Biomedical subjects

David Varon

Publications and source records attributed to David Varon.

28 records · Page 2Linked to original sources

PubMed2003

High incidence of thromboembolism in patients with central nervous system lymphoma.

BACKGROUND: Venous thromboembolism (VTE) is a frequent complication in patients with cancer throughout the course of the disease. Patients with brain tumors are at particularly high risk for VTE, and several risk factors were found in patients with malignant glioma. To the authors' knowledge, the incidence of VTE in patients with central nervous system (CNS) lymphoma is not known, and possible risk factors have not been identified to date. The objective of this study was to evaluate the frequency and risk factors of VTE in patients with CNS lymphoma. METHODS: The authors retrospectively evaluated the medical records of 42 patients with CNS lymphoma who were treated at their center between 1992 and 2001. RESULTS: It was found that 25 patients (59.5%) had VTE, and, in 3 patients (7%), the VTE was fatal. The authors could not demonstrate that age or ambulatory status could predict VTE in this group of patients, but almost all VTE events occurred during the early period of intensive therapy. CONCLUSIONS: The high incidence of VTE found in this study indicates that anticoagulant prophylaxis with low-molecular-weight heparin probably outweighs the risk and cost of such therapy. A prospective evaluation of newly diagnosed patients with CNS lymphoma is underway at the authors' center.

Adult↗

PubMed2003

Thrombospondin-1 mediates platelet adhesion at high shear via glycoprotein Ib (GPIb): an alternative/backup mechanism to von Willebrand factor.

Acute thrombotic arterial occlusion is the leading cause of morbidity and mortality in the Western world. Von Willebrand factor is thought to be the only indispensable adhesive substrate to promote thrombus formation in high shear environments. We found that thrombospondin-1, a glycoprotein enriched in arteriosclerotic plaques, might function as an alternative substrate for thrombus formation. Platelets adhered to thrombospondin-1 in a shear dependent manner with an optimum shear as found in stenosed arteries. Adhesion is extremely firm, with no detachment of platelets up to a shear rate of 4000 s(-1). Experiments using platelets from a patient completely lacking von Willebrand factor showed that von Willebrand factor is not involved in platelet binding to thrombospondin-1. Platelet adhesion to thrombospondin-1 is not mediated via beta3-integrins or GPIa. CD36 partially mediates the adhesion of pre-activated platelets. We identified GPIb as high shear adhesion-receptor for thrombospondin-1. Soluble GPIb, as well as antibodies against the GPIb, blocked platelet adhesion almost completely. The new discovered thrombospondin-1-GPIb adhesion axis under arterial shear conditions might be important, not only during thrombus formation but also for pathological processes where other cells bind to the endothelium or subendothelium, including arteriosclerosis, inflammation and tumor metastasis, and a promising therapeutic target.

Humans↗

PubMed2003

Diagnosis of thrombotic thrombocytopenic purpura based on modulation by patient plasma of normal platelet adhesion under flow condition.

We have designed a simple test for the early diagnosis and treatment monitoring of thrombotic thrombocytopenic purpura (TTP). We examined plasma from 24 TTP patients and normal plasma using a cone and plate(let) analyser (CPA). Test plasma was mixed with citrated normal whole blood (group O) and subjected to flow at a shear rate of 1800/s. Mixing normal plasma (12.5, 25, 50 or 75 microl) with heterologous normal whole blood (final volume of 200 microl) resulted in a decrease of surface coverage (SC, maximally by 63%) and, to a lesser extent, of average size (AS, maximally by 37%) due to dilution of the blood sample. In contrast, mixing the same quantities of acute TTP plasma with normal blood yielded an increase in both SC (up to 125%) and AS (up to 130%). Increased SC and/or AS were detected in all 15 patients in acute phase and in three out of 14 patients in remission. Following repeated plasmapheresis, the enhanced platelet deposition in five patients with acute TTP returned to almost normal patterns. Mixing plasma from patients with other thrombocytopenic conditions in this way resulted in a decrease in both SC and AS, and did not differ from control subjects. In conclusion, the CPA is a simple and specific laboratory test that can be used for the diagnosis and monitoring of plasma exchange therapy in TTP.

