Interleukin 1 or endotoxin increases the release of von Willebrand factor from human endothelial cells

The gut microbiota - a modulator of endothelial cell function and a contributing environmental factor to arterial thrombosis

Introduction: There is emerging evidence linking the commensal gut microbiota with the development of cardiovascular disease and arterial thrombosis. In immunothrombosis, the host clotting system protects against the dissemination of invading microbes, not considering the huge number of microbes that interact with host physiology in a mutualistic fashion. Areas covered: Interestingly, recent research revealed that colonizing gut microbes profoundly influence host innate immune pathways that support arterial thrombus growth. The gut microbiota promotes arterial thrombus formation by enhancing the pro-adhesive capacity of the vascular endothelium, triggering hepatic von Willebrand factor synthesis and its release by Weibel-Palade body exocytosis, resulting in elevated von Willebrand factor levels and enhancing FVIII stability in plasma. Furthermore, the metabolic capacity of gut resident microbes promotes agonist-induced platelet activation and deposition. Here, we give an overview, with a focus on the vascular endothelium, on how this gut-resident microbial ecosystem contributes to arterial thrombus formation. Expert opinion: The gut microbiota and its metabolites not only act on agonist-induced platelet reactivity, but also influence the hepatic endothelial phenotype via remote signaling, facilitating arterial thrombus growth at the arterial injury site.

von Willebrand factor and procoagulant imbalance predict outcome in patients with cirrhosis and thrombocytopenia

BACKGROUND & AIMS

Several lines of evidence suggest that the hemostatic disorders of cirrhosis may have a significant clinical impact. We investigated the independent predictive value of components of the hemostatic system on the occurrence of ascites, variceal bleeding (VB), and survival.

METHODS

One hundred and two patients with thrombocytopenia (Child-Pugh class A/B/C: 34/34/34) were enrolled. Platelet counts, factors (F) II, V, VII, and VIII, antithrombin, protein C (PC), FVIII-to-PC ratio as an index of procoagulant imbalance, von Willebrand factor antigen (vWF-Ag), and model for end-stage liver disease (MELD) were evaluated. Two multivariate analyses were performed: one excluding (model 1) and one including MELD (model 2).

RESULTS

Higher vWF-Ag levels and FVIII-to-PC ratios were the most prominent hemostatic disorders in patients with cirrhosis. Increased levels of vWF-Ag and FVIII, and higher FVIII-to-PC ratios independently predicted the presence of ascites and varices at baseline. Independent predictors of ascites and VB during follow-up were vWF-Ag (model 1/2: p=0.001/p=0.009 and p=0.008/p=0.01, respectively) and FVIII-to-PC ratio (model 1/2: p=0.003/p=0.02 and p=0.01/p=0.03, respectively). vWF-Ag (model 1/2: p=0.007/p=0.002), FVIII-to-PC ratio (model 1/2: p=0.001/p=0.01), and MELD (p=0.02) independently predicted mortality. Patient groups with significantly higher probability of new-onset ascites, VB, and mortality were identified by certain cut-offs of vWF-Ag (213%, 466%, and 321%, respectively) and FVIII-to-PC ratio (1.99, 3.29, and 2.36, respectively). vWF-Ag and FVIII-to-PC ratio equaled MELD in mortality prediction.

CONCLUSIONS

Advanced cirrhosis is characterized by increased thrombotic potential. vWF-Ag and FVIII-to-PC ratio independently predict new-onset ascites, VB, and mortality. Targeting hypercoagulability could improve the outcome of patients with cirrhosis.

LAY SUMMARY

Higher von Willebrand factor antigen (vWF-Ag) levels and factor VIII-to-protein C (FVIII-to-PC) ratio are the prominent hemostatic disorders in patients with cirrhosis. vWF-Ag and FVIII-to-PC ratio independently predict new-onset ascites, variceal bleeding, and mortality in these patients.

Relevance of ADAMTS13 to liver transplantation and surgery

A disintegrin-like and metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS13) specifically cleaves unusually-large von Willebrand factor (VWF) multimers under high shear stress, and down-regulates VWF function to form platelet thrombi. Deficiency of plasma ADAMTS13 activity induces a life-threatening systemic disease, termed thrombotic microangiopathy (TMA) including thrombotic thrombocytopenic purpura (TTP). Children with advanced biliary cirrhosis due to congenital biliary atresia sometimes showed pathological features of TMA, with a concomitant decrease of plasma ADAMTS13 activity. Disappearance of their clinical findings of TTP after successful liver transplantation suggested that the liver is a major organ producing plasma ADAMTS13. In situ hybridization analysis showed that ADAMTS13 was produced by hepatic stellate cells. Subsequently, it was found that ADADTS13 was not merely responsible to development of TMA and TTP, but also related to some kinds of liver dysfunction after liver transplantation. Ischemia-reperfusion injury and acute rejection in liver transplant recipients were often associated with marked decrease of ADAMTS13 and concomitant formation of unusually large VWF multimers without findings of TMA/TTP. The similar phenomenon was observed also in patients who underwent hepatectomy for liver tumors. Imbalance between ADAMTS13 and VWF in the hepatic sinusoid might cause liver damage due to microcirculatory disturbance. It can be called as “local TTP like mechanism” which plays a crucial role in liver dysfunction after liver transplantation and surgery.

The role of endothelial cell adhesion molecules in the development of atherosclerosis

The vascular endothelium serves as a dynamic interface between circulating blood elements and the interstitial tissues. As such, it communicates to cells within the vessel wall as well as to the surrounding tissue, sensing its environment and responding accordingly. The vasculature must maintain a delicate balance when initiating a functional response by producing both proinflammatory and antiinflammatory mediators, vasoconstrictors and vasodilators, growth stimulators and inhibitors, and prothrombogenic and antithrombogenic factors. Any response to injurious agents could lead to pathology. Confounding this complex interplay is the fact that the very response to injury that may have developed to undo the damage may itself be even more deleterious. One response to injury by the endothelium is the new or increased expression of surface receptors for immune elements. In atherosclerosis, the adhesion of monocytes (and T cells) to the endothelium is a key event triggered by some form of insult. Subsequent events include monocytic infiltration of the vessel wall, alterations in lipid metabolism, and the activation of these cells into foam cells. The presence of large numbers of foam cells in the intima may produce a high concentration of cytokines and growth factors within a localized area, extracellular matrix perturbations, smooth muscle cell proliferation, and ultimately platelet aggregation at the site of stenosis. Endothelial cells themselves will not only elaborate factors after the initial injury to the vessel wall but also in response to the factors produced by foam cells within the plaque. These endothelial cell factors include MCP-1, a chemoattractant for monocytes (179,180), IL-1 (63,64), IL-6 (interleukin-6) (65-67), IL-8 (interleukin 8) (181), and PDGF, a potent smooth muscle mitogen (4,72) (Fig. 3). Endothelial cells will propagate an inflammatory response long after the initial insult to the arterial vessel. A chronic cycle of endothelial cell activation and leukocyte infiltration is constitutively activated. Thus, all of the cellular elements of the vessel wall, as well as the atherosclerotic plaque itself, elaborate cytokines and growth factors that amplify and propagate the pathological process.

Imbalance of von Willebrand factor and its cleaving protease ADAMTS13 during systemic inflammation superimposed on advanced cirrhosis

BACKGROUND & AIMS

Systemic inflammation in advanced cirrhosis represents a spectrum ranging from subclinical pathological bacterial translocation and immune activation to overt bacterial infection and sepsis. We hypothesized that systemic inflammation in cirrhosis is accompanied by a failure of ADAMTS13 to control the prothrombotic function of von Willebrand factor (VWF), which is increased in portal hypertension and hepatic fibrosis.

METHODS

Patients with Child A cirrhosis (n = 25), Child B/C cirrhosis without clinical features of systemic inflammation (n = 31), and Child B/C cirrhosis with overt bacterial infections or systemic inflammatory response syndrome (n = 24) were analysed for ADAMTS13 and associated parameters and were followed to determine transplant-free survival.

RESULTS

Plasma concentration and activity of ADAMTS13 were decreased in patients with systemic inflammation. Furthermore, ADAMTS13 inversely correlated with the extent of bacterial translocation and the severity of acute-phase reaction. As a function of reduced ADAMTS13 activity and increased VWF antigen, plasma from patients with superimposed inflammation strongly aggregated the platelet receptor glycoprotein Ib in presence of ristocetin. VWF:RCo correlated with higher concentrations of leucocytes and lipopolysaccharide-binding protein, organ dysfunction, augmented turnover of cross-linked intravascular fibrin, and the occurrence of acute kidney injury during follow-up. VWF:RCo of 390% or more predicted transplant-free survival in univariate analysis [HR = 8.24 (3.30-20.54)] and after adjustment for MELD [HR = 3.58 (1.30-9.88)]. However, adverse outcome was not associated with the accumulation of high-molecular weight VWF multimers.

