Differentiation of Patients with Symptomatic Low von Willebrand Factor from Those with Asymptomatic Low von Willebrand Factor

BACKGROUND

 Accurate diagnosis of symptomatic low von Willebrand factor (VWF) remains a major challenge in von Willebrand disease (VWD). However, present tests do not adequately take into account flow forces that, at very high shear rates, reveal a weakness in the VWF-platelet glycoprotein glycoprotein Ib bond in normal subjects. The degree of this weakness is greater in symptomatic, but not asymptomatic, low VWF.

OBJECTIVE

 The aim of this study is to distinguish patients with symptomatic low VWF (levels in the 30-50 IU/dL range) from those with asymptomatic low VWF and normal subjects.

METHODS

 We measured platelet adhesion (PA)/aggregation in our novel microfluidic flow system that permits real-time assessment of PA (surface coverage) and PA/aggregation (V, aggregate volume) using epifluorescence digital videomicroscopy in flowing noncitrated whole blood at 4,000 second^-1. Blood samples from 24 low VWF patients and 15 normal subjects were collected into plastic tubes containing 4 U/mL enoxaparin. MetaMorph software was used to quantify rates of PA and V increase.

RESULTS

 Rates of PA increase showed a bimodal distribution, with values for 16/24 patients (Group I) all below the 2.5th percentile of normal, and values for 8/24 patients (Group II) similar to controls. Bleeding scores (mean ± standard error) were 5.50 ± 0.45 versus 2.75 ± 0.45 (p = 0.00077), and 10 clinically significant bleeding events were observed in seven versus zero (p = 0.0295) Group I and Group II subjects, respectively.

CONCLUSION

 The present approach may offer a definitive means to distinguish symptomatic low VWF from either asymptomatic low VWF or normal controls.

Risk of Intracranial Hemorrhage Following Intravenous tPA (Tissue-Type Plasminogen Activator) for Acute Stroke Is Low in Children

Background and Purpose—

Data regarding the safety and efficacy of intravenous tPA (tissue-type plasminogen activator) in childhood acute arterial ischemic stroke are inadequate. The TIPS trial (Thrombolysis in Pediatric Stroke; National Institutes of Health grant R01NS065848)—a prospective safety and dose-finding trial of intravenous tPA in acute childhood stroke—was closed for lack of accrual. TIPS sites have subsequently treated children with acute stroke in accordance with established institutional protocols supporting data collection on outcomes.

Methods—

Data on children treated with intravenous tPA for neuroimaging-confirmed arterial ischemic stroke were collected retrospectively from 16 former TIPS sites to establish preliminary safety data. Participating sites were required to report all children who were treated with intravenous tPA to minimize reporting bias. Symptomatic intracranial hemorrhage (SICH) was defined as ECASS (European Cooperative Acute Stroke Study) II parenchymal hematoma type 2 or any intracranial hemorrhage associated with neurological deterioration within 36 following tPA administration. A Bayesian beta-binomial model for risk of SICH following intravenous tPA was fit using a prior distribution based on the risk level in young adults (1.7%); to test for robustness, the model was also fit with uninformative and conservative priors.

Results—

Twenty-six children (age range, 1.1–17 years; median, 14 years; 12 boys) with stroke and a median pediatric National Institutes of Health Stroke Scale score of 14 were treated with intravenous tPA within 2 to 4.5 hours (median, 3.0 hours) after stroke onset. No patient had SICH. Two children developed epistaxis.

Conclusions—

The estimated risk of SICH after tPA in children is 2.1% (95% highest posterior density interval, 0.0%–6.7%; mode, 0.9%). Regardless of prior assumption, there is at least a 98% chance that the risk is <15% and at least a 93% chance that the risk is <10%. These results suggest that the overall risk of SICH after intravenous tPA in children with acute arterial ischemic stroke, when given within 4.5 hours after symptom onset, is low.

Mortality After Pediatric Arterial Ischemic Stroke

OBJECTIVES

Cerebrovascular disease is among the top 10 causes of death in US children, but risk factors for mortality are poorly understood. Within an international registry, we identify predictors of in-hospital mortality after pediatric arterial ischemic stroke (AIS).

METHODS

Neonates (0-28 days) and children (29 days-<19 years) with AIS were enrolled from January 2003 to July 2014 in a multinational stroke registry. Death during hospitalization and cause of death were ascertained from medical records. Logistic regression was used to analyze associations between risk factors and in-hospital mortality.

RESULTS

Fourteen of 915 neonates (1.5%) and 70 of 2273 children (3.1%) died during hospitalization. Of 48 cases with reported causes of death, 31 (64.6%) were stroke-related, with remaining deaths attributed to medical disease. In multivariable analysis, congenital heart disease (odds ratio [OR]: 3.88; 95% confidence interval [CI]: 1.23-12.29; P = .021), posterior plus anterior circulation stroke (OR: 5.36; 95% CI: 1.70-16.85; P = .004), and stroke presentation without seizures (OR: 3.95; 95% CI: 1.26-12.37; P = .019) were associated with in-hospital mortality for neonates. Hispanic ethnicity (OR: 3.12; 95% CI: 1.56-6.24; P = .001), congenital heart disease (OR: 3.14; 95% CI: 1.75-5.61; P < .001), and posterior plus anterior circulation stroke (OR: 2.71; 95% CI: 1.40-5.25; P = .003) were associated with in-hospital mortality for children.

CONCLUSIONS

In-hospital mortality occurred in 2.6% of pediatric AIS cases. Most deaths were attributable to stroke. Risk factors for in-hospital mortality included congenital heart disease and posterior plus anterior circulation stroke. Presentation without seizures and Hispanic ethnicity were also associated with mortality for neonates and children, respectively. Awareness and study of risk factors for mortality represent opportunities to increase survival.

