Platelet serotonin promotes the recruitment of neutrophils to sites of acute inflammation in mice.

The majority of peripheral serotonin is stored in platelets, which secrete it on activation. Serotonin releases Weibel-Palade bodies (WPBs) and we asked whether absence of platelet serotonin affects neutrophil recruitment in inflammatory responses. Tryptophan hydroxylase (Tph)1­deficient mice, lacking non-neuronal serotonin, showed mild leukocytosis compared with wild-type (WT), primarily driven by an elevated neutrophil count. Despite this, 50% fewer leukocytes rolled on unstimulated mesenteric venous endothelium of Tph1(-/-) mice. The velocity of rolling leukocytes was higher in Tph1(-/-) mice, indicating fewer selectin-mediated interactions with endothelium. Stimulation of endothelium with histamine, a secretagogue of WPBs, or injection of serotonin normalized the rolling in Tph1(-/-) mice. Diminished rolling in Tph1(-/-) mice resulted in reduced firm adhesion of leukocytes after lipopolysaccharide treatment. Blocking platelet serotonin uptake with fluoxetine in WT mice reduced serum serotonin by > 80% and similarly reduced leukocyte rolling and adhesion. Four hours after inflammatory stimulation, neutrophil extravasation into lung, peritoneum, and skin wounds was reduced in Tph1(-/-) mice, whereas in vitro neutrophil chemotaxis was independent of serotonin. Survival of lipopolysaccharide-induced endotoxic shock was improved in Tph1(-/-) mice. In conclusion, platelet serotonin promotes the recruitment of neutrophils in acute inflammation, supporting an important role for platelet serotonin in innate immunity.

Extracellular DNA traps are associated with the pathogenesis of TRALI in humans and mice.

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion-related death. The biologic processes contributing to TRALI are poorly understood. All blood products can cause TRALI, and no specific treatment is available. A "2-event model" has been proposed as the trigger. The first event may include surgery, trauma, or infection; the second involves the transfusion of antileukocyte antibodies or bioactive lipids within the blood product. Together, these events induce neutrophil activation in the lungs, causing endothelial damage and capillary leakage. Neutrophils, in response to pathogens or under stress, can release their chromatin coated with granule contents, thus forming neutrophil extracellular traps (NETs). Although protective against infection, these NETs are injurious to tissue. Here we show that NET biomarkers are present in TRALI patients' blood and that NETs are produced in vitro by primed human neutrophils when challenged with anti-HNA-3a antibodies previously implicated in TRALI. NETs are found in alveoli of mice experiencing antibody-mediated TRALI. DNase 1 inhalation prevents their alveolar accumulation and improves arterial oxygen saturation even when administered 90 minutes after TRALI onset. We suggest that NETs form in the lungs during TRALI, contribute to the disease process, and thus could be targeted to prevent or treat TRALI.

Isoflurane inhibits neutrophil recruitment in the cutaneous Arthus reaction model.

PURPOSE: Neutrophil recruitment to the inflammatory sites is regulated by a variety of adhesion molecules including ß2 integrins. The dependency of neutrophil recruitment on ß2 integrins is variable in different tissues, but has not yet been verified in the cutaneous passive reverse Arthus reaction. We examined this question and also evaluated the impact of isoflurane on neutrophil recruitment to the skin because we previously showed in vitro that isoflurane binds and inhibits ß2 integrins. METHODS: The dependency on ß2 integrins in neutrophil recruitment to the skin in the Arthus reaction was examined using αL, αM and ß2 knockout mice. Then, we evaluated the effect of isoflurane on neutrophil recruitment to the skin. In addition, the effects of isoflurane on neutrophil binding to intercellular adhesion molecule-1 (ICAM-1), one of the ß2 integrin ligands, were studied in vitro using cell adhesion assays. RESULTS: Neutrophil recruitment to the skin in the Arthus reaction model was totally dependent on ß2 integrins, as ß2 knockout mice completely abolished it. However, the defect of only one of the ß2 integrins was not sufficient to abolish neutrophil recruitment. Isoflurane reduced neutrophil recruitment to the skin by approximately 90 %. Also, isoflurane inhibited neutrophil adhesion to ß2 integrin ligand ICAM-1. CONCLUSIONS: We demonstrated that (1) neutrophil recruitment to the skin was totally dependent on ß2 integrins, and (2) isoflurane significantly impaired neutrophil recruitment. Based on the previous studies on the contribution of other adhesion molecules in neutrophil recruitment, it is likely that isoflurane at least partially affects on ß2 integrins in this model.

