Oxygen metabolism and the microbicidal activity of macrophages.

Like neutrophils, phagocytizing macrophages undergo a "respiratory burst" in which significant quantities of oxygen are drawn into the cell. The consumed oxygen is not used in oxidative phosphorylation but, rather, in the formation of superoxide anion (O2) and H2O2. These oxygen metabolites and the products of their interaction, in particular hydroxyl radical (OH), have been implicated in the killing of ingested bacteria by neutrophils. Their role in macrophage microbicidal activity has not been fully defined. However, activated macrophages, which mediate increased resistance to infection in vivo, have a markedly increased capacity to generate O2 and H2O2 in vitro when stimulated by phagocytosis or surface perturbation. The enhanced capacity of activated macrophages to generate highly reactive oxygen metabolites during phagocytosis could contribute to the improved microbicidal and tumoricidal activity of these cells.     

The role of free radicals in asbestos-induced diseases.

Asbestos exposure causes pulmonary fibrosis and malignant neoplasms by mechanisms that remain uncertain. In this review, we explore the evidence supporting the hypothesis that free radicals and other reactive oxygen species (ROS) are an important mechanism by which asbestos mediates tissue damage. There appears to be at least two principal mechanisms by which asbestos can induce ROS production; one operates in cell-free systems and the other involves mediation by phagocytic cells. Asbestos and other synthetic mineral fibers can generate free radicals in cell-free systems containing atmospheric oxygen. In particular, the hydroxyl radical often appears to be involved, and the iron content of the fibers has an important role in the generation of this reactive radical. However, asbestos also appears to catalyze electron transfer reactions that do not require iron. Iron chelators either inhibit or augment asbestos-catalyzed generation of the hydroxyl radical and/or pathological changes, depending on the chelator and the nature of the asbestos sample used. The second principal mechanism for asbestos-induced ROS generation involves the activation of phagocytic cells. A variety of mineral fibers have been shown to augment the release of reactive oxygen intermediates from phagocytic cells such as neutrophils and alveolar macrophages. The molecular mechanisms involved are unclear but may involve incomplete phagocytosis with subsequent oxidant release, stimulation of the phospholipase C pathway, and/or IgG-fragment receptor activation. Reactive oxygen species are important mediators of asbestos-induced toxicity to a number of pulmonary cells including alveolar macrophages, epithelial cells, mesothelial cells, and endothelial cells. Reactive oxygen species may contribute to the well-known synergistic effects of asbestos and cigarette smoke on the lung, and the reasons for this synergy are discussed. We conclude that there is strong evidence supporting the premise that reactive oxygen species and/or free radicals contribute to asbestos-induced and cigarette smoke/asbestos-induced lung injury and that strategies aimed at reducing the oxidant stress on pulmonary cells may attenuate the deleterious effects of asbestos.     

Chemiluminescence response of phagocytes in E. coli induced experimental ascending pyelonephritis.

The mechanism of tissue injury at the cellular level by following the chemiluminescence response of various phagocytes in E. coli induced experimental pyelonephritis in mice was investigated. There was a marked increase in the capacity of various phagocytic cells viz; renal neutrophils and macrophages peritoneal macrophages, blood monocytes and neutrophils to produce reactive oxygens species through the respiratory burst activity as monitored by the chemiluminescence response. The chemiluminescence response was observed to be increased significantly (p less than 0.001) with increasing days post infection in all phagocytic cells. However, the quantity of total reactive oxygen species produced per million cells was much more in the renal and peritoneal macrophages as compared to blood monocytes and neutrophils. The peak chemiluminescence response time was observed to be decreased from 4 to 2 minutes with the progression of the diseases. The implications of these findings have been discussed.     

Immunocytochemical identification of metallothionein- positive cells in rheumatoid synovium and analysis of their cell lineage

Metallothionein is a ubiquitous low molecular weight metalloprotein with powerful protective properties against oxygen radical-mediated cytotoxicity associated with inflammatory processes. In rheumatoid arthritis, the inflammatory damage to the synovium appears to be mediated by free radicals released by the high concentration of neutrophils found in the synovial fluid of the inflamed joint. Synovial tissue obtained during routine surgery on rheumatoid and non-rheumatoid joints was subjected to an indirect immunoperoxidase protocol for the immunolocalization of metallothionein using mouse monoclonal anti-metallothionein antibody E9, reactive against the two major isoforms of mammalian metallothionein. A layer of large dendritic-like cells situated subsynovially in the rheumatoid synovium stained very positively for the metalloprotein, both cytoplasmically and in their nuclei. These cells were not found in non-rheumatoid osteoarthritic or in undamaged synovial tissue associated with traumatic joint injury. An attempt was made to investigate their lineage using a series of antibody markers against epithelial cells, endothelial cells, smooth muscle, mesothelial cells, fibroblasts, neutrophils, dermal dendrocytes, macrophages, low and high molecular weight cytokeratin as well as a cell proliferation marker. From our results, it is suggested that these metallothionein-positive cells are probably myofibroblasts similar to the highly motile cells present in granulation tissue. They may originate from perivascular areas of synovium and their movement into the inflamed synovium may reflect the cytoprotective role of metallothionein acting as a free radical scavenger against oxidative damage     