Abstract 15: Mortality After Pediatric Arterial Ischemic Stroke: Results From the International Paediatric Stroke Study

Introduction: Stroke is reported among the top 10 causes of death in children in the US. In the Kids’ Inpatient Database, older age and Hispanic ethnicity were risk factors for mortality after pediatric ICH. Limited data is available regarding risk factors for death after pediatric arterial ischemic stroke (AIS).

Objective: To identify predictors of in-hospital mortality in pediatric patients hospitalized with AIS.

Methods: Neonates (0-28 days) and children (29 days- <19 years) with AIS were enrolled from 1/2003 to 7/2014 in the IPSS multinational stroke registry. Death prior to hospital discharge and cause of death was ascertained from medical records. Logistic regression was used to analyze associations between risk factors and in-hospital mortality.

Results: Fourteen of 915 neonates (1.5%) and 74/2,285 children (3.2%) died during hospitalization. Of 54 cases with reported causes of death, 32 (59%) were related to AIS (herniation 2, brain death 10, ICH/hemorrhagic transformation 5, care withdrawal due to stroke severity 15), with the remaining deaths attributed to underlying medical disease. Of 356 children with Pediatric NIH Stroke Scale (PedNIHSS) scores, median PedNIHSS was 19 (IQR 14-27) among the 13 children who died and 7 (IQR 3-12) among the 343 children who did not die. In multivariable analysis, congenital heart disease (OR 4.1, 95%CI 1.3-13, p=0.018) and posterior plus anterior circulation stroke (OR 4.3, 95%CI 1.3-14, p=0.017) were associated with in-hospital mortality for neonates, while higher PedNIHSS [OR 1.11 (per 1 point PedNIHSS increase), 95%CI 1.03-1.19, p=0.004], Hispanic ethnicity (OR 7.6, 95%CI 1.8-32.3, p=0.006), and cardiac disease (OR 7.5, 95%CI 1.5-38.6, p=0.015) were associated with in-hospital mortality for children.

Conclusions: In-hospital mortality occurred in about 2% of pediatric AIS cases with nearly 60% attributable to stroke. Risk factors for in-hospital mortality included cardiac disease and stroke severity, factors also associated with mortality in adults. Hispanic ethnicity, a factor associated with mortality in childhood ICH, was also associated with mortality after childhood AIS; the underlying reasons are unclear. Additional information is needed on stroke-related deaths after hospitalization.

Thrombophilia and pregnancy complications

The implications of currently available data on the association of gestational vascular complications with thrombophilia are presented in this consensus report. Screening is recommended for women with the following previous complications: fetal loss including three or more first trimester loss, two or more second trimester loss, or any stillbirth; early, severe or recurrent preeclampsia and severe intrauterine growth restriction. Maternal antithrombotic therapy is currently evaluated in women with thrombophilia and previous complications.

On behalf of the Scientific Subcommittee on Perinatal and Pediatric Hemostasis and Working Group on Women’s health Issues and Standardization Committee of the International Society of Thrombosis and Hemostasis.

The spectrum of bleeding in women and girls with haemophilia B

Although hemophilia B affects 1 in 25,000 males there may be 3 female hemophilia B carriers per affected male. This clinical review highlights the unique challenges faced by hemophilia B carriers including the under-recognition of bleeding symptoms associated with and without FIX deficiency, discrepancies in correlation between genotype and bleeding phenotype and therapeutic considerations utilizing clinical vignettes of common scenarios.

Brain endothelial dysfunction in cerebral adrenoleukodystrophy

See Aubourg (doi:10.1093/awv271) for a scientific commentary on this article.X-linked adrenoleukodystrophy is caused by mutations in the ABCD1 gene leading to accumulation of very long chain fatty acids. Its most severe neurological manifestation is cerebral adrenoleukodystrophy. Here we demonstrate that progressive inflammatory demyelination in cerebral adrenoleukodystrophy coincides with blood-brain barrier dysfunction, increased MMP9 expression, and changes in endothelial tight junction proteins as well as adhesion molecules. ABCD1, but not its closest homologue ABCD2, is highly expressed in human brain microvascular endothelial cells, far exceeding its expression in the systemic vasculature. Silencing of ABCD1 in human brain microvascular endothelial cells causes accumulation of very long chain fatty acids, but much later than the immediate upregulation of adhesion molecules and decrease in tight junction proteins. This results in greater adhesion and transmigration of monocytes across the endothelium. PCR-array screening of human brain microvascular endothelial cells after ABCD1 silencing revealed downregulation of both mRNA and protein levels of the transcription factor c-MYC (encoded by MYC). Interestingly, MYC silencing mimicked the effects of ABCD1 silencing on CLDN5 and ICAM1 without decreasing the levels of ABCD1 protein itself. Together, these data demonstrate that ABCD1 deficiency induces significant alterations in brain endothelium via c-MYC and may thereby contribute to the increased trafficking of leucocytes across the blood-brain barrier as seen in cerebral adrenouleukodystrophy.

Emergence of the primary pediatric stroke center: impact of the thrombolysis in pediatric stroke trial

BACKGROUND AND PURPOSE

In adult stroke, the advent of thrombolytic therapy led to the development of primary stroke centers capable to diagnose and treat patients with acute stroke rapidly. We describe the development of primary pediatric stroke centers through preparation of participating centers in the Thrombolysis in Pediatric Stroke (TIPS) trial.

METHODS

We collected data from the 17 enrolling TIPS centers regarding the process of becoming an acute pediatric stroke center with capability to diagnose, evaluate, and treat pediatric stroke rapidly, including use of thrombolytic therapy.

