Reduction of the anticoagulant activity of glycosaminoglycans on the surface of the vascular endothelium by endotoxin and neutrophils: evaluation by an amidolytic assay

The Interplay between Inflammation, Coagulation and Endothelial Injury in the Early Phase of Acute Pancreatitis: Clinical Implications

Acute pancreatitis (AP) is an inflammatory disease with varied severity, ranging from mild local inflammation to severe systemic involvement resulting in substantial mortality. Early pathologic events in AP, both local and systemic, are associated with vascular derangements, including endothelial activation and injury, dysregulation of vasomotor tone, increased vascular permeability, increased leukocyte migration to tissues, and activation of coagulation. The purpose of the review was to summarize current evidence regarding the interplay between inflammation, coagulation and endothelial dysfunction in the early phase of AP. Practical aspects were emphasized: (1) we summarized available data on diagnostic usefulness of the markers of endothelial dysfunction and activated coagulation in early prediction of severe AP; (2) we reviewed in detail the results of experimental studies and clinical trials targeting coagulation-inflammation interactions in severe AP. Among laboratory tests, d-dimer and angiopoietin-2 measurements seem the most useful in early prediction of severe AP. Although most clinical trials evaluating anticoagulants in treatment of severe AP did not show benefits, they also did not show significantly increased bleeding risk. Promising results of human trials were published for low molecular weight heparin treatment. Several anticoagulants that proved beneficial in animal experiments are thus worth testing in patients.

Coagulation and inflammation

The protein C anticoagulant pathway is critical for controlling microvascular thrombosis and is initiated when thrombin binds to thrombomodulin (TM) on the surface of the endothelium. Protein C activation is augmented by an endothelial cell protein C receptor (EPCR). EPCR is shed from the vasculature by inflammatory mediators and thrombin. EPCR binds to activated neutrophils in a process that involves proteinase 3 and Mac-1 and appears to inhibit leukocyte extravasation. EPCR can undergo translocation from the plasma membrane to the nucleus where it re-directs gene expression. During translocation, EPCR can carry activated protein C (APC) to the nucleus, possibly accounting for the ability of APC to modulate inflammatory mediator responses in the endothelium. TNF-α and other inflammatory mediators can down-regulate EPCR and TM. Inhibition of protein C pathway function increases cytokine elaboration, endothelial cell injury and leukocyte extravasation in response to endotoxin and infusion of APC reverses these processes. In vitro, APC has been reported to inhibit TNF-α elaboration from monocytes and to block leukocyte adhesion to selectins. Since thrombin can elicit many inflammatory responses in microvascular endothelium, loss of control of microvascular thrombin generation due to impaired protein C pathway function probably contributes to microvascular dysfunction in sepsis.

Serum heparan sulfate levels are elevated in endotoxemia

BACKGROUND

Increased vascular permeability is a characteristic feature of sepsis which, in the past, has been ascribed exclusively to a malfunction of endothelial cells. However, recently it has become evident that the endothelial glycocalyx is of considerable importance concerning various aspects of vascular physiology, e.g. the vascular barrier and inflammation. Heparan sulfate, one of its essential components is characteristically traceable in blood, in case the endothelial glycocalyx is damaged or destroyed.

METHODS

In 15 pigs we investigated whether the administration of endotoxin from gram-negative bacteria (Escherichia coli) results in increased serum levels of heparan sulfate, signalizing a shedding of the glycocalyx. In addition, markers of inflammation (white blood cell count, platelet count, tumour necrosis factor-α and interleukin-6) were evaluated over an observation period of 6 hours.

RESULTS

Serum heparan sulfate concentrations significantly increased over time in the endotoxin group and were significantly elevated in comparison to the control group 6 hours after administration of endotoxin (p<0.001). In the endotoxin group all markers of inflammation significantly changed during the time course.

CONCLUSIONS

The administration of bacterial endotoxin induced a significant rise in degradation products of the endothelial glycocalyx.

The link between vascular features and thrombosis

The mechanisms of vascular control of thrombotic events remain unclear. The vasculature possesses essential anticoagulant factors that regulate coagulation. Because the endothelium-to-blood ratios are much higher in the microcirculation, it is likely that stasis contributes to thrombotic risk, due in large part to failure to rapidly access the microcirculation and to gain access to this highly anticoagulant environment. Inflammation can potentiate thrombosis in part through downregulation of the vascular anticoagulants, a process that appears to be exacerbated in aging, a well-known risk factor for thrombosis. Surgery and trauma, two major risk factors for thrombosis, result in the release of a variety of cellular components that trigger coagulation through separate mechanisms.

