Nafazatrom-induced salvage of ischemic myocardium in anesthetized dogs is mediated through inhibition of neutrophil function

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.

Molecular identity of the mitochondrial permeability transition pore and its role in ischemia-reperfusion injury

The mitochondrial permeability transition is a key event in cell death. Intense research efforts have been focused on elucidating the molecular components of the mitochondrial permeability transition pore (mPTP) to improve the understanding and treatment of various pathologies, including neurodegenerative disorders, cancer and cardiac diseases. Several molecular factors have been proposed as core components of the mPTP; however, further investigation has indicated that these factors are among a wide range of regulators. Thus, the scientific community lacks a clear model of the mPTP. Here, we review the molecular factors involved in the regulation and formation of the mPTP. Furthermore, we propose that the mitochondrial ATP synthase, specifically its c subunit, is the central core component of the mPTP complex. Moreover, we discuss the involvement of the mPTP in ischemia and reperfusion as well as the results of clinical studies targeting the mPTP to ameliorate ischemia-reperfusion injury. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".

Pleiotropic effects of neutrophils on myocyte apoptosis and left ventricular remodeling during early volume overload

Most of the available evidence on the role of neutrophils on pathological cardiac remodeling has been pertained after acute myocardial infarction. However, whether neutrophils directly contribute to the pathogenesis of cardiac remodeling after events other than acute myocardial infarction remains unknown. Here we show that acute eccentric hypertrophy induced by aorto-caval fistula (ACF) in the rats induced an increase in the inflammatory response characterized by activation of the STAT pathway and increased infiltration of neutrophils in the myocardium. This early inflammation was associated with a decrease in interstitial collagen accumulation and an increase in myocyte apoptosis. Neutrophil infiltration blockade attenuated MMP activation, ECM degradation, and myocyte apoptosis induced by ACF at 24 hours and attenuated the development of eccentric hypertrophy induced by ACF at 2 and 3 weeks, suggesting a causal relationship between neutrophils and the ACF-induced cardiac remodeling. In contrast, sustained neutrophil depletion over 4 weeks resulted in adverse cardiac remodeling with further increase in cardiac dilatation and macrophage infiltration, but with no change in myocyte apoptosis level. These data support a functional role for neutrophils in MMP activation, ECM degradation, and myocyte apoptosis during eccentric cardiac hypertrophy and underscore the adverse effects of chronic anti-neutrophil therapy on cardiac remodeling induced by early volume overload.

Role of 5-lipoxygenase in myocardial ischemia-reperfusion injury in mice

Myocardial ischemia induces 5-lipoxygenase (LOX) translocation and leukotriene production in the heart. Leukotrienes increase inflammatory responses and could thereby aggravate ischemic injury. However, the role of lipoxygenase and leukotrienes in cardiac ischemia/reperfusion damage has not been well defined. Therefore, we tested the effect of ischemia reperfusion in mice with targeted deletion of 5-lipoxygenase, the enzyme converting arachidonic acid in leukotrienes. 5-LOX deficient (KO) and wild-type (WT) mice underwent 30 min of coronary artery ligation and 24 h of reperfusion in vivo. In mice with equivalent area at risk, infarct size was not significantly different between WT and KO mice (infarct/area at risk 61.7+/-3.9 vs. 55.8+/-6.6%, WT vs. KO, P=n.s.). However, neutrophil infiltration as well as tumor necrosis factor expression were increased in 5-lipoxygenase deficient mice. In summary, inhibition of 5-lipoxygenase does not affect cardiac ischemia-reperfusion injury but the post-ischemic inflammatory response.

Gö 6983: A Fast Acting Protein Kinase C Inhibitor that Attenuates Myocardial Ischemia/Reperfusion Injury

Reperfusion injury is characterized by a decrease in endothelial release of nitric oxide within 5 min after reperfusion, increased leukocyte-endothelium interaction, and transmigration of leukocytes into the myocardium, producing cardiac contractile dysfunction. Gö 6983 is a fast acting, lipid soluble, broad spectrum protein kinase C inhibitor. When administered at the beginning of reperfusion, it can restore cardiac function within 5 min and attenuate the deleterious effects associated with acute ischemia/reperfusion. Gö 6983 may offer greater cardioprotection than other broad-spectrum PKC inhibitors in postischemic reperfusion injury because it inhibits PKC(zeta) as well as four other isoforms. The cardioprotection is associated with decreased leukocyte superoxide release and increased endothelial derived nitric oxide from vascular tissue. In vitro studies of human tissue showed that Gö 6983 significantly inhibited antigen-induced superoxide release from leukocytes of patients previously sensitized to tree pollen. In human vascular tissue, Gö 6983 inhibited intracellular Ca(2+) accumulation, suggesting a mechanism for its vasodilator properties. These studies suggest that Gö 6983 would be an effective compound to use in a clinical ischemia/reperfusion setting of organ transplantation and/or cerebral ischemia where inhibiting superoxide release and vasoconstriction in postischemic tissues would allow for better restoration of organ function during reperfusion. However, given the broad-spectrum action of Gö 6983, careful titration of the dose regimen would be recommended to ensure a successful outcome in the setting of organ transplantation and/or cerebral ischemia.

Linear furanocoumarin protects rat myocardium against lipidperoxidation and membrane damage during experimental myocardial injury

The antioxidant activity and the membrane effects of linear furanocoumarin marmesinin isolated from Aegle marmelose was evaluated during experimental myocardial injury. Isoproterenol (150 mg kg(-1) intraperitonially twice at an interval of 24 h) caused increase in the levels of serum marker enzymes via creatinekinase (CK), creatinekinase-MB (CK-MB) isoenzyme, lactatedehydrogenase (LDH) and lactatedehydrogenase isoenzyme (LDH1). It also produced electrocardiographic changes such as increased heart rate, reduced R amplitude and ST elevation. Marmesinin at a dose of 200 mg kg(-1), when administered orally, demonstrated a decrease in serum enzyme levels and restored the electrocardiographic changes towards normalcy. Myocardial injury was accompanied by the disintegration of lipidperoxides and the impairment of natural scavengers. Marmesinin oral treatment for 2 days before and during isoproterenol administration decreased the effect of lipidperoxidation. It was also shown to have a membrane stabilizing action by inhibiting the release of beta-glucuronidase from the subcellular fractions. Thus, linear furanocoumarin marmesinin could have the protective effect against the damage caused by experimental myocardial injury.

Gö 6983 Exerts Cardioprotective Effects in Myocardial Ischemia/Reperfusion

Ischemia followed by reperfusion (I/R) in the presence of polymorphonuclear leukocytes (PMNs) results in cardiac contractile dysfunction. Inhibiting protein kinase C (PKC) inhibits the release of superoxide from PMNs. The compound Gö 6983 is an inhibitor of all five PKC isoforms present in PMNs. Therefore, we hypothesized that Gö 6983 could attenuate PMN-induced cardiac dysfunction by suppression of superoxide production from PMNs. We studied isolated rat hearts following ischemia (20 minutes) and reperfusion (45 minutes) infused with activated PMNs. In hearts reperfused with PMNs and Gö 6983 (100 nM, n = 7), left ventricular developed pressure (LVDP) and the rate of LVDP (+dP/dt max) recovered to 89 +/- 7% and 74 +/- 2% of baseline values, respectively, at 45 minutes postreperfusion compared with I/R hearts (n = 9) receiving PMNs alone, which only recovered to 55 +/- 3% and 45 +/- 5% of baseline values for LVDP and +dP/dtmax, respectively (P < 0.01). Gö 6983 (100 nM) significantly reduced PMN adherence to the endothelium and infiltration into the myocardium compared with I/R + PMN hearts (P < 0.01), and significantly inhibited superoxide release from PMNs by 90 +/- 2% (P < 0.01). In the presence of PMNs, Gö 6983 attenuated post-I/R cardiac contractile dysfunction, which may be related in part to decreased superoxide production.