CONCLUSIONS

Systemic inflammation complicating advanced cirrhosis is accompanied by reduced activity of ADAMTS13 promoting a prothrombotic function of VWF, which can be employed to predict clinical outcome.

Effects of clopidogrel on horses with experimentally induced endotoxemia

OBJECTIVE

To evaluate the effects of clopidogrel on clinical and clinicopathologic variables in healthy horses with experimentally induced endotoxemia.

ANIMALS

12 adult mares. Procedures-Horses were assigned with a randomization procedure to receive clopidogrel (4 mg/kg, once, then 2 mg/kg, q 24 h; n = 6) or a placebo (6) through a nasogastric tube. After 72 hours of treatment, horses received lipopolysaccharide (LPS; 30 ng/kg, IV). Heart rate, respiratory rate, rectal temperature, CBC variables, plasma fibrinogen concentration, serum tumor necrosis factor-α concentration, plasma von Willebrand factor concentration, and measures of platelet activation (including ADP- and collagen-induced platelet aggregation and closure times, thrombelastography variables, and results of flow cytometric detection of platelet membrane P-selectin, phosphatidylserine, and microparticles) were determined at various times before and after LPS administration by investigators unaware of the treatment groups. Statistical analyses were performed with repeated-measures ANOVA.

RESULTS

4 of 6 clopidogrel-treated horses had significant decreases in ADP-induced platelet aggregation before and after LPS administration. Heart rate increased significantly after LPS administration only for the placebo group. No significant differences were detected between groups for CBC variables, closure time, and plasma concentration of fibrinogen or serum concentration of tumor necrosis factor-α, and no clinically relevant differences were detected for other hemostatic variables.

CONCLUSIONS AND CLINICAL RELEVANCE

In this study, administration of LPS did not induce platelet hyperreactivity in horses on the basis of measures of platelet adhesion, aggregation, degranulation, and procoagulant activity. Administration of clopidogrel was associated with variable platelet antiaggregatory activity and attenuated some clinical signs of endotoxemia.

Disseminated intravascular coagulation in a novel porcine model of severe Staphylococcus aureus sepsis fulfills human clinical criteria

Sepsis is a common and often fatal complication in human patients in intensive care units. Relevant and well characterized animal models of sepsis may provide valuable information on pathophysiological mechanisms and be a mean of testing new therapeutic strategies. Large animal models of Staphylococcus aureus sepsis are rare, even though S. aureus increasingly affects human patients. Sepsis changes the haemostatic balance and leads to endothelial cell (EC) activation, coagulopathy and, in severe cases, disseminated intravascular coagulation (DIC). The aim of this study was to characterize the haemostatic and vascular alterations in a novel porcine model of severe S. aureus sepsis, investigating whether the changes fulfill the human clinical criteria for DIC. Five pigs were inoculated intravenously with S. aureus and two control animals were sham-inoculated. Blood samples were collected for thromboelastography (TEG) and assessment of plasma-based haemostatic parameters. Tissue was collected for histopathology and reverse transcriptase quantitative real-time polymerase chain reaction for measurement of mRNA encoding EC markers. All infected animals developed DIC; including procoagulant activation represented by hypercoagulable TEG profiles and prolonged clotting time. Histologically, numerous pulmonary thrombi were present in one pig. Inhibitor consumption was represented by decreasing antithrombin levels in infected pigs. Hyaline globules were found in three infected pigs, confirming fibrinolytic activation. EC activation was identified by expression of von Willebrand factor in small vessels together with elevated mRNA encoding activated EC markers. Severe haemostatic and vascular changes fulfilling the human criteria for DIC were therefore seen in all infected pigs. A tendency towards uncompensated DIC was seen in two animals.

Plasmatic ADAMTS-13 metalloprotease and von Willebrand factor in children with cyanotic congenital heart disease

Changes in plasma von Willebrand factor concentration (VWF:Ag) and ADAMTS-13 activity (the metalloprotease that cleaves VWF physiologically) have been reported in several cardiovascular disorders with prognostic implications. We therefore determined the level of these proteins in the plasma of children with cyanotic congenital heart disease (CCHD) undergoing surgical treatment. Forty-eight children were enrolled (age 0.83 to 7.58 years). Measurements were performed at baseline and 48 h after surgery. ELISA, collagen-binding assays and Western blotting were used to estimate antigenic and biological activities, and proteolysis of VWF multimers. Preoperatively, VWF:Ag and ADAMTS-13 activity were decreased (65 and 71% of normal levels considered as 113 (105-129) U/dL and 91 ± 24% respectively, P < 0.003) and correlated (r = 0.39, P = 0.0064). High molecular weight VWF multimers were not related, suggesting an interaction of VWF with cell membranes, followed by proteolytic cleavage. A low preoperative ADAMTS-13 activity, a longer activated partial thromboplastin time and the need for cardiopulmonary bypass correlated with postoperative bleeding (P < 0.05). Postoperatively, ADAMTS-13 activity increased but less extensively than VWF:Ag (respectively, 2.23 and 2.83 times baseline, P < 0.0001), resulting in an increased VWF:Ag/ADAMTS-13 activity ratio (1.20 to 1.54, respectively, pre- and postoperative median values, P = 0.0029). ADAMTS-13 consumption was further confirmed by decreased ADAMTS-13 antigenic concentration (0.91 ± 0.30 to 0.70 ± 0.25 µg/mL, P < 0.0001) and persistent proteolysis of VWF multimers. We conclude that, in pediatric CCHD, changes in circulating ADAMTS-13 suggest enzyme consumption, associated with abnormal structure and function of VWF.

Decreased plasma ADAMTS-13 activity as a predictor of postoperative bleeding in cyanotic congenital heart disease

OBJECTIVE

To analyze the preoperative plasma antigenic concentration and activity of von Willebrand factor and its main cleaving protease ADAMTS-13 in pediatric patients with cyanotic congenital heart disease undergoing surgical treatment and investigate possible correlations with postoperative bleeding.

METHODS

Plasma antigenic concentrations (von Willebrand factor:Ag and ADAMTS-13:Ag) were measured using enzyme-linked immunoassays. Collagen-binding assays were developed to measure biological activities (von Willebrand factor:collagen binding and ADAMTS-13 activity). The multimeric structure of von Willebrand factor was analyzed using Western immunoblotting. Demographic, diagnostic, and general and specific laboratory data and surgery-related variables were subjected to univariate, bivariate, and multivariate analysis for the prediction of postoperative bleeding.

RESULTS

Forty-eight patients were enrolled, with ages ranging from 9 months to 7.6 years (median 2.5 years). The plasma concentrations of von Willebrand factor:Ag and ADAMTS-13:Ag were decreased by 65 and 82%, respectively, in the patients compared with the controls (p<0.001). An increased density of low-molecular-weight fractions of von Willebrand factor, which are suggestive of proteolytic degradation (p = 0.0081), was associated with decreased ADAMTS-13 activity, which was likely due to ADAMTS-13 consumption (71% of controls, p = 0.0029) and decreased von Willebrand factor:collagen binding (76% of controls, p = 0.0004). Significant postoperative bleeding occurred in 13 patients. The preoperative ADAMTS-13 activity of <64.6% (mean level for the group), preoperative activated partial thromboplastin time, and the need for cardiopulmonary bypass were characterized as independent risk factors for postoperative bleeding, with respective hazard ratios of 22.35 (95% CI 1.69 to 294.79), 1.096 (95% CI 1.016 to 1.183), and 37.43 (95% CI 1.79 to 782.73).

CONCLUSION

Low plasma ADAMTS-13 activity is a risk factor for postoperative bleeding in children with cyanotic congenital heart disease, particularly in children undergoing cardiopulmonary bypass.

Differential regulation of fibrinogen γ chain splice isoforms by interleukin-6

INTRODUCTION

Fibrinogen is a major structural protein in blood clots, and is also a well-known acute phase reactant. The γ chain gene of fibrinogen has two alternative splice variants, γA and γ' chains. γ' fibrinogen constitutes about 7% of total fibrinogen. Total fibrinogen levels and γ' fibrinogen levels have been associated with cardiovascular disease, but the mechanisms regulating the production of the two isoforms are unknown. Several inflammatory cytokines are known to influence the production of total fibrinogen, but the role of cytokines in the production of γ' fibrinogen has not been examined. However, epidemiologic studies have shown an association between γ' fibrinogen levels and inflammatory markers in humans.

