The independent effects of oxygen radical scavengers on canine infarct size. Reduction by superoxide dismutase but not catalase

Do reactive oxygen species damage or protect the heart in ischemia and reperfusion? Analysis on experimental and clinical data

The role of reactive oxygen species (ROS) in ischemic and reperfusion (I/R) injury of the heart has been discussed for more than 40 years. It has been demonstrated that reperfusion triggers a multiple increase in free radical generation in the isolated heart. Antioxidants were found to have the ability to mitigate I/R injury of the heart. However, it is unclear whether their cardioprotective effect truly depends on the decrease of ROS levels in myocardial tissues. Since high doses and high concentrations of antioxidants were experimentally used, it is highly likely that the cardioprotective effect of antioxidants depends on their interaction not only with free radicals but also with other molecules. It has been demonstrated that the antioxidant N-2-mercaptopropionyl glycine or NDPH oxidase knockout abolished the cardioprotective effect of ischemic preconditioning. Consequently, there is evidence that ROS protect the heart against the I/R injury.

Evaluation of Free Radical Injury in Myocardium

Abundant evidence now is available that free radicals are produced in excess when myocardium is reperfused following an episode of ischemia and that free radicals can injure myocytes and endothelial cells. Free radicals may contribute to either reversible or irreversible manifestations of cell injury from ischemia and reperfusion. Several investigators have observed that postischemic contractile dysfunction (myocardial stunning) can be attenuated by a variety of anti-free radical therapies, and there seems to be general agreement that free radical injury contributes to stunning. Whether free radicals are an important cause of lethal myocyte injury (“lethal reperfusion injury”) remains controversial. Using similar interventions and animal models, both positive and negative results have been reported from a growing number of studies done to test the effect of anti-free radical therapies on infarct size. Proposed explanations include differences in: 1) dose of drug and onset or duration of treatment, 2) duration of occlusion or reperfusion, 3) methods of measuring infarct size or area at risk, and 4) failure of some studies to control for baseline variation in the major determinants of infarct size, e.g., collateral blood flow. At present, none of these explanations seems sufficient to resolve the question.

Multi-organ protection of ulinastatin in traumatic cardiac arrest model

Background

Post-cardiac arrest syndrome, which has no specific curative treatment, contributes to the high mortality rate of victims who suffer traumatic cardiac arrest (TCA) and initially can be resuscitated. In the present study, we investigated the potential of ulinastatin to mitigate multiple organ injury after resuscitation in a swine TCA model.

Methods

Twenty-one male pigs were subjected to hemodynamic shock (40% estimated blood loss in 20 min) followed by cardiac arrest (electrically induced ventricular fibrillation) and respiratory suspension for 5 min, and finally manual resuscitation. At 5 min after resuscitation, pigs were randomized to receive 80,000 U/kg ulinastatin (n = 7) or the same volume of saline (n = 9) in the TCA group. Pigs in the sham group (n = 5) were not exposed to bleeding or cardiac arrest. At baseline and at 1, 3, and 6 h after the return of spontaneous circulation, blood samples were collected and assayed for tumor necrosis factor-alpha, interleukin 6, and other indicators of organ injury. At 24 h after resuscitation, pigs were sacrificed and apoptosis levels were assessed in samples of heart, brain, kidney, and intestine.

Results

One pig died in the ulinastatin group and one pig died in the TCA group; the remaining animals were included in the final analysis. TCA and resuscitation caused significant increases in multiple organ function biomarkers in serum, increases in tumor necrosis factor-alpha, and interleukin 6 in serum and increases in the extent of apoptosis in key organs. All these increases were lower in the ulinastatin group.

Conclusion

Ulinastatin may attenuate multiple organ injury after TCA, which should be explored in clinical studies.

Electronic supplementary material

The online version of this article (10.1186/s13017-018-0212-3) contains supplementary material, which is available to authorized users.

Apelin-induced cardioprotection against ischaemia/reperfusion injury: roles of epidermal growth factor and Src

AIM

Apelin, the ligand of the G-protein-coupled receptor (GPCR) APJ, exerts a post-conditioning-like protection against ischaemia/reperfusion injury through activation of PI3K-Akt-NO signalling. The pathway connecting APJ to PI3K is still unknown. As other GPCR ligands act through transactivation of epidermal growth factor receptor (EGFR) via a matrix metalloproteinase (MMP) or Src kinase, we investigated whether EGFR transactivation is involved in the following three features of apelin-induced cardioprotection: limitation of infarct size, suppression of contracture and improvement of post-ischaemic contractile recovery.

METHOD

Isolated rat hearts underwent 30 min of global ischaemia and 2 h of reperfusion. Apelin (0.5 μm) was infused during the first 20 min of reperfusion. EGFR, MMP or Src was inhibited to study the pathway connecting APJ to PI3K. Key components of RISK pathway, namely PI3K, guanylyl cyclase or mitochondrial K⁺ -ATP channels, were also inhibited. Apelin-induced EGFR and phosphatase and tensing homolog (PTEN) phosphorylation were assessed. Left ventricular pressure and infarct size were measured.

RESULTS

Apelin-induced reductions in infarct size and myocardial contracture were prevented by the inhibition of EGFR, Src, MMP or RISK pathway. The involvement of EGFR was confirmed by its phosphorylation. However, neither direct EGFR nor MMP inhibition affected apelin-induced improvement of early post-ischaemic contractile recovery, which was suppressed by Src and RISK inhibitors only. Apelin also increased PTEN phosphorylation, which was removed by Src inhibition.

CONCLUSION

While EGFR and MMP limit infarct size and contracture, Src or RISK pathway inhibition suppresses the three features of cardioprotection. Src does not only transactivate EGFR, but also inhibits PTEN by phosphorylation thus playing a crucial role in apelin-induced cardioprotection.

Study of oxidants and antioxidants in patients of acute myocardial infarction

BACKGROUND

Oxygen free radicals have become attractive candidates to explain injuries in ischemic heart. An association between raised serum uric acid concentration and increased cardiovascular risk has been recognized, however its role in acute myocardial infarction (AMI) is still unclear. Recently, zinc is also trying to establish its role in tissue injury and oxidative stress.

MATERIALS AND METHODS

This cross-sectional study was carried on 75 AMI patients. 5 ml of blood was drawn from each patient within 6 h of AMI, to estimate plasma malondialdehyde (MDA), serum zinc, whole blood superoxide desmutase, serum uric acid, and whole blood glutathione peroxidase (GPx). The same biochemicals were also determined in 50 age and gender matched controls for comparison.

