Vascular endothelial growth factor is an important determinant of sepsis morbidity and mortality

Admission angiopoietin levels in children with septic shock

Angiopoietin (angpt) 1 and angpt-2 are circulating proteins first ascribed opposing roles in embryonic angiogenesis. Both bind the tyrosine kinase with immunoglobulin-like loop and epidermal growth factor homology domains (Tie) 2 receptor on endothelial cells, but angpt-1 is a Tie-2 agonist, whereas angpt-2 antagonizes Tie-2 signaling. In the developed vasculature, angpt-1 protects against vascular leak, whereas angpt-2 promotes increased vascular permeability. Because alterations in vascular permeability are common in septic shock, we obtained plasma from critically ill children within 24 h of diagnosis of the systemic inflammatory response syndrome (SIRS, n = 20), sepsis (n = 20), or septic shock (n = 61), as well as 15 healthy controls. Plasma levels of angpt-1 and angpt-2 were measured via a commercially available enzyme-linked immunosorbent assay. Plasma angpt-2 levels were significantly elevated in children with septic shock when compared with healthy children, as well as critically ill children with either SIRS or sepsis, and circulating angpt-2 levels seemed to correlate with disease severity and outcome. In addition, plasma angpt-1 levels were significantly decreased in critically ill children with septic shock compared with critically ill children with either SIRS or sepsis. Given the contrasting effects of angpt-2 and angpt-1 on the vascular endothelium, these two factors may play an important role in the pathophysiology of septic shock in children, and further studies are warranted.

Soluble vascular endothelial growth factor receptor-1 protects mice in sepsis

OBJECTIVE

To determine the putative role in the modulation of inflammation of a soluble form of Flt-1 (sFlt), a potent vascular endothelial growth factor antagonist, in experimental endotoxemia and sepsis.

DESIGN

Randomized prospective experimental study.

SETTING

University medical laboratory.

SUBJECTS

Male C56BL/6 strain mice.

INTERVENTIONS

We investigated the expression patterns and the effects of vascular endothelial growth factor and soluble Flt-1 in experimental endotoxic shock and sepsis. The possible anti-inflammatory mechanism of soluble Flt-1 was also evaluated.

MEASUREMENTS AND MAIN RESULTS

Both vascular endothelial growth factor and sFlt-1 were rapidly released from macrophages activated in vitro by lipopolysaccharide and in the plasma of endotoxemic mice. Administration of vascular endothelial growth factor enhanced proinflammatory cytokine production and mediated a dramatic increase in mortality in endotoxemic mice. Treatment with sFlt-1 attenuated inflammatory responses, inhibited recruitment of inflammatory cells into the peritoneal cavity, and improved survival in a lethal endotoxemia and cecal ligation and puncture-induced sepsis model, even when administered as late as 24 hrs after the onset of sepsis.

CONCLUSIONS

These findings support a critical protective role of sFlt-1 in endotoxic shock and sepsis. sFlt-1 may therefore have utility as an adjunctive agent for the treatment of sepsis syndrome.

Release of soluble vascular endothelial growth factor receptor-1 (sFlt-1) during coronary artery bypass surgery

Background

This study was conducted to follow plasma concentrations of sFlt-1 and sKDR, two soluble forms of the vascular endothelial growth factor (VEGF) receptor in patients undergoing coronary artery bypass graft (CABG) surgery with extracorporeal circulation (ECC).

Methods

Plasma samples were obtained before, during and after surgery in 15 patients scheduled to undergo CABG. Levels of sFlt-1 and KDR levels were investigated using specific ELISA.

Results

A 75-fold increase of sFlt-1 was found during cardiac surgery, sFlt-1 levels returning to pre-operative values at the 6^th post-operative hour. In contrast sKDR levels did not change during surgery. The ECC-derived sFlt-1 was functional as judge by its inhibitory effect on the VEGF mitogenic response in human umbilical vein endothelial cells (HUVECs). Kinetic experiments revealed sFlt-1 release immediately after the beginning of ECC suggesting a proteolysis of its membrane form (mFlt-1) rather than an elevated transcription/translation process. Flow cytometry analysis highlighted no effect of ECC on the shedding of mFlt-1 on platelets and leukocytes suggesting vascular endothelial cell as a putative cell source for the ECC-derived sFlt-1.