RESULTS

Before 2004, <25% of TIPS sites had continuous 24-hour availability of acute stroke teams, MRI capability, or stroke order sets, despite significant pediatric stroke expertise. After TIPS preparation, >80% of sites now have these systems in place, and all sites reported increased readiness to treat a child with acute stroke. Use of a 1- to 10-Likert scale on which 10 represented complete readiness, median center readiness increased from 6.2 before site preparation to 8.7 at the time of site activation (P≤0.001).

CONCLUSIONS

Before preparing for TIPS, centers interested in pediatric stroke had not developed systematic strategies to diagnose and treat acute pediatric stroke. TIPS trial preparation has resulted in establishment of pediatric acute stroke centers with clinical and system preparedness for evaluation and care of children with acute stroke, including use of a standardized protocol for evaluation and treatment of acute arterial stroke in children that includes use of intravenous tissue-type plasminogen activator.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01591096.

Shiga toxin downregulates tissue factor pathway inhibitor, modulating an increase in the expression of functional tissue factor on endothelium

INTRODUCTION

Endothelial expression of tissue factor (TF) may play a major role in (Stx)-related hemolytic uremic syndrome. We examined human umbilical vein endothelial cell (HUVEC) monolayers to determine the interaction between TF and TF pathway inhibitor (TFPI), hypothesizing that changes in TFPI modulate TF expression.

MATERIALS AND METHODS

We studied 1) cell surface expression of globotriasylceramide (Gb3, the receptor for Stx) with Stx-1 (10 pM), TNFα (20 Ng/ml), or Stx-1 plus TNFα compared to control, 2) gene expression of TF and TFPI, 3) total cellular and cell surface antigenic TF and TFPI, 4) TFPI secretion into supernatant, and 5) factor Xa production.

RESULTS AND CONCLUSIONS

Gb3 expression, negligible with control and Stx-1 alone, increased significantly with TNFα and with Stx-1 plus TNFα. TF mRNA increased 1.25 ± 0.32- fold (N = 9; p = 0.041) with Stx-1 alone vs. 2.82 ± 0.92-fold (N = 13; p < 0.0005) with TNFα alone. However, Stx-1 plus TNFα yielded a 6.51 ± 3.48-fold increase (N = 17; p < 0.0005). TFPI mRNA decreased with TNFα (p < 0.001) and Stx-1 plus TNFα (p < 0.0005). Total cellular and cell surface TF antigen increased significantly with TNFα, but no further with Stx-1 plus TNFα. Total TFPI cellular and cell surface antigen levels, and TFPI secretion decreased significantly with Stx-1 plus TNFα. Median factor Xa production for Stx-1 plus TNFα vs TNFα alone increased (p < 0.001) 3.24-fold. Our results indicate that a subinhibitory concentration of Stx-1 plus TNFα impairs TFPI gene expression, synthesis, cell-surface association, and secretion, leading to augmented functional TF.

Evaluation of hemostasis in flowing blood

Hemostasis and thrombosis are now increasingly recognized as integrally related to blood rheology and blood flow. Platelets, for example, are known to access the vessel wall in ways which depend upon the small-scale motions of neighboring erythrocytes, and access one another via collisions driven by gradients in blood flow velocity. In this context, flow devices have become a subject of great interest in the clinical assessment of bleeding disorders, especially platelet function defects and von Willebrand disease. While these devices currently lack standardization and outcomes measures which establish clear clinical utility, their promise remains great, particularly in the potential to simulate the microenvironment of arteries vs. veins and in their ability to incorporate such intrinsically flow-dependent phenomena as co-localization of tissue-factor-bearing microparticles with platelets, the weakness of the GPIb-vWF bond at very high shear stresses, and even the hemostatic and antithrombotic function of vascular endothelium. In contrast, currently utilized assays are often performed under static conditions that do not involve flow and therefore are not able to simulate the microenvironment of arteries and veins.

Assessment of a cohort of primarily pediatric patients with a presumptive diagnosis of type 1 von Willebrand disease with a novel high shear rate, non-citrated blood flow device

BACKGROUND

A precise approach to the diagnosis of von Willebrand disease (vWD) remains elusive. One important reason is that vWD is a blood flow-related disorder: a vW Factor-platelet GPIb binding defect exists in this condition under the high shear-rate (> 1000 sec-1 in whole blood; > 3000 sec-1 in PRP) conditions of physiologic blood flow which exist in the arterioles of mucous membranes, from which most bleeding in vWD occurs.

METHODS

We therefore studied 28 patients (mean 18.9 yrs) with vWD, diagnosed according to the 2007 NHLBI clinical guidelines, and 26 healthy controls (mean 17.5 yrs). Blood was collected into a plastic tube containing 4 U/ml FC dalteparin, 1.75 μg/ml of the Tab (anti-CD41) monoclonal antibody directed against platelet GPIIb, and 1.0 μg/ml of an ALEXA 555-conjugated rabbit anti-mouse second antibody. Within 30-90 min, the blood was then withdrawn at 667 and 1330 sec(-1) through a special flow chamber allowing for real-time epifluorescence digital videomicroscopy of platelets interacting with a microfibrillar collagen substrate. With MetaMorph software (Universal Imaging) we quantified the percent area (PA) covered by and total volume (TV) of adherent platelet aggregates within a 435 μm × 580 μm field of view.

RESULTS

At 667 sec(-1) after 1 min PA and TV were similar for patients and controls, but at 1330 sec(-1) PA was 9.32 ± 4.21 (mean ± SD) for patients, a value lower (p < 0.001) than the 12.8 ± 3.39 for controls. TV was (1.43 ± 0.91) x 10(4) for patients, a value also lower (p < 0.001) than the (2.22 ± 0.77) x 10(4) for controls. PA or TV was below the 2.5th percentile for controls in 10 patients (36%) and both PA and TV were below the 2.5th percentile in eight.