Endothelial dysfunction after hematopoietic stem cell transplantation: role of the conditioning regimen and the type of transplantation.

There is endothelial activation and damage in hematopoietic stem cell transplantation (HSCT). The impact of the conditioning and type of HSCT on endothelial dysfunction in the early phases of HSCT has been evaluated. Plasma samples were obtained before and at different times after autologous and allogeneic HSCT with and without early complications. Changes in soluble markers of endothelial damage (VWF, ADAMTS-13, sVCAM-1, sICAM-1, and sTNFRI) were measured. There were changes in all markers evaluated that followed different patterns in auto and allo settings. For VWF and sTNRI, progressive increases from day Pre to day 14 and to day 21 were observed in the auto and the allo group, respectively. ADAMTS-13 activity correlated inversely with VWF levels. Levels of sVCAM-1 decreased until day 7, and raised significantly to day 14 and to day 21 in the auto and the allo HSCT, respectively. No significant changes were detected for sICAM-1. Our results confirm that there is endothelial damage at the early phases of HSCT, apparently induced by the consecutive effects of the conditioning, the proinflammatory agents used during transplantation, the translocation of endotoxins across the damaged gastrointestinal tract, and the engraftment. However, the comparative analysis between patients with and without complications suggests that none of these markers has diagnostic or prognostic value.

Innate immune cells induce hemorrhage in tumors during thrombocytopenia.

Platelets are crucial regulators of tumor vascular homeostasis and continuously prevent tumor hemorrhage through secretion of their granules. However, the reason for tumor bleeding in the absence of platelets remains unknown. Tumors are associated with inflammation, a cause of hemorrhage in thrombocytopenia. Here, we investigated the role of the inflamed tumor microenvironment in the induction of tumor vessel injury in thrombocytopenic mice. Using s.c. injections of vascular endothelial growth factor or tumor necrosis factor-alpha combined with depletion of neutrophils, we demonstrate that enhancing the opening of endothelial cell junctions was not sufficient to cause bleeding in the absence of platelets; instead, induction of tissue hemorrhage in thrombocytopenia required recruitment of leukocytes. Immunohistology revealed that thrombocytopenia-induced tumor hemorrhage occurs at sites of macrophage and neutrophil accumulation. Mice deficient in beta2 or beta3 integrins, which have decreased neutrophil and/or macrophage infiltration in their tumor stroma, were protected from thrombocytopenia-induced tumor hemorrhage, indicating that, in the absence of platelets, stroma-infiltrating leukocytes induced tumor vessel injury. This injury was independent of reactive oxygen species generation and of complement activation, as suggested by the persistence of tumor hemorrhage in C3- and nicotinamide adenine dinucleotide phosphate oxidase-deficient thrombocytopenic mice. Our results show that platelets counteract tumor-associated inflammation and that the absence of this platelet function elicits vascular injuries by tumor-infiltrating innate immune cells.

Inflammation induces hemorrhage in thrombocytopenia.

The role of platelets in hemostasis is to produce a plug to arrest bleeding. During thrombocytopenia, spontaneous bleeding is seen in some patients but not in others; the reason for this is unknown. Here, we subjected thrombocytopenic mice to models of dermatitis, stroke, and lung inflammation. The mice showed massive hemorrhage that was limited to the area of inflammation and was not observed in uninflamed thrombocytopenic mice. Endotoxin-induced lung inflammation during thrombocytopenia triggered substantial intra-alveolar hemorrhage leading to profound anemia and respiratory distress. By imaging the cutaneous Arthus reaction through a skin window, we observed in real time the loss of vascular integrity and the kinetics of skin hemorrhage in thrombocytopenic mice. Bleeding-observed mostly from venules-occurred as early as 20 minutes after challenge, pointing to a continuous need for platelets to maintain vascular integrity in inflamed microcirculation. Inflammatory hemorrhage was not seen in genetically engineered mice lacking major platelet adhesion receptors or their activators (alphaIIbbeta3, glycoprotein Ibalpha [GPIbalpha], GPVI, and calcium and diacylglycerol-regulated guanine nucleotide exchange factor I [CalDAG-GEFI]), thus indicating that firm platelet adhesion was not necessary for their supporting role. While platelets were previously shown to promote endothelial activation and recruitment of inflammatory cells, they also appear indispensable to maintain vascular integrity in inflamed tissue. Based on our observations, we propose that inflammation may cause life-threatening hemorrhage during thrombocytopenia.

