Globin attenuates the innate immune response to endotoxin

Hemeprotein amplifies the innate immune receptors of Ctenopharyngodon idellus kidney cells through NF-κB- and MAPK-dependent reactive oxygen species generation

Infectious bacterial and viral diseases that cause hemolysis are considered life-threatening to grass carp (Ctenopharyngodon idellus), which is a species used in aquaculture worldwide. After heme and hemeproteins (Hb) are released as a result of hemolysis, the effect of excess Hb and heme on tissues remains to be characterized. To decipher the mechanisms, after incubation with Hb, we showed that lipopolysaccharide (LPS), Hb, and heme increased the cytotoxicity and secretion of inflammatory cytokines such as interleukin (IL)-6, chemokine (C-C motif) ligand 1 (CCL1), tumor necrosis factor (TNF)-α, IL-6, and IL-1β in vitro, which was due to stimulation of the expression of innate immune receptors, such as nucleotide-binding oligomerization domain (NOD2), toll-like receptor 2 (TLR2), TLR 4, and TLR3. The formation of reactive oxygen species (ROS) and the activation of mitogen-activated protein kinases (MAPKs) and nuclear factor (NF)-κB were important for increasing the cytokine production to induce heme, Hb, and LPS. Moreover, we confirmed that after LPS, Hb, and heme challenge, superoxide dismutase (SOD) and glutathione (GSH) synthetase (GSS) also caused remarkable destruction. However, catalase (CAT) and heme oxygenase-1 (HO-1) were strongly activated. In summary, our research findings present a framework through which heme and Hb concentrations amplify the secretions of inflammatory cytokines, which are induced by pattern recognition receptor (PRR) activation and present possible paths for immune intervention during infection with viral diseases and hemolytic bacterial.

Mechanisms of haemolysis-induced kidney injury

Intravascular haemolysis is a fundamental feature of chronic hereditary and acquired haemolytic anaemias, including those associated with haemoglobinopathies, complement disorders and infectious diseases such as malaria. Destabilization of red blood cells (RBCs) within the vasculature results in systemic inflammation, vasomotor dysfunction, thrombophilia and proliferative vasculopathy. The haemoprotein scavengers haptoglobin and haemopexin act to limit circulating levels of free haemoglobin, haem and iron - potentially toxic species that are released from injured RBCs. However, these adaptive defence systems can fail owing to ongoing intravascular disintegration of RBCs. Induction of the haem-degrading enzyme haem oxygenase 1 (HO1) - and potentially HO2 - represents a response to, and endogenous defence against, large amounts of cellular haem; however, this system can also become saturated. A frequent adverse consequence of massive and/or chronic haemolysis is kidney injury, which contributes to the morbidity and mortality of chronic haemolytic diseases. Intravascular destruction of RBCs and the resulting accumulation of haemoproteins can induce kidney injury via a number of mechanisms, including oxidative stress and cytotoxicity pathways, through the formation of intratubular casts and through direct as well as indirect proinflammatory effects, the latter via the activation of neutrophils and monocytes. Understanding of the detailed pathophysiology of haemolysis-induced kidney injury offers opportunities for the design and implementation of new therapeutic strategies to counteract the unfavourable and potentially fatal effects of haemolysis on the kidney.

The Evolving Erythrocyte: Red Blood Cells as Modulators of Innate Immunity

The field of red cell biology is undergoing a quiet revolution. Long assumed to be inert oxygen carriers, RBCs are emerging as important modulators of the innate immune response. Erythrocytes bind and scavenge chemokines, nucleic acids, and pathogens in circulation. Depending on the conditions of the microenvironment, erythrocytes may either promote immune activation or maintain immune quiescence. We examine erythrocyte immune function through a comparative and evolutionary lens, as this framework may offer perspective into newly recognized roles of human RBCs. Next, we review the known immune roles of human RBCs and discuss their activity in the context of sepsis where erythrocyte function may prove important to disease pathogenesis. Given the limited success of immunomodulatory therapies in treating inflammatory diseases, we propose that the immunologic function of RBCs provides an understudied and potentially rich area of research that may yield novel insights into mechanisms of immune regulation.