Acute Disease↗

PubMed2003

Platelet-leukocyte aggregation under shear stress: differential involvement of selectins and integrins.

Platelets and leukocytes can form heterotypic aggregates. We studied how shear stress influences platelet-leukocyte aggregation (PLA). Shear stress was applied to hirudinized blood, using a cone-and-plate(let) analyzer. Platelet and leukocyte activation and PLA formation were monitored by flow cytometry. Shear stress per se increased platelet P-selectin expression, leukocyte CD11b expression, and PLA formation. Shear-induced heterotypic aggregation was seen among monocytes and neutrophils, but not lymphocytes. ADP induced marked PLA formation, but this was reduced by shear stress. fMLP mildly increased PLA formation, and this effect was enhanced by shear stress. P-selectin blockade abolished, whilst GPIIb/IIIa blockade enhanced shear- and agonist-induced PLA formation. At 1800 s(-1), shear-and agonist-induced PLA formation were maintained or further enhanced with GPIIb/IIIa blockade alone, but reduced by simultaneous blockade of GPIIb/IIIa, CD11b, and CD18. In conclusion, shear stress per se enhances PLA formation. With agonist stimulation, shear stress enhances PLA formation primarily mediated by integrins, but attenuates PLA formation primarily mediated by P-selectin. The present results indicate that P-selectin-mediated bridging is essential for the initiation of PLA formation, while integrin-bridgings contribute importantly to the stability of heterotypic conjugates under high shear stress.

Adult↗

PubMed2002

Whole blood platelet deposition on extracellular matrix under flow conditions in preterm neonatal sepsis.

UNLABELLED: Platelet function in preterm infants with sepsis was evaluated by measuring their adhesion and aggregation properties using the Cone and Plate(let) Analyser. This may lead to earlier detection of bleeding tendency in septic infants. Platelet function was investigated in 54 preterm infants, of whom 32 had proven neonatal sepsis and 22 were healthy matched controls. Citrated whole blood was subjected to shear stress (1300 s(-1)) for 2 min on tissue culture plates precoated with subendothelial extracellular matrix (ECM). The percentage of ECM surface covered with platelets and the average size of the ECM-bound platelet particles were determined with an image analyser. Assays for von Willebrand factor (vWF) antigen, ristocetin co-factor, and vWF collagen binding activity (CBA) were performed on samples from an additional 47 preterm infants: 38 healthy and 9 septic. Platelets of the preterm infants with sepsis displayed lower adhesion than those of the healthy controls. Mean surface coverage was 16.9+/-8.2% for the septic infants, 15.4+/-7.9% for the septic infants after exclusion of those with coagulase-negative staphylococci sepsis, and 20.8+/-9.6% for the healthy group ( P<0.05). Platelet aggregation, vWF antigen, ristocetin co-factor, and CBA levels were similar between the septic and healthy groups. The most significant factor influencing surface coverage was the presence of sepsis. CONCLUSION: platelet adhesion to extracellular matrix is significantly lower in septic preterm infants than in healthy preterm infants. Intrinsic platelet properties, rather than the concentration or activity of plasma von Willebrand factor, may be responsible for this difference. Surface coverage obtained by the collagen binding activity test under flow conditions, which represents platelet adhesion, may be an earlier, more sensitive indicator of bleeding tendency in neonatal sepsis than decreased platelet count.

Blood Platelets↗

PubMed2002

Venous shear stress enhances platelet mediated staphylococcal adhesion to artificial and damaged biological surfaces.