The release of soluble factors contributing to endothelial activation and damage after hematopoietic stem cell transplantation is not limited to the allogeneic setting and involves several pathogenic mechanisms.

This study evaluated the relative impact of the intensity of the conditioning regimen and the alloreactivity in the endothelial dysfunction occurring after allogeneic hematopoietic stem cell transplantation (allo-HSCT). It involved a comparative analysis of the effect of incubating human umbilical vein endothelial cells (ECs) with serum samples from patients receiving autologous HSCT (auto-HSCT) or unrelated donor allo-HSCT. In both groups, blood samples were collected through a central line before conditioning (Pre), before transplantation (day 0), and at days 7, 14, and 21 after transplantation. Changes in the expression of EC receptors and adhesion proteins, adhesion of leukocytes and platelets under flow, and signaling pathways were analyzed. Endothelial activation and damage were observed in both groups, but with differing patterns. All markers of endothelial dysfunction demonstrated a progressive increase from day Pre to day 14 in the auto-HSCT group and exhibited 2 peaks of maximal expression (at days 0 and 21) in the allo-HSCT group. Both treatments induced a proinflammatory state (ie, expression of adhesion receptors, leukocyte adhesion, and p38 MAPK activation) and cell proliferation (ie, morphology and activation of ErK42/44). Prothrombotic changes (ie, von Willebrand factor expression and platelet adhesion) predominated after allo-HSCT, and a proapoptotic tendency (ie, activation of SAPK/JNK) was seen only in this group. These findings indicate that endothelial activation and damage after HSCT also occur in the autologous setting and affect macrovascular ECs. After the initial damage induced by the conditioning regimen, other factors, such as granulocyte colony-stimulating factor (G-CSF) toxicity, engraftment, and alloreactivity, may contribute to the endothelial damage seen during HSCT. Further studies are needed to explore the association between this endothelial damage and the vascular complications associated with HSCT.

Differential expression of proteins from cultured endothelial cells exposed to uremic versus normal serum.

BACKGROUND: Deficient hemostasis and accelerated atherosclerosis coexist in patients with chronic kidney disease. Endothelial dysfunction may be involved in the high incidence of atherothrombotic events in these patients. We established an in vitro model of endothelial dysfunction by exposing endothelial cells to uremic media and applied a proteomic approach to characterize endothelial cell dysfunction in uremia. STUDY DESIGN: Cross-sectional study. SETTING AND PARTICIPANTS: Serum samples from 8 patients with chronic kidney disease on hemodialysis treatment were collected. PREDICTOR: Exposure of cultured endothelial cells to normal and uremic serum. OUTCOME AND MEASUREMENTS: Proteins from lysed cells were characterized by isoelectric point and molecular weight by using 2-dimensional gel electrophoresis. Spots were visualized by means of silver staining and identified by using mass spectrometry. RESULTS: Identification of the most prominent proteins showed molecules related to inflammation (high mobility group box 1, aldose reductase, and proteasome components) and oxidative stress (superoxide dismutase and glutathione peroxidase), both associated with chronic kidney disease. These changes may be caused by activation of the nuclear factor-kappaB transcription factor. Changes in expression of cytoskeletal proteins (destrin and vimentin) also were detected. LIMITATIONS: In vitro study. CONCLUSION: Proteomic techniques proved to be a powerful tool to investigate endothelial dysfunction in uremia. A more exhaustive analysis will provide answers and potential therapeutic targets in the near future.

Inhibition of tyrosine kinase activity prevents the adhesive and cohesive properties of platelets and the expression of procoagulant activity in response to collagen.

INTRODUCTION: Platelet activation leads to signal transduction mechanisms, in which phosphotyrosine proteins play a relevant role. MATERIAL AND METHODS: Platelet suspensions were independently activated by collagen and thrombin in the absence and in the presence of two tyrosine kinase inhibitors, tyrphostin 47 and genistein. Samples were processed to visualize morphological changes by electron microscopy, to evaluate changes in cytoskeletal assembly, to analyze modifications in the expression of activation dependent antigens, and the procoagulant activity at the surface level by flow cytometry. Additional experiments applying flow conditions were performed to assess the effect of inhibiting tyrosine phosphorylation on primary platelet adhesion and fibrin formation. RESULTS: Inhibition of tyrosine phosphorylation blocked shape change and cytoskeletal assembly induced by collagen, and inhibited, though partially, those effects due to thrombin. Both activating agents induced the expression of the intraplatelet antigens CD62P and CD63 at the surface, although only collagen promoted expression of anionic phospholipids. Both tyrphostin 47 and genistein prevented those effects. The extent of platelet adhesion on both collagen-coated and subendothelial surfaces was significantly diminished by the presence of the tyrosine kinase inhibitors assayed. Fibrin formation was also significantly reduced. CONCLUSIONS: Platelet shape change and secretion during platelet activation depends on tyrosine phosphorylation. In addition, primary adhesion of platelets induces signaling through tyrosine kinases to achieve full spreading, and results in the exposure of a procoagulant surface on platelets.