CONCLUSIONS

The novel flow device found that PA and TV were significantly reduced under high shear stress in vWD patients compared to normal controls. However, there was some overlap between the vWD and the control group, suggesting that some vWD patients had normal platelet adhesion/aggregation under the conditions studied. Further study with a higher shear rate appears indicated.

Efficacy of lower-extremity venous thrombolysis in the setting of congenital absence or atresia of the inferior vena cava

PURPOSE

A rare but described risk factor for deep venous thrombosis (DVT), predominantly in the young, is congenital agenesis or atresia of the inferior vena cava (IVC). The optimal management for DVT in this subset of patients is unknown. We evaluated the efficacy of pharmacomechanical catheter-directed thrombolysis (PCDT) followed by systemic anticoagulation in the treatment of acute lower-extremity DVT in the setting of congenital IVC agenesis or atresia.

MATERIALS AND METHODS

Between November of 2005 and May of 2010, six patients (three women [average age 21 years]) were referred to our department with acute lower-extremity DVT and subsequently found to have IVC agenesis or atresia on magnetic resonance imaging. A standardized technique for PCDT (the Angiojet Rheolytic Thrombectomy System followed by the EKOS Microsonic Accelerated Thrombolysis System) was used for all subjects. Successful thrombolysis was followed by systemic heparinization with transition to Coumadin or low molecular-weight heparin and compression stockings. Subjects were followed-up at 1, 3, and then every 6 months after the procedure with clinical assessment and bilateral lower-extremity venous ultrasound.

RESULTS

All PCDT procedures were technically successful. No venous stenting or angioplasty was performed. The average thrombolysis time was 28.6 h (range 12-72). Two patients experienced heparin-induced thrombocytopenia, and one patient developed a self-limited knee hemarthrosis, No patients were lost to follow-up. The average length of follow-up was 25.8 ± 20.2 months (range 3.8-54.8). No incidence of recurrent DVT was identified. There were no manifestations of postthrombotic syndrome.

CONCLUSIONS

PCDT followed by systemic anticoagulation and the use of compression stockings appears to be safe and effective in relatively long-term follow-up treatment of patients who present with acute DVT and IVC agenesis or atresia.

Prothrombotic risk factors in the evaluation and management of perinatal stroke

The ischemia in children affected by perinatal stroke has long been thought to be driven by nonhematologic maternal and perinatal events. New information from clinical studies, however, tells us that plasma-phase risk factors, such as factor V Leiden, elevated lipoprotein (a), and mutations in MTHFR, may be important in the pathogenesis of perinatal stroke, if not always in the risk of recurrence. With regard to stroke recurrence, this risk is only about 2% according to the largest follow-up study to date, and certainly less than 5%. Nonetheless, when strokes do recur, they tend to be associated with the presence of plasma-phase risk factors in the affected child, suggesting that a small percentage of children with a first perinatal stroke may benefit from anticoagulation therapy, both to prevent stroke recurrence as well as occurence of a second, non-CNS thrombotic event. Counselling of parents with regard to subsequent pregnancies should always include medical management of systemic maternal disorders, such as diabetes, persistently elevated antiphospholipid antibodies, and inherited maternal hypercoagulability states.

Up-regulation of tissue factor activity on human proximal tubular epithelial cells in response to Shiga toxin

BACKGROUND

The pathophysiology of hemolytic uremic syndrome (HUS) is incompletely established. Based on clinical studies demonstrating the presence of prothrombotic plasma markers in patients with HUS, we hypothesized that Shiga toxin might cause activation of the coagulation pathway by augmenting tissue factor, the major initiator of coagulation.

METHODS

Human proximal tubular epithelial cells (PTECs) [human kidney-2 (HK-2 cells)] were exposed to Shiga toxin-1, and expression of tissue factor, cell detachment, protein synthesis, caspase-3 activity, and Shiga toxin-1 binding were examined. Results. HK-2 cells expressed constitutive surface tissue factor activity and increased their tissue factor expression upon exposure to Shiga toxin-1. Shiga toxin-1 bound to HK-2 cells and inhibited protein synthesis. The up-regulation of tissue factor was dose- and time-dependent and strongly correlated with cell detachment and increase in caspase-3 activity caused by Shiga toxin-1 exposure. A general caspase inhibitor simultaneously inhibited HK-2 cell detachment and tissue factor up-regulation while mutant Shiga toxin-1 neither caused cell detachment, protein synthesis inhibition, nor increase in tissue factor activity. Tissue factor activity elicited by Shiga toxin-1 was abrogated by a monoclonal antitissue factor antibody. Calphostin C, a protein kinase C (PKC) inhibitor, partially blocked tissue factor up-regulation, indicating possible involvement of PKC-dependent mechanism.

CONCLUSION

These data, taken together, suggest a strong link between Shiga toxin-induced up-regulation of tissue factor activity, cytotoxicity, and apoptosis in HK-2 cells. The proximal tubule is a target of Shiga toxin in HUS, and it seems plausible that injured proximal tubular cells trigger the activation of the coagulation system, the formation of intrarenal platelet-fibrin thrombi, and the development of acute renal failure in HUS.

Shiga toxin enhances functional tissue factor on human glomerular endothelial cells: implications for the pathophysiology of hemolytic uremic syndrome

BACKGROUND

The pathogenesis of Shiga toxin (Stx)-mediated childhood hemolytic uremic syndrome (HUS) is not fully delineated, although current evidence implicates a prothrombotic state. We hypothesized that the tissue factor (TF) pathway plays a major role in the pathophysiology of HUS.