MATERIALS AND METHODS

The expression of γ' fibrinogen and total fibrinogen by HepG2 liver cells was quantitated after treatment with interleukin-1β, transforming growth factor-β, tumor necrosis factor-α, and interleukin-6.

RESULTS

Interleukin-1β, transforming growth factor-β, and tumor necrosis factor-α, known down-regulators of total fibrinogen synthesis, also downregulate γ' fibrinogen synthesis in HepG2 cells. However, interleukin-6 differentially up-regulates the production of total and γ' fibrinogen, leading to a 3.6-fold increase in γA mRNA, but an 8.3-fold increase in γ' mRNA.

CONCLUSIONS

These findings indicate that γ' fibrinogen is disproportionately up-regulated by inflammatory responses induced by interleukin-6.

ADAMTS13 activity may predict the cumulative survival of patients with liver cirrhosis in comparison with the Child-Turcotte-Pugh score and the Model for End-Stage Liver Disease score

AIM

  Decreased plasma ADAMTS13 activity (ADAMTS13:AC) results in accumulation of unusually large von Willebrand factor multimers and platelet thrombi formation. Our aim was to evaluate whether ADAMTS13:AC is a prognostic marker in patients with liver cirrhosis.

METHODS

  Plasma ADAMTS13:AC and its related parameters were examined in 108 cirrhotic patients.

RESULTS

  ADAMTS13:AC decreased as the severity of liver disease increased (means: controls 100%, Child A-cirrhotics 79%, Child B-cirrhotics 63%, and Child C-cirrhotics 31%). ADAMTS13:AC markedly decreased in the cirrhotics with hepatorenal syndrome, refractory ascites and hepatic encephalopathy. The cumulative survival time was the shortest (median: 4.5 months) in the cirrhotics with severe to moderate ADAMTS13:AC deficiency (<3-25%), followed by those with mild ADAMTS13:AC deficiency (25-50%), and was the longest in those with normal activity (>50%). In contrast, based on the Child-Turcotte-Pugh (CTP) score, Child C-cirrhotics had the worst survival, but the survival probabilities did not differ between Child A and B cirrhotics. Based on the Model for End-Stage Liver Disease (MELD) score, the survival was the worst for the cirrhotics in the fourth quartile, but it was not different among cirrhotics in the first three quartiles. Cox proportional-hazards regression analysis showed that ADAMTS13:AC and serum albumin were independent factors affecting the survival.

CONCLUSIONS

  ADAMTS13:AC concomitantly decreases as the functional liver capacity decreases. This activity may be a useful prognostic marker that is equal or superior to the CTP score and the MELD score to predict not only the short-term prognosis but also the long-term survival of the cirrhotic patients.

Determination of ADAMTS13 and Its Clinical Significance for ADAMTS13 Supplementation Therapy to Improve the Survival of Patients with Decompensated Liver Cirrhosis

The liver plays a central role in hemostasis by synthesizing clotting factors, coagulation inhibitors, and fibrinolytic proteins. Liver cirrhosis (LC), therefore, impacts on both primary and secondary hemostatic mechanisms. ADAMTS13 is a metalloproteinase, produced exclusively in hepatic stellate cells, and specifically cleaves unusually large von Willebrand factor multimers (UL-VWFM). Deficiency of ADAMTS13 results in accumulation of UL-VWFM, which induces platelet clumping or thrombi under high shear stress, followed by sinusoidal microcirculatory disturbances and subsequent progression of liver injuries, eventually leading to multiorgan failure. The marked imbalance between decreased ADAMTS13 activity (ADAMTS13 : AC) and increased production of UL-VWFM indicating a high-risk state of platelet microthrombi formation was closely related to functional liver capacity, hepatic encephalopathy, hepatorenal syndrome, and intractable ascites in advanced LC. Some end-stage LC patients with extremely low ADAMTS13 : AC and its IgG inhibitor may reflect conditions similar to thrombotic thrombocytopenic purpura (TTP) or may reflect "subclinical TTP." Hence, cirrhotic patients with severe to moderate deficiency of ADAMTS13 : AC may be candidates for FFP infusion as a source of ADAMTS13 or for recombinant ADAMTS13 supplementation. Such treatments may improve the survival of patients with decompensated LC.

Pivotal role of ADAMTS13 function in liver diseases

The liver is a major source of clotting and fibrinolytic proteins, and plays a central role in thrombo-regulation. Patients with advanced liver diseases tend to bleed because of reduced plasma levels of several clotting factors and thrombocytopenia, but they do also exhibit thrombotic complications. ADAMTS13 is a metalloproteinase, produced exclusively in hepatic stellate cells, and specifically cleaves highly multimeric von Willebrand factor (VWF). VWF plays a pivotal role in hemostasis and thrombosis, and its function is dependent on its multimeric state. Deficiency of ADAMTS13 results in accumulation of unusually large VWF multimers (UL-VWFM) in plasma, in turn induces platelet clumping or thrombi under high shear stress, followed by microcirculatory disturbances. Considering that UL-VWFM, the substrate of ADAMTS13, is produced in transformed vascular endothelial cells at sites of liver injury, decreased ADAMTS13 activity may be involved in not only sinusoidal microcirculatory disturbances, but also subsequent progression of liver injuries, eventually leading to multiorgan failure. This concept can be applied to the development or aggravation of liver diseases, including liver cirrhosis, alcoholic hepatitis, veno-occlusive disease, and adverse events after liver transplantation. These results promise to bring further understanding of the pathophysiology of liver diseases, and offer new insight for development of therapeutic strategies.

Differential role of von Willebrand factor and P-selectin on microvascular thrombosis in endotoxemia

OBJECTIVE

Endotoxin (lipopolysaccharide [LPS]) enhances microvascular thrombosis in mouse cremaster venules. Because von Willebrand factor (vWF) and P-selectin are suggested to mediate LPS-induced platelet-microvessel interactions, we determined whether vWF and P-selectin contribute to microvascular thrombosis in endotoxemia.

METHODS AND RESULTS

A light/dye-induced thrombosis model was used in cremaster microvessels of saline or LPS-injected mice (wild-type, P-selectin-deficient, vWF-deficient, or littermate controls). In each strain except vWF-deficient mice, LPS enhanced thrombosis in venules, resulting in approximately 30% to 55% reduction in times to thrombotic occlusion. LPS had no effect on thrombosis in vWF-deficient mice, although these mice had similar systemic responses to LPS (tachycardia, thrombocytopenia, and plasma coagulation markers). vWF-deficient mice demonstrated prolonged times to thrombotic occlusion relative to littermates. LPS increased plasma vWF in each strain studied. While immunofluorescence in wild-type mice failed to detect LPS-induced differences in microvascular vWF expression, it revealed markedly higher vWF expression in venules relative to arterioles.

CONCLUSIONS

vWF mediates light/dye-induced microvascular thrombosis and endotoxin-induced enhancement of thrombosis in mouse cremaster venules; P-selectin is not required for enhanced thrombosis in response to endotoxin. Enhanced vWF expression in venules relative to arterioles has potential implications for the differences in thrombotic responses among these microvessels.

von Willebrand factor in cardiovascular disease: focus on acute coronary syndromes

von Willebrand factor (VWF) plays a pivotal role in platelet adhesion and aggregation at sites of high shear rates (eg, in coronary arteries that have stenotic or ruptured atherosclerotic plaque lesions). Numerous studies have investigated the relationship between VWF plasma levels and thromboembolic cardiovascular events. In contrast to the rather weak association in the general population, in patients with preexisting vascular disease, VWF is significantly predictive for adverse cardiac events, including death. Likewise, VWF typically rises during the course of acute coronary syndrome, and the extent of this VWF release is an independent predictor of adverse clinical outcome in these patients. Various lines of evidence indicate that VWF is not only a marker but also actually an important effector in the pathogenesis of myocardial infarction. This central role of VWF in thrombogenesis has made it a promising target for research into new antiplatelet therapies that specifically inhibit VWF. This review focuses on the role of VWF in acute coronary syndrome and further outlines the relevance of therapeutic interventions targeting VWF for acute coronary syndrome patients.

