Integrin-mediated cell adhesion requires extracellular disulfide exchange regulated by protein disulfide isomerase

Cell adhesion to extracellular matrix, mediated by integrin receptors, is crucial for cell survival. Receptor-ligand interaction involves conformational changes in the integrin by a mechanism not fully elucidated. In addition to several direct evidence that there is disulfide re-arrangement of integrins, we previously demonstrated a role for extracellular thiols and protein disulfide isomerase (PDI) in integrin-mediated functions using platelets as model system. Exploring the possible generality of this mechanism, we now show, using three different nucleated cells which depend on adhesion for survival, that non-penetrating blockers of free thiols inhibit α2β1 and α5β1 integrin-mediated adhesion and that disulfide exchange takes place in that process. Inhibiting extracellular PDI mimics thiol blocking. Transfection with WT or enzymatically inactive PDI increased their membrane expression and enhanced cell adhesion, suggesting that PDI level is a limiting factor and that the chaperone activity of the enzyme contributes to adhesion. Exogenously added PDI also enhanced adhesion, further supporting the limiting factor of the enzyme. These data indicate that: a) Dependence on ecto-sulfhydryls for integrin-mediated adhesion is not exclusive to the platelet; b) PDI is involved in integrin-mediated adhesion, catalyzing disulfide bond exchange; c) PDI enhances cell adhesion by both its oxidoreductase activity and as a chaperone.

Regulation of Platelet Aggregation and Adenosine Triphosphate Release In Vitro by 17β-Estradiol and Medroxyprogesterone Acetate in Postmenopausal Women

Clinical studies have suggested that hormone replacement therapy (HRT) may reduce the risk of coronary heart disease in postmenopausal women. Although progestins are commonly added to HRT preparations for uteroprotection, the perceived beneficial cardiovascular effects of HRT are thought to be mediated predominantly by the estrogen component. Platelets play a critical role in the pathogenesis of atherosclerosis and cardiovascular disease and, hence, it is possible that the cardiovascular effects of estrogens are mediated, at least in part, through inhibition of illicit platelet activation. The aim of this study was to examine the effects of sex steroids on adenosine diphosphate (ADP)-induced platelet aggregation and adenosine triphosphate (ATP) release in vitro in postmenopausal women. In addition, the effects of antiestrogens [4-hydroxy tamoxifen (4-OHT) and ICI 182780] and antiprogestins (RU 486 and ZK 98299) were also investigated. Preincubation of platelet-rich plasma (PRP) with antiestrogens or antiprogestins did not alter subsequent platelet aggregation or ATP release in response to ADP. However, preincubation with 17β-estradiol (E2) significantly inhibited ADP-mediated platelet aggregation by a mean (±SEM) of 37% ± 6% (p = 0.02) and ATP release by 82% ± 6% (p = 0.03), an effect that was reversed by the addition of ICI 182780 or 4-OHT but not RU 486 and ZK 98299. Although the progestin medroxyprogesterone acetate (MPA) also significantly inhibited platelet aggregation (by 28% ± 5%, p = 0.02) and ATP release (by 63% ± 9%, p = 0.02), this inhibition was not reversed by the addition of antiprogestins or antiestrogens. These data show that sex steroids can modulate platelet function in vitro. Furthermore, as platelets are devoid of nuclear components, these findings indicate that estrogens may regulate platelet function through binding to a non-nuclear receptor with ligand-binding properties similar or identical to the wild-type receptor. By contrast, MPA appears to exert its effect through a mechanism that does not involve binding to the “classical” progesterone receptor.

Coagulation factor XIII serves as protein disulfide isomerase

Tissue transglutaminase was reported to act as protein disulfide isomerase (PDI). We studied whether plasma transglutaminase – coagulation factor XIII (FXIII) – has PDI activity as well. PDI activity was measured by determining the ability to renature reduced-denatured RNase (rdRNase). We found that FXIII can re-nature rdRNase, with efficiency comparable to commercial PDI. This PDI activity was inhibited by bacitracin. Like tissue transglu-taminase, FXIII-mediated PDI activity is independent of its transglutaminase activity and is located on the A subunit. Surface-associated PDI has been previously shown to catalyse two distinct functions: transnitrosation with subsequent release of intracellular nitric oxide and disulfide bond rearrangement during platelet integrin ligation. Our results imply that FXIII-PDI activity may have a role in platelet function.

Evaluating platelet function disorders in children with bleeding tendency - A single center study

Platelet function disorders (PFDs) are a common cause of mild bleeding tendency. However, they cannot be recognized by standard screening studies. The gold standard test for PFD is platelet aggregation, performed by light transmission aggregometry (LTA). A newer and less validated method is the closure time (CT), performed by the platelet function Analyzer 100 (PFA-100). Data regarding the validity of these tests in children are limited. The aim of this study was to evaluate the usefulness of LTA and PFA-100 for the diagnosis of pediatric patients with bleeding tendency. This retrospective study included patients one month-18 year old that had LTA tests performed at the coagulation laboratory of Rabin Medical Center between the years 2006-2015. Bleeding severity was assessed using a pediatric bleeding score. Patients were excluded from analysis if they had thrombocytopenia, thrombocytosis or coagulation factors deficiencies. One hundred and thirty-seven (137) patients were included in the analysis. The median age was 7.5 years (range one month-18 years). Most patients (93%) had a bleeding score of 2 or more. Abnormal LTA was found in 40% and prolonged CT in 23% of the patients. Abnormal LTA was significantly more common in patients with a bleeding score of 2 or more compared to patients with a lower bleeding scores (P = 0.04). No significant correlation was found between the bleeding severity and the number of agonists which induced abnormal responses (p = 0.52) or the CT (p = 0.35). Furthermore, no correlation was found between abnormal LTA and prolonged CT. To conclude, we were able to diagnose 40% of children who presented with bleeding tendency with platelet aggregation defects by LTA. Abnormal LTA was significantly more prevalent in patients with a bleeding score of 2 and above. In contrast, CT was not found to be sensitive as a screening tool for PFD. Therefore, our data extend the validity of the use of LTA for the evaluation of pediatric patients with bleeding tendency.

The role of protein disulfide isomerase in the post-ligation phase of β3 integrin-dependent cell adhesion

INTRODUCTION

Protein disulfide isomerase (PDI) catalyzes disulfide bond exchange. It is crucial for integrin-mediated platelet adhesion and aggregation and disulfide bond exchange is necessary for αIIbβ3 and αvβ3 activation. However, the role of disulfide bond exchange and PDI in the post-ligation phase of αIIbβ3 and αvβ3 mediated cell adhesion has yet to be determined.

METHODS

To investigate a possible such role, we expressed wild type (WT) human αIIb and either WT human β3, or β3 harboring single or double cysteine to serine substitutions disrupting Cys473-Cys503 or Cys523-Cys544 bonds, in baby hamster kidney (BHK) cells, leading to expression of both human αIIbβ3 and a chimeric hamster/human αvβ3. Adhesion to fibrinogen-coated wells was studied in the presence or absence of bacitracin, a PDI inhibitor, with and without an αvβ3 blocker.

RESULTS

Flow cytometry showed WT and mutant αIIbβ3 expression in BHK cells and indicated that mutated αIIbβ3 receptors were constitutively active while WT αIIbβ3 was inactive. Both αIIbβ3 and αvβ3 integrins, WT and mutants, mediated adhesion to fibrinogen as shown by reduced but still substantial adhesion following treatment with the αvβ3 blocker. Mutated αIIbβ3 integrins disrupted in the Cys523-Cys544 bond still depended on PDI for adhesion as shown by the inhibitory effect of bacitracin in the presence of the αvβ3 blocker. Mutated integrins disrupted in the Cys473-Cys503 bond showed a similar trend.

CONCLUSIONS

PDI-mediated disulfide bond exchange plays a pivotal role in the post-ligation phase of αIIbβ3-mediated adhesion to fibrinogen, while this step in αvβ3-mediated adhesion is independent of disulfide exchange.