Xanthine oxidase, but not neutrophils, contributes to activation of cardiac sympathetic afferents during myocardial ischaemia in cats

Activation of cardiac sympathetic afferents during myocardial ischaemia causes angina and induces important cardiovascular reflex responses. Reactive oxygen species (ROS) are important chemical stimuli of cardiac afferents during and after ischaemia. Iron-catalysed Fenton chemistry constitutes one mechanism of production of hydroxyl radicals. Another potential source of these species is xanthine oxidase-catalysed oxidation of purines. Polymorphonuclear leukocytes (PMNs) also contribute to the production of ROS in some conditions. The present study tested the hypothesis that both xanthine oxidase-catalysed oxidation of purines and neutrophils provide a source of ROS sufficient to activate cardiac afferents during ischaemia. We recorded single-unit activity of cardiac afferents innervating the ventricles recorded from the left thoracic sympathetic chain (T1-5) of anaesthetized cats to identify the afferents' responses to ischaemia. The role of xanthine oxidase in activation of these afferents was determined by infusion of oxypurinol (10 mg kg(-1), I.V.), an inhibitor of xanthine oxidase. The importance of neutrophils as a potential source of ROS in the activation of cardiac afferents during ischaemia was assessed by the infusion of a polyclonal antibody (3 mg ml(-1) kg(-1), I.V.) raised in rabbits immunized with cat PMNs. This antibody decreased the number of circulating PMNs and, to a smaller extent, platelets. Since previous data suggest that platelets release serotonin (5-HT), which activates cardiac afferents through a serotonin receptor (subtype 3,5-HT3 receptor) mechanism, before treatment with the antibody in another group, we blocked 5-HT3 receptors on sensory nerve endings with tropisetron (300 microg kg(-1), I.V.). We observed that oxypurinol significantly decreased the activity of cardiac afferents during myocardial ischaemia from 1.5 +/- 0.4 to 0.8 +/- 0.4 impulses s(-1). Similarly, the polyclonal antibody significantly reduced the discharge frequency of ischaemically sensitive cardiac afferents from 2.5 +/- 0.7 to 1.1 +/- 0.4 impulses s(-1). However, pre-blockade of 5-HT3 receptors eliminated the influence of the antibody on discharge activity of the afferents during ischaemia. This study demonstrates that ROS generated from the oxidation of purines contribute to the stimulation of ischaemically sensitive cardiac sympathetic afferents, whereas PMNs do not play a major role in this process.

alpha(4)-integrin mediates neutrophil-induced free radical injury to cardiac myocytes

Previous work has demonstrated that circulating neutrophils (polymorphonuclear leukocytes [PMNs]) adhere to cardiac myocytes via beta(2)-integrins and cause cellular injury via the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzyme system. Since PMNs induced to leave the vasculature (emigrated PMNs) express the alpha(4)-integrin, we asked whether (a) these PMNs also induce myocyte injury via NADPH oxidase; (b) beta(2)-integrins (CD18) still signal oxidant production, or if this process is now coupled to the alpha(4)-integrin; and (c) dysfunction is superoxide dependent within the myocyte or at the myocyte-PMN interface. Emigrated PMNs exposed to cardiac myocytes quickly induced significant changes in myocyte function. Myocyte shortening was decreased by 30-50% and rates of contraction and relaxation were reduced by 30% within the first 10 min. Both alpha(4)-integrin antibody (Ab)-treated PMNs and NADPH oxidase-deficient PMNs were unable to reduce myocyte shortening. An increased level of oxidative stress was detected in myocytes within 5 min of PMN adhesion. Addition of an anti-alpha(4)-integrin Ab, but not an anti-CD18 Ab, prevented oxidant production, suggesting that in emigrated PMNs the NADPH oxidase system is uncoupled from CD18 and can be activated via the alpha(4)-integrin. Addition of exogenous superoxide dismutase (SOD) inhibited all parameters of dysfunction measured, whereas overexpression of intracellular SOD within the myocytes did not inhibit the oxidative stress or the myocyte dysfunction caused by the emigrated PMNs. These findings demonstrate that profound molecular changes occur within PMNs as they emigrate, such that CD18 and associated intracellular signaling pathways leading to oxidant production are uncoupled and newly expressed alpha(4)-integrin functions as the ligand that signals oxidant production. The results also provide pathological relevance as the emigrated PMNs have the capacity to injure cardiac myocytes through the alpha(4)-integrin-coupled NADPH oxidase pathway that can be inhibited by extracellular, but not intracellular SOD.

Effect of cytochrome c on the linoleic acid-degrading activity of porcine leukocyte 12-lipoxygenase

Hemoproteins are known to have quasilipoxygenase activity that converts linoleic acid (LA) to its hydroperoxides. However, it is not still clear whether, like lipoxygenases, hemoproteins can produce LA hydroperoxides when the LA is part of a mixture containing many different saturated and unsaturated fatty acids. In this study, we found that such hemoprotein as cytochrome c (Cyt c) did not produce LA hydroperoxides from the phospholipase A(2) (PL-A(2)) hydrolysis products of egg yolk phosphatidylcholine (PC). We also found that traces of hydroperoxides and a high concentration of the target unsaturated fatty acid (LA) needs to be present in a fatty acid mixture before the quasi-lipoxygenase activity of Cyt c becomes apparent. We also attempted to elucidate how Cyt c interact with porcine leukocyte 12-lipoxygenase (12-LOX). Hemoproteins are known to possess pseudo-lipohydroperoxidase activity, and can remove the hydroperoxides of unsaturated fatty acids from a reaction mixture. However, we found that Cyt c catalyzed the reaction by which hydroperoxides degrade LA, and thus enhanced the LA-degrading activity of 12-LOX. This hemoprotein-induced promotion of the ability of 12-LOX to degrade LA was observed even when the reaction mixture contained many different saturated and unsaturated fatty acids.

Effect of a novel tetrapeptide derivative in a model of isoproterenol induced myocardial necrosis

Isoproterenol hydrochloride (ISO), a beta adrenergic agonist, is known to cause ischemic necrosis in rats. Cardiotoxicity of three different doses of ISO were studied using physiological, biochemical and histopathological parameters. The effects of single and double dose of ISO were analysed, which illustrated that single ISO dose was more cardiotoxic than double ISO dose due to ischemic preconditioning. The tetrapeptide derivatives L-lysine-L-arginine-L-aspartic acid-L-serine (tetrapeptide A) and di-tert.butyloxycarbonyl-L-lysine-L-arginine-L-aspartic acid-tert.butyl O-tert.butyl-L-serinate (tetrapeptide B) along with acetylsalicylic acid as positive control were analysed at different time points for their cardioprotective effect. The results demonstrated that optimal protective effects were observed by pretreatment with 5 mg/kg of tetrapeptide B and this was found to be slightly better than that of acetylsalicylic acid. A lesser degree of cardioprotection was noticed when low doses of tetrapeptide B were administered. This study clearly showed that single dose of ISO (50 mg/kg, s.c.) induced myocardial necrosis could be used as a model to assess cardiovascular drugs and in this model, it was demonstrated that the tetrapeptide B could exhibit optimal cardioprotective effect.