Identification of neuroglobin as a novel player in anti-bacterial responses in amphioxus

Theoretical considerations support various functions of neuroglobin (Ngb), but further studies are required for full characterization of these functions. In this study, we identified the presence of a single Ngb gene, BjNgb, in the amphioxus Branchiostoma japonicum. BjNgb was expressed in various tissues including the notochord, gonads (ovary and testis) and gill, and up-regulated significantly in response to the challenge with LPS and LTA, suggesting involvement in immune response of amphioxus against bacterial infection. In accord, we demonstrated for the first time that recombinant BjNgb (rBjNgb) not only interacted with the Gram-positive and negative bacteria as well as their conserved surface components LPS and LTA, but also enhanced the phagocytosis of bacteria by macrophages. Collectively, these data suggest that BjNgb is a novel player in amphioxus, via functioning as a pattern recognition molecule and an opsonin.

Characterization of gene expression associated with the adaptation of the nematode C. elegans to hypoxia and reoxygenation stress reveals an unexpected function of the neuroglobin GLB-5 in innate immunity

Oxygen (O₂) is a double-edged sword to cells, for while it is vital for energy production in all aerobic animals and insufficient O₂ (hypoxia) can lead to cell death, the reoxygenation of hypoxic tissues may trigger the generation of reactive oxygen species (ROS) that can destroy any biological molecule. Indeed, both hypoxia and hypoxia-reoxygenation (H/R) stress are harmful, and may play a critical role in the pathophysiology of many human diseases, such as myocardial ischemia and stroke. Therefore, understanding how animals adapt to hypoxia and H/R stress is critical for developing better treatments for these diseases. Previous studies showed that the neuroglobin GLB-5(Haw) is essential for the fast recovery of the nematode Caenorhabditis elegans (C. elegans) from H/R stress. Here, we characterize the changes in neuronal gene expression during the adaptation of worms to hypoxia and recovery from H/R stress. Our analysis shows that innate immunity genes are differentially expressed during both adaptation to hypoxia and recovery from H/R stress. Moreover, we reveal that the prolyl hydroxylase EGL-9, a known regulator of both adaptation to hypoxia and the innate immune response, inhibits the fast recovery from H/R stress through its activity in the O₂-sensing neurons AQR, PQR, and URX. Finally, we show that GLB-5(Haw) acts in AQR, PQR, and URX to increase the tolerance of worms to Pseudomonas aeruginosa pathogenesis. Together, our studies suggest that innate immunity and recovery from H/R stress are regulated by overlapping signaling pathways.

A quartz crystal microbalance sensor for endotoxin assay by monitoring limulus amebocyte lysate protease reaction

Endotoxin is able to trigger strong innate immune responses by interacting with specific receptors on immune cells. Therefore, accurate and rapid detection of endotoxin is of primary importance. In this study, endotoxin induced viscosity variation of limulus amebocyte lysate (LAL) reagent is monitored by a quartz crystal microbalance (QCM) sensor with enhanced signal. Based on the analysis of the relationship between endotoxin concentration and QCM frequency shift with time, an effective sensing strategy is developed for endotoxin assay, which shows excellent sensitivity and specificity in the linear detection range from 0.005 to 10 EU mL^-1. Moreover, this QCM sensor could be reused after a simple regeneration procedure. Therefore, it has potential practical utility for endotoxin determination in various applications.

Liver argininosuccinate synthase binds to bacterial lipopolysaccharides and lipid A and inactivates their biological activities

The liver is known to clear and detoxify circulating lipopolysaccharide (LPS). To characterize the molecules involved in this process in the liver, we attempted to purify mouse liver protein(s) that can interact with lipid A, a biologically active portion of LPS. By partially purifying the inactivating activity against a synthetic lipid A analog, we observed the enrichment of a 45-kDa protein in the active fractions. The internal amino acid sequences of the protein were identical with those of argininosuccinate synthase (EC 6.3.4.5). To examine whether argininosuccinate synthase can interact with lipid A, we purified the enzyme from mouse liver and found the co-elevation of the specific enzyme activity and specific lipid A-inactivating activity, indicating that argininosuccinate synthase is the major lipid A-interacting protein in liver. Argininosuccinate synthase also inhibited the biological activities (macrophage activation and Limulus test) of natural lipid A and rough-type LPS but not smooth-type LPS. The enzyme activity was inhibited by lipid A and rough-type LPS and also by smooth-type LPS. Native gel electrophoresis of a mixture of argininosuccinate synthase and LPS and immunoprecipitation of a mixture of argininosuccinate synthase and [3H]-LPS with anti-argininosuccinate synthase antiserum showed that argininosuccinate synthase stably bound lipid A and LPS. These findings, together, indicate that argininosuccinate synthase can effectively bind LPS in the liver.