Acquired thrombasthenia due to inhibitory effect of glycoprotein IIbIIIa autoantibodies

BACKGROUND

A 75 year old patient presenting with mucocutaneous bleeding was diagnosed with acquired thrombasthenia. The diagnosis was based on lack of platelet aggregation with adenosine diphosphate (ADP), arachidonic acid and collagen, and normal aggregation induced by ristocetin.

OBJECTIVE

To study the mechanism of platelet function inhibition in a patient with acquired thrombasthenia.

METHODS

Aggregation assays of platelets from the patient and healthy controls were performed. In addition, anti-glycoprotein (GP) IIbIIIa antibodies bindingto normal in the presence or absence of the patient's serum was by flow cytometry.

RESULTS

Aggregation of normal platelets in the presence of patient's plasma was inhibited four- and 2.5-fold in the presence of ADP and arachidonic acid respectively, while collagen-induced aggregation was completely abolished. Ristocetin-induced aggregation was normal. The patient's serum inhibited binding of commercial anti-glycoprotein IIbIIIa antibodies to normal platelets twofold by flow cytometry. Treatment with anti-CD20 monoclonal antibody (rituximab) normalized the patient's platelet aggregation.

CONCLUSIONS

These results suggest that the patient developed inhibitory anti-GPIIbIIIa autoantibodies that caused acquired thrombasthenia.

Factor XIII improves platelet adhesion to fibrinogen by protein disulfide isomerase-mediated activity

BACKGROUND

Factor XIII (FXIII), a plasma pro-transglutaminase, consists of two A subunits and two B subunits (FXIIIA2B2). Following activation by thrombin, it cross-links fibrin chains at the final step of coagulation. We previously reported that FXIII subunit A (FXIIIA) serves as a protein disulfide isomerase (PDI), and that PDI promotes platelet adhesion and aggregation.

OBJECTIVE

This study sought to examine possible mechanistic effect of FXIII on platelet adhesion to fibrinogen; specifically, the role of its PDI activity.

METHODS

Ex vivo experiments: Blood platelets derived from five patients with hereditary FXIIIA deficiency before and after treatment with Fibrogammin-P (FXIIIA2B2 concentrate) were washed and incubated on immobilized fibrinogen. Bound platelets were stained and counted by microscopy. In vitro experiments: Platelets derived from patients before treatment and five healthy controls were washed and analyzed for adhesion in the presence or absence of Fibrogammin-P or recombinant FXIII (FXIIIA2 concentrate).

RESULTS

In ex vivo experiments, one hour after Fibrogammin-P treatment, mean (±SEM) platelet adhesion to fibrinogen increased by 27±2.32% (p<0.001). In in vitro experiments, treatment with Fibrogammin-P or recombinant FXIII (10IU/mL each) enhanced platelet adhesion to fibrinogen (in patients, by 29.95±6.7% and 29.05±5.3%, respectively; in controls, by 26.06±3.24% and 26.91±4.72, respectively; p<0.04 for all). Iodoacetamide-treated FXIII (I-FXIII), where transglutaminase activity is blocked, showed similar enhanced adhesion as untreated FXIII. By contrast, addition of an antibody that specifically blocks FXIIIA-PDI activity inhibited FXIII-mediated platelet adhesion to fibrinogen by 65%.

CONCLUSION

These findings indicate that FXIII-induced enhancement of platelet adhesion is mediated by FXIII-PDI activity.

Staphylococcal extracellular adherence protein induces platelet activation by stimulation of thiol isomerases

OBJECTIVE

Staphylococcus aureus can induce platelet aggregation. The rapidity and degree of this correlates with the severity of disseminated intravascular coagulation, and depends on platelet peptidoglycans. Surface-located thiol isomerases play an important role in platelet activation. The staphylococcal extracellular adherence protein (Eap) functions as an adhesin for host plasma proteins. Therefore we tested the effect of Eap on platelets.

METHODS AND RESULTS

We found a strong stimulation of the platelet-surface thiol isomerases protein disulfide isomerase and endoplasmic reticulum stress proteins 57 and 72 by Eap. Eap induced thiol isomerase-dependent glycoprotein IIb/IIIa activation, granule secretion, and platelet aggregation. Treatment of platelets with thiol blockers, bacitracin, and anti-protein disulfide isomerase antibody inhibited Eap-induced platelet activation. The effect of Eap on platelets and protein disulfide isomerase activity was completely blocked by glycosaminoglycans. Inhibition by the hydrophobic probe bis(1-anilinonaphthalene 8-sulfonate) suggested the involvement of hydrophobic sites in protein disulfide isomerase and platelet activation by Eap.

CONCLUSIONS

In the present study, we found an additional and yet unknown mechanism of platelet activation by a bacterial adhesin, involving stimulation of thiol isomerases. The thiol isomerase stimulatory and prothrombotic features of a microbial secreted protein are probably not restricted to S aureus and Eap. Because many microorganisms are coated with amyloidogenic proteins, it is likely that the observed mechanism is a more general one.

Extracellular protein disulfide isomerase regulates feedback activation of platelet thrombin generation via modulation of coagulation factor binding

BACKGROUND

Protein disulfide isomerase (PDI) controls platelet integrin function, tissue-factor (TF) activation, and concentrates at fibrin and thrombus formation sites of vascular injury.

OBJECTIVE

To investigate the involvement of surface thiol isomerases and especially PDI, in thrombin-mediated thrombin amplification on human platelets.

METHODS/RESULTS

Using a newly developed thrombin-dependent platelet thrombin generation assay, we observed that the feedback activation of thrombin generation on the platelet surface does not depend on TF, as anti-TF antibodies inhibiting TF-induced thrombin formation in platelet-depleted plasma had no effect compared with vehicle-treated controls. Feedback activation of thrombin generation in the presence of platelets was significantly diminished by membrane impermeant thiol blockers or by the thiol isomerase-inhibitors bacitracin and anti-PDI antibody RL90, respectively. Platelet thrombin formation depends on binding of coagulation factors to the platelet surface. Therefore, involvement of thiol isomerases in this binding was investigated. As shown by confocal microscopy and flow cytometry, thrombin-stimulated platelets exhibited increased surface-associated PDI as well as extracellular disulfide reductase activity compared with unstimulated platelets. Flow cytometric analysis revealed that membrane impermeant thiol blockers or PDI inhibitors, which had been added after platelet stimulation and after phosphatidylserine exposure to exclude their influence on primary platelet activation, significantly inhibited binding of all coagulation factors to thrombin-stimulated platelets.

CONCLUSIONS

Thus, surface-associated PDI is an important regulator of coagulation factor ligation to thrombin-stimulated platelets and of subsequent feedback activation of platelet thrombin generation. Cell surface thiol isomerases might be therefore powerful targets to control hemostasis and thrombosis.

[Laboratory evaluation of lupus anticoagulant in Israel]

Lupus anticoagulants (LAC) are antibodies which are detected by a prolongation of phospholipid-dependent coagulation assays, and are associated with thrombotic events and pregnancy complications in patients with the antiphospholipid syndrome. The antiphospholipid syndrome is defined by arterial or venous thrombosis and/or pregnancy morbidity and by laboratory diagnosis of antiphospholipid antibodies. The laboratory diagnosis is based on LAC and/or anticardiolipin and/or anti-beta2-glycoprotein I antibodies present in plasma, on two or more occasions at least 12 weeks apart. ALthough the presence of LAC correlates best with thrombosis, the Laboratory testing of LAC is not well standardized. In this article, the Laboratory evaluation of LAC will be explained, including the different tests that are recommended by the Israeli Sub-committee of Thrombosis and Hemostasis Laboratories, the possibility to evaluate LAC in patients treated with antithrombotic therapy, and how to report and interpret the results.

Effect of imatinib on the signal transduction cascade regulating telomerase activity in K562 (BCR-ABL-positive) cells sensitive and resistant to imatinib

OBJECTIVE

Imatinib mesylate (IM) is a tyrosine kinase inhibitor selective for BCR-ABL and indicated for the treatment of chronic myeloid leukemia. It has recently been demonstrated that IM also targets other cellular components. Considering the significant role of telomerase in malignant transformation, we studied the effect of IM on telomerase activity (TA) and regulation in BCR-ABL-positive and -negative cells, sensitive and resistant to IM.