Endotoxin enhances microvascular thrombosis in mouse cremaster venules via a TLR4-dependent, neutrophil-independent mechanism

Endotoxemia promotes adhesive interactions between platelets and microvascular endothelium in vivo. We sought to determine whether endotoxin (lipopolysaccharide, LPS) modified platelet thrombus formation in mouse cremaster venules and whether Toll-like receptor 4 (TLR4) and neutrophils were involved in the response. Intravital videomicroscopy was performed in the cremaster microcirculation of pentobarbital-anesthetized mice; venular platelet thrombi were induced with a light/dye endothelial injury model. C57BL/6 mice treated with Escherichia coli endotoxin had enhanced rates of venular platelet thrombus formation: the time to microvessel occlusion was reduced by approximately 50% (P < 0.005) compared with saline-treated animals. Enhanced microvascular thrombosis was evident as early as 2 h after LPS administration. LPS had no effect on thrombosis in either of two mouse strains with altered TLR4 signaling (C57BL/10ScNJ or C3H/HeJ), whereas it enhanced thrombosis in the control strains (C57BL/10J and C3H/HeN). LPS also enhanced platelet adhesion to endothelium in the absence of light/dye injury. Platelet adhesion, but not enhanced thrombosis, was inhibited by depletion of circulating neutrophils. LPS failed to enhance platelet aggregation ex vivo and did not influence platelet P-selectin expression, a marker of platelet activation. These findings support the notion that endotoxemia promotes platelet thrombus formation independent of neutrophils and without enhancement of platelet aggregation, via a TLR4-dependent mechanism.

A Pilot Study Into Measurements of Markers of Atherosclerosis in Periodontitis

BACKGROUND

Periodontitis may be a possible risk factor for atherosclerosis. The current pilot study explored arterial wall thickness and other variables associated with atherosclerosis in healthy subjects with and without periodontitis.

METHODS

Patients with moderate (N = 34) and severe periodontitis (N = 15) and controls (N = 14) were recruited. Intima media thickness (IMT) of the common carotid arteries (CCA), internal carotid arteries (ICA), and bifurcations of carotid arteries (BCA) was estimated bilaterally using B-mode ultrasound. An overall IMT was calculated as the mean of these six measurements. C reactive protein (CRP), fibrinogen, and von Willebrand factor (vWf) were measured in plasma as indicators of systemic inflammation and atherosclerotic disease. Microalbuminuria was determined as a marker of endothelial cell dysfunction.

RESULTS

IMT for CCA were 0.64, 0.68, and 0.69 mm for control, moderate, and severe periodontitis, respectively (not significant). IMT for BCA did not vary among groups. IMT of ICA was largest for severe periodontitis (0.81 mm); corresponding values for controls and moderate periodontitis were 0.58 and 0.55 mm, respectively (P= 0.023). Severe periodontitis patients had an overall IMT of 0.76 mm, while moderate periodontitis patients and controls had lower values (0.64 and 0.65 mm, respectively; P= 0.153). After adjusting for potential confounding factors, the increased IMT for ICA in severe periodontitis was also significant (Padj = 0.040). CRP (P= 0.020, Padj = 0.050) and vWf (P= 0.019, Padj = 0.013) were higher in periodontitis than controls; microalbuminuria was not different between groups. Power calculations suggest that a 4-fold expansion of the severe patient and control groups will result in a high chance (power level 80%) that a clinically significant association between the overall IMT and periodontitis will be observed.

CONCLUSION

The present pilot study indicates that a full study investigating the relationship between periodontitis and atherosclerosis is warranted.

Increased levels of hemostatic proteins are independent of inflammation in glycogen storage disease type Ia

OBJECTIVES

Glycogen storage disease type Ia (GSD-Ia), a congenital deficiency of hepatic glucose-6-phosphatase activity, is often associated with hyperproteinemia. To document the mechanism of hyperproteinemia, the proteins of the hemostatic system were analyzed according to their site of synthesis: hepatocyte, endothelial cell, or both. The role of inflammation was investigated by the measurement of tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) levels in plasma.

METHODS

Twenty-seven patients with GSD-Ia were evaluated, as were 14 patients with other types of GSD and 30 healthy control subjects. Of the 41 patients with GSD, 15 also had hepatic adenoma (14 patients with GSD-Ia and 1 with GSD type III).

RESULTS

In patients with GSD-Ia, there was a two-fold increase in all hepatocyte-synthesized proteins (i.e., factor VII, protein C, C4b binding protein) compared with control subjects and patients with other types of GSD. The proteins with mixed endothelial and hepatocyte origin (i.e., antithrombin and protein S) also were significantly increased but to a lesser extent. In contrast, the mean concentration of von Willebrand factor, which is exclusively synthesized in endothelial cells, was normal, as was the concentration of TNF-alpha and IL-6.

CONCLUSIONS

These results suggest that the hyperproteinemia of GSD-Ia (including hemostatic proteins) is attributable to hepatocyte dysfunction and not related to an inflammatory process.

Cardiovascular diseases and periodontology

BACKGROUND

Cardiovascular diseases represent a widespread heterogeneous group of conditions that have significant morbidity and mortality. The various diseases and their treatments can have an impact upon the periodontium and the delivery of periodontal care.

AIM

In this paper we consider three main topics and explore their relationship to the periodontist and the provision of periodontal treatment.

METHOD

The areas reviewed include the effect of cardiovascular drugs on the periodontium and management of patients with periodontal diseases; the risk of infective endocarditis arising from periodontal procedures; the inter-relationship between periodontal disease and coronary artery disease.

RESULTS AND CONCLUSIONS

Calcium-channel blockers and beta-adrenoceptor blockers cause gingival overgrowth and tooth demineralisation, respectively. Evidence suggests that stopping anticoagulant therapy prior to periodontal procedures is putting patients at a greater risk of thromboembolic disorders compared to the risk of prolonged bleeding. The relationship between dentistry and infective endocarditis remains a controversial issue. It would appear that spontaneous bacteraemia arising from a patient's oral hygiene practices is more likely to be the cause of endocarditis than one-off periodontal procedures. The efficacy of antibiotic prophylaxis is uncertain (and unlikely to be proven), and the risk of death from penicillin appears to be greater than the risk of death arising from infective endocarditis. Finally, the association between periodontal disease and coronary artery disease has been explored and there seem to be many issues with respect to data handling interpretation. Many putative mechanisms have been suggested; however, these only further highlight the need for intervention studies.

Markers of endothelial damage in organ dysfunction and sepsis

OBJECTIVES

To review the literature on direct and indirect markers of endothelial activation and damage in patients with sepsis and systemic inflammation and to assess their clinical usefulness for diagnosis and outcome. Various markers derived from or activated by endothelial cells are described, such as adhesion molecules, thrombomodulin, von Willebrand factor, parameters of the coagulation system, and interleukin-6. Furthermore, the association of these markers with the severity of sepsis, systemic inflammation, and outcome is evaluated.

DATA EXTRACTION AND SYNTHESIS

Published research and review articles related to these parameters, with special emphasis on clinical studies.

CONCLUSIONS

Endothelial activation and damage occur early during sepsis and play a major role in the pathophysiology of systemic inflammation. Various markers of endothelial activation are increased during sepsis and systemic inflammation, and in most studies, the level of markers such as soluble intercellular adhesion molecule, vascular cell adhesion molecule, and E selectin correlate well with the severity of inflammation and the course of the disease. However, to date, it remains unclear whether adhesion molecules and coagulation parameters are superior in this respect to interleukin-6 and procalcitonin, as direct comparisons are lacking. In addition, it is evident that markers of endothelial activation and coagulation parameters lack specificity for infection-induced endothelial damage and organ dysfunction.

Inflammatory cytokine release in patients with unstable angina after coronary angioplasty

The aim of the present study was to investigate inflammatory cytokine release and the interaction with platelets in patients with unstable angina (UA) after coronary angioplasty. In 50 patients with stable angina (SA) and 58 patients with UA, serial venous blood samples were obtained immediately before, and 30 minutes, 4, 12, 24, 48 and 72 hours, and 7 days after coronary angioplasty. Plasma concentrations of IL-8 and vWF were determined by immunoassay, while the expression of CD11 b/CD18 on monocytes and the expression of CD41 on platelets were assessed by flow cytometry. Differences in the baseline plasma concentrations of IL-8, vWF and CD11b/CD18, CD41 were found in the UA and SA groups before angioplasty (101.1 +/- 31.28 pg/mL to 55.8 +/- 17.24 pg/mL, 137.67 +/- 38.14% to 107.40 +/- 28.67% and 318.67 +/- 36.85 MFI to 240.72 +/- 28.43 MFI, 147.5 +/- 23.18 MFI to 104.43 +/- 26.68 MFI all p < 0.05). The peak plasma levels of IL-8 (172.24 +/- 37.82 pg/mL at 12 hours) and vWF (256 +/- 42.32% at 4 hours) significantly increased after coronary angioplasty (both p < 0.01), and were associated with significant time course increases in surface expression of CD11b/CD18 (p < 0.01) and CD41 (p < 0.01). The levels of plasma IL-8 and vWF were significantly higher pre- and post-procedure in UA patients with lesion type C compared to types A or B (p < 0.05), but there were no differences for pre-procedure in the SA group patients with different lesion types (p > 0.05). There were significant correlations between plasma IL-8 and monocyte CD11b/CD18, vWF and CD41 in the UA group (r = 0.5248, r = 0.6240 both p < 0.01, respectively). The findings demonstrate increases in plasma IL-8 and CD11b/CD18 as inflammatory mediators, vWF and CD41 as the abnormal coagulation activity may therefore yield a rationale for pharmacological anticytokines in patients with UA after coronary angioplasty.