RESULTS

We found significantly increased level of plasma MDA (5.649 ± 0.1780 vs. 2.757 ± 0.1623), serum uric acid (4.533 ± 0.1526 vs. 3.200 ± 0.1616) and significantly decreased levels of serum zinc (104.5 ± 1.874 vs. 115.3 ± 3.077), whole blood GPx (4599 ± 101.1 vs. 5519 ± 81.63) and superoxide desmutase (166.8 ± 1.896 vs. 188.3 ± 4.120). All the parameters studied also showed similar significant changes in male and female cases separately.

CONCLUSION

Raised MDA and decreased zinc, glutathione peroxidase, and superoxide desmutase levels denote the increased oxidative stress. Even being a defense, uric acid is raised as it is abundantly present in our body. Thus, AMI exhibits oxidative stress dependent changes irrespective of gender.

Redox signalling and cardioprotection: translatability and mechanism

The morbidity and mortality from coronary artery disease (CAD) remain significant worldwide. The treatment for acute myocardial infarction has improved over the past decades, including early reperfusion of culprit coronary arteries. Although it is mandatory to reperfuse the ischaemic territory as soon as possible, paradoxically this leads to additional myocardial injury, namely ischaemia/reperfusion (I/R) injury, in which redox stress plays a pivotal role and for which no effective therapy is currently available. In this review, we report evidence that the redox environment plays a pivotal role not only in I/R injury but also in cardioprotection. In fact, cardioprotective strategies, such as pre- and post-conditioning, result in a robust reduction in infarct size in animals and the role of redox signalling is of paramount importance in these conditioning strategies. Nitrosative signalling and cysteine redox modifications, such as S-nitrosation/S-nitrosylation, are also emerging as very important mechanisms in conditioning cardioprotection. The reasons for the switch from protective oxidative/nitrosative signalling to deleterious oxidative/nitrosative/nitrative stress are not fully understood. The complex regulation of this switch is, at least in part, responsible for the diminished or lack of cardioprotection induced by conditioning protocols observed in ageing animals and with co-morbidities as well as in humans. Therefore, it is important to understand at a mechanistic level the reasons for these differences before proposing a safe and useful transition of ischaemic or pharmacological conditioning. Indeed, more mechanistic novel therapeutic strategies are required to protect the heart from I/R injury and to improve clinical outcomes in patients with CAD.

Design, synthesis, and preliminary cardioprotective effect evaluation of danshensu derivatives

A series of (R)-3,4-dihydroxyphenyllactic acid Danshensu (DSS) derivatives were synthesized, and their cardioprotective effects were evaluated in vitro and in vivo. Among the new derivatives, compound 14 showed significant protective effects in cultured myocardial cells and in the rat model of myocardial ischemia. The therapeutic efficacy of compound 14 was significantly higher than that of its parent compound DSS, and amlodipine, a first-line treatment for angina pain. Compound 14 potently scavenged free radicals, significantly decreased the levels of LDH and MDA, and inhibited the leakage of CK in animal model of ischemia. We had previously found that compound 14 activated PI3K/Akt/GSK-3β and Nrf2//Keap1/heme oxygenase-1 (HO-1) signaling pathways in H9c2 cells. These results suggest that compound 14 has a unique mechanism of action, that is, multifunctional. Compound 14 may be a new potential therapy for ischemic heart diseases.

Over-expression of catalase in myeloid cells confers acute protection following myocardial infarction

Cardiovascular disease is the leading cause of death in the United States and new treatment options are greatly needed. Oxidative stress is increased following myocardial infarction and levels of antioxidants decrease, causing imbalance that leads to dysfunction. Therapy involving catalase, the endogenous scavenger of hydrogen peroxide (H₂O₂), has been met with mixed results. When over-expressed in cardiomyocytes from birth, catalase improves function following injury. When expressed in the same cells in an inducible manner, catalase showed a time-dependent response with no acute benefit, but a chronic benefit due to altered remodeling. In myeloid cells, catalase over-expression reduced angiogenesis during hindlimb ischemia and prevented monocyte migration. In the present study, due to the large inflammatory response following infarction, we examined myeloid-specific catalase over-expression on post-infarct healing. We found a significant increase in catalase levels following infarction that led to a decrease in H₂O₂ levels, leading to improved acute function. This increase in function could be attributed to reduced infarct size and improved angiogenesis. Despite these initial improvements, there was no improvement in chronic function, likely due to increased fibrosis. These data combined with what has been previously shown underscore the need for temporal, cell-specific catalase delivery as a potential therapeutic option.

Reactive oxygen species and excitation-contraction coupling in the context of cardiac pathology

Reactive oxygen species (ROS) are highly reactive oxygen-derived chemical compounds that are by-products of aerobic cellular metabolism as well as crucial second messengers in numerous signaling pathways. In excitation-contraction-coupling (ECC), which links electrical signaling and coordinated cardiac contraction, ROS have a severe impact on several key ion handling proteins such as ion channels and transporters, but also on regulating proteins such as protein kinases (e.g. CaMKII, PKA or PKC), thereby pivotally influencing the delicate balance of this finely tuned system. While essential as second messengers, ROS may be deleterious when excessively produced due to a disturbed balance in Na(+) and Ca(2+) handling, resulting in Na(+) and Ca(2+) overload, SR Ca(2+) loss and contractile dysfunction. This may, in the end, result in systolic and diastolic dysfunction and arrhythmias. This review aims to provide an overview of the single targets of ROS in ECC and to outline the role of ROS in major cardiac pathologies, such as heart failure and arrhythmogenesis. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System"

[A pathophysiological role of cytochrome p450 involved in production of reactive oxygen species]

Dysregulation of the production of reactive oxygen species (ROS) determines cellular function. Cytochrome P450s (CYPs) regulates ROS production and contributes to the process of cell death. This review summarizes our recent findings, focusing on the involvement of CYPs in pathophysiology induced by ROS. 1. Quinone toxicity in hepatocytes: CYPs require electrons supplied from NADPH-cytochrome P450 reductase (NPR) during the process of metabolism. NPR also provides electrons to quinone compounds, which compete with CYPs over electrons. Inhibition of CYPs shifts NPR's electron flow more to quinones, which accelerates the redox cycle to enhance ROS production and quinone toxicity. 2. Myocardial ischemia-reperfusion injury: Reperfusion of blood flow after coronary artery occlusion induces cell damage, as evident by the extension of myocardial infarct size and caspase-independent cell apoptosis. CYP2C6 appears to be a source for ROS production, since sulfaphenazole, a selective inhibitor of CYP2C6, reduces this damage. ROS produced by CYP2C6 during the reperfusion causes translational activation of Noxa and BimEL, as well as the suppression of caspase activation, resulting in caspase-independent apoptosis. 3. Primary hepatocyte apoptosis: Inhibition of catalase and glutathione peroxidase increases intracellular ROS and elicits caspase-independent hepatocyte apoptosis. SKF-525A, a pan-CYP inhibitor, suppresses these ROS increases and hepatocyte apoptosis. Increased ROS activates ERK and AP-1 by inhibition of tyrosine phosphatase, and inhibits BimEL degradation by proteasome. These results in the accumulation of mitochondrial BimEL, which then induces the release of cytochrome c and endonuclease G (EndoG). Increased ROS also keeps caspases inactivated. As a result, EndoG executes nucleosomal DNA fragmentation.