We investigated the role of blood components in the adhesion of staphylococci to biological and artificial surfaces under well-defined flow conditions by using the Cone and Plate(let) Analyzer. An enzyme-linked immunosorbent assay-like binding assay with biotinylated bacteria determined the extent of bacterial adhesion to subendothelial extracellular matrix (ECM), polystyrene (PS) and adult bovine aortic endothelial (ABAE) cell monolayer. The presence of adsorbed plasma proteins on PS and ECM did not increase and in some cases reduced staphylococcal adhesion under flow conditions (200s(-1)). However, their presence on ABAE cells increased bacterial adhesion but to a level still lower than the adhesion to PS and ECM. In contrast, adhered platelets significantly increased staphylococcal adhesion to both PS and ECM, but did not affect the adhesion to ABAE cells. Furthermore, bacterial adhesion to the platelets coated ECM and PS under flow conditions (200s(-1)) was increased by 1.4 to 2.6-fold compare to static conditions. The platelet-enhanced bacterial adhesion was markedly inhibited by blockade of the platelet GPIb receptor. In conclusion, staphylococcal extensive adhesion to ECM and PS surfaces is increased by venous flow and mediated by surface adhered activated platelets via a GPIb dependent mechanism. On the other hand, ABAE cells demonstrated limited bacterial adhesion that is mediated by adsorbed plasma proteins. Our results suggest that under physiological venous flow conditions the intact vessel wall is less prone for bacterial adhesion than damaged vessel wall.

Animals↗

PubMed2002

Role of agr (RNAIII) in Staphylococcus aureus adherence to fibrinogen, fibronectin, platelets and endothelial cells under static and flow conditions.

In the present study, the adherence of Staphylococcus aureus (strain 83254) and its RNAIII mutant (WA400) to immobilised fibrinogen and fibronectin, and to human endothelial cells (EC), was studied. [3H]Thymidine-labelled bacteria in stationary phase were incubated on the test surfaces for 20 min under static or flow (200/s) conditions. The results showed: (a) increased adherence of the RNAIII mutant to fibrinogen under static conditions, and decreased adherence of the mutant to fibronectin and EC under both static and flow conditions compared with the parental strain; (b) stronger ability of the mutant compared with the parental strain to induce platelet aggregation in suspension; (c) greater adherence of the parental strain and the mutant to EC pre-treated with platelet-rich plasma compared with platelet-poor plasma, and to EC pre-treated with platelet-poor plasma compared with control; (d) increased adherence of S. aureus to EC pre-treated with PMA-activated platelets and decreased adherence to EC pre-treated with tirofiban, a platelet glycoprotein IIb-IlIa inhibitor, which paralleled with increased adherence of PMA-activated platelets and decreased adherence of glycoprotein IIb-IIIa-blocked platelets to EC in the absence of bacteria; and (e) adherence of the mutant was more sensitive to pre-treatment of EC with plasma and PMA-activated platelets. In conclusion, RNAIII down-regulates S. aureus adherence to fibrinogen under static condition and up-regulates S. aureus adherence to fibronectin and EC under both static and flow conditions. The potentiating role of activated platelets in the presence of plasma in S. aureus adherence to EC is down-regulated by RNAIII, probably due to down-regulation of adherence to fibrinogen, the important plasma protein bridging S. aureus, platelets and EC.

Bacterial Adhesion↗

PubMed2002

Comparative analysis of various platelet glycoprotein IIb/IIIa antagonists on shear-induced platelet activation and adhesion.