MATERIALS AND METHODS

We measured cell surface TF activity in response to tumor necrosis factor-alpha (TNF-alpha) (20 ng mL(-1), 2-144 h), Stx-1 (10(-11) mol L(-1), 4-144 h), or their combination (TNF-alpha 22 h and Stx-1 for the last 0.5-4 h of TNF-alpha incubation) on human glomerular (microvascular) endothelial cells (HGECs) and human umbilical vein (macrovascular) endothelial cells (HUVECs).

RESULTS AND CONCLUSIONS

We observed that while TNF-alpha caused an increase in cell surface TF activity on both cell types, the combination of TNF-alpha and Stx-1 differentially affected HGECs. On these cells, TF activity was increased further by 2.67 +/- 0.38-fold (n = 38, P < 0.001), consistent with our parallel observation that Stx-1 binds to HGECs but not to HUVECs. Anti-TF antibody abolished functional TF while anti-tissue factor pathway inhibitor antibody enhanced TF activity. Stx-1 alone did not induce TF activity on either cell type. Measurement of TF antigen levels and quantitative real-time polymerase chain reaction demonstrated that exposure to TNF-alpha markedly increased TF protein and TF mRNA for HGECs, but the exposure to the combination of TNF-alpha and Stx-1 did not increase further the amount of either TF protein or TF mRNA. We conclude that cytokine-activated HGECs, but not HUVECs, undergo a significant augmentation of cell surface TF activity following exposure to Stx, suggesting an important role for TF in the coagulopathy observed in HUS.

Effect of granulocyte colony-stimulating factor on functional and histopathologic outcome after traumatic brain injury in mice

OBJECTIVE

Granulocyte colony-stimulating factor has been used to reduce the risk of sepsis in patients with traumatic brain injury. However, granulocyte colony-stimulating factor exerts potent pro- and anti-inflammatory effects that could influence secondary injury, and outcome, after traumatic brain injury. Our objective was to determine the effect of granulocyte colony-stimulating factor on histopathologic, motor, and cognitive outcome after experimental traumatic brain injury in mice.

DESIGN

Experimental study.

SETTING

Research laboratory at the Massachusetts General Hospital, Boston, MA.

SUBJECTS

Forty-eight adult male C57Bl/6 mice.

INTERVENTIONS

Mice (8 wks of age, n = 16/group) were administered granulocyte colony-stimulating factor or saline subcutaneously twice per day for 7 days after controlled cortical impact or sham injury (n = 16). Absolute neutrophil counts, motor function, Morris water maze performance, and lesion volume were determined after controlled cortical impact or sham injury.

MEASUREMENTS AND MAIN RESULTS

At the time of controlled cortical impact, body weight, brain and body temperature, and systemic absolute neutrophil counts did not differ between groups. Compared with control, systemic absolute neutrophil count was increased more than ten-fold in granulocyte colony-stimulating factor-treated mice on posttrauma days 2 and 7 (p < .05, repeated-measures analysis of variance) but did not differ between groups by day 14. There were no differences between groups in tests of motor function or histopathologic outcome. However, compared with control, mice given granulocyte colony-stimulating factor had improved Morris water maze performance after controlled cortical impact (p < .05, repeated-measures analysis of variance) but not sham injury.

CONCLUSIONS

The data suggest a small beneficial effect of granulocyte colony-stimulating factor on functional outcome after traumatic brain injury in adult mice but do not show differences in histopathology or motor outcome between treated and control groups.

Detached endothelial cells and microparticles as sources of tissue factor activity

INTRODUCTION

Cytokine activation of endothelial cell monolayers is associated with cell detachment, microparticle shedding from plasma membranes, and phosphatidylserine appearance in the plasma membrane outer leaflets. While tissue factor expression on activated endothelial cells and microparticles is well documented, the contribution of detached endothelial cells to tissue factor activity is less clear. We studied tissue factor expression and the role of tissue factor pathway inhibitor on adherent and detached endothelial cells and on microparticles following endothelial cell activation with TNF-alpha.

MATERIALS AND METHODS

Detached endothelial cells and microparticles were obtained from cultures of human umbilical vein endothelial cells by differential centrifugation of cell culture supernatant. For microparticle capture, an antibody directed against CD146 was used. Functional tissue factor activity was measured by chromogenic assay and tissue factor antigen by ELISA. Endothelial cell and microparticle morphology was examined by light and transmission electron microscopy.

RESULTS

After cell activation for 22 h, functional tissue factor activity was distributed as follows: 60%, adherent endothelial cells; 35%, detached cells; and 5%, microparticles. Tissue factor protein followed a similar distribution. Cell detachment was 47%. Electron microscopy demonstrated shedding of microparticles with a diameter of 0.1-0.6 mum. Cy3-annexin V revealed increased phosphatidylserine on activated adherent endothelial cells and microparticles. Pre-incubation of adherent and detached endothelial cells and microparticles with anti-tissue factor antibody blocked factor Xa production. Pre-incubation with anti-tissue factor pathway inhibitor antibody increased tissue factor activity of adherent endothelial cells 2.8-fold, detached cells 1.4-fold, and microparticles 45-fold.

CONCLUSIONS

Detached endothelial cells as well as microparticles from activated endothelial cell monolayers express tissue factor activity, and this activity on microparticles is markedly inhibited by microparticle-associated tissue factor pathway inhibitor.

Low-dose tissue plasminogen activator thrombolysis in children

PURPOSE

To compare results of low-dose tissue plasminogen activator (TPA) in children with arterial and venous thrombi relative to standard published dosing.

METHODS

Subjects consisted of all consecutive children with objectively confirmed thrombi for whom TPA thrombolysis was clinically ordered by the authors. Initial dosing used published standard dose (0.1-0.5 mg/kg per hour). With experience, a low-dose regimen (0.01-0.06 mg/kg per hour) was given in an attempt to derive a minimal effective dose.