The cellular and molecular origin of reactive oxygen species generation during myocardial ischemia and reperfusion

Myocardial ischemia-reperfusion injury is an important cause of impaired heart function in the early postoperative period subsequent to cardiac surgery. Reactive oxygen species (ROS) generation increases during both ischemia and reperfusion and it plays a central role in the pathophysiology of intraoperative myocardial injury. Unfortunately, the cellular source of these ROS during ischemia and reperfusion is often poorly defined. Similarly, individual ROS members tend to be grouped together as free radicals with a uniform reactivity towards biomolecules and with deleterious effects collectively ascribed under the vague umbrella of oxidative stress. This review aims to clarify the identity, origin, and progression of ROS during myocardial ischemia and reperfusion. Additionally, this review aims to describe the biochemical reactions and cellular processes that are initiated by specific ROS that work in concert to ultimately yield the clinical manifestations of myocardial ischemia-reperfusion. Lastly, this review provides an overview of several key cardioprotective strategies that target myocardial ischemia-reperfusion injury from the perspective of ROS generation. This overview is illustrated with example clinical studies that have attempted to translate these strategies to reduce the severity of ischemia-reperfusion injury during coronary artery bypass grafting surgery.

Cardiac biomarkers in a model of acute catecholamine cardiotoxicity

Coronary heart disease and in particular its most serious form — acute myocardial infarction (AMI) — represents the most common cause of mortality in developed countries. Better prognosis may be achieved by understanding the etiopathogenetic mechanisms of AMI. Therefore, a catecholamine model of myocardial injury, which has appeared to be very similar to AMI in human in some aspect, was used. Male Wistar:Han rats were randomly divided into two groups: control group (saline) and isoprenaline group (ISO; synthetic catecholamine, 100 mg.kg— 1 subcutaneously [s.c.]). After 24 hours, functional parameters were measured, biochemical markers in the blood and metals content in the heart tissue were analysed and histological examination was performed. ISO caused marked myocardial injury that was associated with myocardial calcium overload. Close correlation between myocardial impairment (i.e. serum TnT, stroke volume index and wet ventricles weight) and the levels of myocardial calcium was observed. Direct reactive oxygen species (ROS) involvement was documented only by non-significant increase in malonyldialdehyde 24 hours after ISO injury. Moreover, myocardial element analysis revealed no significant changes as for the content of zinc and iron while selenium and copper increased in the ISO group although it reached statistical significance only for the latter.

Superoxide dismutase, lipid peroxidation, and bell-shaped dose response curves

Cellular metabolism generates the cytotoxic superoxide free radical, O(2).(-), and a family of enzymes called superoxide dismutases (SOD) protects us from O(2).(-) by catalyzing its conversion to O(2) and H(2)O(2). Superoxide production increases in a wide variety of pathological states, especially those involving inflammation or ischemic injury. Most of the literature has described systems wherein added or over expressed SOD produced beneficial effects, yet in some circumstances SOD provided no benefit, or was clearly detrimental, exacerbating cell injury or death. When broad dose-response studies were finally possible in models of reperfusion injury in the isolated heart, hormesis became clear. We propose that the mechanisms underlying the hormesis are related to the paradoxical abilities of the superoxide radical to serve as both an initiator and a terminator of the free radical-mediated chain reaction that results in lipid peroxidation. Lipid peroxidation is a universal feature of oxidative stress, causing loss of cellular structure and function. Under any given conditions, the optimal concentration of SOD is that which decreases chain initiation without elimination of the chain termination properties of the radical, resulting in a minimum of net lipid peroxidation. Mathematical modeling of this hypothesis yields predictions fully consistent with observed laboratory data.

Free radicals and antioxidants in inflammatory processes and ischemia-reperfusion injury

This article discusses the current understanding of the role of free radicals and antioxidants in inflammatory processes and in ischemia reperfusion injury. It begins by describing the manifestations of acute inflammation and outlining the cellular events that occur during inflammation. It then describes the biochemical mediators of inflammation with special attention to nitric oxide. It details the process of hypoxia reperfusion injury, the enzymes involved, its treatment, and studies involving specific hypoxia reperfusion injuries in various animal species.

Cardioprotective activity of alcoholic extract of Tinospora cordifolia in ischemia-reperfusion induced myocardial infarction in rats

It has been suggested that the beneficial effects of reperfusing the myocardium might be in part reversed by the occurrence of reperfusion injury. Oxidative stress was suggested to be implicating in the pathogenesis of ischemia-reperfusion (I/R) injury. Many antioxidative plants were shown to be cardioprotective in experimental models of myocardial ischemia-reperfusion (I/R) injury. The present study was designed to investigate the effects of pretreatment with alcoholic extract of Tinospora cordifolia in an in vivo rat model. The model adopted was that of surgically-induced myocardial ischemia, performed by means of left anterior descending coronary artery occlusion (LAD) for 30 min followed by reperfusion for another 4 h. Infarct size was measured by using the staining agent TTC (2,3,5-triphenyl tetrazolium chloride). Lipid peroxide levels in serum and in heart tissue were estimated spectrophotometrically by the methods developed by Yagi and Ohkawa et al. respectively. A lead II electrocardiogram was monitored at various intervals throughout the experiment. A dose dependent reduction in infarct size and in lipid peroxide levels of serum and heart tissue were observed with the prior treatment of T. cordifolia with various doses for 7 d compared to control animals. Hence, the present study suggests the cardioprotective activity of T. cordifolia in limiting ischemia-reperfusion induced myocardial infarction.