The effects of aprotinin and steroids on generation of cytokines during coronary artery surgery

OBJECTIVE

To compare the efficacy of aprotinin and methylprednisolone in reducing cardiopulmonary bypass (CPB)-induced cytokine release, to evaluate the effect of myocardial cytokine release on systemic cytokine levels, and to determine the influence of cytokine release on perioperative and postoperative hemodynamics.

DESIGN

Prospective, randomized clinical trial.

SETTING

University teaching hospital and clinics.

PARTICIPANTS

Thirty patients undergoing elective coronary artery bypass graft surgery.

INTERVENTION

Patients were randomly allocated into groups treated with aprotinin (n = 10) or methylprednisolone (n = 10) or into an untreated control group (n = 10). Aprotinin-treated patients received aprotinin as a high-dose regimen (6 x 10(6) KIU), and methylprednisolone-treated patients received methylprednisolone (30 mg/kg intravenously) before CPB.

MEASUREMENTS AND MAIN RESULTS

Patients were analyzed for hemodynamic changes and alveolar-arterial PO2 difference (AaDO2) until the first postoperative day. Plasma levels of proinflammatory cytokines (tumor necrosis factor [TNF]-alpha, interleukin [IL]-1beta, IL-6, and IL-8) were measured in peripheral arterial blood immediately before the induction of anesthesia, 5 minutes before CPB, 3 minutes after the start of CPB, 2 minutes after the release of the aortic cross-clamp, 1 hour after CPB, 6 hours after CPB, and 24 hours after CPB; and in coronary sinus blood immediately before CPB and 2 minutes after the release of the aortic cross-clamp. The hemodynamic parameters did not differ among the groups throughout the study. After CPB, AaDO2 significantly increased (p < 0.05) in all groups. A significant decrease in AaDO2 was observed in aprotinin-treated patients at 24 hours after CPB compared with the other groups (p < 0.05). TNF-alpha level from peripheral arterial blood significantly increased in control patients 1 hour after CPB (p < 0.01) and did not significantly increase in methylprednisolone-treated patients throughout the study. In all groups, IL-6 levels increased after the release of the aortic cross-clamp and reached peak values 6 hours after CPB. At 6 hours after CPB, the increase in IL-6 levels in methylprednisolone-treated patients was significantly less compared with levels measured in control patients and aprotinin-treated patients (p < 0.001). In control patients, IL-8 levels significantly increased 2 minutes after the release of the aortic cross-clamp (p < 0.05), and peak values were observed 1 hour after CPB (p < 0.01). IL-8 levels in control patients were significantly higher compared with patients treated with aprotinin and patients treated with methylprednisolone 1 hour after CPB (p < 0.05).

CONCLUSION

This study showed that methylprednisolone suppresses TNF-alpha, IL-6, and IL-8 release; however, aprotinin attenuates IL-8 release alone. Methylprednisolone does not produce any additional positive hemodynamic and pulmonary effects. An improved postoperative AaDO2 was observed with the use of aprotinin.

BMT: Bone Marrow Transplant Associated Thrombotic Microangiopathy

Thrombotic microangiopathy is a severe microvascular disorder which may occur in up to 70% of patients undergoing bone marrow transplant. Clinically the term thrombotic microangiopathy encompasses a wide spectrum of syndromes, most importantly the thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). Thrombotic microangiopathy is characterized by the presence of thrombocytopenia, microangiopathic hemolytic anemia, renal impairment, neurological disturbances and multiorgan failure. Several causative agents have been advocated as triggering factors for bone marrow transplant associated thrombotic microangiopathy, including cyclosporine, FK506, the use of total body irradiation, infections and the presence of severe graft-versus-host disease. Plasma exchange represents the standard treatment for patients who develop TTP/HUS after bone marrow transplant, however, the mortality rate still remains high despite aggressive therapy.

Differential effects of enzymatic treatments on the storage and secretion of von Willebrand factor by human endothelial cells

Enzymatic treatment used for passaging of endothelial cells may induce release of von Willebrand factor (vWF). Decreased ability to replenish intracellular stores results in decreased secretion of vWF in later passages of cells. Since both trypsin and pancreatin complex have been used for passaging endothelial cells, we analyzed the effects of successive passaging with these two enzyme preparations on the storage and secretion of vWF by human umbilical vein endothelial cells (HUVECs). Measurements were performed after the second to fifth passages. Cytoplasmic vWF was analyzed by indirect immunofluorescence and secreted vWF was measured in the supernatant of cultured HUVECs by ELISA. In trypsin-passaged cells, secreted vWF decreased progressively from passages 2 to 5. Respective concentrations were 355.0 +/- 30.4, 201.0 +/- 84.5, 150.0 +/- 1.4 and 120.5 +/- 38.9 ng vWF/10(5) cells. Comparatively, pancreatin-passaged cells secreted even less vWF protein (P = .001) at passages 4 and 5 (108.5 +/- 12.0 and 100.0 +/- 4.2 ng/10(5) cells, respectively) and had less vWF-positive cytoplasmic granules per cell. Thus, in experiments involving measurements of endothelial vWF, the use of low passage cells is recommendable and passaging with a pure trypsin preparation appears to be more appropriate.

Platelets adhere to and translocate on von Willebrand factor presented by endothelium in stimulated veins

With the use of intravital microscopy, a new type of platelet–endothelial interaction in mouse mesenteric venules at low shear (80-100 seconds−1) is described. Stimulation of these vessels with calcium ionophore A23187, a known secretagogue of Weibel-Palade bodies, induced immediate platelet adhesion (within 15 seconds) and translocation without the formation of aggregates. This stop-and-go process reached a maximum in approximately 1 minute, when approximately 25 000 platelets adhered/mm2·s, and then adhesion progressively decreased. This adhesion process was dependent on von Willebrand factor (vWF) and independent of P-selectin. Immunohistologic analysis showed that the venules were not denuded withA23187 treatment, suggesting that platelets adhered to vWF secreted on the luminal face of the endothelial cells. Histamine treatment induced a similar adhesion phenomenon. Platelet adhesion was not abolished in β3-deficient mice or when the platelets were treated with inhibitory antibodies to PECAM-1 or PSGL-1, indicating that these molecules are not required for platelet–endothelium interaction at low shear. The adhesion was mediated by platelet glycoprotein Ibα (GPIbα) because the adhesion of murine platelets expressing exclusively the human GPIbα could be prevented by a pretreatment with mocarhagin, a snake venom protease that cleaves human GPIbα. The results indicate that vWF released from Weibel-Palade bodies can dramatically increase the concentration of platelets along the vessel wall through an interaction with GPIbα. It is proposed that this process may rapidly recruit platelets to sites of injury or inflammation in veins.

Platelets adhere to and translocate on von Willebrand factor presented by endothelium in stimulated veins

With the use of intravital microscopy, a new type of platelet–endothelial interaction in mouse mesenteric venules at low shear (80-100 seconds−1) is described. Stimulation of these vessels with calcium ionophore A23187, a known secretagogue of Weibel-Palade bodies, induced immediate platelet adhesion (within 15 seconds) and translocation without the formation of aggregates. This stop-and-go process reached a maximum in approximately 1 minute, when approximately 25 000 platelets adhered/mm2·s, and then adhesion progressively decreased. This adhesion process was dependent on von Willebrand factor (vWF) and independent of P-selectin. Immunohistologic analysis showed that the venules were not denuded withA23187 treatment, suggesting that platelets adhered to vWF secreted on the luminal face of the endothelial cells. Histamine treatment induced a similar adhesion phenomenon. Platelet adhesion was not abolished in β3-deficient mice or when the platelets were treated with inhibitory antibodies to PECAM-1 or PSGL-1, indicating that these molecules are not required for platelet–endothelium interaction at low shear. The adhesion was mediated by platelet glycoprotein Ibα (GPIbα) because the adhesion of murine platelets expressing exclusively the human GPIbα could be prevented by a pretreatment with mocarhagin, a snake venom protease that cleaves human GPIbα. The results indicate that vWF released from Weibel-Palade bodies can dramatically increase the concentration of platelets along the vessel wall through an interaction with GPIbα. It is proposed that this process may rapidly recruit platelets to sites of injury or inflammation in veins.