Immunological properties of oxygen-transport proteins: hemoglobin, hemocyanin and hemerythrin

It is now well documented that peptides with enhanced or alternative functionality (termed cryptides) can be liberated from larger, and sometimes inactive, proteins. A primary example of this phenomenon is the oxygen-transport protein hemoglobin. Aside from respiration, hemoglobin and hemoglobin-derived peptides have been associated with immune modulation, hematopoiesis, signal transduction and microbicidal activities in metazoans. Likewise, the functional equivalents to hemoglobin in invertebrates, namely hemocyanin and hemerythrin, act as potent immune effectors under certain physiological conditions. The purpose of this review is to evaluate the true extent of oxygen-transport protein dynamics in innate immunity, and to impress upon the reader the multi-functionality of these ancient proteins on the basis of their structures. In this context, erythrocyte-pathogen antibiosis and the immune competences of various erythroid cells are compared across diverse taxa.

Identification of CD163 as an antiinflammatory receptor for HMGB1-haptoglobin complexes

Secreted by activated cells or passively released by damaged cells, extracellular HMGB1 is a prototypical damage-associated molecular pattern (DAMP) inflammatory mediator. During the course of developing extracorporeal approaches to treating injury and infection, we inadvertently discovered that haptoglobin, the acute phase protein that binds extracellular hemoglobin and targets cellular uptake through CD163, also binds HMGB1. Haptoglobin-HMGB1 complexes elicit the production of antiinflammatory enzymes (heme oxygenase-1) and cytokines (e.g., IL-10) in WT but not in CD163-deficient macrophages. Genetic disruption of haptoglobin or CD163 expression significantly enhances mortality rates in standardized models of intra-abdominal sepsis in mice. Administration of haptoglobin to WT and to haptoglobin gene-deficient animals confers significant protection. These findings reveal a mechanism for haptoglobin modulation of the inflammatory action of HMGB1, with significant implications for developing experimental strategies targeting HMGB1-dependent inflammatory diseases.

Change of hemopexin level is associated with the severity of sepsis in endotoxemic rat model and the outcome of septic patients

PURPOSE

The purpose of the study is to uncover the role of hemopexin (HPX) as anti-inflammatory mediator in animals and humans.

MATERIALS AND METHODS

We injected rats with 5 and 10 mg/kg of lipopolysaccharide to induce low- and high-grade endotoxemia (LGE and HGE), respectively, and we measured serum levels of tumor necrosis factor α, interleukin 6, and HPX at 0, 1, 3, and 6 hours after the injection. In a clinical study, we measured the initial serum HPX concentrations of septic shock patients. We evaluated the correlation between HPX levels and sepsis severity in rats and the predictive value of the HPX level for 28-day mortality of patients.

RESULTS

In rats, serum interleukin 6 and tumor necrosis factor α concentrations were lower in LGE than in HGE, whereas the HPX level in HGE at 6 hours was significantly lower than in LGE (0.88, interquartile range [0.79-1.00] vs 1.33, interquartile range [1.29-1.49] mg/mL, P= .002). In patients, the initial serum HPX level in nonsurvivors was significantly lower than in survivors (0.75 vs 1.02 mg/mL, P< .001). Multivariate logistic regression analysis revealed that HPX exhibited independent prognostic value for 28-day mortality, and its levels were closely related to Acute Physiology and Chronic Health Evaluation II scores.

CONCLUSIONS

Low serum HPX levels are related to sepsis severity and could indicate poor prognosis for septic shock patients.

