Endothelial Barrier Integrity Is Disrupted In Vitro by Heme and by Serum From Sickle Cell Disease Patients.

Free extracellular heme has been shown to activate several compartments of innate immunity, acting as a danger-associated molecular pattern (DAMP) in hemolytic diseases. Although localized endothelial barrier (EB) disruption is an important part of inflammation that allows circulating leukocytes to reach inflamed tissues, non-localized/deregulated disruption of the EB can lead to widespread microvascular hyperpermeability and secondary tissue damage. In mouse models of sickle cell disease (SCD), EB disruption has been associated with the development of a form of acute lung injury that closely resembles acute chest syndrome (ACS), and that can be elicited by acute heme infusion. Here we explored the effect of heme on EB integrity using human endothelial cell monolayers, in experimental conditions that include elements that more closely resemble in vivo conditions. EB integrity was assessed by electric cell-substrate impedance sensing in the presence of varying concentrations of heme and sera from SCD patients or healthy volunteers. Heme caused a dose-dependent decrease of the electrical resistance of cell monolayers, consistent with EB disruption, which was confirmed by staining of junction protein VE-cadherin. In addition, sera from SCD patients, but not from healthy volunteers, were also capable to induce EB disruption. Interestingly, these effects were not associated with total heme levels in serum. However, when heme was added to sera from SCD patients, but not from healthy volunteers, EB disruption could be elicited, and this effect was associated with hemopexin serum levels. Together our in vitro studies provide additional support to the concept of heme as a DAMP in hemolytic conditions.

Circulating levels of the angiogenesis mediators endoglin, HB-EGF, BMP-9 and FGF-2 in patients with severe sepsis and septic shock.

PURPOSE: Endothelial barrier dysfunction is a hallmark of sepsis, and is at least partially mediated by pathways that regulate endothelial barrier assembly during angiogenesis. Not surprisingly, increased levels of key angiogenic proteins such as VEGF-A and Angiopoietin-2 have been described in sepsis. The purpose of this study was to investigate if additional pathways that regulate endothelial barrier integrity during angiogenesis could also be involved in the host response of sepsis. MATERIAL AND METHODS: We evaluated circulating levels of four proteins involved in angiogenesis, not previously studied in sepsis, in a cohort of 50 patients with severe sepsis and septic shock. RESULTS: Circulating levels of BMP-9 and FGF-2 were similar in patients and healthy volunteers. In contrast, patients with septic shock presented 1.5-fold higher levels of endoglin (P=0.004), and 2-fold lower levels of Heparin-Binding EGF-like growth factor (HB-EGF) (P=0.002) when compared to healthy individuals. Of note, HB-EGF deficiency has been recently demonstrated to be detrimental to survival in a murine model of sepsis. CONCLUSIONS: Endoglin and HB-EGF could be involved in the host response of sepsis. Additional studies are warrant to investigate their role as biomarker or therapeutic targets in sepsis.

Tissue factor-dependent coagulation activation by heme: A thromboelastometry study.

Heme has been characterized as potent trigger of inflammation. In hemostasis, although heme has been shown to both induce and inhibit different compartments of hemostasis, its net effect on the hemostatic balance, and the biological relevance of these effects remain to be determined. Herein we evaluated the effect of heme on hemostasis using a global assay able to generate clinically relevant data in several other complex hemostatic diseases. Citrated whole blood samples from healthy participants were stimulated by heme or vehicle and incubated for 4h at 37°C. Rotational thromboelastometry was immediately performed. The participation of tissue factor in coagulation activation was evaluated using inhibitory antibody. Heme was able of inducing ex vivo coagulation activation in whole blood, affecting predominantly parameters associated with the initial phases of clot formation. This activation effect was at least partially dependent on hematopoietic tissue factor, since the effects of heme were partially abrogated by the inhibition of human tissue factor. In conclusion, using a global hemostasis assay, our study confirmed that heme is able to activate coagulation in whole blood, in a tissue factor-dependent way. These findings could explain the disturbance in hemostatic balance observed in conditions associated with the release of heme such as sickle cell disease.

Role of innate immunity-triggered pathways in the pathogenesis of Sickle Cell Disease: a meta-analysis of gene expression studies.

Despite the detailed characterization of the inflammatory and endothelial changes observed in Sickle Cell Disease (SCD), the hierarchical relationship between elements involved in the pathogenesis of this complex disease is yet to be described. Meta-analyses of gene expression studies from public repositories represent a novel strategy, capable to identify key mediators in complex diseases. We performed several meta-analyses of gene expression studies involving SCD, including studies with patient samples, as well as in-vitro models of the disease. Meta-analyses were performed with the Inmex bioinformatics tool, based on the RankProd package, using raw gene expression data. Functional gene set analysis was performed using more than 60 gene-set libraries. Our results demonstrate that the well-characterized association between innate immunity, hemostasis, angiogenesis and heme metabolism with SCD is also consistently observed at the transcriptomic level, across independent studies. The enrichment of genes and pathways associated with innate immunity and damage repair-associated pathways supports the model of erythroid danger-associated molecular patterns (DAMPs) as key mediators of the pathogenesis of SCD. Our study also generated a novel database of candidate genes, pathways and transcription factors not previously associated with the pathogenesis of SCD that warrant further investigation in models and patients of SCD.