RESULTS

Thirty-five children were treated with TPA. Either standard or low-dose infusions of TPA resulted in complete thrombolysis of 28 of 29 (97%) acute thrombi, while all 6 chronic thrombi had a partial response. In contrast to the recommended adult-derived dosages of 0.1 to 0.5 mg/kg per hour, the authors found that initial doses of less than 0.01 mg/kg per hour were effective in 12 of 17 patients with acute thrombosis. Neonates required 0.06 mg/kg per hour. Route of administration (local or systemic) did not affect efficacy. Major bleeding occurred in only one extremely preterm infant. Minor bleeding, primarily oozing at intravenous sites, occurred in 27% of children during TPA infusions. Prophylactic unfractionated or low-molecular-weight heparin was infused concomitant with TPA in 42% of the children and did not increase the risk of bleeding.

CONCLUSIONS

TPA in very low doses appears to be safe and effective for thrombolysis of acute thromboses in most children, given appropriate patient selection.

Arterial ischemic stroke in childhood: the role of plasma-phase risk factors

The role of plasma-phase risk factors for stroke in the pediatric age group is presently unclear due to the lack of sufficiently large prospective studies, and due to the fact that these risk factors do not apply uniformly to newborns, children with sickle cell disease, and older children. Available evidence indicates that factor V Leiden, prothrombin 20210A, and lipoprotein (a) are all important in the pathogenesis of arterial ischemic stroke in older children, but the role of other plasma-phase risk factors remains uncertain. The contribution of these risk factors to newborn stroke and the stroke of children with sickle cell disease is similarly unclear, likely because the ischemia in affected children is predominantly due to nonhematologic perinatal events and erythrocyte adhesion to endothelium with obstruction of flow in the cerebral microcirculation, respectively. Evaluation of childhood stroke should, in our view, always be performed from the standpoint of the presenting clinical symptoms, diagnostic imaging, and determination of plasma-phase risk factors. Therapeutic anticoagulation and use of antiplatelet agents at present focus on the older child.

Shear stress decreases endothelial cell tissue factor activity by augmenting secretion of tissue factor pathway inhibitor

Monolayers of human umbilical vein endothelial cells were activated with 50 U/mL interleukin-1alpha (IL-1alpha) for 3 hours and simultaneously conditioned with shear stresses of 0, 0.68, or 13.2 dyne/cm(2) in a parallel-plate flow chamber. In the presence of an inflow buffer containing 100 nmol/L factor X and 10 nmol/L factor VII, production of factor Xa, a measure of functional tissue factor (TF), was determined as the product of outflow concentration of factor Xa (chromogenic assay performed under quasi-static flow conditions after the shear period) and flow rate. Similarly, production of TF pathway inhibitor (TFPI) was estimated as the product of antigenic TFPI (by enzyme-linked immunosorbent assay) in the supernatant and flow rate. In parallel experiments, total RNA was isolated for determination of amplification products of TF mRNA by reverse transcription-polymerase chain reaction. We found that shear stress reduced factor Xa production (mean+/-SE; n=number of experiments) from 13.33+/-1.14 (n=16) fmol/minxcm(2) at 0 shear stress to 5.70+/-2.51 (n=5) and 0.54+/-0.54 (n=4) fmol/minxcm(2) at shear stresses of 0.68 and 13.2 dyne/cm(2), respectively. At the same time, immunogold labeling showed that TF antigen on the endothelial surface increased >5-fold with shear stress, whereas TFPI antigen on the surface increased 2-fold. The secretion of TFPI (appearance of new supernatant TFPI) rose from 7.4+/-2.4 (n=12) x10(-)(3) fmol/minxcm(2) at 0 shear stress to 23.7+/-7.3 (n=9) and 50.2+/-14.3 (n=4) x10(-)(3) fmol/minxcm(2) at 0.68 and 13.2 dyne/cm(2), respectively. TF mRNA amplification products were not markedly changed by shear stress. We conclude that acute application of shear stress reduces functional, but not antigenic, expression of TF by intact, activated endothelial cell monolayers in a manner associated with shear stress-augmented endothelial cell secretion of TFPI.

Comparison of tissue factor pathway in human umbilical vein and adult saphenous vein endothelial cells: implications for newborn hemostasis and for laboratory models of endothelial cell function

In this work we have undertaken a comparative study of human umbilical vein endothelial cells (HUVECs) and human saphenous vein endothelial cells (HSVECs) with respect to functional and antigenic tissue factor (TF), tissue factor pathway inhibitor (TFPI), and TF mRNA. Monolayers of each cell type (passage 2, except where specified) were grown to confluence and then activated for 4 h with either 50 U/mL IL-1-alpha or 10 microg/mL tumor necrosis factor-alpha. Activated factor X appearing in supernatant was measured using a chromogenic assay, and both Northern blots and quantitative RT-PCR were performed to assess concentrations of TF mRNA accompanying activation. The role of TFPI was separately determined by ELISA for supernatant TFPI antigen, and by measurements of production of activated factor X in the presence of 0, 5, 15, or 50 microg/mL of an antibody directed against TFPI. To address a non-TF pathway endothelial cell function, antigenic concentrations of tissue plasminogen activator for both cell types was also determined by ELISA. HUVECs were found to produce 2.4- to 3.5-fold more functional TF. No significant HUVEC-HSVEC differences were detected in TF antigen, supernatant TFPI, anti-TFPI affinity for endothelial cell-associated TFPI, TF mRNA or its amplification products, and tissue plasminogen activator. Immunostaining for TF antigen, however, may have failed to detect a modest HUVEC-HSVEC difference. Our finding with respect to functional TF indicates that HUVECs and HSVECs are not equivalent in terms of models for endothelial cell function in small children versus adults.