Endothelial cell dysfunction correlates differentially with survival in primary and secondary pulmonary hypertension

BACKGROUND

Plasma von Willebrand factor antigen (vWF:Ag) has been used as a marker of endothelial perturbation in a number of vascular disorders. In this study, vWF:Ag was determined as an attempt to evaluate the severity of endothelial cell dysfunction in primary pulmonary hypertension (PPH) and congenital heart disease-associated pulmonary hypertension (CHD-PH) comparatively and to determine its impact on short-term survival.

METHODS AND RESULTS

Clinical, hemodynamic, and biochemical data were obtained from 11 patients with PPH and 24 with CHD-PH. Patient groups were similar in terms of age and pulmonary artery pressure. vWF:Ag was measured by electroimmunodiffusion. Patients were followed up for 1 year and at that time, data collected at the beginning of the study were subjected to univariate and multivariate analyses. vWF:Ag was increased in patients (normal reference value 87% +/- 23% activity, mean +/- SD), with higher levels in the PPH group (231% +/- 89%) in comparison with the CHD-PH group (127% +/- 68%) (P <.001). Multivariate analysis showed that survival was influenced by the underlying cause of pulmonary hypertension and vWF:Ag levels but not by patient age, sex, or pulmonary artery pressure. Seven of 10 nonsurvivors but only 4 of 25 survivors had PPH (P =.007). vWF:Ag was 255% +/- 90% in the nonsurvivor group and 121% +/- 54% in the survivors (P <.001).

CONCLUSIONS

Our findings suggest that short-term survival is related to the severity of endothelial cell dysfunction in pulmonary hypertension. In addition, exceedingly high vWF:Ag levels in PPH might reflect a particular pattern of endothelial cell dysfunction that could be associated with decreased short-term life expectancy in this disorder compared with secondary forms of pulmonary hypertension.

Intimal deposition of functional von Willebrand factor in atherogenesis

During the formation of intimal thickening in normocholesterolemic rabbits, von Willebrand factor (vWF) is increased in the endothelial cells (ECs) and deposited in the intima. We investigated whether this also occurs during cholesterol-induced plaque formation, whether the synthesis of vWF increases, and whether this influences platelet adhesion. Rabbits were fed a cholesterol-rich (0.3%) diet for 26 weeks. Thereafter, half of the animals received a normal diet for another 26 weeks (cholesterol withdrawal). To induce intimal thickening in normocholesterolemic rabbits, collars were positioned around the carotid artery. Arterial segments were studied using immunohistochemistry, reverse transcription-polymerase chain reaction, electron microscopy, and platelet adhesion tests. Cholesterol treatment induced plaque formation in the aorta. The ECs had a cuboidal aspect, showed a dense immunoreactivity for vWF, a pronounced rough endoplasmic reticulum, and numerous Weibel-Palade bodies. There were subendothelial vWF deposits in the plaques and vWF mRNA was significantly increased as compared with controls. Similar changes were seen after collar-induced intimal thickening. After cholesterol withdrawal, both vWF mRNA and the ultrastructural morphology of the ECs normalized, and the vWF deposits disappeared from the plaque. Perfusion studies with anticoagulated rabbit blood over cross-sections of atherosclerotic aortas revealed increased vWF-mediated platelet adhesion in the subendothelial plaque region. Whereas rabbit platelets perfused through the lumen adhered to the same extent to de-endothelialized aortas of normocholesterolemic and atherosclerotic rabbits, vWF mediated platelet adhesion to endothelium was observed in atherosclerotic but not in normal aortas. Our results show an increased synthesis and (sub)endothelial presence of vWF after vascular injury, with functional consequences for platelet deposition on the vessel wall.

Regulated inhibition of coagulation by porcine endothelial cells expressing P-selectin-tagged hirudin and tissue factor pathway inhibitor fusion proteins

BACKGROUND

Thrombotic vascular occlusion resulting in infarction occurs during hyperacute rejection of allografts transplanted into sensitized patients and remains a major problem in experimental xenotransplantation. A similar process is also found in disorders of diverse etiology including atherosclerosis, vasculitis, and disseminated intravascular coagulation.

METHODS

We have previously constructed two membrane-tethered anticoagulant fusion proteins based on human tissue factor pathway inhibitor and the leech anticoagulant hirudin and demonstrated their functional efficacy in vitro. These constructs have now been modified by the addition of a P-selectin sequence to the cytoplasmic tail to localize them in Weibel-Palade bodies. They have been transfected into Weibel-Palade body-positive endothelial cells isolated from the inferior vena cava of normal pigs.

RESULTS

In resting endothelial cells, fusion protein expression colocalized with P-selectin and was confined to Weibel-Palade bodies. These cells had a procoagulant phenotype in recalcified human plasma. However, after activation with phorbol ester the anticoagulant proteins were rapidly relocated to the cell surface where they specifically inhibited the clotting of human plasma.

CONCLUSIONS

Novel anticoagulant molecules may prove useful therapeutic agents for gene therapy in thrombotic disease and postangioplasty or for transgenic expression in animals whose organs may be used for clinical xenotransplantation. Expression in vascular endothelial cells may be regulated by inclusion of P-selectin cytoplasmic sequence, to restrict cell surface expression to activated endothelium.

Herpesviruses and thrombosis: activation of coagulation on the endothelium

Vascular injury is an initiating event in the development of atherosclerosis and herpesviruses have been proposed as potential mediators of vascular injury. The demonstration that an avian herpesvirus could induce atherosclerosis in chickens [Fabricant CG, Fabricant J, Litrenta MM, Minick CR. Virus induced atherosclerosis. J Exp Med 1978;148:335-340; Fabricant CG, Fabricant J, Minick CR, Litrenta MM. Herpes virus induced atherosclerosis in chickens. Fed Proc 1983;42:2476-2479; Minick CR, Fabricant CG, Fabricant J, Litrenta MM. Atheroarteriosclerosis induced by infection by herpesvirus. Am J Pathol 1978;96:673-706] suggested the potential of these viral agents to cause similar lesions in humans. In addition, epidemiological evidence linking herpesvirus infection and atherosclerosis [Cunningham MJ, Pasternak RC. The potential role of viruses in the pathogenesis of atherosclerosis. Circulation 1988;77:964-996; Melnick JL, Adam E, DeBakey ME. Cytomegalovirus and atherosclerosis. BioEssays 1995;17:899-903; Adam E, Melnick JL, Probesfield JL et al. High levels of cytomegalovirus antibody in patients requiring vascular surgery for atherosclerosis. Lancet 1987;2:291-293] adds further credence to their role as possible etiologic agents. However, the link between herpesviruses and vascular thrombosis is more tenuous. In this review, we highlight some recent advances in this field, from our laboratory and others, to support the hypothesis that herpesviruses act as prothrombotic agents by activating the coagulation cascade.

Serotonin-induced secretion of von Willebrand factor from human umbilical vein endothelial cells via the cyclic AMP-signaling systems independent of increased cytoplasmic calcium concentration

Endothelial cells are able to synthesize von Willebrand factor (vWf) protein, which is then either secreted in a constitutive way or stored within specific cellular secretory granules, the Weibel-Palade bodies. Stimulated secretion of vWf from these organelles is thought to be induced by agonists causing a transient increase in cytoplasmic calcium concentrations. Serotonin (5-hydroxytryptamine, 5-HT), a local transmitter substance released by activated platelets, has also recently been shown to induce the secretion of vWf. In experiments with human umbilical vein endothelial cells (HUVEC), we found that the 5-HT-induced secretion occurred without a significant increase in cellular calcium levels. The 5-HT 1(D) subtype-specific receptor agonist sumatriptan also induced the release of vWf without causing a calcium signal in HUVEC. Stimulation of endothelial cells with the adenylate cyclase inhibitor, MDL-12 A330, led to the secretion of vWf as well. Simultaneous addition of submaximal concentrations of histamine and 5-HT to HUVEC potentiated the effects of either agonist. Together, these results suggest that in HUVEC 5-HT-induced secretion of vWf is mediated by a decrease in cyclic AMP levels and is independent of changes in cytoplasmic calcium levels.