MATERIALS AND METHODS

Through combining telomeric repeat amplification protocol for detecting TA, reverse transcription polymerase chain reaction and Western blots for detecting RNA and protein levels of telomerase regulating proteins and fluorescence-activated cell sorting analysis, we showed that IM targets telomerase and the signal transduction cascade upstream of it.

RESULTS

IM significantly inhibited TA in BCR-ABL-positive and -negative cells and in chronic myeloid leukemia patients. TA inhibition was also observed in BCR-ABL positive cells resistant to IM at drug concentrations that did not lead to a reduction in BCR-ABL expression. In addition, a reduction in phosphorylated AKT and phosphorylated PDK-1 was also detected following IM incubation.

CONCLUSIONS

We demonstrate an inhibitory effect of IM on TA and on the AKT/PDK pathway. Because this effect was observed in cell expressing the BCR-ABL protein as well as cells not expressing it, and in cells sensitive as well as resistant to IM, it is reasonable to assume that the inhibitory effect of IM on TA is not mediated through known IM targets. The results of this study show that cells resistant to IM with regard to its effect on BCR-ABL could still be sensitive to IM treatment regarding other cellular components.

Coagulation factor XIII serves as protein disulfide isomerase

Tissue transglutaminase was reported to act as protein disulfide isomerase (PDI). We studied whether plasma transglutaminase - coagulation factor XIII (FXIII) - has PDI activity as well. PDI activity was measured by determining the ability to renature reduced-denatured RNase (rdRNase). We found that FXIII can renature rdRNase, with efficiency comparable to commercial PDI. This PDI activity was inhibited by bacitracin. Like tissue transglutaminase, FXIII-mediated PDI activity is independent of its transglutaminase activity and is located on the A subunit. Surface-associated PDI has been previously shown to catalyse two distinct functions: transnitrosation with subsequent release of intracellular nitric oxide and disulfide bond rearrangement during platelet integrin ligation. Our results imply that FXIII-PDI activity may have a role in platelet function.

Collagen binding induces changes in its platelet integrin receptor alpha2beta1

Integrins can signal upon binding of their ligand, presumably because of conformational changes induced by ligand-binding. It has been postulated that ligand binding causes changes in the affinity of the integrin to its ligand. In order to test for ligand-induced change in the affinity of platelet alpha2beta1 to collagen, labelled viable platelets were passaged through a column of fibrillar collagen and stringent lysis conditions were used to remove all low-affinity receptors. A high-affinity fraction left on the collagen could be eluted with dithiothreitol (DTT) and 2% Sodium dodecyl sulfate (SDS). Antibodies raised against this fraction, identified alpha2beta1 by Western-blotting. Functional tests performed with the antibodies confirmed the involvement of the high-affinity proteins in platelet-collagen interactions attributed to alpha2beta1: inhibition of collagen-specific platelet adhesion and aggregation. EDTA, chaotropic agents or low pH did not elute the high affinity fraction of alpha2beta1. However, DTT followed by acetic acid did, which indicates that the steps necessary to disrupt the high-affinity collagen alpha2beta1 bond are reduction of disulfide bond(s) followed by disruption of electrostatic interactions. Our data 2 1 suggest that (i) ligand binding induces the formation of a new disulfide bond in a fraction of alpha2beta1, (ii) that this bond is an intrareceptor, and (iii) that this change increases the affinity of the receptor to its ligand.

Antiphospholipid antibodies may be a new prognostic parameter in aggressive non-Hodgkin's lymphoma

OBJECTIVES

Patients with malignancies have an increased prevalence of antiphospholipid antibodies (APA). The aim of this study was to determine the prevalence of IgG, IgM, and IgA anticardiolipin antibodies (aCL) and anti-beta-2 glycoprotein I antibodies (anti-beta2-GPI) in patients with non-Hodgkin's lymphoma (NHL), and to investigate their clinical and prognostic significance.

METHODS

The study group included 86 patients with NHL. Enzyme-linked immunosorbent assay kits were used to measure the concentrations of aCL and anti-beta2-GPI, and coagulation tests, to measure lupus anticoagulant (LAC) activity. Blood was collected at diagnosis in all patients and at follow-up in 15. Median follow-up time was 1.9 yr.

RESULTS

Elevated APA levels were found in 35 patients (41%) at diagnosis: one patient aCL IgG, five patients aCL IgM, five aCL IgA, one anti-beta2-GPI IgG, 14 anti-beta2-GPI IgM, and 19 anti-beta2-GPI IgA; LAC activity was found in three of 67 patients (4.5%). There was no significant correlation between elevated APA levels and patient's age or sex, disease stage or grade, bone marrow involvement, B symptoms, serum lactate dehydrogenase levels, serum beta2 microglobulin levels, International Prognostic Index (IPI) score, performance status, type of treatment, or response to treatment. There was a correlation between elevated APA and absence of extranodal disease (P = 0.045). A strong negative correlation was found between elevated APA at diagnosis and survival time. Two-year survival was 90 +/- 5% for patients without APA at diagnosis compared with 63 +/- 11% for patients with an elevated APA levels (P = 0.0025). APA added to the predictive value of IPI for event-free and overall survival.

CONCLUSIONS

APA are elevated in 41% of NHL patients at diagnosis and are correlated with shortened survival. Their level may serve as an independent prognostic variable in aggressive NHL.

Increased Thromboembolic Events After Lung Transplantation

BACKGROUND

Lung transplantation is a good therapeutic option for end-stage lung disease. Data on thromboembolic complications following lung transplantation are scarce.

STUDY OBJECTIVES

To evaluate the incidence of thromboembolic events following lung transplantation, and to determine their possible association with hypercoagulable state.

DESIGN

Retrospective study in a single, tertiary-care, university-affiliated referral center.

SUBJECTS AND METHOD

The records of 70 patients who underwent lung transplantation in our institution between September 1997 and September 2003 were reviewed for thromboembolic complications. Parameters pertaining to risk of thrombophilia were measured in the patients with thromboembolic complications.

RESULTS

Thromboembolic complications developed in 6 of the 70 patients (8.6%) at 4 to 24 months after transplantation: deep vein thrombosis (DVT) in 2 patients, pulmonary embolism (PE) in 1 patient, both DVT and PE in 1 patient, and retinal vein thrombosis in 2 patients. The fibrinogen level was elevated in all six patients, and factor VIII, IX, and/or XI levels were elevated in five patients. Heterozygosity for 5 10-methylene tetrahydrofolate reductase was documented in two patients, and mutation for factor II or factor V-Leiden mutation was found in one patient. Levels of protein C and protein S and activated protein C resistance were within normal range in all patients. Four patients had mildly elevated levels of at least one antiphospholipid antibody; none had a positive lupus anticoagulant test result. Overall, all patients demonstrated abnormalities on hypercoagulability tests.

CONCLUSIONS

Thromboembolic complications occur at a high rate (8.6%) in lung transplant recipients and are associated with abnormalities in hypercoagulability. The cause remains unclear. Our results should prompt a high index of suspicion for these potentially fatal complications, which would lead to early diagnosis and successful treatment.