Nitric oxide deficiency, leukocyte activation, and resultant ischemia are crucial to the pathogenesis of diabetic retinopathy/neuropathy--preventive potential of antioxidants, essential fatty acids, chromium, ginkgolides, and pentoxifylline

Impaired microcirculatory perfusion appears to be crucial to the pathogenesis of both neuropathy and retinopathy in diabetics. This in turn reflects a hyperglycemically mediated perturbation of vascular endothelial function that entails overactivation of protein kinase C, reduced availability of nitric oxide, increased production of superoxide and endothelin, impaired insulin function, diminished synthesis of prostacyclin/PGE1, and increased activation and endothelial adherence of leukocytes. These dysfunctions may be addressed with a supplementation program that includes high-dose antioxidants, fish oil, gamma-linolenic acid, chromium, arginine, carnitine, and ginkgolides. Pharmaceuticals likely to be of benefit in this regard include pentoxifylline, probucol, replacement estrogens, and inhibitors of angiotensin converting enzyme and aldose reductase.

Metabolism of arachidonic acid by canine polymorphonuclear leukocytes synthesis of lipoxygenase and omega-oxidized metabolites

Both polymorphonuclear (PMN) leukocytes and metabolites of arachidonic acid, especially lipoxygenase products, have been reported to contribute to myocardial damage after coronary artery occlusion and reperfusion. While canine models of myocardial ischemia were used in many of these studies, very little is known about arachidonic acid metabolism by canine PMNs. Moreover, it is unclear whether arachidonic acid metabolites released by canine PMNs affect vascular tone. Therefore, we characterized arachidonic acid metabolism by canine PMNs and determined the effect of these metabolites on vascular tone of isolated canine coronary arteries. Suspensions of canine PMNs were incubated with [14C]arachidonic acid and the calcium ionophore A23187. The incubation media was extracted, and the metabolites resolved by HPLC. 20-Hydroxy-leukotriene B4 (LTB4), 12,20-dihydroxyeicosatetraenoic acid (diHETE), LTB4, 12-hydroxyheptadeclatrienoic acid (HHT), and 12-(S)-hydroxyeicosatetraenoic acid (HETE) were isolated, and their structures confirmed by gas chromatography/mass spectrometry. There was also evidence for the formation of 20-HETE, thromboxane B2 (TXB2), 5-HETE, and several isomers of LTB4. None of the arachidonic acid metabolites that were isolated from incubates of canine PMNs augmented vascular tone, but material migrating with 12,20-diHETE relaxed canine coronary arteries. Authentic 12(S),20-diHETE also produced a concentration-related relaxation of canine coronary artery. 12(R), 20-diHETE was inactive. 20-HETE inhibited A23187-induced PMN aggregation. Thus, arachidonic acid is metabolized in canine PMNs through the cyclooxygenase, lipoxygenases and cytochrome P-450 pathways. Whether these metabolites contribute to myocardial injury remains to be determined.

Neutrophils and myocardial reperfusion injury

Ischaemia induces an acute inflammatory response in myocardial tissue with an early phase of neutrophil accumulation, which is accelerated by reperfusion. In experimental models, interventions that deplete neutrophils or inhibit their function cause a significant reduction in myocardial infarct size. These cells, therefore, may exacerbate tissue injury through the release of free radicals and proteolytic enzymes. Neutrophil recruitment depends on the presence of inflammatory mediators. Leukotriene B4, interleukin 8 and the complement fragment C5a have been implicated in this process. Studies using antibodies to the selectin, integrin and immunoglobulin superfamily adhesion molecules indicate that they also have a crucial role in myocardial neutrophil recruitment.

Inhibition of Na+/H+ exchanger attenuates neutrophil-mediated reperfusion injury

BACKGROUND

The effect of Na+/H+ exchange inhibition in neutrophil-induced reperfusion injury was investigated using a new amiloride analogue, 5-methyl-N-isobutyl amiloride (MIA).

METHODS

Rat neutrophils were separated using Percoll gradient. Luminol chemiluminescence intensity of isolated neutrophils was depressed by MIA in a dose-dependent manner.

RESULTS

The effect of MIA on neutrophil-induced reperfusion injury was evaluated in Langendorff-perfused rat hearts subjected to 30 minutes of normothermic ischemia. Postischemic left ventricular developed pressure recovery was depressed by the reperfusion with neutrophils (60% +/- 7% to 33% +/- 26%) and was reverted by MIA pretreatment (86% +/- 17%, p < 0.05). MIA also improved percent recovery of coronary flow (51% +/- 2% to 70% +/- 13%), reduced creatine kinase (0.28 +/- 0.1 to 0.085 +/- 0.03 IU.L-1.g-1 dry wt), and lactate dehydrogenase leakage (10.6 +/- 3.8 to 5.16 +/- 1.3 IU.L-1.g-1 dry wt) significantly. The incidence of reperfusion-induced ventricular fibrillation also was reduced by MIA.

CONCLUSIONS

The inhibition of Na+/H+ exchange shows a protective effect against neutrophil-induced reperfusion injury possibly by inhibiting the activation of neutrophils.

Role of neutrophils in myocardial ischemia and reperfusion

In the intact organism, ischemic myocardial injury initiates an acute inflammatory response in which polymorphonuclear leukocytes (PMNs) are major participants. Evidence indicates that the interplaying inflammatory reactions are augmented by reperfusion and that accumulating PMNs can contribute to myocardial damage, eg, by release of oxygen-derived free radicals, proteases, and leukotrienes. In experimental models, interventions aimed at PMN inhibition can exert cardioprotective effects, and some of these strategies raise hope for future clinical applications. A greater understanding of the mechanisms involved in PMN-mediated myocardial damage is necessary for designing a rational approach to reduce the putative detrimental effects of PMNs without antagonizing their favorable consequences in tissue healing.

Ticlopidine augments luminol-dependent chemiluminescence in human neutrophils

Neutrophils contribute to the pathophysiology of various ischaemic states. Since many agents thought to be antiplatelet have also been shown to affect neutrophil function, it was of interest to examine the effect of ticlopidine (250 mg, p.o., b.i.d. for three doses), an antiplatelet agent, on fMLP (formyl-methionyl-leucyl-phenylalanine) stimulated neutrophil aggregation and luminol-dependent chemiluminescence in whole blood. Neutrophil aggregation did not significantly change from baseline values during ticlopidine administration. However, luminol-dependent chemiluminescence, an index of respiratory burst metabolism, was noted to be markedly increased during ticlopidine administration. Two hours following the final dose of ticlopidine, the chemiluminescent response (mean +/- SEM, n = 5) was significantly increased from 6.27 +/- 1.88 to 12.66 +/- 2.19 units (p < 0.05). A return to baseline (6.68 +/- 2.24 units) five days following the administration of ticlopidine was noted. It is concluded from this study that the acute oral administration of ticlopidine may affect neutrophil function as demonstrated by the significant increase in stimulated luminol-dependent chemiluminescence.

