Role of leukocytes in coronary vascular endothelial injury due to ischemia and reperfusion

Reducing Cardiac Injury during ST-Elevation Myocardial Infarction: A Reasoned Approach to a Multitarget Therapeutic Strategy

The significant reduction in ‘ischemic time’ through capillary diffusion of primary percutaneous intervention (pPCI) has rendered myocardial-ischemia reperfusion injury (MIRI) prevention a major issue in order to improve the prognosis of ST elevation myocardial infarction (STEMI) patients. In fact, while the ischemic damage increases with the severity and the duration of blood flow reduction, reperfusion injury reaches its maximum with a moderate amount of ischemic injury. MIRI leads to the development of post-STEMI left ventricular remodeling (post-STEMI LVR), thereby increasing the risk of arrhythmias and heart failure. Single pharmacological and mechanical interventions have shown some benefits, but have not satisfactorily reduced mortality. Therefore, a multitarget therapeutic strategy is needed, but no univocal indications have come from the clinical trials performed so far. On the basis of the results of the consistent clinical studies analyzed in this review, we try to design a randomized clinical trial aimed at evaluating the effects of a reasoned multitarget therapeutic strategy on the prevention of post-STEMI LVR. In fact, we believe that the correct timing of pharmacological and mechanical intervention application, according to their specific ability to interfere with survival pathways, may significantly reduce the incidence of post-STEMI LVR and thus improve patient prognosis.

Innate Immune Cells and Hypertension: Neutrophils and Neutrophil Extracellular Traps (NETs)

Uncontrolled immune system activation amplifies end-organ injury in hypertension. Nonetheless, the exact mechanisms initiating this exacerbated inflammatory response, thereby contributing to further increases in blood pressure (BP), are still being revealed. While participation of lymphoid-derived immune cells has been well described in the hypertension literature, the mechanisms by which myeloid-derived innate immune cells contribute to T cell activation, and subsequent BP elevation, remains an active area of investigation. In this article, we critically analyze the literature to understand how monocytes, macrophages, dendritic cells, and polymorphonuclear leukocytes, including mast cells, eosinophils, basophils, and neutrophils, contribute to hypertension and hypertension-associated end-organ injury. The most abundant leukocytes, neutrophils, are indisputably increased in hypertension. However, it is unknown how (and why) they switch from critical first responders of the innate immune system, and homeostatic regulators of BP, to tissue-damaging, pro-hypertensive mediators. We propose that myeloperoxidase-derived pro-oxidants, neutrophil elastase, neutrophil extracellular traps (NETs), and interactions with other innate and adaptive immune cells are novel mechanisms that could contribute to the inflammatory cascade in hypertension. We further posit that the gut microbiota serves as a set point for neutropoiesis and their function. Finally, given that hypertension appears to be a key risk factor for morbidity and mortality in COVID-19 patients, we put forth evidence that neutrophils and NETs cause cardiovascular injury post-coronavirus infection, and thus may be proposed as an intriguing therapeutic target for high-risk individuals. © 2021 American Physiological Society. Compr Physiol 11:1575-1589, 2021.

The Rationale of Neprilysin Inhibition in Prevention of Myocardial Ischemia-Reperfusion Injury during ST-Elevation Myocardial Infarction

During the last three decades, timely myocardial reperfusion using either thrombolytic therapy or primary percutaneous intervention (pPCI) has allowed amazing improvements in outcomes with a more than halving in 1-year ST-elevation myocardial infarction (STEMI) mortality. However, mortality and left ventricle (LV) remodeling remain substantial in these patients. As such, novel therapeutic interventions are required to reduce myocardial infarction size, preserve LV systolic function, and improve survival in reperfused-STEMI patients. Myocardial ischemia-reperfusion injury (MIRI) prevention represents the main goal to reach in order to reduce STEMI mortality. There is currently no effective therapy for MIRI prevention in STEMI patients. A significant reason for the weak and inconsistent results obtained in this field may be the presence of multiple, partially redundant, mechanisms of cell death during ischemia-reperfusion, whose relative importance may depend on the conditions. Therefore, it is always more recognized that it is important to consider a "multi-targeted cardioprotective therapy", defined as an additive or synergistic cardioprotective agents or interventions directed to distinct targets with different timing of application (before, during, or after pPCI). Given that some neprilysin (NEP) substrates (natriuretic peptides, angiotensin II, bradykinin, apelins, substance P, and adrenomedullin) exert a cardioprotective effect against ischemia-reperfusion injury, it is conceivable that antagonism of proteolytic activity by this enzyme may be considered in a multi-targeted strategy for MIRI prevention. In this review, by starting from main pathophysiological mechanisms promoting MIRI, we discuss cardioprotective effects of NEP substrates and the potential benefit of NEP pharmacological inhibition in MIRI prevention.

Myocardial ischaemia-reperfusion injury and cardioprotection in perspective

Despite the increasing use and success of interventional coronary reperfusion strategies, morbidity and mortality from acute myocardial infarction are still substantial. Myocardial infarct size is a major determinant of prognosis in these patients. Therefore, cardioprotective strategies aim to reduce infarct size. However, a perplexing gap exists between the many preclinical studies reporting infarct size reduction with mechanical and pharmacological interventions and the poor translation into better clinical outcomes in patients. This Review revisits the pathophysiology of myocardial ischaemia-reperfusion injury, including the role of autophagy and forms of cell death such as necrosis, apoptosis, necroptosis and pyroptosis. Other cellular compartments in addition to cardiomyocytes are addressed, notably the coronary microcirculation. Preclinical and clinical research developments in mechanical and pharmacological approaches to induce cardioprotection, and their signal transduction pathways, are discussed. Additive cardioprotective interventions are advocated. For clinical translation into treatments for patients with acute myocardial infarction, who typically are of advanced age, have comorbidities and are receiving several medications, not only infarct size reduction but also attenuation of coronary microvascular obstruction, as well as longer-term targets including infarct repair and reverse remodelling, must be considered to improve patient outcomes. Future clinical trials must focus on patients who really need adjunct cardioprotection, that is, those with severe haemodynamic alterations.

Chymase released from hypoxia-activated cardiac mast cells cleaves human apoA-I at Tyr192 and compromises its cardioprotective activity

ApoA-I, the main structural and functional protein of HDL particles, is cardioprotective, but also highly sensitive to proteolytic cleavage. Here, we investigated the effect of cardiac mast cell activation and ensuing chymase secretion on apoA-I degradation using isolated rat hearts in the Langendorff perfusion system. Cardiac mast cells were activated by injection of compound 48/80 into the coronary circulation or by low-flow myocardial ischemia, after which lipid-free apoA-I was injected and collected in the coronary effluent for cleavage analysis. Mast cell activation by 48/80 resulted in apoA-I cleavage at sites Tyr¹⁹² and Phe²²⁹, but hypoxic activation at Tyr¹⁹² only. In vitro, the proteolytic end-product of apoA-I with either rat or human chymase was the Tyr¹⁹²-truncated fragment. This fragment, when compared with intact apoA-I, showed reduced ability to promote migration of cultured human coronary artery endothelial cells in a wound-healing assay. We propose that C-terminal truncation of apoA-I by chymase released from cardiac mast cells during ischemia impairs the ability of apoA-I to heal damaged endothelium in the ischemic myocardium.

The pathophysiology of acute myocardial infarction and strategies of protection beyond reperfusion: a continual challenge

The incidence of ST segment elevation myocardial infarction (STEMI) has decreased over the last two decades in developed countries, but mortality from STEMI despite widespread access to reperfusion therapy is still substantial as is the development of heart failure, particularly among an expanding older population. In developing countries, the incidence of STEMI is increasing and interventional reperfusion is often not available. We here review the pathophysiology of acute myocardial infarction and reperfusion, notably the temporal and spatial evolution of ischaemic and reperfusion injury, the different modes of cell death, and the resulting coronary microvascular dysfunction. We then go on to briefly characterize the cardioprotective phenomena of ischaemic preconditioning, ischaemic postconditioning, and remote ischaemic conditioning and their underlying signal transduction pathways. We discuss in detail the attempts to translate conditioning strategies and drug therapy into the clinical setting. Most attempts have failed so far to reduce infarct size and improve clinical outcomes in STEMI patients, and we discuss potential reasons for such failure. Currently, it appears that remote ischaemic conditioning and a few drugs (atrial natriuretic peptide, exenatide, metoprolol, and esmolol) reduce infarct size, but studies with clinical outcome as primary endpoint are still underway.