The plasma superoxide scavenging activity in canine cancer and hepatic disease

To clarify the relationship between plasma antioxidant activity and diseases in dogs, plasma samples were collected from 6 healthy dogs and 16 diseased dogs (6 dogs with cancer, 5 dogs with hepatic disease, and 5 dogs with inflammation ), and measured superoxide anion scavenging activities. Antioxidant activities of canine plasma were evaluated by measuring their superoxide anion (O(2)(-.)) scavenging activities with electron spin response spectroscopy combined with spin trapping reagent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Total O(2)(-.) scavenging activities in the presence of plasma of diseased dogs tended to be higher than those in healthy controls, especially significant higher activities in the presence of canine plasma of hepatic disease and inflammation were observed. In diseased dogs, KCN-insensitive activities, suggesting the activity of manganese-containing superoxide dismutase (Mn-SOD), were significantly higher than those in healthy controls. Therefore, it seems that there is a possibility of utilizing of plasma O(2)(-.) scavenging activity as one of clinical indicators for oxidative-related diseases such as cancer, hepatic disease and inflammation in dogs.

Polyethylene glycol-superoxide dismutase, a conjugate in search of exploitation

Without a doubt PEG-SOD has been the enzyme most studied in PEGylation. One can say that it represents the preferred model to assess chemistries for PEG activation, analytical procedures suitable for conjugate characterization, the influence of PEG size in conjugate removal from circulation and elimination of immunogenicity and antigenicity, and the effect of route of administration. The effect of PEG conjugation was studied in vitro and in vivo models in comparison with the free enzyme and the following conclusions may be drawn: (1) At the blood vessel level, PEG-SOD has been shown to provide a greater resistance to oxidant stress, to improve endothelium relaxation and inhibit lipid oxidation. (2) In the heart, PEG-SOD proved to be at least as effective as native SOD in treatment of reperfusion-induced arrhythmias and myocardial ischemia. (3) In the lung, PEG-SOD appeared to be able to reduce oxygen toxicity and E. coli-induced lung injury, but not in the treatment of lung physiopathology associated with endotoxin-induced acute respiratory failure and in the reduction of asbestos-induced cell damage. (4) On cerebral ischemia/reperfusion injuries the effect of PEG-SOD was uncertain, also due to the difficulty of cerebral cell penetration. (5) In kidney and liver ischemia both enzyme forms were found to ameliorate reperfusion damage. In view of so much positive research on PEG-SOD, it is surprising that no approved application in human therapy has been established and approved.

Antioxidant vitamins and enzymatic and synthetic oxygen-derived free radical scavengers in the prevention and treatment of cardiovascular disease

Oxygen-derived free radical formation can lead to cellular injury and death. Under normal situations, the human body has a free radical scavenger system (catalase, superoxide dismutase) that can detoxify free radicals. Antioxidant vitamins and enzymatic and synthetic oxygen-derived free radical scavengers have been used clinically to prevent the formation of oxidized LDL and to prevent reperfusion injury, which is often caused by free radicals. In this article, the pathogenesis of free radical production and cell injury are discussed, and therapeutic approaches for disease prevention are presented.

PR-39, a potent neutrophil inhibitor, attenuates myocardial ischemia-reperfusion injury in mice

We investigated the effects of PR-39, a recently discovered neutrophil inhibitor, in a murine model of myocardial ischemia-reperfusion injury. Mice were given an intravenous injection of vehicle (n = 12) or PR-39 (n = 9) and subjected to 30 min of coronary artery occlusion followed by 24 h of reperfusion. In addition, the effects of PR-39 on leukocyte rolling and adhesion were studied utilizing intravital microscopy of the rat mesentery. The area-at-risk per left ventricle was similar in vehicle- and PR-39-treated mice. However, myocardial infarct per risk area was significantly (P < 0.01) reduced in PR-39 treated hearts (21.0 +/- 3.8%) compared with vehicle (47.1 +/- 4.8%). Histological analysis of ischemic reperfused myocardium demonstrated a significant (P < 0.01) reduction in polymorphonuclear neutrophil (PMN) accumulation in PR-39-treated hearts (n = 6, 34.3 +/- 1.7 PMN/mm(2)) compared with vehicle-treated myocardium (n = 6, 59.7 +/- 3.1 PMN/mm(2)). In addition, PR-39 significantly (P < 0.05) attenuated leukocyte rolling and adherence in rat inflamed mesentery. These results indicate that PR-39 inhibits leukocyte recruitment into inflamed tissue and attenuated myocardial reperfusion injury in a murine model of myocardial ischemia-reperfusion.

Radical scavenging properties of novel benzopyran derivatives, TA248 and TA276, and effects of the compounds on ischemic/reperfused myocardium in dogs

Characteristics of novel benzopyran derivatives, TA248 and TA276, and their effects on myocardial contraction in ischemic/reperfused hearts in dogs were examined. TA248 and TA276 inhibited NADPH-dependent lipid peroxidation induced by Fe(3+) in the rat brain homogenate. Both compounds reduced *O(2-) produced by xanthine-xanthine oxidase system in a dose-dependent manner. TA276 scavenged.OH generated by Fenton reaction in a dose-dependent manner. TA248 also inhibited the.OH production, but the effect was neither complete nor dose dependent. Myocardial contraction was assessed as segment shortening of the left ventricular wall in pentobarbital-anesthetized open-chest dogs. The segment shortening was decreased by the left anterior descending coronary artery ligation (ischemia) and returned by release of the ligated artery (reperfusion). The segment shortening did not recover fully during reperfusion. Either TA248 or TA276 injected 10 min before ischemia improved the recovery of myocardial contraction during reperfusion. Both compounds preserved the level of ATP in the 60-min reperfused myocardium. However, the level of lipid peroxides was not changed by TA248 and TA276. TA248 and TA276 may protect myocardium against ischemic/reperfusion insult, partly because of their free radical scavenging activity, but no significant change in myocardial lipid peroxide level was observed.

Oxidative stress and cardiac disease

Reactive oxygen species (ROS) are formed at an accelerated rate in postischemic myocardium. Cardiac myocytes, endothelial cells, and infiltrating neutrophils contribute to this ROS production. Exposure of these cellular components of the myocardium to exogenous ROS can lead to cellular dysfunction and necrosis. While it remains uncertain whether ROS contribute to the pathogenesis of myocardial infarction, there is strong support for ROS as mediators of the reversible ventricular dysfunction (stunning) that often accompanies reperfusion of the ischemic myocardium. The therapeutic potential of free radical-directed drugs in cardiac disease has not been fully realized.