Heme on innate immunity and inflammation

Heme is an essential molecule expressed ubiquitously all through our tissues. Heme plays major functions in cellular physiology and metabolism as the prosthetic group of diverse proteins. Once released from cells and from hemeproteins free heme causes oxidative damage and inflammation, thus acting as a prototypic damage-associated molecular pattern. In this context, free heme is a critical component of the pathological process of sterile and infectious hemolytic conditions including malaria, hemolytic anemias, ischemia-reperfusion, and hemorrhage. The plasma scavenger proteins hemopexin and albumin reduce heme toxicity and are responsible for transporting free heme to intracellular compartments where it is catabolized by heme-oxygenase enzymes. Upon hemolysis or severe cellular damage the serum capacity to scavenge heme may saturate and increase free heme to sufficient amounts to cause tissue damage in various organs. The mechanism by which heme causes reactive oxygen generation, activation of cells of the innate immune system and cell death are not fully understood. Although heme can directly promote lipid peroxidation by its iron atom, heme can also induce reactive oxygen species generation and production of inflammatory mediators through the activation of selective signaling pathways. Heme activates innate immune cells such as macrophages and neutrophils through activation of innate immune receptors. The importance of these events has been demonstrated in infectious and non-infectious diseases models. In this review, we will discuss the mechanisms behind heme-induced cytotoxicity and inflammation and the consequences of these events on different tissues and diseases.

Innate immune activation after transfusion of stored red blood cells

The transfusion of red blood cells (RBCs), although necessary for treatment of anemia and blood loss, has also been linked to increased morbidity and mortality. RBCs stored for longer durations and transfused in larger volumes are often cited as contributory to adverse outcomes. The potential mechanisms underlying deleterious effects of RBC transfusion are just beginning to be elucidated. In this narrative review, we explore the hypothesis that prolonged RBC storage results in elaboration of substances which may function as danger associated molecular pattern molecules that activate the innate immune system with consequences unfavorable to healthy homeostasis. The nature of these chemical mediators and the biological responses to them offers insight into the mechanisms of these pathological responses. Three major areas of activation of the innate immune apparatus by stored RBCs have been tentatively identified: RBC hemolysis, recipient neutrophil priming, and reactive oxygen species production. The possible mechanisms by which each might perturb the innate immune response are reviewed in a search for potential novel pathways through which transfusion can lead to an altered inflammatory response.

A perspective on the role of extracellular hemoglobin on the innate immune system

Host cell-derived danger-associated molecular patterns (DAMPs), such as the hemoglobin (Hb) can interact with the innate immune system either directly or through binding to pathogen-associated molecular patterns (PAMPs). Hemolysis occurs under various pathological conditions, leading to hemoglobinemia. In the extracellular environment, the Hb becomes a redox-reactive DAMP molecule. In severe hemolysis, the massive level of extracellular pro-oxidative Hb generates reactive oxygen species (ROS), which perturbs the innate immune homeostasis. The Hb also binds to PAMPs and triggers Toll-like receptor-mediated signal transduction. In this perspective, we review the roles of cell-free Hb in the innate immune system, focusing on the plausible interactions among Hb, pathogens, host cell components, and innate immune cells, all of which remain to be explored with experiential detail.

Identification of hemopexin as an anti-inflammatory factor that inhibits synergy of hemoglobin with HMGB1 in sterile and infectious inflammation

Hemoglobin is released from lysed RBCs in numerous clinical settings. High mobility group box 1 (HMGB1) is a nuclear and cytosolic DNA-binding protein released from injured cells that has been shown to play an important role in inducing inflammation. Because both of these endogenous molecules are frequently present in sites of necrosis and inflammation, we studied their interaction on the activation of macrophages. We report in this article that hemoglobin and HMGB1 synergize to activate mouse macrophages to release significantly increased proinflammatory cytokines. Addition of microbial ligands that activate through TLR2 or TLR4 resulted in further significant increases, in a "three-way" synergy between endogenous and microbial ligands. The synergy was strongly suppressed by hemopexin (Hx), an endogenous heme-binding plasma protein. The findings suggest that hemoglobin may play an important role in sterile and infectious inflammation, and that endogenous Hx can modulate this response. Administration of Hx may be beneficial in clinical settings characterized by elevated extracellular hemoglobin and HMGB1.