Acute hypoxia-reoxygenation and vascular oxygen sensing in the chicken embryo

Fetal/perinatal hypoxia is one of the most common causes of perinatal morbidity and mortality and is frequently accompannied by vascular dysfunction. However, the mechanisms involved have not been fully delineated. We hypothesized that exposure to acute hypoxia‐reoxygenation induces alterations in vascular O₂ sensing/signaling as well as in endothelial function in the chicken embryo pulmonary artery (PA), mesenteric artery (MA), femoral artery (FA), and ductus arteriosus (DA). Noninternally pipped 19‐day embryos were exposed to 10% O₂ for 30 min followed by reoxygenation with 21% O₂ or 80% O₂. Another group was constantly maintained at 21% O₂ or at 21% O₂ for 30 min and then exposed to 80% O₂. Following treatment, responses of isolated blood vessels to hypoxia as well as endothelium‐dependent (acetylcholine) and ‐independent (sodium nitroprusside and forskolin) relaxation were investigated in a wire myograph. Hypoxia increased venous blood lactate from 2.03 ± 0.18 to 15.98 ± 0.73 mmol/L (P < 0.001) and reduced hatchability to 0%. However, ex vivo hypoxic contraction of PA and MA, hypoxic relaxation of FA, and normoxic contraction of DA were not significantly different in any of the experimental groups. Relaxations induced by acetylcholine, sodium nitroprusside, and forskolin in PA, MA, FA, and DA rings were also similar in the four groups. In conclusion, exposure to acute hypoxia‐reoxygenation did not affect vascular oxygen sensing or reactivity in the chicken embryo. This suggests that direct effects of acute hypoxia‐reoxygenation on vascular function does not play a role in the pathophysiology of hypoxic cardiovascular injury in the perinatal period.

Telmisartan protects against microvascular dysfunction during myocardial ischemia/reperfusion injury by activation of peroxisome proliferator-activated receptor γ

Background

We investigated the potential of telmisartan to improve microvascular dysfunction induced by myocardial ischemia/reperfusion (I/R) injury by activating the peroxisome proliferator-activated receptor gamma (PPARG) pathway.

Methods

Forty-eight male rabbits were randomly allocated into sham-operated, I/R, GW9662, telmisartan, telmisartan–GW9662, or candesartan groups. Rabbits were anesthetized, and the left anterior descending coronary artery (LAD) was ligated for 60 minutes. Following reperfusion for 6 hours, angiotensin II content of the heart was determined using radioimmunoassay. Myocardial neutrophil accumulation and microvessel cross-sectional area were examined histologically. Myocardial capillaries were examined with transmission electron microscopy. Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in the myocardium were measured using enzyme-linked immunosorbent assay. Western blot was utilized for investigating the expression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and PPARG.

Results

Angiotensin II concentration was significantly increased in all treatment groups compared with the sham-operated group (P < 0.05, all). Accumulation of polymorphonuclear neutrophils was significantly lower, while microvessel cross-sectional area was significantly higher in the telmisartan, telmisartan-GW9662, and candesartan groups compared with the I/R group (P < 0.05). ICAM-1 and VCAM-1 levels were also significantly lower, and correlated with lower NF-κB expression in these groups. The effects were the most significant in the telmisartan group compared with the telmisartan–GW9662 and candesartan groups. Telmisartan significantly increased PPARG protein expression compared with all other groups (P < 0.05, all).

Conclusions

Except for the typical effects of angiotensin II-receptor blocker, telmisartan improved microvascular dysfunction during myocardial I/R injury via the PPARG pathway.

Antioxidant activity contributes to flavonol cardioprotection during reperfusion of rat hearts

The mechanism of flavonol-induced cardioprotection is unclear. We compared the protective actions of a flavonol that inhibits calcium utilization and has antioxidant activity, 3',4'-dihydroxyflavonol (DiOHF); a flavonol that affects only calcium activity, 4'-OH-3'-OCH(3)-flavonol (4'-OH-3'-OCH(3)F); and a water-soluble flavonol with selective antioxidant activity, DiOHF-6-succinamic acid (DiOHF-6-SA), in isolated, perfused rat hearts. Hearts were subjected to global ischemia for 20 min followed by 30 min reperfusion and were treated with vehicle (0.05% DMSO), DiOHF, 4'-OH-3'-OCH(3)F, or DiOHF-6-SA (all 10 μM, n=5-8 per group). Flavonols were infused for 10 min before ischemia and during reperfusion. In vehicle-treated hearts, left-ventricular (LV) +dP/dt was reduced by 60% at the end of reperfusion compared to the preischemic level. Lactate dehydrogenase (LDH) release was elevated and endothelial NO synthase (eNOS) expression was lower in vehicle-treated hearts compared to shams. In comparison, DiOHF treatment improved LV function upon reperfusion, decreased LDH, and preserved eNOS expression. The antioxidant DiOHF-6-SA also preserved contractility, reduced LDH, and preserved eNOS expression. In contrast, hearts treated with 4'-OH-3'-OCH(3)F showed a degree of contractile impairment similar to that of the vehicle group. DiOHF and DiOHF-6-SA also exerted cardioprotection when given only during reperfusion and not when administered only before ischemia. Flavonol-induced cardioprotection relies on antioxidant activity and is mainly exerted during reperfusion.

Lipid oxidation by hypochlorous acid: chlorinated lipids in atherosclerosis and myocardial ischemia

Leukocytes, containing myeloperoxidase (MPO), produce the reactive chlorinating species, HOCl, and they have important roles in the pathophysiology of cardiovascular disease. Leukocyte-derived HOCl can target primary amines, alkenes and vinyl ethers of lipids, resulting in chlorinated products. Plasmalogens are vinyl ether-containing phospholipids that are abundant in tissues of the cardiovascular system. The HOCl oxidation products derived from plasmalogens are α-chlorofatty aldehyde and unsaturated molecular species of lysophosphatidylcholine. α-chlorofatty aldehyde is the precursor of both α-chlorofatty alcohol and α-chlorofatty acid. Both α-chlorofatty aldehyde and α-chlorofatty acid accumulate in activated neutrophils and have disparate chemotactic properties. In addition, α-chlorofatty aldehyde increases in activated monocytes, human atherosclerotic lesions and rat infarcted myocardium. This article addresses the pathways for the synthesis of these lipids and their biological targets.

The paradox of the neutrophil's role in tissue injury

The neutrophil is an essential component of the innate immune system, and its function is vital to human life. Its production increases in response to virtually all forms of inflammation, and subsequently, it can accumulate in blood and tissue to varying degrees. Although its participation in the inflammatory response is often salutary by nature of its normal interaction with vascular endothelium and its capability to enter tissues and respond to chemotactic gradients and to phagocytize and kill microrganisms, it can contribute to processes that impair vascular integrity and blood flow. The mechanisms that the neutrophil uses to kill microorganisms also have the potential to injure normal tissue under special circumstances. Its paradoxical role in the pathophysiology of disease is particularly, but not exclusively, notable in seven circumstances: 1) diabetic retinopathy, 2) sickle cell disease, 3) TRALI, 4) ARDS, 5) renal microvasculopathy, 6) stroke, and 7) acute coronary artery syndrome. The activated neutrophil's capability to become adhesive to endothelium, to generate highly ROS, and to secrete proteases gives it the potential to induce local vascular and tissue injury. In this review, we summarize the evidence for its role as a mediator of tissue injury in these seven conditions, making it or its products potential therapeutic targets.