Molecular characterization of an human monoclonal antibody that interacts with a sulfated tyrosine-containing epitope of the GPIb receptor and inhibits platelet functions

Modification of tyrosine residues in extracellular proteins by a sulfate moity plays an important role in many ligand/receptors interactions. In the present work, we describe a unique human monoclonal antibody, termed Y1-scFv, that is specific for a sulfated epitope in the platelat receptor GPIb. The Y1-scFv single chain antibody (scFv) competes with von Willebrand factor (vWF) for binding to human platelets and thus effectively inhibits platelet aggregation. Limited proteolysis of GPIb molecule, using the endoproteases, mocarhagin and cathepsin G, revealed that a seven amino-acid epitope, Tyr-276 to Glu-282, contains the recognition site for Y1-scFv. This GPIb region contains three sulfated tyrosine residues. Binding studies of Y1-scFv to cells and to synthetic peptides in vitro indicated that of the seven residues comprising the epitope only sulfo-Tyr-276 and adjacent Asp-277 are critical for the interaction. To identify the reciprocal sequences in the antibody that recognize the sulfated epitope, we introduced mutations within the complementary-determining region of the heavy chain (CDR3H) of Y1-scFv (MRAPVI). Arginine residue in the second position was critical for the binding. Moreover, a mutant, containing two sequential arginine residues, in the second and third positions of the CDR3H (MRRPVI), showed a nine-fold increased binding to GPIb. This antibody mutant also demonstrated a significant increase in inhibition of vWF-dependent platelet aggregation and adhesion under flow. In conclusion, this unique antibody and mutants, that recognize a sulfated epitope in GP1b receptor, efficiently inhibited platelet adhesion and aggregation, making it a candidate for a new anti-thrombotic agent.

Changes in autoimmune markers of the anti-cardiolipin syndrome on days of extreme geomamagnetic activity

The possible relation between various biological or medical phenomena and changes in environmental physical activity, such as Solar, Geomagnetic Activity (GMA); Cosmic Ray; Proton, and other particle flux, have been reported. These phenomena seem to be reflected, among others, in the immune system, resulting in changes in immunoglobulin (Ig) levels or outbursts of epidemics.

AIM

to examine a possible association of GMA with another aspect of the immune system--autoimmunity. Fluctuations of levels of anticardiolipin (IgG; IgM, IgA subtypes) and lupus anticoagulant (Kaulin clotting time and Dilute Russell's viper venom time) autoantibodies, serving as anticardiolipin syndrome (ACLS) markers, were monitored during days of severe GMA storms and compared with those of lowest/quiet GMA days. Cosmophysical data were obtained from the NOAA National Space Service Center and the National Geophysical Data Center, USA.

RESULTS

A significant rise in the levels of anti beta2Gp1-IgA (p = 0.0001); and KCT (p = 0.019) was observed on days of the GMA storms.

CONCLUSION

On days of major GMA storms, significant changes in the autoimmune marker levels of ACLS were observed compared with quiet days. An involvement of those changes in clinical events related to GMA storms is possible.

Effect of urinary versus recombinant follicle-stimulating hormone on platelet function and other hemostatic variables in controlled ovarian hyperstimulation

OBJECTIVE

To determine the effect of urinary versus recombinant FSH on platelet function and hemostatic variables in women undergoing controlled ovarian hyperstimulation cycles.

DESIGN

Randomized clinical study.

SETTING

Major university-based infertility and in vitro fertilization unit and hemostasis laboratory.

PATIENT(S)

Ten healthy women (in vitro study), and 24 women undergoing routine controlled ovarian hyperstimulation cycles (in vivo study), randomly assigned to receive either urinary (u-FSH) or recombinant gonadotropin (r-FSH).

INTERVENTION(S)

In vitro study: effect of preincubation of plasma with u-FSH or r-FSH, in the presence or absence of estradiol, on platelet function and coagulation parameters. In vivo study: Changes in platelet function and coagulation parameters after treatment with u-FSH or r-FSH during controlled ovarian hyperstimulation cycles.

MAIN OUTCOME MEASURE(S)

Platelet aggregation and ATP release, activated protein C resistance ratio, free protein S.

RESULT(S)

In vitro study: Platelet aggregation and ATP release were significantly inhibited by u-FSH relative to r-FSH in both the presence and absence of estradiol (P=.047). In vivo study: Platelet function was significantly inhibited after treatment with u-FSH (P=.05) but not with r-FSH. In both studies, small changes of minor clinical significance were noted in activated protein C resistance and free protein S levels.

CONCLUSION(S)

The different platelet response to u-FSH and r-FSH may have clinical implications in selected patients, especially those at risk of thromboembolic complications, in decisions regarding the appropriate medication for controlled ovarian hyperstimulation cycles.

Central venous line thrombosis in children and young adults with thalassemia major

High doses of intravenous deferoxamine via central venous line (CVL) has recently been shown to improve survival in patients with noncompliant thalassemia major (TM). The aim of this retrospective study was to evaluate the extent of CVL-related thrombosis and to determine the presence of prothrombotic factors in children and young patients with TM on such a regimen. Twenty-three patients (median age 13, range 5-25 years) with TM in whom a tunneled CVL was inserted for intensification of iron chelation were evaluated for signs and symptoms of thrombosis and for inherited and acquired risk factors of thrombosis. Mean duration of CVL placement was 37 +/- 31 months (range 6-98 months). Eight patients (35%) had CVL-related thrombosis diagnosed clinically or by echocardiography. Nine patients (39%) had prothrombotic factors, but the thrombosis subgroup did not differ from the other group in age, platelet counts, duration of CVL placement, or the presence of predisposing prothrombotic factors. Based on the high rate of CVL-related thrombosis, routine monitoring is suggested for CVL thrombosis in this population.

Administration of eptifibatide to acute coronary syndrome patients receiving enoxaparin or unfractionated heparin: effect on platelet function and thrombus formation

OBJECTIVES

The goal of this study was to compare the antithrombotic effects of enoxaparin versus unfractionated heparin (UFH) when combined with eptifibatide in acute coronary syndrome (ACS) patients.

BACKGROUND

An increasing number of high-risk ACS patients are treated with low-molecular-weight heparin and a glycoprotein (GP) IIb/IIIa inhibitor. There is a paucity of data regarding the antithrombotic properties of such a combination as compared with UFH and GP IIb/IIIa inhibitors.

METHODS

Twenty-six ACS patients scheduled to undergo coronary angiography were treated with subcutaneous enoxaparin (n = 13) or intravenous UFH (n = 13). All patients received eptifibatide just before coronary angiography. Antithrombotic effects were assessed as changes in platelet-thrombus formation using the Badimon ex vivo perfusion chamber. Perfusions were carried out at a high shear rate (HSR) and a low shear rate (LSR). Patients underwent two perfusion studies: at baseline (under enoxaparin or UFH) and 10 min after the eptifibatide bolus. Platelet function was evaluated by ADP-induced platelet aggregation and the rapid platelet function analyzer.

RESULTS

Both therapeutic combinations achieved a marked reduction in platelet aggregation after eptifibatide (83% to 89.7% reduction in the enoxaparin-eptifibatide group and 77.8% to 85.5% reduction in the UFH-eptifibatide group, inter-group differences not significant). Both groups also demonstrated marked reductions in thrombus formation, but the reductions achieved in the enoxaparin-eptifibatide group were significantly higher than those achieved in the UFH-eptifibatide group (HSR: 75.6% reduction vs. 63.9%, respectively, p = 0.01; LSR: 79.7% reduction vs. 66.1%, respectively, p = 0.0001).

CONCLUSIONS

The combination of eptifibatide with enoxaparin appears to have a more potent antithrombotic effect than that of eptifibatide and UFH in the doses tested.

Enzymatically catalyzed disulfide exchange is required for platelet adhesion to collagen via integrin alpha2beta1

Integrin alpha2beta1 is the principal adhesive receptor for collagen but platelets also adhere through glycoprotein VI (GPVI). Integrin alphaIIbbeta3 may augment platelet adhesion. We have shown that disulfide exchange is necessary for platelet adhesion to fibrinogen, fibronectin, and collagen. However 2 questions remained: (1) Can activated alphaIIbbeta3 explain the observed role of disulfide exchange in adhesion to collagen, or is this role common to other integrins? (2) Is disulfide dependence specific to the integrin receptors or shared with GPVI? To discriminate adhesive functions of alpha2beta1 from those of alphaIIbbeta3 we used Glanzmann platelets and alphaIIbbeta3-specific antibodies applied to normal platelets. To resolve adhesive events mediated by alpha2beta1 from those of GPVI we used synthetic peptides specific to each receptor. We addressed direct integrin ligation using purified alpha2beta1 and recombinant I domain. We observed the following: adhesion to the alpha2beta1-specific peptide was disulfide-exchange dependent and protein disulfide isomerase (PDI) mediated; membrane-impermeant thiol blockers inhibited alpha2beta1, but not GPVI mediated, adhesion; direct blockade of PDI revealed that it is involved in adhesion through alpha2beta1 but not GPVI; and purified alpha2beta1, but not recombinant I domain, depended on free thiols for ligation. These data suggest that the enzymatically catalyzed adhesion-associated reorganization of disulfide bonds is common to members of the integrin family and specific to this family.

