subjects; and whether sRAGE or the ratio of AGEs to sRAGE (AGEs/sRAGE) is a predictor/biomarker of NSTEMI.

METHODS

Serum levels of sRAGE, AGEs, TNF-α and sVCAM-1 were measured in 46 men with NSTEMI and 28 age- and sex-matched control subjects. Angiography was performed in the NSTEMI patients.

RESULTS

sRAGE levels were lower, and levels of AGEs, TNF-α, sVCAM-1 and AGEs/sRAGE were higher in NSTEMI patients than in control subjects. sRAGE levels were negatively correlated with the number of diseased coronary vessels, serum AGEs, AGEs/sRAGE, TNF-α and sVCAM-1. The sensitivity of the AGEs/sRAGE test is greater than that of the sRAGE test, while the specificity and predictive values of the sRAGE test are greater than those of the AGEs/sRAGE test for identifying NSTEMI patients.

CONCLUSIONS

Serum levels of sRAGE were low in NSTEMI patients, and were negatively correlated with extent of lesion, inflammatory mediators, AGEs and AGEs/sRAGE. Both sRAGE and AGEs/sRAGE may serve as biomarkers/predictors for identifying NSTEMI patients.

Novel mechanisms of endothelial dysfunction in diabetes

Diabetes mellitus is a major risk factor for cardiovascular morbidity and mortality. This condition increases the risk of developing coronary, cerebrovascular, and peripheral arterial disease fourfold. Endothelial dysfunction is a major contributor to the pathogenesis of vascular disease in diabetes mellitus patients and has recently received increased attention. In this review article, some recent developments that could improve the knowledge of diabetes-induced endothelial dysfunction are discussed.

Effect of Ligusticum wallichii aqueous extract on oxidative injury and immunity activity in myocardial ischemic reperfusion rats

We investigated the efficacy of Ligusticum wallichi aqueous extract (LWE) for myocardial protection against ischemia-reperfusion injury. Rats were fed for five weeks with either a control diet (sham and ischemia reperfusion (IR) model control groups) or a diet mixed with 0.2%, 0.4% or 0.6% Ligusticum wallichi extract. At the end of the five week period, hearts were excised and subjected to global ischemia for 30 min followed by reperfusion for 2 h. The hearts were compared for indices of oxidative stress and immunity activities. Administration of Ligusticum wallichi extract significantly decreased serum TNF-α, IL-6, IL-8, NO, MIP-1α, CRP and myocardium MDA levels, and serum CK, LDH and AST activities, and increased myocardium Na⁺-K⁺-ATPase, Ca²⁺-Mg²⁺-ATPase, NOS, SOD, CAT, GSH-Px and TAOC activities. The results indicate that Ligusticum wallichii extract treatment can enhance myocardial antioxidant status and improve the immunity profile in ischemic-reperfusion rats.

Soluble receptors for advanced glycation end products (sRAGE) as a predictor of restenosis following percutaneous coronary intervention

BACKGROUND

Interaction of advanced glycation end products (AGEs) with their receptor (RAGE) increases expression of inflammatory mediators (tumor necrosis factor alpha [TNF-α] and soluble vascular cell adhesion molecule-1 [sVCAM-1]) and induces oxygen radicals that are implicated in atherosclerosis. Balloon-injury-induced atherosclerosis is associated with increased expression of AGEs and RAGE. The soluble receptor for AGE (sRAGE), which acts as a decoy for RAGE ligands (AGEs), prevents atherosclerosis in this model.

HYPOTHESIS

We evaluated: 1) whether post-percutaneous coronary intervention (PCI) restenosis is associated with low pre-PCI serum sRAGE, high serum AGEs, TNF-α, and sVCAM-1, and high AGE/sRAGE ratio; 2) whether pre-PCI and post-PCI levels of these markers are similar in patients with or without restenosis; and 3) whether sRAGE and AGE/sRAGE ratio have predictive value for post-PCI restenosis.

METHODS

Angiography was performed in 46 patients with non-ST-segment elevation myocardial infarction for assessment of restenosis. Serum sRAGE, AGEs, TNF-α, and sVCAM-1 were measured in these patients and 20 control subjects.

RESULTS

: Nineteen of the 46 patients developed post-PCI restenosis, which was associated with lower sRAGE and higher TNF-α and sVCAM-1 levels, and higher AGE/sRAGE ratio compared with patients without restenosis. Pre-PCI and post-PCI levels of these biomarkers were similar in both groups, except in patients with restenosis, in whom the post-PCI level of sRAGE was lower and TNF-α was higher than the pre-PCI levels. The sensitivity and negative predictive value of sRAGE were 100%, and were higher than those of AGE/sRAGE ratio in identifying post-PCI restenosis.