Synergistic inflammation is induced by blood degradation products with microbial Toll-like receptor agonists and is blocked by hemopexin

Detection of microbial components by immune cells via Toll-like receptors (TLRs) with subsequent induction of inflammation is essential for host defense. However, an overactive immune response can cause tissue damage and sepsis. The endogenous molecule hemoglobin and its derivative heme are often released into tissue compartments where there is infection in the presence of degrading blood. We found that hemoglobin synergizes with multiple TLR agonists to induce high levels of tumor necrosis factor and interleukin-6 from macrophages and that this synergy is independent of TLR4 and MyD88. In contrast, heme synergized with some but not all TLR agonists studied. Furthermore, the synergy of both hemoglobin and heme with lipopolysaccharide was suppressed by hemopexin, a plasma heme-binding protein. These studies suggest that hemoglobin and heme may substantially contribute to microbe-induced inflammation when bacterial or viral infection coexists with blood degradation and that hemopexin may play a role in controlling inflammation in such settings.

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.

Identification and analysis of immune-related transcriptome in Asian seabass Lates calcarifer

Background

Fish diseases caused by pathogens are limiting their production and trade, affecting the economy generated by aquaculture. Innate immunity system is the first line of host defense in opposing pathogenic organisms or any other foreign material. For identification of immune-related genes in Asian seabass Lates calcarifer, an important marine foodfish species, we injected bacterial lipopolysaccharide (LPS), a commonly used elicitor of innate immune responses to eight individuals at the age of 35 days post-hatch and applied the suppression subtractive hybridization (SSH) technique to selectively amplify spleen cDNA of differentially expressed genes.

Results

Sequencing and bioinformatic analysis of 3351 ESTs from two SSH libraries yielded 1692 unique transcripts. Of which, 618 transcripts were unknown/novel genes and the remaining 1074 were similar to 743 known genes and 105 unannotated mRNA sequences available in public databases. A total of 161 transcripts were classified to the category "response to stimulus" and 115 to "immune system process". We identified 25 significantly up-regulated genes (including 2 unknown transcripts) and 4 down-regulated genes associated with immune-related processes upon challenge with LPS. Quantitative real-time PCR confirmed the differential expression of these genes after LPS challenge.

Conclusions

The present study identified 1692 unique transcripts upon LPS challenge for the first time in Asian seabass by using SSH, sequencing and bioinformatic analysis. Some of the identified transcripts are vertebrate homologues and others are hitherto unreported putative defence proteins. The obtained immune-related genes may allow for a better understanding of immunity in Asian seabass, carrying out detailed functional analysis of these genes and developing strategies for efficient immune protection against infections in Asian seabass.

Hemoglobin induces the expression of indoleamine 2,3-dioxygenase in dendritic cells through the activation of PI3K, PKC, and NF-kappaB and the generation of reactive oxygen species

Indoleamine 2,3-dioxygenase (IDO) is the rate-limiting enzyme in the kynurenine (Kyn) pathway of tryptophan (Trp) metabolism. IDO is immunosuppressive and is induced by inflammation in macrophages and dendritic cells (DCs). Previous studies have shown the serum Kyn/Trp levels in patients with hemolytic anemia to be notably high. In the present study, we demonstrated that hemoglobin (Hb), but not hemin or heme-free globin (Apo Hb), induced IDO expression in bone marrow-derived myeloid DCs (BMDCs). Hb induced the phosphorylation and degradation of I kappaB alpha. Hb-induced IDO expression was inhibited by inhibitors of PI3-kinase (PI3K), PKC and nuclear factor (NF)-kappaB. Hb translocated both RelA and p52 from the cytosol to the nucleus and induced the intracellular generation of reactive oxygen species (ROS). Hb-induced IDO expression was inhibited by anti-oxidant N-acetyl-L-cysteine (NAC) or mixtures of SOD and catalase, however, IDO expression was enhanced by 3-amino-1,2,4-triazole, an inhibitor of catalase, suggesting that the generation of ROS such as O(2) (-), H(2)O(2), and hydroxyl radical is required for the induction of IDO expression. The generation of ROS was inhibited by a PKC inhibitor, and this action was further enhanced by addition of a PI3K inhibitor. Hb induced Akt phosphorylation, which was inhibited by a PI3K inhibitor and enhanced by a PKC inhibitor. These results suggest that the activation of NF-kappaB through the PI3K-PKC-ROS and PI3K-Akt pathways is required for the Hb-induced IDO expression in BMDCs.