Cytochemical studies of hydrogen peroxide production in the tadpole tail of Rana japonica during metamorphic climax

Summary The degeneration of tadpole tail tissue was investigated cytochemically by localizing the sites of hydrogen peroxide production. A cerium perhydroxide precipitation method was used. No reaction product was found in resting macrophages and intact muscle fibres during premetamorphosis. In the metamorphosis phase, extensive cerium precipitates were visualized on the outer surface of the plasma membrane of phagocytotic macrophages, fibroblasts, neutrophils, epidermal cells, muscle fibres, notochordal cells, nerve cells and capillary endothelial cells. The reaction products were localized on those parts of the plasma membranes of the macrophages that were in contact with those of adjoining cells. When catalase were added, the amount of deposits decreased. -Tocopherol and indomethacin, but not dexamethasone, significantly inhibited the formation of the reaction products. These findings are taken to indicate that active oxygen is produced on the plasma membrane of activated macrophages and may play a role in the degeneration of the tail tissue.     

Galectins as inflammatory mediators

Over the last decade a vast amount of reports have shown that galectin-1 and galectin-3 are important mediators of inflammation. In this review we describe how the galectins may be involved in several parts of the inflammatory process, including the recruitment of neutrophils into an infected tissue and the recognition and killing of bacteria by activation of the tissue destructive phagocytic respiratory burst. During bacterial infection or aseptic inflammatory processes, galectins are produced and released by e.g. infected epithelium, activated tissue-resident macrophages and endothelial cells. These extracellular galectins may facilitate binding of neutrophils to the endothelium by cross-linking carbohydrates on the respective cells. Further the galectins improve binding of the neutrophil to the extracellular matrix proteins laminin and fibronectin, and are potential chemotactic factors, inducing migration through the extracellular matrix towards the inflammatory focus. When the cells encounter bacteria, galectin-3 could function as an opsonin, cross-linking bacterial lipopolysaccharide or other carbohydrate-containing surface structures to phagocyte surface glycoconjugates. Both galectin-1 and galectin-3 have the capacity to induce a respiratory burst in neutrophils, provided that the cells have been primed by degranulation and receptor upregulation. The reactive oxygen species produced may be destructive to the invading micro-organisms as well as to the surrounding host tissue, pointing out the possible role of galectins, not only in defence toward infection, but also in inflammatory-induced tissue destruction.     

Metal ions and oxygen radical reactions in human inflammatory joint disease

Activated phagocytic cells produce superoxide (O2-) and hydrogen peroxide (H2O2); their production is important in bacterial killing by neutrophils and has been implicated in tissue damage by activated phagocytes. H2O2 and O2- are poorly reactive in aqueous solution and their damaging actions may be related to formation of more reactive species from them. One such species is hydroxyl radical (OH.), formed from H2O2 in the presence of iron- or copper-ion catalysts. A major determinant of the cytotoxicity of O2- and H2O2 is thus the availability and location of metal-ion catalysts of OH. formation. Hydroxyl radical is an initiator of lipid peroxidation. Iron promoters of OH. production present in vivo include ferritin, and loosely bound iron complexes detectable by the 'bleomycin assay'. The chelating agent Desferal (desferrioxamine B methanesulphonate) prevents iron-dependent formation of OH. and protects against phagocyte-dependent tissue injury in several animal models of human disease. The use of Desferal for human treatment should be approached with caution, because preliminary results upon human rheumatoid patients have revealed side effects. It is proposed that OH. radical is a major damaging agent in the inflamed rheumatoid joint and that its formation is facilitated by the release of iron from transferrin, which can be achieved at the low pH present in the micro-environment created by adherent activated phagocytic cells. It is further proposed that one function of lactoferrin is to protect against iron-dependent radical reactions rather than to act as a catalyst of OH. production.     