CONCLUSIONS

Both low serum sRAGE levels and high AGE/sRAGE ratio have predictive value for post-PCI restenosis.

Reconvene and reconnect the antioxidant hypothesis in human health and disease

The antioxidants are essential molecules in human system but are not miracle molecules. They are neither performance enhancers nor can prevent or cure diseases when taken in excess. Their supplemental value is debateable. In fact, many high quality clinical trials on antioxidant supplement have shown no effect or adverse outcomes ranging from morbidity to all cause mortality. Several Chochrane Meta-analysis and Markov Model techniques, which are presently best available statistical models to derive conclusive answers for comparing large number of trials, support these claims. Nevertheless none of these statistical techniques are flawless. Hence, more efforts are needed to develop perfect statistical model to analyze the pooled data and further double blind, placebo controlled interventional clinical trials, which are gold standard, should be implicitly conducted to get explicit answers. Superoxide dismutase (SOD), glutathione peroxidase and catalase are termed as primary antioxidants as these scavenge superoxide anion and hydrogen peroxide. All these three enzymes are inducible enzymes, thereby inherently meaning that body increases or decreases their activity as per requirement. Hence there is no need to attempt to manipulate their activity nor have such efforts been clinically useful. SOD administration has been tried in some conditions especially in cancer and myocardial infarction but has largely failed, probably because SOD is a large molecule and can not cross cell membrane. The dietary antioxidants, including nutrient antioxidants are chain breaking antioxidants and in tandem with enzyme antioxidants temper the reactive oxygen species (ROS) and reactive nitrogen species (RNS) within physiological limits. Since body is able to regulate its own requirements of enzyme antioxidants, the diet must provide adequate quantity of non-enzymic antioxidants to meet the normal requirements and provide protection in exigent condition. So far, there is no evidence that human tissues ever experience the torrent of reactive species and that in chronic conditions with mildly enhanced generation of reactive species, the body can meet them squarely if antioxidants defense system in tissues is biochemically optimized. We are not yet certain about optimal levels of antioxidants in tissues. Two ways have been used to assess them: first by dietary intake and second by measuring plasma levels. Lately determination of plasma/serum level of antioxidants is considered better index for diagnostic and prognostic purposes. The recommended levels for vitamin A, E and C and beta carotene are 2.2-2.8 μmol/l; 27.5-30 μmol/l; 40-50 μmol/l and 0.4-0.5 μmol/l, respectively. The requirement and recommended blood levels of other dietary antioxidants are not established. The resolved issues are (1) essential to scavenge excess of radical species (2) participants in redox homeostasis (3) selective antioxidants activity against radical species (4) there is no universal antioxidant and 5) therapeutic value in case of deficiency. The overarching issues are (1) therapeutic value as adjuvant therapy in management of diseases (2) supplemental value in developing population (3) selective interactivity of antioxidant in different tissues and on different substrates (4) quantitative contribution in redox balance (5) mechanisms of adverse action on excess supplementation (6) advantages and disadvantages of prooxidant behavior of antioxidants (7) behavior in cohorts with polymorphic differences (8) interaction and intervention in radiotherapy, diabetes and diabetic complications and cardiovascular diseases (9) preventive behavior in neurological disorders (10) benefits of non-nutrient dietary antioxidants (11) markers to assess optimized antioxidants status (12) assessment of benefits of supplementation in alcoholics and heavy smokers. The unresolved and intriguing issues are (1) many compounds such as vitamin A and many others possessing both antioxidant and non-antioxidant properties contribute to both the activities in vivo or exclusively only to non-antioxidant activity and (2) since human tissues do not experience the surge of FR, whether there is any need to develop stronger synthetic antioxidants. Theoretically such antioxidants may do more harm than good.

Role of TNF-alpha in vascular dysfunction

Healthy vascular function is primarily regulated by several factors including EDRF (endothelium-dependent relaxing factor), EDCF (endothelium-dependent contracting factor) and EDHF (endothelium-dependent hyperpolarizing factor). Vascular dysfunction or injury induced by aging, smoking, inflammation, trauma, hyperlipidaemia and hyperglycaemia are among a myriad of risk factors that may contribute to the pathogenesis of many cardiovascular diseases, such as hypertension, diabetes and atherosclerosis. However, the exact mechanisms underlying the impaired vascular activity remain unresolved and there is no current scientific consensus. Accumulating evidence suggests that the inflammatory cytokine TNF (tumour necrosis factor)-α plays a pivotal role in the disruption of macrovascular and microvascular circulation both in vivo and in vitro. AGEs (advanced glycation end-products)/RAGE (receptor for AGEs), LOX-1 [lectin-like oxidized low-density lipoprotein receptor-1) and NF-κB (nuclear factor κB) signalling play key roles in TNF-α expression through an increase in circulating and/or local vascular TNF-α production. The increase in TNF-α expression induces the production of ROS (reactive oxygen species), resulting in endothelial dysfunction in many pathophysiological conditions. Lipid metabolism, dietary supplements and physical activity affect TNF-α expression. The interaction between TNF-α and stem cells is also important in terms of vascular repair or regeneration. Careful scrutiny of these factors may help elucidate the mechanisms that induce vascular dysfunction. The focus of the present review is to summarize recent evidence showing the role of TNF-α in vascular dysfunction in cardiovascular disease. We believe these findings may prompt new directions for targeting inflammation in future therapies.

