Heme induces neutrophil migration and reactive oxygen species generation through signaling pathways characteristic of chemotactic receptors

Differential gene expression analysis of placentas with increased vascular resistance and pre-eclampsia using whole-genome microarrays

Pre-eclampsia is a pregnancy complication characterized by hypertension and proteinuria. There are several factors associated with an increased risk of developing pre-eclampsia, one of which is increased uterine artery resistance, referred to as “notching”. However, some women do not progress into pre-eclampsia whereas others may have a higher risk of doing so. The placenta, central in pre-eclampsia pathology, may express genes associated with either protection or progression into pre-eclampsia. In order to search for genes associated with protection or progression, whole-genome profiling was performed. Placental tissue from 15 controls, 10 pre-eclamptic, 5 pre-eclampsia with notching, and 5 with notching only were analyzed using microarray and antibody microarrays to study some of the same gene product and functionally related ones. The microarray showed 148 genes to be significantly altered between the four groups. In the preeclamptic group compared to notch only, there was increased expression of genes related to chemotaxis and the NF-kappa B pathway and decreased expression of genes related to antigen processing and presentation, such as human leukocyte antigen B. Our results indicate that progression of pre-eclampsia from notching may involve the development of inflammation. Increased expression of antigen-presenting genes, as seen in the notch-only placenta, may prevent this inflammatory response and, thereby, protect the patient from developing pre-eclampsia.

Pulmonary proteases in the cystic fibrosis lung induce interleukin 8 expression from bronchial epithelial cells via a heme/meprin/epidermal growth factor receptor/Toll-like receptor pathway

A high intrapulmonary protease burden is characteristic of cystic fibrosis (CF), and the resulting dysregulation of the protease/anti-protease balance has serious implications for inflammation in the CF lung. Because of this inflammation, micro-bleeds can occur releasing hemoglobin into the lung. The aim of this study was to investigate the effect of the protease-rich environment of the CF lung on human hemoglobin and to assess the proinflammatory effect of heme on CF bronchial epithelium. Here, we show that the Pseudomonas proteases (Pseudomonas elastase and alkaline protease) and the neutrophil proteases (neutrophil elastase (NE) and proteinase-3) are capable of almost complete degradation of hemoglobin in vitro but that NE is the predominant protease that cleaves hemoglobin in vivo in CF bronchoalveolar lavage fluid. One of the effects of this is the release of heme, and in this study we show that heme stimulates IL-8 and IL-10 protein production from ΔF508 CFBE41o(-) bronchial epithelial cells. In addition, heme-induced IL-8 expression utilizes a novel pathway involving meprin, EGF receptor, and MyD88. Meprin levels are elevated in CF cell lines and bronchial brushings, thus adding to the proinflammatory milieu. Interestingly, α(1)-antitrypsin, in addition to its ability to neutralize NE and protease-3, can also bind heme and neutralize heme-induced IL-8 from CFBE41o(-) cells. This study illustrates the proinflammatory effects of micro-bleeds in the CF lung, the process by which this occurs, and a potential therapeutic intervention.

Heme oxygenase system in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) limits access to transplantation. Heme oxygenase-1 (HO-1) is a powerful antioxidant enzyme which degrades free heme into biliverdin, free iron and carbon monoxide. HO-1 and its metabolites have the ability to modulate a wide variety of inflammatory disorders including hepatic IRI. Mechanisms of this protective effect include reduction of oxygen free radicals, alteration of macrophage and T cell phenotype. Further work is required to understand the physiological importance of the many actions of HO-1 identified experimentally, and to harness the protective effect of HO-1 for therapeutic potential.

Heme amplifies the innate immune response to microbial molecules through spleen tyrosine kinase (Syk)-dependent reactive oxygen species generation

Infectious diseases that cause hemolysis are among the most threatening human diseases, because of severity and/or global distribution. In these conditions, hemeproteins and heme are released, but whether heme affects the inflammatory response to microorganism molecules remains to be characterized. Here, we show that heme increased the lethality and cytokine secretion induced by LPS in vivo and enhanced the secretion of cytokines by macrophages stimulated with various agonists of innate immune receptors. Activation of nuclear factor κB (NF-κB) and MAPKs and the generation of reactive oxygen species were essential to the increase in cytokine production induced by heme plus LPS. This synergistic effect of heme and LPS was blocked by a selective inhibitor of spleen tyrosine kinase (Syk) and was abrogated in dendritic cells deficient in Syk. Moreover, inhibition of Syk and the downstream molecules PKC and PI3K reduced the reactive oxygen species generation by heme. Our results highlight a mechanism by which heme amplifies the secretion of cytokines triggered by microbial molecule activation and indicates possible pathways for therapeutic intervention during hemolytic infectious diseases.