The minimized extracorporeal circulation system causes less inflammation and organ damage

The minimized extracorporeal circulation system (MECC) is being used to reduce priming volume and blood/polymer contact during cardiac procedures. In this study, we evaluated the efficacy and potential advantages of the system in coronary artery bypass graft (CABG) patients. We included two groups of patients destined for CABG in a prospective, randomized study: Group A was operated on the usual pump (n = 30) while Group B was operated using the MECC (n = 50). Pre-operative demographics, intra-operative times and values as well as a series of post-operative outcome data (blood loss, transfusion requirements, ventilation time, ICU and hospital stay) were recorded. CK, CK-MB, troponin-T, IL-6 and IL-8 were measured. Pre-operative and post-operative lung function were assessed. In the MECC-operated group, patients developed less post-operative troponin-T (0.2 ± 0.3 vs. 0.5 ± 0.5 ng/mL, p=0.031) and less IL-8 (13.8 ± 5 vs. 22.5 ± 0.5 µg/L, p = 0.05). While blood loss was comparable in both groups, packed red blood cells and fresh frozen plasma were given less frequently in the MECC group (p = 0.015 resp. 0.022). The one-tailed Student’s t-test revealed shorter bypass time in the MECC group (74 ± 17 vs. 82 ± 24 min). There was no difference in ventilation and ICU-time (patients were not treated in a fast-track fashion). The FEV1 was better in the MECC group (relative values: 70.1 ± 18.2% vs. 61.1 ± 12.3%, p = 0.02). Utilization of the MECC may cause less cytokine (IL-8) liberation, owing to less blood/tubing contact, as well as less red blood cell and fresh frozen plasma demand. It may also be the circuit in patients with chronic obstructive pulmonary disease (COPD).

Annexin-1 peptide Anx-1(2-26) protects adult rat cardiac myocytes from cellular injury induced by simulated ischaemia

1 The anti-inflammatory properties of annexin-1 peptides have been largely ascribed to their powerful antineutrophil actions in vivo. We have recently reported that the N-terminal fragment of annexin-1, Anx-1(2-26), preserves contractile function of cardiac muscle in vitro. The aim of the present study was to determine if Anx-1(2-26) elicits protective actions specifically on the cardiac myocyte (in the absence of neutrophils), using a model of metabolic inhibition to simulate ischaemia. 2 Metabolic inhibition of cardiac myocytes (4 h incubation at 37 degrees C in HEPES-containing buffer supplemented with 2-deoxy-D-glucose, D,L-lactic acid and pH adjusted to 6.5) followed by 2.5 h recovery in normal medium markedly increased creatine kinase (CK) and lactate dehydrogenase (LDH) levels by 179+/-39 and 26+/-7 IU L(-1) (both n=40, P<0.001), respectively. However, cellular injury was significantly decreased when Anx-1(2-26) (0.3 microM) was present during metabolic inhibition, CK by 74+/-10% and LDH by 71+/-6% (both n=31, P<0.001), respectively. 3 Boc 2 (10 microM), a nonselective formyl peptide receptor antagonist, present during metabolic inhibition, abolished the cardioprotective effect of Anx-1(2-26). 4 Addition of chelerythrine (10 microM), 5-hydroxydecanoate (500 microM) or SB202190 (1 microM) during metabolic inhibition also abolished Anx-1(2-26)-induced cardioprotection. 5 Cellular injury induced by metabolic inhibition was also largely prevented when myocytes were incubated with Anx-1(2-26) for 5 min with 10 min recovery prior to the insult, or when Anx-1(2-26) was present only during the recovery period following drug-free metabolic inhibition. 6 In conclusion, the annexin-1 peptide Anx-1(2-26) potently prevents cardiac myocyte injury induced by metabolic inhibition, an action that was dependent at least in part on the activation of the formyl peptide receptor family of G-protein-coupled receptors, protein kinase C, p38 mitogen-activated protein kinase and ATP-sensitive potassium channels.

Fish oil before cardiac surgery: neutrophil activation is unaffected but myocardial damage is moderated

Could pre-operative dietary intervention with fish oil reduce neutrophil activation and myocardial damage associated with cardiopulmonary bypass (CPB)? Patients were randomised to receive either 8 g/day fish oil (n=22) or placebo (n=18) for 6 weeks. Neutrophil activation, apoptosis and cardiac damage were measured. Demographics and operative variables were similar. Fish oil diet decreased plasma VLDL from 0.69+/-0.34 to 0.51+/-0.24 mmol/l and triglycerides from 1.68+/-0.70 to 1.39+/-0.54 mmol/l. HDL cholesterol increased from 0.94+/-0.27 to 1.03+/-0.26 mmol/l demonstrating significant treatment effects (P=0.007, 0.02 and 0.0003, respectively) as well as compliance with treatment. There were no significant differences in ex vivo N-formyl-methionyl-leucyl-phenylalanine-stimulated neutrophil superoxide anion generation or myeloperoxidase release at recruitment, pre-operatively and at end-CPB. Apoptosis at end-CPB was equally reduced in both groups from 23+/-9% to 13+/-4% in the fish oil group (P<0.001) and 35+/-14% to 15+/-3% in the placebo group (P=0.001). At end-CPB overall troponin I levels averaged 0.91+/-0.60 ng/ml which clearly exceeded diagnostic levels (0.15 ng/ml). At 24h troponin I fell significantly in the fish oil group to 46+/-23% of end-CPB levels (P=0.0002) whereas it peaked in the placebo group to 107+/-72% (P=0.098 vs. end-CPB); this difference was significant: P=0.013. At 48 h the placebo-treated patients had higher troponins but not significantly so (P=0.059). Area-under-the-curve analysis did not conclusively support this (P=0.068). We conclude that fish oil did not significantly decrease post-CPB neutrophil activation (as detected ex vivo) but may moderate post-operative myocardial damage.

Neutrophil depletion reduces myocardial reperfusion morbidity

BACKGROUND

We tested the hypothesis that depletion of neutrophil leukocytes from the cardioplegic and the initial myocardial reperfusion perfusates reduces clinical indices of reperfusion injury in patients undergoing elective coronary artery bypass.

METHODS

We studied 160 consecutive patients who underwent standard coronary revascularization with cardiopulmonary bypass. Patients with recent myocardial infarction or coronary angioplasty were excluded. Cold blood cardioplegia was used. Just before aortic unclamping, the hearts were perfused retrograde with 250 mL of normothermic cardioplegic solution and 750 mL of blood (pump perfusate). Patients were randomly assigned to two groups. In 80 patients (treated), neutrophils and platelets were removed from all cardiac perfusate during aortic crossclamping with leukocyte filtration. In the remaining 80 patients (control group), leukocyte filtration was not used.

RESULTS

There was no significant difference between groups in age, sex, severity of disease, and number of bypass grafts implanted. Treated patients showed lower prevalence of low cardiac index and reperfusion ventricular fibrillation and lower levels of creatinine kinase MB isoenzyme and troponin I early postoperatively (p < 0.05).

CONCLUSIONS

Neutrophil-filtered blood cardioplegia/reperfusion significantly reduced clinical and biochemical indices of myocardial reperfusion injury after elective coronary revascularization with cardiopulmonary bypass.

Hepatic reticuloendothelial system dysfunction after ischemia-reperfusion: role of P-selectin-mediated neutrophil accumulation

The relationship between hepatic ischemia-reperfusion (I-R) and subsequent injury through neutrophil accumulation is well described. Although alterations in reticuloendothelial system (RES) function (specifically Kupffer cell function) after I-R have been delineated, the degree to which discrete components of RES function (phagocytosis and killing) are independently modulated under these conditions has not been quantified. A hepatic segmental I-R model was established in mice, in which blood supply to the left lateral lobe of the liver was occluded for 45 minutes, the liver was reperfused, and the laparotomy incision was closed. Experimental animals were pretreated with either vinblastin (1.5 mg/kg) to induce neutropenia or anti-P-selectin monoclonal antibody (mAb; 50 microg/mice) 4 days and 5 minutes before ischemia, respectively. We previously reported that after intravenous injection of chromium 51 ((51)Cr) and iodine 125 ((125)I) double-labeled Escherichia coli, hepatic (51)Cr levels could be used to reliably quantify hepatic phagocytic clearance (HPC) of bacteria from blood, whereas the subsequent release of (125)I from the liver accurately paralleled hepatic bacterial killing efficiency (HKE). Using this double-label bacteria clearance assay, HPC and HKE were depressed after I-R, in association with hepatic neutrophil accumulation. Segmental I-R resulted in decreased HPC and HKE activity in both ischemic and nonischemic hepatic lobes. Depressions in HPC and HKE were attenuated by either vinblastin-induced neutropenia or blocking neutrophil adhesion to the hepatic endothelium with anti-P-selectin mAb. These findings support the hypothesis that I-R induces hepatic RES dysfunction, at least in part, through P-selectin-mediated neutrophil accumulation.