The role of inflammatory cytokines in endothelial dysfunction

Clinical and experimental data support a link between endothelial dysfunction and inflammation. Inflammatory cytokines are important protagonists in formation of atherosclerotic plaque, eliciting effects throughout the atherosclerotic vessel. Importantly, the development of atherosclerotic lesions, regardless of the risk factor, e.g., diabetes, hypertension, obesity, is characterized by disruption in normal function of the endothelial cells. Endothelial cells, which line the internal lumen of the vasculature, are part of a complex system that regulates vasodilation and vasoconstriction, growth of vascular smooth muscle cells, inflammation, and hemostasis, maintaining a proper blood supply to tissues and regulating inflammation and coagulation. Current concepts suggest that the earliest event in atherogenesis is endothelial dysfunction, manifested by deficiencies in the production of nitric oxide (NO) and prostacyclin. The focus of this review is to summarize recent evidence showing the effects of inflammation on vascular dysfunction in ischemic-heart disease, which may prompt new directions for targeting inflammation in future therapies.

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.

Anti-inflammatory properties of a chimeric recombinant superoxide dismutase: SOD2/3

While superoxide dismutase (SOD) may be useful in treating inflammation, the problems of getting it into the blood in the right concentration, for long enough periods, and to the intended organ, have limited its translation into human clinical medicine. None of the three naturally occurring forms of human SOD is well suited for use as a therapeutic agent. SOD1 and SOD2 are normally intracellular enzymes and are rapidly cleared by the kidney. SOD3 occurs outside cells, but binds so tightly to cell surfaces or to collagen fibrils in the intracellular matrix that it remains largely in the few organs that secrete it. The "stickiness" of SOD3 results from a positively charged region in the hydrophilic C-terminus of each subunit. We have genetically engineered a hybrid chimeric SOD called SOD2/3 with greatly improved pharmacological properties. It has the sequence encoding the mature human SOD2 fused to the C-terminus of human SOD3. This hybrid SOD2/3 is highly expressed and easily purified. The molecule binds to endothelial cells, but less tightly than SOD3, and circulates well enough to become widely attached to extracellular surfaces, presumably in many tissues. The loose binding appears to produce a buffering effect on enzyme concentration, effectively eliminating bell-shaped dose-response curves. Single IV injections of SOD2/3 have protected experimental animals against a variety of models involving inflammation or ischemia/reperfusion.

Attenuation of extracellular ATP response in cardiomyocytes isolated from hearts subjected to ischemia-reperfusion

Extracellular ATP is known to augment cardiac contractility by increasing intracellular Ca2+ concentration ([Ca2+]i) in cardiomyocytes; however, the status of ATP-mediated Ca2+ mobilization in hearts undergoing ischemia-reperfusion (I/R) has not been examined previously. In this study, therefore, isolated rat hearts were subjected to 10-30 min of global ischemia and 30 min of reperfusion, and the effect of extracellular ATP on [Ca2+]i was measured in purified cardiomyocytes by fura-2 microfluorometry. Reperfusion for 30 min of 20-min ischemic hearts, unlike 10-min ischemic hearts, revealed a partial depression in cardiac function and ATP-induced increase in [Ca2+]i; no changes in basal [Ca2+]i were evident in 10- or 20-min I/R preparations. On the other hand, reperfusion of 30-min ischemic hearts for 5, 15, or 30 min showed a marked depression in both cardiac function and ATP-induced increase in [Ca2+]i and a dramatic increase in basal [Ca2+]i. The positive inotropic effect of extracellular ATP was attenuated, and the maximal binding characteristics of 35S-labeled adenosine 5'-[gamma-thio]triphosphate with crude membranes from hearts undergoing I/R was decreased. ATP-induced increase in [Ca2+]i in cardiomyocytes was depressed by verapamil and Cibacron Blue in both control and I/R hearts; however, this response in I/R hearts, unlike control hearts, was not affected by ryanodine. I/R-induced alterations in cardiac function and ATP-induced increase in [Ca2+]i were attenuated by treatment with an antioxidant mixture and by ischemic preconditioning. The observed changes due to I/R were simulated in hearts perfused with H2O2. The results suggest an impairment of extracellular ATP-induced Ca2+ mobilization in I/R hearts, and this defect appears to be mediated through oxidative stress.