In vivo models of myocardial ischemia and reperfusion injury: application to drug discovery and evaluation

This review discusses the pharmacology of regional myocardial ischemia and reperfusion (I/R) injury and the utilization of in vivo animal models in the preclinical development of novel therapeutic compounds. The manuscript aims to provide an overview of a number of different cardioprotective strategies that have been successful from a preclinical perspective and to also present where possible results of clinical trials of the respective compounds. Myocardial ischemia reperfusion injury may be manifested as myocardial stunning, ventricular arrhythmias, coronary vascular dysfunction, or the development of a myocardial infarct. This review is principally concerned with preclinical studies related to reduction of infarct size. The pathophysiology of the reperfusion injury process is complex, including primarily cellular and humoral components of inflammation, as well as myocellular ionic and metabolic disturbances. This review will discuss strategies directed at oxygen-derived free radicals, neutrophils, adenosine, and the sodium-hydrogen exchanger (NHE). The results of preclinical cardioprotective studies are influenced by the paradigm used therefore methodological considerations will also be presented where appropriate.

Antioxidant function of the mitochondrial protein SP-22 in the cardiovascular system

The mitochondrial protein SP-22 has recently been reported to be a member of the thioredoxin-dependent peroxide reductase family, suggesting that it may be one of the antioxidant systems in mitochondria, which are the major site of reactive oxygen intermediate generation. The aim of this study was to examine whether SP-22 is involved in mitochondrial antioxidant mechanisms and whether its expression is induced by oxidative stresses, particularly those in mitochondria. The expression of SP-22 protein was enhanced by about 1.5-4.6-fold when bovine aortic endothelial cells (BAEC) were exposed to various oxidative stresses, including mitochondrial respiratory inhibitors which increased the superoxide generation in BAEC mitochondria. The expression of SP-22 mRNA increased 2.0-3.5-fold with a peak at 3-6 h after exposure to Fe2+/dithiothreitol or a respiratory inhibitor, antimycin A. BAEC with an increased level of SP-22 protein caused by pretreatment with mild oxidative stress became tolerant to subsequent intense oxidative stress. On the other hand, BAEC that had been depleted of SP-22 with an antisense oligodeoxynucleotide against SP-22 mRNA became more labile to oxidative stress than control BAEC. The induction of SP-22 protein by oxidative stress in vivo was demonstrated in an experimental model of myocardial infarction in rat heart. These findings indicate that SP-22 functions as an antioxidant in mitochondria of the cardiovascular system.

The nonspecific inflammatory response to injury

PURPOSE

The role of the nonspecific inflammatory response in causing injury related to surgery has become better understood over the last decade. There are complex interactions between neutrophils, cytokines and nitric oxide metabolites that may cause organ injury following surgery. The purpose of this review is to summarize some of the processes causing injury through these nonspecific pathways.

METHODS

A review of the medical and anaesthetic literature related to inflammation, neutrophils and pro-inflammatory cytokines were performed using Medline. Bibliographies of relevant articles were searched and additional articles were then selected and reviewed.

RESULTS

Pro-inflammatory cytokines, such as tumour necrosis factor, are released in response to a variety of noxious stimuli (e.g. burns, sepsis, or CABG surgery). These cytokines cause activation of neutrophils with increased upregulation of adhesion complexes on neutrophils and vascular endothelium. Nitric oxide synthase activity is also increased with a resultant increased production of nitric oxide. The increased nitric oxide concentration in the presence of superoxide free radicals secreted by activated neutrophils forms peroxynitrite, a more reactive and toxic molecule. Once this process is initiated, diffuse organ injury can result. Although some information related to specific anaesthetics is available, firm recommendations related to clinical practice cannot be made.

CONCLUSIONS

There is a complex interplay of inflammatory mediators that can cause injury. Although specific clinical applications for manipulating these pathways are not yet generally available, this area holds promise to develop new techniques to improve outcomes following surgery.

Overexpression of human copper, zinc-superoxide dismutase (SOD1) prevents postischemic injury

Superoxide and superoxide-derived oxidants have been hypothesized to be important mediators of postischemic injury. Whereas copper, zinc-superoxide dismutase, SOD1, efficiently dismutates superoxide, there has been controversy regarding whether increasing intracellular SOD1 expression would protect against or potentiate cellular injury. To determine whether increased SOD1 protects the heart from ischemia and reperfusion, studies were performed in a newly developed transgenic mouse model in which direct measurement of superoxide, contractile function, bioenergetics, and cell death could be performed. Transgenic mice with overexpression of human SOD1 were studied along with matched nontransgenic controls. Immunoblotting and immunohistology demonstrated that total SOD1 expression was increased 10-fold in hearts from transgenic mice compared with nontransgenic controls, with increased expression in both myocytes and endothelial cells. In nontransgenic hearts following 30 min of global ischemia a reperfusion-associated burst of superoxide generation was demonstrated by electron paramagnetic resonance spin trapping. However, in the transgenic hearts with overexpression of SOD1 the burst of superoxide generation was almost totally quenched, and this was accompanied by a 2-fold increase in the recovery of contractile function, a 2.2-fold decrease in infarct size, and a greatly improved recovery of high energy phosphates compared with that in nontransgenic controls. These results demonstrate that superoxide is an important mediator of postischemic injury and that increasing intracellular SOD1 dramatically protects the heart from this injury. Thus, increasing intracellular SOD1 expression may be a highly effective approach to decrease the cellular injury that occurs following reperfusion of ischemic tissues.

Electrical and mechanical modulations by oxygen-derived free-radical generating systems in guinea-pig heart muscles

The effects of free-radical generating systems and angiotensin-converting enzyme (ACE) inhibitors on the action potentials and contractile force in guinea-pig cardiac muscles were examined using conventional microelectrode and whole-cell voltage-clamp methods at 36 degrees C. Hydrogen peroxide (30-100 microM) prolonged 50%, 75% and 90% repolarization of action-potential duration (APD) approximately 15-25 min after its application. But the longer exposure reversed the APD shortening in a concentration-dependent manner. Other action-potential parameters were not altered to a significant extent. The contractile force was increased. Longer exposure inhibited the enhanced force (but it was still larger than control). The effects on the spontaneous action potential from right atrial muscle were almost the same. In whole-cell voltage-clamp experiments, H2O2 (100 microM) inhibited L-type Ca2+ current and enhanced delayed rectifier K+ current. The effects of light-activated rose bengal (10-100 nM) on the APD were similar to, but more potent than, those of H2O2. The response was observed rapidly after a light illumination. During exposure to rose bengal (100 nM), abnormal spontaneous action potentials or arrhythmias such as a bigeminy occurred, presumably because of early and delayed afterdepolarizations. The responses were irreversible. At 300 microM ACE inhibitors, captopril and enalapril, protected the changes induced by these free radicals. These results indicate that H2O2 has a dual, time-dependent, action on the APD and rose bengal with light illumination produced the responses rapidly. The oxygen-derived free radicals increased [Ca]i and then cellular Ca2+ overload occurred. These responses were protected by ACE inhibitors.