Increased circulating cell-free hemoglobin levels reduce nitric oxide bioavailability in preeclampsia

Contrasting with increased nitric oxide (NO) formation during healthy pregnancy, reduced NO bioavailability plays a role in preeclampsia. However, no study has examined whether increased NO consumption by enhanced circulating levels of cell-free hemoglobin plays a role in preeclampsia. We studied 82 pregnant women (38 healthy pregnant and 44 with preeclampsia). To assess NO bioavailability, we measured plasma and whole blood nitrite concentrations using an ozone-based chemiluminescence assay. Plasma ceruloplasmin concentrations and plasma NO consumption (pNOc) were assessed and plasma hemoglobin (pHb) concentrations were measured with a commercial immunoassay. We found lower whole blood and plasma nitrite concentrations in preeclamptic patients (-48 and -39%, respectively; both P<0.05) compared with healthy pregnant women. Plasma samples from preeclamptic women consumed 63% more NO (P=0.003) and had 53% higher pHb and 10% higher ceruloplasmin levels than those found in healthy pregnant women (P<0.01). We found significant positive correlations between pHb and pNOc (r=0.61; P<0.0001), negative correlations between pNOc and whole blood or plasma nitrite concentrations (P=0.02; r=-0.32 and P=0.01; r=-0.34, respectively), and negative correlations between pHb and whole blood or plasma nitrite concentrations (P=0.03; r=-0.36 and P=0.01; r=-0.38, respectively). These findings suggest that increased pHb levels lead to increased NO consumption and lower NO bioavailability in preeclamptic compared with healthy pregnant women.

Effects of a single sickling event on the mechanical fragility of sickle cell trait erythrocytes

Hemolysis contributes to the pathology associated with sickle cell disease. However, the mechanism of hemolysis or relative contribution of sickling due to hemoglobin (Hb) polymerization vs. oxidative damage remains unknown. Earlier studies aimed at deciphering the relative importance of these two mechanisms have been complicated by the fact that sickle red cells (SS) have already been affected by multiple rounds of sickling and oxidative damage before they are collected. In our study, we examine the mechanical fragility of sickle cell trait cells, which do not sickle in vivo, but can be made to do so in vitro. Thus, our novel approach explores the effects of sickle Hb polymerization on cells that have never been sickled before. We find that the mechanical fragility of these cells increases dramatically after a single sickling event, suggesting that a substantial amount of hemolysis in vivo probably occurs in polymer-containing cells.

Effect of repeated arthrocentesis on cytologic analysis of synovial fluid in dogs

BACKGROUND

Serial arthrocentesis and synovial fluid examination can be used to monitor treatment efficacy in immune-mediated polyarthritis (IMPA), but whether this procedure induces inflammation that interferes with test result interpretation is unknown.

OBJECTIVES

The aim of this study was to determine the effect of repeated arthrocentesis on synovial fluid cytology in healthy dogs.

ANIMALS

Nine healthy client-owned dogs.

METHODS

Prospective study. Arthrocentesis was performed under sedation on 4 joints (both carpi, 1 tarsus, 1 stifle) on each dog every 3 weeks, a total of 4 times. Automated cell counts were done on stifle fluid, smears were made, and differential cell counts done on smears from all joints. Slides were evaluated microscopically for erythrocyte numbers, total nucleated cell count, differential cell count, and cell morphology. Data were analyzed by 2-way analysis of variance.

RESULTS

A total of 144 synovial fluid samples were examined. Repeated arthrocentesis was not associated with increases in synovial fluid neutrophil numbers. Mild mononuclear inflammation was detected in 13 samples from 6 dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Serial arthrocentesis at 3-week intervals can rarely be associated with mild mononuclear joint inflammation, but does not appear to induce neutrophilic inflammation, at least in healthy dogs, and can be useful to monitor treatment response in canine IMPA.

