Impact of Inherited Thrombophilia on Venous Thromboembolism in Children

Background— The aim of the present study was to estimate the impact of inherited thrombophilia (IT) on the risk of venous thromboembolism (VTE) onset and recurrence in children by a meta-analysis of published observational studies.

Methods and Results— A systematic search of electronic databases (Medline, EMBASE, OVID, Web of Science, The Cochrane Library) for studies published from 1970 to 2007 was conducted using key words in combination as both MeSH terms and text words. Citations were independently screened by 2 authors, and those meeting the inclusion criteria defined a priori were retained. Data on year of publication, study design, country of origin, number of patients/controls, ethnicity, VTE type, and frequency of recurrence were abstracted. Heterogeneity across studies was evaluated, and summary odds ratios and 95% CIs were calculated with both fixed-effects and random-effects models. Thirty-five of 50 studies met inclusion criteria. No significant heterogeneity was discerned across studies. Although >70% of patients had at least 1 clinical risk factor for VTE, a statistically significant association with VTE onset was demonstrated for each IT trait evaluated (and for combined IT traits), with summary odds ratios ranging from 2.63 (95% CI, 1.61 to 4.29) for the factor II variant to 9.44 (95% CI, 3.34 to 26.66) for antithrombin deficiency. Furthermore, a significant association with recurrent VTE was found for all IT traits except the factor V variant and elevated lipoprotein(a).

Conclusions— The present meta-analysis indicates that detection of IT is clinically meaningful in children with, or at risk for, VTE and underscores the importance of pediatric thrombophilia screening programs.

A proposal for an international retinoblastoma staging system

BACKGROUND

Although intra-retinal tumor has long been staged presurgically according to the Reese-Ellsworth (R-E) system, retinoblastoma differs from other pediatric neoplasms in never having had a widely accepted classification system that encompasses the entire spectrum of the disease. Comparisons among studies that consider disease extension, risk factors for extra-ocular relapse, and response to therapy require a universally accepted staging system for extra-ocular disease.

PROCEDURE

A committee of retinoblastoma experts from large centers worldwide has developed a consensus classification that can encompass all retinoblastoma cases and is presented herein. Patients are classified according to extent of disease and the presence of overt extra-ocular extension. In addition, a proposal for substaging considering histopathological features of enucleated specimens is presented to further discriminate between Stage I and II patients.

RESULTS

The following is a summary of the classification system developed-Stage 0: Patients treated conservatively (subject to presurgical ophthalmologic classifications); Stage I: Eye enucleated, completely resected histologically; Stage II: Eye enucleated, microscopic residual tumor; Stage III: Regional extension [(a) overt orbital disease, (b) preauricular or cervical lymph node extension]; Stage IV: Metastatic disease [(a) hematogenous metastasis: (1) single lesion, (2) multiple lesions; (b) CNS extension: (1) prechiasmatic lesion, (2) CNS mass, (3) leptomeningeal disease]. A proposal is also presented for substaging of enucleated Stages I and II eyes.

CONCLUSIONS

The proposed staging system is the product of an international effort to adopt a uniform staging system for patients with retinoblastoma to cover the whole spectrum of the disease.

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.

Second nonocular tumors among survivors of retinoblastoma treated with contemporary photon and proton radiotherapy

BACKGROUND

The leading cause of death among patients with hereditary retinoblastoma is second malignancy. Despite its high rate of efficacy, radiotherapy (RT) is often avoided due to fear of inducing a secondary tumor. Proton RT allows for significant sparing of nontarget tissue. The current study compared the risk of second malignancy in patients with retinoblastoma who were treated with photon and proton RT.

METHODS

A retrospective review was performed of patients with retinoblastoma who were treated with proton RT at the Massachusetts General Hospital or photon RT at Boston Children's Hospital between 1986 and 2011.

RESULTS

A total of 86 patients were identified, 55 of whom received proton RT and 31 of whom received photon RT. Patients were followed for a median of 6.9 years (range, 1.0 years-24.4 years) in the proton cohort and 13.1 years (range, 1.4 years-23.9 years) in the photon cohort. The 10-year cumulative incidence of RT-induced or in-field second malignancies was significantly different between radiation modalities (proton vs photon: 0% vs 14%; P = .015). The 10-year cumulative incidence of all second malignancies was also different, although with borderline significance (5% vs 14%; P = .120).