Galectins as inflammatory mediators

Over the last decade a vast amount of reports have shown that galectin-1 and galectin-3 are important mediators of inflammation. In this review we describe how the galectins may be involved in several parts of the inflammatory process, including the recruitment of neutrophils into an infected tissue and the recognition and killing of bacteria by activation of the tissue destructive phagocytic respiratory burst. During bacterial infection or aseptic inflammatory processes, galectins are produced and released by e.g. infected epithelium, activated tissue-resident macrophages and endothelial cells. These extracellular galectins may facilitate binding of neutrophils to the endothelium by cross-linking carbohydrates on the respective cells. Further the galectins improve binding of the neutrophil to the extracellular matrix proteins laminin and fibronectin, and are potential chemotactic factors, inducing migration through the extracellular matrix towards the inflammatory focus. When the cells encounter bacteria, galectin-3 could function as an opsonin, cross-linking bacterial lipopolysaccharide or other carbohydrate-containing surface structures to phagocyte surface glycoconjugates. Both galectin-1 and galectin-3 have the capacity to induce a respiratory burst in neutrophils, provided that the cells have been primed by degranulation and receptor upregulation. The reactive oxygen species produced may be destructive to the invading micro-organisms as well as to the surrounding host tissue, pointing out the possible role of galectins, not only in defence toward infection, but also in inflammatory-induced tissue destruction. Published in 2004.     

Effects of fibronectin on actin organization and respiratory burst activity in neutrophils,monocytes, and macrophages

Previous studies have shown that fibronectin (Fn) enhances phagocytosis and killing of antibody-coated bacteria by neutrophils and macrophages. In an attempt to understand the mechanism of this enhancement, we have investigated the effects of Fn on phagocytosis-related actin organization as well as respiratory burst activity in neutrophils, monocytes and culture-derived macrophages. Employing an NBD-phallacidin flow cytometric analysis of filamentous actin formation, we found that Fn promotes rapid actin polymerization within 30 seconds in neutrophils, monocytes, and macrophages, but not lymphocytes. Enhancement of actin polymerization by Fn was concentration-dependent and mediated by a pertussis toxin- but not cholera toxin- sensitive G protein. Inhibition of protein kinase C by sphingosine (20 μM), calcium influx by verapamil (0.1 mM), or intracellular calcium mobilization by 8-(N, N-diethyl-amino) octyl-3,4,5-trimethoxybenzoate HCI (TMB-8; 0.1 mM) did not block Fn-enhanced actin polymerization in phagocytes. Incubation of neutrophils and macrophages on microtiter plates precoated with Fn suppressed superoxide (O₂^?) production induced by IgG- and IgA- opsonized group B streptococci. In contrast, Fn significantly enhanced IgA- and IgG-mediated O₂^? production by freshly isolated monocytes. These data suggest that Fn enhances phagocytosis, presumably through G protein-coupled cytoskeleton reorganization and augments O₂^? production by circulating monocytes. In contrast, it appears to suppress O₂^? production by the active phagocytic cells, neutrophils and macrophages. This may result in enhanced phagocytosis and intracellular killing of microorganisms without damaging interstitial tissues. © 1994 Wiley-Liss, Inc.     

Oxygen radicals in the adult respiratory distress syndrome, in myocardial ischemia and reperfusion injury, and in cerebral vascular damage

Recent work suggests that oxygen radicals may be important mediators of damage in a wide variety of pathologic conditions. In this review we consider the evidence supporting the participation of oxygen radicals in the adult respiratory distress syndrome, in ischemia reperfusion injury in the myocardium, and in cerebral vascular injury in acute hypertension and traumatic brain injury. In the adult respiratory distress syndrome there is active sequestration of polymorphonuclear neutrophils in the pulmonary vascular system. There is evidence that activation of these neutrophils results in the production of oxygen radicals which injure the capillary membrane and increase permeability, leading to progressive hypoxia and decreased lung compliance which are hallmarks of the syndrome. In acute arterial hypertension or experimental brain injury oxygen radicals are important mediators of vascular damage. The metabolism of arachidonic acid is the source of oxygen free radical production in these conditions. In myocardial ischemia and reperfusion injury, the ischemic myocyte is "primed" for free radical production. With reperfusion and reintroduction of molecular oxygen there is a burst of oxygen radical production resulting in extensive tissue destruction. Myocardial ischemia--reperfusion injury shares in common with the other two syndromes activation of the arachidonic acid cascade and acute inflammation. Thus it would appear that the generation of toxic oxygen species may represent a final common pathway of tissue destruction in several pathophysiologic states.     