Conclusion

sFlt-1 is released during CABG with ECC. It might be suggested that sFlt-1 production, by neutralizing VEGF and/or by inactivating membrane-bound Flt-1 and KDR receptors, might play a role in the occurrence of post-CABG complication.

Cutting edge: Essential role of hypoxia inducible factor-1alpha in development of lipopolysaccharide-induced sepsis

Sepsis, the leading cause of death in intensive care units, reflects a detrimental host response to infection in which bacteria or LPS act as potent activators of immune cells, including monocytes and macrophages. In this report, we show that LPS raises the level of the transcriptional regulator hypoxia-inducible factor-1alpha (HIF-1alpha) in macrophages, increasing HIF-1alpha and decreasing prolyl hydroxylase mRNA production in a TLR4-dependent fashion. Using murine conditional gene targeting of HIF-1alpha in the myeloid lineage, we demonstrate that HIF-1alpha is a critical determinant of the sepsis phenotype. HIF-1alpha promotes the production of inflammatory cytokines, including TNF-alpha, IL-1, IL-4, IL-6, and IL-12, that reach harmful levels in the host during early sepsis. HIF-1alpha deletion in macrophages is protective against LPS-induced mortality and blocks the development of clinical markers including hypotension and hypothermia. Inhibition of HIF-1alpha activity may thus represent a novel therapeutic target for LPS-induced sepsis.

Pathophysiology of sepsis

Sepsis remains a critical problem with significant morbidity and mortality even in the modern era of critical care management. Multiple derangements exist in sepsis involving several different organs and systems, although controversies exist over their individual contribution to the disease process. Septic patients have substantial, life-threatening alterations in their coagulation system, and currently, there is an approved therapy with a component of the coagulation system (activated protein C) to treat patients with severe sepsis. Previously, it was believed that sepsis merely represented an exaggerated, hyperinflammatory response with patients dying from inflammation-induced organ injury. More recent data indicate that substantial heterogeneity exists in septic patients' inflammatory response, with some appearing immuno-stimulated, whereas others appear suppressed. Cellular changes continue the theme of heterogeneity. Some cells work too well such as neutrophils that remain activated for an extended time. Other cellular changes become accelerated in a detrimental fashion including lymphocyte apoptosis. Metabolic changes are clearly present, requiring close and individualized monitoring. At this point in time, the literature richly illustrates that no single mediator/system/pathway/pathogen drives the pathophysiology of sepsis. This review will briefly discuss many of the important alterations that account for the pathophysiology of sepsis.

Roles for VEGF in the adult

The role of VEGF during development and in pathology is well known, but its function in normal adult tissues is poorly understood. Adverse effects associated with the use of anti-angiogenic therapies targeting VEGF in human pathologies have begun to reveal potential functions of VEGF in quiescent vasculature. Further clues from expression studies of VEGF and its receptors in the adult, from the disease preeclampsia, and from experimental neutralization studies, have suggested that VEGF is involved in endothelial cell survival and fenestration, as well as in the signaling and maintenance of non-endothelial cells. The various biochemical properties of VEGF, and its interaction with other growth factors, may be an important point in determining whether VEGF functions as a maintenance factor versus an angiogenic factor. A thorough understanding of the function of VEGF in the adult may lead to more efficacious pro- and anti-angiogenic therapies.

VEGFR-1 and -2 Regulate Inflammation, Myocardial Angiogenesis, and Arteriosclerosis in Chronically Rejecting Cardiac Allografts

OBJECTIVE

Interplay between inflammation and angiogenesis is important in pathological reparative processes such as arteriosclerosis. We investigated how the two vascular endothelial growth factor receptors VEGFR-1 and -2 regulate these events in chronically rejecting cardiac allografts.

METHODS AND RESULTS

Chronic rejection in mouse cardiac allografts induced primitive myocardial, adventitial, and intimal angiogenesis with endothelial expression of CD31, stem cell marker c-kit, and VEGFR-2. Experiments using marker gene mice or rats as cardiac allograft recipients revealed that replacement of cardiac allograft endothelial cells with recipient bone marrow- or non-bone marrow-derived cells was rare and restricted only to sites with severe injury. Targeting VEGFR-1 with neutralizing antibodies in mice reduced allograft CD11b+ myelomonocyte infiltration and allograft arteriosclerosis. VEGFR-2 inhibition prevented myocardial c-kit+ and CD31+ angiogenesis in the allograft, and decreased allograft inflammation and arteriosclerosis.