The effects of gentamicin on the activities of glutathione peroxidase and superoxide dismutase enzymes and malondialdehyde levels in heart tissues of guinea pigs

In this study, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and malondialdehyde (MDA) levels were measured in heart tissues from guinea pigs treated with gentamicin and gentamicin plus vitamin E combination. Mean values were compared with those of the controls treated with only physiological saline solution. The activities of SOD and GSH-Px were found to be lower and the MDA level higher in the hearts from gentamicin-treated animals compared with those of the controls. In the gentamicin plus vitamin E group, however, tissue SOD activity was found to be increased and MDA level decreased significantly relative to the gentamicin group. GSH-Px activity was lowest in this group. Results suggest that gentamicin suppresses SOD and GSH-Px activities in heart tissue, thereby making the tissue more vulnerable to oxidative stress and peroxidative attacks, an important indicator of which is increased MDA level in the heart tissues from gentamicin-treated guinea pigs. This effect might be deleterious when gentamicin is used after cardiac surgery since a potential risk of free radical injury exists in the heart tissue during and/or after cardiac surgery owing to ischaemia and reperfusion processes, and, possibly, in the management of the patients with certain types of heart disease. Our results showed that vitamin E given concomitantly with gentamicin could protect the heart tissue against free radical injury.

Reperfusion Injury: Basic Concepts and Protection Strategies

Prolonged ischemia such as that following myocardial infarction or occurring during long-term coronary bypass procedures causes serious damage to the myocardium. Early reperfusion is an absolute prerequisite for the survival of ischemic tissue. However, reperfusion has been referred to as the "double edged sword" because reperfusing ischemic myocardium carries with it a component of injury known as reperfusion injury. Reperfusion injury includes a number of events, such as reperfusion arrhythmias, myocardial infarction, stunning, vascular damage, and endothelial dysfunction. The underlying mechanism of reperfusion injury is not entirely known, but the existing evidence suggests that oxygen free radicals generated during the first few minutes of reflow lead to damage of cellular membranes, intracellular calcium overload, and uncoupling of excitation-contraction coupling. Although controversial, free radical scavengers, in general, are highly effective in the attenuation of reperfusion injury in animal models. Newer endogenous protection strategies, which include ischemic and heat shock preconditioning, are known to reduce reperfusion injury following ischemia.

Prolonged coronary artery occlusion-reperfusion sequences reduce myocardial free radical production: an electron paramagnetic resonance study

Our purpose was to determine whether prolonged myocardial ischemia attenuates free radical production after early reperfusion. Twenty-two mongrel dogs underwent left anterior descending coronary artery occlusion for 20, 40, or 60 minutes followed by 30 minutes of reperfusion. Electron paramagnetic resonance spectroscopy was used to measure ascorbate free radical in the coronary vein effluent. Ascorbate free radical production during reperfusion was significantly (p < 0.05) reduced in the dogs undergoing 60 minutes of coronary artery occlusion compared with the dogs undergoing 40 and 20 minutes of occlusion. We conclude that prolonged myocardial ischemia results in less free radical production on reperfusion than do shorter periods of ischemia followed by reperfusion.

Myocardial, neural and vascular aspects of ischemic preconditioning

Ischemic preconditioning can be obtained with brief coronary occlusions. It has been studied in different animal species including dogs, pigs, rabbits and rats. The suggested duration of the occlusions ranges from four periods of 5 min, separated from each other by 5 min of reperfusion, to one period of 2.5 min. In addition to the reduction of the size of a subsequent infarction, preconditioning is responsible for the attenuation of the ischemia-reperfusion injury. The protection has a short duration and does not exceed two hours. Myocardial, neural and endothelial factors are involved in preconditioning. The myocardial component includes an increased release of adenosine with activation of A1 adenosine receptors, the activation of a protein-kinase C and possibly of antioxidant enzymes. The neural component includes a reduction in the release of noradrenaline from the postganglionic sympathetic fibers and a reduced myocardial sensitivity to noradrenaline. The increased myocardial release of adenosine, together with the reduced adrenergic activity, is consistent with the reduction in myocardial metabolism which has been observed after preconditioning. The coronary vascular endothelium is concerned in an increased release of nitric oxide which seems to be responsible for a prevention of reperfusion arrhythmias. In addition to the protective effect exerted on the myocardium, ischemic preconditioning seems to be responsible for a change in the coronary responsiveness to short periods of occlusion followed by release. This change in responsiveness is mainly represented by a greater velocity of the increase in flow occurring in the coronary reactive hyperemia.

Catalase inhibition with 3-amino-1,2,4-triazole does not abolish infarct size reduction in heat-shocked rats

BACKGROUND

Recent studies have shown that improved myocardial salvage after heat-shock pretreatment correlates with the amount of induced cardiac heat-shock protein (HSP)72. However, heat shock also induces myocardial catalase activity, potentially reducing free radical-mediated ischemic injury. The aim of the present study was to determine whether catalase inhibition with 3-amino-1,2,4-triazole (3-AT) abolishes the reduction of infarct size conferred by heat-shock treatment in rats.

METHODS AND RESULTS

Myocardial catalase activity was measured in both heat-shocked and control rats 60 minutes after either 3-AT (1000 mg/kg IV) or saline infusion. In separate experiments, heat-shocked and control rats were treated with 3-AT or saline 60 minutes before being subjected to 35 minutes of left coronary artery occlusion and 120 minutes of reperfusion. Infarct size was determined by dual perfusion with triphenyltetrazolium chloride and phthalocyanine blue dye. Heat-shock treatment significantly increased myocardial catalase compared with control animals (180.5 +/- 4.8, n = 6, versus 86.2 +/- 14.7, n = 5, units/g wet wt; P < .05). Treatment with 3-AT significantly reduced myocardial catalase activity in both heat-shocked and control animals (29.6 +/- 5.7, n = 5, and 36.4 +/- 15.3, n = 6, respectively). Heat-shock treatment significantly reduced infarct size in rats that were both treated and untreated with 3-AT compared with respective control groups (22.5 +/- 3.7%, n = 26, 28.2 +/- 4.0%, n = 22, 52.0 +/- 3.0%, n = 23, and 48.6 +/- 3.2%, n = 26, respectively; P < .0001 for both heat-shocked groups versus both control groups; infarct mass/risk area mass x 100).