Superoxide responses of immune complex-stimulated rat alveolar macrophages. Intracellular calcium and priming

ATP is known to induce calcium transients in rat and human neutrophils and to "prime" these cells for enhanced oxygen radical responses after stimulation with chemotactic peptide, FMLP, or immune complexes. Calcium ionophores are also well known for their ability to prime phagocytic cells. In the current studies, nonelicited rat alveolar macrophages were analyzed for the ability of ATP as well as FMLP, C5a, platelet-activating factor and calcium ionophore (A23187) to modify levels of intracellular calcium and to enhance superoxide anion (O2-) production in response to immune complexes. Although none of these agents induced a O2- response under the conditions employed, all, except FMLP and C5a (human, recombinant) increased intracellular calcium, although the temporal features of the increases varied with the agent. In contrast to the inability of FMLP and C5a to cause intracellular calcium increases in macrophages, these same peptides caused dose-dependent intracellular calcium increases in rat neutrophils, whether the cells were derived from the blood or from the peritoneal cavity. On the basis of the effects of EGTA, the calcium increases in alveolar macrophages were caused by intracellular release of calcium in addition to some influx of extracellular calcium. Although ATP caused a dose-related increase in the level of intracellular calcium in alveolar macrophages, the cells were not "primed" for enhanced O2- responses to immune complexes. In contrast, platelet-activating factor and A23187, each of which induced increased intracellular levels of calcium, were able to prime macrophages for enhanced O2- responses. C5a and FMLP neither increased intracellular calcium levels nor primed macrophages for enhanced O2- responses to immune complexes. It is not clear if the inability of ATP to prime alveolar macrophages is caused entirely by insufficient increases in intracellular calcium or if ATP is unable to bring about additional changes that are relevant to the priming phenomenon.     

Live imaging reveals differing roles of macrophages and neutrophils during zebrafish tail fin regeneration

Macrophages and neutrophils are the pivotal immune phagocytes that enter the wound after tissue injury to remove the cell debris and invaded microorganisms, which presumably facilitate the regrowth of injured tissues. Taking advantage of the regeneration abilities of zebrafish and the newly generated leukocyte-specific zebrafish lines with labeling of both leukocyte lineages, we assessed the behaviors and functions of neutrophils and macrophages during tail fin regeneration. Live imaging showed that within 6 hours post amputation, the inflammatory stage, neutrophils were the primary cells scavenging apoptotic bodies and small cell debris, although they had limited phagocytic capacity and quickly underwent apoptosis. From 6 hours post amputation on, the resolution and regeneration stage, macrophages became the dominant scavengers, efficiently resolving inflammation and facilitating tissue remodeling and regrowth. Ablation of macrophages but not neutrophils severely impaired the inflammatory resolution and tissue regeneration, resulting in the formation of large vacuoles in the regenerated fins. In contrast, removal of neutrophils slightly accelerates the regrowth of injured fin. Our study documents the differing behaviors and functions of macrophages and neutrophils during tissue regeneration.     

The heterogenic properties of monocytes/macrophages and neutrophils in inflammatory response in diabetes

Inflammation is a complicated biological process in response to harmful stimuli, which involves the cooperation of immune system and vascular system. Upon pathogen invasion or tissue injury, resident innate immune cells such as macrophages and dendritic cells are activated and release inflammatory mediators, which result in the vasodilation and recruitment of leukocytes, mainly monocytes and neutrophils. As two of the most important inflammation-mediating immune cells, macrophages and neutrophils have long been regarded to have a pro-inflammatory effect. However, increasing evidences suggest the role of macrophage and neutrophil in inflammation is more complicated and diversified than we thought. Differently activated macrophages and neutrophils lead to diverse even opposite activities. Precise understanding of the role of different subpopulations is critical to achieve the effective treatment for inflammatory diseases. In this review, we discuss the two potentially distinct activation routes of macrophages and neutrophils in obesity and diabetes.     

Neutrophil-endothelial interactions: Modulation of neutrophil activation responses by endothelial cells

There is controversy concerning whether intravascular activation of neutrophils during acute inflammation injures contiguous endothelial cells in vivo. Several physiologic defense mechanisms tend to limit such injury. In this paper we have examined evidence for one of these putative protective mechanisms: endothelial cell modulation of the activation responses of neutrophils during adherence and diapedesis. In vitro, endothelial cells co-incubated with neutrophils inhibit the release of superoxide anion when stimulated by receptor-mediated activators. The possible mechanisms include contact-linked down-regulation of neutrophil activation, the release from endothelial cells of soluble mediators which attenuate neutrophil activation responses, and the presence of free radical scavengers in endothelial cells which are active at the interface between endothelial cells and adherent neutrophils. There may be a broad spectrum of mechanisms by which intercellular interactions protect the lining cells of the vascular lumen from 'inadvertent' destruction by phagocytes which become activated while in an intravascular location.     