Von Willebrand factor could be an index of endothelial dysfunction in patients with cirrhosis: relationship to degree of liver failure and nitric oxide levels

BACKGROUND/AIMS

The aim of this study was to evaluate the relationship between plasma levels of von Willebrand factor (vWF), a marker of endothelial cell activation, and nitric oxide, a powerful vasodilator synthesized by endothelial cells, in 27 patients with cirrhosis at different stages of the disease. These results were compared with those of age-matched normal, healthy subjects (n=10).

METHODS

vWF:antigen was measured by electro-immunodiffusion test and serum nitrite and nitrate levels, the stable end products of nitric oxide metabolism, were determined by an enzymatic procedure.

RESULTS

vWF:antigen and nitrite/nitrate levels were significantly higher in cirrhotic patients (367+/-185% and 29.3+/-10.8 micromol/l) than in healthy subjects (92+/-20% and 19.2+/-8.3 micromol/l, p<0.05, respectively). Higher levels of vWF:antigen and nitrites/nitrates were observed in patients with more advanced degrees of liver failure, as reflected by quantitative Child-Pugh's score (516+/-154% and 38.3+/-7.8 micromol/l in Child-Pugh > or = 9 vs 227+/-61% and 21.0+/-6.1 micromol/l in Child-Pugh <9, p<0.001, respectively). Moreover, both endothelial-related factors were higher in patients with ascites than those without ascites (543+/-158% and 37.8+/-8.9 micromol/l vs 262+/-103% and 24.4+/-8.8 micromol/l, p<0.001, respectively). In the overall series, a highly significant linear correlation between nitrites/nitrates and vWF:antigen levels was observed in patients with cirrhosis (r=0.79, p<0.001).

CONCLUSIONS

These results support a cirrhosis-related endothelial dysfunction and suggest that plasma vWF measurement could be useful as a marker of endothelial disturbance in patients with cirrhosis.

Circulating von Willebrand factor antigen as a predictor of short-term prognosis in pulmonary hypertension

STUDY OBJECTIVE

To determine the potential value of plasma von Willebrand factor antigenic activity (vWF:Ag) and other commonly measured clinical variables for predicting which patients with precapillary pulmonary hypertension would be unlikely to survive 1 year.

DESIGN

Prospective clinical study. The data obtained at the beginning of the study were analyzed at the end of the first year of follow-up.

PATIENTS AND METHODS

Forty patients aged 1.2 to 45 years (median, 24 years) entered the study. Eleven patients had primary pulmonary hypertension, and in the remaining ones, pulmonary vascular disease was associated with antiphospholipid syndrome (n = 1), collagen vascular disease (n = 1), schistosomiasis (n = 3), or congenital heart defects (Eisenmenger's syndrome) (n = 24). Plasma vWF:Ag was determined by electroimmunodiffusion, and the results were expressed as the percentage of activity.

RESULTS

Seven of 11 patients with primary pulmonary hypertension but only 4 of 29 patients with secondary pulmonary hypertension died during the follow-up period (p < 0.005). Initial vWF:Ag values were significantly higher in the nonsurvivor group in comparison with the survivors (256.6+/-85.3% and 132.0+/-59.3% activity, respectively; p < 0.0001). The likelihood of fatal outcome as a function of plasma vWF:Ag levels was estimated for primary and secondary pulmonary hypertensive patients using logistic regression analysis. Decreased life expectancy was significantly related to high vWF:Ag levels and an established diagnosis of primary pulmonary hypertension. A plasma vWF:Ag of >240% (p = 0.003) was 54% sensitive and 93% specific for identifying patients who were unlikely to survive 1 year, with an overall predictive value of 75%. No other variables correlated significantly with survival.

CONCLUSION

Plasma vWF:Ag seems to be a useful biochemical index for predicting short-term prognosis in patients with pulmonary hypertension. In contrast to hemodynamic and histopathological predictors of survival, vWF:Ag does not require invasive techniques to be determined. In light of the possibility of false-negative results, serial measurements should be performed over time in patients with vWF:Ag of <240%. This observation proved helpful in two patients in this study.

Tissue Distribution and Regulation of Murine von Willebrand Factor Gene Expression In Vivo

von Willebrand factor (vWF) is frequently used as a biochemical marker for endothelial cells (ECs). Despite this, little is known about the relative level of expression and regulation of this hemostatic factor in ECs in different vascular beds in vivo. In the present study, we used quantitative reverse transcription polymerase chain reaction and in situ hybridization analysis to study vWF gene expression in murine tissues. Large differences in the level of vWF mRNA were observed when comparing highly vascularized tissues, with the lung and brain containing 5 to 50 times higher concentrations of vWF mRNA than the kidney and liver. In this regard, ECs of small vessels and some microvessels in the lung and brain expressed abundant vWF mRNA, whereas ECs of similar sized vessels in the liver and kidney expressed relatively low levels. In general, significantly higher levels of vWF mRNA and antigen were demonstrated in ECs of larger vessels compared with microvessels and in venous ECs compared with arterial ECs. Although intraperitoneal administration of endotoxin (or tumor necrosis factor-) increased plasma vWF levels, it had variable effects on the steady-state level of vWF mRNA in murine tissues (ie, it decreased vWF mRNA in many tissues, increased it in others, and had little effect on still others). These results indicate that vWF is differentially expressed and regulated in ECs present in different tissues and within the same vascular bed.

© 1998 by The American Society of Hematology.

Tissue Distribution and Regulation of Murine von Willebrand Factor Gene Expression In Vivo

von Willebrand factor (vWF) is frequently used as a biochemical marker for endothelial cells (ECs). Despite this, little is known about the relative level of expression and regulation of this hemostatic factor in ECs in different vascular beds in vivo. In the present study, we used quantitative reverse transcription polymerase chain reaction and in situ hybridization analysis to study vWF gene expression in murine tissues. Large differences in the level of vWF mRNA were observed when comparing highly vascularized tissues, with the lung and brain containing 5 to 50 times higher concentrations of vWF mRNA than the kidney and liver. In this regard, ECs of small vessels and some microvessels in the lung and brain expressed abundant vWF mRNA, whereas ECs of similar sized vessels in the liver and kidney expressed relatively low levels. In general, significantly higher levels of vWF mRNA and antigen were demonstrated in ECs of larger vessels compared with microvessels and in venous ECs compared with arterial ECs. Although intraperitoneal administration of endotoxin (or tumor necrosis factor-) increased plasma vWF levels, it had variable effects on the steady-state level of vWF mRNA in murine tissues (ie, it decreased vWF mRNA in many tissues, increased it in others, and had little effect on still others). These results indicate that vWF is differentially expressed and regulated in ECs present in different tissues and within the same vascular bed.

© 1998 by The American Society of Hematology.

Abnormalities in circulating von Willebrand factor and survival in pulmonary hypertension

BACKGROUND

Changes in circulating von Willebrand factor (vWF) have been widely used for evaluating the severity of endothelial dysfunction in vascular disorders. In pulmonary hypertension, quantitative and structural abnormalities in circulating von Willebrand factor have been identified. We therefore hypothesized that these abnormalities could have prognostic implications.

PATIENTS AND METHODS

We studied 30 consecutive medically treated patients with primary (n = 11) or secondary precapillary pulmonary hypertension associated with congenital heart disease (n = 16) or schistosomiasis (n = 3). Plasma antigenic activity of vWF (vWF:Ag) was measured by electroimmunodiffusion. The relative concentration of low molecular weight vWF multimers (vWF:LMW/Total) was determined by Western immunoblotting. Results of initial evaluation were analyzed at the end of the first and third years of follow-up.

RESULTS

Baseline vWF:Ag activity (P <0.0002) and the vWF: LMW/Total ratio (P <0.005) were higher in patients who died during the first year than in survivors. All patients with vWF:Ag activity >250% or a vWF:LMW/Total ratio >70% died in the first year. All 7 patients with vWF:Ag activity <100% were alive at the end of 3 years of follow-up. A vWF:LMW/Total ratio >68% was 67% sensitive and 95% specific for 1-year mortality, with an overall predictive value of 80%. Both vWF:Ag levels and mortality were greater in the patients with primary pulmonary hypertension than in patients with secondary pulmonary hypertension.

CONCLUSION

Patients with pulmonary hypertension who have abnormalities in circulating vWF have reduced 1-year survival. This might affect decisions such as patient assignment to lung transplantation.

Herpesvirus in atherosclerosis and thrombosis: etiologic agents or ubiquitous bystanders?