Melatonin does not prevent the protection of ischemic preconditioning in vivo despite its antioxidant effect against oxidative stress

Free radicals are involved in the protective mechanism of preconditioning (PC), whereas antioxidant compounds abolish this benefit. Melatonin is a hormone with antioxidant properties. The aim of our study was to evaluate the effect of melatonin on infarct size in ischemic preconditioning in vivo. We randomly divided 33 male rabbits into four groups and subjected them to 30 min of myocardial ischemia and 3 h of reperfusion with the following prior interventions: (i) no intervention, (ii) iv melatonin at a total dose of 50 mg/kg, (iii) PC with two cycles of 5 min ischemia and 10 min reperfusion, and (iv) combined melatonin and PC. In a second series of experiments, another antioxidant agent N-acetylcysteine (NAC) was used in a control and in a PC group. Myocardial infarct size was determined and blood samples were drawn at different time points for the determination of lipid peroxidation products, total superoxide dismutase (SOD) activity, and (1)H-NMR spectra to evaluate the changes in the metabolic profile. Melatonin showed no effect on myocardial infarct size in the group of sustained ischemia (42.9 +/- 3.6% vs 47.4 +/- 4.9%) and it did not attenuate the reduction of myocardial infarct size in the PC group (13.6 +/- 2.4% vs 14.0 +/- 1.7%). A similar effect was found in NAC-treated groups (44.8 +/- 3.4% vs 14.3 +/- 1.3%). Lipid peroxidation product levels were significantly elevated in the control and PC groups, whereas melatonin decreased them in both groups. The SOD activity was enhanced in the PC group compared to controls; melatonin kept SOD activity unchanged during ischemia/reperfusion and enhanced its activity when it was combined with PC. Melatonin did not change the metabolic profile of the control and PC groups. Melatonin does not prevent the beneficial effect of ischemic PC on infarct size despite its antioxidant properties.

The water-soluble vitamin E analogue Trolox protects against ischaemia/reperfusion damage in vitro and ex vivo. A comparison with vitamin E

We investigated the activities, both in vitro and ex vivo, of the water-soluble vitamin analogue Trolox in a model of isolated heart ischaemia-reperfusion and we compared them with those of alpha -tocopherol. Isolated rat hearts were perfused with Krebs-Henseleit solution. For in vitro experiments, the hearts were perfused with Trolox (20 micromol l (-1)) and were subsequently subjected to 20 min of global ischaemia and 40 min of post-ischaemic reperfusion. For ex vivo experiments, either Trolox or alpha -tocopherol (10 mg kg(-1) ) were administered by gastric gavage 60 min before excision of the heart. Various parameters of cardiac function were evaluated and oxidative damage was assessed by TBARS production. Trolox significantly enhanced cardiac recovery after ischaemia/reperfusion, both when it was perfused in vitro and after its oral administration. Vitamin E also favourably affected cardiac recovery but did so less effectively than Trolox. Further, the production of TBARS was significantly inhibited by Trolox, suggesting that its beneficial effects are due to its antioxidant activities. In conclusion, perfusion of isolated rat hearts with low concentrations of the water-soluble vitamin E analogue Trolox effectively enhances cardiac recovery after a 20 min ischaemic period and decreases reperfusion-induced oxidative damage. Interestingly, Trolox retains its activities after oral administration. Vitamin E, when administered per os, also increases functional recovery but does so less potently than Trolox. These differential effects are likely due to the scavenging, by Trolox, of reactive oxygen species generated in the water phase.

Networking antioxidants in the isolated rat heart are selectively depleted by ischemia-reperfusion

Although cardiac endogenous antioxidants have been reported to be oxidized and decreased by ischemia-reperfusion, little is known whether the changes in these antioxidants are correlated with each other in a systematic relationship. In this study, isolated rat hearts were subjected to various periods of ischemia-reperfusion using the Langendorff method, and the content and/or redox status of tissue antioxidants were analyzed. Significant losses in the tissue hydrophilic antioxidants, ascorbate, and glutathione were observed. These losses were dependent on the duration of the reperfusion period (between 0-40 min) but not of ischemia (20-60 min). Marked increases of dehydroascorbate and glutathione disulfide, the oxidized forms of ascorbate and glutathione, respectively, were found during reperfusion, but these changes were not observed during ischemia. These findings indicate that the tissue hydrophilic antioxidants are easily oxidized and may be the first line of antioxidant defenses during reperfusion. Lipophilic antioxidants, like ubiquinol 9 and vitamin E, were not decreased during ischemia-reperfusion using regular buffer; however, if oxidative stress was induced by addition of H2O2 to the buffer solution during reperfusion after 20 min of ischemia, decreases in both the hydrophilic and hydrophobic antioxidants were noticeable. With 100 microM H2O2, the tissue antioxidant decreases were ubiquinol 9 (39%), vitamin E (3%), glutathione (44%) and ascorbate (58%). Only with 500 microM H2O2 treatment were marked decreases in tissue vitamin E (65%) observed; this was associated with almost complete depletion of tissue ubiquinol 9 (95%). These results suggest that prior to the consumption of vitamin E, other antioxidants are depleted and that vitamin E may serve as the ultimate antioxidant, protecting the integrity of cellular membranes. Thus, in this work, cardiac antioxidants were demonstrated to change in a systematically organized relationship under ischemia-reperfusion. This graded utilization of antioxidants supports the redox based antioxidant network concept, found to be present in other biological systems.