Immunoregulatory effects of HO-1: how does it work?

The heme-catabolizing enzyme heme oxygenase-1 (HO-1; encoded by the Hmox1 gene) inhibits the pathogenesis of several immune-mediated inflammatory diseases. This unusually broad salutary effect is thought to rely on the immunoregulatory actions of HO-1, exerted on innate and adaptive immune cells. According to this notion, HO-1 'dampens' innate and adaptive immune responses, limiting immune-mediated tissue injury and thus suppressing the pathogenesis of immune-mediated inflammatory diseases. We will argue that the salutary effects of HO-1 are also exerted via its cytoprotective action, which sustains tissue function and prevents unfettered immune activation by endogenous proinflammatory ligands released from injured cells.

On the fate of extracellular hemoglobin and heme in brain

Intracerebral hemorrhage (ICH) is a major cause of disability in adults worldwide. The pathophysiology of this syndrome is complex, involving both inflammatory and redox components triggered by the extravasation of blood into the cerebral parenchyma. Hemoglobin, heme, and iron released therein seem be important in the brain damage observed in ICH. However, there is a lack of information concerning hemoglobin traffic and metabolism in brain cells. Here, we investigated the fate of hemoglobin and heme in cultured neurons and astrocytes, as well as in the cortex of adult rats. Hemoglobin was made traceable by conjugation to Alexa 488, whereas a fluorescent heme analogue (tin-protoporphyrin IX) was prepared to allow heme tracking. Using fluorescence microscopy we observed that neurons were more efficient in uptake hemoglobin and heme than astrocytes. Exposure of cortical neurons to hemoglobin or heme resulted in an oxidative stress condition. Viability assays showed that neurons were more susceptible to both hemoglobin and heme toxicity than astrocytes. Together, these results show that neurons, rather than astrocytes, preferentially take up hemoglobin-derived products, indicating that these cells are actively involved in the ICH-associated brain damage.

Surgical inflammation: a pathophysiological rainbow

Tetrapyrrole molecules are distributed in virtually all living organisms on Earth. In mammals, tetrapyrrole end products are closely linked to oxygen metabolism. Since increasingly complex trophic functional systems for using oxygen are considered in the post-traumatic inflammatory response, it can be suggested that tetrapyrrole molecules and, particularly their derived pigments, play a key role in modulating inflammation.

In this way, the diverse colorfulness that the inflammatory response triggers during its evolution would reflect the major pathophysiological importance of these pigments in each one of its phases. Therefore, the need of exploiting this color resource could be considered for both the diagnosis and treatment of the inflammation.

Loss of red cell chemokine scavenging promotes transfusion-related lung inflammation

Red cell transfusions are associated with the development of acute lung injury in the critically ill. Recent evidence suggests that storage induced alterations of the red blood cell (RBC) collectively termed the "storage lesion" may be linked with adverse biologic consequences. Using a 2-event model of systemic endotoxemia followed by a secondary challenge of RBC transfusion, we investigated whether purified RBC concentrates from syngeneic C57BL/6 mice altered inflammatory responses in murine lungs. Transfusion of RBCs stored for 10 days increased neutrophil counts, macrophage inflammatory protein-2 (MIP-2) and chemokine (KC) concentrations in the airspaces, and lung microvascular permeability compared with transfusion of less than 1-day-old RBCs. Because RBCs have been shown to scavenge inflammatory chemokines through the blood group Duffy antigen, we investigated the expression and function of Duffy during storage. In banked human RBCs, both Duffy expression and chemokine scavenging function were reduced with increasing duration of storage. Transfusion of Duffy knockout RBCs into Duffy wild-type endotoxemic mice increased airspace neutrophils, inflammatory cytokine concentrations, and lung microvascular permeability compared with transfusion of Duffy wild-type RBCs. Thus, reduction in erythrocyte chemokine scavenging is one functional consequence of the storage lesion by which RBC transfusion can augment existing lung inflammation.

Heme induces endothelial tissue factor expression: potential role in hemostatic activation in patients with hemolytic anemia

OBJECTIVES

We explored the possibility that heme, an inflammatory mediator and a product of intravascular hemolysis in patients with hemolytic anemia including sickle cell disease, could modulate hemostasis by an effect on endothelial tissue factor (TF) expression.