Crosstalk between inflammation and thrombosis

Inflammation shifts the hemostatic mechanisms in favor of thrombosis. Multiple mechanisms are at play including up regulation of tissue factor leading to the initiation of clotting, amplification of the clotting process by augmenting exposure of cellular coagulant phospholipids, inhibition of fibrinolysis by elevating plasminogen activator inhibitor 1 (PAI-1) and decreases in natural anticoagulant pathways, particularly targeted toward down regulation of the protein C anticoagulant pathway through multiple mechanisms. The decreased function of the natural anticoagulant pathways may be particularly problematic because these appear to play a role in dampening inflammatory responses. The protein C anticoagulant pathway provides a useful model for the impact of inflammation on coagulation. This pathway plays a major role in preventing microvascular thrombosis. The pathway is initiated when thrombin binds to thrombomodulin (TM) on the surface of the endothelium. An endothelial cell protein C receptor (EPCR) augments protein C activation by the thrombin-TM complex more than 10-fold in vivo. EPCR is shed from the endothelium by inflammatory mediators and thrombin. EPCR binds to activated neutrophils in a process that involves proteinase 3 and Mac-1 and appears to inhibit leukocyte extravisation. EPCR can undergo translocation from the plasma membrane to the nucleus where it redirects gene expression. During translocation it can carry activated protein C (APC) to the nucleus, possibly accounting for the ability of APC to modulate inflammatory mediator responses in the endothelium. TNF alpha and other inflammatory mediators can down-regulate EPCR and TM and IL-6 can depress levels of protein S in experimental animals. Inhibition of protein C pathway function increases cytokine elaboration, endothelial cell injury and leukocyte extravisation in response to endotoxin, processes that are decreased by infusion of APC. In vitro, APC inhibits TNF alpha elaboration from monocytes and to block leukocyte adhesion to selectins. Since thrombin can elicit many inflammatory responses in microvascular endothelium, loss of control of microvascular thrombin generation due to impaired protein C pathway function probably contributes to microvascular dysfunction in sepsis.

Crosstalk between inflammation and thrombosis

Inflammation shifts the hemostatic mechanisms in favor of thrombosis. Multiple mechanisms are at play including up regulation of tissue factor leading to the initiation of clotting, amplification of the clotting process by augmenting exposure of cellular coagulant phospholipids, inhibition of fibrinolysis by elevating plasminogen activator inhibitor 1 (PAI-1) and decreases in natural anticoagulant pathways, particularly targeted toward down regulation of the protein C anticoagulant pathway through multiple mechanisms. The decreased function of the natural anticoagulant pathways may be particularly problematic because these appear to play a role in dampening inflammatory responses. The protein C anticoagulant pathway provides a useful model for the impact of inflammation on coagulation. This pathway plays a major role in preventing microvascular thrombosis. The pathway is initiated when thrombin binds to thrombomodulin (TM) on the surface of the endothelium. An endothelial cell protein C receptor (EPCR) augments protein C activation by the thrombin-TM complex more than 10-fold in vivo. EPCR is shed from the endothelium by inflammatory mediators and thrombin. EPCR binds to activated neutrophils in a process that involves proteinase 3 and Mac-1 and appears to inhibit leukocyte extravisation. EPCR can undergo translocation from the plasma membrane to the nucleus where it redirects gene expression. During translocation it can carry activated protein C (APC) to the nucleus, possibly accounting for the ability of APC to modulate inflammatory mediator responses in the endothelium. TNF alpha and other inflammatory mediators can down-regulate EPCR and TM and IL-6 can depress levels of protein S in experimental animals. Inhibition of protein C pathway function increases cytokine elaboration, endothelial cell injury and leukocyte extravisation in response to endotoxin, processes that are decreased by infusion of APC. In vitro, APC inhibits TNF alpha elaboration from monocytes and to block leukocyte adhesion to selectins. Since thrombin can elicit many inflammatory responses in microvascular endothelium, loss of control of microvascular thrombin generation due to impaired protein C pathway function probably contributes to microvascular dysfunction in sepsis.

New approaches to the treatment of sepsis

The clinical spectrum of sepsis, severe sepsis, and septic shock is responsible for a growing number of deaths and excessive health care expenditures. Until recently, despite multiple clinical trials, no intervention provided a beneficial outcome in septic patients. Within the last 2 years, studies that involved drotrecogin alfa (activated), corticosteroid therapy, and early goal-directed therapy showed efficacy in those with severe sepsis and septic shock. These results have provided optimism for reducing sepsis-related mortality.