Superoxide dismutase does protect the cultured rat cardiac myocytes against hypoxia/reoxygenation injury

The effect of superoxide dismutase (SOD) on membrane integrity and fluidity of the cultured neonatal rat cardiac myocytes in vitro was investigated under the condition of hypoxia and hypoxia/reoxygenation. Lactate dehydrogenase (LDH) concentration was used as the biochemical indicator for the loss of cell membrane integrity. Fluorescence polarization (FP), average microviscosity (eta) and anisotropy (Ast), which are inversely proportional to the fluidity of cell membrane, were assayed. Cells were respectively exposed to hypoxia or hypoxia/reoxygenation for different periods of time in the absence or presence of SOD at various concentrations. Hypoxia alone or hypoxia/reoxygenation brought injury to the cultured myocytes. This was demonstrated by changes in LDH and membrane fluidity. In the former LDH concentration gradually increased in a time-dependent manner and the values of FP, eta and Ast were significantly increased. The changes in membrane integrity and fluidity induced by hypoxia or hypoxia/reoxygenation could be prevented by adding SOD to the culture medium. The results provide a direct evidence that SOD (740 u.ml-1, the effective dose) was effective in protecting cultured myocytes against the injury as well as an indirect evidence of free radical generation. Based on the results obtained from this study and the establishment of concept of optimally effective dose by Bernier and Omar et al, it was suggested that some previous reports, in which no evidence was found both in protective effect of SOD and in free radical generation by using only one dose in hypoxia/reoxygenation model, should be interpreted with caution.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. III. Comparison of the magnitude of damage by hypoxemia/reoxygenation versus ischemia/reperfusion

The immature heart is more tolerant to ischemia than the adult heart, yet infants with cyanosis show myocardial damage after surgical correction of congenital cardiac defects causing hypoxemia. This study tested the hypothesis that the hypoxemic developing heart is susceptible to oxygen-mediated damage when it is reoxygenated during cardiopulmonary bypass and that this hypoxemic/reoxygenation injury is more severe than ischemic/reperfusion stress. Fifteen Duroc-Yorkshire piglets (2 to 3 weeks old, 3 to 5 kg) underwent 60 minutes of 37 degrees C cardiopulmonary bypass. Five piglets (control) were not made ischemic or hypoxemic. Five underwent 30 minutes of normothermic ischemia (aortic clamping) and 25 minutes of reperfusion before cardiopulmonary bypass was discontinued. Five others underwent 30 minutes of hypoxemia (bypass circuit primed with blood with oxygen tension 20 to 30 mm Hg) and 30 minutes of reoxygenation during cardiopulmonary bypass. Functional (left-ventricular contractility) and biochemical (levels of plasma and tissue conjugated dienes and antioxidant reserve capacity) measurements were made before ischemia/hypoxemia and after reperfusion/reoxygenation. Cardiopulmonary bypass (no ischemia or hypoxemia) caused no changes in left-ventricular function or coronary sinus levels of conjugated dienes. The tolerance to normothermic ischemia was confirmed, inasmuch as left-ventricular function returned to 108% of control values and coronary sinus levels of conjugated dienes did not rise after reperfusion. Conversely, reoxygenation raised plasma levels of conjugated dienes in coronary sinus blood in the hypoxic group 57% compared with end-hypoxic levels (p < 0.05 versus end-hypoxic levels and versus ischemia, by analysis of variance). Antioxidant reserve capacity showed the lowest levels (highest production of malondialdehyde) in the hypoxemic group (51% higher than control values; p < 0.05 by analysis of variance). These biochemical changes were associated with a 62% depression of left-ventricular function after bypass because end-systolic elastance recovered only 38% of control levels (p < 0.05 by analysis of variance). These data confirm the tolerance of the immature heart to ischemia and reperfusion and document a hypoxemic/reoxygenation injury that occurs in immature hearts reoxygenated during bypass. Hypoxemia seems to render the developing heart susceptible to reoxygenation damage that depresses postbypass function and is associated with lipid peroxidation. These findings suggest that starting bypass in cyanotic immature subjects causes an unintended reoxygenation injury that may potentially be counteracted by adding antioxidants to the prime of the extracorporeal circuit.