Protective effect of monoclonal antibodies against LFA-1 and ICAM-1 on myocardial reperfusion injury following global ischemia in rat hearts

The effects of anti-LFA-1 and anti-ICAM-1 monoclonal antibodies (MAbs) on the reperfusion injury of rat cardiac tissues after global ischemia were studied. Studies were performed using an isolated blood perfused heart preparation in which hearts were subjected to 30 min of global ischemia followed by 40 min of reperfusion. Isolated rat hearts were perfused with blood from an anesthetized support rat with or without anti-LFA-1 or anti-ICAM-1 monoclonal antibody administration (n = 10 in each group). Ventricular function, myocardial tissue water content and myocardial energy status were evaluated in this model. In the control group, ischemia and reperfusion of isolated hearts resulted in a 63.6 +/- 2.7% recovery of left ventricular developed pressure (LVDP) and a 44 +/- 7% increase in coronary vascular resistance compared with pre-ischemic baseline values. Treatment with anti-LFA-1 MAb or anti-ICAM-1 MAb resulted in a 77.2 +/- 1.5% and a 80.4 +/- 3.0% recovery of LVDP, respectively. In addition, increase in coronary vascular resistance was only 23 +/- 7% and 13 +/- 6% in anti-LFA-1 and anti-ICAM-1-treated groups, respectively. Values are significantly different between the control group and MAb-treated groups. Ischemia and reperfusion resulted in a 16% increase of myocardial tissue water content (3.71 +/- 0.03 in pre-ischemic baseline versus 4.29 +/- 0.08 ml/g dry weight) in the control group, whereas that resulted in only 3.0 and 5.7% increase in anti-LFA and anti-ICAM-1-treated groups, respectively. The difference between the control group and MAb-treated groups was significant. Cardiac energy status as assessed by adenosine triphosphate (ATP) concentration was markedly reduced in the control group at 40 min of reperfusion compared with pre-ischemic baseline values (5.70 +/- 0.27 vs. 14.92 +/- 0.48 mumol/g dry weight). In contrast, the reduction of myocardial ATP concentration at 40 min of reperfusion was significantly inhibited by anti-LFA-1 and anti-ICAM-1 monoclonal antibody treatment (5.70 +/- 0.27 vs. 8.96 +/- 0.52 and 8.10 +/- 0.47 mumol/g dry weight, respectively). These results suggest that a LFA-1/ICAM-1 pathway plays a critical role in the pathogenesis of postischemic myocardial injury during early reperfusion period.

Induction of manganese superoxide dismutase in rat cardiac myocytes increases tolerance to hypoxia 24 hours after preconditioning

Manganese superoxide dismutase (Mn-SOD) is induced in ischemic hearts 24 h after ischemic preconditioning, when tolerance to ischemia is acquired. We examined the relationship between Mn-SOD induction and the protective effect of preconditioning using cultured rat cardiac myocytes. Exposure of cardiac myocytes to brief hypoxia (1 h) decreased creatine kinase release induced by sustained hypoxia (3 h) that follows when the sustained hypoxia was applied 24 h after hypoxic preconditioning (57% of that in cells without preconditioning). The activity and content of Mn-SOD in cardiac myocytes were increased 24 h after hypoxic preconditioning (activity, 170%; content, 139% compared with cells without preconditioning) coincidentally with the acquisition of tolerance to hypoxia. Mn-SOD mRNA was also increased 20-40 min after preconditioning. Antisense oligodeoxyribonucleotides corresponding to the initiation site of Mn-SOD translation inhibited the increases in the Mn-SOD content and activity and abolished the expected decrease in creatine kinase release induced by sustained hypoxia after 24 h of hypoxic preconditioning. Sense oligodeoxyribonucleotides did not abolish either Mn-SOD induction or tolerance to hypoxia. These results suggest that the induction of Mn-SOD in myocytes by preconditioning plays a pivotal role in the acquisition of tolerance to ischemia at a later phase (24 h) of ischemic preconditioning.

Role of cell adhesion molecules in brain injury after transient middle cerebral artery occlusion in the rat

Activated neutrophils appear to be directly involved in tissue injury after focal cerebral ischemia and reperfusion. Intercellular adhesion molecules-1 (ICAM-1) and CD11/CD18 integrins have been implicated in ischemia-reperfusion induced neutrophil endothelial adhesion and transmigration. We therefore investigated the roles of CD11a/CD18 (LFA-1) and ICAM-1 in cerebral ischemia-reperfusion injury by using monoclonal antibodies, WT1 (anti-CD11a), WT3 (anti-CD18), and 1A29 (anti-ICAM-1). Rats were subjected to 1 h of middle cerebral artery occlusion (MCAO). Individual antibodies were administered at a dose of 5 mg/kg intraperitoneally at 15 min before ischemia and immediately after reperfusion. Rats were killed at 24 h after reperfusion, and brain edema, neutrophil infiltration and infarct size were measured. Sustained enhancement of ICAM-1 expression on capillaries was observed up to 24 h (beginning between 1 and 3 h after reperfusion). While, leukocytes began to infiltrate into the ischemic hemisphere between 6 and 12 h after reperfusion. Treatment with individual antibodies against cell adhesion molecules reduced edema formation and infarct size in addition to neutrophil accumulation 24 h after reperfusion. These results strongly implicate the invasion of neutrophils in the development of post-ischemic brain injury, and suggest that interactions between CD11a/CD18 and ICAM-1 contribute to neutrophil infiltration into the ischemic brain.

Effect of duration of ischaemia on reduction of myocardial infarct size by inhibition of neutrophil accumulation using an anti-CD18 monoclonal antibody

1. Neutrophil accumulation is a characteristic feature of the inflammatory response in myocardial tissue which has undergone a period of ischaemia. The aim of this study was to examine whether inhibition of myocardial neutrophil infiltration, using an antibody to the CD18 leukocyte adhesion molecule, was effective in reducing infarct size in anaesthetized rabbits. 2. Anaesthetized rabbits underwent coronary artery occlusion (CAO) for periods of 30 or 45 min followed by reperfusion for 3 h. Animals were treated intravenously 10 min prior to reperfusion with IB4, a monoclonal antibody to CD18 (1 mg kg-1) or saline (1 ml kg-1). In one group undergoing 45 min CAO, a control antibody, OKMI (1 mg kg-1) was given. 3. Following either 30 or 45 min of CAO, administration of IB4 resulted in a < 75% inhibition in neutrophil accumulation in the area at risk myocardium (AR) compared with control animals. 4. With the 30 min occlusion period, IB4 significantly reduced myocardial infarct size, 27.2 +/- 3.2% vs 67.4 +/- 5.6% in the saline control group (n = 5 P < 0.01). In contrast, IB4 did not reduce infarct size following a 45 min period of ischaemia. 5. In the same animals administration of IB4 significantly inhibited oedema formation in skin elicited by intradermal administration of the neutrophil chemoattractant f-Met-Leu-Phe, but had no effect on coronary microvascular plasma protein leakage in the AR. 6. Our results indicate that infiltrating neutrophils exacerbate tissue injury following a relatively short, 30 min period of myocardial ischaemia in the rabbit. However, protection with IB4 was no longer seen if the period of CAO was extended to 45 min. The results in this model suggest neutrophils are not a major determinant of tissue injury following more than a very short period of ischaemia.