Vascular hemostasis in flowing blood in children

This review considers differences in hemostasis among newborns, children, and adults from the standpoint of the vascular endothelium and, where appropriate, in the presence of flowing blood. Special procoagulant features of newborn hemostasis include unusually large von Willebrand factor multimers, augmented platelet transport under flow conditions, and greater ability of newborn endothelium to generate tissue factor. Special anticoagulant features in the newborn include increased vessel wall glycosaminoglycan activity, elevated alpha2-macroglobulin, and increased percentage of free protein S. The net effect of the differences is that hemostasis is generally achieved in all age groups but is developmental in nature. In addition to congenital hypercoagulable states and catheter placement, developmental vascular anomalies appear to constitute a thrombotic risk, at least in some children (and possibly adults).

Variability of platelet degranulation by different contrast media

RATIONALE AND OBJECTIVES

It has been suggested that nonionic but not ionic contrast media degranulate blood platelets when mixtures of blood and contrast media are studied by flow cytometry. This phenomenon was further assessed in the current study not only by performing whole-blood platelet flow cytometry but also by performing flowing blood platelet aggregometry. The latter is a highly sensitive measure of platelet function.

METHODS

Blood samples were collected from six normal donors and mixed with equal volumes of an ionic monomer (diatrizoate), a nonionic monomer (iohexol), an ionic dimer (ioxaglate), and a nonionic dimer (iodixanol). Samples were collected in the presence of no anticoagulant for 1 min prior to the addition of sodium citrate or in the presence of heparin (14.5 U/ml) or recombinant hirudin (60 micrograms/ml). All samples were fixed in formaldehyde within 30 min.

RESULTS

Platelet degranulation was observed with one nonionic agent (iohexol) and one ionic agent (diatrizoate). Degranulation was not seen with iodixanol or ioxaglate.

CONCLUSION

These findings indicate that degranulation is independent of the ionic or nonionic nature per se of contrast media. A possible explanation for this conclusion is suggested.

Thrombolysis, flow, and vessel wall interactions

Vascular endothelium remains a dynamic interface between blood, blood platelets, and the vessel wall. New developments make clear that many antithrombotic and prothrombotic responses of the endothelium depend on flow conditions in an adaptive manner: duration of a certain level of shear stress matters as well as level of shear. In general, over the course of several hours, endothelium appears to be more actively antithrombotic under moderate shear conditions (eg, 15 dyne/cm2) and more fibrinolytic under high shear conditions (eg, 30 dyne/cm2). Pulsatile flow and cyclic wall stress further modify these responses. Special consideration, moreover, must be given to branch points and regions of irregular geometry (ie, stenoses, aneurysms) in the circulation. In such locations-predilection sites for thrombosis, lipid uptake, and atherosclerosis-low levels of shear stress (eg, 0.5 dyne/cm2), large gradients in shear stress, and vessel wall bending stresses all become important. Preliminary work suggests that endothelial cells in such regions can become prothrombotic, leading to localized platelet adhesion/aggregation and fibrin formation on subendothelium and perhaps deeper structures following vessel injury. Flow effects on thrombolysis remain largely unstudied.

Endothelial cell function, including tissue factor expression, under flow conditions

Vascular endothelium remains a dynamic interface between blood and the vessel wall. New developments make clear that many antithrombotic and prothrombotic responses of the endothelium depend on flow conditions in an adaptive manner: duration of a certain level of shear stress matters as well as level of shear. In general, over a time course of several hours, endothelium appears to be more actively antithrombotic under moderate shear conditions (e.g., 15 dynes/cm2), and more fibrinolytic under high (e.g., 30 dynes/cm2). Pulsatile flow and cyclic wall stress further modify these responses. Special consideration, moreover, must be given to branch points and regions of irregular geometry (i.e., stenoses, aneurysms) in the circulation. In such locations, predilection sites for thrombosis, lipid uptake, and atherosclerosis, low levels of fluid shear stress (e.g., 0.5 dynes/cm2), large gradients in fluid shear stress, and vessel wall bending stresses all become important. Preliminary work suggests that endothelial cells in such regions can become prothrombotic, leading to localized platelet adhesion/aggregation and fibrin formation on subendothelium and perhaps deeper structures following vessel injury.

Platelet degranulation induced by some contrast media is independent of their nonionic vs ionic nature

We confirm that the phenomenon of platelet degranulation exists for both iohexol and diatrizoate, as reported earlier. In contrast to previous conclusions, however, we have determined that the degranulation is independent of the nonionic vs. ionic nature of the media per se, since degranulation was neither seen with nonionic iodixanol nor ionic ioxaglate. The degranulation, further, does not significantly augment platelet function, as measured by flowing whole blood platelet aggregometry.

Nonionic contrast media. Procoagulants or clotting innocents?

OBJECTIVES

Compared with ionic contrast media, nonionic contrast media cause fewer adverse reactions, including hemodynamic and electrophysiologic complications, and are better tolerated by patients. However, concern as to whether nonionic agents are associated with more thromboembolic complications has been raised in recent years. This article reviews in-vitro and in-vivo coagulation studies with nonionic contrast media, including the authors' current study using blood samples from percutaneous transluminal coronary angioplasty (PTCA) patients.

METHODS

Articles for this review were selected on the basis of providing viewpoints representative of both sides of the clotting controversy involving nonionic contrast media. In addition, articles were selected that, in toto, include the several relevant aspects of thrombosis during PTCA: whole blood clotting, angiography catheters, angiography syringes, rheology, and vascular endothelium. The preliminary work described used platelet adhesion/aggregation to a collagen-coated surface under controlled conditions of heparinized, whole blood flow. Adhesion/aggregation was quantified by digital analysis of real-time images obtained by epifluorescence videomicroscopy. In parallel studies, changes in markers (membrane glycoproteins) of platelet activation were measured using whole blood flow cytometry.