Interleukin 1 alpha-induced expression of manganous superoxide dismutase reduces myocardial reperfusion injury in the rat

We investigated the effects of pretreatment with interleukin (IL)-1 alpha on the expression of manganous (Mn) superoxide dismutase (SOD) mRNA and reperfusion-induced arrhythmias and the size of myocardial infarct in rats. Male Wistar rats received 10 mg intraperitoneal injections of human recombinant IL-1 alpha. Their hearts were thereafter isolated at 6, 12, 24, 36 h. A Northern analysis showed that Mn-SOD mRNA was mainly expressed in the heart and slightly in kidney, but not in any other organs. The expression of Mn-SOD mRNA peaked at 6 h after the injection of IL-1 alpha. The Mn-SOD protein content was most increased 12 h after injection. In the isolated heart model, the rats were pretreated with IL-1 alpha 24 h earlier and their hearts were perfused by the Langendorff method. After 20 min of ischemia which was induced by a ligation of a coronary artery, reperfusion-induced arrhythmias were observed. There were no significant differences in the incidence of ventricular arrhythmias between the IL-1 alpha pretreated and the untreated hearts. IL-1 alpha pretreatment significantly reduced the mean duration of the ventricular arrhythmias and also delayed the onset of arrhythmias. The effect of IL-1 alpha pretreatment was also investigated in a 30-min model of ischemia followed by a 3-min reperfusion in anesthetized rats. The infarct size expressed as a percentage of the area at risk was significantly reduced in the IL-1 alpha pretreated hearts compared with the untreated hearts. The left ventricular systolic pressure increased significantly in rat hearts pretreated with IL-1 alpha. Our results therefore showed that the pretreatment with IL-1 alpha induced the overexpression of Mn-SOD mRNA in the rat hearts and also suggested that pretreatment with IL-1 alpha 24 h before ischemia reduced the risk of ischemia-reperfusion injury.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. II. Evidence for reoxygenation damage

This study tested the hypothesis that the developing heart is susceptible to oxygen-mediated damage after reintroduction of molecular oxygen and that this "unintended" reoxygenation injury causes lipid peroxidation and functional depression that may contribute to perioperative cardiac dysfunction. Among 49 Duroc-Yorkshire piglets (2 to 3 weeks old, 3 to 5 kg) 15 control studies were done without hypoxemia to test the effects of the surgical preparation (n = 10) and 60 minutes of cardiopulmonary bypass (n = 5). Twenty-nine piglets underwent up to 2 hours of ventilator hypoxemia (with inspired oxygen fraction reduced to 6% to 7%) to lower arterial oxygen tension to approximately 25 mm Hg. Five piglets did not undergo reoxygenation to determine alterations caused by hypoxemia alone. Twenty-four others received reoxygenation by either raising ventilator inspired oxygen fraction to 1.0 (n = 12) or instituting cardiopulmonary bypass at oxygen tension 400 mm Hg (n = 12). Ventilator hypoxemia produced sufficient hemodynamic compromise and metabolic acidosis that 18 piglets required premature reoxygenation (78 +/- 12 minutes). To avoid the influence of acidosis and hemodynamic deterioration during ventilator hypoxemia, five others underwent 30 minutes of hypoxemia during cardiopulmonary bypass (circuit primed with blood at oxygen tension 25 mm Hg) and 30 minutes of reoxygenation (oxygen tension 400 mm Hg) during cardiopulmonary bypass. Biochemical markers of oxidant damage included measurement of coronary sinus and myocardial conjugated dienes to determine lipid peroxidation and antioxidant reserve capacity assessed by incubating myocardial tissue in the oxidant t-butylhydroperoxide. Functional recovery was determined by inscribing pressure volume loops to determine end-systolic elastance and Starling curves by volume infusion. No biochemical or functional changes occurred in control piglets. Hypoxemia without reoxygenation did not change plasma levels of conjugated dienes, but lowered antioxidant reserve capacity 24%. Reoxygenation by ventilator caused refractory ventricular arrhythmias in two piglets (17% mortality), raised levels of conjugated dienes 45%, and reduced antioxidant reserve capacity 40% with recovery of 39% of mechanical function in the survivors. Comparable biochemical and functional changes occurred in piglets undergoing ventilator hypoxemia and/or cardiopulmonary bypass hypoxemia and reoxygenation on cardiopulmonary bypass. We conclude that hypoxemia increases vulnerability to reoxygenation damage by reducing antioxidant reserve capacity and that reoxygenation by either ventilator or cardiopulmonary bypass produces oxidant damage with resultant functional depression that is not a result of cardiopulmonary bypass. These findings suggest that initiation of cardiopulmonary bypass in cyanotic immature subjects causes an unintended reoxygenation injury, which may increase vulnerability to subsequent ischemia during surgical repair.