Endothelial serpins--protectors of the vasculature?

Vascular damage, initiated by host inflammatory cells, is a component of the pathophysiology of many acute and chronic inflammatory disorders. Neutrophil-mediated tissue damage is mediated primarily by proteinases, particularly elastase and cathepsin G. In this study we have identified endothelial binding of two key serine proteinase inhibitors (serpins), alpha 1-antitrypsin, the inhibitor of elastase, and alpha 1-antichymotrypsin, the inhibitor of cathepsin G. These serpins are shed from the endothelium into the supernatant when neutrophils adherent to the endothelium are activated. Endothelium activated by lipopolysaccharide (LPS) augments this process. Serpin-proteinase complexes activate neutrophils and induce further cytokine release, thereby amplifying inflammatory processes. Strategies aimed at preventing endothelial serpin depletion may help minimize vascular damage during inflammation.

Tumor necrosis factor-alpha as a myocardial depressant substance

Most patient with sepsis and septic shock develop significant derangements of myocardial function. The presence of a circulating myocardial depressant substance (MDS) has been suggested to be the major cause of myocardial depression in sepsis and septic shock. MDS is still not fully characterized by chemical means, and there is no consensus regarding its identity. Nevertheless, high levels of MDS activity can be found in sera from patients with sepsis and septic shock. Furthermore, MDS has been shown to have a number of specific characteristics. These characteristics have also been described with tumor necrosis factor-alpha (TNF), a cytokine that is well recognized to be a primary mediator in the pathogenesis of infection, tissue injury, inflammation and shock. In this review it is suggested that TNF is an MDS, and that the cardiovascular injury and myocardial depression during sepsis and septic shock involve a final common pathway, where TNF may have an important role in this common pathway.

Limitation of myocardial infarct size in pigs with a dual lipoxygenase-cyclooxygenase blocking agent by inhibition of neutrophil activity without reduction of neutrophil migration

OBJECTIVES

The purpose of this study was to assess the effect of the dual cyclooxygenase-lipoxygenase blocking agent BW755C on the extent of myocardial infarction in the pig and to identify the mechanisms of any cardioprotective action of this drug.

BACKGROUND

Activated neutrophils contribute to reperfusion injury after myocardial infarction and inhibition of neutrophil function can limit infarct size.

METHODS

In 9 control and 10 study pigs pretreated with intravenous BW755C (10 mg/kg body weight) 30 min before coronary occlusion, ischemia was induced by a 50-min occlusion of the mid-left anterior descending coronary artery, followed by 3 h of reperfusion. Heart rate, arterial pressure, left ventricular end-diastolic pressure, the first derivative of left ventricular pressure (dP/dt) and regional myocardial blood flow were measured during control, occlusion and reperfusion periods. Infarct size was determined by histochemical staining; and myeloperoxidase activity, a marker for tissue neutrophil content, was assessed in normal and infarcted myocardium. The effect of BW755C on the function of isolated neutrophils stimulated with zymosan-activated serum was evaluated by measuring neutrophil degranulation, leukotriene B4 production, superoxide generation and chemotaxis.

RESULTS

Hemodynamic function and regional myocardial blood flow were similar in control and BW755C-treated animals. BW755C significantly reduced myocardial infarct size compared with that in control animals, as measured by infarct/risk areas by histochemical staining (39 +/- 5% vs. 63 +/- 7%, p < 0.05). Myocardial myeloperoxidase activity was similar in normal, salvaged and infarcted areas in the control and treated groups, indicating that neutrophil accumulation in injured myocardium was unaltered by BW755C. However, this agent attenuated function of isolated, stimulated (zymosan-activated serum) neutrophils. At a concentration of 0.03 mg/ml, BW755C inhibited degranulation (-46%), leukotriene B4 production (-48%) and superoxide generation (-74%), but there was minimal inhibition of chemotaxis in vitro.

CONCLUSIONS

These findings demonstrate that myocardial infarct size can be reduced by selective inhibition of neutrophil cytotoxic activity without affecting neutrophil migration into injured myocardium.

Transient rise in serum interleukin-8 concentration during acute myocardial infarction

OBJECTIVE

To determine whether interleukin-8 (IL-8, a potent activator of neutrophils) is involved in tissue injury during ischaemia and reperfusion in patients with acute myocardial infarction.

SETTING

Teaching hospital.

SUBJECTS

Five consecutive patients with acute Q-wave myocardial infarction, two patients with stable angina who underwent elective percutaneous transluminal coronary angioplasty, and 10 normal controls.

MAIN OUTCOME MEASURE

Serum IL-8 concentration measured by enzyme linked immunosorbent assay (ELISA) over time (every four, eight or 12 hours for 36-72 hours).

RESULTS

All five patients with acute myocardial infarction had a transient but significant rise in serum IL-8 concentration (13-1100 ng/l) within 22 hours after the onset of symptoms, whereas IL-8 was not detected in any of the samples from patients with angina pectoris or normal controls. One patient who died of pump failure and two patients who had mild congestive heart failure showed the highest values (1100, 920, and 190 ng/l respectively).

CONCLUSIONS

Serum IL-8 concentration showed a transient rise during the very early phase of acute myocardial infarction. In combination with several recent lines of evidence indicating the importance of injurious activities of neutrophils as a cause of tissue damage in acute myocardial infarction and the potent stimulation of neutrophils by IL-8, these results strongly suggest that IL-8 is important in the development of myocardial injury in acute myocardial infarction.

Inhibition of lipoxygenase and cyclooxygenase augments cardiac injury by H2O2

The role of arachidonic acid metabolites in the cardiac effects of toxic oxygen metabolites (TOM) was investigated in buffer-perfused rat hearts (Langendorff model). Hydrogen peroxide (H2O2, 200 microM) was given for 10 min to generate TOM, followed by 30 min recovery. H2O2 reduced left ventricular developed pressure (LVDP), increased left ventricular end-diastolic pressure (LVEDP), and increased coronary flow (CF). The hydroxyl radical scavenger thiourea inhibited the H2O2-induced effects. Perfusion with three lipoxygenase inhibitors, AA861, BWA4C, and diethylcarbamazine, in addition to H2O2, augmented the decrease of LVDP and the increase of LVEDP induced by H2O2. The cyclooxygenase inhibitor indomethacin had the same effects. The H2O2-induced increase in CF was not influenced by diethylcarbamazine, but inhibited by all other drugs. Control perfusion with drugs alone did not influence cardiac function. In conclusion, inhibition of lipoxygenase and cyclooxygenase augmented the depression of cardiac function induced by TOM. Leukotrienes and prostanoids appear to be protective against H2O2-induced cardiac injury.