Pathophysiology of meningococcal meningitis and septicaemia

Neisseria meningitidis is remarkable for the diversity of interactions that the bacterium has with the human host, ranging from asymptomatic nasopharyngeal colonisation affecting virtually all members of the population; through focal infections of the meninges, joints, or eye; to the devastating and often fatal syndrome of meningococcal septic shock and purpura fulminans.

Dysfunction of endothelial protein C activation in severe meningococcal sepsis

BACKGROUND

Impairment of the protein C anticoagulation pathway is critical to the thrombosis associated with sepsis and to the development of purpura fulminans in meningococcemia. We studied the expression of thrombomodulin and the endothelial protein C receptor in the dermal microvasculature of children with severe meningococcemia and purpuric or petechial lesions.

METHODS

We assessed the integrity of the endothelium and the expression of thrombomodulin and the endothelial protein C receptor in biopsy specimens of purpuric lesions from 21 children with meningococcal sepsis (median age, 41 months), as compared with control skin-biopsy specimens.

RESULTS

The expression of endothelial thrombomodulin and of the endothelial protein C receptor was lower in the patients with meningococcal sepsis than in the controls, both in vessels with thrombosis and in vessels without thrombosis. On electron microscopical examination, the endothelial cells were generally intact in both thrombosed and nonthrombosed vessels. Plasma thrombomodulin levels in the children with meningococcal sepsis (median, 6.4 ng per liter) were higher than those in the controls (median, 3.6 ng per liter; P=0.002). Plasma levels, protein C antigen, protein S antigen, and antithrombin antigen were lower than those in the controls. In two patients treated with unactivated protein C concentrate, activated protein C was undetectable at the time of admission, and plasma levels remained low.

CONCLUSIONS

In severe meningococcal sepsis, protein C activation is impaired, a finding consistent with down-regulation of the endothelial thrombomodulin-endothelial protein C receptor pathway.

New therapies and vaccines for meningococcal disease

Meningococcal disease (MCD) is an important cause of morbidity and mortality. The pathophysiology consists of a complex interaction of bacterial and host factors, triggered by the release of endotoxin which initiates the inflammatory cascade, resulting in multi-organ failure, coagulopathy, capillary leak, metabolic derangement and eventually death. Prompt recognition and aggressive management are essential in reducing mortality. Over the past decade, there has been intense research into novel therapies and vaccines, with largely disappointing results. Therapies have been broadly divided into anti-endotoxin and anti-TNF-alpha therapies, treatment aimed at correcting coagulopathy and at blood purification and anti-inflammatory cytokine therapy. The reasons for the disappointing results in the search for new therapeutic strategies are difficult to identify. The disordered physiology in MCD results from a complex interaction of several mediators; therefore attempts to correct this by altering just one step represents a gross oversimplification of the process. In addition, the experimental model of endotoxaemia, which is often used, is a poor representation of an acutely ill patient with rapidly progressive shock. There have been several small or poorly designed trials, which have failed to reach definite conclusions. In order to yield conclusive results any future trials must be multicentre, randomised, controlled trials, but these are expensive and, in practice, difficult to conduct. The BPI trial (vide infra) was a significant step forward in this regard and demonstrated the ability to organise a large multicentred trial which can act as a template for future trials. Although the results were not significant there was an overall trend towards improved outcome in the treatment arm. Whilst the development of effective therapies and vaccines are awaited, the priorities at present must be the prompt recognition and aggressive management of disease.

Coagulation in severe sepsis: a central role for thrombomodulin and activated protein C

OBJECTIVES

To review the mechanisms that cause coagulation abnormalities in sepsis, focusing on the interaction between the vascular endothelium and the circulating coagulation factors, particularly the role of the protein C pathway and thrombomodulin.

DATA SOURCES/STUDY SELECTION

Published research abstracts and review articles on the experimental and clinical investigation of the pathophysiology of disseminated intravascular coagulation in sepsis.

DATA EXTRACTION AND SYNTHESIS

The data provide increasing evidence that the coagulopathy seen in sepsis is a result of a complex imbalance of pro- and anticoagulant pathways. Whereas previous research has largely studied events in the plasma, it is now apparent that reactions on cell surfaces such as the vascular endothelium are important in the control of the regulatory pathways.

CONCLUSIONS

The plasma components of the protein C pathway are down-regulated in sepsis. Decreased thrombomodulin expression may cause defective function of the endothelial component of this pathway in septic patients. Treatments must be designed to overcome any functional defect.