Relationship between severity of ischemia and oxidant scavenger enzyme activities in the isolated rat heart

It is currently believed that reperfusion injury of the ischemic or hypoxic myocardium can be attributed, at least in part, to an overproduction of reactive oxygen species (ROS). The aim of the present study was to determine whether ischemia (of different severity or duration) followed by reperfusion can affect the activity of endogenous scavenger enzymes in isolated perfused rat hearts. Isolated Langendorff perfused rat hearts were subjected to either total (10, 20 or 30 min; zero-flow) or partial (30, 60 or 90 min; low-flow of 0.10 or 0.35 ml/min) ischemia, followed by 10 min of reperfusion. Enzymatic activities of total superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) were determined in cardiac tissues at the end of the perfusion protocol. Basal scavenger enzyme activities measured in control hearts (perfused under normoxic conditions) were 33.90 +/- 4.88, 31.20 +/- 5.32 and 1.61 +/- 0.29 IU/mg protein (mean +/- SD, n = 6 per group) for SOD, catalase and GPx respectively. Our results indicate that neither total SOD, GPx, nor catalase myocardial activities were changed whatever the perfusion protocol followed. The present study shows that the endogenous pool of catalytic ROS scavengers is not dramatically altered during ischemia or upon reperfusion. This suggests that ROS scavengers are not directly involved in the development of ischemia/reperfusion injuries. These results also support the premise that excessive radical generation does not occur in this model, where the isolated heart is subjected to ischemia.

Reoxygenation-induced cell damage of isolated neonatal rat ventricular myocytes can be reduced by chain-breaking antioxidants

To study the role of chain-breaking antioxidants on reperfusion injury in the ischemic heart, cultured ventricular heart cells (myocytes) were subjected to hypoxia and reoxygenation. The myocytes were prepared from neonatal rats and cultured in F10 medium that was supplemented with serum. As a marker for cell damage, lactate dehydrogenase was analyzed in the medium. Cells subjected to hypoxia for 5 h showed a 1.9 fold increase in lactate dehydrogenase (LD) leakage, while cells subjected to 1 h hypoxia followed by 4 h reoxygenation showed a 5-fold increase in LD intake. Alpha-tocopherol, beta-carotene, nordihydroguairetic acid (NDGA), butylated hydroxyltoluene (BHT), and ICI211965 were added to the cell medium every 24 h for 6 d prior to reoxygenation. All compounds protected against reoxygenation-induced cell damage. In the presence of the 5-lipoxygenase inhibitor ICI211965, protection against LD leakage was found only at high concentrations, which corresponded to the antioxidative effect of ICI211965, and not to inhibition of 5-lipoxygenase. We conclude that cultured ventricular myocytes can be used to evaluate the protective effect of antioxidants on reoxygenation-induced cell damage, and that chain-breaking antioxidants protected well against reoxygenation-induced cell damage.

Comparison of triphenyltetrazolium chloride (TTC) staining versus detection of fibronectin in experimental myocardial infarction

Staining with triphenyltetrazolium chloride (TTC), although controversial, has frequently been used for the delineation of myocardial infarction. This study was performed further to explore the reliability of the TTC method. In 24-h experiments pigs were subjected to closed-chest occlusion of the left anterior descending coronary artery for 30, 60 or 90 min followed by reperfusion with or without superoxide dismutase (SOD) as an adjunct. One TTC-stained slice from each heart was stabilized by microwave irradiation, gelatin-embedded, frozen in hexane chilled with dry ice and cryosectioned. Serial sections were stained with antibodies against fibronectin in order to identify irreversibly injured myocytes and with van Gieson histologically to confirm the necrotic tissue. A close correspondence of the infarct size was found between TTC stained slices and anti-fibronectin stained sections. The infarct size in the van Gieson stained sections also showed good correspondence but the area of infarction tended to be larger. In the experimental group subjected to 30 min ischaemia and with SOD as an adjunct, the estimated infarcted area in the TTC stained slices was significantly smaller than the area estimated from the anti-fibronectin stained sections. In sections viewed in the light microscope an inverse pattern of TTC and anti-fibronectin staining was observed. It was confirmed at the light microscopic level that myocytes containing an abundance of TTC deposits lacked fibronectin whereas myocytes stained with antifibronectin in general lacked TTC staining except for a zone approximately 0.5 mm wide which was located at the intersection between damaged and surviving myocytes where small TTC deposits were present. The width of the stained zone did not differ among the experimental groups. Thus, differences in estimated infarct size by the three methods used reflect problems in correctly delineating the border between living and dead myocardium rather than an interference by SOD on TTC staining.