The role of neutrophils and inflammation in gastric mucosal injury

Gastric inflammation is a highly complex biochemical protective response to cellular/tissue injury. When this process occurs in an uncontrolled manner, the result is excessive cellular/tissue damage that results chronic inflammation and destruction of normal tissue. Current evidence suggests that Helicobacter pylori (H. pylori) infection and nonsteroidal anti-inflammatory drug (NSAID) ingestion are major causative factors in the pathogenesis of gastric mucosal injury in humans. In response to H. pylori infection or NSAID, neutrophils are recruited to the site of inflammation and generate reactive oxygen and nitrogen species and proteases. However, neutrophils are not able to kill the bacteria that live in the gastric mucus, and compounds produced by activated neutrophils themselves may be potentially harmful for normal tissue. It has been shown that leukocyte-vascular endothelial cell interaction is regulated by various cell adhesion molecules, and that this interaction is directly or indirectly modified by many factors, the origin of which is H. pylori and NSAIDs. This review describes the potential role of neutrophils and neutrophil-associated inflammation for gastric oxidative stress and injury induced by H. pylori and/or NSAID.     

Essential role of methionine residues in calmodulin binding to Bordetella pertussis adenylate cyclase, as probed by selective oxidation and repair by the peptide methionine sulfoxide reductases

Bordetella pertussis, the causative agent of whooping cough, secretes among other virulence factors an adenylate cyclase (AC) toxin that is able to enter into eukaryotic cells where it is activated upon binding to endogenous calmodulin (CaM) and synthesizes supraphysiological cAMP levels. In vivo, the AC toxin, through its specific interaction with the CD11b/CD18 integrin, primarily targets phagocytic cells such as neutrophils and macrophages. Because neutrophil priming and activation result in the production of reactive oxygen species that may cause intracellular oxidation, we have examined the biological consequences of the oxidation of CaM methionines upon its interaction with AC. We show here that the interaction of CaM with AC is dependent on the reduced state of methionines, because oxidation of all methionine residues of CaM dramatically decreases its affinity for AC. Peptide methionine sulfoxide reductases A (MsrA) and B (MsrB) were able to partially reduce the oxidized CaM, and these partially "repaired" forms could interact with AC nearly as efficiently as the native protein. We further showed that the CaM.AC complex is resistant to oxidation with tert-butylhydroperoxide, and we identified methionine residues 109, 124, and 145 as critical for binding to AC. The resistance of the AC.CaM complex to oxidation and the ability of AC to be efficiently activated by partially oxidized CaM molecules should allow the toxin to exert its cytotoxic effects on activated neutrophils and contribute to the host colonization.     

Lung injury after deposition of IgA immune complexes. Requirements for CD18 and L-arginine.

Acute lung injury produced by deposition of IgA immune complexes is complement-dependent, neutrophil-independent, oxygen radical-mediated, and may be a result of the formation of the hydroxyl radical (HO) generated directly or indirectly from activated lung macrophages. The current studies were designed to evaluate further the pathophysiologic events that occur after intrapulmonary deposition of IgA immune complexes. Pretreatment of rats with the human recombinant soluble complement receptor-1 resulted in marked attenuation of IgA immune complex-induced lung injury. Intravenous administration of antibody to CD18, but not antibody to CD11b, was highly protective against lung injury. Treatment of animals with either anti-endothelial leukocyte-adhesion molecule-1 or anti-TNF-alpha, both of which were highly protective against IgG immune complex-induced lung injury, had no protective effects in the model of IgA immune complex-induced lung injury. Immunohistochemical analysis revealed up-regulation of the endothelial leukocyte adhesion molecule-1 in the pulmonary vasculature after deposition of IgA immune complexes. This up-regulation was TNF-alpha-dependent. The arginine analog, NG-monomethyl-L-arginine, was highly protective against IgA immune complex-induced lung injury. This protective effect was reversed by the co-presence of L-arginine (but not D-arginine). Protective interventions against IgA immune complex-induced lung injury were inversely correlated with the numbers of macrophages that could be retrieved by lung lavage. These data suggest fundamental differences in the pathogenesis of lung injury after intrapulmonary deposition of IgA immune complexes, as compared with injury caused by deposition of IgG immune complexes. In the latter, neutrophils, intrapulmonary generation of TNF-alpha, and up-regulation of pulmonary vascular endothelial leukocyte-adhesion molecule-1 are required for the full development of lung injury, whereas no such requirements appear in the case of IgA immune complex-induced lung injury. Full expression of IgA immune complex-induced lung injury also appears to require L-arginine, suggesting a possible role for nitric oxide or its derivatives in events ultimately leading to injury.     