The role of herpesvirus infections in the pathogenesis of vascular diseases remains an enigma. Although there is abundant circumstantial evidence of a role for herpesviruses in atherosclerosis and related processes, a cause-and-effect relationship has yet to be definitively established. This article will review the pathological, molecular, and biochemical evidence supporting the hypothesis that herpesviruses are involved in the development of atherosclerosis, restenosis after coronary angioplasty, accelerated atherosclerosis in recipients of heart transplants, and the induction of a prothrombotic phenotype in vascular endothelial cells.

Increased plasma von Willebrand factor in the systemic inflammatory response syndrome is derived from generalized endothelial cell activation

OBJECTIVES

Von Willebrand factor antigen (vWf) is an essential hemostatic protein. Increased plasma levels have been documented in patients suffering from the systemic inflammatory response syndrome (SIRS) and resulted presumably from endothelial cell damage specific to the site of injury. We hypothesize that increased plasma levels result from systemic endothelial cell activation and degranulation.

DESIGN

We compared immunohistochemical vWf staining in dermal biopsy specimens from patients with SIRS to healthy control subjects in the presence and absence of recombinant human tumor necrosis factor (rhTNF)-alpha. Also, we quantified plasma levels of vWf in these groups using a newly available antibody.

SETTING

A tertiary care surgical intensive care unit in a university teaching hospital.

SUBJECTS

Patients with SIRS and healthy controls.

INTERVENTIONS

Biopsies and blood samples were obtained from study groups.

MEASUREMENTS AND MAIN RESULTS

Decreased baseline vWf staining was noted in SIRS patients. The rhTNF-alpha caused a statistically significant decrease in vWf staining in control subjects but not in SIRS patients. Plasma vWf levels were increased an average of 11-fold in SIRS patients compared with control subjects.

CONCLUSION

We postulate that the increased plasma levels of vWf and the decreased staining in the peripheral dermal plexus represent the generalized activation and degranulation of endothelium in vascular beds remote from the original inflammatory focus.

Effects of histamine and nitric oxide synthase inhibition on plasma levels of von Willebrand factor antigen

Endothelial cells release von Willebrand factor (vWf) either constitutively or by a regulated pathway. Based on various studies in vitro, we hypothesized that the stimulatory action of histamine on vWf release could also be induced in vivo and that it may be inhibited by endogenous production of nitric oxide (NO). Nine healthy subjects received placebo or one of two dosages of a primed constant infusion of the NO-synthase inhibitor N-monomethyl-L-arginine (L-NMMA) in a randomized, double-blind, three-way crossover trial. Histamine was coinfused for 15 minutes at 0.16 microg/kg/min after 30 minutes of pretreatment with either placebo or L-NMMA. Thirty minutes after either the low or the high L-NMMA dose was started, which caused, respectively, a 40% decrease and a 60% decrease in exhaled end expiratory NO level (p = 0.008), there was no increase in von Willebrand factor antigen (vWf-Ag) level (p > 0.05). Histamine caused an 11% (95% confidence interval (CI): 0.4% to 22%; p = 0.011) increase in vWf-Ag level at 125 minutes. After pretreatment with the low and the high L-NMMA doses, vWf-Ag level increased by 18% (Cl: 5% to 31%; p = 0.011) and by 29% (CI: 15% to 42%; p = 0.008), respectively. At 125 minutes, vWf-Ag level was significantly higher after either L-NMMA pretreatment when compared with the results after histamine alone (p < 0.05). In conclusion, the infusion of histamine increased vWf-Ag level, and the inhibition of NO-synthase enhanced this effect, whereas it did not by itself elevate vWf-Ag level. Thus endogenously produced NO may dampen the regulated pathway of vWf secretion; it will be interesting to investigate whether endogenous NO production also inhibits vWf release caused by other stimulators.

Fluid Shear Stress Modulates von Willebrand Factor Release From Human Vascular Endothelium

Fluid shear stress generated by blood flow on arterial wall may play a role in the process of atherosclerosis, not only affecting the mass transport phenomena that take place in blood, but also by modulation of synthesis and secretion of humoral factors released by vascular endothelium that mediate platelet-vessel wall interactions. The present study was designed to investigate whether shear stress, induced by laminar flow, modulates von Willebrand factor (vWF ) release from cultured human umbilical vein endothelial cells (HUVEC) and whether this physical stimulation can affect vWF synthesis. Monolayers of HUVEC were exposed to laminar flow of varying magnitude (from 2 to 12 dynes/cm2) using a cone-and-plate device. The release of vWF in cell supernatant and in extracellular matrix by cells exposed to flow or maintained in static conditions was evaluated by enzyme-linked immunosorbent assay. HUVEC exposed to laminar flow released higher amounts of vWF into the cell supernatant within few hours of exposure and vWF secretion was dependent on shear stress magnitude. vWF released in extracellular matrix was also higher in cell monolayers exposed to shear than in static controls. vWF mRNA expression in HUVEC was not affected by exposure of cells to laminar flow, indicating that shear-induced vWF release reflected enhanced secretion without de novo protein synthesis. Immunofluorescence studies showed that the release of vWF is due to exocytosis from Weibel-Palade bodies, the storage organelles of vWF. These data indicate a novel mechanism by which local hemodynamic shear forces modulate endothelial cell function and may play a role in development of arterial thrombotic events.

Fluid Shear Stress Modulates von Willebrand Factor Release From Human Vascular Endothelium

Fluid shear stress generated by blood flow on arterial wall may play a role in the process of atherosclerosis, not only affecting the mass transport phenomena that take place in blood, but also by modulation of synthesis and secretion of humoral factors released by vascular endothelium that mediate platelet-vessel wall interactions. The present study was designed to investigate whether shear stress, induced by laminar flow, modulates von Willebrand factor (vWF ) release from cultured human umbilical vein endothelial cells (HUVEC) and whether this physical stimulation can affect vWF synthesis. Monolayers of HUVEC were exposed to laminar flow of varying magnitude (from 2 to 12 dynes/cm2) using a cone-and-plate device. The release of vWF in cell supernatant and in extracellular matrix by cells exposed to flow or maintained in static conditions was evaluated by enzyme-linked immunosorbent assay. HUVEC exposed to laminar flow released higher amounts of vWF into the cell supernatant within few hours of exposure and vWF secretion was dependent on shear stress magnitude. vWF released in extracellular matrix was also higher in cell monolayers exposed to shear than in static controls. vWF mRNA expression in HUVEC was not affected by exposure of cells to laminar flow, indicating that shear-induced vWF release reflected enhanced secretion without de novo protein synthesis. Immunofluorescence studies showed that the release of vWF is due to exocytosis from Weibel-Palade bodies, the storage organelles of vWF. These data indicate a novel mechanism by which local hemodynamic shear forces modulate endothelial cell function and may play a role in development of arterial thrombotic events.

Induction of the acute-phase reaction increases heparin-binding proteins in plasma

We have previously demonstrated that the nonspecific binding of unfractionated heparin (UFH) to plasma proteins has a marked modulating effect on its anticoagulant activity. Since some heparin-binding proteins are also acute-phase-reactant proteins, we explored the possibility that the induction of the acute-phase response can increase the plasma concentrations of heparin-binding proteins. The recovery of a fixed amount of UFH or low-molecular-weight heparin (LMWH) added in vitro to rat plasma samples obtained at various time intervals after the administration of intravenous endotoxin or subcutaneous turpentine was compared with that of saline-treated control animals. The anti-factor Xa activity was measured in the plasma samples before and after the addition of a chemically modified low-affinity heparin (LAH) to displace the proportion of the added heparin that is reversibly bound to plasma proteins. Our results show that at 6 hours post-endotoxin and at 24 hours post-turpentine treatment, virtually no anti-factor Xa activity could be measured in the plasma samples, while the expected levels were obtained for control plasma. After the addition of LAH to displace protein-bound UFH, essentially the same anti-factor Xa levels were measured in the plasma from all three treatment groups. These results indicate that induction of the acute-phase reaction can dramatically increase the levels of heparin-binding proteins in rat plasma. In addition, we compared the anti-factor Xa recovery of UFH with that of an LMWH from the plasma of endotoxin- and saline-treated rats and demonstrated that LMWH binds less to plasma proteins than UFH, even in plasma in which the levels of heparin-binding proteins are markedly elevated. The recovery of a fixed amount of UFH added in vitro to human plasma from septic patients was also reduced, but not to the same extent as seen in rat plasma. Removal of candidate heparin-binding and acute-phase proteins by immunodepletion indicated that vitronectin plays an important role in the nonspecific binding of UFH in patient plasma.