CONCLUSIONS

Retinoblastoma is highly responsive to radiation. The central objection to the use of RT, the risk of second malignancy, is based on studies of patients treated with antiquated, relatively nonconformal techniques. The current study is, to the authors' knowledge, the first to present a series of patients treated with the most conformal of the currently available external-beam RT modalities. Although longer follow-up is necessary, the preliminary data from the current study suggest that proton RT significantly lowers the risk of RT-induced malignancy.

Platelets, circulating tissue factor, and fibrin colocalize in ex vivo thrombi: real-time fluorescence images of thrombus formation and propagation under defined flow conditions

Although it is generally accepted that the initial event in coagulation and intravascular thrombus formation is the exposure of tissue factor (TF) to blood, there is still little agreement about the mechanisms of thrombus propagation and the identities of the molecular species participating in this process. In this study, we characterized the thrombotic process in real-time and under defined flow conditions to determine the relative contribution and spatial distribution of 3 components of the thrombi: circulating or blood-borne TF (cTF), fibrin, and platelets. For this purpose, we used high-sensitivity, multicolor immunofluorescence microscopy coupled with a laminar flow chamber. Freshly drawn blood, labeled with mepacrine (marker for platelets and white cells), anti-hTF1(Alexa.568) (marker for tissue factor), and anti-T(2)G(Cy-5)(1) (marker for fibrin) was perfused over collagen-coated glass slides at wall shear rates of 100 and 650 s(-1). A motorized filter cube selector facilitated imaging every 5 seconds at 1 of 3 different wavelengths, corresponding to optimal wavelengths for the 3 markers above. Real-time video recordings obtained during each of 10 discrete experiments show rapid deposition of platelets and fibrin onto collagen-coated glass. Overlay images of fluorescent markers corresponding to platelets, fibrin, and cTF clearly demonstrate colocalization of these 3 components in growing thrombi. These data further support our earlier observations that, in addition to TF present in the vessel wall, there is a pool of TF in circulating blood that contributes to the propagation of thrombosis at a site of vascular injury.

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.

Bleeding risks are higher in children versus adults given prophylactic platelet transfusions for treatment-induced hypoproliferative thrombocytopenia

Age-group analyses were conducted of patients in the prophylactic platelet dose trial (PLADO), which evaluated the relation between platelet dose per transfusion and bleeding. Hospitalized patients with treatment-induced hypoproliferative thrombocytopenia were randomly assigned to 1 of 3 platelet doses: 1.1 × 10(11), 2.2 × 10(11), or 4.4 × 10(11) platelets/m(2) per transfusion, given for morning counts of ≤ 10 000 platelets/μL. Daily hemostatic assessments were performed. The primary end point (percentage of patients who developed grade 2 or higher World Health Organization bleeding) was evaluated in 198 children (0-18 years) and 1044 adults. Although platelet dose did not predict bleeding for any age group, children overall had a significantly higher risk of grade 2 or higher bleeding than adults (86%, 88%, 77% vs 67% of patients aged 0-5 years, 6-12 years, 13-18 years, vs adults, respectively) and more days with grade 2 or higher bleeding (median, 3 days in each pediatric group vs 1 day in adults; P < .001). The effect of age on bleeding differed by disease treatment category and was most pronounced among autologous transplant recipients. Pediatric subjects were at higher risk of bleeding over a wide range of platelet counts, indicating that their excess bleeding risk may be because of factors other than platelet counts.

Platelet adhesion to foreign surfaces under controlled conditions of whole blood flow: human vs rabbit, dog, calf, sheep, pig, macaque, and baboon

Our results reveal significant differences between mammalian species with respect to platelet adhesion to foreign surfaces exposed to heparinized, flowing blood. In particular, we have demonstrated the following: 1) At a surface shear rate characteristic of shear rates in mammalian arteries, human platelet adhesion (and that of calf, baboon, macaque, hog or sheep) is negligible in comparison to dog or rabbit platelet adhesion after 10 mins of blood flow. 2) The species differences are biomaterial dependent: the human-dog difference is present with Cuprophan or Avcothane, but absent with compressed Gore-Tex or fluorinated ethylcellulose. (The platelets of humans and dogs adhere to comparable degrees on the latter 2 biomaterials.) 3) With Cuprophan and recirculated blood, the human-dog difference persists at 30 and 180 mins. 4) By means of videomicroscopy, the species differences are unlikely only to be an artifact of the possible formation and embolization of surface-adherent aggregates. Tests for the thromboresistance of candidate biomaterials and for platelet adhesion under controlled flow conditions must therefore begin to take into account differences between humans and other species.