Function-modulating human monoclonal antibodies against platelet-membrane receptors isolated from a phage-display library

Monoclonal antibodies to platelet membrane receptors have been used extensively for analysis of receptor structure and function. Function-blocking human antibodies are being used for the development of antiplatelet drugs. We isolated human monoclonal antibodies from a library of single-chain Fv (scFv) antibodies displayed on the surface of filamentous phage, by selection on whole platelets. Eight different platelet-binding clones were isolated, of which three bound to the platelet-membrane glycoprotein (GP) GPIb in an ELISA assay. Specific elution with a recombinant polypeptide of von Willebrand factor (VWF) spanning the GPIbalpha binding site, yielded the same three phage clones. Two of the three anti-GPIb clones could be purified as scFv monoclonal antibodies, and they competed with each other for binding to intact platelets, suggesting that they bind at or near the same site on GPIb. Their binding affinities differed, however, and the clone with higher affinity inhibited ristocetin-induced platelet aggregation. These data indicate that selection from a phage display library of human scFvs using whole platelets can be applied for the isolation of functional antiplatelet-GPIb antibodies useful for the development of new therapeutic and diagnostic strategies.

Sustained integrin ligation involves extracellular free sulfhydryls and enzymatically catalyzed disulfide exchange

Studies have suggested a pivotal role for free sulfhydryls in platelet integrin function, and enzyme-mediated reduction of disulfide bonds on platelets has been implicated. The platelet fibrinogen receptor alpha(IIb)beta(3) is the best-studied platelet integrin and serves as a model system for studying the structure-function relation in this family of adhesion receptors. The demonstration of free sulfhydryls on the exofacial domain of purified alpha(IIb)beta(3), specifically in its activated conformation, prompted us to explore the potential for activation-dependent, enzymatically catalyzed thiol expression on intact platelets and the possible role of surface-associated protein disulfide isomerase (PDI) in alpha(IIb)beta(3) ligation. Using the membrane-impermeant sulfhydryl blocker para-chloromercuriphenyl sulfonate, the inhibitor of disulfide exchange bacitracin, and the monoclonal anti-PDI antibody RL90, we examined fibrinogen binding to alpha(IIb)beta(3) as well as ligation-induced allosteric changes in the conformation of alpha(IIb)beta(3). We sought to distinguish the possible involvement of disulfide exchange in agonist-induced platelet stimulation from its role in integrin ligation. Analysis of the role of free thiols in platelet aggregation suggested a thiol-independent initial ligation followed by a thiol-dependent stabilization of binding. Flow cytometric analysis showed that sustained binding of fibrinogen, as well as expression of ligand-induced binding site epitopes and ligand-bound conformation, depended on free thiols and disulfide exchange. Expression of P-selectin was minimally affected, even with complete inhibition of alpha(IIb)beta(3) function. These data indicate that although agonist-induced platelet stimulation is independent of ecto-sulfhydryls, engagement of integrin alpha(IIb)beta(3) on the intact platelet depends totally on their enzymatically catalyzed surface expression.

Impaired platelet aggregation in melanoma patients treated with interferon-alpha-2b adjuvant therapy

BACKGROUND

High-dose interferon (INF)- alpha-2b is the only Food and Drug Administration-approved adjuvant treatment for patients with melanoma who are at high risk of recurrence. Although circumstantial evidence points to a potentially harmful effect of INF-alpha-2b on platelet function, to the authors' knowledge this has never been studied in humans.

METHODS

The study group was comprised of patients who had undergone surgery for melanoma and were free of disease but at a high risk of recurrence. All patients were candidates for adjuvant INF treatment (high-dose) and were undergoing routine evaluation to which platelet aggregation was added. Aggregation was triggered in standard fashion with adenosine diphosphate, epinephrine, collagen, thrombin, arachidonic acid, and ristocetin. Blood samples were drawn immediately before treatment, during the intravenous loading phase, during the subcutaneous maintenance phase, and 3-6 weeks after cessation of treatment. Patients receiving low-dose, long-standing INF-alpha-2b treatment also were tested. All results at each phase were compared with those of normal controls.

RESULTS

In those patients receiving high-dose INF-alpha-2b, ristocetin-induced aggregation did not appear to be affected. However, the response to > or = 1 of the other agonists was impaired in 5 of 6 samples during loading, 14 of 15 samples during the maintenance phase, and 8 of 13 samples after treatment, compared with only 1 of 8 samples before treatment (P = 0.025, P = 0.002, and P = 0.067, respectively). During treatment with low-dose INF, platelet function was affected to a lesser extent.

CONCLUSIONS

INF treatment in melanoma patients appears to be associated with severe impairment of platelet aggregation, which appears to be dose-dependent and cumulative-dose-dependent. This is not detectable by the standard coagulation profile. This effect has significant implications in the event of accidental injury or elective surgery. The antiaggregation activity may be the mechanism by which INF delays, reduces, or prevents the formation of melanoma metastases.

Changes in the effects of interleukin-1beta and tumor necrosis factor-alpha on platelet activation in early pregnancy

Platelets are known to be activated in normal pregnancy, and are further activated in pathological pregnancy states, such as preeclampsia. The factors controlling platelet activation are unknown, but cytokines, such as interleukin 1beta (IL-1beta) and tumor necrosis-alpha (TNF-alpha) have been found to affect platelet function and are believed to be involved in early pregnancy. We assessed the effects of these cytokines on platelets from women at various stages of pregnancy. We compared two methods: platelet in vitro aggregation by aggregometry, and platelet P-selectin expression by flow cytometry. IL-1beta and TNF-alpha had no effect on the in vitro aggregation and P-selectin expression of platelets from women in the first trimester of pregnancy as compared to the inhibitory effects of both in late pregnancy. We conclude that maternal platelet function undergoes a marked change throughout pregnancy.

Effect of thrombophylaxis on uterine and fetal circulation in pregnant women with a history of pregnancy complications

PURPOSE

The aim of this study was to investigate the effect of thromboprophylactic therapy on fetal and maternal Doppler flow parameters in pregnant women with severe complications in previous pregnancies and evidence of acquired or congenital thrombophilia in the current pregnancy.

METHODS

Sixty-five patients with a history of recurrent abortions, intrauterine fetal death, intrauterine growth restriction (IUGR), and severe early-onset preeclampsia were tested for the presence of acquired or congenital thrombophilia. Those with positive findings were prescribed low-dose aspirin plus low-molecular-weight heparin (LMWH) (enoxaparin); the remainder received low-dose aspirin only. A Doppler flow study was performed before and after treatment and in the third trimester of pregnancy.

RESULTS

Of the 65 pregnancies, four ended in spontaneous abortion and were excluded from the analysis. Of the 61 women with completed pregnancies, 37 (61%) had evidence of acquired or congenital thrombophilia: 22 (36%) protein S deficiency; 1 (2%) protein C deficiency; 2 (3%) activated protein C resistance (APC-R); 2 (3%) IgG for antiphospholipid antibodies; 1 (2%) circulating anticoagulant; and 9 (15%) a combined defect. This group showed a significant decrease in mean uterine artery pulsatility index (PI) before and after treatment (1.32+/-0.36 vs. 1.04+/-0.23, P=.006), whereas the remaining 24 patients treated with low-dose aspirin only had nonsignificant changes. Pearson's correlation test yielded no correlations of the pregnancy outcome parameters with Doppler flow values in the umbilical or uterine arteries.