Is immune cell activation the missing link in the pathogenesis of post-diarrhoeal HUS?

Haemolytic uraemic syndrome (HUS), which is caused by Shiga toxin (Stx)-producing Escherichia coli, is the commonest cause of acute renal failure in childhood. It is widely believed that HUS develops following the release of Stx, an AB5 toxin that inhibits protein synthesis and has a direct toxic effect on the kidney endothelium. There remains, however, a mismatch between the current understanding of the pathogenesis of HUS and the evolution of the clinical signs of the disease. Our hypothesis is that Stx-mediated immune cell activation in the gut is the missing link in the pathogenesis of this condition, initiating the characteristic renal pathology of HUS either alone or in synergy with Stx. Validation of this hypothesis could lead to a targeted anti-inflammatory approach aimed at modulating immune cell function in HUS.

Increased excretion of urinary glycosaminoglycans in meningococcal septicemia and their relationship to proteinuria

OBJECTIVES

Meningococcal septic shock is a devastating illness associated with an increase in vascular permeability leading to hypovolemia and accumulation of plasma proteins and fluid in tissues. The capillary leak syndrome is often associated with widespread thrombosis in the skin, limbs, and digits. We postulated that the increase in vascular permeability and the intravascular thrombosis might be caused by an inflammation-induced loss of endothelial and basement membrane glycosaminoglycans (GAGs), which play a role in the permeability and thromboresistant properties of the microvasculature.

DESIGN

Prospective, single-center observational study.

SETTING

University-affiliated meningococcal research unit and pediatric intensive care unit.

PATIENTS

Eighteen children requiring intensive care for meningococcal sepsis, 18 children with steroid-responsive nephrotic syndrome, and 18 healthy control children.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Serum concentrations and urine excretion of glycosaminoglycans were measured and related to changes in glomerular permeability to plasma proteins. The size-distribution and nature of glycosaminoglycans were defined by Polyacrylamide Gel Electrophoresis and specific enzyme digestion. Urinary excretion of heparan sulfate, chondroitin-4-sulfate, and chondroitin-6-sulfate were significantly increased in meningococcal disease (MD) relative to healthy controls and children with steroid-responsive nephrotic syndrome. The urinary GAGs in MD were of similar size to those in controls when analyzed after pronase digestion. However, analysis of proteoglycan size before proteolytic digestion showed the urinary GAGs in MD were of lower molecular weight and unattached to proteins. The fractional excretion of albumin and immunoglobulin G in MD increased with severity of disease. Patients with severe or fatal MD had albumin clearances overlapping those seen in steroid-responsive nephrotic syndrome. There was a significant correlation between proteinuria in MD and urinary excretion of heparan sulfate (r2 = 0.611, p < .0001), chondroitin-4-sulfate (r2 = 0.721, p < .0001), and chondroitin-6-sulfate (r2 = 0.395, p < .0001).

CONCLUSIONS

The capillary leak in meningococcal disease is associated with increased plasma and urine concentrations of GAGs, which may be proteolytically cleaved from endothelial and basement membrane sites. The correlation between the severity of protein leakage and the urine excretion of GAGs suggests that loss of GAGs may be causally related to the increase in permeability to proteins.

Disseminated intravascular coagulation and purpura fulminans secondary to infection

Infection is one of the commonest causes of disseminated intravascular coagulation (DIC). DIC is a complex disorder that results from an imbalance of the pro- and anticoagulant regulatory pathways. This chapter will explain the cellular and molecular basis of the disorder and consider the rationale behind current and experimental treatment strategies.

Use of protein-C concentrate, heparin, and haemodiafiltration in meningococcus-induced purpura fulminans

BACKGROUND

Inflammatory and coagulation processes are both affected in meningococcaemia. Severe acquired protein-C deficiency in meningococcaemia is usually associated with substantial mortality: in survivors, skin grafts, amputation, and end-organ failure are not uncommon. Protein C is a natural anticoagulant and also has important anti-inflammatory activity. We assessed the effects of early replacement therapy with protein-C concentrate together with continuous veno-venous haemodiafiltration and conventional treatment in meningococcaemia.