Cytokine mediation of experimental heart failure-induced anhedonia

Immune system dysfunction is hypothesized to influence several disease states, including cardiovascular disease and psychological depression. The comorbidity of depression and coronary artery disease may be influenced by immune system-brain interactions involving proinflammatory cytokines. The present studies evaluated an index of depression in a rodent model of heart failure by measuring responses to rewarding electrical brain stimulation, which provides an experimental procedure to operationally define anhedonia in rats. Heart failure led to a rightward shift in the current-response relationship in the brain stimulation paradigm, indicative of reduced rewarding properties of the brain stimulation (i.e., anhedonia). Acute treatment with a tumor necrosis factor antagonist, etanercept, reduced circulating tumor necrosis factor- levels in rats with heart failure and restored responding for electrical brain stimulation. The current findings have implications for the study of pathophysiological mechanisms underlying the association of cardiovascular disease and depression.

Biological mechanisms in the relationship between depression and heart disease

Psychological depression is shown to be associated with several aspects of coronary artery disease (CAD), including arrhythmias, myocardial infarction, heart failure and sudden death. The physiological mechanisms accounting for this association are unclear. Hypothalamic-pituitary-adrenal dysregulation, diminished heart rate variability, altered blood platelet function and noncompliance with medial treatments have been proposed as mechanisms underlying depression and cardiovascular disease. Recent evidence also suggests that reduced baroreflex sensitivity, impaired immune function, chronic fatigue and the co-morbidity of depression and anxiety may be involved in the relationship between depression and cardiovascular dysregulation. An experimental strategy using animal models for investigating underlying physiological abnormalities in depression is presented. A key to understanding the bidirectional association between depression and heart disease is to determine whether there are common changes in brain systems that are associated with these conditions. Such approaches may hold promise for advancing our understanding of the interaction between this mood disorder and CAD.

Na(+)/H(+) exchange inhibition prevents endothelial dysfunction after I/R injury

Whereas inhibition of the Na(+)/H(+) exchanger (NHE) has been demonstrated to reduce myocardial infarct size in response to ischemia-reperfusion injury, the ability of NHE inhibition to preserve endothelial cell function has not been examined. This study examined whether NHE inhibition could preserve endothelial cell function after 90 min of regional ischemia and 180 min of reperfusion and compared this inhibition with ischemic preconditioning (IPC). In a canine model either IPC, produced by one 5-min coronary artery occlusion (1 x 5'), or the specific NHE-1 inhibitor eniporide (EMD-96785, 3.0 mg/kg) was administered 15 min before a 90-min coronary artery occlusion followed by 3 h of reperfusion. Infarct size (IS) was determined by 2,3,5-triphenyl tetrazolium chloride staining and expressed as a percentage of the area-at-risk (IS/AAR). Endothelial cell function was assessed by measurement of coronary blood flow in response to intracoronary acetylcholine infusion at the end of reperfusion. Whereas neither control nor IPC-treated animals exhibited a significant reduction in IS/AAR or preservation of endothelial cell function, animals treated with the NHE inhibitor eniporide showed a marked reduction in IS/AAR and a significantly preserved endothelial cell function (P < 0.05). Thus NHE-1 inhibition is more efficacious than IPC at reducing IS/AAR and at preserving endothelial cell function in dogs.

Selected contribution: effects of ischemia-reperfusion on vascular contractility and alpha(1)-adrenergic-receptor signaling in the rat tail artery

To determine the effects of ischemia-reperfusion (I/R) on alpha(1)-adrenergic-receptor (alpha(1)-AR) functions, alpha(1)-AR-mediated contraction, inositol phosphate (IP) accumulation, and alpha(1)-AR-G protein coupling were examined in the tail arteries of anesthetized rats after 60 min of ischemia and 60 min of reperfusion. The contractile response to norepinephrine (NE) was significantly increased after I/R, whereas the contractile response to KCl remained unchanged. This was accompanied by a 69% increase in NE-stimulated IP accumulation. Furthermore, receptor-stimulated coupling of alpha(1a)-AR to G alpha(q/11) proteins was increased, whereas the coupling of alpha(1b)-AR or alpha(1d)-AR to their G proteins was not altered by I/R. These changes in vascular alpha(1)-AR function occurred without concurrent alteration in expression levels of membrane alpha(1)-AR subtypes or in the associated G proteins. These data demonstrate that I/R increases alpha(1a)-AR-G(q/11) protein coupling and alpha(1)-AR-stimulated IP accumulation in the tail artery. The alterations in alpha(1)-AR signaling are associated with and may underlie the enhanced contractile response of the tail artery to adrenergic stimulation after I/R.

Blockade of the natriuretic peptide receptor guanylyl cyclase-A inhibits NF-kappaB activation and alleviates myocardial ischemia/reperfusion injury

Acute myocardial infarction (AMI) remains the leading cause of death in developed countries. Although reperfusion of coronary arteries reduces mortality, it is associated with tissue injury. Endothelial P-selectin-mediated infiltration of neutrophils plays a key role in reperfusion injury. However, the mechanism of the P-selectin induction is not known. Here we show that infarct size after ischemia/reperfusion was significantly smaller in mice lacking guanylyl cyclase-A (GC-A), a natriuretic peptide receptor. The decrease was accompanied by decreases in neutrophil infiltration in coronary endothelial P-selectin expression. Pretreatment with HS-142-1, a GC-A antagonist, also decreased infarct size and P-selectin induction in wild-type mice. In cultured endothelial cells, activation of GC-A augmented H2O2-induced P-selectin expression. Furthermore, ischemia/reperfusion-induced activation of NF-kappaB, a transcription factor that is known to promote P-selectin expression, is suppressed in GC-A-deficient mice. These results suggest that inhibition of GC-A alleviates ischemia/reperfusion injury through suppression of NF-kappaB-mediated P-selectin induction. This novel, GC-A-mediated mechanism of ischemia/reperfusion injury may provide the basis for applying GC-A blockade in the clinical treatment of reperfusion injury.

Myocardial protection with leukocyte depletion in cardiac surgery

A role of neutrophils in ischemia-reperfusion injury has been focused on as one of the mediating factors of inflammatory reactions. Current studies have reported the efficacy of leukocyte-depletion in reperfusion by using leukocyte removal filter to attenuate reperfusion injury during open heart surgeries. For clinical application, we have introduced leukocyte-depleted terminal blood cardioplegia (LDTC) in adult patients and leukocyte-depleted blood cardioplegia in pediatric patients. The results of elective surgery in noncompromised LDTC did not significantly alter the results in terms of leakage of creatine kinase (CK)-MB, production of malondialdehyde from myocardium, and dopamine dose required at the weaning from cardiopulmonary bypass compared with the whole-blood reperfusion or with terminal cardioplegia alone. In contrast, the results in emergency coronary artery bypass graft (CABG) patients differed significantly between the LDTC group and the other two groups. Leukocyte-depleted reperfusion was also effective in a similar fashion for patients with severe left ventricular hypertrophy caused by chronic aortic valve disease. Leukocyte-depleted blood cardioplegia was useful in pediatric patients. Thus, leukocyte depletion may be beneficial as an adjunct to terminal blood cardioplegia or blood cardioplegia during cardiac surgery to attenuate leukocyte-mediated ischemia-reperfusion injury in patients with compromised hearts, such as those with preoperative ischemic insults, severe left ventricular hypertrophy, and in pediatric patients.

Mechanisms involved in the augmentation of arachidonic acid-induced free-radical generation from rat neutrophils following hypoxia-reoxygenation

Polymorphonuclear leukocytes are known to play an important role in hypoxia/ischemia and reoxygenation injury. The present study was undertaken to investigate the involvement of protein kinase C, calmodulin, and cyclic adenosine monophosphate in the augmentation of the free-radical generation observed after hypoxia-reoxygenation (H-R). Free-radical generation from the rat polymorphonuclear leukocytes was measured as the arachidonic acid (1-5x10(-5) M)-induced luminol-dependent chemiluminescence response, which was augmented following H-R. The increase in free-radical generation after H-R was completely blocked by the pretreatment of cells with PKC inhibitor H(7), whereas indomethacin (a cyclo-oxygenase inhibitor) or forskolin (an adenylate cyclase activator) failed to modulate the H-R-dependent response. However, W(7)-a calcium/calmodulin (Ca(2+)/CaM) antagonist-partially reduced the augmented free-radical generation observed in the H-R cells. Results obtained thus suggest the possible involvement of protein kinase C and calcium in the augmentation of the free-radical generation response following H-R.