RESULTS

Although nonionic contrast media are weaker anticoagulants than ionic contrast media, no convincing evidence demonstrates that they are procoagulant. On the contrary, in-vitro studies suggest that ionic media may weaken the antithrombotic properties of vascular endothelium by direct endothelial injury. Certain clinical trials of PTCA patients substantially challenge the use of nonionics. Yet, Grabowski et al found no evidence of platelet activation by ioxaglate or iohexol in preliminary work. This result was obtained with two of the most sensitive platelet assays available: flowing whole blood aggregometry and whole blood flow cytometry. Attention should be given to the adequacy of heparinization in future clinical studies.

CONCLUSIONS

Nonionic contrast media are not procoagulant in vitro in the hands of most research groups. The focus of current controversy, therefore, is whether there is a clinical and in-vivo difference in thrombotic events seen with nonionic versus ionic media during PTCA. Elements in this controversy include platelet activation, blood-foreign surface (catheter and syringe) interaction, rheology, vascular endothelium, and adequacy of heparinization.

The functional expression of tissue factor by fibroblasts and endothelial cells under flow conditions

The expression of tissue factor (TF) by a variety of vascular cell types under physiologic flow conditions is critical to factor X activation and in vivo clotting. Therefore, in a parallel-plate flow chamber (volume 40 microL) we mounted monolayers of human embryonic fibroblasts (FBs) or interleukin-1 alpha (IL-1 alpha) (5 U/mL x 4 hours)-stimulated human umbilical vein endothelial cells (ECs). Inflow buffer contained 10 nmol/L factor VIIa, 100 nmol/L factor X, and 2.0 mmol/L CaCl. With FBs, production of factor Xa (product of outflow concentration of factor Xa-and flow rate) increased 200-fold over the range of shear stress from 0 to 2.7 dynes/cm2. Production values (mean +/- SE (N)) were 7.93 +/- 0.024 (6), 312 +/- 7.3 (6), 688 +/- 33.1 (8), 1,033 +/- 119 (6), and 1,601 +/- 183 (7) fmol/cm2.minute at shear stresses of 0, 0.27, 0.68, 1.35, and 2.7 dynes/cm2, respectively. Further experiments at 0.68 dynes/cm2 indicated that factor Xa production increased with factor X concentration over the range from 3 to 100 nmol/L, but changed little from 300 to 1,000 nmol/L. With ECs, production was 0.13 +/- 0.86 (6), 8.17 +/- 1.65 (13), and 1.66 +/- 1.66 (5) fmol/cm2.minute at 0, 0.68, and 2.7 dynes/cm2, respectively. However, in the presence of an antibody directed against tissue factor pathway inhibitor (TFPI) production with ECs was augmented to 16.46 +/- 0.80 (8), 149.8 +/- 18.6 (8), and 48.9 +/- 10.3 (10), respectively, at these same shear stresses. Control experiments with factor VIIa, factor X, or both absent confirm for both cell types the specificity of the reaction for the TF pathway. Similarly, specificity for TF itself is shown by the virtual absence of factor Xa generation in the presence of the monoclonal antibody HTF1-7B8 directed against human TF. We conclude that ECs, even when activated, are normally unable to generate significant quantities of factor Xa in the presence of factors X and VIIa. However, significant quantities of factor Xa are possible in the presence of an inhibitor of TFPI. On the other hand, production of factor Xa by fibroblasts is markedly augmented by shear stress, yet independent of the availability of substrate factor X above an inflow concentration of 100 nmol/L. The latter suggests a direct effect of flow on the fibroblast monolayers, not substrate limitation by convective diffusion.

Coagulation disorders in children

Many new developments have taken place in the field of coagulation during the past year. We focus on the interesting new controversies surrounding vitamin K prophylaxis of the newborn infant, on the increasing information regarding the growth factors responsible for thrombopoiesis, and on the role of protein C in the genesis of thrombosis.

Platelet adhesion/aggregation in an in vitro model of coronary artery stenosis

Platelet adhesion/aggregation (PAA) at a site of coronary artery stenosis is believed to be a process strongly modulated by local shear rates and the functional state of neighboring endothelium. One purpose of the present work, therefore, is to describe an in vitro model for the direct imaging of such PAA. Another is to apply the model to the question as to whether the use of nonionic vs. ionic contrast media (CM) in the presence of vascular endothelium contributes to PAA at the stenosis site. Toward these ends, we utilized a special flow chamber which incorporates a monolayer of endothelial cells (ECs), a step 66% flowpath constriction at a site preadsorbed with microfibrillar collagen, and arterial shear rates. By epifluorescence microscopy and digital image analysis of video recordings, PAA was found to be greater with dysfunctional ECs (pretreated with lysine acetylsalicyclate) than with normal ECs, thereby confirming a modulatory role in PAA of functionally intact ECs. When nonionic (iohexol) or ionic (ioxaglate, diatrizoate) CM was added to the flowing blood at a concentration of 20% by non-red cell volume, PAA was inhibited in the order diatrizoate > ioxaglate > iohexol > saline control. No inhibition by any CM was seen, however, when chamber prefill culture medium containing 20% by volume CM was displaced by CM-free blood, in simulation of bolus administration of CM. In terms of inhibition of PAA during percutaneous transluminal coronary angioplasty (PTCA), therefore, our model provides a conceptual basis by which one may anticipate in flowing blood no clear benefit of ionic over nonionic CM.(ABSTRACT TRUNCATED AT 250 WORDS)