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.

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.

Radiation therapy for retinoblastoma: comparison of results with lens-sparing versus lateral beam techniques

From 1979 through 1986, 170 children were seen at our institution diagnosed with retinoblastoma. Sixty-six of the children with involvement of 121 eyes, were referred for definitive external beam radiation to one or both eyes. During the study period, two distinct radiation techniques were used. From 1980 through mid-1984, a lens-sparing technique included an anterior electron beam with a contact lens mounted lead shield, combined with a lateral field, was used. Since mid-1984, a modified lateral beam technique has been used, mixing lateral electrons and superior and inferior lateral oblique split beam wedged photons. Doses prescribed were similar for both techniques, ranging from 3,850 to 5,000 cGy in 4 to 5 weeks. The lens-sparing and the modified lateral techniques are compared for local control. For eyes with Group I through III disease, the lens-sparing technique resulted in local control in 33% of the eyes treated, where the modified lateral technique controlled 83% of the eyes treated (p = .006). Mean time to relapse was identical in both groups, that is 24 and 26 months respectively. Most relapses were successfully treated with further local therapy, including laser or cryosurgery, or 60Co plaques. Five eyes required enucleation following initial treatment with the lens-sparing technique, but none thus far with the lateral beam technique. For eyes with Group IV and V disease, no significant differences were found between the two techniques in terms of local control or eventual need for enucleation. With a mean follow-up time of 33 months for the entire group, the 4-year survival is 93%. Two of the 4 deaths are due to second primary tumor, and all 4 have occurred in the lens-sparing group. Because follow-up time is more limited in the lateral beam group, this is not statistically significant and direct survival comparisons are premature.

Is antenatal vitamin K prophylaxis needed for pregnant women taking anticonvulsants?

The objective of this cohort study of a consecutive sample of infants exposed during pregnancy to anticonvulsant drugs was to determine if the mother received late pregnancy prophylaxis with vitamin K, and if any infants had signs of hemorrhagic disease. The medical records of 204 neonates exposed to anticonvulsant drugs in utero and 77 unexposed control neonates were retrospectively reviewed. No hemorrhagic disease was observed, and the incidence of bleeding tendencies was not higher in infants exposed to these drugs compared with control infants, despite no prenatal vitamin K supplementation in all but 1 epileptic woman.

Proton radiation therapy for the treatment of retinoblastoma

PURPOSE

To investigate long-term disease and toxicity outcomes for pediatric retinoblastoma patients treated with proton radiation therapy (PRT).

METHODS AND MATERIALS

This is a retrospective analysis of 49 retinoblastoma patients (60 eyes) treated with PRT between 1986 and 2012.

RESULTS

The majority (84%) of patients had bilateral disease, and nearly half (45%) had received prior chemotherapy. At a median follow-up of 8 years (range, 1-24 years), no patients died of retinoblastoma or developed metastatic disease. The post-PRT enucleation rate was low (18%), especially in patients with early-stage disease (11% for patients with International Classification for Intraocular Retinoblastoma [ICIR] stage A-B disease vs 23% for patients with ICIR stage C-D disease). Post-PRT ophthalmologic follow-up was available for 61% of the preserved eyes (30 of 49): 14 of 30 eyes (47%) had 20/40 visual acuity or better, 7 of 30 (23%) had moderate visual acuity (20/40-20/600), and 9 of 30 (30%) had little or no useful vision (worse than 20/600). Twelve of 60 treated eyes (20%) experienced a post-PRT event requiring intervention, with cataracts the most common (4 eyes). No patients developed an in-field second malignancy.

CONCLUSIONS

Long-term follow-up of retinoblastoma patients treated with PRT demonstrates that PRT can achieve high local control rates, even in advanced cases, and many patients retain useful vision in the treated eye. Treatment-related ocular side effects were uncommon, and no radiation-associated malignancies were observed.

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.

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.

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.

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.

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.

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.

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.