CONCLUSIONS

Thromboprophylactic therapy transiently improves maternal circulation parameters in patients with thrombophilia at risk of fetal loss and other severe complications of pregnancy, but not in correlation with their pregnancy outcome. Therefore, Doppler examination of maternofetal circulation in the second trimester is not predictive of pregnancy outcome.

Regulation of platelet aggregation and adenosine triphosphate release in vitro by 17beta-estradiol and medroxyprogesterone acetate in postmenopausal women

Clinical studies have suggested that hormone replacement therapy (HRT) may reduce the risk of coronary heart disease in postmenopausal women. Although progestins are commonly added to HRT preparations for uteroprotection, the perceived beneficial cardiovascular effects of HRT are thought to be mediated predominantly by the estrogen component. Platelets play a critical role in the pathogenesis of atherosclerosis and cardiovascular disease and, hence, it is possible that the cardiovascular effects of estrogens are mediated, at least in part, through inhibition of illicit platelet activation. The aim of this study was to examine the effects of sex steroids on adenosine diphosphate (ADP)-induced platelet aggregation and adenosine triphosphate (ATP) release in vitro in postmenopausal women. In addition, the effects of antiestrogens 14-hydroxy tamoxifen (4-OHT) and ICI 182780] and antiprogestins (RU 486 and ZK 98299) were also investigated. Preincubation of platelet-rich plasma (PRP) with antiestrogens or antiprogestins did not alter subsequent platelet aggregation or ATP release in response to ADP. However, preincubation with 17beta-estradiol (E2) significantly inhibited ADP-mediated platelet aggregation by a mean (+/-SEM) of 37%+/-6% (p = 0.02) and ATP release by 82%+/-6% (p = 0.03), an effect that was reversed by the addition of ICI 182780 or 4-OHT but not RU 486 and ZK 98299. Although the progestin medroxyprogesterone acetate (MPA) also significantly inhibited platelet aggregation (by 28%+/-5%, p = 0.02) and ATP release (by 63%+/-9%, p = 0.02), this inhibition was not reversed by the addition of antiprogestins or antiestrogens. These data show that sex steroids can modulate platelet function in vitro. Furthermore, as platelets are devoid of nuclear components, these findings indicate that estrogens may regulate platelet function through binding to a non-nuclear receptor with ligand-binding properties similar or identical to the wild-type receptor. By contrast, MPA appears to exert its effect through a mechanism that does not involve binding to the "classical" progesterone receptor.

Protein disulfide isomerase mediates integrin-dependent adhesion

Cell adhesion is mediated by the integrin adhesion receptors. Receptor-ligand interaction involves conformational changes in the receptor, but the underlying mechanism remains unclear. Our earlier work implied a role for sulfhydryls in integrin response to ligand binding in the intact blood platelet. We now show that non-penetrating blockers of free sulfhydryls inhibit beta(1) and beta(3) integrin-mediated platelet adhesion regardless of the affinity state of the integrin. Removal of the inhibitors prior to adhesion fully restores adhesion despite the irreversible nature of inhibitor-thiol interaction, indicating sulfhydryl exposure in response to adhesion. We further show that blocking protein disulfide isomerase (PDI) inhibits adhesion. These data indicate that: (a) ecto-sulfhydryls are necessary for integrin-mediated platelet adhesion; (b) disulfide exchange takes place during this process; (c) surface PDI is involved in integrin-mediated adhesion.

Increased D-dimer levels in twin gestation

In normal pregnancy, the hemostatic balance is displaced toward hypercoagulability. The elevation in plasma levels of coagulation factors VII, VIII, and X and fibrinogen and the increased concentrations of plasminogen activator inhibitors [1,2] may predispose individuals to thromboembolism, especially near term [1,3]. Because human multifetal gestation requires still greater physiological alterations, the imbalance in hemostasis is further exaggerated. It has been suggested that the changes in the coagulation system near term may even mimic low-grade disseminated intravascular coagulopathy [4]. However, for the majority of women with multifetal gestation, the coagulopathy observed in the laboratory is not clinically apparent [5]. Despite the large body of research on the physiological adaptation to pregnancy, relatively little is known of the biological adaptation in general and the hemostatic changes in particular associated with multiple gestation.

Low-molecular-weight heparin for thrombophilia in pregnant women

OBJECTIVE

Low-molecular-weight heparin (LMWH) is the anticoagulant of choice during pregnancy because it is associated with a low incidence of osteoporosis and thrombocytopenia. Antithrombotic therapy has recently been used to prevent pregnancy loss in high-risk patients with evidence of acquired or congenital thrombophilia. The aim of the present study was to gain further information on the teratogenic potential of LMWH in this patient group.

METHODS

The study population included 46 patients with a history of recurrent abortions, intrauterine fetal death or intrauterine growth restriction (IUGR) and severe early-onset preeclampsia. Patients with a history of thromboembolism or positive findings for thrombophilia were prescribed LMWH (enoxaparin sodium, 40 mg daily) in combination with low-dose aspirin (100 mg daily) in the first trimester (group 1, n=14) or the second trimester (group 2, n=17); the remaining 15 patients received low-dose aspirin alone (group 3).

RESULTS

No significant differences were noted between the groups in the incidence of congenital malformations or abortions, IUGR or preterm deliveries. One infant in group 1 had familial bilateral postaxial polydactyly of the hands and one in group 3 had patent ductus arteriosus.

CONCLUSION

Despite the small size of the study groups, our results support the assumption that the use of LMWH is safe, at least as a teratogenic agent, in patients with thrombophilia throughout pregnancy.

Increased operative bleeding during orthopaedic surgery in patients with type I Gaucher disease and bone involvement

To aid clinicians in identifying patients with type I Gaucher disease who are at risk of excessive bleeding, we reviewed the coagulation parameters of six affected patients with bone involvement who underwent orthopaedic surgery at two centers, and of 22 patients under treatment at another, seven of whom had total splenectomy. All patients were of Jewish Ashkenazi origin. Among the latter group, prolonged prothrombin time was noted in 81%. Incidence of clotting factor deficiency were as follows: factor XI, 36.3%; V, 31.8%; VIII, 27.2%; IX, 13.6%; and XII, 27.2%. Most of the abnormalities occurred in the non-splenectomized patients. Two of the six orthopaedic surgery patients had excessive intraoperative and postoperative bleeding. One, who underwent spinal decompression had prolonged prothrombin time, and the other, who had total hip replacement, showed a deficiency of factor XI. The second patient's hemoglobin level was maintained with transfusion of fresh frozen plasma during contralateral hip arthroplasty five months later. We suggest that preoperative evaluation of clotting factors and replacement therapy may prevent excessive bleeding in patients with type I Gaucher disease.

Functional changes in the conformation of thrombospondin-1 during complexation with fibronectin or heparin

Thrombospondin-1 (TSP-1) interacts specifically with heparin and fibronectin in vitro and colocalizes with fibronectin and heparan sulfate in the extracellular matrix (ECM). Its conformation is strongly dependent on Ca2+ concentration. We have previously shown that both heparin and fibronectin have two binding sites on the TSP-1 subunit which may require conformational change for their occupancy (R. Dardik and J. Lahav, 1987, Eur. J. Biochem. 168, 347; ibid 1989, 185, 581). To investigate the effect of TSP-1 binding to fibronectin and heparin on its functional conformation, TSP-1 was subjected to proteolysis in the presence and absence of ligands and of Ca2+. We found that while trypsin cleavage of free TSP-1 resulted in the inactivation of ligand binding, TSP-1 bound to either fibronectin or heparin remained stably associated with these ligands. Cleavage by thrombin or tissue plasminogen activator (tPA) showed that Ca2+-depleted TSP-1, when bound to fibronectin or to heparin, yielded proteolytic cleavage patterns typical of the Ca2+-containing form. Cleavage by chymotrypsin was not affected by binding to fibronectin or heparin; hence loss of proteolytic susceptibility was not due to steric hindrance by the ligands. Taken together, these results indicate that: (A) binding of TSP-1 to fibronectin or heparin is a two-step mechanism where binding to one site leads to conformational changes that enable binding to the second site; (B) TSP-1 in complex with fibronectin or heparin adopts the Ca2+-containing conformation in the absence of Ca2+; and (C) such complexes are highly resistant to cleavage by tPA and, if cleaved by other enzymes, the TSP-1 fragments remain bound to other ECM components. These characteristics have profound significance for platelet adhesion and cell migration into wounds where Ca2+ concentrations are reduced.