Neutrophilia and congestive heart failure after acute myocardial infarction

BACKGROUND

Inflammation associated with acute myocardial infarction (AMI) is frequently marked by a peripheral leukocytosis and relative neutrophilia. Whether this process may contribute to the development of postinfarction congestive heart failure (CHF) is not established. The objective of this study was to examine the association between hospital admission peripheral total leukocyte count and the neutrophil percentage and the subsequent development of CHF in patients with AMI. The study was designed as a retrospective cohort study in the setting of a tertiary referral hospital. Participants included 185 patients discharged with a diagnosis of AMI between May 1 and Sept 30, 1996.

METHODS AND RESULTS

Outcome measures included clinical episodes of CHF with confirmatory chest roentgenogram findings and/or echocardiographic evidence of contractile dysfunction. Multivariable logistic regression analyses were performed to examine the relation between the total leukocyte count, neutrophil percentage, and the development of CHF in the first 4 days after AMI while controlling for baseline characteristics and early therapeutic interventions. Thirty-one percent of the cohort had a leukocyte count >11.0 x10(9)/L on admission to the hospital; 65% had a neutrophil percentage >65%, and 61% had a lymphocyte percentage </=25%. CHF developed in 43% of the cohort. Of these, 92. 5% had relative neutrophilia (neutrophil percentage >65%) compared with 45% of those in whom CHF did not develop. Multivariable analysis revealed a highly significant association between relative neutrophilia and the subsequent development of CHF (odds ratio 14.3; 95% confidence interval 5.2 to 39.3).

CONCLUSIONS

Relative neutrophilia on admission to the hospital in patients with AMI is significantly associated with the early development of CHF. This association may help in the identification of individuals at high risk who might benefit from more aggressive interventions to prevent or reduce the risk of CHF.

Pathogenetic potential of leukocytes in diabetic retinopathy

Recently, increasing interest has been directed toward the role of leukocytes in microvascular disorders including diabetic retinopathy because of their large cell volume, high cytoplasmic rigidity, natural tendency to stick to the vascular endothelium, and capacity to generate toxic superoxide radicals and proteolytic enzymes. Leukocytes in diabetes are reported to be less deformable and more activated, and may be involved in capillary non-perfusion, endothelial cell damage, and vascular leakage in the retinal microcirculation. In fact, histological studies show many capillary occlusions by leukocytes and capillary dropout or degeneration associated with leukocytes in the diabetic retina. Serial acridine orange leukocyte fluorography and fluorescein angiography studies also identify trapped leukocytes directly associated with areas of downstream non-perfusion in the diabetic retinal microcirculation. More recent studies suggest that adhesion molecules may mediate retinal leukocyte stasis (leukostasis) in diabetes and a reduction in the leukostasis by anti-adhesion antibodies can suppress retinal vascular leakage. In addition, some agents inhibiting leukostasis are reported to improve retinal abnormalities induced by diabetes. Thus, leukostasis in the retinal microcirculation can be a new promising target in the treatment of diabetic retinopathy.

Effect of ursodeoxycholic acid on ischemia/reperfusion injury in isolated rat heart

In this study, the effects of ursodeoxycholic acid (UDCA) on ischemia/reperfusion injury were investigated on isolated heart perfusion model. Hearts were perfused with oxygenated Krebs-Henseleit solution (pH 7.4, 37 degrees C) on a Langendorff apparatus. After equilibration, isolated hearts were treated with UDCA 20 to 160 microM or vehicle (0.04% DMSO) for 10 min before the onset of ischemia. After global ischemia (30 min), ischemic hearts were reperfused and allowed to recover for 30 min. The physiological (i.e. heart rate, left ventricular developed pressure, coronary flow, double product and time to contracture formation) and biochemical (lactate dehydrogenase; LDH) parameters were evaluated. In vehicle-treated group, time to contracture formation was 21.4 min during ischemia, LVDP was 18.5 mmHg at the endpoint of reperfusion and LDH activity in total reperfusion effluent was 54.0 U/L. Cardioprotective effects of UDCA against ischemia/reperfusion consisted of a reduced TTC (EC25=97.3 microM), reduced LDH release and enhanced recovery of cardiac contractile function during reperfusion. Especially, the treatments of UDCA 80 and 160 microM significantly increased LVDP and reduced LDH release. Our findings suggest that UDCA ameliorates ischemia/reperfusion-induced myocardial damage.

The heart produces but the lungs consume proinflammatory cytokines following cardiopulmonary bypass

OBJECTIVE

Proinflammatory cytokines, such as interleukin-6 (IL-6), and soluble adhesion molecules, such as E-selectin, may play an important role in patient response to cardiopulmonary bypass (CPB). We sought to define whether the heart and the lungs serve as important sources of these inflammatory mediators under clinical conditions of myocardial revascularization using CPB and cardioplegic arrest.

METHODS

Plasma levels of IL-6 and E-selectin were measured in coronary sinus (CS), arterial, pulmonary arterial (PA) and left atrial (LA) blood samples taken from 12 consecutive patients (68.3 +/- 11 years; five females) undergoing coronary artery bypass grafting (CABG). Blood samples were collected preoperatively, after reperfusion, and 1, 6, 12 and 18 h following surgery. CS and LA blood was drawn using transcutaneous catheters. PA artery blood was obtained through a Swan-Ganz catheter. Cytokine levels were determined by standard enzyme linked immunosorbent assay (ELISA) technique.

RESULTS

A mean of 3.8 +/- 1 coronary anastomoses were performed. The CPB time and aortic X-clamp time were 91 +/- 15 and 45 +/- 10 min, respectively. IL-6 levels increased significantly after CPB and peaked 6 h postoperatively. There was also a significant increase of E-selectin levels with an onset at 1 h and a peak at 12 h postoperatively. At all time points the IL-6 and E-selectin concentrations were significantly higher in the CS than in arterial blood. In contrast, the levels of both mediators measured in the LA were significantly lower than those in the PA.

CONCLUSION

The reperfusion of ischemic myocardium during CABG results in a significant increase in plasma levels of IL-6 and E-selectin. Our data indicate that the myocardium, but not the lungs, is a predominant source of IL-6 and E-selectin release following CPB. The lungs may consume rather than release those mediators during reperfusion. Not the CPB per se, but the myocardial ischemia seems to be crucial in the pathogenesis of the inflammatory response observed following open heart surgery.

Nitric Oxide–Mediated Augmentation of Polymorphonuclear Free Radical Generation After Hypoxia-Reoxygenation

Polymorphonuclear leukocytes (PMNLs), nitric oxide (NO), calcium, and free radicals play an important role in hypoxia/ischemia and reoxygenation injury. In the present study, NO donors, sodium nitroprusside (SNP), and diethylamine-NO (DEA-NO) at low concentrations (10 and 100 nmol/L) potentiated, while higher (10 μmol/L to 10 mmol/L) concentrations inhibited free radical generation response in the rat PMNLs. Free radical generation response was found to be significantly augmented when hypoxic PMNLs were reoxygenated (hypoxia-reoxygenation [H-R]). This increase in free radical generation after reoxygenation or SNP (10 nmol/L) was blocked in the absence of extracellular calcium. SNP (10 nmol/L) or H-R–mediated increases in the free radical generation were prevented by the pretreatment of PMNLs with NO scavenger (hemoglobin), the polyadenine diphosphate (ADP)-ribosylation synthase inhibitor (benzamide) or the calcium channel antagonist (felodipine). A significant augmentation in the nitrite and intracellular calcium levels was observed during hypoxia. Hemoglobin pretreatment also blocked the increase in intracellular calcium levels due to SNP (10 nmol/L) or hypoxia. Thus, increased availability of NO during SNP treatment or H-R, may have led to an ADP-ribosylation–mediated increase in intracellular calcium, thereby increasing the free radical generation from the rat PMNLs.