Anaplasma phagocytophilum-infected neutrophils enhance transmigration of Borrelia burgdorferi across the human blood brain barrier in vitro

The manifestations of Lyme disease, caused by Ixodes spp. tick-transmitted Borrelia burgdorferi, range from skin infection to bloodstream invasion into the heart, joints and nervous system. The febrile infection human granulocytic anaplasmosis is caused by a neutrophilic rickettsia called Anaplasma phagocytophilum, also transmitted by Ixodes ticks. Previous studies suggest that co-infection with A. phagocytophilum contributes to increased spirochetal loads and severity of Lyme disease. However, a common link between these tick-transmitted pathogens is dissemination into blood or tissues through blood vessels. Preliminary studies show that B. burgdorferi binds and passes through endothelial barriers in part mediated by host matrix metalloproteases. Since neutrophils infected by A. phagocytophilum are activated to release bioactive metalloproteases and chemokines, we examined the enhanced B. burgdorferi transmigration through vascular barriers with co-infection in vitro. To test whether endothelial transmigration is enhanced with co-infection, B. burgdorferi and A. phagocytophilum-infected neutrophils were co-incubated with EA.hy926 cells (HUVEC-derived) and human brain microvascular endothelial cells in Transwell cultures. Transmigration of B. burgdorferi through endothelial cell barriers was determined and endothelial barrier integrity was measured by transendothelial electrical resistivity. More B. burgdorferi crossed both human BMEC and EA.hy926 cells in the presence of A. phagocytophilum-infected neutrophils than with uninfected neutrophils without affecting endothelial cell integrity. Such a mechanism may contribute to increased blood and tissue spirochete loads.     

Endotoxin-mediated necrosis and regression of established tumours in the mouse

Summary The fractional distribution of cardia output was measured in tumour-bearing mice treated with 50 g intravenous endotoxin, and correlated with ultrastructural changes in tumour morphology.The proportion of the cardiac output going to the tumour decreased to less than 50% of its original value by 2 h and to 10%–30% by 6 h after giving endotoxin. Because endotoxin decreases absolute cardiac output, the actual perfusion of the tumour will be considerably less than these figures suggest.The decrease in perfusion correlated closely with changes in vascular morphology. Venous congestion on the tumour edge started within 1 h of giving endotoxin and by 3 h, endothelial damage and platelet aggregates were visible. At this time, all cells, tumour, connective tissue and infiltrate in the tumour centre were dead or damaged.By 24–48 h a conspicuous infiltrate of neutrophils and macrophages was present on the edge of the tumour and many of these cells were closely related to tumour cells.We suggest that the haemorrhagic necrosis may be caused by vascular obstruction leading to hypoxia and that the subsequent regression is mediated by activated macrophages and perhaps by neutrophils.     

Inhibition of angiotensin-converting enzyme protects endothelial cell against hypoxia/reoxygenation injury

Cardiovascular tissue injury in ischemia/reperfusion has been shown to be prevented by angiotensin-converting enzyme (ACE) inhibitors. However, the mechanism on endothelial cells has not been assessed in detail. Cultured human aortic endothelial cells (HAEC) were exposed to hypoxia with or without reoxygenation. Hypoxia enhanced apoptosis along with the activation of caspase-3. Reoxygenation increased lactate dehydrogenase release time-dependently, along with an increase of intracellular oxygen radicals. ACE inhibitor quinaprilat and bradykinin significantly lessened apoptosis and lactate dehydrogenase release with these effects being diminished by a kinin B2 receptor antagonist and a nitric oxide synthase inhibitor. In conclusion, hypoxia activated the suicide pathway leading to apoptosis of HAEC by enhancing caspase-3 activity, while subsequent reoxygenation induced necrosis by enhancing oxygen radical production. Quinaprilat could ameliorate both apoptosis and necrosis through the upregulation of constitutive endothelial nitric oxide synthase via an increase of bradykinin, with the resulting increase of nitric oxide.