Platelet accretion into arterial thrombus in stenotic arterial vessels involves shear-induced platelet activation and adhesion. The Cone and Plate(let) Analyzer (CPA) is designed to simulate such conditions in vitro under a rotating high shear rate in whole blood. In the present study, we evaluated various experimental conditions (including aspirin, temperature, and calcium concentration) and investigated the effects of small molecules along with peptide glycoprotein IIb/IIIa antagonists on platelet adhesion using the CPA system. Concentration-dependent effect of glycoprotein IIb/IIIa antagonists on shear-induced platelet adhesion showed marked differences in potencies: IC50 = 34, 35, 91, 438, and 606 nM for DPC802 (a specific glycoprotein IIb/IIIa antagonist), roxifiban, sibrafiban, lotrafiban, and orbofiban (free acid forms), respectively, and IC50 values of 43, 430, and 5781 nM for abciximab, tirofiban, and eptifibatide, respectively. Parallel study was also conducted to evaluate the effect of glycoprotein IIb/IIIa inhibitors using optical aggregometry. The potency of fibans in blocking shear-induced platelet adhesion correlated well with their binding affinity to the resting and activated glycoprotein IIb/IIIa receptors, as well as their "off-rates". Nevertheless, none of these fibans was able to effectively block shear-induced platelet adhesion at targeted clinical dosing regimens except for abciximab. These data suggest that glycoprotein IIb/IIIa antagonists that show similar efficacy in the inhibition of platelet aggregation in a static in vitro assay may differ substantially in a shear-based system of platelet adhesion. The clinical significance of this phenomenon awaits further investigation.

Abciximab↗

PubMed2002

The efficacy and safety of perioperative low molecular weight heparin substitution in patients on chronic oral anticoagulant therapy undergoing transurethral prostatectomy for bladder outlet obstruction.

PURPOSE: Candidates for prostatectomy who require chronic anticoagulant therapy present a major perioperative management problem due to the threat of significant hemorrhage associated with surgery and the risk of thromboembolism associated with discontinuation of the anticoagulants. We evaluated prospectively a perioperative routine using low molecular weight heparin substitution to allow safe discontinuation of prophylactic oral anticoagulants in patients undergoing transurethral resection of the prostate. MATERIALS AND METHODS: We treated 20 patients on chronic oral anticoagulant therapy who required prostatectomy for bladder outlet obstruction according to a prospective protocol based on exchange of the oral anticoagulants with perioperative injections of low molecular weight heparin and resumption of oral anticoagulants early postoperatively. The safety and efficacy of this regimen were assessed in comparison to a control group comprised of 20 randomly selected nonwarfarin treated patients who underwent prostatectomy during the same period. RESULTS: The need for blood transfusions and mean number of units transfused did not significantly differ between the 2 groups. Due to persistent hematuria routine removal of the catheter was possible only in 9 of 20 patients (45%) in the heparin group compared to 18 of 20 (90%) in the control group. Average catheterization and hospitalization period in the heparin group was 3.2 days and 4.2 days respectively, compared to 2.1 and 2.1 days in the control group, respectively (p <0.01). No long-term hemorrhagic or thromboembolic complications were noted at 3 months postoperatively. CONCLUSIONS: Despite longer hospitalization in the heparin treated group, our substitution protocol is safe and effective.

Administration, Oral↗

PubMed2002

Flow conditions modulate homocysteine induced changes in the expression of endothelial cell genes associated with cell-cell interaction and cytoskeletal rearrangement.

In the present study we analyzed changes in the pattern of gene expression in endothelial cells (HUVEC) exposed to elevated homocysteine levels under flow conditions. RNA samples of untreated and homocysteine treated EC were analyzed using a human cDNA array containing 588 cDNAs relevant to the cardiovascular system. Exposure to homocysteine under flow resulted in altered expression of 8 genes, the alterations of 3 of which were further confirmed by RT-PCR analysis: upregulation of MCP-1 and of profilin-I, and downregulation of alpha-catenin. The increased expression of profilin-I and the decreased expression of alpha-catenin were also confirmed at the protein level by Western blot analysis. Furthermore, immunostaining for alpha-catenin demonstrated complete loss of the protein from intercellular junctions following exposure to homocysteine under flow. All these changes were not observed in cells exposed to homocysteine under static conditions. We show that under flow conditions, homocysteine modulates the expression of genes/proteins involved in actin cytoskeleton reorganization, as well as in the formation and/or maintenance of cell-cell junction, thus contributing to the morphological changes (e.g. cell retraction) reflecting endothelial cell injury.

Base Sequence↗