CONCLUSIONS

These results suggest interplay of inflammation, primitive donor-derived myocardial angiogenesis, and arteriosclerosis in transplanted hearts, and that targeting VEGFR-1 and -2 differentially regulate these pathological reparative processes.

Temporal dynamics of gene expression in the lung in a baboon model of E. coli sepsis

Background

Bacterial invasion during sepsis induces disregulated systemic responses that could lead to fatal lung failure. The purpose of this study was to relate the temporal dynamics of gene expression to the pathophysiological changes in the lung during the first and second stages of E. coli sepsis in baboons.

Results

Using human oligonucleotide microarrays, we have explored the temporal changes of gene expression in the lung of baboons challenged with sublethal doses of E. coli. Temporal expression pattern and biological significance of the differentially expressed genes were explored using clustering and pathway analysis software. Expression of selected genes was validated by real-time PCR. Cytokine levels in tissue and plasma were assayed by multiplex ELISA. Changes in lung ultrastructure were visualized by electron microscopy. We found that genes involved in primary inflammation, innate immune response, and apoptosis peaked at 2 hrs. Inflammatory and immune response genes that function in the stimulation of monocytes, natural killer and T-cells, and in the modulation of cell adhesion peaked at 8 hrs, while genes involved in wound healing and functional recovery were upregulated at 24 hrs.

Conclusion

The analysis of gene expression modulation in response to sepsis provides the baseline information that is crucial for the understanding of the pathophysiology of systemic inflammation and may facilitate the development of future approaches for sepsis therapy.

Phenotypic Heterogeneity of the Endothelium

Endothelial cells, which form the inner cellular lining of blood vessels and lymphatics, display remarkable heterogeneity in structure and function. This is the first of a 2-part review focused on phenotypic heterogeneity of blood vessel endothelium. This review provides an historical perspective of our understanding of endothelial heterogeneity, discusses the scope of phenotypic diversity across the vascular tree, and addresses proximate and evolutionary mechanisms of endothelial cell heterogeneity. The overall goal is to underscore the importance of phenotypic heterogeneity as a core property of the endothelium.

Decreased Expression of VEGF-A in Rat Experimental Autoimmune Encephalomyelitis and in Cerebrospinal Fluid Mononuclear Cells from Patients with Multiple Sclerosis

Vascular endothelial growth factor A (VEGF-A) stimulates angiogenesis, but is also pro-inflammatory and plays an important role in the development of neurological disease, where it can have both attenuating and exacerbating effects. VEGF-B, a related molecule, is highly expressed in the central nervous system and seems to be important in neurological injury. A few studies have indicated that VEGF-A may play a role in the pathogenesis of multiple sclerosis (MS), but the role of VEGF-B has not been studied. We have studied the expression of VEGF-A, -B and their receptors by mRNA in situ hybridization, immunohistochemistry and real-time PCR in spinal cord from LEW rats with experimental autoimmune encephalomyelitis (EAE) and in cerebrospinal fluid (CSF) and blood samples from MS patients. Whereas VEGF-A is downregulated in glia in EAE, the infiltrating inflammatory cells are positive for VEGF-A. Expression of VEGF-B and the VEGF receptors is unaltered. In addition, the levels of VEGF-A mRNA in mononuclear cells [corrected] in CSF are lower in MS patients compared with controls. These results demonstrate a complex regulation of VEGF-A during neuroinflammation and suggest that VEGF-B is not involved in the pathogenesis of MS.

Promising therapeutic agents for sepsis

The incidence of sepsis is expected to increase at a rate of 1.5% per year. Advances in our understanding of the sepsis syndrome have enabled researchers to identify new therapeutic targets and design therapies for existing mediators of sepsis. Drotrecogin alfa (activated) was the first biological treatment for serious sepsis approved by the Food and Drug Administration in 2001. There have also been promising research results involving ethyl pyruvate, glycogen synthase kinase-3 inhibitors and 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors. Here, we review these four compounds and compound classes as examples of emerging pharmacological treatments of severe sepsis and describe the current status of sepsis research.