METHODS

Levels of TF mRNA, protein and procoagulant activity were measured in heme-treated endothelial cells.

RESULTS

Heme induces TF expression on the surface of both macrovascular and microvascular endothelial cells in a concentration-dependent manner, with 12-fold to 50-fold induction being noted (enzyme-linked immunosorbent assay) between 1 and 100 microm heme (P < 0.05). Complementary flow cytometry studies showed that the heme-mediated endothelial TF expression was quantitatively similar to that of tumor necrosis factor-alpha (TNF-alpha). Heme also upregulated the expression of TF mRNA (8-fold to 26-fold), protein (20-fold to 39-fold) and procoagulant activity (5-fold to 13-fold) in endothelial cells in a time-dependent manner. The time-course of heme-mediated TF antigen expression paralleled the induction of procoagulant activity, with antibody blocking studies demonstrating specificity for TF protein. Interleukin (IL)-1alpha, and TNF-alpha are not involved in mediating the heme effect, as antibodies against these cytokines and IL-1-receptor antagonist failed to block heme-induced TF expression. Inhibition of heme-induced TF mRNA expression by sulfasalazine and curcumin suggested that the transcription factor nuclear factor kappaB is involved in mediating heme-induced TF expression in endothelial cells.

CONCLUSIONS

Our results demonstrate that heme induces TF expression by directly activating endothelial cells, and that heme-induced endothelial TF expression may provide a pathophysiologic link between the intravascular hemolytic milieu and the hemostatic perturbations previously noted in patients with hemolytic anemia including sickle cell disease.

Trypanosoma cruzi infection is enhanced by vector saliva through immunosuppressant mechanisms mediated by lysophosphatidylcholine

Trypanosoma cruzi, the etiological agent of Chagas disease, is transmitted by bug feces deposited on human skin during a blood meal. However, parasite infection occurs through the wound produced by insect mouthparts. Saliva of the Triatominae bug Rhodnius prolixus is a source of lysophosphatidylcholine (LPC). Here, we tested the role of both triatomine saliva and LPC on parasite transmission. We show that vector saliva is a powerful inducer of cell chemotaxis. A massive number of inflammatory cells were found at the sites where LPC or saliva was inoculated into the skin of mice. LPC is a known chemoattractant for monocytes, but neutrophil recruitment induced by saliva is LPC independent. The preincubation of peritoneal macrophages with saliva or LPC increased fivefold the association of T. cruzi with these cells. Moreover, saliva and LPC block nitric oxide production by T. cruzi-exposed macrophages. The injection of saliva or LPC into mouse skin in the presence of the parasite induces an up-to-sixfold increase in blood parasitemia. Together, our data suggest that saliva of the Triatominae enhances T. cruzi transmission and that some of its biological effects are attributed to LPC. This is a demonstration that a vector-derived lysophospholipid may act as an enhancing factor of Chagas disease.

The reaction of hydrogen peroxide with hemoglobin induces extensive alpha-globin crosslinking and impairs the interaction of hemoglobin with endogenous scavenger pathways

Cell-free hemoglobin (Hb) enhances the oxidation-related toxicity associated with inflammation, ischemia, and hemolytic disorders. Hb is highly vulnerable to oxidative damage, and irreversible structural changes involving iron/heme oxidation, heme-adduct products, and amino acid oxidation have been reported. Specific structural features of Hb, such as unconstrained alpha-chains and molecular size, determine the efficiency of interactions between the endogenous Hb scavengers haptoglobin (Hp) and CD163. Using HPLC, mass spectrometry, and Western blotting, we show that H(2)O(2)-mediated Hb oxidation results in the formation of covalently stabilized globin multimers, with prominent intramolecular crosslinking between alpha-globin chains. These structural alterations are associated with reduced Hp binding, reduced CD163 interaction, and severely impaired endocytosis of oxidized Hb by the Hp-CD163 pathway. As a result, when exposed to oxidized Hb, CD163-positive HEK293 cells and human macrophages do not increase hemeoxygenase-1 (HO-1) expression, the physiological anti-oxidative macrophage response to Hb exposure. Failed Hb clearance, inadequate HO-1 expression, and the subsequent accumulation of oxidatively damaged Hb species might thus contribute to pathologies related to oxidative stress.