Nitric Oxide–Mediated Augmentation of Polymorphonuclear Free Radical Generation After Hypoxia-Reoxygenation

Polymorphonuclear leukocytes (PMNLs), nitric oxide (NO), calcium, and free radicals play an important role in hypoxia/ischemia and reoxygenation injury. In the present study, NO donors, sodium nitroprusside (SNP), and diethylamine-NO (DEA-NO) at low concentrations (10 and 100 nmol/L) potentiated, while higher (10 μmol/L to 10 mmol/L) concentrations inhibited free radical generation response in the rat PMNLs. Free radical generation response was found to be significantly augmented when hypoxic PMNLs were reoxygenated (hypoxia-reoxygenation [H-R]). This increase in free radical generation after reoxygenation or SNP (10 nmol/L) was blocked in the absence of extracellular calcium. SNP (10 nmol/L) or H-R–mediated increases in the free radical generation were prevented by the pretreatment of PMNLs with NO scavenger (hemoglobin), the polyadenine diphosphate (ADP)-ribosylation synthase inhibitor (benzamide) or the calcium channel antagonist (felodipine). A significant augmentation in the nitrite and intracellular calcium levels was observed during hypoxia. Hemoglobin pretreatment also blocked the increase in intracellular calcium levels due to SNP (10 nmol/L) or hypoxia. Thus, increased availability of NO during SNP treatment or H-R, may have led to an ADP-ribosylation–mediated increase in intracellular calcium, thereby increasing the free radical generation from the rat PMNLs.

Myocardial ischemia-reperfusion injury in CD18- and ICAM-1-deficient mice

Previous studies have demonstrated that circulating neutrophils (PMNs) contribute to the pathophysiology of myocardial ischemia-reperfusion (MI/R) injury. PMN-endothelial cell interactions are highly regulated by adhesive interactions between PMN CD11/CD18 and coronary endothelial cell intercellular adhesion molecule-1 (ICAM-1). We investigated the effects of MI/R in wild-type, CD18-, and ICAM-1-deficient (-/-) mice. Wild-type (n = 6), CD18 -/- (n = 6), and ICAM-1 -/- (n = 6) mice were subjected to 30 min of myocardial ischemia and 120 min of reperfusion to determine the extent of PMN infiltration and myocardial cell necrosis. Myocardial infarction (% of the area at risk) was 45.1 +/- 5.9 in wild-type mouse hearts. In contrast, the extent of myocardial infarction was significantly (P < 0.05) reduced in the CD18 (19.3 +/- 5.1%)- and ICAM-1 (17.9 +/- 3.2%)-deficient mice. Similarly, PMN infiltration into the ischemic-reperfused myocardium was attenuated by 54% in the CD18 -/- mice and by 32% in ICAM-1 -/- mice compared with wild-type hearts. Deficiency in either CD18 or ICAM-1 expression results in a marked reduction in PMN accumulation and myocardial necrosis after acute MI/R.

Disparate effects of adhesion and degranulation of platelets on myocardial and coronary function in postischaemic hearts

OBJECTIVE

Beside the major effect of acute thrombus formation, little is known about the interaction of platelets with the coronary endothelium in an ischaemia-reperfusion situation. The present study was designed to investigate, separately, the consequences of platelet adhesion and degranulation during myocardial reperfusion.

METHODS

Isolated guinea pig hearts perfused with Krebs-Henseleit buffer and performing pressure-volume work were used. We infringed myocardial function by imposing ischaemia (20 min of low-flow perfusion with 1 ml/min and 10 min of global ischaemia) and reperfusion (15 min with 5 ml/min). During low-flow perfusion, the coronary endothelium was stimulated by thrombin before and during infusion of a bolus: 10(8) washed human platelets +/- the Arg-Gly-Asp (RGD) analogon lamifiban, the supernatant of 10(8) thrombin-stimulated platelets, fibrinogen (2 microM), lamifiban (2 microM) or Tyrode's solution (control group). The parameter external heart work (EHW), determined pre- and postischaemically, served as criterion for recovery of myocardial function. Additionally, the formation of capillary transudate was measured during the reperfusion phase to assess coronary permeability. Coronary perfusion pressure was monitored continuously and myocardial production of lactate and consumption of pyruvate were measured. Electron microscopy of hearts was performed after platelet application to verify platelet adhesion in the coronary system.

RESULTS

Recovery of EHW by hearts without platelet application was 64 +/- 3% and was significantly reduced to 49 +/- 5% by platelet infusion (n = 8 each). Infusion of supernatant of thrombin-stimulated platelets did not impair recovery of heart work. In the reperfusion phase (6th-10th min), hearts that either had received platelets or supernatant of platelets exhibited a significantly reduced production of capillary transudate (70 microliters/min vs. 180 microliters/min for the controls). Intracoronary bolus application of fibrinogen or lamifiban also reduced coronary leak. Coronary perfusion pressure and metabolic parameters were not statistically different between the groups at any time.

CONCLUSIONS

Platelet adhesion to the coronary endothelium in a situation of myocardial ischaemia impairs cardiac recovery, whereas constituents released by platelets may have beneficial effects on the integrity of the coronary endothelium. In particular, fibrinogen seems to contribute to the permeability reducing effect, possibly by interaction with endothelial receptors recognising the RGD sequence.

Prevention of ischaemia-induced coronary vascular dysfunction

Myocardial ischaemia and reperfusion cause dysfunction of the coronary vasculature leading to a sustained reduction in coronary blood flow and an impairment of responses to both endothelium-dependent and endothelium-independent vasodilators. In contrast, when previously ischaemic arteries are removed from the myocardium and vascular function is examined in vitro, it is evident that while endothelial function is impaired, smooth muscle reactivity remains intact. Therefore, other changes must be responsible for the general reduction in vasodilator reserve. Examination of the vasculature in the ischaemic myocardium by electron microscopy reveals adhesion of leukocytes and plugging of capillaries. There also is evidence that polymorphonuclear leukocytes (PMNs) release a factor that constricts coronary arterioles, and that release of this factor is increased by atherosclerosis. The identity of this factor remains uncertain, but the calcium antagonist amlodipine prevents the coronary vasoconstriction. Amlodipine is also able to prevent the impaired perfusion and the reduction in vasodilator reserve that occurs after myocardial ischaemia and reperfusion in the dog. In addition, amlodipine prevents the endothelial dysfunction observed in isolated arteries after ischaemia and reperfusion. The interaction between the endothelium and activated PMNs may be a suitable target for pharmacological intervention to improve postischaemic vascular function.

Postischemic endothelium-dependent vascular reactivity is preserved in adhesion molecule-deficient mice

Previous studies utilizing monoclonal antibodies directed against specific leukocyte-endothelial cell adhesion proteins have suggested that neutrophils mediate endothelial cell injury in a number of vascular beds after ischemia-reperfusion (I/R). In the present study, we investigated superior mesenteric artery (SMA) vascular reactivity to acetylcholine (ACh) and sodium nitroprusside (SNP) after occlusion and reperfusion in wild-type (C57BL/6) mice and in gene-targeted mice that are deficient in either CD11/CD18, intercellular adhesion molecule 1 (ICAM-1), or P-selectin. All mice were 4 wk of age, and the SMA was occluded for 45 min and then reperfused for 45 min. Segments of SMA were isolated and suspended in organ chambers and contracted with phenylephrine (10(-5) M), and the maximal vasorelaxation to ACh (10(-6) M) and SNP (10(-6) M) was measured. SMA from sham-operated C57BL/6 mice relaxed 83.5 +/- 3.3% to ACh and 91.7 +/- 3.4% to SNP. In contrast, segments of SMA from C57BL/6 mice subjected to I/R demonstrated a marked impairment in vasorelaxation to ACh (51.3 +/- 4.7%, P < 0.01 vs. sham) without any impairment in the vasoreactivity to SNP (86.1 +/- 5.5%). In CD11/CD18-deficient mice, SMA reactivity to ACh (84.7 +/- 2.3%) and SNP (91.2 +/- 2.8%) was unaffected by I/R. Similarly, SMA rings from ICAM-1-deficient mice exhibited normal vasorelaxation to ACh and SNP with maximal vasorelaxation of 83.1 +/- 2.9 and 87.4 +/- 3.0%, respectively. We also observed profound preservation of endothelium-dependent vasorelaxation after I/R in P-selectin-deficient mice. These findings indicate that leukocyte-endothelial cell adhesion molecule deficiency is associated with the preservation of endothelium-dependent vascular responses after I/R.