Free radicals as mediators of tissue injury and disease

A radical is any molecule that contains one or more unpaired electrons. Radicals are normally generated in many metabolic pathways. Some of these radicals can exist in a free form and subsequently interact with various tissue components resulting in dysfunction. The potential role of oxygen- or xenobiotic-derived free radicals in the pathology of several human diseases has stimulated extensive research linking the toxicity of numerous xenobiotics and disease processes to a free radical mechanism. However, because free radical-mediated changes are pervasive and often poorly understood, the question of whether such species are a major cause of tissue injury and human disease remains equivocal. This review discusses cellular sources of various radical species and their reactions with vital cellular constituents. Examples of purported free radical-mediated disorders are discussed in detail to provide insights into the controversy over whether free radicals are important mediators of tissue injury.

Enzyme and immunohistochemical assessment of myocardial damage after ischaemia and reperfusion in a closed-chest pig model

The usefulness of different enzyme and immunohistochemical stains to distinguish reversible and irreversible myocardial cell injury after experimental coronary artery occlusion of varying duration and reperfusion with or without superoxide dismutase as adjunct was investigated. Biopsies or parts of the infarcted and non-infarcted area were rapidly frozen and sectioned in series for enzyme and immunohistochemical evaluation. Sections were stained for the demonstration of phosphorylase, myofibrillar ATPase and mitochondrial oxidative enzymes and also with periodic acid-Schiff, alizarin red S and routine histological stains. Other sections in series were stained with antibodies against fibronectin and the intermediate filament proteins desmin and vimentin. In 49 biopsies a blind quantitative estimation of the area stained for fibronectin, phosphorylase and alizarin red S was performed and evaluated statistically. Phosphorylase, periodic acid-Schiff, fibronectin and alizarin red S allowed delineation of affected myocardium after 30 min of ischaemia followed by reperfusion whereas with the other stains, affected myocardium was readily detectable only after 60 or 90 min of ischaemia followed by reperfusion as well as after 24 h of ischaemia without reperfusion. The immunostaining for fibronectin was very distinct and inversely related to the phosphorylase activity. We show that fibronectin is an excellent marker for damaged cells and that these positively stained myocytes are necrotic as confirmed ultrastructurally. Using alizarin red S as a marker of calcium accumulation in myocytes, a marked discrepancy was observed between the area of fibronectin-containing myocytes and that of myocytes stained by alizarin red S. Calcium accumulation in mitochondria is thus not a prerequisite for myocyte necrosis but does occur only in some of the irreversibly damaged cells. Of special interest is the finding that there was a significant reduction of intracellular calcium in pigs where superoxide dismutase had been used as an adjunct at reperfusion, thus supporting the theory that free radicals do play a role during reperfusion of ischaemic myocardium.

Drug antioxidant effects. A basis for drug selection?

A free radical is any species capable of independent existence that contains one or more unpaired electrons. Free radical reactions have been implicated in the pathology of more than 50 human diseases. Radicals and other reactive oxygen species are formed constantly in the human body, both by deliberate synthesis (e.g. by activated phagocytes) and by chemical side-reactions. They are removed by enzymic and nonenzymic antioxidant defence systems. Oxidative stress, occurring when antioxidant defences are inadequate, can damage lipids, proteins, carbohydrates and DNA. A few clinical conditions are caused by oxidative stress, but more often the stress results from the disease. Sometimes it then makes a significant contribution to the disease pathology, and sometimes it does not. Several antioxidants are available for therapeutic use. They include molecules naturally present in the body [superoxide dismutase (SOD), alpha-tocopherol, glutathione and its precursors, ascorbic acid, adenosine, lactoferrin and carotenoids] as well as synthetic antioxidants [such as thiols, ebselen (PZ51), xanthine oxidase inhibitors, inhibitors of phagocyte function, iron ion chelators and probucol]. The therapeutic efficacy of SOD, alpha-tocopherol and ascorbic acid in the treatment of human disease is generally unimpressive to date although dietary deficiencies of the last two molecules should certainly be avoided. Xanthine oxidase inhibitors may be of limited relevance as antioxidants for human use. Exciting preliminary results with probucol (antiatherosclerosis), ebselen (anti-inflammatory), and iron ion chelators (in thalassaemia, leukaemia, malaria, stroke, traumatic brain injury and haemorrhagic shock) need to be confirmed by controlled clinical trials. Clinical testing of N-acetylcysteine in HIV-1-positive subjects may also be merited. A few drugs already in clinical use may have some antioxidant properties, but this ability is not widespread and drug-derived radicals may occasionally cause significant damage.