CONCLUSIONS

Catalase inhibition with 3-AT does not abolish the reduction of infarct size in heat-shocked rats.

Effect of copper-zinc superoxide dismutase on endothelium-dependent vasodilation in patients with essential hypertension

Patients with essential hypertension have abnormal endothelium-dependent vasodilation related to decreased nitric oxide activity. The specific mechanism responsible for this abnormality is unknown. Recent studies in hypertensive animals have suggested an augmented destruction of nitric oxide by superoxide anions. Therefore, in the present study we aimed to investigate whether this mechanism is responsible for the abnormal vasodilator function of hypertensive patients. To this end, we studied the vascular responses to acetylcholine (an endothelium-dependent vasodilator) and sodium nitroprusside (a direct smooth muscle dilator) before and after combined administration of copper-zinc superoxide dismutase (a scavenger of superoxide anions with poor intracellular penetrance; 6000 U/min) in 20 healthy control subjects (11 men and 9 women; aged 50 +/- 6 years) and 20 hypertensive patients (13 men and 7 women; aged 51 +/- 9 years). Drugs were infused into the brachial artery, and the response of the forearm vasculature was measured by plethysmography. The vasodilator response to acetylcholine was significantly blunted in hypertensive patients compared with control subjects (maximal flow: 8.2 +/- 4 versus 12.7 +/- 3 mL/min per 100 mL; P < .02); however, no difference was observed in the response to sodium nitroprusside (8.1 +/- 4 versus 9.5 +/- 3 mL/min per 100 mL). In healthy control subjects superoxide dismutase infusion did not modify the vasodilator response to acetylcholine (maximal flow: 12.7 +/- 3 before versus 12.1 +/- 3 after superoxide dismutase). Similarly, in hypertensive patients superoxide dismutase infusion did not alter the response to acetylcholine (maximal flow: 8.2 +/- 4 versus 7.7 +/- 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that continuous normothermic blood cardioplegia offers better myocardial protection than intermittent hypothermic cardioplegia

OBJECTIVES

To compare transmyocardial ischaemia and oxidative stress, as well as non-infarction myocardial injury, in patients randomised to intermittent hypothermic cardioplegia or continuous normothermic blood-potassium cardioplegia.

DESIGN

Prospective randomised trial.

SETTING

Tertiary cardiac referral centre.

METHODS

24 patients undergoing elective coronary artery bypass surgery were randomised to hypothermic (13 patients, mean (SEM) age 59.5 (2.6) years) or normothermic (11 patients, mean (SEM) age 59.7 (3.3) years) cardioplegia. Transmyocardial oxidative stress and ischaemia were assessed by the difference in plasma concentrations of oxidised glutathione and lactate respectively, from samples taken simultaneously from the coronary sinus and aortic root. Blood samples were taken just before cross clamp application and at intervals up to 15 min after cross clamp release. Non-infarction myocardial injury was assessed by measurement of creatine kinase MB isoenzyme activity from peripheral venous blood taken 2 and 18 h after surgery.

RESULTS

Intermittent hypothermic cardioplegia resulted in a significant increase in transmyocardial ischaemia (P < 0.001) and oxidative stress (P < 0.001). Evidence of significantly increased myocyte damage was also present (P < 0.01). No significant corresponding changes were present with normothermic cardioplegia.

CONCLUSIONS

Normothermic blood cardioplegia seems to avoid significant changes in myocardial ischaemic status and consequent oxidative stress. This study provides direct evidence that normothermic cardioplegia offers enhanced myocardial protection compared with that of hypothermic cardioplegia. Certain subsets of patients may derive more benefit from normothermic cardioplegia, although it is unclear whether this would be the case for all patients.

Protection by pyruvate against inhibition of Na+, K(+)-ATPase by a free radical generating system containing t-butylhydroperoxide

Global tissue damage due to oxygen-derived free radicals has been implicated in several pathological processes including exposure to ionizing radiation, and postischemic reperfusion of the heart or kidney. Recently pyruvate, a hydroperoxide scavenger, has been shown to protect against functional damage during postischemic reperfusion of the heart and in acute renal failure. In the present study, pyruvate was found to protect against inactivation of partially purified guinea pig renal and rat cardiac Na+,K(+)-ATPase which occurred when microsomal membranes were assayed for 1 hr at 37 degrees C (pH 7.5) in the presence of a free radical generating system (FRGS) containing 0.3 mM t-butylhydroperoxide and horseradish peroxidase. The presence of the FRG system inhibited the guinea pig renal Na+,K(+)-ATPase activity by 48.2 +/- 4.8% (N = 10, P < .05) and the presence of 0.2 to 20 mM pyruvate partially protected the Na+,K(+)-ATPase. At 5 mM pyruvate Na+,K(+)-ATPase was inhibited by only 18.8 +/- 2.5% (N = 10, P < .05) but increasing the pyruvate concentration gave no further protection. Equimolar concentrations of glucose, mannitol or lactate were without effect. The protection appeared to require an alpha-keto acid since alpha- but not beta-ketoglutarate was also effective and the mechanism is most probably the scavenging of t-BHO2. The results of the present study therefore support the hypothesis that, if free radical damage to native Na+,K(+)-ATPase does contribute to global tissue injury in certain pathological processes, pyruvate, in addition to being a powerful metabolic effector of recovery, may also protect against oxidative damage.

Do nitroxides protect cardiomyocytes from hydrogen peroxide or superoxide?

The aim of the research was to study the role played by extracellular O2-radicals, which are implicated in cardiac cell damage and the protective effect by cell-permeable, nitroxide, superoxide dismutase-mimics. Cardiomyocytes cultures from 1-day-old rats served as the test-system. Experiments were performed since 5th day in culture when > 80% of the cells were beating myocardial cells. Oxidative damage was induced by 0.5 mM hypoxanthine and 0.06 U/ml xanthine oxidase or by 10 mM glucose and 0.15 U/ml glucose oxidase. The parameters used to evaluate damages were spontaneous beating, lactate dehydrogenase release and ATP level. The rhythmic pulsation was followed microscopically. To determine the kinetics of cytosolic enzyme release from the cells, media samples were collected at various points of time and assayed for enzyme activity. To determine the cellular ATP, cells were washed with sodium phosphate buffer, scraped off and boiled for 3 min with sodium phosphate buffer. Following centrifugation the supernatant was collected and ATP was determined by the chemiluminogenic assay using firefly tails. The present results indicate that nitroxide stable free radicals in the millimolar concentration range, provide full protection without toxic side-effect. Unlike exogenously added SOD that failed to protect, exogenous catalase provided almost full protection. In addition, the metal-chelating agent dipyridyl, but not diethylene-triamine-pentaacetate or desferrioxamine, protected the cultured cells. The present results suggest that H2O2 is the predominant toxic species mediating the oxidative damage whereas extracellular superoxide radical does not contribute to cultured cardiomyocyte damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen free radicals and antioxidants: a review