Prevention of coronary vascular abnormalities early in reperfusion with TGF-beta may not prevent late coronary vascular injury

Endothelial injury, manifest by increased protein leak and decreased endothelium-dependent relaxation, occurs during reperfusion after ischemia. Transforming growth factor-beta (TGF-beta) has been shown to improve endothelium-dependent relaxation and reduce infarct size after short periods (from 20 min to 4.5 h) of reperfusion even when administered 24 h before the ischemic period. However, whether this represents a transient delay in the process leading to endothelial injury or prevention of injury has not been clear. To examine this issue, we measured protein leak, an index of coronary microvascular permeability, and endothelium-dependent relaxation, a measure of coronary endothelial function, after brief (1-h) and lengthy (48-h) reperfusion periods in dogs treated 30 min before ischemia with TGF-beta (30 microg/kg, i.v.) and control dogs. The left anterior descending coronary artery (LAD) was ligated for 1 h followed by 1 h of reperfusion (n = 10) or 48 h of reperfusion (n = 12). Protein leak was assessed by a dual-isotope technique by using radiolabeled transferrin and erythrocytes, and endothelium-dependent relaxation was assessed in epicardial coronary rings by using adenosine diphosphate (ADP), an endothelium-dependent vasodilator, and sodium nitroprusside (SNP), an endothelium-independent dilator. In control animals, there was a marked increase in the protein leak index (PLI) in the infarct zone (8.3 +/- 1.4 in 1-h dogs, and 8.7 +/- 0.9 in 48-h dogs) compared with the nonischemic myocardium (3.1 +/- 0.8 at 1 h, and 3.8 +/- 0.9 at 48 h). In TGF-beta treated dogs, there was a marked improvement in PLI in the infarct zone in 1-h dogs (PLI, 4.1 +/- 1.1; p < 0.05; or a 50% reduction compared with untreated dogs). However, the 48-h dogs treated with TGF-beta failed to demonstrate an improvement in PLI (PLI, 8.5 +/- 0.9; p = NS). Endothelium-dependent relaxation was impaired in the LAD in control dogs, and treatment with TGF-beta failed to improve relaxation after 1 or 48 h of reperfusion. Microvascular permeability was increased and endothelium-dependent relaxation was decreased after ischemia at both 1 and 48 h of reperfusion. Pretreatment with TGF-beta reduced the increase in permeability at 1 h of reperfusion but not at 48 h.

The leukocyte cell adhesion cascade and its role in myocardial ischemia-reperfusion injury

Cell-cell and cell-matrix interactions are known to be mediated by specific cell adhesion receptors expressed on the cell surface. The characterization of these cell adhesion molecules has allowed researchers to examine their roles in a variety of physiologic and pathophysiologic conditions. Numerous studies have demonstrated that myocardial ischemia-reperfusion injury is an acute inflammatory process in which leukocytes are intimately involved. In this review, we summarize the current data on the leukocyte cell adhesion cascade, focus upon studies which have demonstrated specific cell adhesion molecule interactions which mediate the leukocyte involvement in myocardial ischemia-reperfusion injury and suggest future avenues of exploration and possible clinical implications of the studies reviewed.

Bisaramil and antiarrhythmics as inhibitors of free radical generation

The aim of this study was to investigate the effect of bisaramil--an antiarrhythmic drug under clinical trials-on free radical generation of isolated polymorph neutrophil granulocytes (PMN) and furthermore to compare its activity to that of well-known antiarrhythmics which have different modes of action. PMNs were isolated from healthy beagle dogs, and superoxide radical generation was induced by phorbol-myristate-acetate. Stimulated free radical generation capacity of PMNs and the time lag necessary for the initiation of free radical production were measured. All compounds were used at the concentrations of 10, 25, 50, 75, 100 micrograms ml-1. None of the antiarrhythmics stimulated by itself the free radical generation. Bisaramil exerted concentration dependent inhibitory effect on PMA-stimulated free radical generation and prolonged the time lag concentration dependently. At the investigated concentration range of antiarrhythmics only propafenon, mexiletine and diltiazem showed similar activity to bisaramil, but clear concentration dependency could not be seen in any of the cases. According to the results of this study inhibition of the stimulated free radical production of isolated PMNs cannot be closely connected merely to either membrane stabilizing or Ca-antagonistic activity of drugs. In vitro and earlier measured in vivo inhibitory action of bisaramil on free radical generation indicate a possible cardioprotective effect existing independently from its antiarrhythmic one. This observation may be important in outlining of the clinical indication field of bisaramil, and may be useful in the treatment of reperfusional damage.

The effects of cardioplegic arrest and reperfusion on the microvasculature of the heart

OBJECTIVES

Despite laboratory evidence of leucocyte involvement in reperfusion injury, cardiac surgical clinical trials do not support the therapeutic effectiveness of leucocyte filtration. Furthermore, the direct effects of crystalloid cardioplegia and reperfusion on the capillaries of the heart have yet to be elucidated. We tested the effects of cardioplegic arrest and reperfusion both with and without leucocyte depletion, in a model of cardiopulmonary bypass that mimics clinical cardiac surgical conditions.

METHODS

Four groups of Landrace pigs were studied. Group A (n = 6) underwent 30 min of hypothermic (28 degrees C) cardiopulmonary bypass. Groups B (n = 6), C (n = 6) and D (n = 6) also had 90 min of cardioplegic arrest. Group C was then reperfused with whole blood, while Group D was reperfused with leucocyte-depleted blood. Microvascular methylmethacrylate corrosion casts were made at the end of the experimental period. Myocardial vascular anatomy was defined by electron microscopy and capillary abundance derived from this and from the weight of casts from representative areas. Leucocyte deposition was assessed using radioisotope-labelled leucocytes. Ischaemic damage to tissues was graded according to light and electron microscopic findings.

RESULTS

In Group A the mean (+/- S.D.) vascular cast weight/volume of myocardium (density) was 125 +/- 9 mg/mm3. After cardioplegic arrest (Group B), it fell to 74 +/- 7 mg/mm3 (P < 0.0001) due to absence of capillaries, although arterioles, venules and non-nutritive bypass vessels remained patent. Following reperfusion with whole blood (Group C), capillary numbers partially recovered but luminal diameters were reduced with a cast density of 94 +/- 5 mg/mm3 (P < 0.0001 versus Group A and B). Leucocyte-depleted (87-92%) reperfusion in Group D did not affect cast density (90 +/- 3 mg/mm3; P = 0.17). Coronary vascular resistances in Groups C and D rose slightly, but not significantly, during reperfusion.

CONCLUSIONS

Following cardioplegic arrest, microvascular changes are marked. These changes are partially reversed by 30 min reperfusion. Leucocyte depletion does not ameliorate these effects in this model.

Reperfusion injury: a review of the pathophysiology, clinical manifestations and therapeutic options

Lack of blood supply or ischaemia underlies many of the most important cardiovascular and cerebrovascular diseases faced by clinicians in their daily practice. Many of these ischaemic episodes can be reversed at an early stage by surgical or pharmacological means with the ultimate aim of preventing infarction and cell necrosis in the ischaemic tissues. However, reperfusion of ischaemic areas, in particular the readmission of oxygen, may contribute to further tissue damage (reperfusion injury). For example, the use of thrombolytic therapy in acute myocardial infarction and other revascularisation procedures, such as percutaneous transluminal angioplasty and coronary artery bypass surgery, may be associated with reperfusion of ischaemic myocardium. Such ischaemia and reperfusion may result in injury to one of more of the biochemical, cellular and microvascular components of the heart. Our understanding of the significance of reperfusion injury is however restricted by the profuse literature in animal models and limited literature in the clinical situation. This article reviews the pathophysiology, clinical manifestations of reperfusion injury to the heart and discusses the possible therapeutic approaches to avoiding any adverse effects.

Leukocyte activation with platelet adhesion after coronary angioplasty: a mechanism for recurrent disease?