Postischemic dysfunction of the heart induced by small numbers of neutrophils via formation of hypochlorous acid

The role of polymorphonuclear neutrophils (PMN) in the injury of the heart following ischemia and reperfusion is still controversial. The aim of this study was to investigate whether small numbers of PMN may cause myocardial dysfunction in an isolated system, how the resulting loss of function can be characterized and whether the formation of hypochlorous acid (HOCl) can be responsible for the PMN-mediated effect. Isolated working guinea pig hearts were subjected to a 90% reduction of coronary flow for 30 min, with or without intracoronary infusion of homologous PMN (approximately 1-2 x 10(5) cells/min, i.e. about 5-10% of normal blood count). This ischemia was followed by a 15 min reflow period in a non-working ("Langendorff") mode before work was resumed. In hearts perfused only with buffer, post-hypoxic heart function recovered to 75-80% of the initial value. Inclusion of unstimulated PMN did not further attenuate cardiac function. However, cardiac output was decreased to 42% of the initial value, provided thrombin (0.3 U/ml) and H2O2 (10(-5) M) were also present, and the retained PMN (about 10% of those infused) were additionally stimulated during reflow by application of FMLP (10(-6) M for 1 min). In these instances, coronary flow at any time of the experiment and release of lactate or purines during ischemia and reflow did not differ significantly between hearts perfused with or without PMN. There was no substantial release of myoglobin in controls and in PMN-treated hearts. Inotropic stimulation of the hearts with noradrenaline or exogenous Ca2+ caused a sustained increase in contractile force. However, the response was significantly reduced in PMN-perfused hearts in comparison to control hearts. The myocardial contents of high-energy phosphates with and without inotropic stimulation proved to be identical irrespective of whether experiments had been performed in the absence or presence of PMN. A similar loss of myocardial function as mediated by PMN could be produced by infusing chemically generated hypochlorous acid (HOCl, 5 x 10(-7) M for 10 min). Strikingly, that portion of the infused HOCl which actually reacted with cardiac tissue was comparable to the amount shown to be generated by stimulating 10(6) PMN retained in the coronary system (about 7 nmoles). Supplementing the perfusate with the scavengers L-methionine (10(-4) M) or uric acid (5 x 10(-4) M) prevented the attenuation of heart function provoked by PMN. The results indicate that small numbers of PMN, sufficiently activated, can depress cardiac function after 30 min of ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Collagen-induced rat platelet reactivity is enhanced in whole blood in both the presence and absence of dense granule secretion

Collagen induced aggregation, ATP secretion and thromboxane (TxB2) generation of storage pool deficient platelets were compared to normal platelets of closely related rat strains. Platelet function was monitored in citrated-platelet-rich-plasma (PRP) and citrated whole blood. Wistar (W) and fawn-hooded (FH) rat strains and their F2 hybrids were utilized. The W strain, which is ancestral to the FH strain, is not storage pool deficient while the FH strain is. This was manifested by the total lack of collagen induced ATP secretion from platelets of the FH strain while the platelets of the W strain secreted normally. Utilizing platelets from the F2 generation of WxFH matings, the absence of dense granule secretion (ATP) from the FH platelets, as well as other platelet defects of FH rats, were shown to be associated with homozygosity for the red-eyed dilution gene [r]. The non-secreting FH platelets were utilized to determine the effects of secreted dense granule constituents upon collagen induced aggregation and TxB2 generation. The non-secreting storage pool deficient platelets did aggregate and did generate TxB2 upon stimulation with collagen; however, the storage pool deficient FH platelets demonstrated less TxB2 generation and did not aggregate as effectively as the normally secreting platelets of the W strain. When evaluating collagen induced platelet function in whole blood as compared to PRP, the storage pool deficient platelets remained less reactive than normally secreting platelets, but both platelet types demonstrated enhanced aggregation and increased TxB2 generation in whole blood.

The effect of the 21-aminosteroid U74006F in a rabbit model of thromboembolic stroke

U74006F, a novel 21-aminosteroid, is an inhibitor of iron-dependent lipid peroxidation that is devoid of glucocorticoid and mineralocorticoid side effects. The efficacy of U74006F in reducing cerebral infarct size was investigated in a rabbit model of thromboembolic stroke. Each animal received either U74006F (3.0 mg/kg immediately before and 2 hr after embolization, n = 8) or vehicle control (n = 10). Hematocrit, mean arterial pressure, PCO2, PO2, and pH were measured and controlled both before and after the administration of an autologous clot into one internal carotid artery. Regional cerebral blood flow (in ml/100 g/min, mean +/- SEM) measured by hydrogen clearance was similar in both groups, being reduced from 68.2 +/- 9.6 to 5.2 +/- 1.9 in the control group immediately after clot embolization and from 73.3 +/- 14.9 to 7.0 +/- 1.7 in the U74006F group. Four hours after embolization the brain was harvested and cerebral infarct size was determined using the triphenyl-tetrazolium chloride technique (% hemisphere, mean +/- SEM). In the U74006F-treated group, the infarct size was significantly reduced (P < 0.05) to 14.8 +/- 6.4 from a control value of 36.0 +/- 6.4. Additionally, cerebral blood flow values after embolization were consistently higher in the U74006F group, although the differences were not statistically significant. This data suggests that the 21-aminosteroid U74006F may have a protective effect in cerebral ischemia.

Activated neutrophils aggravate endothelial dysfunction after reperfusion of the ischemic feline myocardium

Endothelial dysfunction, as evidenced by decreased stimulated release of endothelium-derived relaxing factor (EDRF), occurs after reperfusion of the ischemic myocardium. To better understand this endothelial dysfunction, isolated cat hearts were perfused under constant flow by the Langendorff procedure with Krebs-Henseleit solution devoid of blood cells. Following global ischemia (90 minutes) and reperfusion (20 minutes), coronary vasorelaxation to the endothelium-dependent vasodilator acetylcholine (ACh) was 70 +/- 3% of initial values (p less than 0.01) compared with 90 +/- 4% in nonischemic control perfused hearts. No decrement occurred in response to the endothelium-independent vasodilator nitroglycerin (NTG). Coronary artery rings isolated from the ischemic left circumflex coronary artery showed a similar degree of endothelial dysfunction to ACh, with normal relaxation in response to NaNO2. Autologous cat neutrophils (100 million cells), activated with 100 nmol/L f-met-leu-phe infused into the heart directly before and throughout reperfusion, resulted in a further decrement in ACh-induced vasodilation, to 55 +/- 5% of initial response, with no effect on NTG-induced vasodilation. Similar results were obtained with coronary artery rings isolated from perfused cat hearts and exposed to neutrophils. This neutrophil-enhanced endothelial dysfunction was inhibited by human superoxide dismutase as well as by an antibody to the adherence glycoprotein complex CD-18 (i.e., MAbR 15.7). Therefore endothelial dysfunction occurs initially upon reperfusion of the previously ischemic heart and is aggravated by superoxide radicals produced by activated neutrophils.

Role of resident macrophages in canatoxin-induced in vivo neutrophil migration

Canatoxin (Cntx), a toxic protein purified from Canavalia ensiformis seeds, was shown to have lipoxygenase-mediated effects either in vivo or in vitro. Data here show that Cntx induced a dose-dependent migration of neutrophils and mononuclear cells when injected into rat peritoneal cavities. Furthermore, Cntx was able to induce neutrophil migration into pleural cavities and into air pouches. These effects were inhibited by dexamethasone but not by inhibitors of arachidonic acid metabolism (indomethacin, NDGA, and BW-755c) or by a PAF antagonist (BN 52021). In the peritoneal cavity Cntx caused an increase in vascular permeability inhibited by dexamethasone and BW-755c. Neutrophil migration induced by this toxin was dependent on the number of resident macrophages, since the migratory effect was enhanced by increasing the peritoneal macrophage population with thioglycollate pretreatment and was diminished when this population was reduced by peritoneal wash. It was also observed that Cntx induced release of a chemotactic factor from macrophage monolayers in vitro. Dexamethasone blocked this release but did not affect in vivo neutrophil recruitment induced by that factor. These data suggest that Cntx-induced neutrophil migration may be mediated by the same macrophage-derived neutrophil chemotactic factor released by other stimuli such as LPS, IL-1, and INF-gamma.