In 1989, nearly 43% of deaths in the United States were due to some form of cardiovascular disease, and 23% were caused by cancer. Thus, two of every three people in this country die from either cardiovascular disease or cancer. Based on both experimental and epidemiological evidence, investigators believe that free radicals play a critical role in the development of both diseases. Low levels of antioxidants, which increases free radical activity, are clearly associated with an increased risk of these diseases. This link has led to the conclusion that use of antioxidant vitamin supplements to scavenge free radicals could potentially decrease the risks of cancer and cardiovascular disease. Results from numerous studies to date have been very promising, although a true protective or preventive causal relationship has not yet been established. Numerous primary and secondary intervention trials currently underway should more definitively assess the role of antioxidants in disease prevention. In the interim, many people feel the evidence is now strong enough to begin supplementation on their own. The pharmacist is in a position to advise patients on the safe and moderate use of antioxidants. The antioxidants discussed in this article are relatively non-toxic, with the exception of vitamin A. The possible benefits of vitamin A are better achieved with the use of beta-carotene. Megadose antioxidant supplementation does not appear to provide any additional benefit beyond what a more moderate supplement can provide and should therefore be discouraged. Taking a trace mineral with antioxidant potential is generally a waste of money, provided the patient is not initially deficient in the element.(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant human superoxide dismutase (h-SOD) fails to improve recovery of ventricular function in patients undergoing coronary angioplasty for acute myocardial infarction

BACKGROUND

Animal studies have demonstrated a burst of oxygen free radical generation after reperfusion of ischemic myocardium that could be blocked by administration of the free radical scavenger recombinant human superoxide dismutase (h-SOD). A multicenter, randomized, placebo-controlled clinical trial was designed to test the hypothesis that free radical-mediated reperfusion injury could be reduced by intravenous administration of h-SOD begun before percutaneous transluminal coronary angioplasty (PTCA) in patients with acute transmural myocardial infarction.

METHODS AND RESULTS

One hundred twenty patients were randomized to receive placebo (n = 59) or h-SOD (n = 61) given as a 10-mg/kg intravenous bolus followed by a 60-minute infusion of 0.2 mg.kg-1.min-1. Left ventricular function was analyzed via paired contrast left ventriculograms performed before PTCA and after 6 to 10 days and paired radionuclide ventriculograms performed within 24 hours of PTCA and after 4 to 6 weeks. Both h-SOD- and placebo-treated patients showed improvement in global and regional left ventricular function after successful reperfusion. Compared with the placebo group, no additional improvement was observed in the patients treated with h-SOD.

CONCLUSIONS

The results of this clinical trial failed to demonstrate a beneficial effect of h-SOD on global or regional left ventricular function in patients who underwent successful PTCA for treatment of acute myocardial infarction.

Free radicals and the heart

Because of the molecular configuration, most free radicals are highly reactive and can cause cell injury. Protective mechanisms have evolved to provide defense against free-radical injury. Any time these defense systems are overwhelmed, such as during disease states, cell dysfunction may occur. In this review we discuss cellular sources as well as the significance of free radicals, oxidative stress, and antioxidants. A probable role of oxidative stress in various cardiac pathologies has been also analyzed. Although some methods for the detection of free radicals as well as oxidative stress have been cited, better methods to study the quantity as well as subcellular distribution of free radicals are needed in order to understand fully the role of free radicals in both health and disease.

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.

Effect of zinc deficiency on lipid peroxidation status and infarct size in rat hearts

The objective of this study was to investigate the effect of dietary zinc on endogenous production of lipid peroxides, and on myocardial infarct size in rats. Male rats were fed a zinc-deficient diet containing 4 ppm zinc, or a standard diet containing 60 ppm zinc. After 3 weeks of diet, half of the animals underwent occlusion of the left coronary artery. The remaining animals underwent sham operation without occlusion. Forty-eight hours later, the hearts were sampled and lipid peroxide levels and infarct size were evaluated. Coronary occlusion was associated with an increase in cardiac lipid peroxide levels which were more pronounced in the zinc deficient group. However, infarct size appeared to be independent from zinc deficiency, despite the free radical-mediated lipid peroxide augmentation reported here. The pharmacological limitation of infarct size in rats with permanent coronary occlusion is discussed.

Involvement of free radicals in cisplatin-induced emesis in Suncus murinus

The participation of free radicals in cisplatin-induced emesis was investigated in the house musk shrew, Suncus murinus. Thiobarbituric acid (TBA) values, which indicate the degree of lipid peroxidation, in brain, liver and small intestine were increased significantly 60 min after the treatment with cisplatin (20 mg/kg, i.p.). Moreover, cisplatin (20 mg/kg, i.p.)-induced emesis was prevented by intraperitoneal injection of N-(2-mercaptopropionyl)glycine (MPG), a radical scavenging agent, with ID50 value of 130 mg/kg. However, MPG did not block the emesis induced by copper sulfate (40 mg/kg, p.o.), veratrine (0.5 mg/kg, s.c.) or serotonin (10 mg/kg, i.p.). We also investigated the effects of superoxide dismutase conjugated to polyethylene glycol and catalase, but the number of vomiting episodes and latency did not change significantly when these agents were intraperitoneally injected 30 min prior to or 20 min after the administration of cisplatin. MPG did not affect the antitumor effect of cisplatin tested in vitro. These results suggest that free radicals mediate emesis caused by cisplatin and that radical scavengers may become a new class of prophylactic drug against cancer-chemotherapeutic drug-induced emesis.

Neutrophil mediated myocardial injury

1. Activated polymorphonuclear neutrophils (PMN) were shown to exacerbate ischemic myocardial injury and their activation is modulated by complement system, platelet activating factor, arachidonic acid metabolites, adenosine and nitric oxide. 2. Mechanisms of injurious PMN effect on ischemic myocardium are related to both mechanical and biochemical processes. 3. Activated PMN aggregate and adhere to endothelium that results in capillary plugging and subsequent impairment of coronary blood flow as well as participating in the development of endothelial cell edema. 4. PMN-related biochemical damage of ischemic myocardium is a result of the release of cytotoxic free oxygen radicals and proteolytic enzymes as well as vasoconstrictor leukotriene B4 and leukotoxin.