METHODS

12 patients aged between 3 months and 27 years with meningococcaemia and severe acquired protein-C deficiency (mean 0.20 IU/mL) were studied. All patients had septic shock, widespread purpura, skin necrosis, and disseminated intravascular coagulopathy. After a test dose of protein-C concentrate, patients received a continuous infusion with the dose adjusted daily to keep the plasma concentration between 0.8 and 1.2 IU/mL. 11 patients were given unfractionated intravenous heparin (10-15 IU kg-1 h-1). Nine patients had haemodiafiltration and one had peritoneal dialysis. The Glasgow meningococcal septicaemia prognostic score and the paediatric risk of mortality score predicted a minimum mortality of 80% and 57%, respectively.

FINDINGS

No patient died. No adverse reactions to the treatment were seen. Two patients had lower-limb amputations, one of whom had a thrombotic cerebrovascular accident; both patients had received the protein-C concentrate and heparin later than the rest of the group (60 h [16.97] vs 12 h [3.13]). One patient developed chronic renal failure despite receiving protein-C infusion 15 h after admission.

INTERPRETATION

The acquired severe deficiency of protein C in meningococcaemia contributes to the pathogenesis of the thrombotic necrotic lesions in the skin and other organs and probably has an important role in the inflammatory response. Protein-C therapy is merely one approach to improve the host response in this syndrome. We suggest that a double-blind, randomised, controlled multicentre trial is needed to confirm our results.

Arterial smooth muscle cell heparan sulfate proteoglycans accelerate thrombin inhibition by heparin cofactor II

Heparin cofactor II (HCII) is a potent thrombin inhibitor in the presence of heparin and dermatan sulfate, glycosaminoglycans that accelerate the inhibition reaction. HCII is postulated to be an extravascular thrombin inhibitor that is stimulated physiologically by dermatan sulfate proteoglycans. To understand how thrombin activity may be downregulated within the artery wall, cultured monkey aorta smooth muscle cell (SMC) proteoglycans were tested for their ability to accelerate thrombin inhibition by HCII. Early confluent SMC monolayers increased thrombin-HCII inhibition rates 2-fold to 4-fold compared with reactions in cell-free control wells (7.3 +/- 0.5 versus 2.7 +/- 0.2 x 10(4) mol.L-1.min-1, with and without SMCs, respectively; n = 7 experiments). Extracellular matrix obtained by cell monolayer removal also accelerated the thrombin-HCII inhibition reaction 3-fold to 5-fold. Rate increases were abolished by Polybrene or protamine sulfate. Pretreatment of monolayers with heparitinase I (and of extracellular matrix with HNO2) to degrade heparan sulfate blocked the thrombin-HCII inhibition rate increase. In contrast, pretreatment with chondroitinase ABC in the presence of proteinase inhibitors had no effect. "Pericellular" (cell surface- and extracellular matrix-derived) SMC heparan sulfate proteoglycans (HSPGs) were purified and fractionated by charge on DEAE-Sephacel. At a concentration of 1 microgram/mL hexuronic acid, high-charge HSPG stimulated a 7-fold thrombin-HCII inhibition rate increase relative to reactions without proteoglycan, whereas low-charge HSPG induced a 2-fold rate increase. In comparison, an 18-fold rate increase was observed with 1 microgram/mL dermatan sulfate proteoglycan purified from SMC culture media. These results indicate that SMC HSPG could contribute significantly to thrombin inhibition by HCII in the artery wall.

Assessment of the effect of candidate anti-inflammatory treatments on the interaction between meningococci and inflammatory cells in vitro in a whole blood model

A wide range of immunomodulating agents are now available which may be of benefit in reducing inflammatory cell activation in meningococcal sepsis. In order to facilitate selection of candidate anti-inflammatory agents for clinical trials, we have used an in vitro whole blood model to evaluate the effects on meningococcal induced neutrophil and monocyte activation, of dexamethasone, prostacyclin, pentoxifylline and a human IgM anti-lipid A monoclonal antibody (HA-1A). Known concentrations of heat and penicillin killed meningococci were added to whole blood and the time course of cellular activation was determined. Using elastase alpha 1-antitrypsin (elastase-alpha 1-AT) and TNF alpha production as markers of neutrophil and monocyte activation respectively, plasma levels of elastase-alpha 1-AT and TNF alpha were found to increase in a dose-dependent manner. Elastase-alpha 1-AT was detected early, with most release occurring between 15-30 min whereas TNF alpha was detected later, between 120-180 min. Dexamethasone, prostacyclin and pentoxifylline caused a dose-dependent inhibition of TNF alpha release but had no effect on elastase release. HA-1A had no effect on either TNF alpha or elastase release. This model may be useful in determining the sequence of inflammatory cell activation and in selecting candidate anti-inflammatory agents for evaluation in clinical trials.