Causes and consequences of coagulation activation in sepsis: an evolutionary medicine perspective.

BACKGROUND: Coagulation and innate immunity have been linked together for at least 450 million years of evolution. Sepsis, one of the world's leading causes of death, is probably the condition in which this evolutionary link is more evident. However, the biological and the clinical relevance of this association have only recently gained the attention of the scientific community. DISCUSSION: During sepsis, the host response to a pathogen is invariably associated with coagulation activation. For several years, coagulation activation has been solely regarded as a mechanism of tissue damage, a concept that led to several clinical trials of anticoagulant agents for sepsis. More recently, this paradigm has been challenged by the failure of these clinical trials, and by a growing bulk of evidence supporting the concept that coagulation activation is beneficial for pathogen clearance. In this article we discuss recent basic and clinical data that point to a more balanced view of the detrimental and beneficial consequences of coagulation activation in sepsis. Reappraisal of the association between coagulation and immune activation from an evolutionary medicine perspective offers a unique opportunity to gain new insights about the pathogenesis of sepsis, paving the way to more successful approaches in both basic and clinical research in this field.

Avaliação clínica de proteínas modeladoras da permeabilidade endotelial como biomarcadores para estratificação de risco na sepse em pacientes com neoplasias hematológicas e neutropenia febril / Clinical evaluation of modulators of endothelial permeability as biomarkers for risk stratification in sepsis patients with hematological malignancies and febrile neutropenia

A neutropenia febril (NF) em pacientes com neoplasias hematológicas é caracterizada pelo alto risco de sepse e choque séptico. Embora a utilização de escores clínicos como o MASCC permita a identificação de pacientes de baixo risco, este escore é menos informativo em pacientes de alto risco, onde se encaixam a maioria dos pacientes com neoplasias hematológicas, além daqueles submetidos a esquemas intensivos de quimioterapia. Ao mesmo tempo, a aplicação de biomarcadores de gravidade como a procalcitonina, validados em pacientes não-neutropênicos, é controversa em pacientes com NF. A quebra da barreira endotelial é um elemento chave no choque séptico, de modo que proteínas envolvidas neste processo são candidatos atrativos como biomarcadores de gravidade na sepse. Neste estudo, avaliamos prospectivamente o valor da dosagem de VEGF-A, sFlt-1, Ang-1 e Ang-2 como biomarcadores da evolução para choque séptico em 120 pacientes com NF. Pacientes internados nas enfermarias de Hematologia e Transplante de Medula Óssea do HC da UNICAMP para tratamento de NF entre março de 2011 e 2012 foram convidados a participar. As amostras foram coletadas na manhã seguinte à entrada no estudo, junto com a coleta de exames de rotina. O estudo foi desenhado com o objetivo de mimetizar as condições de coleta e processamento das amostras, que seriam encontradas na prática clínica real. Foi avaliada a evolução para choque séptico e mortalidade em 28 dias. Os resultados foram comparados com marcadores de prognóstico clássicos como proteína C reativa, e escores MASCC e SOFA. No total, 99 pacientes preencheram os critérios de inclusão, dos quais 19,8% evoluíram com choque séptico. Não foram observadas diferenças clínicas e demográficas entre os pacientes com NF não-complicada e choque séptico, exceto pelo escore SOFA, significativamente mais elevado no segundo grupo.

Febrile neutropenia (FN) in patients with hematologic malignancies is characterized by a high risk of sepsis complications and septic shock. Although the use of clinical scores such as the MASCC allows the identification of low-risk patients, this score is much less informative in high-risk patients, a category in which most patients with hematologic malignancies, and those undergoing intensive chemotherapy regimens, fit in. At the same time, the use of classical biomarkers such as procalcitonin in non-neutropenic patients is controversial in patients with FN. Endothelial barrier breakdown is a key element in septic shock, so that proteins involved in this process are attractive candidates as biomarkers of sepsis severity. In this study, we prospectively evaluated the value of VEGF-A, sFlt-1, Ang-1 and Ang-2 serum levels as biomarkers of progression to septic shock in 120 patients with FN. Patients hospitalized in the Hematology and Bone Marrow Transplantation in-patient units of a university hospital (HC-UNICAMP) for the treatment of FN between March 2011 and March 2012 were invited to participate. Samples were collected in the following morning after study entry, along with the collection of routine labs. The study was designed to mimic the conditions of blood sample collection and processing that would be encountered in "real-world" clinical practice. Clinical outcomes were (1) progression to septic shock and (2) death within 28 days from fever onset. Results were compared with classical prognostic markers such as C-reactive protein, and MASCC and SOFA scores. In total, 99 patients met the inclusion criteria, of which 19.8% progressed to septic shock. No differences clinical and demographic differences were observed between patients with uncomplicated-FN or septic shock, except for a higher SOFA scores in the latter group.