Antibody to CD-18 exerts endothelial and cardiac protective effects in myocardial ischemia and reperfusion

We studied the effects of MAbR15.7, an antibody directed against the common beta-chain (CD-18) of a family of neutrophil adherence glycoproteins, on endothelial dysfunction and myocardial injury in a model of myocardial ischemia and reperfusion in cats. Pentobarbital-anesthetized cats were subjected to 1.5 h occlusion of the left anterior descending coronary artery (LAD) and 4.5 h of reperfusion. MI + R resulted in severe myocardial injury and endothelial dysfunction, including significant elevation of plasma creatine kinase (CK) activity, marked myocardial necrosis, high cardiac myeloperoxidase (MPO) activity in ischemic cardiac tissue, and loss of response of LAD coronary rings to the endothelium-dependent vasodilators, acetylcholine (ACh) and A-23187. In contrast, MAbR15.7-treated cats exhibited a lower plasma CK activity at every time point observed after 2 h, a reduced area of cardiac necrosis (2 +/- 1 vs. 30.8 +/- 2.5% of area-at-risk, P less than 0.001), lower MPO activity in the ischemic region (P less than 0.01), and significantly preserved vasorelaxant responses of LAD coronary rings to endothelium-dependent vasodilators, ACh (P less than 0.001), and A-23187 (P less than 0.001). These results indicate that myocardial ischemia and reperfusion induces significant myocardial injury and endothelial dysfunction in the cat involving a CD18-dependent neutrophil adherence mechanism. Inhibition of neutrophil adherence to the endothelium exerts significant protective effects in this model of reperfusion injury.

Do neutrophils contribute to myocardial stunning?

Although removal of neutrophils from the arterial blood by mechanical filtration has been reported to prevent or reduce the severity of myocardial stunning caused by a 15 minute coronary artery occlusion in the dog, neutrophil filtration does not protect against myocardial dysfunction following a 10-minute occlusion. Nonfilter methods to reduce neutrophil numbers or effectiveness with anti-neutrophil serum, monoclonal anti-CD11b antibodies, or the lipoxygenase inhibitor nafazatrom fail to modify myocardial dysfunction after brief ischemia, even though they effectively reduce infarct size after more prolonged ischemia. The brief durations of ischemia required to produce myocardial stunning but to avoid necrosis are insufficient to produce local activation of complement, formation of chemotactic factors, or activation or infiltration of neutrophils. Microvascular plugging with neutrophils cannot be demonstrated in stunned myocardium, and abnormalities of microvascular function can be dissociated from impaired postischemic myocardial function. Based on the weight of accumulated evidence, neutrophils appear to have no important role in the production of stunned myocardium.

Factor XIII of blood coagulation inhibits the oxidative phagocyte metabolism and suppresses the immune response in vivo

Factor XIII of blood coagulation (F XIII) belongs to the family of transglutaminases and is a major cell product of certain subsets of macrophages. The gene for F XIIIA is coupled to the immune response genes of the HLA-region on chromosome 6. F XIII dose- dependently inhibits the in vitro chemiluminescence response of human phagocytes. About 0.1 units of F XIII/ml (final) decreased the chemiluminescence response to about 50%. In addition, about 0.6 units of F XIII/ml inhibits 50% of the release of the lysosomal hydrolase N-acetyl-beta glucosaminidase in both immune complex stimulated and unstimulated monocytes. Intraperitoneal application of F XIII reduced the activity of phagocytes in a F XIII dose dependent manner. 0.25 units of F XIII reduced the chemiluminescence reaction of murine peritoneal M phi to about 50% of the activity of PBS treated animals after 2 or 24 hours of in vivo incubation. In the Fisher/Lewis rats skin transplantation model, injections of 5 units of F XIII/animal on days 1-7 or on days 10-17 increased the survival times of the transplants from the control value of 17.0 +/- 1.4 to 26.0 +/- 2.0 and 23.0 +/- 2.4 days, respectively. F XIII may represent a novel and physiological immune suppressive agent for a broad range of human diseases of autoimmune character.

Polymorphonuclear leukocyte infiltration into cerebral focal ischemic tissue: myeloperoxidase activity assay and histologic verification

Two different techniques were utilized to identify the infiltration of polymorphonuclear leukocytes (PMN) into cerebral tissue following focal ischemia: histologic analysis and a modified myeloperoxidase (MPO) activity assay. Twenty-four hours after producing permanent cortical ischemia by occluding and severing the middle cerebral artery of male spontaneously hypertensive rats, contralateral hemiparalysis and sensory-motor deficits were observed due to cerebral infarction of the frontal and parietal cortex. In hematoxylin-and-eosin-stained histologic sections, PMN, predominantly neutrophils, were identified at various stages of diapedesis from deep cerebral and meningeal vessels at the periphery of the infarct, into brain parenchyma. When MPO activity in normal brain tissue was studied initially, it could not be demonstrated in normal tissues extracted from non-washed homogenates. However, if tissue was homogenized in phosphate buffer (i.e., washed), MPO activity was expressed upon extraction. Utilizing this modified assay, MPO activity was significantly increased only in the infarcted cortex compared to other normal areas of the brain. This was observed in non-perfused animals and after perfusion with isotonic saline to remove blood constituents from the vasculature prior to brain removal. The increased PMN infiltration and MPO activity were not observed in forebrain tissue of sham-operated control rats. Also, MPO activity was not increased in the ischemic cortex of MCAO rats perfused immediately after middle cerebral artery occlusion, indicating that blood was not trapped in the ischemic area. By using a leukocyte histochemical staining assay, activity of peroxidases was identified within vascular-adhering/infiltrating PMN in the infarcted cortex 24 hr after focal ischemia. An evaluation of several blood components indicated that increased MPO activity was selective for PMN. The observed increase of approximately 0.3 U MPO/g wet weight ischemic tissue vs. nonischemic cerebral tissues probably reflects the increased vascular adherance/infiltration of approximately 600,000 PMN/g wet weight infarcted cortex 24 hr after focal ischemia. This combined biochemical and histological study strongly suggests that PMN adhere within blood vessels and infiltrate into brain tissue injured by focal ischemia and that the associated inflammatory response might contribute to delayed progressive tissue damage in focal stroke. This modified MPO assay is a useful, quantitative index of PMN that can be utilized to elucidate the potential deleterious consequences of neutrophils infiltrating into the central nervous system after cerebral ischemia, trauma, or other pro-inflammatory stimuli.