Cutaneous necrosis as a terminal paraneoplastic thromboembolic event in a patient with non-Hodgkin's lymphoma

Thrombotic complications in non-Hodgkin's lymphoma often originate in the large veins. We describe a patient with refractory advanced high-grade lymphoma who presented with the rare complication of extensive cutaneous necrosis due to thrombosis of dermal vessels; there was also a recent new peak of monoclonal IgM-kappa protein. Direct immunofluorescence demonstrated immune deposits with complement in the dermal vessel wall. Based on these observations and on published data, we suggest that these complexes were the trigger for the thrombotic events and that the monoclonal IgM acted as xenoreactive antibodies, initiating a cascade of events. The first step of this cascade was activation of the complement and the membrane attack complex, which caused secretion of IL-1 alpha by endothelial cells, followed by overexpression of tissue factor on the surface of the dermal vessel wall endothelium. Dermal vessel thrombosis was the final event in this cascade.

Activated protein C resistance in pediatric inflammatory bowel disease

BACKGROUND

There is evidence for a hypercoagulable state in inflammatory bowel disease (IBD), and small vessel thrombosis has been identified in the bowel of patients with Crohn's disease, suggesting thrombosis as a possible etiologic factor. Activated protein C (APC) resistance is the most common inherited disorder leading to thrombosis and accounts for 30% to 40% of episodes of idiopathic venous thrombosis.

METHODS

The prevalence of APC resistance was studied in 23 patients with IBD (17 with Crohn's disease, 6 with ulcerative colitis) and in 11 control subjects with recurrent abdominal pain or celiac disease, using an APC resistance screening method.

RESULTS

One patient with Crohn's disease had a positive screen result, two patients (one with Crohn's, one with ulcerative colitis) had borderline results, and results in all of the control subjects were normal. One patient with Crohn's disease had a history of a thromboembolic event but had a normal screen result.

CONCLUSIONS

Activated protein C resistance does not seem to play a major role in the etiology of the hypercoagulable state in inflammatory bowel disease.

Levels of proteins C and S do not decline subsequent to first line chemotherapy in lymphoma patients

Thromboembolic complications and decrease in protein C and S have been observed in patients while receiving combination chemotherapy for breast cancer. We investigated whether initial cytotoxic treatment of non-Hodgkin's lymphoma (NHL) and Hodgkin's disease (HD) is also associated with changes in these anticoagulant parameters. For this purpose 25 patients with intermediate to high grade NHL and seven with HD, undergoing primary treatment with cytotoxic drugs were evaluated at three time-points: pre-therapy, mid-therapy and post-therapy. In contrast to the breast cancer patients, no significant changes in protein C, protein S and antithrombin III levels were observed in the NHL patients during the various stages of therapy. However in HD patients, the mean protein C values had a tendency to be higher at mid-therapy compared to pre-therapy and protein S levels had a tendency to be higher at mid-therapy compared to post-therapy. In lymphoma patients receiving primary cytotoxic treatment we did not find changes in anticoagulant parameters that can explain a chemotherapy-induced hypercoagulable state, as has been reported in breast cancer patients.

Affinity modulation in platelet alpha 2 beta 1 following ligand binding

In order to test for ligand-induced change in the affinity of platelet alpha 2 beta 1 to collagen we passaged labeled viable platelets through a column of fibrillar collagen and used stringent lysis conditions to remove all low-affinity receptors. A high affinity fraction left on the collagen could be eluted with DTT and 2% SDS. Antibodies raised against it Western-blotted alpha 2 beta 1. Functional tests performed with the antibodies confirmed the involvement of the high affinity proteins in platelet-collagen interactions attributed to alpha 2 beta 1: inhibition of collagen-specific platelet adhesion and aggregation. EDTA, chaotropic agents or low pH did not elute the high affinity fraction of alpha 2 beta 1. However, DTT followed by acetic acid did. Our data suggest that 1) ligand binding induces the formation of a new disulfide bond in a fraction of alpha 2 beta 1, 2) that this bond is intrareceptor and 3) that this change increases the affinity of the receptor to its ligand.

A human monoclonal IgA autoantibody--185/12--behaves like an autoimmune antiphospholipid antibody

A human monoclonal anticardiolipin autoantibody (ACA) of the IgA-k isotype, designated 185/12, is described. The antibody was prepared from peripheral B cells, obtained from a patient with a history of habitual abortion, by immortalization with Epstein-Barr virus (EBV). The antibody displays a strong binding activity to cardiolipin and phosphatidyl L-serine, but not to phosphatidylcholine, phosphatidylinositol, ssDNA and dsDNA. It binds to cardiolipin in a concentration-related and saturable manner (Kd = 3.0 x 10(-8) M). This reaction is dependent upon the presence of bovine serum, and is fully inhibited by cardiolipin vesicles. The 185/12 antibody exhibits different binding patterns to the solid-phase bound cardiolipin-serum complex and to its individual components (cardiolipin and bovine serum). The Bmax of 185/12 binding to the complex (0.968 OD units) is higher than the sum of the Bmax values calculated for each one of the complex components (0.352 + 0.179 = 0.531 OD units). Bovine serum as well as purified beta 2-glycoprotein I (beta 2-GPI) in suspension inhibit the binding of 185/12 to the complex. 185/12 binding capacity increases in direct relation to the rising concentration of beta 2-GPI. Collectively, these data may be interpreted to suggest that 185/12 antibody, which is an IgA isotype, exhibits characteristics usually attributed only to antiphospholipid autoantibodies (APA) of the IgG isotype, that are associated with the clinical spectrum of APA syndrome (APA-S). It is, therefore, possible that autoantibodies of the IgA isotype could play a pathogenic role, which may be different from that of the IgG isotype, in the development of autoimmune phenomena.

The functions of thrombospondin and its involvement in physiology and pathophysiology

The thrombospondin family of molecules is expressed in many different tissues. Its expression is highly regulated by different hormones and cytokines and is developmentally controlled. It can bind to many different cell types, probably via an array of receptors which are similarly regulated. The level of thrombospondins in body fluids and their distribution in tissue change in correlation with various pathological states. It is linked to the growth of primary tumors and to metastasis, to development of the atherosclerotic plaque, to malaria infection and other diseases. The role(s) of thrombospondin(s) are by and large unknown, though specific interaction seem to affect particular cell functions. The wide-spread spatial and temporal regulation, multiple interactions and correlation with major diseases imply important roles in cell function and call for concerted effort to unravel the mystery.

Lupus anticoagulant antibodies inhibit collagen-induced adhesion and aggregation of human platelets in vitro

The effect of circulating lupus anticoagulant on platelet interaction with collagen and other proteins was tested, with the aim of understanding the role of membrane phospholipids in platelet function. Plasma samples from 26 systemic lupus erythematosus (SLE) patients, containing circulating lupus anticoagulant (LAC), were examined for their effect on adhesion and aggregation of normal human platelets. We find that SLE plasma, but not normal plasma, inhibits platelet adhesion to collagen in a concentration-dependent manner. At a plasma concentration of 1% the inhibition was 73 +/- 9% (mean +/- SD). In sharp contrast, there was no effect on platelet adhesion to fibronectin. Purified IgG from the same plasma samples also had an inhibitory effect. At 15 micrograms/ml (comparable in IgG concentration to 0.1% plasma) it inhibited adhesion to collagen by 33 +/- 11%. Inhibition could be abolished by preincubation of the LAC-containing plasma with cardiolipin (CL), phosphatidylinositol (PI), and, to a lesser extent, phosphatidylserine (PS) but not with phosphatidylcholine (PC) or phosphatidylethanolamine (PE). Inhibition could also be abolished by preincubation of the LAC-containing plasma with a 10-fold excess of washed normal platelets. The effect of 1% LAC plasma on platelet aggregation was as striking, showing 79 +/- 26% inhibition of collagen-induced aggregation, and it could also be abolished by preincubation of the LAC plasma with cardiolipin. In contrast, the effect of LAC plasma on thrombin-induced aggregation was rather modest. Our results indicate that antiphospholipid antibodies interfere with platelet adhesion and stimulation by collagen in vitro and point to an important role of external plasma membrane phospholipids, particularly PI, in collagen-induced platelet activation.