Structural stabilization in tetrameric or polymeric hemoglobin determines its interaction with endogenous antioxidant scavenger pathways

Hemoglobin (Hb) released into the circulation during hemolysis and chemically modified Hb proposed for use as oxygen therapeutics exert toxic effects that are partially attributable to heme's oxidant activity. Native extracellular Hb is scavenged by haptoglobin (Hp) after alphabeta-subunit dimerization. In the absence of Hp, monocyte/macrophage cell-surface CD163 binds and clears Hb. We evaluated several chemically modified Hbs to establish the role of chemical cross-linking patterns and molecular sizes on binding and clearance by each pathway. We found that Hbs possessing beta-globin cross-linking, irrespective of polymerization, demonstrate increased Hp affinity compared with alpha-globin-stabilized Hbs. These data suggest that Hb alpha-subunit accessibility is critical for Hp binding in the absence of dimerization. beta-Globin chain cross-linked tetramers/polymers displayed strong polyvalent Hp binding with increased viscosity and formation of visible gel matrices. Modified Hb interaction with CD163 and cellular uptake demonstrated an inverse relation with molecular size, irrespective of alpha and beta cross-linking. These findings were confirmed by HO-1 induction and intracellular ferritin accumulation in CD163-expressing HEK293 cells. Based on these results, a rational and systematic approach to HBOC design may be used to optimize interaction with endogenous Hb clearance and detoxification pathways.

A central role for free heme in the pathogenesis of severe malaria: the missing link?

Malaria, the disease caused by Plasmodium infection, is endemic to poverty in so-called underdeveloped countries. Plasmodium falciparum, the main infectious Plasmodium species in sub-Saharan countries, can trigger the development of severe malaria, including cerebral malaria, a neurological syndrome that claims the lives of more than one million children (<5 years old) per year. Attempts to eradicate Plasmodium infection, and in particular its lethal outcomes, have so far been unsuccessful. Using well-established rodent models of malaria infection, we found that survival of a Plasmodium-infected host is strictly dependent on the host's ability to up-regulate the expression of heme oxygenase-1 (HO-1 encoded by the gene Hmox1). HO-1 is a stress-responsive enzyme that catabolizes free heme into biliverdin, via a reaction that releases Fe and generates the gas carbon monoxide (CO). Generation of CO through heme catabolism by HO-1 prevents the onset of cerebral malaria. The protective effect of CO is mediated via its binding to cell-free hemoglobin (Hb) released from infected red blood cells during the blood stage of Plasmodium infection. Binding of CO to cell-free Hb prevents heme release and thus generation of free heme, which we found to play a central role in the pathogenesis of cerebral malaria. We will address hereby how defense mechanisms that prevent the deleterious effects of free heme, including the expression of HO-1, impact on the pathologic outcome of Plasmodium infection and how these may be used therapeutically to suppress its lethal outcomes.

Placental expression profiling in preeclampsia: local overproduction of hemoglobin may drive pathological changes

OBJECTIVE

To create a library enriched in cDNAs from preeclamptic placentas to print onto microarrays for placental profiling of preeclampsia (PE) and high risk pregnancies.

DESIGN

Prospective study.

SETTING

University women's clinic and academic research laboratory.

PATIENT(S)

Ten patients with PE, 5 with PE and bilateral notching, 5 with bilateral notching without PE, and 15 normotensive patients were recruited.

INTERVENTION(S)

Placenta and placenta bed biopsies were collected after delivery.

MAIN OUTCOME MEASURE(S)

Subtracted libraries of PE transcripts were produced, and cDNAs from these libraries were used to make PE-specific cDNA arrays. Results were verified quantitatively using real-time polymerase chain reaction (PCR) and histologically using in situ hybridization and immunohistochemistry.

RESULT(S)

Thirty genes were significantly altered in at least one group comparison. Differences in two candidate genes were confirmed using quantitative real-time PCR. Hemoglobin alpha2 and gamma transcripts were significantly overexpressed in the PE placenta. Scattered cells in the placenta and placental blood vessels were shown to express genes encoding these hemoglobin chains.

CONCLUSION(S)

We demonstrate increased hemoglobin production in the PE placenta. The hemoglobin may be released into the placenta blood vessel lumen. Free heme and hemoglobin are potent toxins that cause endothelial damage and inflammation.