Cardioprotective and endothelial protective effects of [Ala-IL8]77 in a rabbit model of myocardial ischaemia and reperfusion

1 We studied the effects of a form of interleukin-8 (i.e., [Ala-IL8]77) on endothelial dysfunction and myocardial injury in rabbits. Pentobarbitone-anaesthetized rabbits were subjected to 1.5 h occlusion of the marginal coronary artery and 3.5 h reperfusion. [Ala-IL8]77 (50 micrograms or its vehicle) was given i.v. as a bolus 10 min prior to reperfusion. [Ala-IL8]77 was also studied in isolated perfused hearts of rabbits. 2 Myocardial ischaemia plus reperfusion in untreated rabbits produced severe endothelial dysfunction and myocardial injury, including marked myocardial necrosis, elevated cardiac myeloperoxidase (MPO) activity in ischaemic cardiac tissue, and loss of response of marginal coronary rings to the endothelium-dependent vasodilators, acetylcholine (ACh) and A23187. 3 Administration of [Ala-IL8]77 10 min prior to reperfusion resulted in significant protective effects in post-ischaemic reperfusion. Compared with untreated rabbits, [Ala-IL8]77 caused a reduced necrotic zone (P less than 0.01), lower MPO activity in the necrotic zone (P less than 0.05), and significantly preserved vasorelaxant responses of marginal coronary artery rings to endothelium-dependent vasodilators, ACh (P less than 0.001) and A23187 (P less than 0.001). 4 These results indicate that myocardial ischaemia and reperfusion result in a severe endothelial dysfunction and myocardial injury which involved the interaction of neutrophils and endothelial cells. However, [Ala-IL8]77 did not appear to exert a direct endothelial protective effect in the absence of neutrophils in rabbit isolated perfused hearts. 5 Inhibition of neutrophil accumulation in the myocardium, perhaps by prevention of endothelial dysfunction resulting from [Ala-IL8]77, leads to significant protective effects in ischaemia and reperfusion in rabbits.

The role of neutrophils and platelets in a rabbit model of thromboembolic stroke

Cerebral ischemia is accompanied by many of the cardinal features of acute inflammation such as neutrophil and platelet activation and accumulation. We sought to determine whether circulating neutrophils or platelets contribute to brain injury in a rabbit model of thromboembolic stroke that includes a fixed duration of superimposed systemic hypotension. We randomized 18 rabbits to receive either antineutrophil antiserum (n = 6), antiplatelet antiserum (n = 5), or nonimmune serum (n = 7). We assessed brain ischemia by measuring cerebral blood flow, intracranial pressure, and infarct size. Following the intracarotid administration of an autologous clot, cerebral blood flow in all groups fell to less than 5 ml/100 g/min during induced hypotension. After restoration of baseline blood pressure, mean cerebral blood flow in neutropenic animals recovered to 20-30 ml/100 g/min while that in control and thrombocytopenic rabbits remained at less than 10 ml/100 g/min. Intracranial pressure in control animals rose steadily to a final value of 241% of baseline, while a much smaller increase (148% of baseline) was noted in the thrombocytopenic group; no change from baseline was evident in the neutropenic group. Infarct size was significantly (p less than 0.05) reduced in the neutropenic group but not in the thrombocytopenic group. These results suggest that neutrophils may be important contributors to ischemia-induced brain injury whereas the role of platelets is more subtle.

The triphasic pattern of skeletal muscle blood flow in reperfusion injury: an experimental model with implications for surgery on the acutely ischaemic lower limb

A new model of acute lower limb ischaemia has been developed in the rat hind limb. The model has been used to examine the influence on skeletal muscle blood flow of increasing periods of ischaemia and reperfusion. Following restoration of blood flow after 2-6h ischaemia initial gastrocnemius muscle blood flow was reduced. The severity of initial low reflow, indicated by mean perfusion ratios at 0 and 10 min, correlated with the duration of preceding ischaemia (r = 0.83, p less than 0.05) and was greatest in limbs subjected to 6h ischaemia (p less than 0.01 vs. controls at 0, 10 and 60 min after revascularisation). After 60-240 min, reperfusion muscle blood flow returned to normal in limbs subjected to 3, 4 or 5 h ischaemia. In contrast, peak muscle blood flow in limbs that had been ischaemic for 6 h occurred after 120 min, although perfusion remained less than that measured in control limbs (p less than 0.05:6 h ischaemia, 120 min vs. control)-(relative reperfusion). Limbs reperfused after 6 h ischaemia demonstrated a subsequent decline in muscle blood flow between 120 min and 240 min following revascularisation (p less than 0.05). In addition, muscle blood flow at 240 min was no different to that in a totally ischaemic limb (p less than 0.01 vs. controls; ns vs. ischaemic limb) thus representing reperfusion injury.

Reduction in infarct size by the phospholipase inhibitor quinacrine in dogs with coronary artery occlusion

It has been suggested that activation of tissue phospholipases may contribute to the development of ischemic cell injury. In the present study we sought to assess whether administration of the phospholipase inhibitor quinacrine would reduce the extent of myocardial necrosis after coronary artery occlusion. In open-chest, anesthetized dogs the left anterior descending coronary artery was ligated, and technetium-99-labeled albumin microspheres were injected into the left atrium to measure the area at risk. The animals were then randomly divided into a control group (n = 8) and a group receiving quinacrine (5 mg/kg intravenous bolus followed by a 40 micrograms/kg/min infusion for 6 hours; n = 9). The animals were killed 6 hours after occlusion, and the infarcted area was delineated by triphenyltetrazolium chloride staining. The extent of the risk region was similar in the two groups (32.3 +/- 2.1% of the left ventricle in control dogs and 34.2 +/- 3.4% in quinacrine-treated dogs). Infarct size was 86.4 +/- 8.8% of the risk region in control animals, whereas in treated dogs it averaged 62.3 +/- 6.4% of the risk region (p = 0.05). No differences were found in heart rate, arterial pressure, and rate-pressure product between the two groups. Thus administration of the phospholipase inhibitor quinacrine reduced the extent of myocardial necrosis in a model of fixed coronary artery occlusion. Preservation of membrane phospholipids, reduced formation of lipoxygenase metabolites, or both may mediate this phenomenon.

Platelet-activating factor and progressive brain damage following focal brain injury

The effects of a platelet-activating factor (PAF) antagonist on brain edema, cortical microcirculation, blood-brain barrier (BBB) disruption, and neuronal death following focal brain injury are reported. A neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was used to induce highly reproducible focal cortical lesions in anesthetized rats. Secondary brain damage in this model was characterized by progressive cortical hypoperfusion, edema, and BBB disruption in the vicinity of the hemispheroid lesion occurring acutely after injury. The histopathological evolution was followed for up to 4 days. Neuronal damage in the cortex and the hippocampus (CA-1) was assessed quantitatively, revealing secondary and progressive loss of neuronal tissue within the first 24 hours following injury. Pretreatment with the PAF antagonist BN 50739 ameliorated the severe hypoperfusion in 12 rats (increasing local cerebral blood flow from a mean +/- standard error of the mean of 40.5% +/- 8.3% to 80.2% +/- 7.8%, p less than 0.01) and reduced edema by 70% in 10 rats (p less than 0.05) acutely after injury. The PAF antagonist also reduced the progression of neuronal damage in the cortex and the CA-1 hippocampal neurons (decrease of neuronal death from 88.0% +/- 3.9% to 49.8% +/- 4.2% at 24 hours in the cortex and from 40.2 +/- 5.0% to 13.2% +/- 2.1% in the hippocampus in 30 rats; p less than 0.05). This study provides evidence to support progressive brain damage following focal brain injury, associated with secondary loss of neuronal cells. In this latter process, PAF antagonists may provide significant therapeutic protection in arresting secondary brain damage following cerebral ischemia and neurological trauma.