Differentiation-controlled synthesis and binding of thrombospondin to granulosa cells

Thrombospondin (TSP) is a large glycoprotein, synthesized by several matrix-forming cells and incorporated into their extracellular matrix. In several cell types its presence supports cell growth and proliferation. To investigate the role of this protein in cell differentiation, we studied the hormonal effect of TSP production and receptor-mediated binding to primary granulosa cells prepared from diethylstilbestrol-treated immature female rats. These cells can be induced to differentiate by FSH, 8-bromo-cAMP (8-Br-cAMP), or forskolin. Progesterone production is induced during differentiation, and its level of synthesis is an important manifestation of the differentiated phenotype. We find that undifferentiated granulosa cells synthesize and secrete TSP. The protein comprises about 0.5% of the total cell protein, and it is the major protein secreted in culture. Treatment of the cells with FSH or 8-Br-cAMP reduces TSP production dramatically, and forskolin completely inhibits it. In parallel, we observed that the undifferentiated cells bind TSP specifically with a Kd of 1.8 nM, and the number of binding sites per cell is 1.7 x 10(5). This binding can be prevented by excess TSP or an anti-TSP monoclonal antibody (B7-3). This ability to bind TSP is completely lost after induction of differentiation by FSH or 8-Br-cAMP. Our findings show that both the production and binding of TSP to granulosa cells are tightly controlled by normal cell differentiation and indicate that changes in TSP are correlated with the passage of the cell through the stages of maturation, a passage that also involves changes in cell shape and extracellular interactions and in the steroidogenic capacity of these cells.

Cell-binding domain of endothelial cell thrombospondin: localization to the 70-kDa core fragment and determination of binding characteristics

Endothelial and other cell types synthesize thrombospondin (TSP), secrete it into their culture medium, and incorporate it into their extracellular matrix. TSP is a large multifunctional protein capable of specific interactions with other matrix components, as well as with cell surfaces, and can modulate cell adhesion to the extracellular matrix. With the aim of understanding the mechanism by which TSP exerts its effect on cell adhesion, we studied the interaction of endothelial cell TSP (EC-TSP) with three different cell types: endothelial cells, granulosa cells, and myoblasts. We find that endothelial cells specifically bind radiolabeled EC-TSP with a Kd of 25 nM, and the number of binding sites is 2.6 X 10(6)/cell. Binding is not inhibitable by the cell-adhesion peptide GRGDS, indicating that the cell-binding site of EC-TSP is not in the RGD-containing domain. Localization of the cell-binding site was achieved by testing two chymotryptic fragments representing different regions of the TSP molecule, the 70-kDa core fragment and the 27-kDa N-terminal fragment, for their ability to bind to the cells. Cell-binding capacity was demonstrated by the 70-kDa fragment but not by the 27-kDa fragment. Binding of both intact [125I]EC-TSP and of the 125I-labeled 70-kDa fragment was inhibited by unlabeled TSP, heparin, fibronectin (FN), monoclonal anti-TSP antibody directed against the 70-kDa fragment (B7-3), and by full serum, but not by heparin-absorbed serum or the cell-adhesion peptide GRGDS. The 70-kDa fragment binds to endothelial cells with a Kd of 47 nM, and the number of binding sites is 5.0 x 10(6)/cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple domains are involved in the interaction of endothelial cell thrombospondin with fibronectin

Thrombospondin is a large multifunctional glycoprotein synthesized, secreted and incorporated into the extracellular matrix by several cell types in culture. It is also present in the blood platelet and is secreted following platelet activation. We have previously shown that thrombospondin co-distributes with fibronectin in the extracellular matrix and that it can bind directly to purified fibronectin. In order to elucidate the chemical aspects of thrombospondin incorporation into the extracellular matrix, we studied the interaction of endothelial cell thrombospondin and fibronectin. We find that endothelial cell thrombospondin has two distinct binding domains for fibronectin. One domain is on the 70-kDa core fragment, probably similar to that of platelet thrombospondin. The other domain is on the 27-kDa N-terminal fragment and is unique to endothelial cell thrombospondin. The dissociation constant of the intact endothelial-cell-derived molecule is 0.7 +/- 0.2 x 10(-7) M. Following fragmentation, the separate domains bind with somewhat lower affinity: the core domain binds with a Kd of 3.4 +/- 1.5 x 10(-7) M and the N-terminal domain binds with a Kd of 8.8 +/- 1.8 x 10(-7) M. Binding of the intact molecule is Ca2+-independent. By contrast, following tryptic fragmentation, binding of the 70-kDa fragment is practically lost. It can be restored, however, by removal of Ca2+, indicating that the binding site on this domain is either sequestered or becomes so following fragmentation. Heparin, which also binds to both fragments, competed with fibronectin binding to the 27-kDa fragment but not to the 70-kDa domain. The fact that heparin also competitively inhibits fibronectin binding of the intact molecule further supports sequestration of the fibronectin-binding domain on the 70-kDa core fragment. Our data suggest that endothelial-cell thrombospondin possesses two distinct binding sites for fibronectin, a low-affinity constitutively available one and a high-affinity one, possibly sequestered on the intact unbound molecule.

The build-up of the thrombospondin extracellular matrix. An apparent dependence on synthesis and on preformed fibrillar matrix

Thrombospondin (TSP) is a multifunctional protein synthesized by several cell types in culture, among them endothelial cells, and incorporated into the extracellular matrix (ECM) of these cells. In vitro it has been detected in most interstitial spaces, and its presence has been suggested to be developmentally controlled. With the aim of elucidating the role of TSP in the extracellular matrix, we studied the build-up of this protein in the matrix as a function of cell type density and age in culture. The development of the TSP matrix was compared to that of fibronectin (FN) and of von Willebrand Factor (VWF) in the same cultures using our monoclonal anti-TSP antibody B7-3 and monospecific anti-FN or anti-VWF antibodies. In cultures of bovine aortic endothelial cells (BAEC) we observed that both the pattern and distribution of TSP in the matrix changed with cell density and time in culture; it started as a completely amorphous dense layer of protein when the cells were sparse and changed to well organized fibrils when the cells had been confluent for a while. The first appearance of the fibrillar arrays of TSP coincides perfectly with that of the FN fibers; extracellular VWF also was first detected at this point. From this time in culture, there was an increasing coincidence of the TSP with the FN and the VWF matrices suggesting the formation of a complex multicomponent structure of the fibrillar network.(ABSTRACT TRUNCATED AT 250 WORDS)

Gray platelet syndrome in the elderly

A 68-year-old male who suffered from thrombocytopenia and mild splenomegaly for 18 years was found to present agranular gray platelets on peripheral blood smear. Bone biopsy revealed a mild, diffuse, reticular fibrosis with no collagen, and electron microscopy of the platelets showed an absence of almost all the alpha-granules. Platelet thrombospondin and fibronectin analysed by SDS-polyacrylamide gel electrophoresis and Rocket immunoelectrophoresis were absent. Follow-up of 4 years showed the same parameters with no evidence of active myeloproliferative or dysmyelopoietic disorders. Hemorrhagic diathesis was limited to ecchymoses and postprostatectomy bleeding, necessitating platelet transfusion. This led us to conclude that our patient probably had a constitutional primary alpha-granule deficiency or gray platelet syndrome. This extremely rare defect has been described in less than 10 patients, all of them very young. Our observation shows that these patients may have a long, uneventful survival.