OBJECTIVES

The purpose of this pilot study was to determine whether leukocyte activation occurs, whether leukocyte-platelet complexes develop and whether there is any association between these findings and clinical outcome after coronary angioplasty.

BACKGROUND

Increased expression of CD11b on monocytes and neutrophils promotes their adhesion to endothelial cells, extracellular matrix and smooth muscle cells. Thrombin-activated platelets adhere to monocytes and neutrophils through P-selectin. These cell complexes may affect the inflammatory process and, thus, the outcome of coronary angioplasty.

METHODS

During elective single-vessel coronary angioplasty in 11 men, samples were obtained for flow cytometric detection of CD11b, as well as the percent of leukocytes with adherent platelets and the intensity of bound platelet fluorescence (number of platelets/leukocyte).

RESULTS

After angioplasty, there was an increase in CD11b (monocytes: p = 0.001, neutrophils: p = 0.02) and leukocytes with adherent platelets (p = 0.02). During follow-up, five patients remained in stable condition and six had subsequent clinical events: restenosis and progression of disease requiring coronary artery bypass grafting (n = 3), myocardial infarction involving the dilated artery (n = 1) and unstable angina (n = 2). Values for leukocyte CD11b expression, the percent of leukocytes with adherent platelets and the intensity of bound platelet fluorescence were higher both before and after angioplasty in the six patients experiencing clinical events.

CONCLUSIONS

Despite standard aspirin and heparin therapy, leukocyte activation with platelet adherence occurs after coronary angioplasty. The magnitude of leukocyte activation and platelet adherence appears to be higher in patients experiencing late clinical events.

Biochemistry and cell biology of phospholipase D in human neutrophils

Neutrophils play a major role host defense against invading microbes. Recent studies have emphasized the importance of the phospholipase D (PLD) in the signalling cascade leading to neutrophil activation. Phospholipase D catalyzes the hydrolysis of phospholipids to generate phosphatidic acid with secondarily generation of diradylglycerol; both of these products have been implicated as second messengers. Herein, we discuss the regulation and the biochemistry of the receptor-regulated PLD in human neutrophils. In vivo and in vitro studies suggest an activation mode in which initial receptor-linked activation of phospholipase C generates diacylglycerol and inositol trisphosphate. The resulting calcium flux along with the diacylglycerol activate a conventional isoform of protein kinase C (PKC), probably PKC beta 1. This PKC, in turn phosphorylates a plasma membrane component resulting in PLD activation and a second outpouring of diradylglycerol. The small GTP-binding proteins, RhoA and ARF, also participate in this process, and synergize with a 50 kDa cytosolic regulatory factor.

The microvascular cell and ischemia-reperfusion injury

The vascular endothelium has a number of functions that may mediate many of the ischemia-reperfusion (IR) phenomena. The gatekeeper function is disturbed and increased capillary permeability results in edema and organ dysfunction. Vasomotor function is altered, with impairment of relaxation and augmentation of constrictor responses. Coagulation becomes imbalanced, favoring the procoagulant pathways that lead to thrombosis. Vascular adhesion molecules (integrins, selectins) are upregulated or expressed to mediate the adherence and subsequent destructive effects of neutrophils as they interact with the endothelium and the underlying organs. Finally, the more chronic vascular endothelial response may be proliferation of all cellular components of the vessel wall, leading, e.g., to intimal hyperplasia or restenosis. Ultimately, the endothelium plays a significant role either in the reparative processes that lead to recovery of the organ (myocardial stunning) or in the destructive processes that lead to cell or organ death (myocardial infarction). Our research group has been interested in the selectins, particularly E-selectin (endothelial) and P-selectin (platelet). E-selectin is not constitutively present on endothelial cells but can be upregulated by inflammatory mediators such as the cytokines tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), and endotoxin. We have investigated the upregulation of E-selectin with cytokines in both hypoxia and hypothermia. Hypoxia appears to enhance E-selectin upregulation on stimulation with IL-1 or TNF-alpha, although hypothermia (to 25 degrees C) blunts this response. With rewarming to 37 degrees C, the transduction and surface expression return.

Clinical biology of nitric oxide

Nitric oxide is a pluripotential molecule that acts as both an autocrine and paracrine mediator of homoeostasis, and derangement of its metabolism can be linked with many pathophysiological events. This review provides a broad overview of the basic and clinical scientific aspects of nitric oxide.

Endothelium, coronary vasodilation, and organic nitrates

Recent investigations have suggested that the vascular endothelium is an active participant in the regulation of arterial tone and blood flow. In a state of health, the endothelium contributes to hemodynamic equilibrium; however, it rapidly becomes dysfunctional in hypercholesterolemia and diabetes mellitus or with exposure to the stress of hypertension or long-term smoking. Among the deficits observed during endothelial dysfunction is a reduction in the synthesis and release or an excessive degradation of EDRF. This potent vasorelaxant is derived from the amino acid L-arginine and has been characterized as NO or a closely related substance. EDRF relaxes vascular smooth muscle by activating guanylate cyclase. A deficiency in the activity of EDRF may be the mechanism of diminished coronary vasodilation in patients with ischemic heart disease. Organic nitrates, which are metabolized to NO or S-nitrosothiol at the cellular level, are often used in the management of myocardial ischemia; they also induce vasodilation by activating guanylate cyclase. The similarities between organic nitrates and endogenous EDRF and their interactions are discussed in this review.

Modulation of neutrophil activity by nitric oxide during acute myocardial ischaemia and reperfusion

Nitric oxide (NO) exerts an inhibitory effect on polymorphonuclear neutrophil (PMN) function, via a cyclic GMP-mediated mechanism, while PMNs are known to play an important role in myocardial ischaemia-reperfusion injury (MI-R). Since the major source of NO, vascular endothelium, becomes functionally impaired during MI-R, it is attractive to hypothesize that it is this loss of endothelial nitric oxide production that allows PMN adherence and activation. The studies reviewed here add substance to this hypothesis. Authentic NO, administered during MI-R both reduces myocardial necrosis and PMN accumulation, while basal NO release, as estimated by coronary artery ring responses to L-NAME, an NO synthase inhibitor, declines during reperfusion with a time-course mirrored by PMN adherence in the same preparation. Reduction in infarct size and decreased PMN accumulation can also be demonstrated with L-arginine and NO donors. Since endothelial dysfunction leads to PMN adherence and PMNs have been shown to contribute to endothelial dysfunction, it seems probable that a positive feedback loop is generated during MI-R, leading to the amplification of PMN activity and subsequent myocardial damage.

Attenuation of coronary flow reserve and myocardial function after temporary subtotal coronary artery occlusion and increased myocardial oxygen demand in dogs

OBJECTIVES

We examined whether subtotal coronary artery occlusion and reperfusion alter coronary flow reserve and regional myocardial function.

BACKGROUND

Total coronary artery occlusion followed by reperfusion results in decreased coronary flow reserve and regional myocardial dysfunction.

METHODS

Thirteen anesthetized dogs were subjected to subtotal occlusion of the left anterior descending coronary artery for 1 h, followed by reperfusion for 1 h. During subtotal left anterior descending occlusion, heart rate was increased by atrial pacing. After reperfusion, coronary flow reserve, indicated by reactive hyperemia, as well as coronary flow responses to acetylcholine and nitroglycerin, regional myocardial function and myocardial leukocyte accumulation were measured.

RESULTS

After reperfusion, coronary flow reserve was decreased in the ischemic left anterior descending but not the nonischemic circumflex coronary artery region. Myocardial function was also depressed in the left anterior descending coronary region and did not improve on reperfusion. Histologic study showed no leukocyte infiltration in the ischemic left anterior descending coronary region. Myeloperoxidase, an index of myocardial leukocyte accumulation, was similar in the left anterior descending and circumflex coronary regions. Sensitivity of epicardial left anterior descending coronary artery rings to the thromboxane A2 analog U46,619 was enhanced, and relaxation of these rings in response to endothelium-dependent relaxants was decreased.

CONCLUSIONS

Coronary flow reserve is reduced and regional myocardial function depressed after subtotal coronary artery occlusion and increased heart rate. A decreased synthesis or increased breakdown of endothelium-derived relaxing factor may be related to a decrease in coronary flow reserve. However, the reduction in coronary flow reserve appears to be unrelated to leukocyte accumulation in the reperfused region.