Effect of two different dialysis membranes on leukocyte adhesion and aggregation.

AIMS: We evaluated modifications in formation of heterotypic platelet-leukocyte aggregation induced by dialysis through cellulosic or synthetic membranes and evaluated the effects of such procedures promoting adhesive interactions between leukocytes and normal endothelial cells (ECs). METHODS: Samples were obtained from arterial and venous lines at baseline, after 15 and 120 min of hemodialysis. Heterotypic aggregation was assessed using flow-cytometric techniques. Experiments to determine leukocyte adhesion to ECs were performed in parallel plate perfusion chambers at 450 s(-1). RESULTS: Patients dialyzed with a cellulosic membrane showed a significantly higher baseline granulocyte heterotypic aggregation (median 22.5%, range 8.6-32%) versus healthy subjects (median 10%, range 3.2-14.6%; p < 0.05). Granulocyte heterotypic aggregation values remained increased throughout the hemodialysis session not only in the arterial line (median 18 and 24.5%, range 7-30 and 8.7-36% at 15 and 2 h, respectively) but also in the venous line (median 20 and 25%, range 8.6-32 and 11.5-35% at 15 min and 2 h, respectively). Basal lymphocytes heterotypic aggregation values observed in uremic patients were 6% (0.1-7.1%) versus 1.0% (0.5-2.8%) in the control group (p < 0.05). The increase remained during the hemodialysis session both in the arterial line (median 5 and 4%, range 0.2-14 and 0.5-7.1 % at 15 min and 2 h, respectively) and in the venous line (median 7 and 7%, range 1.4-14 and 0.5-10.6% at 15 min and 2 h). In contrast, patients dialyzed with a synthetic membrane showed a decreased basal granulocyte heterotypic aggregation compared to healthy subjects (median 3.5 vs. 10%, range 2.8-7 vs. 3.2-14.6%, respectively; p < 0.05). For lymphocytes, basal heterotypic aggregation values were 0.2% (range 0.1-0.5%) in dialyzed patients vs. 0.98% (range 0.5-2.8%) in healthy subjects (p < 0.05), without changes throughout the dialysis session. Changes in leukocyte adhesion during hemodialysis did not reach statistical significance with either hemodialysis membrane. Our studies confirm a differential activation of platelets and leukocytes depending on the nature of the dialysis membranes. However, activation of circulating cellular elements by hemodialysis procedures did not enhance cross-talk interactions between leukocytes and unaltered ECs.

Integrin-independent role of CalDAG-GEFI in neutrophil chemotaxis.

Chemotaxis and integrin activation are essential processes for neutrophil transmigration in response to injury. CalDAG-GEFI plays a key role in the activation of beta1, beta2, and beta3 integrins in platelets and neutrophils by exchanging a GDP for a GTP on Rap1. Here, we explored the role of CalDAG-GEFI and Rap1b in integrin-independent neutrophil chemotaxis. In a transwell assay, CalDAG-GEFI-/- neutrophils had a 46% reduction in transmigration compared with WT in response to a low concentration of LTB4. Visualization of migrating neutrophils in the presence of 10 mM EDTA revealed that CalDAG-GEFI-/- neutrophils had abnormal chemotactic behavior compared with WT neutrophils, including reduced speed and directionality. Interestingly, Rap1b-/- neutrophils had a similar phenotype in this assay, suggesting that CalDAG-GEFI may be acting through Rap1b. We investigated whether the deficit in integrin-independent chemotaxis in CalDAG-GEFI-/- neutrophils could be explained by defective cytoskeleton rearrangement. Indeed, we found that CalDAG-GEFI-/- neutrophils had reduced formation of F-actin pseudopodia after LTB4 stimulation, suggesting that they have a defect in polarization. Overall, our studies show that CalDAG-GEFI helps regulate neutrophil chemotaxis, independent of its established role in integrin activation, through a mechanism that involves actin cytoskeleton and cellular polarization.