Hemoglobin and LPS act in synergy to amplify the inflammatory response

Vascular disruption and bleeding during periodontitis likely increase the levels of hemoglobin in gingival crevicular fluid. The aim of this study was to investigate the effect of hemoglobin on the inflammatory responses of human macrophages stimulated with lipopolysaccharides (LPS) isolated from periodontopathogens. The production of interleukin-1 beta (IL-1beta), IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha) by macrophages following challenges with Porphyromonas gingivalis and Fusobacterium nucleatum LPS in the presence or absence of human hemoglobin was analyzed by ELISA. The effect of hemoglobin on LPS-binding to macrophages was evaluated with (3)H-LPS. Hemoglobin and LPS from periodontopathogens acted in synergy to stimulate the production of high levels of IL-1beta, IL-6, IL-8, and TNF-alpha by macrophages. Hemoglobin also enhanced LPS-binding to macrophages. This study suggests that hemoglobin contributes to increases in the levels of pro-inflammatory mediators in periodontal sites by acting in synergy with LPS from periodontopathogens, thus favoring the progression of periodontitis.

Unraveling the lethal synergism betweenTrypanosoma cruzi infection and LPS: A role for increased macrophage reactivity

Various infections sensitize to lethal shock by promoting hyperactivation of macrophages to LPS stimulation. Although macrophages are thought to be deactivated upon contact with apoptotic cells during Trypanosoma cruzi infection, T. cruzi infection also sensitizes mice to endotoxemia. Herein, we studied the mechanisms of sensitization to endotoxemia in T. cruzi-infected mice in order to solve the paradox. Live (but not fixed) trypomastigotes from various stocks sensitized mice to endotoxemia. Mice deficient in glycolipid recognition (TLR2(-/-) and CD1d(-/-)) were sensitized by infection to challenge with LPS. Infected mice hyperproduced TNF and IL-10 upon LPS challenge. Infected TNF-R1(-/-), macrophage migration inhibitory factor (MIF)(-/-) and IFN-gamma(-/-) mice were lethally sensitized, but infected TNF-R1(-/-) mice administered anti-MIF survived shock with LPS. Macrophages from infected mice hyperproduced TNF in response to LPS stimulation and displayed increased expression of TLR4 compared to non-infected controls. Treatment with the PGE(2) synthesis inhibitor acetylsalicylic acid (AAS) in vivo reduced parasitemia and enhanced LPS-stimulated production of TNF by macrophages, but the effect was less in infected mice than in normal mice. Nevertheless, AAS treatment did not increase the susceptibility of infected mice to sublethal shock with LPS. Our results point to independent MIF and TNF/TNF-R1 lethal pathways and suggest a role for hyperactivated macrophages in T. cruzi-sensitized LPS-induced shock.

Monocyte and macrophage activation by lipoteichoic Acid is independent of alanine and is potentiated by hemoglobin

Lipoteichoic acids (LTAs) are Gram-positive bacterial cell wall components that elicit mononuclear cell cytokine secretion. Cytokine-stimulating activity is thought to be dependent on retaining a high level of ester-linked D-alanine residues along the polyglycerol phosphate backbone. However, Streptococcus pyogenes LTA essentially devoid of D-alanine caused human and mouse cells to secrete as much IL-6 as LTA with a much higher D-alanine content. Furthermore, hemoglobin (Hb) markedly potentiates the stimulatory effect of various LTAs on mouse macrophages or human blood cells, regardless of their d-alanine content. LTA and Hb appear to form a molecular complex, based on the ability of each to affect the other's migration on native acrylamide gels, their comigration on these gels, and the ability of LTA to alter the absorption spectra of Hb. Because S. pyogenes is known to release LTA and secrete at least two potent hemolytic toxins, LTA-Hb interactions could occur during streptococcal infections and might result in a profound alteration of the local inflammatory response.

Amelioration of sepsis-induced hepatic and ileal injury in rats by the leukotriene receptor blocker montelukast

BACKGROUND

Sepsis is a generalized inflammatory response, which involves organ systems remote from the locus of the initial infectious insult, involves the release of cytokines and the subsequent formation of reactive oxygen and nitrogen species.

OBJECTIVE

The aim of this study was to investigate the possible protective effect of montelukast, a leukotriene receptor blocker, against oxidative damage in the liver and ileum of septic rats.

METHODS

Sepsis was induced by cecal ligation and puncture method in female Wistar albino rats. Sepsis and sham operated (control) groups received either saline or montelukast (10 mg/kg, ip) immediately after the operation and at 12 h. Twenty-four hours after the surgery, rats were decapitated and malondialdehyde (MDA) content--an index of lipid peroxidation, glutathione (GSH) levels--a key antioxidant, myeloperoxidase (MPO) activity--an index of neutrophil infiltration, and collagen contents were determined in the liver and ileum. Formation of reactive oxygen species in liver and ileal tissue samples was monitored by using chemiluminescence (CL) technique with luminol and lucigenin probes. Both tissues were also analyzed histologically. Serum lactate dehydrogenase (LDH) and tumor necrosis factor-alpha (TNF-alpha) level were assessed in trunk blood.

RESULTS

Sepsis resulted in decreased GSH levels, and increased MDA levels, MPO activity, CL levels and collagen contents in both the liver and the ileum (P < 0.05-P < 0.001) indicating the presence of the oxidative damage. Similarly, serum TNF-alpha and LDH were elevated in the sepsis group as compared to control group. On the other hand, montelukast treatment reversed all these biochemical indices, as well as histopathological alterations, which were induced by sepsis.

CONCLUSION

Findings of the present study suggest that montelukast possesses an anti-inflammatory effect on sepsis-induced hepatic and intestinal damage and protects against oxidative injury by a neutrophil-dependent mechanism.

Vascular damage by unstable hemoglobins: The role of heme-depleted globin

The study compared the damage inflicted to endothelial cells (ECs) by intact hemoglobin (Hb) and isolated chains. To compare optional in vivo contact of acellular Hb with the endothelium, oxy-forms of Hb and its isolated alpha- and beta-chains existing in the thalassemias were added to primary confluent cultures of bovine aorta EC. Cell damage was followed by morphological changes or leakage of lactic dehydrogenase and pre-inserted 51Cr from the cells, followed for 27 h. Under these experimental conditions, Hb did not affect the cells but its chains inflicted damage, beta- more than alpha-chains. Based on the literature and our data, we hypothesized that hemin and/or globin should be responsible for the increased endothelial damage by beta-chains. While hemin hardly affected ECs, globin, unlike the plasma protein hemopexin, was harmful. Since hemin release leaves globin with a large hydrophobic surface, the globin-damage appears to result from adsorptive pinocytosis to endothelial membrane.

Redox active hemoglobin enhances lipopolysaccharide-induced injury to cultured bovine endothelial cells

The interaction of cell-free hemoglobin with lipopolysaccharide (LPS) is thought to aggravate the pathophysiology of sepsis and/or septic shock. This study examines the possible modulatory role of cell-free hemoglobin on LPS-induced apoptosis of cultured bovine aortic endothelial cells. Experiments were performed with or without fetal bovine serum, a source of LPS-binding protein and soluble CD14. In the absence of serum, LPS alone or coincubated with purified bovine hemoglobin (BvHb), human hemoglobin (Hb), or alpha-cross-linked Hb (alphaalphaHb) did not induce apoptosis. In the presence of serum, LPS induced significant apoptosis. LPS combined with BvHb, Hb, or alphaalphaHb produced the same extent of apoptosis as LPS alone. To examine whether the H(2)O(2)-driven redox activity of hemoglobin alters LPS-induced apoptosis, glucose oxidase was added to the system to generate a subtoxic flux of H(2)O(2). The combined treatment of LPS, glucose oxidase, and BvHb, Hb, or alphaalphaHb enhanced apoptosis compared with LPS alone. These findings support a possible mechanism whereby the redox cycling of hemoglobin, and not its direct interaction with LPS, contributes to the hemoglobin-mediated enhancement of LPS-related pathophysiology.